2seventy bio (TSVT) 10-Q 1 Dec 21 2021 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2021	Nov. 26, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
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, Address Line Two	Suite 200
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	2142
City Area Code	339
Local Phone Number	499-9300
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	TSVT
Security Exchange Name	NASDAQ
Entity Current Reporting Status	No
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		23,369,088
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001860782
Current Fiscal Year End Date	--12-31

Condensed Combined Balance Shee

Condensed Combined Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets, Current [Abstract]
Prepaid expenses	$ 8,460	$ 14,413
Receivables	16,135	10,691
Total current assets	24,595	25,104
Property, plant and equipment, net	33,752	144,025
Intangible assets, net	11,009	5,644
Goodwill	12,056	13,128
Operating lease right-of-use assets	105,310	116,456
Other non-current assets	6,237	8,263
Total assets	192,959	312,620
Current liabilities:
Accounts payable	6,197	7,152
Accrued expenses and other current liabilities	76,273	43,347
Operating lease liability, current portion	14,480	15,313
Deferred revenue, current portion	0	820
Collaboration research advancement, current portion	9,130	9,236
Total current liabilities	106,080	75,868
Deferred revenue, net of current portion	25,762	25,762
Collaboration research advancement, net of current portion	16,767	21,581
Operating lease liability, net of current portion	99,819	112,290
Other non-current liabilities	2,938	2,490
Total liabilities	251,366	237,991
Commitments and contingencies (Note 7)
Equity (deficit):
Net parent investment	(58,407)	74,629
Total equity (deficit)	(58,407)	74,629
Total liabilities and equity (deficit)	$ 192,959	$ 312,620

Condensed Combined Statements o

Condensed Combined Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue:
Collaborative arrangement revenue	$ 12,337	$ 2,422	$ 15,527	$ 114,398
Total revenues	19,257	18,434	38,488	238,217
Operating expenses:
Research and development	61,131	72,253	202,394	227,585
Selling, general and administrative	22,996	22,105	69,025	68,951
Share of collaboration loss	0	0	10,071	0
Cost of royalty and other revenue	320	1,318	2,111	3,897
Change in fair value of contingent consideration	48	(828)	464	(5,591)
Total operating expenses	84,495	94,848	284,065	294,842
Loss from operations	(65,238)	(76,414)	(245,577)	(56,625)
Other income, net	5,237	4,339	14,340	13,312
Loss before income taxes	(60,001)	(72,075)	(231,237)	(43,313)
Income tax (expense) benefit	0	0	0	0
Net loss and comprehensive loss	(60,001)	(72,075)	(231,237)	(43,313)
Service
Revenue:
Revenue	6,312	12,513	17,544	106,733
Royalty and other revenue
Revenue:
Revenue	$ 608	$ 3,499	$ 5,417	$ 17,086

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Net Parent Investment
Beginning balance at Dec. 31, 2019		$ 43,692
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation		14,359
Transfers from (to) bluebird bio		88,018
Net loss		(74,424)
Ending balance at Mar. 31, 2020		71,645
Beginning balance at Dec. 31, 2019		43,692
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	$ (43,313)
Ending balance at Sep. 30, 2020		78,161
Beginning balance at Mar. 31, 2020		71,645
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation		18,944
Transfers from (to) bluebird bio		(125,378)
Net loss		103,186
Ending balance at Jun. 30, 2020		68,397
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation		15,255
Transfers from (to) bluebird bio		66,584
Net loss	(72,075)	(72,075)
Ending balance at Sep. 30, 2020		78,161
Beginning balance at Dec. 31, 2020	74,629	74,629
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation		17,109
Transfers from (to) bluebird bio		71,101
Net loss		(87,196)
Ending balance at Mar. 31, 2021		75,643
Beginning balance at Dec. 31, 2020	74,629	74,629
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(231,237)
Ending balance at Sep. 30, 2021	(58,407)	(58,407)
Beginning balance at Mar. 31, 2021		75,643
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation		11,967
Transfers from (to) bluebird bio		45,119
Net loss		(84,040)
Ending balance at Jun. 30, 2021		48,689
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation		11,230
Transfers from (to) bluebird bio		(58,325)
Net loss	(60,001)	(60,001)
Ending balance at Sep. 30, 2021	$ (58,407)	$ (58,407)

Condensed Combined Statements_2

Condensed Combined Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net loss	$ (231,237)	$ (43,313)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Change in fair value of contingent consideration	464	(5,591)
Depreciation and amortization	12,815	9,869
Stock-based compensation expense	40,306	48,558
Other non-cash items	247	76
Changes in operating assets and liabilities:
Prepaid expenses and other assets	3,036	(3,074)
Operating lease right-of-use assets	11,146	10,186
Accounts payable	607	(11,355)
Accrued expenses and other liabilities	32,066	(12,160)
Operating lease liabilities	(13,305)	(9,516)
Deferred revenue	(820)	8,558
Collaboration research advancement	(4,920)	(6,202)
Net cash used in operating activities	(149,595)	(13,964)
Cash flows from investing activities:
Purchases of property, plant and equipment	(10,600)	(15,260)
Purchase of intangible assets	(8,000)	0
Net cash used in investing activities	(18,600)	(15,260)
Cash flows from financing activities:
Transfers from bluebird bio	168,195	29,224
Net cash provided by financing activities	168,195	29,224
Increase (decrease) in cash, cash equivalents and restricted cash	0	0
Cash, cash equivalents and restricted cash at beginning of period	0	0
Cash, cash equivalents and restricted cash at end of period	0	0
Supplemental cash flow disclosures:
Purchases of property, plant and equipment included in accounts payable and accrued expenses	321	1,590
Right-of-use assets obtained in exchange for operating lease liabilities	0	4,484
Non-cash return of bRT-related assets to bluebird bio	110,300	0
Cash paid during the period for interest	0	0
Cash paid during the period for income taxes	$ 0	$ 0

Description of the business

Description of the business	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of the business	Description of the business 2seventy bio, Inc. (the “Company” or “2seventy bio”) was incorporated in Delaware on April 26, 2021 and is headquartered in Cambridge, Massachusetts. The Company is a cell and gene therapy company focused on the research, development, and commercialization of transformative treatments for cancer. It is led by a team with significant expertise and experience in this field, from discovery through clinical development to regulatory approval of idecabtagene vicleucel (ide-cel, marketed as ABECMA ® ), the first FDA-approved chimeric antigen receptor technology (CAR T) cell therapy for multiple myeloma. 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 innovative, targeted cellular therapies for patients with cancer. The Company is advancing multiple preclinical and clinical programs in oncology and, together with its partner Bristol-Myers Squibb (BMS), delivering ide-cel to multiple myeloma patients in the United States following approval by the FDA of ide-cel in March 2021 for the treatment of adults with multiple myeloma who have received at least four prior lines of therapy, including an immunomodulatory agent, a proteasome inhibitor and an anti-CD38 monoclonal antibody. For further discussion of the Company’s collaboration with BMS, please refer to Note 8, Collaborative arrangements and strategic partnerships. The separation from bluebird bio, Inc. In January 2021, bluebird bio, Inc. (“bluebird bio”) announced its plans to separate its oncology portfolio and programs from its severe genetic disease portfolio and programs, and spin off its oncology portfolio and programs into a separate publicly traded company. In furtherance of this plan, on September 30, 2021, bluebird bio’s board of directors approved the distribution of all of the issued and outstanding shares of 2seventy bio common stock on the basis of one share of 2seventy bio common stock for every three shares of bluebird bio common stock issued and outstanding on October 19, 2021, the record date for the distribution. As a result of the distribution, which occurred on November 4, 2021, 2seventy bio became an independent, publicly traded company. On November 3, 2021, the Company also entered into a separation agreement with bluebird bio, which is referred to in this quarterly report as the separation agreement, as well as various other agreements with bluebird bio, including a tax matters agreement, an employee matters agreement, an intellectual property license agreement, a transition services agreement under which 2seventy bio temporarily receives certain services from bluebird bio, and a second transition services agreement under which 2seventy bio temporarily provides certain services to bluebird bio. These agreements also govern certain of 2seventy bio’s relationships with bluebird bio after the separation. For additional information regarding the separation agreement and the other related agreements, see "Risk Factors—Risks Related to the Separation" and "Transactions with Related and Certain Other Parties." Going concern In accordance with Accounting Standards Codification (“ASC”) 205-40, Going Concern , the Company evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about its ability to continue as a going concern within one year after the date that the condensed combined financial statements are issued. The Company has incurred losses and has experienced negative operating cash flows for all historical periods presented. During the nine months ended September 30, 2021, the Company incurred a loss of $231.2 million and used $149.6 million of cash in operations. The Company expects to continue to generate operating losses and negative operating cash flows for the next few years. As further described in Note 13, Subsequent events, upon the Company’s separation from bluebird bio on November 4, 2021, bluebird bio made a cash contribution to the Company of approximately $441.5 million, a portion of which is considered restricted, which alleviated the conditions that previously raised substantial doubt about the Company’s ability to continue as a going concern. Accordingly, as of the date of issuance of these condensed combined financial statements, the Company expects its cash, cash equivalents, and marketable securities will be sufficient to fund current planned operations for at least the next twelve months. The Company previously concluded that there was substantial doubt about its ability to continue as a going concern in prior periods due to the Company’s need to obtain additional funding. The Company intends to pursue additional cash resources through a combination of public or private equity offerings, debt financings, collaborations, strategic alliances or licensing arrangements with third parties. There can be no assurance that such financing will be available in sufficient amounts or on acceptable terms, if at all, and some could be dilutive to existing stockholders. If the Company is unable to obtain additional funding on a timely basis, it may be forced to significantly curtail, delay, or discontinue one or more of its planned research or development programs or be unable to expand its operations.

