Allakos (ALLK) 10-K 1 Mar 22 2021 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Feb. 23, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Trading Symbol	ALLK
Entity Registrant Name	Allakos Inc.
Entity Central Index Key	0001564824
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 3,236.6
Entity Common Stock, Shares Outstanding		54,691,012
ICFR Auditor Attestation Flag	true
Entity File Number	001-38582
Entity Tax Identification Number	45-4798831
Entity Address, Address Line One	975 Island Drive
Entity Address, Address Line Two	Suite 201
Entity Address, City or Town	Redwood City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94065
City Area Code	650
Local Phone Number	597-5002
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, par value $0.001
Security Exchange Name	NASDAQ
Document Annual Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	DE
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP
Auditor Location	Redwood City, California
Documents Incorporated by Reference	Portions of the Registrant’s Definitive Proxy Statement relating to the registrant’s 2022 Annual Meeting of Shareholders are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such Definitive Proxy Statement will be filed with the Securities and Exchange Commission within 120 days after the end of the registrant’s 2021 fiscal year ended December 31, 2021.

BALANCE SHEETS

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 152,822	$ 207,177
Investments in marketable securities	271,416	451,820
Prepaid expenses and other current assets	27,343	10,270
Total current assets	451,581	669,267
Property and equipment, net	43,100	8,345
Operating lease right-of-use assets	31,707	39,731
Other long-term assets	8,436	2,275
Total assets	534,824	719,618
Current liabilities:
Accounts payable	13,692	13,960
Accrued expenses and other current liabilities	26,557	8,490
Total current liabilities	40,249	22,450
Operating lease liabilities, net of current portion	49,099	42,773
Total liabilities	89,348	65,223
Commitments and contingencies (Notes 6 and 7)
Stockholders’ equity:
Preferred stock, $0.001 par value per share; 20,000 shares authorized as of December 31, 2021 and 2020; no shares issued and outstanding as of December 31, 2021 and 2020	0	0
Common stock, $0.001 par value per share; 200,000 shares authorized as of December 31, 2021 and 2020; 54,622 and 53,081 shares issued and outstanding as of December 31, 2021 and 2020, respectively	54	53
Additional paid-in capital	1,058,399	997,298
Accumulated other comprehensive gain (loss)	(153)	8
Accumulated deficit	(612,824)	(342,964)
Total stockholders’ equity	445,476	654,395
Total liabilities and stockholders’ equity	$ 534,824	$ 719,618

BALANCE SHEETS (Parenthetical)

BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	54,622,363	53,081,000
Common stock, shares outstanding	54,622,363	53,081,000

STATEMENTS OF OPERATIONS AND CO

STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating expenses
Research and development	$ 196,328	$ 105,533	$ 61,858
General and administrative	75,147	51,524	29,560
Total operating expenses	271,475	157,057	91,418
Loss from operations	(271,475)	(157,057)	(91,418)
Interest income	377	4,313	6,201
Other income (expense), net	1,238	(736)	(155)
Net loss	(269,860)	(153,480)	(85,372)
Unrealized gain (loss) on marketable securities	(161)	(129)	152
Comprehensive loss	$ (270,021)	$ (153,609)	$ (85,220)
Net loss per common share:
Basic and diluted	$ (5.01)	$ (3.10)	$ (1.89)
Weighted-average number of common shares outstanding:
Basic and diluted	53,832	49,492	45,191

STATEMENTS OF STOCKHOLDERS' EQU

STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit
Balance, Shares at Dec. 31, 2018		42,117
Balance at Dec. 31, 2018	$ 183,994,000	$ 42,000	$ 288,079,000	$ (15,000)	$ (104,112,000)
Stock-based compensation expense	15,764,000	0	15,764,000	0	0
Issuance of common stock upon exercise of stock options	2,448,000	$ 1,000	2,447,000	0	0
Issuance of common stock upon exercise of stock options, Shares		1,250
Issuance of common stock upon 2018 ESPP purchase	1,190,000	$ 0	1,190,000	0	0
Issuance of common stock upon 2018 ESPP purchase, Shares		74
Issuance of common stock upon follow-on offering, net of offering costs	377,525,000	$ 5,000	377,520,000	0	0
Issuance of common stock upon follow-on offering, net of offering costs, shares		5,227
Vesting of restricted common stock	20,000	$ 0	20,000	0	0
Unrealized gain on marketable securities, net of tax	152,000	0	0	152,000	0
Unrealized gain (loss) on marketable securities	152,000
Net loss	(85,372,000)	$ 0	0	0	(85,372,000)
Balance, Shares at Dec. 31, 2019		48,668
Balance at Dec. 31, 2019	495,721,000	$ 48,000	685,020,000	137,000	(189,484,000)
Stock-based compensation expense	33,446,000	0	33,446,000	0	0
Issuance of common stock upon exercise of stock options	5,696,000	$ 1,000	5,695,000	0	0
Issuance of common stock upon exercise of stock options, Shares		700
Issuance of common stock upon 2018 ESPP purchase	1,454,000	$ 0	1,454,000	0	0
Issuance of common stock upon 2018 ESPP purchase, Shares		70
Issuance of common stock upon follow-on offering, net of offering costs	271,687,000	$ 4,000	271,683,000
Issuance of common stock upon follow-on offering, net of offering costs, shares		3,506
Issuance of common stock upon vesting of restricted stock units	0	$ 0	0	0	0
Issuance of common stock upon vesting of restricted stock units, Shares		137
Unrealized gain (loss) on marketable securities	(129,000)	$ 0	0	(129,000)	0
Net loss	(153,480,000)	$ 0	0	0	(153,480,000)
Balance, Shares at Dec. 31, 2020		53,081
Balance at Dec. 31, 2020	654,395,000	$ 53,000	997,298,000	8,000	(342,964,000)
Stock-based compensation expense	50,842,000	0	50,842,000	0	0
Issuance of common stock upon exercise of stock options	8,492,000	$ 1,000	8,491,000	0	0
Issuance of common stock upon exercise of stock options, Shares		1,227
Issuance of common stock upon 2018 ESPP purchase	1,768,000	$ 0	1,768,000	0	0
Issuance of common stock upon 2018 ESPP purchase, Shares		29
Issuance of common stock upon vesting of restricted stock units	0	$ 0	0	0	0
Issuance of common stock upon vesting of restricted stock units, Shares		285
Unrealized gain (loss) on marketable securities	(161,000)	$ 0	0	(161,000)	0
Net loss	(269,860,000)	$ 0	0	0	(269,860,000)
Balance, Shares at Dec. 31, 2021		54,622
Balance at Dec. 31, 2021	$ 445,476,000	$ 54,000	$ 1,058,399,000	$ (153,000)	$ (612,824,000)

STATEMENTS OF STOCKHOLDERS' E_2

STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Common Stock
Stock issuance costs	$ 15,813	$ 24,975

STATEMENTS OF CASH FLOWS

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities
Net loss	$ (269,860)	$ (153,480)	$ (85,372)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	50,842	33,446	15,764
Net amortization of premiums and discounts on marketable securities	3,389	2,358	(2,664)
Depreciation and amortization	2,310	1,545	1,508
Noncash lease expense	2,570	794	275
Gain on lease modification	(1,873)	0	0
Loss on disposal of property and equipment	46	0	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(16,678)	(7,601)	463
Other long-term assets	(6,161)	0	(564)
Accounts payable	(232)	7,644	3,571
Accrued expenses and other current liabilities	13,594	900	4,077
Operating lease liabilities, net of current portion	14,200	470	(70)
Net cash used in operating activities	(207,853)	(113,924)	(63,012)
Cash flows from investing activities
Purchases of marketable securities	(387,541)	(542,273)	(541,701)
Proceeds from maturities of marketable securities	564,000	546,800	230,500
Purchases of property and equipment	(33,221)	(630)	(770)
Net cash provided by (used in) investing activities	143,238	3,897	(311,971)
Cash flows from financing activities
Proceeds from issuance of common stock, net of issuance costs	0	271,687	377,525
Proceeds from exercise of stock options, net of repurchases	8,492	5,696	2,448
Proceeds from issuance of common stock under 2018 ESPP	1,768	1,454	1,190
Net cash provided by financing activities	10,260	278,837	381,163
Net increase (decrease) in cash, cash equivalents and restricted cash	(54,355)	168,810	6,180
Cash, cash equivalents and restricted cash, beginning of period	209,452	40,642	34,462
Cash, cash equivalents and restricted cash, end of period	155,097	209,452	40,642
Supplemental disclosures
Right-of-use assets obtained in exchange for lease obligations	200	34,750	6,050
Vesting of restricted common stock subject to repurchase	0	0	20
Property and equipment purchased but unpaid	$ 3,890	$ 353	$ 0

