Gritstone bio (GRTSQ) 10-Q 5 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 31, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Document Quarterly Report	true
Document Transition Report	false
Trading Symbol	GRTS
Entity Registrant Name	Gritstone Oncology, Inc.
Entity Central Index Key	0001656634
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		37,764,085
Entity Emerging Growth Company	true
Entity Small Business	true
Entity Ex Transition Period	true
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity File Number	001-38663
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-4859534
Entity Address, Address Line One	5959 Horton Street
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	Emeryville
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94608
City Area Code	510
Local Phone Number	871-6100
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Security Exchange Name	NASDAQ

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 57,648	$ 57,408
Marketable securities	12,897	70,368
Prepaid expenses and other current assets	3,202	3,497
Total current assets	73,747	131,273
Property and equipment, net	23,306	26,911
Operating lease right-of-use assets	22,706	23,427
Deposits and other long-term assets	2,749	2,778
Total assets	122,508	184,389
Current liabilities:
Accounts payable	3,284	4,621
Accrued compensation	4,911	4,598
Accrued liabilities	664	1,041
Accrued research and development expenses	2,557	1,779
Lease liabilities, current portion	5,069	2,505
Deferred revenue, current portion	5,528	4,956
Total current liabilities	22,013	19,500
Other non-current liabilities	634
Lease liabilities, net of current portion	20,791	20,985
Deferred revenue, net of current portion	7,086	9,560
Total liabilities	50,524	50,045
Commitments and contingencies (Notes 6 and 8)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $0.0001 par value; 300,000,000 shares authorized at September 30, 2020 and December 31, 2019; 37,763,266 and 36,332,956 shares issued and outstanding at September 30, 2020 and December 31, 2019	17	17
Additional paid-in capital	371,097	355,291
Accumulated other comprehensive gain	5	24
Accumulated deficit	(299,135)	(220,988)
Total stockholders’ equity	71,984	134,344
Total liabilities and stockholders’ equity	$ 122,508	$ 184,389

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
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	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	37,763,266	36,332,956
Common stock, shares outstanding	37,763,266	36,332,956

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Total revenues	$ 939	$ 984	$ 2,688	$ 3,481
Operating expenses:
Research and development	22,050	24,886	65,807	59,314
General and administrative	5,031	4,582	15,751	13,794
Total operating expenses	27,081	29,468	81,558	73,108
Loss from operations	(26,142)	(28,484)	(78,870)	(69,627)
Interest income, net	69	936	723	2,898
Net loss	(26,073)	(27,548)	(78,147)	(66,729)
Other comprehensive gain:
Unrealized (loss) gain on marketable securities, net of tax	(45)	(45)	(19)	116
Net and comprehensive loss	$ (26,118)	$ (27,593)	$ (78,166)	$ (66,613)
Net loss per share, basic and diluted	$ (0.69)	$ (0.77)	$ (2.10)	$ (2.04)
Weighted-average number of shares used in computing net loss per share, basic and diluted	37,750,145	35,690,600	37,268,318	32,762,176
Collaboration [Member]
Total revenues	$ 795	$ 984	$ 2,544	$ 3,481
Contribution [Member]
Total revenues	$ 144		$ 144

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Revision of Prior Period, Accounting Standards Update, Adjustment [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Gain/(Loss) [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member]Revision of Prior Period, Accounting Standards Update, Adjustment [Member]
Balance at Dec. 31, 2018	$ 149,122	$ (153)	$ 16	$ 275,593	$ (85)	$ (126,402)	$ (153)
Balance, shares at Dec. 31, 2018			28,823,130
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201602Member
Issuance of stock, net of issuance costs	$ 69,709		$ 1	69,708
Issuance of common stock under at the market ("ATM") equity offering program, net of issuance costs, shares			6,500,000
Unrealized (loss) gain on marketable securities, net of tax	116				116
Lapse of repurchase rights related to common stock issued pursuant to early exercises	51			51
Lapse of repurchase rights related to common stock issued pursuant to early exercises, shares			149,051
Issuance of common stock upon exercise of stock options	423			423
Issuance of common stock upon exercise of stock options, shares			261,900
Stock-based compensation	3,856			3,856
Net loss	(66,729)					(66,729)
Balance at Sep. 30, 2019	156,395		$ 17	349,631	31	(193,284)
Balance, shares at Sep. 30, 2019			35,734,081
Balance at Dec. 31, 2018	149,122	$ (153)	$ 16	275,593	(85)	(126,402)	$ (153)
Balance, shares at Dec. 31, 2018			28,823,130
Balance at Dec. 31, 2019	134,344		$ 17	355,291	24	(220,988)
Balance, shares at Dec. 31, 2019			36,332,956
Balance at Jun. 30, 2019	182,378		$ 17	348,021	76	(165,736)
Balance, shares at Jun. 30, 2019			35,654,631
Unrealized (loss) gain on marketable securities, net of tax	(45)				(45)
Lapse of repurchase rights related to common stock issued pursuant to early exercises	17			17
Lapse of repurchase rights related to common stock issued pursuant to early exercises, shares			48,174
Issuance of common stock upon exercise of stock options	61			61
Issuance of common stock upon exercise of stock options, shares			31,276
Stock-based compensation	1,532			1,532
Net loss	(27,548)					(27,548)
Balance at Sep. 30, 2019	156,395		$ 17	349,631	31	(193,284)
Balance, shares at Sep. 30, 2019			35,734,081
Balance at Dec. 31, 2019	134,344		$ 17	355,291	24	(220,988)
Balance, shares at Dec. 31, 2019			36,332,956
Issuance of stock, net of issuance costs	9,670			9,670
Issuance of common stock under at the market ("ATM") equity offering program, net of issuance costs, shares			1,160,963
Issuance of common stock under employees tock purchase plan (“ESPP”)	527			527
Issuance of common stock under employee stock purchase plan ("ESPP"), shares			96,234
Unrealized (loss) gain on marketable securities, net of tax	(19)				(19)
Lapse of repurchase rights related to common stock issued pursuant to early exercises	11			11
Lapse of repurchase rights related to common stock issued pursuant to early exercises, shares			30,874
Issuance of common stock upon exercise of stock options	$ 183			183
Issuance of common stock upon exercise of stock options, shares	142,239		142,239
Stock-based compensation	$ 5,415			5,415
Net loss	(78,147)					(78,147)
Balance at Sep. 30, 2020	71,984		$ 17	371,097	5	(299,135)
Balance, shares at Sep. 30, 2020			37,763,266
Balance at Jun. 30, 2020	96,228		$ 17	369,223	50	(273,062)
Balance, shares at Jun. 30, 2020			37,713,218
Unrealized (loss) gain on marketable securities, net of tax	(45)				(45)
Issuance of common stock upon exercise of stock options	37			37
Issuance of common stock upon exercise of stock options, shares			50,048
Stock-based compensation	1,837			1,837
Net loss	(26,073)					(26,073)
Balance at Sep. 30, 2020	$ 71,984		$ 17	$ 371,097	$ 5	$ (299,135)
Balance, shares at Sep. 30, 2020			37,763,266

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' Equity (Parenthetical) - Common Stock [Member] - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
ATM Equity Offering Program [Member]
Issuance costs	$ 104
Follow-on Public Offering [Member]
Issuance costs		$ 556
Shares issued price per share		$ 11.50

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities
Net loss	$ (78,147)	$ (66,729)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	4,951	3,303
Net amortization of premiums and discounts on marketable securities	(123)	(1,248)
Stock-based compensation	5,415	3,856
Non-cash operating lease expense	5,621	4,491
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	853	(1,785)
Operating lease right-of-use assets	0	(3,328)
Deposits and other long-term assets	29	(281)
Accounts payable	(200)	1,600
Accrued compensation	311	(226)
Accrued and other non-current liabilities	1,041	104
Accrued research and development expenses	778	2,989
Lease liability	(2,512)	(1,824)
Deferred revenue	(1,902)	(3,481)
Net cash used in operating activities	(63,885)	(62,559)
Investing activities
Purchase of marketable securities	(8,809)	(28,329)
Maturities of marketable securities	60,982	96,094
Sales of marketable securities	5,401	0
Purchase of property and equipment	(3,243)	(10,575)
Net cash provided by investing activities	54,331	57,190
Financing activities
Proceeds from issuance of common stock, net of issuance costs	10,473	70,684
Payments of deferred financing costs	(104)	(556)
Net cash provided by financing activities	10,369	70,128
Net increase in cash, cash equivalents and restricted cash	815	64,759
Cash, cash equivalents and restricted cash at beginning of period	58,400	53,175
Cash, cash equivalents and restricted cash at end of period	59,215	117,934
Supplemental disclosures of non-cash investing and financing information
Property and equipment purchases accrued but not yet paid	96	3,615
Remeasurement of operating lease right-of-use asset for lease modification	$ 3,174	$ 99