Summary of significant accounti

Summary of significant accounting policies and basis of presentation	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of significant accounting policies and basis of presentation	Summary of significant accounting policies and basis of presentation Basis of presentation Because the previously described distribution occurred subsequent to September 30, 2021, the accompanying condensed combined financial statements have been prepared on a carve-out basis and are derived from bluebird bio's consolidated financial statements and accounting records. The accompanying condensed combined financial statements reflect the historical results of 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 United States GAAP as included in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board (“FASB”). Certain information and footnote disclosures included in the Company’s annual financial statements have been condensed or omitted. These condensed combined financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position and results of operations for the interim periods ended September 30, 2021 and 2020. The historical results of operations, financial position and cash flows of 2seventy bio presented in these condensed combined financial statements may not be indicative of what they would have been had 2seventy bio been an independent stand-alone entity, nor are they necessarily indicative of 2seventy bio's future results of operations, financial position and cash flows. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These condensed combined financial statements should be read in conjunction with the audited combined financial statements as of and for the year ended December 31, 2020 and the notes thereto, which are included in Exhibit 99.1 to the Company’s Form 10, which was most recently filed with the Securities and Exchange Commission on October 8, 2021. As part of bluebird bio, the Company was dependent upon bluebird bio for all of its working capital and financing requirements, as bluebird bio used a centralized approach to cash management and financing its operations. There were no cash amounts specifically attributable to the Company for the historical periods presented; therefore, cash and cash equivalents have not been allocated to the Company in the condensed combined financial statements. Financing transactions related to bluebird bio are accounted for as a component of net parent investment in the condensed combined balance sheets and as a financing activity on the accompanying condensed combined statements of cash flows. The Company’s condensed combined financial statements include an allocation of expenses related to certain bluebird bio corporate functions, including senior management, legal, human resources, finance and information technology. In addition, the Company's condensed combined financial statements include an allocation of certain research and development costs not directly attributable to individual programs. These expenses have been allocated to the Company based on direct usage or benefit where specifically identifiable, with the remainder allocated based on employee time spent on projects, square footage or other measures that management believes are consistent and reasonable. These allocations may not be indicative of the actual expense that would have been incurred had the Company operated as an independent, publicly traded company for the periods presented. See Note 11, Related-party transactions , for a further description of the accounting for the separation from bluebird bio. The condensed combined balance sheets of the Company include assets and liabilities that were allocated principally on a specific identification basis. As 2seventy bio's operations were not historically held by a single legal entity or separate legal entities, net parent investment is shown in lieu of stockholder's equity in the condensed combined financial statements. Net parent investment represents the cumulative investment by bluebird bio in the Company through the dates presented, inclusive of operating results. Balances between the Company and bluebird bio that were not historically settled in cash are included in net parent investment. All significant transactions between the Company and bluebird bio have been included in the accompanying condensed combined financial statements. Transactions with bluebird bio are reflected in the accompanying condensed combined statements of equity (deficit) as net transfers from (to) parent and in the accompanying condensed combined balance sheets within net parent investment. Amounts reported are computed based on thousands, except percentages or as otherwise noted. As a result, certain totals may not sum due to rounding. Principles of combination and consolidation The accompanying condensed combined financial statements include the attribution of certain assets and liabilities that have historically been held by bluebird bio but which are specifically identifiable or attributable to the Company. All intercompany balances and transactions with bluebird bio are deemed to be effectively settled in the condensed combined financial statements at the time the transaction is recorded. Expenses related to corporate allocations from bluebird bio to the Company are considered to be effectively settled for cash in the condensed combined financial statements at the time the transaction is recorded. The Company continually assesses whether it is the primary beneficiary of a variable interest entity as changes to existing relationships or future transactions may result in consolidation or deconsolidation of one or more collaborators or partners. In determining whether it is the primary beneficiary of an entity in which the Company has a variable interest, management applies a qualitative approach that determines whether the Company has both (1) the power to direct the economically significant activities of the entity and (2) the obligation to absorb losses of, or the right to receive benefits from, the entity that could potentially be significant to that entity. Use of estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts in the financial statements and accompanying notes. Actual results could materially differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes and management must select an amount that falls within that range of reasonable estimates. This process may result in actual results differing materially from those estimated amounts used in the preparation of the financial statements. Estimates and judgments are used in the following areas, among others: allocations of revenue, expenses, assets and liabilities from bluebird bio's historical consolidated financial statements to the Company, future undiscounted cash flows and subsequent fair value estimates used to assess potential and measure any impairment of long-lived assets, including goodwill and intangible assets, the measurement of right-of-use assets and lease liabilities, contingent consideration, stock-based compensation expense, accrued expenses, income taxes, and the assessment of the Company's ability to fund its operations for at least the next twelve months from the date of issuance of these financial statements. In addition, estimates and judgments are used in the Company’s accounting for its revenue-generating arrangements, in particular as it relates to determining the stand-alone selling price of performance obligations, evaluating whether an option to acquire additional goods and services represents a material right, estimating the total transaction price, including estimating variable consideration and the probability of achieving future potential development and regulatory milestones, assessing the period of performance over which revenue may be recognized, and accounting for modifications to revenue-generating arrangements. Significant accounting policies The significant accounting policies used in preparation of these condensed combined financial statements for the three and nine months ended September 30, 2021 and 2020 are consistent with those discussed in Note 2 to the combined financial statements for the year ended December 31, 2020 included in Exhibit 99.1 to the Company’s Form 10, except as noted immediately below and as noted within the " Recent accounting pronouncements - Recently adopted " section. Collaborative arrangement revenue The Company analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements ("ASC 808"), which includes determining whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of ASC 808 and those that are more reflective of a vendor-customer relationship and therefore within the scope of ASC 606, Revenue from Contracts with Customers ("Topic 606" or "ASC 606"). For elements of collaboration arrangements that are accounted for pursuant to ASC 808, an appropriate recognition method is determined and applied consistently, generally by analogy to Topic 606. In arrangements where the Company does not deem its collaborator to be its customer, payments to and from its collaborator are presented in the condensed combined statements of operations and comprehensive loss based on the nature of the payments, as summarized in the table and further described below. Nature of Payment Statement of Operations Presentation The Company's share of profits in connection with commercialization of products Collaborative arrangement revenue The Company's share of losses in connection with commercialization of products Share of collaboration loss Net reimbursement of the Company's research and development expenses Collaborative arrangement revenue Net reimbursement of the collaborator's research and development expenses Research and development expense Where the collaborator is the principal in the product sales, the Company recognizes its share of any profits or losses, representing net product sales less cost of goods sold and shared commercial and other expenses, in the period in which such underlying sales occur and costs are incurred by the collaborator. The Company also recognizes its share of costs arising from research and development activities performed by collaborators in the period its collaborators incur such expenses. Recent accounting pronouncements Recently adopted ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify the accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The new standard was effective beginning January 1, 2021. The adoption of ASU 2019-12 did not have a material impact on the Company's financial position or results of operations upon adoption. ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity In August 2020, the FASB issued ASU 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU 2020-06”). ASU 2020-06 simplifies the complexity associated with applying U.S. GAAP for certain financial instruments with characteristics of liabilities and equity. More specifically, the amendments focus on the guidance for convertible instruments and derivative scope exception for contracts in an entity's own equity. The Company early adopted the new standard, effective January 1, 2021. The adoption of ASU 2020-06 did not have an impact on the Company's financial position or results of operations upon adoption. ASU No. 2020-08, Codification Improvements to Subtopic 310-20, Receivables - Nonrefundable Fees and Other Costs In October 2020, the FASB issued ASU 2020-08, Codification Improvements to Subtopic 310-20, Receivables - Nonrefundable Fees and Other Costs (“ASU 2020-08”) to provide further clarification and update the previously issued guidance in ASU 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20: Premium Amortization on Purchased Callable Debt Securities) (“ASU 2017-08”). ASU 2017-08 shortened the amortization period for certain callable debt securities purchased at a premium by requiring that the premium be amortized to the earliest call date. ASU 2020-08 requires that at each reporting period, to the extent that the amortized cost of an individual callable debt security exceeds the amount repayable by the issuer at the next call date, the excess premium shall be amortized to the next call date. The new standard was effective beginning January 1, 2021. The adoption of ASU 2020-08 did not have a material impact on the Company's financial position or results of operations upon adoption. ASU No. 2020-10, Codification Improvements In October 2020, the FASB issued ASU 2020-10, Codification Improvements ("ASU 2020-10"). The amendments in this ASU represent changes to clarify the ASC, correct unintended application of the guidance, or make minor improvements to the ASC that are not expected to have a significant effect on current accounting practice or create a significant administrative cost to most entities. This new standard was effective beginning January 1, 2021. The adoption of ASU 2020-10 did not have a material impact on the Company's financial position or results of operations upon adoption.

Fair value measurements

Fair value measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair value measurements	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, 2021 and December 31, 2020 (in thousands): Total Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) September 30, 2021 Liabilities: Contingent consideration $ 1,973 $ — $ — $ 1,973 Total liabilities $ 1,973 $ — $ — $ 1,973 December 31, 2020 Liabilities: Contingent consideration $ 1,509 $ — $ — $ 1,509 Total liabilities $ 1,509 $ — $ — $ 1,509 As of September 30, 2021 and December 31, 2020, the Company did not have any assets that are measured at fair value on a recurring basis. Contingent consideration In connection with bluebird bio's prior acquisition of Precision Genome Engineering, Inc. (“Pregenen”), the Company may be required to pay future consideration that is contingent upon the achievement of certain commercial milestone events. Contingent consideration is measured at fair value and is based on significant unobservable inputs, which represents a Level 3 measurement within the fair value hierarchy. The valuation of contingent consideration uses assumptions the Company believes would be made by a market participant. The Company assesses these estimates on an on-going basis as additional data impacting the assumptions is obtained. Future changes in the fair value of contingent consideration related to updated assumptions and estimates are recognized within the condensed combined statements of operations and comprehensive loss. In the absence of new information related to the probability of milestone achievement, changes in fair value will reflect changing discount rates and the passage of time. Contingent consideration is included in other non-current liabilities on the condensed combined balance sheets. The table below provides a roll-forward of fair value of the Company’s contingent consideration obligations that include Level 3 inputs (in thousands): Nine Months Ended September 30, 2021 2020 Beginning balance $ 1,509 $ 7,977 Additions — — Changes in fair value 464 (5,591) Payments — — Ending balance $ 1,973 $ 2,386 Please refer to Note 7, Commitments and contingencies , for further information.

