0001860782-23-000113 | 10-Q | XBRL Viewer

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Collaborative arrangements and strategic partnerships - Collaborative Arrangement Revenue (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	$ 5,859			$ 7,903			$ 64,265	$ 18,425
Share of collaboration loss	0			0			0	(9,642)
Ide Cel Commercial Activities \| Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	(582)	$ 23,272	$ 21,581	2,849	$ (5,931)	$ (6,709)	44,271	(9,791)
Share of collaboration loss	1,118	1,271	1,380	1,215	1,641	1,357	3,769	4,213
ABECMA Commercial Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	$ 536	$ 24,543	$ 22,961	4,064	0	0	$ 48,040	4,064
Share of collaboration loss				$ 0	$ (4,290)	$ (5,352)		$ (9,642)

Net Loss Per Share

9 Months Ended

Sep. 30, 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 and nine months ended September 30,
	2023	2022
Outstanding stock options (1)	3,369	2,607
Restricted stock units (1)	2,335	1,332
ESPP shares	—	30
	5,704	3,969

(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.

Commitments and contingencies - Narrative (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Jul. 31, 2021	Sep. 30, 2023
Resilience
Commitments And Contingencies Disclosure [Line Items]
Net operating losses, percentage of reimbursement	50.00%
Reimbursement cap	$ 15.0
Portion of net operating losses paid		$ 14.2
Pregenen
Commitments And Contingencies Disclosure [Line Items]
Contingent future cash payments		$ 99.9

Collaborative arrangements and strategic partnerships - Summary of Transaction Price Allocation (Details) - Regeneron - Regeneron Collaboration Agreement, Original And Amendment Combined $ in Thousands	Sep. 30, 2023 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Allocation of Transaction Price	$ 11,259
Unsatisfied Portion of Transaction Price	9,104
MUC-16 Mono/Combo & Next Gen Therapies
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Allocation of Transaction Price	1,905
Unsatisfied Portion of Transaction Price	556
MAGE-A4
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Allocation of Transaction Price	178
Unsatisfied Portion of Transaction Price	5
Early Research Target (1)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Allocation of Transaction Price	8,701
Unsatisfied Portion of Transaction Price	8,105
Early Research Target (2)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Allocation of Transaction Price	475
Unsatisfied Portion of Transaction Price	$ 438

Leases	9 Months Ended
Leases	Sep. 30, 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.

Goodwill (Tables)

9 Months Ended

Sep. 30, 2023

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Goodwill

The following table summarizes the activity of goodwill for the nine months ended September 30, 2023 (in thousands):


	Balance at December 31, 2022		Additions		Impairment		Balance at September, 2023
Goodwill	$	12,056	$	—	$	(12,056)	$	—

- Definition

Tabular disclosure of goodwill by reportable segment and in total which includes a rollforward schedule.

+ References

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

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						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	$ (51,315)			$ (58,155)			$ (179,541)	$ (188,591)
Ide-cel Research And Development Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	(6,120)	$ (5,652)	$ (4,871)	(9,252)	$ (5,463)	$ (6,893)	(16,643)	(21,608)
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	(6,980)	(7,195)	(9,461)	(10,672)	(7,418)	(8,118)	(23,636)	(26,208)
Reimbursements For Research And Development Expenses Under Collaborative Arrangement	860	$ 1,543	$ 4,590	1,420	$ 1,955	$ 1,225	6,993	4,600
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	$ 3,324			$ 3,122			$ 12,435	$ 9,437

Net Loss Per Share - Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 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)	5,704,000	3,969,000	5,704,000	3,969,000
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)	3,369,000	2,607,000	3,369,000	2,607,000
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)	2,335,000	1,332,000	2,335,000	1,332,000
ESPP shares
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	30,000	0	30,000

Accrued expenses and other current liabilities

9 Months Ended

Sep. 30, 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 September 30, 2023		As of December 31, 2022
Employee compensation, including severances for restructuring	$	15,210	$	14,845
Royalties	8,626		13,094
Manufacturing costs	5,067		17,962
Collaboration research costs	2,880		2,005
Clinical and contract research organization costs	1,584		1,619
Property, plant, and equipment	1,157		1,498
Professional fees	320		239
Other	2,564		3,416
Total accrued expenses and other current liabilities	$	37,408	$	54,678

Royalty and other revenue - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Royalty and other revenue
License And Royalty Revenue [Line Items]
Revenue	$ 1,227	$ 863	$ 4,642	$ 2,531

- 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.

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+ Details

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities:
Net loss	$ (160,748)	$ (231,010)
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of contingent consideration	180	181
Depreciation and amortization	7,255	9,208
Stock-based compensation expense	27,206	31,635
Goodwill impairment charge	12,056	0
Other non-cash items	(4,881)	1,074
Changes in operating assets and liabilities:
Prepaid expenses and other assets	9,611	753
Operating lease right-of-use assets	16,332	22,076
Accounts payable	(1,015)	422
Accrued expenses and other liabilities	(16,603)	(1,598)
Operating lease liabilities	(10,016)	(8,927)
Deferred revenue	21,104	10,000
Collaboration research advancement	(3,744)	(14,361)
Net cash used in operating activities	(103,263)	(180,547)
Cash flows from investing activities:
Purchases of property, plant and equipment	(12,794)	(19,676)
Purchases of marketable securities	(237,151)	(115,692)
Proceeds from maturities of marketable securities	245,899	147,597
Purchases of restricted investments	(6,983)	(1,976)
Proceeds from maturities of restricted investments	7,000	2,000
Net cash (used in) provided by investing activities	(4,029)	12,253
Cash flows from financing activities:
Proceeds from issuance of common stock in public offering, net of issuance costs	117,004	0
Proceeds from issuance of common stock to Regeneron, net of issuance costs	9,859	0
Proceeds from the issuance of common stock in private placement, net of issuance costs	0	165,531
Proceeds from exercise of stock options and ESPP contributions	274	466
Net cash provided by financing activities	127,137	165,997
Increase (decrease) in cash, cash equivalents and restricted cash and cash equivalents	19,845	(2,297)
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	92,135	128,151
Reconciliation of cash, cash equivalents, and restricted cash and cash equivalents
Cash and cash equivalents	90,226	127,021
Restricted cash and cash equivalents included in restricted investments and other non-current assets	1,909	1,130
Total cash, cash equivalents, and restricted cash and cash equivalents	92,135	128,151
Supplemental cash flow disclosures:
Purchases of property, plant and equipment included in accounts payable and accrued expenses	1,605	2,828
Financing issuance costs included in accounts payable or accrued expenses	$ 35	$ 0

Collaborative arrangements and strategic partnerships

9 Months Ended

Sep. 30, 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 second quarter of 2023, the Company entered into an amendment to the collaboration agreement with BMS to assign future manufacturing of lentiviral vector to BMS, as further described in Note 8, Other funding commitments.