Organization

Organization	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization	1. Organization Description of Business Gritstone Oncology, Inc. (“Gritstone” or the “Company”) is an immuno-oncology company developing personalized cancer immunotherapies to fight multiple cancer types. The Company was incorporated in the state of Delaware on August 5, 2015, and is based in Emeryville, California and Cambridge, Massachusetts, with a manufacturing facility in Pleasanton, California. The Company operates in one segment.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying interim condensed consolidated financial statements are unaudited and are comprised of the consolidation of the Company and its wholly-owned subsidiary. All intercompany balances and transactions have been eliminated in consolidation. The Company has no unconsolidated subsidiaries or investments accounted for under the equity method. The accompanying condensed consolidated financial statements have been prepared in accordance with United States generally accepted accounting principles (“U.S. GAAP”) and the rules and regulations of Securities and Exchange Commission (“SEC”) for interim reporting. The condensed consolidated financial statements are unaudited and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, necessary for the fair presentation for interim reporting. The results of operations for any interim period are not necessarily indicative of results of operations for any future period. Certain information and footnote disclosures typically included in annual financial statements prepared in accordance with U.S. GAAP have been condensed or omitted. Accordingly, these unaudited interim condensed consolidated financial statements should be read in conjunction with the Company’s financial statements as of and for the year ended December 31, 2019, which are included in the Company’s Annual Report on Form 10-K, as filed with the SEC on March 11, 2020 . Need for Additional Capital The Company has incurred operating losses and has an accumulated deficit as a result of ongoing efforts to develop drug product candidates, including conducting preclinical and clinical trials and providing general and administrative support for these operations. The Company had cash, cash equivalents, and marketable securities of $70.5 million and $127.8 million as of September 30, 2020 and December 31, 2019, respectively. million and $221.0 million as of September 30, 2020 and December 31, 2019, respectively. The Company had net losses of $26.1 78.1 $27.5 million and $66.7 million for the three and nine months ended September 30, 2019, respectively, and of $63.9 million $62.6 property rights to its product candidates and sell unsecured assets, or a combination of the above, any of which may have a material adverse effect on the Company’s business, results of operations, financial condition and/or its ability to fund its scheduled obligations on a timely basis or at all. Failure to manage discretionary spending or raise additional capital , as needed, may adversely impact the Company’s ability to achieve its intended business objectives. Th e accompanying condensed consolidated financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the settlement of liabilities and commitments in the normal course of business. The condensed consolidated financial statements do not reflect any adjustments relating to the recoverability and classification of assets or the amounts and classification of liabilities that might be necessary if the Company is unable to continue as a going concern. Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and judgments that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities as of the date of the condensed consolidated financial statements and the reported amounts of revenue and expenses in the condensed consolidated financial statements and accompanying notes during the reporting period. On an ongoing basis, management evaluates its estimates, including those related to preclinical and clinical study trial accruals, fair value of assets and liabilities, the fair value of right-of-use assets (“ROU assets”) and lease liabilities, revenue recognition, and the fair value of stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates . Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist of cash, cash equivalents, and marketable securities. Cash, cash equivalents and marketable securities are invested through banks and other financial institutions in the United States. Such deposits may be in excess of federally insured limits. The Company maintains cash equivalents and marketable securities with various high-credit-quality and capitalized financial institutions. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. The Company’s investment policy limits investments to certain types of securities issued by the U.S. government, its agencies, and institutions with investment-grade credit ratings and places restrictions on maturities and concentration by type and issuer. The Company is exposed to credit risk in the event of a default by the financial institutions holding its cash, cash equivalents, and marketable securities and issuers of marketable securities to the extent recorded on the balance sheets. Through September 30, 2020, the Company has no off-balance sheet concentrations of credit risk. Other Risks and Uncertainties The Company is subject to a number of risks similar to those of other early-stage immuno-oncology companies, including dependence on key individuals; the need to develop commercially viable therapeutics; competition from other companies, many of which are larger and better capitalized; and the need to obtain adequate additional financing to fund the development of its product candidates. The Company currently depends on third-party suppliers for key materials and services used in its research and development manufacturing process, and is subject to certain risks related to the loss of these third-party suppliers or their inability to supply the Company with adequate materials and services. In March 2020, the World Health Organization declared the global novel coronavirus disease (“COVID-19”) outbreak a pandemic. To date, the Company’s business has not been materially impacted by the COVID-19 pandemic. However, the Company has experienced slowing of patient recruitment and sample collection in its ongoing clinical trials and cannot at this time predict the specific extent, duration, or full impact that the 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 outbreak and related governmental advisories and restrictions. These developments and the impact of COVID-19 on the financial markets and the overall economy are highly uncertain. If the financial markets and/or the overall economy are impacted for an extended period, the Company’s results may be adversely affected. Cash, Cash Equivalents, and Restricted Cash Cash equivalents, which consist primarily of highly liquid investments with original maturities of three months or less when purchased, are stated at cost which approximates fair value. These assets include investments in money market funds that invest in U.S. Treasury obligations and certificates of deposit which are stated at fair value. The Company has issued a letter of credit under a lease agreement which has been collateralized by a cash deposit for an equal amount and is recorded within deposits and other long-term assets on the condensed consolidated balance sheets based on the term of the underlying lease. Additionally, the Company has received cash proceeds from a philanthropic institution which is restricted and to be spent in accordance with the contribution agreement and is recorded as restricted cash within prepaid expenses and other current assets on the condensed consolidated balance sheet. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the balance sheets that sum to the total of the same amounts shown in the statements of cash flows (in thousands): September 30, December 31, 2020 2019 Cash and cash equivalents $ 57,648 $ 57,408 Restricted cash 1,567 992 Total cash, cash equivalents and restricted cash $ 59,215 $ 58,400 Leases The Company determines whether the arrangement is or contains a lease at the inception of the arrangement and if such a lease is classified as a financing lease or operating lease. All of the Company’s leases are classified as operating leases. Leases with a term greater than one year are included in operating lease ROU assets, lease liabilities, current portion, and in the Company’s condensed consolidated balance sheets at September 30, 2020 and December 31, 2019 In determining the net present value of lease payments, t The Company considers a lease term to be the noncancelable period that it has the right to use the underlying asset, including any periods where it is reasonably assured the Company will exercise the option to extend the contract. Periods covered by an option to extend are included in the lease term if the lessor controls the exercise of that option. The Company recognizes lease expense on a straight-line basis over the expected lease term. The Company has elected to not separate lease and non-lease components for its leased assets and accounts for all lease and non-lease components of its agreements as a single lease component. The lease components resulting in a ROU asset have been recorded on the condensed consolidated balance sheets and amortized as lease expense on a straight-line basis over the lease term. Revenue Recognition The Company analyzes its collaboration agreements to assess 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 that are considered to be in the scope of the collaboration guidance and that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of the collaboration guidance and those that are more reflective of a vendor-customer relationship and, therefore, within the scope of the revenue with contracts with customer guidance. For elements of collaboration arrangements that are accounted for pursuant to the revenue from contracts with customer guidance, an appropriate recognition method is determined and applied consistently, generally by analogy to the revenue from contracts with customers guidance. The terms of the licensing and collaboration agreements entered into typically include payment of one or more of the following: non-refundable, up-front fees; development, regulatory, and commercial milestone payments; payments for manufacturing supply services; and royalties on net sales of licensed products. Each of these payments results in license, collaboration, and other revenues, except for revenues from royalties on net sales of licensed products, which are classified as royalty revenues. The core principle of the accounting for revenue from contracts with customers guidance is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received in exchange for those goods or services. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue in the Company’s condensed consolidated balance sheets. If the related performance obligation is expected to be satisfied within the next twelve months this will be classified in current liabilities. Amounts recognized as revenue prior to receipt are recorded as contract assets in the Company’s condensed consolidated balance sheets. If the Company expects to have an unconditional right to receive consideration in the next twelve months, this will be classified in current assets. A net contract asset or liability is presented for each contract with a customer. At contract inception, the Company assesses the goods or services promised in a contract with a customer and identifies those distinct goods and services that represent a performance obligation. A promised good or service may not be identified as a performance obligation if it is immaterial in the context of the contract with the customer, if it is not separately identifiable from other promises in the contract (either because it is not capable of being separated or because it is not separable in the context of the contract), or if the performance obligation does not provide the customer with a material right. The Company considers the terms of the contract and its customary business practices to determine the transaction price. The transaction price is the amount of consideration to which the Company expects to be entitled in exchange for transferring promised goods or services to a customer. The consideration promised in a contract with a customer may include fixed amounts, variable amounts, or both. Variable consideration will only be included in the transaction price when it is not considered constrained, which is when it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur. If it is determined that multiple performance obligations exist, the transaction price is allocated at the inception of the agreement to all identified performance obligations based on the relative standalone selling prices. The relative selling price for each deliverable is estimated using objective evidence if it is available. If objective evidence is not available, the Company uses its best estimate of the selling price for the deliverable. Revenue is recognized when, or as, the Company satisfies a performance obligation by transferring a promised good or service to a customer. An asset is transferred when, or as, the customer obtains control of that asset, which for a service, is considered to be as the services are received and used. The Company recognizes revenue over time by measuring the progress toward complete satisfaction of the relevant performance obligation using an appropriate input or output method based on the nature of the good or service promised to the customer. After contract inception, the transaction price is reassessed at every period end and updated for changes such as resolution of uncertain events. Any change in the transaction price is allocated to the performance obligations on the same basis as at contract inception. Management may be required to exercise considerable judgment in estimating revenue to be recognized. Judgment is required in identifying performance obligations, estimating the transaction price, estimating the stand-alone selling prices of identified performance obligations, which may include forecasted revenue, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success, and estimating the progress towards satisfaction of performance obligations. Income Taxes On March 18, 2020, the Families First Coronavirus Response Act (“FFCR Act”), and on March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (“CARES Act”) were each enacted in response to the COVID-19 pandemic. The FFCR Act and the CARES Act contain numerous income tax provisions relating to refundable payroll tax credits, deferment of employer side social security payments, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations and technical corrections to tax depreciation methods for qualified improvement property. On June 29, 2020, Assembly Bill 85 (“A.B. 85”) was signed into California law. A.B. 85 provides for a three-year three-year The FFCR Act, CARES Act and A.B. 85 did not have a material impact on the Company’s condensed consolidated financial statements as of September 30, 2020; however, the Company continues to examine the impacts the FFCR Act, CARES Act and A.B. 85 may have on its business, results of operations, financial condition, liquidity and related disclosures. Recently Adopted Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13— Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement. The Company adopted this standard on January 1, 2020 with no material impact on its condensed consolidated financial statements and related disclosures. In August 2018, the FASB issued ASU No. 2018-15, Intangibles (Topic 350): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract 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 is effective for annual reporting periods beginning after December 15, 2019, and interim periods within that year. This new standard can be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. The Company adopted this standard on January 1, 2020 with no material impact on its condensed consolidated financial statements and related disclosures. In November 2018, the FASB issued ASU 2018-18— Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 December 15, 2019 . The Company adopted this standard on January 1, 2020 with no material impact on its condensed consolidated financial statements and related disclosures. In December 2019, the FASB (“Financial Accounting Standards Board”) issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities	9 Months Ended
	Sep. 30, 2020
Cash And Cash Equivalents [Abstract]
Cash Equivalents and Marketable Securities	3. Cash Equivalents and Marketable Securities The amortized costs, unrealized gains and losses and fair values of cash equivalents and marketable securities were as follows (in thousands): September 30, 2020 Description Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds $ 43,852 $ — $ — $ 43,852 Commercial paper 2,000 — — 2,000 Total cash equivalents 45,852 — — 45,852 Short-term marketable securities: Commercial paper 5,496 3 — 5,499 Corporate debt securities 4,390 2 — 4,392 U.S. government treasuries 3,006 — — 3,006 Total short-term marketable securities 12,892 5 — 12,897 Total $ 58,744 $ 5 $ — $ 58,749 December 31, 2019 Description Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds $ 42,133 $ — $ — $ 42,133 Commercial paper 1,749 — — 1,749 Corporate debt securities 2,500 — — 2,500 Total cash equivalents 46,382 — — 46,382 Short-term marketable securities: Certificates of deposit 631 — — 631 Commercial paper 31,476 15 — 31,491 Corporate debt securities 38,237 15 (6 ) 38,246 Total short-term marketable securities 70,344 30 (6 ) 70,368 Total $ 116,726 $ 30 $ (6 ) $ 116,750 All marketable securities held as of September 30, 2020, had contractual maturities of less than one year. There have been no material realized gains or losses on marketable securities for the periods presented. As of September 30, 2020, the Company did not hold any individual securities in an unrealized loss position for 12 months or less. . No significant facts or circumstances have arisen to indicate that there has been any significant deterioration in the creditworthiness of the issuers of the securities held by us. The Company considered the current and expected future economic and market conditions surrounding the COVID-19 pandemic and determined that the estimate of credit losses was not significantly impacted. the current and expected future economic and market conditions surrounding the COVID-19 pandemic, as further development arises. As of September 30 , 2020, the Company does not have any marketable securities in an unrealized loss position and thus has not recorded an allowance for credit losses. See Note 4 for further information regarding the fair value of the Company’s financial instruments.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. Fair Value Measurements The Company determines the fair value of financial and non-financial assets and liabilities based on the assumptions that market participants would use in pricing the asset or liability in orderly transaction between market participants at the measurement date. The identification of market participant assumptions provides a basis for determining what inputs are to be used for pricing each asset or liability. A fair value hierarchy has been established which gives precedence to fair value measurements calculated using observable inputs over those using unobservable inputs. This hierarchy prioritizes the inputs into three broad levels as follows: • Level 1 inputs are quoted prices in active markets that are accessible at the market date for identical assets or liabilities. • Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. • Level 3 inputs are unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the assets or liability. Financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The carrying amounts reflected on the balance sheets for cash and cash equivalents, prepaid expenses and other current assets, accounts payable, accrued compensation and accrued liabilities approximate their fair values due to their short-term nature. The Company’s financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements were as follows (in thousands): September 30, 2020 Description Total Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 43,852 $ 43,852 $ — $ — Commercial paper 2,000 — 2,000 — Total cash equivalents 45,852 43,852 2,000 — Short-term marketable securities: Commercial paper 5,499 — 5,499 — Corporate debt securities 4,392 — 4,392 — U.S. government securities 3,006 3,006 — — Total short-term marketable securities 12,897 3,006 9,891 — Total $ 58,749 $ 46,858 $ 11,891 $ — December 31, 2019 Description Total Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 42,133 $ 42,133 $ — $ — Commercial paper 1,749 — 1,749 — Corporate debt securities 2,500 — 2,500 — Total cash equivalents 46,382 42,133 4,249 — Short-term marketable securities: Certificates of deposit 631 — 631 — Commercial paper 31,491 — 31,491 — Corporate debt securities 38,246 — 38,246 — Total short-term marketable securities 70,368 — 70,368 — Total $ 116,750 $ 42,133 $ 74,617 $ — The Company measures the fair value of money market funds based on quoted prices in active markets for identical securities. Commercial paper , corporate debt securities , certificates of deposits, and U.S. government securities are valued taking into consideration valuations obtained from third-party pricing services. 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, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads; benchmark securities; prepayment/default projections based on historical data; and other observable inputs. There were no transfers between Level 1 and Level 2 during the periods presented. See Note 3 for further information regarding the amortized cost of our financial instruments.