Organization and Business

Organization and Business	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Business	1. Organization and Business Allakos Inc. (“Allakos” or the “Company”) was incorporated in the state of Delaware in March 2012. Allakos is a clinical stage biopharmaceutical company focused on the development of lirentelimab for the treatment of eosinophil and mast cell related diseases. The Company’s primary activities to date have included establishing its facilities, recruiting personnel, conducting research and development of its product candidates and raising capital. The Company’s operations are located in Redwood City, California. Liquidity Matters Since inception, the Company has incurred net losses and negative cash flows from operations. During the year ended December 31, 2021, the Company incurred a net loss of $ 269.9 million and used $ 207.9 million of cash in operations. As of December 31, 2021, the Company had an accumulated deficit of $ 612.8 million and does not expect to experience positive cash flows from operating activities in the foreseeable future. The Company has financed its operations to date primarily through the sale of common stock. Management expects to incur additional operating losses in the future as the Company continues to further develop, seek regulatory approval for and, if approved, commence commercialization of its product candidates. Due to the clinical study results released in December 2021, our Board of Directors approved in February 2022 plans to reduce our contractual commitments with Lonza and a reorganization plan (the “Reorganization Plan”) to reduce operating costs and better align our workforce with the clinical development plans of our business. Refer to Note 12 “Subsequent Events” for additional information. The Company had $ 424.2 million of cash, cash equivalents and marketable securities at December 31, 2021. Management believes that this amount is sufficient to fund the Company’s operations for at least the next 12 months from the issuance date of these financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The financial statements have been prepared in accordance with United States generally accepted accounting principles (“U.S. GAAP”). The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts and disclosures reported in the financial statements and accompanying notes. Use of Estimates Management uses significant judgment when making estimates related to common stock valuation and related stock-based compensation expense, accrued research and development expense, and lease related assets and liabilities. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results could differ from those estimates under different assumptions or conditions, and those differences could be material to the financial position and results of operations. Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to credit risk principally consist of cash, cash equivalents and marketable securities. These financial instruments are held in accounts at a single financial institution that management believes possesses high credit quality. Amounts on deposit with this financial institution have and will continue to exceed federally-insured limits. The Company has not experienced any losses on its cash deposits. Additionally, the Company’s investment policy limits its investments to certain types of securities issued by the United States government and its agencies. The Company is subject to a number of risks similar to that of other early-stage biopharmaceutical companies, including, but not limited to, the need to obtain adequate additional funding, possible failure of current or future clinical trials, its reliance on third-parties to conduct its clinical trials, the need to obtain regulatory and marketing approvals for its product candidates, competitive developments, the need to successfully commercialize and gain market acceptance of the Company’s product candidates, its right to develop and commercialize its product candidates pursuant to the terms and conditions of the licenses granted to the Company, protection of proprietary technology, the ability to make milestone, royalty or other payments due under licensing agreements, and the need to secure and maintain adequate manufacturing arrangements with third-parties. If the Company does not successfully commercialize or partner its product candidates, it will be unable to generate product revenue or achieve profitability. Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company’s balance sheets and which, in aggregate, represent the amounts reported in the statements of cash flows (in thousands): December 31, 2021 2020 2019 Cash and cash equivalents $ 152,822 $ 207,177 $ 38,367 Restricted cash 2,275 2,275 2,275 Total $ 155,097 $ 209,452 $ 40,642 Restricted cash at December 31, 2021 represents $ 2.3 million of security deposits for the lease of the Company’s facilities in Redwood City, California and San Carlos, California. Both security deposits are in the form of letters of credit secured by restricted cash. Restricted cash amounts are included within other long-term assets on the Company’s balance sheets. Marketable Securities The Company invests in marketable securities, primarily securities issued by the United States government and its agencies. The Company’s marketable securities are considered available-for-sale and are classified as current assets even when the stated maturities of the underlying securities exceed one year from the date of the current balance sheet being reported. This classification reflects management’s ability and intent to utilize proceeds from the sale of such investments to fund ongoing operations. Unrealized gains and losses are excluded from earnings and are reported as a component of accumulated other comprehensive gain. The cost of securities sold is determined using the specific-identification method. Interest earned and adjustments for the amortization of premiums and discounts on investments are included in interest income, net, on the statements of operations and comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on investments in marketable securities are included in other expense, net, on the statements of operations and comprehensive loss. Fair Value Measurements The Company accounts for fair value of its financial instruments in accordance with Financial Accounting Standards Board (the “FASB”) Accounting Standards Codification (“ASC”) Topic No. 820, Fair Value Measurements (“ASC 820”). ASC 820 establishes a common definition for fair value, establishes a framework for measuring fair value and expands disclosures about such fair value measurements. Additionally, ASC 820 defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The Company measures fair value based on a three-level hierarchy of inputs, of which the first two are considered observable and the last unobservable. Unobservable inputs reflect the Company’s own assumptions about current market conditions. The three-level hierarchy of inputs is as follows: Level 1 – Quoted prices in active markets for identical assets or liabilities. Level 2 – Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 – Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of assets or liabilities. To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The carrying amounts reflected in the Company’s balance sheets for cash and cash equivalents, prepaid expenses and other current assets, other long-term assets, accounts payable, and accrued expenses and other current liabilities approximate fair value, due to their short-term nature. The Company’s investments in marketable securities are measured at fair value in accordance with the levels above. Property and Equipment, Net Property and equipment are stated at cost, net of accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the assets. Generally, the useful lives of laboratory equipment are five years , furniture and office equipment are three to five years , and leasehold improvements property and equipment are the shorter of the remaining lease term or the estimated life of the assets . Any resulting gains or losses on dispositions of property and equipment are included as a component of other income (expense), net, within the Company’s statements of operations and comprehensive loss. Repair and maintenance costs that do not significantly add value to the property and equipment, or prolong its life, are charged to operating expense as incurred. Operating Leases The Company accounts for its leases in accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 842, “Leases” (“ASC 842”). Right-of-use assets represent the Company’s right to use an underlying asset over the lease term and include any lease payments made prior to the lease commencement date and are reduced by lease incentives. Lease liabilities represent the present value of the total lease payments over the lease term, calculated using the Company’s incremental borrowing rate. In determining the Company’s incremental borrowing rate, consideration is given to the term of the lease and the Company’s credit risk. The Company recognizes options to extend a lease when it is reasonably certain that it will exercise such extension. The Company does not recognize options to terminate a lease when it is reasonably certain that it will not exercise such early termination options. Lease expense is recognized on a straight-line basis over the expected lease term. Accrued Research and Development Expense Service agreements with contract development and manufacturing organizations (“CDMOs”), clinical contract research organizations (“CROs”) and clinical investigative sites comprise a significant component of the Company’s research and development activities. External costs for these vendors are recognized as the services are incurred. The Company accrues for expenses resulting from obligations under agreements with its third-parties for which the timing of payments does not match the periods over which the materials or services are provided to the Company. Accruals are recorded based on estimates of services received and efforts expended pursuant to agreements established with CDMOs, clinical CROs, clinical investigative sites and other outside service providers. These estimates are typically based on contracted amounts applied to the proportion of work performed and determined through analysis with internal personnel and external service providers as to the progress or stage of completion of the services. The Company makes judgements and estimates in determining the accrual balance in each reporting period. In the event advance payments are made to a CDMO, clinical CRO, clinical investigative site or other outside service provider, the payments are recorded within prepaid expenses and other current assets and subsequently recognized as research and development expense when the associated services have been performed. As actual costs become known, the Company adjusts its liabilities and assets. Inputs, such as the extent of services received and the duration of services to be performed, may vary from the Company’s estimates, which will result in adjustments to research and development expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect the Company’s results of operations. The Company’s historical estimates have not been materially different from actual amounts recorded. Research and Development Expense Research and development costs are expensed as incurred. Research and development costs include, among others, consulting costs, salaries, benefits, travel, stock-based compensation, laboratory supplies and other non-capital equipment utilized for in-house research, allocation of facilities and overhead costs and external costs paid to third-parties that conduct research and development activities on the Company’s behalf. Amounts incurred in connection with license agreements, including milestone payments, are also included in research and development expense. Advance payments for goods or services to be rendered in the future for use in research and development activities are deferred and included in prepaid expenses and other current assets. The deferred amounts are expensed as the related goods are delivered or the services are performed. Segments Operating segments are defined as components of an entity about which separate discrete information is available for evaluation by the chief operating decision maker or decision-making group, in deciding how to allocate resources and in assessing performance. The Company’s chief operating decision maker, its Chief Executive Officer, views its operations and manages its business in one operating segment operating exclusively in the United States. Patent Costs The Company expenses patent application and related legal costs as incurred and classifies such costs as general and administrative expenses in the statements of operations and comprehensive loss. Stock-Based Compensation The Company accounts for its stock-based compensation in accordance with FASB ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all stock-based awards issued to employees and nonemployees to be recognized as expense in the statements of operations and comprehensive loss based on their grant date fair values. Stock-based awards issued to nonemployee consultants are accounted for based on the fair value of services to be received or of the intrinsic value of equity instruments to be issued, whichever is more reliably measured. The measurement date for awards issued to nonemployee consultants is the date of grant. For purposes of determining the estimated fair value of stock options granted to employees and nonemployees, the Company uses the Black-Scholes option pricing model. The Black-Scholes option pricing model requires the input of certain assumptions that involve judgment, for which changes can materially affect the resulting estimates of fair value. The assumptions used to determine the fair value of stock options granted were as follows: Expected volatility – As there is insufficient trading history for the Company’s common stock, the Company has based its computation of expected volatility on the historical volatility of a representative group of public companies with similar characteristics to the Company, including stage of product development and life science industry focus. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. Expected term – The Company determines the expected term in accordance with the “simplified method” described by SEC Staff Accounting Bulletin No. 107, Share-Based Payment , as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. Risk-free interest rate – The Company bases the risk-free interest rate on United States Treasury securities with terms consistent to the expected term of the stock option being valued. Expected dividends – The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. The fair value of restricted stock units (“RSUs”) is determined using the quoted market price of the Company’s common stock on the date of grant. The Company uses historical data to estimate pre-vesting forfeitures and records stock-based compensation expense only for those awards expected to vest. To the extent that actual forfeitures differ from estimates, the difference is recorded as a cumulative adjustment in the period the estimate are revised. The Company expenses the fair value of its stock-based compensation awards to employees and nonemployees on a straight-line basis over the requisite service period, which is generally the vesting period. The Company recognizes the stock-based compensation expense related to performance-based stock awards or performance-based RSUs ("PSUs") if the performance targets are deemed probable of being achieved. The vesting of PSUs requires that certain performance conditions are achieved during the performance period and is subject to the employee’s continued service requirements. Income Taxes We account for income taxes under the asset and liability method. Current income tax expense or benefit represents the amount of income taxes we expect to pay or have refunded in the current year. Our deferred income tax assets and liabilities are determined based on differences between financial statement reporting and tax basis accounting of assets and liabilities and net operating loss and credit carryforwards, which we measure using the enacted tax rates and laws that will be in effect when such items are expected to reverse. We reduce deferred income tax assets, as necessary, by applying a valuation allowance to the extent that we determined it is more likely than not that some or all of our tax benefits will not be realized. We account for uncertain tax positions in accordance with ASC 740-10, Accounting for Uncertainty in Income Taxes. We assess all material positions reflected in our income tax returns, including all significant uncertain positions, for all tax years that are subject to assessment or challenge by relevant taxing authorities. Upon determining the sustainability of our positions, we measure the largest amount of benefit possessing greater than fifty percent likelihood of being realized upon ultimate settlement. We reassess such positions at each balance sheet date to determine whether any factors underlying the sustainability assertion have changed and whether or not the amount of the recognized tax benefit is still appropriate. Comprehensive Loss Comprehensive loss is defined as the change in stockholders’ equity during a period from transactions and other events and circumstances from non-owner sources. The difference between net loss and comprehensive loss for the years ended December 31, 2021, 2020 and 2019 are a result of unrealized gains and losses on the Company’s investments in marketable securities included in current assets on the balance sheets. Net Loss per Share The Company calculates basic net loss per share by dividing the net loss attributable to common stockholders by the weighted-average shares of common stock outstanding during the period. The Company calculates diluted net loss per share after giving consideration to all potentially dilutive securities outstanding during the period using the treasury-stock and if-converted methods, except where the effect of including such securities would be anti-dilutive. Because the Company has reported net losses since inception, the effect from potentially dilutive securities would have been anti-dilutive and therefore has been excluded from the calculation of diluted net loss per share. Basic and diluted net loss per share was calculated as follows (in thousands, except per share data): Year Ended December 31, 2021 2020 2019 Numerator: Net loss $ ( 269,860 ) $ ( 153,480 ) $ ( 85,372 ) Denominator: Weighted-average shares of common stock 53,832 49,492 45,191 Net loss per share, basic and diluted $ ( 5.01 ) $ ( 3.10 ) $ ( 1.89 ) The following table sets forth the potentially dilutive securities that have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect for the periods indicated (in thousands): Year Ended December 31, 2021 2020 2019 Options to purchase common stock 5,530 6,616 7,148 Unvested restricted stock units 1,506 1,161 542 Unvested performance stock unit 113 — — Shares issuable under employee stock purchase plans 118 14 31 Total 7,267 7,791 7,721 Foreign Currency Transactions The Company is party to multiple contract manufacturing and clinical research agreements for which services to be performed are denominated in foreign currencies other than the United States Dollar. The Company records gains and losses attributable to fluctuations in foreign currencies as a component of other income (expense), net, on the statements of operations and comprehensive loss. Recently Issued and Adopted Accounting Pronouncements The Company has reviewed recently issued accounting pronouncements and concluded they are either not applicable to the business or that no material effect is expected on the Financial Statements as a result of future adoption.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The Company measures and reports certain financial instruments as assets and liabilities at fair value on a recurring basis. The Company’s financial assets measured at fair value on a recurring basis were as follows (in thousands): December 31, 2021 Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 150,781 $ — $ — $ 150,781 Total cash equivalents 150,781 — — 150,781 Short-term marketable securities U.S. treasuries 271,416 — — 271,416 Total short-term marketable securities 271,416 — — 271,416 Total cash equivalents and short-term $ 422,197 $ — $ — $ 422,197 December 31, 2020 Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 205,408 $ — $ — $ 205,408 Total cash equivalents 205,408 — — 205,408 Short-term marketable securities U.S. treasuries 451,820 — — 451,820 Total short-term marketable securities 451,820 — — 451,820 Total cash equivalents and short-term $ 657,228 $ — $ — $ 657,228 The Company evaluates transfers between levels at the end of each reporting period. There were no transfers of assets or liabilities between levels during the years ended December 31, 2021 and 2020.

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities All marketable securities were considered available-for-sale at December 31, 2021 and 2020. The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s marketable securities by major security type are summarized in the table below (in thousands): December 31, 2021 Amortized Unrealized Unrealized Fair Available-for-sale securities U.S. treasuries classified as investments $ 271,570 $ 2 $ ( 156 ) $ 271,416 Total $ 271,570 $ 2 $ ( 156 ) $ 271,416 December 31, 2020 Amortized Unrealized Unrealized Fair Available-for-sale securities U.S. treasuries classified as investments $ 451,812 $ 26 $ ( 18 ) $ 451,820 Total $ 451,812 $ 26 $ ( 18 ) $ 451,820 The amortized cost of available-for-sale securities is adjusted for amortization of premiums and accretion of discounts to maturity. As of December 31, 2021 and 2020, the aggregate fair value of securities held by the Company in an unrealized loss position for less than twelve months was $ 241.4 million and $ 91.4 million, respectively. All of these securities had remaining maturities of less than one year . The Company has the intent and ability to hold such securities until recovery and has determined that there has been no material change to their credit risk. As a result, the Company determined it did not hold any investments with a credit loss at December 31, 2021 and 2020. There were no material realized gains or losses recognized on the sale or maturity of available-for-sale securities during the years ended December 31, 2021, 2020 and 2019, and as a result, there were no material reclassifications out of accumulated other comprehensive gain (loss) for the same periods.

