0001293971-23-000055 | 10-Q | XBRL Viewer

Marketable securities

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

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


Description	Amortized cost / Cost		Unrealized gains		Unrealized losses		Fair value
September 30, 2023
U.S. government agency securities and treasuries	8,949		—		(3)		8,946
Total	$	8,949	$	—	$	(3)	$	8,946
December 31, 2022
U.S. government agency securities and treasuries	$	67,970	$	—	$	(1,733)	$	66,237
Corporate bonds	2,524		—		(26)		2,498
Total	$	70,494	$	—	$	(1,759)	$	68,735

No available-for-sale debt securities held as of September 30, 2023 or December 31, 2022 had remaining maturities greater than one year.

Stock-based compensation - Schedule of Stock-Based Compensation Expense by Classification (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 4,868	$ 9,212	$ 16,013	$ 30,509
Cost of product revenue
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	342	0	435	0
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2,461	3,975	7,503	13,462
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 2,065	$ 5,237	$ 8,075	$ 17,047

- Definition

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

+ References

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

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

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

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

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

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

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

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

+ Details

Fair value measurements - Schedule of Unrealized Loss on Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair value
Less than 12 months	$ 8,946	$ 0
12 months or greater	0	68,735
Total	8,946	68,735
Unrealized losses
Less than 12 months	(3)	0
12 months or greater	0	(1,759)
Total	(3)	(1,759)
U.S. government agency securities and treasuries
Fair value
Less than 12 months	8,946	0
12 months or greater	0	66,237
Total	8,946	66,237
Unrealized losses
Less than 12 months	(3)	0
12 months or greater	0	(1,733)
Total	$ (3)	(1,733)
Corporate bonds
Fair value
Less than 12 months		0
12 months or greater		2,498
Total		2,498
Unrealized losses
Less than 12 months		0
12 months or greater		(26)
Total		$ (26)

Inventory

9 Months Ended

Sep. 30, 2023

Inventory Disclosure [Abstract]

Inventory

Inventory, net, consists of the following (in thousands):


	As of September 30, 2023		As of December 31, 2022
Raw materials	$	7,392	$	—
Work in progress	9,725		—
Finished goods	3,852		—
Inventory	$	20,969	$	—

Raw materials inventory consists of completed materials meeting quality acceptance standards to be used in the manufacture of drug product. Materials may include small molecules, plasmids, or vector products. Work in progress inventory consists of materials that are either partially completed or fully manufactured but are pending quality acceptance. Finished goods are completed drug product having full quality acceptance that may be shipped to a qualified treatment center, but has not yet been infused in the patient.

As of December 31, 2022, the Company did not have any manufactured inventory that was in progress or had received final quality acceptance after the FDA approval of ZYNTEGLO or SKYSONA. Prior to FDA approval, the existing inventory was expensed to research and development expense.

Basis of presentation, principles of consolidation and significant accounting policies	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Basis of presentation, principles of consolidation and significant accounting policies	Basis of presentation, principles of consolidation and significant accounting policies Basis of presentation The accompanying condensed consolidated financial statements are unaudited 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 ASC and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board (“FASB”). Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These condensed consolidated 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, 2023 and 2022. 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 consolidated financial statements should be read in conjunction with the audited consolidated financial statements as of and for the year ended December 31, 2022, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2022, filed with the Securities and Exchange Commission (the “SEC”) on March 29, 2023 (the "2022 Annual Report on Form 10-K"). Amounts reported are computed based on thousands, except percentages, per share amounts or as otherwise noted. As a result, certain totals may not sum due to rounding. The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Company views its operations and manages its business in one operating segment. Significant accounting policies The significant accounting policies used in preparation of these condensed consolidated financial statements for the three and nine months ended September 30, 2023 are consistent with those discussed in Note 2 to the consolidated financial statements included in the Company’s 2022 Annual Report on Form 10-K. Use of estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts in the financial statements and accompanying notes. Actual results could materially differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes and management must select an amount that falls within that range of reasonable estimates. This process may result in actual results differing materially from those estimated amounts used in the preparation of the financial statements. Estimates and judgments are used in the following areas, among others: future undiscounted cash flows and subsequent fair value estimates used to assess potential and measure any impairment of long-lived assets, including goodwill and intangible assets, and the measurement of right-of-use assets and lease liabilities, stock-based compensation expense, accrued expenses, income taxes, gross to net revenue reserves, inventory reserved, 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. Inventory Inventories are stated at the lower of cost or net realizable value under the first-expired, first-out ("FEFO") methodology. Given human gene therapy products are a new and novel category of therapeutics and future economic benefit is not probable until regulatory approval for the product has been obtained, the Company has only considered inventory for capitalization upon and after regulatory approval. Manufacturing costs incurred prior to regulatory approval for pre-launch inventory that did not qualify for capitalization and clinical manufacturing costs were charged to research and development expense in the Company’s consolidated statements of operations and comprehensive loss as costs were incurred. Additionally, inventory that initially qualifies for capitalization but that may ultimately be used for the production of clinical drug product is expensed as research and development expense when it has been designated for the manufacture of clinical drug product. Inventory consists of cell banks, plasmids, LVV, other materials and compounds sourced from third party suppliers and utilized in the manufacturing process, and drug product, which has been produced for the treatment of specific patients, that are owned by the Company. Management periodically reviews inventories for excess or obsolescence, considering factors such as sales forecasts compared to quantities on hand and firm purchase commitments as well as remaining shelf life of on hand inventories. The Company writes-down its inventory that is obsolete or otherwise unmarketable to its estimated net realizable value in the period in which the impairment is first identified. Any such adjustments are included as a component of cost of goods sold within cost of product revenue on the Company’s consolidated statements of operations and comprehensive loss. Revenue recognition Under ASC Topic 606, Revenue from Contracts with Customers (“Topic 606”), an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price, including variable consideration, if any; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration to which it is entitled in exchange for the goods or services it transfers to the customer. Once a contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and if so, they are considered performance obligations. The Company assesses whether each promised good or service is distinct for the purpose of identifying the performance obligations in the contract. This assessment involves subjective determinations and requires management to make judgments about the individual promised goods or services and whether such are separable from the other aspects of the contractual relationship. Promised goods and services are considered distinct provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer (that is, the good or service is capable of being distinct) and (ii) the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract (that is, the promise to transfer the good or service is distinct within the context of the contract). The transaction price is then determined and allocated to the identified performance obligations in proportion to their standalone selling prices (“SSP”) on a relative SSP basis. SSP is determined at contract inception and is not updated to reflect changes between contract inception and when the performance obligations are satisfied. If the consideration promised in a contract includes a variable amount, the Company estimates the amount of consideration to which it will be entitled in exchange for transferring the promised goods or services to a customer. The Company determines the amount of variable consideration by using the expected value method or the most likely amount method. The Company includes the unconstrained amount of estimated variable consideration in the transaction price. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. At the end of each subsequent reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis in the period of adjustment. If a license arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. The Company has assessed each of its revenue generating arrangements in order to determine whether a significant financing component exists and concluded that a significant financing component does not exist in any of its arrangements. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied, at a point in time. The Company recognizes revenue within the following financial statement captions: Product revenue, net The Company recognizes product revenue, net in accordance with Topic 606. Product revenue, net represents sales of ZYNTEGLO and SKYSONA. In 2022, the Company received approval of ZYNTEGLO and SKYSONA from the FDA. The amount of revenue recognized by the Company is equal to the amount of consideration that is expected to be received from the sale of product to its customers. The Company has Specialty Distributors ("SD") and Specialty Pharmacies ("SP") that deliver product to the Qualified Treatment Centers ("QTC"). Revenue is only recognized when the performance obligation is satisfied. The Company recognizes revenue upon infusion to the patient. To determine whether a significant reversal will occur in future periods, the Company assesses both the likelihood and magnitude of any such potential reversal of revenue. Other revenue In 2021, the Company entered into a grant agreement with the Bill and Melinda Gates Foundation. The Company recognizes grant revenue in accordance with ASC 958-605, Revenue Recognition Not-for-Profit Entities, when qualifying costs are incurred and barriers to restriction have been overcome. When grant funds are received after costs have been incurred, the Company records revenue and a corresponding grant receivable. Cash received from grants in advance of incurring qualifying costs is recorded as deferred revenue and recognized as revenue when qualifying costs are incurred. In 2023, the Company ceased further research work and is in the process of winding down such collaboration. Recent accounting pronouncements During the periods presented, the Company was not required to adopt any recently issued accounting standards. The Company does not expect any recently issued accounting standards to have a material impact on its financial statements.