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 First Amendment to the Amended and Restated Co-Development, Co-Promote and Profit Share Agreement (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 and nine months ended September 30, 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						For the nine months ended
Abecma U.S. Collaboration Profit/Loss Share	March 31, 2023		June 30, 2023		September 30, 2023		September 30, 2023
2seventy's share of profits (losses), net of 2seventy's share of BMS costs for commercial activities	$	21,581	$	23,272	$	(582)	$	44,271
Reimbursement from BMS for 2seventy costs of commercial manufacturing and commercial activities	1,380		1,271		1,118		3,769
Collaborative arrangement revenue (1)	$	22,961	$	24,543	$	536	$	48,040


	For the three months ended						For the nine months ended
Abecma U.S. Collaboration Profit/Loss Share	March 31, 2022		June 30, 2022		September 30, 2022		September 30, 2022
2seventy's share of profits (losses), net of 2seventy's share of BMS costs for commercial activities	$	(6,709)	$	(5,931)	$	2,849	$	(9,791)
Reimbursement from BMS for 2seventy costs of commercial manufacturing and commercial activities	1,357		1,641		1,215		4,213
Collaborative arrangement revenue (1)	$	—	$	—	$	4,064	$	4,064
Share of collaboration loss (1)	$	(5,352)	$	(4,290)	$	—	$	(9,642)

(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 tables summarize 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 and nine months ended September 30, 2023 and 2022 (in thousands):


	For the three months ended						For the nine months ended
Abecma U.S. Collaboration Net R&D Expenses	March 31, 2023		June 30, 2023		September 30, 2023		September 30, 2023
2seventy's obligation for its share of BMS research and development expenses	$	(9,461)	$	(7,195)	$	(6,980)	$	(23,636)
Reimbursement from BMS for 2seventy research and development expenses	4,590		1,543		860		6,993
Net R&D expense (1)	$	(4,871)	$	(5,652)	$	(6,120)	$	(16,643)


	For the three months ended						For the nine months ended
Abecma U.S. Collaboration Net R&D Expenses	March 31, 2022		June 30, 2022		September 30, 2022		September 30, 2022
2seventy's obligation for its share of BMS research and development expenses	$	(8,118)	$	(7,418)	$	(10,672)	$	(26,208)
Reimbursement from BMS for 2seventy research and development expenses	1,225		1,955		1,420		4,600
Net R&D expense (1)	$	(6,893)	$	(5,463)	$	(9,252)	$	(21,608)

(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 and nine months ended September 30, 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 September 30,				For the nine months ended September 30,
	2023		2022		2023		2022
ASC 606 ide-cel license and manufacturing revenue – ex-U.S. (included as a component of service revenue) (1)	$	3,324	$	3,122	$	12,435	$	9,437

(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

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 nine months ended September 30, 2023 (in thousands):


	Balance at December 31, 2022		Additions		Deductions		Balance at September, 2023
Receivables	$	4,537	$	46,212	$	(50,749)	$	—
Contract liabilities:
Deferred revenue	$	—	$	—	$	—	$	—

The decrease in the receivables balance for the nine months ended September 30, 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 Investigational New Drug (“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 payment 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. As of December 31, 2022, $1.1 million of the premium remained to be recognized.

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. The research credit was fully utilized in the first quarter of 2023.

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 four targets outlined in the joint research activities within the Amendment are now four distinct performance obligations. Based on this, the Company treated the modification as a termination of the existing contract and a creation of a new contract. The remaining premium of $1.1 million that had not been recognized as of December 31, 2022 was allocated with the $10.1 million premium attributed to joint research activities from the Amendment, for a total of $11.2 million. This amount is recognized through the filing of IND for each individual target, allocated among the four distinct performance obligations based on the stand-alone selling price of each target performance obligation. 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 four performance obligations 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. Any changes to these estimates will be recognized in the period in which they change as a cumulative catch-up.

As noted, the four targets represent four distinct performance obligations and as such, the Company has allocated the total transaction price of $11.2 million among the four performance obligations based on the stand-alone selling price of each target.

The following table summarizes the allocation of the transaction price to each performance obligation and the amount of the allocated transaction price that is unsatisfied or partially unsatisfied as of September 30, 2023, which the Company expects to recognized as revenue as the targets progress through each of the target’s respective IND filing (in thousands):


Performance Obligation	Allocation of Transaction Price		Unsatisfied Portion of Transaction Price
MUC-16 Mono/Combo & Next Gen Therapies	$	1,905	$	556
MAGE-A4	178		5
Early Research Target (1)	8,701		8,105
Early Research Target (2)	475		438
Total	$	11,259	$	9,104

As of September 30, 2023, approximately $9.1 million remains in collaboration deferred revenue, of which $4.0 million is included in deferred revenue, current portion and $5.1 million is included in deferred revenue, net of current portion on the condensed consolidated balance sheets.

The Company recognized $5.3 million and $16.2 million of collaborative arrangement revenue from the Regeneron Collaboration Agreement for the three and nine months ended September 30, 2023, respectively. The Company recognized $3.8 million and $14.4 million of collaborative arrangement revenue from the Regeneron Collaboration Agreement for the three and nine months ended September 30, 2022, respectively. As of September 30, 2023, amounts due from Regeneron total $4.6 million, included within receivables and other current assets on the condensed consolidated balance sheets.

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 shared 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 which the Company will also share equally with Regeneron. During the third quarter of 2023, the Company completed a transfer of vector supply to JW of approximately $0.5 million. During the nine months ended September 30, 2023, the Company has transferred a total of $0.6 million of vector supply to JW.

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 a mid-single digit percentage of 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.

In April 2023, the Company achieved positive proof of concept, preclinical data related to its joint research and development collaboration with Novo Nordisk. This achievement triggered a $15.0 million milestone payment to the Company under the terms of the Novo Collaboration Agreement. Following the achievement of this milestone, Novo may elect to exercise an option to in-license technology from a third party in connection with the Novo Collaboration Agreement, for which the Company is responsible in making a $9.0 million payment to such third party. This amount is allocated to the research and development performance obligation. As such, the Company has recorded this as a contract liability as of September 30, 2023, which is included in deferred revenue, current portion on the condensed consolidated balance sheet. In November 2023, Novo exercised its option to in-license technology from a third party in connection with the Novo Collaboration Agreement, which triggered the aforementioned $9.0 million payment by the Company to such third party. The remaining $6.0 million, of the $15.0 million proof of concept milestone, is allocated to the material right alongside the $5.0 million upfront payment. The total $11.0 million is included in deferred revenue, net of current portion, as of September 30, 2023, and will be recognized when Novo exercises its option to obtain a license to commercialize the product developed.

Revenue associated with the research and development performance obligation will be recognized as services are provided and costs are incurred. For the three and nine months ended September 30, 2023, the Company recognized $1.1 million and $4.7 million of service revenue under this agreement, respectively. For the three and nine months ended September 30, 2022, the Company recognized $1.5 million and $4.9 million of service revenue under this agreement, respectively.