Balance Sheet Components and Su

Balance Sheet Components and Supplemental Disclosures	12 Months Ended
	Dec. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components and Supplemental Disclosures	5. Balance Sheet Components and Supplemental Disclosures Property and Equipment, Net Property and equipment, net, consisted of the following (in thousands): December 31, 2021 2020 Laboratory equipment $ 4,676 $ 4,236 Furniture and office equipment 1,947 1,784 Leasehold improvements 4,581 4,581 Construction-in-progress 37,704 1,325 48,908 11,926 Less accumulated depreciation ( 5,808 ) ( 3,581 ) Property and equipment, net $ 43,100 $ 8,345 Depreciation and amortization expense for the years ended December 31, 2021, 2020 and 2019 was $ 2.3 million, $ 1.5 million and $ 1.5 million, respectively. The increase in construction-in-progress assets in 2021 primarily relate to tenant improvements at the Company’s new corporate headquarters and is expected to be completed and put into service during the first quarter of 2022. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, 2021 2020 Accrued contract research and development expense $ 16,215 $ 4,697 Accrued compensation and benefits expense 3,172 3,214 Current portion of operating lease liabilities 2,316 492 Other current liabilities 4,854 87 Total $ 26,557 $ 8,490

Leases

Leases	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Leases	6. Leases Operating Leases The Company’s lease obligations primarily relate to leased office and laboratory space under noncancelable operating leases. In accordance with ASC 842, the Company has performed an evaluation of its other contracts with vendors and has determined that, except for the leases described below, none of its other contracts contain a lease. 2018 Redwood City Lease In January 2018 , the Company entered into an operating lease agreement for approximately 25,000 square feet of office and laboratory space in Redwood City, California (the “2018 Redwood City Lease”). The contractual term of the 2018 Redwood City Lease was 10.75 years beginning from the substantial completion and delivery of the premises, which occurred in November 2018, and originally terminating in July 2029 . The 2018 Redwood City Lease includes monthly base rent amounts escalating over the term of the lease. In addition, the lessor provided for a tenant improvement allowance ("TIA") up to $ 1.4 million, which was fully utilized. The TIA was recorded as leasehold improvements, with offsetting adjustments recorded to the associated operating lease right of use asset included on the balance sheets as of December 31, 2021 and 2020. In November 2021 , the Company entered into a lease termination agreement (the “Termination Agreement”) with respect to the 2018 Redwood City Lease. Pursuant to the Termination Agreement, the 2018 Redwood City Lease will be terminated effective April 30, 2022 . The Company accounted for this change in lease term as a modification of the original lease. As a result of the modification, the operating right-of-use asset and lease liability were remeasured. As of December 31, 2021, the remaining lease liability of $ 0.6 million was recognized on the balance sheet. There is no remaining right-of-use asset as of December 31, 2021. The Company recognized $ 1.9 million as gain on lease modifications in the fourth quarter of 2021, which is included in other income (expense), net on the statements of operations and comprehensive loss. In connection with the early termination and upon satisfaction of certain conditions including the delivery of certain equipment and other assets related to the building, the landlord agreed to pay to the Company $ 1.1 million. 2019 San Carlos Lease In December 2019 , the Company entered into an additional operating lease agreement for approximately 98,000 square feet of office and laboratory space in San Carlos, California (the “2019 San Carlos Lease”). The contractual term of the 2019 San Carlos Lease is 10.25 years from August 2021 until October 2031 . The 2019 San Carlos Lease provides rent abatements and includes a one-time option to extend the lease term for five years . This option to extend the lease term was not determined to be reasonably certain and therefore has not been included in the Company’s calculation of the associated operating lease liability under ASC 842. The 2019 San Carlos Lease includes monthly base rent amounts escalating over the term of the lease. In addition, the lessor provided for a TIA of up to $ 14.7 million, which is expected to be fully utilized and are recorded in lease obligations. The Company utilized its incremental borrowing rate to calculate the present value of the lease payments for the 2019 San Carlos Lease based on information available on November 1, 2020, the lease commencement date for accounting purposes, which was the date the Company was deemed to have obtained control of the premises. Calculation of the operating lease liability also included estimated future TIA reimbursements that had not yet been received as of the lease commencement date. TIA reimbursements received subsequent to lease commencement date are recorded as reductions to the operating lease liability. Classification of Operating Leases The 2018 Redwood City Lease and the 2019 San Carlos Lease required security deposits of $ 0.8 million and $ 1.5 million, respectively, which the Company satisfied by establishing letters of credit secured by restricted cash. Restricted cash related to the Company’s lease agreements are recorded in other long-term assets on the Company’s balance sheets. Classification of the Company’s operating lease liabilities included in the Company’s balance sheets at December 31, 2021 and 2020 was as follows (in thousands): December 31, 2021 2020 Operating lease liabilities Current portion included in accrued expenses and $ 2,316 $ 492 Operating lease liabilities, net of current portion 49,099 42,773 Total operating lease liabilities $ 51,415 $ 43,265 The components of lease costs, which are included in operating expenses in the Company’s statements of operations and comprehensive loss were as follows (in thousands): Year ended December 31, 2021 2020 Operating lease costs $ 6,676 $ 2,087 Variable costs 1,663 364 Total lease costs $ 8,339 $ 2,451 Variable costs included in the table above represent amounts the Company pays related to property taxes, insurance, maintenance and repair costs. Cash paid for amounts included in the measurement of the Company’s operating lease liabilities and presented within cash used in operating activities in the statements of cash flows was $ 1.7 million, $ 1.2 million and $ 0.5 million for the years ended December 31, 2021, 2020 and 2019. Cash received for amounts related to tenant improvement allowances from lessors was $ 12.9 million, $ 0.2 million and $ 0 million for the years ended December 31, 2021, 2020 and 2019, respectively. Operating Lease Obligations Future lease payments required under operating leases included on the Company’s balance sheet at December 31, 2021 are as follows (in thousands): Fiscal Year Ending December 31, 2022 $ 7,445 2023 7,061 2024 7,273 2025 7,492 2026 7,716 Thereafter 40,677 Total future lease payments 77,664 Less: Present value adjustment 25,276 Present value of future lease incentives 973 Operating lease liabilities $ 51,415 Operating lease liabilities are based on the net present value of the remaining lease payments over the remaining lease term. In determining the present value of lease payments, the Company used its incremental borrowing rate based on the information available at the lease commencement date. As of December 31, 2021, the weighted-average remaining lease term of the Company’s leases was 9.8 years and the weighted-average discount rate used to determine the operating lease liabilities included on the balance sheet was 8.5 %. As of December 31, 2021, the Company has not been party to any lease agreements containing material residual value guarantees or material restrictive covenants.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Loss Contingency [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies As of December 31, 2021, the Company had $ 284.8 million noncancelable purchase commitments under various master service agreements primarily relating to our contract development and manufacturing organizations (“CDMOs”). Refer to Note 12 “Subsequent Events” for additional details. Additionally, we enter into contracts in the normal course of business with clinical contract research organizations (“CROs”), clinical investigative sites and other counterparties assisting with our preclinical studies and clinical trials. Such contracts are generally cancellable, with varying provisions regarding termination. In the event of a contract being terminated, we would only be obligated for services received as of the effective date of the termination, along with cancellation fees, as applicable. In-Licensing Agreements The Company has entered into exclusive and non-exclusive, royalty bearing license agreements with third-parties for certain intellectual property. Under the terms of the license agreements, the Company is obligated to pay milestone payments upon the achievement of specified clinical, regulatory and commercial milestones. Research and development expense associated with the Company’s milestone payments are recognized when such milestone has been achieved. Actual amounts due under the license agreements will vary depending on factors including, but not limited to, the number of products developed and the Company’s ability to further develop and commercialize the licensed products. The Company is also subject to future royalty payments based on sales of the licensed products. In-licensing payments to third-parties for milestones are recognized as research and development expense in the period of achievement. The Company did no t recognize any milestone expense for the years ended December 31, 2021 and 2019. The Company recognized $ 3.4 million of milestone expense for the year ended December 31, 2020 related to development milestones associated with the first patient dosed in the Company’s Phase 3 study with lirentelimab. Milestone payments are not creditable against royalties. As of December 31, 2021, the Company has no t incurred any royalty liabilities related to its license agreements, as product sales have not yet commenced. Exclusive License Agreement with The Johns Hopkins University In December 2013, the Company entered into a license agreement with The Johns Hopkins University (“JHU”) for a worldwide exclusive license to develop, use, manufacture and commercialize covered product candidates including lirentelimab, which was amended in September 30, 2016. Under the terms of the agreement, the Company has made upfront and milestone payments of $ 0.7 million through December 31, 2021 and may be required to make aggregate additional milestone payments of up to $ 1.8 million. The Company also issued 88,887 shares of common stock as consideration under the JHU license agreement. In addition to milestone payments, the Company is also subject to single-digit royalties to JHU based on future net sales of each licensed therapeutic product candidate by the Company and its affiliates and sublicensees, with up to a low six-digit dollar minimum annual royalty payment. Non-exclusive License Agreement with BioWa Inc. and Lonza Sales AG In October 2013, the Company entered into a tripartite agreement with BioWa Inc. (“BioWa”), and Lonza Sales AG (“Lonza”), for the non-exclusive worldwide license to develop and commercialize product candidates including lirentelimab that are manufactured using a technology jointly developed and owned by BioWa and Lonza. Under the terms of the agreement, the Company has made milestone payments of $ 3.4 million through December 31, 2020 and may be required to make aggregate additional milestone payments of up to $ 38.0 million. In addition to milestone payments, the Company is also subject to minimum annual commercial license fees of $ 40,000 per year to BioWa until such time as BioWa receives royalty payments, as well as low single-digit royalties to BioWa and to Lonza. Royalties are based on future net sales by the Company and its affiliates and sublicensees. Indemnification Agreements The Company has entered into indemnification agreements with certain directors and officers that require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. To date, no such matters have arisen and the Company does not believe that the outcome of any claims under indemnification arrangements will have a material adverse effect on its financial positions, results of operations or cash flows. Accordingly, the Company has not recorded a liability related to such indemnifications at December 31, 2021. Legal Contingencies On March 10, 2020, a putative securities class action complaint captioned Kim v. Allakos et al., No. 20-cv-01720 (N.D. Cal.) was filed in the United States District Court for the Northern District of California against the Company, its Chief Executive Officer, Dr. Robert Alexander, and its former Chief Financial Officer, Mr. Leo Redmond. The complaint asserts claims for violations of Sections 10(b) and 20(a) of the Securities Exchange Act of 1934 and Rule 10b-5 promulgated thereunder and seeks damages based on alleged material misrepresentations and omissions concerning its Phase 2 clinical trials of lirentelimab. The proposed class period is August 5, 2019, through December 17, 2019, inclusive. On August 28, 2020, the plaintiff filed an amended complaint, adding as defendants Adam Tomasi, the Company’s President and Chief Operating Officer, and Henrik Rasmussen, the Company’s former Chief Medical Officer. Given the early stage of this litigation matter, the Company cannot reasonably estimate a potential future loss or a range of potential future losses, if any, and has not recorded a contingent liability accrual as of December 31, 2021.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2021
Stockholders' Equity Note [Abstract]