Inventory - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended
Inventory - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Inventory Disclosure [Abstract]
Excess inventory reserve	$ 5,333	$ 7,519

Condensed Consolidated Statements of Stockholders' Equity (unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Accumulated deficit
Beginning balance (in shares) at Dec. 31, 2021		71,115
Beginning balance at Dec. 31, 2021	$ 374,277	$ 711	$ 4,096,402	$ (2,911)	$ (3,719,925)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		310
Vesting of restricted stock units	0	$ 3	(3)
Exercise of stock options (in shares)		1
Exercise of stock options	1		1
Stock-based compensation	12,681		12,681
Issuance of stock awards (in shares)		12
Other comprehensive income (loss)	(1,548)			(1,548)
Net income (loss)	(122,152)				(122,152)
Ending balance, shares (in shares) at Mar. 31, 2022		71,438
Ending balance at Mar. 31, 2022	263,259	$ 714	4,109,081	(4,459)	(3,842,077)
Beginning balance (in shares) at Dec. 31, 2021		71,115
Beginning balance at Dec. 31, 2021	374,277	$ 711	4,096,402	(2,911)	(3,719,925)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss)	(1,719)
Net income (loss)	(298,810)
Ending balance, shares (in shares) at Sep. 30, 2022		82,880
Ending balance at Sep. 30, 2022	158,857	$ 829	4,181,393	(4,630)	(4,018,735)
Beginning balance (in shares) at Mar. 31, 2022		71,438
Beginning balance at Mar. 31, 2022	263,259	$ 714	4,109,081	(4,459)	(3,842,077)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		60
Vesting of restricted stock units	0	$ 1	(1)
Exercise of stock options (in shares)		1
Exercise of stock options	1		1
Issuance of common stock (in shares)		2,052
Issuance of common stock	8,043	$ 20	8,023
Stock-based compensation	8,908		8,908
Other comprehensive income (loss)	43			43
Net income (loss)	(100,138)				(100,138)
Ending balance, shares (in shares) at Jun. 30, 2022		73,551
Ending balance at Jun. 30, 2022	180,116	$ 735	4,126,012	(4,416)	(3,942,215)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		572
Vesting of restricted stock units	0	$ 6	(6)
Purchase of common stock under ESPP (in shares)		67
Purchase of common stock under employee stock purchase plan (ESPP)	239	$ 1	238
Issuance of common stock (in shares)		8,690
Issuance of common stock	46,024	$ 87	45,937
Stock-based compensation	9,212		9,212
Other comprehensive income (loss)	(214)			(214)
Net income (loss)	(76,520)				(76,520)
Ending balance, shares (in shares) at Sep. 30, 2022		82,880
Ending balance at Sep. 30, 2022	$ 158,857	$ 829	4,181,393	(4,630)	(4,018,735)
Beginning balance (in shares) at Dec. 31, 2022	82,923	82,923
Beginning balance at Dec. 31, 2022	$ 196,343	$ 830	4,186,086	(4,070)	(3,986,503)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		382
Vesting of restricted stock units	(195)	$ 3	(198)
Exercise of stock options (in shares)		3
Exercise of stock options	7		7
Purchase of common stock under ESPP (in shares)		62
Purchase of common stock under employee stock purchase plan (ESPP)	227	$ 1	226
Issuance of common stock (in shares)		23,000
Issuance of common stock	130,291	$ 230	130,061
Stock-based compensation	5,843		5,843
Other comprehensive income (loss)	984			984
Net income (loss)	21,240				21,240
Ending balance, shares (in shares) at Mar. 31, 2023		106,370
Ending balance at Mar. 31, 2023	$ 354,740	$ 1,064	4,322,025	(3,086)	(3,965,263)
Beginning balance (in shares) at Dec. 31, 2022	82,923	82,923
Beginning balance at Dec. 31, 2022	$ 196,343	$ 830	4,186,086	(4,070)	(3,986,503)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	3
Other comprehensive income (loss)	$ 1,843
Net income (loss)	$ (123,399)
Ending balance, shares (in shares) at Sep. 30, 2023	107,022	107,022
Ending balance at Sep. 30, 2023	$ 222,536	$ 1,071	4,333,594	(2,227)	(4,109,902)
Beginning balance (in shares) at Mar. 31, 2023		106,370
Beginning balance at Mar. 31, 2023	354,740	$ 1,064	4,322,025	(3,086)	(3,965,263)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		65
Vesting of restricted stock units	0	$ 1	(1)
Exercise of stock options (in shares)		19
Exercise of stock options	77		77
Stock-based compensation	6,388		6,388
Other comprehensive income (loss)	722			722
Net income (loss)	(72,908)				(72,908)
Ending balance, shares (in shares) at Jun. 30, 2023		106,454
Ending balance at Jun. 30, 2023	289,019	$ 1,065	4,328,489	(2,364)	(4,038,171)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		566
Vesting of restricted stock units	0	$ 6	(6)
Exercise of stock options (in shares)		2
Exercise of stock options	8		8
Issuance of common stock (in shares)		0
Issuance of common stock	(50)	$ 0	(50)
Stock-based compensation	5,153		5,153
Other comprehensive income (loss)	137			137
Net income (loss)	$ (71,731)				(71,731)
Ending balance, shares (in shares) at Sep. 30, 2023	107,022	107,022
Ending balance at Sep. 30, 2023	$ 222,536	$ 1,071	$ 4,333,594	$ (2,227)	$ (4,109,902)

Fair value measurements

9 Months Ended

Sep. 30, 2023

Fair Value Disclosures [Abstract]

Fair value measurements

The following table sets forth the Company’s assets and liabilities that are measured at fair value on a recurring basis as of September 30, 2023 and December 31, 2022 (in thousands):


Description	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
September 30, 2023
Assets:
Cash and cash equivalents	$	165,347	$	165,347	$	—	$	—
Marketable securities:
U.S. government agency securities and treasuries	8,946		—		8,946		—
Total	$	174,293	$	165,347	$	8,946	$	—
December 31, 2022
Assets:
Cash and cash equivalents	$	113,006	$	113,006	$	—	$	—
Marketable securities:
U.S. government agency securities and treasuries	66,237		—		66,237		—
Corporate bonds	2,498		—		2,498		—
Total	$	181,741	$	113,006	$	68,735	$	—

Cash and cash equivalents

The Company considers all highly liquid securities with original final maturities of 90 days or less from the date of purchase to be cash equivalents. As of September 30, 2023 and December 31, 2022, cash and cash equivalents comprise funds in cash and money market accounts held at multiple banking and asset management institutions.

Marketable securities

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

The amortized cost of available-for-sale debt securities is adjusted for amortization of premiums and accretion of discounts to the earliest call date for premiums or to maturity for discounts. At September 30, 2023 and December 31, 2022, the balance in the Company’s accumulated other comprehensive loss was composed primarily of activity related to the Company’s available-for-sale debt securities. There were no realized losses recognized on the sale or maturity of available-for-sale debt securities during the three months ended September 30, 2023 and 2022. There were $0.1 million and no realized losses recognized on the sale or maturity of available-for-sale debt securities during the nine months ended September 30, 2023 and 2022, respectively.

Accrued interest receivable on the Company's available-for-sale debt securities totaled $0.3 million and $0.1 million as of September 30, 2023 and December 31, 2022, respectively. No accrued interest receivable was written off during the three and nine months ended September 30, 2023 or 2022.

