0001737287-21-000009 | 10-K | XBRL Viewer | Allogene Therapeutics INC

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Cover Page - USD ($) $ in Millions	12 Months Ended
Cover Page - USD ($) $ in Millions	Dec. 31, 2020	Feb. 22, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-38693
Entity Registrant Name	Allogene Therapeutics, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-3562771
Entity Address, Address Line One	210 East Grand Avenue
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	457-2700
Title of 12(b) Security	Common Stock, Par Value $0.001 Per Share
Trading Symbol	ALLO
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
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
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 3,509
Entity Common Stock, Shares Outstanding (in shares)		140,647,818
Documents Incorporated by Reference	Portions of the Registrant’s Definitive Proxy Statement relating to the 2021 Annual Meeting of Stockholders, which will be filed with the Securities and Exchange Commission within 120 days after the end of the Registrant’s fiscal year ended December 31, 2020, are incorporated by reference into Part III of this Report.
Entity Central Index Key	0001737287
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 183,351	$ 175,126
Short-term investments	644,559	355,407
Prepaid expenses and other current assets	17,220	14,043
Total current assets	845,130	544,576
Long-term investments	204,208	58,322
Operating lease right-of-use asset	41,295	44,495
Property and equipment, net	118,840	56,449
Intangible assets, net	0	151
Restricted cash	9,449	4,299
Other long-term assets	5,169	4,618
Equity method investment	3,738	4,892
Total assets	1,227,829	717,802
Current liabilities:
Accounts payable	10,390	9,250
Accrued and other current liabilities	44,938	23,829
Deferred revenue	38,992	0
Total current liabilities	94,320	33,079
Lease liability, noncurrent	50,809	51,349
Other long-term liabilities	3,083	4,351
Total liabilities	148,212	88,779
Commitments and Contingencies (Notes 6, 7 and 8)
Stockholders’ equity:
Preferred stock, $0.001 par value: 10,000,000 authorized as of December 31, 2020 and December 31, 2019; no shares were issued and outstanding as of December 31, 2020 and December 31, 2019	0	0
Common stock, $0.001 par value: 200,000,000 authorized as of December 31, 2020 and December 31, 2019; 140,474,305 and 124,267,358 shares issued and outstanding as of December 31, 2020 and December 31, 2019, respectively	140	124
Additional paid-in capital	1,725,552	1,023,876
Accumulated deficit	(646,343)	(396,122)
Accumulated other comprehensive income	268	1,145
Total stockholders’ equity	1,079,617	629,023
Total liabilities and stockholders’ equity	$ 1,227,829	$ 717,802

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Preferred stock, par or stated value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	140,474,305	124,267,358
Common stock, shares outstanding (in shares)	140,474,305	124,267,358

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating expenses:
Research and development	$ 192,987	$ 144,535	$ 151,860
General and administrative	65,256	57,473	40,982
Total operating expenses	258,243	202,008	192,842
Loss from operations	(258,243)	(202,008)	(192,842)
Other income (expense), net:
Change in fair value of convertible note payable	0	0	(21,211)
Interest expense	0	0	(3,358)
Interest and other income, net	9,164	17,351	5,789
Other expenses	(1,142)	(268)	0
Total other income (expense), net	8,022	17,083	(18,780)
Loss before income taxes	(250,221)	(184,925)	(211,622)
Benefit from income taxes	0	331	117
Net loss	(250,221)	(184,594)	(211,505)
Other comprehensive income:
Net unrealized (loss) gain on available-for-sale investments, net of tax	(877)	839	306
Net comprehensive loss	$ (251,098)	$ (183,755)	$ (211,199)
Net loss per share, basic and diluted (in dollars per share)	$ (2.08)	$ (1.83)	$ (7.31)
Weighted-average number of shares used in computing net loss per share, basic and diluted (in shares)	120,370,177	101,061,149	28,948,386

Consolidated Statements of Convertible Preferred Stock and Stockholders’ Equity (Deficit) - USD ($) $ in Thousands	Total	IPO	ATM offering	Series A Convertible Preferred Stock	Series A Convertible Preferred Stock Series A1 Convertible Preferred Shares	Subscriptions Receivables from Preferred Stockholders	Common Stock	Common Stock IPO	Common Stock ATM offering	Notes Receivable from Common Stockholders	Additional Paid-in Capital	Additional Paid-in Capital IPO	Additional Paid-in Capital ATM offering	Accumulated Deficit	Accumulated Other Comprehensive Income
Balance (in shares) at Dec. 31, 2017				0			26,249,993
Balance at Dec. 31, 2017	$ (2)			$ 0		$ 0	$ 26			$ (5)	$ 0			$ (23)	$ 0
Issuance of Series A convertible preferred shares at $35.06 per share, net of issuance costs of $635 and $84 (in shares)				7,557,990	998,225
Issuance of Series A convertible preferred shares at $35.06 per share, net of issuance costs of $635 and $84				$ 264,365	$ 34,917
Issuance of Series A-1 convertible preferred shares at $35.06 per share in connection with asset acquisition (in shares)					3,187,772
Issuance of Series A-1 convertible preferred shares at $35.06 per share in connection with asset acquisition					$ 111,770
Proceeds received from common stockholders for issuance of founders' stock at inception	5									5
Subscriptions receivable from preferred stockholders	(150,000)					(150,000)
Proceeds received from preferred stockholders	150,000					150,000
Issuance of common stock for exercise of stock options (in shares)							5,020,580
Issuance of common stock for early exercise of stock options	5						$ 5
Issuance of common stock, net of issuance costs (in shares)								20,700,000
Issuance of common stock, net of issuance costs		$ 343,329						$ 21				$ 343,308
Conversion of Series A convertible preferred stock (in shares)				(11,743,987)			61,655,922
Conversion of Series A convertible preferred stock	411,052			$ (411,052)			$ 62				410,990
Issuance of common stock upon conversion of convertible stock (in shares)							7,856,176
Issuance of common stock upon conversion of convertible notes	141,410						$ 7				141,403
Adjustment for fractional shares from forward stock split	(2)										(2)
Stock-based compensation	18,566										18,566
Net loss	(211,505)													(211,505)
Net unrealized loss on available-for-sale investments	306														306
Balance (in shares) at Dec. 31, 2018				0			121,482,671
Balance at Dec. 31, 2018	703,164			$ 0		$ 0	$ 121			$ 0	914,265			(211,528)	306
Issuance of common stock for exercise of stock options (in shares)							711,623
Issuance of common stock for early exercise of stock options	2,959						$ 1				2,958
Employee stock purchase plan (in shares)							107,982
Employee stock purchase plan	1,783										1,783
Issuance of common stock, net of issuance costs (in shares)							1,965,082
Issuance of common stock, net of issuance costs	54,219						$ 2				54,217
Vesting of early exercised common stock	4,590										4,590
Stock-based compensation	46,063										46,063
Net loss	(184,594)													(184,594)
Net unrealized loss on available-for-sale investments	$ 839														839
Balance (in shares) at Dec. 31, 2019	124,267,358						124,267,358
Balance at Dec. 31, 2019	$ 629,023						$ 124				1,023,876			(396,122)	1,145
Issuance of common stock for exercise of stock options (in shares)							1,725,695
Issuance of common stock for early exercise of stock options	8,815						$ 2				8,813
Employee stock purchase plan (in shares)							175,142
Employee stock purchase plan	2,843										2,843
Issuance of common stock, net of issuance costs (in shares)			848,663				13,457,447		848,663
Issuance of common stock, net of issuance costs	595,730		$ 26,203				$ 13		$ 1		595,717		$ 26,202
Vesting of early exercised common stock	2,840										2,840
Stock-based compensation	65,261										65,261
Net loss	(250,221)													(250,221)
Net unrealized loss on available-for-sale investments	$ (877)														(877)
Balance (in shares) at Dec. 31, 2020	140,474,305						140,474,305
Balance at Dec. 31, 2020	$ 1,079,617						$ 140				$ 1,725,552			$ (646,343)	$ 268

Consolidated Statements of Convertible Preferred Stock and Stockholders’ Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2018
Preferred stock, par or stated value (in dollars per share)	$ 0.001
Series A1 Convertible Preferred Shares
Preferred stock, par or stated value (in dollars per share)		$ 35.06
Net issuance cost on equity		$ 84
IPO
Net issuance cost on equity		$ 29,300
Public offering
Net issuance cost on equity	$ 36,800
ATM offering
Net issuance cost on equity	$ 600
Series A Convertible Preferred Stock
Preferred stock, par or stated value (in dollars per share)		$ 35.06
Net issuance cost on equity		$ 635

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (250,221)	$ (184,594)	$ (211,505)
Adjustments to reconcile net loss to net cash used in operating activities:
Acquired in-process research and development	0	0	109,436
Stock-based compensation	65,261	46,063	18,566
Amortization of other intangible assets acquired	151	603	452
Depreciation and amortization	7,435	4,424	1,048
Net amortization/accretion on investment securities	3,250	(3,596)	(1,036)
Non-cash rent expense	3,955	6,777	1,832
Change in fair value of convertible notes payable	0	0	21,211
Debt issuance costs on convertible notes payable	0	0	3,358
Income tax benefit	0	(331)	(117)
Share of losses from equity method investments	1,154	182	0
Other	0	0	6
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(3,177)	(5,445)	(8,598)
Other long-term assets	34	(4,374)	(244)
Accounts payable	615	(985)	8,800
Accrued and other current liabilities	18,726	6,351	12,138
Deferred revenue	38,992	0	0
Other long-term liabilities	(1,268)	(2,425)	0
Net cash used in operating activities	(115,093)	(137,350)	(44,653)
Cash flows from investing activities:
Purchases of property and equipment	(65,958)	(50,791)	(3,234)
Purchase of stock in equity method investment	0	(5,075)	0
Proceeds from sales of investments	4,799	0	2,606
Proceeds from maturities of investments	593,627	472,578	19,235
Purchase of investments	(1,037,591)	(252,628)	(649,307)
Cash paid for acquisition of assets	0	0	(2,098)
Net cash provided by (used in) investing activities	(505,123)	164,084	(632,798)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs	0	0	299,281
Proceeds from issuance of convertible notes, net of issuance costs	0	0	116,842
Proceeds from early exercise of stock options	0	0	11,370
Proceeds from issuance of common stock, net of commissions and issuance costs	621,933	54,219	343,689
Proceeds from issuance of common stock and upon exercise of stock options	8,815	2,958	0
Proceeds from issuance of common stock under the employee stock purchase plan	2,843	1,783	0
Net cash provided by financing activities	633,591	58,960	771,182
Net increase in cash, cash equivalents and restricted cash	13,375	85,694	93,731
Cash, cash equivalents and restricted cash — beginning of period	179,425	93,731	0
Cash, cash equivalents and restricted cash — end of period	192,800	179,425	93,731
Non-cash operating, investing and financing activities:
Common stock issued on conversion of convertible preferred stock	0	0	411,052
Common stock issued on conversion of convertible notes payable	0	0	141,410
Series A-1 convertible preferred stock issued in asset acquisition	0	0	111,770
PP&E and other assets acquired in asset acquisition	0	0	111,770
Right-of-use asset obtained in exchange for lease liability	0	13,827	33,015
Property and equipment purchases in accounts payable and accrued and other current liabilities	8,567	4,668	3,182
Capitalized cloud computing costs included in accounts payable and accrued and other current liabilities	584	0	0
Deferred offering costs included in accounts payable and accrued and other current liabilities	0	135	356
Supplemental disclosure:
Cash paid for amounts included in the measurement of lease liabilities	(6,244)	(3,563)	(31)
Cash received for amounts related to tenant improvement allowances from lessors	$ 2,809	$ 4,473	$ 0

Description of Business and Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2020

Disclosure Text Block [Abstract]

Description of Business and Summary of Significant Accounting Policies

Allogene Therapeutics, Inc. (the Company or Allogene) was incorporated on November 30, 2017 in the State of Delaware and is headquartered in South San Francisco, California. Allogene is a clinical-stage immuno-oncology company pioneering the development and commercialization of genetically engineered allogeneic T cell therapies for the treatment of cancer. The Company is developing a pipeline of off-the-shelf T cell product candidates that are designed to target and kill cancer cells.

For the period from November 30, 2017 (inception) to December 31, 2017, the Company incurred $2,000 in start-up costs to establish the Company. Principal operations commenced in April 2018 when Allogene acquired certain assets from Pfizer Inc. (Pfizer) (see Note 6) and completed a Series A and A-1 preferred stock financing (see Note 11).

Public Offerings

In October 2018, the Company completed an initial public offering (IPO) of its common stock. In connection with its IPO, the Company issued and sold 20,700,000 shares of its common stock, which included 2,700,000 shares of its common stock issued pursuant to the over-allotment option granted to the underwriters, at a price to the public of $18.00 per share. As a result of the IPO, the Company received $343.3 million in net proceeds, after deducting underwriting discounts and commissions of $26.1 million and offering expenses of $3.2 million payable by the Company. At the closing of the IPO, 11,743,987 shares of outstanding convertible preferred stock were automatically converted into 61,655,922 shares of common stock and the 2018 Notes (see Note 11) were automatically converted into 7,856,176 shares of common stock. Following the IPO, there were no shares of convertible preferred stock or preferred stock outstanding.

In November 2019, the Company entered into a sales agreement with Cowen and Company, LLC (Cowen), under which the Company may from time to time issue and sell shares of its common stock through Cowen in at-the-market (ATM) offerings for an aggregate offering price of up to $250.0 million. The aggregate compensation payable to Cowen as the Company's sales agent equals up to 3.0% of the gross sales price of the shares sold through it pursuant to the sales agreement. During the year ended December 31, 2020, we sold an aggregate of 848,663 shares of common stock in ATM offerings resulting in net proceeds of $26.2 million.

In June 2020, the Company sold 13,457,447 shares of its common stock, which included 1,755,319 shares sold pursuant to the full exercise of the underwriters' option to purchase additional shares, in an underwritten public offering at a price of $47.00 per share, which resulted in gross proceeds of approximately $632.5 million. Net proceeds to the Company after deducting the underwriting discounts and commissions and other expenses were approximately $595.7 million.

Forward Stock Split

On October 1, 2018, the Company filed an amendment to the Company’s amended and restated certificate of incorporation to effect a forward split of shares of the Company’s common stock on a 1-for-5.25 basis (the Forward Stock Split). In connection with the Forward Stock Split, the conversion ratio for the Company’s outstanding convertible preferred stock was proportionately adjusted such that the common stock issuable upon conversion of such preferred stock was increased in proportion to the Forward Stock Split. The par value of the common stock was not adjusted as a result of the Forward Stock Split. All references to common stock, options to purchase common stock, early exercised options, share data, per share data, convertible preferred stock (to the extent presented on an as-converted to common stock basis) and related information contained in these financial statements have been retrospectively adjusted to reflect the effect of the Forward Stock Split for all periods presented.

Need for Additional Capital

The Company has sustained operating losses and expects to continue to generate operating losses for the foreseeable future. The Company’s ultimate success depends on the outcome of its research and development activities as well as the ability to commercialize the Company’s product candidates. The Company had cash, cash equivalents and investments of $1.0 billion as of December 31, 2020. Since inception through December 31, 2020, the Company has incurred cumulative net losses of $646.3 million. Management expects to incur additional losses in the future to fund its operations and conduct product research and development and recognizes the need to raise additional capital to fully implement its business plan.

The Company intends to raise additional capital through the issuance of equity securities, debt financings or other sources in order to further implement its business plan. However, if such financing is not available at adequate levels, the Company will need to reevaluate its operating plan and may be required to delay the development of its product candidates. The Company expects that its cash and cash equivalents and investments will be sufficient to fund its operations for at least the next 12 months from the date the Company’s Annual Report on Form 10-K is filed with the Securities and Exchange Commission (SEC).

The Company cannot at this time predict the specific extent, duration, or full impact that the ongoing COVID-19 pandemic will have on its financial condition and operations, including ongoing and planned clinical trials. The impact of the COVID-19 pandemic on the financial performance of the Company will depend on future developments, including the duration and spread of the pandemic and related governmental advisories and restrictions. These developments and the impact of the COVID-19 pandemic on the financial markets and the overall economy are highly uncertain. If business conditions, financial markets and/or the overall economy are impacted for an extended period, the Company’s results may be adversely affected.

Basis of Presentation

The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP).

In June 2020, the Company formed a wholly-owned, Netherlands-based subsidiary, Allogene Therapeutics, B.V., to help prepare for and assist with the Company's activities in Europe. The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All material intercompany balances and transactions have been eliminated during consolidation.

Use of Estimates

The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying consolidated financial statements include but are not limited to the fair value of common stock, the fair value of stock options, the fair value of investments, the fair value of convertible notes payable upon conversion, income tax uncertainties, and certain accruals. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances change. Actual results could differ from those estimates.

Concentration of Credit and other Risks and Uncertainties

Financial instruments, which potentially subject the Company to significant concentrations of credit risk, consist primarily of cash and cash equivalents and investments. The primary objectives for the Company’s investment portfolio are the preservation of capital and the maintenance of liquidity. The Company does not enter into any investment transaction for trading or speculative purposes.

The Company’s investment policy limits investments to certain types of instruments such as certificates of deposit, commercial paper, money market instruments, obligations issued by the U.S. government and U.S. government agencies as well as corporate debt securities, and places restrictions on maturities and concentration by type and issuer. The Company maintains cash balances in excess of amounts insured by the FDIC and concentrated within a limited number of financial institutions. The accounts are monitored by management and management believes that the financial institutions are financially sound, and, accordingly, minimal credit risk exists with respect to these financial institutions. As of December 31, 2020 and 2019, the Company has not experienced any credit losses in such accounts or investments.

The Company is subject to a number of risks common for early-stage biopharmaceutical companies including, but not limited to, dependency on the clinical and commercial success of its product candidates, ability to obtain regulatory approval of its product candidates, the need for substantial additional financing to achieve its goals, uncertainty of broad adoption of its approved products, if any, by physicians and patients, significant competition and untested manufacturing capabilities.

Segments

Operating segments are defined as components of an entity for which separate financial information is available and that is regularly reviewed by the Chief Operating Decision Maker (CODM) in deciding how to allocate resources to an individual segment and in assessing performance. The Company’s CODM is its Chief Executive Officer. The Company has determined it operates in a single operating segment and has one reportable segment.

Cash, Cash Equivalents and Restricted Cash

The Company considers all highly liquid investments purchased with original maturities of three months or less from the purchase date to be cash equivalents. Cash equivalents consist primarily of amounts invested in bank money market accounts and money market mutual funds.

The Company has issued letters of credit under separate lease and other agreements which have been collateralized by restricted cash. This cash is classified as long-term restricted cash on the accompanying consolidated balance sheet based on the terms of the underlying agreements.

Investments

Investments are available-for-sale and are carried at estimated fair value. The Company’s valuations of marketable securities are generally derived from independent pricing services based upon quoted prices in active markets for similar securities, with prices adjusted for yield and number of days to maturity, or based on industry models using data inputs, such as interest rates and prices that can be directly observed or corroborated in active markets. Management determines the appropriate classification of its investments in debt securities at the time of purchase and at the end of each reporting period. Investments with original maturities of less than three months at the date of purchase are classified as cash and cash equivalents. Investments with original maturities beyond three months at the date of purchase and which mature at, or less than twelve months from the consolidated balance sheet date are classified as current.

