Annexon (ANNX) 10-K 1 Mar 22 2021 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Feb. 25, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Amendment Flag	false
Document Period End Date	Dec. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Trading Symbol	ANNX
Entity Registrant Name	ANNEXON, INC.
Entity Central Index Key	0001528115
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Title of 12(b) Security	Common stock, par value $0.001 per share
Security Exchange Name	NASDAQ
Entity File Number	001-39402
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	27-5414423
Entity Address, Address Line One	1400 Sierra Point Parkway
Entity Address, Address Line Two	Bldg C
Entity Address, Address Line Three	Suite 200
Entity Address, City or Town	Brisbane
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94005
City Area Code	650
Local Phone Number	822-5500
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		38,563,565
Entity Public Float			$ 750
ICFR Auditor Attestation Flag	true
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Auditor Name	KPMG LLP
Auditor Location	San Francisco, CA
Auditor Firm ID	185
Documents Incorporated by Reference	Portions of the Registrant’s definitive proxy statement relating to the 2022 Annual Meeting of Stockholders, which will be filed with the Securities and Exchange Commission within 120 days after the end of the Registrant’s fiscal year ended December 31, 2021, are incorporated by reference into Part III of this Annual Report on Form 10-K.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 74,843	$ 268,565
Short-term investments	167,872	82,641
Prepaid expenses and other current assets	4,978	2,805
Total current assets	247,693	354,011
Restricted cash	1,166
Property and equipment, net	17,848	1,935
Operating lease right-of-use assets	20,333
Total assets	287,040	355,946
Current liabilities:
Accounts payable	11,153	3,734
Accrued liabilities	9,250	6,497
Deferred rent, current		391
Operating lease liabilities, current	1,202
Other current liabilities	139
Total current liabilities	21,744	10,622
Deferred rent		1,046
Operating lease liabilities, non-current	33,387
Total liabilities	55,131	11,668
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized as of December 31, 2021 and 2020, respectively; no shares issued and outstanding as of December 31, 2021 and 2020, respectively
Common stock, $0.001 par value; 300,000,000 shares authorized as of December 31, 2021 and 2020, respectively; 38,560,854 and 38,157,618 shares issued and outstanding as of December 31, 2021 and 2020, respectively	39	38
Additional paid-in capital	528,365	510,309
Accumulated other comprehensive loss	(180)	(77)
Accumulated deficit	(296,315)	(165,992)
Total stockholders' equity	231,909	344,278
Total liabilities and stockholders’ equity	$ 287,040	$ 355,946

Consolidated Balance Sheets (Pa

Consolidated 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	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value per share	$ 0.001	$ 0.001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	38,560,854	38,157,618
Common stock, shares outstanding	38,560,854	38,157,618

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating expenses:
Research and development	$ 100,066	$ 49,271
General and administrative	30,647	14,198
Total operating expenses	130,713	63,469
Loss from operations	(130,713)	(63,469)
Interest and other income, net	390	57
Net loss	(130,323)	(63,412)
Accretion on redeemable convertible preferred stock		(705)
Deemed dividend – beneficial conversion feature on redeemable convertible preferred stock		(6,219)
Net loss attributable to common stockholders	$ (130,323)	$ (70,336)
Net loss per share attributable to common stockholders, basic and diluted	$ (3.40)	$ (4.15)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted	38,316,273	16,962,398

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (130,323,000)	$ (63,412,000)
Other comprehensive gain (loss):
Foreign currency translation adjustment	(5,000)	9,000
Unrealized loss on available for sale securities	(98,000)	(6,000)
Comprehensive loss	$ (130,426,000)	$ (63,409,000)

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($)	Total	Redeemable Convertible Preferred Stock [Member]	Series D Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Beginning Balance, Values at Dec. 31, 2019		$ 143,984,000
Beginning Balance, Shares at Dec. 31, 2019		111,748,065
Beginning Balance, Shares at Dec. 31, 2019				433,749
Beginning Balance, Values at Dec. 31, 2019	$ (100,454,000)			$ 4,000	$ 2,202,000	$ (80,000)	$ (102,580,000)
Accretion on redeemable convertible preferred stock		$ 705,000
Accretion on redeemable convertible preferred stock	(705,000)				(705,000)
Issuance of redeemable convertible preferred stock, net of issuance costs			$ 96,807,000
Issuance of redeemable convertible preferred stock, net of issuance costs and value of redeemable convertible preferred stock liability, Shares			71,719,859
Beneficial conversion feature on Series D redeemable convertible preferred stock			$ (6,297,000)
Beneficial conversion feature on Series D redeemable convertible preferred stock	6,297,000				6,297,000
Conversion of redeemable convertible preferred stock to common stock upon initial public offering	6,297,000	$ (241,418,000)
Conversion of redeemable convertible preferred stock to common stock upon initial public offering, Shares		(183,467,924)
Conversion of redeemable convertible preferred stock to common stock upon initial public offering	241,418,000			$ 21,000	241,397,000
Conversion of redeemable convertible preferred stock to common stock upon initial public offering, Shares				20,824,938
Deemed dividend of beneficial conversion feature on conversion of redeemable convertible preferred stock		$ 6,219,000
Deemed dividend of beneficial conversion feature on conversion of redeemable convertible preferred stock	(6,219,000)				(6,219,000)
Issuance of common stock in connection with initial public offering, net of issuance costs of $24,700	262,440,000			$ 13,000	262,427,000
Issuance of common stock in connection with initial public offering, net of issuance costs of $24,700, Shares				16,889,403
Stock-based compensation	4,888,000				4,888,000
Stock option exercises	22,000				22,000
Stock option exercises, Shares				9,528
Foreign currency translation adjustment	9,000					9,000
Unrealized loss on available-for-sale securities	(6,000)					(6,000)
Net loss	(63,412,000)						(63,412,000)
Ending Balance, Values at Dec. 31, 2020		$ 0
Ending Balance, Shares at Dec. 31, 2020		0
Ending Balance, Values at Dec. 31, 2020	344,278,000			$ 38,000	510,309,000	(77,000)	(165,992,000)
Ending Balance, Shares at Dec. 31, 2020				38,157,618
Stock-based compensation	16,262,000				16,262,000
Stock option exercises	$ 1,610,000			$ 1,000	1,609,000
Stock option exercises, Shares	391,349			391,349
Issuance of common stock per ESPP purchase	$ 185,000				185,000
Issuance of common stock per ESPP purchase, Shares				11,887
Foreign currency translation adjustment	(5,000)					(5,000)
Unrealized loss on available-for-sale securities	(98,000)					(98,000)
Net loss	(130,323,000)						(130,323,000)
Ending Balance, Values at Dec. 31, 2021	$ 231,909,000			$ 39,000	$ 528,365,000	$ (180,000)	$ (296,315,000)
Ending Balance, Shares at Dec. 31, 2021				38,560,854

