0001860782-22-000005 | 10-K | XBRL Viewer

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Consolidated and Combined Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 130,414	$ 0
Marketable securities	134,643	0
Prepaid expenses	9,512	14,413
Receivables and other current assets	16,995	10,691
Total current assets	291,564	25,104
Property, plant and equipment, net	34,913	144,025
Marketable securities	97,124	0
Intangible assets, net	9,892	5,644
Goodwill	12,056	13,128
Operating lease right-of-use assets	275,534	116,456
Restricted cash and other non-current assets	38,592	8,263
Total assets	759,675	312,620
Current liabilities:
Accounts payable	6,024	7,152
Accrued expenses and other current liabilities	55,410	43,347
Operating lease liability, current portion	9,769	15,313
Deferred revenue, current portion	5,000	820
Collaboration research advancement, current portion	22,185	9,236
Total current liabilities	98,388	75,868
Deferred revenue, net of current portion	25,762	25,762
Collaboration research advancement, net of current portion	1,135	21,581
Operating lease liability, net of current portion	272,446	112,290
Other non-current liabilities	2,122	2,490
Total liabilities	399,853	237,991
Commitments and contingencies (Note 8)
Stockholders’ equity:
Net parent investment	0	74,629
Preferred stock, $0.0001 par value; 10,000 shares authorized, 0 shares issued and outstanding at December 31, 2021; no shares authorized, issued and outstanding at December 31, 2020	0	0
Common stock, $0.0001 par value; 200,000 shares authorized, 23,585 shares issued and outstanding at December 31, 2021; no shares authorized, issued and outstanding at December 31, 2020	2	0
Additional paid-in capital	400,026	0
Accumulated other comprehensive loss	(712)	0
Accumulated deficit	(39,494)	0
Total stockholders’ equity	359,822	74,629
Total liabilities and stockholders’ equity	$ 759,675	$ 312,620
Common stock, shares authorized (in shares)	200,000,000	0

Consolidated and Combined Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Preferred stock, par value per share (in dollars per share)	$ 0.1000	$ 0.1000
Preferred stock, shares authorized (in shares)	10,000,000	0
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.1000	$ 0.1000
Common stock, shares authorized (in shares)	200,000,000	0
Common stock, shares issued (in shares)	23,585,000	0
Common stock, shares outstanding (in shares)	23,585,000	0

Consolidated and Combined Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue:
Collaborative arrangement revenue	$ 26,921	$ 115,594	$ 5,740
Total revenues	54,522	248,122	44,296
Operating expenses:
Research and development	261,937	296,467	297,645
Selling, general and administrative	93,506	90,897	81,646
Share of collaboration loss	10,071	0	0
Cost of royalty and other revenue	2,517	5,396	2,978
Change in fair value of contingent consideration	439	(6,468)	2,747
Total operating expenses	368,470	386,292	385,016
Loss from operations	(313,948)	(138,170)	(340,720)
Interest income, net	88	0	0
Other income, net	21,647	18,056	20,126
Loss before income taxes	(292,213)	(120,114)	(320,594)
Income tax (expense) benefit	0	0	0
Net loss	$ (292,213)	$ (120,114)	$ (320,594)
Net loss per share - basic (in dollars per share)	$ (12.44)	$ (5.14)	$ (13.72)
Net loss per share - diluted (in dollars per share)	$ (12.44)	$ (5.14)	$ (13.72)
Weighted-average number of common shares used in computing net loss per share - basic	23,499	23,369	23,369
Weighted-average number of common shares used in computing net loss per share - diluted	23,499	23,369	23,369
Other comprehensive loss:
Other comprehensive loss, net of tax benefit (expense) of $0.0 million, $0.0 million, and $0.0 million for the years ended December 31, 2021, 2020 and 2019, respectively	$ (712)	$ 0	$ 0
Comprehensive loss	(292,925)	(120,114)	(320,594)
Service revenue
Revenue:
Revenue	21,381	111,452	30,351
Royalty and other revenue
Revenue:
Revenue	$ 6,220	$ 21,076	$ 8,205

Consolidated and Combined Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Other Comprehensive Income (Loss), Tax	$ 0.0	$ 0.0	$ 0.0

- Definition

Amount of tax expense (benefit) allocated to other comprehensive income (loss).

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+ Details

Consolidated and Combined Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common stock	Net parent investment	Net parent investment Cumulative Effect, Period of Adoption, Adjustment	Additional paid-in capital	Accumulated other comprehensive loss	Accumulated deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustment to beginning net parent investment from adoption of ASU		$ 6,564			$ 6,564
Beginning balance at Dec. 31, 2018	$ 27,951			$ 27,951
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	62,049			62,049
Transfers from bluebird bio	267,722			267,722
Net loss	(320,594)			(320,594)
Ending balance at Dec. 31, 2019	43,692			43,692
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	60,997			60,997
Transfers from bluebird bio	90,054			90,054
Net loss	$ (120,114)			(120,114)
Ending balance (in shares) at Dec. 31, 2020	0
Ending balance at Dec. 31, 2020	$ 74,629			74,629
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation - bluebird allocation	44,626			44,626
Stock-based compensation	9,012					$ 9,012
Transfers from bluebird bio	517,706			517,936			$ (230)
Consummation of spin-off transaction (in shares)			23,369,000
Consummation of spin-off transaction, which includes issuance of pre-funded warrants to purchase 757,575 shares of common stock (refer to Note 9, Stockholders’ equity)			$ 2	(384,472)		384,470
Vesting of restricted stock units (in shares)			7,000
Issuance of unrestricted stock awards to settle accrued employee compensation (in shares)			209,000
Issuance of unrestricted stock awards to settle accrued employee compensation	6,544					6,544
Other comprehensive loss	(482)						(482)
Net loss	$ (292,213)			(252,719)				$ (39,494)
Ending balance (in shares) at Dec. 31, 2021	23,585,000		23,585,000
Ending balance at Dec. 31, 2021	$ 359,822		$ 2	$ 0		$ 400,026	$ (712)	$ (39,494)

Consolidated Statements of Equity (Parenthetical)	12 Months Ended
Consolidated Statements of Equity (Parenthetical)	Dec. 31, 2018
Accounting Standards Update [Extensible Enumeration]	us-gaap:AccountingStandardsUpdate201602Member

- Definition

Indicates amendment to accounting standards.

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+ Details

Consolidated and Combined Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (292,213)	$ (120,114)	$ (320,594)
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of contingent consideration	439	(6,468)	2,747
Depreciation and amortization	16,350	13,188	12,587
Stock-based compensation expense	54,629	60,997	62,049
Other non-cash items	430	73	110
Changes in operating assets and liabilities:
Prepaid expenses and other assets	1,578	1,526	6,700
Operating lease right-of-use assets	15,541	13,764	12,214
Accounts payable	(6)	(13,240)	14,611
Accrued expenses and other liabilities	15,733	(7,479)	26,341
Operating lease liabilities	(16,199)	(10,960)	(2,309)
Deferred revenue	4,180	8,317	(16,674)
Collaboration research advancement	(7,496)	(7,397)	(5,739)
Net cash used in operating activities	(207,034)	(67,793)	(207,957)
Cash flows from investing activities:
Purchases of property, plant and equipment	(11,575)	(22,261)	(59,765)
Proceeds from maturities of marketable securities	34,986	0	0
Purchase of intangible assets	(8,000)	0	0
Net cash provided by (used in) investing activities	15,411	(22,261)	(59,765)
Cash flows from financing activities:
Transfers from bluebird bio	354,889	90,054	267,722
Net cash provided by financing activities	354,889	90,054	267,722
Increase (decrease) in cash, cash equivalents and restricted cash	163,266	0	0
Cash, cash equivalents and restricted cash at beginning of year	0	0	0
Cash, cash equivalents and restricted cash at end of year	163,266	0	0
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	130,414	0	0
Restricted cash included in restricted cash and other non-current assets	32,852	0	0
Total cash, cash equivalents and restricted cash	163,266	0	0
Supplemental cash flow disclosures:
Purchases of property, plant and equipment included in accounts payable and accrued expenses	3,703	2,039	3,064
Right-of-use assets obtained in exchange for operating lease liabilities	0	4,989	9,745
Non-cash return of bRT-related assets to bluebird bio	110,300	0	0
Increase of right-of-use asset and associated lease liability due to lease reassessment	174,618	0	0
Issuance of unrestricted stock awards to settle accrued employee compensation	6,544	0	0
Cash paid during the period for interest	0	0	0
Cash paid during the period for income taxes	$ 0	$ 0	$ 0

Description of the business	12 Months Ended
Description of the business	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of the business	Description of the business 2seventy bio, Inc. (the “Company” or “2seventy bio”) is a cell and gene therapy company focused on the research, development, and commercialization of transformative treatments for cancer. The Company’s approach combines its expertise in T cell engineering technology and lentiviral vector gene delivery approaches, experience in research, development, and manufacturing of cell therapies and a suite of technologies that can be selectively deployed to develop highly innovative, targeted cellular therapies for patients with cancer. The Company is advancing multiple preclinical and clinical programs in oncology and, together with Bristol Myers Squibb (“BMS”), delivering the first FDA-approved CAR T therapy in multiple myeloma, ABECMA (idecabtagene vicleucel, or ide-cel), to patients in the United States. Please refer to Note 10, Collaborative arrangements and strategic partnerships, for further discussion of the collaboration with BMS. 2seventy bio Securities Corporation is a wholly-owned subsidiary of the Company which was incorporated in Massachusetts on December 13, 2021 and was granted securities corporation status in Massachusetts for the 2021 tax year. 2seventy bio Securities Corporation has no employees. The separation In January 2021, bluebird bio, Inc. ("bluebird bio") announced its plans to separate its oncology portfolio and programs from its severe genetic disease (“SGD”) portfolio and programs through a pro rata distribution of 2seventy bio's common stock to stockholders of bluebird bio. As a part of the separation, bluebird bio transferred the assets, liabilities and operations of its oncology portfolio and programs to 2seventy bio, pursuant to the terms of the separation agreement entered into between 2seventy bio and bluebird bio on November 3, 2021. On November 4, 2021, the distribution date, each bluebird bio stockholder received a pro rata share of 2seventy bio's common stock for every share of bluebird bio common stock held of record at the close of business on the record date for the distribution. Registered stockholders received cash in lieu of any fractional shares of 2seventy bio's common stock that they would have received as a result of the application of the distribution ratio. Following the distribution, 2seventy bio began to operate as a separate, independent, publicly traded company. Going concern In accordance with Accounting Standards Codification (“ASC”) 205-40, Going Concern, the Company evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about its ability to continue as a going concern within one year after the date that the consolidated and combined financial statements are issued. The Company has incurred losses and has experienced negative operating cash flows for all historical periods presented. During the year ended December 31, 2021, the Company incurred a net loss of $292.2 million and used $207.0 million of cash in operations. The Company expects to continue to generate operating losses and negative operating cash flows for the next few years. The Company's continued operations are dependent on its ability to raise additional funding. As of December 31, 2021, the Company had cash, cash equivalents, and marketable securities of $362.2 million. The Company expects that its cash, cash equivalents, and marketable securities will be sufficient to fund current planned operations for at least the next twelve months from the date of issuance of these financial statements. The Company intends to pursue additional cash resources through a combination of public or private equity offerings, debt financings, collaborations, strategic alliances or licensing arrangements with third parties. There can be no assurance that such financing will be available in sufficient amounts or on acceptable terms, if at all, and some could be dilutive to existing stockholders. If the Company is unable to obtain additional funding on a timely basis, it may be forced to significantly curtail, delay, or discontinue one or more of its planned research or development programs or be unable to expand its operations.

Summary of significant accounting policies and basis of presentation

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Summary of significant accounting policies and basis of presentation

Basis of presentation

The Company did not operate as a separate, stand-alone entity prior to its separation from bluebird bio. The Company’s consolidated balance sheet as of December 31, 2021 consists of the consolidated balances of the Company as prepared on a stand-alone basis. The Company’s consolidated and combined statements of operations and comprehensive loss, stockholders’ equity and cash flows for the year ended December 31, 2021 have been prepared on a carve out basis, derived from bluebird bio’s consolidated financial statements and accounting records, for the period prior to the separation on November 4, 2021 and on a stand-alone basis for the period following the separation through December 31, 2021. The Company’s combined balance sheet as of December 31, 2020 and combined statements of operations and comprehensive loss, stockholders’ equity and cash flows for the years ended December 31, 2020 and 2019 have been prepared on a carve-out basis, derived from bluebird bio's consolidated financial statements and accounting records.

The accompanying consolidated and combined financial statements reflect the historical results of the operations, financial position and cash flows of the Company and have been prepared by the Company in accordance with accounting principles generally accepted in the United States (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as included in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board (“FASB”).

The historical results of operations, financial position and cash flows of 2seventy bio presented in these consolidated and combined financial statements may not be indicative of what they would have been had 2seventy bio been an independent stand-alone entity for each of the years presented, nor are they necessarily indicative of 2seventy bio's future results of operations, financial position and cash flows.

Prior to the separation, the Company was dependent upon bluebird bio for all of its working capital and financing requirements, as bluebird bio used a centralized approach to cash management and financing its operations. There were no cash amounts specifically attributable to the Company for the periods prior to the separation; therefore, cash and cash equivalents were not allocated to the Company for periods prior to the separation. Financing transactions related to bluebird bio for periods prior to the separation are accounted for as a component of net parent investment in the consolidated and combined balance sheets and as a financing activity on the accompanying consolidated and combined statements of cash flows. In 2021, net cash transferred to us from bluebird bio of $354.9 million, as indicated in our consolidated and combined statements of cash flows, includes both the net changes in our cash used for operating and investing activities prior to the separation and the cash and cash equivalents distributed to us upon separation.

Prior to the separation, the Company’s combined financial statements included an allocation of expenses related to certain bluebird bio corporate functions, including senior management, legal, human resources, finance and information technology. In addition, prior to the separation the Company's combined financial statements include an allocation of certain research and development costs not directly attributable to individual programs. These expenses were allocated to the Company based on direct usage or benefit where specifically identifiable, with the remainder allocated based on employee time spent on projects, square footage or other measures that management believes are consistent and reasonable. These allocations may not be indicative of the actual expense that would have been incurred had the Company operated as an independent, publicly traded company for the periods prior to the separation. See Note 14, Related-party transactions, for a further description of the accounting for the separation from bluebird bio.

Prior to the separation, the combined balance sheets of the Company included assets and liabilities that were allocated principally on a specific identification basis. These allocations may not be indicative of the actual assets and liabilities that would have been recorded had the Company operated as an independent, publicly traded company for the periods prior to the separation. As 2seventy bio's operations were not historically held by a single legal entity or separate legal entities, net parent investment was shown in lieu of stockholder's equity in the combined financial

statements for periods prior to the separation. As a result of the separation, the Company’s net parent investment balance was reclassified to additional paid-in capital.

For periods prior to the separation, the taxable income (loss) of bluebird bio entities, including 2seventy bio, Inc. prior to the separation, was included in bluebird bio’s consolidated tax returns. As such, separate income tax returns were not prepared for the entities included within the combined financial statements prior to separation.

In connection with the separation, certain assets and liabilities, including certain accounts receivables and accounts payables, included on the consolidated and combined balance sheets prior to the separation have been retained by bluebird bio post-separation and, therefore, were adjusted through net parent investment in the Company’s consolidated and combined financial statements. In addition, in connection with the separation, certain equity awards were converted in accordance with the Employee Matters Agreement, as further described in Note 13, Stock-based compensation. Upon separation, bluebird bio contributed $384.5 million of net assets to the Company.

Amounts reported are computed based on thousands, except percentages or as otherwise noted. As a result, certain totals may not sum due to rounding.

Principles of consolidation and combination

Periods prior to separation

The accompanying combined financial statements included the attribution of certain assets and liabilities that were historically held by bluebird bio but which were specifically identifiable or attributable to the Company. All intercompany balances and transactions with bluebird bio were deemed to be effectively settled in the combined financial statements at the time the transaction was recorded. Expenses related to corporate allocations from bluebird bio to the Company were considered to be effectively settled for cash in the combined financial statements at the time the transaction was recorded.

Periods after the separation

The accompanying consolidated and combined financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany transactions and accounts within the Company have been eliminated. Certain amounts presented in the prior period have been reclassified to conform to the current period presentation.

As a standalone entity, the Company will file tax returns on its own behalf, and tax balances and the effective income tax rate may differ from the amounts reported in the historical periods. As of November 4, 2021 and in connection with the separation, the Company adjusted its deferred tax balances and computed its related tax provision to reflect operations as a standalone entity.

Variable interest entities

The Company continually assesses whether it is the primary beneficiary of a variable interest entity as changes to existing relationships or future transactions may result in consolidation or deconsolidation of one or more collaborators or partners. In determining whether it is the primary beneficiary of an entity in which the Company has a variable interest, management applies a qualitative approach that determines whether the Company has both (1) the power to direct the economically significant activities of the entity and (2) the obligation to absorb losses of, or the right to receive benefits from, the entity that could potentially be significant to that entity.

Use of estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts in the financial statements and accompanying notes. Actual results could materially differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of

future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes and management must select an amount that falls within that range of reasonable estimates. This process may result in actual results differing materially from those estimated amounts used in the preparation of the financial statements.

Estimates and judgments are used in the following areas, among others: allocations of revenue, expenses, assets and liabilities from bluebird bio's historical consolidated financial statements to the Company for periods prior to the separation, future undiscounted cash flows and subsequent fair value estimates used to assess potential and measure any impairment of long-lived assets, including goodwill and intangible assets, the measurement of right-of-use assets and lease liabilities, contingent consideration, stock-based compensation expense, accrued expenses, income taxes, and the assessment of the Company's ability to fund its operations for at least the next twelve months from the date of issuance of these financial statements. In addition, estimates and judgments are used in the Company’s accounting for its revenue-generating arrangements, in particular as it relates to determining the stand-alone selling price of performance obligations, evaluating whether an option to acquire additional goods and services represents a material right, estimating the total transaction price, including estimating variable consideration and the probability of achieving future potential development and regulatory milestones, assessing the period of performance over which revenue may be recognized, and accounting for modifications to revenue-generating arrangements.

Segment information

The Company operates in a single segment, focusing on researching, developing and commercializing potentially transformative treatments for cancer. Consistent with its operational structure, its chief operating decision maker manages and allocates resources for the Company at a consolidated level. Therefore, results of the Company's operations are reported on a consolidated basis for purposes of segment reporting. All material long-lived assets of the Company reside in the United States.

Cash and cash equivalents

The Company considers all highly liquid investments purchased with original final maturities of 90 days or less from the date of purchase to be cash equivalents. Cash equivalents may consist of marketable securities with maturities of less than 90 days when purchased. Cash equivalents are reported at fair value. There were no cash or cash equivalents specifically attributable to 2seventy bio for the historical periods presented prior to the separation.

Restricted cash

Restricted cash consists primarily of letters of credit totaling $30.0 million that are required to be maintained in connection with the Company’s lease arrangements. The letters of credit are in the name of the Company’s landlords and are required to fulfill lease requirements in the event the Company should default on its lease obligations. As of December 31, 2021, the Company classified its restricted cash as non-current on the consolidated and combined balance sheet based on the release dates of the restrictions. As of December 31, 2020, the Company did not have any restricted cash. For further information on the Company’s letters of credit, see Note 7, Leases.

Marketable securities

The Company’s marketable securities are maintained by investment managers and consist of U.S. government agency securities and treasuries, corporate bonds and commercial paper. Debt securities are carried at fair value with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ equity until realized. Any premium arising at purchase is amortized to the earliest call date and any discount arising at purchase is accreted to maturity. Amortization and accretion of premiums and discounts are recorded in interest income, net. Realized gains and losses on debt securities are determined using the specific identification method and are included in other income, net.

The Company classifies marketable securities with a remaining maturity when purchased of greater than three months as available-for-sale. Marketable securities with a remaining maturity date greater than one year are classified as non-current assets although these securities are available for use in the Company’s current operations.

There were no marketable securities specifically attributable to 2seventy bio for the historical periods presented prior to the separation.

Effective January 1, 2020, the Company adopted ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Statements (“ASU 2016-13” or “ASC 326”), using the effective date method. As the Company had never recorded any other-than-temporary-impairment adjustments to its available-for-sale debt securities prior to the effective date, no transition provisions are applicable to the Company.

The Company assesses its available-for-sale debt securities under the available-for-sale debt security impairment model in ASC 326 as of each reporting date in order to determine if a portion of any decline in fair value below carrying value recognized on its available-for-sale debt securities is the result of a credit loss. The Company records credit losses in the consolidated and combined statements of operations and comprehensive loss as credit loss expense within other income, net, which is limited to the difference between the fair value and the amortized cost of the security. To date, the Company has not recorded any credit losses on its available-for-sale debt securities.

Accrued interest receivable related to the Company's available-for-sale debt securities is presented within receivables and other current assets on the Company's consolidated and combined balance sheets. The Company has elected the practical expedient available to exclude accrued interest receivable from both the fair value and the amortized cost basis of available-for-sale debt securities for the purposes of identifying and measuring any impairment. The Company writes off accrued interest receivable once it has determined that the asset is not realizable. Any write offs of accrued interest receivable are recorded by reversing interest income, recognizing credit loss expense, or a combination of both. To date, the Company has not written off any accrued interest receivables associated with its marketable securities.

Concentrations of credit risk and off-balance sheet risk

Financial instruments that subject the Company to credit risk primarily consist of cash and cash equivalents, available-for-sale securities, and accounts receivable. The Company maintains its cash and cash equivalent balances with high-quality financial institutions and, consequently, the Company believes that such funds are subject to minimal credit risk. The Company’s marketable securities, which primarily consist of U.S. government agency securities and treasuries, corporate bonds and commercial paper, potentially subject the Company to concentrations of credit risk. The Company has adopted an investment policy that limits the amounts the Company may invest in any one type of investment and requires all investments held by the Company to be at least AA+/Aa1 rated, thereby reducing credit risk exposure. The Company’s accounts receivable balance primarily consists of amounts owed from collaborative arrangement partners and royalties receivable under out-license agreements with various third parties. The Company monitors economic conditions to identify facts or circumstances that may indicate that any of its accounts receivable are at risk of collection.