Unrealized gains and losses are excluded from earnings and are reported as a component of other comprehensive income. The Company periodically evaluates whether declines in fair values of its available-for-sale securities below their book value are other-than-temporary. This evaluation consists of several qualitative and quantitative factors regarding the severity and duration of the unrealized loss as well as the Company’s ability and intent to hold the available-for-sale security until a forecasted recovery occurs. Additionally, the Company assesses whether it has plans to sell the security or it is more likely than not it will be required to sell any available-for-sale securities before recovery of its amortized cost basis. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in interest and other income, net. The cost of investments sold is based on the specific-identification method. Interest income on investments is included in interest and other income, net.

Fair Value Measurement

Assets and liabilities recorded at fair value on a recurring basis in the consolidated balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows:

Level 1—Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date.

Level 2—Inputs (other than quoted prices included in Level 1) are either directly or indirectly observable for the asset or liability. These include quoted prices for similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active.

Level 3— Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

Property and Equipment, Net

Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation is computed on a straight-line basis over the estimated useful lives of the related assets, generally three to seven years. Maintenance and

repairs are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in other expense.

The Company has determined the estimated life of assets to be as follows:


Laboratory equipment			5 years
Computer equipment and purchased software			3 - 5 years
Fixtures and furniture			7 years
Leasehold improvements			Shorter of lease term or useful life

The Company adopted Accounting Standards Update ("ASU") No. 2018-15, Intangibles – Goodwill and other – Internal-Use Software (Subtopic 350-40) on January 1, 2020 on a prospective basis. The Company capitalizes implementation costs associated with internal use cloud computing arrangements in alignment with ASC 350-40 internal-use software. Costs incurred in preliminary project stage and post implementation stage are expensed as incurred. Costs incurred during the application development stage of implementation are capitalized in other long term assets on the consolidated balance sheet. Capitalized implementation costs from cloud computing arrangements are amortized over the term of the cloud-based service arrangement.

Leases

The Company early adopted ASU No. 2016-2, Leases on January 1, 2018. For its long-term operating leases, the Company recognizes a right-of-use asset and a lease liability on its consolidated balance sheets. The lease liability is determined as the present value of future lease payments using an estimated rate of interest that the Company would pay to borrow equivalent funds on a collateralized basis at the lease commencement date. The right-of-use asset is based on the liability adjusted for any prepaid or deferred rent. The lease term at the commencement date is determined by considering whether renewal options and termination options are reasonably assured of exercise.

Rent expense for the operating lease is recognized on a straight-line basis over the lease term and is included in operating expenses on the consolidated statements of operations and comprehensive loss. Variable lease payments include lease operating expenses.

The Company elected to exclude from its consolidated balance sheets recognition of leases having a term of 12 months or less (short-term leases) and elected to not separate lease components and non-lease components for its long-term real-estate leases.

Equity Method Investments

The Company uses the equity method of accounting for equity investments in companies if the investment provides the ability to exercise significant influence, but not control, over operating and financial policies of the investee. The Company's proportionate share of the net income or loss of these companies is included in other expenses in the consolidated statement of operations. Judgment regarding the level of influence over each equity method investment includes considering key factors such as our ownership interest, representation on the board of directors, participation in policy-making decisions and material purchase and sale transactions.

The Company evaluates equity method investments for impairment whenever events or changes in circumstances indicate that the carrying amount of the investment might not be recoverable. Factors considered when reviewing an equity method investment for impairment include the length of time (duration) and the extent (severity) to which the fair value of the equity method investment has been less than cost, the investee’s financial condition and near-term prospects and the intent and ability to hold the investment for a period of time sufficient to allow for anticipated recovery. An impairment that is other-than-temporary is recognized in the period identified.

Variable Interest Entities

For entities in which the Company has variable interests, the Company focuses on identifying if one of the entities is the primary beneficiary through having the power to direct the activities that most significantly impact the variable interest entity’s economic performance and having the obligation to absorb losses or the right to receive benefits from the variable

interest entity. If the Company is the primary beneficiary of a variable interest entity, the assets, liabilities, and results of operations of the variable interest entity will be included in the Company’s consolidated financial statements. The Company did not consolidate any variable interest entities in any of the periods presented because the Company determined that it was not the primary beneficiary.

Accrued Research and Development Costs

The Company records accrued liabilities for estimated costs of research and development activities conducted by collaboration partners and third-party service providers, which include the conduct of preclinical studies and clinical trials, and contract manufacturing activities. The Company records the estimated costs of research and development activities based upon the estimated amount of services provided but not yet invoiced and includes these costs in accrued and other current liabilities on the consolidated balance sheets and within research and development expenses on the consolidated statements of operations and comprehensive loss.

The Company accrues for these costs based on factors such as estimates of the work completed and in accordance with agreements established with its collaboration partners and third-party service providers. The Company makes significant judgments and estimates in determining the accrued liabilities balance at the end of each reporting period. As actual costs become known, the Company adjusts its accrued liabilities. The Company has not experienced any material differences between accrued costs and actual costs incurred since its inception.

Income Taxes

Income taxes are accounted for under the asset and liability method. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to affect taxable income. Management makes an assessment of the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to the Company’s historical operating performance and net losses, the net deferred tax assets have been fully offset by a valuation allowance.

The Company recognizes uncertain income tax positions at the largest amount that is more likely than not to be sustained upon audit by the relevant taxing authority. An uncertain income tax position will not be recognized if it has less than a 50% likelihood of being sustained. Changes in recognition or measurement are reflected in the period in which judgment occurs. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of the provision for income taxes.

Stock-Based Compensation

The Company measures its stock-based awards granted to employees, consultants and directors based on the estimated fair values of the awards and recognizes the compensation over the requisite service period. The Company uses the Black-Scholes option-pricing model to estimate the fair value of its stock-based awards. Stock-based compensation is recognized using the straight-line method. As the stock compensation expense is based on awards ultimately expected to vest, it is reduced by forfeitures. The Company accounts for forfeitures as they occur.

Net Loss Per Share

Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding for the period, without consideration for potential dilutive shares of common stock. Since the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share since the effects of potentially dilutive securities are antidilutive. Shares of common stock subject to repurchase are excluded from the weighted-average shares.

Comprehensive Loss

Comprehensive loss includes net loss and certain changes in stockholders’ equity (deficit) that are excluded from net loss. For the years ended December 31, 2020, 2019 and 2018 this was comprised of unrealized gains and losses, net of tax, on the Company’s investments.

Definite-Lived Intangible Assets

Identifiable intangible assets consist of in-process research and development and workforce associated with the Pfizer asset acquisition. Intangible assets with finite lives are amortized over their estimated useful lives on a straight-line basis, generally two years. Acquired in-process research and development intangible assets with no alternative future use are charged to research and development expense when acquired. The straight-line method of amortization represents the Company’s best estimate of the distribution of the economic value of the identifiable intangible assets. Intangible assets are carried at cost less accumulated amortization. Amortization of intangible assets is included in research and development expenses.

Impairment of Long-Lived Assets

Long-lived assets are reviewed annually for impairment or whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amount of an asset group to the future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows arising from the asset. There were impairment losses related to equipment disposals of zero and $0.2 million for the years ended December 31, 2020 and 2019, respectively.

Revenue Recognition

In the near future, the Company’s revenue is anticipated to be generated through collaboration research and license agreements. The terms of these agreements are anticipated to contain multiple deliverables which may include (i) grant of licenses, (ii) transfer of know-how, (iii) research and development activities, (iii) clinical manufacturing and, (iv) product supply. The payment terms of these agreements may include nonrefundable upfront fees, payments for research and development activities, payments based upon the achievement of certain milestones, royalty payments based on product sales derived from the collaboration, and payments for supplying product.

The Company will analyze its collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements (ASC 808) to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of ASC 808 and those that are more reflective of a vendor-customer relationship and, therefore, within the scope of Topic 606, Revenue from Contracts with Customers (ASC 606). For elements of collaboration arrangements that are accounted for pursuant to ASC 808, an appropriate recognition method is determined and applied consistently, generally by analogy to Topic 606.

For elements of those arrangements that the Company determines should be accounted for under ASC 606, the Company assesses which activities in the collaboration agreements are performance obligations that should be accounted for separately and determine the transaction price of the arrangement, which includes the assessment of the probability of achievement of future milestones and other potential consideration. A performance obligation represents a promise in a contract to transfer a distinct good or service to a customer, which represents a unit of accounting in accordance with ASC 606. A performance obligation is considered distinct from other obligations in a contract when it provides a benefit to the customer either on its own or together with other resources that are readily available to the customer and is separately identified in the contract. The Company considers a performance obligation satisfied once the Company has transferred control of a good or service to the customer, meaning the customer has the ability to use and obtain the benefit of the good or service. A portion of the consideration should be allocated to each distinct performance obligation and recognized as revenue when, or as, the performance obligation is satisfied. The total consideration which the Company expects to collect in exchange for the Company’s products is an estimate and may be fixed or variable. The Company constrains the estimated variable consideration when it assesses it is probable that a significant reversal in the amount of cumulative revenue recognized may occur in future periods. The transaction price is re-evaluated, including the estimated variable consideration included in the transaction price and all constrained amounts, in each reporting period and as uncertain events are resolved or other changes in circumstances occur. The allocation of the transaction price is performed based on standalone selling prices, which are based on estimated amounts that the Company would charge for a performance obligation if it were sold separately. Revenue is recognized when, or as, performance obligations in the contracts are satisfied, in the amount reflecting the expected consideration to be received from the goods or services transferred to the customers. Funds received in advance are recorded as deferred revenue and are recognized as the related performance obligation is satisfied.

Research and Development Expenses

Research and development costs are expensed as incurred and consist of salaries and benefits, including associated stock-based compensation, and laboratory supplies and facility costs, as well as fees paid to other entities that conduct certain research and development activities on the Company’s behalf. Research and development expenses also include costs incurred for internal and sponsored collaborative research and development activities. Costs associated with co-development activities performed under the various license and collaboration agreements are included in research and development expenses.

Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are capitalized and then expensed as the related goods are delivered or the services are performed.

Recent Accounting Guidance	12 Months Ended
Recent Accounting Guidance	Dec. 31, 2020
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Guidance	Recent Accounting Guidance Recently Adopted Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses: Measurement of Credit Losses on Financial Instruments and also issued subsequent amendments to the initial guidance: ASU 2018-19, ASU 2019-04, ASU 2019-05, and ASU 2019-11. The standard requires measurement and recognition of expected credit losses for financial assets by requiring an allowance to be recorded as an offset to the amortized cost of such assets. For available-for-sale debt securities, expected credit losses should be estimated when the fair value of the debt securities is below their associated amortized costs. This standard became effective for fiscal years beginning after December 15, 2019, with early adoption permitted beginning the first quarter of 2019. The Company’s financial instruments that are in the scope of ASU 2016-13 include, but are not limited to, other receivables and available-for-sale debt securities. The Company adopted this standard on January 1, 2020 and applied the modified retrospective approach. Adoption of the new guidance had no significant impact on the Company’s consolidated financial statements. In August 2018, the FASB issued Accounting Standards Update No. 2018-15, Intangibles – Goodwill and other – Internal-Use Software (Subtopic 350-40), which amended its guidance for costs of implementing a cloud computing service arrangement and aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. This new standard also requires customers to expense the capitalized implementation costs of a hosting arrangement that is a service contract over the term of the hosting arrangement. This standard became effective for fiscal years beginning after December 15, 2019, with early adoption permitted. The Company adopted this standard on January 1, 2020, on a prospective basis for applicable implementation costs. As of December 31, 2020, $4.2 million of implementation costs related to cloud computing service arrangements were capitalized and included in other long term assets on the consolidated balance sheets. In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606, which clarifies that certain transactions between participants in a collaborative arrangement should be accounted for under ASC 606 when the counterparty is a customer. In addition, Topic 808 precludes an entity from presenting consideration from a transaction in a collaborative arrangement as revenue from contracts with customers if the counterparty is not a customer for that transaction. This standard is effective for fiscal years beginning after December 31, 2019, with early adoption permitted. The Company adopted this standard on January 1, 2020. Adoption of the new guidance had no significant impact on the Company’s consolidated financial statements. In December 2019, the FASB issued Accounting Standards Update No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (ASU 2019-12), which simplifies the accounting for income taxes, eliminates certain exceptions within ASC 740, Income Taxes, and clarifies certain aspects of the current guidance to promote consistency among reporting entities. This standard is effective for fiscal years beginning after December 15, 2020, with early adoption permitted. The Company early adopted this standard as of January 1, 2020 on a prospective basis in accordance with ASC 250, Accounting Changes and Error Corrections. The adoption resulted in the Company no longer needing to determine the tax effect from unrealized gains on available for sale securities, which previously had been disclosed in the consolidated statement of operations as a benefit from income taxes. Adoption of the new guidance had no significant impact on the Company's consolidated financial statements. Recent Accounting Pronouncements Not Yet Adopted In January 2020, the FASB issues Accounting Standard Update No. 2020-01, Investments – Equity Securities (Topic 321), Investments – Equity Method and Joint Ventures (Topic 323), which clarifies the interactions between topics 321 and 323 in applying or discontinuing the equity method of accounting for investments. This guidance will be effective for the Company in the first quarter of 2021, and early adoption is permitted. The Company is currently evaluating the impact of the new guidance on its consolidated financial statements.

- Definition

The entire disclosure for change in accounting principle. Includes, but is not limited to, nature, reason, and method of adopting amendment to accounting standards or other change in accounting principle.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 65
-Paragraph 1
-Subparagraph (g)(2)
-URI http://asc.fasb.org/extlink&oid=113356391&loc=SL49131195-203048

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-URI http://asc.fasb.org/topic&trid=2122394

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
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-Section 65
-Paragraph 1
-Subparagraph (i)
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 1
-Subparagraph (i)(2)
-URI http://asc.fasb.org/extlink&oid=113356391&loc=SL49131195-203048

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 2
-Subparagraph (g)(2)(iii)
-URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(4)
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
-Section 65
-Paragraph 15
-Subparagraph (g)(1)
-URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=120154821&loc=SL120154904-197079

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
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-Section S99
-Paragraph 5
-Subparagraph (SAB Topic 11.M.Q2)
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
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Reference 19: http://www.xbrl.org/2003/role/disclosureRef
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Reference 20: http://www.xbrl.org/2003/role/disclosureRef
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Reference 22: http://www.xbrl.org/2003/role/disclosureRef
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Reference 23: http://www.xbrl.org/2003/role/disclosureRef
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Reference 24: http://www.xbrl.org/2003/role/disclosureRef
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Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 65
-Paragraph 8
-Subparagraph (e)(3)

+ Details

Fair Value Measurements

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

The Company follows authoritative accounting guidance, which among other things, defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability.

The Company measures and reports its cash equivalents, restricted cash, investments and convertible notes payable at fair value.

Money market funds are measured at fair value on a recurring basis using quoted prices and are classified as Level 1. Investments are measured at fair value based on inputs other than quoted prices that are derived from observable market data and are classified as Level 2 inputs, except for investments in U.S. treasury securities which are classified as Level 1.

There were no Level 3 assets or liabilities at December 31, 2020 or 2019.

Financial assets subject to fair value measurements on a recurring basis and the level of inputs used in such measurements by major security type as of December 31, 2020 are presented in the following table:


	December 31, 2020
	Level 1		Level 2		Level 3		Fair Value
	(in thousands)
Financial Assets:
Money market funds ¹	$	102,039	$	—	$	—	$	102,039
Commercial paper	—		58,975		—		58,975
Corporate bonds	—		262,757		—		262,757
U.S. treasury securities	446,996		—		—		446,996
U.S. agency securities	—		80,039		—		80,039
Total financial assets	$	549,035	$	401,771	$	—	$	950,806

¹ Included within cash and cash equivalents on the Company’s consolidated balance sheet

Financial assets subject to fair value measurements on a recurring basis and the level of inputs used in such measurements by major security type as of December 31, 2019 are presented in the following table:


	December 31, 2019
	Level 1		Level 2		Level 3		Fair Value
	(in thousands)
Financial Assets:
Money market funds ¹	$	122,900	$	—	$	—	$	122,900
Corporate bonds	—		205,011		—		205,011
U.S. treasury securities	181,894		—		—		181,894
U.S. agency securities	—		25,824		—		25,824
Certificates of deposit	—		1,000		—		1,000
Total financial assets	$	304,794	$	231,835	$	—	$	536,629

¹ Included within cash and cash equivalents on the Company’s consolidated balance sheet

The carrying amounts of accounts payable and accrued liabilities approximate their fair values due to their short-term maturities. The Company’s Level 2 securities are valued using third-party pricing sources. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly.

There were no transfers of assets between the fair value measurement levels during the years ended December 31, 2020 or 2019.

- Definition

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

+ References + Details

Investments

12 Months Ended

Dec. 31, 2020

Investments, All Other Investments [Abstract]

Investments

The fair value and amortized cost of cash equivalents and available-for-sale securities by major security type as of December 31, 2020 are presented in the following table:


	December 31, 2020
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
	(in thousands)
Money market funds	$	102,039	$	—	$	—	$	102,039
Commercial paper	58,969		8		(2)		58,975
Corporate bonds	262,349		444		(36)		262,757
U.S. treasury securities	446,726		282		(12)		446,996
U.S. agency securities	80,012		30		(3)		80,039
Total cash equivalents and investments	$	950,095	$	764	$	(53)	$	950,806

Classified as:
Cash equivalents							$	102,039
Short-term investments							644,559
Long-term investments							204,208
Total cash equivalents, and investments							$	950,806

The fair value and amortized cost of cash equivalents and available-for-sale securities by major security type as of December 31, 2019 are presented in the following table:


	December 31, 2019
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
	(in thousands)
Money market funds	$	122,900	$	—	$	—	$	122,900
Corporate bonds	204,144		871		(4)		205,011
U.S. treasury securities	181,340		557		(3)		181,894
U.S. agency securities	25,658		167		(1)		25,824
Certificates of deposit	1,000		—		—		1,000
Total cash equivalents and investments	$	535,042	$	1,595	$	(8)	$	536,629

Classified as:
Cash equivalents							$	122,900
Short-term investments							355,407
Long-term investments							58,322
Total cash equivalents, and investments							$	536,629

The Company believes that it is more-likely-than-not that investments in an unrealized loss position will be held until maturity and all interest and principal will be received. The Company does not intent to sell these investments and it is not more likely than not that the Company will be required to sell the investment before recovery of its amortized cost basis.

