0001860782-24-000116 | 10-Q | XBRL Viewer

Print Document

Leases	9 Months Ended
Leases	Sep. 30, 2024
Leases [Abstract]
Leases	Leases The Company leases certain office and laboratory space, primarily located in Cambridge, Massachusetts and Seattle, Washington, which was assigned to it in connection with its separation from bluebird bio. The lease at 60 Binney Street, Cambridge, Massachusetts for 253,108 square feet (the “Prime Lease”) was previously entered into by bluebird bio with ARE-MA Region No. 40, LLC on September 21, 2015. The lease at 188 East Blaine Street in Seattle, Washington for 36,126 square feet was previously entered into by bluebird bio on July 18, 2018. In connection with the Regeneron Transaction, Regeneron agreed to fully sublease the Company’s facilities in Seattle, Washington and sublease a portion of the Company’s facilities in Cambridge, Massachusetts. As part of the sublease agreement with Regeneron (the “Subtenant”), the Company agreed to sublease to Regeneron approximately 159,106 square feet of space in Cambridge and approximately 36,126 square feet of space in Seattle. The Company remains the primary obligor of the leases. In each case, the monthly base rent for the sublease is equal to the rate per square foot paid by the Company, which is subject to annual rent increases. For the Prime Lease, in addition to base rent, the Subtenant is responsible for its allocated share of costs incurred and expenditures made by the Company in the operation and management of the subleased space. The Subtenant has agreed to pay its proportionate share (63%) of all operating expenses, taxes, insurance, utilities storage, parking fees and all other additional rent payable by the Company under the Prime Lease. Sublease income from Regeneron will cover a majority of the Company’s future minimum lease commitments through 2027. Total sublease income for the three and nine months ended September 30, 2024 related to the sublease of the Prime Lease was approximately $4.9 million and $9.8 million, respectively. Total sublease income for the three and nine months ended September 30, 2024 related to the sublease of the Seattle lease was approximately $0.6 million and $1.2 million, respectively, which covers all of the Company’s costs for the Seattle facility. This income is netted against the Company’s rent expense, which is included within operating expenses, in the condensed consolidated statements of operations and comprehensive loss.

Corporate Restructuring

9 Months Ended

Sep. 30, 2024

Restructuring and Related Activities [Abstract]

Corporate Restructuring

2023 Restructuring Plan

In August 2023, the Company’s board of directors approved a restructuring plan (the “2023 Restructuring Plan”) to conserve financial resources and better align the Company’s workforce with current business needs. As part of the 2023 Restructuring Plan, the Company's workforce was reduced by approximately 40% in September 2023. The Company’s 2023 Restructuring Plan was complete as of June 30, 2024.

In connection with the 2023 Restructuring Plan, the Company incurred $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 were included in restructuring expenses on the condensed consolidated statements of operations and comprehensive loss. Since inception of the 2023 Restructuring

Plan, the Company has paid $8.6 million of restructuring costs. All payments associated with the plan have been made and no accrued costs remain as of September 30, 2024.

2024 Restructuring Plan

In January 2024, the Company announced a strategic path forward to focus exclusively on the commercialization and development of Abecma. In connection with the Company’s strategic re-alignment, the Company entered into an asset purchase agreement with Regeneron to sell the Company’s oncology and autoimmune research and development programs, clinical manufacturing capabilities, and related platform technologies which closed on April 1, 2024. Approximately 62% of the workforce that was left following completion of the 2023 Restructuring Plan transitioned to Regeneron as a part of the Regeneron Transaction. Additionally, as part of the strategic re-alignment, the Company’s board of directors approved a restructuring plan (the “2024 Restructuring Plan”) to further reduce its remaining workforce by approximately 14%. The Company expects the 2024 Restructuring Plan to be substantially complete during the first half of 2025, as certain transition activities related to the Company’s strategic re-alignment will extend into 2025.

In connection with the 2024 Restructuring Plan, the Company expects to incur approximately $6.6 million of costs for severance and related benefits and stock-based compensation expense. These costs will be recognized over the period from January 2024 through March 2025, and are disclosed as restructuring expenses on the condensed consolidated statements of operations and comprehensive loss. The table below summarizes the expenses recognized and expected to be recognized under the 2024 Restructuring Plan as of September 30, 2024:


	Expense recognized for the three months ended September 30, 2024		Expense recognized for the nine months ended September 30, 2024		Total expense expected to be recognized
Cash-related restructuring expenses:
Severance and related benefits	$	228	$	5,376	$	5,607
Non-cash expenses:
Stock-based compensation expense	—		1,037		1,037
Total restructuring expenses	$	228	$	6,413	$	6,644

The following table summarizes the cash-related restructuring accrued liabilities activity recorded in connection with the 2024 Restructuring Plan for the nine months ended September 30, 2024:


	For the nine months ended September 30, 2024
Beginning balance at January 1, 2024	$	—
Cash-related expenses recognized	5,376
Cash-related expenses paid	(3,814)
Reversal of excess accrual	—
Remaining accrual at September 30, 2024 (1)	$	1,562

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

Collaborative arrangements and strategic partnerships - Summary of Transaction Price Allocation (Details) - Regeneron - Regeneron Collaboration Agreement, Original And Amendment Combined $ in Thousands	Sep. 30, 2024 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Allocation of Transaction Price	$ 11,259
MUC16 Mono/Combo & Next Gen Therapies
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Allocation of Transaction Price	1,905
MAGE-A4
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Allocation of Transaction Price	178
Early Research Target 1
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Allocation of Transaction Price	8,701
Early Research Target 2
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Allocation of Transaction Price	$ 475

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

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive (loss) income	Accumulated deficit
Beginning balance (in shares) at Dec. 31, 2022		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 public offering, 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
Purchases of shares under ESPP (in shares)		39,000
Purchases of shares under ESPP	451		451
Other comprehensive income (loss)	927			927
Net income (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
Beginning balance at Dec. 31, 2022	310,466	$ 4	606,986	(2,877)	(293,647)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(160,748)
Ending balance (in shares) at Sep. 30, 2023		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 (loss)	520			520
Net income (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
Purchases of shares under ESPP (in shares)		75,000
Purchases of shares under ESPP	251		251
Other comprehensive income (loss)	514			514
Net income (loss)	(71,638)				(71,638)
Ending balance (in shares) at Sep. 30, 2023		50,616,000
Ending balance at Sep. 30, 2023	$ 306,422	$ 5	761,728	(916)	(454,395)
Beginning balance (in shares) at Dec. 31, 2023	50,632,000	50,632,000
Beginning balance at Dec. 31, 2023	$ 255,300	$ 5	766,716	(204)	(511,217)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		695,000
Stock-based compensation	4,684		4,684
Purchases of shares under ESPP (in shares)		77,000
Purchases of shares under ESPP	260		260
Other comprehensive income (loss)	(132)			(132)
Net income (loss)	(52,673)				(52,673)
Ending balance (in shares) at Mar. 31, 2024		51,404,000
Ending balance at Mar. 31, 2024	$ 207,439	$ 5	771,660	(336)	(563,890)
Beginning balance (in shares) at Dec. 31, 2023	50,632,000	50,632,000
Beginning balance at Dec. 31, 2023	$ 255,300	$ 5	766,716	(204)	(511,217)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ (37,727)
Ending balance (in shares) at Sep. 30, 2024	51,512,000	51,512,000
Ending balance at Sep. 30, 2024	$ 228,102	$ 5	776,736	305	(548,944)
Beginning balance (in shares) at Mar. 31, 2024		51,404,000
Beginning balance at Mar. 31, 2024	207,439	$ 5	771,660	(336)	(563,890)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		89,000
Exercise of stock options	1		1
Stock-based compensation	2,385		2,385
Other comprehensive income (loss)	100			100
Net income (loss)	24,879				24,879
Ending balance (in shares) at Jun. 30, 2024		51,493,000
Ending balance at Jun. 30, 2024	234,804	$ 5	774,046	(236)	(539,011)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		7,000
Exercise of stock options	19		19
Stock-based compensation	2,643		2,643
Purchases of shares under ESPP (in shares)		7,000
Purchases of shares under ESPP	28		28
Other comprehensive income (loss)	541			541
Net income (loss)	$ (9,933)				(9,933)
Ending balance (in shares) at Sep. 30, 2024	51,512,000	51,512,000
Ending balance at Sep. 30, 2024	$ 228,102	$ 5	$ 776,736	$ 305	$ (548,944)

Related-party transactions	9 Months Ended
Related-party transactions	Sep. 30, 2024
Related Party Transactions [Abstract]
Related-party transactions	Related-party transactions Relationship with bluebird bio In January 2021, bluebird bio, Inc. (“bluebird bio”) announced its plans to separate 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 (the “Separation”). In connection with the Separation, 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 2023 annual report on Form 10-K. The transition services agreements have since been terminated. 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.