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Property and Equipment, Net	5. Property and Equipment, Net Property and equipment and related accumulated depreciation and amortization are as follows (in thousands): September 30, December 31, 2020 2019 Computer equipment and software $ 971 $ 863 Furniture and fixtures 2,054 2,007 Laboratory equipment 21,873 21,025 Leasehold improvements 13,640 11,102 Construction-in-progress 28 2,224 38,566 37,221 Less accumulated depreciation and amortization (15,260 ) (10,310 ) Total property and equipment, net $ 23,306 $ 26,911 Depreciation and amortization expense was $1.7 million $1.2 million and $3.3 million for the three and nine months ended September 30, 2019, respectively

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Leases In November 2015, the Company entered into an 84-month non-cancelable operating lease, effective March 2016, for a facility in Emeryville, California, with laboratory and office space. In conjunction with signing the lease, the Company paid a cash security deposit of $50,000. The lease agreement includes an escalation clause for increased rent and a renewal provision allowing the Company to extend this lease for an additional three years at the prevailing rental rate. In September 2018 the Emeryville lease was amended whereby the Company entered into a 12-month operating lease for additional temporary space. The Company may terminate the temporary space lease agreement with 30 days advanced written notice to the landlord. In January 2019, the Company entered into a 120-month operating lease for a new facility in Emeryville, California with office and laboratory space for the Company’s new principal executive offices. In conjunction with signing the lease, the Company paid a cash security deposit of $0.6 million, which is recorded as a deposit on the Company’s condensed consolidated balance sheet as of September 30, 2020 and December 31, 2019. The lease agreement includes a free rent period, an escalation clause for increased rent and a renewal provision allowing the Company to extend this lease for an additional two five-year In connection with the new lease agreement, the Company also entered into an agreement (the “Lease Termination Agreement”) to early terminate the Company’s existing lease dated November 2015 for its current premises. The then existing lease terminated in October 2019. The Company accounted for the Lease Termination Agreement as a separate contract and recorded an adjustment of $ 1.8 million to the ROU a sset and l ease l iability to reflect the remaining term of the modified agreement through October 2019. In February 2016, the Company entered into a 67-month non-cancelable operating lease effective October 2016 for a facility in Cambridge, Massachusetts, with laboratory and office space. In conjunction with signing the lease, the Company paid a cash security deposit of $0.3 million, which is recorded in deposits and other long-term assets on the Company’s condensed consolidated balance sheet as of September 30, 2020. The lease agreement includes an escalation clause for increased rent and a renewal provision allowing the Company to extend this lease for an additional three years at the prevailing rental rate. The lessor provided the Company a tenant improvement allowance for a total of $2.1 million to complete the laboratory and office renovation. In March 2017, the Company entered into a noncancelable operating lease (the “Pleasanton Lease”) to lease 42,620 square feet of office, cleanroom, and laboratory support manufacturing space in Pleasanton, California (the “Pleasanton Facility”). Subsequently, in April 2017, the Company took possession of the space. The Pleasanton Lease includes a free rent period, escalating rent payments and a term that expires on November 30, 2024. The Company has the option to extend the lease term for a period of five years at the then market rental rate. The Company’s obligation to pay rent commenced in December 2017. The Company obtained an irrevocable letter of credit in March 2017 in the initial amount of approximately $1.0 million as a security deposit to the Pleasanton Lease, which may be drawn down by the landlord in the event the Company fails to fully and faithfully perform all of its obligations. The letter of credit may be reduced based on certain levels of cash and cash equivalents the Company holds. As of September 30, 2020, none of the irrevocable letter of credit amount had been drawn. The Pleasanton Lease further provides that the Company is obligated to pay to the landlord its proportionate share of certain basic operating costs, including taxes and operating expenses. In connection with the Pleasanton Lease, the Company received a tenant improvement allowance of $1.2 million from the landlord for the costs associated with the design, development and construction of tenant improvements for the Pleasanton Facility. The unamortized tenant improvement balance as of January 1, 2019 has been recognized as a component of operating lease ROU assets on the condensed consolidated balance sheets as of September 30, 2020 and December 31, 2019. In September 2018, the Company entered into a 24-month non-cancellable operating lease for an additional facility in Cambridge, Massachusetts with laboratory and office space. In conjunction with signing the lease, the Company prepaid the first twelve months base rent in the amount of $1.3 million, of of $0.9 million $0.3 million, which included $0.1 million for the last month’s rent and In July 2019, the Company amended its Cambridge, Massachusetts laboratory and office space facility lease. of $3.2 million, $0.3 million, which included $0.1 million for the last month’s rent and has been classified as part of In May 2020, the Company executed an additional amendment to its Cambridge, Massachusetts laboratory and office space facility lease. The amendment extended the lease term by an additional 12 months through August 2022. Upon six months written notice, the Company has the right to terminate the amended lease agreement. The amendment provides for annual base rent of approximately $3.6 million, effective September 2021. This amendment resulted in an increase to the ROU assets and lease liabilities of $3.1 million. In May 2019, the Company entered into a 64-month non-cancellable operating lease for additional office space in Pleasanton, California. The lessor provided the Company a tenant improvement allowance for a total of $0.1 million to complete the office renovation. The Company’s obligation to pay rent commenced on August 1, 2019. The Company has determined the tenant improvements to be lessee owned and therefore has recorded a $0.3 million ROU asset and a $0.4 million lease liability on the condensed consolidated balance sheet as of September 30, 2020. The Company’s operating leases include various covenants, indemnities, defaults, termination rights, security deposits and other provisions customary for lease transactions of this nature. The components of lease costs, which were included in our condensed consolidated statements of operations and comprehensive loss, were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Lease cost Operating lease cost $ 1,906 $ 1,653 $ 5,621 $ 4,491 Short-term lease cost — 76 8 198 Total lease cost $ 1,906 $ 1,729 $ 5,629 $ 4,689 Supplemental information related to leases was as follows (in thousands): Nine Months Ended September 30, 2020 2019 Cash paid for amounts included in the measurement of lease liabilities (in thousands): Operating cash flows from operating leases $ 3,446 $ 1,939 New right-of-use assets obtained in exchange for lease obligations (in thousands): Operating leases $ 3,174 $ 1,447 Weighted average remaining lease term (years): Operating leases 6.1 7.9 Weighted average discount rate: Operating leases 9.0 % 9.0 % As of September 30, 2020, minimum annual rental payments under the Company’s operating lease agreements are as follows (in thousands): Lease Financing Obligation Year ending December 31, 2020 (remaining three months) $ 1,951 2021 7,905 2022 5,836 2023 3,459 2024 3,459 Thereafter 12,531 Total minimum payments 35,141 Less: Amounts representing interest expense (8,629 ) Less: Amounts representing tenant improvement allowance (652 ) Present value of future minimum lease payments 25,860 Less: Current portion of lease liability (5,069 ) Noncurrent portion of lease liability $ 20,791 The a mount s representing the tenant improvement allowance are expected to be received by the Company in 2020. Agreements with CROs In September 2017, the Company entered into a contract research and development agreement with a third-party contract research organization (“CRO”) to provide research, analysis and antibody samples to further the Company’s development of its drug candidates. The Company is also obligated to pay the CRO certain milestone payments of up to $36.4 million on achievement of specified events. None of these events had occurred as of September 30, 2020. During the three and nine months ended September 30, 2020, the Company had no research and development expense under the agreement. The Company recognized an insignificant amount of research and development expense under the agreement during the three and nine months ended September 30, 2019. In May 2019, the Company entered into a contract research and testing agreement with a third-party contract research organization to provide antibody discovery related services. The Company is also obligated to pay the CRO certain milestone payments of up to $34.8 million on achievement of specified events. None of these events had occurred as of September 30, 2020. No research and development expense was recorded under the agreement during the three months ended September 30, 2020. During the nine months ended September 30, 2020, the Company recognized an insignificant amount of research and development expense under the agreement. During the three and nine months ended September 30, 2019, the Company recognized a total of $0.6 million and $0.8 million, respectively, of research and development expense under the agreement. Guarantees and Indemnifications The Company, as permitted under Delaware law and in accordance with its certification of incorporation and bylaws, and pursuant to indemnification agreements with certain of its officers and directors, indemnifies its officers and directors for certain events or occurrences, subject to certain limits, which the officer or director is or was serving at the Company’s request in such capacity. The term of the indemnification period lasts as long as an officer or director may be subject to any proceeding arising out of acts or omissions of such officer or director in such capacity. The maximum amount of potential future indemnification is unlimited; however, the Company currently holds director and officer liability insurance. This insurance limits the Company’s exposure and may enable it to recover a portion of any future amounts paid. The Company believes that the fair value of these indemnification obligations is minimal. Accordingly, the Company has not recognized any liabilities relating to these obligations for any period presented.

