Allogene Therapeutics (ALLO) 10-Q 7 May 19 2019 Q1 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2019	May 03, 2019
Document And Entity Information [Abstract]
Entity Registrant Name	Allogene Therapeutics, Inc.
Document Type	10-Q
Trading Symbol	ALLO
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding		121,539,320
Amendment Flag	false
Entity Central Index Key	0001737287
Entity Filer Category	Non-accelerated Filer
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Entity Emerging Growth Company	true
Entity Small Business	false
Entity Ex Transition Period	false

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	[1]
Current assets:
Cash and cash equivalents	$ 92,748	$ 92,432
Short-term investments	373,392	366,952
Prepaid expenses and other current assets	10,487	8,598
Total current assets	476,627	467,982
Long-term investments	214,588	261,966
Operating lease right-of-use asset	32,394	33,015
Property and equipment, net	20,426	8,595
Intangible assets, net	603	754
Restricted cash	4,299	1,299
Other long-term assets	432	244
Total assets	749,369	773,855
Current liabilities:
Accounts payable	12,976	12,338
Accrued and other current liabilities	14,289	17,121
Total current liabilities	27,265	29,459
Lease liability, noncurrent	34,811	34,456
Other long-term liabilities	6,065	6,776
Total liabilities	68,141	70,691
Commitments and Contingencies (Notes 6 and 7)
Stockholders’ equity:
Preferred stock, $0.001 par value: 10,000,000 shares authorized as of March 31, 2019 and December 31, 2018; no shares were issued and outstanding as of March 31, 2019 and December 31, 2018
Common stock, $0.001 par value: 200,000,000 shares authorized as of March 31, 2019 and December 31, 2018; 121,527,320 and 121,482,671 shares issued and outstanding as of March 31, 2019 and December 31, 2018, respectively	121	121
Additional paid-in capital	922,816	914,265
Accumulated deficit	(243,114)	(211,528)
Accumulated other comprehensive income	1,405	306
Total stockholders’ equity	681,228	703,164
Total liabilities and stockholders’ equity	$ 749,369	$ 773,855
[1]	The balance sheet as of December 31, 2018 is derived from the audited financial statements as of that date.

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value per share	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	121,527,320	121,482,671
Common stock, shares outstanding	121,527,320	121,482,671

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating expenses:
Research and development	$ 23,403
General and administrative	13,058	$ 2,597
Total operating expenses	36,461	2,597
Loss from operations	(36,461)	(2,597)
Interest and other income, net	4,825
Loss before income taxes	(31,636)	(2,597)
Benefit from income taxes	50
Net Loss	(31,586)	(2,597)
Other comprehensive income:
Net unrealized gain on available-for-sale investments, net of tax	1,099
Net comprehensive loss	$ (30,487)	$ (2,597)
Net loss per share, basic and diluted	$ (0.32)	$ (0.10)
Weighted-average number of shares used in computing net loss per share, basic and diluted	97,315,890	26,249,993

Condensed Statement of Stockhol

Condensed Statement of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total		Common Stock	Notes Receivable from Common Stockholders	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income
Balance at Dec. 31, 2017	$ (2)		$ 26	$ (5)		$ (23)
Balance, Shares at Dec. 31, 2017			26,249,993
Proceeds received from common stockholders for issuance of founders' stock at inception	5			$ 5
Net loss	(2,597)					(2,597)
Balance at Mar. 31, 2018	(2,594)		$ 26			(2,620)
Balance, Shares at Mar. 31, 2018			26,249,993
Balance at Dec. 31, 2018	$ 703,164	[1]	$ 121		$ 914,265	(211,528)	$ 306
Balance, Shares at Dec. 31, 2018	121,482,671		121,482,671
Stock-based compensation	$ 7,867				7,867
Employee stock purchase plan	684				684
Employee stock purchase plan, Shares			44,649
Net loss	(31,586)					(31,586)
Net unrealized gain on available-for-sale investments	1,099						1,099
Balance at Mar. 31, 2019	$ 681,228		$ 121		$ 922,816	$ (243,114)	$ 1,405
Balance, Shares at Mar. 31, 2019	121,527,320		121,527,320
[1]	The balance sheet as of December 31, 2018 is derived from the audited financial statements as of that date.

Condensed Statement of Cash Flo

Condensed Statement of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (31,586)	$ (2,597)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Stock-based compensation	7,867	0
Amortization of other intangible assets acquired	151	0
Depreciation and amortization	544	0
Net amortization/accretion on investment securities	(1,223)	0
Non-cash rent expense	1,275	0
Deferred income taxes	(50)	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,892)	5
Other long-term assets	(188)	0
Accounts payable	(348)	0
Accrued and other current liabilities	(4,095)	2,597
Other long-term liabilities	(711)	0
Net cash (used in) provided by operating activities	(30,256)	5
Cash flows from investing activities:
Purchases of property and equipment	(10,423)	0
Proceeds from sales or maturities of investments	95,708	0
Purchase of investments	(52,397)	0
Net cash provided by investing activities	32,888	0
Cash flows from financing activities:
Proceeds from employee stock purchase plan	684	0
Net cash provided by financing activities	684	0
Net increase in cash, cash equivalents and restricted cash	3,316	5
Cash, cash equivalents and restricted cash — beginning of period	93,731	0
Cash, cash equivalents and restricted cash — end of period	97,047	5
Non-cash investing and financing activities:
Property and equipment purchase in accounts payable and accrued liabilities	5,134	0
Supplemental disclosure:
Cash paid for amounts included in the measurement of lease liabilities	$ 391	$ 0