Property, plant and equipment,

Property, plant and equipment, net	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Property, plant and equipment, net	Property, plant and equipment, net Property, plant and equipment, net, consists of the following (in thousands): As of September 30, 2021 As of December 31, 2020 Land $ — $ 1,210 Building — 15,745 Computer equipment and software 5,252 6,503 Office equipment 6,080 6,588 Laboratory equipment 30,818 24,080 Leasehold improvements 28,479 28,305 Construction-in-progress 799 91,631 Total property, plant and equipment 71,428 174,062 Less accumulated depreciation and amortization (37,676) (30,037) Property, plant and equipment, net $ 33,752 $ 144,025 Depreciation and amortization expense related to property, plant and equipment was $3.5 million and $2.4 million for the three months ended September 30, 2021 and 2020, respectively. Depreciation and amortization expense related to property, plant and equipment was $9.7 million and $7.0 million for the nine months ended September 30, 2021 and 2020, respectively. North Carolina manufacturing facility In November 2017, bluebird bio acquired a manufacturing facility in Durham, North Carolina for the future manufacture of lentiviral vectors for the Company’s gene therapies. This manufacturing facility was primarily dedicated to the Company's operations and, accordingly, prior to the sale of the facility as described below, was to be attributed to the Company in connection with the separation. Construction-in-progress as of December 31, 2020 includes $91.1 million related to the North Carolina manufacturing facility. In July 2021, bluebird bio and National Resilience, Inc. ("Resilience") announced a strategic manufacturing collaboration aimed to accelerate the early research, development, and delivery of cell therapies. Agreements related to the collaboration were executed in September 2021. As part of the agreement, Resilience acquired bluebird bio's manufacturing facility in Durham and retained all staff employed at the site. As a result of the transaction, bluebird bio disposed of $111.2 million of net assets, primarily consisting of the building and laboratory equipment. In connection with the separation, the manufacturing facility was expected to be assigned to 2seventy bio and, accordingly, the manufacturing facility was included within the 2seventy bio carve-out financial statements in prior periods. The disposition of the net assets of the manufacturing facility previously assigned to 2seventy bio has been reflected as a transfer to bluebird bio via net parent investment as a result of bluebird bio’s sale of such facility. Please refer to Note 8, Collaborative arrangements and strategic partnerships , for further discussion.

Accrued expenses and other curr

Accrued expenses and other current liabilities	9 Months Ended
	Sep. 30, 2021
Payables and Accruals [Abstract]
Accrued expenses and other current liabilities	Accrued expenses and other current liabilities Accrued expenses and other current liabilities consist of the following (in thousands): As of September 30, 2021 As of December 31, 2020 Employee compensation $ 28,465 $ 9,451 Collaboration research costs 27,553 19,605 Manufacturing costs 5,676 6,808 Clinical and contract research organization costs 2,497 2,854 Property, plant, and equipment 618 440 License and milestone fees 236 278 Other 11,228 3,911 Total accrued expenses and other current liabilities $ 76,273 $ 43,347

Leases

Leases	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Leases	Leases The leases for certain office and laboratory space to which bluebird bio was a party were assigned to the Company in connection with the separation, and, therefore, are included in these condensed combined financial statements. Except as described below, there have been no material changes to the lease obligations from those disclosed in Note 6, Leases , to the annual combined financial statements included in Exhibit 99.1 to the Company’s Form 10. 60 Binney Street lease In October 2021, bluebird bio entered into a consent to assignment and amendment to its lease agreement for its 60 Binney Street lease, pursuant to which bluebird bio's interest in the lease was assigned to 2seventy bio. In November 2021, 2seventy bio executed a $25.0 million letter of credit related to this lease. Seattle, Washington leases In October 2021, bluebird bio entered into a consent to assignment and amendment to its lease agreement for office and laboratory space in Seattle, Washington and the related sublease that was executed in September 2020 for a portion of the space. The agreement reassigns bluebird bio’s interest in the lease and the sublease to 2seventy bio. As part of the assignment, the sublease agreement associated with the expanded space was also assigned to 2seventy bio. In November 2021, 2seventy bio executed a $5.0 million letter of credit related to this lease.

Commitments and contingencies

Commitments and contingencies	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	Commitments and contingencies Contingent consideration related to business combinations On June 30, 2014, bluebird bio acquired Pregenen. All assets, liabilities and future obligations related to the Pregenen acquisition, including the resulting goodwill and contingent consideration, were assumed by the Company in connection with the separation. As of September 30, 2021, 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 combined balance sheets at fair value. Estimating the fair value of contingent consideration requires the use of significant assumptions primarily relating to probabilities of successful achievement of certain clinical and commercial milestones, the expected timing in which these milestones will be achieved and discount rates. The use of different assumptions could result in materially different estimates of fair value. Other funding commitments Certain agreements that were assigned by bluebird bio to the Company in connection with the separation relate principally to licensed technology and may require future payments relating to milestones that may be met in subsequent periods or royalties on future sales of specified products. These agreements include the collaboration agreements entered into with BMS and Regeneron Pharmaceuticals, Inc. ("Regeneron") and the agreements entered into with Resilience, all of which were assigned to the Company in connection with the separation. Additionally, to the extent an agreement relating to licensed technology was not 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 8, Collaborative arrangements and strategic partnerships , for further information on the BMS, Regeneron and Resilience agreements and to Note 9, Royalty and other revenue , for further information on license agreements. Based on the Company's development plans as of September 30, 2021, the Company may be obligated to make future development, regulatory and commercial milestone payments and royalty payments on future sales of specified products. Payments under these agreements generally become due and payable upon achievement of such milestones or sales. When the achievement of these milestones or sales has not occurred, such contingencies are not recorded in the Company’s financial statements. As further discussed in Note 8, 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® and bb21217. Concurrent with the sale of the manufacturing facility in Durham, North Carolina, bluebird bio also entered into a commercial supply agreement and a development manufacturing supply agreement with Resilience. Certain rights and obligations under the asset purchase agreement and certain of the ancillary agreements, including these two manufacturing agreements, among others, were assigned by bluebird bio to 2seventy bio on November 4, 2021 upon the separation of 2seventy bio from bluebird bio. The assignments under the asset purchase agreement and the development manufacturing supply agreement commit the Company to reimburse Resilience for an amount equal to 50% of the net operating losses of and relating to the manufacturing facility’s business incurred during the twelve-month period ending on the first anniversary of the closing of the transaction, as calculated in accordance with the asset purchase agreement, subject to a cap of $15.0 million. In exchange, under the terms of the development manufacturing supply agreement, the Company will receive up to eight batches of lentiviral vector during the twelve-month period ending on the first anniversary of the closing of the transaction. The Company has therefore committed to a minimum purchase of at least the Company's 50% share of the net operating losses during the twelve-month period ending on the first anniversary of the closing of the transaction. Please refer to Note 8, Collaborative arrangements and strategic partnerships , for further discussion. Additionally, bluebird bio is party to various contracts with contract research organizations and contract manufacturers that generally provide for termination on notice, with the exact amounts in the event of termination to be based on the timing of the termination and the terms of the agreement. There have been no material changes in future minimum purchase commitments from those disclosed in Note 7, Commitments and Contingencies , to the annual combined financial statements included in Exhibit 99.1 to the Company’s Form 10 . Litigation From time to time, bluebird bio has been and the Company expects to be party to various claims and complaints arising in the ordinary course of business, including securities class action litigation. bluebird bio has entered into, and the Company expects to enter into, standard indemnification agreements in the ordinary course of business. Pursuant to these agreements, bluebird bio indemnifies, holds harmless, and agrees to reimburse the indemnified party for losses suffered or incurred by the indemnified party, generally bluebird bio’s business partners. Pursuant to the separation agreement, the Company indemnifies, holds harmless, and agrees to reimburse bluebird bio for its indemnification obligations with respect to the Company’s business partners, relating to the Company’s business or arising out of the Company’s activities, in the past or to be conducted in the future. The term of these indemnification agreements is generally perpetual any time after execution of the agreement. The maximum potential amount of future payments bluebird bio or the Company could be required to make under these indemnification agreements is unlimited. Management does not believe that any ultimate liability resulting from any such claims or indemnification agreements 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.

