0001860782-23-000076 | 10-Q | XBRL Viewer

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Cover Page - shares	3 Months Ended
Cover Page - shares	Mar. 31, 2023	May 04, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2023
Document Transition Report	false
Entity File Number	001-40791
Entity Registrant Name	2seventy bio, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	86-3658454
Entity Address, Address Line One	60 Binney Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	339
Local Phone Number	499-9300
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	TSVT
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		50,199,268
Amendment Flag	false
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q1
Entity Central Index Key	0001860782
Current Fiscal Year End Date	--12-31

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 193,629	$ 71,032
Marketable securities	146,301	195,238
Prepaid expenses	8,635	13,652
Receivables and other current assets	41,252	20,960
Total current assets	389,817	300,882
Property, plant and equipment, net	59,153	55,735
Marketable securities	1,432	1,414
Intangible assets, net	7,125	7,302
Goodwill	12,056	12,056
Operating lease right-of-use assets	235,264	240,885
Restricted investments and other non-current assets	37,590	38,391
Total assets	742,437	656,665
Current liabilities:
Accounts payable	13,399	7,208
Accrued expenses and other current liabilities	43,568	54,678
Operating lease liability, current portion	11,482	11,164
Deferred revenue, current portion	8,480	3,000
Collaboration research advancement	0	3,744
Total current liabilities	76,929	79,794
Deferred revenue, net of current portion	6,311	5,000
Operating lease liability, net of current portion	255,472	259,008
Other non-current liabilities	2,401	2,397
Total liabilities	341,113	346,199
Commitments and contingencies (Note 8)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized, 0 shares issued and outstanding at March 31, 2023 and December 31, 2022	0	0
Common stock, $0.0001 par value; 200,000 shares authorized, 50,190 and 37,928 shares issued and outstanding at March 31, 2023 and December 31, 2022, respectively	5	4
Additional paid-in capital	743,937	606,986
Accumulated other comprehensive loss	(1,950)	(2,877)
Accumulated deficit	(340,668)	(293,647)
Total stockholders’ equity	401,324	310,466
Total liabilities and stockholders’ equity	$ 742,437	$ 656,665

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par value per share (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	50,190,000	37,928,000
Common stock, shares outstanding (in shares)	50,190,000	37,928,000

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Revenue:
Collaborative arrangement revenue	$ 29,372	$ 3,487
Total revenues	41,621	8,429
Operating expenses:
Research and development	68,246	65,879
Cost of manufacturing for commercial collaboration	3,654	3,366
Selling, general and administrative	20,720	23,861
Share of collaboration loss	0	5,352
Cost of royalty and other revenue	641	511
Change in fair value of contingent consideration	73	48
Total operating expenses	93,334	99,017
Loss from operations	(51,713)	(90,588)
Interest income, net	2,049	115
Other income, net	2,643	4,762
Loss before income taxes	(47,021)	(85,711)
Income tax (expense) benefit	0	0
Net loss	$ (47,021)	$ (85,711)
Net loss per share - basic (in dollars per share)	$ (1.08)	$ (3.20)
Net loss per share - diluted (in dollars per share)	$ (1.08)	$ (3.20)
Weighted-average number of common shares used in computing net loss per share - basic (in shares)	43,468,000	26,751,000
Weighted-average number of common shares used in computing net loss per share - diluted (in shares)	43,468,000	26,751,000
Other comprehensive income (loss):
Other comprehensive income (loss), net of tax benefit (expense) of $0.0 million and $0.0 million for the three months ended March 31, 2023 and 2022, respectively.	$ 927	$ (2,092)
Comprehensive loss	(46,094)	(87,803)
Service revenue
Revenue:
Revenue	10,826	4,055
Royalty and other revenue
Revenue:
Revenue	$ 1,423	$ 887

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Income Statement [Abstract]
Tax benefit (expense)	$ 0.0	$ 0.0

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org/extlink&oid=6450520&loc=d3e32583-110901

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-URI https://asc.fasb.org/extlink&oid=126968391&loc=d3e640-108580

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+ Details

Condensed Consolidated and Combined Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive loss	Accumulated deficit
Beginning balance (in shares) at Dec. 31, 2021		23,585,000
Beginning balance at Dec. 31, 2021	$ 359,822	$ 2	$ 400,026	$ (712)	$ (39,494)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		97,000
Exercise of stock options	1		1
Issuance of common stock in private placement, net of issuance costs (in shares)		13,934,000
Issuance of common stock in public offering, net of issuance costs	165,657	$ 2	165,655
Stock-based compensation	9,739		9,739
Other comprehensive income	(2,092)			(2,092)
Net loss	(85,711)				(85,711)
Ending balance (in shares) at Mar. 31, 2022		37,616,000
Ending balance at Mar. 31, 2022	$ 447,416	$ 4	575,421	(2,804)	(125,205)
Beginning balance (in shares) at Dec. 31, 2022	37,928,000	37,928,000
Beginning balance at Dec. 31, 2022	$ 310,466	$ 4	606,986	(2,877)	(293,647)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		237,000
Exercise of stock options (in shares)	1,000
Exercise of stock options	$ 7		7
Issuance of common stock in private placement, net of issuance costs (in shares)		10,870,000
Issuance of common stock in public offering, net of issuance costs	116,969	$ 1	116,968
Issuance of common stock to Regeneron (in shares)		1,115,000
Issuance of common stock to Regeneron	9,859		9,859
Stock-based compensation	9,666		9,666
Purchase of common stock under ESPP (in shares)		39,000
Purchases of shares under ESPP	451		451
Other comprehensive income	927			927
Net loss	$ (47,021)				(47,021)
Ending balance (in shares) at Mar. 31, 2023	50,190,000	50,190,000
Ending balance at Mar. 31, 2023	$ 401,324	$ 5	$ 743,937	$ (1,950)	$ (340,668)

Condensed Consolidated Statements of Cash Flows $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($)	Mar. 31, 2022 USD ($)
Cash flows from operating activities:
Net loss	$ (47,021)	$ (85,711)
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of contingent consideration	73	48
Depreciation and amortization	2,255	3,530
Stock-based compensation expense	9,666	9,739
Other non-cash items	(1,204)	1,227
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(14,103)	(7,186)
Operating lease right-of-use assets	5,621	4,710
Accounts payable	7,072	6,228
Accrued expenses and other liabilities	(11,276)	280
Operating lease liabilities	(3,218)	(2,860)
Deferred revenue	6,791	0
Collaboration research advancement	(3,744)	(3,487)
Net cash used in operating activities	(49,088)	(73,482)
Cash flows from investing activities:
Purchases of property, plant and equipment	(6,079)	(3,585)
Purchases of marketable securities	(36,093)	(22,450)
Proceeds from maturities of marketable securities	86,976	70,784
Purchases of restricted investments	(2,506)	0
Proceeds from maturities of restricted investments	2,500	0
Net cash provided by investing activities	44,798	44,749
Cash flows from financing activities:
Proceeds from issuance of common stock in public offering, net of issuance costs	117,058	0
Proceeds from issuance of common stock to Regeneron, net of issuance costs	9,876	0
Proceeds from the issuance of common stock in private placement	0	170,000
Proceeds from exercise of stock options and ESPP contributions	150	99
Net cash provided by financing activities	127,084	170,099
Increase in cash, cash equivalents and restricted cash and cash equivalents	122,794	141,366
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period	72,290	130,448
Cash, cash equivalents and restricted cash and cash equivalents at end of period	195,084	271,814
Reconciliation of cash, cash equivalents, and restricted cash and cash equivalents
Cash and cash equivalents	193,629	270,893
Restricted cash and cash equivalents included in restricted investments and other non-current assets	1,455	921
Total cash, cash equivalents, and restricted cash and cash equivalents	195,084	271,814
Supplemental cash flow disclosures:
Purchases of property, plant and equipment included in accounts payable and accrued expenses	2,342	2,925
Private placement issuance costs included in accounts payable and accrued expenses	0	4,343
Financing issuance costs included in accounts payable or accrued expenses	$ 106	$ 0

Description of the business	3 Months Ended
Description of the business	Mar. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of the business	Description of the business 2seventy bio, Inc. (the “Company” or “2seventy bio”) was incorporated in Delaware on April 26, 2021 and 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 U.S. Food and Drug Administration (“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 beginning in 2021. 2seventy bio Securities Corporation has no employees. The separation from bluebird bio, Inc. In January 2021, bluebird bio, Inc. (“bluebird bio”) announced its plans to separate its oncology portfolio and programs from its severe genetic disease portfolio and programs, and spin off its oncology portfolio and programs into a separate, publicly traded company. In furtherance of this plan, on September 30, 2021, bluebird bio’s board of directors approved the distribution of all of the issued and outstanding shares of 2seventy bio common stock on the basis of one share of 2seventy bio common stock for every three shares of bluebird bio common stock issued and outstanding on October 19, 2021, the record date for the distribution. As a result of the distribution, which occurred on November 4, 2021, 2seventy bio became an independent, publicly traded company. On November 3, 2021, the Company also entered into a separation agreement with bluebird bio, which is referred to in this quarterly report as the “Separation Agreement”, as well as various other agreements with bluebird bio, including a tax matters agreement, an employee matters agreement, an intellectual property license agreement, a transition services agreement under which 2seventy bio temporarily receives certain services from bluebird bio, and a second transition services agreement under which 2seventy bio temporarily provides certain services to bluebird bio. These agreements also govern certain of 2seventy bio’s relationships with bluebird bio after the separation. For additional information regarding the Separation Agreement and the other related agreements, refer to Note 13, Related-party transactions and the section captioned “Part III. Item 13. Certain Relationships and Related Transactions, and Director Independence,” included in our annual report on Form 10-K, which was filed with the SEC on March 16, 2023. Going concern In accordance with Accounting Standards Codification 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 condensed consolidated financial statements are issued. The Company has incurred losses and has experienced negative operating cash flows for all historical periods presented. During the three months ended March 31, 2023, the Company incurred a net loss of $47.0 million and used $49.1 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 and generate operating cash flows from the commercialization of its product candidates, if approved. As of March 31, 2023, the Company had cash, cash equivalents, and marketable securities of $341.4 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. This includes the potential sale of shares of our common stock of up to $150.0 million in gross proceeds under the at-the-market (“ATM”) facility established in November 2022 with Cowen and Company, LLC. No sales of common stock have occurred under this ATM as of the date of this Quarterly Report on Form 10-Q. 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

3 Months Ended

Mar. 31, 2023

Accounting Policies [Abstract]

Summary of significant accounting policies and basis of presentation

Significant accounting policies

The significant accounting policies used in preparation of these condensed consolidated financial statements are consistent with those discussed in Note 2 to the consolidated financial statements for the year ended December 31, 2022 included in the Company’s 2022 annual report on Form 10-K.