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance Sheet Components	7. Balance Sheet Components Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consist of the following (in thousands): September 30, December 31, 2020 2019 Prepaid insurance $ 24 $ 1,252 Interest and other receivables 61 482 Prepaid research and development-related expenses 2,139 1,473 Restricted cash 575 — Other 403 290 Total prepaid expenses and other current assets $ 3,202 $ 3,497 Deposits and Other Long-Term Assets Deposits and other long-term assets consist of the following (in thousands): September 30, December 31, 2020 2019 Lease security deposit $ 1,218 $ 1,201 Prepaid research and development-related expenses 539 585 Restricted cash 992 992 Total deposits and other long-term assets $ 2,749 $ 2,778

Collaboration and License Agree

Collaboration and License Agreements	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration and License Agreements	8. Collaboration and License Agreements bluebird bio, Inc. In August 2018, the Company entered into a Research Collaboration and License Agreement (“Collaboration Agreement”) with bluebird bio, Inc. (“bluebird”). Under the terms of the Collaboration Agreement, the Company will provide to bluebird tumor-specific targets across several tumor types and, in certain cases, T cell receptors (“TCR”) directed to those targets. The Company received a non-refundable upfront payment of $20.0 million and bluebird also concurrently acquired 768,115 shares of the Company’s Series C convertible preferred stock for $10.0 million at $13.04 per share. Per the Collaboration Agreement, bluebird was also provided an option to acquire shares of the Company’s common stock at the same price as all other investors in connection with the IPO. In October 2018, bluebird purchased 666,667 shares of the Company’s common stock at the price to the public of $15.00 per share for a total of $10.0 million. Under the terms of the Collaboration Agreement, the Company is eligible to earn development, regulatory, and sales-based milestones in an amount of up to $1.2 billion, and single-digit royalties on sales of products that utilize the technology subject to the Collaboration Agreement. None of these events had occurred as of September 30, 2020 and no royalties were due from the sale of licensed products. In August 2019, the Company entered into a First Amendment to the Research Collaboration and License Agreement which extended the timeline for the Company and bluebird to execute a Patient Selection Services Agreement to within two years after the Effective Date of the Research Collaboration and License Agreement. In August 2020, the Company entered into a Second Amendment which extended the timeline of the Patient Selection Services Agreement to within three years and Both amendments were entered into for administrative purposes and the Company determined the amendments were not a modification of contract under ASC 606. bluebird may terminate the Collaboration Agreement by giving a 120-day prior written notice to the Company at any time after the effective date of the agreement. Unless terminated early the agreement has a term that ends upon the last payment owed by Gritstone on a licensed product. The Collaboration Agreement may be terminated for cause by either party based on uncured material breach by the other party or bankruptcy of the other party. Upon early termination, all ongoing activities under the agreement and all mutual collaboration, development and commercialization licenses and sublicenses will terminate. The licenses granted by the Company to bluebird under the licensed intellectual property will remain in effect in accordance with their respective terms. Additionally, all of bluebird’s payment obligations that have not yet accrued related to future milestone and royalty payments will be reduced by fifty percent for the remainder of the agreement term. The Company concluded that bluebird is a customer, and the contract is not subject to accounting literature on collaborative arrangements. This is because the Company granted to bluebird a license to its intellectual property, and provided research and development services, all of which are outputs of the Company’s ongoing activities, in exchange for consideration. The Company identified the following three material promises under the Collaboration Agreement: 1) transfer of a license to intellectual property and related technology know-how (“License and Know-How”); 2) the obligation to perform target selection and TCR generation services (“Research and Development Services”); and 3) participation on the Joint Steering Committee (“JSC”). The Company provided to bluebird standard indemnification and protection of licensed intellectual property, which is part of assurance that the license meets the contract’s specifications and is not an obligation to provide goods or services. The Company considered that the License and Know-How has standalone functionality, was considered to be functional intellectual property, and is capable of being distinct. However, the Company determined that the License and Know-How is not distinct from the Research and Development Services or participation on the JSC within the context of the agreement because bluebird is dependent on the Company to execute the Research and Development Services and participate on the JSC in order for bluebird to benefit from the License and Know-How. As such, the License and Know-How is combined with the Research and Development Services and participation on the JSC into a single performance obligation. As such, the transaction price under this arrangement will be allocated to this single performance obligation. The Company has also determined that all other goods or services which are contingent upon bluebird reaching various milestones are not considered performance obligations at the inception of the arrangement. The transaction price at the inception of the Collaboration Agreement consisted of the upfront payment of $20.0 million and the $10.0 million received from bluebird for the purchase of the Company’s Series C convertible preferred stock. The sale of the Series C convertible preferred stock was not considered to be a performance obligation as it was a separate financing component of the transaction. Accordingly, $10.0 million of the transaction price was allocated to the issuance of 768,115 shares of Series C convertible preferred stock at fair value of $13.04 per share and recorded in stockholders’ equity. The variable consideration related to the remaining development, regulatory, and sales-based milestones payments has not been included in the initial transaction price and continues to be fully constrained as of September 30, 2020. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon initiation of clinical trials for early stage targets and bluebird’s development efforts. Any variable consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur as they were determined to relate predominantly to the License and Know-How granted to bluebird. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. For revenue recognition purposes, the Company determined that the duration of the contract began on the effective date in August 2018 and ends upon completion of the Research and Development Services which is also when the participation on the JSC is no longer an obligation. The contract duration is defined as the period in which parties to the contract have present enforceable rights and obligations. We analyzed the impact of bluebird terminating the agreement prior to August 2023 and determined that there were substantive non-monetary penalties to bluebird for doing so. We considered quantitative and qualitative factors to reach this conclusion. Revenue is recognized when, or as, the Company satisfies its performance obligation by transferring the promised services to bluebird. Revenue will be recognized over time using a cost-based input method, based on internal labor cost effort to perform the research services, since the internal labor cost incurred over time is thought to best reflect the transfer of services to bluebird. In applying a cost-based input method of revenue recognition, we use actual costs incurred relative to budgeted costs to fulfill the combined performance obligation. A cost-based input method of revenue recognition requires us to make estimates of costs to complete the performance obligation. The cumulative effect of any revisions to estimated costs to complete the performance obligation will be recorded in the period in which changes are identified and amounts can be reasonably estimated. A significant change in these assumptions and estimates could have a material impact on the timing and amount of revenue recognized in future periods. For the three and nine months ended September 30, 2020, the Company has recognized $0.8 million and $1.9 million, respectively, as collaboration revenue as a result of satisfying its performance obligation by transferring the promised services estimated by the labor cost incurred. A deferred revenue balance of $12.6 million is recorded on the condensed consolidated balance sheets in both current and long-term liabilities as of September 30, 2020, which relates to the performance obligation identified, with such amounts to be recognized over the period the performance obligation is expected to be satisfied, which is currently expected to be through mid-2023. Changes in the deferred revenue balance during the nine months ended September 30, 2020 are as follows (in thousands): Deferred Revenue Balance at December 31, 2019 $ 14,516 Additions — Deductions (1,902 ) Balance at September 30, 2020 $ 12,614 There were no receivables or net contract assets recorded as of September 30, 2020 or December 31, 2019 associated with the Collaboration Agreement. The Company expensed all incremental costs of obtaining the Collaboration Agreement in 2018 as such amounts were insignificant. Arbutus Biopharma Corporation In October 2017, the Company entered into an Exclusive License Agreement by and between Arbutus Biopharma Corporation (“Arbutus”) and Protiva Biotherapeutics Inc. a wholly owned subsidiary of Arbutus. Certain terms of the agreement were modified by amendment in July 2018. Under the license agreement, the Company has an exclusive license to utilize certain Arbutus intellectual property including patents and know-how relating to immunotherapy. During the three and nine months ended September 30, 2020, the Company had no research and development expense under the agreement. During the three and nine months ended September 30, 2019, the Company reimbursed Arbutus for $0.2 million and $0.3 million, respectively, for materials and personnel costs following the initial patient treatment of SLATE in the Company’s GO-005 clinical trial. In 2019, the Company Non-Profit Hospital Cancer Center In January 2016, the Company entered into an Exclusive License Agreement with a non-profit hospital cancer center. Under the license agreement, the Company has an exclusive license to utilize certain patents and know-how relating to immunotherapy for an insignificant upfront payment, cash milestone payments on achievement of specified events, and a low single digit royalty on sales of licensed products. The achievement of the milestones and payment of royalties is dependent upon obtaining regulatory approval. Upon achievement of a milestone related to the Company’s Phase 1 clinical trial for GRANITE, GO-004, in December 2018 the Company recorded an insignificant amount to research and development expense for amounts owed to the Hospital Cancer Center, which was paid to the hospital in February 2019. None of the other milestone events had occurred

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Stockholders' Equity	9. Stockholders’ Equity In connection with the completion of its IPO, in October 2018, the Company’s certificate of incorporation was amended and restated to provide for 300,000,000 authorized shares of common stock with a par value of $0.0001 per share and 10,000,000 authorized shares of preferred stock with a par value of $0.0001 per share. The Company has 10,000,000 shares of preferred stock authorized for issuance, par value of $0.0001 The Company has 300,000,000 shares of common stock authorized for issuance, par value $0.0001 Sale of Common Stock In April 2019, the Company completed an underwritten public offering and sold and issued an aggregate of 6,500,000 shares of common stock at a price to the public of $11.50 per share. The Company received aggregate net proceeds from the offering of approximately $69.7 million, after deducting underwriting discounts and commissions and offering costs. In October 2019, the Company filed a Registration Statement on Form S-3 (the “Shelf Registration Statement”) with the SEC, covering the offering of up to $250.0 million of common stock, preferred stock, debt securities, warrants and units. The Shelf Registration Statement included a prospectus covering the offering, issuance and sale of up to $75.0 million of the Company’s common stock from time to time through an at the market offering under the Securities Act of 1933, as amended (the “ATM Offering Program”). The SEC declared the Shelf Registration Statement effective on November 8, 2019. In October 2019, the Company also entered into a sales agreement (the “Sales Agreement”) with Cowen and Company, LLC (“Cowen”) to sell shares of the Company’s common stock, from time to time, with aggregate gross sales proceeds of up to $75.0 million, through an at the market offering under which Cowen will act as its sales agent Cowen is entitled to compensation for its services equal to up to 3.0% of the gross proceeds of any shares of common stock sold through Cowen under the Sales Agreement. In addition, the Company has agreed to reimburse a portion of the expenses of Cowen in connection with the offering up to a maximum of $50,000. During the year ended December 31, 2019, the Company issued and sold 490,880 shares of its common stock through its ATM Offering Program and received net proceeds of approximately $3.8 million, after deducting commissions of $0.1 million and other offering expenses of $0.3 million. During the nine months ended September 30, 2020, the Company issued and sold 1,160,963 shares of its common stock through its ATM Offering Program and received net proceeds of approximately $9.8 million, after deducting commissions of $0.3