Collaborative arrangements and

Collaborative arrangements and strategic partnerships	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaborative arrangements and strategic partnerships	Collaborative arrangements and strategic partnerships To date, the Company’s service and collaborative arrangement revenue has been primarily generated from collaboration arrangements with BMS and Regeneron, each as further described below. These agreements were assumed by the Company in connection with the separation. Bristol-Myers Squibb BMS Original 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 8, Collaborative arrangements , to the annual combined financial statements included in Exhibit 99.1 to the Company’s Form 10. During the third quarter of 2021, there have been no changes to the terms of the collaboration agreement with BMS. Ide-cel 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. 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 ide-cel 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 In March 2021, BMS received marketing approval from the U.S. Food and Drug Administration for ide-cel as a treatment for adult patients with relapsed or refractory multiple myeloma after four or more prior lines of therapy, including an immunomodulatory agent, a proteasome inhibitor, and an anti-CD38 monoclonal antibody. BMS is primarily responsible for the commercialization of ide-cel and they are the principal for commercial activity. On a quarterly basis, the Company determines its share of collaboration profit or loss for commercial activities. The Company’s share of any collaboration profit for commercial activities is recognized as collaborative arrangement revenue and its share of any collaboration loss for commercial activity is recognized as an operating expense and classified as share of collaboration loss on the Company's condensed combined statement of operations and comprehensive loss. The Company recognized the following on the condensed combined statements of operations and comprehensive loss related to its share of collaboration profit or loss associated with ide-cel commercial activities following approval (in thousands). These amounts represent the Company’s share of BMS’ ide-cel product revenue, cost of goods sold, and selling costs, offset by any reimbursement of commercial costs incurred by the Company, and exclude expenses related to ongoing development, which are separately reflected in the combined statements of operations and comprehensive loss as described below. Amounts incurred prior to commercial approval were not material. Three months ended Nine months ended March 31, 2021 June 30, 2021 September 30, 2021 September 30, 2021 Collaborative arrangement revenue from ide-cel commercial activities (1) $ — $ — $ 10,607 $ 10,607 Share of collaboration loss from ide-cel commercial activities (1) $ — $ (10,071) $ — $ (10,071) _________________ (1) As noted above, the calculation is performed on a quarterly basis. The calculation is independent of previous activity, which may result in fluctuations between revenue and expense recognition period over period. The Company’s year-to-date collaboration profit for commercial activities was $0.5 million. The Company also is 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 is classified as research and development expense on the condensed combined statement of operations and comprehensive loss. If BMS is obligated to reimburse the Company because the Company’s research and development costs exceeds BMS’ research and development costs, the net amount is recorded as collaborative arrangement revenue. The following table summarizes the amounts associated with the research activities under the collaboration included in research and development expense or recognized as collaborative arrangement revenue for the three and nine months ended September 30, 2021 and 2020 (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 ASC 808 ide-cel research and development revenue - U.S. (1)(2) $ — $ — $ — $ 108,196 ASC 808 ide-cel research and development expense - U.S. (1) $ (5,660) $ (16,084) $ (31,678) $ (21,164) _________________ (1) As noted above, the calculation of collaborative arrangement activity to be recognized for joint ide-cel efforts in the United States is performed on a quarterly basis. The calculation is independent of previous activity, which may result in fluctuations between revenue and expense recognition period over period, depending on the varying extent of effort performed by each party during the period. (2) In the second quarter of 2020, the Company recognized $169.2 million as a cumulative catch-up adjustment to revenue recorded in connection with the May 2020 First Amendment to the Amended and Restated Co-Development, Co-Promote and Profit Share Agreement (“Amended Ide-cel CCPS”), a portion of which was recognized as ASC 808 research and development collaboration revenue. Refer to Note 8, Collaborative arrangements , to the annual combined financial statements included in Exhibit 99.1 to the Company’s Form 10 for further discussion on the Amended Ide-cel CCPS. Ide-cel ex-U.S. Service Revenue The following table summarizes the revenue recognized related to ide-cel ex-U.S. activities for the three and nine months ended September 30, 2021 and 2020 (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 ASC 606 ide-cel license and manufacturing revenue - ex-U.S. (1) $ 5,314 $ 6,913 $ 14,698 $ 94,733 ________________ (1) In the second quarter of 2020, the Company recognized $169.2 million as a cumulative catch-up adjustment to revenue recorded in connection with the Amended Ide-cel CCPS, a portion of which was recognized as ASC 606 license and manufacturing revenue. Refer to Note 8, Collaborative arrangements , to the annual combined financial statements included in Exhibit 99.1 to the Company’s Form 10 for further discussion on the Amended Ide-cel CCPS. bb21217 In addition to the activities related to ide-cel, BMS previously exercised its option to obtain an exclusive worldwide license to develop and commercialize bb21217, the second product candidate under the collaboration arrangement with BMS which is further described in Note 8, Collaborative arrangements , to the annual combined financial statements included in Exhibit 99.1 to the Company’s Form 10. Under the collaboration arrangement with BMS, the Company has an option to co-develop and co-promote bb21217 within the United States. The Company is in the process of reviewing data from CRB-402, the on-going phase 1 clinical trial of bb21217, and its related decision to enter into an agreement to co-develop and co-promote bb21217 within the United States. The Company’s election to co-develop and co-promote bb21217 within the United States must be made by the substantial completion of CRB-402. If elected, the Company expects the responsibilities of the parties to remain largely unchanged, however, the Company expects it will share equally in all profits and losses relating to developing, commercializing and manufacturing bb21217 within the United States and have the right to participate in the development and promotion of bb21217 within the United States. Under this scenario, the U.S. milestones and royalties payable would be adjusted and the Company would be eligible to receive a $10.0 million development milestone payment related to the development of bb21217 within the United States. The Company would not be eligible for royalties on U.S. sales of bb21217 under this scenario. In the event the Company does not exercise its option to co-develop and co-promote bb21217, the Company will receive an additional fee in the amount of $10.0 million. Under this scenario, the Company is eligible to receive U.S. milestones of up to $85.0 million for the first indication to be addressed by bb21217 and royalties for U.S. sales of bb21217. All of the remaining development, regulatory, and commercial milestones related to U.S. development, regulatory and commercialization activities are fully constrained and are therefore excluded from the transaction price. As part of its evaluation of the constraint, the Company considered numerous factors, including the fact that achievement of the milestones is outside the control of the Company and contingent upon the future success of its clinical trials, the licensee’s efforts, or the receipt of regulatory approval. Any consideration related to U.S. sales-based milestones (including royalties) will be recognized when the related sales occur as these amounts have been determined to relate predominantly to the license granted to BMS and therefore are recognized at the later of when the performance obligation is satisfied or the related sales occur. The transaction price associated with the collaboration arrangement consists of $31.0 million of upfront payments and option payments received from BMS and $1.8 million in variable consideration which represents reimbursement to be received from BMS for manufacturing vector and associated payloads through development. The Company has identified two performance obligations with respect to the arrangement with BMS. The initial performance obligation was for research and development services that were substantially completed in September 2019, associated with the initial phase 1 clinical trial of bb21217. The Company allocated $5.4 million of consideration to the research and development services performance obligation and fully recognized the consideration through September 2019. The other performance obligation relates to a combined performance obligation for the bb21217 license and vector manufacturing services through development, and the remaining $27.3 million in consideration was allocated to this combined performance obligation. The Company will satisfy this combined performance obligation as the bb21217 manufacturing services are performed . As of September 30, 2021, the Company has not commenced manufacturing and the full amount of the allocated transaction price remains unsatisfied. The Company re-evaluates the transaction price, including the estimated variable consideration included in the transaction price and all constrained amounts, each reporting period and as uncertain events are resolved or other changes in circumstances occur. Contract assets and liabilities – ide-cel and bb21217 The Company receives payments from its collaborative partners based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due until such time as the Company satisfies its performance obligations under these arrangements. A contract asset is a conditional right to consideration in exchange for goods or services that the Company has transferred to a customer. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The following table presents changes in the balances of the Company’s BMS receivables and contract liabilities during the nine months ended September 30, 2021 (in thousands): Balance at December 31, 2020 Additions Deductions Balance at September 30, 2021 Receivables $ 400 $ 10,261 $ (400) $ 10,261 Contract liabilities: Deferred revenue $ 26,582 $ — $ (820) $ 25,762 The increase in the receivables balance for the nine months ended September 30, 2021 is driven by amounts owed to the Company from BMS in the period under the settlement terms of the collaboration agreement. The decrease in deferred revenue during the nine months ended September 30, 2021 is driven by the release of the remaining $0.8 million of deferred revenue associated with the combined performance obligation consisting of the ide-cel license and manufacturing services. Regeneron Regeneron Collaboration Agreement In August 2018, bluebird bio entered into a Collaboration Agreement (the “Regeneron Collaboration Agreement”) with Regeneron pursuant to which the parties will apply their respective technology platforms to the discovery, development, and commercialization of novel immune cell therapies for cancer. In August 2018, following the completion of required regulatory reviews, the Regeneron Collaboration Agreement became effective. As noted above, the agreement was assumed by the Company in connection with the separation. Under the terms of the agreement, the parties will leverage Regeneron’s proprietary platform technologies for the discovery and characterization of fully human antibodies, as well as T cell receptors directed against tumor-specific proteins and peptides and the Company will contribute its field-leading expertise in gene therapy. In accordance with the Regeneron Collaboration Agreement, the parties jointly selected six initial targets and intend to equally share the costs of research up to the point of submitting an IND application for a potential gene therapy product directed to a particular target. Additional targets may be selected to add to or replace any of the initial targets during the five-year research collaboration term as agreed to by the parties. Regeneron will accrue a certain number of option rights exercisable against targets as the parties reach certain milestones under the terms of the agreement. Upon the acceptance of an IND for the first product candidate directed to a target, Regeneron will have the right to exercise an option for co-development/co-commercialization of product candidates directed to such target on a worldwide or applicable opt-in territory basis, with certain exceptions. Where Regeneron chooses to opt-in, the parties will share equally in the costs of development and commercialization and will share equally in any profits or losses therefrom in applicable opt-in territories. Outside of the applicable opt-in territories, the target becomes a licensed target and Regeneron would be eligible to receive, with respect to any resulting product, milestone payments of up to $130.0 million per product and royalties on net sales outside of the applicable opt-in territories at a rate ranging from the mid-single digits to low-double digits. A target would also become a licensed target in the event Regeneron does not have an option to such target, or Regeneron does not exercise its option with respect to such target. Either party may terminate a given research program directed to a particular target for convenience, and the other party may elect to continue such research program at its expense, receiving applicable cross-licenses. The terminating party will receive licensed product royalties and milestone payments on the potential applicable gene therapy products. Where the Company terminates a given research program for convenience, and Regeneron elects to continue such research program, the parties will enter into a transitional services agreement. Under certain conditions, following its opt-in, Regeneron may terminate a given collaboration program and the Company may elect to continue the development and commercialization of the applicable potential gene therapy products as licensed products. Regeneron Share Purchase Agreement A Share Purchase Agreement (“SPA”) was entered into by bluebird bio and Regeneron in August 2018. In August 2018, on the closing date of the transaction, bluebird bio issued Regeneron 0.4 million shares of bluebird bio’s common stock, subject to certain restrictions, for $238.10 per share, or $100.0 million in the aggregate. The purchase price represents $63.0 million worth of common stock plus a $37.0 million premium, which represents a collaboration research advancement, or credit to be applied to Regeneron’s initial 50 percent funding obligation for collaboration research, after which the collaborators will continue to fund ongoing research equally. The collaboration research advancement only applies to pre-IND research activities and is not refundable or creditable against post-IND research activities for any programs where Regeneron exercises its opt-in rights. Accounting analysis – Regeneron At the commencement of the arrangement, two units of accounting were identified, which are the issuance of 0.4 million shares of bluebird bio’s common stock and joint research activities during the five-year research collaboration term. The Company determined the total transaction price to be $100.0 million, which comprises $54.5 million attributed to the bluebird bio equity sold to Regeneron and $45.5 million attributed to the joint research activities. In determining the fair value of the bluebird bio common stock at closing, the Company considered the closing price of the bluebird bio common stock on the closing date of the transaction and included a lack of marketability discount because Regeneron received shares subject to certain restrictions. The Company analyzed the joint research activities to assess whether they fall within the scope of ASC 808, and will reassess this throughout the life of the arrangement based on changes in the roles and responsibilities of the parties. Based on the terms of the arrangement as outlined above, for the collaboration research performed prior to submission of an IND application for a potential gene therapy product, both parties are deemed to be active participants in the collaboration. Both parties are performing research and development activities and will share equally in these costs through IND. Additionally, Regeneron and the Company are exposed to significant risks and rewards dependent on the commercial success of any product candidates that may result from the collaboration. As such, the collaboration arrangement is deemed to be within the scope of ASC 808. The $45.5 million attributed to the joint research activities includes the $37.0 million creditable against amounts owed to the Company by Regeneron. The collaboration research advancement will be reduced over time for amounts due to the Company by Regeneron as a result of the parties agreeing to share in the costs of collaboration research equally. The remainder of the amount attributed to the joint research activities will be recognized over the five-year research collaboration term. Consistent with its collaboration accounting policy, the Company will recognize collaborative arrangement 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 collaborative arrangement revenue and reduce the original $37.0 million advance by the amount due from Regeneron until such advancement is fully utilized, after which the Company would record an amount due from Regeneron. If Regeneron’s research costs incurred exceed those research costs incurred by the Company in a given quarter, the Company will record research and development expense and record a liability for the amount due to Regeneron. As of September 30, 2021 and December 31, 2020, the Company has $25.9 million and $30.8 million, respectively, of the amount attributed to the joint research activities remaining to be recognized, which is classified as collaboration research advancement, current portion and collaboration research advancement, net of current portion on the condensed combined balance sheets. The Company recognized $1.7 million and $4.9 million of collaborative arrangement revenue from the Regeneron Collaboration Agreement during the three and nine months ended September 30, 2021, respectively. The Company recognized $2.4 million and $6.2 million of collaborative arrangement revenue from the Regeneron Collaboration Agreement during the three and nine months ended September 30, 2020, respectively. Resilience Background In July 2021, bluebird bio and Resilience US, Inc. (formerly known as Resilience Boston, Inc.), an affiliate of Resilience, signed an Asset Purchase Agreement (the “Agreement”). As part of the Agreement, and upon the closing of the transaction which occurred in September 2021, Resilience acquired bluebird bio's lentiviral vector manufacturing facility located in Durham, North Carolina and retained staff employed at the site. In exchange, bluebird bio received $110.3 million for the facility and related fixed assets. Upon the completion of the separation in November 2021, 2seventy bio was assigned certain rights and obligations under the Agreement as well as certain Ancillary Agreements described below. Upon closing, bluebird bio entered into certain ancillary agreements, including two manufacturing agreements and a license agreement (the “License Agreement”), among others (together referred to as the “Ancillary Agreements”). One manufacturing agreement will support the future manufacturing of lentiviral vector for the Company’s commercial product in collaboration with BMS, ide-cel (the “Commercial Supply Agreement”), while the other will support ongoing manufacturing for lentiviral vector for the Company's development candidates (the “Development Manufacturing Supply Agreement”). The Company also agreed to reimburse Resilience for an amount equal to 50% of the net operating losses of and relating to the manufacturing facility’s business incurred during the twelve-month period ending on the first anniversary of the closing of the transaction, as calculated in accordance with the Agreement, subject to a cap of $15.0 million. In exchange, under the terms of the Development Manufacturing Supply Agreement, the Company will receive up to eight batches of lentiviral vector during the twelve-month period ending on the first anniversary of the closing of the transaction. The License Agreement grants Resilience a worldwide, co-exclusive license to intellectual property controlled by the Company to perform Resilience’s obligations and exercise Resilience’s rights under the supply agreements, and a worldwide, nonexclusive right to offer certain manufacturing services to third-party customers under certain of the Company's intellectual property. Under the terms of the License Agreement, the Company may receive a high single-digit to low double-digit percentage tiered royalty based on Resilience’s gross margins for transactions entered into with parties other than the Company in which the Company's proprietary intellectual property is utilized as part of such transaction. Under the Commercial Supply Agreement, the Company will pay fully burdened manufacturing cost plus a markup for production of vector. Under the Development Manufacturing Supply Agreement, services, manufacture, and delivery of batches of lentiviral vector during the first twelve months from the execution of this agreement will be free of cost, as the costs of these services are represented by the net operating loss sharing arrangement outlined within the Agreement. As such, the Company has committed to a minimum purchase of at least the Company's 50% share of the net operating losses during the first twelve months from the execution of such agreement. After the first twelve months, the Company will pay Resilience the fully burdened manufacturing cost plus a markup for production of vector. Upon separation of 2seventy bio from bluebird bio, effective November 4, 2021, certain rights and obligations under the Agreement and certain Ancillary Agreements were assigned by bluebird bio to 2seventy bio with 2seventy bio assuming all rights and obligations these agreements convey. Accounting analysis - Resilience Since the January 2021 announcement by bluebird bio of its plans to separate and spin-off of 2seventy bio from its severe genetic disease portfolio and programs, the manufacturing facility was expected to be assigned to 2seventy bio and was therefore accounted for within the 2seventy bio carve-out financial statements. The disposition of the net assets of the manufacturing facility previously assigned to 2seventy bio has been reflected as a transfer to bluebird bio via net parent investment as a result of bluebird bio’s sale of such facility. 2seventy bio is not a party to the sale of the manufacturing facility and, therefore, did not recognize any gain or loss arising from the transaction.

