bluebird bio (BLUE) 10-Q 5 May 21 2021 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
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	60 Binney Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	339
Local Phone Number	499-9300
Title of 12(b) Security	Common Stock, $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	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		67,447,548
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Central Index Key	0001293971
Current Fiscal Year End Date	--12-31

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 439,714	$ 317,705
Marketable securities	572,722	833,546
Prepaid expenses	42,258	37,472
Receivables and other current assets	24,762	16,116
Inventory	18,079	10,698
Total current assets	1,097,535	1,215,537
Marketable securities	81,115	122,891
Property, plant and equipment, net	165,198	162,831
Intangible assets, net	11,469	10,041
Goodwill	13,128	13,128
Operating lease right-of-use assets	197,970	184,019
Restricted cash and other non-current assets	70,864	72,805
Total assets	1,637,279	1,781,252
Current liabilities:
Accounts payable	20,232	21,602
Accrued expenses and other current liabilities	146,791	145,406
Operating lease liability, current portion	28,063	25,024
Deferred revenue, current portion	1,330	2,320
Collaboration research advancement, current portion	9,899	9,236
Total current liabilities	206,315	203,588
Deferred revenue, net of current portion	25,762	25,762
Collaboration research advancement, net of current portion	19,399	21,581
Operating lease liability, net of current portion	177,702	167,997
Other non-current liabilities	7,768	7,268
Total liabilities	436,946	426,196
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock, $0.01 par value, 5,000 shares authorized; 0 shares issued and outstanding at March 31, 2021 and December 31, 2020	0	0
Common stock, $0.01 par value, 125,000 shares authorized; 67,422 and 66,432 shares issued and outstanding at March 31, 2021 and December 31, 2020, respectively	675	665
Additional paid-in capital	4,311,462	4,260,443
Accumulated other comprehensive loss	(5,449)	(5,505)
Accumulated deficit	(3,106,355)	(2,900,547)
Total stockholders’ equity	1,200,333	1,355,056
Total liabilities and stockholders’ equity	$ 1,637,279	$ 1,781,252

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
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 or stated value per share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	125,000,000	125,000,000
Common stock, shares, issued (in shares)	67,422,000	66,432,000
Common stock, shares, outstanding (in shares)	67,422,000	66,432,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue:
Collaborative arrangement revenue	$ 1,519	$ 2,302
Total revenues	12,794	21,863
Operating expenses:
Research and development	154,478	154,123
Selling, general and administrative	86,874	73,248
Cost of royalty and other revenue	2,281	1,025
Change in fair value of contingent consideration	369	(3,108)
Total operating expenses	244,002	225,288
Loss from operations	(231,208)	(203,425)
Interest income, net	710	5,355
Other income (expense), net	24,756	(4,447)
Loss before income taxes	(205,742)	(202,517)
Income tax expense	(66)	(94)
Net loss	$ (205,808)	$ (202,611)
Net loss per share - basic and diluted: (in dollars per share)	$ (3.07)	$ (3.64)
Weighted-average number of common shares used in computing net loss per share - basic and diluted: (in shares)	66,976	55,590
Other comprehensive income (loss):
Other comprehensive income (loss), net of tax benefit (expense) of $0.0 million for the three months ended March 31, 2021 and 2020	$ 56	$ (906)
Comprehensive loss	(205,752)	(203,517)
Service revenue
Revenue:
Revenue	5,918	16,833
Royalty and other revenue
Revenue:
Revenue	$ 5,357	$ 2,728

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Income Statement [Abstract]
Other comprehensive income (loss), tax	$ 0

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' Equity (unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive loss	Accumulated deficit
Beginning balance (in shares) at Dec. 31, 2019		55,368
Beginning balance at Dec. 31, 2019	$ 1,284,993	$ 554	$ 3,568,184	$ (1,893)	$ (2,281,852)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		204
Vesting of restricted stock units	0	$ 2	(2)
Exercise of stock options, shares (in shares)		20
Exercise of stock options	750		750
Purchase of common stock under ESPP (in shares)		28
Purchase of common stock under ESPP	1,872		1,872
Stock-based compensation	36,335		36,335
Other comprehensive income (loss)	(906)			(906)
Net loss	(202,611)				(202,611)
Ending balance, shares (in shares) at Mar. 31, 2020		55,620
Ending balance at Mar. 31, 2020	$ 1,120,433	$ 556	3,607,139	(2,799)	(2,484,463)
Beginning balance (in shares) at Dec. 31, 2020	66,432	66,432
Beginning balance at Dec. 31, 2020	$ 1,355,056	$ 665	4,260,443	(5,505)	(2,900,547)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		294
Vesting of restricted stock units	$ 0	$ 3	(3)
Exercise of stock options, shares (in shares)	207	207
Exercise of stock options	$ 1,219	$ 2	1,217
Purchase of common stock under ESPP (in shares)		67
Purchase of common stock under ESPP	1,707	$ 1	1,706
Stock-based compensation	36,090		36,090
Issuance of stock to settle liability-classified restricted stock units (in shares)		422
Issuance of unrestricted stock awards to settle accrued employee compensation	12,013	$ 4	12,009
Other comprehensive income (loss)	56			56
Net loss	$ (205,808)				(205,808)
Ending balance, shares (in shares) at Mar. 31, 2021	67,422	67,422
Ending balance at Mar. 31, 2021	$ 1,200,333	$ 675	$ 4,311,462	$ (5,449)	$ (3,106,355)

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net loss	$ (205,808)	$ (202,611)
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of contingent consideration	369	(3,108)
Depreciation and amortization	5,360	4,880
Stock-based compensation expense	42,527	36,293
(Gain) loss on equity securities	(28,372)	4,520
Other non-cash items	2,513	(1,387)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(8,979)	(9,285)
Inventory	(7,103)	(1,699)
Operating lease right-of-use assets	8,098	5,842
Accounts payable	67	(9,519)
Accrued expenses and other liabilities	(184)	(20,557)
Operating lease liabilities	(9,306)	(5,070)
Deferred revenue	(990)	(2,118)
Collaboration research advancement	(1,519)	(2,302)
Net cash used in operating activities	(203,327)	(206,121)
Cash flows from investing activities:
Purchase of property, plant and equipment	(7,626)	(10,676)
Purchases of marketable securities	(53,200)	(101,421)
Proceeds from maturities of marketable securities	350,860	336,675
Proceeds from sales of marketable securities	31,318	0
Net cash provided by investing activities	321,352	224,578
Cash flows from financing activities:
Proceeds from exercise of stock options and ESPP contributions	3,796	963
Net cash provided by financing activities	3,796	963
Increase in cash, cash equivalents and restricted cash	121,821	19,420
Cash, cash equivalents and restricted cash at beginning of period	373,728	381,709
Cash, cash equivalents and restricted cash at end of period	495,549	401,129
Reconciliation of cash, cash equivalents and restricted cash:
Total cash, cash equivalents and restricted cash	495,549	401,129
Supplemental cash flow disclosures from investing and financing activities:
Purchases of property, plant and equipment included in accounts payable and accrued expenses	2,238	1,125
Right-of-use assets obtained in exchange for operating lease liabilities	22,049	14,425
Issuance of unrestricted stock awards to settle accrued employee compensation	$ 12,013	$ 0

Description of the business

Description of the business	3 Months Ended
	Mar. 31, 2021
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 Cambridge, Massachusetts. The Company is a biotechnology company committed to researching, developing and commercializing potentially transformative gene therapies for severe genetic diseases and cancer. Since its inception, the Company has devoted substantially all of its resources to its research and development efforts relating to its product candidates, including activities to manufacture product candidates, conduct clinical studies of its product candidates, perform preclinical research to identify new product candidates and provide selling, general and administrative support for these operations, including commercial-readiness activities. The Company’s programs in severe genetic diseases include programs for transfusion-dependent β-thalassemia, or TDT, sickle cell disease, or SCD, and cerebral adrenoleukodystrophy, or CALD. The Company’s programs in oncology are focused on developing novel engineered cell and gene therapies for cancer, including the anti-BCMA CAR T programs for multiple myeloma under the Company’s collaboration arrangement with Bristol-Myers Squibb ("BMS"). Please refer to Note 10, Collaborative arrangements, for further discussion of the Company’s collaboration with BMS. In March 2021, BMS received marketing approval from the U.S. Food and Drug Administration for ABECMA ® (idecabtagene vicleucel; ide-cel) as a treatment of adult patients with relapsed or refractory multiple myeloma after four or more prior lines of therapy, including an immunomodulatory agent, a proteasome inhibitor, and an anti-CD38 monoclonal antibody. In October 2020, the Company's marketing authorization application was accepted by the European Medicines Agency, or EMA, for elivaldogene autotemcel (eli-cel; formerly Lenti-D gene therapy) as a treatment for cerebral adrenoleukodystrophy. In June 2019, the Company received conditional marketing authorization from the European Commission for betibeglogene autotemcel (beti-cel; formerly LentiGlobin for β-thalassemia gene therapy) as a treatment of patients 12 years and older with TDT who do not have a β 0 /β 0 genotype, for whom hematopoietic stem cell (HSC) transplantation is appropriate but a human leukocyte-matched related HSC donor is not available. beti-cel is being marketed as ZYNTEGLO™ in the European Union. The Company began recognizing product revenue from product sales of ZYNTEGLO during the first quarter of 2021. In February 2021, the Company temporarily suspended marketing of ZYNTEGLO in light of safety events in the HGB-206 study of LentiGlobin gene therapy for SCD, which is manufactured using the same vector as ZYNTEGLO. Additionally, the EMA has paused the renewal procedure for ZYNTEGLO's conditional marketing authorization while the EMA's pharmacovigilance risk assessment committee reviews the risk-benefit assessment for ZYNTEGLO and determines whether any additional pharmacovigilance measures are necessary. In January 2021, the Company announced its intent to separate its severe genetic disease and oncology programs into two separate, independent publicly traded companies, bluebird bio, Inc. and 2seventy bio, Inc., a newly-formed Delaware corporation and wholly-owned subsidiary of the Company prior to the separation. bluebird bio, Inc. intends to retain focus on its severe genetic disease programs and 2seventy bio, Inc. is expected to focus on the Company's oncology programs. The transaction is expected to be completed in late 2021 and is anticipated to be tax-free, subject to receipt of a favorable Internal Revenue Service (“IRS”) ruling. In accordance with Accounting Standards Codification (“ASC”) 205-40, Going Concern , the Company evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about its ability to continue as a going concern within one year after the date that the consolidated financial statements are issued. The Company has incurred losses since inception and to date has financed its operations primarily through the sale of equity securities and, to a lesser extent, through collaboration agreements and grants from governmental agencies and charitable foundations. As of March 31, 2021, the Company had an accumulated deficit of $3.11 billion. During the three months ended March 31, 2021, the Company incurred a loss of $205.8 million and used $203.3 million of cash in operations. The Company expects to continue to generate operating losses and negative operating cash flows for the next few years and will need additional funding to support its planned operating activities through profitability. The transition to profitability is dependent upon the successful development, approval, and commercialization of the Company’s product and product candidates and the achievement of a level of revenues adequate to support its cost structure. As of March 31, 2021, the Company had cash, cash equivalents and marketable securities of $1.09 billion. The Company expects its cash, cash equivalents and marketable securities will be sufficient to fund current planned operations for at least the next twelve months from the date of issuance of these financial statements, though it may pursue additional cash resources