- 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
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480990/946-20-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480990/946-20-50-6

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-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
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(e))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org/850/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483326/850-10-50-6

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483326/850-10-50-1

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

+ Details

Royalty and other revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Royalty and other revenue
License And Royalty Revenue [Line Items]
Revenue	$ 0	$ 1,227	$ 0	$ 4,642

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 41
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-41

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 270
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482964/270-10-50-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (ee)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-32

Reference 4: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-32

Reference 5: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-32

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 924
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479941/924-10-S99-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-5

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 30
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-30

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-42

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-22

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 40
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-40

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-22

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-4

+ Details

Net Loss Per Share (Tables)

9 Months Ended

Sep. 30, 2024

Earnings Per Share [Abstract]

Common Stock Equivalents Excluded from Calculation of Diluted 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,
	2024	2023
Outstanding stock options (1)	3,962	3,369
Restricted stock units (1)	3,601	2,335
ESPP Shares	—	—
	7,563	5,704

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

Collaborative arrangements and strategic partnerships

9 Months Ended

Sep. 30, 2024

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 from bluebird bio as described in Note 14. Concurrent with the closings of the Regeneron Transaction and the Novo Transaction, the Regeneron Collaboration Agreement and the Novo Collaboration Agreement were terminated, respectively, as further described below.

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 2023 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, Commitments and contingencies, to the consolidated financial statements included in the Company's 2023 annual report on Form 10-K.

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). If the Company were to choose to terminate its existing agreement with BMS, it would be entitled to a mid-single digit to low teens royalty based on a percentage of net sales of Abecma in the United States with 90 days’ notice. 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 (i.e. commercial sales of Abecma by BMS). The Company’s share of any collaboration profit for commercial activities is recognized as collaborative arrangement revenue and its share of any collaboration loss for commercial activity is recognized as an operating expense and classified as share of collaboration loss on the Company's 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. 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 income (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, 2024 and 2023 (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, 2024		June 30, 2024		September 30, 2024		September 30, 2024
2seventy's share of profits (losses), net of 2seventy's share of BMS costs for commercial activities	$	(1,975)	$	3,549	$	9,617	$	11,191
Reimbursement from BMS for 2seventy costs of commercial manufacturing and commercial activities	745		815		1,067		2,627
Collaborative arrangement revenue (1)	$	—	$	4,364	$	10,684	$	15,048
Share of collaboration loss (1)	$	(1,230)	$	—	$	—	$	(1,230)


	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

(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, 2024 and 2023 (in thousands):


	For the three months ended						For the nine months ended
Abecma U.S. Collaboration Net R&D Expenses	March 31, 2024		June 30, 2024		September 30, 2024		September 30, 2024
2seventy's obligation for its share of BMS research and development expenses	$	(6,963)	$	(8,625)	$	(8,225)	$	(23,813)
Reimbursement from BMS for 2seventy research and development expenses	224		192		57		473
Net R&D expense (1)	$	(6,739)	$	(8,433)	$	(8,168)	$	(23,340)


	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)

(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, 2024 and 2023 (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,
	2024		2023		2024		2023
ASC 606 ide-cel license and manufacturing revenue – ex-U.S. (included as a component of service revenue) (1)	$	2,850	$	3,324	$	7,685	$	12,435

(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.

One-time restructuring expenses

In the second quarter of 2024, the Company recognized one-time expense of $5.4 million representing its share of costs associated with BMS’ early exit from a commercial manufacturing and supply agreement as a result of its transition to the use of suspension lentiviral vector in the manufacturing of Abecma. An additional $0.3 million of final exit costs were incurred and recognized in the third quarter of 2024. These costs are included in restructuring expenses on the condensed consolidated statements of operations and comprehensive loss.

Regeneron

Upon closing of the Regeneron Transaction, on April 1, 2024, the Regeneron Collaboration Agreement described below was terminated. Please refer to Note 3, Asset Purchase Agreements for further information regarding the accounting treatment for the termination.

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 the corresponding milestone payment 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 SPA with Regeneron pursuant to which the Company sold 1.1 million shares of its common stock, subject to certain restrictions, for $17.94 per share, to Regeneron for an aggregate cash price of approximately $20.0 million. The purchase price represents $9.9 million worth of common stock plus a $10.1 million premium, which represents deferred revenue.

Accounting analysis – 2018 Regeneron Collaboration Agreement

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

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

The $45.5 million attributed to the joint research activities includes the $37.0 million creditable against amounts owed to the Company by Regeneron. The collaboration research advancement will be reduced over time for amounts due to the Company by Regeneron as a result of the parties agreeing to share in the costs of collaboration research equally. The remainder of $8.5 million will be attributed to the joint research activities and recognized over the five-year research collaboration term.

Consistent with its collaboration accounting policy, the Company will recognize collaboration revenue or research and development expense related to the joint research activities in future periods depending on the amounts incurred by each party in a given reporting period. That is, if the Company’s research costs incurred exceed those research costs incurred by Regeneron in a given quarter, the Company will record collaboration revenue and reduce the original $37.0 million advance by the amount due from Regeneron until such advancement is fully utilized, after which the Company would record an amount due from Regeneron. If Regeneron’s research costs incurred exceed those research costs incurred by the Company in a given quarter, the Company will record research and development expense and record a liability for the amount due to Regeneron. The collaboration research advancement 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 received the benefit of the research activities as the activities were performed. The Company determined the most appropriate method to track progress towards completion of the four performance obligations was an input method that was based on costs incurred. There were 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 included a number of objective and subjective factors, including the likelihood that a target would 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 would be recognized in the period in which they change as a cumulative catch-up.

As noted, the four targets represented four distinct performance obligations and as such, the Company had 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 (in thousands):


Performance Obligation	Allocation of Transaction Price
MUC16 Mono/Combo & Next Gen Therapies	$	1,905
MAGE-A4	178
Early Research Target (1)	8,701
Early Research Target (2)	475
Total	$	11,259

As of September 30, 2024, as the Regeneron Collaboration Agreement has been terminated concurrently with the closing of the Regeneron Transaction, there is no unsatisfied portion of the transaction price remaining and there is no remaining deferred revenue. The remaining deferred revenue amount of $7.8 million as of April 1, 2024, was derecognized as part of the Regeneron Transaction. Refer to Note 3, Asset Purchase Agreements, for further detail.

During the first quarter of 2024, the Company received a milestone payment of $4.0 million from Regeneron relating to IND acceptance for the MUC16 target. As the filing of IND for the target is complete, the performance obligation relating to the target is satisfied and the Company recognized the full $4.0 million as service revenue in the first quarter of 2024, and on the condensed consolidated statement of operations for the nine months ended September 30, 2024 under ASC 606.

The Regeneron Collaboration Agreement has terminated concurrently with the closing of the Regeneron Transaction, and as such the Company did not recognize revenue in the third quarter of 2024. For the nine months ended September 30, 2024, the Company recognized $4.7 million of collaborative arrangement revenue from the Regeneron Collaboration Agreement relating to the first quarter of 2024. For the three and nine months ended September 30, 2023, the Company recognized $5.3 million and $16.2 million of collaborative arrangement revenue, respectively.

JW Therapeutics

Please refer to Note 3, Asset Purchase Agreements, for further information on the terms of the Asset Sale. Upon closing of the Asset Sale on April 1, 2024, this program was assumed by Regeneron, including all upfront milestone and royalty payments to be made by JW (Cayman) Therapeutics Co., Ltd. (“JW”), if any.

In October 2022, the Company entered into a strategic alliance with 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 granted JW a license for the MAGE-A4 cell therapy in the Chinese mainland, Hong Kong (China), and Macao (China). JW is responsible for development, manufacturing, and commercialization of the initial product within China. The Company was eligible to receive milestones and royalties on product revenues in China. The Company and Regeneron were to 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 were also to 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 was 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 had concluded the manufacturing and supply of vector was a distinct performance obligation from the license for MAGE-A4 cell therapy because there were 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 consisting of 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 in the development and commercialization for the initial Phase 1 clinical trial which the Company will also share equally with Regeneron. The agreement with JW was assumed by

Regeneron as a part of the Regeneron Transaction. As of September 30, 2024, no unsatisfied portion of the variable consideration for the reimbursement of vector supply remains.

Novo Nordisk

Upon the closing of an asset purchase agreement with Novo Nordisk in June 2024, the Collaboration and License Agreement with Novo Nordisk was terminated. Please refer to Note 3, Asset Purchase Agreements, for further information regarding the accounting treatment for the termination.

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. 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. 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. Prior to the Novo Transaction, the total of $11.0 million was included in deferred revenue, net of current portion. This amount was derecognized as part of the accounting for the Novo Transaction. Please refer to Note 3, Asset Purchase Agreements, for further detail.

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, 2024, the Company recognized no service revenue and $3.5 million of service revenue under this agreement, respectively. 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. The collaboration has been terminated following the signing of the asset purchase agreement with Novo in June 2024. Refer to Note 3, Asset Purchase Agreements, for further details.

Marketable securities - Schedule of Unrealized Loss on Restricted Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Fair value
Less than 12 months	$ 1,973	$ 3,496
12 months or greater	5,963	13,266
Total	7,936	16,762
Unrealized losses
Less than 12 months	(2)	(4)
12 months or greater	(32)	(361)
Total	(34)	(365)
U.S. government agency securities and treasuries
Fair value
Less than 12 months	1,973	3,496
12 months or greater	5,963	13,266
Total	7,936	16,762
Unrealized losses
Less than 12 months	(2)	(4)
12 months or greater	(32)	(361)
Total	$ (34)	$ (365)

Accrued expenses and other current liabilities

9 Months Ended

Sep. 30, 2024

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, 2024		As of December 31, 2023
Collaboration research costs	$	7,053	$	5,681
Employee compensation, including severance for restructuring	6,591		4,639
Royalties	4,022		9,702
Clinical and contract research organization costs	904		990
Deferred transition services income (1)	457		—
Manufacturing costs	—		1,764
Property, plant, and equipment	—		279
Other	4,195		2,633
Total accrued expenses and other current liabilities	$	23,222	$	25,688

(1) Refer to Note 3, Asset Purchase Agreements, for further information regarding deferred transition services income relating to the Novo Transaction.