Stockholders' Equity	8. Stockholders’ Equity The Company’s amended and restated certificate of incorporation filed on July 23, 2018 authorizes the issuance of a total of 220,000,000 shares of stock. Of these shares, 200,000,000 are designated as common stock and 20,000,000 are designated as preferred stock. Common Stock There were 54,622,363 shares of common stock issued and outstanding at December 31, 2021. Common shares reserved for future issuance upon the exercise, issuance or conversion of the respective equity instruments are as follows (in thousands): December 31, 2021 2020 Exercise of common stock options outstanding 5,530 6,616 Shares reserved for issuance under equity incentive plans 7,154 5,271 Vesting of restricted stock units 1,506 1,161 Shares reserved for issuance under employee stock purchase plans 1,766 1,265 Total 15,956 14,313 Common stockholders are entitled to dividends if and when declared by the Board of Directors subject to the prior rights of preferred stockholders. As of December 31, 2021, no dividends on common stock had been declared by the Board of Directors. Preferred Stock There were no shares of preferred stock issued and outstanding at December 31, 2021.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	9. Stock-Based Compensation Total stock-based compensation expense recognized is as follows (in thousands): Year Ended December 31, 2021 2020 2019 Research and development $ 19,872 $ 11,583 $ 5,351 General and administrative 30,970 21,863 10,413 Total $ 50,842 $ 33,446 $ 15,764 No income tax benefits for stock-based compensation expense have been recognized for the years ended December 31, 2021, 2020 and 2019 as a result of the Company’s full valuation allowance applied to net deferred tax assets and net operating loss carryforwards. Equity Incentive Plans In July 2018, the Board of Directors adopted the 2018 Equity Incentive Plan (the “2018 Plan”). The 2018 Plan provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock units (“RSUs”), stock appreciation rights, performance-based awards ("PSUs") and other stock-based awards. The number of shares of common stock that may be issued under the 2018 Plan will automatically increase on each January 1, beginning with the fiscal year ending December 31, 2019, equal to the least of (i) 5,000,000 shares, (ii) 5 % of the outstanding shares of common stock as of the last day of the preceding fiscal year and (iii) such other amount as the Board of Directors may determine. Stock options and RSUs granted under the 2018 Plan generally vest over four years and expire no more than 10 years from the date of grant. Following the IPO and upon the effectiveness of the 2018 Plan, the Company’s 2012 Equity Incentive Plan, as amended, (the “2012 Plan”), terminated and no further awards will be granted thereunder. All outstanding awards under the 2012 Plan will continue to be governed by their existing terms. Any shares subject to awards granted under the 2012 Plan that, on or after the termination of the 2012 Plan, expire or terminate and shares previously issued pursuant to awards granted under the 2012 Plan that, on or after the termination of the 2012 Plan, are forfeited or repurchased by the Company will be transferred into the 2018 Plan. As of December 31, 2021, the maximum number of shares that may be added to the 2018 Plan pursuant to the preceding clause is 3,587,158 shares. Prior to its termination, the 2012 Plan provided for the grant of stock options, stock appreciation rights, restricted stock and restricted stock units to employees, directors and consultants. Stock options granted under the 2012 Plan generally vest over four years and expire no more than 10 years from the date of grant. As of December 31, 2021, the number of shares available for issuance under the 2018 Plan was 7,040,500 . Stock Options Stock option activity under the 2018 Plan and the 2012 Plan during the year ended December 31, 2021 is summarized as follows (in thousands, except per share data): Weighted- Weighted- Average Average Aggregate Options Exercise Remaining Intrinsic Outstanding Price Years Value Balance at December 31, 2020 6,616 $ 15.53 7.1 $ 823,532 Authorized — Granted 375 $ 94.89 Exercised ( 1,228 ) $ 6.92 Forfeited ( 233 ) $ 46.54 Balance at December 31, 2021 5,530 $ 21.51 6.3 $ 25,750 Options exercisable 4,625 $ 13.12 5.9 $ 25,251 Options vested and expected to vest 5,514 $ 21.34 6.3 $ 25,749 The following weighted-average assumptions were used to calculate the fair value of stock options granted during the periods indicated: Year Ended December 31, 2021 2020 2019 Risk-free interest rate 1.01 % 0.50 % 1.91 % Expected volatility 70.40 % 70.78 % 67.22 % Expected dividend yield — — — Expected term (in years) 6.00 5.95 6.01 The weighted-average fair value of options granted during the years ended December 31, 2021, 2020 and 2019 was $ 59.00 , $ 51.59 and $ 28.66 per share, respectively. The aggregate fair value of stock options that vested during the years ended December 31, 2021, 2020 and 2019 was $ 17.1 million, $ 18.0 million and $ 12.6 million, respectively. The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. Following the IPO, the aggregate intrinsic value represents the value of the Company’s closing stock price on the last trading day of the year in excess of the weighted-average exercise price multiplied by the number of options outstanding or exercisable. The aggregate intrinsic value of stock options exercised during the years ended December 31, 2021, 2020 and 2019 was $ 109.2 million, $ 62.2 million and $ 55.8 million, respectively. As of December 31, 2021, total unrecognized stock-based compensation expense relating to unvested stock options was $ 30.6 million. This amount is expected to be recognized over a weighted-average period of 2.6 years. Restricted Stock Awards The 2012 Plan allows for the issuance of restricted common stock and early exercise of unvested stock options in exchange for restricted common stock. Unvested shares of restricted common stock are subject to repurchase by the Company at the original issuance price in the event of the employee’s termination, either voluntarily or involuntarily. Consideration received for unvested stock-based awards is initially recorded as a liability and subsequently reclassified into stockholders’ deficit as the related awards vest. There were no unvested shares of restricted common stock at December 31, 2021 and 2020. The fair value of restricted common stock that vested during the years ended December 31, 2021, 2020 and 2019 was $ 0 , $ 0 and $ 20,000 , respectively. Time-based Restricted Stock Units Each time-based restricted stock unit (“RSU”) represents one equivalent share of our common stock to be awarded after satisfying the applicable continued service-based vesting criteria over a specified period. The fair value for these RSUs is based on the closing price of our common stock on the date of grant. The RSUs do not entitle participants to the rights of holders of common stock, such as voting rights, until the shares are issued. RSUs that are expected to vest are net of estimated future forfeitures. RSU activity under the 2018 Plan is summarized as follows (in thousands, except per share data): Weighted- Average Number Grant Date of Shares Fair Value Balance at December 31, 2020 1,161 $ 102.24 Granted 833 $ 84.80 Vested ( 285 ) $ 100.11 Forfeited ( 203 ) $ 101.12 Balance at December 31, 2021 1,506 $ 93.14 The weighted-average fair value of RSUs granted during the year ended December 31, 2021, 2020 and 2019 was $ 84.80 , $ 106.56 and $ 93.67 , respectively. As of December 31, 2021, total unrecognized stock-based compensation expense relating to unvested RSUs was $ 130.0 million and the weighted-average remaining vesting period was 3.2 years. The aggregate intrinsic value of RSUs is calculated as the closing price per share of the Company’s common stock on the last trading day of the fiscal period, multiplied by the number of RSUs expected to vest as of December 31, 2021. As of December 31, 2021, the aggregate intrinsic value of RSUs was $ 14.7 million. Performance-based Restricted Stock Units During the year ended December 31, 2021, the Compensation Committee of the Board of Directors approved awards of restricted stock units with performance-based vesting (“PSUs”) from the 2018 Plan to certain executive officers. Each PSU represents one equivalent share of our common stock to be awarded upon vesting at the end of the performance periods, if specific performance goals set by the Compensation Committee of the Board of Directors are achieved. No PSUs will vest if the performance goals are not met. The fair value of these PSUs is based on the closing price of our common stock on the date of grant. The Company assesses the probability of achieving the performance goals on a quarterly basis. Changes in our assessment of the probability results in adjustments to stock-based compensation, which may include either a cumulative catch-up of expense or a reduction of expense depending on whether the likelihood of vesting has increased or decreased, that is recognized in the period such determination is made. The PSUs do not entitle participants to the rights of holders of common stock, such as voting rights, until the shares are issued. PSUs that are expected to vest are net of estimated future forfeitures. The following table summarizes the PSUs activity for the year ended December 31, 2021 (in thousands, except per share data): Weighted- Average Number Grant Date of Shares Fair Value Balance at December 31, 2020 — $ — Granted 113 $ 79.60 Balance at December 31, 2021 113 $ 76.60 The Company did no t grant any stock options or awards with performance-based or market-based vesting conditions during the years ended December 31, 2020 and 2019. As of December 31, 2021, the vesting of the PSUs was not deemed probable. Accordingly, no stock-based compensation expense related to these awards has been recognized during the year ended December 31, 2021. As of December 31, 2021, total unrecognized compensation expense relating to PSUs was $ 9.0 million over a weighted-averag e period of 2.2 years and the aggregate intrinsic value of PSUs was $ 1.1 million. Employee Stock Purchase Plan In July 2018, the Company’s Board of Directors and stockholders approved the 2018 Employee Stock Purchase Plan (the “2018 ESPP”). The number of shares of common stock that may be issued under the 2018 ESPP shall automatically increase on each January 1, beginning with the fiscal year ending December 31, 2019, equal to the least of (i) 1,000,000 shares, (ii) 1 % of the outstanding shares of common stock as of the last day of the immediately preceding fiscal year and (iii) such other amount determined by the 2018 ESPP administrator. As of December 31, 2021, the number of shares available for issuance under the 2018 ESPP was 1,765,958 . Under the 2018 ESPP, employees may purchase shares of the Company’s common stock at a price per share equal to 85 % of the lower of the fair market value of the common stock on the first trading day of the offering period or on the exercise date. The 2018 ESPP provides for consecutive, overlapping 24 -month offering periods, each of which will include purchase periods. The first offering period commenced on July 18, 2018 . During the year ended December 31, 2021, 2020 and 2019, stock-based compensation related to the 2018 ESPP was $ 1.2 million, $ 0.9 million and $ 0.7 million, respectively. The following weighted-average assumptions were used to calculate the fair value of ESPP shares during the periods indicated: Year Ended December 31, 2021 2020 2019 Risk-free interest rate 0.11 % 0.58 % 2.37 % Expected volatility 68.40 % 61.80 % 64.26 % Expected dividend yield — — — Expected term (in years) 1.20 1.20 1.22 As of December 31, 2021, total unrecognized compensation expense relating to shares to be purchased under the 2018 ESPP was $ 1.5 million over a weighted-average period of 1.3 years.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes The Company’s deferred income tax assets include operating losses and tax credit carryforwards, as well as certain temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Total deferred income tax assets, net of valuation allowance, at December 31, 2021 and 2020 were as follows (in thousands): December 31, 2021 2020 Deferred tax assets Net operating loss carryforwards $ 157,277 $ 87,124 Research and development credits 33,341 18,139 Accruals and reserves 3,889 1,368 Stock-based compensation 4,932 5,661 Lease liability 10,854 9,151 Gross deferred tax assets 210,293 121,443 Less: valuation allowance ( 203,516 ) ( 112,680 ) Deferred tax assets, net of valuation allowance 6,777 8,763 Deferred tax liabilities Fixed and intangible assets 84 360 Right-of-use asset 6,693 8,403 Gross deferred tax liabilities 6,777 8,763 Net deferred tax assets $ — $ — Management has evaluated the positive and negative evidence surrounding the realizability of its deferred tax assets and has determined that it is more likely than not that the Company will not recognize the benefits of its federal and state deferred tax assets, and as a result, a valuation allowance of $ 203.5 million and $ 112.7 million has been established at December 31, 2021 and 2020, respectively. The change in the valuation allowance was $ 90.8 million and $ 52.8 million for the years ended December 31, 2021 and 2020, respectively. The Company has incurred net operating losses (“NOL”) since inception. As of December 31, 2021, the Company had federal and state NOL carryforwards of $ 715.5 million and $ 95.1 million, respectively. Federal NOL carryforwards of $ 653.6 million, which were generated after December 31, 2017, do not expire. The remaining $ 61.9 million of Federal NOL carryforwards expire beginning in 2032 . As of December 31, 2021, the Company had federal and California research and other tax credit carryforwards of $ 38.4 million and $ 8.0 million, respectively. The federal tax credits expire beginning in 2033 . The California tax credits can be carried forward indefinitely. The Internal Revenue Code of 1986, as amended (the “Code”), provides for a limitation of the annual use of net operating losses and other tax attributes (such as research and development tax credit carryforwards) following certain ownership changes defined by the Code that could limit the Company’s ability to utilize these carryforwards in the future. The Company may have experienced or may in the future experience ownership changes, as defined by the Code and may not be able to take full advantage of these carryforwards for federal or state income tax purposes. The effective tax rate for the years ended December 31, 2021 and 2020 is different from the federal statutory rate primarily due to the valuation allowance against deferred tax assets as a result of insufficient income. The Company’s effective tax rate differs from the federal statutory tax rate as follows: Year Ended December 31, 2021 2020 Federal statutory tax rate 21.0 % 21.0 % Change in deferred tax asset valuation allowance ( 33.7 )% ( 34.4 )% State taxes, net of federal benefit 1.9 % 0.8 % Research and development tax credits 5.2 % 5.6 % Stock-based compensation 6.9 % 6.9 % Other ( 1.3 )% 0.1 % Effective tax rate — % — % Uncertain Tax Positions The Company accounts for its uncertain tax positions in accordance with FASB ASC Topic No. 740-10, Accounting for Uncertainty in Income Taxes (“ASC 740-10”). Per ASC 740-10, the Company determines its uncertain tax positions based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings is more likely than not to be sustained upon examination by the relevant income tax authorities. A reconciliation of the beginning and ending amount of unrecognized benefits is as follows (in thousands): Year Ended December 31, 2021 2020 Balance at the beginning of the year $ 6,932 $ 3,545 Increase related to current year tax positions 5,345 3,387 Increase related to prior year tax positions ( 324 ) — Balance at the end of the year $ 11,953 $ 6,932 The entire amount of the unrecognized tax benefits would not impact the Company’s effective tax rate if recognized. During the years ended December 31, 2021 and 2020, the Company did not recognize accrued interest and penalties related to unrecognized tax benefits. The Company does not anticipate that the amount of existing unrecognized tax benefits will significantly increase or decrease during the next twelve months. The Company files income tax returns in the U.S. federal and multiple state tax jurisdictions. The federal and state income tax returns from inception to December 31, 2021 remain subject to examination. During the third quarter of 2020, the U.S. Internal Revenue Service (“IRS”) commenced an examination of the Company’s federal corporate income tax return for the year ended December 31, 2018. The Company believes that it has adequately provided for any adjustments that may result from the IRS examination, however, the outcome of tax examinations cannot be predicted with certainty. The examination was not yet completed as of December 31, 2021. It is the Company’s policy to include penalties and interest expense related to income taxes as a component of the income tax provision as necessary. Management determined that no accrual for interest and penalties was required at December 31, 2021 and 2020. Since the Company is in a loss carryforward position, it is generally subject to examination by the U.S. federal, state and local income tax authorities for all tax years in which a loss carryforward is available.