Description of Business

Description of Business	3 Months Ended
	Mar. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Description of Business	1. Description of Business 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. Initial Public Offering 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 approximately $343.0 million in net proceeds, after deducting underwriting discounts and commissions of $26.1 million and offering expenses of approximately $3.2 million payable by the Company. At the closing of the IPO, all 11,743,987 shares of outstanding convertible preferred stock were automatically converted into 61,655,922 shares of common stock and our outstanding convertible promissory notes in $120.2 million principal amount 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. 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. The Company had cash and cash equivalents and investments of $680.7 million as of March 31, 2019. Since inception through March 31, 2019, the Company has incurred cumulative net losses of $243.1 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 when needed and 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 a period of at least one year from the date the accompanying unaudited condensed financial statements are filed with the Securities and Exchange Commission (SEC). 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 then-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 condensed financial statements have been retrospectively adjusted to reflect the effect of the Forward Stock Split for all periods presented.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP) for interim financial information and pursuant to Form 10-Q and Article 10 of Regulation S-X of the SEC. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the Company’s opinion, all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation of the results of operations and cash flows for the periods presented have been included. The condensed balance sheet as of March 31, 2019, the condensed statements of operations and comprehensive loss for the three months ended March 31, 2019 and 2018, the condensed statements of stockholders’ equity (deficit) as of March 31, 2019 and 2018, the condensed statements of cash flows for the three months ended March 31, 2019 and 2018, and the financial data and other financial information disclosed in the notes to the condensed financial statements are unaudited. The results of operations for the three months ended March 31, 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019, or for any other future annual or interim period. These condensed financial statements should be read in conjunction with the Company’s audited financial statements and related notes for the year ended December 31, 2018, included in the Company’s Annual Report on Form 10-K filed with the SEC on March 8, 2019. Use of Estimates The preparation of 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 financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying financial statements include but are not limited to the fair value of common stock, the fair value of stock options, the fair value of convertible notes payable, 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 dictate. Actual results could differ from those estimates. Significant Accounting Policies There have been no significant changes to the accounting policies during the three months ended March 31, 2019, as compared to the significant accounting policies described in Note 1 of the “Notes to Financial Statements” in the Company’s audited financial statements included in its Annual Report. Recently Adopted Accounting Pronouncements In February 2018, the FASB issued Accounting Standards Update No. 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income Recent Accounting Pronouncements Not Yet Adopted In August 2018, the FASB issued Accounting Standards Update No. 2018-15, Intangibles – Goodwill and other – Internal-Use Software (Subtopic 350-40)

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The Company measures and reports its cash equivalents, restricted cash, and investments at fair value. Money market funds are measured at fair value on a recurring basis using quoted prices and are classified as Level 1. I nvestments 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. There were no Level 3 assets or liabilities at March 31, 2019. Financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements by major security type as of March 31, 2019, are presented in the following tables: March 31, 2019 Level 1 Level 2 Level 3 Fair Value (in thousands) Financial Assets: Money market funds (1) $ 17,162 $ — $ — $ 17,162 Commercial paper — 4,952 — 4,952 Corporate bonds — 246,697 — 246,697 U.S. treasury securities 284,893 — — 284,893 U.S. agency securities — 55,238 — 55,238 Total financial assets $ 302,055 $ 306,887 $ — $ 608,942 December 31, 2018 Level 1 Level 2 Level 3 Fair Value (in thousands) Financial Assets: Money market funds (1) $ 61,023 $ — $ — $ 61,023 Commercial paper — 4,917 — 4,917 Corporate bonds — 244,076 — 244,076 U.S. treasury securities 342,001 — — 342,001 U.S. agency securities — 62,115 — 62,115 Total financial assets $ 403,024 $ 311,108 $ — $ 714,132 (1) Included within cash and cash equivalents on the Company’s balance sheets There were no transfers between Levels 1, 2 or 3 for the period presented.

Financial Instruments

Financial Instruments	3 Months Ended
	Mar. 31, 2019
Investments All Other Investments [Abstract]
Financial Instruments	4. Financial Instruments The fair value and amortized cost of cash equivalents and available-for-sale securities by major security type as of March 31, 2019 are presented in the following table: March 31, 2019 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Money market funds $ 17,162 $ — $ — $ 17,162 Commercial paper 4,952 — — 4,952 Corporate bonds 245,892 827 (22 ) 246,697 U.S. treasury securities 284,335 560 (2 ) 284,893 U.S. agency securities 55,029 209 — 55,238 Total cash equivalents and investments $ 607,370 $ 1,596 $ (24 ) $ 608,942 Classified as: Cash equivalents $ 20,962 Short-term investments 373,392 Long-term investments 214,588 Total cash equivalents and investments $ 608,942 December 31, 2018 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Money market funds $ 61,023 $ — $ — $ 61,023 Commercial paper 4,917 — — 4,917 Corporate bonds 244,136 220 (280 ) 244,076 U.S. treasury securities 341,696 342 (37 ) 342,001 U.S. agency securities 61,937 181 (3 ) 62,115 Total cash equivalents and investments $ 713,709 $ 743 $ (320 ) $ 714,132 Classified as: Cash equivalents $ 85,214 Short-term investments 366,952 Long-term investments 261,966 Total cash equivalents and investments $ 714,132 As of March 31, 2019, the remaining contractual maturities of available-for-sale securities were less than three years. There have been no significant realized losses on available-for-sale securities for the period presented. Based on the Company’s review of its available-for-sale securities, the Company believes it had no other-than-temporary impairments on these securities as of March 31, 2019, because the Company does not intend to sell these securities nor does the Company believe that it will be required to sell these securities before the recovery of their amortized cost basis. Gross realized gains and gross realized losses were immaterial for the three months ended March 31, 2019.