Consolidated Statements of Re_2

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Series D Redeemable Convertible Preferred Stock [Member]
Stock issuance costs	$ 5,200
Common Stock [Member]
Stock issuance costs	$ 24,700

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating activities:
Net loss	$ (130,323)	$ (63,412)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,141	667
Accretion of discount on available-for sale securities	1,253	53
Stock-based compensation	16,262	4,888
Reduction in the carrying amount of right-of-use assets	1,273
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,612)	(1,330)
Other long-term assets		96
Accounts payable	3,859	1,513
Accrued liabilities	773	4,804
Deferred rent		(366)
Operating lease liabilities	1,125
Other current liabilities	139
Net cash used in operating activities	(106,110)	(53,087)
Investing activities:
Purchases of property and equipment	(1,654)	(464)
Purchases of available-for-sale securities	(225,601)	(82,700)
Proceeds from sale of available-for-sale securities	5,993
Proceeds from maturities of available-for-sale securities	133,026
Net cash used in investing activities	(88,236)	(83,164)
Financing activities:
Proceeds from the exercise of common stock options	1,610	22
Proceeds from employee stock purchase plan	185
Proceeds from Paycheck Protection Program loan		500
Repayments of Paycheck Protection Program loan		(500)
Proceeds from issuance of redeemable convertible preferred stock (including $13,900 of proceeds from the related parties)		102,000
Payments of issuance costs related to redeemable convertible preferred stock		(5,193)
Proceeds from issuance of common stock upon initial public offering, net of underwriting discounts and commissions		267,021
Payments of offering costs related to initial public offering		(2,974)
Net cash provided by financing activities	1,795	360,876
(Decrease) increase in cash, cash equivalents, and restricted cash	(192,551)	224,625
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(5)	9
Cash, cash equivalents, and restricted cash at beginning of year	268,565	43,931
Cash, cash equivalents, and restricted cash at end of year	76,009	268,565
Supplemental disclosures of cash flow information:
Cash paid for amounts included in the measurement of lease liability	996
Non-cash investing and financing activities:
Reclassification of redeemable convertible preferred stock to common stock upon initial public offering		241,418
Accretion on redeemable convertible preferred stock		705
Right-of-use assets obtained in exchange for lease liability	21,084
Leasehold improvements obtained in exchange for tenant improvement allowance from lessors	10,860
Purchase of property and equipment included in accounts payable and accrued liabilities	$ 5,540
Beneficial conversion feature recognized upon issuance of redeemable convertible preferred stock		6,297
Deemed dividend arising from conversion of beneficial conversion feature		$ 6,219

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Proceeds from issuance of redeemable convertible preferred stock	$ 102,000
Related Parties [Member]
Proceeds from issuance of redeemable convertible preferred stock	$ 13,900

Organization

Organization	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Organization	1. Organization Annexon, Inc., or the Company, is a clinical-stage biopharmaceutical company pioneering a new class of complement medicines designed to stop the classical complement pathway at its start, C1q, in order to bring therapies to patients suffering from serious complement-mediated autoimmune, neurodegenerative and ophthalmic disorders. The Company is located in Brisbane, California and was incorporated in Delaware in March 2011. The Company’s wholly-owned subsidiary, Annexon Biosciences Australia Pty Ltd, or the Subsidiary, is a proprietary limited company incorporated in 2016 and domiciled in Australia. The Subsidiary is also engaged in research and development activities in support of its parent company. Initial Public Offering On July 23 14,750,000 2,139,403 262.4 Reverse Stock Split On July 17, 2020, the Company’s board of directors approved an amendment to the Company’s certificate of incorporation to effect a reverse split of shares of the Company’s common stock on a one-for- 8.81 Liquidity Since inception, the Company has been involved primarily in performing research and development activities, conducting clinical trials, hiring personnel, and raising capital to support and expand these activities. The Company has experienced losses and negative cash flows from operations since its inception and, as of December 31, 2021, had an accumulated deficit of $296.3 million and cash and cash equivalents and short-term investments of $242.7 million. The Company has historically funded its operations through the issuance of shares of its redeemable convertible preferred stock and common stock. Based on projected activities, management projects that cash on hand is sufficient to support operations for at least the next 12 months following issuance of these consolidated financial statements. Management expects to continue to incur losses and negative cash flows from operations for at least the next several years.