The following table summarizes available-for-sale debt securities in a continuous unrealized loss position for less than and greater than twelve months, and for which an allowance for credit losses has not been recorded at September 30, 2023 and December 31, 2022 (in thousands):


	Less than 12 months				12 months or greater				Total
Description	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
September 30, 2023
U.S. government agency securities and treasuries	$	8,946	$	(3)	$	—	$	—	$	8,946	$	(3)
Total	$	8,946	$	(3)	$	—	$	—	$	8,946	$	(3)
December 31, 2022
U.S. government agency securities and treasuries	$	—	$	—	$	66,237	$	(1,733)	$	66,237	$	(1,733)
Corporate bonds	—		—		2,498		(26)		2,498		(26)
Total	$	—	$	—	$	68,735	$	(1,759)	$	68,735	$	(1,759)

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

- Definition

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

+ References + Details

Property, plant and equipment, net

9 Months Ended

Sep. 30, 2023

Property, Plant and Equipment [Abstract]

Property, plant and equipment, net

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


	As of September 30, 2023		As of December 31, 2022
Laboratory equipment	$	18,591	$	25,092
Computer equipment and software	2,267		1,854
Office equipment	4,646		4,348
Leasehold improvements	1,140		—
Construction-in-progress	410		—
Total property, plant and equipment	27,054		31,294
Less accumulated depreciation and amortization	(17,082)		(21,932)
Property, plant and equipment, net	$	9,972	$	9,362

Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) - $ / shares	Sep. 30, 2023	Dec. 31, 2022
Stockholders’ equity:
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	250,000,000	250,000,000
Common stock, shares issued (in shares)	107,022,000	82,923,000
Common stock, shares outstanding (in shares)	107,022,000	82,923,000

Stock-based compensation (Tables)

9 Months Ended

Sep. 30, 2023

Share-Based Payment Arrangement [Abstract]

Summary of Stock-Based Compensation Expense by Award Type

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


	For the three months ended September 30,				For the nine months ended September 30,
	2023		2022		2023		2022
Stock options	$	1,758	$	2,886	$	5,192	$	11,829
Restricted stock units	2,916		6,142		10,552		18,027
Employee stock purchase plan and other	194		184		269		653
	$	4,868	$	9,212	$	16,013	$	30,509

Schedule of Stock-Based Compensation Expense by Classification

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


	For the three months ended September 30,				For the nine months ended September 30,
	2023		2022		2023		2022
Cost of product revenue	342		—		435		—
Selling, general and administrative	2,461		3,975		7,503		13,462
Research and development	2,065		5,237		8,075		17,047
	$	4,868	$	9,212	$	16,013	$	30,509

Summary of Stock Option Activity Under Plan

The following table summarizes the stock option activity under the Company’s equity award plans and have been adjusted to reflect the effects of the November 2021 separation of our severe genetic disease and oncology programs into two separate, publicly traded companies:


	Shares (in thousands)	Weighted- average exercise price per share
Outstanding at December 31, 2022	2,668	$	24.38
Granted	2,015	$	4.95
Exercised	(3)	$	2.74
Canceled, forfeited, or expired	(453)	$	31.39
Outstanding at September 30, 2023	4,227	$	14.35
Exercisable at September 30, 2023	1,347	$	30.52
Vested and expected to vest at September 30, 2023	4,227	$	14.35

Summary of Restricted Common Stock Awards

The following table summarizes the restricted stock unit activity under the Company’s equity award plans and have been adjusted to reflect the effects of the November 2021 separation of our severe genetic disease and oncology programs into two separate, publicly traded companies:


	Shares (in thousands)	Weighted- average grant date fair value
Unvested at December 31, 2022	2,415	$	11.44
Granted	3,117	$	4.90
Vested	(987)	$	14.71
Forfeited	(395)	$	8.50
Unvested at September 30, 2023	4,150	$	6.33

Basis of presentation, principles of consolidation and significant accounting policies (Detail)	9 Months Ended
	Sep. 30, 2023 segment
Accounting Policies [Abstract]
Number of operating segments	1

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities:
Net income (loss)	$ (123,399)	$ (298,810)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Depreciation and amortization	3,124	3,745
Stock-based compensation expense	16,013	30,509
Gain from sale of priority review voucher	(92,930)	0
Loss (gain) on equity securities	0	3,135
Excess inventory reserve	5,333	7,519
Other non-cash items	19	2,890
Changes in operating assets and liabilities:
Accounts receivable	(23,000)	0
Prepaid expenses and other assets	(523)	(6,197)
Inventory	(24,931)	0
Operating lease right-of-use assets	40,101	29,650
Accounts payable	(5,787)	(7,552)
Accrued expenses and other liabilities	7,125	(39,046)
Operating lease liabilities	(30,506)	(22,523)
Deferred revenue	8,152	0
Net cash used in operating activities	(221,209)	(296,680)
Cash flows from investing activities:
Purchase of property, plant and equipment	(2,975)	(8,100)
Purchases of marketable securities	(43,297)	0
Proceeds from maturities of marketable securities	99,521	125,095
Proceeds from sales of marketable securities	5,853	30,216
Purchase of intangible assets	(868)	0
Proceeds from sale of priority review voucher	92,930	0
Net cash provided by investing activities	151,164	147,211
Cash flows from financing activities:
Proceeds from exercise of stock options and ESPP contributions	93	3
Net cash provided by financing activities	129,969	54,368
(Decrease) increase in cash, cash equivalents and restricted cash	59,924	(95,101)
Cash, cash equivalents and restricted cash at beginning of period	158,445	206,693
Cash, cash equivalents and restricted cash at end of period	218,369	111,592
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	165,347	66,478
Restricted cash included in other current assets	8,885	1,565
Restricted cash included in restricted cash and other non-current assets	44,137	43,549
Total cash, cash equivalents and restricted cash	218,369	111,592
Supplemental cash flow disclosures from investing and financing activities:
Purchases of property, plant and equipment included in accounts payable and accrued expenses	941	176
Offering expenses accrued or in accounts payable	248	298
Right-of-use assets obtained in exchange for operating lease liabilities	44,819	229,636
Increase (Reduction) of right of use asset and associated lease liability due to lease reassessment	8,003	(2,833)
Cash paid during the period for income taxes	5	0
Private Placement
Cash flows from financing activities:
Proceeds from issuance of common stock	(196)	0
Public Offering
Cash flows from financing activities:
Proceeds from issuance of common stock	$ 130,072	$ 54,365

Commitments and contingencies	9 Months Ended
Commitments and contingencies	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	Commitments and contingencies Other funding commitments The Company is party to various agreements, principally relating to licensed technology, that require future payments relating to milestones that may be met in subsequent periods or royalties on future sales of specified products. The Company may be obligated to make future development, regulatory, and commercial milestone payments, and royalty payments on future sales of specified products associated with its collaboration and license agreements. Payments under these agreements generally become due and payable upon achievement of such milestones or sales. When the achievement of these milestones or sales have occurred, the corresponding amounts are recognized in the Company’s financial statements. Additionally, the Company is party to various contracts with contract research organizations and contract manufacturers that generally provide for termination on notice, with the exact amounts in the event of termination to be based on the timing of the termination and the terms of the agreement. As compared to the contractual obligations and commitments as disclosed in the Company's 2022 Annual Report on Form 10-K, the Company's future minimum purchase commitments as of the nine months ended September 30, 2023 decreased by $0.6 million. The Company is, and may become, party to various claims and complaints arising in the ordinary course of business, including securities class action and intellectual property litigation. The Company enters into standard indemnification agreements in the ordinary course of business. Pursuant to the agreements, the Company indemnifies, holds harmless, and agrees to reimburse the indemnified party for losses suffered or incurred by the indemnified party, generally the Company’s business partners. The term of these indemnification agreements is generally perpetual any time after execution of the agreement. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is generally unlimited. Management does not believe that any ultimate liability resulting from any of these claims will have a material adverse effect on its results of operations, financial position, or liquidity. However, management cannot give any assurance regarding the ultimate outcome of any claims, and their resolution could be material to operating results for any particular period. The Company also indemnifies each of its officers and directors for certain events or occurrences, subject to certain limits, while the officer or director is or was serving at the Company's request in such capacity, as permitted under Delaware law and in accordance with its certificate of incorporation and by-laws. The term of the indemnification period lasts as long as such officer or director may be subject to any proceeding arising out of acts or omissions of such officer or director in such capacity. The maximum amount of potential future indemnification is unlimited; however, the Company currently holds director and officer liability insurance. This insurance allows the transfer of risk associated with the Company's exposure and may enable it to recover a portion of any future amounts paid. The Company believes that the fair value of these indemnification obligations is minimal. Accordingly, it has not recognized any liabilities relating to these obligations.