The fair values of available-for-sale debt investments by contractual maturity as of December 31, 2020 and 2019 were as follows:


	December 31,
	2020		2019
	(in thousands)
Due in 1 year or less	$	644,559	$	355,407
Due in 1 - 2 years	148,211		58,322
Due in 3 years	55,997		—
Instruments not due at a single maturity date	102,039		122,900
Total cash equivalents and investments	$	950,806	$	536,629

As of December 31, 2020 and 2019, the remaining contractual maturities of available-for-sale securities were less than three years and two years, respectively. There have been no significant realized losses on available-for-sale securities for the years ended December 31, 2020, 2019 and 2018. As of December 31, 2020 and 2019, unrealized losses on available-for-sale investments are not attributed to credit risk. The Company believes that it is more-likely-than-not that investments in an unrealized loss position will be held until maturity and all interest and principal will be received. The Company believes that an allowance for credit losses is unnecessary because the unrealized losses on certain of the Company’s marketable securities are due to market factors. As of December 31, 2020 and 2019, securities with a fair value of $5.0 million and zero respectively, were in a net unrealized loss position for more than 12 months. To date, the Company has not recorded any impairment charges on marketable securities.

As of December 31, 2020 and 2019, the Company recognized $2.8 million and $2.4 million of accrued interest receivable from available-for-sale investments within prepaid expenses and other current assets on the consolidated balance sheets.

Balance Sheet Components

12 Months Ended

Dec. 31, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Balance Sheet Components

Property and Equipment, Net


	December 31,
	2020		2019
	(in thousands)
Construction in progress	$	68,944	$	12,390
Leasehold improvements	31,518		29,924
Laboratory equipment	23,810		13,117
Computers equipment and purchased software	4,088		3,726
Furniture and fixtures	3,388		2,764
Total	131,748		61,921
Less: accumulated depreciation	(12,908)		(5,472)
Total property and equipment, net	$	118,840	$	56,449

Depreciation expense for the years ended December 31, 2020, 2019 and 2018 was $7.4 million, $4.6 million and $1.0 million respectively. Disposals of property and equipment were zero , $0.2 million and zero for the years ended December 31, 2020, 2019 and 2018, respectively.

Accrued Liabilities

Accrued liabilities consist of the following:


	December 31,
	2020		2019
	(in thousands)
Accrued compensation and related benefits	$	15,943	$	9,560
Accrued research and development expenses	13,887		4,833
Accrued property and equipment	7,475		3,575
Unvested shares liability	2,842		2,843
Other	4,791		3,018
Total accrued and other current liabilities	$	44,938	$	23,829

Asset Acquisition

12 Months Ended

Dec. 31, 2020

Business Combinations [Abstract]

Asset Acquisition

In April 2018, the Company entered into an Asset Contribution Agreement (the Pfizer Agreement) with Pfizer pursuant to which the Company acquired certain assets, including certain contracts described in Note 7, and intellectual property for the development and administration of chimeric antigen receptor (CAR) T cells for the treatment of cancer.

As consideration for the purchased assets, the Company issued Pfizer 3,187,772 shares of its Series A-1 convertible preferred stock with an estimated fair value of $111.8 million or $35.06 per share. The Company also incurred $2.1 million of direct expenses related to the asset acquisition, bringing the total consideration to $113.9 million. The fair value of the Series A-1 convertible preferred stock was established using the price per share paid by third-party investors in the concurrent closing of the Series A and A-1 convertible preferred stock financing at $35.06 per share as well as the price per share paid by Pfizer to purchase additional shares of Series A-1 convertible preferred stock at $35.06 per share at the same time and at the same price per share as the rest of Series A and A-1 shares sold in such financing (see Note 11 for additional details). The Series A-1 convertible preferred shares issued to Pfizer had the same rights, preferences and privileges as the Series A convertible preferred shares issued to the third-party investors.

The Company accounted for the transaction as an asset acquisition as substantially all of the estimated fair value of the gross assets acquired was concentrated in a single identified asset, anti-CD19 CAR T cell therapy, thus satisfying the requirements of the screen test in ASU 2017-1. The assets acquired in the transaction were measured based on the fair value of the Series A-1 convertible preferred stock issued to Pfizer and direct transaction costs of $2.1 million, as the fair value of the equity given was more readily determinable than the fair value of the assets received. The following table summarizes the fair value of assets acquired (in thousands):


Property and equipment	$	3,258
In-process research and development (IPR&D):
Anti-CD19 CAR T cell therapy	103,936
Anti-BCMA CAR T cell therapy	5,500
Assembled workforce	1,206
Total assets acquired	$	113,900

The estimated fair values of anti-CD19 CAR T cell therapy and anti-BCMA CAR T cell therapy were determined using a risk-adjusted discounted cash flow approach, which used the present value of the direct cash flows expected to be generated by anti-CD19 CAR T cell therapy and anti-BCMA CAR T cell therapy during their estimated economic lives, net of returns on contributory assets such as working capital, property and equipment, and the assembled workforce. The discount rate of 16.5% was based on rates of return available from alternative investments of similar type and quality as of the valuation date. The remaining IPR&D targets were determined to be more conceptual in nature with nominal value being attributed to them. The estimate of the fair value of the assembled workforce was determined using a replacement cost approach, based on the estimated cost of recruiting and training an equivalent workforce as of the acquisition date.

The amount allocated to intangible IPR&D assets was charged to research and development expenses as these assets had no alternative future use at the time of the acquisition transaction. The remaining intangible asset relates to the assembled workforce which was capitalized and is being amortized over its estimated economic life of two years to research and development expenses.

In addition, under the terms of the Pfizer Agreement, the Company was also required to make milestone payments to Pfizer of $30.0 million or $60.0 million per target (depending on the target, and up to $840.0 million in the aggregate for all targets) upon successful completion of certain regulatory and sales milestones for certain targets covered by the Pfizer Agreement. No milestone payments were made or became due in the years ended December 31, 2020, 2019 and 2018. These contingent payments were not part of the consideration for the purchased assets.

As part of the asset acquisition, the Company also assumed licensing agreements Pfizer had entered into with two third-party entities holding certain intellectual property. Both agreements cover use of the intellectual property held by the parties and certain research collaboration activities. See Note 7 for additional details on these agreements.

Under the Pfizer Agreement, the Company was required to use commercially reasonable efforts to develop and seek regulatory approval in and for the United States and the European Union for certain products covered by the Pfizer Agreement and to commercialize each product covered by the Pfizer Agreement in the applicable royalty territory in which regulatory approval for such product has been obtained.

License and Collaboration Agreements	12 Months Ended
License and Collaboration Agreements	Dec. 31, 2020
Research and Development [Abstract]
License and Collaboration Agreements	License and Collaboration Agreements Asset Contribution Agreement with Pfizer In connection with the Pfizer Agreement (see Note 6), the Company is required to make milestone payments upon successful completion of regulatory and sales milestones on a target-by-target basis for the targets including CD19 and B-cell maturation antigen (BCMA), covered by the Pfizer Agreement. The aggregate potential milestone payments upon successful completion of various regulatory milestones in the United States and the European Union are $30.0 million or $60.0 million, depending on the target, with aggregate potential regulatory and development milestones of up to $840.0 million, provided that the Company is not obligated to pay a milestone for regulatory approval in the European Union for an anti-CD19 allogeneic CAR T cell product, to the extent Servier has commercial rights to such territory. The aggregate potential milestone payments upon reaching certain annual net sales thresholds in North America, Europe, Asia, Australia and Oceania (the Territory) for a certain number of targets covered by the Pfizer Agreement are $325.0 million per target. The sales milestones in the foregoing sentence are payable on a country-by-country basis until the last to expire of any Pfizer Royalty Term, as described below, for any product in such country in the Territory. In October 2019, the Territory was expanded to all countries in the world. No milestone or royalty payments were made in the years ended December 31, 2020, 2019 and 2018. Pfizer is also eligible to receive, on a product-by-product and country-by-country basis, royalties in single-digit percentages on annual net sales for products covered by the Pfizer Agreement or that use certain Pfizer intellectual property and for which an IND is first filed on or before April 6, 2023. The Company’s royalty obligation with respect to a given product in a given country begins upon the first sale of such product in such country and ends on the later of (i) expiration of the last claim of any applicable patent or (ii) 12 years from the first sale of such product in such country. Research Collaboration and License Agreement with Cellectis As part of the Pfizer Agreement (see Note 6), Pfizer assigned to the Company a Research Collaboration and License Agreement (the Original Cellectis Agreement) with Cellectis S.A. (Cellectis). On March 8, 2019, the Company entered into a License Agreement (the Cellectis Agreement) with Cellectis. In connection with the execution of the Cellectis Agreement, on March 8, 2019, the Company and Cellectis also entered into a letter agreement (the Letter Agreement), pursuant to which the Company and Cellectis agreed to terminate the Original Cellectis Agreement. The Original Cellectis Agreement included a research collaboration to conduct discovery and pre-clinical development activities to generate CAR T cells directed at targets selected by each party, which was completed in June 2018. Pursuant to the Cellectis Agreement, Cellectis granted to the Company an exclusive, worldwide, royalty-bearing license, on a target-by-target basis, with sublicensing rights under certain conditions, under certain of Cellectis’s intellectual property, including its TALEN and electroporation technology, to make, use, sell, import, and otherwise exploit and commercialize CAR T products directed at certain targets, including BCMA, FLT3, DLL3 and CD70 (the Allogene Targets), for human oncologic therapeutic, diagnostic, prophylactic and prognostic purposes. In addition, certain Cellectis intellectual property rights granted by Cellectis to the Company and to Servier pursuant to the Exclusive License and Collaboration Agreement by and between Servier and Pfizer, dated October 30, 2016, which Pfizer assigned to the Company in April 2018, will survive the termination of the Original Cellectis Agreement. Pursuant to the Cellectis Agreement, the Company granted Cellectis a non-exclusive, worldwide, royalty-free, perpetual and irrevocable license, with sublicensing rights under certain conditions, under certain of the Company's intellectual property, to make, use, sell, import and otherwise commercialize CAR T products directed at certain targets (the Cellectis Targets). The Cellectis Agreement provides for development and sales milestone payments by the Company of up to $185.0 million per product that is directed against an Allogene Target, with aggregate potential development and sales milestone payments totaling up to $2.8 billion. Cellectis is also eligible to receive tiered royalties on annual worldwide net sales of any products that are commercialized by the Company that contain or incorporate, are made using or are claimed or covered by, Cellectis intellectual property licensed to the Company under the Cellectis Agreement (the Allogene Products), at rates in the high single-digit percentages. Such royalties may be reduced, on a licensed product-by-licensed product and country-by-country basis, for generic entry and for payments due under licenses of third party patents. Pursuant to the Cellectis Agreement, and subject to certain exceptions, the Company is required to indemnify Cellectis against all third party claims related to the development, manufacturing, commercialization or use of any Allogene Product or arising out of the Company’s material breach of the representations, warranties or covenants set forth in the Cellectis Agreement, and Cellectis is required, subject to certain exceptions, to indemnify the Company against all third party claims related to the development, manufacturing, commercialization or use of CAR T products directed at Cellectis Targets or arising out of Cellectis’s material breach of the representations, warranties or covenants set forth in the Cellectis Agreement. The royalties are payable, on a licensed product-by-licensed product and country-by-country basis, until the later of (i) the expiration of the last to expire of the licensed patents covering such product; (ii) the loss of regulatory exclusivity afforded such product in such country, and (iii) the tenth anniversary of the date of the first commercial sale of such product in such country; however, in no event shall such royalties be payable, with respect to a particular licensed product, past the twentieth anniversary of the first commercial sale for such product. Depending on the Cellectis Target, the Company has a right of first refusal or right of first negotiation to purchase or license from Cellectis rights to develop and commercialize products against such Cellectis Targets. Under the Cellectis Agreement, the Company has certain diligence obligations to progress the development of CAR T product candidates and to commercialize one CAR T product per Allogene Target in one major market country where the Company has received regulatory approval. If the Company materially breaches any of its diligence obligations and fails to cure within 90 days, then with respect to certain targets, such target will cease to be an Allogene Target and instead will become a Cellectis Target. Unless earlier terminated in accordance with its terms, the Cellectis Agreement will expire on a product-by-product and country-by-country basis, upon expiration of all royalty payment obligations with respect to such licensed product in such country. The Company has the right to terminate the Cellectis Agreement at will upon 60 days’ prior written notice, either in its entirety or on a target-by-target basis. Either party may terminate the Cellectis Agreement, in its entirety or on a target-by-target basis, upon 90 days’ prior written notice in the event of the other party’s uncured material breach. The Cellectis Agreement may also be terminated by the Company upon written notice at any time in the event that Cellectis becomes bankrupt or insolvent or upon written notice within 60 days of a consummation of a change of control of Cellectis. All costs the Company incurred in connection with this agreement were recognized as research and development expenses in the consolidated statement of operations. For the year ended December 31, 2019, $5.0 million of costs were incurred related to the achievement of a clinical development milestone under this agreement. No clinical development milestones were achieved for the years ended December 31, 2020 and 2018. License and Collaboration Agreement with Servier As part of the Pfizer Agreement (see Note 6), Pfizer assigned to the Company an Exclusive License and Collaboration Agreement (the Servier Agreement), with Les Laboratoires Servier SAS and Institut de Recherches Internationales Servier SAS (collectively, Servier) to develop, manufacture and commercialize certain allogeneic anti-CD19 CAR T cell product candidates, including UCART19, in the United States with the option to obtain the rights over additional anti-CD19 product candidates and for allogeneic CAR T cell product candidates directed against one additional target. In October 2019, the Company agreed to waive its rights to the one additional target. Under the Servier Agreement, the Company has an exclusive license to develop, manufacture and commercialize UCART19 in the field of anti-tumor adoptive immunotherapy in the United States, with an exclusive option to obtain the same rights for additional product candidates in the United States and, if Servier does not elect to pursue development or commercialization of those product candidates in certain markets outside of the United States pursuant to its license, outside of the United States as well. The Company is not required to make any additional payments to Servier to exercise an option. If the Company opts-in to another product candidate, Servier has the right to obtain rights to such product candidate outside the United States and to share development costs for such product candidate. Under the Servier Agreement, the Company is required to use commercially reasonable efforts to develop and obtain marketing approval in the United States in the field of anti-tumor adoptive immunotherapy for at least one product directed against CD19, and Servier is required to use commercially reasonable efforts to develop and obtain marketing approval in the European Union, and one other country in a group of specified countries outside of the European Union and the United States, in the field of anti-tumor adoptive immunotherapy for at least one allogeneic adaptive T cell product directed against a certain Company-selected target. For product candidates that the Company is co-developing with Servier, including UCART19, ALLO-501 and ALLO-501A, the Company is responsible for 60% of the specified development costs and Servier is responsible for the remaining 40% of the specified development costs under the applicable global research and development plan. Subject to certain restrictions, each party has the right to conduct activities that are specific to its territory outside the global research and development plan at such party’s sole expense. In addition, each party is solely responsible for commercialization activities in its territory at such party’s sole expense. The Company is required to make milestone payments to Servier upon successful completion of regulatory and sales milestones. The Servier Agreement provides for aggregate potential payments by the Company to Servier of up to $137.5 million upon successful completion of various regulatory milestones, and aggregate potential payments by the Company to Servier of up to $78.0 million upon successful completion of various sales milestones. Similarly, Servier is required to make milestone payments upon successful completion of regulatory and sales milestones for products directed at the Allogene-target covered by the Servier Agreement that achieves such milestones. The total potential payments that Servier is obligated to make to the Company under the Servier Agreement upon successful completion of regulatory and sales milestones are $42 million and €70.5 million ($86.6 million), respectively. The foregoing milestones are subject to certain adjustments if the Company obtains rights for certain products outside of the United States upon Servier’s election not to pursue such rights. Each party is also eligible to receive tiered royalties on annual net sales in countries within the paying party’s respective territory of any licensed products that are commercialized by such party that are directed at the targets licensed by such party under the Servier Agreement. The royalty rates are in a range from the low tens to the high teen percentages. Such royalties may be reduced for interchangeable drug entry, expiration of patent rights and amounts paid pursuant to licenses of third-party patents. The royalty obligation for each party with respect to a given licensed product in a given country in each party’s respective territory (the Servier Royalty Term) begins upon the first commercial sale of such product in such country and ends after a defined number of years. Unless earlier terminated in accordance with the Servier Agreement, the Servier Agreement will continue, on a licensed product-by-licensed product and country-by-country basis, until the Servier Royalty Term with respect to the sale of such licensed product in such country expires. For the year ended December 31, 2020, the Company recorded $8.5 million of net cost recoveries under the cost-sharing terms as a reduction to research and development expenses. For the years ended December 31, 2019 and 2018, the Company recorded $7.3 million and $4.2 million, respectively, of costs incurred under the collaboration agreement with Servier as research and development expenses. As of December 31, 2020, amounts due from Servier of $3.8 million were recorded in other current assets in the accompanying consolidated balance sheets. As of December 31, 2019, amounts due to Servier of $2.2 million were recorded in accrued and other current liabilities in the accompanying consolidated balance sheets. Research Collaboration and License Agreement with Notch Therapeutics On November 1, 2019, the Company entered into a Collaboration and License Agreement (the Notch Agreement) with Notch Therapeutics Inc. (Notch), pursuant to which Notch granted to Allogene an exclusive, worldwide, royalty-bearing, sublicensable license under certain of Notch’s intellectual property to develop, make, use, sell, import, and otherwise commercialize therapeutic gene-edited T cell and/or natural killer (NK) cell products from induced pluripotent stem cells directed at certain CAR targets for initial application in non-Hodgkin lymphoma, acute lymphoblastic leukemia and multiple myeloma. In addition, Notch has granted Allogene an option to add certain specified targets to its exclusive license in exchange for an agreed per-target option fee. The Notch Agreement includes a research collaboration to conduct research and pre-clinical development activities to generate engineered cells directed to Allogene’s exclusive targets, which will be conducted in accordance with an agreed research plan and budget under the oversight of a joint development committee. Allogene will reimburse Notch’s costs incurred in accordance with such plan and budget. The term of the research collaboration will expire upon the earlier of (i) the fifth anniversary of the date of the Notch Agreement, (ii) at Allogene’s election, following the joint development committee’s determination that for each exclusive target, Notch has met certain success criteria, or (iii) the joint development committee’s determination that the research collaboration cannot be reasonably pursued against any exclusive target due to technical infeasibility or safety issues. In connection with the execution of the Notch Agreement, Allogene made an upfront payment to Notch of $10.0 million in return for a license to access Notch's technology in order to conduct research pursuant to the Notch Agreement. The Company recognized a research and development expense of $10 million during the year ended December 31, 2019 as the license had no foreseeable alternative future use. In addition, Allogene made a $5.0 million investment in Notch’s series seed convertible preferred stock, resulting in Allogene having a 25% ownership interest in Notch’s outstanding capital stock on a fully diluted basis immediately following the investment. In connection with this investment, David Chang, M.D., Ph.D., the Company's President, Chief Executive Officer and Board member, was appointed to Notch’s board of directors. Under the Notch Agreement, Notch will be eligible to receive up to $7.25 million upon achieving certain agreed research milestones, up to $4.0 million per exclusive target upon achieving certain pre-clinical development milestones, and up to $283.0 million per exclusive target and cell type (i.e., T cell or NK cell) upon achieving certain clinical, regulatory and commercial milestones. Notch is also entitled to receive tiered royalties in the mid to high single digit range on Allogene’s sales of licensed products, subject to certain reductions, for a term, on a country-by-country and product-by-product basis, commencing on first commercial sale of such product in such country and continuing until the latest of (i) the date upon which there is no valid claim of the licensed patents in such country of sale that covers such product, (ii) the expiration of applicable data or other regulatory exclusivity in such country of sale or (iii) a defined period from the first commercial sale of such product in such country. The terms of the Notch Agreement will continue on a product-by-product and country-by-country basis until Allogene’s payment obligations with respect to such product in such country have expired. Following such expiration, Allogene’s license with respect to such product and country shall be perpetual, irrevocable, fully paid up and royalty-free. Allogene may terminate the Collaboration Agreement in whole or on a product-by-product basis upon ninety days’ prior written notice to Notch. Either party may also terminate the Collaboration Agreement with written notice upon material breach by the other party, if such breach has not been cured within a defined period of receiving such notice, or in the event of the other party’s insolvency. The Company has determined that Notch is a variable interest entity as of December 31, 2020 and 2019, respectively. The Company does not have the power to direct the activities which most significantly affect Notch's economic performance. Accordingly, for the years ended December 31, 2020 and 2019, the Company did not consolidate Notch because the Company determined that it was not the primary beneficiary. For the years ended December 31, 2020 and 2019, the Company recorded $3.2 million and $0.1 million, respectively, in collaboration costs as research and development expenses. Strategic Alliance with The University of Texas MD Anderson Cancer Center On October 6, 2020, the Company entered into a strategic five-year collaboration agreement with The University of Texas MD Anderson Cancer Center (MD Anderson) for the preclinical and clinical investigation of allogeneic CAR T cell product candidates. The Company and MD Anderson are collaborating on the design and conduct of preclinical and clinical studies with oversight from a joint steering committee. Under the terms of the agreement, the Company has committed up to $15.0 million of funding for the duration of the agreement. Payment of this funding is contingent on mutual agreement to study orders in order for any study to be included under the alliance. The Company made an upfront payment of $3.0 million to MD Anderson in the year ended December 31, 2020. The Company is obligated to make further payments to MD Anderson each year upon the anniversary of the agreement effective date through the duration of the agreement term. These costs are expensed to research and development as MD Anderson renders the services under the strategic alliance. As of December 31, 2020, no research and development costs had been incurred under the alliance. The agreement may be terminated by either party for material breach by the other party. Individual studies may be terminated for, among other things, material breach, health and safety concerns or where the institutional review board, the review board at the clinical site with oversight of the clinical study, requests termination of any study. Where any legal or regulatory authorization is finally withdrawn or terminated, the relevant study will also terminate automatically. Joint Venture and License Agreement with Allogene Overland Biopharm (CY) Limited On December 14, 2020, the Company entered into a License Agreement with Allogene Overland Biopharm (CY) Limited (Allogene Overland), a joint venture established by the Company and Overland Pharmaceuticals (CY) Inc. (Overland), pursuant to a Share Purchase Agreement, dated December 14, 2020, for the purpose of developing, manufacturing and commercializing certain allogeneic CAR T cell therapies for patients in greater China, Taiwan, South Korea and Singapore (the JV Territory). Pursuant to the Share Purchase Agreement, the Company acquired Seed Preferred Shares in Allogene Overland representing 49% of Allogene Overland's outstanding stock as partial consideration for the License Agreement, and Overland acquired Seed Preferred Shares representing 51% of Allogene Overland's outstanding stock for $117.0 million in upfront and certain quarterly cash payments, to support operations of Allogene Overland. As of December 31, 2020, the Company and Overland are the sole equity holders in Allogene Overland. The Company received $40 million from Allogene Overland as partial consideration for the License Agreement. Pursuant to the License Agreement, the Company granted Allogene Overland an exclusive license to develop, manufacture and commercialize certain allogeneic CAR T cell candidates directed at four targets, BCMA, CD70, FLT3, and DLL3, in the JV Territory. As consideration, the Company would also be entitled to additional regulatory milestone payments of up to $40.0 million and, subject to certain conditions, tiered low-to-mid single-digit sales royalties. Promises that the Company concluded were distinct performance obligations in the License Agreement included: (1) the license of intellectual property and delivery of know-how, (2) the manufacturing license, related know-how and support, (3) if and when available know-how developed in future periods, and (4) participation in the joint steering committee. In order to determine the transaction price, the Company evaluated all the payments to be received during the duration of the contract. Fixed consideration exists in the form of the upfront payment. Regulatory milestones and royalties were considered variable consideration. The Company constrains the estimated variable consideration when it assesses it is probable that a significant reversal in the amount of cumulative revenue recognized may occur in future periods. Milestone fees were constrained and not included in the transaction price due to the uncertainties of research and development. The Company re-evaluates the transaction price, including the estimated variable consideration included in the transaction price and all constrained amounts, in each reporting period and as uncertain events are resolved or other changes in circumstances occur. The shares of Series Seed Preferred Stock were accounted for as part of the Company’s joint venture and equity method accounting upon formation of the joint venture, and as such, were excluded from the transaction price. The Company determined that the initial transaction price consists of the upfront payment of $40.0 million. The allocation of the transaction price is performed based on standalone selling prices, which are based on estimated amounts that the Company would charge for a performance obligation if it were sold separately. The transaction price allocated to the license of intellectual property and delivery of know-how will be recognized upon grant of license and delivery of know-how. The transaction price allocated to (i) the manufacturing license, related know-how and support services, (ii) if and when available know-how developed in future periods, and (iii) participation in the joint steering committee, will be recognized over time as the services are delivered. Funds received in advance are recorded as deferred revenue and will be recognized as the performance obligations are satisfied. The Company has determined that Allogene Overland is a variable interest entity as of December 31, 2020. The Company does not have the power to independently direct the activities which most significantly affect Allogene Overland's economic performance. Accordingly, for the year ended December 31, 2020, the Company did not consolidate Allogene Overland because the Company determined that it was not the primary beneficiary. For the year ended December 31, 2020, the Company recorded the $40.0 million upfront cash payment received from Allogene Overland as deferred revenue, of which $39.0 million was current, on the consolidated balance sheet.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2020