Basis of Presentation and Signi

Basis of Presentation and Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	2 . Basis of Presentation Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported expenses during the reporting period. Management evaluates its estimates, including but not limited to the fair value of investments, stock options, income taxes, clinical trial accruals and stock-based compensation. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates. Principles The consolidated financial statements include the operations of Annexon, Inc. and its wholly owned subsidiary and include the results of operations and cash flows of these entities. All intercompany balances and transactions have been eliminated in consolidation. Segments The Company’s chief operating decision maker is its Chief Executive Officer. The Chief Executive Officer reviews financial information on an aggregate basis for the purposes of evaluating financial performance and allocating the Company’s resources. Accordingly, the Company has determined that it operates in one segment. Cash, Cash Equivalents and Restricted Cash The considers Restricted cash as of December 31, 2021 relates to the letters of credit established for the Company’s office leases. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheets that sum to the total of the same amounts shown in the consolidated statements of cash flows: December 31, 2021 2020 Cash $ 734 $ 597 Cash equivalents 74,109 267,968 Cash and cash equivalents 74,843 268,565 Restricted cash 1,166 — Cash, cash equivalents and restricted cash $ 76,009 $ 268,565 Short-Term Investments Short-term investments have been classified as available-for-sale and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. The Company determines the appropriate classification of its investments in debt securities at the time of purchase. Available-for-sale securities with original maturities beyond three months at the date of purchase are classified as current based on their availability for use in current operations. The Company evaluates, on a quarterly basis, its available-for-sale debt securities for potential impairment. For available-for-sale debt securities in an unrealized loss position, the Company assesses whether such declines are due to credit loss based on factors such as changes to the rating of the security by a ratings agency, market conditions and supportable forecasts of economic and market conditions, among others. If credit loss exists, the Company assess es whether it has plans to sell the security or it is more likely than not it will be required to sell any available-for-sale debt security before recovery of its amortized cost basis. If either condition is met, the security’s amortized cost basis is written down to fair value and is recognized through interest and other income (expense) , net. If neither condition is met, declines as a result of credit losses, if any, are recognized as an allowance for credit loss, limited to the amount of unrealized loss, through interest and other income (expense) , net. Any portion of the unrealized loss that is not a result of a credit loss, is recognized in other comprehensive income (loss) . Realized gains and losses, if any, on available-for-sale debt securities are included in interest and other income (expense) , net. The cost of investments sold is based on the specific-identification method. Interest on available-for-sale debt Property and Equipment, Net Property and equipment are carried at cost less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets. Depreciation begins at the time the asset is placed in service. Maintenance and repairs are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the balance sheet and the resulting gain or loss is reflected in operations in the period realized. The useful Laboratory equipment 5 years Office and computer equipment 3 years Leasehold improvements Shorter of remaining lease term or estimated useful life Impairment of Long-Lived Assets The Company evaluates its long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying amount of these assets may not be recoverable. Recoverability of these assets is measured by comparison of the carrying amount of each asset to the future undiscounted cash flows the asset is expected to generate over its remaining life. When indications of impairment are present and the estimated undiscounted future cash flows from the use of these assets is less than the assets’ carrying value, the related assets will be written down to fair value. There were no impairments of the Company’s long-lived assets for the periods presented. Leases The Company determines if an arrangement is a lease at inception. Upon adoption of Accounting Standards Codification 842, Leases As a practical expedient, the Company elected, for all facility leases, not to separate non-lease components from lease components and instead to account for each separate lease component and its associated non-lease components as a single lease component. The Company elected to exclude from its balance sheets recognition of leases having a term of 12 months or less (short-term leases). Income Taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carry forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. Valuation allowances are established when necessary to reduce deferred taxes to the amounts expected to be realized. The examination Commitments and Contingencies Liabilities for loss contingencies arising from claims, assessments, litigation, fines, and penalties and other sources are recorded when it is probable that a liability has been incurred and the amount can be reasonably estimated. Legal costs incurred in connection with loss contingencies are expensed as incurred. Foreign Currencies The Dollar Gains Research and Development Expense Research and development expenses consist primarily of direct and indirect costs incurred for the development of the Company’s product candidates. Direct expenses include (i) preclinical and clinical outside service costs associated with discovery, preclinical and clinical testing of the Company’s product candidates; (ii) professional services agreements with third-party contract organizations, investigative clinical trial sites and consultants that conduct research and development activities on the Company’s behalf; (iii) contract manufacturing costs to produce clinical trial materials; and (iv) laboratory supplies and materials. Indirect expenses include (A) compensation and personnel-related expenses (including stock-based compensation), (B) allocated expenses for facilities and depreciation; and (C) other indirect costs. Research and development costs are expensed as incurred. Payments made to third parties are under agreements that are generally cancelable by the Company. Advance payments for research and development activities are deferred as prepaid expenses. The prepaid amounts are expensed as the related services are performed. The Company estimates preclinical studies and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on the Company’s behalf. The Company also estimates manufacturing costs based on services performed pursuant to contracts with contract manufacturing organizations that develop and manufacture product on the Company’s behalf. In accruing service fees, the Company estimates the period over which services will be performed and the level of effort to be expended in each period. These estimates are based on the Company’s communications with the third-party service providers and on information available at each balance sheet date. If the actual timing of the performance of services or the level of effort varies significantly from the estimate, the Company will adjust Stock-Based Compensation The Company accounts for stock-based compensation arrangements with employees and non-employee directors and consultants using a fair value method which requires the recognition of compensation expense for costs related to all stock-based payments, including stock options and restricted stock units, or RSUs. The fair value method requires the Company to estimate the fair value of stock options to employees and non-employees on the date of grant using the Black-Scholes option pricing model. The fair value of RSU awards are based on the fair value of the underlying common stock as of the grant date. The Company grants certain employees performance-based stock options. For awards that include performance conditions, no compensation cost is recognized until the performance goals are probable of being met, at which time the cumulative compensation expense from the service inception date would be recognized. Stock-based compensation costs are based on the fair value of the underlying option calculated using the Black-Scholes option pricing model and recognized as expense on a straight-line basis (for all but performance-based awards for which the accelerated method is used) over the requisite service period, which is the vesting period. Determining the appropriate fair value model and related assumptions requires judgment, including estimating expected term, expected stock price volatility, risk-free interest rate and dividend yield. The Company accounts for forfeitures Accounting for Non-Recurring Grant Income Non-recurring grant income is recognized when the research and development activities have been undertaken and the Company has completed its assessment of whether such activities meet the relevant qualifying criteria. Grants received from government and other agencies in advance of the specific research and development costs to which they relate are deferred and recognized in the consolidated statement of operations in the period they are earned and when the related research and development costs are incurred. Non-recurring grant income recognized in interest and other income (expense), net was $135,000 for the year ended December 31, 2021. No non-recurring grant income was recognized during 2020. Net Loss Per Share Attributable Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period, without consideration for potential dilutive shares of common stock. As the Company was in a loss position for all periods presented, basic net loss per share attributable to common stockholders is the same as diluted net loss per share attributable to common stockholders because the effects of potentially dilutive securities are antidilutive. Concentration of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash and cash equivalents and short-term investments. The Company’s cash and Management Recently Adopted Accounting Pronouncements In August 2018, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (Topic 350) The standard requires implementation costs incurred by customers in cloud computing arrangements to be deferred over the noncancelable term of the cloud computing arrangements plus any optional renewal periods (1) that are reasonably certain to be exercised by the customer or (2) for which exercise of the renewal option is controlled by the cloud service provider. The effective date of this pronouncement is for fiscal years beginning after December 15, 2020 and early adoption is permitted. The standard can be adopted either using the prospective or retrospective transition approach. The Company adopted ASU No. 2018-15 on January 1, 2021 and the adoption did not have a material impact on its consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), , Leases In the second quarter of 2021, the Company adopted ASU No. 2016-02 The adoption of Topic 842 as of January 1, 2021 resulted in the recognition of ROU assets of $0.5 million, corresponding lease liabilities of $0.6 million, the derecognition of Commitments and Contingencies T As part of the Topic 842 adoption, the Company elected certain practical expedients outlined in the guidance. The Company has chosen to apply the package of practical expedients for existing leases, which provides relief from reassessing: (i) whether a contract is or contains a lease, (ii) lease classification, and (iii) whether initial direct costs can be capitalized. The Company did not elect the hindsight practical expedient to reassess the lease term for existing leases. The Company elected the short-term lease exemption, under which any lease less than 12 months is excluded from recognition on the balance sheet. Additionally, the Company elected the non-separation of lease and non-lease components. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments Codification Improvements to Topic 326, Financial Instrument s —Credit Losses . This ASU does not change the core principle of the guidance in ASU 2016-13, instead these amendments are intended to clarify and improve operability of certain topics included within the credit losses guidance. The FASB also subsequently issued ASU No. 2019-04, Codification Improvements to Topic 326, Financial Instruments—Credit Losses, Derivatives and Hedging (Topic 815), and Financial Instruments (Topic 825), which did not change the core principle of the guidance in ASU 2016-13 but clarified that expected recoveries of amounts previously written off and expected to be written off should be included in the valuation account and should not exceed amounts previously written off and expected to be written off. In March 2020, the FASB issued ASU No. 2020-3, Codification Improvements to Financial Instruments which makes narrow-scope improvements to various financial instruments topics, including the new credit losses standard and clarifies the following areas ( i ) the contractual term of a net investment in a lease should be the contractual term used to measure expected credit losses; (ii) when an entity regains control of financial assets sold, an allowance for credit losses should be recorded. The guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2019 for public business entities, excluding smaller reporting companies. The Company adopted this guidance on a modified-retrospective basis effective January 1, 2021 and noted no material impact to the Company’s consolidated financial statements. Recently The Company has reviewed the FASB issued ASU accounting pronouncements and interpretations thereof that have effectiveness dates during the periods reported and in future periods. The Company has carefully considered the new pronouncements that alter previous generally accepted accounting principles and do not believe that any new or modified principles will have a material impact on the Company’s reported financial position or operations in the near term. The applicability of any standard is subject to the formal review of the Company’s financial management.