Balance Sheets Components

Balance Sheets Components	3 Months Ended
	Mar. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance Sheets Components	5 . Balance Sheets Components Prepaid expenses and Other Current Assets Prepaid expenses and Other Current Assets consist of the following: March 31, 2019 December 31, 2018 (In thousands) Prepaid research and development expenses $ 4,183 $ 2,356 Accrued interest on investments 3,391 3,108 Prepaid insurance 1,629 2,376 Other prepaid and current assets 1,284 758 Total prepaid expenses and other current assets $ 10,487 $ 8,598 Property and Equipment Property and Equipment consist of the following: March 31, 2019 December 31, 2018 (In thousands) Laboratory equipment $ 7,417 $ 5,534 Leasehold improvements 127 15 Computers equipment and purchased software 1,962 1,327 Furniture and fixtures 799 64 Construction in progress 11,713 2,703 Total 22,018 9,643 Less: accumulated depreciation (1,592 ) (1,048 ) Total property and equipment, net $ 20,426 $ 8,595 Accrued Liabilities Accrued liabilities consist of the following: March 31, 2019 December 31, 2018 (In thousands) Unvested shares liabilities $ 5,300 $ 4,590 Accrued research and development expenses 4,872 7,808 Accrued compensation and related benefits 2,719 4,111 Other 1,398 612 Total accrued and other current liabilities $ 14,289 $ 17,121

License Agreements

License Agreements	3 Months Ended
	Mar. 31, 2019
Research And Development [Abstract]
License Agreements	6 . License Agreements Asset Contribution Agreement with Pfizer 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 and intellectual property for the development and administration of chimeric antigen receptor (CAR) T cells for the treatment of cancer. 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. No such payments were made in the three-months ended March 31, 2019. 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 investigational new drug application ( Research Collaboration and License Agreement with Cellectis As part of the Pfizer Agreement, 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 our 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. The Company expects to pay Cellectis $5.0 million upon the dosing of the first patient in its Phase 1 clinical trial of ALLO-715. 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. License and Collaboration Agreement with Servier As part of the Pfizer Agreement, 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 products, including other anti-CD19 product candidates. 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 generally not required to make any additional payments to Servier to exercise an option, except for products directed at a certain target, for which the Company is required to pay Servier an option fee in the low tens of millions of dollars range upon exercise. 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 and ALLO-501, 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 on a target-by-target basis. For products directed against CD19, including UCART19, 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. The total potential payments that the Company is obligated to make under the Servier Agreement upon successful completion of regulatory and sales milestones are $381.5 million, including the CD19-related milestone payments described above. 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 ($79.1 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 three months ended March 31, 2019, the Company recorded $0.7 million As of March 31, 2019, amounts due to Servier of $2.2 million was recorded in the accounts payable and $1.0 million in accrued and other current liabilities in the accompanying condensed balance sheet

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Leases	7. 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. In connection with the lease, the Company has maintained a letter of credit for the benefit of the landlord in the amount of $1.0 million In connection with this lease, the Company recognized an operating lease right-of-use asset of $24.2 million as of March 31, 2019 and an aggregate lease liability of $26.7 million in the accompanying condensed balance sheet. The remaining lease term is 9 years and 11 months, and the estimated incremental borrowing rate is 8.0%. In October 2018, the Company entered into an operating lease agreement for new office and laboratory space which consists of approximately 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 the right to make 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 connection with the lease, the Company has maintained a letter of credit for the benefit of the landlord in the amount of $0.2 million. In connection with this lease, the Company recognized an operating lease right-of-use asset of $6.1 million as of March 31, 2019 and an aggregate lease liability of $6.3 million in the accompanying balance sheet. The remaining lease term is 9 years and 11 months, and the estimated incremental borrowing rate is 8.0%. In December 2018, the Company entered into two operating leases for office space in New York and Los Angeles for approximately 4,358 and 1,293 square feet respectively. The Company recognized operating lease right-of-use assets of $1.9 million and $0.2 million as of March 31, 2019 and aggregate lease liabilities of $1.9 million and $0.2 million respectively for these leases. The lease term for the New York operating lease is 6 years and 7 months, with no option for renewal. The lease term for the Los Angeles operating lease is 3 years with an option to extend the lease term for another two years which is not reasonably certain of exercise. There were no lease incentive allowances for either location. In connection with the New York lease, the Company maintains a letter of credit for the benefit of the landlord in the amount of $0.1 million. The remaining lease terms were 6 years and 3 months and 2 years and 8 months at March 31, 2019 and the estimated incremental borrowing rates applied were 8% and 7%, respectively. 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 has a term of 15 years and 8 months and is expected to commence in May 2020. Upon certain conditions, the Company has two ten-year options to extend the lease $2.9 million for costs related to the design and construction of certain Company improvements. In connection with the lease, the Company maintains a letter of credit for the benefit of the landlord in the amount of $3.0 million. The undiscounted future lease payments under the lease liabilities as of March 31, 2019 were as follows: Year ending December 31: (in thousands) 2019 (remaining 9 months) $ 3,168 2020 5,971 2021 7,792 2022 7,958 2023 8,213 2024 and thereafter 63,517 Total undiscounted lease payments 96,619 Less: Undiscounted lease payments related to Newark lease (36,231 ) Less: Present value adjustment (19,333 ) Less: Tenant improvement allowance (5,942 ) Total $ 35,113 Rent expense for all operating leases was $1.4 million for the three months ended March 31, 2019. Short-term lease expense was $1.0 million for the three months ended March 31, 2019. Variable lease payments for operating expenses was $0.3 million for the three months ended March 31, 2019. There was a total commitment of $0.7 million at March 31, 2019 related to short-term leases.