Commitments and contingencies (Tables)

9 Months Ended

Sep. 30, 2023

Commitments and Contingencies Disclosure [Abstract]

Schedule of Non-cancelable Contractual Obligations

The following table summarizes the Company’s non-cancelable contractual obligations as of September 30, 2023 (in thousands):


Years ended December 31,	Purchase commitment
2023	$	9,868
2024	3,565
2025 and thereafter	—
Total purchase commitments	$	13,433

Fair value measurements

9 Months Ended

Sep. 30, 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 September 30, 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)
September 30, 2023
Assets:
Cash and cash equivalents	$	90,226	$	70,678	$	19,548	$	—
Marketable securities:
U.S. government agency securities and treasuries	121,565		—		121,565		—
Commercial paper	72,487		—		72,487		—
Restricted cash and cash equivalents	1,909		1,909		—		—
Restricted investments	32,072		—		32,072		—
Total assets	$	318,259	$	72,587	$	245,672	$	—
Liabilities:
Contingent consideration	$	2,360	$	—	$	—	$	2,360
Total liabilities	$	2,360	$	—	$	—	$	2,360
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”) in 2014, 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 nine months ended September 30, 2023
Beginning balance	$	2,180
Additions	—
Changes in fair value	180
Payments	—
Ending balance	$	2,360

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

Stock-based compensation - Schedule of Stock-Based Compensation Expense by Classification (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 9,800	$ 12,207	$ 27,206	$ 31,635
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	3,812	5,314	10,802	14,263
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 5,988	$ 6,893	$ 16,404	$ 17,372

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 1D
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480483/718-10-35-1D

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480483/718-10-35-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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+ Details

Condensed Consolidated 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, 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]
Net loss	(231,010)
Ending balance (in shares) at Sep. 30, 2022		37,912,000
Ending balance at Sep. 30, 2022	323,180	$ 4	597,566	(3,886)	(270,504)
Beginning balance (in shares) at Mar. 31, 2022		37,616,000
Beginning balance at Mar. 31, 2022	447,416	$ 4	575,421	(2,804)	(125,205)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		18,000
Exercise of stock options	1		1
Issuance of common stock in public offering, net of issuance costs	(124)		(124)
Stock-based compensation	9,689		9,689
Other comprehensive income	(578)			(578)
Net loss	(77,420)				(77,420)
Ending balance (in shares) at Jun. 30, 2022		37,634,000
Ending balance at Jun. 30, 2022	378,984	$ 4	584,987	(3,382)	(202,625)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		245,000
Stock-based compensation	12,207		12,207
Purchase of common stock under ESPP (in shares)		33,000
Purchases of shares under ESPP	372		372
Other comprehensive income	(504)			(504)
Net loss	(67,879)				(67,879)
Ending balance (in shares) at Sep. 30, 2022		37,912,000
Ending balance at Sep. 30, 2022	$ 323,180	$ 4	597,566	(3,886)	(270,504)
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
Ending balance at Mar. 31, 2023	$ 401,324	$ 5	743,937	(1,950)	(340,668)
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]
Net loss	$ (160,748)
Ending balance (in shares) at Sep. 30, 2023	50,616,000	50,616,000
Ending balance at Sep. 30, 2023	$ 306,422	$ 5	761,728	(916)	(454,395)
Beginning balance (in shares) at Mar. 31, 2023		50,190,000
Beginning balance at Mar. 31, 2023	401,324	$ 5	743,937	(1,950)	(340,668)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		48,000
Stock-based compensation	7,740		7,740
Other comprehensive income	520			520
Net loss	(42,089)				(42,089)
Ending balance (in shares) at Jun. 30, 2023		50,238,000
Ending balance at Jun. 30, 2023	367,495	$ 5	751,677	(1,430)	(382,757)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		303,000
Stock-based compensation	9,800		9,800
Purchase of common stock under ESPP (in shares)		75,000
Purchases of shares under ESPP	251		251
Other comprehensive income	514			514
Net loss	$ (71,638)				(71,638)
Ending balance (in shares) at Sep. 30, 2023	50,616,000	50,616,000
Ending balance at Sep. 30, 2023	$ 306,422	$ 5	$ 761,728	$ (916)	$ (454,395)

Goodwill

9 Months Ended

Sep. 30, 2023

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill

On June 30, 2014, bluebird bio acquired Pregenen. All assets and liabilities related to the Pregenen acquisition, including the resulting goodwill and contingent consideration, were attributed to the Company in connection with the separation from bluebird bio. Prior to the impairment test described further below, the balance of the Company’s goodwill was $12.1 million. The Company operates in a single segment, focusing on researching, developing and commercializing potentially transformative treatments for cancer. Consistent with its operational structure, its chief operating decision maker manages and allocates resources for the Company at a consolidated level. Additionally, the Company determined that its single operating segment is also its only reporting unit. As such, the Company has allocated its entire goodwill balance to its single reporting unit and the goodwill impairment test is completed at this level.

During the third quarter of 2023, and more recently, the Company experienced a sustained decline in the price of its common stock in part due to decreased external expectations for future Abecma sales resulting from increased competitive dynamics, which was considered a triggering event. Management concluded it was more likely than not that the fair value of its reporting unit is less than its carrying amount. The Company then performed a one-step quantitative test and recorded the amount of goodwill impairment as the excess of the reporting unit’s carrying amount over its fair value, not to exceed the total amount of goodwill allocated to the reporting unit.

At September 30, 2023, the Company estimated the fair value of the Company’s single reporting unit using both a market approach and an income approach. Major assumptions were applied in the income approach, including (i) forecasted growth rates (ii) forecasted profitability and (iii) discount rate. Considerable management judgment is necessary to evaluate the impact of operating changes and business initiatives on estimated future growth rates and profitability in order to estimate future cash flows.

Upon completing the impairment test, the Company determined that the estimated fair value of the reporting unit was less than its carrying value, thus indicating an impairment. The Company recognized a goodwill

impairment charge of $12.1 million during the third quarter of 2023, which represented the entire goodwill balance prior to impairment charge.

The following table summarizes the activity of goodwill for the nine months ended September 30, 2023 (in thousands):


	Balance at December 31, 2022		Additions		Impairment		Balance at September, 2023
Goodwill	$	12,056	$	—	$	(12,056)	$	—

Fair value measurements - Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021
Assets:
Marketable securities:	$ 194,052	$ 196,652
Restricted cash and cash equivalents	92,135	72,290	$ 128,151	$ 130,448
U.S. government agency securities and treasuries
Assets:
Marketable securities:	121,565	118,779
Corporate bonds
Assets:
Marketable securities:		2,498
Commercial paper
Assets:
Marketable securities:	72,487	75,375
Fair value, measurements, recurring
Assets:
Cash and cash equivalents	90,226	71,032
Restricted cash and cash equivalents	1,909	1,257
Restricted investments	32,072	31,768
Total assets	318,259	300,709
Liabilities:
Contingent consideration	2,360
Total liabilities	2,360	2,180
Fair value, measurements, recurring \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	121,565	118,779
Fair value, measurements, recurring \| Corporate bonds
Assets:
Marketable securities:		2,498
Fair value, measurements, recurring \| Commercial paper
Assets:
Marketable securities:	72,487	75,375
Fair value, measurements, recurring \| Quoted prices in active markets (Level 1)
Assets:
Cash and cash equivalents	70,678	71,032
Restricted cash and cash equivalents	1,909	1,257
Restricted investments	0	0
Total assets	72,587	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
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	19,548	0
Restricted cash and cash equivalents	0	0
Restricted investments	32,072	31,768
Total assets	245,672	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:	121,565	118,779
Fair value, measurements, recurring \| Significant other observable inputs (Level 2) \| Corporate bonds
Assets:
Marketable securities:		2,498
Fair value, measurements, recurring \| Significant other observable inputs (Level 2) \| Commercial paper
Assets:
Marketable securities:	72,487	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	2,360
Total liabilities	2,360	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
Fair value, measurements, recurring \| Significant unobservable inputs (Level 3) \| Commercial paper
Assets:
Marketable securities:	$ 0	$ 0

Description of the business	9 Months Ended
Description of the business	Sep. 30, 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 nine months ended September 30, 2023, the Company incurred a net loss of $160.7 million and used $103.3 million of cash in operations. The Company expects to continue to generate operating losses and negative operating cash flows for the foreseeable future. The Company's continued operations are dependent on its ability to raise additional funding and generate operating cash flows from Abecma sales and the commercialization of its product candidates, if approved. As of September 30, 2023, the Company had cash, cash equivalents, and marketable securities of $284.3 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’s current operating plan is based on various assumptions. If the Company uses its capital resources sooner than expected, it would evaluate further reductions in its expense or obtaining additional financing. This may include pursuing 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 the Company’s 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.