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Leases

In August 2018, the Company entered into an operating lease agreement for new office and laboratory space which consists of approximately 68,000 square feet located in South San Francisco, California. The lease term is 127 months beginning August 2018 through February 2029 with an option to extend the term for another seven years which is not reasonably assured of exercise. The Company has made certain tenant improvements, including the addition of laboratory space, and has received $5.0 million of tenant improvement allowances up to December 31, 2020. The rent payments began on March 1, 2019 after an abatement period.

In October 2018, the Company entered into an operating lease agreement for new office and laboratory space which consists of 14,943 square feet located in South San Francisco, California. The lease term is 124 months beginning November 2018 through February 2029, with an option to extend the term for another seven years which is not reasonably assured of exercise. The Company has made certain tenant improvements, including the upgrading of current office and laboratory space with a lease incentive allowance of $0.8 million. Rent payments began in November 2018.

In February 2019, the Company entered into a lease agreement for approximately 118,000 square feet of space to develop a cell therapy manufacturing facility in Newark, California. The lease term is 188 months beginning November 2020 through July 2036. Upon certain conditions, the Company has two ten-year options to extend the lease, both of which are not reasonably assured of exercise. The Company is entitled to a tenant improvement allowance of $2.9 million for costs related to the design and construction of certain Company improvements, and has received $1.6 million of tenant improvement allowances up to December 31, 2020.

The Company maintains letters of credit for the benefit of landlords which is disclosed as restricted cash in the consolidated balance sheet. Restricted cash related to letters of credit due to landlords was $5.2 million and $4.3 million as of December 31, 2020 and 2019, respectively.

The balance sheet classification of our lease liabilities were as follows (in thousands):


	December 31, 2020		December 31, 2019
Operating lease liabilities
Current portion included in accrued and other current liabilities	$	2,974	$	1,679
Long-term portion of lease liabilities	50,809		51,349
Total operating lease liabilities	$	53,783	$	53,028

The components of lease costs for operating leases, which were recognized in operating expenses, were as follows (in thousands):


	Twelve Months Ended December 31,
	2020		2019		2018
Operating lease cost	$	7,390	$	5,945	$	1,863
Variable lease cost	1,382		1,087		32
Total lease costs	$	8,771	$	7,033	$	1,895

Cash paid for amounts included in the measurement of lease liabilities for the twelve months ended December 31, 2020 was $6.2 million and was included in net cash used in operating activities in our consolidated statements of cash flows.

The undiscounted future non-cancellable lease payments under our operating leases as of December 31, 2020 is as follows:


Year ending December 31:	(in thousands)
2021	$	6,485
2022	7,917
2023	8,168
2024	8,430
2025 and thereafter	56,654
Total undiscounted lease payments	87,653
Less: Present value adjustment	(32,313)
Less: Tenant improvement allowance	(1,557)
Total	$	53,783

Operating lease liabilities are based on the net present value of the remaining lease payments over the remaining lease term. In determining the present value of lease payments, we use our estimated incremental borrowing rate. The weighted average discount rate used to determine the operating lease liability was 8.37%. As of December 31, 2020, the weighted average remaining lease term for our operating leases is 10.28 years.

Rent expense for short-term leases was $0.2 million, $2.4 million and $2.6 million for the years ended December 31, 2020, 2019 and 2018 respectively.

Certain lease agreements require the Company to return designated areas of leased space to its original condition upon termination of the lease agreement. At the inception of such leases, the Company records an asset retirement obligation and a corresponding capital asset in an amount equal to the estimated fair value of the obligation. To determine the fair value of the obligation, we estimate the cost for a third-party to perform the restoration work. In subsequent periods, for each asset retirement obligation, the Company records interest expense to accrete the asset retirement obligation liability to full value and depreciate each capitalized asset retirement obligation asset, both over the term of the associated lease agreement. Asset retirement obligations were $0.5 million and $0.4 million as of December 31, 2020 and 2019 respectively.

Other Commitments

Solar Power Purchase and Energy Services Agreement

In July 2020, the Company entered into a Solar Power Purchase and Energy Services Agreement for the installation and operation of a solar photovoltaic generating system and battery energy storage system at the Company's cell therapy manufacturing facility in Newark, California. The agreement has a term of 20 years and is expected to commence in the first half of 2021. The Company is obligated to pay for electricity generated from the system at an agreed rate for the duration of the agreement term. Termination of the agreement by the Company will result in a termination payment due of approximately $4.3 million. In connection with the agreement, the Company maintains a letter of credit for the benefit of the service provider in the amount of $4.3 million which is disclosed as restricted cash in the consolidated balance sheet as of December 31, 2020.

License Agreements for Intellectual Property

The Company has entered into certain license agreements for intellectual property which is used as part of our development and manufacturing processes. Each of these respective agreements are generally cancellable by the Company. These agreements require payment of annual license fees and may include conditional milestone payments for achievement of specific research, clinical and commercial events, and royalty payments. The timing and likelihood of any significant conditional milestone payments or royalty payments becoming due was not probable as of December 31, 2020.

Purchase Commitments

In the normal course of business, the Company enters into various purchase commitments with third-party contract manufacturers for the manufacture and processing of our product candidates and related raw materials, and we have entered into other contracts in the normal course of business with contract research organizations for clinical trials and other vendors for other services and products for operating purposes. These agreements generally provide for termination or cancellation, other than for costs already incurred. As of December 31, 2020, the Company had non-cancellable purchase commitments of $5.4 million.

Contingencies

In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnifications. The Company’s exposure under these agreements is unknown, because it involves claims that may be made against the Company in the future, but have not yet been made. The Company accrues a liability for such matters when it is probable that future expenditures will be made and such expenditures can be reasonably estimated.

Indemnification

In accordance with the Company’s amended and restated certificate of incorporation and amended and restated bylaws, the Company has indemnification obligations to its officers and directors for certain events or occurrences, subject to certain limits, while they are serving in such capacity. There have been no claims to date, and the Company has a directors and officers liability insurance policy that may enable it to recover a portion of any amounts paid for future claims.

Equity Method Investment	12 Months Ended
Equity Method Investment	Dec. 31, 2020
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investment	Equity Method InvestmentsNotch Therapeutics In conjunction with the execution of the Notch Agreement (see Note 7), the Company also entered into a Share Purchase Agreement with the Company acquiring shares of Notch’s Series Seed convertible preferred stock for a total investment cost of $5.1 million which includes transaction costs of $0.1 million, resulting in a 25% ownership interest in Notch. The Company’s total equity investment in Notch as of December 31, 2020 and 2019 was $3.7 million and $4.9 million, respectively, based on the cost method of accounting. During the years ended December 31, 2020 and 2019, the Company recognized its share of Notch's net loss under the other expenses caption within the consolidated statement of operations. Allogene Overland Biopharm (CY) Limited In conjunction with the execution of the License Agreement with Allogene Overland (see Note 7), the Company also entered into a Share Purchase Agreement and Shareholders' Agreement with the joint venture company acquiring shares of Allogene Overland’s Seed Preferred Shares representing a 49% ownership interest in exchange for entering into a License Agreement which had a carrying value of zero. The Company accounts for its investment in Allogene Overland as an equity method investment at carrying value. The Company's total equity investment is Allogene Overland was zero as of December 31, 2020. The Company’s equity investment in Allogene Overland as of December 31, 2020 had a zero carryover basis. Therefore, the Company did not account for its share of losses incurred by Allogene Overland. See Note 7 for further details.

Convertible Notes Payable (2018 Notes)	12 Months Ended
Convertible Notes Payable (2018 Notes)	Dec. 31, 2020
Debt Disclosure [Abstract]
Convertible Notes Payable (2018 Notes)	Convertible Notes Payable (2018 Notes) In September 2018, the Company entered into a note purchase agreement pursuant to which it sold and issued an aggregate of $120.2 million in convertible promissory notes (convertible notes payable or 2018 Notes) and received net cash proceeds of $116.8 million. On issuance, the fair value of the 2018 Notes was determined to be equal to $120.2 million, which is the principal amount of the 2018 Notes. The 2018 Notes did not accrue interest. The 2018 Notes were settled in 7,856,176 shares of common stock in connection with the closing of the Company’s IPO (see Note 1) at a settlement price equal to 85% of the IPO price per share. On issuance, the Company elected to account for the 2018 Notes at fair value with any changes in estimated fair value being recognized through the statements of operations and comprehensive loss until the 2018 Notes settled. The fair value of the 2018 Notes was determined to be $141.4 million upon settlement. For the years ended December 31, 2020 and 2019, the Company recognized zero and $21.2 million, respectively, of expense in the accompanying statements of operations and comprehensive loss for the change in fair value of the 2018 Notes. On issuance, total debt issuance costs of $3.4 million were expensed and recognized as interest expense in the accompanying statements of operations and comprehensive loss.

Convertible Preferred Stock and Stockholders' Equity	12 Months Ended
Convertible Preferred Stock and Stockholders' Equity	Dec. 31, 2020
Equity [Abstract]
Convertible Preferred Stock and Stockholders’ Equity	Convertible Preferred Stock and Stockholders’ Equity Convertible Preferred Stock As discussed in Note 6, the Company issued 3,187,772 shares of its Series A-1 convertible preferred stock to Pfizer in connection with the Pfizer Agreement entered into in April 2018. In April 2018, the Company issued 7,557,990 shares of its Series A convertible preferred stock at a price per share of $35.06 for net cash proceeds of $264.4 million and issued 998,225 shares of Series A-1 convertible preferred stock at a price per share of $35.06 for net cash proceeds of $34.9 million. Fifty percent of the aggregate purchase price of $300.0 million was paid in April 2018. The remaining subscriptions receivable of $150.0 million was received in July and August 2018, at the election of the Company’s board of directors. On the completion of the IPO (see Note 1), all outstanding shares of convertible preferred stock were automatically converted into 61,655,922 shares of common stock. Preferred Stock Pursuant to the Amended and Restated Certificate of Incorporation filed on October 15, 2018, as amended, the Company is authorized to issue a total of 10,000,000 shares of preferred stock, of which no shares were issued and outstanding at December 31, 2020 and 2019. Common Stock Pursuant to the Amended and Restated Certificate of Incorporation filed on October 15, 2018, as amended, the Company is authorized to issue a total of 200,000,000 shares of common stock, of which 140,474,305 and 124,267,358 shares were issued and outstanding at December 31, 2020 and 2019, respectively. In connection with the issuance of the Company’s Series A convertible preferred stock in April 2018, the Company’s founders agreed to modify their common shares outstanding to include vesting provisions that require continued service to the Company in order to vest in those shares. As such, the 26,249,993 modified shares of common stock became compensatory upon such modification. The total compensation cost resulting from the modification is approximately $59.5 million and is being recognized over the four year vesting term. Common stockholders are entitled to dividends if and when declared by the Company’s Board of Directors subject to the prior rights of the preferred stockholders. As of December 31, 2020 and 2019, no dividends on common stock had been declared by the Company’s Board of Directors.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Stock-Based Compensation

2018 Equity Incentive Plan

In June 2018, the Company adopted its 2018 Equity Incentive Plan (Prior 2018 Plan). The 2018 Plan provided for the Company to sell or issue common stock or restricted common stock, or to grant incentive stock options or nonqualified stock options for the purchase of common stock, to employees, members of the Company’s Board of Directors and consultants of the Company under terms and provisions established by the Company’s Board of Directors. In September 2018, the Board of Directors adopted a new amended and restated 2018 Equity Incentive Plan as a successor to and continuation of the Prior 2018 Plan, which became effective in October 2018 (the 2018 Plan), which authorized additional shares for issuance and provided for an automatic annual increase to the number of shares issuable under the 2018 Plan by an amount equal to 5% of the total number of shares of common stock outstanding on December 31st of the preceding calendar year. The term of any stock option granted under the 2018 Plan cannot exceed 10 years. The Company generally grants stock-based awards with service conditions only. Options granted typically vest over a four-year period but may be granted with different vesting terms. Restricted Stock Units granted typically vest annually over a four-year period but may be granted with different vesting terms. Options shall not have an exercise price less than 100% of the fair market value of the Company’s common stock on the grant date. If the individual possesses more than 10% of the combined voting power of all classes of stock of the Company, the exercise price shall not be less than 110% of the fair market value of a common share of stock on the date of grant. This requirement is applicable to incentive stock options only.

As of December 31, 2020 and 2019, there were 12,308,848 and 9,642,503 shares reserved by the Company under the 2018 Plan for the future issuance of equity awards.