Net loss per share (Tables)

9 Months Ended

Sep. 30, 2023

Earnings Per Share [Abstract]

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

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


	For the three months ended September 30,
	2023	2022
Outstanding stock options	5,875	4,548
Restricted stock units	4,194	2,473
ESPP shares and other	—	67
	10,069	7,088

Marketable securities (Detail) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Amortized cost / Cost
Marketable securities	$ 8,949,000	$ 70,494,000
Unrealized gains
Marketable securities	0	0
Unrealized losses
Marketable securities	(3,000)	(1,759,000)
Fair value
Marketable securities	8,946,000	68,735,000
Debt securities, available-for-sale, noncurrent	0	0
U.S. government agency securities and treasuries
Amortized cost / Cost
Debt securities	8,949,000	67,970,000
Unrealized gains
Debt securities	0	0
Unrealized losses
Debt securities	(3,000)	(1,733,000)
Fair value
Debt securities	$ 8,946,000	66,237,000
Corporate bonds
Amortized cost / Cost
Debt securities		2,524,000
Unrealized gains
Debt securities		0
Unrealized losses
Debt securities		(26,000)
Fair value
Debt securities		$ 2,498,000

Cover Page - shares	9 Months Ended
Cover Page - shares	Sep. 30, 2023	Nov. 03, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Transition Report	false
Entity File Number	001-35966
Entity Registrant Name	bluebird bio, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	13-3680878
Entity Address, Address Line One	455 Grand Union Boulevard
Entity Address, City or Town	Somerville
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02145
City Area Code	339
Local Phone Number	499-9300
Title of 12(b) Security	Common Stock, $0.01 par value per share
Trading Symbol	BLUE
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		109,336,211
Amendment Flag	false
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001293971
Current Fiscal Year End Date	--12-31

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Pay vs Performance Disclosure
Net income (loss)	$ (71,731)	$ (72,908)	$ 21,240	$ (76,520)	$ (100,138)	$ (122,152)	$ (123,399)	$ (298,810)

- Definition

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

+ References

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

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481687/323-10-50-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-28

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482765/220-10-50-6

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-3

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

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

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

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

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

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-4

Reference 13: http://www.xbrl.org/2003/role/exampleRef
-Topic 946
-SubTopic 830
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480167/946-830-55-10

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section 45
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483581/946-220-45-7

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(18))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(9))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-09(1)(d))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-3

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(i))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 20: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(ii))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iii)(A))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

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

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(5))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(i))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iii)(A))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 26: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iii)(B))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

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

Reference 28: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(5))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 29: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 30
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-30

Reference 30: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 31: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 60B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-60B

Reference 32: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 31
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-31

Reference 33: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 34: http://www.xbrl.org/2003/role/disclosureRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483499/205-20-50-7

Reference 35: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

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

Reference 37: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-1B

Reference 38: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(20))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

Reference 39: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(22))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1

+ Details

Inventory (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Inventory Disclosure [Abstract]
Raw materials	$ 7,392	$ 0
Work in progress	9,725	0
Finished goods	3,852	0
Inventory	$ 20,969	$ 0

Equity	9 Months Ended
Equity	Sep. 30, 2023
Equity [Abstract]
Equity	EquityOn January 18, 2023, the Company entered into an underwriting agreement (the “Underwriting Agreement”) with Goldman Sachs & Co. LLC and J.P. Morgan Securities LLC in connection with the public offering, issuance and sale by the Company of 20.0 million shares of the Company’s common stock, $0.01 par value per share, at a public offering price of $6.00 per share, less underwriting discounts and commissions. Under the terms of the Underwriting Agreement, the Company also granted the underwriters an option exercisable for 30 days to purchase up to an additional 3.0 million shares of Common Stock at the public offering price, less underwriting discounts and commissions, which the underwriters exercised in full. The offering closed on January 23, 2023.For the nine months ended September 30, 2023, the Company sold 23.0 million shares of common stock for gross proceeds of $138.0 million ($130.5 million net of offering costs), pursuant to the Underwriting Agreement.

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

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

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

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481004/946-505-50-6

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

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

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

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

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

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

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

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

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

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

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

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

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

+ Details

Income taxes	9 Months Ended
Income taxes	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Income taxes	Income taxes Deferred tax assets and deferred tax liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using statutory rates. 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 tax benefit recognized during the three and nine months ended September 30, 2023 was $0.0 million and $0.1 million, respectively, due to the wind down of our operations in Europe and the full valuation allowance. On August 16, 2022, the Inflation Reduction Act (“IRA”) was enacted and introduced a 15% corporate alternative minimum tax ("CAMT"), effective for tax years beginning after December 31, 2022, for corporations with average annual adjusted financial statement income for any consecutive three-year tax period ending after December 31, 2021 and preceding the tax year that exceeds $1 billion, as well as a 1% excise tax on stock repurchases made by public companies. The Company has concluded that the provisions in the IRA have an immaterial impact on the Company’s income tax expense due to its cumulative losses and full valuation allowance position.

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

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

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

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

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

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

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

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

+ Details

Description of the business (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended						6 Months Ended	9 Months Ended
	Oct. 30, 2023	Oct. 18, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Subsidiary, Sale of Stock [Line Items]
Gain from sale of priority review voucher, net			$ 0		$ 92,900	$ 0				$ 92,930	$ 0
Proceeds from sale of priority review voucher										$ 92,930	0
Shares of common stock sold (in shares)										23,000,000
Offering costs										$ 130,500
Cash, cash equivalents and marketable securities			174,300							174,300
Accumulated deficit			4,109,902							4,109,902		$ 3,986,503
Net income (loss)			$ (71,731)	$ (72,908)	$ 21,240	$ (76,520)	$ (100,138)	$ (122,152)		(123,399)	(298,810)
Net cash used in operating activities										$ 221,209	$ 296,680
Subsequent Event
Subsidiary, Sale of Stock [Line Items]
Shares of common stock sold (in shares)		2,264,916
Third Priority Review Voucher \| Subsequent Event
Subsidiary, Sale of Stock [Line Items]
Proceeds from sale of priority review voucher	$ 103,000
Public Stock Offering
Subsidiary, Sale of Stock [Line Items]
Shares of common stock sold (in shares)					23,000,000
Common stock price per share (in dollars per share)					$ 6.00
Proceeds from stock offering					$ 130,500
April 2022 Reduction
Subsidiary, Sale of Stock [Line Items]
Plans to reduce workforce, as a percent									30.00%

Marketable securities (Tables)

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Summary of Marketable Securities Held

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


Description	Amortized cost / Cost		Unrealized gains		Unrealized losses		Fair value
September 30, 2023
U.S. government agency securities and treasuries	8,949		—		(3)		8,946
Total	$	8,949	$	—	$	(3)	$	8,946
December 31, 2022
U.S. government agency securities and treasuries	$	67,970	$	—	$	(1,733)	$	66,237
Corporate bonds	2,524		—		(26)		2,498
Total	$	70,494	$	—	$	(1,759)	$	68,735

Fair value measurements (Tables)

9 Months Ended

Sep. 30, 2023

Fair Value Disclosures [Abstract]

Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis

The following table sets forth the Company’s assets and liabilities that are measured at fair value on a recurring basis as of September 30, 2023 and December 31, 2022 (in thousands):


Description	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
September 30, 2023
Assets:
Cash and cash equivalents	$	165,347	$	165,347	$	—	$	—
Marketable securities:
U.S. government agency securities and treasuries	8,946		—		8,946		—
Total	$	174,293	$	165,347	$	8,946	$	—
December 31, 2022
Assets:
Cash and cash equivalents	$	113,006	$	113,006	$	—	$	—
Marketable securities:
U.S. government agency securities and treasuries	66,237		—		66,237		—
Corporate bonds	2,498		—		2,498		—
Total	$	181,741	$	113,006	$	68,735	$	—