Corporate Restructuring (Tables)

9 Months Ended

Sep. 30, 2023

Restructuring and Related Activities [Abstract]

Summary of Accrued Liability Activity

The following table summarizes the accrued liabilities activity recorded in connection with the Restructuring Plan as of September 30, 2023:


	As of September 30, 2023
Beginning balance	$	—
Total estimated expenses	8,614
Expenses paid from inception through September 30, 2023	(795)
Reversal of excess accrual through September 30, 2023	—
Remaining accrual at September 30, 2023 (1)	$	7,819

(1)This balance is included within accrued expense and other current liabilities on the condensed consolidated balance sheets.

Summary of significant accounting policies and basis of presentation - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net cash used in operating activities	$ (103,263)	$ (180,547)
Net cash provided by investing activities	(4,029)	12,253
Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net cash used in operating activities	8,000	1,107
Net cash provided by investing activities	$ 8,000	$ 24

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

Equity	9 Months Ended
Equity	Sep. 30, 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 September 30, 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. Details regarding the recognition of this deferred revenue as revenue are included below in Note 10, Collaborative arrangements and strategic partnerships. 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 equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480237/815-40-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-16

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

+ Details

Commitments and contingencies - Schedule of Non-cancelable Contractual Obligations (Detail) $ in Thousands	Sep. 30, 2023 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2023	$ 9,868
2024	3,565
2025 and thereafter	0
Total purchase commitments	$ 13,433

Marketable securities - Narrative (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Interest receivable	$ 800		$ 800		$ 300
Interest receivable, write-off	$ 0	$ 0	$ 0	$ 0

Marketable securities (Tables)

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Summary of Marketable Securities

The following table summarizes the marketable securities held at September 30, 2023 and December 31, 2022 (in thousands):


	Amortized cost/ cost		Unrealized gains		Unrealized losses		Fair Value
September 30, 2023
U.S. government agency securities and treasuries	$	121,834	$	11	$	(280)	$	121,565
Commercial paper	72,544		2		(59)		72,487
Total	$	194,378	$	13	$	(339)	$	194,052
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

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 September 30, 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
September 30, 2023
U.S. government agency securities and treasuries	$	108,319	$	(236)	$	1,456	$	(44)	$	109,775	$	(280)
Commercial paper	55,551		(59)		—		—		55,551		(59)
Total	$	163,870	$	(295)	$	1,456	$	(44)	$	165,326	$	(339)
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 nine months ended September 30, 2023
Beginning balance	$	2,180
Additions	—
Changes in fair value	180
Payments	—
Ending balance	$	2,360

Summary or Restricted Investments

The following table summarizes restricted investments held at September 30, 2023 and December 31, 2022 (in thousands):


	Amortized cost/ cost		Unrealized gains		Unrealized losses		Fair Value
September 30, 2023
U.S. government agency securities and treasuries	$	32,666	$	—	$	(594)	$	32,072
Total	$	32,666	$	—	$	(594)	$	32,072
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

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 September 30, 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
September 30, 2023
U.S. government agency securities and treasuries	$	6,460	$	(28)	$	25,113	$	(566)	$	31,573	$	(594)
Total	$	6,460	$	(28)	$	25,113	$	(566)	$	31,573	$	(594)
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)

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Statement [Abstract]
Tax benefit (expense)	$ 0.0	$ 0.0	$ 0.0	$ 0.0

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 12
-SubTopic 10
-Topic 220
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-12

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482765/220-10-50-4

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 830
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481674/830-30-50-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 830
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481694/830-30-45-17

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 830
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 20
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481694/830-30-45-20

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(19))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-10

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 11
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482659/740-20-45-11

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(21))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(23))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482659/740-20-45-2

+ Details

Property, plant and equipment, net - Summary of Property, Plant and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 114,739	$ 103,573
Less accumulated depreciation and amortization	(54,058)	(47,838)
Property, plant and equipment, net	60,681	55,735
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	6,054	5,670
Office equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	6,726	6,159
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	43,083	36,216
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	58,595	27,416
Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 281	$ 28,112

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 90,226	$ 71,032
Marketable securities	160,393	195,238
Prepaid expenses	7,120	13,652
Receivables and other current assets	19,515	20,960
Total current assets	277,254	300,882
Property, plant and equipment, net	60,681	55,735
Marketable securities	33,659	1,414
Intangible assets, net	6,771	7,302
Goodwill	0	12,056
Operating lease right-of-use assets	224,553	240,885
Restricted investments and other non-current assets	37,888	38,391
Total assets	640,806	656,665
Current liabilities:
Accounts payable	5,307	7,208
Accrued expenses and other current liabilities	37,408	54,678
Operating lease liability, current portion	12,267	11,164
Deferred revenue, current portion	13,026	3,000
Collaboration research advancement	0	3,744
Total current liabilities	68,008	79,794
Deferred revenue, net of current portion	16,077	5,000
Operating lease liability, net of current portion	247,890	259,008
Other non-current liabilities	2,409	2,397
Total liabilities	334,384	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 September 30, 2023 and December 31, 2022	0	0
Common stock, $0.0001 par value; 200,000 shares authorized, 50,616 and 37,928 shares issued and outstanding at September 30, 2023 and December 31, 2022, respectively	5	4
Additional paid-in capital	761,728	606,986
Accumulated other comprehensive loss	(916)	(2,877)
Accumulated deficit	(454,395)	(293,647)
Total stockholders’ equity	306,422	310,466
Total liabilities and stockholders’ equity	$ 640,806	$ 656,665

Stock-based compensation (Tables)

9 Months Ended

Sep. 30, 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 September 30,				For the nine months ended September 30,
	2023		2022		2023		2022
Stock options	$	2,655	$	4,519	$	9,237	$	13,577
Restricted stock units	7,046		7,615		17,697		17,901
Employee Stock Purchase Plan	99		73		272		157
	$	9,800	$	12,207	$	27,206	$	31,635

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 September 30,				For the nine months ended September 30,
	2023		2022		2023		2022
Research and development	$	3,812	$	5,314	$	10,802	$	14,263
Selling, general and administrative	5,988		6,893		16,404		17,372
	$	9,800	$	12,207	$	27,206	$	31,635

Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended				9 Months Ended
	Dec. 13, 2021	Mar. 31, 2023	Jan. 31, 2023	Nov. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued (in shares)						50,616,000		37,928,000
Proceeds from issuance of common stock to Regeneron, net of issuance costs						$ 9,859	$ 0
Common stock						5		$ 4
Regeneron
Subsidiary, Sale of Stock [Line Items]
Contract with customer liability						$ 4,600
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
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
Common stock price per share (in dollars per share)					$ 12.20
Proceeds from issuance of common stock to Regeneron, net of issuance costs					$ 165,500