Royalty and other revenue

Royalty and other revenue	9 Months Ended
	Sep. 30, 2021
License And Royalty Revenue [Abstract]
Royalty and other revenue	Royalty and other revenue bluebird bio has out-licensed intellectual property to various third parties. Under the terms of these agreements, some of which were assumed by the Company in connection with the separation, bluebird bio and the Company may be entitled to royalties and milestone payments. Novartis Pharma AG In April 2017, bluebird bio entered into a worldwide license agreement with Novartis, which is further described in Note 9, Royalty and other revenue, to the annual combined financial statements included in Exhibit 99.1 to the Company’s Form 10. Under the terms of the agreement, Novartis non-exclusively licensed certain patent rights related to lentiviral vector technology to develop and commercialize CAR T cell therapies for oncology, including Kymriah (formerly known as CTL19), Novartis’s anti-CD19 CAR T therapy. The agreement was to be assumed by the Company in connection with the separation. Beginning in the fourth quarter of 2017, the Company began recognizing royalty revenue from sales of tisagenlecleucel under the agreement. This license agreement was terminated effective March 2021, at which point in time Novartis was no longer required to pay the Company royalty or other payments on net sales of tisagenlecleucel or any future products. The Company recognized $0.6 million and $3.5 million of royalty revenue in the three months ended September 30, 2021 and 2020, respectively, from sales of tisagenlecleucel. The Company recognized $2.9 million and $9.6 million of royalty revenue in the nine months ended September 30, 2021 and 2020, respectively, from sales of tisagenlecleucel. Such amounts are included within royalty and other revenue in the condensed combined statement of operations and comprehensive loss. Juno Therapeutics In May 2020, bluebird bio entered into a non-exclusive license agreement with Juno Therapeutics, Inc. (“Juno”), a wholly-owned subsidiary of BMS, related to lentiviral vector technology to develop and commercialize CD-19-directed CAR T cell therapies. The agreement was assumed by the Company in connection with the separation. Upon regulatory approval of lisocabtagene maraleucel during the first quarter of 2021, bluebird bio received a $2.5 million milestone payment from Juno, which is included within royalty and other revenue in the Company’s condensed combined financial statements. Royalty revenue recognized from sales of lisocabtagene maraleucel is also included within royalty and other revenue in the condensed combined statement of operations and comprehensive loss.

Stock-based compensation

Stock-based compensation	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Stock-based compensation	Stock-based compensation During the first quarter of 2021, bluebird bio implemented a retention program designed to incentivize and retain employees through the separation of its severe genetic disease and oncology programs, which is intended to occur by the end of 2021. Under the retention program, employees are entitled to a one-time bonus payment, consisting of both a cash payment and unrestricted stock awards, with the condition that the employee remains employed at the end of 2021. All awards granted under bluebird bio’s equity plans consist of shares of bluebird bio’s common stock. Accordingly, the amounts presented are not necessarily indicative of future stock-based compensation and do not necessarily reflect the amounts that the Company would have recorded as an independent, publicly traded company for the periods presented. Stock-based compensation expense Stock-based compensation expense was allocated to the Company using a combination of specific identification and time spent on projects at various levels of the organization, which management believes are consistent and reasonable. Stock-based compensation expense under bluebird bio's stock option and incentive plans allocated to the Company by classification included within the condensed combined statements of operations and comprehensive loss was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Research and development $ 5,523 $ 7,916 $ 22,429 $ 24,765 Selling, general and administrative 5,707 7,339 17,877 23,793 $ 11,230 $ 15,255 $ 40,306 $ 48,558