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	10. Stock-Based Compensation Award Incentive Plans In August 2015, the Board of Directors approved the 2015 Equity Incentive Plan (“2015 Plan”). In connection with the Company’s IPO and the effectiveness of the 2018 Award Incentive Plan (“2018 Plan”), the 2015 Plan terminated and no further awards will be granted under the 2015 Plan. The 92,815 shares of common stock shares that were then unissued and available for future issuance under the 2015 Plan became available under the 2018 Plan. In September 2018, the Company’s Board of Directors approved the 2018 Plan. Under the 2018 Plan, a total of 2,690,000 shares of our common stock were initially reserved for issuance under the 2018 Plan, plus the number of shares remaining available for future awards under the 2015 Plan, as of the effective date of the 2018 Plan. The number of shares of common stock reserved for issuance under the 2018 Plan will automatically increase on January 1 of each year, beginning on January 1, 2019 and continuing through and including January 1, 2028, by 4% of the total number of shares of our stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s Board of Directors. The maximum number of shares that may be issued upon the exercise of ISOs under the 2018 Plan is 45,000,000. The Company’s Board of Directors has the authority to determine to whom options will be granted, the number of shares, the term, and the exercise price. If an individual owns stock representing 10% or more of the outstanding shares, the price of each share shall be at least 110% of the fair market value, as determined by the board of directors. Options granted have a term of up to 10 years and generally vest over a 4-year period with a straight-line vesting. Stock Option Activity A summary of the 2015 Plan and 2018 Plan activity is as follows: Options Outstanding Number of Shares Available for Issuance Number of Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Balance at December 31, 2019 2,851,883 3,165,961 $ 7.83 8.45 $ 8,875 Authorized 1,454,553 Granted (1,800,700 ) 1,800,700 $ 8.48 Exercised — (142,239 ) $ 1.31 Cancelled 332,955 (332,955 ) $ 10.74 Balance at September 30, 2020 2,838,691 4,491,467 $ 8.08 8.37 $ 1,188 Vested and exercisable – September 30, 2020 1,767,271 $ 6.63 7.63 $ 1,051 Vested and expected to vest – September 30, 2020 4,136,041 $ 7.99 8.32 $ 1,184 For the nine months ended September 30, 2020 and 2019, the total intrinsic value of stock option awards exercised was $0.8 million $2.8 million At September 30 , 2020, $13.9 million of total unrecognized compensation cost related to non-vested employee and consultant options is expected to be recognized over a weighted-average period of 2.62 years. The total fair value of shares vested during the period ended September 30, 2020 was $5.1 million. Stock-based compensation expense and awards granted to non-employees were immaterial for the nine months ended September 30, 2020 and 2019. Stock-Based Compensation Expense Total stock-based compensation for all awards granted to employees, consultants and our 2018 Employee Stock Purchase Plan (“ESPP”), before taxes, is as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Research and development expenses $ 1,133 $ 965 $ 3,387 $ 2,522 General and administrative expenses 704 567 2,028 1,334 Total $ 1,837 $ 1,532 $ 5,415 $ 3,856

Net Loss Per Common Share

Net Loss Per Common Share	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Net Loss Per Common Share	11. Net Loss Per Common Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented. The following table sets forth the computation of the basic and diluted net loss per share (in thousands, except for share and per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Numerator: Net loss $ (26,073 ) $ (27,548 ) $ (78,147 ) $ (66,729 ) Denominator: Weighted-average common shares outstanding, basic and diluted 37,750,145 35,690,600 37,268,318 32,762,176 Net loss per share, basic and diluted $ (0.69 ) $ (0.77 ) $ (2.10 ) $ (2.04 ) 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 for all periods as the inclusion of all potential common shares outstanding 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: September 30, December 31, 2020 2019 Options issued and outstanding and ESPP shares issuable and outstanding 4,624,285 3,179,041 Early exercised common stock subject to future vesting — 30,874 Total 4,624,285 3,209,915

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2020
Subsequent Events [Abstract]
Subsequent Events	12. Subsequent Events On October 20, 2020, the Company entered into an Option and License and Development Agreement with a biopharma company. Under the agreement, the Company agreed to pay the biopharma company an upfront payment of $2.0 million, up to an aggregate of $21.0 million in specified development and regulatory milestones and up to an aggregate of $50.0 million in specified commercial milestones, as well as a low to mid-single digit royalties on net sales of licensed products for a royalty term lasting until the later of expiration of the last covered patent under the license.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying interim condensed consolidated financial statements are unaudited and are comprised of the consolidation of the Company and its wholly-owned subsidiary. All intercompany balances and transactions have been eliminated in consolidation. The Company has no unconsolidated subsidiaries or investments accounted for under the equity method. The accompanying condensed consolidated financial statements have been prepared in accordance with United States generally accepted accounting principles (“U.S. GAAP”) and the rules and regulations of Securities and Exchange Commission (“SEC”) for interim reporting. The condensed consolidated financial statements are unaudited and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, necessary for the fair presentation for interim reporting. The results of operations for any interim period are not necessarily indicative of results of operations for any future period. Certain information and footnote disclosures typically included in annual financial statements prepared in accordance with U.S. GAAP have been condensed or omitted. Accordingly, these unaudited interim condensed consolidated financial statements should be read in conjunction with the Company’s financial statements as of and for the year ended December 31, 2019, which are included in the Company’s Annual Report on Form 10-K, as filed with the SEC on March 11, 2020 .
Need for Additional Capital	Need for Additional Capital The Company has incurred operating losses and has an accumulated deficit as a result of ongoing efforts to develop drug product candidates, including conducting preclinical and clinical trials and providing general and administrative support for these operations. The Company had cash, cash equivalents, and marketable securities of $70.5 million and $127.8 million as of September 30, 2020 and December 31, 2019, respectively. million and $221.0 million as of September 30, 2020 and December 31, 2019, respectively. The Company had net losses of $26.1 78.1 $27.5 million and $66.7 million for the three and nine months ended September 30, 2019, respectively, and of $63.9 million $62.6 property rights to its product candidates and sell unsecured assets, or a combination of the above, any of which may have a material adverse effect on the Company’s business, results of operations, financial condition and/or its ability to fund its scheduled obligations on a timely basis or at all. Failure to manage discretionary spending or raise additional capital , as needed, may adversely impact the Company’s ability to achieve its intended business objectives. Th e accompanying condensed consolidated financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the settlement of liabilities and commitments in the normal course of business. The condensed consolidated financial statements do not reflect any adjustments relating to the recoverability and classification of assets or the amounts and classification of liabilities that might be necessary if the Company is unable to continue as a going concern.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and judgments that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities as of the date of the condensed consolidated financial statements and the reported amounts of revenue and expenses in the condensed consolidated financial statements and accompanying notes during the reporting period. On an ongoing basis, management evaluates its estimates, including those related to preclinical and clinical study trial accruals, fair value of assets and liabilities, the fair value of right-of-use assets (“ROU assets”) and lease liabilities, revenue recognition, and the fair value of stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates .
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist of cash, cash equivalents, and marketable securities. Cash, cash equivalents and marketable securities are invested through banks and other financial institutions in the United States. Such deposits may be in excess of federally insured limits. The Company maintains cash equivalents and marketable securities with various high-credit-quality and capitalized financial institutions. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. The Company’s investment policy limits investments to certain types of securities issued by the U.S. government, its agencies, and institutions with investment-grade credit ratings and places restrictions on maturities and concentration by type and issuer. The Company is exposed to credit risk in the event of a default by the financial institutions holding its cash, cash equivalents, and marketable securities and issuers of marketable securities to the extent recorded on the balance sheets. Through September 30, 2020, the Company has no off-balance sheet concentrations of credit risk.
Other Risks and Uncertainties	Other Risks and Uncertainties The Company is subject to a number of risks similar to those of other early-stage immuno-oncology companies, including dependence on key individuals; the need to develop commercially viable therapeutics; competition from other companies, many of which are larger and better capitalized; and the need to obtain adequate additional financing to fund the development of its product candidates. The Company currently depends on third-party suppliers for key materials and services used in its research and development manufacturing process, and is subject to certain risks related to the loss of these third-party suppliers or their inability to supply the Company with adequate materials and services. In March 2020, the World Health Organization declared the global novel coronavirus disease (“COVID-19”) outbreak a pandemic. To date, the Company’s business has not been materially impacted by the COVID-19 pandemic. However, the Company has experienced slowing of patient recruitment and sample collection in its ongoing clinical trials and cannot at this time predict the specific extent, duration, or full impact that the 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 outbreak and related governmental advisories and restrictions. These developments and the impact of COVID-19 on the financial markets and the overall economy are highly uncertain. If the financial markets and/or the overall economy are impacted for an extended period, the Company’s results may be adversely affected.
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents, and Restricted Cash Cash equivalents, which consist primarily of highly liquid investments with original maturities of three months or less when purchased, are stated at cost which approximates fair value. These assets include investments in money market funds that invest in U.S. Treasury obligations and certificates of deposit which are stated at fair value. The Company has issued a letter of credit under a lease agreement which has been collateralized by a cash deposit for an equal amount and is recorded within deposits and other long-term assets on the condensed consolidated balance sheets based on the term of the underlying lease. Additionally, the Company has received cash proceeds from a philanthropic institution which is restricted and to be spent in accordance with the contribution agreement and is recorded as restricted cash within prepaid expenses and other current assets on the condensed consolidated balance sheet. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the balance sheets that sum to the total of the same amounts shown in the statements of cash flows (in thousands): September 30, December 31, 2020 2019 Cash and cash equivalents $ 57,648 $ 57,408 Restricted cash 1,567 992 Total cash, cash equivalents and restricted cash $ 59,215 $ 58,400
Leases	Leases The Company determines whether the arrangement is or contains a lease at the inception of the arrangement and if such a lease is classified as a financing lease or operating lease. All of the Company’s leases are classified as operating leases. Leases with a term greater than one year are included in operating lease ROU assets, lease liabilities, current portion, and in the Company’s condensed consolidated balance sheets at September 30, 2020 and December 31, 2019 In determining the net present value of lease payments, t The Company considers a lease term to be the noncancelable period that it has the right to use the underlying asset, including any periods where it is reasonably assured the Company will exercise the option to extend the contract. Periods covered by an option to extend are included in the lease term if the lessor controls the exercise of that option. The Company recognizes lease expense on a straight-line basis over the expected lease term. The Company has elected to not separate lease and non-lease components for its leased assets and accounts for all lease and non-lease components of its agreements as a single lease component. The lease components resulting in a ROU asset have been recorded on the condensed consolidated balance sheets and amortized as lease expense on a straight-line basis over the lease term.
Revenue Recognition	Revenue Recognition The Company analyzes its collaboration agreements to assess 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 that are considered to be in the scope of the collaboration guidance and that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of the collaboration guidance and those that are more reflective of a vendor-customer relationship and, therefore, within the scope of the revenue with contracts with customer guidance. For elements of collaboration arrangements that are accounted for pursuant to the revenue from contracts with customer guidance, an appropriate recognition method is determined and applied consistently, generally by analogy to the revenue from contracts with customers guidance. The terms of the licensing and collaboration agreements entered into typically include payment of one or more of the following: non-refundable, up-front fees; development, regulatory, and commercial milestone payments; payments for manufacturing supply services; and royalties on net sales of licensed products. Each of these payments results in license, collaboration, and other revenues, except for revenues from royalties on net sales of licensed products, which are classified as royalty revenues. The core principle of the accounting for revenue from contracts with customers guidance is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received in exchange for those goods or services. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue in the Company’s condensed consolidated balance sheets. If the related performance obligation is expected to be satisfied within the next twelve months this will be classified in current liabilities. Amounts recognized as revenue prior to receipt are recorded as contract assets in the Company’s condensed consolidated balance sheets. If the Company expects to have an unconditional right to receive consideration in the next twelve months, this will be classified in current assets. A net contract asset or liability is presented for each contract with a customer. At contract inception, the Company assesses the goods or services promised in a contract with a customer and identifies those distinct goods and services that represent a performance obligation. A promised good or service may not be identified as a performance obligation if it is immaterial in the context of the contract with the customer, if it is not separately identifiable from other promises in the contract (either because it is not capable of being separated or because it is not separable in the context of the contract), or if the performance obligation does not provide the customer with a material right. The Company considers the terms of the contract and its customary business practices to determine the transaction price. The transaction price is the amount of consideration to which the Company expects to be entitled in exchange for transferring promised goods or services to a customer. The consideration promised in a contract with a customer may include fixed amounts, variable amounts, or both. Variable consideration will only be included in the transaction price when it is not considered constrained, which is when it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur. If it is determined that multiple performance obligations exist, the transaction price is allocated at the inception of the agreement to all identified performance obligations based on the relative standalone selling prices. The relative selling price for each deliverable is estimated using objective evidence if it is available. If objective evidence is not available, the Company uses its best estimate of the selling price for the deliverable. Revenue is recognized when, or as, the Company satisfies a performance obligation by transferring a promised good or service to a customer. An asset is transferred when, or as, the customer obtains control of that asset, which for a service, is considered to be as the services are received and used. The Company recognizes revenue over time by measuring the progress toward complete satisfaction of the relevant performance obligation using an appropriate input or output method based on the nature of the good or service promised to the customer. After contract inception, the transaction price is reassessed at every period end and updated for changes such as resolution of uncertain events. Any change in the transaction price is allocated to the performance obligations on the same basis as at contract inception. Management may be required to exercise considerable judgment in estimating revenue to be recognized. Judgment is required in identifying performance obligations, estimating the transaction price, estimating the stand-alone selling prices of identified performance obligations, which may include forecasted revenue, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success, and estimating the progress towards satisfaction of performance obligations.
Income Taxes	Income Taxes On March 18, 2020, the Families First Coronavirus Response Act (“FFCR Act”), and on March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (“CARES Act”) were each enacted in response to the COVID-19 pandemic. The FFCR Act and the CARES Act contain numerous income tax provisions relating to refundable payroll tax credits, deferment of employer side social security payments, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations and technical corrections to tax depreciation methods for qualified improvement property. On June 29, 2020, Assembly Bill 85 (“A.B. 85”) was signed into California law. A.B. 85 provides for a three-year three-year The FFCR Act, CARES Act and A.B. 85 did not have a material impact on the Company’s condensed consolidated financial statements as of September 30, 2020; however, the Company continues to examine the impacts the FFCR Act, CARES Act and A.B. 85 may have on its business, results of operations, financial condition, liquidity and related disclosures.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13— Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement. The Company adopted this standard on January 1, 2020 with no material impact on its condensed consolidated financial statements and related disclosures. In August 2018, the FASB issued ASU No. 2018-15, Intangibles (Topic 350): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract 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 is effective for annual reporting periods beginning after December 15, 2019, and interim periods within that year. This new standard can be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. The Company adopted this standard on January 1, 2020 with no material impact on its condensed consolidated financial statements and related disclosures. In November 2018, the FASB issued ASU 2018-18— Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 December 15, 2019 . The Company adopted this standard on January 1, 2020 with no material impact on its condensed consolidated financial statements and related disclosures. In December 2019, the FASB (“Financial Accounting Standards Board”) issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Cash, Cash Equivalents, and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the balance sheets that sum to the total of the same amounts shown in the statements of cash flows (in thousands): September 30, December 31, 2020 2019 Cash and cash equivalents $ 57,648 $ 57,408 Restricted cash 1,567 992 Total cash, cash equivalents and restricted cash $ 59,215 $ 58,400