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	8 . Stock-Based Compensation In June 2018, the Company adopted the 2018 Equity Incentive Plan (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 October 2018, the Board of Directors approved an amendment and restatement of the 2018 Plan, increasing the shares of common stock issuable under the 2018 Plan as well as allowing for an automatic annual increase to the shares issuance under the 2018 Plan to the amount equal to 5% of the total number of shares of common stock outstanding on December 31 st 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. As of March 31, 2019, there were 12,546,247 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: Number of Options Weighted- Average Exercise Price Weighted- Average Remaining Contract Term (In years) Balance, December 31, 2018 7,235,545 $ 7.72 9.62 Options granted 1,834,111 27.29 9.94 Options exercised — — — Options forfeited (130,100 ) 4.60 9.28 Balance, March 31, 2019 8,939,556 $ 11.78 9.49 Exercisable, March 31, 2019 3,692,378 $ 10.02 9.48 Vested and expected to vest, March 31, 2019 8,939,556 $ 11.78 9.49 Restricted Stock Unit Activity The following summarizes restricted stock unit activity under the 2018 Plan: Restricted Stock Units Weighted- Average Fair Value at Date of Grant per Share Unvested at December 31, 2018 — — Granted 1,102,028 $ 27.29 Vested — — Forfeited — — Unvested at March 31, 2019 1,102,028 $ 27.29 Vested and expected to vest, March 31, 2019 1,102,028 $ 27.29 Total stock-based compensation related to stock options, restricted stock units, employee stock purchase plan and vesting of the founders’ common stock was as follows: Three Months Ended March 31, 2019 (In thousands) Research and development $ 2,732 General and administrative 5,135 Total stock-based compensation $ 7,867 Early Exercised Options The Company allows certain of its employees and its directors to exercise options granted under 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. As of March 31, 2019, there was $5.3 million recorded in accrued and other liabilities and $6.1 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 condensed financial statements since the exercise date.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2019
Related Party Transactions [Abstract]
Related Party Transactions	9 . Related Party Transactions As of March 31, 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. For the three months ended March 31, 2019, the costs incurred under the Pfizer TSA were $2.7 million. The Company also purchased certain lab supplies from Pfizer in connection with its research and development activities. For the three months ended March 31, 2019, the total lab supplies and services purchased from Pfizer was $0.6 million. As of March 31, 2019, the Company had an amount payable to Pfizer of $1.7 million, which was recorded in the accrued and other current liabilities on the accompanying condensed balance sheets. Sublease Agreement In February 2019, the Company subleased approximately 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. Two of the Company’s board members have beneficial ownership in ByHeart and one serves on the board of directors of ByHeart. Sublease income for the three months ended March 31, 2019 was $0.1 million and was recognized as other income. 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 was $0.2 million for the three months ended March 31, 2019. In August 2018, the Company entered into a consulting agreement with Bellco Capital LLC (Bellco). The Company’s executive chairman, Arie Belldegrun, M.D., FACS, is the Chairman and an owner of 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 pays Bellco $33,333.33 per month in arrears commencing January 2019 and, in the Company’s discretion, may 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 cost incurred for services provided and out-of-pocket expenses incurred under this consulting agreement were $0.2 million for the three months ended March 31, 2019.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	10. The Company has a history of losses, and expects to record a loss in 2019. The Company continues to maintain a full valuation allowance against its net deferred tax assets.

Net Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Net Loss Per Share	1 1 . Net Loss Per Share The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the period presented due to their anti-dilutive effect: Three Months Ended March 31, 2019 2018 Stock options to purchase common stock 8,939,556 — Restricted stock units subject to vesting 1,102,028 — Expected shares purchased under Employee Stock Purchase Plan 265,455 — Founder shares of common stock subject to future vesting 18,173,066 — Early exercised stock options subject to future vesting 5,020,580 — Total 33,500,685 —

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP) for interim financial information and pursuant to Form 10-Q and Article 10 of Regulation S-X of the SEC. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the Company’s opinion, all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation of the results of operations and cash flows for the periods presented have been included. The condensed balance sheet as of March 31, 2019, the condensed statements of operations and comprehensive loss for the three months ended March 31, 2019 and 2018, the condensed statements of stockholders’ equity (deficit) as of March 31, 2019 and 2018, the condensed statements of cash flows for the three months ended March 31, 2019 and 2018, and the financial data and other financial information disclosed in the notes to the condensed financial statements are unaudited. The results of operations for the three months ended March 31, 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019, or for any other future annual or interim period. These condensed financial statements should be read in conjunction with the Company’s audited financial statements and related notes for the year ended December 31, 2018, included in the Company’s Annual Report on Form 10-K filed with the SEC on March 8, 2019.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying financial statements include but are not limited to the fair value of common stock, the fair value of stock options, the fair value of convertible notes payable, 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 dictate. Actual results could differ from those estimates.
Significant Accounting Policies	Significant Accounting Policies There have been no significant changes to the accounting policies during the three months ended March 31, 2019, as compared to the significant accounting policies described in Note 1 of the “Notes to Financial Statements” in the Company’s audited financial statements included in its Annual Report.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In February 2018, the FASB issued Accounting Standards Update No. 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income
Recent Accounting Pronouncements Not Yet Adopted	Recent Accounting Pronouncements Not Yet Adopted In August 2018, the FASB issued Accounting Standards Update No. 2018-15, Intangibles – Goodwill and other – Internal-Use Software (Subtopic 350-40)