Basis of presentation

The accompanying condensed consolidated 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”).

In the opinion of management, the unaudited interim condensed consolidated financial statements reflect all normal recurring adjustments considered necessary for a fair presentation of the Company’s financial position and the results of its operations for the interim periods presented.

Correction of immaterial error

During the first quarter of 2023, the Company identified two immaterial errors in its previously issued 2022 quarterly reports on Form 10-Q and 2021 and 2022 annual reports on Form 10-K related to: 1) restricted investments previously presented as restricted cash on its consolidated balance sheets and consolidated statements of cash flows; and 2) cash outflows related to the purchase of property, plant and equipment previously presented within operating cash outflows instead of investing cash outflows in its 2022 annual consolidated statements of cash flows.

Based on the analysis of quantitative and qualitative factors in accordance with SEC Staff Accounting Bulletin (SAB) Topic 1.M “Assessing Materiality” and SAB Topic 1.N “Considering the Effects of Prior Year Misstatements when Quantifying Misstatements in Current Year Financial Statements”, the Company concluded that these errors were immaterial, individually and in the aggregate, to its consolidated balance sheets and consolidated statements of cash flows as presented in its previously filed quarterly and annual financial statements. There was no impact to any other statements for any period presented.

To correct for the immaterial error related to restricted investments, the Company:

•changed the caption “Restricted cash and other non-current assets” to “Restricted investments and other non-current assets” on the balance sheet;

•included additional disclosures around the restricted investments within Note 3, Marketable securities and Note 4, Fair value measurements; and

•adjusted its previously filed consolidated statement of cash flows as follows:


	For the three months ended March 31, 2022
in thousands	As previously reported		Adjustment		As revised
Cash flows from operating activities:
Changes in operating assets and liabilities:
Prepaid expenses and other assets	$	(7,768)	$	582	$	(7,186)
Net cash used in operating activities	$	(74,064)	$	582	$	(73,482)
Increase in cash, cash equivalents and restricted cash and cash equivalents	$	140,784	$	582	$	141,366
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period	$	163,266	$	(32,818)	$	130,448
Cash, cash equivalents and restricted cash and cash equivalents at end of period	$	304,050	$	(32,236)	$	271,814
Reconciliation of cash, cash equivalents and restricted cash and cash equivalents
Restricted cash and cash equivalents included in restricted investments and other non-current assets	$	33,157	$	(32,236)	$	921
Total cash, cash equivalents and restricted cash and cash equivalents	$	304,050	$	(32,236)	$	271,814

The Company will correct its prior period presentation for this error in its future 2023 quarterly financial statements on Form 10-Q and 2023 annual report on Form 10-K.

To correct for the immaterial misclassification of cash outflows noted above, the Company will adjust its 2022 statement of cash flows within its 2023 annual report on Form 10-K by reclassifying $8.0 million of cash outflows from net cash used in operating activities to net cash provided by investing activities.

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: 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.

Marketable securities

3 Months Ended

Mar. 31, 2023

Investments, Debt and Equity Securities [Abstract]

Marketable securities

The following table summarizes the marketable securities held at March 31, 2023 and December 31, 2022 (in thousands):


	Amortized cost/ cost		Unrealized gains		Unrealized losses		Fair Value
March 31, 2023
U.S. government agency securities and treasuries	$	97,174	$	13	$	(1,020)	$	96,167
Corporate bonds	1,001		—		(14)		987
Commercial paper	50,651		1		(73)		50,579
Total	$	148,826	$	14	$	(1,107)	$	147,733
December 31, 2022
U.S. government agency securities and treasuries	$	120,739	$	3	$	(1,963)	$	118,779
Corporate bonds	2,524		—		(26)		2,498
Commercial paper	75,491		3		(119)		75,375
Total	$	198,754	$	6	$	(2,108)	$	196,652

No available-for-sale debt securities held as of March 31, 2023 or December 31, 2022 had remaining maturities greater than five years.

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 March 31, 2023 and December 31, 2022 (in thousands):


	Less than 12 months				12 months or greater				Total
	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
March 31, 2023
U.S. government agency securities and treasuries	$	1,952	$	(1)	$	74,463	$	(1,019)	$	76,415	$	(1,020)
Corporate bonds	—		—		987		(14)		987		(14)
Commercial paper	43,580		(73)		—		—		43,580		(73)
Total	$	45,532	$	(74)	$	75,450	$	(1,033)	$	120,982	$	(1,107)
December 31, 2022
U.S. government agency securities and treasuries	$	28,749	$	(159)	$	86,176	$	(1,804)	$	114,925	$	(1,963)
Corporate bonds	—		—		2,498		(26)		2,498		(26)
Commercial paper	62,636		(119)		—		—		62,636		(119)
Total	$	91,385	$	(278)	$	88,674	$	(1,830)	$	180,059	$	(2,108)

As discussed further in Note 7, Leases, to the consolidated financial statements included in the Company's 2022 annual report on Form 10-K, the Company maintains letters of credit related to its leases in Cambridge and Seattle. A portion of this collateral is classified as restricted investments and included within restricted investments and other non-current assets on the condensed consolidated balance sheets.

The following table summarizes restricted investments held at March 31, 2023 and December 31, 2022 (in thousands):


	Amortized cost/ cost		Unrealized gains		Unrealized losses		Fair Value
March 31, 2023
U.S. government agency securities and treasuries	$	32,806	$	—	$	(865)	$	31,941
Total	$	32,806	$	—	$	(865)	$	31,941
December 31, 2022
U.S. government agency securities and treasuries	$	32,880	$	—	$	(1,112)	$	31,768
Total	$	32,880	$	—	$	(1,112)	$	31,768

The following table summarizes restricted investments 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 March 31, 2023 and December 31, 2022 (in thousands):


	Less than 12 months				12 months or greater				Total
	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
March 31, 2023
U.S. government agency securities and treasuries	$	4,450	$	(27)	$	27,491	$	(838)	$	31,941	$	(865)
Total	$	4,450	$	(27)	$	27,491	$	(838)	$	31,941	$	(865)
December 31, 2022
U.S. government agency securities and treasuries	$	1,942	$	(27)	$	29,826	$	(1,085)	$	31,768	$	(1,112)
Total	$	1,942	$	(27)	$	29,826	$	(1,085)	$	31,768	$	(1,112)

Accrued interest receivables on the Company's available-for-sale debt securities and restricted investments, included within receivables and other current assets in the Company’s condensed consolidated balance sheet, totaled $0.7 million and $0.3 million as of March 31, 2023 and December 31, 2022, respectively. No accrued interest receivable was written off during the three months ended March 31, 2023 or 2022.

The amortized cost of available-for-sale debt securities and restricted investments is adjusted for amortization of premiums and accretion of discounts to the earliest call date for premiums or to maturity for discounts. At March 31, 2023 and December 31, 2022, 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 and restricted investments. There were no material realized gains or losses recognized on the sale or maturity of available-for-sale securities or restricted investments during the three months ended March 31, 2023 and 2022.

The Company determined that there was no material change in the credit risk of the above investments during the three months ended March 31, 2023. As such, an allowance for credit losses was not recognized. As of

March 31, 2023, 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.

Fair value measurements

3 Months Ended

Mar. 31, 2023

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 March 31, 2023 and December 31, 2022 (in thousands):


	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
March 31, 2023
Assets:
Cash and cash equivalents	$	193,629	$	175,713	$	17,916	$	—
Marketable securities:
U.S. government agency securities and treasuries	96,167		—		96,167		—
Corporate bonds	987		—		987		—
Commercial paper	50,579		—		50,579		—
Restricted cash and cash equivalents	1,455		1,455		—		—
Restricted investments	31,941		—		31,941		—
Total assets	$	374,758	$	177,168	$	197,590	$	—
Liabilities:
Contingent consideration	$	2,253	$	—	$	—	$	2,253
Total liabilities	$	2,253	$	—	$	—	$	2,253
December 31, 2022
Assets:
Cash and cash equivalents	$	71,032	$	71,032	$	—	$	—
Marketable securities:
U.S. government agency securities and treasuries	118,779		—		118,779		—
Corporate bonds	2,498		—		2,498		—
Commercial paper	75,375		—		75,375		—
Restricted cash and cash equivalents	1,257		1,257		—		—
Restricted investments	31,768		—		31,768		—
Total assets	$	300,709	$	72,289	$	228,420	$	—
Liabilities:
Contingent consideration	$	2,180	$	—	$	—	$	2,180
Total liabilities	$	2,180	$	—	$	—	$	2,180

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 certain commercial 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 condensed consolidated 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 condensed consolidated 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):


	For the three months ended March 31, 2023
Beginning balance	$	2,180
Additions	—
Changes in fair value	73
Payments	—
Ending balance	$	2,253

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

3 Months Ended

Mar. 31, 2023

Property, Plant and Equipment [Abstract]

Property, plant and equipment, net

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


	As of March 31, 2023		As of December 31, 2022
Computer equipment and software	$	5,899	$	5,670
Office equipment	6,159		6,159
Laboratory equipment	36,534		36,216
Leasehold improvements	27,428		27,416
Construction-in-progress	33,048		28,112
Total property, plant and equipment	109,068		103,573
Less accumulated depreciation and amortization	(49,915)		(47,838)
Property, plant and equipment, net	$	59,153	$	55,735

Cambridge, Massachusetts drug product manufacturing facility

In February 2022, the Company began construction of a drug product manufacturing facility within its Cambridge, Massachusetts headquarters. The facility will enable rapid translational research in clinical trials and the manufacture of drug product for use in Phase 1 clinical development activities. Construction-in-progress as of March 31, 2023 includes $31.7 million related to the ongoing build-out of the facility. As of December 31, 2022, construction-in-progress included $27.0 million related to the build-out of the facility. The build out of the facility was substantially completed in February 2023 and is anticipated to be operational by mid-2023.