Basis of presentation, principl

Basis of presentation, principles of consolidation and significant accounting policies	3 Months Ended
	Mar. 31, 2021
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”) as found in the Accounting Standards Codification ("ASC") and Accounting Standards Updates (“ASU”) 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 March 31, 2021 and 2020. 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, 2020, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on February 23, 2021. Inventory in the prior year’s condensed consolidated financial statements have been reclassified to conform to the current presentation on the condensed consolidated balance sheets and condensed consolidated statements of cash flows. However, no subtotals in the prior year condensed consolidated financial statements were impacted as a result. Amounts reported are computed based on thousands. 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. Any reference in these notes to applicable guidance is meant to refer to GAAP. 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 months ended March 31, 2021 are consistent with those discussed in Note 2 to the consolidated financial statements included in the Company’s 2020 Annual Report on Form 10-K, except as noted immediately below and as noted within the "Recent accounting pronouncements - Recently adopted" section. Royalty and other revenue During the first quarter of 2021, the Company recognized an immaterial amount of product revenue related to the sale of ZYNTEGLO in the European Union and the related cost of goods sold, which is included within royalty and other revenue and cost of royalty and other revenue, respectively. 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 regulatory approval. Manufacturing costs incurred prior to regulatory approval for pre-launch inventory that did not qualify for capitalization and clinical manufacturing costs are charged to research and development expense in the Company’s condensed consolidated statements of operations and comprehensive loss as costs are 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, vectors, 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. 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 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, contingent consideration, stock-based compensation expense, accrued expenses, revenue recognition, income taxes, inventory capitalization, 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. Recent accounting pronouncements Recently adopted ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify the accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The new standard was effective beginning January 1, 2021. The adoption of ASU 2019-12 did not have a material impact on the Company's financial position or results of operations upon adoption. ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity In August 2020, the FASB issued ASU 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU 2020-06”). ASU 2020-06 simplifies the complexity associated with applying U.S. GAAP for certain financial instruments with characteristics of liabilities and equity. More specifically, the amendments focus on the guidance for convertible instruments and derivative scope exception for contracts in an entity's own equity. The Company early adopted the new standard, effective January 1, 2021. The adoption of ASU 2020-06 did not have an impact on the Company's financial position or results of operations upon adoption. ASU No. 2020-08, Codification Improvements to Subtopic 310-20, Receivables - Nonrefundable Fees and Other Costs In October 2020, the FASB issued ASU 2020-08, Codification Improvements to Subtopic 310-20, Receivables - Nonrefundable Fees and Other Costs (“ASU 2020-08”) to provide further clarification and update the previously issued guidance in ASU 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20: Premium Amortization on Purchased Callable Debt Securities) (“ASU 2017-08”). ASU 2017-08 shortened the amortization period for certain callable debt securities purchased at a premium by requiring that the premium be amortized to the earliest call date. ASU 2020-08 requires that at each reporting period, to the extent that the amortized cost of an individual callable debt security exceeds the amount repayable by the issuer at the next call date, the excess premium shall be amortized to the next call date. The new standard was effective beginning January 1, 2021. The adoption of ASU 2020-08 did not have a material impact on the Company's financial position or results of operations upon adoption. ASU No. 2020-10, Codification Improvements In October 2020, the FASB issued ASU 2020-10, Codification Improvements ("ASU 2020-10"). The amendments in this ASU represent changes to clarify the ASC, correct unintended application of the guidance, or make minor improvements to the ASC that are not expected to have a significant effect on current accounting practice or create a significant administrative cost to most entities. This new standard was effective beginning January 1, 2021. The adoption of ASU 2020-10 did not have a material impact on the Company's financial position or results of operations upon adoption.

Marketable Securities

Marketable Securities	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Marketable securities	Marketable securities The following table summarizes the marketable securities held at March 31, 2021 and December 31, 2020 (in thousands): Description Amortized cost / Cost Unrealized gains Unrealized losses Fair value March 31, 2021 U.S. government agency securities and treasuries $ 429,039 $ 256 $ (16) $ 429,279 Corporate bonds 142,773 163 (40) 142,896 Commercial paper 78,955 — — 78,955 Equity securities 4,305 — (1,598) 2,707 Total $ 655,072 $ 419 $ (1,654) $ 653,837 December 31, 2020 U.S. government agency securities and treasuries $ 675,043 $ 302 $ (74) $ 675,271 Corporate bonds 197,171 432 (40) 197,563 Commercial paper 77,949 1 — 77,950 Equity securities 20,017 — (14,364) 5,653 Total $ 970,180 $ 735 $ (14,478) $ 956,437 No available-for-sale debt securities held as of March 31, 2021 or December 31, 2020 had remaining maturities greater than five years.

Fair value measurements

Fair value measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair value measurements	Fair value measurements The following table sets forth the Company’s assets and liabilities that are measured at fair value on a recurring basis as of March 31, 2021 and December 31, 2020 (in thousands): Description Total Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) March 31, 2021 Assets: Cash and cash equivalents $ 439,714 $ 410,715 $ 28,999 $ — Marketable securities: U.S. government agency securities and treasuries 429,279 — 429,279 — Corporate bonds 142,896 — 142,896 — Commercial paper 78,955 — 78,955 — Equity securities 2,707 2,707 — — Total $ 1,093,551 $ 413,422 $ 680,129 $ — Liabilities: Contingent consideration $ 1,878 $ — $ — $ 1,878 Total $ 1,878 $ — $ — $ 1,878 December 31, 2020 Assets: Cash and cash equivalents $ 317,705 $ 317,705 $ — $ — Marketable securities: U.S. government agency securities and treasuries 675,271 — 675,271 — Corporate bonds 197,563 — 197,563 — Commercial paper 77,950 — 77,950 — Equity securities 5,653 5,653 — — Total $ 1,274,142 $ 323,358 $ 950,784 $ — Liabilities: Contingent consideration $ 1,509 $ — $ — $ 1,509 Total $ 1,509 $ — $ — $ 1,509 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 March 31, 2021, cash and cash equivalents comprise funds in cash, money market accounts, and commercial paper. As of December 31, 2020, cash and cash equivalents comprise funds in cash and money market accounts. 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 next call date for premiums or to maturity for discounts. At March 31, 2021 and December 31, 2020, the balance in the Company’s accumulated other comprehensive loss includes activity related to the Company’s available-for-sale debt securities. There were no material realized gains or losses recognized on the sale or maturity of available-for-sale debt securities during the three months ended March 31, 2021 or 2020. Accrued interest receivable on the Company's available-for-sale debt securities totaled $2.2 million and $3.1 million as of March 31, 2021 and December 31, 2020, respectively. No accrued interest receivable was written off during the three months ended March 31, 2021 or 2020. The following table summarizes available-for-sale debt securities in a continuous unrealized loss position for less than and greater than twelve months, and for which an allowance for credit losses has not been recorded at March 31, 2021 and December 31, 2020 (in thousands): Less than 12 months 12 months or greater Total Description Fair value Unrealized losses Fair value Unrealized losses Fair value Unrealized losses March 31, 2021 U.S. government agency securities $ 48,802 $ (16) $ — $ — $ 48,802 $ (16) Corporate bonds 92,855 (40) — — 92,855 (40) Total $ 141,657 $ (56) $ — $ — $ 141,657 $ (56) December 31, 2020 U.S. government agency securities $ 211,384 $ (74) $ — $ — $ 211,384 $ (74) Corporate bonds 76,598 (40) 1,205 — 77,803 (40) Total $ 287,982 $ (114) $ 1,205 $ — $ 289,187 $ (114) The Company determined that there was no material change in the credit risk of the above investments during the three months ended March 31, 2021. As such, an allowance for credit losses was not recognized. As of March 31, 2021, the Company does not intend to sell such securities and it is not more likely than not that the Company will be required to sell the securities before recovery of their amortized cost bases. The Company held equity securities with an aggregate fair value of $2.7 million and $5.7 million as of March 31, 2021 and December 31, 2020, respectively, within short-term marketable securities on its condensed consolidated balance sheets. In January 2021, the Company sold a portion of its equity securities for proceeds of $31.3 million. During the three months ended March 31, 2021 and 2020, the Company recorded gains of $28.4 million and losses of $4.5 million, respectively, related to its equity securities, which are included in other income (expense), net on the condensed consolidated statements of operations and comprehensive loss. Contingent consideration In connection with its prior acquisition of Precision Genome Engineering, Inc. (“Pregenen”), the Company may be required to pay future consideration that is contingent upon the achievement of specified development, regulatory approvals or sales-based milestone events. Contingent consideration is measured at fair value and is based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. The valuation of contingent consideration uses assumptions the Company believes would be made by a market participant. The Company assesses these estimates on an on-going basis as additional data impacting the assumptions is obtained. Future changes in the fair value of contingent consideration related to updated assumptions and estimates are recognized within the condensed consolidated statements of operations and comprehensive loss. In the absence of new information, changes in fair value will reflect changing discount rates and the passage of time. Contingent consideration is included in accrued expenses and other current liabilities and other non-current liabilities on the condensed consolidated balance sheets. Please refer to Note 9, Commitments and contingencies, for further information.

Inventory

Inventory	3 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
Inventory	Inventory Inventory consists of the following (in thousands): As of March 31, 2021 As of December 31, 2020 Raw materials $ 16,892 $ 8,967 Finished goods 1,187 1,731 Inventory $ 18,079 $ 10,698

Property, plant and equipment,

Property, plant and equipment, net	3 Months Ended
	Mar. 31, 2021
Property, Plant and Equipment [Abstract]
Property, plant and equipment, net	Property, plant and equipment, net Property, plant and equipment, net, consists of the following (in thousands): As of March 31, 2021 As of December 31, 2020 Land $ 1,210 $ 1,210 Building 88,591 15,745 Computer equipment and software 6,919 6,950 Office equipment 7,633 7,665 Laboratory equipment 66,600 55,521 Leasehold improvements 34,104 34,286 Construction-in-progress 14,939 92,514 Total property, plant and equipment 219,996 213,891 Less accumulated depreciation and amortization (54,798) (51,060) Property, plant and equipment, net $ 165,198 $ 162,831 North Carolina manufacturing facility In November 2017, the Company acquired a manufacturing facility in Durham, North Carolina for the future manufacture of lentiviral vector for the Company’s gene therapies. As of March 31, 2021, the majority of the facility has been placed into service. The remainder of the facility is still in process of qualification, which is required for the facility to be ready for its intended use. Construction-in-progress as of March 31, 2021 and December 31, 2020 includes $14.2 million and $91.1 million, respectively, related to the North Carolina manufacturing facility.