The increase in accrued collaboration research costs is attributable to an increase in the Company’s accrual of amounts due under its collaboration with BMS. The increase in accrued employee compensation was primarily driven by 2024 retention bonuses for remaining 2seventy employees and the timing of the 2023 annual bonus payout, which occurred in December 2023.

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 (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net R&D expense	$ (8,320)			$ (51,315)			$ (68,264)	$ (179,541)
Collaborative arrangement revenue	10,684			5,859			19,744	64,265
Income (loss) from collaborative arrangements	0			0			(1,230)	0
Ide-cel Research And Development Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net R&D expense	(8,168)	$ (8,433)	$ (6,739)	(6,120)	$ (5,652)	$ (4,871)	(23,340)	(16,643)
ABECMA Commercial Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	10,684	4,364	0	536	24,543	22,961	15,048	48,040
Income (loss) from collaborative arrangements	0	0	(1,230)				(1,230)
Bristol-Myers Squibb \| Ide-cel Research And Development Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
2seventy's obligation for its share of BMS research and development expenses	(8,225)	(8,625)	(6,963)	(6,980)	(7,195)	(9,461)	(23,813)	(23,636)
Reimbursement from BMS for 2seventy research and development expenses	57	192	224	860	1,543	4,590	473	6,993
Bristol-Myers Squibb \| Ide Cel Commercial Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	9,617	3,549	(1,975)	(582)	23,272	21,581	11,191	44,271
Income (loss) from collaborative arrangements	1,067	$ 815	$ 745	1,118	$ 1,271	$ 1,380	2,627	3,769
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	$ 2,850			$ 3,324			$ 7,685	$ 12,435

Property, plant and equipment, net (Tables)

9 Months Ended

Sep. 30, 2024

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, 2024		As of December 31, 2023
Computer equipment and software	$	4,965	$	6,156
Office equipment	6,330		6,726
Laboratory equipment	4,162		43,209
Leasehold improvements	48,340		58,832
Construction-in-progress	—		138
Total property, plant and equipment	63,797		115,061
Less accumulated depreciation and amortization	(28,560)		(56,911)
Property, plant and equipment, net	$	35,237	$	58,150

Summary of significant accounting policies and basis of presentation (Policies)	9 Months Ended
	Sep. 30, 2024
Accounting Policies [Abstract]
Contingent consideration receivable	Contingent consideration receivable Under ASC 810, Consolidations, the Company has elected to use the loss recovery approach to account for contingent consideration receivable. Under this approach, if it is probable that contingent consideration will be received, an asset would be recognized and measured initially at the lesser of (i) the amount of probable future proceeds or (ii) the difference between the fair value of the consideration received, excluding the contingent consideration, and the carrying amount of the deconsolidated net assets.
Gain or Loss on Transaction	Gain or Loss on Transaction The Company accounts for the disposition or sale of a business in accordance with Topic 810, Consolidations. This includes derecognizing assets related to the disposal group and then recognizing a gain or loss for the difference between the fair value of the consideration received and the book value of the disposal group under Topic 810.
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 of the Financial Accounting Standards Board. 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 these condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts in the condensed consolidated 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 condensed consolidated 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 condensed consolidated 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 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 condensed consolidated financial statements. In addition, estimates and judgments are used in the Company’s accounting for its revenue-generating arrangements, in particular as it relates to determining the stand-alone selling price of performance obligations, evaluating whether an option to acquire additional goods and services represents a material right, estimating the total transaction price, including estimating variable consideration and the probability of achieving future potential development and regulatory milestones, assessing the period of performance over which revenue may be recognized, and accounting for modifications to revenue-generating arrangements.

Summary of significant accounting policies and basis of presentation	9 Months Ended
	Sep. 30, 2024
Accounting Policies [Abstract]
Summary of significant accounting policies and basis of presentation	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, 2023 included in the Company’s 2023 annual report on Form 10-K, except as disclosed below: Contingent consideration receivable Under ASC 810, Consolidations, the Company has elected to use the loss recovery approach to account for contingent consideration receivable. Under this approach, if it is probable that contingent consideration will be received, an asset would be recognized and measured initially at the lesser of (i) the amount of probable future proceeds or (ii) the difference between the fair value of the consideration received, excluding the contingent consideration, and the carrying amount of the deconsolidated net assets. Gain or Loss on Transaction The Company accounts for the disposition or sale of a business in accordance with Topic 810, Consolidations. This includes derecognizing assets related to the disposal group and then recognizing a gain or loss for the difference between the fair value of the consideration received and the book value of the disposal group under Topic 810. 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 of the Financial Accounting Standards Board. 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 The preparation of these condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts in the condensed consolidated 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 condensed consolidated 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 condensed consolidated 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 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 condensed consolidated 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.

Fair value measurements - Roll-Forward of Fair Value of the Company's Contingent Consideration Obligations (Details) - Significant unobservable inputs (Level 3) - Contingent Consideration Obligations $ in Thousands	9 Months Ended
	Sep. 30, 2024 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 2,415
Additions	0
Changes in fair value	(2,415)
Payments	0
Ending balance	$ 0

Corporate Restructuring - Narrative (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended	7 Months Ended	9 Months Ended	11 Months Ended
	Apr. 02, 2024	Sep. 30, 2023	Sep. 30, 2023	Oct. 31, 2024	Sep. 30, 2024	Jun. 30, 2024
Restructuring Cost and Reserve [Line Items]
Restructuring expenses					$ 5,376
Payments for restructuring					3,814
August 2023 Reduction
Restructuring Cost and Reserve [Line Items]
Percentage of workforce reduction		40.00%
Restructuring expenses			$ 8,600
Payments for restructuring						$ 8,600
January 2024 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Percentage of workforce remaining	62.00%
Total restructuring expenses					$ 6,644
January 2024 Restructuring Plan \| Subsequent Event
Restructuring Cost and Reserve [Line Items]
Percentage of workforce reduction				14.00%

- 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

Corporate Restructuring (Tables)

9 Months Ended

Sep. 30, 2024

Restructuring and Related Activities [Abstract]

Summary of Accrued Liability Activity

The table below summarizes the expenses recognized and expected to be recognized under the 2024 Restructuring Plan as of September 30, 2024:


	Expense recognized for the three months ended September 30, 2024		Expense recognized for the nine months ended September 30, 2024		Total expense expected to be recognized
Cash-related restructuring expenses:
Severance and related benefits	$	228	$	5,376	$	5,607
Non-cash expenses:
Stock-based compensation expense	—		1,037		1,037
Total restructuring expenses	$	228	$	6,413	$	6,644

The following table summarizes the cash-related restructuring accrued liabilities activity recorded in connection with the 2024 Restructuring Plan for the nine months ended September 30, 2024:


	For the nine months ended September 30, 2024
Beginning balance at January 1, 2024	$	—
Cash-related expenses recognized	5,376
Cash-related expenses paid	(3,814)
Reversal of excess accrual	—
Remaining accrual at September 30, 2024 (1)	$	1,562

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

Marketable securities - Narrative (Detail) - USD ($)	3 Months Ended		9 Months Ended
Marketable securities - Narrative (Detail) - USD ($)	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Interest receivable	$ 1,000,000		$ 1,000,000		$ 800,000
Interest receivable, write-off	$ 0	$ 0	$ 0	$ 0

Marketable securities (Tables)

9 Months Ended

Sep. 30, 2024

Investments, Debt and Equity Securities [Abstract]

Summary of Marketable Securities

The following table summarizes the marketable securities held at September 30, 2024 and December 31, 2023 (in thousands):


	Cost or amortized cost		Unrealized gains		Unrealized losses		Fair Value
September 30, 2024
U.S. government agency securities and treasuries	$	81,085	$	182	$	(3)	$	81,264
Corporate bonds	2,016		—		(1)		2,015
Commercial paper	49,084		74		(22)		49,136
Total	$	132,185	$	256	$	(26)	$	132,415
December 31, 2023
U.S. government agency securities and treasuries	$	101,566	$	144	$	(85)	$	101,625
Commercial paper	45,188		34		—		45,222
Total	$	146,754	$	178	$	(85)	$	146,847

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 twelve months and twelve months or greater, and for which an allowance for credit losses has not been recorded at September 30, 2024 and December 31, 2023 (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, 2024
U.S. government agency securities and treasuries	$	1,930	$	(2)	$	4,992	$	(1)	$	6,922	$	(3)
Corporate bonds	2,015		(1)		—		—		2,015		(1)
Commercial paper	10,795		(22)		—		—		10,795		(22)
Total	$	14,740	$	(25)	$	4,992	$	(1)	$	19,732	$	(26)
December 31, 2023
U.S. government agency securities and treasuries	$	45,850	$	(60)	$	1,475	$	(25)	$	47,325	$	(85)
Total	$	45,850	$	(60)	$	1,475	$	(25)	$	47,325	$	(85)

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, 2024
Beginning balance	$	2,415
Additions	—
Changes in fair value	(2,415)
Payments	—
Ending balance	$	—

Summary or Restricted Investments

The following table summarizes restricted investments held at September 30, 2024 and December 31, 2023 (in thousands):