Defined Contribution Plans

Defined Contribution Plans	12 Months Ended
	Dec. 31, 2021
Retirement Benefits [Abstract]
Defined Contribution Plans	11. Defined Contribution Plans In January 2018, the Company established a defined contribution plan under Section 401(k) of the Internal Revenue Code (the “401(k) plan”). The 401(k) plan covers all employees who meet defined minimum age and service requirements. Employee contributions are voluntary and are determined on an individual basis, limited to the maximum amount allowable under U.S. federal tax regulations. The Company makes matching contributions of up to 4 % of the eligible employees’ compensation to the 401(k) plan. During the years ended December 31, 2021, 2020 and 2019, the Company made contributions to the 401(k) plan of $ 0.7 million, $ 0.7 million and $ 0.5 million, respectively.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	12. Subsequent Events In February 2022, we began implementing a reorganization plan to reduce operating costs, contractual commitments and better align our workforce with the clinical development plans of our business (the "Reorganization Plan"). Vendor Termination Agreement Approximately $ 231.2 million of the $ 284.8 million total noncancellable purchase obligations as of December 31, related to various manufacturing services agreements with Lonza AG or affiliates (such agreements, the “MSAs”) On February 14, 2022 (the “Effective Date”), the Company entered into a termination agreement (the “Termination Agreement”) with Lonza AG, Lonza Sales Ltd and Lonza Sales AG (collectively, “Lonza”) regarding all outstanding manufacturing service agreements. Lonza will continue to provide certain services to us, including completion of cGMP batches already underway and other services to assist with the transition post-termination. The Termination Agreement provides that the Company shall pay approximately $ 136.1 million ( 126 million Swiss Francs) (the “Termination Amount”) to Lonza as a result of such termination, 95% of which is to be paid within 30 days after the Effective Date, and 5% of which is be paid within 30 days of the release of the remaining cGMP batches. If the Company fails to pay the first 95% of the Termination Amount to Lonza within 30 days of the Effective Date, Lonza may at its option give notice to the Company that the Termination Agreement is terminated. The Termination Agreement contains mutual releases by all parties thereto, for all claims known and unknown, relating and arising out of, or connected with, the MSAs and the subject matter(s) thereof, subject to certain exceptions . In addition, Lonza held or had placed orders for raw materials to be used in the course of services Lonza was to provide to the Company. Pursuant to the Termination Agreement, the cost of such raw materials is included in the Termination Amount. Although the Company will hold title to such raw materials and may repurpose where possible, the recoverable value, if any, is currently not estimable. As the agreement was terminated on February 14, 2022, there was no impact of the termination agreement to the financial statements for the year ended December 31, 2021. The Company is still evaluating the impact of the termination agreement to our 2022 financial statements including the total amount and value, if any, of raw materials and its ability to utilize or repurpose such materials and the total value of services remaining to be rendered. However, the Company expects that the termination will result in a charge to our financial statements in amounts totaling up to $ 137 million during 2022. Employment Related Subsequent Events Under the plan, the Company is reducing its workforce by approximately 35 %. Impacted employees received notice that their positions will be eliminated on February 16, 2022 . At the time of departure from the Company, impacted employees are eligible to receive severance benefits and Company funded COBRA premiums, contingent upon an impacted employee’s execution (and non-revocation) of a customary separation agreement, which includes a general release of claims against the Company. In connection with the Reorganization Plan, the Company estimates that it will incur aggregate restructuring charges of approximately $ 5.3 million, which will be recognized primarily in the first quarter of 2022 , related to severance payments and other employee-related separation costs. The Company may also incur additional costs not currently contemplated due to events that may occur as a result of, or that are associated with, the reduction in workforce. In addition, the Board determined that it is in the best interests of the Company and its stockholder to put in place arrangements designed to provide that the Company will have the continued dedication and commitment of those employees, including executives, determined to be key to the planned go-forward operations. The Board approved, and management has implemented a retention program for employees staying with the company and includes cash retention bonuses totaling approximately $ 3 million for certain retained employees and grants of RSUs totaling 8.2 million awards in aggregate to all employees. Half of these RSUs are time-based RSUs with four-year vesting and half are performance-based with full vesting in the event that the Company achieves all primary endpoints in any of its Phase 2/3 clinical studies other than the Phase 3 Eosinophilic Duodenitis study expected to readout data in Q3 2022.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The financial statements have been prepared in accordance with United States generally accepted accounting principles (“U.S. GAAP”). The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts and disclosures reported in the financial statements and accompanying notes.
Use of Estimates	Use of Estimates Management uses significant judgment when making estimates related to common stock valuation and related stock-based compensation expense, accrued research and development expense, and lease related assets and liabilities. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results could differ from those estimates under different assumptions or conditions, and those differences could be material to the financial position and results of operations.
Concentration of Credit Risk and Other Risks and Uncertainties	Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to credit risk principally consist of cash, cash equivalents and marketable securities. These financial instruments are held in accounts at a single financial institution that management believes possesses high credit quality. Amounts on deposit with this financial institution have and will continue to exceed federally-insured limits. The Company has not experienced any losses on its cash deposits. Additionally, the Company’s investment policy limits its investments to certain types of securities issued by the United States government and its agencies. The Company is subject to a number of risks similar to that of other early-stage biopharmaceutical companies, including, but not limited to, the need to obtain adequate additional funding, possible failure of current or future clinical trials, its reliance on third-parties to conduct its clinical trials, the need to obtain regulatory and marketing approvals for its product candidates, competitive developments, the need to successfully commercialize and gain market acceptance of the Company’s product candidates, its right to develop and commercialize its product candidates pursuant to the terms and conditions of the licenses granted to the Company, protection of proprietary technology, the ability to make milestone, royalty or other payments due under licensing agreements, and the need to secure and maintain adequate manufacturing arrangements with third-parties. If the Company does not successfully commercialize or partner its product candidates, it will be unable to generate product revenue or achieve profitability.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company’s balance sheets and which, in aggregate, represent the amounts reported in the statements of cash flows (in thousands): December 31, 2021 2020 2019 Cash and cash equivalents $ 152,822 $ 207,177 $ 38,367 Restricted cash 2,275 2,275 2,275 Total $ 155,097 $ 209,452 $ 40,642 Restricted cash at December 31, 2021 represents $ 2.3 million of security deposits for the lease of the Company’s facilities in Redwood City, California and San Carlos, California. Both security deposits are in the form of letters of credit secured by restricted cash. Restricted cash amounts are included within other long-term assets on the Company’s balance sheets.
Marketable Securities	Marketable Securities The Company invests in marketable securities, primarily securities issued by the United States government and its agencies. The Company’s marketable securities are considered available-for-sale and are classified as current assets even when the stated maturities of the underlying securities exceed one year from the date of the current balance sheet being reported. This classification reflects management’s ability and intent to utilize proceeds from the sale of such investments to fund ongoing operations. Unrealized gains and losses are excluded from earnings and are reported as a component of accumulated other comprehensive gain. The cost of securities sold is determined using the specific-identification method. Interest earned and adjustments for the amortization of premiums and discounts on investments are included in interest income, net, on the statements of operations and comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on investments in marketable securities are included in other expense, net, on the statements of operations and comprehensive loss.
Fair Value Measurements	Fair Value Measurements The Company accounts for fair value of its financial instruments in accordance with Financial Accounting Standards Board (the “FASB”) Accounting Standards Codification (“ASC”) Topic No. 820, Fair Value Measurements (“ASC 820”). ASC 820 establishes a common definition for fair value, establishes a framework for measuring fair value and expands disclosures about such fair value measurements. Additionally, ASC 820 defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The Company measures fair value based on a three-level hierarchy of inputs, of which the first two are considered observable and the last unobservable. Unobservable inputs reflect the Company’s own assumptions about current market conditions. The three-level hierarchy of inputs is as follows: Level 1 – Quoted prices in active markets for identical assets or liabilities. Level 2 – Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 – Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of assets or liabilities. To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The carrying amounts reflected in the Company’s balance sheets for cash and cash equivalents, prepaid expenses and other current assets, other long-term assets, accounts payable, and accrued expenses and other current liabilities approximate fair value, due to their short-term nature. The Company’s investments in marketable securities are measured at fair value in accordance with the levels above.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are stated at cost, net of accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the assets. Generally, the useful lives of laboratory equipment are five years , furniture and office equipment are three to five years , and leasehold improvements property and equipment are the shorter of the remaining lease term or the estimated life of the assets . Any resulting gains or losses on dispositions of property and equipment are included as a component of other income (expense), net, within the Company’s statements of operations and comprehensive loss. Repair and maintenance costs that do not significantly add value to the property and equipment, or prolong its life, are charged to operating expense as incurred.
Operating Leases	Operating Leases The Company accounts for its leases in accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 842, “Leases” (“ASC 842”). Right-of-use assets represent the Company’s right to use an underlying asset over the lease term and include any lease payments made prior to the lease commencement date and are reduced by lease incentives. Lease liabilities represent the present value of the total lease payments over the lease term, calculated using the Company’s incremental borrowing rate. In determining the Company’s incremental borrowing rate, consideration is given to the term of the lease and the Company’s credit risk. The Company recognizes options to extend a lease when it is reasonably certain that it will exercise such extension. The Company does not recognize options to terminate a lease when it is reasonably certain that it will not exercise such early termination options. Lease expense is recognized on a straight-line basis over the expected lease term.
Accrued Research and Development Expense	Accrued Research and Development Expense Service agreements with contract development and manufacturing organizations (“CDMOs”), clinical contract research organizations (“CROs”) and clinical investigative sites comprise a significant component of the Company’s research and development activities. External costs for these vendors are recognized as the services are incurred. The Company accrues for expenses resulting from obligations under agreements with its third-parties for which the timing of payments does not match the periods over which the materials or services are provided to the Company. Accruals are recorded based on estimates of services received and efforts expended pursuant to agreements established with CDMOs, clinical CROs, clinical investigative sites and other outside service providers. These estimates are typically based on contracted amounts applied to the proportion of work performed and determined through analysis with internal personnel and external service providers as to the progress or stage of completion of the services. The Company makes judgements and estimates in determining the accrual balance in each reporting period. In the event advance payments are made to a CDMO, clinical CRO, clinical investigative site or other outside service provider, the payments are recorded within prepaid expenses and other current assets and subsequently recognized as research and development expense when the associated services have been performed. As actual costs become known, the Company adjusts its liabilities and assets. Inputs, such as the extent of services received and the duration of services to be performed, may vary from the Company’s estimates, which will result in adjustments to research and development expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect the Company’s results of operations. The Company’s historical estimates have not been materially different from actual amounts recorded.
Research and Development Expense	Research and Development Expense Research and development costs are expensed as incurred. Research and development costs include, among others, consulting costs, salaries, benefits, travel, stock-based compensation, laboratory supplies and other non-capital equipment utilized for in-house research, allocation of facilities and overhead costs and external costs paid to third-parties that conduct research and development activities on the Company’s behalf. Amounts incurred in connection with license agreements, including milestone payments, are also included in research and development expense. Advance payments for goods or services to be rendered in the future for use in research and development activities are deferred and included in prepaid expenses and other current assets. The deferred amounts are expensed as the related goods are delivered or the services are performed.
Segments	Segments Operating segments are defined as components of an entity about which separate discrete information is available for evaluation by the chief operating decision maker or decision-making group, in deciding how to allocate resources and in assessing performance. The Company’s chief operating decision maker, its Chief Executive Officer, views its operations and manages its business in one operating segment operating exclusively in the United States.
Patent Costs	Patent Costs The Company expenses patent application and related legal costs as incurred and classifies such costs as general and administrative expenses in the statements of operations and comprehensive loss.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for its stock-based compensation in accordance with FASB ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all stock-based awards issued to employees and nonemployees to be recognized as expense in the statements of operations and comprehensive loss based on their grant date fair values. Stock-based awards issued to nonemployee consultants are accounted for based on the fair value of services to be received or of the intrinsic value of equity instruments to be issued, whichever is more reliably measured. The measurement date for awards issued to nonemployee consultants is the date of grant. For purposes of determining the estimated fair value of stock options granted to employees and nonemployees, the Company uses the Black-Scholes option pricing model. The Black-Scholes option pricing model requires the input of certain assumptions that involve judgment, for which changes can materially affect the resulting estimates of fair value. The assumptions used to determine the fair value of stock options granted were as follows: Expected volatility – As there is insufficient trading history for the Company’s common stock, the Company has based its computation of expected volatility on the historical volatility of a representative group of public companies with similar characteristics to the Company, including stage of product development and life science industry focus. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. Expected term – The Company determines the expected term in accordance with the “simplified method” described by SEC Staff Accounting Bulletin No. 107, Share-Based Payment , as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. Risk-free interest rate – The Company bases the risk-free interest rate on United States Treasury securities with terms consistent to the expected term of the stock option being valued. Expected dividends – The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. The fair value of restricted stock units (“RSUs”) is determined using the quoted market price of the Company’s common stock on the date of grant. The Company uses historical data to estimate pre-vesting forfeitures and records stock-based compensation expense only for those awards expected to vest. To the extent that actual forfeitures differ from estimates, the difference is recorded as a cumulative adjustment in the period the estimate are revised. The Company expenses the fair value of its stock-based compensation awards to employees and nonemployees on a straight-line basis over the requisite service period, which is generally the vesting period. The Company recognizes the stock-based compensation expense related to performance-based stock awards or performance-based RSUs ("PSUs") if the performance targets are deemed probable of being achieved. The vesting of PSUs requires that certain performance conditions are achieved during the performance period and is subject to the employee’s continued service requirements.
Income Taxes	Income Taxes We account for income taxes under the asset and liability method. Current income tax expense or benefit represents the amount of income taxes we expect to pay or have refunded in the current year. Our deferred income tax assets and liabilities are determined based on differences between financial statement reporting and tax basis accounting of assets and liabilities and net operating loss and credit carryforwards, which we measure using the enacted tax rates and laws that will be in effect when such items are expected to reverse. We reduce deferred income tax assets, as necessary, by applying a valuation allowance to the extent that we determined it is more likely than not that some or all of our tax benefits will not be realized. We account for uncertain tax positions in accordance with ASC 740-10, Accounting for Uncertainty in Income Taxes. We assess all material positions reflected in our income tax returns, including all significant uncertain positions, for all tax years that are subject to assessment or challenge by relevant taxing authorities. Upon determining the sustainability of our positions, we measure the largest amount of benefit possessing greater than fifty percent likelihood of being realized upon ultimate settlement. We reassess such positions at each balance sheet date to determine whether any factors underlying the sustainability assertion have changed and whether or not the amount of the recognized tax benefit is still appropriate.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as the change in stockholders’ equity during a period from transactions and other events and circumstances from non-owner sources. The difference between net loss and comprehensive loss for the years ended December 31, 2021, 2020 and 2019 are a result of unrealized gains and losses on the Company’s investments in marketable securities included in current assets on the balance sheets.
Net Loss per Share	Net Loss per Share The Company calculates basic net loss per share by dividing the net loss attributable to common stockholders by the weighted-average shares of common stock outstanding during the period. The Company calculates diluted net loss per share after giving consideration to all potentially dilutive securities outstanding during the period using the treasury-stock and if-converted methods, except where the effect of including such securities would be anti-dilutive. Because the Company has reported net losses since inception, the effect from potentially dilutive securities would have been anti-dilutive and therefore has been excluded from the calculation of diluted net loss per share. Basic and diluted net loss per share was calculated as follows (in thousands, except per share data): Year Ended December 31, 2021 2020 2019 Numerator: Net loss $ ( 269,860 ) $ ( 153,480 ) $ ( 85,372 ) Denominator: Weighted-average shares of common stock 53,832 49,492 45,191 Net loss per share, basic and diluted $ ( 5.01 ) $ ( 3.10 ) $ ( 1.89 ) The following table sets forth the potentially dilutive securities that have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect for the periods indicated (in thousands): Year Ended December 31, 2021 2020 2019 Options to purchase common stock 5,530 6,616 7,148 Unvested restricted stock units 1,506 1,161 542 Unvested performance stock unit 113 — — Shares issuable under employee stock purchase plans 118 14 31 Total 7,267 7,791 7,721
Foreign Currency Transactions	Foreign Currency Transactions The Company is party to multiple contract manufacturing and clinical research agreements for which services to be performed are denominated in foreign currencies other than the United States Dollar. The Company records gains and losses attributable to fluctuations in foreign currencies as a component of other income (expense), net, on the statements of operations and comprehensive loss.
Recently Issued and Adopted Accounting Pronouncements	Recently Issued and Adopted Accounting Pronouncements The Company has reviewed recently issued accounting pronouncements and concluded they are either not applicable to the business or that no material effect is expected on the Financial Statements as a result of future adoption.
Uncertain Tax Positions	Uncertain Tax Positions The Company accounts for its uncertain tax positions in accordance with FASB ASC Topic No. 740-10, Accounting for Uncertainty in Income Taxes (“ASC 740-10”). Per ASC 740-10, the Company determines its uncertain tax positions based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings is more likely than not to be sustained upon examination by the relevant income tax authorities. It is the Company’s policy to include penalties and interest expense related to income taxes as a component of the income tax provision as necessary.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company’s balance sheets and which, in aggregate, represent the amounts reported in the statements of cash flows (in thousands): December 31, 2021 2020 2019 Cash and cash equivalents $ 152,822 $ 207,177 $ 38,367 Restricted cash 2,275 2,275 2,275 Total $ 155,097 $ 209,452 $ 40,642
Calculation of Basic and Diluted Net Loss per Share	Basic and diluted net loss per share was calculated as follows (in thousands, except per share data): Year Ended December 31, 2021 2020 2019 Numerator: Net loss $ ( 269,860 ) $ ( 153,480 ) $ ( 85,372 ) Denominator: Weighted-average shares of common stock 53,832 49,492 45,191 Net loss per share, basic and diluted $ ( 5.01 ) $ ( 3.10 ) $ ( 1.89 )
Summary of Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share	The following table sets forth the potentially dilutive securities that have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect for the periods indicated (in thousands): Year Ended December 31, 2021 2020 2019 Options to purchase common stock 5,530 6,616 7,148 Unvested restricted stock units 1,506 1,161 542 Unvested performance stock unit 113 — — Shares issuable under employee stock purchase plans 118 14 31 Total 7,267 7,791 7,721