Accrued expenses and other curr

Accrued expenses and other current liabilities	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Accrued expenses and other current liabilities	Accrued expenses and other current liabilities Accrued expenses and other current liabilities consist of the following (in thousands): As of March 31, 2021 As of December 31, 2020 Employee compensation $ 45,916 $ 55,802 Manufacturing costs 24,726 22,571 Clinical and contract research organization costs 23,377 23,766 Collaboration research costs 23,679 20,004 Property, plant and equipment 1,543 789 License and milestone fees 303 278 Professional fees 1,993 1,541 Other 25,254 20,655 Accrued expenses and other current liabilities $ 146,791 $ 145,406

Leases

Leases	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Leases	Leases The Company leases certain office and laboratory space, primarily located in Cambridge, Massachusetts and Seattle, Washington. Additionally, the Company has embedded leases at various 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 2020 Annual Report on Form 10-K. Embedded operating leases In July 2020, 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 a controlled environment room at the facility is designated for the Company's exclusive use during the term of the agreement, with the option to sublease the space if the Company provides notice that it will not utilize it for a specified duration of time. Under the terms of the agreement, the Company will be required to pay up to $5.4 million per year in maintenance fees in addition to the cost of any services provided and may terminate this agreement with eighteen months' notice. The term of the agreement is five years, with the option to extend. The Company recorded a right-of-use asset and lease liability for this operating lease upon lease commencement in March 2021 and is recognizing rent expense on a straight-line basis throughout the remaining term of the embedded lease.

Commitments and contingencies

Commitments and contingencies	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	Commitments and contingencies Contingent consideration related to business combinations In June 2014, the Company acquired Pregenen. The Company may be required to make up to $120.0 million in remaining future contingent cash payments to the former equity holders of Pregenen upon the achievement of certain clinical and commercial milestones related to the Pregenen technology, of which $20.1 million relates to clinical milestones and $99.9 million relates to commercial milestones. In accordance with accounting guidance for business combinations, contingent consideration liabilities are required to be recognized on the condensed consolidated balance sheets at fair value. Estimating the fair value of contingent consideration requires the use of significant assumptions primarily relating to probabilities of successful achievement of certain clinical and commercial milestones, the expected timing in which these milestones will be achieved, and discount rates. The use of different assumptions could result in materially different estimates of fair value. Other funding commitments 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. Please refer to Note 10, Collaborative arrangements, for further information on the Company's collaboration agreements and to Note 11, Royalty and other revenue , for further information on the Company's license agreements. 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. There have been no material changes in future minimum purchase commitments from those disclosed in Note 9 to the consolidated financial statements included in the Company's 2020 Annual Report on Form 10-K. While there are no material legal proceedings the Company is aware of, the Company may become party to various claims and complaints arising in the ordinary course of business. 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 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.