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Financial Assets And Liabilities Subject To Fair Value Measurements On Recurring Basis And Level Of Inputs Used In Such Measurements By Major Security Type	Financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements by major security type as of March 31, 2019, are presented in the following tables: March 31, 2019 Level 1 Level 2 Level 3 Fair Value (in thousands) Financial Assets: Money market funds (1) $ 17,162 $ — $ — $ 17,162 Commercial paper — 4,952 — 4,952 Corporate bonds — 246,697 — 246,697 U.S. treasury securities 284,893 — — 284,893 U.S. agency securities — 55,238 — 55,238 Total financial assets $ 302,055 $ 306,887 $ — $ 608,942 December 31, 2018 Level 1 Level 2 Level 3 Fair Value (in thousands) Financial Assets: Money market funds (1) $ 61,023 $ — $ — $ 61,023 Commercial paper — 4,917 — 4,917 Corporate bonds — 244,076 — 244,076 U.S. treasury securities 342,001 — — 342,001 U.S. agency securities — 62,115 — 62,115 Total financial assets $ 403,024 $ 311,108 $ — $ 714,132 (1) Included within cash and cash equivalents on the Company’s balance sheets

Financial Instruments (Tables)

Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2019
Investments All Other Investments [Abstract]
Summary of Cash Equivalents, Restricted Cash and Investments, Classified as Available-for-Sale Securities	The fair value and amortized cost of cash equivalents and available-for-sale securities by major security type as of March 31, 2019 are presented in the following table: March 31, 2019 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Money market funds $ 17,162 $ — $ — $ 17,162 Commercial paper 4,952 — — 4,952 Corporate bonds 245,892 827 (22 ) 246,697 U.S. treasury securities 284,335 560 (2 ) 284,893 U.S. agency securities 55,029 209 — 55,238 Total cash equivalents and investments $ 607,370 $ 1,596 $ (24 ) $ 608,942 Classified as: Cash equivalents $ 20,962 Short-term investments 373,392 Long-term investments 214,588 Total cash equivalents and investments $ 608,942 December 31, 2018 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Money market funds $ 61,023 $ — $ — $ 61,023 Commercial paper 4,917 — — 4,917 Corporate bonds 244,136 220 (280 ) 244,076 U.S. treasury securities 341,696 342 (37 ) 342,001 U.S. agency securities 61,937 181 (3 ) 62,115 Total cash equivalents and investments $ 713,709 $ 743 $ (320 ) $ 714,132 Classified as: Cash equivalents $ 85,214 Short-term investments 366,952 Long-term investments 261,966 Total cash equivalents and investments $ 714,132

Balance Sheets Components (Tabl

Balance Sheets Components (Tables)	3 Months Ended
	Mar. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Prepaid and Other Current Assets	Prepaid expenses and Other Current Assets Prepaid expenses and Other Current Assets consist of the following: March 31, 2019 December 31, 2018 (In thousands) Prepaid research and development expenses $ 4,183 $ 2,356 Accrued interest on investments 3,391 3,108 Prepaid insurance 1,629 2,376 Other prepaid and current assets 1,284 758 Total prepaid expenses and other current assets $ 10,487 $ 8,598
Schedule of Property and Equipment	Property and Equipment Property and Equipment consist of the following: March 31, 2019 December 31, 2018 (In thousands) Laboratory equipment $ 7,417 $ 5,534 Leasehold improvements 127 15 Computers equipment and purchased software 1,962 1,327 Furniture and fixtures 799 64 Construction in progress 11,713 2,703 Total 22,018 9,643 Less: accumulated depreciation (1,592 ) (1,048 ) Total property and equipment, net $ 20,426 $ 8,595
Schedule of Accrued Liabilities	Accrued Liabilities Accrued liabilities consist of the following: March 31, 2019 December 31, 2018 (In thousands) Unvested shares liabilities $ 5,300 $ 4,590 Accrued research and development expenses 4,872 7,808 Accrued compensation and related benefits 2,719 4,111 Other 1,398 612 Total accrued and other current liabilities $ 14,289 $ 17,121

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Summary of Undiscounted Future Lease Payments Under Lease Liability	The undiscounted future lease payments under the lease liabilities as of March 31, 2019 were as follows: Year ending December 31: (in thousands) 2019 (remaining 9 months) $ 3,168 2020 5,971 2021 7,792 2022 7,958 2023 8,213 2024 and thereafter 63,517 Total undiscounted lease payments 96,619 Less: Undiscounted lease payments related to Newark lease (36,231 ) Less: Present value adjustment (19,333 ) Less: Tenant improvement allowance (5,942 ) Total $ 35,113

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Option Activity Under Plan	The following summarizes option activity under the 2018 Plan: Number of Options Weighted- Average Exercise Price Weighted- Average Remaining Contract Term (In years) Balance, December 31, 2018 7,235,545 $ 7.72 9.62 Options granted 1,834,111 27.29 9.94 Options exercised — — — Options forfeited (130,100 ) 4.60 9.28 Balance, March 31, 2019 8,939,556 $ 11.78 9.49 Exercisable, March 31, 2019 3,692,378 $ 10.02 9.48 Vested and expected to vest, March 31, 2019 8,939,556 $ 11.78 9.49
Schedule of Restricted Stock Units Activity Under Plan	The following summarizes restricted stock unit activity under the 2018 Plan: Restricted Stock Units Weighted- Average Fair Value at Date of Grant per Share Unvested at December 31, 2018 — — Granted 1,102,028 $ 27.29 Vested — — Forfeited — — Unvested at March 31, 2019 1,102,028 $ 27.29 Vested and expected to vest, March 31, 2019 1,102,028 $ 27.29
Schedule of Stock-Based Compensation Expense	Total stock-based compensation related to stock options, restricted stock units, employee stock purchase plan and vesting of the founders’ common stock was as follows: Three Months Ended March 31, 2019 (In thousands) Research and development $ 2,732 General and administrative 5,135 Total stock-based compensation $ 7,867