Fair value of financial instruments

The Company has certain financial assets and liabilities recorded at fair value which have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements:

Level 1—Fair values are determined utilizing quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

Level 2—Fair values are determined utilizing quoted prices for identical assets or liabilities in non-active markets, quoted prices for similar assets or liabilities in active markets, or other market observable inputs such as interest rates, yield curves and foreign currency spot rates.

Level 3—Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable.

To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level

within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Items measured at fair value on a recurring basis include marketable securities (see Note 3, Marketable securities, and Note 4, Fair value measurements) and contingent consideration (see Note 4, Fair value measurements). The carrying amounts of accounts receivable, accounts payable and accrued expenses approximate their fair values due to their short-term nature.

Business combinations

Business combinations are accounted for using the acquisition method of accounting. Using this method, the tangible and intangible assets acquired and the liabilities assumed are recorded as of the acquisition date at their respective fair values. The Company evaluates a business as an integrated set of activities and assets that is capable of being managed for the purpose of providing a return in the form of dividends, lower costs or other economic benefits and consists of inputs and processes that provide or have the ability to provide outputs. In an acquisition of a business, the excess of the fair value of the consideration transferred over the fair value of the net assets acquired is recorded as goodwill. In an acquisition of net assets that does not constitute a business, no goodwill is recognized.

The consolidated and combined financial statements include the results of operations of an acquired business after the completion of the acquisition.

Goodwill

Goodwill represents the excess of the purchase price over the fair value of the net assets acquired when accounted for using the acquisition method of accounting. Goodwill is not amortized; rather, it is evaluated for impairment within the Company’s single reporting unit on an annual basis, during the fourth quarter, or more frequently if an event occurs or circumstances change that would more-likely-than-not reduce the fair value of the Company’s reporting unit below its carrying amount. The Company performs a one-step quantitative test and records the amount of goodwill impairment, if any, as the excess of a reporting unit's carrying amount over its fair value, not to exceed the total amount of goodwill allocated to the reporting unit. The Company has not recognized any impairment charges related to goodwill to date.

Intangible assets, net

Intangible assets, net primarily consist of acquired core technology, net of accumulated amortization. The Company amortizes its intangible assets using the straight-line method over their estimated economic lives and periodically reviews for impairment. The Company has not recognized any impairment charges related to intangible assets to date.

Contingent consideration

Each reporting period, the Company remeasures the contingent consideration obligations associated with business combinations to their fair value and records within operating expenses increases or decreases in their fair value as change in fair value of contingent consideration within the consolidated and combined statements of operations and comprehensive loss. Changes in contingent consideration result from changes in the assumptions regarding probabilities of successful achievement of related milestones, the estimated timing in which the milestones may be achieved, and the discount rate used to estimate the fair value of the liability. Contingent consideration may change significantly as development of the Company’s programs in certain indications progress and additional data is obtained, impacting the Company’s assumptions. The assumptions used in estimating fair value require significant judgment. The use of different assumptions and judgments could result in a materially different estimate of fair value. See Note 4, Fair value measurements, for additional information.

Property, plant and equipment

Property, plant and equipment is stated at cost. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred. Depreciation and amortization is calculated using the straight-line method over the estimated useful lives of the assets, which are as follows:


Asset						Estimated useful life
Building						40 years
Computer equipment and software						3 years
Furniture and fixtures						2-5 years
Laboratory equipment						2-5 years
Leasehold improvements						Shorter of the useful life or remaining lease term

Impairment of long-lived assets

The Company reviews long-lived assets when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparison of the book values of the assets to future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value, which is measured based on the projected discounted future net cash flows arising from the assets.

Leases

Effective January 1, 2019, the Company adopted ASC 842, Leases (“ASC 842”) using the required modified retrospective approach and utilizing the effective date as its date of initial application.

At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the relevant facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and current and non-current lease liabilities, as applicable. The Company does not have material financing leases.

Operating lease liabilities and their corresponding right-of-use assets are initially recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate to discount lease payments, which reflects the rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. To estimate its incremental borrowing rate, a credit rating applicable to the Company is estimated using a synthetic credit rating analysis since the Company does not currently have a rating agency-based credit rating.

The Company has elected not to recognize leases with an original term of one year or less on the balance sheet. The Company typically only includes an initial lease term in its assessment of a lease arrangement. Options to renew a lease are not included in the Company’s assessment unless it is reasonably certain that the Company will exercise its renewal option.

Assumptions made by the Company at the commencement date are re-evaluated upon occurrence of certain events, including a lease modification. A lease modification results in a separate contract when the modification grants the lessee an additional right of use not included in the original lease and when lease payments increase commensurate with the stand-alone price for the additional right of use. When a lease modification results in a separate contract, it is accounted for in the same manner as a new lease.

In accordance with ASC 842, components of a lease should be separated into lease components and non-lease components. The fixed and in-substance fixed contract consideration must be allocated based on the relative stand-alone prices to the lease components and non-lease components.

Entities may elect not to separate lease and non-lease components. Rather, entities would account for each lease component and related non-lease component together as a single lease component. The Company has elected to account for lease and non-lease components together as a single lease component for all underlying assets and allocate all of the contract consideration to the lease component only.

For purposes of distinguishing between operating and financing leases, ASC 842 allows for the use of judgment in determining whether the lease term is for a major part of the remaining economic life of the underlying asset and whether the present value of lease payments represents substantially all of the fair value of the underlying asset. The Company applies the bright line thresholds referenced in ASC 842-10-55-2 to assist in evaluating leases for appropriate classification. The aforementioned bright lines are applied consistently to the Company’s entire portfolio of leases.

Common stock warrants

The Company's common stock warrants are evaluated pursuant to ASC 480, Distinguishing Liabilities from Equity ("ASC 480"), and ASC 815, Derivatives and Hedging ("ASC 815"). Management classifies its freestanding warrants as (i) liabilities, if the warrant terms allow settlement of the warrant exercise in cash, or (ii) equity, if the warrant terms only allow settlement in shares of common stock.

Revenue recognition

Under ASC Topic 606, Revenue from Contracts with Customers (“Topic 606”), an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price, including variable consideration, if any; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration to which it is entitled in exchange for the goods or services it transfers to the customer.

Once a contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and if so, they are considered performance obligations. The identification of material rights requires judgments related to the determination of the value of the underlying good or service relative to the option exercise price. The exercise of a material right is accounted for as a contract modification for accounting purposes.

The Company assesses whether each promised good or service is distinct for the purpose of identifying the performance obligations in the contract. This assessment involves subjective determinations and requires management to make judgments about the individual promised goods or services and whether such are separable from the other aspects of the contractual relationship. Promised goods and services are considered distinct provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer (that is, the good or service is capable of being distinct) and (ii) the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract (that is, the promise to transfer the good or service is distinct within the context of the contract). In assessing whether a promised good or service is distinct, the Company considers factors such as the license terms, the research, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. The Company also considers the intended benefit of the contract in assessing whether a promised good or service is separately identifiable from other promises in the contract. If a

promised good or service is not distinct, an entity is required to combine that good or service with other promised goods or services until it identifies a bundle of goods or services that is distinct.

The transaction price is determined and allocated to the identified performance obligations in proportion to their stand-alone selling prices (“SSP”) on a relative SSP basis. SSP is determined at contract inception and is not updated to reflect changes between contract inception and when the performance obligations are satisfied. Determining the SSP for performance obligations requires significant judgment. In developing the SSP for a performance obligation, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. The Company validates the SSP for performance obligations by evaluating whether changes in the key assumptions used to determine the SSP will have a significant effect on the allocation of arrangement consideration between multiple performance obligations.

If the consideration promised in a contract includes a variable amount, the Company estimates the amount of consideration to which it will be entitled in exchange for transferring the promised goods or services to a customer. The Company determines the amount of variable consideration by using the expected value method or the most likely amount method. The amount of variable consideration included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur when the uncertainty related to the variable consideration is resolved. At the end of each subsequent reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis in the period of adjustment.

If an arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received.

For arrangements with licenses of intellectual property that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes royalty revenue and sales-based milestones at the later of (i) when the related sales occur, or (ii) when the performance obligation to which the royalty has been allocated has been satisfied.

In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. The Company assessed each of its revenue generating arrangements in order to determine whether a significant financing component exists and concluded that a significant financing component does not exist in any of its arrangements.

The Company recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied, either at a point in time or over time, and if over time recognition is based on the use of an output or input method.

The Company recognizes revenue within the following financial statement captions:

Service revenue

To date, the Company’s service revenue has primarily been generated from the elements of its collaboration arrangement with BMS that are accounted for pursuant to Topic 606, using the five-step model described above. As discussed further below, the Company analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements (“ASC 808”) or Topic 606. For the elements of a collaboration arrangement which are more reflective of a vendor-customer relationship and therefore within the scope of Topic 606, the Company records the related revenue as service revenue on the consolidated and combined statement of

operations and comprehensive loss. Refer below for additional discussion around the Company’s policy for recognizing collaborative arrangement revenue and the determination of whether elements of a collaboration arrangement are within the scope of ASC 808 or Topic 606.

Collaborative arrangement revenue

To date, the Company’s collaborative arrangement revenue has been generated from its collaboration arrangements with BMS and Regeneron Pharmaceuticals, Inc. (“Regeneron”), as further described in Note 10, Collaborative arrangements and strategic partnerships.

The Company analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808, which includes determining whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of ASC 808 and those that are more reflective of a vendor-customer relationship and therefore within the scope of Topic 606 (refer above for further discussion of the Company's policy for recognizing service revenue pursuant to Topic 606). For elements of collaboration arrangements that are accounted for pursuant to ASC 808, an appropriate recognition method is determined and applied consistently, generally by analogy to Topic 606.

In arrangements where the Company does not deem its collaborator to be its customer, payments to and from its collaborator are presented in the consolidated and combined statements of operations and comprehensive loss based on the nature of the payments, as summarized in the table and further described below.


Nature of Payment						Statement of Operations Presentation
The Company's share of net profits in connection with commercialization of products						Collaborative arrangement revenue
The Company's share of net losses in connection with commercialization of products						Share of collaboration loss
Net reimbursement of the Company's research and development expenses						Collaborative arrangement revenue
Net reimbursement of the collaborator's research and development expenses						Research and development expense

Where the collaborator is the principal in the product sales, the Company recognizes its share of any profits or losses, representing net product sales less cost of goods sold and shared commercial and other expenses, in the period in which such underlying sales occur and costs are incurred by the collaborator. The Company also recognizes its share of costs arising from research and development activities performed by collaborators in the period its collaborators incur such expenses

Royalty and other revenue

The Company enters into out-licensing agreements that are within the scope of Topic 606. The Company does not have any material license arrangements that contain more than one performance obligation. The terms of such out-license agreements include the license of functional intellectual property, given the functionality of the intellectual property is not expected to change substantially as a result of the licensor’s ongoing activities, and typically include payment of one or more of the following: non-refundable up-front license fees; development and regulatory milestone payments and milestone payments based on the level of sales; and royalties on net sales of licensed products. Nonrefundable up-front license fees are recognized as revenue at a point in time when the licensed intellectual property is made available for the customer’s use and benefit, which is generally at the inception of the arrangement. Development and regulatory milestone fees, which are a type of variable consideration, are recognized as revenue to the extent that it is probable that a significant reversal will not occur. The

Company recognizes royalty revenue and sales-based milestones at the later of (i) when the related sales occur, or (ii) when the performance obligation to which the royalty has been allocated has been satisfied.

For a complete discussion of accounting for collaboration and other revenue-generating arrangements, see Note 10, Collaborative arrangements and strategic partnerships, and Note 11, Royalty and other revenue.

Research and development expenses

Research and development costs are charged to expense as costs are incurred in performing research and development activities, including salaries and benefits, facilities costs, overhead costs, clinical study and related clinical manufacturing costs, license and milestone fees, contract services, manufacturing costs for pre-launch inventory that did not qualify for capitalization, and other related costs. Up-front fees and milestones paid to third parties in connection with technologies that have not reached technological feasibility and do not have an alternative future use are expensed as research and development expense as incurred. In circumstances where amounts have been paid in excess of costs incurred, the Company records a prepaid expense. The Company accrues costs for clinical trial activities based upon estimates of the services received and related expenses incurred that have yet to be invoiced by the contract research organizations, clinical study sites, laboratories, consultants, or other clinical trial vendors that perform the activities. Where amounts owed to a collaboration partner exceed the Company’s collaborative arrangement revenues in each quarterly period, such amounts are classified as research and development expense.

Cost of royalty and other revenue

Cost of royalty and other revenue represents expense associated with amounts owed to third parties as a result of revenue recognized under the Company’s out-license arrangements.

Stock-based compensation

The Company’s share-based compensation programs grant awards that include stock options, restricted stock units, restricted stock awards, and shares issued under an employee stock purchase plan. Grants are awarded to employees and non-employees, including the Company's board of directors.

The Company accounts for its stock-based compensation awards in accordance with FASB ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all stock-based payments, including grants of stock options and restricted stock units and modifications to existing stock options, to be recognized in the consolidated and combined statements of operations and comprehensive loss based on their fair values.

The Company’s stock-based awards are subject to either service, performance-based, or market-based vesting conditions. Compensation expense related to awards with service-based vesting conditions is recognized on a straight-line basis based on the grant date fair value over the associated service period of the award, which is generally the vesting term. Compensation expense related to awards with performance-based vesting conditions is recognized based on the grant date fair value over the requisite service period using the accelerated attribution method to the extent achievement of the performance condition is probable.

The Company estimates the fair value of its option awards using the Black-Scholes option pricing model, which requires the input of subjective assumptions, including (i) the expected stock price volatility, (ii) the calculation of expected term of the award, (iii) the risk-free interest rate, and (iv) expected dividends. Due to the lack of company specific historical and implied volatility data, the Company bases its estimate of expected volatility on the estimate and expected volatilities of a representative group of publicly traded companies. For these analyses, the Company selects companies with comparable characteristics including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected life of the stock-based awards. It will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. The Company has estimated the expected term of its employee stock options using the “simplified” method, whereby, the expected term equals the arithmetic average of the vesting term and the original contractual term of the option due to its lack of sufficient historical data. For stock options that were converted in accordance with the Employee Matters Agreement, as further described in Note 13, Stock-based

compensation, the Company estimated the expected term to be the remaining contractual term of the awards as of the date of the separation. The risk-free interest rates for periods within the expected term of the option are based on the U.S. Treasury securities with a maturity date commensurate with the expected term of the associated award. The Company has never paid, and does not expect to pay, dividends in the foreseeable future.

For performance-based restricted stock units that vest based on a total shareholder return metric, the vesting condition is considered a market condition as it vests based on the movement in share price of a company. The impact of the market condition is reflected in the award’s fair value on the grant date, and the expense is recognized irrespective of whether the market condition is achieved as long as the required service is provided.

The Company accounts for forfeitures as they occur. Stock-based compensation expense recognized in the financial statements is based on awards for which performance or service conditions are expected to be satisfied.

Other income, net

For periods prior to the separation, other income, net consisted primarily of income resulting from the allocation of facility-related, depreciation and amortization expense to bluebird bio for its proportional use of assets that were attributed to the Company as well as expense resulting from the allocation of facility-related, depreciation and amortization expense to the Company for its proportional use of bluebird bio assets that were not attributed to the Company. Other income, net also includes immaterial gains and losses on disposal of assets.

Net loss per share

Basic net loss per share is calculated by dividing net loss attributable to common stockholders by the weighted average number of common shares outstanding during the period, including the shares of common stock issuable upon the exercise of warrants that are exercisable for little or no consideration. Diluted net income per share is calculated by dividing the net income attributable to common stockholders by the weighted-average number of common equivalent shares outstanding for the period, including the shares of common stock issuable upon the exercise of warrants that are exercisable for little or no consideration as well as any dilutive effect from outstanding stock options, unvested restricted stock, restricted stock units, and employee stock purchase plan stock using the treasury stock method. Given that the Company recorded a net loss for each of the periods presented, there is no difference between basic and diluted net loss per share since the effect of common stock equivalents would be anti-dilutive and are, therefore, excluded from the diluted net loss per share calculation.

The Company follows the two-class method when computing net loss per share in periods when issued shares that meet the definition of participating securities are outstanding. The two-class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to received dividends as if all income for the period had been distributed. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders when participating securities are outstanding, losses are not allocated to the participating securities.

Prior to November 4, 2021, there were no shares of the Company outstanding. As such, the shares outstanding immediately after the distribution, including the shares of common stock issuable upon the exercise of warrants that are exercisable for little or no consideration, were used to calculate the basic and diluted net loss per share for all historical periods presented.

Income taxes

For periods prior to the separation, income taxes as presented in the combined financial statements of 2seventy bio attribute current and deferred income taxes of bluebird bio to 2seventy bio in a manner that is systematic, rational and consistent with the asset and liability method prescribed by FASB ASC Topic 740: Income Taxes (“ASC 740”). Accordingly, 2seventy bio’s income tax provision for periods prior to the separation was prepared following the separate return method. The separate return method applies ASC 740 to the stand-alone financial statements of each member of the consolidated group as if each group member was a separate taxpayer and

a stand-alone enterprise. The calculation of the Company's income taxes on a separate return basis requires a considerable amount of judgment and use of both estimates and allocations. As a result, actual transactions included in the consolidated financial statements of bluebird bio may not be included in the separate combined financial statements of 2seventy bio. Similarly, the tax treatment of certain items reflected in the combined financial statements of 2seventy bio may not be reflected in the consolidated financial statements and tax returns of bluebird bio. Therefore, items such as net operating losses, credit carryforwards and valuation allowances may exist in the Company's stand-alone financial statements that may or may not exist in bluebird bio’s consolidated financial statements. As such, the income taxes of 2seventy bio as presented for periods prior to the separation may not be indicative of the income taxes that 2seventy bio will generate in the future.

The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Valuation allowances are provided, if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. The Company accrues for potential interest and penalties related to unrecognized tax benefits in income tax expense.

In general, for periods prior to the separation, the taxable income (loss) of bluebird bio, including any taxable income (loss) attributed to 2seventy bio, was included in bluebird bio’s consolidated tax returns. As such, separate income tax returns were not prepared for 2seventy bio prior to the separation. Consequently, for periods prior to the separation any income taxes currently payable by 2seventy bio are deemed to have been remitted to bluebird bio, in cash, in the period prior to the separation in which the liability arose, and income taxes currently receivable by 2seventy bio are deemed to have been received from bluebird bio in the period in which the receivable arose.

Comprehensive loss

Comprehensive loss is composed of net loss and other comprehensive income (loss). Other comprehensive income (loss) consists of unrealized gains and losses on debt securities.

Recent accounting pronouncements

Recently adopted

ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes

In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify the accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The new standard was effective beginning January 1, 2021. The adoption of ASU 2019-12 did not have a material impact on the Company's financial position or results of operations upon adoption.

ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity

In August 2020, the FASB issued ASU 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU 2020-06”). ASU 2020-06 simplifies the complexity associated with applying U.S. GAAP for certain financial instruments with characteristics of liabilities

and equity. More specifically, the amendments focus on the guidance for convertible instruments and the derivative scope exception for contracts in an entity's own equity. The Company early adopted the new standard, effective January 1, 2021. The adoption of ASU 2020-06 did not have an impact on the Company's financial position or results of operations upon adoption.

ASU No. 2020-08, Codification Improvements to Subtopic 310-20, Receivables - Nonrefundable Fees and Other Costs

In October 2020, the FASB issued ASU 2020-08, Codification Improvements to Subtopic 310-20, Receivables - Nonrefundable Fees and Other Costs (“ASU 2020-08”) to provide further clarification and update the previously issued guidance in ASU 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20: Premium Amortization on Purchased Callable Debt Securities) (“ASU 2017-08”). ASU 2017-08 shortened the amortization period for certain callable debt securities purchased at a premium by requiring that the premium be amortized to the earliest call date. ASU 2020-08 requires that at each reporting period, to the extent that the amortized cost of an individual callable debt security exceeds the amount repayable by the issuer at the next call date, the excess premium shall be amortized to the next call date. The new standard was effective beginning January 1, 2021. The adoption of ASU 2020-08 did not have a material impact on the Company's financial position or results of operations upon adoption.

ASU No. 2020-10, Codification Improvements

In October 2020, the FASB issued ASU 2020-10, Codification Improvements ("ASU 2020-10"). The amendments in this ASU represent changes to clarify the ASC, correct unintended application of the guidance, or make minor improvements to the ASC that are not expected to have a significant effect on current accounting practice or create a significant administrative cost to most entities. This new standard was effective beginning January 1, 2021. The adoption of ASU 2020-10 did not have a material impact on the Company's financial position or results of operations upon adoption.

Marketable securities

12 Months Ended

Dec. 31, 2021

Investments, Debt and Equity Securities [Abstract]

Marketable securities

The following table summarizes the marketable securities held at December 31, 2021 (in thousands):


	Amortized cost/ cost		Unrealized gains		Unrealized losses		Fair Value
December 31, 2021
U.S. government agency securities and treasuries	$	128,899	$	—	$	(507)	$	128,392
Corporate bonds	49,368		$	—	(58)		49,310
Commercial paper	54,065		$	—	—		54,065
Total	$	232,332	$	—	$	(565)	$	231,767

As of December 31, 2020, the Company did not have any marketable securities. No available-for-sale debt securities held as of December 31, 2021 had remaining maturities greater than five years.