Collaborative arrangements

Collaborative arrangements	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaborative arrangements	Collaborative arrangements To date, the Company’s revenue has been primarily generated from its collaboration arrangements with BMS and Regeneron Pharmaceuticals, Inc. ("Regeneron"), each as further described below. Bristol-Myers Squibb BMS Original Collaboration Agreement In March 2013, the Company entered into a Master Collaboration Agreement (the “BMS Collaboration Agreement”) with Celgene (now BMS following its acquisition of Celgene in November 2019) to discover, develop and commercialize potentially disease-altering gene therapies in oncology. The collaboration is focused on applying gene therapy technology to genetically modify a patient’s own T cells, known as chimeric antigen receptor, or CAR T cells, to target and destroy cancer cells. Additionally, in March 2013, the Company entered into a Platform Technology Sublicense Agreement (the “Sublicense Agreement”) with BMS pursuant to which the Company obtained a sublicense to certain intellectual property from BMS, originating under BMS’s license from Baylor College of Medicine, for use in the collaboration. Under the terms of the BMS Collaboration Agreement, the Company received an up-front, non-refundable, non-creditable payment of $75.0 million. The Company was responsible for conducting discovery, research and development activities through completion of phase 1 clinical studies, if any, during the initial term of the BMS Collaboration Agreement, or three years. BMS Amended Collaboration Agreement In June 2015, the Company and BMS amended and restated the BMS Collaboration Agreement (the “Amended BMS Collaboration Agreement”). Under the Amended BMS Collaboration Agreement, the parties narrowed the focus of the collaboration to exclusively work on anti- B-cell maturation antigen (“BCMA”) product candidates for a new three-year term. In connection with the Amended BMS Collaboration Agreement, the Company received an up-front, non-refundable, non-creditable payment of $25.0 million to fund research and development under the collaboration. Under the terms of the Amended BMS Collaboration Agreement, for up to two product candidates selected for development under the collaboration, the Company was responsible for conducting and funding all research and development activities performed up through completion of the initial phase 1 clinical study of such product candidate. On a product candidate-by-product candidate basis, up through a specified period following enrollment of the first patient in an initial phase 1 clinical study for such product candidate, the Company had granted BMS an option to obtain an exclusive worldwide license to develop and commercialize such product. Following BMS’s license of each product candidate, the Company is entitled to elect to co-develop and co-promote each product candidate in the U.S. BMS Ide-cel License Agreement In February 2016, BMS exercised its option to obtain an exclusive worldwide license to develop and commercialize ide-cel, the first product candidate under the Amended BMS Collaboration Agreement, pursuant to an executed license agreement (“Ide-cel License Agreement”) entered into by the parties in February 2016 and paid to the Company the associated $10.0 million option fee. Pursuant to the Ide-cel License Agreement, BMS was responsible for development and related funding of ide-cel after the substantial completion of the phase 1 clinical trial. The Company was responsible for the manufacture of vector and associated payload throughout development and upon BMS’s request, throughout commercialization, the costs of which were reimbursable by BMS in accordance with the terms of the Amended and Restated Co-Development, Co-Promote and Profit Share Agreement, as further described below. BMS was responsible for the manufacture of drug product throughout development and commercialization. Under the Ide-cel License Agreement, the Company was eligible to receive U.S. milestones of up to $85.0 million for the first indication to be addressed by ide-cel and royalties for U.S. sales of ide-cel. Additionally, the Company was eligible to receive ex-U.S. milestones of up to $55.0 million and royalties for ex-U.S. sales of ide-cel. BMS Ide-cel Co-Development, Co-Promote and Profit Share Agreement In March 2018, the Company elected to co-develop and co-promote ide-cel within the U.S. pursuant to the execution of the Amended and Restated Co-Development, Co-Promote and Profit Share Agreement (“Ide-cel CCPS”), which replaced the Ide-cel License Agreement. As a result of executing the Ide-cel CCPS, the responsibilities of the parties remained unchanged from those under the Ide-cel License Agreement, however, the Company will share equally in all profits and losses relating to developing, commercializing and manufacturing ide-cel within the U.S. and has the right to participate in the development and promotion of ide-cel in the U.S. BMS is responsible for the costs incurred to manufacture vector and associated payload for use outside of the U.S., plus a mark-up. As a result of electing to co-develop and co-promote ide-cel within the U.S., the milestones and royalties payable under the Ide-cel License Agreement were adjusted. Under the Ide-cel CCPS, the Company was eligible to receive a $10.0 million milestone related to the development of ide-cel in the U.S. and, for the first indication to be addressed by ide-cel, ex-U.S. regulatory and commercial milestones of up to $60.0 million. Additionally, the Company was eligible to receive royalties for ex-U.S. sales of ide-cel, but not for U.S. sales of ide-cel. Under the Ide-cel CCPS, the $10.0 million development milestone was achieved in the second quarter of 2019 and subsequently paid by BMS. In May 2020, the First Amendment to the Amended and Restated Co-Development, Co-Promote and Profit Share Agreement (as amended, the "Amended Ide-cel CCPS") was executed, which amended the Ide-cel CCPS. Under the Amended Ide-cel CCPS, the parties will continue to share equally in all profits and losses relating to developing, commercializing and manufacturing ide-cel within the U.S. Under the Amended Ide-cel CCPS and the Amended bb21217 License Agreement, described further below, BMS was relieved of its obligations to pay the Company for future ex-U.S. milestones and royalties on ex-U.S. sales for each of ide-cel and bb21217 in exchange for an up-front, non-refundable, non-creditable payment of $200.0 million, which represents the aggregate of the probability-weighted, net present value of the future ex-U.S. milestones and royalties on ex-U.S. sales for each of ide-cel and bb21217. In connection with these amendments, BMS assumed the contract manufacturing agreements relating to ide-cel adherent lentiviral vector. Over time, BMS is assuming responsibility for manufacturing ide-cel suspension lentiviral vector outside of the U.S., with bluebird responsible for manufacturing ide-cel suspension lentiviral vector in the U.S. In addition, under the Amended Ide-cel CCPS and the Amended bb21217 License Agreement, described further below, the parties are released from future exclusivity related to BCMA-directed T cell therapies. There are no remaining milestones or royalties under the Amended Ide-cel CCPS. Ide-cel is marketed as ABECMA in the U.S. following its approval by the FDA in March 2021 for the treatment of adult patients with relapsed or refractory multiple myeloma after four or more prior lines of therapy, including an immunomodulatory agent, a proteasome inhibitor, and an anti-CD38 monoclonal antibody. Under the Amended Ide-cel CCPS, BMS is primarily responsible for the commercialization of ABECMA and the Company has concluded BMS is the principal for purposes of recognition of product sales. Accordingly, the Company will continue to account for its share of the profits and losses relating to developing, commercializing, and manufacturing ABECMA in the U.S. as collaborative arrangement revenue (expense). There were no product sales of ABECMA during the first quarter of 2021. BMS bb21217 License Agreement In September 2017, BMS exercised its option to obtain an exclusive worldwide license to develop and commercialize bb21217, the second product candidate under the Amended BMS Collaboration Agreement, pursuant to an executed license agreement (“bb21217 License Agreement”) entered into by the parties in September 2017 and paid the Company an option fee of $15.0 million. Pursuant to the bb21217 License Agreement, BMS is responsible for development and related funding of bb21217 after the substantial completion of the ongoing phase 1 clinical trial. In 2019, the parties amended the protocol for the ongoing phase 1 clinical trial to enroll additional patients for which the Company will be reimbursed based upon an agreed-upon amount per patient. Under the bb21217 License Agreement, the Company is eligible to receive U.S. milestones of up to $85.0 million for the first indication to be addressed by bb21217 and royalties for U.S. sales of bb21217. Additionally, the Company was eligible to receive ex-U.S. milestones of up to $55.0 million and royalties for ex-U.S. sales of bb21217. In May 2020, the Second Amended and Restated License Agreement ("Amended bb21217 License Agreement") was executed, which replaced the bb21217 License Agreement. Under the Amended bb21217 License Agreement, over time, BMS is assuming responsibility for manufacturing suspension lentiviral vector outside of the U.S., with bluebird responsible for manufacturing suspension lentiviral vector in the U.S. Under the Amended bb21217 License Agreement, expenses incurred by the Company associated with these activities are fully reimbursable by BMS at cost plus a mark-up. Throughout both development and commercialization, BMS is responsible for the manufacture of drug product. There are no remaining milestones and royalties related to the ex-U.S. development or commercialization of bb21217 following execution of the Amended bb21217 License Agreement. The Company currently expects it will exercise its option to co-develop and co-promote bb21217 within the U.S. The Company’s election to co-develop and co-promote bb21217 must be made by the substantial completion of the on-going phase 1 clinical trial of bb21217. If elected, the Company expects the responsibilities of the parties to remain largely unchanged, however, the Company expects it will share equally in all profits and losses relating to developing, commercializing and manufacturing bb21217 within the U.S. and to have the right to participate in the development and promotion of bb21217 in the U.S. Under this scenario, the U.S. milestones and royalties payable under the Amended bb21217 License Agreement would be adjusted and the Company would be eligible to receive a $10.0 million development milestone payment related to the development of bb21217 within the U.S. The Company would not be eligible for royalties on U.S. sales of bb21217 under this scenario. In the event the Company does not exercise its option to co-develop and co-promote bb21217, the Company will receive an additional fee in the amount of $10.0 million. Under this scenario, there would be no change to the U.S. milestones and royalties for U.S. sales of bb21217, as previously described above, for which the Company would be eligible to receive. Accounting Analysis – Amended Ide-cel CCPS and Amended bb21217 License Agreement In accordance with the Company’s accounting policies related to variable consideration, as further described in the Company’s Annual Report on Form 10-K filed with the SEC on February 23, 2021, if an arrangement includes variable consideration, including milestone payments, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount to be included in the transaction price of an arrangement. 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, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. The Company recognizes royalty revenue and sales-based milestones at the later of (i) when the related sales occur, or (ii) when the performance obligation to which the royalty has been allocated has been satisfied. Prior to the May 2020 amendments, the Company had constrained all variable consideration related to the remaining ex-U.S. milestones and royalties for ex-U.S. sales under the Ide-cel CCPS and bb21217 License Agreement. As a result of the May 2020 amendments, the uncertainty associated with the previously constrained variable consideration for future ex-U.S. milestones and royalties on ex-U.S. sales for each of ide-cel and bb21217 was resolved in exchange for an up-front, non-refundable, non-creditable payment of $200.0 million. While the Ide-cel CCPS and bb21217 License Agreement were historically accounted for as separate contracts, the May 2020 amendments to each agreement were negotiated as a package with a single commercial objective and, as such, the Amended Ide-cel CCPS and Amended bb21217 License Agreement were combined for accounting purposes and treated as a single arrangement. At the time of the May 2020 amendments, there was one remaining performance obligation under each of the Ide-cel CCPS and bb21217 License Agreement, neither of which were fully satisfied: a combined performance obligation of the ide-cel license and ide-cel vector manufacturing through development; and a combined performance obligation of the bb21217 license and bb21217 vector manufacturing through development. Subsequent to the May 2020 amendments, the Company concluded the two performance obligations are distinct from each other as BMS can benefit from each license and associated manufacturing services separately and the respective licenses and manufacturing services do not modify one another and are not interdependent. Accordingly, the Company will continue to account for each performance obligation separately. The Company allocated the $200.0 million up-front payment received in connection with the May 2020 amendments to the remaining performance obligations described above based on the general allocation principles of Topic 606. In applying these principles, the Company considered the $200.0 million up-front payment is representative of previously constrained variable consideration that has been changed and the related uncertainties resolved by the May 2020 amendments. Moreover, the Company considered that a portion of the $200.0 million was specifically attributable to each remaining performance obligation as the amount represents the aggregate of the probability-weighted, net present value of the future ex-U.S. milestones and royalties on ex-U.S. sales for each of ide-cel and bb21217 and that each respective portion therefore (i) relates specifically to the Company's satisfaction of each of its remaining performance obligations and (ii) is representative of the amount of consideration the Company expects to be entitled to in exchange for satisfying the respective performance obligations. As such, the Company concluded that the portion of the $200.0 million up-front payment specifically attributable to each of ide-cel and bb21217 should be allocated to each respective performance obligation pursuant to the variable consideration allocation exception. The Amended Ide-cel CCPS and Amended bb21217 License Agreement represent a contract modification to an existing contract under Topic 606 given the May 2020 amendments resulted in a reduction in scope of the Company's responsibilities under each performance obligation described above. Specifically, the May 2020 amendments reduced the scope of the Company's obligation to provide ex-U.S. vector manufacturing services through development for both ide-cel and bb21217 as those activities will transition to BMS over time. In addition, the May 2020 amendments resulted in a change in the overall transaction price under the arrangement. The May 2020 amendments did not include any additional promised goods and services. The remaining goods and services to be provided in order to fully satisfy each performance obligation described above are not distinct from those previously provided with respect to each performance obligation. Therefore, for each performance obligation, the remaining goods and services are part of a single performance obligation that is partially satisfied at the date of the contract modification. Accordingly, the effect that the contract modification had on the transaction price and the measure of progress toward complete satisfaction of each respective performance obligation has been recognized on a cumulative catch-up basis. The accounting for any previously satisfied performance obligations as of the contract modification date are not affected by the modification. Ide-cel transaction price The following tables summarize the total transaction price, the allocation of the total transaction price to the identified performance obligations under the arrangement (including those performance obligations that were completed as of the May 2020 contract modification date), and the amount of the transaction price unsatisfied as of March 31, 2021 (in thousands): Ide-cel transaction price as of March 31, Up-front non-refundable payments, option fee and milestone payments received prior to May 2020 $ 120,000 Allocated portion of the up-front non-refundable payment received in connection with the Amended Ide-cel CCPS and bb21217 License Agreement (2) 184,029 Estimated variable consideration (3) 83,900 $ 387,929 (1) Composed of all up-front payments and option fee and milestone payments received under the BMS Collaboration Agreement, Amended BMS Collaboration Agreement, Ide-cel License Agreement, and Ide-cel CCPS. This consideration was allocated to the performance obligations under the Ide-cel CCPS based on a relative standalone selling price (“SSP”) basis. The Company estimated the SSP of the ide-cel license after considering potential future cash flows under the license. The Company then discounted these probability-weighted cash flows to their present value. The Company estimated the SSP of each of the ide-cel research and development services and ide-cel manufacturing services to be provided based on the Company’s estimated cost of providing the services plus an applicable profit margin commensurate with observable market data for similar services. (2) This represents the portion of the $200.0 million up-front payment received under the Amended Ide-cel CCPS and Amended bb21217 License Agreement which was allocated to ide-cel. (3) Estimated variable consideration represents the estimated reimbursement from BMS for the manufacture of vectors and associated payload through development. Allocation of Transaction price unsatisfied as of March 31, 2021 Ide-cel research and development services $ 40,912 $ — Ide-cel license and manufacturing services 347,017 — $ 387,929 $ — Ide-cel research and development services The Company satisfied this performance obligation as the research and development services were performed. The Company determined that the period of performance of the research and development services was three years through projected initial phase 1 clinical study substantial completion, or through May 2018. The research and development performance obligation was satisfied prior to the May 2020 amendments and, as a result, the accounting for this previously satisfied performance obligation was not affected by the modification. The Company recognized no revenue related to ide-cel research and development services for the three months ended March 31, 2021 and 2020. Ide-cel license and manufacturing services The Company accounts for its vector manufacturing services for development in the U.S. and BMS’s U.S. development efforts within the scope of ASC 808, Collaborative Arrangements ("ASC 808") given that both parties are active participants in the activities and both parties are exposed to significant risks and rewards dependent on the commercial success of the activities. The Company recognizes revenue for its U.S. manufacturing services by analogy to Topic 606. The portion of BMS’s U.S. development costs that the Company is responsible for are recognized as a reduction to its collaborative arrangement revenues, or, if in excess of such revenues in a given quarter, the excess is recorded as research and development expense. The Company recognizes revenue associated with the combined performance obligation using the proportional performance method, as the Company will satisfy this performance obligation as the manufacturing services are performed through development. In using this method, the Company estimated its development plan for ide-cel, including expected demand from BMS, and the costs associated with the manufacture of vectors and associated payload for incorporation into ide-cel. On a quarterly basis, the Company determines the proportion of effort incurred as a percentage of total effort it expects to expend. This ratio is applied to the transaction price, which includes variable consideration, allocated to the combined performance obligation consisting of the ide-cel license and manufacturing services. Management has applied significant judgment in the process of developing its budget estimates and any changes to these estimates will be recognized in the period in which they change as a cumulative catch-up. The following table summarizes the net collaborative arrangement revenue recognized or expense incurred for the joint ide-cel development efforts in the U.S. under ASC 808 related to the combined performance obligation for the license and vector manufacturing of ide-cel in the U.S. for the three months ended March 31, 2021, and 2020 (in thousands): For the three months ended March 31, 2021 2020 ASC 808 ide-cel research and development expense - U.S. (1) $ (16,825) $ (5,080) (1) As noted above, the calculation of collaborative arrangement revenue or research and development expense to be recognized for joint ide-cel development efforts in the U.S. is performed on a quarterly basis. The calculation is independent of previous activity, which may result in fluctuations between revenue and expense recognition period over period, depending on the varying extent of effort performed by each party during the period. Revenue related to the combined unit of accounting for the ex-U.S. license and vector manufacturing services is accounted for in accordance with Topic 606. The following table summarizes the revenue recognized related to the combined unit of accounting for the ide-cel ex-U.S. license and vector manufacturing services for the three months ended March 31, 2021, and 2020 (in thousands): For the three months ended March 31, 2021 2020 ASC 606 ide-cel license and manufacturing revenue - ex-U.S. $ 5,104 $ 13,970 As of March 31, 2021, the Company has satisfied its performance obligation related to ide-cel license and manufacturing services and thus, the aggregate amount of the transaction price allocated to the combined performance obligation that is unsatisfied, or partially unsatisfied, is $0.0 million. As of March 31, 2021 and December 31, 2020, the Company had $0.0 million and $0.8 million, respectively, of deferred revenue associated with the combined performance obligation consisting of the ide-cel license and manufacturing services. bb21217 transaction price The following tables summarize the total transaction price, the allocation of the total transaction price to the identified performance obligations under the arrangement (including those performance obligations that were completed as of the May 2020 contract modification date), and the amount of the transaction price unsatisfied as of March 31, 2021 (in thousands): bb21217 transaction price as of March 31, 2021 Up-front non-refundable payment received prior to May 2020 contract modification (1) $ 15,000 Allocated portion of the up-front non-refundable payment received in connection with the Amended Ide-cel CCPS and bb21217 License Agreement (2) 15,971 Estimated variable consideration (3) 1,803 $ 32,774 (1) Composed of the up-front non-refundable payment received under the bb21217 License Agreement. This consideration was allocated to the performance obligations under the bb21217 License Agreement based on a relative SSP basis. The Company estimated the SSP of the bb21217 license after considering potential future cash flows under the license. The Company then discounted these probability-weighted cash flows to their present value. The Company estimated the SSP of each of the bb21217 research and development services and bb21217 manufacturing services to be provided based on the Company’s estimated cost of providing the services plus an applicable profit margin commensurate with observable market data for similar services. (2) This represents the portion of the $200.0 million up-front payment received under the Amended Ide-cel CCPS and Amended bb21217 License Agreement which was allocated to bb21217. (3) Estimated variable consideration represents the estimated reimbursement from BMS for the manufacture of vectors and associated payload through development. Allocation of transaction Transaction price unsatisfied as of March 31, 2021 bb21217 research and development services $ 5,444 $ — bb21217 license and manufacturing services 27,330 27,330 $ 32,774 $ 27,330 All of the remaining development, regulatory, and commercial milestones under the Amended bb21217 License Agreement are related to U.S. development, regulatory and commercialization activities and are fully constrained and are therefore excluded from the transaction price. As part of its evaluation of the constraint, the Company considered numerous factors, including the fact that achievement of the milestones is outside the control of the Company and contingent upon the future success of its clinical trials, the licensee’s efforts, or the receipt of regulatory approval. Any consideration related to U.S. sales-based milestones (including royalties) will be recognized when the related sales occur as these amounts have been determined to relate predominantly to the license granted to BMS and therefore are recognized at the later of when the performance obligation is satisfied, or the related sales occur. The Company re-evaluates the transaction price, including its estimated variable consideration included in the transaction price and all constrained amounts, each reporting period and as uncertain events are resolved or other changes in circumstances occur. bb21217 research and development services The Company satisfied this performance obligation as the research and development services were performed. The Company determined that the period of performance of the research and development services was two years through projected substantial completion of the initial phase 1 clinical study, or through September 2019. The research and development performance obligation was satisfied prior to the May 2020 amendments, and as a result, the accounting for this previously satisfied performance obligation was not affected by the modification. The agreement to expand the bb21217 phase 1 trial that occurred in 2019 was previously treated as a separate contract for accounting purposes, because the trial expansion was for the addition of a promised good or service that is distinct and the associated consideration reflected the standalone selling price of the additional promised good or service. This contract was not affected by the May 2020 amendments and, accordingly, the accounting for this agreement was not impacted by the May 2020 amendments. The transaction price associated with these additional patients consists of variable consideration and is based upon an agreed-upon amount per patient which will be recognized as revenue as the patients are treated. The Company began fulfilling the performance obligation in the fourth quarter of 2019 and it was satisfied in the fourth quarter of 2020. In connection with treating additional patients in the phase 1 trial, the Company recognized revenue of $0.0 million and $2.4 million for the three months ended March 31, 2021 and 2020, respectively. bb21217 license and manufacturing services The Company will satisfy its performance obligation related to the manufacture of vectors and associated payload for incorporation into bb21217 through development as the bb21217 manufacturing services are performed. As of March 31, 2021, the manufacturing services for bb21217 had not yet commenced. Therefore, no amounts have been recognized for the combined performance obligation in the condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020. The aggregate amount of the transaction price allocated to the combined performance obligation, which consists of the bb21217 license and manufacturing services, is $27.3 million. The Company does not expect that recognition will begin in the next twelve months and has therefore classified deferred revenue associated with the combined performance obligation as deferred revenue, net of current portion on its condensed consolidated balance sheets. The Company had $25.8 million of remaining deferred revenue as of March 31, 2021 and as of December 31, 2020, associated with the combined performance obligation consisting of the bb21217 license and manufacturing services. Contract assets and liabilities – ide-cel and bb21217 The Company receives payments from its collaborative partners based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due until such time as the Company satisfies its performance obligations under these arrangements. A contract asset is a conditional right to consideration in exchange for goods or services that the Company has transferred to a customer. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The following table presents changes in the balances of the Company’s BMS receivables and contract liabilities during the three months ended March 31, 2021 (in thousands): Balance at December 31, Additions Deductions Balance at Receivables $ 400 $ — $ (400) $ — Contract liabilities: Deferred revenue $ 26,582 $ — $ (820) $ 25,762 The decrease in the receivables balance for the three months ended March 31, 2021 is driven by amounts collected from BMS in the period. The decrease in deferred revenue during the three months ended March 31, 2021 is driven by the release of the remaining $0.8 million of deferred revenue associated with the combined performance obligation consisting of the ide-cel license and manufacturing services. Regeneron Regeneron Collaboration Agreement In August 2018, the Company entered into a Collaboration Agreement (the “Regeneron Collaboration Agreement”) with Regeneron pursuant to which the parties will apply their respective technology platforms to the discovery, development, and commercialization of novel immune cell therapies for cancer. In August 2018, following the completion of required regulatory reviews, the Regeneron Collaboration Agreement became effective. Under the terms of the agreement, the parties will leverage Regeneron’s proprietary platform technologies for the discovery and characterization of fully human antibodies, as well as T cell receptors directed against tumor-specific proteins and peptides and the Company will contribute its field-leading expertise in gene therapy. In accordance with the Regeneron Collaboration Agreement, the parties jointly selected six initial targets and intend to equally share the costs of research up to the point of submitting an IND application for a potential gene therapy product directed to a particular target. Additional targets may be selected to add to or replace any of the initial targets during the five-year research collaboration term as agreed to by the parties. Regeneron will accrue a certain number of option rights exercisable against targets as the parties reach certain milestones under the terms of the agreement. Upon the acceptance of an IND for the first product candidate directed to a target, Regeneron will have the right to exercise an option for co-development/co-commercialization of product candidates directed to such target on a worldwide or applicable opt-in territory basis, with certain exceptions. Where Regeneron chooses to opt-in, the parties