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 utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The Company determines fair value based on assumptions that market participants would use in pricing an asset or liability in the principal or most advantageous market. When considering market participant assumptions in fair value measurements, the following fair value hierarchy distinguishes between observable and unobservable inputs, which are categorized in one of the following levels: • Level 1 Inputs: Unadjusted quoted prices in active markets for identical assets or liabilities accessible to the reporting entity at the measurement date. • Level 2 Inputs: Other than quoted prices included in Level 1 inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the asset or liability. • Level 3 Inputs: Unobservable inputs for the asset or liability used to measure fair value to the extent that observable inputs are not available, thereby allowing for situations in which there is little, if any, market activity for the asset or liability at measurement date. On a recurring basis, the Company measures certain financial assets and liabilities at fair value. The following tables summarize the fair value of the Company’s financial assets and liabilities measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): December 31, 2021 Valuation Hierarchy Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Assets: Cash equivalents: Money market funds Level 1 $ 74,109 $ — $ — $ 74,109 Short-term investments: Commercial paper Level 2 85,352 — (27 ) 85,325 Corporate debt Level 2 48,814 — (24 ) 48,790 Government bonds Level 2 33,809 — (52 ) 33,757 Total assets $ 242,084 $ — $ (103 ) $ 241,981 December 31, 2020 Valuation Hierarchy Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Assets: Cash equivalents: Money market funds Level 1 $ 267,968 $ — $ — $ 267,968 Short-term investments: Commercial paper Level 2 59,930 — — 59,930 Corporate bonds Level 2 22,717 1 (7 ) 22,711 Total assets $ 350,615 $ 1 $ (7 ) $ 350,609 All of the investments held as of December 31, 2021 had maturities of less than two years. For the years ended December 31, 2021 and 2020, the Company recognized no material realized gains or losses on financial instruments.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2021
Disclosure Of Balance Sheet Components [Abstract]
Balance Sheet Components	4 . Balance Sheet Components Prepaid Expenses and Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2021 2020 Prepaid insurance $ 1,282 $ 1,236 Prepaid research and development costs 3,002 1,039 Other prepaid expenses 231 527 Other receivables — 3 Other current assets 463 — Total prepaid expenses and other current assets $ 4,978 $ 2,805 Property and Property and equipment, net consisted of the following (in thousands): December 31, 2021 2020 Leasehold improvements $ 16,594 $ 3,061 Laboratory equipment 1,353 555 Furniture and fixtures 649 263 Computer equipment and software 41 27 Total property and equipment, gross $ 18,637 $ 3,906 Less: accumulated depreciation (789 ) (1,971 ) Total property and equipment, net $ 17,848 $ 1,935 Total depreciation expense recognized for the years ended December 31, 2021 and 2020 was $2.1 million and $0.7 million, respectively. Accrued Liabilities Accrued liabilities consisted of the following (in thousands): December 31, 2021 2020 Accrued research and development expenses $ 2,404 $ 3,260 Accrued compensation 3,573 2,543 Accrued professional services 1,274 524 Accrued construction costs 1,917 — Other accrued expenses 82 170 Total accrued liabilities $ 9,250 $ 6,497