Fair value measurements

12 Months Ended

Dec. 31, 2021

Fair Value Disclosures [Abstract]

Fair value measurements

The following table sets forth the Company’s assets and liabilities that are measured at fair value on a recurring basis as of December 31, 2021 and 2020 (in thousands):


	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
December 31, 2021
Assets:
Cash and cash equivalents	$	130,414	$	130,414	$	—	$	—
Marketable securities:
U.S. government agency securities and treasuries	128,392		—		128,392		—
Corporate bonds	49,310		—		49,310		—
Commercial paper	54,065		—		54,065		—
Total assets	$	362,181	$	130,414	$	231,767	$	—
Liabilities:
Contingent consideration	$	1,948	$	—	$	—	$	1,948
Total liabilities	$	1,948	$	—	$	—	$	1,948
December 31, 2020
Liabilities:
Contingent consideration	$	1,509	$	—	$	—	$	1,509
Total liabilities	$	1,509	$	—	$	—	$	1,509

As of December 31, 2020, the Company did not hold any assets that were measured at fair value on a recurring basis.

Marketable securities

Marketable securities classified as Level 2 within the valuation hierarchy generally consist of U.S. government agency securities and treasuries, corporate bonds, and commercial paper. The Company estimates the fair values of these marketable securities by taking into consideration valuations obtained from third-party pricing sources. These pricing sources utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include market pricing based on real-time trade data for the same or similar securities, issuer credit spreads, benchmark yields, and other observable inputs. The Company validates the prices provided by its third-party pricing sources by understanding the models used, obtaining market values from other pricing sources and analyzing pricing data in certain instances.

The amortized cost of available-for-sale debt securities is adjusted for amortization of premiums and accretion of discounts to the earliest call date for premiums or to maturity for discounts. At December 31, 2021, the balance in the Company’s accumulated other comprehensive loss was composed primarily of activity related to the Company’s available-for-sale debt securities. There were no material realized gains or losses recognized on the sale or maturity of available-for-sale securities during the year ended December 31, 2021.

Accrued interest receivable on the Company's available-for-sale debt securities totaled $0.4 million as of December 31, 2021. No accrued interest receivable was written off during the twelve months ended December 31, 2021.

The following table summarizes available-for-sale debt securities in a continuous unrealized loss position for less than and greater than twelve months, and for which an allowance for credit losses has not been recorded at December 31, 2021 (in thousands):


	Less than 12 months				12 months or greater				Total
Description	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
December 31, 2021
U.S. government agency securities and treasuries	$	111,190	$	(507)	$	—	$	—	$	111,190	$	(507)
Corporate bonds	48,940		(58)		—		—		48,940		(58)
Total	$	160,130	$	(565)	$	—	$	—	$	160,130	$	(565)

The Company determined that there was no material change in the credit risk of the above investments during the twelve months ended December 31, 2021. As such, an allowance for credit losses was not recognized. As of December 31, 2021, the Company does not intend to sell such securities and it is not more likely than not that the Company will be required to sell the securities before recovery of their amortized cost bases.

Contingent consideration

In connection with bluebird bio's prior acquisition of Precision Genome Engineering, Inc. (“Pregenen”), the Company may be required to pay future consideration that is contingent upon the achievement of specified development, regulatory approvals or sales-based milestone events. Contingent consideration is measured at fair value and is based on significant unobservable inputs, which represents a Level 3 measurement within the fair value hierarchy. The valuation of contingent consideration uses assumptions the Company believes would be made by a market participant. The Company assesses these estimates on an on-going basis as additional data impacting the assumptions is obtained. Future changes in the fair value of contingent consideration related to updated assumptions and estimates are recognized within the consolidated and combined statements of operations and comprehensive loss. In the absence of new information related to the probability of milestone achievement, changes in fair value will reflect changing discount rates and the passage of time. Contingent consideration is included in other non-current liabilities on the consolidated and combined balance sheets.

The table below provides a roll-forward of fair value of the Company’s contingent consideration obligations that include Level 3 inputs (in thousands):


	Year ended December 31,
	2021		2020
Beginning balance	$	1,509	$	7,977
Additions	—		—
Changes in fair value	439		(6,468)
Payments	—		—
Ending balance	$	1,948	$	1,509

Please refer to Note 8, Commitments and contingencies, for further information.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Property, plant and equipment, net

12 Months Ended

Dec. 31, 2021

Property, Plant and Equipment [Abstract]

Property, plant and equipment, net

Property, plant and equipment, net, consists of the following (in thousands):


	As of December 31,
	2021		2020
Land	$	—	$	1,210
Building	—		15,745
Computer equipment and software	5,260		6,503
Office equipment	6,080		6,588
Laboratory equipment	31,710		24,080
Leasehold improvements	28,479		28,305
Construction-in-progress	3,462		91,631
Total property, plant and equipment	74,991		174,062
Less accumulated depreciation and amortization	(40,078)		(30,037)
Property, plant and equipment, net	$	34,913	$	144,025

Depreciation and amortization expense related to property, plant and equipment was $12.1 million, $9.4 million, and $8.8 million for the years ended December 31, 2021, 2020, and 2019, respectively.

North Carolina manufacturing facility

In November 2017, bluebird bio acquired a manufacturing facility in Durham, North Carolina for the future manufacture of lentiviral vectors for its gene therapies. This manufacturing facility was primarily dedicated to the Company's operations and, accordingly, prior to the sale of the facility as described below, was to be attributed to the Company in connection with the separation. Construction-in-progress as of December 31, 2020 includes $91.1 million related to the North Carolina manufacturing facility.

In July 2021, bluebird bio and National Resilience, Inc. ("Resilience") announced a strategic manufacturing collaboration aimed to accelerate the early research, development, and delivery of cell therapies. Agreements related to the collaboration were executed in September 2021. As part of the agreements, Resilience acquired bluebird bio's North Carolina manufacturing facility and retained all staff employed at the site. As a result, bluebird bio disposed of $111.2 million of net assets, primarily consisting of the building and laboratory equipment. Prior to its disposal by bluebird bio, the North Carolina manufacturing facility was to be attributed to the Company and, accordingly, the manufacturing facility was included within the Company’s financial statements prior to its disposal. The disposition of the net assets of the North Carolina manufacturing facility has been reflected as a transfer to bluebird bio via net parent investment as a result of bluebird bio’s sale of such facility. Please refer to Note 10, Collaborative arrangements and strategic partnerships, for further discussion.

Accrued expenses and other current liabilities

12 Months Ended

Dec. 31, 2021

Payables and Accruals [Abstract]

Accrued expenses and other current liabilities

Accrued expenses and other current liabilities consist of the following (in thousands):


	As of December 31,
	2021		2020
Employee compensation	$	24,655	$	9,451
Royalties	6,768		1,493
Manufacturing costs	5,459		6,808
Clinical and contract research organization costs	3,229		2,854
Collaboration research costs	2,576		19,605
Property, plant, and equipment	2,241		440
Professional fees	1,688		—
Separation related costs	762		—
License and milestone fees	123		278
Other	7,909		2,418
Total accrued expenses and other current liabilities	$	55,410	$	43,347

Leases

12 Months Ended

Dec. 31, 2021

Leases [Abstract]

Leases

The Company leases certain office and laboratory space that was attributed to it in connection with the separation.

60 Binney Street lease

In September, 2015, bluebird bio entered into a lease agreement, which was attributed to the Company in connection with the separation. This is the Company’s corporate headquarters and includes office and laboratory space located in a building (the “Building”) at 60 Binney Street, Cambridge, Massachusetts (the “60 Binney Street Lease”). Under the terms of the 60 Binney Street Lease, starting on October 1, 2016, bluebird bio leased approximately 253,108 square feet of office and laboratory space at $72.50 per square foot per year, or $18.4 million per year in base rent, which is subject to scheduled annual rent increases of 1.75% plus certain operating expenses and taxes. bluebird bio historically maintained a $13.8 million collateralized letter of credit which, subject to the terms of the lease and certain reduction requirements specified therein, including market capitalization requirements, may decrease to $9.2 million over time. As the Company did not have legal ownership over any bank accounts prior to the separation, there were no cash and cash equivalent balances specifically attributable to the Company for the periods prior to the separation and, accordingly, no restricted cash is reflected in the consolidated and combined financial statements related to the letter of credit for periods prior to the separation. Pursuant to a work letter entered into in connection with the 60 Binney Street Lease, the landlord contributed an aggregate of $42.4 million toward the cost of construction and tenant improvements for the Building. The lease would continue until March 31, 2027.

In October 2021, bluebird bio entered into a consent to assignment and amendment to its lease agreement for its 60 Binney Street lease, pursuant to which bluebird bio's interest in the lease was assigned to the Company. In November 2021, the Company executed a $25.0 million letter of credit related to this lease. Under the assigned and amended lease agreement, the lease term was extended through March 31, 2034 with the 2022 base rent being $90.00 per square foot per year, or $22.8 million per year in base rent, subject to scheduled annual rent increases of 3.0% plus certain operating expenses and taxes. Starting April 1, 2026, the base rent will reset to $118.41 per square foot per year, or $30.0 million per year in base rent, subject to scheduled annual rent increases of 3.0% plus certain operating expenses and taxes. Pursuant to a work letter entered into in connection with the 60 Binney Street assignment and amended lease agreement, the landlord agreed to contribute up to an aggregate of $19.1 million toward the cost of tenant improvements for the leased space. As of December 31, 2021, the Company did not incur any tenant improvement costs.

The Company has classified this lease as an operating lease and recorded a right-of-use asset and lease liability. The Company is recognizing rent expense on a straight-line basis throughout the remaining term of the lease.

Seattle, Washington leases

In July 2018, bluebird bio entered into a lease agreement for office and laboratory space located in a portion of a building in Seattle, Washington, and moved into the facility in June 2019. This lease was assigned to the Company in connection with the separation. The lease was amended in October 2018 to increase the total rentable space to approximately 36,126 square feet at $54.00 per square foot in base rent per year, which is subject to scheduled annual rent increases of 2.5% plus certain operating expenses and taxes. The lease commenced on January 1, 2019 and the lease term will continue through January 31, 2027. The Company has classified this lease as an operating lease and recorded a right-of-use asset and lease liability at lease commencement.

In September 2019, bluebird bio entered into a second amendment to the lease (the “Second Amendment”). The Second Amendment added approximately 22,188 square feet to the existing space and extended the lease term of the entire premises by 16 months, or until April 2028. Fixed monthly rent for the expanded space will be incurred at a rate of $62.80 per square foot per year beginning in January 2021, subject to annual increases of 2.5%. The Second Amendment includes a five-year option to extend the term.

The execution of the Second Amendment was deemed to be a lease modification representing two separate contracts under ASC 842. One contract is related to a new right-of-use for the expanded 22,188 square feet of space, which is to be accounted for as a new lease, and the other is related to the modification of term for the original 36,126 square feet of space. An additional right-of-use asset and lease liability was recognized upon lease commencement of the expanded space. In September 2020, bluebird bio entered into a sublease agreement for the 22,188 square feet added under the Second Amendment at a fixed monthly rent of $62.80 per square foot per year beginning in January 2021, subject to annual increases of 2.5%. The sublease term will continue through April 2028.

In October 2021, bluebird bio entered into a consent to assignment and amendment to its lease agreement for office and laboratory space in Seattle, Washington and the related sublease that was executed in September 2020 for a portion of the space. The agreement reassigns bluebird bio’s interest in the lease and the sublease to the Company. In November 2021, the Company executed a $5.0 million letter of credit related to this lease.

The Company is recognizing rent expense on a straight-line basis through the remaining extended term of the respective leases. The head lease and the sublease will be accounted for as two separate contracts with the income from the sublease presented separately from the lease expense on the head lease.

Summary of all lease costs recognized under ASC 842

The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the years ended December 31, 2021, 2020 and 2019 (in thousands):


	For the year ended December 31,
	2021			2020			2019
Lease cost (1)
Operating lease cost	$	24,838		$	22,454		$	21,406
Total lease cost	$	24,838		$	22,454		$	21,406

Other information
Operating cash flows used for operating leases	$	25,489		$	19,632		$	19,521
Weighted average remaining lease term	11.8 years			6.4 years			7.4 years
Weighted average discount rate	5.47		%	6.72		%	6.73		%

________________

(1)Short-term lease costs and variable lease costs incurred by the Company for the twelve months ended December 31, 2021, 2020 and 2019 were immaterial.

Rent expense is calculated on a straight-line basis over the term of the lease. Rent expense recognized under all leases, including additional charges for utilities, parking, maintenance, and real estate taxes that are not included

within lease costs in the table above, was $34.5 million, $32.5 million, and $30.6 million for the years ended December 31, 2021, 2020 and 2019, respectively.

As of December 31, 2021, future minimum commitments under ASC 842 under the Company’s operating leases were as follows (in thousands):


Maturity of lease liabilities	As of December 31, 2021
2022	$	27,078
2023	27,864
2024	28,675
2025	29,501
2026	32,920
2027 and thereafter	250,383
Total lease payments	396,421
Less: imputed interest	(114,206)
Total operating lease liabilities	$	282,215

Commitments and contingencies

12 Months Ended

Dec. 31, 2021

Commitments and Contingencies Disclosure [Abstract]

Commitments and contingencies

Lease commitments

2seventy bio leases certain office and laboratory space. Refer to Note 7, Leases, for further information on the terms of these lease agreements.

Contingent consideration related to business combinations

On June 30, 2014, bluebird bio acquired Pregenen. All assets and liabilities related to the Pregenen acquisition, including the resulting goodwill and contingent consideration, were attributed to the Company in connection with the separation. The Company may be required to make up to an additional $99.9 million in remaining future contingent cash payments to the former equityholders of Pregenen upon the achievement of certain commercial milestones related to the Pregenen technology. In accordance with accounting guidance for business combinations, contingent consideration liabilities are required to be recognized on the consolidated and combined balance sheets at fair value. Estimating the fair value of contingent consideration requires the use of significant assumptions primarily relating to probabilities of successful achievement of certain clinical and commercial milestones, the expected timing in which these milestones will be achieved and discount rates. The use of different assumptions could result in materially different estimates of fair value.

Other funding commitments

Certain agreements that were assigned by bluebird bio to the Company in connection with the separation relate principally to licensed technology and may require future payments relating to milestones that may be met in subsequent periods or royalties on future sales of specified products. These agreements include the collaboration agreements entered into with BMS and Regeneron and the agreements entered into with Resilience, all of which were assigned to the Company in connection with the separation. Additionally, to the extent an agreement relating to licensed technology was not attributed to the Company, bluebird bio entered into a sublicense with the Company, which may require future milestone and/or royalty payments. Please refer to Note 10, Collaborative arrangements and strategic partnerships, for further information on the BMS, Regeneron, and Resilience agreements and Note 11, Royalty and other revenue, for further information on license agreements.

Based on the Company's development plans as of December 31, 2021, the Company may be obligated to make future development, regulatory and commercial milestone payments and royalty payments on future sales of specified products. Payments under these agreements generally become due and payable upon achievement of such milestones or sales. When the achievement of these milestones or sales has not occurred, such contingencies are not

recorded in the Company’s financial statements. As further discussed in Note 10, Collaborative arrangements and strategic partnerships, BMS assumed responsibility for amounts due to licensors as a result of any future ex-U.S. sales of ABECMA.

Concurrent with the sale of the manufacturing facility in Durham, North Carolina, bluebird bio also entered into a commercial supply agreement and a development manufacturing supply agreement with Resilience. Certain rights and obligations under the asset purchase agreement and certain of the ancillary agreements, including these two manufacturing agreements, among others, were assigned by bluebird bio to 2seventy bio on November 4, 2021 upon the separation of 2seventy bio from bluebird bio. The assignments under the asset purchase agreement and the development manufacturing supply agreement commit the Company to reimburse Resilience for an amount equal to 50% of the net operating losses of and relating to the manufacturing facility’s business incurred during the twelve-month period ending on the first anniversary of the closing of the transaction, as calculated in accordance with the asset purchase agreement, subject to a cap of $15.0 million. As of December 31, 2021, the Company has accrued $2.6 million related to the net operating losses of Resilience. In exchange, under the terms of the development manufacturing supply agreement, the Company will receive up to eight batches of lentiviral vector during the twelve-month period ending on the first anniversary of the closing of the transaction. The Company has therefore committed to a minimum purchase equal to at least the Company's 50% share of the net operating losses during the twelve-month period ending on the first anniversary of the closing of the transaction. Please refer to Note 10, Collaborative arrangements and strategic partnerships, for further discussion.

Additionally, 2seventy bio is party to various contracts with contract research organizations and contract manufacturers that generally provide for termination on notice, with the exact amounts in the event of termination to be based on the timing of the termination and the terms of the agreement.

The Company has various manufacturing development and license agreements to support clinical and commercial product needs. The following table presents non-cancelable contractual obligations arising from these arrangements:


Years ended December 31,	Purchase commitment
2022	$	15,750
Total purchase commitments	$	15,750

In January 2022, the Company entered into an agreement with a contract manufacturer which includes non-cancelable contractual obligations of $7.2 million for the year ended December 31, 2022.

Litigation

From time to time, the Company expects to be party to various claims and complaints arising in the ordinary course of business. However, the Company is not currently a party to any litigation or legal proceedings that, in the opinion of its management, are probable of having a material adverse effect on its business. The Company enters into standard indemnification agreements in the ordinary course of business. Pursuant to these agreements, the Company indemnifies, holds harmless, and agrees to reimburse the indemnified party for losses suffered or incurred by the indemnified party, generally the Company’s business partners. In addition, pursuant to the separation agreement, the Company indemnifies, holds harmless, and agrees to reimburse bluebird bio for its indemnification obligations with respect to the Company’s business partners, relating to the Company’s business or arising out of the Company’s activities, in the past or to be conducted in the future. The term of these indemnification agreements is generally perpetual any time after execution of the agreement. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited. Management does not believe that any ultimate liability resulting from any of these claims will have a material adverse effect on its results of operations, financial position, or liquidity. However, management cannot give any assurance regarding the ultimate outcome of any claims, and their resolution could be material to operating results for any particular period.

The Company indemnifies each of its directors and officers for certain events or occurrences, subject to certain limits, while the officer or director is or was serving at the Company’s request in such capacity, as permitted under

Delaware law and in accordance with its certificate of incorporation and by-laws. The term of the indemnification period will last as long as a director or officer may be subject to any proceeding arising out of acts or omissions of such director or officer in such capacity. The maximum amount of potential future indemnification is unlimited; however, the Company holds director and officer liability insurance .

Stockholders' equity

12 Months Ended

Dec. 31, 2021

Equity [Abstract]

Stockholders' equity

Stockholders’ equity

The Company is authorized to issue 200.0 million shares of common stock. Holders of common stock are entitled to one vote per share. Holders of common stock are entitled to receive dividends, if and when declared by the Company’s board of directors, and to share ratably in the Company’s assets legally available for distribution to the Company’s shareholders in the event of liquidation. Holders of common stock have no preemptive, subscription, redemption or conversion rights. As of December 31, 2021, the Company had 23.6 million shares of common stock issued and outstanding. As of December 31, 2020, the Company had no shares of common stock authorized, issued or outstanding.

In November 2021, the Company issued 23,368,988 shares of its common stock to bluebird bio in connection with the separation.

In November 2021, the Company issued to certain institutional investors (who previously purchased pre-funded warrants to purchase shares of bluebird bio common stock) pre-funded warrants to purchase 757,575 shares of the Company’s common stock at an exercise price of $0.0001 per share. The pre-funded warrants can be exercised at any time or times on or after November 4, 2021, until exercised in full. The warrants have been evaluated to determine the appropriate accounting and classification pursuant to ASC 480 and ASC 815. Based on the terms of the pre-funded warrants, management concluded that they should be classified within stockholders’ equity on the Company’s consolidated and combined balance sheets, with no subsequent remeasurement as long as the underlying warrant agreements are not modified or amended.

The Company is authorized to issue 10.0 million shares of preferred stock in one or more series and to fix the powers, designations, preferences and relative participating option or other rights thereof, including dividend rights, conversion rights, voting rights, redemption terms, liquidation preferences and the number of shares constituting any series, without any further vote or action by the Company’s shareholders. As of December 31, 2021, the Company had no shares of preferred stock issued or outstanding. As of December 31, 2020, the Company had no shares of preferred stock authorized, issued or outstanding.

Reserved for future issuance

The Company has reserved for future issuance the following number of shares of common stock (in thousands):


	As of December 31,
	2021		2020
Options to purchase common stock (1)	$	1,490	$	—
Restricted stock units (1)	1,080		—
2021 Stock Option and Incentive Plan	2,125		—
2021 Employee Stock Purchase Plan	233		—
Pre-funded warrants to purchase common stock	758
Total	$	5,686	$	—

(1)Outstanding stock options and restricted stock units include awards outstanding to employees of bluebird bio.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-Subparagraph (b)
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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-Section 50
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-Subparagraph (d)
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496180-112644

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
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-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Collaborative arrangements and strategic partnerships

12 Months Ended

Dec. 31, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Collaborative arrangements and strategic partnerships

Bristol Myers Squibb

BMS Collaboration Agreement

In March 2013, bluebird bio entered into a Master Collaboration Agreement (the “BMS Collaboration Agreement”) with Celgene (now BMS following its acquisition of Celgene in November 2019) to discover, develop and commercialize potentially disease-altering gene therapies in oncology and a Platform Technology Sublicense Agreement (the “Sublicense Agreement”) with BMS pursuant to which bluebird bio obtained a sublicense to certain intellectual property from BMS, originating under BMS’s license from Baylor College of Medicine, for use in the collaboration.

Under the terms of the BMS Collaboration Agreement, the Company received an up-front, non-refundable, non-creditable payment of $75.0 million. The Company was responsible for conducting discovery, research, and development activities through completion of phase 1 clinical trials, if any, during the initial term of the BMS Collaboration Agreement, or three years.

Subsequently, bluebird bio and BMS executed various amendments, summarized as follows. These agreements were assumed by the Company in connection with the separation.

In June 2015, both parties amended and restated the BMS Collaboration Agreement (the “Amended BMS Collaboration Agreement”) to narrow the focus of the collaboration to exclusively work on anti-B-cell maturation antigen (“BCMA”) product candidates for a new three-year term. In connection with the Amended BMS Collaboration Agreement, the Company received an up-front, non-refundable, non-creditable payment of $25.0 million to fund research and development under the collaboration.

On a product candidate-by-product candidate basis, up through a specified period following enrollment of the first patient in an initial phase 1 clinical trial for such product candidate, BMS had an option to obtain an exclusive worldwide license to develop and commercialize such product. Following BMS’s license of each product candidate, the Company is entitled to elect to co-develop and co-promote each product candidate in the United States.