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Summary of Financial Assets Measured at Fair Value on Recurring Basis	The Company measures and reports certain financial instruments as assets and liabilities at fair value on a recurring basis. The Company’s financial assets measured at fair value on a recurring basis were as follows (in thousands): December 31, 2021 Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 150,781 $ — $ — $ 150,781 Total cash equivalents 150,781 — — 150,781 Short-term marketable securities U.S. treasuries 271,416 — — 271,416 Total short-term marketable securities 271,416 — — 271,416 Total cash equivalents and short-term $ 422,197 $ — $ — $ 422,197 December 31, 2020 Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 205,408 $ — $ — $ 205,408 Total cash equivalents 205,408 — — 205,408 Short-term marketable securities U.S. treasuries 451,820 — — 451,820 Total short-term marketable securities 451,820 — — 451,820 Total cash equivalents and short-term $ 657,228 $ — $ — $ 657,228

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Summary of Amortized Cost, Gross Unrealized Holding Gains or Losses, and Fair Value of Marketable Securities	All marketable securities were considered available-for-sale at December 31, 2021 and 2020. The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s marketable securities by major security type are summarized in the table below (in thousands): December 31, 2021 Amortized Unrealized Unrealized Fair Available-for-sale securities U.S. treasuries classified as investments $ 271,570 $ 2 $ ( 156 ) $ 271,416 Total $ 271,570 $ 2 $ ( 156 ) $ 271,416 December 31, 2020 Amortized Unrealized Unrealized Fair Available-for-sale securities U.S. treasuries classified as investments $ 451,812 $ 26 $ ( 18 ) $ 451,820 Total $ 451,812 $ 26 $ ( 18 ) $ 451,820

Balance Sheet Components and _2

Balance Sheet Components and Supplemental Disclosures (Tables)	12 Months Ended
	Dec. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net, consisted of the following (in thousands): December 31, 2021 2020 Laboratory equipment $ 4,676 $ 4,236 Furniture and office equipment 1,947 1,784 Leasehold improvements 4,581 4,581 Construction-in-progress 37,704 1,325 48,908 11,926 Less accumulated depreciation ( 5,808 ) ( 3,581 ) Property and equipment, net $ 43,100 $ 8,345
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, 2021 2020 Accrued contract research and development expense $ 16,215 $ 4,697 Accrued compensation and benefits expense 3,172 3,214 Current portion of operating lease liabilities 2,316 492 Other current liabilities 4,854 87 Total $ 26,557 $ 8,490

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Summary of Classification of Company's Operating Lease Liabilities	Classification of the Company’s operating lease liabilities included in the Company’s balance sheets at December 31, 2021 and 2020 was as follows (in thousands): December 31, 2021 2020 Operating lease liabilities Current portion included in accrued expenses and $ 2,316 $ 492 Operating lease liabilities, net of current portion 49,099 42,773 Total operating lease liabilities $ 51,415 $ 43,265
Summary of Components of Lease Costs	The components of lease costs, which are included in operating expenses in the Company’s statements of operations and comprehensive loss were as follows (in thousands): Year ended December 31, 2021 2020 Operating lease costs $ 6,676 $ 2,087 Variable costs 1,663 364 Total lease costs $ 8,339 $ 2,451
Summary of Future Lease Payments Required Under Operating Leases	Future lease payments required under operating leases included on the Company’s balance sheet at December 31, 2021 are as follows (in thousands): Fiscal Year Ending December 31, 2022 $ 7,445 2023 7,061 2024 7,273 2025 7,492 2026 7,716 Thereafter 40,677 Total future lease payments 77,664 Less: Present value adjustment 25,276 Present value of future lease incentives 973 Operating lease liabilities $ 51,415

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2021
Stockholders' Equity Note [Abstract]
Summary of Common Stock Shares Reserved for Future Issuance	Common shares reserved for future issuance upon the exercise, issuance or conversion of the respective equity instruments are as follows (in thousands): December 31, 2021 2020 Exercise of common stock options outstanding 5,530 6,616 Shares reserved for issuance under equity incentive plans 7,154 5,271 Vesting of restricted stock units 1,506 1,161 Shares reserved for issuance under employee stock purchase plans 1,766 1,265 Total 15,956 14,313