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Schedule of Anti-dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share	The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the period presented due to their anti-dilutive effect: Three Months Ended March 31, 2019 2018 Stock options to purchase common stock 8,939,556 — Restricted stock units subject to vesting 1,102,028 — Expected shares purchased under Employee Stock Purchase Plan 265,455 — Founder shares of common stock subject to future vesting 18,173,066 — Early exercised stock options subject to future vesting 5,020,580 — Total 33,500,685 —

Description of Business - Addit

Description of Business - Additional Information (Details) $ / shares in Units, $ in Thousands	Oct. 10, 2018USD ($)$ / sharesshares	Oct. 01, 2018	Mar. 31, 2019USD ($)shares	Mar. 31, 2018USD ($)	Mar. 31, 2019USD ($)shares	Dec. 31, 2018shares
Subsidiary Sale Of Stock [Line Items]
Date of incorporation			Nov. 30, 2017
Net proceeds | $	$ 343,000
preferred stock, shares outstanding			0		0	0
Cash and cash equivalents and marketable securities | $			$ 680,700		$ 680,700
Net loss | $			$ (31,586)	$ (2,597)	$ (243,100)
Common stock, stock split description		1-for-5.25
Common stock forward split ratio		0.1905
IPO
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock, shares	20,700,000
Common stock price per share | $ / shares	$ 18
Underwriting discounts and commissions | $	$ 26,100
Offering costs | $	$ 3,200
Outstanding convertible preferred stock	11,743,987
preferred stock, shares outstanding	0
IPO | Convertible Promissory Notes [Member]
Subsidiary Sale Of Stock [Line Items]
Outstanding convertible promissory notes | $	$ 120,200
Over-Allotment Option
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock, shares	2,700,000
Common Stock | IPO
Subsidiary Sale Of Stock [Line Items]
Number of convertible preferred stock converted to shares of common stock	61,655,922
Number of 2018 Notes converted into common stock	7,856,176

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - Fair Value, Measurements, Recurring - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	$ 608,942,000	$ 714,132,000
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	0	$ 0
Financial Liabilities	$ 0

Fair Value Measurements - Finan

Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	$ 608,942,000	$ 714,132,000
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	17,162,000	61,023,000
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	4,952,000	4,917,000
Corporate Bond Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	246,697,000	244,076,000
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	284,893,000	342,001,000
U.S. Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	55,238,000	62,115,000
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	302,055,000	403,024,000
Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	17,162,000	61,023,000
Level 1 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	0	0
Level 1 | Corporate Bond Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	0	0
Level 1 | U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	284,893,000	342,001,000
Level 1 | U.S. Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	0	0
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	306,887,000	311,108,000
Level 2 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	0	0
Level 2 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	4,952,000	4,917,000
Level 2 | Corporate Bond Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	246,697,000	244,076,000
Level 2 | U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	0	0
Level 2 | U.S. Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	55,238,000	62,115,000
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	0	0
Level 3 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	0	0
Level 3 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	0	0
Level 3 | Corporate Bond Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	0	0
Level 3 | U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	0	0
Level 3 | U.S. Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	$ 0	$ 0

Financial Instruments - Summary

Financial Instruments - Summary of Cash Equivalents, Restricted Cash and Investments, Classified as Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 607,370	$ 713,709
Unrealized Gains	1,596	743
Unrealized Losses	(24)	(320)
Fair Value	608,942	714,132
Cash equivalents	20,962	85,214
Short-term investments	373,392	366,952
Long-term investments	214,588	261,966
Total cash equivalents and investments	608,942	714,132
Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	17,162	61,023
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	17,162	61,023
Corporate Bond Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	245,892	244,136
Unrealized Gains	827	220
Unrealized Losses	(22)	(280)
Fair Value	246,697	244,076
Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	4,952	4,917
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	4,952	4,917
U.S. Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	284,335	341,696
Unrealized Gains	560	342
Unrealized Losses	(2)	(37)
Fair Value	284,893	342,001
U.S. Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	55,029	61,937
Unrealized Gains	209	181
Unrealized Losses	0	(3)
Fair Value	$ 55,238	$ 62,115

Financial Instruments - Additio

Financial Instruments - Additional Information (Details)	Mar. 31, 2019
Investments Debt And Equity Securities [Abstract]
Maximum remaining contractual maturities of available-for-sale securities	3 years

Balance Sheets Components - Sch

Balance Sheets Components - Schedule of Prepaid and Other Current Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Prepaid research and development expenses	$ 4,183	$ 2,356
Accrued interest on investments	3,391	3,108
Prepaid insurance	1,629	2,376
Other prepaid and current assets	1,284	758
Total prepaid expenses and other current assets	$ 10,487	$ 8,598	[1]
[1]	The balance sheet as of December 31, 2018 is derived from the audited financial statements as of that date.

Balance Sheets Components - S_2

Balance Sheets Components - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property plant and equipment, gross	$ 22,018	$ 9,643
Less: accumulated depreciation	(1,592)	(1,048)
Total property and equipment, net	20,426	8,595	[1]
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property plant and equipment, gross	7,417	5,534
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property plant and equipment, gross	127	15
Computers Equipment and Purchased Software
Property Plant And Equipment [Line Items]
Property plant and equipment, gross	1,962	1,327
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property plant and equipment, gross	799	64
Construction in Progress
Property Plant And Equipment [Line Items]
Property plant and equipment, gross	$ 11,713	$ 2,703
[1]	The balance sheet as of December 31, 2018 is derived from the audited financial statements as of that date.