Cash Equivalents and Marketab_2

Cash Equivalents and Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2020
Cash And Cash Equivalents [Abstract]
Cash Equivalents and Marketable Securities	The amortized costs, unrealized gains and losses and fair values of cash equivalents and marketable securities were as follows (in thousands): September 30, 2020 Description Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds $ 43,852 $ — $ — $ 43,852 Commercial paper 2,000 — — 2,000 Total cash equivalents 45,852 — — 45,852 Short-term marketable securities: Commercial paper 5,496 3 — 5,499 Corporate debt securities 4,390 2 — 4,392 U.S. government treasuries 3,006 — — 3,006 Total short-term marketable securities 12,892 5 — 12,897 Total $ 58,744 $ 5 $ — $ 58,749 December 31, 2019 Description Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds $ 42,133 $ — $ — $ 42,133 Commercial paper 1,749 — — 1,749 Corporate debt securities 2,500 — — 2,500 Total cash equivalents 46,382 — — 46,382 Short-term marketable securities: Certificates of deposit 631 — — 631 Commercial paper 31,476 15 — 31,491 Corporate debt securities 38,237 15 (6 ) 38,246 Total short-term marketable securities 70,344 30 (6 ) 70,368 Total $ 116,726 $ 30 $ (6 ) $ 116,750

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Assets and Liabilities Measured at Fair Value	The Company’s financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements were as follows (in thousands): September 30, 2020 Description Total Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 43,852 $ 43,852 $ — $ — Commercial paper 2,000 — 2,000 — Total cash equivalents 45,852 43,852 2,000 — Short-term marketable securities: Commercial paper 5,499 — 5,499 — Corporate debt securities 4,392 — 4,392 — U.S. government securities 3,006 3,006 — — Total short-term marketable securities 12,897 3,006 9,891 — Total $ 58,749 $ 46,858 $ 11,891 $ — December 31, 2019 Description Total Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 42,133 $ 42,133 $ — $ — Commercial paper 1,749 — 1,749 — Corporate debt securities 2,500 — 2,500 — Total cash equivalents 46,382 42,133 4,249 — Short-term marketable securities: Certificates of deposit 631 — 631 — Commercial paper 31,491 — 31,491 — Corporate debt securities 38,246 — 38,246 — Total short-term marketable securities 70,368 — 70,368 — Total $ 116,750 $ 42,133 $ 74,617 $ —

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment and related accumulated depreciation and amortization are as follows (in thousands): September 30, December 31, 2020 2019 Computer equipment and software $ 971 $ 863 Furniture and fixtures 2,054 2,007 Laboratory equipment 21,873 21,025 Leasehold improvements 13,640 11,102 Construction-in-progress 28 2,224 38,566 37,221 Less accumulated depreciation and amortization (15,260 ) (10,310 ) Total property and equipment, net $ 23,306 $ 26,911

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Schedule of Components of Lease Costs	The components of lease costs, which were included in our condensed consolidated statements of operations and comprehensive loss, were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Lease cost Operating lease cost $ 1,906 $ 1,653 $ 5,621 $ 4,491 Short-term lease cost — 76 8 198 Total lease cost $ 1,906 $ 1,729 $ 5,629 $ 4,689
Schedule of Supplemental Information Related to Leases	Supplemental information related to leases was as follows (in thousands): Nine Months Ended September 30, 2020 2019 Cash paid for amounts included in the measurement of lease liabilities (in thousands): Operating cash flows from operating leases $ 3,446 $ 1,939 New right-of-use assets obtained in exchange for lease obligations (in thousands): Operating leases $ 3,174 $ 1,447 Weighted average remaining lease term (years): Operating leases 6.1 7.9 Weighted average discount rate: Operating leases 9.0 % 9.0 %
Schedule of Minimum Annual Rental Payments Under Operating Lease Agreements	As of September 30, 2020, minimum annual rental payments under the Company’s operating lease agreements are as follows (in thousands): Lease Financing Obligation Year ending December 31, 2020 (remaining three months) $ 1,951 2021 7,905 2022 5,836 2023 3,459 2024 3,459 Thereafter 12,531 Total minimum payments 35,141 Less: Amounts representing interest expense (8,629 ) Less: Amounts representing tenant improvement allowance (652 ) Present value of future minimum lease payments 25,860 Less: Current portion of lease liability (5,069 ) Noncurrent portion of lease liability $ 20,791

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consist of the following (in thousands): September 30, December 31, 2020 2019 Prepaid insurance $ 24 $ 1,252 Interest and other receivables 61 482 Prepaid research and development-related expenses 2,139 1,473 Restricted cash 575 — Other 403 290 Total prepaid expenses and other current assets $ 3,202 $ 3,497
Schedule of Deposits and Other Long-Term Assets	Deposits and other long-term assets consist of the following (in thousands): September 30, December 31, 2020 2019 Lease security deposit $ 1,218 $ 1,201 Prepaid research and development-related expenses 539 585 Restricted cash 992 992 Total deposits and other long-term assets $ 2,749 $ 2,778

Collaboration and License Agr_2

Collaboration and License Agreements (Tables)	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Changes in Deferred Revenue Balance	Changes in the deferred revenue balance during the nine months ended September 30, 2020 are as follows (in thousands): Deferred Revenue Balance at December 31, 2019 $ 14,516 Additions — Deductions (1,902 ) Balance at September 30, 2020 $ 12,614

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Stock Options Activity	A summary of the 2015 Plan and 2018 Plan activity is as follows: Options Outstanding Number of Shares Available for Issuance Number of Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Balance at December 31, 2019 2,851,883 3,165,961 $ 7.83 8.45 $ 8,875 Authorized 1,454,553 Granted (1,800,700 ) 1,800,700 $ 8.48 Exercised — (142,239 ) $ 1.31 Cancelled 332,955 (332,955 ) $ 10.74 Balance at September 30, 2020 2,838,691 4,491,467 $ 8.08 8.37 $ 1,188 Vested and exercisable – September 30, 2020 1,767,271 $ 6.63 7.63 $ 1,051 Vested and expected to vest – September 30, 2020 4,136,041 $ 7.99 8.32 $ 1,184
Schedule of Stock Based Compensation Expense	Total stock-based compensation for all awards granted to employees, consultants and our 2018 Employee Stock Purchase Plan (“ESPP”), before taxes, is as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Research and development expenses $ 1,133 $ 965 $ 3,387 $ 2,522 General and administrative expenses 704 567 2,028 1,334 Total $ 1,837 $ 1,532 $ 5,415 $ 3,856