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Total Stock-Based Compensation Expense Recognized	Total stock-based compensation expense recognized is as follows (in thousands): Year Ended December 31, 2021 2020 2019 Research and development $ 19,872 $ 11,583 $ 5,351 General and administrative 30,970 21,863 10,413 Total $ 50,842 $ 33,446 $ 15,764
Summary of Stock Option Activity	Stock option activity under the 2018 Plan and the 2012 Plan during the year ended December 31, 2021 is summarized as follows (in thousands, except per share data): Weighted- Weighted- Average Average Aggregate Options Exercise Remaining Intrinsic Outstanding Price Years Value Balance at December 31, 2020 6,616 $ 15.53 7.1 $ 823,532 Authorized — Granted 375 $ 94.89 Exercised ( 1,228 ) $ 6.92 Forfeited ( 233 ) $ 46.54 Balance at December 31, 2021 5,530 $ 21.51 6.3 $ 25,750 Options exercisable 4,625 $ 13.12 5.9 $ 25,251 Options vested and expected to vest 5,514 $ 21.34 6.3 $ 25,749
Summary of Weighted-Average Assumptions Used to Calculate Fair Value of Stock Options Granted	The following weighted-average assumptions were used to calculate the fair value of stock options granted during the periods indicated: Year Ended December 31, 2021 2020 2019 Risk-free interest rate 1.01 % 0.50 % 1.91 % Expected volatility 70.40 % 70.78 % 67.22 % Expected dividend yield — — — Expected term (in years) 6.00 5.95 6.01
Summary of Weighted-Average Assumptions Used to Calculate Fair Value of ESPP Shares	The following weighted-average assumptions were used to calculate the fair value of ESPP shares during the periods indicated: Year Ended December 31, 2021 2020 2019 Risk-free interest rate 0.11 % 0.58 % 2.37 % Expected volatility 68.40 % 61.80 % 64.26 % Expected dividend yield — — — Expected term (in years) 1.20 1.20 1.22
Time-based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Restricted Stock Units	RSU activity under the 2018 Plan is summarized as follows (in thousands, except per share data): Weighted- Average Number Grant Date of Shares Fair Value Balance at December 31, 2020 1,161 $ 102.24 Granted 833 $ 84.80 Vested ( 285 ) $ 100.11 Forfeited ( 203 ) $ 101.12 Balance at December 31, 2021 1,506 $ 93.14
Performance-based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Restricted Stock Units	The following table summarizes the PSUs activity for the year ended December 31, 2021 (in thousands, except per share data): Weighted- Average Number Grant Date of Shares Fair Value Balance at December 31, 2020 — $ — Granted 113 $ 79.60 Balance at December 31, 2021 113 $ 76.60

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Summary of Total Deferred Income Tax Assets, Net of Valuation Allowance	Total deferred income tax assets, net of valuation allowance, at December 31, 2021 and 2020 were as follows (in thousands): December 31, 2021 2020 Deferred tax assets Net operating loss carryforwards $ 157,277 $ 87,124 Research and development credits 33,341 18,139 Accruals and reserves 3,889 1,368 Stock-based compensation 4,932 5,661 Lease liability 10,854 9,151 Gross deferred tax assets 210,293 121,443 Less: valuation allowance ( 203,516 ) ( 112,680 ) Deferred tax assets, net of valuation allowance 6,777 8,763 Deferred tax liabilities Fixed and intangible assets 84 360 Right-of-use asset 6,693 8,403 Gross deferred tax liabilities 6,777 8,763 Net deferred tax assets $ — $ —
Summary of Effective Tax Rate Differs From Federal Statutory Tax Rate	The Company’s effective tax rate differs from the federal statutory tax rate as follows: Year Ended December 31, 2021 2020 Federal statutory tax rate 21.0 % 21.0 % Change in deferred tax asset valuation allowance ( 33.7 )% ( 34.4 )% State taxes, net of federal benefit 1.9 % 0.8 % Research and development tax credits 5.2 % 5.6 % Stock-based compensation 6.9 % 6.9 % Other ( 1.3 )% 0.1 % Effective tax rate — % — %
Reconciliation of Beginning and Ending Amount of Unrecognized Benefits	A reconciliation of the beginning and ending amount of unrecognized benefits is as follows (in thousands): Year Ended December 31, 2021 2020 Balance at the beginning of the year $ 6,932 $ 3,545 Increase related to current year tax positions 5,345 3,387 Increase related to prior year tax positions ( 324 ) — Balance at the end of the year $ 11,953 $ 6,932

Organization and Business - Add

Organization and Business - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net loss	$ 269,860	$ 153,480	$ 85,372
Cash used in operations	(207,853)	(113,924)	$ (63,012)
Accumulated deficit	612,824	$ 342,964
Cash, cash equivalents and marketable securities	$ 424,200

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)Segment	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Summary Of Significant Accounting Policies [Line Items]
Restricted cash in other long term assets, deposit for lease facility | $	$ 2,275	$ 2,275	$ 2,275
Number of operating segments | Segment	1
Expected dividend yield	0.00%	0.00%	0.00%
Income tax rate	21.00%	21.00%
Leasehold Improvements
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, Useful life	shorter of the remaining lease term or the estimated life of the assets
Laboratory Equipment
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, Useful life	5 years
Furniture and Office Equipment | Minimum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, Useful life	3 years
Furniture and Office Equipment | Maximum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, Useful life	5 years

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 152,822	$ 207,177	$ 38,367
Restricted cash	2,275	2,275	2,275
Total	$ 155,097	$ 209,452	$ 40,642	$ 34,462

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Calculation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Numerator:
Net loss	$ (269,860)	$ (153,480)	$ (85,372)
Weighted-average number of common shares outstanding:
Weighted-average shares of common stock outstanding, basic and diluted	53,832	49,492	45,191
Net loss per share, basic and diluted	$ (5.01)	$ (3.10)	$ (1.89)

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Summary of Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	7,267,000	7,791,000	7,721,000
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	5,530,000	6,616,000	7,148,000
Unvested Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	1,506,000	1,161,000	542
Unvested Performance Stock Unit
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	113,000	0	0
Shares Issuable under Employee Stock Purchase Plans
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	118,000	14,000	31,000

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	$ 271,416	$ 451,820
Fair Value, Measurements, Recurring Basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	150,781	205,408
Short-term marketable securities	271,416	451,820
Total cash equivalents and short-term marketable securities	422,197	657,228
Fair Value, Measurements, Recurring Basis | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	150,781	205,408
Short-term marketable securities	271,416	451,820
Total cash equivalents and short-term marketable securities	422,197	657,228
Fair Value, Measurements, Recurring Basis | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term marketable securities	0	0
Total cash equivalents and short-term marketable securities	0	0
Fair Value, Measurements, Recurring Basis | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term marketable securities	0	0
Total cash equivalents and short-term marketable securities	0	0
Fair Value, Measurements, Recurring Basis | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	150,781	205,408
Fair Value, Measurements, Recurring Basis | Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	150,781	205,408
Fair Value, Measurements, Recurring Basis | Money Market Funds | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Fair Value, Measurements, Recurring Basis | Money Market Funds | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Fair Value, Measurements, Recurring Basis | U.S. Treasuries
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	271,416	451,820
Fair Value, Measurements, Recurring Basis | U.S. Treasuries | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	271,416	451,820
Fair Value, Measurements, Recurring Basis | U.S. Treasuries | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	0	0
Fair Value, Measurements, Recurring Basis | U.S. Treasuries | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	$ 0	$ 0

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Transfers of assets between level 1 to level 2	$ 0	$ 0
Transfers of assets between level 2 to level 1	0	0
Transfers of liabilities between level 1 to level 2	0	0
Transfers of liabilities between level 2 to level 1	0	0
Transfers of assets into level 3	0	0
Transfers of assets out of level 3	0	0
Transfers of liabilities into level 3	0	0
Transfers of liabilities out of level 3	$ 0	$ 0

Marketable Securities - Summary

Marketable Securities - Summary of Amortized Cost, Gross Unrealized Holding Gains or Losses, and Fair Value of Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	$ 271,570	$ 451,812
Unrealized Gains	2	26
Unrealized Losses	(156)	(18)
Fair Value	271,416	451,820
Investments | U.S. Treasuries
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	271,570	451,812
Unrealized Gains	2	26
Unrealized Losses	(156)	(18)
Fair Value	$ 271,416	$ 451,820

Marketable Securities - Additio

Marketable Securities - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities in an unrealized loss position, fair value	$ 241,400,000	$ 91,400,000
Available for sale securities gross recognized gains on sale or maturity	0	0	$ 0
Available for sale securities gross recognized losses on sale or maturity	$ 0	$ 0	$ 0
Maximum
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities, remaining maturity period	1 year

Balance Sheet Components and _3

Balance Sheet Components and Supplemental Disclosures - Schedule of Property and Equipment, Net (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 48,908,000	$ 11,926,000
Less accumulated depreciation	(5,808,000)	(3,581,000)
Property and equipment, net	43,100,000	8,345,000
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,676,000	4,236,000
Furniture And Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,947,000	1,784,000
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,581,000	4,581,000
Construction In Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 37,704	$ 1,325,000

Balance Sheet Components and _4

Balance Sheet Components and Supplemental Disclosures - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Depreciation and amortization	$ 2,310	$ 1,545	$ 1,508

Balance Sheet Components and _5

Balance Sheet Components and Supplemental Disclosures - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Accrued contract research and development expense	$ 16,215	$ 4,697
Accrued compensation and benefits expense	3,172	3,214
Current portion of operating lease liabilities	2,316	492
Other current liabilities	4,854	87
Total	$ 26,557	$ 8,490

Leases - Additional Information

Leases - Additional Information (Details)	Nov. 30, 2021	Dec. 31, 2019USD ($)ft²	Jan. 31, 2018USD ($)ft²	Dec. 31, 2021USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)ft²
Lessee, Lease, Description [Line Items]
Cash paid for amounts included in measurement of operating lease liabilities					$ 1,700,000	$ 1,200,000	$ 500,000
Cash received for amounts related to tenant improvement allowances from lessors					$ 12,900,000	200,000	$ 0
Operating lease, weighted-average remaining lease term				9 years 9 months 18 days	9 years 9 months 18 days
Operating lease, weighted-average discount rate				8.50%	8.50%
Remaining lease liability				$ 49,099,000	$ 49,099,000	42,773,000
Remaining right-of-use assets				31,707,000	31,707,000	$ 39,731,000
2019 San Carlos Lease Agreement
Lessee, Lease, Description [Line Items]
Operating lease agreement initiation period		2019-12
Base term of lease		10 years 3 months					10 years 3 months
Lessee operating lease expected termination Period		2031-10
Lease term extension period		5 years					5 years
Area of office and laboratory space | ft²		98,000					98,000
Security deposit in the form of letter of credit secured by restricted cash				1,500,000	1,500,000
2019 San Carlos Lease Agreement | Maximum
Lessee, Lease, Description [Line Items]
Tenant improvement allowance		$ 14,700,000					$ 14,700,000
2018 Redwood City Lease Agreement
Lessee, Lease, Description [Line Items]
Operating lease agreement initiation period			2018-01
Base term of lease			10 years 9 months
Lessee operating lease expected termination Period			2029-07
Area of office and laboratory space | ft²			25,000
Tenant improvement allowance			$ 1,400,000
Security deposit in the form of letter of credit secured by restricted cash				800,000	$ 800,000
Lease termination date					2021-11
Remaining lease liability				600,000	$ 600,000
Remaining right-of-use assets				0	0
Early Lease Termination Payment Receivable				1,100,000	$ 1,100,000
2018 Redwood City Lease Agreement | Other Income (Expense)
Lessee, Lease, Description [Line Items]
Gain on lease modifications				$ 1,900,000
2018 Redwood City Lease Agreement | Lease Termination Agreement [Member]
Lessee, Lease, Description [Line Items]
Lease termination date	Apr. 30, 2022

Leases - Summary of Classificat

Leases - Summary of Classification of Company's Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Operating lease liabilities
Current portion included in accrued expenses and other current liabilities	$ 2,316	$ 492
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Accrued Liabilities, Current	Accrued Liabilities, Current
Operating lease liabilities, net of current portion	$ 49,099	$ 42,773
Total operating lease liabilities	$ 51,415	$ 43,265

Leases - Summary of Components

Leases - Summary of Components of Lease Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Leases [Abstract]
Operating lease costs	$ 6,676	$ 2,087
Variable costs	1,663	364
Total lease costs	$ 8,339	$ 2,451

Leases - Summary of Future Leas

Leases - Summary of Future Lease Payments Required Under Operating Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2022	$ 7,445
2023	7,061
2024	7,273
2025	7,492
2026	7,716
Thereafter	40,677
Total future lease payments	77,664
Present value adjustment	25,276
Present value of future lease incentives	973
Operating lease liabilities	$ 51,415	$ 43,265

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($)	12 Months Ended			96 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2021
Loss Contingencies [Line Items]
Noncancelable purchase commitments	$ 284,800,000			$ 284,800,000
Accrued Royalties	$ 0			$ 0
Common stock, shares issued	54,622,363	53,081,000		54,622,363
In-Licensing Agreements
Loss Contingencies [Line Items]
Milestone expense	$ 0	$ 3,400,000	$ 0
Exclusive License Agreement with The Johns Hopkins University
Loss Contingencies [Line Items]
Upfront and milestone payments				$ 700,000
Common stock, shares issued	88,887			88,887
Non-exclusive License Agreement with BioWa Inc. and Lonza Sales AG
Loss Contingencies [Line Items]
Milestone payments		$ 3,400,000
Minimum | Non-exclusive License Agreement with BioWa Inc. and Lonza Sales AG
Loss Contingencies [Line Items]
Annual commercial license fees				$ 40,000
Maximum | Exclusive License Agreement with The Johns Hopkins University
Loss Contingencies [Line Items]
Aggregate additional milestone payments				1,800,000
Maximum | Non-exclusive License Agreement with BioWa Inc. and Lonza Sales AG
Loss Contingencies [Line Items]
Aggregate additional milestone payments				$ 38,000,000