Balance Sheets Components - S_3

Balance Sheets Components - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Unvested shares liabilities	$ 5,300	$ 4,590
Accrued research and development expenses	4,872	7,808
Accrued compensation and related benefits	2,719	4,111
Other	1,398	612
Total accrued and other current liabilities	$ 14,289	$ 17,121	[1]
[1]	The balance sheet as of December 31, 2018 is derived from the audited financial statements as of that date.

License Agreements - Additional

License Agreements - Additional Information (Details) € in Millions	3 Months Ended
	Mar. 31, 2019USD ($)	Mar. 31, 2019EUR (€)	Dec. 31, 2018USD ($)	[1]
License Agreements [Line Items]
Research and development	$ 23,403,000
Accrued and other current liabilities	$ 14,289,000		$ 17,121,000
License and Collaboration Agreement
License Agreements [Line Items]
Percentage of development cost responsible for	60.00%
Pfizer | Asset Contribution Agreement | UNITED STATES
License Agreements [Line Items]
Aggregate potential milestone payments	$ 30,000,000
Pfizer | Asset Contribution Agreement | European Union
License Agreements [Line Items]
Aggregate potential milestone payments	60,000,000
Pfizer | Asset Contribution Agreement | European Union | Maximum
License Agreements [Line Items]
Aggregate potential regulatory and development milestones	840,000,000
Pfizer | Asset Contribution Agreement | North America, Europe, Asia, Australia and Oceania
License Agreements [Line Items]
Aggregate potential milestone payments	325,000,000
Cellectis | Research Collaboration and License Agreement
License Agreements [Line Items]
Maximum payments required per product against selected target	185,000,000
Accounts payable, related parties	5,000,000
Research and development	0
Accrued and other current liabilities	0
Cellectis | Maximum | Research Collaboration and License Agreement
License Agreements [Line Items]
Aggregate potential milestone payments	2,800,000,000
Servier | License and Collaboration Agreement
License Agreements [Line Items]
Research and development	700,000
Accrued and other current liabilities	$ 1,000,000
Percentage of development cost responsible for	40.00%
Accounts payable	$ 2,200,000
Servier | Regulatory Milestone | License and Collaboration Agreement
License Agreements [Line Items]
Aggregate potential milestone receivable	42,000,000
Servier | Regulatory Milestone | Maximum | License and Collaboration Agreement
License Agreements [Line Items]
Aggregate potential milestone payments	137,500,000
Servier | Sales Milestone | License and Collaboration Agreement
License Agreements [Line Items]
Aggregate potential milestone receivable	79,100,000	€ 70.5
Servier | Sales Milestone | Maximum | License and Collaboration Agreement
License Agreements [Line Items]
Aggregate potential milestone payments	78,000,000
Servier | Regulatory And Sales Milestone | License and Collaboration Agreement
License Agreements [Line Items]
Payments to milestone	$ 381,500,000
[1]	The balance sheet as of December 31, 2018 is derived from the audited financial statements as of that date.

Leases - Additional Information

Leases - Additional Information (Details)	1 Months Ended			3 Months Ended
	Feb. 28, 2019USD ($)ft²Renewal	Oct. 31, 2018USD ($)Sq.Ft	Aug. 31, 2018USD ($)Sq.Ft	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)Sq.FtOperatingLease
Operating Leased Assets [Line Items]
Area of office and laboratory | Sq.Ft		14,943	68,000
Operating lease term	15 years 8 months	124 months	127 months
Operating lease expiration period		Feb. 28, 2029	Feb. 28, 2029
Operating lease, option to extend term	10 years	7 years	7 years
Allowance for tenant improvements	$ 2,900,000	$ 800,000	$ 5,100,000	$ 5,942,000
Letter of credit	$ 3,000,000	$ 200,000	$ 1,000,000
Operating lease right-of-use asset				32,394,000	$ 33,015,000	[1]
Aggregate lease liability, noncurrent				34,811,000	$ 34,456,000	[1]
Number of operating Leases for office space | OperatingLease					2
Area of operating lease | ft²	118,000
Operating lease commencement date	May 31, 2020
Lease, Option to extend	Upon certain conditions, the Company has two ten-year options to extend the lease
Number of options to extend lease | Renewal	2
Payment of lease rental per month	$ 159,150
Lessee, Operating Lease, Variable Lease Payment, Terms and Conditions	Subject to rent abatement for the second through nine months of the lease, the Company will be required to pay $159,150 per month for rent for the first twelve months of the lease term which will increase at a rate of 3% per year.
Increase in rate for rent per year for lease term	3.00%
Rent expense				1,400,000
Short term lease expense				1,000,000
Variable Lease, Payment				300,000
Total commitment related to short-term leases				700,000
New York
Operating Leased Assets [Line Items]
Area of office and laboratory | Sq.Ft					4,358
Operating lease term					6 years 7 months
Allowance for tenant improvements					$ 0
Letter of credit					$ 100,000
Operating lease right-of-use asset				1,900,000
Aggregate lease liability, noncurrent				$ 1,900,000
Estimated incremental borrowing rate of lease				8.00%
Remaining Lease term				6 years 3 months
Los Angeles
Operating Leased Assets [Line Items]
Area of office and laboratory | Sq.Ft					1,293
Operating lease term					3 years
Operating lease, option to extend term					2 years
Allowance for tenant improvements					$ 0
Operating lease right-of-use asset				$ 200,000
Aggregate lease liability, noncurrent				$ 200,000
Estimated incremental borrowing rate of lease				7.00%
Remaining Lease term				2 years 8 months
Newark
Operating Leased Assets [Line Items]
Undiscounted lease payments				$ 36,231,000
127 Months Lease Term
Operating Leased Assets [Line Items]
Operating lease right-of-use asset				24,200,000
Aggregate lease liability, noncurrent				$ 26,700,000
Remaining Lease term				9 years 11 months
Estimated incremental borrowing rate of lease				8.00%
124 Months Lease Term
Operating Leased Assets [Line Items]
Operating lease right-of-use asset				$ 6,100,000
Aggregate lease liability, noncurrent				$ 6,300,000
Remaining Lease term				9 years 11 months
Estimated incremental borrowing rate of lease				8.00%
[1]	The balance sheet as of December 31, 2018 is derived from the audited financial statements as of that date.