Accrued expenses and other current liabilities

3 Months Ended

Mar. 31, 2023

Payables and Accruals [Abstract]

Accrued expenses and other current liabilities

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


	As of March 31, 2023		As of December 31, 2022
Manufacturing costs	$	19,244	$	17,962
Royalties	11,629		13,094
Employee compensation	4,547		14,845
Property, plant, and equipment	1,858		1,498
Clinical and contract research organization costs	1,692		1,619
Professional fees	858		239
Collaboration research costs	505		2,005
Other	3,235		3,416
Total accrued expenses and other current liabilities	$	43,568	$	54,678

Leases	3 Months Ended
Leases	Mar. 31, 2023
Leases [Abstract]
Leases	LeasesThe Company leases certain office and laboratory space, primarily located in Cambridge, Massachusetts and Seattle, Washington, that was assigned to it in connection with the separation. There have been no material changes to the lease obligations from those disclosed in Note 7, Leases, to the consolidated financial statements included in the Company's 2022 annual report on Form 10-K.

Commitments and contingencies	3 Months Ended
Commitments and contingencies	Mar. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	Commitments and contingencies Contingent consideration related to business combinations On June 30, 2014, bluebird bio acquired Pregenen. All assets, liabilities and future obligations related to the Pregenen acquisition, including the resulting goodwill and contingent consideration, were assumed by the Company in connection with the separation. As of March 31, 2023, the Company may be required to make up to $99.9 million in contingent cash payments to the former equity holders 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 condensed consolidated 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. Please refer to Note 4, Fair value measurements, for further information. 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. Additionally, to the extent an agreement relating to licensed technology was not assigned to the Company, bluebird bio entered into a sublicense with the Company, which may require the Company to make future milestone and/or royalty payments. Please refer to Note 10, Collaborative arrangements and strategic partnerships, for further information on the BMS, Regeneron Pharmaceuticals, Inc. (“Regeneron”), and Novo Nordisk A/S (“Novo”) agreements and to Note 11, Royalty and other revenue, for further information on license agreements. Based on the Company's development plans as of March 31, 2023, 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. 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 agreement, Resilience acquired bluebird bio's North Carolina manufacturing facility and retained all staff employed at the site. Concurrent with the sale of the manufacturing facility in Durham, North Carolina, bluebird bio entered into certain ancillary agreements, including two manufacturing agreements and a license agreement (the “Resilience License Agreement”), among others (together referred to as the “Ancillary Agreements”). One manufacturing agreement will support the future manufacturing of lentiviral vector for the commercial product marketed in collaboration with BMS, Abecma (the “Commercial Supply Agreement”), while the other will support ongoing manufacturing for lentiviral vector for development candidates (the “Development Manufacturing Supply Agreement”). Certain rights and obligations under these agreements 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. In exchange, under the terms of the development manufacturing supply agreement, the Company was entitled to 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 therefore committed to a minimum purchase of 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, which occurred in September 2022. As of March 31, 2023, the Company has accrued $14.8 million representing our estimated share of the net operating losses of Resilience. The disposition of the net assets of the manufacturing facility previously assigned to 2seventy bio was reflected as a transfer to bluebird bio via net parent investment as a result of bluebird bio’s sale of such facility in the Company’s 2021 annual report on Form 10-K. As a result of the separation, the Company’s net parent investment balance was reclassified to additional paid-in capital. 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. 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. There have been no material changes in future minimum purchase commitments from those disclosed in Note 8, Commitments and Contingencies, to the consolidated financial statements included in the Company's 2022 annual report on Form 10-K. 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 and indemnification agreements entered into with each of its directors and officers. 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.

Equity	3 Months Ended
Equity	Mar. 31, 2023
Equity [Abstract]
Equity	Equity In 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 net proceeds to the Company of approximately $165.5 million, after deducting placement agent fees and other offering expenses payable by the Company. In November 2022, the Company entered into a sales agreement with Cowen and Company, LLC (“Cowen”), relating to shares of the Company’s common stock through an “at the market” equity offering program under which Cowen will act as the Company’s sales agent (the “ATM Facility”). Pursuant to the terms of the sales agreement, the Company may offer and sell shares of common stock, having an aggregate price of up to $150.0 million, from time to time. As of March 31, 2023, the Company had not made any sales under the ATM Facility. In January 2023, the Company entered into a Share Purchase Agreement with Regeneron, pursuant to which it sold 1,114,827 shares of its common stock to Regeneron, subject to certain restrictions, for an aggregate cash price of approximately $20.0 million. The purchase price represents $9.9 million worth of common stock plus a $10.1 million premium, which represents collaboration deferred revenue. In March 2023, the Company sold 10,869,566 shares of common stock through an underwritten public offering at a price per share of $11.50. This resulted in aggregate net proceeds to the Company of approximately $117.0 million, after deducting underwriting fees and offering expenses. The underwriters did not exercise their option to purchase up to 1,630,434 additional shares of common stock and therefore no additional proceeds were received.

- 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-URI https://asc.fasb.org/topic&trid=2208762

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 14
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496171-112644

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 14
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496171-112644

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI https://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496189-112644

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (g)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496189-112644

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

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
-Name Accounting Standards Codification
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-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496189-112644

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 16
-Subparagraph (b)
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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-Paragraph 13
-Subparagraph (i)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 1
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Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126731327&loc=SL126733271-114008

+ Details

Collaborative arrangements and strategic partnerships

3 Months Ended

Mar. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Collaborative arrangements and strategic partnerships

To date, the Company’s service and collaborative arrangement revenue has been primarily generated from collaboration arrangements with BMS, Regeneron, and Novo, each as further described below. These agreements were assumed by the Company in connection with the separation.

Bristol-Myers Squibb

BMS Collaboration Agreement

In March 2013, bluebird bio entered into a collaboration agreement with BMS. The details of the collaboration agreements and the payments the Company has received, and is entitled to receive, are further described in Note 10,

Collaborative arrangements and strategic partnerships, to the consolidated financial statements included in the Company's 2022 annual report on Form 10-K. During the first quarter of 2023, there have been no changes to the terms of the collaboration agreement with BMS.

Abecma

Under the collaboration agreement with BMS, the Company shares equally in the profit and loss related to the development and commercialization of ide-cel in the United States (marketed as Abecma). The Company has no remaining financial rights with respect to the development or commercialization of ide-cel outside of the United States. The Company accounts for its collaborative arrangement efforts with BMS in the United States within the scope of ASC 808 given that both parties are active participants in the activities and both parties are exposed to significant risks and rewards dependent on the commercial success of the activities. The calculation of collaborative activity to be recognized for joint Abecma efforts in the United States is performed on a quarterly basis and is independent of previous quarterly activity. This 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. The Company recognizes revenue related to the combined unit of accounting for the ex-U.S. license and lentiviral vector manufacturing services under Topic 606.

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. 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 condensed consolidated statement of operations and comprehensive loss.

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 and both companies continue to develop suspension lentiviral vector to be used in the manufacture of Abecma. 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 tables summarize the components utilized in the Company’s quarterly calculation of collaborative arrangement revenue or share of collaboration loss under the BMS collaboration arrangement for the three months ended March 31, 2023, and 2022 (in thousands). The amounts reported for these periods represent the Company’s share of BMS’ Abecma 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 consolidated statements of operations and comprehensive loss as described below.


	For the three months ended March 31,
Abecma U.S. Collaboration Profit/Loss Share	2023		2022
2seventy's share of profits (losses), net of 2seventy's share of BMS costs for commercial activities	$	21,581	$	(6,709)
Reimbursement from BMS for 2seventy costs of commercial manufacturing and commercial activities	1,380		1,357
Collaborative arrangement revenue (1)	$	22,961	$	—
Share of collaboration loss (1)	$	—	$	(5,352)

(1)As noted above, the calculation is performed on a quarterly basis and consists of 2seventy's share of profits, net of 2seventy's share of BMS costs for commercial activities, offset by reimbursement from BMS for 2seventy commercial activities. The calculation is independent of previous activity, which may result in fluctuations between revenue and expense recognition period over period.

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 the three months ended March 31, 2023 and 2022 (in thousands):


	For the three months ended March 31,
Abecma U.S. Collaboration Net R&D Expenses	2023		2022
2seventy's obligation for its share of BMS research and development expenses	$	(9,461)	$	(8,118)
Reimbursement from BMS for 2seventy research and development expenses	4,590		1,225
Net R&D expense (1)	$	(4,871)	$	(6,893)

(1)As noted above, the calculation is performed on a quarterly basis and consists of 2seventy bio's obligation for its share of BMS research and development expenses, offset by reimbursement from BMS for 2seventy bio’s research and development expenses.