Related-party transactions

Related-party transactions	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Related-party transactions	Related-party transactionsHistorically, the Company was managed and operated in the normal course of business under bluebird bio. Accordingly, certain shared costs have been allocated to the Company and reflected as expenses in the Company's stand-alone condensed combined financial statements. The expenses reflected in the condensed combined financial statements may not be indicative of expenses that will be incurred by the Company in the future. Corporate allocations The condensed combined financial statements reflect allocations of certain expenses from bluebird bio, including, but not limited to, general corporate expenses, such as senior management, legal, human resources, accounting, other financial services (such as treasury, audit and purchasing), tax, information technology, and corporate employee benefits, incentives and stock-based compensation included within selling, general and administrative expense. These expenses have been allocated to the Company based on direct usage or benefit where specifically identifiable, with the remainder allocated based on employee time spent on projects, square footage or other measures that management believes are consistent and reasonable. Allocations for management costs and corporate support services provided to the Company totaled $14.5 million and $18.9 million for the three months ended September 30, 2021 and 2020, respectively. Allocations for management costs and corporate support services provided to the Company totaled $49.9 million and $59.2 million for the nine months ended September 30, 2021 and 2020, respectively. The financial information in these condensed combined financial statements does not necessarily include all the expenses that would have been incurred by the Company had it been a separate, stand-alone entity. Actual costs that may have been incurred if the Company had been a stand-alone company would depend on a number of factors, including the chosen organization structure and functions outsourced or performed by employees. See Note 2, Summary of significant accounting policies and basis of presentation , for additional information on the preparation and basis of presentation of these condensed combined financial statements, including the treatment of certain research and development costs not directly attributable to individual programs. Usage of the Company's assets by bluebird bio and of bluebird bio's assets by the Company Certain assets have been reflected in these condensed combined financial statements as the underlying assets were assumed by the Company; however, bluebird bio has historically utilized a portion of the underlying asset as part of its operations. Accordingly, the expense related to the underlying asset has been reflected in the condensed combined financial statements. The Company has also recorded an imputed charge to bluebird bio to reflect the cost of bluebird bio's proportional usage. In addition, the Company has recorded as an expense an imputed charge to reflect the cost of the Company's proportional usage of certain underlying assets not reflected in the condensed combined financial statements but for which the Company has historically utilized a portion of the underlying asset as part of its operations. The income and expense recognized by the Company resulting from these imputed charges is recorded as other income, net in the condensed combined financial statements and was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Imputed charge to bluebird bio for leases $ 4,519 $ 4,085 $ 13,440 $ 12,410 Imputed charge from bluebird bio for leases (209) (261) (836) (714) Imputed charge to bluebird bio for property, plant and equipment 507 571 1,714 1,695 Imputed charge from bluebird bio for property, plant and equipment (13) (57) (1,125) (174) Imputed charge to bluebird bio for intangible assets 9 39 82 155 Other — 61 (1) 86 $ 4,813 $ 4,438 $ 13,274 $ 13,458 Other components of other income, net, that are not shown in the table above primarily include immaterial rental income and gains and losses on disposals of fixed assets. Stock-based compensation As discussed in Note 10, Stock-based compensation , 2seventy bio’s employees participate in bluebird bio's stock-based compensation plans, the costs of which have been allocated to 2seventy bio and recorded in research and development and selling, general and administrative expenses in the condensed combined statements of operations and comprehensive loss. Retirement plans 2seventy bio’s employees participate in bluebird bio's 401(k) Savings plan, the costs of which have been allocated to 2seventy bio and recorded in research and development and selling, general and administrative expenses in the condensed combined statements of operations and comprehensive loss. Transaction costs As of September 30, 2021, bluebird bio had incurred costs related to the separation of the Company. To the extent separation costs are incurred that will directly benefit the Company as a stand-alone company, such costs will be allocated to the Company. Centralized cash management No separate cash accounts for 2seventy bio were historically maintained and, therefore, bluebird bio is presumed to have funded 2seventy bio’s operating, investing and financing activities as necessary. As cash is disbursed and received by bluebird bio, for purposes of the condensed combined financial statements, funding of 2seventy bio’s expenditures is reflected in the condensed combined financial statements as a component of net parent investment.

Income taxes

Income taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income taxes	Income taxes Deferred 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. The Company did not operate as a stand-alone entity (or group of entities) prior to the separation and, accordingly, the amount and composition of its tax losses, credits, and other deferred tax assets included in the condensed combined financial statements may change as the result of the Company’s separation from bluebird bio. In March 2020, the Coronavirus Aid, Relief and Economic Security Act (“CARES Act”) was enacted. This law temporarily suspends and adjusts certain law changes enacted in the Tax Cuts and Jobs Act in 2017. In December 2020, the Consolidated Appropriations Act was enacted. This law modified the employee retention credit under the CARES Act and created credit extenders for certain credits. The Company has concluded that the provisions in the CARES Act and Consolidated Appropriations Act have an immaterial impact on the Company’s income tax expense due to its cumulative losses and full valuation allowance position.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	Subsequent events On November 4, 2021, bluebird bio completed the separation of its oncology portfolio and programs into 2seventy bio, retaining its severe genetic disease portfolio and programs. The separation was effected by means of a distribution of all of the outstanding shares of common stock of 2seventy bio on the basis of one share of 2seventy bio common stock for every three shares of bluebird bio common stock issued and outstanding on October 19, 2021, the record date for the distribution. The distribution was effected at 12:01 a.m. on November 4, 2021. Immediately following the distribution, the Company had 23,369,088 shares of common stock and pre-funded warrants to purchase 757,575 shares of common stock outstanding. In connection with the separation, on November 3, 2021, bluebird bio and 2seventy bio executed a separation agreement, a tax matters agreement, an employee matters agreement, an intellectual property license agreement, and transition services agreements, under which both companies will temporarily provide and receive certain services from each other. These agreements effectuated the separation and govern 2seventy bio's relationship with bluebird bio following the distribution. In addition, in connection with the separation, bluebird bio made a cash contribution to the Company of approximately $441.5 million

Summary of significant accoun_2

Summary of significant accounting policies and basis of presentation (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of presentation	Basis of presentation Because the previously described distribution occurred subsequent to September 30, 2021, the accompanying condensed combined financial statements have been prepared on a carve-out basis and are derived from bluebird bio's consolidated financial statements and accounting records. The accompanying condensed combined financial statements reflect the historical results of 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 United States GAAP as included in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board (“FASB”). Certain information and footnote disclosures included in the Company’s annual financial statements have been condensed or omitted. These condensed combined financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position and results of operations for the interim periods ended September 30, 2021 and 2020. The historical results of operations, financial position and cash flows of 2seventy bio presented in these condensed combined financial statements may not be indicative of what they would have been had 2seventy bio been an independent stand-alone entity, nor are they necessarily indicative of 2seventy bio's future results of operations, financial position and cash flows. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These condensed combined financial statements should be read in conjunction with the audited combined financial statements as of and for the year ended December 31, 2020 and the notes thereto, which are included in Exhibit 99.1 to the Company’s Form 10, which was most recently filed with the Securities and Exchange Commission on October 8, 2021. As part of bluebird bio, the Company was dependent upon bluebird bio for all of its working capital and financing requirements, as bluebird bio used a centralized approach to cash management and financing its operations. There were no cash amounts specifically attributable to the Company for the historical periods presented; therefore, cash and cash equivalents have not been allocated to the Company in the condensed combined financial statements. Financing transactions related to bluebird bio are accounted for as a component of net parent investment in the condensed combined balance sheets and as a financing activity on the accompanying condensed combined statements of cash flows. The Company’s condensed combined financial statements include an allocation of expenses related to certain bluebird bio corporate functions, including senior management, legal, human resources, finance and information technology. In addition, the Company's condensed combined financial statements include an allocation of certain research and development costs not directly attributable to individual programs. These expenses have been allocated to the Company based on direct usage or benefit where specifically identifiable, with the remainder allocated based on employee time spent on projects, square footage or other measures that management believes are consistent and reasonable. These allocations may not be indicative of the actual expense that would have been incurred had the Company operated as an independent, publicly traded company for the periods presented. See Note 11, Related-party transactions , for a further description of the accounting for the separation from bluebird bio. The condensed combined balance sheets of the Company include assets and liabilities that were allocated principally on a specific identification basis. As 2seventy bio's operations were not historically held by a single legal entity or separate legal entities, net parent investment is shown in lieu of stockholder's equity in the condensed combined financial statements. Net parent investment represents the cumulative investment by bluebird bio in the Company through the dates presented, inclusive of operating results. Balances between the Company and bluebird bio that were not historically settled in cash are included in net parent investment. All significant transactions between the Company and bluebird bio have been included in the accompanying condensed combined financial statements. Transactions with bluebird bio are reflected in the accompanying condensed combined statements of equity (deficit) as net transfers from (to) parent and in the accompanying condensed combined balance sheets within net parent investment. Amounts reported are computed based on thousands, except percentages or as otherwise noted. As a result, certain totals may not sum due to rounding.
Principles of combination and consolidation	Principles of combination and consolidation The accompanying condensed combined financial statements include the attribution of certain assets and liabilities that have historically been held by bluebird bio but which are specifically identifiable or attributable to the Company. All intercompany balances and transactions with bluebird bio are deemed to be effectively settled in the condensed combined financial statements at the time the transaction is recorded. Expenses related to corporate allocations from bluebird bio to the Company are considered to be effectively settled for cash in the condensed combined financial statements at the time the transaction is recorded. The Company continually assesses whether it is the primary beneficiary of a variable interest entity as changes to existing relationships or future transactions may result in consolidation or deconsolidation of one or more collaborators or partners. In determining whether it is the primary beneficiary of an entity in which the Company has a variable interest, management applies a qualitative approach that determines whether the Company has both (1) the power to direct the economically significant activities of the entity and (2) the obligation to absorb losses of, or the right to receive benefits from, the entity that could potentially be significant to that entity.
Use of estimates	Use of estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts in the financial statements and accompanying notes. Actual results could materially differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes and management must select an amount that falls within that range of reasonable estimates. This process may result in actual results differing materially from those estimated amounts used in the preparation of the financial statements. Estimates and judgments are used in the following areas, among others: allocations of revenue, expenses, assets and liabilities from bluebird bio's historical consolidated financial statements to the Company, future undiscounted cash flows and subsequent fair value estimates used to assess potential and measure any impairment of long-lived assets, including goodwill and intangible assets, the measurement of right-of-use assets and lease liabilities,
Collaborative arrangement revenue	Collaborative arrangement revenue The Company analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements ("ASC 808"), which includes determining whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of ASC 808 and those that are more reflective of a vendor-customer relationship and therefore within the scope of ASC 606, Revenue from Contracts with Customers ("Topic 606" or "ASC 606"). For elements of collaboration arrangements that are accounted for pursuant to ASC 808, an appropriate recognition method is determined and applied consistently, generally by analogy to Topic 606. In arrangements where the Company does not deem its collaborator to be its customer, payments to and from its collaborator are presented in the condensed combined statements of operations and comprehensive loss based on the nature of the payments, as summarized in the table and further described below. Nature of Payment Statement of Operations Presentation The Company's share of profits in connection with commercialization of products Collaborative arrangement revenue The Company's share of losses in connection with commercialization of products Share of collaboration loss Net reimbursement of the Company's research and development expenses Collaborative arrangement revenue Net reimbursement of the collaborator's research and development expenses Research and development expense Where the collaborator is the principal in the product sales, the Company recognizes its share of any profits or losses, representing net product sales less cost of goods sold and shared commercial and other expenses, in the period in which such underlying sales occur and costs are incurred by the collaborator. The Company also recognizes its share of costs arising from research and development activities performed by collaborators in the period its collaborators incur such expenses.
Recent accounting pronouncements	Recent accounting pronouncements Recently adopted ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify the accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The new standard was effective beginning January 1, 2021. The adoption of ASU 2019-12 did not have a material impact on the Company's financial position or results of operations upon adoption. ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity In August 2020, the FASB issued ASU 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU 2020-06”). ASU 2020-06 simplifies the complexity associated with applying U.S. GAAP for certain financial instruments with characteristics of liabilities and equity. More specifically, the amendments focus on the guidance for convertible instruments and derivative scope exception for contracts in an entity's own equity. The Company early adopted the new standard, effective January 1, 2021. The adoption of ASU 2020-06 did not have an impact on the Company's financial position or results of operations upon adoption. ASU No. 2020-08, Codification Improvements to Subtopic 310-20, Receivables - Nonrefundable Fees and Other Costs In October 2020, the FASB issued ASU 2020-08, Codification Improvements to Subtopic 310-20, Receivables - Nonrefundable Fees and Other Costs (“ASU 2020-08”) to provide further clarification and update the previously issued guidance in ASU 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20: Premium Amortization on Purchased Callable Debt Securities) (“ASU 2017-08”). ASU 2017-08 shortened the amortization period for certain callable debt securities purchased at a premium by requiring that the premium be amortized to the earliest call date. ASU 2020-08 requires that at each reporting period, to the extent that the amortized cost of an individual callable debt security exceeds the amount repayable by the issuer at the next call date, the excess premium shall be amortized to the next call date. The new standard was effective beginning January 1, 2021. The adoption of ASU 2020-08 did not have a material impact on the Company's financial position or results of operations upon adoption. ASU No. 2020-10, Codification Improvements In October 2020, the FASB issued ASU 2020-10, Codification Improvements ("ASU 2020-10"). The amendments in this ASU represent changes to clarify the ASC, correct unintended application of the guidance, or make minor improvements to the ASC that are not expected to have a significant effect on current accounting practice or create a significant administrative cost to most entities. This new standard was effective beginning January 1, 2021. The adoption of ASU 2020-10 did not have a material impact on the Company's financial position or results of operations upon adoption.