BMS Ide-cel related agreements

In February 2016, BMS exercised its option to obtain an exclusive worldwide license to develop and commercialize ide-cel, the first product candidate under the Amended BMS Collaboration Agreement, pursuant to an executed license agreement (“Ide-cel License Agreement”) and paid the Company the associated $10.0 million option fee. Pursuant to the Ide-cel License Agreement, BMS was responsible for development and related funding of ide-cel after the substantial completion of the phase 1 clinical trial. The Company was responsible for the manufacture of vector and associated payload throughout development and, upon BMS’s request, throughout commercialization, the costs of which were reimbursable by BMS in accordance with the terms of the Amended and Restated Co-Development, Co-Promote and Profit Share Agreement, as further described below. BMS was responsible for the manufacture of drug product throughout development and commercialization. Under the Ide-cel License Agreement, the Company was eligible to receive (i) U.S. milestones of up to $85.0 million for the first indication to be addressed by ide-cel and royalties for U.S. sales of ide-cel and (ii) ex-U.S. milestones of up to $55.0 million and royalties for ex-U.S. sales of ide-cel.

In March 2018, the Company elected to co-develop and co-promote ide-cel within the United States pursuant to the execution of the Amended and Restated Co-Development, Co-Promote and Profit Share Agreement (“Ide-cel CCPS”), which replaced the Ide-cel License Agreement. As a result of executing the Ide-cel CCPS, the Company will share equally in all profits and losses relating to developing, commercializing and manufacturing ide-cel within the United States and has the right to participate in the development and promotion of ide-cel in the United States. BMS is responsible for the costs incurred to manufacture vector and associated payload for use outside of the United States, plus a markup. As a result of electing to co-develop and co-promote ide-cel within the United States, the milestones and royalties payable under the Ide-cel License Agreement were adjusted. Under the Ide-cel CCPS, the Company was eligible to receive a $10.0 million milestone related to the development of ide-cel in the United States and, for the first indication to be addressed by ide-cel, ex-U.S. regulatory and commercial milestones of up to $60.0 million. Under the Ide-cel CCPS, the $10.0 million milestone related to the development of ide-cel in the United States was achieved in the second quarter of 2019 and subsequently paid by BMS.

BMS bb21217 License Agreement

In September 2017, BMS exercised its option to obtain an exclusive worldwide license to develop and commercialize bb21217, an investigational BCMA-targeted CAR T cell therapy, the second product candidate under the Amended BMS Collaboration Agreement, pursuant to an executed license agreement (“bb21217 License Agreement”) and paid the Company an option fee of $15.0 million. Pursuant to the bb21217 License Agreement, BMS is responsible for development and related funding of bb21217 after the substantial completion of the ongoing phase 1 clinical trial. In 2019, the parties amended the protocol for the ongoing phase 1 clinical trial to enroll additional patients for which the Company will be reimbursed based upon an agreed-upon amount per patient. Under the bb21217 License Agreement, the Company is eligible to receive U.S. milestones of up to $85.0 million for the first indication to be addressed by bb21217 and royalties for U.S. sales of bb21217. Additionally, the Company was eligible to receive ex-U.S. milestones of up to $55.0 million and royalties for ex-U.S. sales of bb21217.

May 2020 Amendments to Ide-cel and bb21217 agreements

In May 2020, the First Amendment to the Amended and Restated Co-Development, Co-Promote and Profit Share Agreement (as amended, the "Amended Ide-cel CCPS") and the Second Amended and Restated License Agreement ("Amended bb21217 License Agreement" and, collectively with the Amended Ide-cel CCPS, the “May 2020 Amendments”), which replaced the bb21217 License Agreement, was executed. Under the Amended Ide-cel CCPS, the parties will continue to share equally in all profits and losses related to developing, commercializing and manufacturing ide-cel within the United States. However, the Amended Ide-cel CCPS changed the Company’s responsibilities with respect to manufacturing activities. Under the Amended Ide-cel CCPS, BMS assumed the contract manufacturing agreements related to ide-cel adherent lentiviral vector. Over time, BMS is also assuming responsibility for manufacturing ide-cel suspension lentiviral vector outside of the United States, with the Company responsible for manufacturing ide-cel suspension lentiviral vector in the United States.

Under the Amended bb21217 License Agreement, over time, BMS is assuming responsibility for manufacturing suspension lentiviral vector outside of the United States, with the Company responsible for manufacturing suspension lentiviral vector in the United States. Under the Amended bb21217 License Agreement, expenses incurred by the Company associated with these activities are fully reimbursable by BMS at cost plus a mark-up. Throughout both development and commercialization, BMS is responsible for the manufacture of drug product.

The May 2020 Amendments relieved BMS of its obligations to pay the Company for future ex-U.S. milestones and royalties on ex-U.S. sales for each of ide-cel and bb21217 in exchange for an up-front, non-refundable, non-creditable payment of $200.0 million, which represents the aggregate of the probability-weighted, net present value of the future ex-U.S. milestones and royalties on ex-U.S. sales for each of ide-cel and bb21217. In addition, the parties are released from future exclusivity related to BCMA-directed T cell therapies. There are no remaining milestones or royalties under the Amended Ide-cel CCPS.

In March 2021, the FDA approved the marketing of Ide-cel as ABECMA in the United States for the treatment of adult patients with relapsed or refractory multiple myeloma after four or more prior lines of therapy, including an immunomodulatory agent, a proteasome inhibitor, and an anti-CD38 monoclonal antibody. Under the Amended Ide-cel CCPS, BMS is primarily responsible for the commercialization of ABECMA and the Company has concluded BMS is the principal for such activities for purposes of applying its ASC 808 accounting policy to the Amended Ide-cel CCPS. As previously described, under the collaboration arrangement with BMS, the Company has an option to co-develop and co-promote bb21217 within the United States. However, following completion of the CRB-402 clinical trial, and based in part on ABECMA clinical data and commercial sales to date, in January 2022 the Company, along with BMS, evaluated its plans with respect to bb21217 and does not expect to co-develop and co-promote bb21217. Because the Company does not intend to exercise this option, it expects to receive an additional fee in the amount of $10.0 million from BMS pursuant to the terms of the collaboration arrangement. Under this scenario, there would be no change to the U.S. milestones and royalties for U.S. sales of bb21217, as previously described above, for which the Company would be eligible to receive.

Accounting Analysis

Amended Ide-cel CCPS and Amended bb21217 License Agreement

Prior to the Amended Ide-cel CCPS and Amended bb21217 License Agreement, the Company had constrained all variable consideration related to the remaining ex-U.S. milestones and royalties for ex-U.S. sales under the Ide-cel CCPS and bb21217 License Agreement, as these milestones and royalties for ex-U.S sales were not considered to be probable. As a result of the Amended Ide-cel CCPS and Amended bb21217 License Agreement, the uncertainty associated with the previously constrained variable consideration for future ex-U.S. milestones and royalties on ex-U.S. sales for each of ide-cel and bb21217 was resolved in exchange for an up-front, non-refundable, non-creditable payment of $200.0 million. The Amended Ide-cel CCPS and Amended bb21217 License Agreement were negotiated as a package with a single commercial objective and, as such, the Amended Ide-cel CCPS and Amended bb21217 License Agreement were combined for accounting purposes and treated as a single arrangement.

At the time of execution of the Amended Ide-cel CCPS and Amended bb21217 License Agreement, there was one remaining performance obligation under each agreements: a combined performance obligation of the ide-cel license and ide-cel vector manufacturing through development; and a combined performance obligation of the bb21217 license and bb21217 vector manufacturing through development, neither of which were fully satisfied. The Company concluded each performance obligation was distinct from each other as BMS can benefit from each license and associated manufacturing services separately and the respective licenses and manufacturing services do not modify one another and are not interdependent. Accordingly, the Company continues to account for each performance obligation separately.

The Company allocated the $200.0 million up-front payment received in connection with the Amended Ide-cel CCPS and Amended bb21217 License Agreement to the remaining performance obligations described above based on the general allocation principles of Topic 606. The Company considered that a portion of the $200.0 million was specifically attributable to each remaining performance obligation as the amount represents the aggregate of the probability-weighted, net present value of the future ex-U.S. milestones and royalties on ex-U.S. sales for each of ide-cel and bb21217 and that each respective portion therefore (i) relates specifically to the Company's satisfaction of each of its remaining performance obligations and (ii) is representative of the amount of consideration the Company expects to be entitled to in exchange for satisfying the respective performance obligations. As such, the Company concluded that the portion of the $200.0 million up-front payment specifically attributable to each of ide-cel and bb21217 should be allocated to each respective performance obligation pursuant to the variable consideration allocation exception.

The Amended Ide-cel CCPS and Amended bb21217 License Agreement represent a contract modification to an existing contract under Topic 606 resulting in a reduction in scope of the Company's responsibilities under each performance obligation described above. This resulted in a change in the overall transaction price under the arrangement. The Amended Ide-cel CCPS and Amended bb21217 License Agreement did not include any additional promised goods and services.

The remaining goods and services to be provided to fully satisfy each performance obligation described above are not distinct from those previously provided with respect to each performance obligation. Therefore, for each performance obligation, the remaining goods and services are part of a single performance obligation that is partially satisfied at the date of the contract modification. Accordingly, the effect that the contract modification had on the transaction price and the measure of progress toward complete satisfaction of each respective performance obligation has been recognized on a cumulative catch-up basis. The accounting for any previously satisfied performance obligations as of the contract modification date are not affected by the modification.

The following table summarizes the total transaction price, the allocation of the total transaction price to the identified performance obligations under the arrangement (including those performance obligations that were completed as of the May 2020 contract modification date as of December 31, 2021 (in thousands):


	Transaction price as of December 31, 2021
	Ide-cel		bb21217
Upfront non-refundable payments received prior to May 2020 contract modification (1)	$	120,000	$	15,000
Allocated portion of the upfront non-refundable payment received in connection with the Amended Ide-cel CCPS and bb21217 License Agreement (2)	184,029		15,971
Estimated variable consideration (3)	83,900		1,803
	$	387,929	$	32,774

(1) Composed of all up-front payments and fees and milestone payments received under the related agreements. This consideration was allocated to the performance obligations under the agreements based on a relative standalone selling price (“SSP”) basis.

(2) This represents the portion of the $200.0 million up-front payment received under the Amended Ide-cel CCPS and Amended bb21217 License Agreement which was allocated to ide-cel and bb21217.

(3) Estimated variable consideration represents the estimated reimbursement from BMS for the manufacture of vectors and associated payload through development.

Ide-cel research and development services

The Company allocated $40.9 million of the ide-cel transaction price to the ide-cel research and development services. The research and development performance obligation was satisfied prior to the May 2020 Amendments and, as a result, the accounting for this previously satisfied performance obligation was not affected by the modification. The Company recognized no revenue related to ide-cel research and development services for the years ended December 31, 2021 and 2020. The Company recognized $2.3 million related to ide-cel research and development services for the year ended December 31, 2019.

Ide-cel license and manufacturing services

The Company allocated $347.0 million of the ide-cel transaction price to the combined unit of accounting which consists of the license and manufacture of vectors and associated payload for incorporation into ide-cel through development. As of December 31, 2021, there was no unsatisfied transaction price and the remaining deferred revenue as of December 31, 2020 related to the performance obligation was recognized when the performance obligation was satisfied during the first quarter of 2021, upon ABECMA commercial approval. The following table summarizes the net collaboration revenue recognized or expense incurred for the joint ide-cel development efforts in the U.S. under ASC 808, including revenue or expense related to the combined performance obligation for license and manufacturing of ide-cel in the U.S. for the years ended December 31, 2021, 2020 and 2019 (in thousands):


	For the years ended December 31,
	2021		2020		2019
ASC 808 ide-cel license and manufacturing revenue - U.S. (1)(2)	$	—	$	108,196	$	—
ASC 808 ide-cel license and manufacturing expense - U.S. (1)	$	—	$	(41,599)	$	(32,415)

(1) As noted above, the calculation of collaborative arrangement activity to be recognized for joint ide-cel efforts in the United States is performed on a quarterly basis. The calculation is independent of previous activity, which may result in fluctuations between revenue and expense recognition period over period, depending on the varying extent of effort performed by each party during the period.

(2) In the second quarter of 2020, the Company recognized $169.2 million as a cumulative catch-up adjustment to revenue recorded in connection with the Amended Ide-cel CCPS, a portion of which was recognized as ASC 808 research and development collaboration revenue.

Ide-cel U.S. Share of Collaboration Profit or Loss

The U.S. commercial and development activities under the Amended Ide-Cel CCPS are within the scope of ASC 808. On a quarterly basis, the Company determines its share of collaboration profit or loss for commercial activities (i.e., commercial sales of ABECMA by BMS). The Company’s share of any collaboration profit for commercial activities is recognized as collaborative arrangement revenue and its share of any collaboration loss for commercial activity is recognized as an operating expense and classified as share of collaboration loss on the Company's statements of operations and comprehensive loss. The Company recognized the following on the statements of operations and comprehensive loss related to its share of collaboration profit or loss associated with

ide-cel commercial activities following approval (in thousands). These amounts represent the Company’s share of BMS’ ide-cel product revenue, cost of goods sold, and selling costs, along with reimbursement by BMS of commercial costs incurred by the Company, and exclude expenses related to ongoing development, which are separately reflected in the statements of operations and comprehensive loss as described below. Amounts incurred prior to commercial approval in March 2021 were not material.


	For the three months ended March 31, 2021		For the three months ended June 30, 2021		For the three months ended September 30, 2021		For the three months ended December 31, 2021
Net revenue	$	—	$	—	$	10,607	$	8,818
Net expense	$	—	$	(10,071)	$	—	$	—

The Company’s collaboration profit for commercial activities was $9.4 million for the year ended December 31, 2021.

The Company is also responsible for equally sharing in the ongoing ide-cel research and development activities being conducted by BMS in the United States as BMS continues conducting ongoing clinical studies to support the use of ABECMA in earlier lines of therapy. The net amount owed to BMS for research and development activities determined on a quarterly basis is classified as research and development expense on the statements of operations and comprehensive loss. If BMS is obligated to reimburse the Company because the Company’s research and development costs exceeds BMS’ research and development costs in a particular quarterly period, the net amount is recorded as collaborative arrangement revenue. The following table summarizes the amounts associated with the research activities under the collaboration included in research and development expense or recognized as collaborative arrangement revenue for each quarter during the year ended December 31, 2021 (in thousands):


	For the three months ended March 31, 2021		For the three months ended June 30, 2021		For the three months ended September 30, 2021		For the three months ended December 31, 2021
Net expense	$	(16,825)	$	(9,193)	$	(5,660)	$	(7,835)

Ide-cel ex-U.S. Service Revenue

The Company accounts for any ex-U.S. activities under the Amended Ide-cel CCPS pursuant to ASC 606. The following table summarizes the revenue recognized related to ide-cel ex-U.S. activities for the years ended December 31, 2021, 2020, and 2019 (in thousands):


	For the years ended December 31,
	2021		2020		2019
ASC 606 ide-cel license and manufacturing revenue – ex-U.S. (1)	$	16,895	$	99,053	$	25,522

(1)In the second quarter of 2020, the Company recognized $169.2 million as a cumulative catch-up adjustment to revenue recorded in connection with the Amended Ide-cel CCPS, a portion of which was recognized as ASC 606 license and manufacturing revenue.

bb21217 research and development services

The Company allocated $5.4 million of the bb21217 transaction price to the research and development services. The research and development performance obligation was satisfied prior to the May 2020 amendments, and as a result, the accounting for this previously satisfied performance obligation was not affected by the modification. The Company recognized no revenue related to bb21217 research and developments services for the years ended December 31, 2021 and 2020, and revenue of $2.2 million for the year ended December 31, 2019.

The agreement to expand the bb21217 phase 1 trial that occurred in 2019 was previously treated as a separate contract for accounting purposes. The transaction price associated with these additional patients consists of variable consideration and is based upon an agreed-upon amount per patient which will be recognized as revenue as the patients are treated. The Company began fulfilling the performance obligation in the fourth quarter of 2019 and it was satisfied in the fourth quarter of 2020. In connection with treating additional patients in the phase 1 trial, the Company recognized revenue of $0.0 million, $12.4 million, and $0.4 million for the years ended December 31, 2021, 2020, and 2019, respectively.

bb21217 license and manufacturing services

The Company will satisfy its performance obligation related to the manufacture of vectors and associated payload for incorporation into bb21217 through development as the bb21217 manufacturing services are performed. The aggregate amount of the transaction price allocated to the combined performance obligation, which consists of the bb21217 license and manufacturing services, is $27.3 million, of which $1.8 million has not yet been received as of December 31, 2021. As of December 31, 2021, the manufacturing services for bb21217 had not yet commenced. Therefore, no amounts have been recognized as revenue for the combined performance obligation in the statements of operations and comprehensive loss for the years ended December 31, 2021, 2020, and 2019.

The Company had $25.8 million of deferred revenue as of December 31, 2021 and 2020 associated with the combined performance obligation consisting of the bb21217 license and manufacturing services.

Contract assets and liabilities – ide-cel and bb21217

The Company receives payments from its collaborative partners based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due until such time as the Company satisfies its performance obligations under these arrangements. A contract asset is a conditional right to consideration in exchange for goods or services that the Company has transferred to a customer. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional.

The following table presents changes in the balances of the Company’s BMS receivables and contract liabilities during the twelve months ended December 31, 2021 (in thousands):


	Balance at December 31, 2020		Additions		Deductions		Balance at December 31, 2021
Receivables	$	400	$	13,441	$	(13,189)	$	652
Contract liabilities:
Deferred revenue	$	26,582	$	—	$	(820)	$	25,762

The increase in the receivables balance for the twelve months ended December 31, 2021 is driven by amounts owed to the Company from BMS in the period under the settlement terms of the collaboration agreement, offset by amounts collected from BMS in the period.

The decrease in deferred revenue during the twelve months ended December 31, 2021 is driven by the release of the remaining $0.8 million of deferred revenue associated with the combined performance obligation consisting of the ide-cel license and manufacturing services.

Regeneron

Regeneron Collaboration Agreement

In August 2018, bluebird bio entered into a Collaboration Agreement (the “Regeneron Collaboration Agreement”) with Regeneron pursuant to which the parties will apply their respective technology platforms to the discovery, development, and commercialization of novel immune cell therapies for cancer. In August 2018, following the completion of required regulatory reviews, the Regeneron Collaboration Agreement became effective. As noted above, the agreement will be attributed to the Company in connection with the separation. Under the terms of the agreement, the parties will leverage Regeneron’s proprietary platform technologies for the discovery

and characterization of fully human antibodies, as well as T cell receptors directed against tumor-specific proteins and peptides and the Company will contribute its field-leading expertise in gene therapy.

In accordance with the Regeneron Collaboration Agreement, the parties jointly selected six initial targets and intend to equally share the costs of research up to the point of submitting an IND application for a potential gene therapy product directed to a particular target. Additional targets may be selected to add to or replace any of the initial targets during the five-year research collaboration term as agreed to by the parties.

Regeneron will accrue a certain number of option rights exercisable against targets as the parties reach certain milestones under the terms of the agreement. Upon the acceptance of an IND for the first product candidate directed to a target, Regeneron will have the right to exercise an option for co-development/co-commercialization of product candidates directed to such target on a worldwide or applicable opt-in territory basis, with certain exceptions. Where Regeneron chooses to opt-in, the parties will share equally in the costs of development and commercialization, and will share equally in any profits or losses therefrom in applicable opt-in territories. Outside of the applicable opt-in territories, the target becomes a licensed target and Regeneron would be eligible to receive, with respect to any resulting product, milestone payments of up to $130.0 million per product and royalties on net sales outside of the applicable opt-in territories at a rate ranging from the mid-single digits to low-double digits. A target would also become a licensed target in the event Regeneron does not have an option to such target, or Regeneron does not exercise its option with respect to such target.

Either party may terminate a given research program directed to a particular target for convenience, and the other party may elect to continue such research program at its expense, receiving applicable cross-licenses. The terminating party will receive licensed product royalties and milestone payments on the potential applicable gene therapy products. Where the Company terminates a given research program for convenience, and Regeneron elects to continue such research program, the parties will enter into a transitional services agreement. Under certain conditions, following its opt-in, Regeneron may terminate a given collaboration program and the Company may elect to continue the development and commercialization of the applicable potential gene therapy products as licensed products.

Regeneron Share Purchase Agreement

A Share Purchase Agreement (“SPA”) was entered into by bluebird bio and Regeneron in August 2018. In August 2018, on the closing date of the transaction, bluebird bio issued Regeneron 0.4 million shares of bluebird bio’s common stock, subject to certain restrictions, for $238.10 per share, or $100.0 million in the aggregate. The purchase price represents $63.0 million worth of common stock plus a $37.0 million premium, which represents a collaboration research advancement, or credit to be applied to Regeneron’s initial 50 percent funding obligation for collaboration research, after which the collaborators will continue to fund ongoing research equally. The collaboration research advancement only applies to pre-IND research activities and is not refundable or creditable against post-IND research activities for any programs where Regeneron exercises its opt-in rights.

Accounting analysis – Regeneron

At the commencement of the arrangement, two units of accounting were identified, which are the issuance of 0.4 million shares of bluebird bio’s common stock and joint research activities during the five year research collaboration term. The Company determined the total transaction price to be $100.0 million, which comprises $54.5 million attributed to the bluebird bio equity sold to Regeneron and $45.5 million attributed to the joint research activities. In determining the fair value of the bluebird bio common stock at closing, the Company considered the closing price of the bluebird bio common stock on the closing date of the transaction and included a lack of marketability discount because Regeneron received shares subject to certain restrictions.