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	5 . Commitments Leases The Company leased its offices and laboratory in South San Francisco, California, or the South San Francisco Lease, under a 7-year noncancelable lease agreement that ends in June 2024 with a 5-year renewal option. In December 2020, the Company entered into an agreement to lease office and laboratory space in Brisbane, California, or the Brisbane Lease, with an affiliate of the South San Francisco Lease landlord. November 2021 ten-year Concurrent with the execution of the Brisbane Lease, the Company entered into an agreement to terminate the South San Francisco Lease, immediately effective when the tenant improvements of the Brisbane Lease were completed in December 2021. The South San Francisco Lease and the Brisbane Lease are accounted for as one lease with two lease components. Accordingly, upon adoption of Topic 842, the total consideration for the lease was reallocated to each lease component based on standalone selling price. As the Brisbane Lease commenced in May 2021, $1.3 million of the consideration allocated to the Brisbane Lease was recorded as a liability as of January 1, 2021 when the deferred rent balance of the South San Francisco Lease was derecognized. In November 2021, the Company subleased space that has no immediate needs for the Company’s operations for two years starting from December 2021 for the aggregate sublease payments of $3.4 million. The sublease income, while it reduces the rent expense, is not considered in the value of the right-of-use asset or lease liability. The Company’s sublease income was $0.1 million for the year ended December 31, 2021. In connection The weighted average incremental borrowing rate used to measure the operating lease liability is 8.4%. Operating lease cost for the year ended December 31, 2021 was $2.9 million. Variable lease payments for the year ended December 31, 2021 were $0.4 million. Rent expense for the year ended December 31, 2020 was $0.4 million. Future minimum lease payments and related lease liabilities as of December 31, 2021, were as follows: As of December 31: (in thousands) 2022 $ 4,203 2023 4,742 2024 4,907 2025 5,079 2026 and thereafter 32,833 Total undiscounted lease payments 51,764 Less: Imputed interest (17,175 ) Total 34,589 The Company’s future undiscounted lease payments under non-cancellable operating leases (as defined by prior guidance) as of December 31, 2020 were as follows: As of December 31: (in thousands) 2021 $ 618 2022 4,189 2023 4,756 2024 5,035 2025 and thereafter 38,332 Total 52,930 License and In November 2011, the Company entered into an exclusive licensing agreement , or the Stanford Agreement, with The Board of Trustees of the Leland Stanford Junior University, or Stanford, whereby the Company was granted an exclusive, worldwide, royalty-bearing, sublicensable license, under certain patent rights, or the Licensed Patents, to make, use, offer for sale, sell, import and otherwise commercialize products covered by the Licensed Patents for human or animal diseases, disorders or conditions. Under the Stanford Agreement, the Company made an upfront payment and is obligated to pay Stanford annual license maintenance fees, potential future milestone payments totaling up to $500,000, and royalty payments at a rate equal to a low single-digit percentage of worldwide net sales of licensed products. The Company did not achieve any milestones or make any milestone payments for the years ended December 31, 2021 and 2020. In December 2016, the Company entered into a Sponsored Research Agreement with a not-for-profit entity to perform research on multiple sclerosis. The Sponsored Research Agreement was amended in March 2019. Under the terms of the Sponsored Research Agreement, as amended, the Company may receive up to $651,000 No Guarantees and In the normal course of business, the Company enters into agreements that contain a variety of representations and provide for general indemnification. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. As of December 31, 2021, the Company did not have any material indemnification claims or guarantees that were probable or reasonably possible and consequently has not recorded related liabilities.

Stockholder's Equity

Stockholder's Equity	12 Months Ended
	Dec. 31, 2021
Stockholders Equity Note [Abstract]
Stockholder's Equity	6 . Stockholder’s Equity Common Stock The holders of the Company’s common stock have one vote for each share of common stock. Common stockholders are entitled to dividends when, as, and if declared by the Board of Directors. The holders have no preemptive or other subscription rights and there are no redemption or sinking fund provisions with respect to such shares. As of December 31, 2021, no dividends had been declared by the Board of Directors. The Company reserved the following shares of common stock for issuance as follows: December 31, 2021 2020 Options issued and outstanding 5,662,824 3,909,873 Reserve for 2020 Incentive Plan 2,039,951 2,707,947 Unvested restricted stock units outstanding 50,000 — Common stock reserved for 2021 ATM program 5,265,929 — Reserved for employee stock purchase plan 729,775 360,086 Total common stock reserved 13,748,479 6,977,906 At-the-Market Offering In August 2021, the Company entered into a sales agreement with Cowen and Company LLC, or Cowen, as sales agent, pursuant to which the Company may issue and sell shares of its common stock for an aggregate maximum offering price of $100.0 million under an at-the-market offering program, or 2021 ATM program. The Company will pay Cowen up to 3% of gross proceeds for the common stock sold through the 2021 ATM program. As of December 31, 2021, no shares of common stock have been sold under the 2021 ATM program.