Stock Option Activity

The following summarizes option activity under the 2018 Plan:


	Outstanding Options
	Number of Options	Weighted- Average Exercise Price		Weighted- Average Remaining Contract Term	Aggregate Intrinsic Value
				(in years)	(in thousands)
Balance, December 31, 2019	9,190,522	$	14.51	8.82	$	110,490
Options granted	3,252,687	21.86
Options exercised	(1,260,275)	7.05			$	36,264
Options forfeited	(748,900)	13.99
Balance, December 31, 2020	10,434,034	$	17.73	8.29	$	93,149
Exercisable, December 31, 2020	6,473,752	$	15.77	8.17	$	65,818
Vested and expected to vest, December 31, 2020	10,434,034	$	17.73	8.29	$	93,149

The aggregate intrinsic values of options exercised, outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the options and the closing price of the Company’s common stock on the Nasdaq Global Select Market on December 31, 2020. During the years ended December 31, 2020 and 2019, the estimated weighted-average grant-date fair value of employee options granted was $13.79 per share and $18.42 per share, respectively. As of December 31, 2020 and 2019, there was $81.1 million and $74.7 million, respectively, of unrecognized stock-based compensation related to unvested stock options, which is expected to be recognized over a weighted-average period of 2 years, 222 days and 3 years, 15 days, respectively.

The fair value of employee, consultant and director stock option awards was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions:


	Year Ended December 31,
	2020	2019
Fair value of common stock	$18.22 - $48.94	$25.94 - $31.99
Expected term in years	5.31 - 6.09	5.27 - 6.08
Expected volatility	71.42% - 72.14%	74.14% - 74.92%
Expected risk-free interest rate	0.31% - 1.65%	1.54% - 2.62%
Expected dividend	0%	0%

The Black-Scholes option-pricing model requires the use of subjective assumptions which determine the fair value of stock-based awards. These assumptions include:

Fair value of common stock—For grants before October 2018 when the Company was private and there was no public market for the Company’s common stock, the fair value of the Company’s common stock underlying share-based awards was estimated on each grant date by the Company’s Board of Directors. In order to determine the fair value of the Company’s common stock underlying option grants, the Company’s Board of Directors considered, among other things, valuations of the Company’s common stock prepared by an unrelated third-party valuation firm in accordance with the guidance provided by the American Institute of Certified Public Accountants Practice Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation. For all grants subsequent to the Company’s IPO in October 2018, the fair value of common stock was determined by taking the closing price per share of common stock per Nasdaq.

Expected term— The expected term represents the period that stock-based awards are expected to be outstanding. The expected term for option grants is determined using the simplified method. The simplified method deems the term to be the average of the time-to-vesting and the contractual life of the stock-based awards.

Expected volatility— The Company uses an average historical stock price volatility of comparable public companies within the biotechnology and pharmaceutical industry that were deemed to be representative of future stock price trends as the Company does not have sufficient trading history for its common stock. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available.

Risk-free interest rate—The risk-free interest rate is based on the U.S. Treasury zero coupon issues in effect at the time of grant for periods corresponding with the expected term of option.

Expected dividend—The Company has never paid dividends on its common stock and has no plans to pay dividends on its common stock. Therefore, the Company used an expected dividend yield of zero.

For the years ended December 31, 2020 and 2019, total stock-based compensation expense related to stock options was $31.8 million and $21.9 million, respectively.

Restricted Stock Unit Activity

The following summarizes restricted stock unit activity under the 2018 Plan:


	Outstanding Restricted Stock Units
	Restricted Stock Units	Weighted- Average Grant Date Fair Value per Share		Weighted Average Remaining Vesting Life	Aggregate Intrinsic Value
				(in years)	(in thousands)
Unvested December 31, 2019	1,941,155	$	27.45	1.98	50,431
Granted	1,269,499	24.40		1.68
Vested	(490,470)	27.41
Forfeited	(226,264)	24.87
Unvested December 31, 2020	2,493,920	$	26.14	1.66	$	62,947
Vested and expected to vest, December 31, 2020	2,493,920	$	26.14	1.66	$	62,947

For the years ended December 31, 2020 and 2019, the Company granted zero and 57,361 performance based restricted stock units to a certain executive officer pursuant to the 2018 Plan. The 2019 granted performance awards are subject to the holder's continued service to the Company through each applicable vesting event. Through December 31, 2020, the Company believes that the achievement of the requisite performance conditions for these awards are not probable and as a result, no compensation expense has been recognized related to these awards in the year ended December 31, 2020.

For the years ended December 31, 2020 and 2019, total stock-based compensation expense related to restricted stock units was $17.2 million and $8.8 million, respectively. As of December 31, 2020 and 2019, there was $51.1 million and $43.0 million, respectively, of unrecognized stock-based compensation which is expected to be recognized over a weighted average period of 2.84 years.

Employee Stock Purchase Plan

In October 2018, the shareholders approved the 2018 Employee Stock Purchase Plan (ESPP), which initially reserved 1,160,000 shares of our common stock for employee purchases under terms and provisions established by the Board of Directors. Effective January 1, 2020 and 2019, the number of shares authorized under the ESPP for employee purchases increased by 1,242,673 and 1,214,826 shares respectively. The ESPP is intended to qualify as an ‘employee stock purchase plan’ under Section 423 of the Internal Revenue Code. Under the current offering adopted pursuant to the ESPP, each offering period is approximately 24 months, which is generally divided into four purchase periods of approximately six months.

Employees are eligible to participate if they are employed by the Company. Under the ESPP, employees may purchase common stock through payroll deductions at a price equal to 85% of the lower of the fair market value of common stock on the first trading day of each offering period or on the purchase date. The ESPP provides for consecutive, overlapping 24-month offering periods. The offering periods are scheduled to start on the first trading day on or after March 16 or September 16 of each year, except for the first offering period which commenced on October 11, 2018, the first trading day after the effective date of the Company’s registration statement. Contributions under the ESPP are limited to a maximum of 15% of an employee’s eligible compensation.

The fair values of the rights granted under the ESPP were calculated using the following assumptions:


	Year ended December 31,
	2020	2019
Expected term (in years)	0.50 – 2.00	0.50 – 2.00
Volatility	63.88% - 72.75%	60.4% - 76.0%
Risk-free interest rate	0.12%-0.36%	1.72% - 2.49%
Dividend yield	—	—

For the years ended December 31, 2020 and 2019, total stock-based compensation expense related to ESPP was $2.5 million and $1.6 million, respectively.

Founders’ Stock

Stock-based compensation expense is recognized for shares of founders’ stock as vesting conditions are met. In relation to the modification described in Note 11, 24,230,750 shares of founders’ stock remained unvested at the modification date in April 2018. For the years ended December 31, 2020 and 2019, $13.7 million and $13.7 million of stock-based compensation expense was recognized related to the vesting of 6,057,684 and 6,057,684 shares, respectively, of founders' stock. At December 31, 2020 and 2019, there was $17.1 million and $30.9 million of unrecognized stock-based compensation expense related to 7,572,119 and 13,629,803 shares of unvested founders’ stock which is expected to be recognized over 1 year, 3 months and 2 years, 3 months, respectively. The weighted-average fair value at grant date for founders’ stock was $2.27 per share.

Total stock-based compensation expense related to stock options, restricted stock units, employee stock purchase plans and vesting of the founders’ common stock was as follows:


	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Research and development	$	31,309	$	19,429	$	1,657
General and administrative	33,952		26,634		16,909
Total stock-based compensation expense	$	65,261	$	46,063	$	18,566

Early Exercised Options

The Company allows certain of its employees and its directors to exercise options granted under the Prior 2018 Plan and the 2018 Plan prior to vesting. The shares related to early exercised stock options are subject to the Company’s lapsing repurchase right upon termination of employment or service on the Company’s Board of Directors at the lesser of the original purchase price or fair market value at the time of repurchase. In order to vest, the holders are required to provide continued service to the Company. The proceeds are initially recorded in accrued and other liabilities and other long-term liabilities for the noncurrent portion. The proceeds are reclassified to paid-in capital as the repurchase right lapses. During the years ended December 31, 2020 and 2019, zero options were early exercised. As of December 31, 2020 and 2019, there was $2.8 million and $2.8 million recorded in accrued and other liabilities and $1.1 million and $3.9 million recorded in other long-term liabilities related to shares held by employees and directors that were subject to repurchase. The underlying shares are shown as outstanding in the consolidated financial statements since the exercise date but the shares which are subject to future vesting conditions are not included in the calculation of earnings per share.

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Pfizer Inc. As of December 31, 2020 and 2019, Pfizer held 22,032,040 shares of Common Stock and had appointed one member to the Company’s Board of Directors. In April 2018, the Company and Pfizer entered into a transition services agreement (the Pfizer TSA) for Pfizer to provide professional services to the Company related to research and development, project management, and other administrative functions. In September 2019, the Company and Pfizer terminated the Pfizer TSA. For the years ended December 31, 2020, 2019 and 2018, the costs incurred under the Pfizer TSA were zero, $4.5 million and $10.1 million, respectively. The Company also purchased certain lab supplies and services from Pfizer in connection with its research and development activities. For the years ended December 31, 2020, 2019 and 2018, total lab supplies and services purchased from Pfizer were zero, $1.4 million and $10.4 million, respectively. As of December 31, 2020 and 2019, the Company had amounts payable to Pfizer of zero and $0.1 million, respectively, which were recorded in the accompanying consolidated balance sheets. Consulting Agreements In June 2018, the Company entered into a services agreement with Two River Consulting LLC (Two River) a firm affiliated with the Company’s President and Chief Executive Officer, the Company’s Executive Chairman of the board of directors, and a director of the Company to provide various managerial, administrative, accounting and financial services to the Company. The costs incurred for services provided under this agreement were $0.4 million, $0.6 million and $0.6 million for the years ended December 31, 2020, 2019 and 2018, respectively. In August 2018, the Company entered into a consulting agreement with Bellco Capital LLC (Bellco). Pursuant to the consulting agreement, Bellco provides certain services for the Company, which are performed by Dr. Belldegrun and include without limitation, providing advice and analysis with respect to the Company’s business, business strategy and potential opportunities in the field of allogeneic CAR T cell therapy and any other aspect of the CAR T cell therapy business as the Company may agree. In consideration for these services, the Company paid Bellco $33,333 per month in arrears commencing January 2019 and $37,000 per month in arrears commencing January 2020. The Company may also, at its discretion, pay Bellco an annual performance award in an amount up to 60% of the aggregate compensation payable to Bellco in a calendar year. The Company also reimburses Bellco for out of pocket expenses incurred in performing the services. The costs incurred for services provided, bonus and out-of-pocket expenses incurred under this consulting agreement were $0.9 million, $0.8 million and $0.5 million for the years ended December 31, 2020, 2019 and 2018, respectively. As of December 31, 2020 and 2019, amounts due to Bellco of $0.3 million and $0.3 million, respectively, were recorded in accrued and other current liabilities in the accompanying consolidated balance sheets. Sublease Agreements In December 2018, the Company entered into a sublease with Bellco for 1,293 square feet of office space in Los Angeles, California for a three year term. On April 1, 2020, Bellco Capital Advisors Inc. assumed all rights, title, interests and obligations under the sublease from Bellco Capital LLC. The Company’s executive chairman, Arie Belldegrun, M.D., FACS, is a trustee of the Belldegrun Family Trust, which controls Bellco Capital Advisors Inc. The total right of use asset and associated liability recorded related to this related party lease was $0.1 million and $0.1 million at December 31, 2020 and 2019, respectively. In February 2019, the Company subleased 2,180 square feet of its office space in New York, New York, to ByHeart, Inc., formerly known as Second Science, Inc. (ByHeart). ByHeart is a development-stage infant formula company. Certain of the Company’s board members and executive officers have beneficial ownership in ByHeart and two serve on the board of directors of ByHeart. In September 2019, the Company entered into an amendment to the sublease agreement and increased the subleased space to 2,907 square feet. In October 2020, the sublease agreement between the Company and ByHeart was terminated. Sublease income for the years ended December 31, 2020 and 2019 was $0.3 million and $0.3 million, respectively, and was recognized as other income. Allogene Overland Biopharm (CY) Limited On December 14, 2020, the Company entered into an agreement with Overland to create a joint venture for the purpose of developing, manufacturing and commercializing certain allogeneic CAR T cell therapies for patients in greater China, Taiwan, South Korea and Singapore. In December 2020, the joint venture company, Allogene Overland, was established and obtained its business license in the Cayman Islands. Upon consummation of the joint venture, the Company and Overland received a 49% and 51% equity interest, respectively, in the entity in exchange for their contributions to the entity. See Notes 7 and 9 for further discussion.

401(k) Plan	12 Months Ended
401(k) Plan	Dec. 31, 2020
Retirement Benefits [Abstract]
401(k) Plan	401(k) PlanIn April 2018, the Company began to sponsor a 401(k) retirement savings plan for the benefit of its employees. All employees are eligible to participate, provided they meet the requirements of the plan. The Company made contributions to the plan for eligible participants, and recorded contribution expenses of $1.4 million, $0.9 million and $0.4 million related to matched contributions for the years ended December 31, 2020, 2019 and 2018, respectively.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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-Section 55
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Income Taxes

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Income Taxes

For the years ended December 31, 2020, 2019 and 2018, the Company recorded income tax related to minimum state taxes. The Company has incurred net operating losses for all the periods presented. The Company has not reflected any benefit of such net operating loss carryforwards in the accompanying consolidated financial statements.

The Company has established a full valuation allowance against its deferred tax assets due to the uncertainty surrounding the realization of such assets.


	Year Ended December 31,
	2020		2019		2018
Current:	(in thousands)
Federal	$	—	$	—	$	—
State	—		1		2
	—		1		2
Deferred:
Federal	—		(251)		(89)
State	—		(81)		(30)
	—		(332)		(119)
Benefit for income taxes	$	—	$	(331)	$	(117)

Reconciliation of the benefit for income taxes calculated at the statutory rate to our benefit for income taxes is as follows:


	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Tax benefit at federal statutory rate	$	(52,546)	$	(38,834)	$	(44,441)
State taxes, net of federal benefit	(18,656)		(12,951)		(10,652)
Stock-based compensation	997		2,037		3,629
Research tax credits	(2,319)		(1,714)		(708)
Write-off of in-process R&D	—		—		5,247
Change in fair value of convertible notes	—		—		4,454
Change in valuation allowance	72,538		49,989		41,916
Other	(14)		1,142		438
Benefit for incomes taxes	$	—	$	(331)	$	(117)

Deferred income taxes reflect the net tax effects of (a) temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes, and (b) operating losses and tax credit carryforwards.

Significant components of our deferred tax assets and liabilities are as follows:


	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	115,199	$	54,018	$	16,437
Tax credit carryforwards	8,297		4,239		1,239
Intangibles	20,582		22,770		23,086
Accrued expenses	3,888		2,375		952
Lease liabilities	15,050		14,839		9,730
Stock based compensation	12,970		6,870		360
Investments	175		—		—
Other	12		—		—
Total deferred tax assets	176,173		105,111		51,804
Deferred tax liabilities:
Fixed assets	(172)		(361)		(531)
Right of use leased assets	(11,556)		(12,453)		(9,239)
Investments	—		(393)		(118)
Other	—		—		—
Total deferred tax liabilities	(11,728)		(13,207)		(9,888)
Net deferred tax assets	164,445		91,904		41,916
Valuation allowance	(164,445)		(91,904)		(41,916)
Net deferred tax assets	$	—	$	—	$	—

Realization of deferred tax assets is dependent upon future earnings, if any, the timing and amount of which are uncertain. Due to the lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance. The valuation allowance increased by approximately $72.5 million, $50.0 million and $41.9 million during the years ended December 31, 2020, 2019 and 2018, respectively.

The following table sets forth our federal and state NOL carryforwards and federal research and development tax credits as of December 31, 2020:


	Amount		Expiration
	(in thousands)
Net operating losses, federal	$	413,920	Indefinite
Net operating losses, federal	$	2	2037
Net operating losses, state	$	404,881	2037-2039
Tax credits, federal	$	7,902	2037-2039
Tax credits, state	$	7,502	Indefinite

Current federal and California tax laws include substantial restrictions on the utilization of NOLs and tax credit carryforwards in the event of an ownership change of a corporation. Accordingly, the Company's ability to utilize NOLs and tax credit carryforwards may be limited as a result of such ownership changes. Such a limitation could result in the expiration of carryforwards before they are utilized.

In December 2019, the FASB issued Accounting Standards Update No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (ASU 2019-12), which simplifies the accounting for income taxes, eliminates certain exceptions within ASC 740, Income Taxes, and clarifies certain aspects of the current guidance to promote consistency among reporting entities. This guidance will be effective for the Company in the first quarter of 2021 on a prospective basis, and early adoption is permitted. The Company early adopted this standard as of January 1, 2020 on a prospective basis in accordance with ASC 250, Accounting Changes and Error Corrections. The adoption resulted in the Company no longer needing to determine the tax effect from unrealized gains on available for sale securities, which previously had been disclosed in the consolidated statement of operations as a benefit from income taxes. The impact of the adoption is that the benefit from income taxes in the consolidated statement of operations and comprehensive loss is zero. For the years ended December 31,

2019 and 2018, the Company recorded a tax benefit of $0.3 million and $0.1 million respectively, in other comprehensive income, related to available-for-sale securities.

We apply the provisions of ASC Topic 740 to account for uncertain income tax positions. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows:


	December 31,
	2020		2019		2018
	(in thousands)
Balance at beginning of the year:	3,148		920		—
Additions based on tax positions related to current year	3,013		2,228		920
Additions to tax position of prior year	—		—		—
Reductions to tax position of prior years	—		—		—
Lapse of the applicable statute of limitations	—		—		—
Balance at end of the year	$	6,161	$	3,148	$	920

It is the Company’s policy to include penalties and interest expense related to income taxes as a component of interest and other income, net, as necessary. As of December 31, 2020, 2019 and 2018, there were no accrued interest and penalties related to uncertain tax positions. The reversal of the uncertain tax benefits would not affect the effective tax rate to the extent that the Company continues to maintain a full valuation allowance against its deferred tax assets. Unrecognized tax benefits may change during the next 12 months for items that arise in the ordinary course of business. We are subject to examination by U.S. federal or state tax authorities for all years since inception.

- Definition

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

+ References + Details

Net Loss and Net Loss Per Share

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Net Loss and Net Loss Per Share

The following table sets forth the computation of the basic and diluted net loss per share (in thousands, except share and per share data):


	Year Ended December 31,
	2020		2019		2018
Numerator:
Net loss	$	(250,221)	$	(184,594)	$	(211,505)
Denominator:
Weighted average common shares outstanding	120,370,177		101,061,149		28,948,386
Net loss per share, basic and diluted	$	(2.08)	$	(1.83)	$	(7.31)

Since the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share as the inclusion of all potential dilutive securities would have been anti-dilutive. Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:


	Year Ended December 31,
	2020	2019	2018
Stock options to purchase common stock	10,434,034	9,190,522	7,235,545
Restricted stock units subject to vesting	2,493,920	1,941,155	—
Expected shares purchased under Employee Stock Purchase Plan	312,750	195,161	144,272
Founder shares subject to future vesting	7,572,119	13,629,803	19,687,487
Early exercised stock options subject to future vesting	1,737,137	2,992,290	5,020,580
Total	22,549,960	27,948,931	32,087,884

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	Subsequent EventsIn February 2021, the Company made a $15.9 million investment in Notch's Series A preferred stock. Immediately following this transaction, the Company's share in Notch was 17% on a fully diluted basis.