The Company analyzed the joint research activities to assess whether they fall within the scope of ASC 808, and will reassess this throughout the life of the arrangement based on changes in the roles and responsibilities of the parties. Based on the terms of the arrangement as outlined above, for the collaboration research performed prior to submission of an IND application for a potential gene therapy product, both parties are deemed to be active participants in the collaboration. Both parties are performing research and development activities and will share equally in these costs through IND. Additionally, Regeneron and the Company are exposed to significant risks and

rewards dependent on the commercial success of any product candidates that may result from the collaboration. As such, the collaboration arrangement is deemed to be within the scope of ASC 808.

The $45.5 million attributed to the joint research activities includes the $37.0 million creditable against amounts owed to the Company by Regeneron. The collaboration research advancement will be reduced over time for amounts due to the Company by Regeneron as a result of the parties agreeing to share in the costs of collaboration research equally. The remainder of the amount attributed to the joint research activities will be recognized over the five-year research collaboration term.

Consistent with its collaboration accounting policy, the Company will recognize collaboration revenue or research and development expense related to the joint research activities in future periods depending on the amounts incurred by each party in a given reporting period. That is, if the Company’s research costs incurred exceed those research costs incurred by Regeneron in a given quarter, the Company will record collaboration revenue and reduce the original $37.0 million advance by the amount due from Regeneron until such advancement is fully utilized, after which the Company would record an amount due from Regeneron. If Regeneron’s research costs incurred exceed those research costs incurred by the Company in a given quarter, the Company will record research and development expense and record a liability for the amount due to Regeneron. As of December 31, 2021 and 2020, the Company has $23.3 million and $30.8 million, respectively, of the amount attributed to the joint research activities remaining to be recognized which is classified as collaboration research advancement, current portion and collaboration research advancement, net of current portion on the consolidated and combined balance sheet.

The Company recognized $7.5 million and $7.4 million of collaboration revenue from the Regeneron Collaboration Agreement during the years ended December 31, 2021 and 2020, respectively.

Resilience

Background

In July 2021, bluebird bio and Resilience US, Inc. (formerly known as Resilience Boston, Inc.), an affiliate of Resilience, signed an Asset Purchase Agreement (the “Agreement”). As part of the Agreement, and upon the closing of the transaction which occurred in September 2021, Resilience acquired bluebird bio's lentiviral vector manufacturing facility located in Durham, North Carolina and retained staff employed at the site. In exchange, bluebird bio received $110.3 million for the facility and related fixed assets.

Upon closing, bluebird bio entered into certain ancillary agreements, including two manufacturing agreements and a license agreement (the “License Agreement”), among others (together referred to as the “Ancillary Agreements”). Upon separation of 2seventy bio from bluebird bio, effective November 4, 2021, certain rights and obligations under the Agreement and certain Ancillary Agreements were assigned by bluebrid bio to 2seventy bio with 2seventy bio assuming all rights and obligations these agreements convey.

One manufacturing agreement will support the future manufacturing of lentiviral vector for the Company’s commercial product in collaboration with BMS, ide-cel (the “Commercial Supply Agreement”), while the other will support ongoing manufacturing for lentiviral vector for the Company's development candidates (the “Development Manufacturing Supply Agreement”). The Company also agreed to reimburse Resilience for an amount equal to 50% of the net operating losses of and relating to the manufacturing facility’s business incurred during the twelve-month period ending on the first anniversary of the closing of the transaction, as calculated in accordance with the Agreement, subject to a cap of $15.0 million. In exchange, under the terms of the Development Manufacturing Supply Agreement, the Company will receive up to eight batches of lentiviral vector during the twelve-month period ending on the first anniversary of the closing of the transaction. The License Agreement grants Resilience a worldwide, co-exclusive license to intellectual property controlled by the Company to perform Resilience’s obligations and exercise Resilience’s rights under the supply agreements, and a worldwide, nonexclusive right to offer certain manufacturing services to third-party customers under certain of the Company's intellectual property. Under the terms of the License Agreement, the Company may receive a high single-digit to low double-digit percentage tiered royalty based on Resilience’s gross margins for transactions entered into with parties other than the Company in which the Company's proprietary intellectual property is utilized as part of such transaction.

Under the Commercial Supply Agreement, the Company will pay fully burdened manufacturing cost plus a markup for production of vector. Under the Development Manufacturing Supply Agreement, services, manufacture, and delivery of batches of lentiviral vector during the first twelve months from the execution of this agreement will be free of cost, as the costs of these services are represented by the net operating loss sharing arrangement outlined within the Agreement. As such, the Company has committed to a minimum purchase of at least the Company's 50% share of the net operating losses during the first twelve months from the execution of such agreement. After the first twelve months, the Company will pay Resilience the fully burdened manufacturing cost plus a markup for production of vector.

Accounting analysis - Resilience

Since the January 2021 announcement by bluebird bio of its plans to separate and spin-off of 2seventy bio from its severe genetic disease portfolio and programs, the manufacturing facility was expected to be assigned to 2seventy bio and was therefore accounted for within the 2seventy bio carve-out financial statements. The disposition of the net assets of the manufacturing facility previously assigned to 2seventy bio has been reflected as a transfer to bluebird bio via net parent investment as a result of bluebird bio’s sale of such facility. 2seventy bio is not a party to the sale of the manufacturing facility and, therefore, did not recognize any gain or loss arising from the transaction.

Future royalty payments under the License Agreement (which was assigned to the Company as previously described) are considered part of the consideration associated with the disposition of the manufacturing facility. In accordance with ASC 450, the Company will recognize future royalties received under the License Agreement in the period the contingencies are resolved as an adjustment to the consideration received as other income in the consolidated and combined statements of operations and comprehensive loss.

Novo Nordisk

Novo Collaboration and License Agreement

On December 23, 2021, the Company entered into a Collaboration and License Agreement (the “Novo Collaboration Agreement”) with Novo Nordisk A/S (“Novo”) for the discovery, development, and commercialization of a potential new gene therapy in hemophilia A. The Company and Novo have agreed to develop an initial research program with the goal of researching and developing a lead candidate directed to hemophilia A. The Company will provide Novo with research licenses to support the companies’ activities during the initial research program and an option to enable Novo to obtain an exclusive license to commercialize the product derived from or containing compounds developed during the initial research program.

Under the terms of the Novo Collaboration Agreement, Novo agreed to pay the Company:

•a non-refundable, non-creditable upfront payment of $5.0 million;

•$15.0 million upon achievement of certain scientific milestones during the initial research program, or $9.0 million should Novo decide to continue the initial research program without achieving the scientific milestones;

•up to $26.0 million of exclusive license fees for the development, manufacture, and commercialization of the product should Novo exercise its option; and,

•up to $72.0 million in development and commercialization milestones.

Novo also agreed to reimburse the Company for research costs incurred in connection with the initial research program up to a mutually agreed upon amount, initially budgeted at $6.7 million. If Novo exercises its option to obtain a license to commercialize the product developed during the initial research program, the Company is also eligible to receive mid-single digit royalties on product sales on a country-by-country and product-by-product basis, subject to certain royalty step-down provisions set forth in the agreement.

Accounting Analysis - Novo

The Company concluded that Novo is a customer, and as such, the arrangement falls within the scope of Topic 606. The Company identified two performance obligations consisting of (i) the research license and research and development services to be provided during the initial research program and (ii) a material right related to Novo’s option to obtain an exclusive license for the development, manufacture, and commercialization of the product developed during the initial research program. The Company determined that the research license and research and development services promises were not separately identifiable and were not distinct or distinct within the context of the contract due to the specialized nature of the services to be provided by 2seventy, specifically with respect to the Company’s expertise related to gene therapy and the interdependent relationship between the promises. The material right is considered a separate performance obligation pursuant to the provisions of Topic 606.

At contract inception, the Company determined the unconstrained transaction price was $11.7 million, consisting of the $5.0 million in up-front consideration and the $6.7 million in reimbursement for the research and development services. Variable consideration associated with the scientific milestones was fully constrained due to the uncertainty associated with the outcome of the research efforts under the initial research program. The Company allocated $6.7 million of the transaction price to the research services and $5.0 million to the material right using a relative selling price methodology. Management will re-evaluate the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur and adjust the transaction price as necessary.

Revenue associated with the research and development performance obligation will be recognized as services are provided and costs are incurred. The portion of the transaction price attributed to the material right will be deferred and recognized as revenue upon Novo exercising its option to license the product.

No revenue was recognized under the Novo Collaboration Agreement during the year ended December 31, 2021. The $5.0 million upfront payment was recorded as a receivable as of December 31, 2021, and no amount has been invoiced or received related to the research and development services as the services did not commence until 2022. The aggregate amount of the consideration receivable under the arrangement as of December 31, 2021, relates to the material right performance obligation which was unsatisfied as of December 31, 2021.

Royalty and other revenue	12 Months Ended
Royalty and other revenue	Dec. 31, 2021
License And Royalty Revenue [Abstract]
Royalty and other revenue	Royalty and other revenue bluebird bio has out-licensed intellectual property to various third parties. Under the terms of these agreements, some of which were assumed by the Company in connection with the separation, bluebird bio and the Company may be entitled to royalties and milestone payments. The Company recognized $6.2 million, $21.1 million, and $8.2 million of royalty and other revenue in the years ended December 31, 2021, 2020, and 2019, respectively. Novartis Pharma AG In April 2017, bluebird bio entered into a worldwide license agreement with Novartis. Under the terms of the agreement, Novartis non-exclusively licensed certain patent rights related to lentiviral vector technology to develop and commercialize CAR T cell therapies for oncology, including Kymriah (formerly known as CTL19), Novartis’s anti-CD19 CAR T therapy. The agreement was assumed by the Company in connection with the separation. Beginning in the fourth quarter of 2017, bluebird bio began receiving royalties from sales of tisagenlecleucel under the agreement. This license agreement was terminated effective March 2021, at which point in time Novartis was no longer required to make royalty or other payments on net sales of tisagenlecleucel or any future products. Royalty revenue recognized from sales of tisagenlecleucel is included within royalty and other revenue in the condensed consolidated and combined statement of operations and comprehensive loss. Juno Therapeutics In May 2020, bluebird bio entered into a non-exclusive license agreement with Juno Therapeutics, Inc. (“Juno”), a wholly-owned subsidiary of BMS, related to lentiviral vector technology to develop and commercialize CD-19-directed CAR T cell therapies. The agreement was assumed by the Company in connection with the separation. Upon regulatory approval of lisocabtagene maraleucel during the first quarter of 2021, bluebird bio received a $2.5 million milestone payment from Juno, which is included within royalty and other revenue in the Company’s consolidated and combined financial statements. Royalty revenue recognized from sales of lisocabtagene maraleucel is also included within royalty and other revenue in the consolidated and combined statement of operations and comprehensive loss.

Intangible assets

12 Months Ended

Dec. 31, 2021

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible assets

Intangible assets, net of accumulated amortization, are summarized as follows (in thousands):


	As of December 31,						As of December 31,
	2021						2020
	Cost		Accumulated amortization		Net		Cost		Accumulated amortization		Net
Developed technology	$	30,100	$	(28,218)	$	1,882	$	30,100	$	(24,456)	$	5,644
In-licensed rights	8,500		(490)		8,010		—		—		—
Total	$	38,600	$	(28,708)	$	9,892	$	30,100	$	(24,456)	$	5,644

Amortization expense for intangible assets was $4.3 million, $3.8 million, and $3.8 million for the years ended December 31, 2021, 2020 and 2019, respectively.

Developed technology

The Company's developed technology was obtained through the acquisition in 2014 of Pregenen, a privately-held biotechnology company includes gene editing and cell signaling technology with a broad range of potential therapeutic applications. The gene editing platform intangible asset is being amortized on a straight-line basis over its expected useful life of approximately eight years from the date of the acquisition.

In-licensed rights

In-licensed rights consist of capitalized milestone payments made to third parties upon receiving regulatory approval of ABECMA in the U.S. The in-licensed rights are being amortized on a straight-line basis over the remaining life of the related patents of approximately twelve years, as the life of the related patents reflects the expected time period that the Company will benefit from the in-licensed rights.

The following table summarizes the estimated future amortization for intangible assets for the next five years and thereafter (in thousands):


	As of December 31, 2021
2022	$	2,590
2023	708
2024	708
2025	708
2026	708
2027 and thereafter	4,470
Total	$	9,892

Stock-based compensation

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

Stock-based compensation

The Company’s employees have historically participated in bluebird bio’s various stock-based compensation plans.

In connection with 2seventy’s separation from bluebird bio on November 4, 2021, under the provisions of the existing plans, the outstanding bluebird bio equity awards were adjusted in accordance with the terms of the

Employee Matters Agreement (equitable adjustment) to preserve the intrinsic value of the awards immediately before and after distribution.

Upon the distribution, employees holding stock options, restricted stock units (“RSUs”) and performance restricted stock units (“PRSUs”) denominated in pre-distribution bluebird bio stock received a number of otherwise-similar awards either in post-distribution 2seventy stock or in a combination of post-distribution bluebird stock and 2seventy stock based on conversion ratios outlined for each group of employees in the Employee Matters Agreement that the Company entered into in connection with the distribution.

The equity awards that were granted prior to 2021 were converted under the shareholder method, wherein employees holding outstanding equity awards received equity awards in both bluebird and 2seventy. The conversion ratio for the shareholder method took into consideration a distribution ratio of one share of 2seventy common stock for every three shares of bluebird bio common stock. For equity awards granted in 2021, the number of awards that were outstanding at the time of the spin-off were proportionately adjusted to maintain the aggregate intrinsic value of the awards at the date of the spin-off. The conversion ratio was determined based on the volume weighted-average trading price for bluebird common stock for the five trading days before and the volume weighted-average trading price for 2seventy common stock for the five trading days after the spin.

These modified awards otherwise retained substantially the same terms and conditions, including term and vesting provisions. Due to the modification of the equity awards as a result of the distribution, the Company compared the fair value of the outstanding equity awards immediately before and after the distribution. The modification resulted in an incremental fair value of $1.5 million, of which $1.3 million was immediately recognized as of the distribution.

The Company will incur future compensation cost related to bluebird bio equity awards held by its employees but will not incur future compensation cost related to bluebird employees holding equity awards in 2seventy.

In October 2021, the Company’s board of directors adopted its 2021 Stock Option and Incentive Plan (“2021 Plan”), which was subsequently approved by bluebird bio, then the Company’s sole stockholders. The 2021 Plan became effective on October 17, 2021, the day immediately prior to the effectiveness of the Company’s Registration Statement on Form 10.

The 2021 Plan allows for the granting of incentive stock options, non-qualified stock options, RSUs, PRSUs, and restricted stock awards to 2seventy bio’s employees, members of the board of directors, and consultants of 2seventy bio, including those of 2seventy bio who became employees of the Company in connection with the separation. All awards granted under the 2021 Plan consist of shares of 2seventy bio’s common stock.

Stock-based compensation expense

For periods prior to the separation, stock-based compensation expense was allocated to the Company using a combination of specific identification and time spent on projects at various levels of the organization, which management believes are consistent and reasonable.

The Company recognized stock-based compensation expense totaling $54.6 million, $61.0 million, and $62.0 million during the years ended December 31, 2021, 2020, and 2019, respectively. Stock-based compensation expense recognized by award type is as follows (in thousands):


	Year Ended December 31,
	2021		2020		2019
Stock options	$	26,185	$	36,685	$	36,792
Restricted stock units	21,414		19,185		24,744
Employee stock purchase plan and other	7,030		5,127		512
	$	54,629	$	60,997	$	62,049

Stock-based compensation expense by classification included within the consolidated statements of operations and comprehensive loss was as follows (in thousands):


	Year Ended December 31,
	2021		2020		2019
Research and development	$	29,746	$	30,935	$	33,853
Selling, general and administrative	24,883		30,062		28,196
	$	54,629	$	60,997	$	62,049

As of December 31, 2021, the Company had $25.0 million, $38.5 million, and $1.2 million of unrecognized compensation expense related to unvested stock options, RSUs, and PRSUs (exclusive of those with service and performance conditions that have not yet been achieved), respectively, that is expected to be recognized over a weighted-average period of 1.83 years, 2.03 years, and 2.09 years, respectively. The Company had no unrecognized compensation expense related to the ESPP described below as of December 31, 2021.

Stock options

The following table summarizes the stock option activity under the Company’s equity awards plans for 2seventy employees:


	Shares (in thousands)	Weighted-average exercise price per share		Weighted-average contractual life (in years)	Aggregate intrinsic value (a) (in thousands)
Outstanding at December 31, 2020	—	$	—
Granted	—	$	—
Converted in distribution	875	$	129.67
Exercised	—	$	—
Canceled or forfeited	(2)	$	157.43
Outstanding at December 31, 2021	873	$	129.60	6.6	$	131
Exercisable at December 31, 2021	518	$	161.76	5.2	$	131
Vested and expected to vest at December 31, 2021	873	$	129.60	6.6	$	131

(a) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the fair value of the common stock for the options that were in the money at December 31, 2021.

Restricted stock units

The following table summarizes the restricted stock unit activity under the Company’s equity award plans for 2seventy employees:


	Shares (in thousands)	Weighted-average exercise price per share
Unvested balance at December 31, 2020	—	$	—
Granted	9	36.14
Converted in distribution	969	50.93
Vested	(3)	137.65
Forfeited	(4)	86.12
Unvested balance at December 31, 2021	971	$	50.56

The intrinsic value of RSUs vested during the year ended December 31, 2021 was $0.1 million.

On February 1, 2021, the Company’s CEO was granted 27,000 PRSUs by bluebird. Each PRSU related to one share of common stock of bluebird. The number of PRSUs earned and vested would be determined based on bluebird’s total shareholder return (“TSR”) compared against the median TSR of a peer group over the performance period January 1, 2021 through December 31, 2023. Upon spin-off, the PRSUs were converted to 17,387 2seventy PRSUs. The TSR was kept whole by treating the value of bluebird at spin as a dividend that is reinvested into 2seventy stock. As of December 31, 2021, expense of $0.4 million related to the PRSUs was recognized, and $1.3 million of unrecognized expense is expected to be recognized over the remaining duration of the award’s life.

Unrestricted stock awards

During the fourth quarter of 2021, the Company granted 0.2 million unrestricted stock awards to employees as part of its 2021 retention program which was designed to incentivize and retain employees through the spin-off. Under the retention program, employees were entitled to a one-time bonus payment, consisting of both a cash payment and unrestricted stock awards, with the condition that the employee remained employed through the end of 2021. Expense recognized on the unrestricted stock awards during the year ended December 31, 2021 totaled $6.5 million.

Employee Stock Purchase Plan

In October 2021, the Company’s board of directors adopted its 2021 Employee Stock Purchase Plan (“2021 ESPP”), which was subsequently approved by bluebird bio, then its sole stockholders. The 2021 ESPP became effective on October 17, 2021, the day immediately prior to the effectiveness of the Company’s Registration Statement on Form 10. The 2021 ESPP authorizes the initial issuance of a specified number of shares of the Company’s common stock to participating employees. For the year ended December 31, 2021, no shares of common stock were issued under the 2021 ESPP.

Related-party transactions

12 Months Ended

Dec. 31, 2021

Related-party transactions

Relationship with Bluebird Bio

Following the separation, bluebird bio is considered a related party.

In connection with the separation, the Company entered into a separation agreement (the “Separation Agreement”) with bluebird bio, dated as of November 3, 2021, that, among other things, set forth bluebird bio’s agreements with 2seventy bio regarding the principal actions to be taken in connection with the separation, including the distribution. The effective time of the distribution was 12:01 a.m. on November 4, 2021. The Separation Agreement identifies assets transferred to, liabilities assumed by and contracts assigned to 2seventy bio as part of the separation, and it provides for when and how these transfers, assumptions and assignments occur. The purpose of the Separation Agreement is to provide 2seventy bio and bluebird bio with assets to operate their respective businesses and retain or assume liabilities related to those assets. Each of 2seventy bio and bluebird bio agreed to releases, with respect to pre-separation claims, and cross indemnities with respect to post-separation claims, that are principally designed to place financial responsibility for the obligations and liabilities allocated to 2seventy bio under the Separation Agreement with 2seventy bio and financial responsibility for the obligations and liabilities allocated to bluebird bio under the Separation Agreement. bluebird bio and 2seventy bio are also each subject to mutual 12-month employee non-solicit and non-hire restrictions, subject to certain customary exceptions. In accordance with the Separation Agreement with bluebird bio, there were certain other transactions and adjustments post-Separation between the Company and bluebird bio. For the two months since separation through to December 31, 2021, the Company recorded a net charge to operating expense of $0.2 million related to the Separation Agreement.

The Company and bluebird bio also entered into a tax matters agreement, dated as of November 3, 2021, governing bluebird bio’s and 2seventy bio's respective rights, responsibilities and obligations with respect to taxes (including taxes arising in the ordinary course of business and taxes, if any, incurred as a result of any failure of the distribution and certain related transactions to qualify as tax-free for U.S. federal income tax purposes, tax attributes, the preparation and filing of tax returns, the control of audits and other tax proceedings, and assistance and cooperation in respect of tax matters).

In connection with the separation, the Company also entered into an employee matters agreement with bluebird bio, dated as of November 3, 2021. The employee matters agreement allocates assets, liabilities and responsibilities relating to the employment, compensation and employee benefits of bluebird bio and 2seventy bio employees, and other related matters, in connection with the separation, including the treatment of outstanding bluebird bio incentive equity awards and certain retirement and welfare benefit obligations. The employee matters agreement generally provides that, unless otherwise specified, 2seventy bio is responsible for liabilities associated with employees who transfer to 2seventy bio and employees whose employment terminated prior to the distribution but who primarily supported the 2seventy bio business, and bluebird bio is responsible for liabilities associated with other employees, including employees retained by bluebird bio. Included in the agreement are also specific clauses relating to liabilities assumed by bluebird bio for the costs incurred prior to the separation. For the two months since separation through to December 31, 2021, the Company recorded a net charge to operating expense of $1.8 million for costs stipulated by the agreement.