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 three months ended March 31, 2023 and 2022 (in thousands). These amounts are reflected in service revenue in the consolidated statements of operations and comprehensive loss:


	For the three months ended March 31,
	2023		2022
ASC 606 ide-cel license and manufacturing revenue – ex-U.S. (included as a component of service revenue) (1)	$	6,123	$	2,790

(1)These amounts include reimbursements from BMS to the Company for the Company’s ex-U.S. quality and other manufacturing costs associated with the manufacture of Abecma inventory.

bb21217

In addition to the activities related to ide-cel, BMS previously exercised its option to obtain an exclusive worldwide license to develop and commercialize bb21217, the second product candidate under the collaboration arrangement with BMS which is further described in Note 10, Collaborative arrangements and strategic partnerships, to the consolidated financial statements included in the Company's 2022 annual report on Form 10-K.

Under the collaboration arrangement with BMS, the Company had an option to co-develop and co-promote bb21217 within the United States. However, following completion of the CRB-402 clinical trial, in January 2022 the Company, along with BMS, evaluated its plans with respect to bb21217. Based in part on the strength of Abecma clinical data and commercial sales to date, the Company and BMS elected to discontinue development of bb21217 and, as such, the Company did not exercise its option to co-develop and co-promote bb21217 within the United States. The Company is still eligible to receive U.S. milestones and royalties for U.S. sales of bb21217, if further developed by BMS. Additionally, pursuant to the terms of the collaboration agreement, because it did not exercise its option to co-develop and co-promote bb21217, the Company received an additional fee in the amount of $10.0 million from BMS during the second quarter of 2022. Pursuant to the variable consideration allocation exception, the $10.0 million of consideration received was allocated to the combined performance obligation for the bb21217 license and vector manufacturing services through development, described further below.

The transaction price associated with the collaboration arrangement consisted of $31.0 million of upfront payments and option payments received from BMS, the $10.0 million bb21217 opt-out payment discussed above, and $1.8 million in variable consideration which represented reimbursement to be received from BMS for manufacturing vector and associated payloads through development (which will never be received by the Company given the decision to discontinue development of bb21217 in 2022). The Company identified two performance obligations with respect to the arrangement with BMS. The initial performance obligation was for research and development services that were substantially completed in September 2019, associated with the initial phase 1 clinical trial of bb21217. The Company allocated $5.4 million of consideration to the research and development services performance obligation and fully recognized the consideration through September 2019. The other performance obligation relates to a combined performance obligation for the bb21217 license and vector manufacturing services through development, and the remaining $37.4 million in consideration was allocated to this combined performance obligation. All of the remaining development, regulatory, and commercial milestones related to U.S. development, regulatory and commercialization activities are fully constrained and are therefore excluded from the transaction price.

In December 2022, BMS formally notified the Company that its license and vector manufacturing services for bb21217 will no longer be required, thus releasing it from the combined performance obligation for the bb21217 license and vector manufacturing services through development. As a result, the Company recognized the remaining deferred revenue of $35.8 million associated with bb21217 performance obligations as a component of service revenue during the fourth quarter of 2022.

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 three months ended March 31, 2023 (in thousands):


	Balance at December 31, 2022		Additions		Deductions		Balance at March 31, 2023
Receivables	$	4,537	$	24,212	$	(4,537)	$	24,212
Contract liabilities:
Deferred revenue	$	—	$	—	$	—	$	—

The increase in the receivables balance for the three months ended March 31, 2023 is driven by amounts owed less amounts paid to the Company by BMS in the period under the settlement terms of the collaboration agreement.

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 was assumed by 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.

First Amendment to the Regeneron Collaboration Agreement

In January 2023, 2seventy bio and Regeneron announced an amendment to the Regeneron Collaboration Agreement (the “Amendment”), to amend and extend their current agreement, applying their respective technology platforms to the discovery, development and commercialization of novel immune cell therapies for cancer. Under the Amendment, the parties have identified four research targets to advance the next stage of research therapies. The parties will continue sharing costs for these activities in a manner largely consistent with the existing agreement, with Regeneron now covering 75% of eligible late-stage research costs to study combinations and 100% of the costs for the arms of clinical studies that include Regeneron agents through regulatory approval of two of the four targets. For other programs, cost-sharing will follow the existing 50/50 cost sharing agreement.

Additionally, Regeneron will make one-time milestone payments for each of the first Clinical Candidate directed to MUC-16 and the first Clinical Candidate directed to a selected early stage research target to achieve the applicable milestones. Clinical Candidate milestone events and payments include:

•$2.0 million payment from Regeneron for Development Candidate Nomination;

•$3.0 million payment from Regeneron for IND Acceptance; and

•$5.0 million pay from Regeneron for the Earlier of (i) last patient dosed with a Monotherapy Regimen and (ii) dosing of the 10th patient in a Clinical Trial included in an Approved Research/ Development Plan.

The Development Candidate Nomination for MUC-16 has already occurred and will not be due until the Clinical Candidate milestone event (IND Acceptance) is achieved for MUC-16 at which time the first milestone will be reduced to $1.0 million for a total amount due for the two milestones related to MUC-16 of $4.0 million.

Regeneron Share Purchase Agreements

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 to 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. Following the spin-off, Regeneron held approximately 0.1 million shares of 2seventy bio’s common stock, subject to certain restrictions. 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.

In connection with the Amendment, the Company entered into a Share Purchase Agreement with Regeneron pursuant to which the Company sold 1.1 million shares of its common stock, subject to certain restrictions, for $17.94 per share, to Regeneron for an aggregate cash price of approximately $20.0 million. The purchase price represents $9.9 million worth of common stock plus a $10.1 million premium, which represents deferred revenue.

Accounting analysis – 2018 Regeneron Collaboration Agreement

At the commencement of the original Regeneron Collaboration Agreement, 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 submission. 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 $8.5 million will be attributed to the joint research activities and 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, 2022, the Company had $3.7 million of collaboration research advancement credit attributed to the joint research activities still to be recognized. As of March 31, 2023, this amount was fully utilized and there is no collaboration research advancement credit remaining.

Accounting analysis - Regeneron Amendment

At the commencement of the Amendment, the Company identified two units of accounting, including the issuance of 1.1 million shares of 2seventy bio common stock and joint research activities under the amended agreement. The Company determined the total transaction price to be $20.0 million, which comprises $9.9 million of 2seventy bio equity sold to Regeneron and $10.1 million attributed to joint research activities. In determining the fair value of 2seventy bio common stock at closing, the Company considered the closing price of 2seventy 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.

Consistent with the original Regeneron Collaboration Agreement, the Company assessed whether the joint research activities under the Amendment fell 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 amended arrangement as outlined above, for the collaboration research performed prior to submission of an IND application for a potential gene therapy product, both parties continue to be active participants in the collaboration. Both parties continue to perform research and development activities and will share in these costs through IND submission. Additionally, Regeneron and the Company continue to be 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 Company continues to apply ASC 606 by analogy to determine the measurement and recognition of the consideration received from Regeneron.

The Company analogized to the contract modification guidance in ASC 606 to account for the scope and pricing changes contained in the Amendment. The Company concluded the performance obligation under the Amended Agreement continues to be a single performance obligation and the remaining services under the Amendment are not distinct from those already provided. The Company therefore accounted for the modification by updating the transaction price and measure of progress prospectively with a cumulative catch-up entry recorded as of the effective date of the Amendment. The updated transaction price is based on the Company’s total spend from the original agreement and total estimated spend until the targets outlined in the Amendment clear IND filing, at which point, the Company will reassess whether the collaboration is still within the scope of ASC 808. The Company then combined the $10.1 million premium attributed to the joint research activities in the Amendment with the $8.5 million premium from the original Regeneron Collaboration Agreement for a total of $18.6 million. Future milestones continue to be fully constrained until such time as the achievement of such milestones are considered probable.

The Company concluded that it continues to satisfy its obligations over-time as Regeneron receives the benefit of the research activities as the activities are performed. The Company determined the most appropriate method to track progress towards completion of the performance obligation is an input method that is based on costs incurred. There are significant judgments and estimates inherent in the determination of the costs to be incurred for the research and development activities related to the collaboration with Regeneron. These estimates and assumptions include a number of objective and subjective factors, including the likelihood that a target will be successfully developed through its IND filing and the estimated costs associated with such development, including the potential third-party costs related to each target’s IND-enabling study.

As of March 31, 2023, the Company estimates the contract is approximately 47% complete and therefore approximately $9.8 million remains in collaboration deferred revenue, of which $3.5 million is included in short-term deferred revenue and $6.3 million is included in long-term deferred revenue on the condensed consolidated balance sheets.

The Company recognized $6.4 million of collaborative arrangement revenue, including a $0.7 million catch-up adjustment under the Amendment, for the three months ended March 31, 2023. The Company recognized $3.5 million of collaborative arrangement revenue from the Regeneron Collaboration Agreement for the three months ended March 31, 2022. As of March 31, 2023, amounts due from Regeneron include $2.3 million of receivables from the collaborative arrangement revenue recognized in the first quarter of 2023.

JW Therapeutics

In October 2022, the Company entered into a strategic alliance with JW (Cayman) Therapeutics Co., Ltd. (“JW”) to establish a translational and clinical cell therapy development platform designed to more rapidly explore T cell-based immunotherapy therapy products in the Chinese mainland, Hong Kong (China), and Macao (China). The initial focus of the collaboration is the Company’s MAGE-A4 TCR program in solid tumors which is being developed as part of its collaboration with Regeneron.