Description of Business and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Disclosure Text Block [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP). In June 2020, the Company formed a wholly-owned, Netherlands-based subsidiary, Allogene Therapeutics, B.V., to help prepare for and assist with the Company's activities in Europe. The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All material intercompany balances and transactions have been eliminated during consolidation.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying consolidated financial statements include but are not limited to the fair value of common stock, the fair value of stock options, the fair value of investments, the fair value of convertible notes payable upon conversion, income tax uncertainties, and certain accruals. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances change. Actual results could differ from those estimates.
Concentration of Credit and other Risks and Uncertainties	Concentration of Credit and other Risks and Uncertainties Financial instruments, which potentially subject the Company to significant concentrations of credit risk, consist primarily of cash and cash equivalents and investments. The primary objectives for the Company’s investment portfolio are the preservation of capital and the maintenance of liquidity. The Company does not enter into any investment transaction for trading or speculative purposes. The Company’s investment policy limits investments to certain types of instruments such as certificates of deposit, commercial paper, money market instruments, obligations issued by the U.S. government and U.S. government agencies as well as corporate debt securities, and places restrictions on maturities and concentration by type and issuer. The Company maintains cash balances in excess of amounts insured by the FDIC and concentrated within a limited number of financial institutions. The accounts are monitored by management and management believes that the financial institutions are financially sound, and, accordingly, minimal credit risk exists with respect to these financial institutions. As of December 31, 2020 and 2019, the Company has not experienced any credit losses in such accounts or investments. The Company is subject to a number of risks common for early-stage biopharmaceutical companies including, but not limited to, dependency on the clinical and commercial success of its product candidates, ability to obtain regulatory approval of its product candidates, the need for substantial additional financing to achieve its goals, uncertainty of broad adoption of its approved products, if any, by physicians and patients, significant competition and untested manufacturing capabilities.
Segments	SegmentsOperating segments are defined as components of an entity for which separate financial information is available and that is regularly reviewed by the Chief Operating Decision Maker (CODM) in deciding how to allocate resources to an individual segment and in assessing performance. The Company’s CODM is its Chief Executive Officer. The Company has determined it operates in a single operating segment and has one reportable segment.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments purchased with original maturities of three months or less from the purchase date to be cash equivalents. Cash equivalents consist primarily of amounts invested in bank money market accounts and money market mutual funds. The Company has issued letters of credit under separate lease and other agreements which have been collateralized by restricted cash. This cash is classified as long-term restricted cash on the accompanying consolidated balance sheet based on the terms of the underlying agreements.
Investments	Investments Investments are available-for-sale and are carried at estimated fair value. The Company’s valuations of marketable securities are generally derived from independent pricing services based upon quoted prices in active markets for similar securities, with prices adjusted for yield and number of days to maturity, or based on industry models using data inputs, such as interest rates and prices that can be directly observed or corroborated in active markets. Management determines the appropriate classification of its investments in debt securities at the time of purchase and at the end of each reporting period. Investments with original maturities of less than three months at the date of purchase are classified as cash and cash equivalents. Investments with original maturities beyond three months at the date of purchase and which mature at, or less than twelve months from the consolidated balance sheet date are classified as current. Unrealized gains and losses are excluded from earnings and are reported as a component of other comprehensive income. The Company periodically evaluates whether declines in fair values of its available-for-sale securities below their book value are other-than-temporary. This evaluation consists of several qualitative and quantitative factors regarding the severity and duration of the unrealized loss as well as the Company’s ability and intent to hold the available-for-sale security until a forecasted recovery occurs. Additionally, the Company assesses whether it has plans to sell the security or it is more likely than not it will be required to sell any available-for-sale securities before recovery of its amortized cost basis. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in interest and other income, net. The cost of investments sold is based on the specific-identification method. Interest income on investments is included in interest and other income, net.
Fair Value Measurement	Fair Value Measurement Assets and liabilities recorded at fair value on a recurring basis in the consolidated balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1—Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2—Inputs (other than quoted prices included in Level 1) are either directly or indirectly observable for the asset or liability. These include quoted prices for similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active. Level 3— Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation is computed on a straight-line basis over the estimated useful lives of the related assets, generally three to seven years. Maintenance and repairs are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in other expense.The Company adopted Accounting Standards Update ("ASU") No. 2018-15, Intangibles – Goodwill and other – Internal-Use Software (Subtopic 350-40) on January 1, 2020 on a prospective basis. The Company capitalizes implementation costs associated with internal use cloud computing arrangements in alignment with ASC 350-40 internal-use software. Costs incurred in preliminary project stage and post implementation stage are expensed as incurred. Costs incurred during the application development stage of implementation are capitalized in other long term assets on the consolidated balance sheet. Capitalized implementation costs from cloud computing arrangements are amortized over the term of the cloud-based service arrangement.
Leases	Leases The Company early adopted ASU No. 2016-2, Leases on January 1, 2018. For its long-term operating leases, the Company recognizes a right-of-use asset and a lease liability on its consolidated balance sheets. The lease liability is determined as the present value of future lease payments using an estimated rate of interest that the Company would pay to borrow equivalent funds on a collateralized basis at the lease commencement date. The right-of-use asset is based on the liability adjusted for any prepaid or deferred rent. The lease term at the commencement date is determined by considering whether renewal options and termination options are reasonably assured of exercise. Rent expense for the operating lease is recognized on a straight-line basis over the lease term and is included in operating expenses on the consolidated statements of operations and comprehensive loss. Variable lease payments include lease operating expenses. The Company elected to exclude from its consolidated balance sheets recognition of leases having a term of 12 months or less (short-term leases) and elected to not separate lease components and non-lease components for its long-term real-estate leases.
Equity Method Investments and Variable Interest Entities	Equity Method Investments The Company uses the equity method of accounting for equity investments in companies if the investment provides the ability to exercise significant influence, but not control, over operating and financial policies of the investee. The Company's proportionate share of the net income or loss of these companies is included in other expenses in the consolidated statement of operations. Judgment regarding the level of influence over each equity method investment includes considering key factors such as our ownership interest, representation on the board of directors, participation in policy-making decisions and material purchase and sale transactions. The Company evaluates equity method investments for impairment whenever events or changes in circumstances indicate that the carrying amount of the investment might not be recoverable. Factors considered when reviewing an equity method investment for impairment include the length of time (duration) and the extent (severity) to which the fair value of the equity method investment has been less than cost, the investee’s financial condition and near-term prospects and the intent and ability to hold the investment for a period of time sufficient to allow for anticipated recovery. An impairment that is other-than-temporary is recognized in the period identified. Variable Interest Entities For entities in which the Company has variable interests, the Company focuses on identifying if one of the entities is the primary beneficiary through having the power to direct the activities that most significantly impact the variable interest entity’s economic performance and having the obligation to absorb losses or the right to receive benefits from the variable interest entity. If the Company is the primary beneficiary of a variable interest entity, the assets, liabilities, and results of operations of the variable interest entity will be included in the Company’s consolidated financial statements. The Company did not consolidate any variable interest entities in any of the periods presented because the Company determined that it was not the primary beneficiary.
Accrued Research and Development Costs	Accrued Research and Development Costs The Company records accrued liabilities for estimated costs of research and development activities conducted by collaboration partners and third-party service providers, which include the conduct of preclinical studies and clinical trials, and contract manufacturing activities. The Company records the estimated costs of research and development activities based upon the estimated amount of services provided but not yet invoiced and includes these costs in accrued and other current liabilities on the consolidated balance sheets and within research and development expenses on the consolidated statements of operations and comprehensive loss. The Company accrues for these costs based on factors such as estimates of the work completed and in accordance with agreements established with its collaboration partners and third-party service providers. The Company makes significant judgments and estimates in determining the accrued liabilities balance at the end of each reporting period. As actual costs become known, the Company adjusts its accrued liabilities. The Company has not experienced any material differences between accrued costs and actual costs incurred since its inception.
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to affect taxable income. Management makes an assessment of the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to the Company’s historical operating performance and net losses, the net deferred tax assets have been fully offset by a valuation allowance. The Company recognizes uncertain income tax positions at the largest amount that is more likely than not to be sustained upon audit by the relevant taxing authority. An uncertain income tax position will not be recognized if it has less than a 50% likelihood of being sustained. Changes in recognition or measurement are reflected in the period in which judgment occurs. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of the provision for income taxes.
Stock-Based Compensation	Stock-Based Compensation The Company measures its stock-based awards granted to employees, consultants and directors based on the estimated fair values of the awards and recognizes the compensation over the requisite service period. The Company uses the Black-Scholes option-pricing model to estimate the fair value of its stock-based awards. Stock-based compensation is recognized using the straight-line method. As the stock compensation expense is based on awards ultimately expected to vest, it is reduced by forfeitures. The Company accounts for forfeitures as they occur.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding for the period, without consideration for potential dilutive shares of common stock. Since the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share since the effects of potentially dilutive securities are antidilutive. Shares of common stock subject to repurchase are excluded from the weighted-average shares.
Comprehensive Loss	Comprehensive LossComprehensive loss includes net loss and certain changes in stockholders’ equity (deficit) that are excluded from net loss. For the years ended December 31, 2020, 2019 and 2018 this was comprised of unrealized gains and losses, net of tax, on the Company’s investments.
Definite-Lived Intangible Assets	Definite-Lived Intangible AssetsIdentifiable intangible assets consist of in-process research and development and workforce associated with the Pfizer asset acquisition. Intangible assets with finite lives are amortized over their estimated useful lives on a straight-line basis, generally two years. Acquired in-process research and development intangible assets with no alternative future use are charged to research and development expense when acquired. The straight-line method of amortization represents the Company’s best estimate of the distribution of the economic value of the identifiable intangible assets. Intangible assets are carried at cost less accumulated amortization. Amortization of intangible assets is included in research and development expenses.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets are reviewed annually for impairment or whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amount of an asset group to the future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows arising from the asset. There were impairment losses related to equipment disposals of zero and $0.2 million for the years ended December 31, 2020 and 2019, respectively.
Revenue Recognition	Revenue Recognition In the near future, the Company’s revenue is anticipated to be generated through collaboration research and license agreements. The terms of these agreements are anticipated to contain multiple deliverables which may include (i) grant of licenses, (ii) transfer of know-how, (iii) research and development activities, (iii) clinical manufacturing and, (iv) product supply. The payment terms of these agreements may include nonrefundable upfront fees, payments for research and development activities, payments based upon the achievement of certain milestones, royalty payments based on product sales derived from the collaboration, and payments for supplying product. The Company will analyze its collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements (ASC 808) to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of ASC 808 and those that are more reflective of a vendor-customer relationship and, therefore, within the scope of Topic 606, Revenue from Contracts with Customers (ASC 606). For elements of collaboration arrangements that are accounted for pursuant to ASC 808, an appropriate recognition method is determined and applied consistently, generally by analogy to Topic 606. For elements of those arrangements that the Company determines should be accounted for under ASC 606, the Company assesses which activities in the collaboration agreements are performance obligations that should be accounted for separately and determine the transaction price of the arrangement, which includes the assessment of the probability of achievement of future milestones and other potential consideration. A performance obligation represents a promise in a contract to transfer a distinct good or service to a customer, which represents a unit of accounting in accordance with ASC 606. A performance obligation is considered distinct from other obligations in a contract when it provides a benefit to the customer either on its own or together with other resources that are readily available to the customer and is separately identified in the contract. The Company considers a performance obligation satisfied once the Company has transferred control of a good or service to the customer, meaning the customer has the ability to use and obtain the benefit of the good or service. A portion of the consideration should be allocated to each distinct performance obligation and recognized as revenue when, or as, the performance obligation is satisfied. The total consideration which the Company expects to collect in exchange for the Company’s products is an estimate and may be fixed or variable. The Company constrains the estimated variable consideration when it assesses it is probable that a significant reversal in the amount of cumulative revenue recognized may occur in future periods. The transaction price is re-evaluated, including the estimated variable consideration included in the transaction price and all constrained amounts, in each reporting period and as uncertain events are resolved or other changes in circumstances occur. The allocation of the transaction price is performed based on standalone selling prices, which are based on estimated amounts that the Company would charge for a performance obligation if it were sold separately. Revenue is recognized when, or as, performance obligations in the contracts are satisfied, in the amount reflecting the expected consideration to be received from the goods or services transferred to the customers. Funds received in advance are recorded as deferred revenue and are recognized as the related performance obligation is satisfied.
Research and Development Expenses	Research and Development Expenses Research and development costs are expensed as incurred and consist of salaries and benefits, including associated stock-based compensation, and laboratory supplies and facility costs, as well as fees paid to other entities that conduct certain research and development activities on the Company’s behalf. Research and development expenses also include costs incurred for internal and sponsored collaborative research and development activities. Costs associated with co-development activities performed under the various license and collaboration agreements are included in research and development expenses. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are capitalized and then expensed as the related goods are delivered or the services are performed.

Description of Business and Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Text Block [Abstract]

Estimated Life Of Assets

The Company has determined the estimated life of assets to be as follows:


Laboratory equipment			5 years
Computer equipment and purchased software			3 - 5 years
Fixtures and furniture			7 years
Leasehold improvements			Shorter of lease term or useful life

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Financial Assets Subject to Fair Value Measurements on Recurring Basis and Level of Inputs Used in Such Measurements by Major Security Type


	December 31, 2020
	Level 1		Level 2		Level 3		Fair Value
	(in thousands)
Financial Assets:
Money market funds ¹	$	102,039	$	—	$	—	$	102,039
Commercial paper	—		58,975		—		58,975
Corporate bonds	—		262,757		—		262,757
U.S. treasury securities	446,996		—		—		446,996
U.S. agency securities	—		80,039		—		80,039
Total financial assets	$	549,035	$	401,771	$	—	$	950,806

¹ Included within cash and cash equivalents on the Company’s consolidated balance sheet


	December 31, 2019
	Level 1		Level 2		Level 3		Fair Value
	(in thousands)
Financial Assets:
Money market funds ¹	$	122,900	$	—	$	—	$	122,900
Corporate bonds	—		205,011		—		205,011
U.S. treasury securities	181,894		—		—		181,894
U.S. agency securities	—		25,824		—		25,824
Certificates of deposit	—		1,000		—		1,000
Total financial assets	$	304,794	$	231,835	$	—	$	536,629

¹ Included within cash and cash equivalents on the Company’s consolidated balance sheet

Investment (Tables)

12 Months Ended

Dec. 31, 2020

Investments, All Other Investments [Abstract]

Summary of Cash Equivalents and Available-for-Sale Securities

The fair value and amortized cost of cash equivalents and available-for-sale securities by major security type as of December 31, 2020 are presented in the following table:


	December 31, 2020
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
	(in thousands)
Money market funds	$	102,039	$	—	$	—	$	102,039
Commercial paper	58,969		8		(2)		58,975
Corporate bonds	262,349		444		(36)		262,757
U.S. treasury securities	446,726		282		(12)		446,996
U.S. agency securities	80,012		30		(3)		80,039
Total cash equivalents and investments	$	950,095	$	764	$	(53)	$	950,806

Classified as:
Cash equivalents							$	102,039
Short-term investments							644,559
Long-term investments							204,208
Total cash equivalents, and investments							$	950,806

The fair value and amortized cost of cash equivalents and available-for-sale securities by major security type as of December 31, 2019 are presented in the following table:


	December 31, 2019
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
	(in thousands)
Money market funds	$	122,900	$	—	$	—	$	122,900
Corporate bonds	204,144		871		(4)		205,011
U.S. treasury securities	181,340		557		(3)		181,894
U.S. agency securities	25,658		167		(1)		25,824
Certificates of deposit	1,000		—		—		1,000
Total cash equivalents and investments	$	535,042	$	1,595	$	(8)	$	536,629

Classified as:
Cash equivalents							$	122,900
Short-term investments							355,407
Long-term investments							58,322
Total cash equivalents, and investments							$	536,629

Schedule of Available For Sale Debt Investments by Contractual Maturity

The fair values of available-for-sale debt investments by contractual maturity as of December 31, 2020 and 2019 were as follows:


	December 31,
	2020		2019
	(in thousands)
Due in 1 year or less	$	644,559	$	355,407
Due in 1 - 2 years	148,211		58,322
Due in 3 years	55,997		—
Instruments not due at a single maturity date	102,039		122,900
Total cash equivalents and investments	$	950,806	$	536,629

Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Property and Equipment, Net

Property and Equipment, Net


	December 31,
	2020		2019
	(in thousands)
Construction in progress	$	68,944	$	12,390
Leasehold improvements	31,518		29,924
Laboratory equipment	23,810		13,117
Computers equipment and purchased software	4,088		3,726
Furniture and fixtures	3,388		2,764
Total	131,748		61,921
Less: accumulated depreciation	(12,908)		(5,472)
Total property and equipment, net	$	118,840	$	56,449

Schedule of Accrued Liabilities

Accrued Liabilities

Accrued liabilities consist of the following:


	December 31,
	2020		2019
	(in thousands)
Accrued compensation and related benefits	$	15,943	$	9,560
Accrued research and development expenses	13,887		4,833
Accrued property and equipment	7,475		3,575
Unvested shares liability	2,842		2,843
Other	4,791		3,018
Total accrued and other current liabilities	$	44,938	$	23,829

Asset Acquisition (Tables)

12 Months Ended

Dec. 31, 2020

Business Combinations [Abstract]

Schedule of Fair Value of Assets Acquired

The following table summarizes the fair value of assets acquired (in thousands):


Property and equipment	$	3,258
In-process research and development (IPR&D):
Anti-CD19 CAR T cell therapy	103,936
Anti-BCMA CAR T cell therapy	5,500
Assembled workforce	1,206
Total assets acquired	$	113,900

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2020

Commitments and Contingencies Disclosure [Abstract]

Schedule of Lease Liabilities

The balance sheet classification of our lease liabilities were as follows (in thousands):


	December 31, 2020		December 31, 2019
Operating lease liabilities
Current portion included in accrued and other current liabilities	$	2,974	$	1,679
Long-term portion of lease liabilities	50,809		51,349
Total operating lease liabilities	$	53,783	$	53,028

Schedule of Lease Costs

The components of lease costs for operating leases, which were recognized in operating expenses, were as follows (in thousands):


	Twelve Months Ended December 31,
	2020		2019		2018
Operating lease cost	$	7,390	$	5,945	$	1,863
Variable lease cost	1,382		1,087		32
Total lease costs	$	8,771	$	7,033	$	1,895

Summary of Undiscounted Future Non-Cancellable Lease Payments Under Operating Leases

The undiscounted future non-cancellable lease payments under our operating leases as of December 31, 2020 is as follows:


Year ending December 31:	(in thousands)
2021	$	6,485
2022	7,917
2023	8,168
2024	8,430
2025 and thereafter	56,654
Total undiscounted lease payments	87,653
Less: Present value adjustment	(32,313)
Less: Tenant improvement allowance	(1,557)
Total	$	53,783

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Summary of Stock Option Activity Under Plan

The following summarizes option activity under the 2018 Plan:


	Outstanding Options
	Number of Options	Weighted- Average Exercise Price		Weighted- Average Remaining Contract Term	Aggregate Intrinsic Value
				(in years)	(in thousands)
Balance, December 31, 2019	9,190,522	$	14.51	8.82	$	110,490
Options granted	3,252,687	21.86
Options exercised	(1,260,275)	7.05			$	36,264
Options forfeited	(748,900)	13.99
Balance, December 31, 2020	10,434,034	$	17.73	8.29	$	93,149
Exercisable, December 31, 2020	6,473,752	$	15.77	8.17	$	65,818
Vested and expected to vest, December 31, 2020	10,434,034	$	17.73	8.29	$	93,149

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

The fair value of employee, consultant and director stock option awards was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions:


	Year Ended December 31,
	2020	2019
Fair value of common stock	$18.22 - $48.94	$25.94 - $31.99
Expected term in years	5.31 - 6.09	5.27 - 6.08
Expected volatility	71.42% - 72.14%	74.14% - 74.92%
Expected risk-free interest rate	0.31% - 1.65%	1.54% - 2.62%
Expected dividend	0%	0%

Schedule of Restricted Stock Units Activity

The following summarizes restricted stock unit activity under the 2018 Plan:


	Outstanding Restricted Stock Units
	Restricted Stock Units	Weighted- Average Grant Date Fair Value per Share		Weighted Average Remaining Vesting Life	Aggregate Intrinsic Value
				(in years)	(in thousands)
Unvested December 31, 2019	1,941,155	$	27.45	1.98	50,431
Granted	1,269,499	24.40		1.68
Vested	(490,470)	27.41
Forfeited	(226,264)	24.87
Unvested December 31, 2020	2,493,920	$	26.14	1.66	$	62,947
Vested and expected to vest, December 31, 2020	2,493,920	$	26.14	1.66	$	62,947

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions

The fair values of the rights granted under the ESPP were calculated using the following assumptions:


	Year ended December 31,
	2020	2019
Expected term (in years)	0.50 – 2.00	0.50 – 2.00
Volatility	63.88% - 72.75%	60.4% - 76.0%
Risk-free interest rate	0.12%-0.36%	1.72% - 2.49%
Dividend yield	—	—

Schedule of Stock-Based Compensation Expense

Total stock-based compensation expense related to stock options, restricted stock units, employee stock purchase plans and vesting of the founders’ common stock was as follows:


	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Research and development	$	31,309	$	19,429	$	1,657
General and administrative	33,952		26,634		16,909
Total stock-based compensation expense	$	65,261	$	46,063	$	18,566

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Summary of Valuation Allowance

The Company has established a full valuation allowance against its deferred tax assets due to the uncertainty surrounding the realization of such assets.