The Company and bluebird bio also entered into an intellectual property license agreement on November 3, 2021, pursuant to which each party granted a license to certain intellectual property and technology to the other. bluebird bio granted 2seventy bio a perpetual, worldwide, non-exclusive, royalty-free, fully paid-up license (or, as the case may be, sublicense) to certain intellectual property to allow 2seventy bio to use such intellectual property in connection with 2seventy bio's ongoing and future research and development activities and product candidates. 2seventy bio granted bluebird bio a perpetual, worldwide, non-exclusive, royalty-free, fully paid-up license (or, as the case may be, sublicense) to certain intellectual property for use in bluebird bio’s existing products and product candidates. Such licenses between the parties generally allow current or future uses of the intellectual property in connection with each party's respective fields. Charges associated to the intellectual property license agreement will commenced in 2022, there were no costs associated to the period since separation through to December 31, 2021.

The Company and bluebird bio entered into two transition services agreements on November 3, 2021, pursuant to which bluebird bio will provide 2seventy bio with corporate and shared services and resources related to corporate functions such as finance, human resources, internal audit, research and development, financial reporting, and information technology, and to which 2seventy bio will provide certain services to bluebird bio, each for an initial term of two years, unless earlier terminated or extended according to the terms of the transition services agreement. The Company recorded a $1.4 million in other income, reflecting services provided to bluebird bio and $0.7 million of operating expenses for activities related to the transition services.

Additionally, under the transition services agreements, 2seventy bio will sublease 30% of its headquarters at 60 Binney Street in Cambridge, Massachusetts to bluebird bio through the first quarter of 2022. Beginning in the second quarter of 2022, this percentage will decrease to 23% for the remainder of the year. The Company recorded $0.8 million in other income related to sublease income from bluebird under this arrangement during the year ended December 31, 2021.

As of December 31, 2021, amounts due to bluebird bio under the above agreements were $1.5 million, of which $1.2 million was included in accrued expenses and other current liabilities and $0.3 million was included in accounts payable. As of December 31, 2021, amounts due from bluebird bio under the above agreements were $1.6 million and were included in receivables and other current assets.

Corporate allocations

Prior to the separation, the Company did not operate as a separate, stand-alone entity, but rather was managed and operated in the normal course of business under bluebird bio. Accordingly, certain shared costs have been allocated to the Company and reflected as expenses in the Company's stand-alone consolidated and combined financial statements for periods prior to the separation as described b. The expenses reflected in the consolidated and combined financial statements may not be indicative of expenses that will be incurred by the Company in the future.

For periods prior to the separation, the consolidated and combined financial statements reflect allocations of certain expenses from bluebird bio, including, but not limited to, general corporate expenses, such as senior management, legal, human resources, accounting, other financial services (such as treasury, audit and purchasing),

tax, information technology, and corporate employee benefits, incentives and stock-based compensation included within selling, general and administrative expense.

These expenses have been allocated to the Company based on direct usage or benefit where specifically identifiable, with the remainder allocated based on employee time spent on projects, square footage or other measures that management believes are consistent and reasonable. Allocations for management costs and corporate support services provided to the Company totaled $55.3 million, $76.6 million, and $67.8 million for the years ended December 31, 2021, 2020 and 2019, respectively.

The financial information in these consolidated and combined financial statements for periods prior to the separation does not necessarily include all the expenses that would have been incurred by the Company had it been a separate, stand-alone entity. Actual costs that may have been incurred if the Company had been a stand-alone company would depend on a number of factors, including the chosen organization structure and functions outsourced or performed by employees. See Note 2, Summary of significant accounting policies and basis of presentation, for additional information on the preparation and basis of presentation of these consolidated and combined financial statements, including the treatment of certain research and development costs not directly attributable to individual programs.

Usage of the Company's assets by bluebird bio and of bluebird bio's assets by the Company prior to the separation

Certain assets have been reflected in these consolidated and combined financial statements as the underlying assets were attributed to the Company; however, bluebird bio has historically utilized a portion of the underlying asset as part of its operations. Accordingly, the expense related to the underlying asset has been reflected in the combined financial statements. The Company has also recorded an imputed charge to bluebird bio to reflect the cost of bluebird bio's proportional usage. In addition, the Company has recorded as an expense an imputed charge to reflect the cost of the Company's proportional usage of certain underlying assets not reflected in the consolidated and combined financial statements but for which the Company has historically utilized a portion of the underlying asset as part of its operations. The income and expense recognized by the Company for periods prior to the separation resulting from these imputed charges was recorded as other income, net in the combined financial statements and was as follows:


	Year ended December 31,
	2021		2020		2019
Imputed charge to bluebird bio for leases	$	14,833	$	16,562	$	17,694
Imputed charge from bluebird bio for leases	(908)		(1,072)		(696)
Imputed charge to bluebird bio for property, plant and equipment	1,891		2,225		3,385
Imputed charge from bluebird bio for property, plant and equipment	(1,130)		(229)		(99)
Imputed charge to bluebird bio for intangible assets	82		199		65
Other	(1)		155		(116)
	$	14,767	$	17,840	$	20,233

Other components of other income, net, that are not shown in the table above include immaterial gains and losses on disposals of fixed assets.

Stock-based compensation

As discussed in Note 13, Stock-based compensation, prior to the separation, 2seventy bio’s employees participated in bluebird bio's stock-based compensation plans, the costs of which have been allocated to 2seventy bio and recorded in research and development and selling, general and administrative expenses in the consolidated and combined statements of operations and comprehensive loss.

Retirement plans

As discussed in Note 15, 401(k) Savings plan, prior to the separation, 2seventy bio’s employees participated in bluebird bio's 401(k) Savings plan, the costs of which have been allocated to 2seventy bio and recorded in research and development and selling, general and administrative expenses in the consolidated and combined statements of operations and comprehensive loss.

Transaction costs

Prior to the separation, bluebird bio had incurred costs related to the separation of the Company. To the extent separation costs are incurred that will directly benefit the Company as a stand-alone company, such costs were allocated to the Company.

Centralized cash management

Prior to the separation, no separate cash accounts for 2seventy bio were maintained and, therefore, bluebird bio was presumed to have funded 2seventy bio’s operating, investing and financing activities as necessary. As cash was disbursed and received by bluebird bio, for purposes of the consolidated and combined financial statements, funding of 2seventy bio’s expenditures was reflected in the consolidated and combined financial statements as a component of net parent investment.

401(k) Savings plan	12 Months Ended
401(k) Savings plan	Dec. 31, 2021
Retirement Benefits [Abstract]
401(k) Savings plan	401(k) Savings planPrior to the spin-off, all 2seventy employees were covered by bluebird bio’s defined-contribution savings plan under Section 401(k) of the Internal Revenue Code (“bluebird 401(k) Plan”), which was established in 1997. Upon spin-off, 2seventy bio established a defined-contribution savings plan under Section 401(k) of the Internal Revenue Code (“2seventy 401(k) Plan”), which covers all employees who meet defined minimum age and service requirements, including those who became employees of the Company, and allows participants to defer a portion of their annual compensation on a pretax basis. Expense related to the bluebird and 2seventy 401(k) Plans for 2seventy employees totaled $2.4 million, $2.2 million, $2.0 million for the years ended December 31, 2021, 2020, and 2019, respectively.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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+ Details

Income taxes

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Income taxes

The Company did not operate as a separate, stand-alone entity for periods prior to the separation. The Company’s statement of operations for periods prior to separation have been prepared on a carve out basis. The Company’s income tax provision for the year ended December 31, 2021 has been prepared on a stand alone basis for the period in which the Company was an independent, publicly traded Company from November 4, 2021 through December 31, 2021. Accordingly, the amount and composition of its tax losses, credits, and other deferred tax assets included in the consolidated and combined financial statements has change as the result of the Company’s separation from bluebird bio.

The components of loss before income taxes were as follows (in thousands):


	Year ended December 31,
	2021		2020		2019
Domestic	$	(292,213)	$	(120,114)	$	(320,594)
Foreign	—		—		—
Total	$	(292,213)	$	(120,114)	$	(320,594)

The Company has not recorded a provision for federal or state income taxes as it has had cumulative net operating losses since inception.

For the years ended December 31, 2021, 2020 and 2019, the Company did not recognize any income tax expense (benefit) as the Company was subject to a full valuation allowance. A reconciliation of income tax expense

(benefit) computed at the statutory federal income tax rate to the Company’s effective income tax rate as reflected in the financial statements is as follows:


	Year ended December 31,
	2021		2020		2019
Federal income tax expense at statutory rate	21.0	%	21.0	%	21.0	%
State income tax, net of federal benefit	0.6	%	3.8	%	5.5	%
Permanent differences	—	%	0.3	%	(0.1)	%
Stock-based compensation	0.3	%	(4.1)	%	(0.5)	%
Research and development credit	0.2	%	13.8	%	5.6	%
Officer compensation limitation	(0.4)	%	(1.6)	%	(0.7)	%
Uncertain tax positions	—	%	(1.1)	%	(0.4)	%
Other	(1.1)	%	—	%	(0.2)	%
Change in valuation allowance	64.8	%	(32.1)	%	(30.2)	%
Separation adjustment	(85.4)	%	—	%	—	%
Effective income tax rate (expense) benefit	—	%	—	%	—	%

Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets and liabilities are composed of the following (in thousands):


	Year ended December 31,
	2021		2020
Deferred tax assets:
U.S. net operating loss carryforwards (federal and state)	$	12,142	$	149,570
Tax credit carryforwards (federal and state)	466		49,379
Capitalized license fees and research and development expenses	11,905		13,091
Deferred revenue	13,724		15,348
Stock-based compensation	15,824		21,400
Lease liabilities	71,941		34,119
Accruals and other	5,395		2,715
Total deferred tax assets	131,397		285,622
Intangible assets	(476)		(1,509)
Right-of-use assets	(69,693)		(31,139)
Fixed assets	(2,958)		(5,477)
Less: valuation allowance	(58,270)		(247,497)
Net deferred taxes	$	—	$	—

For the year ended December 31, 2020, deferred tax assets and liabilities are a result of the separate return calculation presentation and may not represent deferred tax assets and liability balances after the separation.

As of December 31, 2021, the Company had U.S. federal net operating loss carryforwards of approximately $47.9 million, which may be available to offset future income tax liabilities and which will carryforward indefinitely. As of December 31, 2021, the Company also had U.S. state net operating loss carryforwards of approximately $34.3 million, which may be available to offset future income tax liabilities and expire at various dates through 2041.

As of December 31, 2021, the Company had federal research and development and orphan drug tax credit carryforwards of approximately $0.5 million, available to reduce future tax liabilities which expire at various dates through 2041. An analysis of the U.S. research and development and orphan drug credits has not yet been

completed. Until a study is completed by the Company and any limitation is known, no amounts are being presented as an uncertain tax position.

Utilization of the net operating loss carryforwards and research and development tax credit carryforwards may be subject to an annual limitation under Section 382 of the Internal Revenue Code of 1986, as amended (the “Internal Revenue Code”), and corresponding provisions of state law, due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50 percent over a three-year period. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards would be subject to an annual limitation under Section 382, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed and any limitation is known, no amounts are being presented as an uncertain tax position.

A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. Due to the uncertainty surrounding the realization of the favorable tax attributes in future tax returns, the Company has recorded a full valuation allowance against the Company’s otherwise recognizable net deferred tax assets. With respect to the period from separation through December 31, 2021, the valuation allowance increased on a net basis by approximately $58.3 million.

In March 2020, the Coronavirus Aid, Relief and Economic Security Act (“CARES Act”) was enacted. This law temporarily suspends and adjusts certain law changes enacted in the Tax Cuts and Jobs Act in 2017. In December 2020, the Consolidated Appropriations Act was enacted. This law modified the employee retention credit under the CARES Act and created credit extenders for certain credits. The Company has concluded that the provisions in the CARES Act and Consolidated Appropriations Act have an immaterial impact on the Company’s income tax expense due to its cumulative losses and full valuation allowance position.

The Company is in the process of filing its first tax return and has no history of tax audits on a standalone basis and will regularly assesses the outcome of potential examinations in each of the taxing jurisdictions when determining the adequacy of the amount of unrecognized tax benefit recorded.

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands):


	Unrecognized tax benefits
Balance as of December 31, 2019	$	3,070
Increases (decreases) for tax positions related to current period	1,333
Increases (decreases) for tax positions related to prior periods	—
Balance as of December 31, 2020	4,403
Increases (decreases) for tax positions related to current period	36
Increases (decreases) for tax positions as part of separation adjustment	(4,403)
Balance as of December 31, 2021	$	36

The unrecognized tax benefits at December 31, 2021 is not material and, if recognized, would not affect the Company’s effective tax rate due to its full valuation allowance position. The Company does not anticipate that the amount of existing unrecognized tax benefits will significantly increase or decrease within the next 12 months. The Company has elected to include interest and penalties related to uncertain tax positions as a component of its

provision for income taxes. For the year ended December 31, 2021, the Company’s accrued interest and penalties related to uncertain tax positions were not material.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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-Section 50
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-URI http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 270
-Section 50
-Paragraph 1
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-URI http://asc.fasb.org/topic&trid=2144680

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Net loss per share

12 Months Ended

Dec. 31, 2021

Earnings Per Share [Abstract]

Net loss per share

The following common stock equivalents were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect (in thousands):


	Year ended December 31,
	2021	2020	2019
Outstanding stock options (1)	1,490	—	—
Restricted stock units (1)	1,080	—	—
	2,570	—	—

(1)Outstanding stock options and restricted stock units include awards outstanding to employees of bluebird bio.

Subsequent events	12 Months Ended
Subsequent events	Dec. 31, 2021
Subsequent Events [Abstract]
Subsequent events	Subsequent eventsIn March 2022, the Company entered into stock purchase agreements with certain investors, pursuant to which the Company agreed to sell and issue, in a private placement, an aggregate of 13,934,427 shares of the Company’s common stock at a purchase price per share of $12.20. This resulted in aggregate gross proceeds to the Company of approximately $170 million, before deducting placement agent fees and other offering expenses payable by the Company.

Summary of significant accounting policies and basis of presentation (Policies)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Basis of presentation

statements for periods prior to the separation. As a result of the separation, the Company’s net parent investment balance was reclassified to additional paid-in capital.

Amounts reported are computed based on thousands, except percentages or as otherwise noted. As a result, certain totals may not sum due to rounding.

Principles of combination

Principles of consolidation and combination

Periods prior to separation

Periods after the separation

Variable interest entities

Use of estimates

Segment information

Cash and cash equivalents

Restricted cash

Marketable securities

There were no marketable securities specifically attributable to 2seventy bio for the historical periods presented prior to the separation.

Concentrations of credit risk and off-balance sheet risk

Fair value of financial instruments

Level 1—Fair values are determined utilizing quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

Level 3—Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable.

within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Business combinations

The consolidated and combined financial statements include the results of operations of an acquired business after the completion of the acquisition.

Goodwill

GoodwillGoodwill represents the excess of the purchase price over the fair value of the net assets acquired when accounted for using the acquisition method of accounting. Goodwill is not amortized; rather, it is evaluated for impairment within the Company’s single reporting unit on an annual basis, during the fourth quarter, or more frequently if an event occurs or circumstances change that would more-likely-than-not reduce the fair value of the Company’s reporting unit below its carrying amount. The Company performs a one-step quantitative test and records the amount of goodwill impairment, if any, as the excess of a reporting unit's carrying amount over its fair value, not to exceed the total amount of goodwill allocated to the reporting unit.

Intangible assets, net

Contingent consideration

Property, plant and equipment


Asset						Estimated useful life
Building						40 years
Computer equipment and software						3 years
Furniture and fixtures						2-5 years
Laboratory equipment						2-5 years
Leasehold improvements						Shorter of the useful life or remaining lease term

Impairment of long-lived assets

Leases

Effective January 1, 2019, the Company adopted ASC 842, Leases (“ASC 842”) using the required modified retrospective approach and utilizing the effective date as its date of initial application.

Common stock warrants

Revenue recognition

The Company recognizes revenue within the following financial statement captions:

Service revenue

Collaborative arrangement revenue


Nature of Payment						Statement of Operations Presentation
The Company's share of net profits in connection with commercialization of products						Collaborative arrangement revenue
The Company's share of net losses in connection with commercialization of products						Share of collaboration loss
Net reimbursement of the Company's research and development expenses						Collaborative arrangement revenue
Net reimbursement of the collaborator's research and development expenses						Research and development expense

Royalty and other revenue

Research and development expenses

Cost of royalty and other revenue

Cost of royalty and other revenue represents expense associated with amounts owed to third parties as a result of revenue recognized under the Company’s out-license arrangements.

Stock-based compensation

Comprehensive loss is composed of net loss and other comprehensive income (loss). Other comprehensive income (loss) consists of unrealized gains and losses on debt securities.

Recent accounting pronouncements

Recently adopted

ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes

ASU No. 2020-08, Codification Improvements to Subtopic 310-20, Receivables - Nonrefundable Fees and Other Costs

ASU No. 2020-10, Codification Improvements

Summary of significant accounting policies and basis of presentation (Tables)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Estimated Useful Lives of Assets

Depreciation and amortization is calculated using the straight-line method over the estimated useful lives of the assets, which are as follows:


Asset						Estimated useful life
Building						40 years
Computer equipment and software						3 years
Furniture and fixtures						2-5 years
Laboratory equipment						2-5 years
Leasehold improvements						Shorter of the useful life or remaining lease term

Investments, Debt and Equity Securities (Tables)

12 Months Ended

Dec. 31, 2021

Investments, Debt and Equity Securities [Abstract]

Summary of Marketable Securities

The following table summarizes the marketable securities held at December 31, 2021 (in thousands):


	Amortized cost/ cost		Unrealized gains		Unrealized losses		Fair Value
December 31, 2021
U.S. government agency securities and treasuries	$	128,899	$	—	$	(507)	$	128,392
Corporate bonds	49,368		$	—	(58)		49,310
Commercial paper	54,065		$	—	—		54,065
Total	$	232,332	$	—	$	(565)	$	231,767

As of December 31, 2020, the Company did not have any marketable securities. No available-for-sale debt securities held as of December 31, 2021 had remaining maturities greater than five years.

Fair value measurements (Tables)

12 Months Ended

Dec. 31, 2021

Fair Value Disclosures [Abstract]

Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis

The following table sets forth the Company’s assets and liabilities that are measured at fair value on a recurring basis as of December 31, 2021 and 2020 (in thousands):


	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
December 31, 2021
Assets:
Cash and cash equivalents	$	130,414	$	130,414	$	—	$	—
Marketable securities:
U.S. government agency securities and treasuries	128,392		—		128,392		—
Corporate bonds	49,310		—		49,310		—
Commercial paper	54,065		—		54,065		—
Total assets	$	362,181	$	130,414	$	231,767	$	—
Liabilities:
Contingent consideration	$	1,948	$	—	$	—	$	1,948
Total liabilities	$	1,948	$	—	$	—	$	1,948
December 31, 2020
Liabilities:
Contingent consideration	$	1,509	$	—	$	—	$	1,509
Total liabilities	$	1,509	$	—	$	—	$	1,509

Summary of Available-for-sale Debt Securities in a Continuous Unrealized Loss Position


	Less than 12 months				12 months or greater				Total
Description	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
December 31, 2021
U.S. government agency securities and treasuries	$	111,190	$	(507)	$	—	$	—	$	111,190	$	(507)
Corporate bonds	48,940		(58)		—		—		48,940		(58)
Total	$	160,130	$	(565)	$	—	$	—	$	160,130	$	(565)

Roll-Forward of Fair Value of the Company's Contingent Consideration Obligations

The table below provides a roll-forward of fair value of the Company’s contingent consideration obligations that include Level 3 inputs (in thousands):


	Year ended December 31,
	2021		2020
Beginning balance	$	1,509	$	7,977
Additions	—		—
Changes in fair value	439		(6,468)
Payments	—		—
Ending balance	$	1,948	$	1,509

Property, plant and equipment, net (Tables)

12 Months Ended

Dec. 31, 2021

Property, Plant and Equipment [Abstract]

Summary of Property, Plant and Equipment, Net

Property, plant and equipment, net, consists of the following (in thousands):


	As of December 31,
	2021		2020
Land	$	—	$	1,210
Building	—		15,745
Computer equipment and software	5,260		6,503
Office equipment	6,080		6,588
Laboratory equipment	31,710		24,080
Leasehold improvements	28,479		28,305
Construction-in-progress	3,462		91,631
Total property, plant and equipment	74,991		174,062
Less accumulated depreciation and amortization	(40,078)		(30,037)
Property, plant and equipment, net	$	34,913	$	144,025

Accrued expenses and other current liabilities (Tables)

12 Months Ended

Dec. 31, 2021

Payables and Accruals [Abstract]

Summary of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consist of the following (in thousands):


	As of December 31,
	2021		2020
Employee compensation	$	24,655	$	9,451
Royalties	6,768		1,493
Manufacturing costs	5,459		6,808
Clinical and contract research organization costs	3,229		2,854
Collaboration research costs	2,576		19,605
Property, plant, and equipment	2,241		440
Professional fees	1,688		—
Separation related costs	762		—
License and milestone fees	123		278
Other	7,909		2,418
Total accrued expenses and other current liabilities	$	55,410	$	43,347

Leases (Tables)

12 Months Ended

Dec. 31, 2021

Leases [Abstract]

Summary of Lease Costs and Other Information Pertaining to Operating Leases


	For the year ended December 31,
	2021			2020			2019
Lease cost (1)
Operating lease cost	$	24,838		$	22,454		$	21,406
Total lease cost	$	24,838		$	22,454		$	21,406

Other information
Operating cash flows used for operating leases	$	25,489		$	19,632		$	19,521
Weighted average remaining lease term	11.8 years			6.4 years			7.4 years
Weighted average discount rate	5.47		%	6.72		%	6.73		%

________________

(1)Short-term lease costs and variable lease costs incurred by the Company for the twelve months ended December 31, 2021, 2020 and 2019 were immaterial.