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


	Less than 12 months				12 months or greater				Total
Description	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
September 30, 2023
U.S. government agency securities and treasuries	$	8,946	$	(3)	$	—	$	—	$	8,946	$	(3)
Total	$	8,946	$	(3)	$	—	$	—	$	8,946	$	(3)
December 31, 2022
U.S. government agency securities and treasuries	$	—	$	—	$	66,237	$	(1,733)	$	66,237	$	(1,733)
Corporate bonds	—		—		2,498		(26)		2,498		(26)
Total	$	—	$	—	$	68,735	$	(1,759)	$	68,735	$	(1,759)

Leases	9 Months Ended
Leases	Sep. 30, 2023
Leases [Abstract]
Leases	Leases The Company leases certain office and laboratory space, primarily located in Somerville, Massachusetts. Additionally, the Company has embedded leases through its agreements with contract manufacturing organizations in both the United States and internationally. Except as described below, there have been no material changes in lease obligations from those disclosed in Note 8 to the consolidated financial statements included in the Company's 2022 Annual Report on Form 10-K. 60 Binney Street lease & sublease In August 2023, the Company completed the construction of its new office and laboratory space and terminated the 60 Binney Street sublease. On the termination date the remaining right-of-use asset and lease liability were removed. Embedded operating leases In September 2023, the Company entered into a second amendment to the June 2016 commercial manufacturing agreement with Lonza Houston, Inc. to manufacture gene therapies ZYNTEGLO and SKYSONA. Pursuant to the amendment, both parties agreed to increased manufacturing capacity, a revised fee schedule and modified payment terms on invoices. The revised fee schedule replaced the fixed suite fee with manufacturing slot fees. The amended contract terms continue to provide exclusive use during the term of the agreement and the classification of the lease remained accounted for as an operating lease. The Company determined that the amendment should be accounted for as a lease modification applicable under ASC 842, not as a separate contract. For contract manufacturing arrangements, the Company has elected to account for lease and non-lease components separately. At the effective date of modification, the Company recorded an increase to the right-of-use asset and lease liability in the amount of $6.5 million. In connection with the modified payment terms, the Company is required to post a letter of credit in the amount of $6.9 million for the benefit of the manufacturer, subject to gradual decreases upon payment of invoices. The letter of credit has been secured by cash and is presented as restricted cash and other current assets. In December 2022, the Company entered into an agreement reserving manufacturing capacity with a contract manufacturing organization. The Company concluded that this agreement contains an embedded operating lease as the Company is using the entire capacity of a manufacturing suite at the facility. Under the terms of the agreement, the Company will be required to pay suite fees of $13.5 million in 2023 and $18.0 million per year in 2024 and 2025, in addition to the cost of any services provided. The term of the agreement is three years. The Company recorded a right-of-use asset and lease liability for this operating lease upon lease commencement in April 2023 and is recognizing rent expense on a straight-line basis throughout the remaining term of the embedded lease.

Description of the business	9 Months Ended
Description of the business	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of the business	Description of the business bluebird bio, Inc. (the “Company” or “bluebird”) was incorporated in Delaware on April 16, 1992, and is headquartered in Somerville, Massachusetts. The Company is a biotechnology company committed to researching, developing, and commercializing potentially curative transformative gene therapies for severe genetic diseases based on our lentiviral vector (“LVV”) gene addition platform. In 2022, following more than a decade of leadership in research and clinical development, the Company received approval from the U.S. Food and Drug Administration (the “FDA”) for two gene therapies, both of which were recently launched. On August 17, 2022, ZYNTEGLO (betibeglogene autotemcel, also known as beti-cel), was approved by the FDA for the treatment of adult and pediatric patients with ß-thalassemia who require regular red blood cell transfusions. On September 16, 2022, the FDA granted Accelerated Approval of SKYSONA (elivaldogene autotemcel, also known as eli-cel), to slow the progression of neurologic dysfunction in boys 4-17 years of age with early active cerebral adrenoleukodystrophy (“CALD”). On June 21, 2023, the Company announced that the FDA had accepted for priority review the Company's biologics licensing application (“BLA”) for its third gene therapy candidate (lovotibeglogene autotemcel, also known as lovo-cel) which was submitted with a proposed indication for the treatment of patients 12 and older with sickle cell disease (“SCD”) with a history of vaso-occlusive-events. The FDA set a Prescription Drug User Fee Act (PDUFA) goal date for lovo-cel of December 20, 2023 and if approved, the Company anticipates commercial launch in early 2024. The Company is focusing its development and commercialization efforts in the U.S. market. The Company has obtained the withdrawal of the marketing authorization for beti-cel in the European Union, which became effective on March 24, 2022. On November 18, 2021, the Company obtained the withdrawal of the marketing authorization for eli-cel in the European Union. The Company withdrew its marketing applications for beti-cel and eli-cel from the MHRA in the United Kingdom. The Company is continuing the long-term follow-up of patients previously enrolled within the clinical trial programs in Europe as planned but do not intend to initiate any new clinical trials in Europe for β-thalassemia, CALD or SCD. Since its inception in 1992, the Company has devoted substantially all of its resources to its development and commercialization efforts relating to its products and product candidates, including activities to manufacture product candidates in compliance with good manufacturing practices ("GMP") to conduct clinical studies of its product candidates, to provide selling, general and administrative support for these operations, to market, commercially manufacture and distribute its approved products and to protect its intellectual property. The Company has not generated material revenue from product sales. The Company has funded its operations primarily through the sale of common stock in its public offerings, private placements of preferred stock and warrants, the sale of two Rare Pediatric Disease Priority Review Vouchers ("PRVs") and through collaborations. In August 2022 and September 2022 the Company received the two PRVs under an FDA program intended to encourage the development of treatments for rare pediatric diseases. In the first quarter of 2023, the Company sold its second PRV for aggregate net proceeds of $92.9 million. In October 2023, the Company entered into an advance agreement to sell a third PRV, if granted in connection with the potential approval of lovo-cel, for $103.0 million. In the first quarter of 2023, the Company sold 23.0 million shares of common stock (inclusive of shares sold pursuant to an option to the underwriters in connection with the offering) through an underwritten public offering at a price of $6.00 per share for aggregate net proceeds of $130.5 million. In April 2022, the board of directors of the Company (the "Board of Directors") approved a comprehensive restructuring plan intended to reduce operating expenses and enhance the Company’s focus on achieving FDA approval for its programs in the U.S. As part of the restructuring, the Company reduced its workforce by approximately 30% across the second and third quarters of 2022. Refer to Note 14, Restructuring, for more information on this restructuring. In accordance with Accounting Standards Codification (“ASC”) 205-40, Going Concern, the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that these consolidated financial statements are issued. As of September 30, 2023, the Company had an accumulated deficit of $4.11 billion. During the nine months ended September 30, 2023, the Company had a net loss of $123.4 million and used $221.2 million of cash in operations. As of September 30, 2023, the Company had cash, cash equivalents and marketable securities of $174.3 million. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the Company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that these consolidated financial statements are issued. In performing its analysis, management excluded certain elements of its operating plan that cannot be considered probable. Under ASC 205-40, the future receipt of potential funding from future equity or debt issuances and the release of restricted cash related to the Company’s 50 Binney Street sublease cannot be considered probable at this time because these plans are not entirely within the Company’s control nor have been approved by the Board of Directors as of the date of these condensed consolidated financial statements. The Company's expectation to generate operating losses and negative operating cash flows in the future and the need for additional funding to support its planned operations raise substantial doubt regarding the Company’s ability to continue as a going concern for a period of one year after the date that these consolidated financial statements are issued. Management's plans to alleviate the conditions that raise substantial doubt include evaluating 2023 spending and the pursuit of additional cash resources through public or private equity or debt financings. Management has concluded the likelihood that its plan to successfully obtain sufficient funding from one or more of these sources, or adequately reduce expenditures, while reasonably possible, is less than probable. Accordingly, the Company has concluded that substantial doubt exists about the Company’s ability to continue as a going concern for a period of at least 12 months from the date of issuance of these consolidated financial statements. The Company will assess on a quarterly basis whether the determination for estimates remain appropriate based on actual data observed. However, the Company has based this estimate on assumptions that may prove to be wrong, and its operating plan may change as a result of many factors currently unknown to it. As a result, the Company could deplete its capital resources sooner than it currently expects. The Company expects to finance its future cash needs through the issuance of equity, or debt, or other alternative means. If the Company is unable to obtain funding on a timely basis, or if revenues from collaboration arrangements or product sales are less than it has projected, the Company may be required to further revise its business plan and strategy, which may result in the Company significantly curtailing, delaying or discontinuing one or more of its research or development programs or the commercialization of any product candidates or may result in the Company being unable to expand its operations or otherwise capitalize on its business opportunities. As a result, the Company's business, financial condition and results of operations could be materially affected. The accompanying financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of the uncertainties described above.