	Cost or amortized cost		Unrealized gains		Unrealized losses		Fair Value
September 30, 2024
U.S. government agency securities and treasuries	$	34,784	$	109	$	(34)	$	34,859
Total	$	34,784	$	109	$	(34)	$	34,859
December 31, 2023
U.S. government agency securities and treasuries	$	33,072	$	67	$	(365)	$	32,774
Total	$	33,072	$	67	$	(365)	$	32,774

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 twelve months and twelve months or greater, and for which an allowance for credit losses has not been recorded at September 30, 2024 and December 31, 2023 (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, 2024
U.S. government agency securities and treasuries	$	1,973	$	(2)	$	5,963	$	(32)	$	7,936	$	(34)
Total	$	1,973	$	(2)	$	5,963	$	(32)	$	7,936	$	(34)
December 31, 2023
U.S. government agency securities and treasuries	$	3,496	$	(4)	$	13,266	$	(361)	$	16,762	$	(365)
Total	$	3,496	$	(4)	$	13,266	$	(361)	$	16,762	$	(365)

Fair value measurements

9 Months Ended

Sep. 30, 2024

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, 2024 and December 31, 2023 (in thousands):


	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
September 30, 2024
Assets:
Cash and cash equivalents	$	59,984	$	59,984	$	—	$	—
Marketable securities:
U.S. government agency securities and treasuries	81,264		—		81,264		—
Corporate bonds	2,015		—		2,015		—
Commercial paper	49,136		—		49,136		—
Restricted cash and cash equivalents	363		363		—		—
Restricted investments	34,859		—		34,859		—
Total assets	$	227,621	$	60,347	$	167,274	$	—
December 31, 2023
Assets:
Cash and cash equivalents	$	74,958	$	74,958	$	—	$	—
Marketable securities:
U.S. government agency securities and treasuries	101,625		—		101,625		—
Commercial paper	45,222		—		45,222		—
Restricted cash and cash equivalents	1,725		1,725		—
Restricted investments	32,774		—		32,774		—
Total assets	$	256,304	$	76,683	$	179,621	$	—
Liabilities:
Contingent consideration	$	2,415	$	—	$	—	$	2,415
Total liabilities	$	2,415	$	—	$	—	$	2,415

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. As of September 30, 2024, the Company determined the probability of milestone achievement to be zero and as a result reduced the fair value of contingent consideration included in other non-current liabilities on the condensed consolidated balance sheets to zero.

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, 2024
Beginning balance	$	2,415
Additions	—
Changes in fair value	(2,415)
Payments	—
Ending balance	$	—

Please refer to Note 9, 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

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 107
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-107

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 100
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-100

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2E
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2E

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 940
-SubTopic 820
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478119/940-820-50-1

+ Details

Accrued expenses and other current liabilities (Tables)

9 Months Ended

Sep. 30, 2024

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, 2024		As of December 31, 2023
Collaboration research costs	$	7,053	$	5,681
Employee compensation, including severance for restructuring	6,591		4,639
Royalties	4,022		9,702
Clinical and contract research organization costs	904		990
Deferred transition services income (1)	457		—
Manufacturing costs	—		1,764
Property, plant, and equipment	—		279
Other	4,195		2,633
Total accrued expenses and other current liabilities	$	23,222	$	25,688

(1) Refer to Note 3, Asset Purchase Agreements, for further information regarding deferred transition services income relating to the Novo Transaction.

Leases - Narrative (Details) $ in Millions			3 Months Ended	9 Months Ended
Leases - Narrative (Details) $ in Millions	Jul. 18, 2018 ft²	Sep. 21, 2015 ft²	Sep. 30, 2024 USD ($)	Sep. 30, 2024 USD ($) ft²
Lessee, Lease, Description [Line Items]
Lease rent, annual increase percentage				63.00%
60 Binney Street Lease
Lessee, Lease, Description [Line Items]
Sublease income \| $			$ 4.9	$ 9.8
60 Binney Street Lease \| Cambridge, Massachusetts
Lessee, Lease, Description [Line Items]
Lease building space (in sq ft) \| ft²		253,108		159,106
188 East Blaine Street Lease
Lessee, Lease, Description [Line Items]
Sublease income \| $			$ 0.6	$ 1.2
188 East Blaine Street Lease \| Seattle, Washington
Lessee, Lease, Description [Line Items]
Lease building space (in sq ft) \| ft²	36,126			36,126

Net Loss Per Share - Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
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)	7,563,000	5,704,000	7,563,000	5,704,000
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)	3,962,000	3,369,000	3,962,000	3,369,000
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)	3,601,000	2,335,000	3,601,000	2,335,000
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	0	0	0

Income taxes	9 Months Ended
Income taxes	Sep. 30, 2024
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 tax.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-12

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 231
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482663/740-10-55-231

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12C
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-12C

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-12B

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477891/740-270-50-1

Reference 6: 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 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480990/946-20-50-13

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org/740/tableOfContent

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-14

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-21

Reference 12: 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 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479360/740-10-S99-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482603/740-30-50-2

+ Details

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2024	Dec. 31, 2023
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)	51,512,000	50,632,000
Common stock, shares outstanding (in shares)	51,512,000	50,632,000

Collaborative arrangements and strategic partnerships - Narrative (Details) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended				9 Months Ended
	Jan. 31, 2023 USD ($) $ / shares shares	Aug. 31, 2018 USD ($) target accounting_unit $ / shares shares	Sep. 30, 2024 USD ($)	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Apr. 30, 2023 USD ($)	Oct. 31, 2022 USD ($)	Dec. 31, 2021 USD ($) performance_obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
One time restructuring expenses			$ 300	$ 5,400
Proceeds from issuance of common stock to Regeneron, net of issuance costs							$ 0	$ 9,859
Common stock, $0.0001 par value; 200,000 shares authorized, 51,512 and 50,632 shares issued and outstanding at September 30, 2024 and December 31, 2023, respectively			5				$ 5		$ 5
Number of accounting units \| accounting_unit		2
Bristol-Myers Squibb \| Abecma Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Agreement termination notice period							90 days
Regeneron \| Collaboration Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue balance recognized as gross revenues						$ 5,300	$ 4,700	16,200
Regeneron \| Research and Development Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Purchase price premium		$ 37,000					1,100
Collaborative arrangement amortization period		5 years
Collaboration agreement, transaction price		$ 100,000
Collaborative arrangement amount attributed to joint research activities		45,500
Collaborative arrangement amount attributed to joint research activities, net funding advancement		8,500
Regeneron \| Research and Development Services \| Bluebird Bio
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement amount attributed to equity sold		$ 54,500
Regeneron \| 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			7,800				7,800
Regeneron \| Regeneron Collaboration Agreement, Amendment One \| Pre-Clinical Costs To Study Combinations
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement research initial funding obligation, percentage	75.00%
Regeneron \| Regeneron Collaboration Agreement, Amendment One \| Clinical Study Costs Involving Regeneron Agents
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement research initial funding obligation, percentage	100.00%
Regeneron \| Regeneron Collaboration Agreement, Amendment One \| MUC-16 Development Candidate Nomination
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	$ 2,000
Regeneron \| Regeneron Collaboration Agreement, Amendment One \| MUC-16 IND Acceptance
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	3,000
Regeneron \| Regeneron Collaboration Agreement, Amendment One \| Last Patient Dosed Or Dosing Of The 10th Patient
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	5,000
Regeneron \| Regeneron Collaboration Agreement, Amendment One \| MUC-16 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, Amendment One \| MUC-16
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	$ 4,000
Revenue					$ 4,000
Regeneron \| Share Purchase Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock shares issued (in shares) \| shares	1,114,827	100,000
Common stock price per share (in dollars per share) \| $ / shares	$ 17.94
Proceeds from issuance of common stock to Regeneron, net of issuance costs	$ 20,000
Common stock, $0.0001 par value; 200,000 shares authorized, 51,512 and 50,632 shares issued and outstanding at September 30, 2024 and December 31, 2023, respectively	9,900
Contract with customer liability	$ 10,100
Regeneron \| Share Purchase Agreement \| Bluebird Bio
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement research initial funding obligation, percentage		50.00%
Common stock price per share (in dollars per share) \| $ / shares		$ 238.10
Proceeds from issuance of common stock to Regeneron, net of issuance costs		$ 100,000
Purchase price premium		$ 37,000
Regeneron \| Share Purchase Agreement \| Common stock \| Bluebird Bio
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock shares issued (in shares) \| shares		400,000
Proceeds from issuance of common stock to Regeneron, net of issuance costs		$ 63,000
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
JW Therapeutics
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability											$ 3,000
Estimated variable consideration											7,300
Estimated variable consideration reimbursement											$ 4,300
Novo Nordisk A/S \| Novo Collaboration and License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability												$ 5,000
Revenue			0			$ 1,100	3,500	$ 4,700
Estimated variable consideration												$ 11,700
Number of performance obligations \| performance_obligation												2
Estimated variable consideration, upfront payment												$ 5,000
Estimated variable consideration, research reimbursement												6,700
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 \| 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 \| 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