Net Loss Per Common Share (Tabl

Net Loss Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Computation of Basic and Diluted 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 during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented. The following table sets forth the computation of the basic and diluted net loss per share (in thousands, except for share and per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Numerator: Net loss $ (26,073 ) $ (27,548 ) $ (78,147 ) $ (66,729 ) Denominator: Weighted-average common shares outstanding, basic and diluted 37,750,145 35,690,600 37,268,318 32,762,176 Net loss per share, basic and diluted $ (0.69 ) $ (0.77 ) $ (2.10 ) $ (2.04 )
Computation of Potentially Anti-Dilutive Securities	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 for all periods as the inclusion of all potential common shares outstanding 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: September 30, December 31, 2020 2019 Options issued and outstanding and ESPP shares issuable and outstanding 4,624,285 3,179,041 Early exercised common stock subject to future vesting — 30,874 Total 4,624,285 3,209,915

Organization - Additional Infor

Organization - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2020Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segments	1

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	Jun. 29, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Summary Of Significant Accounting Policies [Line Items]
Cash, cash equivalents and marketable securities		$ 70,500,000		$ 70,500,000		$ 127,800,000
Accumulated deficit		(299,135,000)		(299,135,000)		$ (220,988,000)
Net loss		$ (26,073,000)	$ (27,548,000)	(78,147,000)	$ (66,729,000)
Net cash used in operating activities				$ (63,885,000)	$ (62,559,000)
Use of net operating losses suspension period for medium and large business	3 years
Use of business incentive tax credits period cap	3 years
ASU 2016-13 [Member]
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted		true		true
Change in accounting principle, accounting standards update, adoption date		Jan. 1, 2020		Jan. 1, 2020
Change in accounting principle, accounting standards update, immaterial effect		true		true
ASU 2018-13 [Member]
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted		true		true
Change in accounting principle, accounting standards update, adoption date		Jan. 1, 2020		Jan. 1, 2020
Change in accounting principle, accounting standards update, immaterial effect		true		true
ASU 2018-15 [Member]
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted		true		true
Change in accounting principle, accounting standards update, adoption date		Jan. 1, 2020		Jan. 1, 2020
Change in accounting principle, accounting standards update, immaterial effect		true		true
ASU 2018-18 [Member]
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted		true		true
Change in accounting principle, accounting standards update, adoption date		Jan. 1, 2020		Jan. 1, 2020
Change in accounting principle, accounting standards update, immaterial effect		true		true
ASU 2019-12 [Member]
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted		true		true
Change in accounting principle, accounting standards update, adoption date		Apr. 1, 2020		Apr. 1, 2020
Change in accounting principle, accounting standards update, immaterial effect		true		true
Taxable Years 2020, 2021 and 2022 [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Business incentive tax credits to offset	$ 5,000,000
Taxable Years 2020, 2021 and 2022 [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Net operating carryforward loss for certain tax payers with taxable income	$ 1,000,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 57,648	$ 57,408
Restricted cash	1,567	992
Total cash, cash equivalents and restricted cash	$ 59,215	$ 58,400	$ 117,934	$ 53,175

Cash Equivalents and Marketab_3

Cash Equivalents and Marketable Securities - Schedule of Amortized Cost, Unrealized Gains and Losses and Fair Value of Cash Equivalent and Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Cash equivalents and marketable securities [Line Items]
Amortized Cost	$ 57,648	$ 57,408
Unrealized Losses		(6)
Amortized Cost	58,744	116,726
Unrealized Gains	5	30
Fair Value	58,749	116,750
Cash Equivalents [Member]
Cash equivalents and marketable securities [Line Items]
Amortized Cost	45,852	46,382
Fair Value	45,852	46,382
Cash Equivalents [Member] | Money Market Funds [Member]
Cash equivalents and marketable securities [Line Items]
Amortized Cost	43,852	42,133
Fair Value	43,852	42,133
Cash Equivalents [Member] | Corporate Debt Securities [Member]
Cash equivalents and marketable securities [Line Items]
Amortized Cost		2,500
Fair Value		2,500
Cash Equivalents [Member] | Commercial Paper [Member]
Cash equivalents and marketable securities [Line Items]
Amortized Cost	2,000	1,749
Fair Value	2,000	1,749
Short-Term Marketable Securities [Member]
Cash equivalents and marketable securities [Line Items]
Amortized Cost	12,892	70,344
Unrealized Gains	5	30
Unrealized Losses		(6)
Fair Value	12,897	70,368
Short-Term Marketable Securities [Member] | Corporate Debt Securities [Member]
Cash equivalents and marketable securities [Line Items]
Amortized Cost	4,390	38,237
Unrealized Gains	2	15
Unrealized Losses		(6)
Fair Value	4,392	38,246
Short-Term Marketable Securities [Member] | Commercial Paper [Member]
Cash equivalents and marketable securities [Line Items]
Amortized Cost	5,496	31,476
Unrealized Gains	3	15
Fair Value	5,499	31,491
Short-Term Marketable Securities [Member] | U.S. Government Treasuries [Member]
Cash equivalents and marketable securities [Line Items]
Amortized Cost	3,006
Fair Value	$ 3,006
Short-Term Marketable Securities [Member] | Certificates of Deposit [Member]
Cash equivalents and marketable securities [Line Items]
Amortized Cost		631
Fair Value		$ 631

Cash Equivalents and Marketab_4

Cash Equivalents and Marketable Securities - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2020USD ($)Security
Cash equivalents and marketable securities [Line Items]
Realized gains or losses on marketable securities, description	no material realized gains or losses
Number of individual securities in an unrealized loss position for 12 months or less | Security	0
Credit loss | $	$ 0
Maximum [Member]
Cash equivalents and marketable securities [Line Items]
Marketable securities contractual maturities period	1 year

Fair Value Measurements - Finan

Fair Value Measurements - Financial Assets and Liabilities Subject To Fair Value Measurements on a Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	$ 58,749	$ 116,750
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	46,858	42,133
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	11,891	74,617
Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	45,852	46,382
Cash Equivalents [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	43,852	42,133
Cash Equivalents [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	2,000	1,749
Cash Equivalents [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value		2,500
Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	43,852	42,133
Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	43,852	42,133
Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	2,000	4,249
Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	2,000	1,749
Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value		2,500
Short-Term Marketable Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	12,897	70,368
Short-Term Marketable Securities [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	5,499	31,491
Short-Term Marketable Securities [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	4,392	38,246
Short-Term Marketable Securities [Member] | U.S. Government Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	3,006
Short-Term Marketable Securities [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value		631
Short-Term Marketable Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	3,006
Short-Term Marketable Securities [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Government Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	3,006
Short-Term Marketable Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	9,891	70,368
Short-Term Marketable Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	5,499	31,491
Short-Term Marketable Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value	$ 4,392	38,246
Short-Term Marketable Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets fair value		$ 631

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value, Assets, Level 1 to Level 2 Transfers	$ 0	$ 0
Fair Value, Liabilities, Level 1 to Level 2 Transfers	0	0
Fair Value, Assets, Level 2 to Level 1 Transfers	0	0
Fair Value, Liabilities, Level 2 to Level 1 Transfers	$ 0	$ 0

Property and Equipment, Net - S

Property and Equipment, Net - Summary of Property and Equipment and Related Accumulated Depreciation and Amortization (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 38,566	$ 37,221
Less accumulated depreciation and amortization	(15,260)	(10,310)
Total property and equipment, net	23,306	26,911
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	971	863
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,054	2,007
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	21,873	21,025
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	13,640	11,102
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 28	$ 2,224

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 1,700	$ 1,200	$ 4,951	$ 3,303

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	1 Months Ended						3 Months Ended		9 Months Ended
	May 31, 2020USD ($)	Jul. 31, 2019USD ($)	Jan. 31, 2019USD ($)renewal_term	Sep. 30, 2018USD ($)	Mar. 31, 2017USD ($)ft²	Nov. 30, 2015USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)	May 31, 2019USD ($)	Jan. 01, 2019USD ($)	Sep. 30, 2017USD ($)	Feb. 28, 2016USD ($)
Commitments and Contingencies Disclosure [Line Items]
Operating lease cash security deposit							$ 1,218,000		$ 1,218,000		$ 1,201,000
Operating lease right-of-use assets							22,706,000		22,706,000		23,427,000
Lease liability							25,860,000		25,860,000
Research and Development Expense							22,050,000	$ 24,886,000	65,807,000	$ 59,314,000
Contract Research Organization [Member]
Commitments and Contingencies Disclosure [Line Items]
Maximum milestone payments												$ 34,800,000		$ 36,400,000
Research and Development Expense							0	$ 600,000	0	$ 800,000
Emeryville California [Member]
Commitments and Contingencies Disclosure [Line Items]
Operating leasing term			120 months			84 months
Operating lease cash security deposit						$ 50,000	600,000		600,000		$ 600,000
Operating leasing renewal option to extend lease			5 years			3 years
Operating lease for additional temporary space				12 months
Temporary space lease termination notice period				30 days
Operating leases number of renewal terms | renewal_term			2
Tenant improvement allowance			$ 4,000,000
Operating lease right-of-use assets							9,500,000		9,500,000
Lease liability							14,400,000		14,400,000
Operating lease termination date						2019-10
Adjustment to right-of-use assets and lease liability									1,800,000
Cambridge Massachusetts [Member]
Commitments and Contingencies Disclosure [Line Items]
Operating leasing term		24 months		24 months											67 months
Operating lease cash security deposit		$ 300,000		$ 300,000											$ 300,000
Operating leasing renewal option to extend lease	12 months	12 months													3 years
Tenant improvement allowance															$ 2,100,000
Operating lease right-of-use assets	$ 3,100,000
Lease liability	$ 3,100,000
Operating lease termination date	2022-08	2021-08		2020-08
Operating leases rent expense		$ 100,000		$ 100,000
Base rent paid for the year		3,200,000		$ 1,300,000
Annual base rent	$ 3,600,000	$ 3,400,000
Cambridge Massachusetts [Member] | Accounting Standards Update 2016-02 [Member]
Commitments and Contingencies Disclosure [Line Items]
Operating lease right-of-use assets													$ 900,000
Pleasanton [Member]
Commitments and Contingencies Disclosure [Line Items]
Operating leasing term												64 months
Operating leasing renewal option to extend lease					5 years
Tenant improvement allowance					$ 1,200,000							$ 100,000
Operating lease right-of-use assets							300,000		300,000
Lease liability							400,000		400,000
Net rentable area | ft²					42,620
Lease expiration date					Nov. 30, 2024
Letters of credit outstanding, amount					$ 1,000,000
Withdrawal from irrevocable letters of credit							$ 0		$ 0