Net loss per share - Anti-dilutive shares (Detail) - shares shares in Thousands	3 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	10,069	7,088
Outstanding stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	5,875	4,548
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	4,194	2,473
ESPP shares and other
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	0	67

Commitments and contingencies (Details) $ in Millions	Sep. 30, 2023 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Decrease in purchase commitments	$ 0.6

Property, plant and equipment, net - Summary of Property, Plant and Equipment Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 27,054	$ 31,294
Less accumulated depreciation and amortization	(17,082)	(21,932)
Property, plant and equipment, net	9,972	9,362
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	18,591	25,092
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	2,267	1,854
Office equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	4,646	4,348
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	1,140	0
Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 410	$ 0

Stock-based compensation - Summary of Stock Option Activity Under Plan (Detail) - $ / shares shares in Thousands	9 Months Ended
	Sep. 30, 2023
Shares (in thousands)
Outstanding at beginning of period (in shares)	2,668
Granted (in shares)	2,015
Exercised (in shares)	(3)
Canceled, forfeited, or expired (in shares)	(453)
Outstanding at end of period (in shares)	4,227
Exercisable at end of period (in shares)	1,347
Vested and expected to vest at end of period (in shares)	4,227
Weighted- average exercise price per share
Outstanding at beginning of period (in dollars per share)	$ 24.38
Granted (in dollars per share)	4.95
Exercised (in dollars per share)	2.74
Canceled, forfeited, or expired (in dollars per share)	31.39
Outstanding at end of period (in dollars per share)	14.35
Exercisable at end of period (in dollars per share)	30.52
Vested and expected to vest at end of period (in dollars per share)	$ 14.35

Stock-based compensation - Summary of Restricted Stock Units (Detail) - Restricted stock units shares in Thousands	9 Months Ended
	Sep. 30, 2023 $ / shares shares
Shares (in thousands)
Unvested balance at beginning of period (in shares) \| shares	2,415
Granted (in shares) \| shares	3,117
Vested (in shares) \| shares	(987)
Forfeited (in shares) \| shares	(395)
Unvested balance at end of period (in shares) \| shares	4,150
Weighted- average grant date fair value
Unvested balance at beginning of period (in dollars per share) \| $ / shares	$ 11.44
Granted (in dollars per share) \| $ / shares	4.90
Vested (in dollars per share) \| $ / shares	14.71
Forfeited (in dollars per share) \| $ / shares	8.50
Unvested balance at end of period (in dollars per share) \| $ / shares	$ 6.33

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 165,347	$ 113,006
Marketable securities	8,946	67,321
Accounts receivable	23,000	0
Prepaid expenses	11,431	8,374
Inventory	20,969	0
Other current assets	17,383	10,787
Total current assets	247,076	199,488
Marketable securities	0	1,414
Property, plant and equipment, net	9,972	9,362
Goodwill	5,646	5,646
Intangible assets	5,368	4,868
Operating lease right-of-use assets	294,717	281,996
Restricted cash and other non-current assets	50,829	52,128
Total assets	613,608	554,902
Current liabilities:
Accounts payable	19,852	25,092
Deferred revenue	9,653	1,502
Accrued expenses and other current liabilities	57,768	50,483
Operating lease liability, current portion	71,684	51,160
Total current liabilities	158,957	128,237
Operating lease liability, net of current portion	232,023	230,230
Other non-current liabilities	92	92
Total liabilities	391,072	358,559
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock, $0.01 par value, 5,000 shares authorized; 0 shares issued and outstanding at September 30, 2023 and December 31, 2022	0	0
Common stock, $0.01 par value, 250,000 shares authorized; 107,022 and 82,923 shares issued and outstanding at September 30, 2023 and December 31, 2022, respectively	1,071	830
Additional paid-in capital	4,333,594	4,186,086
Accumulated other comprehensive loss	(2,227)	(4,070)
Accumulated deficit	(4,109,902)	(3,986,503)
Total stockholders’ equity	222,536	196,343
Total liabilities and stockholders’ equity	$ 613,608	$ 554,902

Leases - Narrative (Details) - Manufacturing Facility - USD ($) $ in Millions	1 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Lessee, Lease, Description [Line Items]
Increase (decrease) in operating lease liability	$ 6.5
Lease period		3 years
Letter of Credit \| Line of Credit
Lessee, Lease, Description [Line Items]
Line of credit	$ 6.9
Manufacturing Facility Lease, Year One
Lessee, Lease, Description [Line Items]
Annual expense		$ 13.5
Manufacturing Facility Lease, Years Two And Three
Lessee, Lease, Description [Line Items]
Annual expense		$ 18.0

Restructuring	9 Months Ended
Restructuring	Sep. 30, 2023
Restructuring and Related Activities [Abstract]
Restructuring	RestructuringIn April 2022, the Board of Directors approved a comprehensive restructuring plan intended to reduce operating expenses. As part of the restructuring, the Company reduced its workforce by nearly 30% across the second and third quarters of 2022. The Company incurred approximately $4.9 million in costs to implement the restructuring, comprised primarily of severance payments and continuing health care coverage over the severance period. The restructuring actions associated with these charges commenced in April 2022, and were completed by September 30, 2022.

Condensed Consolidated Statements of Operations and Comprehensive Loss (unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Statement [Abstract]
Other comprehensive income (loss), tax	$ 0.0	$ 0.0	$ 0.0	$ 0.0

- Definition

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

+ References

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

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

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

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

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

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

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

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

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

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

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

+ Details

Net loss per share

9 Months Ended

Sep. 30, 2023

Earnings Per Share [Abstract]

Net loss per share


	For the three months ended September 30,
	2023	2022
Outstanding stock options	5,875	4,548
Restricted stock units	4,194	2,473
ESPP shares and other	—	67
	10,069	7,088

Income taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Income taxes (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 0	$ (7)	$ 80	$ (7)

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Subsequent events	9 Months Ended
Subsequent events	Sep. 30, 2023
Subsequent Events [Abstract]
Subsequent events	Subsequent events Pre-funded warrants On October 18, 2023, the Company received exercise notifications for all pre-funded warrants issued in September 2021. The exercises were done as a cashless exercise and resulted in the issuance of 2,264,916 common shares. Sale of priority review voucher On October 30, 2023, the Company announced that it had entered into an advance agreement to sell a third PRV, if granted, in connection with the potential approval of lovo-cel, for $103.0 million. Closing of the transaction remains subject to the approval of lovo-cel and receipt of a PRV, as well as customary closing conditions.

Accrued expenses and other current liabilities (Tables)

9 Months Ended

Sep. 30, 2023

Payables and Accruals [Abstract]

Summary of Accrued Expenses and Other Current Liabilities

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


	As of September 30, 2023		As of December 31, 2022
Accrued manufacturing costs	$	6,183	$	7,199
Accrued goods and services	7,709		8,134
Accrued clinical and contract research organization costs	13,689		12,368
Accrued employee compensation	19,442		20,095
Accrued professional fees	2,748		1,939
Other	7,997		748
Total accrued expenses and other current liabilities	$	57,768	$	50,483

Stock-based compensation

9 Months Ended

Sep. 30, 2023

Share-Based Payment Arrangement [Abstract]

Stock-based compensation

In January 2023 and 2022, the number of shares of common stock available for issuance under the 2013 Stock Option and Incentive Plan (“2013 Plan”) was increased by approximately 3.3 million and 2.8 million shares, respectively, as a result of the automatic increase provision of the 2013 Plan. On June 16, 2023, the Company’s stockholders approved the 2023 Incentive Award Plan (the “2023 Plan”), which replaced the 2013 Plan. Following approval of the 2023 Plan, no further awards will be granted under the 2013 Plan. As of September 30, 2023, the total number of shares of common stock available for issuance under the 2023 Plan was approximately 4.8 million.