Under the terms of the agreement, the Company will grant JW a license for the MAGE-A4 cell therapy in the Chinese mainland, Hong Kong (China), and Macao (China). JW will be responsible for development, manufacturing, and commercialization of the Initial Product within China. The Company is eligible to receive milestones and royalties on product revenues in China. The Company and Regeneron will equally share all payments received from JW, including but not limited to all upfront, milestone and royalty payments made by JW to the Company. The Company and Regeneron will also equally share all costs for any eligible expenses incurred in accordance with the terms of the Regeneron Collaboration Agreement. Additionally, the Company may leverage the early clinical data generated under the collaboration to support development in other geographies.

Accounting Analysis - JW

The Company concluded JW is a customer, and as such, the arrangement falls within the scope of Topic 606. Two performance obligations were identified within the contract consisting of (i) a license for the MAGE-A4 cell therapy, including a transfer of technology as agreed upon by both parties and (ii) vector supply necessary to conduct a Phase 1 clinical trial. The Company has concluded the manufacturing and supply of vector is a distinct performance obligation from the license for MAGE-A4 cell therapy because there are other vendors that could provide the necessary supply.

At contract inception, the Company determined the unconstrained transaction price was $7.3 million, consisting of the $3.0 million up-front consideration and $4.3 million variable consideration for the reimbursement of vector supply. JW provided the Company with a $3.0 million upfront payment related to the granting of a license for MAGE-A4 cell therapy and the transfer of technology for the development of the Initial Product in which the Company will share equally with Regeneron. During the first quarter of 2023, the Company completed the full transfer of the license of IP related to MAGEA4 cell therapy along with the technology transfer, and as such, the upfront payment received from JW was recognized as service revenue during the first quarter of 2023. The transaction price of $4.3 million related to the supply of vector consists of variable consideration based upon the estimated amount of vector needed for the initial Phase 1 clinical trial. As of March 31, 2023, the manufacturing and transfer of vector to JW has not yet occurred and therefore the Company has not received any payments related to this performance obligation.

Novo Nordisk

Novo Collaboration and License Agreement

In December 2021, the Company entered into a Collaboration and License Agreement (the “Novo Collaboration Agreement”) with 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 research program up to a mutually agreed upon amount. 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. For the three months ended March 31, 2023, and 2022 the Company recognized $1.7 million and $1.3 million of service revenue under this agreement, respectively.

Royalty and other revenue	3 Months Ended
Royalty and other revenue	Mar. 31, 2023
License And Royalty Revenue [Abstract]
Royalty and other revenue	Royalty and other revenuebluebird 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 $1.4 million and $0.9 million of royalty and other revenue in the three months ended March 31, 2023 and 2022, respectively. 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. Royalty revenue recognized from sales of lisocabtagene maraleucel is included within royalty and other revenue in the condensed consolidated statement of operations and comprehensive loss.

Stock-based compensation

3 Months Ended

Mar. 31, 2023

Share-Based Payment Arrangement [Abstract]

Stock-based compensation

In connection with 2seventy bio’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. Refer to Note 13, Stock-based compensation, to the consolidated financial statements included in our annual report on Form 10-K for the year ended December 31, 2022 for details on the conversion methodology of the equity awards.

In October 2021, the Company’s board of directors adopted the 2021 Stock Option and Incentive Plan (“2021 Plan”) which allows for the granting of incentive stock options, non-qualified stock options, restricted stock units (“RSUs”), performance-based restricted stock units (“PRSUs”), and restricted stock awards to 2seventy bio’s employees, members of the board of directors, and consultants of 2seventy bio, including those who became employees of the Company in connection with the separation. Shares of the Company’s common stock underlie all awards granted under the 2021 Plan.

Stock-based compensation expense

Stock-based compensation expense includes compensation cost related to 2seventy bio equity awards held by its employees as well as bluebird bio equity awards issued upon separation to its employees.

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


	For the three months ended March 31,
	2023		2022
Stock options	$	3,865	$	4,404
Restricted stock units	5,727		5,314
Employee stock purchase plan and other	74		21
	$	9,666	$	9,739

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


	For the three months ended March 31,
	2023		2022
Research and development	$	3,618	$	4,218
Selling, general and administrative	6,048		5,521
	$	9,666	$	9,739

Employee Stock Purchase Plan

During the three months ended March 31, 2023, less than 0.1 million shares of common stock were issued under the Company’s 2021 Employee Stock Purchase Plan.

Related-party transactions	3 Months Ended
Related-party transactions	Mar. 31, 2023
Related Party Transactions [Abstract]
Related-party transactions	Related-party transactions Relationship with bluebird bio In connection with the separation from bluebird bio, Inc, the Company entered into certain agreements pursuant to which the separation of its business from bluebird bio was effected and that govern its relationship with bluebird bio going forward. The separation agreement, tax matters agreement, employee matters agreement, intellectual property license agreement (“License Agreement”) and two transition services agreements are described in Note 14, Related-party transactions, to the consolidated financial statements included in the Company’s 2022 annual report on Form 10-K. Aside from a Partial Assignment and Assumption Agreement entered in February 2023, as described below, there have been no material changes to the existing agreements from those previously disclosed. Prior to the separation, all of Company’s outstanding shares of common stock were owned by bluebird bio and therefore the transactions under those agreements were considered and disclosed as related party transactions. Following the completion of the separation and distribution, the Company and bluebird bio have operated separately, each as independent public company and bluebird bio no longer owns any shares of the Company’s common stock. Therefore, transactions under those agreements are no longer accounted for as related party transactions. On February 23, 2023, the Company entered into a Partial Assignment and Assumption Agreement (the “Assignment and Assumption Agreement”) with Institut Pasteur (“Institut Pasteur”) and bluebird bio. Pursuant to the Assignment and Assumption Agreement, bluebird bio assigned to the Company bluebird bio’s rights, obligations and interests under a license agreement with Institut Pasteur that were previously licensed to the Company by bluebird bio under the License Agreement. The Company will pay Institut Pasteur an annual maintenance payment, a percentage of income received in the event of sublicensing arrangements and, upon commercialization of certain products, a percentage of net sales as a royalty, which varies depending on the indication of the product.

Income taxes	3 Months Ended
Income taxes	Mar. 31, 2023
Income Tax Disclosure [Abstract]
Income taxes	Income taxesDeferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. 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.

- 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
-SubTopic 10
-Section 50
-Paragraph 21
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32857-109319

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-URI https://asc.fasb.org/extlink&oid=122134291&loc=d3e330215-122817

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 17
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32809-109319

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-URI https://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
-SubTopic 10
-Section 50
-Paragraph 14
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32705-109319

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 270
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6424409&loc=d3e44925-109338

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-URI https://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 https://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 https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Net Loss Per Share

3 Months Ended

Mar. 31, 2023

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):


	For the three months ended March 31,
	2023	2022
Outstanding stock options (1)	3,571	2,780
Restricted stock units (1)	2,678	1,655
ESPP shares and other	—	35
	6,249	4,470

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

As described further in Note 9, Stockholders’ equity, to the consolidated financial statements included in the Company’s 2022 annual report on Form 10-K, 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. Based on the terms of the pre-funded warrants, management concluded that they should be considered outstanding shares in the computation of basic and diluted net loss per share.

Subsequent events	3 Months Ended
Subsequent events	Mar. 31, 2023
Subsequent Events [Abstract]
Subsequent events	Subsequent eventsIn April 2023, the Company achieved positive proof of concept, preclinical data related to its joint research and development collaboration with Novo Nordisk, which is focused on an in vivo gene editing treatment for hemophilia A. This achievement triggered a $15.0 million milestone payment under the terms of the Novo Collaboration Agreement. Following the achievement of this milestone, the Company and/or Novo Nordisk may elect to exercise an option to in-license technology from a third party in connection with the Novo Collaboration Agreement, which would result in the Company making a $9.0 million payment to the third party.

Summary of significant accounting policies and basis of presentation (Policies)	3 Months Ended
	Mar. 31, 2023
Accounting Policies [Abstract]
Basis of presentation	Basis of presentation The accompanying condensed consolidated 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”). In the opinion of management, the unaudited interim condensed consolidated financial statements reflect all normal recurring adjustments considered necessary for a fair presentation of the Company’s financial position and the results of its operations for the interim periods presented.
Use of estimates	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: 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.

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

3 Months Ended

Mar. 31, 2023

Accounting Policies [Abstract]

Schedule of Error Corrections and Prior Period Adjustments

adjusted its previously filed consolidated statement of cash flows as follows:


	For the three months ended March 31, 2022
in thousands	As previously reported		Adjustment		As revised
Cash flows from operating activities:
Changes in operating assets and liabilities:
Prepaid expenses and other assets	$	(7,768)	$	582	$	(7,186)
Net cash used in operating activities	$	(74,064)	$	582	$	(73,482)
Increase in cash, cash equivalents and restricted cash and cash equivalents	$	140,784	$	582	$	141,366
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period	$	163,266	$	(32,818)	$	130,448
Cash, cash equivalents and restricted cash and cash equivalents at end of period	$	304,050	$	(32,236)	$	271,814
Reconciliation of cash, cash equivalents and restricted cash and cash equivalents
Restricted cash and cash equivalents included in restricted investments and other non-current assets	$	33,157	$	(32,236)	$	921
Total cash, cash equivalents and restricted cash and cash equivalents	$	304,050	$	(32,236)	$	271,814

Marketable securities (Tables)

3 Months Ended

Mar. 31, 2023

Investments, Debt and Equity Securities [Abstract]

Summary of Marketable Securities

The following table summarizes the marketable securities held at March 31, 2023 and December 31, 2022 (in thousands):