Leases - Summary of Undiscounte

Leases - Summary of Undiscounted Future Lease Payments Under Lease Liability (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Feb. 28, 2019	Oct. 31, 2018	Aug. 31, 2018
2019 (remaining 9 months)	$ 3,168
2020	5,971
2021	7,792
2022	7,958
2023	8,213
2024 and thereafter	63,517
Total undiscounted lease payments	96,619
Less: Present value adjustment	(19,333)
Less: Tenant improvement allowance	(5,942)	$ (2,900)	$ (800)	$ (5,100)
Total	35,113
Newark
Less: Undiscounted lease payments related to Newark lease	$ (36,231)

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Accrued and other liabilities, related to shares held by employees and directors that were subject to repurchase	$ 5.3
Other long term liabilities, related to shares held by employees and directors that were subject to repurchase	$ 6.1
2018 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares as percentage of common shares outstanding	5.00%
Share-based compensation arrangement by share-based payment award, Description	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. 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. 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
Vesting term	4 years
Number of shares reserved for future issuance | shares	12,546,247
2018 Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option granted period	10 years
Option exercise price as percentage of fair value of common stock on grate date	100.00%

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity Under Plan (Details) - 2018 Plan - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Shares
Number of Options, Balance	7,235,545
Number of Options, Options granted	1,834,111
Number of Options, Options exercised	0
Number of Options, Options forfeited	(130,100)
Number of Options, Balance	8,939,556	7,235,545
Number of Options, Exercisable	3,692,378
Number of Options, Vested and expected to vest	8,939,556
Weighted-Average Exercise Price, Balance	$ 7.72
Weighted-Average Exercise Price, Options granted	27.29
Weighted-Average Exercise Price, Options exercised	0
Weighted-Average Exercise Price, Options forfeited	4.60
Weighted-Average Exercise Price, Balance	11.78	$ 7.72
Weighted-Average Exercise Price, Exercisable	10.02
Weighted-Average Exercise Price, Vested and expected to vest	$ 11.78
Weighted-Average Remaining Contract Term, Balance	9 years 5 months 27 days	9 years 7 months 13 days
Weighted-Average Remaining Contract Term, Option granted	9 years 11 months 8 days
Weighted-Average Remaining Contract Term, Option Forfeited	9 years 3 months 11 days
Weighted-Average Remaining Contract Term, Exercisable	9 years 5 months 23 days
Weighted-Average Remaining Contract Term, Vested and expected to vest	9 years 5 months 27 days

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Restricted Stock Units Activity Under Plan (Details) - Restricted Stock Unit - 2018 Plan	3 Months Ended
	Mar. 31, 2019$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of unvested, shares granted | shares	1,102,028
Number of unvested shares, Balance | shares	1,102,028
Number of unvested shares, Vested and expected to vest | shares	1,102,028
Weighted-Average Fair Value at Date of Grant per Share, granted | $ / shares	$ 27.29
Weighted-Average Fair Value at Date of Grant per Share, Balance | $ / shares	27.29
Weighted-Average Fair Value at Date of Grant per Share, Vested and expected to vest | $ / shares	$ 27.29

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 7,867
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	2,732
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 5,135

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details)	1 Months Ended	3 Months Ended
	Aug. 31, 2018USD ($)	Mar. 31, 2019USD ($)Sq.FtDirectorshares	Dec. 31, 2018shares
Related Party Transaction [Line Items]
Common stock, shares outstanding | shares		121,527,320	121,482,671
Pfizer
Related Party Transaction [Line Items]
Common stock, shares outstanding | shares		22,032,040
Number of members appointed to board of directors | Director		1
Pfizer | Accrued and Other Current Liabilities
Related Party Transaction [Line Items]
Payable to related party, current		$ 1,700,000
Pfizer | Transition Services Agreement
Related Party Transaction [Line Items]
Related party costs		2,700,000
Pfizer | Transition Services Agreement | Research and development
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions with related party		$ 600,000
ByHeart | Sublease Agreement [Member]
Related Party Transaction [Line Items]
Area of office space | Sq.Ft		2,180
Sublease income		$ 100,000
Two River | Consulting Agreements
Related Party Transaction [Line Items]
Related party costs		200,000
Bellco | Consulting Agreements
Related Party Transaction [Line Items]
Related party costs		$ 200,000
Related party transaction monthly payment in arrears	$ 33,333,330
Related party transaction agreement commencement date	Jan. 31, 2019
Bellco | Consulting Agreements | Maximum
Related Party Transaction [Line Items]
Related party transaction compensation percentage	60.00%

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Anti-dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted net loss per share	33,500,685	0
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	8,939,556	0
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	1,102,028	0
Founder Shares of Common Stock 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	18,173,066	0
Expected Shares Purchased Under Employee Stock Purchase Plans
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted net loss per share	265,455	0
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	5,020,580	0