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Revenue:
Collaborative arrangement revenue	$ 10,684	$ 5,859	$ 19,744	$ 64,265
Total revenues	13,534	12,034	34,936	89,703
Operating expenses:
Research and development	8,320	51,315	68,264	179,541
Cost of manufacturing for commercial collaboration	5,768	4,408	12,490	11,672
Selling, general and administrative	12,884	13,004	35,400	53,213
Share of collaboration loss	0	0	1,230	0
Restructuring expenses	503	8,614	12,131	8,614
Cost of royalty and other revenue	0	551	0	2,099
Change in fair value of contingent consideration	0	54	(2,415)	180
Goodwill impairment charge	0	12,056	0	12,056
Total operating expenses	27,475	90,002	127,100	267,375
Loss from operations	(13,941)	(77,968)	(92,164)	(177,672)
Interest income, net	2,855	3,626	8,243	8,765
Other income, net	1,153	2,704	3,233	8,159
Loss before income taxes	(9,933)	(71,638)	(37,727)	(160,748)
Income tax (expense) benefit	0	0	0	0
Net loss	$ (9,933)	$ (71,638)	$ (37,727)	$ (160,748)
Net loss per share - basic (in dollars per share)	$ (0.19)	$ (1.40)	$ (0.72)	$ (3.31)
Net loss per share - diluted (in dollars per share)	$ (0.19)	$ (1.40)	$ (0.72)	$ (3.31)
Weighted-average number of common shares used in computing net loss per share - basic (in shares)	52,263,000	51,179,000	52,176,000	48,566,000
Weighted-average number of common shares used in computing net loss per share - diluted (in shares)	52,263,000	51,179,000	52,176,000	48,566,000
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, 2024 and 2023, respectively.	$ 541	$ 514	$ 509	$ 1,961
Comprehensive loss	(9,392)	(71,124)	(37,218)	(158,787)
Novo Nordisk
Operating expenses:
Loss on assets held for sale to Regeneron	0	0	47,987	0
Regeneron
Operating expenses:
Loss on assets held for sale to Regeneron	0	0	(5,026)	0
Service revenue
Revenue:
Revenue	2,850	4,948	15,192	20,796
Royalty and other revenue
Revenue:
Revenue	$ 0	$ 1,227	$ 0	$ 4,642

Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Collaboration research costs	$ 7,053	$ 5,681
Employee compensation, including severance for restructuring	6,591	4,639
Royalties	4,022	9,702
Clinical and contract research organization costs	904	990
Deferred transition services income	457	0
Manufacturing costs	0	1,764
Property, plant, and equipment	0	279
Other	4,195	2,633
Total accrued expenses and other current liabilities	$ 23,222	$ 25,688

Collaborative arrangements and strategic partnerships (Tables)

9 Months Ended

Sep. 30, 2024

Organization, Consolidation and Presentation of Financial Statements [Abstract]

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

The amounts reported for these periods represent the Company’s share of BMS’ Abecma product revenue, cost of goods sold, and selling costs, along with reimbursement by BMS of commercial costs incurred by the Company, and exclude expenses related to ongoing development, which are separately reflected in the consolidated statements of operations and comprehensive loss as described below.


	For the three months ended						For the nine months ended
Abecma U.S. Collaboration Profit/Loss Share	March 31, 2024		June 30, 2024		September 30, 2024		September 30, 2024
2seventy's share of profits (losses), net of 2seventy's share of BMS costs for commercial activities	$	(1,975)	$	3,549	$	9,617	$	11,191
Reimbursement from BMS for 2seventy costs of commercial manufacturing and commercial activities	745		815		1,067		2,627
Collaborative arrangement revenue (1)	$	—	$	4,364	$	10,684	$	15,048
Share of collaboration loss (1)	$	(1,230)	$	—	$	—	$	(1,230)


	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 Net R&D Expenses	March 31, 2024		June 30, 2024		September 30, 2024		September 30, 2024
2seventy's obligation for its share of BMS research and development expenses	$	(6,963)	$	(8,625)	$	(8,225)	$	(23,813)
Reimbursement from BMS for 2seventy research and development expenses	224		192		57		473
Net R&D expense (1)	$	(6,739)	$	(8,433)	$	(8,168)	$	(23,340)


	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 September 30,				For the nine months ended September 30,
	2024		2023		2024		2023
ASC 606 ide-cel license and manufacturing revenue – ex-U.S. (included as a component of service revenue) (1)	$	2,850	$	3,324	$	7,685	$	12,435

(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 summarizes the allocation of the transaction price to each performance obligation and the amount of the allocated transaction price (in thousands):


Performance Obligation	Allocation of Transaction Price
MUC16 Mono/Combo & Next Gen Therapies	$	1,905
MAGE-A4	178
Early Research Target (1)	8,701
Early Research Target (2)	475
Total	$	11,259

Corporate Restructuring - Summary of Accrued Liability Activity (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2024 USD ($)
Restructuring Reserve [Roll Forward]
Beginning balance	$ 0
Cash-related expenses recognized	5,376
Cash-related expenses paid	(3,814)
Reversal of excess accrual	0
Ending balance	$ 1,562

Asset purchase agreements (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Apr. 01, 2024	Jan. 31, 2024	Dec. 31, 2023
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Receivables and other current assets		$ 22,275				$ 13,411
Regeneron Purchase Agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset held-for-sale, deferred revenue totals		12,800
Novo Nordsk Purchase Agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset held-for-sale, deferred revenue totals			$ 48,000
Discontinued Operations, Held-for-Sale \| Regeneron Purchase Agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received				$ 5,000	$ 5,000
Property, plant and equipment and prepaid expenses classified as held for sale	$ 17,800
Deferred revenue derecognized				$ 7,800
Gain (loss) on asset sale and assets held for sale	$ 5,000
Receivables and other current assets		$ 5,000
Discontinued Operations, Held-for-Sale \| Novo Nordsk Purchase Agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received			38,000
Deferred revenue derecognized			11,000
Contingent consideration			2,000
Initial purchase price			$ 1,000

Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			9 Months Ended
	Mar. 31, 2023	Jan. 31, 2023	Aug. 31, 2018	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Subsidiary, Sale of Stock [Line Items]
Proceeds from issuance of common stock to Regeneron, net of issuance costs				$ 0	$ 9,859
Common stock				$ 5		$ 5
Underwritten Public Offering
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in transaction (in shares)	10,869,566
Common stock price per share (in dollars per share)	$ 11.50
Aggregate net proceeds	$ 117,000
Additional shares available for purchase (in shares)	1,630,434
Regeneron \| Share Purchase Agreement
Subsidiary, Sale of Stock [Line Items]
Common stock shares issued (in shares)		1,114,827	100,000
Proceeds from issuance of common stock to Regeneron, net of issuance costs		$ 20,000
Common stock		9,900
Contract with customer liability		$ 10,100
Common stock price per share (in dollars per share)		$ 17.94

Cover Page - shares	9 Months Ended
Cover Page - shares	Sep. 30, 2024	Nov. 06, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2024
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	617
Local Phone Number	675-7270
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		51,588,420
Amendment Flag	false
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001860782
Current Fiscal Year End Date	--12-31

Stock-based compensation

9 Months Ended

Sep. 30, 2024

Share-Based Payment Arrangement [Abstract]

Stock-based compensation

In connection with 2seventy bio’s separation from bluebird bio in 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, 2023 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,

performance-based restricted stock units, 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,
	2024		2023		2024		2023
Stock options	$	881	$	2,655	$	3,782	$	9,237
Restricted stock units	1,748		7,046		5,840		17,697
Employee Stock Purchase Plan	14		99		90		272
	$	2,643	$	9,800	$	9,712	$	27,206

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,
	2024		2023		2024		2023
Research and development	$	75	$	3,812	$	2,070	$	10,802
Selling, general and administrative	2,568		5,988		6,605		16,404
Restructuring expenses	—		—		1,037		—
	$	2,643	$	9,800	$	9,712	$	27,206

Employee Stock Purchase Plan

During the nine months ended September 30, 2024, 0.1 million shares of common stock were issued under the Company’s 2021 Employee Stock Purchase Plan (“ESPP”).

Commitments and contingencies	9 Months Ended
Commitments and contingencies	Sep. 30, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	Commitments and contingencies Contingent consideration related to business combination 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. 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. As of September 30, 2024, the Company determined the probability of milestone achievement to be zero and as a result reduced the fair value of contingent consideration included in other non-current liabilities on the condensed consolidated balance sheets to zero. Please refer to Note 5, 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 11, Collaborative arrangements and strategic partnerships, for further information on the BMS, Regeneron, and Novo Nordisk A/S agreements and to Note 12, Royalty and other revenue, for further information on license agreements. Based on the Company's development plans as of September 30, 2024, 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 condensed consolidated financial statements. As further discussed in Note 11, 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. Additionally, 2seventy bio was party to various contracts with contract research organizations and contract manufacturers that generally provide for termination on notice, with the exact amounts in the event of termination to be based on the timing of the termination and the terms of the agreement. The majority of these contracts were assumed by Regeneron upon or after closing of the Regeneron Transaction. For any contracts remaining, other than a decrease in committed spend due to the payment of these obligations in the normal course of business, there have been no material changes in future minimum purchase commitments from those disclosed in Note 8, Commitments and Contingencies, to the consolidated financial statements included in the Company's 2023 annual report on Form 10-K. Litigation From time to time, the Company expects to be party to various claims and complaints arising in the ordinary course of business. However, the Company is not currently a party to any litigation or legal proceedings that, in the opinion of its management, are probable of having a material adverse effect on its business. The Company enters into standard indemnification agreements in the ordinary course of business. Pursuant to these agreements, the Company indemnifies, holds harmless, and agrees to reimburse the indemnified party for losses suffered or incurred by the indemnified party, generally the Company’s business partners. In addition, pursuant to the separation agreement with bluebird bio, 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.