Royalty and other revenue

Royalty and other revenue	3 Months Ended
	Mar. 31, 2021
License And Royalty Revenue [Abstract]
Royalty and other revenue	Royalty and other revenue The Company has out-licensed intellectual property to various third parties. Under the terms of these agreements, the Company may be entitled to royalties and milestone payments. In April 2017, the Company entered into a worldwide license agreement with Novartis, which is further described in the Company’s Annual Report on Form 10-K filed with the SEC on February 23, 2021. Beginning in the fourth quarter of 2017, the Company began recognizing royalty revenue from sales of tisagenlecleucel under the agreement. This license agreement was terminated effective March 2021, at which point in time Novartis was no longer required to pay the Company royalty or other payments on net sales of tisagenlecleucel or any future products. Royalty revenue recognized from sales of tisagenlecleucel is included within royalty and other revenue on the condensed consolidated statement of operations and comprehensive loss. In May 2020, the Company entered into a non-exclusive license agreement with Juno Therapeutics, Inc. (“Juno”), a wholly-owned subsidiary of BMS, related to lentiviral vector technology to develop and commercialize CD-19-directed CAR T cell therapies. Upon regulatory approval of lisocabtagene maraleucel during the first quarter of 2021, the Company received a $2.5 million milestone payment from Juno, which is included within royalty and other revenue. The Company may also be obligated to pay third-party licensors as a result of revenue recognized under out-license agreements, which is included within cost of royalty and other revenue on the condensed consolidated statement of operations and comprehensive loss. During the first quarter of 2021, the Company recognized an immaterial amount of product revenue related to the sale of ZYNTEGLO in the European Union and the related cost of goods sold, which is included within royalty and other revenue and cost of royalty and other revenue, respectively.

Stock-based compensation

Stock-based compensation	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Stock-based compensation	Stock-based compensation In January 2021 and 2020, the number of shares of common stock available for issuance under the 2013 Stock Option and Incentive Plan (“2013 Plan”) was increased by approximately 2.7 million and 2.2 million shares, respectively, as a result of the automatic increase provision of the 2013 Plan. As of March 31, 2021, the total number of shares of common stock available for issuance under the 2013 Plan was approximately 3.5 million. Stock-based compensation expense The Company recognized stock-based compensation expense totaling $42.5 million and $36.3 million for the three months ended March 31, 2021 and 2020, respectively. Stock-based compensation expense by award type included within the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands): For the three months ended March 31, 2021 2020 Stock options $ 20,659 $ 24,440 Restricted stock units 14,733 11,853 Employee stock purchase plan and other 7,082 — $ 42,474 $ 36,293 Stock-based compensation expense by classification included within the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands): For the three months ended March 31, 2021 2020 Research and development $ 19,868 $ 16,269 Selling, general and administrative 22,606 20,024 $ 42,474 $ 36,293 Stock-based compensation of $0.3 million and less than $0.1 million was capitalized into inventory for the three months ended March 31, 2021 and 2020, respectively. During the three months ended March 31, 2021, capitalized stock-based compensation of less than $0.1 million was recognized within cost of royalty and other revenue when the related product was sold. As of March 31, 2021, the Company had approximately $252.4 million of unrecognized stock-based compensation expense, which is expected to be recognized over a weighted-average period of approximately 2.2 years. Unrestricted stock awards During the first quarter of 2021, the Company granted 0.4 million unrestricted stock awards to employees as part of its 2020 annual incentive program. In addition, the Company implemented a retention program designed to incentivize and retain employees through the separation of its severe genetic disease and oncology programs, which is intended to occur by the end of 2021. Under the retention program, employees are entitled to a one-time bonus payment, consisting of both a cash payment and unrestricted stock awards, with the condition that the employee remains employed at the end of 2021. For the three months ended March 31, 2021, the Company recognized $13.3 million in expense related to this program, which includes $6.7 million in stock compensation expense related to the anticipated grants of stock. Stock option activity The following table summarizes the stock option activity under the Company’s equity award plans: Shares (in thousands) Weighted- average exercise price per share Outstanding at December 31, 2020 6,262 $ 105.02 Granted 671 $ 29.17 Exercised (207) $ 5.88 Canceled, forfeited, or expired (268) $ 110.62 Outstanding at March 31, 2021 6,458 $ 100.08 Exercisable at March 31, 2021 3,829 $ 111.17 Vested and expected to vest at March 31, 2021 6,458 $ 100.08 During the three months ended March 31, 2021, 0.2 million stock options were exercised, resulting in total proceeds to the Company of $1.2 million. Restricted stock unit activity The following table summarizes the restricted stock unit activity under the Company’s equity award plans: Shares Weighted- Unvested balance at December 31, 2020 1,495 $ 102.34 Granted 990 $ 29.17 Vested (294) $ 108.85 Forfeited (118) $ 84.63 Unvested balance at March 31, 2021 2,073 $ 67.48 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. During each of the three months ended March 31, 2021 and 2020, less than 0.1 million shares of common stock were issued under the 2013 ESPP.

Income taxes

Income taxes	3 Months Ended
	Mar. 31, 2021
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 expense recognized during the three months ended March 31, 2021 is due to income taxes on foreign earnings. In March 2020, the Coronavirus Aid, Relief and Economic Security Act (“CARES Act”) was enacted. This law temporarily suspends and adjusts certain law changes enacted in the Tax Cuts and Jobs Act in 2017. In December 2020, the Consolidated Appropriations Act was enacted. This law modified the employee retention credit under the CARES Act and created credit extenders for certain credits. In March 2021, the American Rescue Plan Act (“ARPA”) was enacted and contained extenders to the refundable employee retention credit and provided further limitations to executive compensation effective for tax years beginning after 2026. The Company has concluded that the provisions in the CARES Act, Consolidated Appropriations Act, and ARPA have an immaterial impact on the Company’s income tax expense due to its cumulative losses and full valuation allowance position.