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Components of Lease Costs (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Lease cost
Operating lease cost	$ 1,906	$ 1,653	$ 5,621	$ 4,491
Short-term lease cost		76	8	198
Total lease cost	$ 1,906	$ 1,729	$ 5,629	$ 4,689

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Supplemental Information Related to Leases (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash paid for amounts included in the measurement of lease liabilities (in thousands):
Operating cash flows from operating leases	$ 3,446	$ 1,939
New right-of-use assets obtained in exchange for lease obligations (in thousands):
Operating leases	$ 3,174	$ 1,447
Weighted average remaining lease term (years):
Operating leases	6 years 1 month 6 days	7 years 10 months 24 days
Weighted average discount rate:
Operating leases	9.00%	9.00%

Commitments and Contingencies_4

Commitments and Contingencies - Schedule of Minimum Annual Rental Payments Under Company's Operating Lease Agreements (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Operating Leases
2020 (remaining three months)	$ 1,951
2021	7,905
2022	5,836
2023	3,459
2024	3,459
Thereafter	12,531
Total minimum payments	35,141
Less: Amounts representing interest expense	(8,629)
Less: Amounts representing tenant improvement allowance	(652)
Present value of future minimum lease payments	25,860
Less: Current portion of lease liability	(5,069)	$ (2,505)
Noncurrent portion of lease liability	$ 20,791	$ 20,985

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Prepaid Expense And Other Assets Current [Abstract]
Prepaid insurance	$ 24	$ 1,252
Interest and other receivables	61	482
Prepaid research and development-related expenses	2,139	1,473
Restricted cash	575
Other	403	290
Total prepaid expenses and other current assets	$ 3,202	$ 3,497

Balance Sheet Components - Sc_2

Balance Sheet Components - Schedule of Deposits and Other Long-Term Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Other Assets Unclassified [Abstract]
Lease security deposit	$ 1,218	$ 1,201
Prepaid research and development-related expenses	539	585
Restricted cash	992	992
Total deposits and other long-term assets	$ 2,749	$ 2,778

Collaboration and License Agr_3

Collaboration and License Agreements - Additional Information (Detail) - USD ($)	1 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 31, 2018	Sep. 30, 2018	Aug. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Preferred stock shares issued				0		0		0
Purchase of common stock upon Company IPO						$ 10,473,000	$ 70,684,000
Collaboration and license revenue						(1,902,000)
Deferred revenue				$ 12,614,000		12,614,000		$ 14,516,000
Research and development				22,050,000	$ 24,886,000	65,807,000	59,314,000
Bluebird Bio Inc [Member] | Collaboration Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from non refundable upfront payment			$ 20,000,000
Proceeds from issuance of preferred stock			$ 10,000,000
Offering price per share	$ 15
Purchase of common stock upon Company IPO	$ 10,000,000
Number of common shares sold	666,667
Development, regulatory, and commercial milestones				1,200,000,000		$ 1,200,000,000
Collaboration agreement early termination notice period						120 days
Early termination reduction of future milestone and royalty payments, description						Additionally, all of bluebird’s payment obligations that have not yet accrued related to future milestone and royalty payments will be reduced by fifty percent for the remainder of the agreement term.
Revenue recognition contract start month year						2018-08
Revenue recognition contract end month year						2023-08
Collaboration and license revenue				800,000		$ 1,900,000
Deferred revenue				12,600,000		12,600,000
Receivables				0		0		0
Contract assets				0		0		0
Bluebird Bio Inc [Member] | Collaboration Agreement [Member] | Series C [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Preferred stock shares issued			768,115
Offering price per share			$ 13.04
Arbutus Biopharma Corporation and Protiva Biotherapeutics Inc [Member] | Collaboration Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum milestone consideration payable				$ 123,500,000		$ 123,500,000
Development milestone payment		$ 2,500,000
Royalty consideration as a percentage of sales of licensed product				3.50%		3.50%
Research and development				$ 0		$ 0
Milestone payment included in research and development expense								$ 3,000,000
Reimbursements expense materials and personnel costs					$ 200,000		$ 300,000

Collaboration and License Agr_4

Collaboration and License Agreements - Schedule of Changes in Deferred Revenue Balance (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Revenue From Contract With Customer [Abstract]
Balance at December 31, 2019	$ 14,516
Additions	0
Deductions	(1,902)
Balance at September 30, 2020	$ 12,614

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended		9 Months Ended		12 Months Ended
	Oct. 31, 2019	Apr. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Oct. 31, 2018
Subsidiary Sale Of Stock [Line Items]
Common stock, shares authorized			300,000,000		300,000,000
Common stock, par value			$ 0.0001		$ 0.0001
Preferred stock, shares authorized			10,000,000		10,000,000
Preferred stock, par value			$ 0.0001		$ 0.0001
Preferred stock, shares issued			0		0
Preferred stock, shares outstanding			0		0
Common stock, shares issued			37,763,266		36,332,956
Common stock, shares outstanding			37,763,266		36,332,956
Common stock voting rights			Holders of the Company’s common stock are entitled to one vote per share.
Net proceeds from issuance of stock			$ 10,473,000	$ 70,684,000
Common stock, preferred stock, debt securities, warrants and units covered in Registration Statement	$ 250,000,000
Percentage of gross proceeds as underwriter compensation	3.00%
Maximum offering expense agreed to be reimbursed	$ 50,000
Maximum [Member]
Subsidiary Sale Of Stock [Line Items]
Net proceeds from issuance of stock	$ 75,000,000
Common Stock [Member]
Subsidiary Sale Of Stock [Line Items]
Stock issued, number of shares			1,160,963	6,500,000
Amended and Restated Certificate of Incorporation [Member]
Subsidiary Sale Of Stock [Line Items]
Common stock, shares authorized						300,000,000
Common stock, par value						$ 0.0001
Preferred stock, shares authorized						10,000,000
Preferred stock, par value						$ 0.0001
Underwritten Public Offering [Member]
Subsidiary Sale Of Stock [Line Items]
Stock issued, price per share		$ 11.50
Net proceeds from issuance of stock		$ 69,700,000
Underwritten Public Offering [Member] | Common Stock [Member]
Subsidiary Sale Of Stock [Line Items]
Stock issued, number of shares		6,500,000
ATM Equity Offering Program [Member]
Subsidiary Sale Of Stock [Line Items]
Stock issued, number of shares			1,160,963		490,880
Net proceeds from issuance of stock			$ 9,800,000		$ 3,800,000
Payment of commissions on sale of shares			300,000		100,000
Payment of other offering costs on sale of shares			$ 100,000		$ 300,000

Stock Based Compensation - Addi

Stock Based Compensation - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for issuance	2,838,691		2,851,883
Intrinsic value of stock option awards exercised	$ 0.8	$ 2.8
Unrecognized compensation cost related to non-vested employee and consultant options	$ 13.9
Recognition period of unrecognized compensation cost related to non-vested employee and consultant	2 years 7 months 13 days
Fair value of shares vested	$ 5.1
2018 Award Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for issuance				92,815
Number of shares available for future issuance				2,690,000
Increase in shares available for issuance	4.00%
Share-based Compensation Arrangement by Share-based Payment Award, maximum number of shares authorized	45,000,000
Minimum percentage of outstanding shares held by individual	10.00%
Minimum percentage fair market value of share price	110.00%
Option vesting period	4 years
Share based compensation by shared based payment award, description	If an individual owns stock representing 10% or more of the outstanding shares, the price of each share shall be at least 110% of the fair market value, as determined by the board of directors. Options granted have a term of up to 10 years and generally vest over a 4-year period with a straight-line vesting.
2018 Award Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option granted expiration period	10 years

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Stock Options Activity (Detail) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares
Number of Shares Available for Issuance
Number of options beginning balance	2,851,883
Authorized	1,454,553
Granted	(1,800,700)
Exercised	0
Cancelled	332,955
Number of options ending balance	2,838,691	2,851,883
Number of Shares
Outstanding at beginning of period	3,165,961
Granted	1,800,700
Exercised	(142,239)
Cancelled	(332,955)
Outstanding at end of period	4,491,467	3,165,961
Options Outstanding, Number of Shares, Vested and exercisable	1,767,271
Options Outstanding, Number of Shares, Vested and expected to vest	4,136,041
Weighted-Average Exercise Price
Beginning Balance | $ / shares	$ 7.83
Granted | $ / shares	8.48
Exercised | $ / shares	1.31
Cancelled | $ / shares	10.74
Ending Balance | $ / shares	8.08	$ 7.83
Weighted-Average Exercise Price, Vested and exercisable | $ / shares	6.63
Weighted-Average Exercise Price, Vested and expected to vest | $ / shares	$ 7.99
Options Outstanding, Weighted-Average Remaining Contractual Term (in years)	8 years 4 months 13 days	8 years 5 months 12 days
Options Outstanding, Weighted-Average Remaining Contractual Term, Vested and exercisable (in years)	7 years 7 months 17 days
Options Outstanding, Weighted-Average Remaining Contractual Term, Vested and expected to vest (in years)	8 years 3 months 25 days
Options Outstanding, Aggregate Intrinsic Value | $	$ 1,188	$ 8,875
Options Outstanding, Aggregate Intrinsic Value, Vested and exercisable | $	1,051
Options Outstanding, Aggregate Intrinsic Value, Vested and expected to vest | $	$ 1,184

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock Based Compensation Expense	$ 1,837	$ 1,532	$ 5,415	$ 3,856
Research and Development Expense [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock Based Compensation Expense	1,133	965	3,387	2,522
General and Administrative Expense [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock Based Compensation Expense	$ 704	$ 567	$ 2,028	$ 1,334

Net Loss Per Common Share - Com

Net Loss Per Common Share - Computation of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net loss	$ (26,073)	$ (27,548)	$ (78,147)	$ (66,729)
Denominator:
Weighted-average common shares outstanding, basic and diluted	37,750,145	35,690,600	37,268,318	32,762,176
Net loss per share, basic and diluted	$ (0.69)	$ (0.77)	$ (2.10)	$ (2.04)

Net Loss Per Common Share - C_2

Net Loss Per Common Share - Computation of Potentially Anti-dilutive Securities (Detail) - shares	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities that were not included in the diluted per share calculations	4,624,285	3,209,915
Options Issued and Outstanding and ESPP Shares Issuable and Outstanding [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities that were not included in the diluted per share calculations	4,624,285	3,179,041
Early Exercised Common Stock Subject To Future Vesting [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities that were not included in the diluted per share calculations		30,874

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - Subsequent Event [Member] - Option and License and Development Agreement [Member]	Oct. 20, 2020USD ($)
Subsequent Event [Line Items]
Upfront payment	$ 2,000,000
Maximum [Member]
Subsequent Event [Line Items]
Aggregate upfront payment in specified development and regulatory milestone	21,000,000
Aggregate upfront payment in specified commercial milestone	$ 50,000,000