	Amortized cost/ cost		Unrealized gains		Unrealized losses		Fair Value
March 31, 2023
U.S. government agency securities and treasuries	$	97,174	$	13	$	(1,020)	$	96,167
Corporate bonds	1,001		—		(14)		987
Commercial paper	50,651		1		(73)		50,579
Total	$	148,826	$	14	$	(1,107)	$	147,733
December 31, 2022
U.S. government agency securities and treasuries	$	120,739	$	3	$	(1,963)	$	118,779
Corporate bonds	2,524		—		(26)		2,498
Commercial paper	75,491		3		(119)		75,375
Total	$	198,754	$	6	$	(2,108)	$	196,652

Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value


	Less than 12 months				12 months or greater				Total
	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
March 31, 2023
U.S. government agency securities and treasuries	$	1,952	$	(1)	$	74,463	$	(1,019)	$	76,415	$	(1,020)
Corporate bonds	—		—		987		(14)		987		(14)
Commercial paper	43,580		(73)		—		—		43,580		(73)
Total	$	45,532	$	(74)	$	75,450	$	(1,033)	$	120,982	$	(1,107)
December 31, 2022
U.S. government agency securities and treasuries	$	28,749	$	(159)	$	86,176	$	(1,804)	$	114,925	$	(1,963)
Corporate bonds	—		—		2,498		(26)		2,498		(26)
Commercial paper	62,636		(119)		—		—		62,636		(119)
Total	$	91,385	$	(278)	$	88,674	$	(1,830)	$	180,059	$	(2,108)

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


	For the three months ended March 31, 2023
Beginning balance	$	2,180
Additions	—
Changes in fair value	73
Payments	—
Ending balance	$	2,253

Summary or Restricted Investments

The following table summarizes restricted investments held at March 31, 2023 and December 31, 2022 (in thousands):


	Amortized cost/ cost		Unrealized gains		Unrealized losses		Fair Value
March 31, 2023
U.S. government agency securities and treasuries	$	32,806	$	—	$	(865)	$	31,941
Total	$	32,806	$	—	$	(865)	$	31,941
December 31, 2022
U.S. government agency securities and treasuries	$	32,880	$	—	$	(1,112)	$	31,768
Total	$	32,880	$	—	$	(1,112)	$	31,768

Restricted Investments, Available-for-Sale, Unrealized Loss Position, Fair Value


	Less than 12 months				12 months or greater				Total
	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
March 31, 2023
U.S. government agency securities and treasuries	$	4,450	$	(27)	$	27,491	$	(838)	$	31,941	$	(865)
Total	$	4,450	$	(27)	$	27,491	$	(838)	$	31,941	$	(865)
December 31, 2022
U.S. government agency securities and treasuries	$	1,942	$	(27)	$	29,826	$	(1,085)	$	31,768	$	(1,112)
Total	$	1,942	$	(27)	$	29,826	$	(1,085)	$	31,768	$	(1,112)

Fair value measurements (Tables)

3 Months Ended

Mar. 31, 2023

Fair Value Disclosures [Abstract]

Recorded Amount of Assets and Liabilities Measured at Fair Value on 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 March 31, 2023 and December 31, 2022 (in thousands):


	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
March 31, 2023
Assets:
Cash and cash equivalents	$	193,629	$	175,713	$	17,916	$	—
Marketable securities:
U.S. government agency securities and treasuries	96,167		—		96,167		—
Corporate bonds	987		—		987		—
Commercial paper	50,579		—		50,579		—
Restricted cash and cash equivalents	1,455		1,455		—		—
Restricted investments	31,941		—		31,941		—
Total assets	$	374,758	$	177,168	$	197,590	$	—
Liabilities:
Contingent consideration	$	2,253	$	—	$	—	$	2,253
Total liabilities	$	2,253	$	—	$	—	$	2,253
December 31, 2022
Assets:
Cash and cash equivalents	$	71,032	$	71,032	$	—	$	—
Marketable securities:
U.S. government agency securities and treasuries	118,779		—		118,779		—
Corporate bonds	2,498		—		2,498		—
Commercial paper	75,375		—		75,375		—
Restricted cash and cash equivalents	1,257		1,257		—		—
Restricted investments	31,768		—		31,768		—
Total assets	$	300,709	$	72,289	$	228,420	$	—
Liabilities:
Contingent consideration	$	2,180	$	—	$	—	$	2,180
Total liabilities	$	2,180	$	—	$	—	$	2,180

Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value


	Less than 12 months				12 months or greater				Total
	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
March 31, 2023
U.S. government agency securities and treasuries	$	1,952	$	(1)	$	74,463	$	(1,019)	$	76,415	$	(1,020)
Corporate bonds	—		—		987		(14)		987		(14)
Commercial paper	43,580		(73)		—		—		43,580		(73)
Total	$	45,532	$	(74)	$	75,450	$	(1,033)	$	120,982	$	(1,107)
December 31, 2022
U.S. government agency securities and treasuries	$	28,749	$	(159)	$	86,176	$	(1,804)	$	114,925	$	(1,963)
Corporate bonds	—		—		2,498		(26)		2,498		(26)
Commercial paper	62,636		(119)		—		—		62,636		(119)
Total	$	91,385	$	(278)	$	88,674	$	(1,830)	$	180,059	$	(2,108)

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


	For the three months ended March 31, 2023
Beginning balance	$	2,180
Additions	—
Changes in fair value	73
Payments	—
Ending balance	$	2,253

Property, plant and equipment, net (Tables)

3 Months Ended

Mar. 31, 2023

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 March 31, 2023		As of December 31, 2022
Computer equipment and software	$	5,899	$	5,670
Office equipment	6,159		6,159
Laboratory equipment	36,534		36,216
Leasehold improvements	27,428		27,416
Construction-in-progress	33,048		28,112
Total property, plant and equipment	109,068		103,573
Less accumulated depreciation and amortization	(49,915)		(47,838)
Property, plant and equipment, net	$	59,153	$	55,735

Accrued expenses and other current liabilities (Tables)

3 Months Ended

Mar. 31, 2023

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 March 31, 2023		As of December 31, 2022
Manufacturing costs	$	19,244	$	17,962
Royalties	11,629		13,094
Employee compensation	4,547		14,845
Property, plant, and equipment	1,858		1,498
Clinical and contract research organization costs	1,692		1,619
Professional fees	858		239
Collaboration research costs	505		2,005
Other	3,235		3,416
Total accrued expenses and other current liabilities	$	43,568	$	54,678

Collaborative arrangements and strategic partnerships (Tables)

3 Months Ended

Mar. 31, 2023

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

The amounts reported for these periods represent the Company’s share of BMS’ Abecma 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 consolidated statements of operations and comprehensive loss as described below.


	For the three months ended March 31,
Abecma U.S. Collaboration Profit/Loss Share	2023		2022
2seventy's share of profits (losses), net of 2seventy's share of BMS costs for commercial activities	$	21,581	$	(6,709)
Reimbursement from BMS for 2seventy costs of commercial manufacturing and commercial activities	1,380		1,357
Collaborative arrangement revenue (1)	$	22,961	$	—
Share of collaboration loss (1)	$	—	$	(5,352)


	For the three months ended March 31,
Abecma U.S. Collaboration Net R&D Expenses	2023		2022
2seventy's obligation for its share of BMS research and development expenses	$	(9,461)	$	(8,118)
Reimbursement from BMS for 2seventy research and development expenses	4,590		1,225
Net R&D expense (1)	$	(4,871)	$	(6,893)


	For the three months ended March 31,
	2023		2022
ASC 606 ide-cel license and manufacturing revenue – ex-U.S. (included as a component of service revenue) (1)	$	6,123	$	2,790

(1)These amounts include reimbursements from BMS to the Company for the Company’s ex-U.S. quality and other manufacturing costs associated with the manufacture of Abecma inventory.

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 three months ended March 31, 2023 (in thousands):


	Balance at December 31, 2022		Additions		Deductions		Balance at March 31, 2023
Receivables	$	4,537	$	24,212	$	(4,537)	$	24,212
Contract liabilities:
Deferred revenue	$	—	$	—	$	—	$	—

Stock-based compensation (Tables)

3 Months Ended

Mar. 31, 2023

Share-Based Payment Arrangement [Abstract]

Summary of Stock-Based Compensation Expense by Award Type

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


	For the three months ended March 31,
	2023		2022
Stock options	$	3,865	$	4,404
Restricted stock units	5,727		5,314
Employee stock purchase plan and other	74		21
	$	9,666	$	9,739

Schedule of Stock-Based Compensation Expense by Classification

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


	For the three months ended March 31,
	2023		2022
Research and development	$	3,618	$	4,218
Selling, general and administrative	6,048		5,521
	$	9,666	$	9,739

Net Loss Per Share (Tables)

3 Months Ended

Mar. 31, 2023

Earnings Per Share [Abstract]

Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share


	For the three months ended March 31,
	2023	2022
Outstanding stock options (1)	3,571	2,780
Restricted stock units (1)	2,678	1,655
ESPP shares and other	—	35
	6,249	4,470

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

Description of the business - Narrative (Detail) $ in Thousands	1 Months Ended	3 Months Ended
	Nov. 30, 2022 USD ($)	Mar. 31, 2023 USD ($) employee	Mar. 31, 2022 USD ($)	Sep. 30, 2021
Subsequent Event [Line Items]
Conversion ratio				0.3333
Net loss		$ 47,021	$ 85,711
Net cash used in operating activities		49,088	$ 73,482
Cash, cash equivalents, and marketable securities		$ 341,400
At The Market Facility \| Cowen And Company LLC
Subsequent Event [Line Items]
Aggregate gross proceeds (up to)	$ 150,000
2seventy bio Securities Corporation
Subsequent Event [Line Items]
Number of employees \| employee		0