Stock-based compensation expense

The Company recognized stock-based compensation expense totaling $4.9 million and $9.2 million during the three months ended September 30, 2023 and 2022, respectively. The Company recognized stock-based compensation expense totaling $16.0 million and $30.5 million for the nine months ended September 30, 2023 and 2022, respectively. Stock-based compensation expense recognized by award type is included within the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands):


	For the three months ended September 30,				For the nine months ended September 30,
	2023		2022		2023		2022
Stock options	$	1,758	$	2,886	$	5,192	$	11,829
Restricted stock units	2,916		6,142		10,552		18,027
Employee stock purchase plan and other	194		184		269		653
	$	4,868	$	9,212	$	16,013	$	30,509

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


	For the three months ended September 30,				For the nine months ended September 30,
	2023		2022		2023		2022
Cost of product revenue	342		—		435		—
Selling, general and administrative	2,461		3,975		7,503		13,462
Research and development	2,065		5,237		8,075		17,047
	$	4,868	$	9,212	$	16,013	$	30,509

During the nine months ended September 30, 2023, the Company had $1.4 million of stock compensation expense that was capitalized into inventory.

Stock options


	Shares (in thousands)	Weighted- average exercise price per share
Outstanding at December 31, 2022	2,668	$	24.38
Granted	2,015	$	4.95
Exercised	(3)	$	2.74
Canceled, forfeited, or expired	(453)	$	31.39
Outstanding at September 30, 2023	4,227	$	14.35
Exercisable at September 30, 2023	1,347	$	30.52
Vested and expected to vest at September 30, 2023	4,227	$	14.35

During the nine months ended September 30, 2023, less than 0.1 million stock options were exercised, resulting in total proceeds to the Company of less than $0.1 million.

Restricted stock units


	Shares (in thousands)	Weighted- average grant date fair value
Unvested at December 31, 2022	2,415	$	11.44
Granted	3,117	$	4.90
Vested	(987)	$	14.71
Forfeited	(395)	$	8.50
Unvested at September 30, 2023	4,150	$	6.33

Employee stock purchase plan

In June 2013, the Company adopted its 2013 Employee Stock Purchase Plan (“2013 ESPP”), which authorized the initial issuance of up to a total of 0.2 million shares of the Company’s common stock to participating employees. In June 2021, the Company amended the 2013 ESPP to authorize an additional 1.4 million shares of the Company’s common stock available to participating employees. During each of the nine months ended September 30, 2023 and 2022, less than 0.1 million shares and less than 0.1 million shares, respectively, of common stock were issued under the 2013 ESPP.

Inventory (Tables)

9 Months Ended

Sep. 30, 2023

Inventory Disclosure [Abstract]

Schedule of Inventory, Current

Inventory, net, consists of the following (in thousands):


	As of September 30, 2023		As of December 31, 2022
Raw materials	$	7,392	$	—
Work in progress	9,725		—
Finished goods	3,852		—
Inventory	$	20,969	$	—

Stock-based compensation - Narrative (Detail) - USD ($) shares in Thousands, $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
	Jan. 31, 2023	Jan. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2021	Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increased number of issuance of awards under the 2013 Plan (in shares)	3,300	2,800
Number of shares available for issuance (in shares)			4,800		4,800
Stock-based compensation expense			$ 4,868	$ 9,212	$ 16,013	$ 30,509
Amount capitalized					$ 1,400
Stock option share exercised (in shares)					3
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option share exercised (in shares)					100
Proceeds from exercise of stock options and ESPP contributions					$ 100
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			1,758	2,886	5,192	11,829
Employee stock purchase plan and other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 194	$ 184	$ 269	$ 653
Common shares reserved for future issuance (in shares)								200
Increase in shares authorized (in shares)							1,400
Employee stock purchase plan and other \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock issued under plan (in shares)					100	100

Property, plant and equipment, net (Tables)

9 Months Ended

Sep. 30, 2023

Property, Plant and Equipment [Abstract]

Summary of Property, Plant and Equipment Net

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


	As of September 30, 2023		As of December 31, 2022
Laboratory equipment	$	18,591	$	25,092
Computer equipment and software	2,267		1,854
Office equipment	4,646		4,348
Leasehold improvements	1,140		—
Construction-in-progress	410		—
Total property, plant and equipment	27,054		31,294
Less accumulated depreciation and amortization	(17,082)		(21,932)
Property, plant and equipment, net	$	9,972	$	9,362

Subsequent Events (Details) - USD ($) $ in Thousands			9 Months Ended
Subsequent Events (Details) - USD ($) $ in Thousands	Oct. 30, 2023	Oct. 18, 2023	Sep. 30, 2023	Sep. 30, 2022
Subsequent Event [Line Items]
Shares of common stock sold (in shares)			23,000,000
Proceeds from sale of priority review voucher			$ 92,930	$ 0
Subsequent Event
Subsequent Event [Line Items]
Shares of common stock sold (in shares)		2,264,916
Subsequent Event \| Third Priority Review Voucher
Subsequent Event [Line Items]
Proceeds from sale of priority review voucher	$ 103,000

Fair value measurements - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Realized gain (loss) on available-for-sale securities	$ 0.0	$ 0.0	$ (0.1)	$ 0.0
Interest receivable	0.3		0.3		$ 0.1
Interest receivable, write-offs	$ 0.0	$ 0.0	$ 0.0	$ 0.0

Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		9 Months Ended
	Jan. 18, 2023	Sep. 30, 2023	Dec. 31, 2022
Equity [Abstract]
Issuance of common stock (in shares)	20.0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01
Shares issued, price per share (in dollars per share)	$ 6.00
Option to purchase additional shares, exercise period	30 days
Option to purchase additional shares (in shares)	3.0
Shares of common stock sold (in shares)		23.0
Gross proceeds		$ 138.0
Offering costs		$ 130.5