Net Loss Per Share

9 Months Ended

Sep. 30, 2024

Earnings Per Share [Abstract]

Net Loss Per Share


	For the three and nine months ended September 30,
	2024	2023
Outstanding stock options (1)	3,962	3,369
Restricted stock units (1)	3,601	2,335
ESPP Shares	—	—
	7,563	5,704

(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 2023 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.

Stock-based compensation - Summary of Stock-Based Compensation Expense by Award Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 2,643	$ 9,800	$ 9,712	$ 27,206
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	881	2,655	3,782	9,237
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,748	7,046	5,840	17,697
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 14	$ 99	$ 90	$ 272

- 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
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(01)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(02)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(03)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(04)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(ii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(01)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(02)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(03)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(ii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 26: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 27: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iv)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 28: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(v)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Cash flows from operating activities:
Net loss	$ (9,933)	$ (71,638)	$ (37,727)	$ (160,748)
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of contingent consideration	0	54	(2,415)	180
Depreciation and amortization			5,441	7,255
Stock-based compensation expense			9,712	27,206
Goodwill impairment charge	0	12,056	0	12,056
Other non-cash items			(3,448)	(4,881)
Changes in operating assets and liabilities:
Prepaid expenses and other assets			(4,917)	9,611
Operating lease right-of-use assets			14,234	16,332
Accounts payable			(376)	(1,015)
Accrued expenses and other liabilities			(3,304)	(16,603)
Operating lease liabilities			(9,228)	(10,016)
Deferred revenue			(535)	21,104
Collaboration research advancement			0	(3,744)
Net cash used in operating activities			(75,524)	(103,263)
Cash flows from investing activities:
Purchases of property, plant and equipment			(707)	(12,794)
Proceeds from sale of equipment			176	0
Purchases of marketable securities			(104,452)	(237,151)
Proceeds from maturities of marketable securities			122,505	245,899
Purchases of restricted investments			(16,808)	(6,983)
Proceeds from maturities of restricted investments			15,060	7,000
Net cash provided by (used in) investing activities			58,774	(4,029)
Cash flows from financing activities:
Proceeds from issuance of common stock in public offering, net of issuance costs			0	117,004
Proceeds from issuance of common stock to Regeneron, net of issuance costs			0	9,859
Proceeds from exercise of stock options and ESPP contributions			414	274
Net cash provided by financing activities			414	127,137
(Decrease) increase in cash, cash equivalents and restricted cash and cash equivalents			(16,336)	19,845
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period			76,683	72,290
Cash, cash equivalents and restricted cash and cash equivalents at end of period	60,347	92,135	60,347	92,135
Reconciliation of cash, cash equivalents, and restricted cash and cash equivalents
Cash and cash equivalents	59,984	90,226	59,984	90,226
Restricted cash and cash equivalents included in restricted investments and other non-current assets	363	1,909	363	1,909
Total cash, cash equivalents, and restricted cash and cash equivalents	60,347	92,135	60,347	92,135
Supplemental cash flow disclosures:
Purchases of property, plant and equipment included in accounts payable and accrued expenses			0	1,605
Financing issuance costs included in accounts payable or accrued expenses			0	35
Novo Nordisk
Adjustments to reconcile net loss to net cash used in operating activities:
Gain (loss) on asset sale and assets held for sale	0	0	(47,987)	0
Cash flows from investing activities:
Proceeds from asset sale			38,000	0
Regeneron
Adjustments to reconcile net loss to net cash used in operating activities:
Gain (loss) on asset sale and assets held for sale	$ 0	$ 0	5,026	0
Cash flows from investing activities:
Proceeds from asset sale			$ 5,000	$ 0

Commitments and contingencies (Details) $ in Millions	Sep. 30, 2024 USD ($)
Pregenen
Commitments And Contingencies Disclosure [Line Items]
Contingent future cash payments	$ 99.9

Stock-based compensation - Schedule of Stock-Based Compensation Expense by Classification (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 2,643	$ 9,800	$ 9,712	$ 27,206
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	75	3,812	2,070	10,802
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2,568	5,988	6,605	16,404
Restructuring expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 0	$ 0	$ 1,037	$ 0

- 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

Property, plant and equipment, net - Summary of Property, Plant and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 63,797	$ 115,061
Less accumulated depreciation and amortization	(28,560)	(56,911)
Property, plant and equipment, net	35,237	58,150
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	4,965	6,156
Office equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	6,330	6,726
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	4,162	43,209
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	48,340	58,832
Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 0	$ 138

Description of the business (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended						9 Months Ended
	Nov. 30, 2022	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Subsequent Event [Line Items]
Net loss		$ (9,933)	$ 24,879	$ (52,673)	$ (71,638)	$ (42,089)	$ (47,021)	$ (37,727)	$ (160,748)
Net cash used in operating activities								75,524	$ 103,263
Cash, cash equivalents, and marketable securities		$ 192,400						$ 192,400
At The Market Facility \| Cowen And Company LLC
Subsequent Event [Line Items]
Aggregate gross proceeds (up to)	$ 150,000

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-9

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 805
-SubTopic 60
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147476176/805-60-65-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 323
-Name Accounting Standards Codification
-Section 65
-Paragraph 2
-Subparagraph (g)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478666/740-323-65-2

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(20))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481687/323-10-50-3

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-28

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482765/220-10-50-6

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-3

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-1

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480175/815-40-65-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-8

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-11

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-11

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-4

Reference 17: http://www.xbrl.org/2003/role/exampleRef
-Topic 946
-SubTopic 830
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479168/946-830-55-10

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section 45
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479105/946-220-45-7

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(18))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(9))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-09(1)(d))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-3

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(i))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1A

Reference 23: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(ii))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1A

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iii)(A))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1A

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iv))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1A

Reference 26: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(5))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1A

Reference 27: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(i))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1B

Reference 28: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iii)(A))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1B

Reference 29: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iii)(B))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1B

Reference 30: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iv))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1B

Reference 31: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(5))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1B

Reference 32: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 60B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482689/260-10-45-60B

Reference 33: http://www.xbrl.org/2003/role/disclosureRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483499/205-20-50-7

Reference 34: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

Reference 35: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482790/220-10-45-1A

Reference 36: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482790/220-10-45-1B

Reference 37: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(22))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478524/942-220-S99-1

+ Details

Stock-based compensation (Tables)

9 Months Ended

Sep. 30, 2024

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,
	2024		2023		2024		2023
Stock options	$	881	$	2,655	$	3,782	$	9,237
Restricted stock units	1,748		7,046		5,840		17,697
Employee Stock Purchase Plan	14		99		90		272
	$	2,643	$	9,800	$	9,712	$	27,206

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,
	2024		2023		2024		2023
Research and development	$	75	$	3,812	$	2,070	$	10,802
Selling, general and administrative	2,568		5,988		6,605		16,404
Restructuring expenses	—		—		1,037		—
	$	2,643	$	9,800	$	9,712	$	27,206

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 59,984	$ 74,958
Marketable securities	132,415	142,031
Prepaid expenses	3,805	7,365
Receivables and other current assets	22,275	13,411
Total current assets	218,479	237,765
Property, plant and equipment, net	35,237	58,150
Marketable securities	0	4,816
Intangible assets, net	6,063	6,594
Operating lease right-of-use assets	205,724	219,958
Restricted investments and other non-current assets	38,343	38,143
Total assets	503,846	565,426
Current liabilities:
Accounts payable	5,076	6,028
Accrued expenses and other current liabilities	23,222	25,688
Operating lease liability, current portion	15,797	12,660
Deferred revenue, current portion	0	15,403
Total current liabilities	44,095	59,779
Deferred revenue, net of current portion	0	3,918
Operating lease liability, net of current portion	231,649	244,013
Other non-current liabilities	0	2,416
Total liabilities	275,744	310,126
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized, 0 shares issued and outstanding at September 30, 2024 and December 31, 2023	0	0
Common stock, $0.0001 par value; 200,000 shares authorized, 51,512 and 50,632 shares issued and outstanding at September 30, 2024 and December 31, 2023, respectively	5	5
Additional paid-in capital	776,736	766,716
Accumulated other comprehensive income (loss)	305	(204)
Accumulated deficit	(548,944)	(511,217)
Total stockholders’ equity	228,102	255,300
Total liabilities and stockholders’ equity	$ 503,846	$ 565,426

Fair value measurements - Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022
Assets:
Marketable securities:	$ 132,415	$ 146,847
Restricted cash and cash equivalents	60,347	76,683	$ 92,135	$ 72,290
U.S. government agency securities and treasuries
Assets:
Marketable securities:	81,264	101,625
Corporate bonds
Assets:
Marketable securities:	2,015
Commercial paper
Assets:
Marketable securities:	49,136	45,222
Fair Value, Measurements, Recurring
Assets:
Cash and cash equivalents	59,984	74,958
Restricted cash and cash equivalents	363	1,725
Restricted investments	34,859	32,774
Total assets	227,621	256,304
Liabilities:
Contingent consideration		2,415
Total liabilities		2,415
Fair Value, Measurements, Recurring \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	81,264	101,625
Fair Value, Measurements, Recurring \| Corporate bonds
Assets:
Marketable securities:	2,015
Fair Value, Measurements, Recurring \| Commercial paper
Assets:
Marketable securities:	49,136	45,222
Fair Value, Measurements, Recurring \| Quoted prices in active markets (Level 1)
Assets:
Cash and cash equivalents	59,984	74,958
Restricted cash and cash equivalents	363	1,725
Restricted investments	0	0
Total assets	60,347	76,683
Liabilities:
Contingent consideration		0
Total liabilities		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	0	0
Restricted cash and cash equivalents	0	0
Restricted investments	34,859	32,774
Total assets	167,274	179,621
Liabilities:
Contingent consideration		0
Total liabilities		0
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	81,264	101,625
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| Corporate bonds
Assets:
Marketable securities:	2,015
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| Commercial paper
Assets:
Marketable securities:	49,136	45,222
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Restricted cash and cash equivalents	0
Restricted investments	0	0
Total assets	0	0
Liabilities:
Contingent consideration		2,415
Total liabilities		2,415
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