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Jul. 23, 2018
Stockholders' Equity Note [Abstract]
Total number of shares authorized			220,000,000
Common stock, shares authorized	200,000,000	200,000,000	200,000,000
Preferred stock, shares authorized	20,000,000	20,000,000	20,000,000
Common stock, shares issued	54,622,363	53,081,000
Common stock, shares outstanding	54,622,363	53,081,000
Common stock dividends declared	$ 0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Details) - shares shares in Thousands	Dec. 31, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Common shares reserved for future issuance	15,956	14,313
Exercise of Common Stock Options Outstanding
Class Of Stock [Line Items]
Common shares reserved for future issuance	5,530	6,616
Shares Reserved for Issuance Under Equity Incentive Plans
Class Of Stock [Line Items]
Common shares reserved for future issuance	7,154	5,271
Vesting of Restricted Stock Units
Class Of Stock [Line Items]
Common shares reserved for future issuance	1,506	1,161
Shares Reserved for Issuance Under Employee Stock Purchase Plans
Class Of Stock [Line Items]
Common shares reserved for future issuance	1,766	1,265

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Total Stock-Based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 50,842	$ 33,446	$ 15,764
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	19,872	11,583	5,351
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 30,970	$ 21,863	$ 10,413

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jul. 31, 2018	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Tax benefits for stock-based compensation expense recognized		$ 0	$ 0	$ 0
Weighted-average fair value of options granted		$ 59	$ 51.59	$ 28.66
Aggregate fair value of stock options vested		$ 17,100,000	$ 18,000,000	$ 12,600,000
Aggregate intrinsic value of stock options exercised		109,200,000	62,200,000	55,800,000
Total unrecognized stock-based compensation expense relating to unvested stock options		$ 30,600,000
Weighted-average recognition period		2 years 7 months 6 days
Total stock-based compensation expense		$ 50,842,000	$ 33,446,000	$ 15,764,000
Market-Based Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted			0	0
Time-based Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average recognition period		3 years 2 months 12 days
Shares of restricted common stock unvested		1,506,000	1,161,000
Description of terms of award		Each time-based restricted stock unit (“RSU”) represents one equivalent share of our common stock to be awarded after satisfying the applicable continued service-based vesting criteria over a specified period. The fair value for these RSUs is based on the closing price of our common stock on the date of grant. The RSUs do not entitle participants to the rights of holders of common stock, such as voting rights, until the shares are issued. RSUs that are expected to vest are net of estimated future forfeitures.
Weighted-average fair value of RSUs granted		$ 84.80	$ 106.56	$ 93.67
Total unrecognized stock-based compensation expense		$ 130,000,000
Aggregate intrinsic value		$ 14,700,000
Performance-based Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted			0	0
Weighted-average recognition period		2 years 2 months 12 days
Shares of restricted common stock unvested		113,000	0
Description of terms of award		During the year ended December 31, 2021, the Compensation Committee of the Board of Directors approved awards of restricted stock units with performance-based vesting (“PSUs”) from the 2018 Plan to certain executive officers. Each PSU represents one equivalent share of our common stock to be awarded upon vesting at the end of the performance periods, if specific performance goals set by the Compensation Committee of the Board of Directors are achieved. No PSUs will vest if the performance goals are not met. The fair value of these PSUs is based on the closing price of our common stock on the date of grant. The Company assesses the probability of achieving the performance goals on a quarterly basis. Changes in our assessment of the probability results in adjustments to stock-based compensation, which may include either a cumulative catch-up of expense or a reduction of expense depending on whether the likelihood of vesting has increased or decreased, that is recognized in the period such determination is made. The PSUs do not entitle participants to the rights of holders of common stock, such as voting rights, until the shares are issued. PSUs that are expected to vest are net of estimated future forfeitures.
Weighted-average fair value of RSUs granted		$ 79.60
Total unrecognized stock-based compensation expense		$ 9,000,000
Aggregate intrinsic value		1,100,000
Total stock-based compensation expense		$ 0
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in number of common stock shares reserved for issuance per year	1,000,000
Percentage increase in shares reserved for issuance per year	1.00%
Number of shares available for issuance		1,765,958
Weighted-average recognition period		1 year 3 months 18 days
Total unrecognized stock-based compensation expense		$ 1,500,000
Price as a percentage of fair market value of common stock	85.00%
Consecutive overlapping offering period	24 months
First offering period commence date	Jul. 18, 2018
Total stock-based compensation expense		$ 1,200,000	$ 900,000	$ 700,000
Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of restricted common stock unvested		0	0
Fair value of restricted common stock vested		$ 0	$ 0	$ 20,000
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in number of common stock shares reserved for issuance per year	5,000,000
Percentage increase in shares reserved for issuance per year	5.00%
Award vesting period	4 years
Maximum number of additional shares authorized to be added to the Plan		3,587,158
Number of shares available for issuance		7,040,500
2018 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option expiration period	10 years
2012 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period	4 years
2012 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option expiration period	10 years

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate Intrinsic Value, Exercised	$ 109,200	$ 62,200	$ 55,800
2018 and 2012 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options Outstanding, Beginning balance	6,616
Options Outstanding, Granted	375
Options Outstanding, Exercised	(1,228)
Options Outstanding, forfeited	(233)
Options Outstanding, Ending balance	5,530	6,616
Options Outstanding, Options exercisable	4,625
Options Outstanding, Options vested and expected to vest	5,514
Weighted Average Exercise Price, Beginning balance	$ 15.53
Weighted Average Exercise Price, Granted	94.89
Weighted Average Exercise Price, Exercised	6.92
Weighted Average Exercise Price, Forfeited	46.54
Weighted Average Exercise Price, Ending balance	21.51	$ 15.53
Weighted Average Exercise Price, Options exercisable	13.12
Weighted Average Exercise Price, Options vested and expected to vest	$ 21.34
Weighted Average Remaining Years	6 years 3 months 18 days	7 years 1 month 6 days
Weighted Average Remaining Years, Options exercisable	5 years 10 months 24 days
Weighted Average Remaining Years, Options vested and expected to vest	6 years 3 months 18 days
Aggregate Intrinsic Value, Beginning balance	$ 823,532
Aggregate Intrinsic Value, Ending balance	25,750	$ 823,532
Aggregate Intrinsic Value, Options exercisable	25,251
Aggregate Intrinsic Value, Options vested and expected to vest	$ 25,749

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Weighted-Average Assumptions Used to Calculate Fair Value of Stock Options Granted and ESPP Shares (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	1.01%	0.50%	1.91%
Expected volatility	70.40%	70.78%	67.22%
Expected dividend yield	0.00%	0.00%	0.00%
Expected term (in years)	6 years	5 years 11 months 12 days	6 years 3 days
ESPP Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	0.11%	0.58%	2.37%
Expected volatility	68.40%	61.80%	64.26%
Expected dividend yield	0.00%	0.00%	0.00%
Expected term (in years)	1 year 2 months 12 days	1 year 2 months 12 days	1 year 2 months 19 days

Stock-Based Compensation - Su_4

Stock-Based Compensation - Summary of RSU Activity (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Time-based Restricted Stock Units
Number of Shares
Balance at December 31, 2020	1,161
Granted	833
Vested	(285)
Forfeited	(203)
Balance at December 31, 2021	1,506	1,161
Weighted-Average Grant Date Fair Value
Balance at December 31, 2020	$ 102.24
Granted	84.80	$ 106.56	$ 93.67
Vested	100.11
Forfeited	101.12
Balance at December 31, 2021	$ 93.14	$ 102.24
Performance-based Restricted Stock Units
Number of Shares
Balance at December 31, 2020	0
Granted	113
Balance at December 31, 2021	113	0
Weighted-Average Grant Date Fair Value
Balance at December 31, 2020	$ 0
Granted	79.60
Balance at December 31, 2021	$ 76.60	$ 0

Income Taxes - Summary of Total

Income Taxes - Summary of Total Deferred Income Tax Assets, Net of Valuation Allowance (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets
Net operating loss carryforwards	$ 157,277	$ 87,124
Research and development credits	33,341	18,139
Accruals and reserves	3,889	1,368
Stock-based compensation	4,932	5,661
Lease liability	10,854	9,151
Gross deferred tax assets	210,293	121,443
Less: valuation allowance	(203,516)	(112,680)
Deferred tax assets, net of valuation allowance	6,777	8,763
Deferred tax liabilities
Fixed and intangible assets	84	360
Right-of-use asset	6,693	8,403
Gross deferred tax liabilities	6,777	8,763
Net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Line Items]
Deferred tax assets, valuation allowance	$ 203,516,000	$ 112,680,000
Increase in valuation allowance	90,800,000	52,800,000
Federal NOL carryforwards	715,500,000
State NOL carryforwards	95,100,000
Research and development credits	33,341,000	18,139,000
Accrual for interest and penalties	$ 0	$ 0
Federal
Income Tax Disclosure [Line Items]
NOL carryforwards, expiration year	2032
Research and development credits	$ 38,400,000
Research and development tax credit carryforwards, expiration year	2033
Federal | Generated After December 31, 2017
Income Tax Disclosure [Line Items]
Federal NOL carryforwards	$ 653,600,000
Federal | 2032 Expiration Period
Income Tax Disclosure [Line Items]
Federal NOL carryforwards	61,900,000
State
Income Tax Disclosure [Line Items]
Research and development credits	$ 8,000,000

Income Taxes - Summary of Effec

Income Taxes - Summary of Effective Tax Rate Differs From Federal Statutory Tax Rate (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Federal statutory tax rate	21.00%	21.00%
Change in deferred tax asset valuation allowance	(33.70%)	(34.40%)
State taxes, net of federal benefit	1.90%	0.80%
Research and development tax credits	5.20%	5.60%
Stock-based compensation	6.90%	6.90%
Other	(1.30%)	0.10%
Effective tax rate	0.00%	0.00%

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Balance at the beginning of the year	$ 6,932	$ 3,545
Increase related to current year tax positions	5,345	3,387
Increase related to prior year tax positions	324
Balance at the end of the year	$ 11,953	$ 6,932

Defined Contribution Plans - Ad

Defined Contribution Plans - Additional Information (Details) - 401(K) Plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Contribution Plan Disclosure [Line Items]
Contributions made by employer	$ 0.7	$ 0.7	$ 0.5
Employer contribution matching percentage	4.00%

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) shares in Millions, SFr in Millions, $ in Millions	Feb. 15, 2022USD ($)shares	Feb. 14, 2022USD ($)	Feb. 14, 2022CHF (SFr)	Dec. 31, 2021USD ($)
Subsequent Event [Line Items]
Noncancellable purchase obligations				$ 284.8
Lonza AG
Subsequent Event [Line Items]
Noncancellable purchase obligations				$ 231.2
Termination agreement date		Feb. 14, 2022	Feb. 14, 2022
Termination agreement description		95% of which is to be paid within 30 days after the Effective Date, and 5% of which is be paid within 30 days of the release of the remaining cGMP batches. If the Company fails to pay the first 95% of the Termination Amount to Lonza within 30 days of the Effective Date, Lonza may at its option give notice to the Company that the Termination Agreement is terminated.	95% of which is to be paid within 30 days after the Effective Date, and 5% of which is be paid within 30 days of the release of the remaining cGMP batches. If the Company fails to pay the first 95% of the Termination Amount to Lonza within 30 days of the Effective Date, Lonza may at its option give notice to the Company that the Termination Agreement is terminated.
Lonza AG | Subsequent Event
Subsequent Event [Line Items]
Termination fee payable		$ 136.1	SFr 126
Expected termination charges against earnings		$ 137
Re-organization Plan [Member] | Subsequent Event
Subsequent Event [Line Items]
Re-organization plan, initiation Date	Feb. 15, 2022
Re-organization plan completion date	Mar. 31, 2022
Workforce reduction percentage	35.00%
Date of elimination	Feb. 16, 2022
Restructuring charges	$ 5.3
Cash retention bonuses	$ 3
Re-organization Plan [Member] | Restricted Stock Units | Subsequent Event
Subsequent Event [Line Items]
Grants of RSUs | shares	8.2
Re-organization Plan [Member] | Time-based Restricted Stock Units | Subsequent Event
Subsequent Event [Line Items]
Vesting period	4 years