Summary of significant accounting policies and basis of presentation - Correction of Immaterial Error (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Changes in operating assets and liabilities:
Prepaid expenses and other assets	$ (14,103)	$ (7,186)
Net cash used in operating activities	(49,088)	(73,482)
Increase in cash, cash equivalents and restricted cash and cash equivalents	122,794	141,366
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period	72,290	130,448
Cash, cash equivalents and restricted cash and cash equivalents at end of period	195,084	271,814
Reconciliation of cash, cash equivalents, and restricted cash and cash equivalents
Restricted cash and cash equivalents included in restricted investments and other non-current assets	1,455	921
Total cash, cash equivalents, and restricted cash and cash equivalents	195,084	271,814
As previously reported
Changes in operating assets and liabilities:
Prepaid expenses and other assets		(7,768)
Net cash used in operating activities		(74,064)
Increase in cash, cash equivalents and restricted cash and cash equivalents		140,784
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period		163,266
Cash, cash equivalents and restricted cash and cash equivalents at end of period		304,050
Reconciliation of cash, cash equivalents, and restricted cash and cash equivalents
Restricted cash and cash equivalents included in restricted investments and other non-current assets		33,157
Total cash, cash equivalents, and restricted cash and cash equivalents		304,050
Adjustment
Changes in operating assets and liabilities:
Prepaid expenses and other assets		582
Net cash used in operating activities	$ 8,000	582
Increase in cash, cash equivalents and restricted cash and cash equivalents		582
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period		(32,818)
Cash, cash equivalents and restricted cash and cash equivalents at end of period		(32,236)
Reconciliation of cash, cash equivalents, and restricted cash and cash equivalents
Restricted cash and cash equivalents included in restricted investments and other non-current assets		(32,236)
Total cash, cash equivalents, and restricted cash and cash equivalents		$ (32,236)

Summary of significant accounting policies and basis of presentation - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net cash used in operating activities	$ (49,088)	$ (73,482)
Net cash provided by investing activities	44,798	44,749
Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net cash used in operating activities	8,000	$ 582
Net cash provided by investing activities	$ 8,000

Marketable securities - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Marketable Securities [Line Items]
Amortized cost/ cost	$ 148,826	$ 198,754
Unrealized gains	14	6
Unrealized losses	(1,107)	(2,108)
Fair Value	147,733	196,652
U.S. government agency securities and treasuries
Marketable Securities [Line Items]
Amortized cost/ cost	97,174	120,739
Unrealized gains	13	3
Unrealized losses	(1,020)	(1,963)
Fair Value	96,167	118,779
Corporate bonds
Marketable Securities [Line Items]
Amortized cost/ cost	1,001	2,524
Unrealized gains	0	0
Unrealized losses	(14)	(26)
Fair Value	987	2,498
Commercial paper
Marketable Securities [Line Items]
Amortized cost/ cost	50,651	75,491
Unrealized gains	1	3
Unrealized losses	(73)	(119)
Fair Value	$ 50,579	$ 75,375

Marketable securities - Schedule of Unrealized Loss on Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Fair value
Less than 12 months	$ 45,532	$ 91,385
12 months or greater	75,450	88,674
Total	120,982	180,059
Unrealized losses
Less than 12 months	(74)	(278)
12 months or greater	(1,033)	(1,830)
Total	(1,107)	(2,108)
U.S. government agency securities and treasuries
Fair value
Less than 12 months	1,952	28,749
12 months or greater	74,463	86,176
Total	76,415	114,925
Unrealized losses
Less than 12 months	(1)	(159)
12 months or greater	(1,019)	(1,804)
Total	(1,020)	(1,963)
Corporate bonds
Fair value
Less than 12 months	0	0
12 months or greater	987	2,498
Total	987	2,498
Unrealized losses
Less than 12 months	0	0
12 months or greater	(14)	(26)
Total	(14)	(26)
Commercial paper
Fair value
Less than 12 months	43,580	62,636
12 months or greater	0	0
Total	43,580	62,636
Unrealized losses
Less than 12 months	(73)	(119)
12 months or greater	0	0
Total	$ (73)	$ (119)

Marketable securities - Summary of Restricted Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized cost/ cost	$ 32,806	$ 32,880
Unrealized gains	0	0
Unrealized losses	(865)	(1,112)
Fair Value	31,941	31,768
U.S. government agency securities and treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized cost/ cost	32,806	32,880
Unrealized gains	0	0
Unrealized losses	(865)	(1,112)
Fair Value	$ 31,941	$ 31,768

Marketable securities - Schedule of Unrealized Loss on Restricted Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Fair value
Less than 12 months	$ 4,450	$ 1,942
12 months or greater	27,491	29,826
Total	31,941	31,768
Unrealized losses
Less than 12 months	(27)	(27)
12 months or greater	(838)	(1,085)
Total	(865)	(1,112)
U.S. government agency securities and treasuries
Fair value
Less than 12 months	4,450	1,942
12 months or greater	27,491	29,826
Total	31,941	31,768
Unrealized losses
Less than 12 months	(27)	(27)
12 months or greater	(838)	(1,085)
Total	$ (865)	$ (1,112)

Marketable securities - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Interest receivable	$ 0.7		$ 0.3
Interest receivable, write-off	$ 0.0	$ 0.0

Fair value measurements - Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
Assets:
Marketable securities:	$ 147,733	$ 196,652
Restricted cash and cash equivalents	195,084	72,290	$ 271,814	$ 130,448
U.S. government agency securities and treasuries
Assets:
Marketable securities:	96,167	118,779
Corporate bonds
Assets:
Marketable securities:	987	2,498
Commercial paper
Assets:
Marketable securities:	50,579	75,375
Fair value, measurements, recurring
Assets:
Cash and cash equivalents	193,629	71,032
Restricted cash and cash equivalents	1,455	1,257
Restricted investments	31,941	31,768
Total assets	374,758	300,709
Liabilities:
Contingent consideration	2,253
Total liabilities	2,253	2,180
Fair value, measurements, recurring \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	96,167	118,779
Fair value, measurements, recurring \| Corporate bonds
Assets:
Marketable securities:	987	2,498
Fair value, measurements, recurring \| Commercial paper
Assets:
Marketable securities:	50,579	75,375
Fair value, measurements, recurring \| Quoted prices in active markets (Level 1)
Assets:
Cash and cash equivalents	175,713	71,032
Restricted cash and cash equivalents	1,455	1,257
Restricted investments	0	0
Total assets	177,168	72,289
Liabilities:
Contingent consideration	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	0
Fair value, measurements, recurring \| Quoted prices in active markets (Level 1) \| Corporate bonds
Assets:
Marketable securities:	0	0
Fair value, measurements, recurring \| Quoted prices in active markets (Level 1) \| Commercial paper
Assets:
Marketable securities:	0	0
Fair value, measurements, recurring \| Significant other observable inputs (Level 2)
Assets:
Cash and cash equivalents	17,916	0
Restricted cash and cash equivalents	0	0
Restricted investments	31,941	31,768
Total assets	197,590	228,420
Liabilities:
Contingent consideration	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:	96,167	118,779
Fair value, measurements, recurring \| Significant other observable inputs (Level 2) \| Corporate bonds
Assets:
Marketable securities:	987	2,498
Fair value, measurements, recurring \| Significant other observable inputs (Level 2) \| Commercial paper
Assets:
Marketable securities:	50,579	75,375
Fair value, measurements, recurring \| Significant unobservable inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Restricted cash and cash equivalents	0	0
Restricted investments	0	0
Total assets	0	0
Liabilities:
Contingent consideration	2,253
Total liabilities	2,253	2,180
Fair value, measurements, recurring \| Significant unobservable inputs (Level 3) \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	0	0
Fair value, measurements, recurring \| Significant unobservable inputs (Level 3) \| Corporate bonds
Assets:
Marketable securities:	0	0
Fair value, measurements, recurring \| Significant unobservable inputs (Level 3) \| Commercial paper
Assets:
Marketable securities:	$ 0	$ 0

Fair value measurements - Roll-Forward of Fair Value of the Company's Contingent Consideration Obligations (Detail) - Significant unobservable inputs (Level 3) - Contingent consideration obligations $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 2,180
Additions	0
Changes in fair value	73
Payments	0
Ending balance	$ 2,253

Property, plant and equipment, net - Summary of Property, Plant and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 109,068	$ 103,573
Less accumulated depreciation and amortization	(49,915)	(47,838)
Property, plant and equipment, net	59,153	55,735
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	5,899	5,670
Office equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	6,159	6,159
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	36,534	36,216
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	27,428	27,416
Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 33,048	$ 28,112

Property, plant and equipment, net - Narrative (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 109,068	$ 103,573
Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	33,048	28,112
Cambridge, Massachusetts \| Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 31,700	$ 27,000

Accrued expenses and other current liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Manufacturing costs	$ 19,244	$ 17,962
Royalties	11,629	13,094
Employee compensation	4,547	14,845
Property, plant, and equipment	1,858	1,498
Clinical and contract research organization costs	1,692	1,619
Professional fees	858	239
Collaboration research costs	505	2,005
Other	3,235	3,416
Total accrued expenses and other current liabilities	$ 43,568	$ 54,678

Commitments and contingencies - Narrative (Detail) $ in Millions	1 Months Ended
	Jul. 31, 2021 USD ($) batch	Mar. 31, 2023 USD ($)
Resilience
Commitments And Contingencies Disclosure [Line Items]
Net operating losses, percentage of reimbursement	50.00%
Reimbursement cap	$ 15.0
Net operating losses, percentage of minimum purchase amount	50.00%
Accrued Liabilities		$ 14.8
Maximum \| Resilience
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

Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended				3 Months Ended
	Dec. 13, 2021	Mar. 31, 2023	Jan. 31, 2023	Nov. 30, 2022	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued (in shares)		50,190,000				50,190,000		37,928,000
Proceeds from issuance of common stock to Regeneron, net of issuance costs						$ 9,876	$ 0
Common stock		$ 5				5		$ 4
Regeneron
Subsidiary, Sale of Stock [Line Items]
Contract with customer liability		$ 2,300				$ 2,300
Regeneron \| Share purchase agreement
Subsidiary, Sale of Stock [Line Items]
Common stock price per share (in dollars per share)			$ 17.94
Proceeds from issuance of common stock to Regeneron, net of issuance costs			$ 20,000
Common stock shares issued (in shares)	100,000		1,114,827
Common stock			$ 9,900
Contract with customer liability			$ 10,100
Underwritten Public Offering
Subsidiary, Sale of Stock [Line Items]
Common stock price per share (in dollars per share)		$ 11.50				$ 11.50
Number of shares issued in transaction (in shares)		10,869,566
Aggregate net proceeds		$ 117,000
Additional shares available for purchase (in shares)		1,630,434
At The Market Facility \| Cowen And Company LLC
Subsidiary, Sale of Stock [Line Items]
Aggregate gross proceeds (up to)				$ 150,000
Private Placement
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued (in shares)					13,934,427		13,934,427
Common stock price per share (in dollars per share)					$ 12.20		$ 12.20
Proceeds from issuance of common stock to Regeneron, net of issuance costs					$ 165,500

Collaborative arrangements and strategic partnerships - Collaborative Arrangement Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	$ 29,372	$ 3,487
Share of collaboration loss	0	(5,352)
Ide Cel Commercial Activities \| Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	21,581	(6,709)
Share of collaboration loss	1,380	1,357
ABECMA Commercial Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	22,961	0
Share of collaboration loss	$ 0	$ (5,352)

Collaborative arrangements and strategic partnerships - Narrative (Detail) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended
	Dec. 13, 2021 shares	Jan. 31, 2023 USD ($) $ / shares shares	Aug. 31, 2018 USD ($) target accounting_unit $ / shares shares	Mar. 31, 2023 USD ($) performance_obligation	Mar. 31, 2022 USD ($)	Dec. 31, 2022 USD ($)	Oct. 27, 2022 USD ($)	Dec. 31, 2021 USD ($) performance_obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Income (loss) from collaborative arrangements				$ 0	$ (5,352)
Number of performance obligations \| performance_obligation				2
Investment in common stock				$ 9,876	0
Number of accounting units \| accounting_unit			2
Deferred revenue, current portion				8,480		$ 3,000
Deferred revenue, net of current portion				6,311		5,000
Revenues				41,621	8,429
Common stock				5		4
Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement, transaction price				31,000
Estimated variable consideration				1,800
Contract with customer liability				0		0
Bristol-Myers Squibb \| Phase I, Additional Obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated variable consideration				37,400
Bristol-Myers Squibb \| Research and development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated variable consideration				5,400
Bristol-Myers Squibb \| bb21217 license agreement \| U.S.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional fee receivable if option to co-develop and co-promote is not exercised				10,000
Bristol-Myers Squibb \| Bb Two One Two One Seven License And Manufacturing Services \| License and manufacturing services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability						35,800
Regeneron
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Joint research activities remaining to be recognized						$ 3,700
Contract with customer liability				2,300
Regeneron \| Collaboration
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue balance recognized as gross revenues				$ 6,400	3,500
Regeneron \| Research and development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement, transaction price			$ 100,000
Purchase price premium			$ 37,000
Collaborative arrangement amortization period			5 years
Collaborative arrangement amount attributed to joint research activities			$ 45,500
Collaborative Arrangement Amount Attributed To Joint Research Activities, Net Funding Advancement			8,500
Regeneron \| Research and development services \| Bluebird Bio
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement amount attributed to equity sold			$ 54,500
Regeneron \| Share purchase agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Issuance of common stock to Regeneron (in shares) \| shares	100,000	1,114,827
Common stock price per share (in dollars per share) \| $ / shares		$ 17.94
Investment in common stock		$ 20,000
Contract with customer liability		10,100
Common stock		$ 9,900
Regeneron \| Share purchase agreement \| Bluebird Bio
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock price per share (in dollars per share) \| $ / shares			$ 238.10
Investment in common stock			$ 100,000
Purchase price premium			$ 37,000
Collaborative arrangement research initial funding obligation, percentage			50.00%
Regeneron \| Share purchase agreement \| Common stock \| Bluebird Bio
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
Regeneron \| Regeneron Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of initial collaboration targets \| target			6
Research collaboration term			5 years
Regeneron \| Regeneron Collaboration Agreement \| Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable			$ 130,000
Regeneron \| Regeneron Collaboration Agreement, Amendment One
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement research initial funding obligation, percentage		50.00%
Percent complete				47.00%
Deferred revenue, current portion				$ 3,500
Deferred revenue, net of current portion				6,300
Revenues				700
Contract with customer liability				9,800
Regeneron \| Regeneron Collaboration Agreement, Amendment One \| Pre-Clinical Costs To Study Combinations
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement research initial funding obligation, percentage		75.00%
Regeneron \| Regeneron Collaboration Agreement, Amendment One \| Clinical Study Costs Involving Regeneron Agents
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement research initial funding obligation, percentage		100.00%
Regeneron \| Regeneron Collaboration Agreement, Amendment One \| MUC-16 Development Candidate Nomination
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable		$ 2,000
Regeneron \| Regeneron Collaboration Agreement, Amendment One \| MUC-16 IND Acceptance
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable		3,000
Regeneron \| Regeneron Collaboration Agreement, Amendment One \| Last Patient Dosed Or Dosing Of The 10th Patient
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable		5,000
Regeneron \| Regeneron Collaboration Agreement, Amendment One \| MUC-16
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable		4,000
Regeneron \| Regeneron Collaboration Agreement, Amendment One \| MUC-16 Development Candidate Nomination After Achievement Of IND Acceptance
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable		$ 1,000
Regeneron \| Regeneron Collaboration Agreement, Original And Amendment Combined
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability				18,600
Novo Nordisk A/S \| Novo Collaboration and License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated variable consideration								$ 11,700
Number of performance obligations \| performance_obligation								2
Contract with customer liability								$ 5,000
Estimated variable consideration, research reimbursement								6,700
Estimated variable consideration, upfront payment								5,000
Revenue				$ 1,700	$ 1,300
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
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
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
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
JW Therapeutics
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated variable consideration							$ 7,300
Contract with customer liability							3,000
Estimated variable consideration reimbursement							$ 4,300

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
	Mar. 31, 2023	Mar. 31, 2022
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	$ (68,246)	$ (65,879)
Ide-cel Research And Development Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	(4,871)	(6,893)
Bristol-Myers Squibb \| Ide-cel Research And Development Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research And Development Expense Obligation Under Collaborative Arrangement	(9,461)	(8,118)
Reimbursements For Research And Development Expenses Under Collaborative Arrangement	4,590	1,225
Bristol-Myers Squibb \| Outside of U.S. \| Ide-cel license and manufacturing services \| License and manufacturing services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue	$ 6,123	$ 2,790

Collaborative arrangements and strategic partnerships - Changes in Balances of Company's Receivables and Contract Liabilities (Detail) - Bristol-Myers Squibb $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($)
Receivables
Balance at December 31, 2022	$ 4,537
Additions	24,212
Deductions	(4,537)
Balance at March 31, 2023	24,212
Contract liabilities:
Balance at December 31, 2022	0
Additions	0
Deductions	0
Balance at March 31, 2023	$ 0

Royalty and other revenue - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Royalty and other revenue
License And Royalty Revenue [Line Items]
Revenue	$ 1,423	$ 887

- 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 https://asc.fasb.org/extlink&oid=126901519&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 https://asc.fasb.org/extlink&oid=126901519&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 https://asc.fasb.org/extlink&oid=126901519&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 https://asc.fasb.org/extlink&oid=126901519&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 https://asc.fasb.org/extlink&oid=126901519&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 https://asc.fasb.org/extlink&oid=126920106&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 https://asc.fasb.org/extlink&oid=126901519&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 https://asc.fasb.org/extlink&oid=126901519&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 https://asc.fasb.org/extlink&oid=126901519&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 https://asc.fasb.org/extlink&oid=126920106&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 https://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856

+ Details

Stock-based compensation - Summary of Stock-Based Compensation Expense by Award Type (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 9,666	$ 9,739
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	3,865	4,404
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	5,727	5,314
Employee stock purchase plan and other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 74	$ 21

Stock-based compensation - Schedule of Stock-Based Compensation Expense by Classification (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 9,666	$ 9,739
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	3,618	4,218
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 6,048	$ 5,521

Stock-based compensation - Narrative (Detail)	3 Months Ended
Stock-based compensation - Narrative (Detail)	Mar. 31, 2023 shares
2021 Employee Stock Purchase 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)	100,000

Net Loss Per Share - Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
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)	6,249,000	4,470,000
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)	3,571,000	2,780,000
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)	2,678,000	1,655,000
ESPP shares and other
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)	0	35,000

Net Loss Per Share - Narrative (Details) - Pre-funded Warrants - Private Placement	Nov. 30, 2021 $ / shares shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Pre-funded warrants issued (in shares) \| shares	757,575
Exercise price of warrants (in dollars per share) \| $ / shares	$ 0.0001

Subsequent events (Details) - Subsequent Event $ in Millions	1 Months Ended
	Apr. 30, 2023 USD ($)
Subsequent Event [Line Items]
Optional in-license technology payment	$ 9.0
Novo Nordisk A/S
Subsequent Event [Line Items]
Revenue	$ 15.0

- Definition

+ References

+ Details