Collaborative arrangements and strategic partnerships - Changes in Balances of Company's Receivables and Contract Liabilities (Detail) - Bristol-Myers Squibb $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Receivables
Balance at December 31, 2022	$ 4,537
Additions	46,212
Deductions	(50,749)
Balance at September, 2023	0
Contract liabilities:
Balance at December 31, 2022	0
Additions	0
Deductions	0
Balance at September, 2023	$ 0

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

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	9 Months Ended
	Sep. 30, 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	180
Payments	0
Ending balance	$ 2,360

Summary of significant accounting policies and basis of presentation

9 Months Ended

Sep. 30, 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 2022 and 2021 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 nine months ended September 30, 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	$	(354)	$	1,107	$	753
Net cash used in operating activities	$	(181,654)	$	1,107	$	(180,547)
Cash flows from investing activities:
Purchases of restricted investments	$	—	$	(1,976)	$	(1,976)
Maturities of restricted investments	$	—	$	2,000	$	2,000
Net cash provided by investing activities	$	12,229	$	24	$	12,253
Decrease in cash, cash equivalents and restricted cash and cash equivalents	$	(3,428)	$	1,131	$	(2,297)
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	$	159,838	$	(31,687)	$	128,151
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	$	32,817	$	(31,687)	$	1,130
Total cash, cash equivalents and restricted cash and cash equivalents	$	159,838	$	(31,687)	$	128,151

The Company will correct its prior period presentation for this error in the 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.

Property, plant and equipment, net - Narrative (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 114,739	$ 103,573
Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	281	28,112
Cambridge, Massachusetts \| Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 36,400	$ 27,000

Property, plant and equipment, net

9 Months Ended

Sep. 30, 2023

Property, Plant and Equipment [Abstract]

Property, plant and equipment, net

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


	As of September 30, 2023		As of December 31, 2022
Computer equipment and software	$	6,054	$	5,670
Office equipment	6,726		6,159
Laboratory equipment	43,083		36,216
Leasehold improvements	58,595		27,416
Construction-in-progress	281		28,112
Total property, plant and equipment	114,739		103,573
Less accumulated depreciation and amortization	(54,058)		(47,838)
Property, plant and equipment, net	$	60,681	$	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. The build-out of the facility was substantially completed in February 2023 and the facility is fully operational as of August 2023. Construction-in-progress totaling $36.4 million related to the build-out of the facility was placed into service. As of December 31, 2022, construction-in-progress included $27.0 million related to the build-out of the facility.

Property, plant and equipment, net (Tables)

9 Months Ended

Sep. 30, 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 September 30, 2023		As of December 31, 2022
Computer equipment and software	$	6,054	$	5,670
Office equipment	6,726		6,159
Laboratory equipment	43,083		36,216
Leasehold improvements	58,595		27,416
Construction-in-progress	281		28,112
Total property, plant and equipment	114,739		103,573
Less accumulated depreciation and amortization	(54,058)		(47,838)
Property, plant and equipment, net	$	60,681	$	55,735

Marketable securities - Schedule of Unrealized Loss on Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair value
Less than 12 months	$ 163,870	$ 91,385
12 months or greater	1,456	88,674
Total	165,326	180,059
Unrealized losses
Less than 12 months	(295)	(278)
12 months or greater	(44)	(1,830)
Total	(339)	(2,108)
U.S. government agency securities and treasuries
Fair value
Less than 12 months	108,319	28,749
12 months or greater	1,456	86,176
Total	109,775	114,925
Unrealized losses
Less than 12 months	(236)	(159)
12 months or greater	(44)	(1,804)
Total	(280)	(1,963)
Corporate bonds
Fair value
Less than 12 months		0
12 months or greater		2,498
Total		2,498
Unrealized losses
Less than 12 months		0
12 months or greater		(26)
Total		(26)
Commercial paper
Fair value
Less than 12 months	55,551	62,636
12 months or greater	0	0
Total	55,551	62,636
Unrealized losses
Less than 12 months	(59)	(119)
12 months or greater	0	0
Total	$ (59)	$ (119)

Royalty and other revenue	9 Months Ended
Royalty and other revenue	Sep. 30, 2023
License And Royalty Revenue [Abstract]
Royalty and other revenue	Royalty and other revenue bluebird bio has out-licensed intellectual property to various third parties. Under the terms of these agreements, some of which were assumed by the Company in connection with the separation, bluebird bio and the Company may be entitled to royalties and milestone payments. The Company recognized $1.2 million and $4.6 million of royalty and other revenue for the three and nine months ended September 30, 2023, respectively. The Company recognized $0.9 million and $2.5 million of royalty and other revenue in the three and nine months ended September 30, 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. As of August 24, 2023, the royalty term of this license agreement ended, and the Company will no longer receive royalties from sales of lisocabtagene maraleucel.

Accrued expenses and other current liabilities (Tables)

9 Months Ended

Sep. 30, 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 September 30, 2023		As of December 31, 2022
Employee compensation, including severances for restructuring	$	15,210	$	14,845
Royalties	8,626		13,094
Manufacturing costs	5,067		17,962
Collaboration research costs	2,880		2,005
Clinical and contract research organization costs	1,584		1,619
Property, plant, and equipment	1,157		1,498
Professional fees	320		239
Other	2,564		3,416
Total accrued expenses and other current liabilities	$	37,408	$	54,678

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

9 Months Ended

Sep. 30, 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 nine months ended September 30, 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	$	(354)	$	1,107	$	753
Net cash used in operating activities	$	(181,654)	$	1,107	$	(180,547)
Cash flows from investing activities:
Purchases of restricted investments	$	—	$	(1,976)	$	(1,976)
Maturities of restricted investments	$	—	$	2,000	$	2,000
Net cash provided by investing activities	$	12,229	$	24	$	12,253
Decrease in cash, cash equivalents and restricted cash and cash equivalents	$	(3,428)	$	1,131	$	(2,297)
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	$	159,838	$	(31,687)	$	128,151
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	$	32,817	$	(31,687)	$	1,130
Total cash, cash equivalents and restricted cash and cash equivalents	$	159,838	$	(31,687)	$	128,151

Collaborative arrangements and strategic partnerships (Tables)

9 Months Ended

Sep. 30, 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


	For the three months ended						For the nine months ended
Abecma U.S. Collaboration Profit/Loss Share	March 31, 2023		June 30, 2023		September 30, 2023		September 30, 2023
2seventy's share of profits (losses), net of 2seventy's share of BMS costs for commercial activities	$	21,581	$	23,272	$	(582)	$	44,271
Reimbursement from BMS for 2seventy costs of commercial manufacturing and commercial activities	1,380		1,271		1,118		3,769
Collaborative arrangement revenue (1)	$	22,961	$	24,543	$	536	$	48,040