Net loss per share

Net loss per share	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Net loss per share	Net loss per share The following common stock equivalents were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect (in thousands): For the three months ended March 31, 2021 2020 Outstanding stock options 6,458 6,478 Restricted stock units 2,073 1,585 ESPP shares and other 884 — 9,415 8,063

Basis of presentation, princi_2

Basis of presentation, principles of consolidation and significant accounting policies (Policies)	3 Months Ended
	Mar. 31, 2021
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”) as found in the Accounting Standards Codification ("ASC") and Accounting Standards Updates (“ASU”) 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 March 31, 2021 and 2020.
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. Any reference in these notes to applicable guidance is meant to refer to GAAP. The Company views its operations and manages its business in one operating segment.
Royalty and other revenue	Royalty and other revenue During the first quarter of 2021, the Company recognized an immaterial amount of product revenue related to the sale of ZYNTEGLO in the European Union and the related cost of goods sold, which is included within royalty and other revenue and cost of royalty and other revenue, respectively.
Inventories	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 regulatory approval. Manufacturing costs incurred prior to regulatory approval for pre-launch inventory that did not qualify for capitalization and clinical manufacturing costs are charged to research and development expense in the Company’s condensed consolidated statements of operations and comprehensive loss as costs are 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, vectors, 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.
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 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, contingent consideration, stock-based compensation expense, accrued expenses, revenue recognition, income taxes, inventory capitalization, 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.
Recent accounting pronouncements	Recent accounting pronouncements Recently adopted ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify the accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The new standard was effective beginning January 1, 2021. The adoption of ASU 2019-12 did not have a material impact on the Company's financial position or results of operations upon adoption. ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity In August 2020, the FASB issued ASU 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU 2020-06”). ASU 2020-06 simplifies the complexity associated with applying U.S. GAAP for certain financial instruments with characteristics of liabilities and equity. More specifically, the amendments focus on the guidance for convertible instruments and derivative scope exception for contracts in an entity's own equity. The Company early adopted the new standard, effective January 1, 2021. The adoption of ASU 2020-06 did not have an impact on the Company's financial position or results of operations upon adoption. ASU No. 2020-08, Codification Improvements to Subtopic 310-20, Receivables - Nonrefundable Fees and Other Costs In October 2020, the FASB issued ASU 2020-08, Codification Improvements to Subtopic 310-20, Receivables - Nonrefundable Fees and Other Costs (“ASU 2020-08”) to provide further clarification and update the previously issued guidance in ASU 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20: Premium Amortization on Purchased Callable Debt Securities) (“ASU 2017-08”). ASU 2017-08 shortened the amortization period for certain callable debt securities purchased at a premium by requiring that the premium be amortized to the earliest call date. ASU 2020-08 requires that at each reporting period, to the extent that the amortized cost of an individual callable debt security exceeds the amount repayable by the issuer at the next call date, the excess premium shall be amortized to the next call date. The new standard was effective beginning January 1, 2021. The adoption of ASU 2020-08 did not have a material impact on the Company's financial position or results of operations upon adoption. ASU No. 2020-10, Codification Improvements In October 2020, the FASB issued ASU 2020-10, Codification Improvements ("ASU 2020-10"). The amendments in this ASU represent changes to clarify the ASC, correct unintended application of the guidance, or make minor improvements to the ASC that are not expected to have a significant effect on current accounting practice or create a significant administrative cost to most entities. This new standard was effective beginning January 1, 2021. The adoption of ASU 2020-10 did not have a material impact on the Company's financial position or results of operations upon adoption.

Marketable Securities (Tables)

Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Summary of Marketable Securities Held	The following table summarizes the marketable securities held at March 31, 2021 and December 31, 2020 (in thousands): Description Amortized cost / Cost Unrealized gains Unrealized losses Fair value March 31, 2021 U.S. government agency securities and treasuries $ 429,039 $ 256 $ (16) $ 429,279 Corporate bonds 142,773 163 (40) 142,896 Commercial paper 78,955 — — 78,955 Equity securities 4,305 — (1,598) 2,707 Total $ 655,072 $ 419 $ (1,654) $ 653,837 December 31, 2020 U.S. government agency securities and treasuries $ 675,043 $ 302 $ (74) $ 675,271 Corporate bonds 197,171 432 (40) 197,563 Commercial paper 77,949 1 — 77,950 Equity securities 20,017 — (14,364) 5,653 Total $ 970,180 $ 735 $ (14,478) $ 956,437

Fair value measurements (Tables

Fair value measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis	The following table sets forth the Company’s assets and liabilities that are measured at fair value on a recurring basis as of March 31, 2021 and December 31, 2020 (in thousands): Description Total Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) March 31, 2021 Assets: Cash and cash equivalents $ 439,714 $ 410,715 $ 28,999 $ — Marketable securities: U.S. government agency securities and treasuries 429,279 — 429,279 — Corporate bonds 142,896 — 142,896 — Commercial paper 78,955 — 78,955 — Equity securities 2,707 2,707 — — Total $ 1,093,551 $ 413,422 $ 680,129 $ — Liabilities: Contingent consideration $ 1,878 $ — $ — $ 1,878 Total $ 1,878 $ — $ — $ 1,878 December 31, 2020 Assets: Cash and cash equivalents $ 317,705 $ 317,705 $ — $ — Marketable securities: U.S. government agency securities and treasuries 675,271 — 675,271 — Corporate bonds 197,563 — 197,563 — Commercial paper 77,950 — 77,950 — Equity securities 5,653 5,653 — — Total $ 1,274,142 $ 323,358 $ 950,784 $ — Liabilities: Contingent consideration $ 1,509 $ — $ — $ 1,509 Total $ 1,509 $ — $ — $ 1,509
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value	The following table summarizes available-for-sale debt securities in a continuous unrealized loss position for less than and greater than twelve months, and for which an allowance for credit losses has not been recorded at March 31, 2021 and December 31, 2020 (in thousands): Less than 12 months 12 months or greater Total Description Fair value Unrealized losses Fair value Unrealized losses Fair value Unrealized losses March 31, 2021 U.S. government agency securities $ 48,802 $ (16) $ — $ — $ 48,802 $ (16) Corporate bonds 92,855 (40) — — 92,855 (40) Total $ 141,657 $ (56) $ — $ — $ 141,657 $ (56) December 31, 2020 U.S. government agency securities $ 211,384 $ (74) $ — $ — $ 211,384 $ (74) Corporate bonds 76,598 (40) 1,205 — 77,803 (40) Total $ 287,982 $ (114) $ 1,205 $ — $ 289,187 $ (114)

Inventory (Tables)

Inventory (Tables)	3 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
Schedule of Inventory, Current	Inventory consists of the following (in thousands): As of March 31, 2021 As of December 31, 2020 Raw materials $ 16,892 $ 8,967 Finished goods 1,187 1,731 Inventory $ 18,079 $ 10,698

Property, plant and equipment_2

Property, plant and equipment, net (Tables)	3 Months Ended
	Mar. 31, 2021
Property, Plant and Equipment [Abstract]
Summary of Property, Plant and Equipment Net	Property, plant and equipment, net, consists of the following (in thousands): As of March 31, 2021 As of December 31, 2020 Land $ 1,210 $ 1,210 Building 88,591 15,745 Computer equipment and software 6,919 6,950 Office equipment 7,633 7,665 Laboratory equipment 66,600 55,521 Leasehold improvements 34,104 34,286 Construction-in-progress 14,939 92,514 Total property, plant and equipment 219,996 213,891 Less accumulated depreciation and amortization (54,798) (51,060) Property, plant and equipment, net $ 165,198 $ 162,831

Accrued expenses and other cu_2

Accrued expenses and other current liabilities (Tables)	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following (in thousands): As of March 31, 2021 As of December 31, 2020 Employee compensation $ 45,916 $ 55,802 Manufacturing costs 24,726 22,571 Clinical and contract research organization costs 23,377 23,766 Collaboration research costs 23,679 20,004 Property, plant and equipment 1,543 789 License and milestone fees 303 278 Professional fees 1,993 1,541 Other 25,254 20,655 Accrued expenses and other current liabilities $ 146,791 $ 145,406

Collaborative arrangements (Tab

Collaborative arrangements (Tables)	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of Agreement Transaction Price	The following tables summarize the total transaction price, the allocation of the total transaction price to the identified performance obligations under the arrangement (including those performance obligations that were completed as of the May 2020 contract modification date), and the amount of the transaction price unsatisfied as of March 31, 2021 (in thousands): Ide-cel transaction price as of March 31, Up-front non-refundable payments, option fee and milestone payments received prior to May 2020 $ 120,000 Allocated portion of the up-front non-refundable payment received in connection with the Amended Ide-cel CCPS and bb21217 License Agreement (2) 184,029 Estimated variable consideration (3) 83,900 $ 387,929 (1) Composed of all up-front payments and option fee and milestone payments received under the BMS Collaboration Agreement, Amended BMS Collaboration Agreement, Ide-cel License Agreement, and Ide-cel CCPS. This consideration was allocated to the performance obligations under the Ide-cel CCPS based on a relative standalone selling price (“SSP”) basis. The Company estimated the SSP of the ide-cel license after considering potential future cash flows under the license. The Company then discounted these probability-weighted cash flows to their present value. The Company estimated the SSP of each of the ide-cel research and development services and ide-cel manufacturing services to be provided based on the Company’s estimated cost of providing the services plus an applicable profit margin commensurate with observable market data for similar services. (2) This represents the portion of the $200.0 million up-front payment received under the Amended Ide-cel CCPS and Amended bb21217 License Agreement which was allocated to ide-cel. (3) Estimated variable consideration represents the estimated reimbursement from BMS for the manufacture of vectors and associated payload through development. Allocation of Transaction price unsatisfied as of March 31, 2021 Ide-cel research and development services $ 40,912 $ — Ide-cel license and manufacturing services 347,017 — $ 387,929 $ — The following table summarizes the net collaborative arrangement revenue recognized or expense incurred for the joint ide-cel development efforts in the U.S. under ASC 808 related to the combined performance obligation for the license and vector manufacturing of ide-cel in the U.S. for the three months ended March 31, 2021, and 2020 (in thousands): For the three months ended March 31, 2021 2020 ASC 808 ide-cel research and development expense - U.S. (1) $ (16,825) $ (5,080) (1) As noted above, the calculation of collaborative arrangement revenue or research and development expense to be recognized for joint ide-cel development efforts in the U.S. is performed on a quarterly basis. The calculation is independent of previous activity, which may result in fluctuations between revenue and expense recognition period over period, depending on the varying extent of effort performed by each party during the period. Revenue related to the combined unit of accounting for the ex-U.S. license and vector manufacturing services is accounted for in accordance with Topic 606. The following table summarizes the revenue recognized related to the combined unit of accounting for the ide-cel ex-U.S. license and vector manufacturing services for the three months ended March 31, 2021, and 2020 (in thousands): For the three months ended March 31, 2021 2020 ASC 606 ide-cel license and manufacturing revenue - ex-U.S. $ 5,104 $ 13,970 The following tables summarize the total transaction price, the allocation of the total transaction price to the identified performance obligations under the arrangement (including those performance obligations that were completed as of the May 2020 contract modification date), and the amount of the transaction price unsatisfied as of March 31, 2021 (in thousands): bb21217 transaction price as of March 31, 2021 Up-front non-refundable payment received prior to May 2020 contract modification (1) $ 15,000 Allocated portion of the up-front non-refundable payment received in connection with the Amended Ide-cel CCPS and bb21217 License Agreement (2) 15,971 Estimated variable consideration (3) 1,803 $ 32,774 (1) Composed of the up-front non-refundable payment received under the bb21217 License Agreement. This consideration was allocated to the performance obligations under the bb21217 License Agreement based on a relative SSP basis. The Company estimated the SSP of the bb21217 license after considering potential future cash flows under the license. The Company then discounted these probability-weighted cash flows to their present value. The Company estimated the SSP of each of the bb21217 research and development services and bb21217 manufacturing services to be provided based on the Company’s estimated cost of providing the services plus an applicable profit margin commensurate with observable market data for similar services. (2) This represents the portion of the $200.0 million up-front payment received under the Amended Ide-cel CCPS and Amended bb21217 License Agreement which was allocated to bb21217. (3) Estimated variable consideration represents the estimated reimbursement from BMS for the manufacture of vectors and associated payload through development. Allocation of transaction Transaction price unsatisfied as of March 31, 2021 bb21217 research and development services $ 5,444 $ — bb21217 license and manufacturing services 27,330 27,330 $ 32,774 $ 27,330
Summary of Contract Assets and Liabilities	The following table presents changes in the balances of the Company’s BMS receivables and contract liabilities during the three months ended March 31, 2021 (in thousands): Balance at December 31, Additions Deductions Balance at Receivables $ 400 $ — $ (400) $ — Contract liabilities: Deferred revenue $ 26,582 $ — $ (820) $ 25,762