Equity Incentive Plan

Equity Incentive Plan	12 Months Ended
	Dec. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity Incentive Plan	7 . Equity Incentive In July 2020, the Company’s board of directors and stockholders adopted and approved the 2020 Incentive Award Plan, or the 2020 Plan, and the Employee Stock Purchase Plan, or the ESPP, which became effective in connection with the IPO. The Company may not grant any additional awards under the 2011 Equity Incentive Plan, or the 2011 Plan. The 2011 Plan will continue to govern outstanding equity awards granted thereunder. 2020 Equity Incentive Plan The number of shares of common stock reserved for issuance under the 2020 Plan automatically increase on the first day of January, in an amount equal to 4% of the total number of shares of the Company’s capital stock outstanding on the last day of the preceding year, or a lesser number of shares determined by the Company’s board of directors. Awards granted under the 2020 Plan expire no later than ten years from the date of grant. For the Incentive Stock Options, or ISOs, and Nonstatutory Stock Options, or NSOs, the option price shall not be less than 100% of the estimated fair value on the date of grant. Options granted typically vest over a four-year 2,039,951 Stock options Stock option activity under the 2011 Plan and the 2020 Plan was as follows: Number of Shares Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Balances as of December 31, 2020 3,909,873 $ 10.78 8.40 $ 56,128 Additional shares authorized Stock options granted 2,871,400 $ 25.54 Stock options exercised (391,349 ) $ 4.11 Stock options cancelled (727,100 ) $ 24.41 Balances as of December 31, 2021 5,662,824 $ 16.98 8.26 $ 10,186 Exercisable as of December 31, 2021 2,065,942 $ 11.34 7.08 $ 8,120 The total intrinsic value of options exercised during the years ended December 31, 2021 and 2020 was $6.4 million and $0.2 million, respectively. The intrinsic value is the difference between the fair value of the Company’s common stock at the time of exercise and the exercise price of the stock option. The weighted-average grant date fair value of options granted to employees during the years ended December 31, 2021 and 2020 was $18.83 and $12.33 per share, respectively. As of December 31, 2021, the total unrecognized stock-based compensation cost related to outstanding unvested stock options that are expected to vest was $51.9 million, which the Company expects to recognize over an estimated weighted-average period of 3.03 years. Restricted Stock Units RSUs are share awards that entitle the holder to receive freely tradeable shares of the Company’s common stock upon vesting. The RSUs cannot be transferred and the awards are subject to forfeiture if the holder’s employment terminates prior to the release of the vesting restrictions. The RSUs generally vest over a three-year period in equal amounts on an annual basis, provided the employee remains continuously employed with the Company. The fair value of the RSUs is equal to the closing price of the Company’s common stock on the grant date. A summary of RSU activity under our equity incentive plan and related information is as follows: Number of Shares Weighted-Average Grant Date Fair Value Per Share Unvested as of December 31, 2020 — $ — Granted 50,000 12.84 Unvested as of December 31, 2021 50,000 $ 12.84 As of December 31, 2021, unrecognized stock-based compensation expense related to outstanding unvested RSUs was $0.6 million, which is expected to be recognized over a weighted-average period of 2.98 years. Employee Stock Purchase Plan The ESPP enables eligible employees to purchase shares of the Company's common stock at the end of each offering period at a price equal to 85% of the fair market value of the shares on the first business day or the last business day of the offering period, whichever is lower. Eligible employees generally included all employees. Share purchases are funded through payroll deductions of at least 1%, and up to 15% of an employee’s eligible compensation for each payroll period. The number of shares reserved for issuance under the ESPP increase automatically on the first day of each fiscal year, by a number equal to, 1% of the shares of common stock outstanding on the last day of the immediately preceding fiscal year, or such number of shares determined by the Company’s board of directors. As of December 31, 2021, 729,775 shares were available for future purchase. The ESPP generally provides for six-month consecutive offering periods beginning on May 15 th th The ESPP is a compensatory plan as defined by the authoritative guidance for stock compensation. As such, stock-based compensation expense has been recorded for the years ended December 31, 2021 and 2020. Stock-Based Compensation Expense The total stock-based compensation expense recognized was as follows (in thousands): Year Ended December 31, 2021 2020 Research and development $ 8,610 $ 2,274 General and administrative 7,652 2,614 Total stock-based compensation expense $ 16,262 $ 4,888 The stock-based compensation expense related to the ESPP for the years ended December 31, 2021 and 2020 were $0.1 million and $0.1 million, respectively. To determine the value of stock option awards for stock-based compensation purposes, the Company uses the Black-Scholes option pricing model and the assumptions discussed below. Fair Value of Common Stock— Historically, for all periods prior to the IPO in July 2020, fair values of the shares of common stock underlying the Company’s share-based awards were estimated on each grant date by the Company’s board of directors. The board of directors considered, among other things, valuations of the Company’s common stock which were prepared by an independent third-party valuation firm in accordance with the guidance provided by the American Institute of Certified Public Accountants 2013 Practice Aid, Valuation of Privately-Held-Company Equity Securities Issued as Compensation. After the completion of the IPO, the fair value of each share of underlying common stock is based on the closing price of the Company’s common stock as reported on the date of grant on the Nasdaq Global Select Market. Expected Term —The Company’s expected term represents the period that the Company’s stock-based awards are expected to be outstanding. The Company’s historical share option exercise information is limited due to a lack of sufficient data points, and did not provide a reasonable basis upon which to estimate an expected term. The expected term for option grants is therefore determined using the simplified method (based on the mid-point between the vesting date and the end of the contractual term). Expected Volatility —Because the Company does not have sufficient trading history for its common stock, the expected volatility was estimated based on the average volatility for comparable publicly traded life science companies over a period equal to the expected term of the stock option grants. The comparable companies were chosen based on the similar size, stage in the life cycle, or area of specialty. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available and to align with the Company’s expected term. Risk-Free Interest Rate —The risk-free interest rate is based on the U.S. Treasury zero coupon issues in effect at the time of grant for periods corresponding with the expected term of the option. Dividend Yield —The Company has never paid dividends on its common stock and has no plans to pay dividends on its common stock. Therefore, the Company used an expected dividend yield of zero. The fair value of each award issued was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions: Year Ended December 31, 2021 2020 Expected term (in years) 4.33-6.08 5.00-6.08 Expected volatility 88%-91% 85%-93% Risk-free interest rate 0.35%-1.31% 0.33%-1.45% Dividend yield — —