Basis of presentation, principles of consolidation and significant accounting policies (Policies)	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Basis of presentation	Basis of presentation The accompanying condensed consolidated financial statements are unaudited 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 ASC and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board (“FASB”). Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These condensed consolidated 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, 2023 and 2022.
Consolidation	The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Company views its operations and manages its business in one operating segment.
Use of estimates	Use of estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts in the financial statements and accompanying notes. Actual results could materially differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes and management must select an amount that falls within that range of reasonable estimates. This process may result in actual results differing materially from those estimated amounts used in the preparation of the financial statements. Estimates and judgments are used in the following areas, among others: future undiscounted cash flows and subsequent fair value estimates used to assess potential and measure any impairment of long-lived assets, including goodwill and intangible assets, and the measurement of right-of-use assets and lease liabilities, stock-based compensation expense, accrued expenses, income taxes, gross to net revenue reserves, inventory reserved, 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.
Inventory	Inventory Inventories are stated at the lower of cost or net realizable value under the first-expired, first-out ("FEFO") methodology. Given human gene therapy products are a new and novel category of therapeutics and future economic benefit is not probable until regulatory approval for the product has been obtained, the Company has only considered inventory for capitalization upon and after regulatory approval. Manufacturing costs incurred prior to regulatory approval for pre-launch inventory that did not qualify for capitalization and clinical manufacturing costs were charged to research and development expense in the Company’s consolidated statements of operations and comprehensive loss as costs were incurred. Additionally, inventory that initially qualifies for capitalization but that may ultimately be used for the production of clinical drug product is expensed as research and development expense when it has been designated for the manufacture of clinical drug product. Inventory consists of cell banks, plasmids, LVV, other materials and compounds sourced from third party suppliers and utilized in the manufacturing process, and drug product, which has been produced for the treatment of specific patients, that are owned by the Company. Management periodically reviews inventories for excess or obsolescence, considering factors such as sales forecasts compared to quantities on hand and firm purchase commitments as well as remaining shelf life of on hand inventories. The Company writes-down its inventory that is obsolete or otherwise unmarketable to its estimated net realizable value in the period in which the impairment is first identified. Any such adjustments are included as a component of cost of goods sold within cost of product revenue on the Company’s consolidated statements of operations and comprehensive loss.
Revenue recognition	Revenue recognition Under ASC Topic 606, Revenue from Contracts with Customers (“Topic 606”), an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price, including variable consideration, if any; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration to which it is entitled in exchange for the goods or services it transfers to the customer. Once a contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and if so, they are considered performance obligations. The Company assesses whether each promised good or service is distinct for the purpose of identifying the performance obligations in the contract. This assessment involves subjective determinations and requires management to make judgments about the individual promised goods or services and whether such are separable from the other aspects of the contractual relationship. Promised goods and services are considered distinct provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer (that is, the good or service is capable of being distinct) and (ii) the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract (that is, the promise to transfer the good or service is distinct within the context of the contract). The transaction price is then determined and allocated to the identified performance obligations in proportion to their standalone selling prices (“SSP”) on a relative SSP basis. SSP is determined at contract inception and is not updated to reflect changes between contract inception and when the performance obligations are satisfied. If the consideration promised in a contract includes a variable amount, the Company estimates the amount of consideration to which it will be entitled in exchange for transferring the promised goods or services to a customer. The Company determines the amount of variable consideration by using the expected value method or the most likely amount method. The Company includes the unconstrained amount of estimated variable consideration in the transaction price. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. At the end of each subsequent reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis in the period of adjustment. If a license arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. The Company has assessed each of its revenue generating arrangements in order to determine whether a significant financing component exists and concluded that a significant financing component does not exist in any of its arrangements. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied, at a point in time. The Company recognizes revenue within the following financial statement captions: Product revenue, net The Company recognizes product revenue, net in accordance with Topic 606. Product revenue, net represents sales of ZYNTEGLO and SKYSONA. In 2022, the Company received approval of ZYNTEGLO and SKYSONA from the FDA. The amount of revenue recognized by the Company is equal to the amount of consideration that is expected to be received from the sale of product to its customers. The Company has Specialty Distributors ("SD") and Specialty Pharmacies ("SP") that deliver product to the Qualified Treatment Centers ("QTC"). Revenue is only recognized when the performance obligation is satisfied. The Company recognizes revenue upon infusion to the patient. To determine whether a significant reversal will occur in future periods, the Company assesses both the likelihood and magnitude of any such potential reversal of revenue. Other revenue In 2021, the Company entered into a grant agreement with the Bill and Melinda Gates Foundation. The Company recognizes grant revenue in accordance with ASC 958-605, Revenue Recognition Not-for-Profit Entities, when qualifying costs are incurred and barriers to restriction have been overcome. When grant funds are received after costs have been incurred, the Company records revenue and a corresponding grant receivable. Cash received from grants in advance of incurring qualifying costs is recorded as deferred revenue and recognized as revenue when qualifying costs are incurred. In 2023, the Company ceased further research work and is in the process of winding down such collaboration.
Recent accounting pronouncements	Recent accounting pronouncements During the periods presented, the Company was not required to adopt any recently issued accounting standards. The Company does not expect any recently issued accounting standards to have a material impact on its financial statements.

- Definition

Disclosure of inventory accounting policy for inventory classes, including, but not limited to, basis for determining inventory amounts, methods by which amounts are added and removed from inventory classes, loss recognition on impairment of inventories, and situations in which inventories are stated above cost.

+ References + Details

- Definition

Disclosure of accounting policy for revenue from contract with customer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 19
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-19

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-18

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-18

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 20
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-20

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 20
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-20

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 20
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-20

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 20
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-20

Reference 9: http://www.xbrl.org/2003/role/exampleRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (e)
-SubTopic 10
-Topic 235
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483426/235-10-50-4

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Name Accounting Standards Codification
-Topic 606
-Publisher FASB
-URI https://asc.fasb.org//606/tableOfContent

+ Details

Stock-based compensation - Summary of Stock-Based Compensation Expense by Award Type (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 4,868	$ 9,212	$ 16,013	$ 30,509
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,758	2,886	5,192	11,829
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2,916	6,142	10,552	18,027
Employee stock purchase plan and other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 194	$ 184	$ 269	$ 653

- Definition

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

+ References

+ Details

Condensed Consolidated Statements of Operations and Comprehensive Loss (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenue:
Total revenues	$ 12,392	$ 71	$ 21,663	$ 3,534
Cost of product revenue	10,955	0	23,895	10,056
Gross margin	1,437	71	(2,232)	(6,522)
Operating expenses:
Selling, general and administrative	40,703	33,402	118,406	106,201
Research and development	45,463	53,149	133,881	194,864
Restructuring expenses	0	(1,699)	0	4,940
Total operating expenses	86,166	84,852	252,287	306,005
Gain from sale of priority review voucher, net	0	0	92,930	0
Income (loss) from operations	(84,729)	(84,781)	(161,589)	(312,527)
Interest income, net	2,454	383	7,958	663
Other income (expense), net	10,544	7,885	30,152	13,061
Income (loss) before income taxes	(71,731)	(76,513)	(123,479)	(298,803)
Income tax (expense) benefit	0	(7)	80	(7)
Net income (loss)	$ (71,731)	$ (76,520)	$ (123,399)	$ (298,810)
Net income (loss) per share - basic (in dollars per share)	$ (0.66)	$ (0.94)	$ (1.15)	$ (3.91)
Net income (loss) per share - diluted (in dollars per share)	$ (0.66)	$ (0.94)	$ (1.15)	$ (3.91)
Weighted-average number of common shares used in computing net income (loss) per share - basic (in shares)	109,098	81,543	106,924	76,361
Weighted-average number of common shares used in computing net income (loss) per share - diluted (in shares)	109,098	81,543	106,924	76,361
Other comprehensive income (loss):
Total other comprehensive income (loss)	$ 137	$ (214)	$ 1,843	$ (1,719)
Comprehensive income (loss)	(71,594)	(76,734)	(121,556)	(300,529)
Product revenue, net
Revenue:
Revenue	12,281	0	21,414	2,739
Other revenue
Revenue:
Revenue	$ 111	$ 71	$ 249	$ 795

Accrued expenses and other current liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued manufacturing costs	$ 6,183	$ 7,199
Accrued goods and services	7,709	8,134
Accrued clinical and contract research organization costs	13,689	12,368
Accrued employee compensation	19,442	20,095
Accrued professional fees	2,748	1,939
Other	7,997	748
Total accrued expenses and other current liabilities	$ 57,768	$ 50,483

Accrued expenses and other current liabilities

9 Months Ended

Sep. 30, 2023

Payables and Accruals [Abstract]

Accrued expenses and other current liabilities

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


	As of September 30, 2023		As of December 31, 2022
Accrued manufacturing costs	$	6,183	$	7,199
Accrued goods and services	7,709		8,134
Accrued clinical and contract research organization costs	13,689		12,368
Accrued employee compensation	19,442		20,095
Accrued professional fees	2,748		1,939
Other	7,997		748
Total accrued expenses and other current liabilities	$	57,768	$	50,483

Fair value measurements - Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Assets:
Marketable securities:	$ 8,946	$ 68,735
Fair Value, Measurements, Recurring
Assets:
Cash and cash equivalents	165,347	113,006
Total	174,293	181,741
Fair Value, Measurements, Recurring \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	8,946	66,237
Fair Value, Measurements, Recurring \| Corporate bonds
Assets:
Marketable securities:		2,498
Fair Value, Measurements, Recurring \| Quoted prices in active markets (Level 1)
Assets:
Cash and cash equivalents	165,347	113,006
Total	165,347	113,006
Fair Value, Measurements, Recurring \| Quoted prices in active markets (Level 1) \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring \| Quoted prices in active markets (Level 1) \| Corporate bonds
Assets:
Marketable securities:		0
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2)
Assets:
Cash and cash equivalents	0	0
Total	8,946	68,735
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	8,946	66,237
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| Corporate bonds
Assets:
Marketable securities:		2,498
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Total	0	0
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3) \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	$ 0	0
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3) \| Corporate bonds
Assets:
Marketable securities:		$ 0

Restructuring - Narrative (Details) - April 2022 Reduction $ in Millions	6 Months Ended
	Sep. 30, 2022 USD ($)
Restructuring Cost and Reserve [Line Items]
Plans to reduce workforce, as a percent	30.00%
Payments for restructuring	$ 4.9

- Definition

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

+ References + Details