Marketable securities - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Marketable Securities [Line Items]
Cost or amortized cost	$ 132,185	$ 146,754
Unrealized gains	256	178
Unrealized losses	(26)	(85)
Fair Value	132,415	146,847
U.S. government agency securities and treasuries
Marketable Securities [Line Items]
Cost or amortized cost	81,085	101,566
Unrealized gains	182	144
Unrealized losses	(3)	(85)
Fair Value	81,264	101,625
Corporate bonds
Marketable Securities [Line Items]
Cost or amortized cost	2,016
Unrealized gains	0
Unrealized losses	(1)
Fair Value	2,015
Commercial paper
Marketable Securities [Line Items]
Cost or amortized cost	49,084	45,188
Unrealized gains	74	34
Unrealized losses	(22)	0
Fair Value	$ 49,136	$ 45,222

Property, plant and equipment, net - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Apr. 01, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	$ 35,237		$ 58,150
Regeneron
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net		$ 17,700
Regeneron \| Laboratory equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net		12,100
Regeneron \| Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net		5,500
Regeneron \| Software and Office Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net		$ 100

Property, plant and equipment, net

9 Months Ended

Sep. 30, 2024

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, 2024		As of December 31, 2023
Computer equipment and software	$	4,965	$	6,156
Office equipment	6,330		6,726
Laboratory equipment	4,162		43,209
Leasehold improvements	48,340		58,832
Construction-in-progress	—		138
Total property, plant and equipment	63,797		115,061
Less accumulated depreciation and amortization	(28,560)		(56,911)
Property, plant and equipment, net	$	35,237	$	58,150

As part of the Regeneron Transaction, the Company transferred fixed assets with a net book value, prior to impairment, of $17.7 million to Regeneron. This consisted of laboratory equipment, leasehold improvements, and software and office equipment with net book values, prior to impairment, of $12.1 million, $5.5 million, and $0.1 million, respectively. For further detail regarding the Asset Sale to Regeneron, please refer to Note 3, Asset Purchase Agreements.

Collaborative arrangements and strategic partnerships - Collaborative Arrangement Revenue (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	$ 10,684			$ 5,859			$ 19,744	$ 64,265
Share of collaboration loss	0			0			(1,230)	0
Ide Cel Commercial Activities \| Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	9,617	$ 3,549	$ (1,975)	(582)	$ 23,272	$ 21,581	11,191	44,271
Share of collaboration loss	1,067	815	745	1,118	1,271	1,380	2,627	3,769
ABECMA Commercial Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	10,684	4,364	0	$ 536	$ 24,543	$ 22,961	15,048	$ 48,040
Share of collaboration loss	$ 0	$ 0	$ (1,230)				$ (1,230)

Stock-based compensation - Narrative (Details)	9 Months Ended
Stock-based compensation - Narrative (Details)	Sep. 30, 2024 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

Insider Trading Arrangements	3 Months Ended	9 Months Ended
Insider Trading Arrangements	Sep. 30, 2024 shares	Sep. 30, 2024 shares
Trading Arrangements, by Individual
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false
Jessica Snow [Member]
Trading Arrangements, by Individual
Material Terms of Trading Arrangement		On September 13, 2024, Jessica Snow, our Senior Vice President of Quality and Head of Operations, adopted a Rule 10b5-1 trading plan, which is intended to satisfy the affirmative defense conditions of Exchange Act Rule 10b5-1(c), with respect to the sale of up to an aggregate of 48,089 shares of common stock of the Company pursuant to the terms of such trading plan. Her Rule 10b5-1 trading arrangement is active through October 13, 2025.
Name	Jessica Snow
Title	Senior Vice President
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	September 13, 2024
Expiration Date	October 13, 2025
Arrangement Duration	395 days
Aggregate Available	48,089	48,089

Marketable securities - Schedule of Unrealized Loss on Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Fair value
Less than 12 months	$ 14,740	$ 45,850
12 months or greater	4,992	1,475
Total	19,732	47,325
Unrealized losses
Less than 12 months	(25)	(60)
12 months or greater	(1)	(25)
Total	(26)	(85)
U.S. government agency securities and treasuries
Fair value
Less than 12 months	1,930	45,850
12 months or greater	4,992	1,475
Total	6,922	47,325
Unrealized losses
Less than 12 months	(2)	(60)
12 months or greater	(1)	(25)
Total	(3)	$ (85)
Corporate bonds
Fair value
Less than 12 months	2,015
12 months or greater	0
Total	2,015
Unrealized losses
Less than 12 months	(1)
12 months or greater	0
Total	(1)
Commercial paper
Fair value
Less than 12 months	10,795
12 months or greater	0
Total	10,795
Unrealized losses
Less than 12 months	(22)
12 months or greater	0
Total	$ (22)

Marketable securities - Summary of Restricted Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Cost or amortized cost	$ 34,784	$ 33,072
Unrealized gains	109	67
Unrealized losses	(34)	(365)
Fair Value	34,859	32,774
U.S. government agency securities and treasuries
Debt Securities, Available-for-sale [Line Items]
Cost or amortized cost	34,784	33,072
Unrealized gains	109	67
Unrealized losses	(34)	(365)
Fair Value	$ 34,859	$ 32,774

- 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
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

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

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

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

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

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

+ Details

Description of the business	9 Months Ended
Description of the business	Sep. 30, 2024
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, together with BMS, is delivering the first U.S. Food and Drug Administration (“FDA”) approved CAR T therapy in multiple myeloma, Abecma, to patients in the United States. Please refer to Note 11, 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 and was granted securities corporation status in Massachusetts for the 2021 tax year. 2seventy bio Securities Corporation has no employees. On January 29, 2024, the Company began undertaking a strategic realignment to focus on the development and commercialization of Abecma. In connection with the strategic realignment, the Company entered into an asset purchase agreement with Regeneron Pharmaceuticals, Inc. (“Regeneron”), to sell to Regeneron substantially all of the assets related to its oncology and autoimmune cell therapy programs (the “Regeneron Transaction”). The Regeneron Transaction closed on April 1, 2024 and Regeneron assumed all of the ongoing programs, infrastructure and personnel costs related to these programs. In June 2024, the Company announced the completion of an asset purchase agreement with Novo Nordisk (“Novo”) as part of its strategic realignment. Under the terms of the Novo Transaction, Novo acquired the Company’s program for the research, development, manufacture, regulatory approval, and commercialization of gene therapy products exploiting the megaTAL Platform that is directed to the treatment, diagnosis and prevention of hemophilia (the “megaTAL Sale”). 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 normal operating losses and has experienced negative operating cash flows for all historical periods presented. During the nine months ended September 30, 2024, the Company incurred a net loss of $37.7 million and used $75.5 million of cash in operations. The Company expects to continue to generate operating losses and negative operating cash flows for the near future. As of September 30, 2024, the Company had cash, cash equivalents, and marketable securities of $192.4 million. Based on the Company’s current operating plans, including with respect to the ongoing commercialization of Abecma, 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 condensed consolidated 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 may also include 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 and the Company does not currently have any plans to sell shares under the ATM.

Corporate Restructuring - Summary of Expenses Recognized and Expected to be Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Expense recognized for the nine months ended September 30, 2024
Severance and related benefits			$ 5,376
Total restructuring expenses	$ 503	$ 8,614	12,131	$ 8,614
January 2024 Restructuring Plan
Expense recognized for the nine months ended September 30, 2024
Stock-based compensation expense	0		1,037
Total restructuring expenses	228		6,413
Total expense expected to be recognized
Stock-based compensation expense	1,037		1,037
Total restructuring expenses	6,644		6,644
January 2024 Restructuring Plan \| Severance and related benefits
Expense recognized for the nine months ended September 30, 2024
Severance and related benefits	228		5,376
Total expense expected to be recognized
Cash-related restructuring expenses	$ 5,607		$ 5,607

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Pay vs Performance Disclosure
Net loss	$ (9,933)	$ 24,879	$ (52,673)	$ (71,638)	$ (42,089)	$ (47,021)	$ (37,727)	$ (160,748)

- Definition

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

+ References

+ Details

Royalty and other revenue	9 Months Ended
Royalty and other revenue	Sep. 30, 2024
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. Juno Therapeutics In May 2020, bluebird bio entered into a non-exclusive license agreement with Juno Therapeutics, Inc., 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. The Company did not recognize royalty and other revenue for the three and nine months ended September 30, 2024. 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.