Summary of significant accoun_3

Summary of significant accounting policies and basis of presentation (Tables)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Collaborative Arrangements, Nature Of Payment And Presentation	In arrangements where the Company does not deem its collaborator to be its customer, payments to and from its collaborator are presented in the condensed combined statements of operations and comprehensive loss based on the nature of the payments, as summarized in the table and further described below. Nature of Payment Statement of Operations Presentation The Company's share of profits in connection with commercialization of products Collaborative arrangement revenue The Company's share of losses in connection with commercialization of products Share of collaboration loss Net reimbursement of the Company's research and development expenses Collaborative arrangement revenue Net reimbursement of the collaborator's research and development expenses Research and development expense

Fair value measurements (Tables

Fair value measurements (Tables)	9 Months Ended
	Sep. 30, 2021
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, 2021 and December 31, 2020 (in thousands): Total Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) September 30, 2021 Liabilities: Contingent consideration $ 1,973 $ — $ — $ 1,973 Total liabilities $ 1,973 $ — $ — $ 1,973 December 31, 2020 Liabilities: Contingent consideration $ 1,509 $ — $ — $ 1,509 Total liabilities $ 1,509 $ — $ — $ 1,509
Roll-Forward of Fair Value of the Company's Contingent Consideration Obligations	The table below provides a roll-forward of fair value of the Company’s contingent consideration obligations that include Level 3 inputs (in thousands): Nine Months Ended September 30, 2021 2020 Beginning balance $ 1,509 $ 7,977 Additions — — Changes in fair value 464 (5,591) Payments — — Ending balance $ 1,973 $ 2,386

Property, plant and equipment_2

Property, plant and equipment, net (Tables)	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Summary of Property, Plant and Equipment, Net	Property, plant and equipment, net, consists of the following (in thousands): As of September 30, 2021 As of December 31, 2020 Land $ — $ 1,210 Building — 15,745 Computer equipment and software 5,252 6,503 Office equipment 6,080 6,588 Laboratory equipment 30,818 24,080 Leasehold improvements 28,479 28,305 Construction-in-progress 799 91,631 Total property, plant and equipment 71,428 174,062 Less accumulated depreciation and amortization (37,676) (30,037) Property, plant and equipment, net $ 33,752 $ 144,025

Accrued expenses and other cu_2

Accrued expenses and other current liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Payables and Accruals [Abstract]
Summary of accrued expenses and other current liabilities	Accrued expenses and other current liabilities consist of the following (in thousands): As of September 30, 2021 As of December 31, 2020 Employee compensation $ 28,465 $ 9,451 Collaboration research costs 27,553 19,605 Manufacturing costs 5,676 6,808 Clinical and contract research organization costs 2,497 2,854 Property, plant, and equipment 618 440 License and milestone fees 236 278 Other 11,228 3,911 Total accrued expenses and other current liabilities $ 76,273 $ 43,347

Collaborative arrangements an_2

Collaborative arrangements and strategic partnerships (Tables)	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of Total Transaction Price, Allocation of Total Transaction Price to Identified Performance Obligations Under Arrangement and Amount of Transaction Price Unsatisfied	These amounts represent the Company’s share of BMS’ ide-cel product revenue, cost of goods sold, and selling costs, offset by any reimbursement of commercial costs incurred by the Company, and exclude expenses related to ongoing development, which are separately reflected in the combined statements of operations and comprehensive loss as described below. Amounts incurred prior to commercial approval were not material. Three months ended Nine months ended March 31, 2021 June 30, 2021 September 30, 2021 September 30, 2021 Collaborative arrangement revenue from ide-cel commercial activities (1) $ — $ — $ 10,607 $ 10,607 Share of collaboration loss from ide-cel commercial activities (1) $ — $ (10,071) $ — $ (10,071) _________________ (1) As noted above, the calculation is performed on a quarterly basis. The calculation is independent of previous activity, which may result in fluctuations between revenue and expense recognition period over period. The following table summarizes the amounts associated with the research activities under the collaboration included in research and development expense or recognized as collaborative arrangement revenue for the three and nine months ended September 30, 2021 and 2020 (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 ASC 808 ide-cel research and development revenue - U.S. (1)(2) $ — $ — $ — $ 108,196 ASC 808 ide-cel research and development expense - U.S. (1) $ (5,660) $ (16,084) $ (31,678) $ (21,164) _________________ (1) As noted above, the calculation of collaborative arrangement activity to be recognized for joint ide-cel efforts in the United States is performed on a quarterly basis. The calculation is independent of previous activity, which may result in fluctuations between revenue and expense recognition period over period, depending on the varying extent of effort performed by each party during the period. (2) In the second quarter of 2020, the Company recognized $169.2 million as a cumulative catch-up adjustment to revenue recorded in connection with the May 2020 First Amendment to the Amended and Restated Co-Development, Co-Promote and Profit Share Agreement (“Amended Ide-cel CCPS”), a portion of which was recognized as ASC 808 research and development collaboration revenue. Refer to Note 8, Collaborative arrangements , to the annual combined financial statements included in Exhibit 99.1 to the Company’s Form 10 for further discussion on the Amended Ide-cel CCPS. Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 ASC 606 ide-cel license and manufacturing revenue - ex-U.S. (1) $ 5,314 $ 6,913 $ 14,698 $ 94,733 ________________ (1) In the second quarter of 2020, the Company recognized $169.2 million as a cumulative catch-up adjustment to revenue recorded in connection with the Amended Ide-cel CCPS, a portion of which was recognized as ASC 606 license and manufacturing revenue. Refer to Note 8, Collaborative arrangements , to the annual combined financial statements included in Exhibit 99.1 to the Company’s Form 10 for further discussion on the Amended Ide-cel CCPS.
Changes in Balances of Company's Receivables and Contract Liabilities	The following table presents changes in the balances of the Company’s BMS receivables and contract liabilities during the nine months ended September 30, 2021 (in thousands): Balance at December 31, 2020 Additions Deductions Balance at September 30, 2021 Receivables $ 400 $ 10,261 $ (400) $ 10,261 Contract liabilities: Deferred revenue $ 26,582 $ — $ (820) $ 25,762

Stock-based compensation (Table

Stock-based compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Schedule of Stock-Based Compensation Expense by Classification	Stock-based compensation expense under bluebird bio's stock option and incentive plans allocated to the Company by classification included within the condensed combined statements of operations and comprehensive loss was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Research and development $ 5,523 $ 7,916 $ 22,429 $ 24,765 Selling, general and administrative 5,707 7,339 17,877 23,793 $ 11,230 $ 15,255 $ 40,306 $ 48,558

Related-party transactions (Tab

Related-party transactions (Tables)	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Schedule of Related Party Transactions	The income and expense recognized by the Company resulting from these imputed charges is recorded as other income, net in the condensed combined financial statements and was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Imputed charge to bluebird bio for leases $ 4,519 $ 4,085 $ 13,440 $ 12,410 Imputed charge from bluebird bio for leases (209) (261) (836) (714) Imputed charge to bluebird bio for property, plant and equipment 507 571 1,714 1,695 Imputed charge from bluebird bio for property, plant and equipment (13) (57) (1,125) (174) Imputed charge to bluebird bio for intangible assets 9 39 82 155 Other — 61 (1) 86 $ 4,813 $ 4,438 $ 13,274 $ 13,458

Description of the business - N

Description of the business - Narrative (Detail) $ in Thousands	Nov. 04, 2021USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)
Subsequent Event [Line Items]
Net loss		$ (60,001)	$ (72,075)	$ (231,237)	$ (43,313)
Net cash used in operating activities				(149,595)	(13,964)
Proceeds from contributions from parent				$ 168,195	$ 29,224
Conversion ratio		0.3333		0.3333
Subsequent Event
Subsequent Event [Line Items]
Proceeds from contributions from parent	$ 441,500