	For the three months ended						For the nine months ended
Abecma U.S. Collaboration Profit/Loss Share	March 31, 2022		June 30, 2022		September 30, 2022		September 30, 2022
2seventy's share of profits (losses), net of 2seventy's share of BMS costs for commercial activities	$	(6,709)	$	(5,931)	$	2,849	$	(9,791)
Reimbursement from BMS for 2seventy costs of commercial manufacturing and commercial activities	1,357		1,641		1,215		4,213
Collaborative arrangement revenue (1)	$	—	$	—	$	4,064	$	4,064
Share of collaboration loss (1)	$	(5,352)	$	(4,290)	$	—	$	(9,642)


	For the three months ended						For the nine months ended
Abecma U.S. Collaboration Net R&D Expenses	March 31, 2023		June 30, 2023		September 30, 2023		September 30, 2023
2seventy's obligation for its share of BMS research and development expenses	$	(9,461)	$	(7,195)	$	(6,980)	$	(23,636)
Reimbursement from BMS for 2seventy research and development expenses	4,590		1,543		860		6,993
Net R&D expense (1)	$	(4,871)	$	(5,652)	$	(6,120)	$	(16,643)


	For the three months ended						For the nine months ended
Abecma U.S. Collaboration Net R&D Expenses	March 31, 2022		June 30, 2022		September 30, 2022		September 30, 2022
2seventy's obligation for its share of BMS research and development expenses	$	(8,118)	$	(7,418)	$	(10,672)	$	(26,208)
Reimbursement from BMS for 2seventy research and development expenses	1,225		1,955		1,420		4,600
Net R&D expense (1)	$	(6,893)	$	(5,463)	$	(9,252)	$	(21,608)


	For the three months ended September 30,				For the nine months ended September 30,
	2023		2022		2023		2022
ASC 606 ide-cel license and manufacturing revenue – ex-U.S. (included as a component of service revenue) (1)	$	3,324	$	3,122	$	12,435	$	9,437

(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.

Summary of contract liabilities

The following table presents changes in the balances of the Company’s BMS receivables and contract liabilities during the nine months ended September 30, 2023 (in thousands):


	Balance at December 31, 2022		Additions		Deductions		Balance at September, 2023
Receivables	$	4,537	$	46,212	$	(50,749)	$	—
Contract liabilities:
Deferred revenue	$	—	$	—	$	—	$	—


Performance Obligation	Allocation of Transaction Price		Unsatisfied Portion of Transaction Price
MUC-16 Mono/Combo & Next Gen Therapies	$	1,905	$	556
MAGE-A4	178		5
Early Research Target (1)	8,701		8,105
Early Research Target (2)	475		438
Total	$	11,259	$	9,104

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 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)	50,616,000	37,928,000
Common stock, shares outstanding (in shares)	50,616,000	37,928,000

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Pay vs Performance Disclosure
Net loss	$ (71,638)	$ (42,089)	$ (47,021)	$ (67,879)	$ (77,420)	$ (85,711)	$ (160,748)	$ (231,010)

- Definition

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

+ References

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+ Details

Corporate Restructuring - Summary of Accrued Liability Activity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Restructuring Reserve [Roll Forward]
Beginning balance			$ 0
Total estimated expenses	$ 8,614	$ 0	8,614	$ 0
Expenses paid from inception through September 30, 2023			(795)
Reversal of excess accrual through September 30, 2023			0
Ending balance	$ 7,819		$ 7,819

Net Loss Per Share (Tables)

9 Months Ended

Sep. 30, 2023

Earnings Per Share [Abstract]

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


	For the three and nine months ended September 30,
	2023	2022
Outstanding stock options (1)	3,369	2,607
Restricted stock units (1)	2,335	1,332
ESPP shares	—	30
	5,704	3,969

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

Income taxes	9 Months Ended
Income taxes	Sep. 30, 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

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-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Marketable securities - Summary of Restricted Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized cost/ cost	$ 32,666	$ 32,880
Unrealized gains	0	0
Unrealized losses	(594)	(1,112)
Fair Value	32,072	31,768
U.S. government agency securities and treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized cost/ cost	32,666	32,880
Unrealized gains	0	0
Unrealized losses	(594)	(1,112)
Fair Value	$ 32,072	$ 31,768

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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-Subparagraph (aa)
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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-Paragraph 2
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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-Name Accounting Standards Codification
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-Paragraph 2
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-Publisher FASB
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
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-Paragraph 3
-Subparagraph (a)
-Publisher FASB
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
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-Section 50
-Paragraph 3
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

+ Details

Summary of significant accounting policies and basis of presentation (Policies)	9 Months Ended
	Sep. 30, 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.

Goodwill - Summary of Goodwill Activity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Goodwill [Roll Forward]
Beginning balance	$ 12,100		$ 12,056
Additions			0
Goodwill impairment charge	(12,056)	$ 0	(12,056)	$ 0
Ending balance	$ 0		$ 0

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References + Details

Commitments and contingencies

9 Months Ended

Sep. 30, 2023

Commitments and Contingencies Disclosure [Abstract]

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 from bluebird bio. As of September 30, 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 September 30, 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 of the manufacturing agreements supports ongoing manufacturing for lentiviral vector for development candidates (the “Development Manufacturing Supply Agreement”). The other manufacturing agreement for the future manufacturing of lentiviral vector for the commercial product marketed in collaboration with BMS, Abecma (the “Commercial Supply Agreement”) was assigned by the Company to BMS on June 23, 2023. Certain rights and obligations under the Ancillary 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 committed 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. During the second quarter of 2023, the Company paid a total of $14.2 million to Resilience for its share of net operating losses. 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. As noted above, the Company assigned its Commercial Supply Agreement with Resilience to BMS in June 2023. As a result of the assignment, the Company’s future minimum commitments related to the Commercial Supply Agreement have materially decreased from amounts disclosed as of December 31, 2022 in Note 8, Commitments and Contingencies, to the consolidated financial statements included in the Company's 2022 annual report on Form 10-K. The following table summarizes the Company’s non-cancelable contractual obligations as of September 30, 2023 (in thousands):


Years ended December 31,	Purchase commitment
2023	$	9,868
2024	3,565
2025 and thereafter	—
Total purchase commitments	$	13,433

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.

Related-party transactions	9 Months Ended
Related-party transactions	Sep. 30, 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 an 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.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Paragraph 5
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-URI https://asc.fasb.org//1943274/2147480990/946-20-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-URI https://asc.fasb.org//1943274/2147480990/946-20-50-6

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 2
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 2
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 220
-Name Accounting Standards Codification
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-Paragraph 1
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
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-URI https://asc.fasb.org//850/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
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-URI https://asc.fasb.org//1943274/2147483326/850-10-50-6

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

+ Details

Stock-based compensation - Summary of Stock-Based Compensation Expense by Award Type (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 9,800	$ 12,207	$ 27,206	$ 31,635
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	3,812	5,314	10,802	14,263
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	5,988	6,893	16,404	17,372
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2,655	4,519	9,237	13,577
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	7,046	7,615	17,697	17,901
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 99	$ 73	$ 272	$ 157

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Marketable securities - Schedule of Unrealized Loss on Restricted Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair value
Less than 12 months	$ 6,460	$ 1,942
12 months or greater	25,113	29,826
Total	31,573	31,768
Unrealized losses
Less than 12 months	(28)	(27)
12 months or greater	(566)	(1,085)
Total	(594)	(1,112)
U.S. government agency securities and treasuries
Fair value
Less than 12 months	6,460	1,942
12 months or greater	25,113	29,826
Total	31,573	31,768
Unrealized losses
Less than 12 months	(28)	(27)
12 months or greater	(566)	(1,085)
Total	$ (594)	$ (1,112)

Marketable securities

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Marketable securities

The following table summarizes the marketable securities held at September 30, 2023 and December 31, 2022 (in thousands):


	Amortized cost/ cost		Unrealized gains		Unrealized losses		Fair Value
September 30, 2023
U.S. government agency securities and treasuries	$	121,834	$	11	$	(280)	$	121,565
Commercial paper	72,544		2		(59)		72,487
Total	$	194,378	$	13	$	(339)	$	194,052
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 September 30, 2023 or December 31, 2022 had remaining maturities greater than five years.