Summary of Future Minimum Commitments

As of December 31, 2021, future minimum commitments under ASC 842 under the Company’s operating leases were as follows (in thousands):


Maturity of lease liabilities	As of December 31, 2021
2022	$	27,078
2023	27,864
2024	28,675
2025	29,501
2026	32,920
2027 and thereafter	250,383
Total lease payments	396,421
Less: imputed interest	(114,206)
Total operating lease liabilities	$	282,215

Commitments and contingencies (Tables)

12 Months Ended

Dec. 31, 2021

Commitments and Contingencies Disclosure [Abstract]

Schedule of Non-cancelable Contractual Obligations

The following table presents non-cancelable contractual obligations arising from these arrangements:


Years ended December 31,	Purchase commitment
2022	$	15,750
Total purchase commitments	$	15,750

Stockholders' equity (Tables)

12 Months Ended

Dec. 31, 2021

Equity [Abstract]

Schedule of Common Stock Reserved for Future Issuance

The Company has reserved for future issuance the following number of shares of common stock (in thousands):


	As of December 31,
	2021		2020
Options to purchase common stock (1)	$	1,490	$	—
Restricted stock units (1)	1,080		—
2021 Stock Option and Incentive Plan	2,125		—
2021 Employee Stock Purchase Plan	233		—
Pre-funded warrants to purchase common stock	758
Total	$	5,686	$	—

(1)Outstanding stock options and restricted stock units include awards outstanding to employees of bluebird bio.

Collaborative arrangements and strategic partnerships (Tables)

12 Months Ended

Dec. 31, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Summary of Total Transaction Price, Allocation of Total Transaction Price to Identified Performance Obligations Under Arrangement and Amount of Transaction Price Unsatisfied


	Transaction price as of December 31, 2021
	Ide-cel		bb21217
Upfront non-refundable payments received prior to May 2020 contract modification (1)	$	120,000	$	15,000
Allocated portion of the upfront non-refundable payment received in connection with the Amended Ide-cel CCPS and bb21217 License Agreement (2)	184,029		15,971
Estimated variable consideration (3)	83,900		1,803
	$	387,929	$	32,774

(2) This represents the portion of the $200.0 million up-front payment received under the Amended Ide-cel CCPS and Amended bb21217 License Agreement which was allocated to ide-cel and bb21217.

(3) Estimated variable consideration represents the estimated reimbursement from BMS for the manufacture of vectors and associated payload through development.

The following table summarizes the net collaboration revenue recognized or expense incurred for the joint ide-cel development efforts in the U.S. under ASC 808, including revenue or expense related to the combined performance obligation for license and manufacturing of ide-cel in the U.S. for the years ended December 31, 2021, 2020 and 2019 (in thousands):


	For the years ended December 31,
	2021		2020		2019
ASC 808 ide-cel license and manufacturing revenue - U.S. (1)(2)	$	—	$	108,196	$	—
ASC 808 ide-cel license and manufacturing expense - U.S. (1)	$	—	$	(41,599)	$	(32,415)

The Company recognized the following on the statements of operations and comprehensive loss related to its share of collaboration profit or loss associated with


	For the three months ended March 31, 2021		For the three months ended June 30, 2021		For the three months ended September 30, 2021		For the three months ended December 31, 2021
Net revenue	$	—	$	—	$	10,607	$	8,818
Net expense	$	—	$	(10,071)	$	—	$	—

The following table summarizes the amounts associated with the research activities under the collaboration included in research and development expense or recognized as collaborative arrangement revenue for each quarter during the year ended December 31, 2021 (in thousands):


	For the three months ended March 31, 2021		For the three months ended June 30, 2021		For the three months ended September 30, 2021		For the three months ended December 31, 2021
Net expense	$	(16,825)	$	(9,193)	$	(5,660)	$	(7,835)


	For the years ended December 31,
	2021		2020		2019
ASC 606 ide-cel license and manufacturing revenue – ex-U.S. (1)	$	16,895	$	99,053	$	25,522

Changes in Balances of Company's Receivables and Contract Liabilities

The following table presents changes in the balances of the Company’s BMS receivables and contract liabilities during the twelve months ended December 31, 2021 (in thousands):


	Balance at December 31, 2020		Additions		Deductions		Balance at December 31, 2021
Receivables	$	400	$	13,441	$	(13,189)	$	652
Contract liabilities:
Deferred revenue	$	26,582	$	—	$	(820)	$	25,762

Intangible assets (Tables)

12 Months Ended

Dec. 31, 2021

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Finite-Lived Intangible Assets

Intangible assets, net of accumulated amortization, are summarized as follows (in thousands):


	As of December 31,						As of December 31,
	2021						2020
	Cost		Accumulated amortization		Net		Cost		Accumulated amortization		Net
Developed technology	$	30,100	$	(28,218)	$	1,882	$	30,100	$	(24,456)	$	5,644
In-licensed rights	8,500		(490)		8,010		—		—		—
Total	$	38,600	$	(28,708)	$	9,892	$	30,100	$	(24,456)	$	5,644

Schedule of Finite-Lived Intangible Assets, Future Amortization Expense

The following table summarizes the estimated future amortization for intangible assets for the next five years and thereafter (in thousands):


	As of December 31, 2021
2022	$	2,590
2023	708
2024	708
2025	708
2026	708
2027 and thereafter	4,470
Total	$	9,892

Stock-based compensation (Tables)

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

Stock-based Compensation Expense Recognized by Award Type

Stock-based compensation expense recognized by award type is as follows (in thousands):


	Year Ended December 31,
	2021		2020		2019
Stock options	$	26,185	$	36,685	$	36,792
Restricted stock units	21,414		19,185		24,744
Employee stock purchase plan and other	7,030		5,127		512
	$	54,629	$	60,997	$	62,049

Schedule of Stock-Based Compensation Expense by Classification

Stock-based compensation expense by classification included within the consolidated statements of operations and comprehensive loss was as follows (in thousands):


	Year Ended December 31,
	2021		2020		2019
Research and development	$	29,746	$	30,935	$	33,853
Selling, general and administrative	24,883		30,062		28,196
	$	54,629	$	60,997	$	62,049

Summary of Stock Option Activity

The following table summarizes the stock option activity under the Company’s equity awards plans for 2seventy employees:


	Shares (in thousands)	Weighted-average exercise price per share		Weighted-average contractual life (in years)	Aggregate intrinsic value (a) (in thousands)
Outstanding at December 31, 2020	—	$	—
Granted	—	$	—
Converted in distribution	875	$	129.67
Exercised	—	$	—
Canceled or forfeited	(2)	$	157.43
Outstanding at December 31, 2021	873	$	129.60	6.6	$	131
Exercisable at December 31, 2021	518	$	161.76	5.2	$	131
Vested and expected to vest at December 31, 2021	873	$	129.60	6.6	$	131

Summary of Restricted Stock Unit Activity

The following table summarizes the restricted stock unit activity under the Company’s equity award plans for 2seventy employees:


	Shares (in thousands)	Weighted-average exercise price per share
Unvested balance at December 31, 2020	—	$	—
Granted	9	36.14
Converted in distribution	969	50.93
Vested	(3)	137.65
Forfeited	(4)	86.12
Unvested balance at December 31, 2021	971	$	50.56

Related-party transactions (Tables)

12 Months Ended

Dec. 31, 2021

Schedule of Income and Expense Resulting from Imputed Charges

The income and expense recognized by the Company for periods prior to the separation resulting from these imputed charges was recorded as other income, net in the combined financial statements and was as follows:


	Year ended December 31,
	2021		2020		2019
Imputed charge to bluebird bio for leases	$	14,833	$	16,562	$	17,694
Imputed charge from bluebird bio for leases	(908)		(1,072)		(696)
Imputed charge to bluebird bio for property, plant and equipment	1,891		2,225		3,385
Imputed charge from bluebird bio for property, plant and equipment	(1,130)		(229)		(99)
Imputed charge to bluebird bio for intangible assets	82		199		65
Other	(1)		155		(116)
	$	14,767	$	17,840	$	20,233

Income taxes (Tables)

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Schedule Components of Loss Before Income Taxes

The components of loss before income taxes were as follows (in thousands):


	Year ended December 31,
	2021		2020		2019
Domestic	$	(292,213)	$	(120,114)	$	(320,594)
Foreign	—		—		—
Total	$	(292,213)	$	(120,114)	$	(320,594)

Reconciliation of Income Tax Provision (Benefit) Computed at the Statutory Federal Income Tax Rate to Effective Income Tax Rate (Provision) Benefit as Reflected in the Financial Statements


	Year ended December 31,
	2021		2020		2019
Federal income tax expense at statutory rate	21.0	%	21.0	%	21.0	%
State income tax, net of federal benefit	0.6	%	3.8	%	5.5	%
Permanent differences	—	%	0.3	%	(0.1)	%
Stock-based compensation	0.3	%	(4.1)	%	(0.5)	%
Research and development credit	0.2	%	13.8	%	5.6	%
Officer compensation limitation	(0.4)	%	(1.6)	%	(0.7)	%
Uncertain tax positions	—	%	(1.1)	%	(0.4)	%
Other	(1.1)	%	—	%	(0.2)	%
Change in valuation allowance	64.8	%	(32.1)	%	(30.2)	%
Separation adjustment	(85.4)	%	—	%	—	%
Effective income tax rate (expense) benefit	—	%	—	%	—	%

Components of Deferred Tax Assets and Liabilities


	Year ended December 31,
	2021		2020
Deferred tax assets:
U.S. net operating loss carryforwards (federal and state)	$	12,142	$	149,570
Tax credit carryforwards (federal and state)	466		49,379
Capitalized license fees and research and development expenses	11,905		13,091
Deferred revenue	13,724		15,348
Stock-based compensation	15,824		21,400
Lease liabilities	71,941		34,119
Accruals and other	5,395		2,715
Total deferred tax assets	131,397		285,622
Intangible assets	(476)		(1,509)
Right-of-use assets	(69,693)		(31,139)
Fixed assets	(2,958)		(5,477)
Less: valuation allowance	(58,270)		(247,497)
Net deferred taxes	$	—	$	—

Reconciliation of Unrecognized Tax Benefits

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands):


	Unrecognized tax benefits
Balance as of December 31, 2019	$	3,070
Increases (decreases) for tax positions related to current period	1,333
Increases (decreases) for tax positions related to prior periods	—
Balance as of December 31, 2020	4,403
Increases (decreases) for tax positions related to current period	36
Increases (decreases) for tax positions as part of separation adjustment	(4,403)
Balance as of December 31, 2021	$	36

Net loss per share (Tables)

12 Months Ended

Dec. 31, 2021

Earnings Per Share [Abstract]

Schedule of Common Stock Equivalents Excluded from the Calculation of Diluted Net Loss per Share


	Year ended December 31,
	2021	2020	2019
Outstanding stock options (1)	1,490	—	—
Restricted stock units (1)	1,080	—	—
	2,570	—	—

(1)Outstanding stock options and restricted stock units include awards outstanding to employees of bluebird bio.

Description of the business - Narrative (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net loss	$ 292,213	$ 120,114	$ 320,594
Net cash used in operating activities	207,034	$ 67,793	$ 207,957
Cash, cash equivalents, and marketable securities	$ 362,200

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(22))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=124431687&loc=d3e22595-107794

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(18))
-URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 40
-Section 65
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=123482062&loc=SL123482106-238011

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=124431353&loc=SL124452729-227067

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
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+ Details

Summary of significant accounting policies and basis of presentation - Narrative (Detail)	12 Months Ended
	Dec. 31, 2021 USD ($) segment shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($)	Nov. 04, 2021 USD ($)	Nov. 03, 2021 shares
Restricted Cash and Cash Equivalents Items [Line Items]
Transfers from bluebird bio	$ 354,889,000	$ 90,054,000	$ 267,722,000
Net assets				$ 384,500,000
Number of operating segments \| segment	1
Accumulated goodwill impairment loss	$ 0
Interest income	$ 88,000	$ 0	0
Common stock, shares outstanding (in shares) \| shares	23,585,000	0			0
Restricted cash included in restricted cash and other non-current assets	$ 32,852,000	$ 0	$ 0
Letter of credit
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash included in restricted cash and other non-current assets	$ 30,000,000

Summary of significant accounting policies and basis of presentation - Estimated Useful Lives of Assets (Detail)	12 Months Ended
	Dec. 31, 2021
Building
Property, Plant and Equipment [Line Items]
Estimated useful life	40 years
Computer equipment and software
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Furniture and fixtures \| Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	2 years
Furniture and fixtures \| Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Laboratory equipment \| Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	2 years
Laboratory equipment \| Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years

Marketable securities - Summary of Marketable Securities (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Marketable Securities [Line Items]
Amortized cost/ cost	$ 232,332,000
Unrealized gains	0
Unrealized losses	(565,000)
Fair Value	231,767,000	$ 0
U.S. government agency securities and treasuries
Marketable Securities [Line Items]
Amortized cost/ cost	128,899,000
Unrealized gains	0
Unrealized losses	(507,000)
Fair Value	128,392,000
Corporate bonds
Marketable Securities [Line Items]
Amortized cost/ cost	49,368,000
Unrealized gains	0
Unrealized losses	(58,000)
Fair Value	49,310,000
Commercial paper
Marketable Securities [Line Items]
Amortized cost/ cost	54,065,000
Unrealized gains	0
Unrealized losses	0
Fair Value	$ 54,065,000

Fair value measurements - Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Assets:
Marketable securities:	$ 231,767,000	$ 0
U.S. government agency securities and treasuries
Assets:
Marketable securities:	128,392,000
Corporate bonds
Assets:
Marketable securities:	49,310,000
Commercial paper
Assets:
Marketable securities:	54,065,000
Fair value, measurements, recurring
Assets:
Cash and cash equivalents	130,414,000
Total assets	362,181,000	0
Liabilities:
Contingent consideration	1,948,000	1,509,000
Total liabilities	1,948,000	1,509,000
Fair value, measurements, recurring \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	128,392,000
Fair value, measurements, recurring \| Corporate bonds
Assets:
Marketable securities:	49,310,000
Fair value, measurements, recurring \| Commercial paper
Assets:
Marketable securities:	54,065,000
Fair value, measurements, recurring \| Quoted prices in active markets (Level 1)
Assets:
Cash and cash equivalents	130,414,000
Total assets	130,414,000
Liabilities:
Contingent consideration	0	0
Total liabilities	0	0
Fair value, measurements, recurring \| Quoted prices in active markets (Level 1) \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	0
Fair value, measurements, recurring \| Quoted prices in active markets (Level 1) \| Corporate bonds
Assets:
Marketable securities:	0
Fair value, measurements, recurring \| Quoted prices in active markets (Level 1) \| Commercial paper
Assets:
Marketable securities:	0
Fair value, measurements, recurring \| Significant other observable inputs (Level 2)
Assets:
Cash and cash equivalents	0
Total assets	231,767,000
Liabilities:
Contingent consideration	0	0
Total liabilities	0	0
Fair value, measurements, recurring \| Significant other observable inputs (Level 2) \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	128,392,000
Fair value, measurements, recurring \| Significant other observable inputs (Level 2) \| Corporate bonds
Assets:
Marketable securities:	49,310,000
Fair value, measurements, recurring \| Significant other observable inputs (Level 2) \| Commercial paper
Assets:
Marketable securities:	54,065,000
Fair value, measurements, recurring \| Significant unobservable inputs (Level 3)
Assets:
Cash and cash equivalents	0
Total assets	0
Liabilities:
Contingent consideration	1,948,000	1,509,000
Total liabilities	1,948,000	$ 1,509,000
Fair value, measurements, recurring \| Significant unobservable inputs (Level 3) \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	0
Fair value, measurements, recurring \| Significant unobservable inputs (Level 3) \| Corporate bonds
Assets:
Marketable securities:	0
Fair value, measurements, recurring \| Significant unobservable inputs (Level 3) \| Commercial paper
Assets:
Marketable securities:	$ 0

Fair value measurements - Narrative (Detail)	12 Months Ended
Fair value measurements - Narrative (Detail)	Dec. 31, 2021 USD ($)
Fair Value Disclosures [Abstract]
Realized gain (loss) recognized on sale	$ 0
Interest receivable	400,000
Interest receivable, write-off	$ 0

Fair value measurements - Schedule of Unrealized Loss on Investments (Details) $ in Thousands	Dec. 31, 2021 USD ($)
Fair value
Less than 12 months	$ 160,130
12 months or greater	0
Total	160,130
Unrealized losses
Less than 12 months	(565)
12 months or greater	0
Total	(565)
U.S. government agency securities and treasuries
Fair value
Less than 12 months	111,190
12 months or greater	0
Total	111,190
Unrealized losses
Less than 12 months	(507)
12 months or greater	0
Total	(507)
Corporate bonds
Fair value
Less than 12 months	48,940
12 months or greater	0
Total	48,940
Unrealized losses
Less than 12 months	(58)
12 months or greater	0
Total	$ (58)

Fair value measurements - Roll-Forward of Fair Value of the Company's Contingent Consideration Obligations (Detail) - Significant unobservable inputs (Level 3) - Contingent consideration obligations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 1,509	$ 7,977
Additions	0	0
Changes in fair value	439	(6,468)
Payments	0	0
Ending balance	$ 1,948	$ 1,509

Property, plant and equipment, net - Summary of Property, Plant and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 74,991	$ 174,062
Less accumulated depreciation and amortization	(40,078)	(30,037)
Property, plant and equipment, net	34,913	144,025
Land
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	1,210
Building
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	15,745
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	5,260	6,503
Office equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	6,080	6,588
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	31,710	24,080
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	28,479	28,305
Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 3,462	$ 91,631

Property, plant and equipment, net - Narrative (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2021
Property, Plant and Equipment [Line Items]
Depreciation	$ 12,100	$ 9,400	$ 8,800
Construction in progress	$ 74,991	174,062
Lentiviral Vector Manufacturing Facility
Property, Plant and Equipment [Line Items]
Net assets disposed of				$ 111,200
Construction In Progress North Carolina Manufacturing Facility
Property, Plant and Equipment [Line Items]
Construction in progress		$ 91,100

Accrued expenses and other current liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Employee compensation	$ 24,655	$ 9,451
Royalties	6,768	1,493
Manufacturing costs	5,459	6,808
Clinical and contract research organization costs	3,229	2,854
Collaboration research costs	2,576	19,605
Property, plant, and equipment	2,241	440
Professional fees	1,688	0
Separation related costs	762	0
License and milestone fees	123	278
Other	7,909	2,418
Total accrued expenses and other current liabilities	$ 55,410	$ 43,347

Leases - Narrative (Details)			1 Months Ended				12 Months Ended
Leases - Narrative (Details)	Apr. 01, 2026 USD ($) $ / ft²	Oct. 01, 2016 USD ($) ft² $ / ft²	Nov. 30, 2021 USD ($) $ / ft²	Sep. 30, 2020 ft²	Sep. 30, 2019 ft² lease_term $ / ft²	Jul. 31, 2018 ft² $ / ft²	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($) $ / ft²	Dec. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Letter of credit							$ 32,852,000	$ 0	$ 0
Operating lease, expense							34,500,000	$ 32,500,000	$ 30,600,000
Letter of credit
Lessee, Lease, Description [Line Items]
Letter of credit							$ 30,000,000
Seattle, Washington
Lessee, Lease, Description [Line Items]
Lease building space (in sq ft) \| ft²				22,188	22,188	36,126
Annual lease rent per square foot (in dollars per sq ft) \| $ / ft²					62.80	54.00		62.80
Lease rent, annual increase percentage					2.50%	2.50%		2.50%
Lessee, operating lease, term of contract extension					16 months
Lease extension terms					5 years
Lessee, operating lease, number of contracts \| lease_term					2
60 Binney Street lease
Lessee, Lease, Description [Line Items]
Lease building space (in sq ft) \| ft²		253,108
Annual lease rent per square foot (in dollars per sq ft) \| $ / ft²		72.50	90.00
Lease payments base annual rent		$ 18,400,000	$ 22,800,000
Lease rent, annual increase percentage		1.75%	3.00%
Collateralized letter of credit		$ 13,800,000
Decrease in letter of credit under the terms of the lease		9,200,000
Landlord contribution for cost of construction and tenant improvements		$ 42,400,000	$ 19,100,000
60 Binney Street lease \| Letter of credit
Lessee, Lease, Description [Line Items]
Letter of credit			25,000,000
60 Binney Street lease \| Forecast
Lessee, Lease, Description [Line Items]
Annual lease rent per square foot (in dollars per sq ft) \| $ / ft²	118.41
Lease payments base annual rent	$ 30,000,000
Lease rent, annual increase percentage	3.00%
Office and Laboratory Space Lease \| Seattle, Washington \| Letter of credit
Lessee, Lease, Description [Line Items]
Letter of credit			$ 5,000,000

Leases - Summary of Lease Costs and Other Information Pertaining to Operating Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease cost	$ 24,838	$ 22,454	$ 21,406
Total lease cost	24,838	22,454	21,406
Operating cash flows used for operating leases	$ 25,489	$ 19,632	$ 19,521
Weighted average remaining lease term	11 years 9 months 18 days	6 years 4 months 24 days	7 years 4 months 24 days
Weighted average discount rate	5.47%	6.72%	6.73%

Leases - Schedule of Future Minimum Commitments Under Operating Leases (Details) $ in Thousands	Dec. 31, 2021 USD ($)
Leases [Abstract]
2022	$ 27,078
2023	27,864
2024	28,675
2025	29,501
2026	32,920
2027 and thereafter	250,383
Total lease payments	396,421
Less: imputed interest	(114,206)
Total operating lease liabilities	$ 282,215

Commitments and contingencies - Narrative (Detail) $ in Millions	1 Months Ended
	Jul. 31, 2021 USD ($) agreement batch	Jan. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Jun. 30, 2014 USD ($)
Subsequent Event
Commitments And Contingencies Disclosure [Line Items]
Non-cancelable contractual obligation		$ 7.2
Resilience
Commitments And Contingencies Disclosure [Line Items]
Number of manufacturing agreements \| agreement	2
Net operating losses, percentage of reimbursement	50.00%
Reimbursement cap	$ 15.0
Accrued liabilities			$ 2.6
Net operating losses, percentage of minimum purchase amount	50.00%
Resilience \| Maximum
Commitments And Contingencies Disclosure [Line Items]
Number of lentiviral vector batches \| batch	8
Pregenen
Commitments And Contingencies Disclosure [Line Items]
Contingent future cash payments				$ 99.9