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	8 . Income Taxes For financial reporting purposes, loss before provision for income taxes, includes the following components (in thousands): Year Ended December 31, 2021 2020 Domestic $ 130,313 $ 63,406 Foreign 10 6 Loss before income taxes $ 130,323 $ 63,412 For each of the years ended December 31, 2021 and 2020, the Company incurred insignificant amounts for an income tax provision. The U.S. federal and California deferred tax assets generated from the Company’s net operating losses have been fully reserved, as the Company believes it is more likely than not that the benefit will not be realized. Reconciliation of income tax computed at federal statutory rates to the reported provision for income taxes was as follows (in thousands): Year Ended December 31, 2021 2020 Tax provision at U.S. statutory rate $ (27,368 ) $ (13,316 ) Stock-based compensation 794 426 R&D tax credits (2,392 ) (1,031 ) Change in valuation allowance 25,911 13,906 Section 382 limitations 2,922 — Other 133 15 Provision for income taxes $ — $ — Deferred The tax effects of temporary differences that give rise to significant portions of the Company’s deferred tax assets and liabilities are as follows (in thousands): December 31, 2021 2020 Deferred Tax Assets: Net operating loss carryforwards $ 57,073 $ 36,922 Research and development credits 7,367 6,246 Other intangibles 5 5 Accruals and reserves 686 583 Stock-based compensation 3,041 995 Tenant improvement allowances — 257 Lease liabilities 7,340 — Unrealized gain/loss on investments 240 — Total gross deferred tax assets 75,752 45,008 Less: valuation allowance (69,147 ) (44,745 ) Total deferred tax assets, net $ 6,605 $ 263 Deferred Tax Liabilities: Fixed assets $ (2,290 ) $ (263 ) Right-of-use assets (4,315 ) — Total gross deferred tax liabilities (6,605 ) (263 ) Net deferred tax assets $ — $ — As of December 31, 2021, the Company had $257.9 million of federal and $70.7 million of state net operating loss, or NOL, carryforwards available to offset future taxable income. Under the Tax Cuts and Jobs Act of 2017, or the Tax Act, federal NOLs generated after December 31, 2017 will be carried forward indefinitely with the yearly NOL utilization limited to 80 percent of taxable income. The Company had $197.1 million of such federal NOLs that do not expire. If not utilized, the federal carryforward losses generated prior to 2018 and the state carryforward losses will expire in various amounts beginning in 2031. As of December 31, 2021, the Company had $7.3 million of federal and $5.6 million of state credit carryforwards available to offset future taxable income. If not utilized, these credit carryforwards will expire in various amounts for federal purposes beginning in 2031. The state credits do not expire. In assessing the realization of deferred tax assets, management considers whether it is more likely than not that some or all of the deferred tax assets will not be realized. Management believes that, based on available evidence, both positive and negative, it is more likely than not that the deferred tax assets will not be utilized; therefore, a full valuation allowance has been recorded. The Company’s valuation allowance increased by $24.4 million and $14.8 million Utilization of the net operating loss carryforwards and credits may be subject to an annual limitation due to the ownership change limitations provided by the Internal Revenue Code of 1986, as amended, and similar state provisions. The annual limitations may result in the expiration of net operating losses and credits before utilization. The Company performed a Section 382 analysis through June 30, 2021. Federal net operating losses carryforwards of $257.8 million and state and local net operating loss carryforwards of $30.8 million are not expected to expire unutilized as a result of ownership changes identified through June 30, 2021. The Company has identified $0.1 million and $39.9 million of federal and state net operating losses, respectively, that will expire unused due to ownership changes, and federal credits of $3.7 million that will not be able to be utilized due to ownership change limitation; these amounts have been excluded from the deferred tax assets table above. Uncertain Tax The Company has the following activity relating to the gross amount of unrecognized tax benefits (in thousands): Year Ended December 31, 2021 2020 Beginning balance $ 1,576 $ 1,116 Decreases based on tax positions related to prior year (789 ) — Additions based on tax positions related to current year 1,007 460 Ending balance $ 1,794 $ 1,576 None of these uncertain tax positions will impact the Company’s effective tax rate if assessed. The Company’s policy is to classify interest and penalties associated with unrecognized tax benefits as income tax expense. The Company had no interest or penalty accruals associated with uncertain tax benefits in its consolidated balance sheet and consolidated statement of operations for the years ended December 31, 2021 and 2020. The Company files income tax returns in the US, California, Georgia, Indiana, Maryland, Massachusetts, Nebraska, New Jersey, North Carolina, Pennsylvania, Texas and in Australia. The Company is not currently under examination by any major tax jurisdictions nor has it been in the past. The tax years 2011 through 2021 remain effectively open for examination by the Internal Revenue Service and most state tax authorities. Although it is reasonably possible that certain unrecognized tax benefits may increase or decrease within the next 12 months due to tax examination changes, settlement activities, expirations of statute of limitations, or the impact on recognition and measurement considerations related to the results of published tax cases or other similar activities, the Company does not anticipate any significant changes to unrecognized tax benefits over the next 12 months.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Stockholders	9 . Net Loss Per Share Attributable As the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share for all periods as the inclusion of all potential common securities outstanding would have been anti-dilutive . The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect: Year Ended December 31, 2021 2020 Stock options to purchase common stock 5,662,824 3,909,873 Shares subject to employee stock purchase plan 15,924 275 Unvested restricted stock units 50,000 — Total 5,728,748 3,910,148