	Less than 12 months				12 months or greater				Total
	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
September 30, 2023
U.S. government agency securities and treasuries	$	108,319	$	(236)	$	1,456	$	(44)	$	109,775	$	(280)
Commercial paper	55,551		(59)		—		—		55,551		(59)
Total	$	163,870	$	(295)	$	1,456	$	(44)	$	165,326	$	(339)
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 September 30, 2023 and December 31, 2022 (in thousands):


	Amortized cost/ cost		Unrealized gains		Unrealized losses		Fair Value
September 30, 2023
U.S. government agency securities and treasuries	$	32,666	$	—	$	(594)	$	32,072
Total	$	32,666	$	—	$	(594)	$	32,072
December 31, 2022
U.S. government agency securities and treasuries	$	32,880	$	—	$	(1,112)	$	31,768
Total	$	32,880	$	—	$	(1,112)	$	31,768


	Less than 12 months				12 months or greater				Total
	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
September 30, 2023
U.S. government agency securities and treasuries	$	6,460	$	(28)	$	25,113	$	(566)	$	31,573	$	(594)
Total	$	6,460	$	(28)	$	25,113	$	(566)	$	31,573	$	(594)
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 $0.8 million and $0.3 million as of September 30, 2023 and December 31, 2022, respectively. No accrued interest receivable was written off during the three and nine months ended September 30, 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 September 30, 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 and nine months ended September 30, 2023 and 2022.

The Company determined that there was no material change in the credit risk of the above investments during the nine months ended September 30, 2023. As such, an allowance for credit losses was not recognized. As of September 30, 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.

Description of the business - Narrative (Detail) $ in Thousands	1 Months Ended	3 Months Ended						9 Months Ended
	Nov. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) employee	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Sep. 30, 2023 USD ($) employee	Sep. 30, 2022 USD ($)	Sep. 30, 2021
Subsequent Event [Line Items]
Conversion ratio										0.3333
Net loss		$ 71,638	$ 42,089	$ 47,021	$ 67,879	$ 77,420	$ 85,711	$ 160,748	$ 231,010
Net cash used in operating activities								103,263	$ 180,547
Cash, cash equivalents, and marketable securities		$ 284,300						$ 284,300
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						0

Collaborative arrangements and strategic partnerships - Narrative (Detail) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended		9 Months Ended
	Dec. 13, 2021 shares	Jan. 31, 2023 USD ($) $ / shares shares	Aug. 31, 2018 USD ($) target accounting_unit $ / shares shares	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Apr. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)	Oct. 27, 2022 USD ($)	Jun. 30, 2022 USD ($) performance_obligation	Dec. 31, 2021 USD ($) performance_obligation	Sep. 30, 2019 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Income (loss) from collaborative arrangements				$ 0	$ 0	$ 0	$ (9,642)
Number of performance obligations \| performance_obligation											2
Investment in common stock						9,859	0
Number of accounting units \| accounting_unit			2
Contract with customer liability, current				13,026		13,026			$ 3,000
Contract with customer liability, noncurrent				16,077		16,077			5,000
Revenues				12,034	13,408	89,703	35,319
Common stock				5		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			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				4,600		4,600
Regeneron \| Collaboration
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue balance recognized as gross revenues				5,300	3,800	16,200	14,400
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			1,100
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
Contract with customer liability									$ 1,100
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%
Contract with customer liability, current				4,000		4,000
Contract with customer liability, noncurrent				5,100		5,100
Contract with customer liability				9,100		9,100
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				11,200		11,200
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				1,100	$ 1,500	4,700	$ 4,900
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				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
Novo Nordisk A/S \| Novo Collaboration and License Agreement \| Milestone Achievement, Option To In-License Technology From Third Party
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable								9,000
Contract with customer liability								$ 6,000
Novo Nordisk A/S \| Novo Collaboration and License Agreement \| Milestone Achievement, Option To In-License Technology From Third Party And Upfront Payment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability				11,000		11,000
JW Therapeutics
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated variable consideration										$ 7,300
Contract with customer liability, current				500		500
Contract with customer liability				$ 600		$ 600				3,000
Estimated variable consideration reimbursement										$ 4,300

Cover Page - shares	9 Months Ended
Cover Page - shares	Sep. 30, 2023	Nov. 08, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 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		50,624,606
Amendment Flag	false
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001860782
Current Fiscal Year End Date	--12-31

Goodwill - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended
Goodwill - Narrative (Details) $ in Thousands	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) reporting_unit segment	Sep. 30, 2022 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	$ 0		$ 0		$ 12,100	$ 12,056
Number of operating segments \| segment			1
Number of reporting units \| reporting_unit			1
Goodwill impairment charge	$ 12,056	$ 0	$ 12,056	$ 0

- Definition

+ References + Details

Fair value measurements (Tables)

9 Months Ended

Sep. 30, 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 September 30, 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)
September 30, 2023
Assets:
Cash and cash equivalents	$	90,226	$	70,678	$	19,548	$	—
Marketable securities:
U.S. government agency securities and treasuries	121,565		—		121,565		—
Commercial paper	72,487		—		72,487		—
Restricted cash and cash equivalents	1,909		1,909		—		—
Restricted investments	32,072		—		32,072		—
Total assets	$	318,259	$	72,587	$	245,672	$	—
Liabilities:
Contingent consideration	$	2,360	$	—	$	—	$	2,360
Total liabilities	$	2,360	$	—	$	—	$	2,360
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
September 30, 2023
U.S. government agency securities and treasuries	$	108,319	$	(236)	$	1,456	$	(44)	$	109,775	$	(280)
Commercial paper	55,551		(59)		—		—		55,551		(59)
Total	$	163,870	$	(295)	$	1,456	$	(44)	$	165,326	$	(339)
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 nine months ended September 30, 2023
Beginning balance	$	2,180
Additions	—
Changes in fair value	180
Payments	—
Ending balance	$	2,360