Commitments and contingencies - Schedule of Non-cancelable Contractual Obligations (Detail) $ in Thousands	Dec. 31, 2021 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2022	$ 15,750
Total purchase commitments	$ 15,750

Stockholders' equity - Narrative (Details)	Dec. 31, 2021 vote shares	Nov. 30, 2021 $ / shares shares	Nov. 03, 2021 shares	Dec. 31, 2020 shares
Subsidiary, Sale of Stock [Line Items]
Common stock, shares authorized (in shares)	200,000,000			0
Common stock, number of votes (in votes per share) \| vote	1
Common stock, shares issued (in shares)	23,585,000			0
Common stock, shares outstanding (in shares)	23,585,000		0	0
Preferred stock, shares authorized (in shares)	10,000,000			0
Preferred stock, shares issued (in shares)	0			0
Preferred stock, shares outstanding (in shares)	0			0
Private Placement \| Bluebird Bio
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued (in shares)		23,368,988
Pre-funded Warrants \| Private Placement
Subsidiary, Sale of Stock [Line Items]
Pre-funded warrants issued (in shares)		757,575
Exercise price of warrants (in dollars per share) \| $ / shares		$ 0.0001

Stockholders' equity - Common Stock Reserved for Future Issuance (Details) - shares shares in Thousands	Dec. 31, 2021	Dec. 31, 2020
Subsidiary, Sale of Stock [Line Items]
Common stock reserved for future issuance (in shares)	5,686	0
Pre-funded Warrants
Subsidiary, Sale of Stock [Line Items]
Common stock reserved for future issuance (in shares)	758
2021 Stock Option and Incentive Plan
Subsidiary, Sale of Stock [Line Items]
Common stock reserved for future issuance (in shares)	2,125	0
2021 Employee Stock Purchase Plan
Subsidiary, Sale of Stock [Line Items]
Common stock reserved for future issuance (in shares)	233	0
Options to purchase common stock
Subsidiary, Sale of Stock [Line Items]
Common stock reserved for future issuance (in shares)	1,490	0
Restricted stock units
Subsidiary, Sale of Stock [Line Items]
Common stock reserved for future issuance (in shares)	1,080	0

Collaborative arrangements and strategic partnerships - Narrative (Detail)	1 Months Ended						3 Months Ended	12 Months Ended
	Jul. 31, 2021 USD ($) agreement batch	Aug. 31, 2018 USD ($) target accounting_unit $ / shares shares	Sep. 30, 2017 USD ($)	Feb. 29, 2016 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2013 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 23, 2021 USD ($) performance_obligation	Mar. 31, 2021 USD ($)	May 31, 2020 USD ($)	Mar. 31, 2018 USD ($)
Lentiviral Vector Manufacturing Facility
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from divestiture of business	$ 110,300,000
Number of manufacturing agreements \| agreement	2
Net operating losses reimbursement, percent	50.00%
Reimbursement cap	$ 15,000,000
Maximum \| Lentiviral Vector Manufacturing Facility
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of batches to be received \| batch	8
Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability								$ 25,762,000	$ 26,582,000
Term of collaboration agreement						3 years
Bristol-Myers Squibb \| Research and development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement, transaction price								40,900,000
Bristol-Myers Squibb \| bb21217 research and development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement, transaction price								5,400,000
Bristol-Myers Squibb \| BMS collaborative arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability						$ 75,000,000
Gross profit								9,400,000
Bristol-Myers Squibb \| Amended collaborative agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability					$ 25,000,000
Term of collaboration agreement					3 years
Bristol-Myers Squibb \| Ide-cel license agreement \| First product candidates
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement, option fee received				$ 10,000,000
Bristol-Myers Squibb \| Ide-cel license agreement \| First product candidates \| U.S.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable				85,000,000
Bristol-Myers Squibb \| Ide-cel license agreement \| First product candidates \| Outside of U.S.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable				$ 55,000,000
Bristol-Myers Squibb \| Ide-cel co development co promote and profit share agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development milestone payments receivable								387,929,000
Contract with customer development milestone payment achieved							$ 10,000,000
Bristol-Myers Squibb \| Ide-cel co development co promote and profit share agreement \| Outside of U.S.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable														$ 60,000,000
Bristol-Myers Squibb \| Ide-cel co development co promote and profit share agreement \| Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development milestone payments receivable														$ 10,000,000
Bristol-Myers Squibb \| Amended Ide-cel co development, co-promote and profit share agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone and royalty obligation buy-out								184,029,000				$ 10,000,000	$ 200,000,000
Bristol-Myers Squibb \| bb21217 license agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement, option fee received			$ 15,000,000
Development milestone payments receivable								32,774,000
Milestone and royalty obligation buy-out								15,971,000
Estimated variable consideration								1,803,000
Bristol-Myers Squibb \| bb21217 license agreement \| U.S.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable			85,000,000
Bristol-Myers Squibb \| bb21217 license agreement \| Outside of U.S.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable			$ 55,000,000
Bristol-Myers Squibb \| Ide-cel research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue								0	0	$ 2,300,000
Bristol-Myers Squibb \| Ide-cel license and manufacturing services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement, transaction price								347,000,000
Bristol-Myers Squibb \| Ide-cel license and manufacturing services \| License and manufacturing services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability								800,000
Bristol-Myers Squibb \| Ide-cel license and manufacturing services \| License and manufacturing services \| Outside of U.S.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue								16,895,000	99,053,000	25,522,000
Bristol-Myers Squibb \| bb21217 research and development services \| Phase I, initial obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue								0	0	2,200,000
Bristol-Myers Squibb \| bb21217 research and development services \| Phase I, additional obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue								0	12,400,000	400,000
Bristol-Myers Squibb \| bb21217 license and manufacturing services \| License and manufacturing services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability								25,800,000
Revenue								0	0	$ 0
Combined performance obligation, remaining								27,300,000
Remaining performance obligation not yet received								1,800,000
Regeneron Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of initial collaboration targets \| target		6
Research collaboration term		5 years
Number of accounting units \| accounting_unit		2
Joint research activities remaining to be recognized								23,300,000	30,800,000
Regeneron Collaboration Agreement \| Collaboration
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue balance recognized as gross revenues								7,500,000	$ 7,400,000
Regeneron Collaboration Agreement \| Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable		$ 130,000,000
Regeneron Collaboration Agreement \| Research and development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement, transaction price								100,000,000
Purchase price premium								$ 37,000,000
Collaborative arrangement amortization period								5 years
Collaborative arrangement amount attributed to equity sold								$ 54,500,000
Collaborative arrangement amount attributed to joint research activities								$ 45,500,000
Regeneron Collaboration Agreement \| Share purchase agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Issuance of common stock to Regeneron (in shares) \| shares		400,000
Common stock price per share (in dollars per share) \| $ / shares		$ 238.10
Investment in common stock		$ 100,000,000
Purchase price premium		$ 37,000,000
Collaborative arrangement research initial funding obligation, percentage		50.00%
Regeneron Collaboration Agreement \| Share purchase agreement \| Common stock
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Issuance of common stock to Regeneron (in shares) \| shares								400,000
Investment in common stock		$ 63,000,000
Novo Nordisk A/S \| Novo Collaboration and License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability											$ 5,000,000
Number of performance obligations \| performance_obligation											2
Estimated variable consideration								$ 11,700,000
Estimated variable consideration, upfront payment								5,000,000
Estimated variable consideration, research reimbursement								$ 6,700,000
Novo Nordisk A/S \| Novo Collaboration and License Agreement \| License and manufacturing services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable											$ 26,000,000
Novo Nordisk A/S \| Novo Collaboration and License Agreement \| Development and Commercialization Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable											72,000,000
Novo Nordisk A/S \| Novo Collaboration and License Agreement \| Scientific milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable											15,000,000
Novo Nordisk A/S \| Novo Collaboration and License Agreement \| Extension of research plan without achieving scientific milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable											$ 9,000,000

Collaborative arrangements and strategic partnerships - Summary of Total Transaction Price, Allocation of Total Transaction Price to Identified Performance Obligations Under Arrangement and Amount of Transaction Price Unsatisfied (Detail) - Bristol-Myers Squibb - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2021	Mar. 31, 2021	May 31, 2020
BMS collaborative arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront non refundable fees		$ 120,000
Amended Ide-cel co development, co-promote and profit share agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone and royalty obligation buy-out		184,029	$ 10,000	$ 200,000
Vectors and associated payload
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated variable consideration		83,900
Ide-cel co development co promote and profit share agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development milestone payments receivable		387,929
Ide-cel license and manufacturing services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement, transaction price		347,000
bb21217 license agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront non refundable fees		15,000
Collaboration agreement, option fee received	$ 15,000
Milestone and royalty obligation buy-out		15,971
Estimated variable consideration		1,803
Development milestone payments receivable		$ 32,774

Collaborative arrangements and strategic partnerships - Summary of Revenue Recognized or Expense Incurred for Joint Ide-cel Development Efforts Related to Combined Unit of Accounting for its License and Vector Manufacturing of Ide-cel (Detail) - USD ($) $ in Thousands	3 Months Ended					12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues						$ 54,522	$ 248,122	$ 44,296
Total operating expenses						(368,470)	(386,292)	(385,016)
Research and development						(261,937)	(296,467)	(297,645)
Ide-cel research and development services \| Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total operating expenses	$ (7,835)	$ (5,660)	$ (9,193)	$ (16,825)
Ide-cel license and manufacturing services \| Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues	8,818	10,607	0	0
Total operating expenses	$ 0	$ 0	$ (10,071)	$ 0
U.S. \| Ide Cel revenue services \| License and manufacturing services \| Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues					$ 169,200
U.S. \| Ide Cel revenue services \| License and manufacturing services \| Accounting Standards Update 2014-09 \| Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue						0	108,196	0
U.S. \| Ide-cel research and development services \| License and manufacturing services \| Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development						0	(41,599)	(32,415)
Outside of U.S. \| Ide-cel license and manufacturing services \| License and manufacturing services \| Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue						$ 16,895	$ 99,053	$ 25,522

Collaborative arrangements and strategic partnerships - Changes in Balances of Company's Receivables and Contract Liabilities (Detail) - Bristol-Myers Squibb $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($)
Receivables
Beginning balance	$ 400
Additions	13,441
Deductions	(13,189)
Ending balance	652
Contract liabilities:
Beginning balance	26,582
Additions	0
Deductions	(820)
Ending balance	$ 25,762

Royalty and other revenue - Narrative (Detail) - Royalty and other revenue - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
License And Royalty Revenue [Line Items]
Milestone payment	$ 6,200	$ 21,100	$ 8,200	$ 6,220	$ 21,076	$ 8,205
Juno Therapeutics
License And Royalty Revenue [Line Items]
Milestone payment	$ 2,500

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8906-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e9031-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e9038-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130543-203045

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e9054-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130545-203045

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 924
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-URI http://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856

+ Details

Intangible assets - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Cost	$ 38,600	$ 30,100
Accumulated amortization	(28,708)	(24,456)
Net	9,892	5,644
Developed technology
Finite-Lived Intangible Assets [Line Items]
Cost	30,100	30,100
Accumulated amortization	(28,218)	(24,456)
Net	1,882	5,644
In-licensed rights
Finite-Lived Intangible Assets [Line Items]
Cost	8,500	0
Accumulated amortization	(490)	0
Net	$ 8,010	$ 0

Intangible assets - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 4.3	$ 3.8	$ 3.8
Developed technology
Finite-Lived Intangible Assets [Line Items]
Expected useful life	8 years
In-licensed rights
Finite-Lived Intangible Assets [Line Items]
Expected useful life	12 years

Intangible assets - Schedule of Finite-Lived Intangible Assets, Future Amortization Expense (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
2022	$ 2,590
2023	708
2024	708
2025	708
2026	708
2027 and thereafter	4,470
Net	$ 9,892	$ 5,644

Stock-based compensation - Narrative (Detail)			3 Months Ended	12 Months Ended
Stock-based compensation - Narrative (Detail)	Nov. 04, 2021 USD ($) shares	Feb. 01, 2021 shares	Dec. 31, 2021 USD ($) shares	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion ratio			0.3333	0.3333
Incremental fair value of equity award modification	$ 1,300,000			$ 1,500,000
Stock-based compensation expense				54,629,000	$ 60,997,000	$ 62,049,000
Unrecognized stock- based compensation expense related to unvested stock options, restricted stock awards and employee stock purchase plan			$ 25,000,000	$ 25,000,000	$ 38,500,000	$ 1,200,000
Expected weighted-average period related to unvested stock options, restricted stock awards and employee stock purchase plan				1 year 9 months 29 days	2 years 10 days	2 years 1 month 2 days
Intrinsic value of restricted stock units vested				$ 100,000
Performance and service condition based restricted stock unit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense				400,000
Unrecognized stock- based compensation expense related to unvested stock options, restricted stock awards and employee stock purchase plan			$ 1,300,000	1,300,000
Share-based compensation arrangement by share-based payment award, shares issued in period (less than) (in shares) \| shares	17,387	27,000
2021 Stock Option and Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, shares issued in period (less than) (in shares) \| shares			200,000
2021 Stock Option and Incentive Plan \| Unrestricted stock awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense				6,500,000
2021 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock- based compensation expense related to unvested stock options, restricted stock awards and employee stock purchase plan			$ 0	$ 0
Share-based compensation arrangement by share-based payment award, shares issued in period (less than) (in shares) \| shares				0

Stock-based compensation - Schedule of Stock-Based Compensation Expense by Classification (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 54,629	$ 60,997	$ 62,049
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	29,746	30,935	33,853
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 24,883	$ 30,062	$ 28,196

Stock-based compensation - Summary of Stock-Based Compensation Expense by Award Type (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 54,629	$ 60,997	$ 62,049
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	26,185	36,685	36,792
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	21,414	19,185	24,744
Employee stock purchase plan and other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 7,030	$ 5,127	$ 512

Stock-based compensation - Summary of Stock Option Activity Under Plan (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at beginning of period (in shares) \| shares	0
Granted (in shares) \| shares	0
Converted in distribution (in shares) \| shares	875
Exercised (in shares) \| shares	0
Canceled or forfeited (in shares) \| shares	(2)
Outstanding at end of period (in shares) \| shares	873
Exercisable at end of period (in shares) \| shares	518
Vested and expected to vest at end of period (in shares) \| shares	873
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding at beginning of period (in dollars per share) \| $ / shares	$ 0
Granted (in dollars per share) \| $ / shares	0
Converted in distribution (in dollars per share) \| $ / shares	129.67
Exercised (in dollars per share) \| $ / shares	0
Canceled or forfeited (in dollars per share) \| $ / shares	157.43
Outstanding at end of period (in dollars per share) \| $ / shares	129.60
Exercisable at end of period (in dollars per share) \| $ / shares	161.76
Vested and expected to vest at end of period (in dollars per share) \| $ / shares	$ 129.60
Weighted-average contractual life (in years)
Outstanding at end of period	6 years 7 months 6 days
Exercisable at end of period	5 years 2 months 12 days
Vested and expected to vest at end of period	6 years 7 months 6 days
Aggregate intrinsic value (in thousands)
Outstanding at end of period \| $	$ 131
Exercisable at end of period \| $	131
Vested and expected to vest at end of period \| $	$ 131

Stock-based compensation - Summary of Restricted Stock Units (Detail) - Restricted stock units shares in Thousands	12 Months Ended
	Dec. 31, 2021 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested balance at beginning of period (in shares) \| shares	0
Granted (in shares) \| shares	9
Converted in distribution (in shares) \| shares	969
Vested (in shares) \| shares	(3)
Forfeited (in shares) \| shares	(4)
Unvested balance at end of period (in shares) \| shares	971
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Unvested balance at beginning of period (in dollars per share) \| $ / shares	$ 0
Granted (in dollars per share) \| $ / shares	36.14
Converted in distribution (in dollars per share) \| $ / shares	50.93
Vested (in dollars per share) \| $ / shares	137.65
Forfeited (in dollars per share) \| $ / shares	86.12
Unvested balance at end of period (in dollars per share) \| $ / shares	$ 50.56

Related-party transactions - Narrative (Details) $ in Thousands	2 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2021 USD ($)	Jun. 30, 2022	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Nov. 03, 2021 agreement
Related Party Transaction [Line Items]
Total operating expenses			$ 368,470	$ 386,292	$ 385,016
Number of transition services agreements \| agreement						2
Initial term of transition services agreement						2 years
Other income, net			21,647	18,056	20,126
Accrued expenses and other current liabilities	$ 55,410		55,410	43,347
Accounts payable	6,024		6,024	7,152
Bluebird Bio \| Separation Agreement
Related Party Transaction [Line Items]
Total operating expenses	200
Bluebird Bio \| Employment Matters Agreement
Related Party Transaction [Line Items]
Total operating expenses	1,800
Bluebird Bio \| Transition Services Agreement
Related Party Transaction [Line Items]
Total operating expenses	700
Other income, net	$ 1,400
Area of sublease, as a percent	30.00%
Sublease income	$ 800
Amount due to related party	1,500		1,500
Accrued expenses and other current liabilities	1,200		1,200
Accounts payable	300		300
Amount due from related party	$ 1,600		1,600
Bluebird Bio \| Transition Services Agreement \| Forecast
Related Party Transaction [Line Items]
Area of sublease, as a percent		23.00%
Bluebird Bio \| Management Costs and Corporate Support Services
Related Party Transaction [Line Items]
Allocations for management costs and corporate support services provided to the Company			$ 55,300	$ 76,600	$ 67,800

Related-party transactions - Imputed Charges (Details) - Bluebird Bio - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	$ 14,767	$ 17,840	$ 20,233
Imputed charge to bluebird bio for leases
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	14,833	16,562	17,694
Imputed charge from bluebird bio for leases
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	(908)	(1,072)	(696)
Imputed charge to bluebird bio for property, plant and equipment
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	1,891	2,225	3,385
Imputed charge from bluebird bio for property, plant and equipment
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	(1,130)	(229)	(99)
Imputed charge to bluebird bio for intangible assets
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	82	199	65
Other
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	$ (1)	$ 155	$ (116)

401(k) Savings plan - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Retirement Benefits [Abstract]
Expenses related to 401(k) plan	$ 2.4	$ 2.2	$ 2.0

Income taxes - Schedule of Components of Loss Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Domestic	$ (292,213)	$ (120,114)	$ (320,594)
Foreign	0	0	0
Loss before income taxes	$ (292,213)	$ (120,114)	$ (320,594)

- Definition

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8906-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=123384075&loc=d3e41242-110953

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(10))
-URI http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(8))
-URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 235
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05(b)(2))
-URI http://asc.fasb.org/extlink&oid=120399901&loc=d3e537907-122884

Reference 9: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8924-108599

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

+ Details

Income taxes - Reconciliation of Income Tax Provision (Benefit) (Detail)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Federal income tax expense at statutory rate	21.00%	21.00%	21.00%
State income tax, net of federal benefit	0.60%	3.80%	5.50%
Permanent differences	0.00%	0.30%	(0.10%)
Stock-based compensation	0.30%	(4.10%)	(0.50%)
Research and development credit	0.20%	13.80%	5.60%
Officer compensation limitation	(0.40%)	(1.60%)	(0.70%)
Uncertain tax positions	0.00%	(1.10%)	(0.40%)
Other	(1.10%)	0.00%	(0.20%)
Change in valuation allowance	64.80%	(32.10%)	(30.20%)
Separation adjustment	(85.40%)	0.00%	0.00%
Effective income tax rate (expense) benefit	0.00%	0.00%	0.00%

Income taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
U.S. net operating loss carryforwards (federal and state)	$ 12,142	$ 149,570
Tax credit carryforwards (federal and state)	466	49,379
Capitalized license fees and research and development expenses	11,905	13,091
Deferred revenue	13,724	15,348
Stock-based compensation	15,824	21,400
Lease liabilities	71,941	34,119
Accruals and other	5,395	2,715
Total deferred tax assets	131,397	285,622
Intangible assets	(476)	(1,509)
Right-of-use assets	(69,693)	(31,139)
Fixed assets	(2,958)	(5,477)
Less: valuation allowance	(58,270)	(247,497)
Net deferred taxes	$ 0	$ 0

Income taxes - Narrative (Detail) - USD ($)	12 Months Ended
Income taxes - Narrative (Detail) - USD ($)	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Components Of Income Tax Expense Benefit [Line Items]
Valuation allowance	$ 58,270,000	$ 247,497,000
Income tax examination, penalties and interest accrued	$ 0	$ 0	$ 0
Research Tax Credit Carryforward
Components Of Income Tax Expense Benefit [Line Items]
Limitations on use of net operating losses and tax credit carryforwards, percentage	50.00%
Limitations on use of net operating losses and tax credit carryforwards, period	3 years
U.S.
Components Of Income Tax Expense Benefit [Line Items]
Operating loss carryforwards	$ 47,900,000
U.S. \| Research Tax Credit Carryforward
Components Of Income Tax Expense Benefit [Line Items]
Tax credit carryforward amount	500,000
State and Local Jurisdiction
Components Of Income Tax Expense Benefit [Line Items]
Operating loss carryforwards	$ 34,300,000

Income taxes - Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of beginning of period	$ 4,403	$ 3,070
Increases (decreases) for tax positions related to current period	36	1,333
Increases (decreases) for tax positions related to prior periods		0
Increases (decreases) for tax positions as part of separation adjustment	(4,403)
Balance as of end of period	$ 36	$ 4,403

Net loss per share - Common Stock Equivalents Excluded from the Calculation of Diluted Net Loss per Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	2,570	0	0
Outstanding stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	1,490	0	0
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	1,080	0	0

Subsequent Events (Details) - Subsequent Event - Private Placement $ / shares in Units, $ in Millions	1 Months Ended
	Mar. 22, 2022 USD ($) $ / shares shares
Subsequent Event [Line Items]
Shares issued in private placement offering (in shares) \| shares	13,934,427
Common stock price per share (in dollars per share) \| $ / shares	$ 12.20
Gross proceeds from private placement offering \| $	$ 170