Fair value measurements - Recor

Fair value measurements - Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair value, measurements, recurring - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration	$ 1,973	$ 1,509
Total liabilities	1,973	1,509
Quoted prices in active markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration	0	0
Total liabilities	0	0
Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration	0	0
Total liabilities	0	0
Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration	1,973	1,509
Total liabilities	$ 1,973	$ 1,509

Fair value measurements - Roll-

Fair value measurements - Roll-Forward of Fair Value of the Company's Contingent Consideration Obligations (Detail) - Significant unobservable inputs (Level 3) - Contingent consideration obligations - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 1,509	$ 7,977
Additions	0	0
Changes in fair value	464	(5,591)
Payments	0	0
Ending balance	$ 1,973	$ 2,386

Property, plant and equipment_3

Property, plant and equipment, net - Summary of Property, Plant and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 71,428	$ 174,062
Less accumulated depreciation and amortization	(37,676)	(30,037)
Property, plant and equipment, net	33,752	144,025
Land
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	1,210
Building
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	15,745
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	5,252	6,503
Office equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	6,080	6,588
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	30,818	24,080
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	28,479	28,305
Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 799	$ 91,631

Property, plant and equipment_4

Property, plant and equipment, net - Narrative (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Depreciation	$ 3,500	$ 2,400	$ 9,700	$ 7,000
Construction in progress	71,428		71,428		$ 174,062
Lentiviral Vector Manufacturing Facility
Property, Plant and Equipment [Line Items]
Net assets disposed of	$ 111,200		$ 111,200
Construction In Progress North Carolina Manufacturing Facility
Property, Plant and Equipment [Line Items]
Construction in progress					$ 91,100

Accrued expenses and other cu_3

Accrued expenses and other current liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Employee compensation	$ 28,465	$ 9,451
Collaboration research costs	27,553	19,605
Manufacturing costs	5,676	6,808
Clinical and contract research organization costs	2,497	2,854
Property, plant, and equipment	618	440
License and milestone fees	236	278
Other	11,228	3,911
Total accrued expenses and other current liabilities	$ 76,273	$ 43,347

Leases - Narrative (Details)

Leases - Narrative (Details) - Subsequent Event $ in Millions	1 Months Ended
	Nov. 30, 2021USD ($)
Seattle, Washington
Lessee, Lease, Description [Line Items]
Collateralized letter of credit	$ 5
60 Binney Street lease
Lessee, Lease, Description [Line Items]
Collateralized letter of credit	$ 25

Commitments and contingencies -

Commitments and contingencies - Narrative (Detail) $ in Millions	1 Months Ended
	Jul. 31, 2021USD ($)batchagreement	Sep. 30, 2021USD ($)
Resilience
Commitments And Contingencies Disclosure [Line Items]
Number of manufacturing agreements | agreement	2
Net operating losses, percentage of reimbursement	50.00%
Reimbursement cap	$ 15
Net operating losses, percentage of minimum purchase amount	50.00%
Maximum | Resilience
Commitments And Contingencies Disclosure [Line Items]
Number of lentiviral vector batches | batch	8
Pregenen
Commitments And Contingencies Disclosure [Line Items]
Contingent future cash payments		$ 99.9

Collaborative arrangements an_3

Collaborative arrangements and strategic partnerships - Collaborative Arrangement Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	$ 12,337	$ 2,422	$ 15,527	$ 114,398
Share of collaboration loss	0	0	(10,071)	0
Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Share of collaboration loss			500
Ide Cel Commercial Activities | Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	0	0	10,607	10,607
Share of collaboration loss	$ 0	$ (10,071)	$ 0	$ (10,071)

Collaborative arrangements an_4

Collaborative arrangements and strategic partnerships - Narrative (Detail) $ / shares in Units, $ in Thousands, shares in Millions	Aug. 24, 2018USD ($)accounting_unit$ / sharesshares	Jul. 31, 2021USD ($)batchagreement	Aug. 31, 2018target	Sep. 30, 2021USD ($)performance_obligation	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)performance_obligation	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Sep. 30, 2019USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Income (loss) from collaborative arrangements				$ 0	$ 0	$ (10,071)	$ 0
Number of performance obligations | performance_obligation				2		2
Decrease to deferred revenue						$ 820	(8,558)
Number of accounting units | accounting_unit	2
Lentiviral Vector Manufacturing Facility | Bluebird Bio
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from divestiture of business		$ 110,300
Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Income (loss) from collaborative arrangements						500
Collaboration agreement, transaction price				$ 31,000		31,000
Estimated variable consideration				1,800		1,800
Decrease to deferred revenue						800
Bristol-Myers Squibb | Phase I, Additional Obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated variable consideration									$ 27,300
Bristol-Myers Squibb | Research and development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated variable consideration									$ 5,400
Bristol-Myers Squibb | Ide Cel Commercial Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Income (loss) from collaborative arrangements				0	(10,071)	0	(10,071)
Bristol-Myers Squibb | bb21217 license agreement | U.S.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional fee receivable if option to co-develop and co-promote is not exercised				10,000		10,000
Milestone payments receivable				85,000		85,000
Bristol-Myers Squibb | bb21217 research and development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer development milestone payment achieved						10,000
Regeneron Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of initial collaboration targets | target			6
Research collaboration term			5 years
Joint research activities remaining to be recognized				25,900		25,900		$ 30,800
Regeneron Collaboration Agreement | Collaboration
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue balance recognized as gross revenues				$ 1,700	$ 2,400	$ 4,900	$ 6,200
Regeneron Collaboration Agreement | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	$ 130,000
Regeneron Collaboration Agreement | Research and development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement, transaction price	100,000
Purchase price premium	$ 37,000
Collaborative arrangement amortization period	5 years
Collaborative arrangement amount attributed to joint research activities	$ 45,500
Regeneron Collaboration Agreement | 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 Collaboration Agreement | Share purchase agreement | Bluebird Bio
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock price per share (in dollars per share) | $ / shares	$ 238.10
Investment in common stock	$ 100,000
Purchase price premium	$ 37,000
Collaborative arrangement research initial funding obligation, percentage	50.00%
Regeneron Collaboration Agreement | Share purchase agreement | Common shares | Bluebird Bio
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Issuance of common stock to Regeneron (in shares) | shares	0.4
Investment in common stock	$ 63,000
Resilience
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of manufacturing agreements | agreement		2
Net operating losses, percentage of reimbursement		50.00%
Reimbursement cap		$ 15,000
Net operating losses, percentage of minimum purchase amount		50.00%
Resilience | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of lentiviral vector batches | batch		8

Collaborative arrangements an_5

Collaborative arrangements and strategic partnerships - Summary of Revenue Recognized or Expense Incurred for Joint Ide-cel Development Efforts Related to Combined Unit of Accounting for its License and Vector Manufacturing of Ide-cel (Detail) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	$ 12,337	$ 2,422		$ 15,527	$ 114,398
Research and development expense	(61,131)	(72,253)		(202,394)	(227,585)
Revenues	19,257	18,434		38,488	238,217
Bristol-Myers Squibb | U.S. | Ide-cel Research And Development Services | License and manufacturing services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	(5,660)	(16,084)		(31,678)	(21,164)
Bristol-Myers Squibb | U.S. | Ide Cel Revenue Services | License and manufacturing services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement revenue	0	0		0	108,196
Revenues			$ 169,200
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	$ 5,314	$ 6,913		$ 14,698	$ 94,733
Revenues			$ 169,200

Collaborative arrangements an_6

Collaborative arrangements and strategic partnerships - Changes in Balances of Company's Receivables and Contract Liabilities (Detail) - Bristol-Myers Squibb $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Receivables
Balance at December 31, 2020	$ 400
Additions	10,261
Deductions	(400)
Balance at September 30, 2021	10,261
Contract liabilities:
Balance at December 31, 2020	26,582
Additions	0
Deductions	(820)
Balance at September 30, 2021	$ 25,762

Royalty and other revenue - Add

Royalty and other revenue - Additional Information (Detail) - Royalty and other revenue - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
License And Royalty Revenue [Line Items]
Revenue	$ 608		$ 3,499	$ 5,417	$ 17,086
Novartis Pharma AG
License And Royalty Revenue [Line Items]
Revenue	$ 600		$ 3,500	$ 2,900	$ 9,600
Juno Therapeutics | Bluebird Bio
License And Royalty Revenue [Line Items]
Revenue		$ 2,500

Stock-based compensation - Sche

Stock-based compensation - Schedule of Stock-Based Compensation Expense by Classification (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 11,230	$ 15,255	$ 40,306	$ 48,558
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	5,523	7,916	22,429	24,765
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 5,707	$ 7,339	$ 17,877	$ 23,793

Related-party transactions - Na

Related-party transactions - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Bluebird Bio | Management Costs and Corporate Support Services
Related Party Transaction [Line Items]
Allocations for management costs and corporate support services provided to the Company	$ 14.5	$ 18.9	$ 49.9	$ 59.2

Related Party Disclosures - Imp

Related Party Disclosures - Imputed Charges (Details) - Bluebird Bio - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	$ 4,813	$ 4,438	$ 13,274	$ 13,458
Imputed charge to bluebird bio for leases
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	4,519	4,085	13,440	12,410
Imputed charge from bluebird bio for leases
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	(209)	(261)	(836)	(714)
Imputed charge to bluebird bio for property, plant and equipment
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	507	571	1,714	1,695
Imputed charge from bluebird bio for property, plant and equipment
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	(13)	(57)	(1,125)	(174)
Imputed charge to bluebird bio for intangible assets
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	9	39	82	155
Other
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	$ 0	$ 61	$ (1)	$ 86

Subsequent Events (Details)

Subsequent Events (Details) $ in Thousands	Nov. 04, 2021USD ($)shares	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)
Subsequent Event [Line Items]
Transfers from bluebird bio | $		$ 168,195	$ 29,224
Subsequent Event
Subsequent Event [Line Items]
Share distribution ratio	0.33
Common stock, shares outstanding (in shares) | shares	23,369,088
Transfers from bluebird bio | $	$ 441,500
Subsequent Event | Pre-funded Warrants
Subsequent Event [Line Items]
Pre-funded warrants issued (in shares) | shares	757,575