Stock-based compensation (Table

Stock-based compensation (Tables)	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Summary of Stock-Based Compensation Expense by Award Type	Stock-based compensation expense by award type included within the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands): For the three months ended March 31, 2021 2020 Stock options $ 20,659 $ 24,440 Restricted stock units 14,733 11,853 Employee stock purchase plan and other 7,082 — $ 42,474 $ 36,293
Schedule of Stock-Based Compensation Expense by Classification	Stock-based compensation expense by classification included within the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands): For the three months ended March 31, 2021 2020 Research and development $ 19,868 $ 16,269 Selling, general and administrative 22,606 20,024 $ 42,474 $ 36,293
Summary of Stock Option Activity Under Plan	The following table summarizes the stock option activity under the Company’s equity award plans: Shares (in thousands) Weighted- average exercise price per share Outstanding at December 31, 2020 6,262 $ 105.02 Granted 671 $ 29.17 Exercised (207) $ 5.88 Canceled, forfeited, or expired (268) $ 110.62 Outstanding at March 31, 2021 6,458 $ 100.08 Exercisable at March 31, 2021 3,829 $ 111.17 Vested and expected to vest at March 31, 2021 6,458 $ 100.08
Summary of Restricted Common Stock Awards	The following table summarizes the restricted stock unit activity under the Company’s equity award plans: Shares Weighted- Unvested balance at December 31, 2020 1,495 $ 102.34 Granted 990 $ 29.17 Vested (294) $ 108.85 Forfeited (118) $ 84.63 Unvested balance at March 31, 2021 2,073 $ 67.48

Net loss per share (Tables)

Net loss per share (Tables)	3 Months Ended
	Mar. 31, 2021
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 March 31, 2021 2020 Outstanding stock options 6,458 6,478 Restricted stock units 2,073 1,585 ESPP shares and other 884 — 9,415 8,063

Description of the business - A

Description of the business - Additional Information (Detail) $ in Millions	Mar. 31, 2021USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash, cash equivalents and marketable securities	$ 1,090

Basis of presentation, princi_3

Basis of presentation, principles of consolidation and significant accounting policies - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021segment
Accounting Policies [Abstract]
Number of operating segments	1

Marketable Securities - Summary

Marketable Securities - Summary of Marketable Securities Held (Detail) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Amortized cost / Cost
Equity securities	$ 4,305,000	$ 20,017,000
Marketable securities	655,072,000	970,180,000
Unrealized gains
Equity securities	0	0
Marketable securities	419,000	735,000
Unrealized losses
Equity securities	(1,598,000)	(14,364,000)
Marketable securities	(1,654,000)	(14,478,000)
Fair value
Equity securities	2,707,000	5,653,000
Marketable securities:	653,837,000	956,437,000
Debt securities, available-for-sale, noncurrent	0	0
U.S. government agency securities and treasuries
Amortized cost / Cost
Debt securities	429,039,000	675,043,000
Unrealized gains
Debt securities	256,000	302,000
Unrealized losses
Debt securities	(16,000)	(74,000)
Fair value
Debt securities	429,279,000	675,271,000
Corporate bonds
Amortized cost / Cost
Debt securities	142,773,000	197,171,000
Unrealized gains
Debt securities	163,000	432,000
Unrealized losses
Debt securities	(40,000)	(40,000)
Fair value
Debt securities	142,896,000	197,563,000
Commercial paper
Amortized cost / Cost
Debt securities	78,955,000	77,949,000
Unrealized gains
Debt securities	0	1,000
Unrealized losses
Debt securities	0	0
Fair value
Debt securities	$ 78,955,000	$ 77,950,000

Fair value measurements - Recor

Fair value measurements - Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets:
Marketable securities:	$ 653,837	$ 956,437
Equity securities	2,707	5,653
Fair Value, Measurements, Recurring
Assets:
Cash and cash equivalents	439,714	317,705
Equity securities	2,707	5,653
Total	1,093,551	1,274,142
Liabilities:
Contingent consideration	1,878	1,509
Total	1,878	1,509
Fair Value, Measurements, Recurring | U.S. government agency securities and treasuries
Assets:
Marketable securities:	429,279	675,271
Fair Value, Measurements, Recurring | Corporate bonds
Assets:
Marketable securities:	142,896	197,563
Fair Value, Measurements, Recurring | Commercial paper
Assets:
Marketable securities:	78,955	77,950
Fair Value, Measurements, Recurring | Quoted prices in active markets (Level 1)
Assets:
Cash and cash equivalents	410,715	317,705
Equity securities	2,707	5,653
Total	413,422	323,358
Liabilities:
Contingent consideration	0	0
Total	0	0
Fair Value, Measurements, Recurring | Quoted prices in active markets (Level 1) | U.S. government agency securities and treasuries
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring | Quoted prices in active markets (Level 1) | Corporate bonds
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring | Quoted prices in active markets (Level 1) | Commercial paper
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets:
Cash and cash equivalents	28,999	0
Equity securities	0	0
Total	680,129	950,784
Liabilities:
Contingent consideration	0	0
Total	0	0
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | U.S. government agency securities and treasuries
Assets:
Marketable securities:	429,279	675,271
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | Corporate bonds
Assets:
Marketable securities:	142,896	197,563
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | Commercial paper
Assets:
Marketable securities:	78,955	77,950
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Equity securities	0	0
Total	0	0
Liabilities:
Contingent consideration	1,878	1,509
Total	1,878	1,509
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | U.S. government agency securities and treasuries
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | Corporate bonds
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | Commercial paper
Assets:
Marketable securities:	$ 0	$ 0

Fair value measurements - Narra

Fair value measurements - Narrative (Detail) - USD ($)	1 Months Ended	3 Months Ended
	Jan. 31, 2021	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized gain (loss) on available-for-sale securities		$ 0	$ 0
Interest receivable		2,200,000		$ 3,100,000
Interest receivable, write-offs		0	0
Investment at fair value		2,707,000		$ 5,653,000
Proceeds from sale of equity securities	$ 31,300,000
Other (Expense) Income, Net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) on equity securities		$ (28,400,000)	$ (4,500,000)

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Unrealized Loss on Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair value
Less than 12 months	$ 141,657	$ 287,982
12 months or greater	0	1,205
Total	141,657	289,187
Unrealized losses
Less than 12 months	(56)	(114)
12 months or greater	0	0
Total	(56)	(114)
U.S. government agency securities and treasuries
Fair value
Less than 12 months	48,802	211,384
12 months or greater	0	0
Total	48,802	211,384
Unrealized losses
Less than 12 months	(16)	(74)
12 months or greater	0	0
Total	(16)	(74)
Corporate bonds
Fair value
Less than 12 months	92,855	76,598
12 months or greater	0	1,205
Total	92,855	77,803
Unrealized losses
Less than 12 months	(40)	(40)
12 months or greater	0	0
Total	$ (40)	$ (40)

Inventory (Details)

Inventory (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
Raw materials	$ 16,892	$ 8,967
Finished goods	1,187	1,731
Inventory	$ 18,079	$ 10,698

Property, plant and equipment_3

Property, plant and equipment, net - Summary of Property, Plant and Equipment Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 219,996	$ 213,891
Less accumulated depreciation and amortization	(54,798)	(51,060)
Property, plant and equipment, net	165,198	162,831
Land
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	1,210	1,210
Building
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	88,591	15,745
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	6,919	6,950
Office equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	7,633	7,665
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	66,600	55,521
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	34,104	34,286
Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 14,939	$ 92,514

Property, plant and equipment_4

Property, plant and equipment, net - Narrative (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 219,996	$ 213,891
Remaining Construction In Progress North Carolina Manufacturing Facility
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 14,200	$ 91,100

Accrued expenses and other cu_3

Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Employee compensation	$ 45,916	$ 55,802
Manufacturing costs	24,726	22,571
Clinical and contract research organization costs	23,377	23,766
Collaboration research costs	23,679	20,004
Property, plant and equipment	1,543	789
License and milestone fees	303	278
Professional fees	1,993	1,541
Other	25,254	20,655
Accrued expenses and other current liabilities	$ 146,791	$ 145,406

Leases - Embedded Operating Lea

Leases - Embedded Operating Leases Narrative (Details) - Manufacturing Facility $ in Millions	1 Months Ended
	Jul. 31, 2020USD ($)
Lessee, Lease, Description [Line Items]
Annual maintenance fees	$ 5.4
Lease notice period	18 months
Lease period	5 years

Commitments and contingencies -

Commitments and contingencies - Narrative (Detail) - Pregenen $ in Millions	Jun. 30, 2014USD ($)
Commitments And Contingencies Disclosure [Line Items]
Contingent cash payments	$ 120
Clinical Milestone Payments
Commitments And Contingencies Disclosure [Line Items]
Contingent cash payments	20.1
Commercial Milestones Payments
Commitments And Contingencies Disclosure [Line Items]
Contingent cash payments	$ 99.9

Collaborative arrangements - Na

Collaborative arrangements - Narrative (Detail)

Aug. 24, 2018USD ($)$ / sharesshares

Aug. 31, 2018target

Sep. 30, 2017USD ($)

Feb. 29, 2016USD ($)

Jun. 30, 2015USD ($)product

Mar. 31, 2013USD ($)

Mar. 31, 2021USD ($)

Mar. 31, 2020USD ($)

Jun. 30, 2019USD ($)

Dec. 31, 2020USD ($)

May 31, 2020USD ($)

Mar. 31, 2018USD ($)

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Deferred revenue

$ 990,000

$ 2,118,000

Bristol-Myers Squibb

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Contract with customer liability

25,762,000

$ 26,582,000

Term of collaboration agreement

3 years

Deferred revenue

(800,000)

Bristol-Myers Squibb | Collaborative Arrangement

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Contract with customer liability

$ 75,000,000

Bristol-Myers Squibb | Amended Collaborative Arrangement

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Contract with customer liability

$ 25,000,000

Term of collaboration agreement

3 years

Number of product candidates | product

2

Bristol-Myers Squibb | Ide-cel License Agreement | First Product Candidates

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Collaboration agreement, option fee received

$ 10,000,000

Bristol-Myers Squibb | Ide-cel License Agreement | First Product Candidates | U.S.