Fair value measurements (Tables)

9 Months Ended

Sep. 30, 2024

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, 2024 and December 31, 2023 (in thousands):


	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
September 30, 2024
Assets:
Cash and cash equivalents	$	59,984	$	59,984	$	—	$	—
Marketable securities:
U.S. government agency securities and treasuries	81,264		—		81,264		—
Corporate bonds	2,015		—		2,015		—
Commercial paper	49,136		—		49,136		—
Restricted cash and cash equivalents	363		363		—		—
Restricted investments	34,859		—		34,859		—
Total assets	$	227,621	$	60,347	$	167,274	$	—
December 31, 2023
Assets:
Cash and cash equivalents	$	74,958	$	74,958	$	—	$	—
Marketable securities:
U.S. government agency securities and treasuries	101,625		—		101,625		—
Commercial paper	45,222		—		45,222		—
Restricted cash and cash equivalents	1,725		1,725		—
Restricted investments	32,774		—		32,774		—
Total assets	$	256,304	$	76,683	$	179,621	$	—
Liabilities:
Contingent consideration	$	2,415	$	—	$	—	$	2,415
Total liabilities	$	2,415	$	—	$	—	$	2,415

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, 2024
U.S. government agency securities and treasuries	$	1,930	$	(2)	$	4,992	$	(1)	$	6,922	$	(3)
Corporate bonds	2,015		(1)		—		—		2,015		(1)
Commercial paper	10,795		(22)		—		—		10,795		(22)
Total	$	14,740	$	(25)	$	4,992	$	(1)	$	19,732	$	(26)
December 31, 2023
U.S. government agency securities and treasuries	$	45,850	$	(60)	$	1,475	$	(25)	$	47,325	$	(85)
Total	$	45,850	$	(60)	$	1,475	$	(25)	$	47,325	$	(85)

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, 2024
Beginning balance	$	2,415
Additions	—
Changes in fair value	(2,415)
Payments	—
Ending balance	$	—

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
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/1943274/2147477250/944-220-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/1943274/2147478524/942-220-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

Asset purchase agreements	9 Months Ended
Asset purchase agreements	Sep. 30, 2024
Discontinued Operations and Disposal Groups [Abstract]
Asset purchase agreements	Asset purchase agreements Regeneron Asset Purchase Agreement In January 2024, the Company and Regeneron entered into an asset purchase agreement for the Regeneron Transaction. The assets consisted of property, plant and equipment and prepaid expenses. As consideration for the Asset Sale, Regeneron agreed to pay the Company an upfront payment of $5.0 million and contingent consideration based on regulatory approval and sales-based royalties. Regeneron assumed certain programs, infrastructure and personnel costs related to the programs purchased. In accordance with Topic 360, Property, Plant, and Equipment, the Company determined that as of the signing of the asset purchase agreement in January 2024, the criterion to classify the assets to be sold to Regeneron as assets held for sale was met. The $17.8 million of property, plant and equipment and prepaid expenses to be sold to Regeneron were classified as assets held for sale on the Company’s condensed consolidated balance sheets as of March 31, 2024. As noted above, the Company received an upfront payment of $5.0 million upon closing of the Regeneron Transaction, which occurred on April 1, 2024. Moreover, the termination of the Company’s existing Collaboration Agreement with Regeneron (as described in Note 11) was negotiated concurrently with the asset purchase agreement and as such, the Company derecognized $7.8 million of deferred revenue associated with the Regeneron Collaboration Agreement as part of the Asset Sale. The cash received by the Company combined with the derecognition of the remaining deferred revenue totals $12.8 million and represents the approximate combined fair value of the assets sold to Regeneron under the asset purchase agreement. As such, in the first quarter of 2024, the Company recorded an impairment loss of $5.0 million, disclosed as the “loss on assets held for sale to Regeneron” on the condensed consolidated statements of operations and comprehensive loss. This represents the excess of the carrying value of the assets to be transferred to Regeneron at the time the held for sale criteria was met. This is presented as loss on assets held for sale on the condensed consolidated statements of operations and comprehensive loss. Upon the closing of the Regeneron Transaction on April 1, 2024 and the receipt of the $5.0 million upfront payment, the Company derecognized the assets held for sale and the deferred revenue discussed above from its condensed consolidated balance sheets. In connection with the Asset Sale, the Company entered into transition services agreements with Regeneron, under which the Company provides certain services to Regeneron to help facilitate an orderly transition of the business following the Asset Sale. In return for these services, Regeneron is required to pay certain agreed upon fees to reimburse the Company for costs incurred, without markup. As of September 30, 2024, $5.0 million of receivables associated with these transition services agreements are included within receivables and other current assets on the Company’s condensed consolidated balance sheets. Income for services provided by the Company to Regeneron is included within other income, net within the condensed consolidated statements of operations and comprehensive loss. Reimbursement for costs incurred, without markup, are netted against operating expenses on the condensed consolidated statements of operations and comprehensive loss. Novo Asset Purchase Agreement In June 2024, the Company announced the completion of the Novo Transaction. As consideration, Novo paid the Company upfront consideration of $38.0 million, plus up to an additional $2.0 million that will be held back by Novo for 12 months and may be used to settle certain indemnification claims. No assets on the Company’s condensed consolidated balance sheet were identified to be transferred to Novo as part of the transaction. The termination of the Company’s existing Collaboration and License Agreement with Novo (as described in Note 11) was negotiated concurrently with the asset purchase agreement and as such, the Company derecognized $11.0 million of deferred revenue associated with the Company’s Novo Collaboration Agreement as part of the megaTAL Sale. In connection with the megaTAL Sale, the Company entered into a transition service agreement with Novo under which the Company will provide certain services to Novo to help facilitate an orderly transition of the business following the sale. Consideration for these services was included in the initial purchase price and as such, $1.0 million, which represents the fair market value of the services to be performed, is deferred from the gain on the sale and will be recognized over the six month term of the transition services agreement. The balance of deferred transition service income is included within accrued expenses and other current liabilities on the condensed consolidated balance sheets. The $38.0 million cash consideration received by the Company (less the $1.0 million received for transition services to be provided by the Company) combined with the derecognition of the deferred revenue totals $48.0 million and represents the gain on the sale of asset to Novo. This is disclosed as the “gain on sale to Novo Nordisk”, on the condensed consolidated statements of operations and comprehensive loss. As the Company has elected to use the loss recovery approach to account for contingent consideration receivable, the $2.0 million cash consideration held back by Novo will not be recognized until it is probable to be received.

Equity	9 Months Ended
Equity	Sep. 30, 2024
Equity [Abstract]
Equity	Equity 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 11, 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
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478448/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-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

Marketable securities

9 Months Ended

Sep. 30, 2024

Investments, Debt and Equity Securities [Abstract]

Marketable securities

The following table summarizes the marketable securities held at September 30, 2024 and December 31, 2023 (in thousands):


	Cost or amortized cost		Unrealized gains		Unrealized losses		Fair Value
September 30, 2024
U.S. government agency securities and treasuries	$	81,085	$	182	$	(3)	$	81,264
Corporate bonds	2,016		—		(1)		2,015
Commercial paper	49,084		74		(22)		49,136
Total	$	132,185	$	256	$	(26)	$	132,415
December 31, 2023
U.S. government agency securities and treasuries	$	101,566	$	144	$	(85)	$	101,625
Commercial paper	45,188		34		—		45,222
Total	$	146,754	$	178	$	(85)	$	146,847

No available-for-sale debt securities held as of September 30, 2024 or December 31, 2023 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, 2024
U.S. government agency securities and treasuries	$	1,930	$	(2)	$	4,992	$	(1)	$	6,922	$	(3)
Corporate bonds	2,015		(1)		—		—		2,015		(1)
Commercial paper	10,795		(22)		—		—		10,795		(22)
Total	$	14,740	$	(25)	$	4,992	$	(1)	$	19,732	$	(26)
December 31, 2023
U.S. government agency securities and treasuries	$	45,850	$	(60)	$	1,475	$	(25)	$	47,325	$	(85)
Total	$	45,850	$	(60)	$	1,475	$	(25)	$	47,325	$	(85)

As discussed further in Note 8, Leases, to the consolidated financial statements included in the Company's 2023 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, 2024 and December 31, 2023 (in thousands):


	Cost or amortized cost		Unrealized gains		Unrealized losses		Fair Value
September 30, 2024
U.S. government agency securities and treasuries	$	34,784	$	109	$	(34)	$	34,859
Total	$	34,784	$	109	$	(34)	$	34,859
December 31, 2023
U.S. government agency securities and treasuries	$	33,072	$	67	$	(365)	$	32,774
Total	$	33,072	$	67	$	(365)	$	32,774


	Less than 12 months				12 months or greater				Total
	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
September 30, 2024
U.S. government agency securities and treasuries	$	1,973	$	(2)	$	5,963	$	(32)	$	7,936	$	(34)
Total	$	1,973	$	(2)	$	5,963	$	(32)	$	7,936	$	(34)
December 31, 2023
U.S. government agency securities and treasuries	$	3,496	$	(4)	$	13,266	$	(361)	$	16,762	$	(365)
Total	$	3,496	$	(4)	$	13,266	$	(361)	$	16,762	$	(365)

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 $1.0 million as of September 30, 2024 and $0.8 million as of December 31, 2023. No accrued interest receivable was written off during the three and nine months ended September 30, 2024 or 2023.

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, 2024 and December 31, 2023, the balance in the Company’s accumulated other comprehensive income 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, 2024 and 2023.

The Company determined that there was no material change in the credit risk of the above investments during the three and nine months ended September 30, 2024. As such, an allowance for credit losses was not recognized. As of September 30, 2024, 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.