	Year Ended December 31,
	2020		2019		2018
Current:	(in thousands)
Federal	$	—	$	—	$	—
State	—		1		2
	—		1		2
Deferred:
Federal	—		(251)		(89)
State	—		(81)		(30)
	—		(332)		(119)
Benefit for income taxes	$	—	$	(331)	$	(117)

Schedule of Income Tax Rate Reconciliation

Reconciliation of the benefit for income taxes calculated at the statutory rate to our benefit for income taxes is as follows:


	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Tax benefit at federal statutory rate	$	(52,546)	$	(38,834)	$	(44,441)
State taxes, net of federal benefit	(18,656)		(12,951)		(10,652)
Stock-based compensation	997		2,037		3,629
Research tax credits	(2,319)		(1,714)		(708)
Write-off of in-process R&D	—		—		5,247
Change in fair value of convertible notes	—		—		4,454
Change in valuation allowance	72,538		49,989		41,916
Other	(14)		1,142		438
Benefit for incomes taxes	$	—	$	(331)	$	(117)

Schedule of Deferred Tax Assets and Liabilities

Significant components of our deferred tax assets and liabilities are as follows:


	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	115,199	$	54,018	$	16,437
Tax credit carryforwards	8,297		4,239		1,239
Intangibles	20,582		22,770		23,086
Accrued expenses	3,888		2,375		952
Lease liabilities	15,050		14,839		9,730
Stock based compensation	12,970		6,870		360
Investments	175		—		—
Other	12		—		—
Total deferred tax assets	176,173		105,111		51,804
Deferred tax liabilities:
Fixed assets	(172)		(361)		(531)
Right of use leased assets	(11,556)		(12,453)		(9,239)
Investments	—		(393)		(118)
Other	—		—		—
Total deferred tax liabilities	(11,728)		(13,207)		(9,888)
Net deferred tax assets	164,445		91,904		41,916
Valuation allowance	(164,445)		(91,904)		(41,916)
Net deferred tax assets	$	—	$	—	$	—

Summary of Operating Loss Carryforwards

The following table sets forth our federal and state NOL carryforwards and federal research and development tax credits as of December 31, 2020:


	Amount		Expiration
	(in thousands)
Net operating losses, federal	$	413,920	Indefinite
Net operating losses, federal	$	2	2037
Net operating losses, state	$	404,881	2037-2039
Tax credits, federal	$	7,902	2037-2039
Tax credits, state	$	7,502	Indefinite

Schedule of Reconciliation of Unrecognized Tax Benefits

We apply the provisions of ASC Topic 740 to account for uncertain income tax positions. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows:


	December 31,
	2020		2019		2018
	(in thousands)
Balance at beginning of the year:	3,148		920		—
Additions based on tax positions related to current year	3,013		2,228		920
Additions to tax position of prior year	—		—		—
Reductions to tax position of prior years	—		—		—
Lapse of the applicable statute of limitations	—		—		—
Balance at end of the year	$	6,161	$	3,148	$	920

Net Loss and Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Schedule of Earnings Per Share Basic and Diluted

The following table sets forth the computation of the basic and diluted net loss per share (in thousands, except share and per share data):


	Year Ended December 31,
	2020		2019		2018
Numerator:
Net loss	$	(250,221)	$	(184,594)	$	(211,505)
Denominator:
Weighted average common shares outstanding	120,370,177		101,061,149		28,948,386
Net loss per share, basic and diluted	$	(2.08)	$	(1.83)	$	(7.31)

Schedule of Anti-dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share

Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:


	Year Ended December 31,
	2020	2019	2018
Stock options to purchase common stock	10,434,034	9,190,522	7,235,545
Restricted stock units subject to vesting	2,493,920	1,941,155	—
Expected shares purchased under Employee Stock Purchase Plan	312,750	195,161	144,272
Founder shares subject to future vesting	7,572,119	13,629,803	19,687,487
Early exercised stock options subject to future vesting	1,737,137	2,992,290	5,020,580
Total	22,549,960	27,948,931	32,087,884

Description of Business and Summary of Significant Accounting Policies - Additional Information (Details)		1 Months Ended			12 Months Ended			37 Months Ended
	Oct. 01, 2018	Jun. 30, 2020 USD ($) $ / shares shares	Oct. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($)	Dec. 31, 2020 USD ($) segment shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2020 USD ($) shares	Nov. 30, 2019 USD ($)	Oct. 10, 2018 shares
Subsidiary, Sale of Stock [Line Items]
Start up costs				$ 2,000
Common stock price (in dollars per share) \| $ / shares		$ 47.00
Preferred stock outstanding (in shares) \| shares					0	0		0
Stock issuance, maximum value									$ 250,000,000.0
Stock issuance, maximum compensation due to third party (as a percentage of stock sales)						3.00%
Stock issued, value		$ 595,700,000			$ 595,730,000	$ 54,219,000
Shares sold in transaction (in shares) \| shares		13,457,447
Sale of stock, consideration received on transaction		$ 632,500,000
Common stock forward split ratio	0.1905
Cash and cash equivalents and marketable securities					1,000,000,000.0			$ 1,000,000,000.0
Net loss and comprehensive loss					$ (250,221,000)	(184,594,000)	$ (211,505,000)	$ (646,300,000)
Reportable segments \| segment					1
Finite-lived intangible asset, useful life					2 years
Disposal of property, plant, and equipment					$ 0	200,000	0
IPO
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock (in shares) \| shares			20,700,000
Net proceeds			$ 343,300,000
Common stock price (in dollars per share) \| $ / shares			$ 18.00
Underwriting discounts and commissions			$ 26,100,000
Offering costs			$ 3,200,000				29,300,000
Convertible preferred stock, shares outstanding (in shares) \| shares			11,743,987
Number of 2018 Notes converted into common stock (in shares) \| shares			7,856,176
Preferred stock outstanding (in shares) \| shares			0
Stock issued, value							$ 343,329,000
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock (in shares) \| shares			2,700,000
Shares sold in transaction (in shares) \| shares		1,755,319
ATM offering
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock (in shares) \| shares					848,663
Offering costs					$ 600,000	$ 1,600,000
Stock issued, value					$ 26,203,000
Common Stock
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock (in shares) \| shares					13,457,447	1,965,082
Number of 2018 Notes converted into common stock (in shares) \| shares			7,856,176				7,856,176
Stock issued, value					$ 13,000	$ 2,000
Common Stock \| IPO
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock (in shares) \| shares							20,700,000
Number of convertible preferred stock converted to shares of common stock (in shares) \| shares			61,655,922							61,655,922
Stock issued, value							$ 21,000
Common Stock \| ATM offering
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock (in shares) \| shares					848,663
Stock issued, value					$ 1,000

Description of Business and Summary of Significant Accounting Policies - Schedule of Estimated Life of Assets (Details)	12 Months Ended
	Dec. 31, 2020
Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	3 years
Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	7 years
Laboratory equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	5 years
Computer Equipment and purchased software \| Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	3 years
Computer Equipment and purchased software \| Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	5 years
Fixtures and Furniture
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	7 years

Recent Accounting Guidance (Details) $ in Millions	Dec. 31, 2020 USD ($)
Accounting Changes and Error Corrections [Abstract]
Implementation costs capitalized	$ 4.2

Fair Value Measurements - Additional Information (Detail) - Fair Value, Measurements, Recurring - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets	$ 950,806,000	$ 536,629,000
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets	$ 0	$ 0

Investments - Summary of Cash Equivalents, Restricted Cash and Investments, Classified as Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 950,095	$ 535,042
Unrealized Gains	764	1,595
Unrealized Losses	(53)	(8)
Fair Value	950,806	536,629
Cash equivalents	102,039	122,900
Short-term investments	644,559	355,407
Long-term investments	204,208	58,322
Total cash equivalents, and investments	950,806	536,629
Money Market Funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	102,039	122,900
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	102,039	122,900
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	58,969
Unrealized Gains	8
Unrealized Losses	(2)
Fair Value	58,975
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	262,349	204,144
Unrealized Gains	444	871
Unrealized Losses	(36)	(4)
Fair Value	262,757	205,011
U.S. treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	446,726	181,340
Unrealized Gains	282	557
Unrealized Losses	(12)	(3)
Fair Value	446,996	181,894
U.S. agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	80,012	25,658
Unrealized Gains	30	167
Unrealized Losses	(3)	(1)
Fair Value	$ 80,039	25,824
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		1,000
Unrealized Gains		0
Unrealized Losses		0
Fair Value		$ 1,000

Investments - Schedule of Fair Values of Available For Sale Debt Investments by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Investments, All Other Investments [Abstract]
Due in 1 year or less	$ 644,559	$ 355,407
Due in 1 - 2 years	148,211	58,322
Due in 3 years	55,997	0
Instruments not due at a single maturity date	102,039	122,900
Total cash equivalents and investments	$ 950,806	$ 536,629

Investment - Additional Information (Details) - USD ($)	12 Months Ended
Investment - Additional Information (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments, All Other Investments [Abstract]
Maximum remaining contractual maturities of available-for-sale securities	3 years	2 years
Other than temporary impairment losses of available-for-sale securities	$ 0	$ 0	$ 0
Net unrealized loss position	5,000,000.0	0
Accrued interest receivable from available-fore-sale investments	$ 2,800,000	$ 2,400,000

Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	$ 131,748	$ 61,921
Less: accumulated depreciation	(12,908)	(5,472)
Total property and equipment, net	118,840	56,449
Construction in progress
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	68,944	12,390
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	31,518	29,924
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	23,810	13,117
Computers equipment and purchased software
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	4,088	3,726
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	$ 3,388	$ 2,764

Balance Sheet Components - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Depreciation and amortization expense	$ 7,400,000	$ 4,600,000	$ 1,000,000.0
Disposal of property, plant, and equipment	$ 0	$ 200,000	$ 0

Balance Sheet Components - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued compensation and related benefits	$ 15,943	$ 9,560
Accrued research and development expenses	13,887	4,833
Accrued property and equipment	7,475	3,575
Unvested shares liability	2,842	2,843
Other	4,791	3,018
Total accrued and other current liabilities	$ 44,938	$ 23,829

Asset Acquisition - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Apr. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Asset Acquisition [Line Items]
Total asset acquisition	$ 113,900,000
Discount rate for valuation	16.50%
Finite-lived intangible asset, useful life		2 years
Pfizer \| Asset Contribution Agreement
Asset Acquisition [Line Items]
Finite-lived intangible asset, useful life	2 years
Milestone payments		$ 0	$ 0	$ 0
Aggregate milestone payments	$ 840,000,000.0
Pfizer \| Asset Contribution Agreement \| United States
Asset Acquisition [Line Items]
Milestone payments	30,000,000.0
Pfizer \| Asset Contribution Agreement \| European Union
Asset Acquisition [Line Items]
Milestone payments	$ 60,000,000.0
Series A1 Convertible Preferred Shares
Asset Acquisition [Line Items]
Share issued in connection with asset acquisition (in shares)	3,187,772
Share issued in connection with asset acquisition, fair value	$ 111,800,000
Convertible preferred stock, price per share (in usd per share)	$ 35.06
Costs from issuance of preferred shares	$ 2,100,000
Total asset acquisition	$ 113,900,000

Asset Acquisition - Schedule of Fair Value of Assets Acquired (Details) $ in Thousands	Apr. 30, 2018 USD ($)
Asset Acquisition [Line Items]
Property and equipment	$ 3,258
Total assets acquired	113,900
In Process Research and Development \| Anti-CD19 CAR T cell therapy
Asset Acquisition [Line Items]
Total assets acquired	103,936
In Process Research and Development \| Anti-BCMA CAR T cell therapy
Asset Acquisition [Line Items]
Total assets acquired	5,500
In Process Research and Development \| Assembled workforce
Asset Acquisition [Line Items]
Total assets acquired	$ 1,206

License and Collaboration Agreements (Details) € in Millions			12 Months Ended
	Dec. 14, 2020 USD ($)	Oct. 06, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 EUR (€)	Nov. 01, 2019 USD ($)
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development			$ 192,987,000	$ 144,535,000	$ 151,860,000
Accrued and other current liabilities			44,938,000	23,829,000
Equity method investment			3,738,000	4,892,000
University Of Texas M D Anderson Cancer Center
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development			0	0
Collaboration agreement, upfront payment			$ 3,000,000.0
Collaboration agreement, term		5 years
Committed funding		$ 15,000,000.0
Company and Overland Pharmaceuticals Inc.
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Ownership percentage	51.00%
License and Collaboration Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Percentage of development cost the company responsible for			60.00%
Joint Venture \| Company and Overland Pharmaceuticals Inc.
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payments	$ 40,000,000.0
Upfront and quarterly cash payments	117,000,000.0
Joint venture capital support payments	40,000,000
Joint Venture \| Company and Overland Pharmaceuticals Inc. \| Deferred Revenue
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration agreement, upfront payment			$ 40,000,000.0
Joint Venture \| Company and Overland Pharmaceuticals Inc. \| Deferred Revenue, Current
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration agreement, upfront payment			$ 39,000,000.0
Maximum \| Joint Venture \| Company and Overland Pharmaceuticals Inc.
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payments	$ 40,000,000.0
Pfizer
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Royalty obligation period from date of first sale			12 years
Pfizer \| Asset Contribution Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payments			$ 0	0	0
Pfizer \| Asset Contribution Agreement \| United States
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payments			30,000,000.0
Pfizer \| Asset Contribution Agreement \| European Union
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payments			60,000,000.0
Pfizer \| Asset Contribution Agreement \| North America, Europe, Asia, Australia and Oceania
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate potential milestone payments per target			325,000,000.0
Pfizer \| Asset Contribution Agreement \| Maximum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payments			840,000,000.0
Cellectis \| Research Collaboration and License Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Maximum payments required per product against selected target			185,000,000.0
Cellectis \| Regulatory and Sales Milestone \| Maximum \| Research Collaboration and License Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate potential milestone payable			2,800,000,000
Cellectis \| Pre-Clinical Development Milestone \| Research Collaboration and License Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development				5,000,000.0
Servier \| License and Collaboration Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development			$ 8,500,000	7,300,000	$ 4,200,000
Percentage of development cost the company responsible for			40.00%
Other current assets			$ 3,800,000
Accrued and other current liabilities				2,200,000
Servier \| Regulatory Milestone \| License and Collaboration Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate potential milestone payable			42,000,000
Servier \| Regulatory Milestone \| Maximum \| License and Collaboration Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate potential milestone payments per target			137,500,000
Servier \| Sales Milestone \| License and Collaboration Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate potential milestone payable			86,600,000			€ 70.5
Servier \| Sales Milestone \| Maximum \| License and Collaboration Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate potential milestone payments per target			78,000,000.0
Notch Therapeutics, Inc. \| Research and development
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration costs			3,200,000	100,000
Notch Therapeutics, Inc. \| Research Collaboration and License Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate potential milestone payable			7,250,000
Notch Therapeutics, Inc. \| License and Collaboration Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development				10,000,000
Collaboration agreement, upfront payment							$ 10,000,000.0
Notch Therapeutics, Inc. \| Pre-Clinical Development Milestone \| Maximum \| License and Collaboration Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate potential milestone payments per target			4,000,000.0
Notch Therapeutics, Inc. \| Clinical, Regulatory, and Commercial Milestone \| Maximum \| License and Collaboration Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate potential milestone payments per target			283,000,000.0
Notch Therapeutics, Inc.
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Equity method investment			$ 3,700,000	$ 4,900,000			$ 5,000,000.0
Ownership percentage			25.00%			25.00%	25.00%
Allogene
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Equity method investment			$ 0
Ownership percentage	49.00%

Commitments and Contingencies - Additional Information (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 28, 2019 ft² option	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jul. 31, 2020	Oct. 31, 2018 USD ($) ft²	Aug. 31, 2018 USD ($) ft²
Operating Leased Assets [Line Items]
Allowance for tenant improvements		$ 1,557
Tenant improvement allowances received		2,809	$ 4,473	$ 0
Cash paid for amounts included in measurement of lease liabilities		$ 6,200
Weighted average discount rate (as a percent)		8.37%
Remaining lease term		10 years 3 months 10 days
Rent expense for short-term leases		$ 200	2,400	$ 2,600
Asset retirement obligation		500	400
Operating lease liability		53,783	53,028
Letter of credit		5,200	$ 4,300
Non-cancellable purchase commitments		5,400
Onyx Development Group LLC
Operating Leased Assets [Line Items]
Agreement term					20 years
Termination payment		4,300
Onyx Development Group LLC \| Letter of Credit
Operating Leased Assets [Line Items]
Letter of credit		4,300
Newark
Operating Leased Assets [Line Items]
Area of lease (in sq ft) \| ft²	118,000
Operating lease term						188 months
Operating lease, extended term	10 years
Allowance for tenant improvements		2,900
Operating lease, options to extend term \| option	2
Tenant improvement allowances received		$ 1,600
127 Months Lease Term
Operating Leased Assets [Line Items]
Area of lease (in sq ft) \| ft²							68,000
Operating lease term							127 months
Operating lease, extended term							7 years
Allowance for tenant improvements							$ 5,000
124 Months Lease Term
Operating Leased Assets [Line Items]
Area of lease (in sq ft) \| ft²						14,943
Operating lease term						124 months
Operating lease, extended term						7 years
Allowance for tenant improvements						$ 800