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Milestone payments receivable

85,000,000

Bristol-Myers Squibb | Ide-cel License Agreement | First Product Candidates | Outside of U.S.

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Milestone payments receivable

$ 55,000,000

Bristol-Myers Squibb | Ide-cel Co-Development, Co-Promote and Profit Share Agreement

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Milestone payment achieved

$ 10,000,000

Bristol-Myers Squibb | Ide-cel Co-Development, Co-Promote and Profit Share Agreement | U.S.

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Milestone payments receivable

$ 10,000,000

Bristol-Myers Squibb | Ide-cel Co-Development, Co-Promote and Profit Share Agreement | Outside of U.S.

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Milestone payments receivable

$ 60,000,000

Bristol-Myers Squibb | Amended Ide Cel Co Development, Co-Promote And Profit Share Agreement

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Milestone and royalty obligation buy-out

184,029,000

$ 200,000,000

Bristol-Myers Squibb | bb21217 License Agreement

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Collaboration agreement, option fee received

$ 15,000,000

15,000,000

Milestone payment achieved

10,000,000

Milestone and royalty obligation buy-out

$ 15,971,000

Additional fee receivable if option to co-develop and co-promote is not exercised

10,000,000

Deferred revenue recognition period

2 years

Bristol-Myers Squibb | bb21217 License Agreement | U.S.

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Milestone payments receivable

85,000,000

Bristol-Myers Squibb | bb21217 License Agreement | Outside of U.S.

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Milestone payments receivable

$ 55,000,000

Bristol-Myers Squibb | Ide-cel License and Manufacturing Services

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Collaboration agreement, transaction price

$ 347,017,000

Remaining performance obligation revenue

0

Bristol-Myers Squibb | Ide-cel License and Manufacturing Services | License and Manufacturing Services

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Contract with customer liability

0

800,000

Remaining performance obligation revenue

0

Bristol-Myers Squibb | Ide-cel License and Manufacturing Services | License and Manufacturing Services | Outside of U.S.

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Revenue

5,104,000

13,970,000

Bristol-Myers Squibb | Ide-cel Research and Development

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Revenue

0

0

Bristol-Myers Squibb | bb21217 Research and Development Services

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Collaboration agreement, transaction price

5,444,000

Remaining performance obligation revenue

0

Bristol-Myers Squibb | bb21217 Research and Development Services | Phase I, Additional Obligation

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Revenue

0

2,400,000

Bristol-Myers Squibb | bb21217 license and manufacturing services

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Collaboration agreement, transaction price

27,330,000

Remaining performance obligation revenue

27,330,000

Bristol-Myers Squibb | bb21217 license and manufacturing services | License and Manufacturing Services

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Contract with customer liability

25,800,000

25,800,000

Liability, revenue recognized

0

0

Remaining performance obligation revenue

27,300,000

Regeneron Collaboration Agreement

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Number of initial collaboration targets | target

6

Research collaboration term

5 years

5 years

Joint research activities remaining to be recognized

29,300,000

$ 30,800,000

Regeneron Collaboration Agreement | Collaboration

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Liability, revenue recognized

$ 1,500,000

$ 2,300,000

Regeneron Collaboration Agreement | Maximum

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Milestone payments receivable

$ 130,000,000

Regeneron Collaboration Agreement | Research and Development Services

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Collaboration agreement, transaction price

100,000,000

Purchase price premium

$ 37,000,000

Collaborative arrangement amortization period

5 years

Collaborative arrangement amount attributed to equity sold

$ 54,500,000

Collaborative arrangement amount attributed to joint research activities

$ 45,500,000

Regeneron Collaboration Agreement | Share Purchase Agreement

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Common stock shares issued (in shares) | shares

400,000

Common stock price per share | $ / shares

$ 238.10

Investment in common stock

$ 100,000,000

Purchase price premium

$ 37,000,000

Collaborative arrangement research initial funding obligation, percentage

50.00%

Regeneron Collaboration Agreement | Share Purchase Agreement | Common Shares

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Common stock shares issued (in shares) | shares

400,000

Investment in common stock

$ 63,000,000

Collaborative arrangements - Su

Collaborative arrangements - Summary of Total Transaction Price, Allocation of Total Transaction Price to Identified Performance Obligations Under Arrangement and Amount of Transaction Price Unsatisfied (Detail) - Bristol-Myers Squibb - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Sep. 30, 2017	Mar. 31, 2021	May 31, 2020
Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Up-front non-refundable payment		$ 120,000
Amended Ide Cel Co Development, Co-Promote And Profit Share Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone and royalty obligation buy-out		184,029	$ 200,000
Vectors and Associated Payload
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Estimated variable consideration		83,900
Ide-cel Research and Development Services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, transaction price		40,912
Transaction price unsatisfied		0
Ide-cel Transaction Price
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, transaction price		387,929
Transaction price unsatisfied		0
bb21217 License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone and royalty obligation buy-out		15,971
Collaboration agreement, license fee	$ 15,000	15,000
Manufacturing Services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Estimated variable consideration		1,803
bb21217 Transaction Price
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, transaction price		32,774
Transaction price unsatisfied		27,330
bb21217 Research and Development Services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, transaction price		5,444
Transaction price unsatisfied		0
bb21217 license and manufacturing services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, transaction price		27,330
Transaction price unsatisfied		27,330
Ide-cel License and Manufacturing Services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, transaction price		347,017
Transaction price unsatisfied		$ 0

Collaborative arrangements - _2

Collaborative arrangements - Summary of Revenue Recognized or Expense Incurred for Joint Ide-cel Development Efforts Related to Combined Unit of Accounting for its License and Vector Manufacturing of Ide-cel (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense	$ (154,478)	$ (154,123)
Bristol-Myers Squibb | U.S. | Ide-cel Research and Development Services | License and Manufacturing Services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense	(16,825)	(5,080)
Bristol-Myers Squibb | Outside of U.S. | Ide-cel License and Manufacturing Services | License and Manufacturing Services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue	$ 5,104	$ 13,970

Collaborative arrangements - Ch

Collaborative arrangements - Changes in Balances of Company's Receivables and Contract Liabilities (Detail) - Bristol-Myers Squibb $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)
Receivables
Balance at beginning of period	$ 400
Additions	0
Deductions	(400)
Balance at end of period	0
Contract liabilities:
Balance at beginning of period	26,582
Additions	0
Deductions	(820)
Balance at end of period	$ 25,762

Royalty and other revenue - Add

Royalty and other revenue - Additional Information (Detail) - Royalty and other revenue - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
License And Royalty Revenue [Line Items]
Revenue	$ 5,357	$ 2,728
Juno Therapeutics
License And Royalty Revenue [Line Items]
Revenue	$ 2,500

Stock-based compensation - Narr

Stock-based compensation - Narrative (Detail) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended
	Jan. 31, 2021	Jan. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	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)	2,700,000	2,200,000
Number of shares available for issuance (in shares)			3,500,000
Stock-based compensation expense			$ 42,474	$ 36,293
Amount capitalized			300
Unrecognized stock- based compensation expense related to unvested stock options, restricted stock units, performance-based restricted stock units and employee stock purchase plan			$ 252,400
Expected weighted-average period related to unvested stock options, restricted stock units, performance-based restricted stock units and employee stock purchase plan			2 years 2 months 12 days
Granted (in shares)			671,000
Stock option share exercised (in shares)			207,000
Proceed from option share exercised			$ 1,200
Retention Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee benefits and share-based compensation expense			13,300
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount capitalized				100
Maximum | Cost Of Royalty And Other Revenue
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount capitalized			100
Employee stock purchase plan and other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 7,082	$ 0
Common shares reserved for future issuance (in shares)					200,000
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)			100,000	100,000
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 14,733	$ 11,853
Unrestricted Stock Awards | 2020 Annual Incentive Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)			400,000
Unrestricted Stock Awards | Retention Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 6,700

Stock-based compensation - Summ

Stock-based compensation - Summary of Stock-Based Compensation Expense by Award Type (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 42,474	$ 36,293
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	20,659	24,440
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	14,733	11,853
Employee stock purchase plan and other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 7,082	$ 0

Stock-based compensation - Sche

Stock-based compensation - Schedule of Stock-Based Compensation Expense by Classification (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 42,474	$ 36,293
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	19,868	16,269
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 22,606	$ 20,024

Stock-based compensation - Su_2

Stock-based compensation - Summary of Stock Option Activity Under Plan (Detail) shares in Thousands	3 Months Ended
	Mar. 31, 2021$ / sharesshares
Shares (in thousands)
Outstanding at beginning of period (in shares) | shares	6,262
Granted (in shares) | shares	671
Exercised (in shares) | shares	(207)
Canceled, forfeited, or expired (in shares) | shares	(268)
Outstanding at end of period (in shares) | shares	6,458
Exercisable at end of period (in shares) | shares	3,829
Vested and expected to vest at end of period (in shares) | shares	6,458
Weighted- average exercise price per share
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 105.02
Granted (in dollars per share) | $ / shares	29.17
Exercised (in dollars per share) | $ / shares	5.88
Canceled, forfeited, or expired (in dollars per share) | $ / shares	110.62
Outstanding at end of period (in dollars per share) | $ / shares	100.08
Exercisable at end of period (in dollars per share) | $ / shares	111.17
Vested and expected to vest at end of period (in dollars per share) | $ / shares	$ 100.08

Stock-based compensation - Su_3

Stock-based compensation - Summary of Restricted Stock Units (Detail) - Restricted stock units shares in Thousands	3 Months Ended
	Mar. 31, 2021$ / sharesshares
Shares (in thousands)
Unvested balance at beginning of period (in shares) | shares	1,495
Granted (in shares) | shares	990
Vested (in shares) | shares	(294)
Forfeited (in shares) | shares	(118)
Unvested balance at end of period (in shares) | shares	2,073
Weighted- average grant date fair value
Unvested balance at beginning of period (in dollars per share) | $ / shares	$ 102.34
Granted (in dollars per share) | $ / shares	29.17
Vested (in dollars per share) | $ / shares	108.85
Forfeited (in dollars per share) | $ / shares	84.63
Unvested balance at end of period (in dollars per share) | $ / shares	$ 67.48

Net loss per share - Common Sto

Net loss per share - Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
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)	9,415	8,063
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)	6,458	6,478
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	2,073	1,585
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)	884	0

Uncategorized Items - blue-2021

Label	Element	Value
Restricted Cash, Current	us-gaap_RestrictedCashCurrent	$ 0
Restricted Cash, Current	us-gaap_RestrictedCashCurrent	1,330,000
Restricted Cash, Noncurrent	us-gaap_RestrictedCashNoncurrent	54,500,000
Restricted Cash, Noncurrent	us-gaap_RestrictedCashNoncurrent	$ 54,505,000