Summary of significant accounting policies and basis of presentation - Correction of Immaterial Error (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Changes in operating assets and liabilities:
Prepaid expenses and other assets	$ 9,611	$ 753
Net cash used in operating activities	(103,263)	(180,547)
Payments for (Proceeds from) Investments [Abstract]
Purchases of restricted investments	(6,983)	(1,976)
Proceeds from maturities of restricted investments	7,000	2,000
Net cash (used in) provided by investing activities	(4,029)	12,253
Increase (decrease) in cash, cash equivalents and restricted cash and cash equivalents	19,845	(2,297)
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	92,135	128,151
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	1,909	1,130
Total cash, cash equivalents, and restricted cash and cash equivalents	92,135	128,151
As previously reported
Changes in operating assets and liabilities:
Prepaid expenses and other assets		(354)
Net cash used in operating activities		(181,654)
Payments for (Proceeds from) Investments [Abstract]
Purchases of restricted investments		0
Proceeds from maturities of restricted investments		0
Net cash (used in) provided by investing activities		12,229
Increase (decrease) in cash, cash equivalents and restricted cash and cash equivalents		(3,428)
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		159,838
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		32,817
Total cash, cash equivalents, and restricted cash and cash equivalents		159,838
Adjustment
Changes in operating assets and liabilities:
Prepaid expenses and other assets		1,107
Net cash used in operating activities	8,000	1,107
Payments for (Proceeds from) Investments [Abstract]
Purchases of restricted investments		(1,976)
Proceeds from maturities of restricted investments		2,000
Net cash (used in) provided by investing activities	$ 8,000	24
Increase (decrease) in cash, cash equivalents and restricted cash and cash equivalents		1,131
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		(31,687)
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		(31,687)
Total cash, cash equivalents, and restricted cash and cash equivalents		$ (31,687)

Stock-based compensation

9 Months Ended

Sep. 30, 2023

Share-Based Payment Arrangement [Abstract]

Stock-based compensation

Stock-based compensationIn 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 September 30,				For the nine months ended September 30,
	2023		2022		2023		2022
Stock options	$	2,655	$	4,519	$	9,237	$	13,577
Restricted stock units	7,046		7,615		17,697		17,901
Employee Stock Purchase Plan	99		73		272		157
	$	9,800	$	12,207	$	27,206	$	31,635

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 September 30,				For the nine months ended September 30,
	2023		2022		2023		2022
Research and development	$	3,812	$	5,314	$	10,802	$	14,263
Selling, general and administrative	5,988		6,893		16,404		17,372
	$	9,800	$	12,207	$	27,206	$	31,635

Employee Stock Purchase Plan

During the nine months ended September 30, 2023, 0.1 million shares of common stock were issued under the Company’s 2021 Employee Stock Purchase Plan (“ESPP”).

Corporate Restructuring

9 Months Ended

Sep. 30, 2023

Restructuring and Related Activities [Abstract]

Corporate Restructuring

Corporate RestructuringIn August 2023, the Company’s board of directors approved a restructuring plan (the “Restructuring Plan”) to conserve financial resources and better align the Company’s workforce with current business needs. As part of the

Restructuring Plan, the Company's workforce was reduced by approximately 40% in September 2023. The Company anticipates the Restructuring Plan will be substantially complete by December 31, 2023.

In connection with the Restructuring Plan, the Company estimates it will incur $8.6 million of one-time costs relating to severance and retention packages and related benefits. These costs were recognized in the third quarter of 2023, in accordance with ASC 420, Exit and Disposal Activities, and are included in Restructuring expenses in the condensed consolidated statement of operations and comprehensive loss. The following table summarizes the accrued liabilities activity recorded in connection with the Restructuring Plan as of September 30, 2023:


	As of September 30, 2023
Beginning balance	$	—
Total estimated expenses	8,614
Expenses paid from inception through September 30, 2023	(795)
Reversal of excess accrual through September 30, 2023	—
Remaining accrual at September 30, 2023 (1)	$	7,819

(1)This balance is included within accrued expense and other current liabilities on the condensed consolidated balance sheets.

Marketable securities - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Marketable Securities [Line Items]
Amortized cost/ cost	$ 194,378	$ 198,754
Unrealized gains	13	6
Unrealized losses	(339)	(2,108)
Fair Value	194,052	196,652
U.S. government agency securities and treasuries
Marketable Securities [Line Items]
Amortized cost/ cost	121,834	120,739
Unrealized gains	11	3
Unrealized losses	(280)	(1,963)
Fair Value	121,565	118,779
Corporate bonds
Marketable Securities [Line Items]
Amortized cost/ cost		2,524
Unrealized gains		0
Unrealized losses		(26)
Fair Value		2,498
Commercial paper
Marketable Securities [Line Items]
Amortized cost/ cost	72,544	75,491
Unrealized gains	2	3
Unrealized losses	(59)	(119)
Fair Value	$ 72,487	$ 75,375

Accrued expenses and other current liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Employee compensation, including severances for restructuring	$ 15,210	$ 14,845
Royalties	8,626	13,094
Manufacturing costs	5,067	17,962
Collaboration research costs	2,880	2,005
Clinical and contract research organization costs	1,584	1,619
Property, plant, and equipment	1,157	1,498
Professional fees	320	239
Other	2,564	3,416
Total accrued expenses and other current liabilities	$ 37,408	$ 54,678

Stock-based compensation - Narrative (Detail)	9 Months Ended
Stock-based compensation - Narrative (Detail)	Sep. 30, 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 (in shares)	100,000

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenue:
Collaborative arrangement revenue	$ 5,859	$ 7,903	$ 64,265	$ 18,425
Total revenues	12,034	13,408	89,703	35,319
Operating expenses:
Research and development	51,315	58,155	179,541	188,591
Cost of manufacturing for commercial collaboration	4,408	3,584	11,672	10,832
Selling, general and administrative	13,004	19,610	53,213	60,749
Share of collaboration loss	0	0	0	9,642
Restructuring expenses	8,614	0	8,614	0
Cost of royalty and other revenue	551	377	2,099	1,252
Change in fair value of contingent consideration	54	50	180	181
Goodwill impairment charge	12,056	0	12,056	0
Total operating expenses	90,002	81,776	267,375	271,247
Loss from operations	(77,968)	(68,368)	(177,672)	(235,928)
Interest income, net	3,626	1,113	8,765	1,441
Other income (expense), net	2,704	(624)	8,159	3,477
Loss before income taxes	(71,638)	(67,879)	(160,748)	(231,010)
Income tax (expense) benefit	0	0	0	0
Net loss	$ (71,638)	$ (67,879)	$ (160,748)	$ (231,010)
Net loss per share - basic (in dollars per share)	$ (1.40)	$ (1.76)	$ (3.31)	$ (6.67)
Net loss per share - diluted (in dollars per share)	$ (1.40)	$ (1.76)	$ (3.31)	$ (6.67)
Weighted-average number of common shares used in computing net loss per share - basic (in shares)	51,179,000	38,573,000	48,566,000	34,612,000
Weighted-average number of common shares used in computing net loss per share - diluted (in shares)	51,179,000	38,573,000	48,566,000	34,612,000
Other comprehensive income (loss):
Other comprehensive income (loss), net of tax benefit (expense) of $0.0 million and $0.0 million for the three and nine months ended September 30, 2023 and 2022, respectively.	$ 514	$ (504)	$ 1,961	$ (3,174)
Comprehensive loss	(71,124)	(68,383)	(158,787)	(234,184)
Service revenue
Revenue:
Revenue	4,948	4,642	20,796	14,363
Royalty and other revenue
Revenue:
Revenue	$ 1,227	$ 863	$ 4,642	$ 2,531

Corporate Restructuring - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Restructuring Cost and Reserve [Line Items]
Restructuring expenses		$ 8,614	$ 0	$ 8,614	$ 0
August 2023 Reduction
Restructuring Cost and Reserve [Line Items]
Percentage of workforce reduction	40.00%
Restructuring expenses		$ 8,600

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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