Commitments and Contingencies - Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Current portion included in accrued and other current liabilities	$ 2,974	$ 1,679
Long-term portion of lease liabilities	50,809	51,349
Total operating lease liabilities	$ 53,783	$ 53,028
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	allo:AccruedAndOtherLiabilitiesCurrent	allo:AccruedAndOtherLiabilitiesCurrent

Commitments and Contingencies - Lease Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Operating lease cost	$ 7,390	$ 5,945	$ 1,863
Variable lease cost	1,382	1,087	32
Total lease costs	$ 8,771	$ 7,033	$ 1,895

Commitments and Contingencies - Summary of Undiscounted Future Non-Cancellable Lease Payments Under Operating Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
2021	$ 6,485
2022	7,917
2023	8,168
2024	8,430
2025 and thereafter	56,654
Total undiscounted lease payments	87,653
Less: Present value adjustment	(32,313)
Less: Tenant improvement allowance	(1,557)
Total	$ 53,783	$ 53,028

Equity Method Investment (Details) - USD ($)	12 Months Ended
Equity Method Investment (Details) - USD ($)	Dec. 31, 2020	Dec. 14, 2020	Dec. 31, 2019	Nov. 01, 2019
Schedule of Equity Method Investments [Line Items]
Equity method investment	$ 3,738,000		$ 4,892,000
Notch Therapeutics, Inc.
Schedule of Equity Method Investments [Line Items]
Payments to acquire interest in Notch	5,100,000
Transaction costs	$ 100,000
Ownership percentage	25.00%			25.00%
Equity method investment	$ 3,700,000		$ 4,900,000	$ 5,000,000.0
Allogene
Schedule of Equity Method Investments [Line Items]
Ownership percentage		49.00%
Equity method investment	$ 0

Convertible Notes Payable (2018 Notes) (Details) - USD ($)	1 Months Ended		12 Months Ended
	Oct. 31, 2018	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Aggregate principal amount		$ 120,200,000
Proceeds from issuance of convertible notes, net of issuance costs		116,800,000	$ 0	$ 0	$ 116,842,000
Fair value of notes	$ 141,400,000	$ 120,200,000
Debt conversion settlement price as a percentage of IPO price per share	85.00%
Change in fair value of convertible notes payable			0	$ 21,200,000
Debt issuance of cost			$ 3,400,000
IPO
Short-term Debt [Line Items]
Number of 2018 Notes converted into common stock (in shares)	7,856,176

Convertible Preferred Stock and Stockholders' Deficit (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Apr. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	Oct. 31, 2018	Oct. 10, 2018	Aug. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock price (in dollars per share)					$ 47.00
Proceeds from issuance of convertible preferred stock, net of issuance costs		$ 0	$ 0	$ 299,281
Aggregate purchase price, shares value	$ 300,000
Subscriptions receivable								$ 150,000
Preferred stock, shares authorized (in shares)		10,000,000	10,000,000
Preferred stock, shares issued (in shares)		0	0
Preferred stock, shares outstanding (in shares)		0	0
Common stock, shares authorized (in shares)		200,000,000	200,000,000
Common stock, shares issued (in shares)		140,474,305	124,267,358
Common stock, shares outstanding (in shares)		140,474,305	124,267,358
Modified shares of common stock (in shares)		26,249,993
Compensation cost resulting from the modification		$ 59,500
Vesting term		4 years
Dividends declared on common stock (in dollars per share)		$ 0	$ 0
IPO
Class of Stock [Line Items]
Common stock price (in dollars per share)						$ 18.00
Preferred stock, shares outstanding (in shares)						0
Common Stock
Class of Stock [Line Items]
Common stock, shares outstanding (in shares)		140,474,305	124,267,358	121,482,671					26,249,993
Common Stock \| IPO
Class of Stock [Line Items]
Number of convertible preferred stock converted to shares of common stock (in shares)						61,655,922	61,655,922
Series A1 Convertible Preferred Shares
Class of Stock [Line Items]
Convertible preferred stock, shares issued (in shares)	3,187,772
Convertible preferred stock, shares issued (in shares)	998,225
Common stock price (in dollars per share)	$ 35.06
Proceeds from issuance of convertible preferred stock, net of issuance costs	$ 34,900
Series A Convertible Preferred Shares
Class of Stock [Line Items]
Convertible preferred stock, shares issued (in shares)	7,557,990
Common stock price (in dollars per share)	$ 35.06
Proceeds from issuance of convertible preferred stock, net of issuance costs	$ 264,400

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Apr. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares as percentage of common shares outstanding		5.00%
Vesting term		4 years
Share-based compensation expense		$ 65,261	$ 46,063	$ 18,566
Accrued and other liabilities, related to shares held by employees and directors that were subject to repurchase		$ 2,800	$ 2,800
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted period		10 years
2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance (in shares)		12,308,848	9,642,503
Issuance of common stock for exercise of stock options (in shares)		1,260,275
2018 Plan \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Combined voting power by individual		10.00%
2018 Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option exercise price as percentage of fair value of common stock on grate date		100.00%
Option exercise price as percentage of fair value of common stock on grate date		110.00%
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated weighted average grant date fair value of employee options granted (in dollars per share)		$ 13.79	$ 18.42
Unrecognized stock based compensation		$ 81,100	$ 74,700
Weighted-average period recognized		2 years 222 days	3 years 15 days
Period of recognized compensation cost		2 years 222 days	3 years 15 days
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting term		4 years
Unrecognized stock based compensation		$ 51,100	$ 43,000
Weighted-average period recognized		2 years 10 months 2 days
Share-based compensation expense		$ 17,200	$ 8,800
Restricted stock units, granted (in shares)		1,269,499
Period of recognized compensation cost		2 years 10 months 2 days
Restricted stock units, weighted average grant date fair value, grants (in dollars per share)		$ 24.40
Restricted Stock Units \| Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units, granted (in shares)		0	57,361
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense		$ 2,500	$ 1,600
Initially reserved common stock for employee purchase (in shares)	1,160,000	1,242,673	1,214,826
Current offering period	24 months
Purchase of common stock through payroll deductions to equal price of lower fair market value	85.00%
Percentage of eligible compensation contribution by employee	15.00%
2018 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense		$ 31,800	$ 21,900
Founders Stock Award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock based compensation		$ 17,100	$ 30,900
Weighted-average period recognized		1 year 3 months	2 years 3 months
Share-based compensation expense		$ 13,700	$ 13,700
Number of shares unvested (in shares)		7,572,119	13,629,803
Number of vested shares (in shares)		6,057,684	6,057,684
Period of recognized compensation cost		1 year 3 months	2 years 3 months
Restricted stock units, weighted average grant date fair value, grants (in dollars per share)		$ 2.27
Founders Stock Award \| Founders
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares unvested (in shares)					24,230,750
Early Exercised Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock for exercise of stock options (in shares)		0	0
Other long term liabilities, related to shares held by employees and directors that were subject to repurchase		$ 1,100	$ 3,900
Equity Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting term		4 years

Stock-Based Compensation - Summary of Stock Option Activity Under Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value, vested and expected to vest	$ 93,149
2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options, beginning balance (in shares)	9,190,522
Number of options, options granted	3,252,687
Number of options, options exercised (in shares)	(1,260,275)
Number of options, options forfeited (in shares)	(748,900)
Number of options, ending balance (in shares)	10,434,034	9,190,522
Number of options, exercisable (in shares)	6,473,752
Number of options, vested and expected to vest (in shares)	10,434,034
Weighted-average exercise price, beginning balance (in dollars per share)	$ 14.51
Weighted-average exercise price, options granted (in dollars per share)	21.86
Weighted-average exercise price, options exercised (in dollars per share)	7.05
Weighted-average exercise price, options forfeited (in dollars per share)	13.99
Weighted-average exercise price, ending balance (in dollars per share)	17.73	$ 14.51
Weighted-average exercise price, exercisable (in dollars per share)	15.77
Weighted-average exercise price, vested and expected to vest (in dollars per share)	$ 17.73
Weighted-average remaining contract term, vested and expected to vest	8 years 3 months 14 days	8 years 9 months 25 days
Weighted-average remaining contract term, exercisable	8 years 2 months 1 day
Weighted-average remaining contract term	8 years 3 months 14 days
Aggregate intrinsic value, balance	$ 93,149	$ 110,490
Aggregate intrinsic value, exercised	36,264
Aggregate intrinsic value, exercisable	$ 65,818

Stock-Based Compensation - Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions (Details) - 2018 Equity Incentive Plan - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	71.42%	74.14%
Expected volatility, maximum	72.14%	74.92%
Expected risk-free interest rate, minimum	0.31%	1.54%
Expected risk-free interest rate, maximum	1.65%	2.62%
Expected dividend	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of common stock	$ 18.22	$ 25.94
Expected term in years	5 years 3 months 21 days	5 years 3 months 7 days
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of common stock	$ 48.94	$ 31.99
Expected term in years	6 years 1 month 2 days	6 years 29 days

Stock-Based Compensation - Summary of Restricted Stock Activity (Details) - Restricted stock units subject to vesting - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units, unvested, beginning balance (in shares)	1,941,155
Restricted stock units, granted (in shares)	1,269,499
Restricted stock units, vested (in shares)	(490,470)
Restricted stock units, forfeited (in shares)	(226,264)
Restricted stock units, unvested, ending balance (in shares)	2,493,920	1,941,155
Restricted stock units, vested and expected to vest (in shares)	2,493,920
Restricted stock units, weighted average grant date fair value, beginning balance (in dollars per share)	$ 27.45
Restricted stock units, weighted average grant date fair value, grants (in dollars per share)	24.40
Restricted stock units, weighted average grant date fair value, vested (in dollars per share)	27.41
Restricted stock units, weighted average grant date fair value, forfeited (in dollars per share)	24.87
Restricted stock units, weighted average grant date fair value, ending balance (in dollars per share)	26.14	$ 27.45
Restricted stock units, weighted average grant date fair value, vested and expected to vest (in dollars per share)	$ 26.14
Restricted stock units, unvested, weighted average remaining vesting life	1 year 7 months 28 days	1 year 11 months 23 days
Restricted stock units, granted, weighted average remaining vesting life	1 year 8 months 4 days
Restricted stock units, vested and expected to vest, weighted average remaining vesting life	1 year 7 months 28 days
Restricted stock units, aggregate intrinsic value, beginning balance	$ 50,431
Restricted stock units, aggregate intrinsic value, ending balance	62,947	$ 50,431
Restricted stock units, aggregate intrinsic value, vested and expected to vest	$ 62,947

Stock-Based Compensation - Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions (Details) - Employee Stock Purchase Plan	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	63.88%	60.40%
Expected volatility, maximum	72.75%	76.00%
Expected risk-free interest rate, minimum	0.12%	1.72%
Expected risk-free interest rate, maximum	0.36%	2.49%
Expected dividend	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term in years	6 months	6 months
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term in years	2 years	2 years

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 65,261	$ 46,063	$ 18,566
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	31,309	19,429	1,657
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 33,952	$ 26,634	$ 16,909

Related Party Transactions (Details)	1 Months Ended	12 Months Ended
Related Party Transactions (Details)	Aug. 31, 2018 USD ($)	Dec. 31, 2020 USD ($) director shares	Dec. 31, 2019 USD ($) director shares	Dec. 31, 2018 USD ($) ft²	Dec. 14, 2020	Sep. 30, 2019 ft²	Feb. 28, 2019 ft²
Related Party Transaction [Line Items]
Common stock, shares outstanding (in shares) \| shares		140,474,305	124,267,358
Operating lease right-of-use asset		$ 41,295,000	$ 44,495,000
Company and Overland Pharmaceuticals Inc.
Related Party Transaction [Line Items]
Ownership percentage					51.00%
Allogene
Related Party Transaction [Line Items]
Ownership percentage					49.00%
Two River Consulting LLC
Related Party Transaction [Line Items]
Related party costs		$ 400,000	$ 600,000	$ 600,000
Pfizer
Related Party Transaction [Line Items]
Common stock, shares outstanding (in shares) \| shares		22,032,040	22,032,040
Number of members appointed to board of directors \| director		1	1
Payable to related party, current		$ 0	$ 100,000
Pfizer \| Transition services agreement
Related Party Transaction [Line Items]
Related party costs		0	4,500,000	10,100,000
Pfizer \| Research and development \| Transition services agreement \| Lab Supplies
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions with related party		0	1,400,000	$ 10,400,000
Bellco
Related Party Transaction [Line Items]
Due to related party		300,000	300,000
Bellco \| Los Angeles California
Related Party Transaction [Line Items]
Area of lease (in sq ft) \| ft²				1,293
Operating lease term				3 years
Operating lease right-of-use asset		100,000	100,000
Bellco \| Consulting agreements
Related Party Transaction [Line Items]
Related party costs		900,000	800,000	$ 500,000
Bellco \| Consulting agreements \| Maximum
Related Party Transaction [Line Items]
Related party transaction compensation percentage	60.00%
Bellco \| Payments Commencing January 2019 \| Consulting agreements
Related Party Transaction [Line Items]
Related party transaction monthly payment in arrears	$ 33,333
Bellco \| Payments Commencing January2020 \| Consulting agreements
Related Party Transaction [Line Items]
Related party transaction monthly payment in arrears	$ 37,000
ByHeart
Related Party Transaction [Line Items]
Sublease Income		$ 300,000	$ 300,000
ByHeart \| New York
Related Party Transaction [Line Items]
Area of lease (in sq ft) \| ft²						2,907	2,180

401(k) Plan (Details) - USD ($) $ in Millions	12 Months Ended
401(k) Plan (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Contribution expenses	$ 1.4	$ 0.9	$ 0.4

- Definition

Amount of contribution received by defined benefit plan from employer which increases plan assets.

+ References + Details

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Increase in valuation allowance	$ 72,500,000	$ 50,000,000.0	$ 41,900,000
Tax benefit		300,000	100,000
Accrued interest and penalties	$ 0	$ 0	$ 0

- Definition

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

+ References

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+ Details

Income Taxes - Summary of Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current:
Federal	$ 0	$ 0	$ 0
State	0	1	2
Current federal, state and local, tax expense (benefit)	0	1	2
Deferred:
Federal	0	(251)	(89)
State	0	(81)	(30)
Deferred federal, state and local, tax expense (benefit)	0	(332)	(119)
Benefit for income taxes	$ 0	$ (331)	$ (117)

- Definition

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

+ References + Details

Income Taxes - Schedule of Income Tax Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Tax benefit at federal statutory rate	$ (52,546)	$ (38,834)	$ (44,441)
State taxes, net of federal benefit	(18,656)	(12,951)	(10,652)
Stock-based compensation	997	2,037	3,629
Research tax credits	(2,319)	(1,714)	(708)
Write-off of in-process R&D	0	0	5,247
Change in fair value of convertible notes	0	0	4,454
Change in valuation allowance	72,538	49,989	41,916
Other	(14)	1,142	438
Benefit for income taxes	$ 0	$ (331)	$ (117)

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 115,199	$ 54,018	$ 16,437
Tax credit carryforwards	8,297	4,239	1,239
Intangibles	20,582	22,770	23,086
Accrued expenses	3,888	2,375	952
Lease liabilities	15,050	14,839	9,730
Stock based compensation	12,970	6,870	360
Investments	175	0	0
Other	12	0	0
Total deferred tax assets	176,173	105,111	51,804
Deferred tax liabilities:
Fixed assets	(172)	(361)	(531)
Right of use leased assets	(11,556)	(12,453)	(9,239)
Investments	0	(393)	(118)
Other	0	0	0
Total deferred tax liabilities	(11,728)	(13,207)	(9,888)
Net deferred tax assets	164,445	91,904	41,916
Valuation allowance	(164,445)	(91,904)	(41,916)
Net deferred tax assets	$ 0	$ 0	$ 0

Income Taxes - Summary of Operating Loss Carryforwards and Tax Credits (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Federal \| Indefinite
Operating Loss Carryforwards [Line Items]
Net operating losses carryforwards	$ 413,920
Federal \| 2037
Operating Loss Carryforwards [Line Items]
Net operating losses carryforwards	2
Federal \| 2037-2039
Operating Loss Carryforwards [Line Items]
Tax credits	7,902
State \| Indefinite
Operating Loss Carryforwards [Line Items]
Tax credits	7,502
State \| 2037-2039
Operating Loss Carryforwards [Line Items]
Net operating losses carryforwards	$ 404,881

Income Taxes - Schedule of Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Balance at beginning of the year	$ 3,148	$ 920	$ 0
Additions based on tax positions related to current year	3,013	2,228	920
Additions to tax position of prior year	0	0	0
Reductions to tax position of prior years	0	0	0
Lapse of the applicable statute of limitations	0	0	0
Balance at end of the year	$ 6,161	$ 3,148	$ 920

Net Loss and Net Loss Per Share - Schedule of Earnings Per Share Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended			37 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
Numerator:
Net loss	$ (250,221)	$ (184,594)	$ (211,505)	$ (646,300)
Denominator:
Weighted average common shares outstanding (in shares)	120,370,177	101,061,149	28,948,386
Net loss per share, basic and diluted (in dollars per share)	$ (2.08)	$ (1.83)	$ (7.31)

- Definition

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

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+ Details

Net Loss and Net Loss Per Share - Schedule of Anti-dilutive Shares (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted net loss per share (in shares)	22,549,960	27,948,931	32,087,884
Stock options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted net loss per share (in shares)	10,434,034	9,190,522	7,235,545
Restricted stock units subject to vesting
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted net loss per share (in shares)	2,493,920	1,941,155	0
Expected shares purchased under Employee Stock Purchase Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted net loss per share (in shares)	312,750	195,161	144,272
Founder shares subject to future vesting
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted net loss per share (in shares)	7,572,119	13,629,803	19,687,487
Early exercised stock options subject to future vesting
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted net loss per share (in shares)	1,737,137	2,992,290	5,020,580

Subsequent Events (Details) - Notch Therapeutics, Inc. - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Feb. 25, 2021	Dec. 31, 2020	Nov. 01, 2019
Subsequent Event [Line Items]
Payments to acquire interest in Notch		$ 5.1
Ownership percentage		25.00%	25.00%
Subsequent Event
Subsequent Event [Line Items]
Payments to acquire interest in Notch	$ 15.9
Ownership percentage	17.00%