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported expenses during the reporting period. Management evaluates its estimates, including but not limited to the fair value of investments, stock options, income taxes, clinical trial accruals and stock-based compensation. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates.
Principles of Consolidation	Principles The consolidated financial statements include the operations of Annexon, Inc. and its wholly owned subsidiary and include the results of operations and cash flows of these entities. All intercompany balances and transactions have been eliminated in consolidation.
Segments	Segments The Company’s chief operating decision maker is its Chief Executive Officer. The Chief Executive Officer reviews financial information on an aggregate basis for the purposes of evaluating financial performance and allocating the Company’s resources. Accordingly, the Company has determined that it operates in one segment.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash The considers Restricted cash as of December 31, 2021 relates to the letters of credit established for the Company’s office leases. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheets that sum to the total of the same amounts shown in the consolidated statements of cash flows: December 31, 2021 2020 Cash $ 734 $ 597 Cash equivalents 74,109 267,968 Cash and cash equivalents 74,843 268,565 Restricted cash 1,166 — Cash, cash equivalents and restricted cash $ 76,009 $ 268,565
Short-Term Investments	Short-Term Investments Short-term investments have been classified as available-for-sale and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. The Company determines the appropriate classification of its investments in debt securities at the time of purchase. Available-for-sale securities with original maturities beyond three months at the date of purchase are classified as current based on their availability for use in current operations. The Company evaluates, on a quarterly basis, its available-for-sale debt securities for potential impairment. For available-for-sale debt securities in an unrealized loss position, the Company assesses whether such declines are due to credit loss based on factors such as changes to the rating of the security by a ratings agency, market conditions and supportable forecasts of economic and market conditions, among others. If credit loss exists, the Company assess es whether it has plans to sell the security or it is more likely than not it will be required to sell any available-for-sale debt security before recovery of its amortized cost basis. If either condition is met, the security’s amortized cost basis is written down to fair value and is recognized through interest and other income (expense) , net. If neither condition is met, declines as a result of credit losses, if any, are recognized as an allowance for credit loss, limited to the amount of unrealized loss, through interest and other income (expense) , net. Any portion of the unrealized loss that is not a result of a credit loss, is recognized in other comprehensive income (loss) . Realized gains and losses, if any, on available-for-sale debt securities are included in interest and other income (expense) , net. The cost of investments sold is based on the specific-identification method. Interest on available-for-sale debt
Property and Equipment, Net	Property and Equipment, Net Property and equipment are carried at cost less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets. Depreciation begins at the time the asset is placed in service. Maintenance and repairs are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the balance sheet and the resulting gain or loss is reflected in operations in the period realized. The useful Laboratory equipment 5 years Office and computer equipment 3 years Leasehold improvements Shorter of remaining lease term or estimated useful life
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates its long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying amount of these assets may not be recoverable. Recoverability of these assets is measured by comparison of the carrying amount of each asset to the future undiscounted cash flows the asset is expected to generate over its remaining life. When indications of impairment are present and the estimated undiscounted future cash flows from the use of these assets is less than the assets’ carrying value, the related assets will be written down to fair value. There were no impairments of the Company’s long-lived assets for the periods presented.
Leases	Leases The Company determines if an arrangement is a lease at inception. Upon adoption of Accounting Standards Codification 842, Leases As a practical expedient, the Company elected, for all facility leases, not to separate non-lease components from lease components and instead to account for each separate lease component and its associated non-lease components as a single lease component. The Company elected to exclude from its balance sheets recognition of leases having a term of 12 months or less (short-term leases).
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carry forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. Valuation allowances are established when necessary to reduce deferred taxes to the amounts expected to be realized. The examination
Commitments and Contingencies	Commitments and Contingencies Liabilities for loss contingencies arising from claims, assessments, litigation, fines, and penalties and other sources are recorded when it is probable that a liability has been incurred and the amount can be reasonably estimated. Legal costs incurred in connection with loss contingencies are expensed as incurred.
Foreign Currencies	Foreign Currencies The Dollar Gains
Research and Development Expense	Research and Development Expense Research and development expenses consist primarily of direct and indirect costs incurred for the development of the Company’s product candidates. Direct expenses include (i) preclinical and clinical outside service costs associated with discovery, preclinical and clinical testing of the Company’s product candidates; (ii) professional services agreements with third-party contract organizations, investigative clinical trial sites and consultants that conduct research and development activities on the Company’s behalf; (iii) contract manufacturing costs to produce clinical trial materials; and (iv) laboratory supplies and materials. Indirect expenses include (A) compensation and personnel-related expenses (including stock-based compensation), (B) allocated expenses for facilities and depreciation; and (C) other indirect costs. Research and development costs are expensed as incurred. Payments made to third parties are under agreements that are generally cancelable by the Company. Advance payments for research and development activities are deferred as prepaid expenses. The prepaid amounts are expensed as the related services are performed. The Company estimates preclinical studies and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on the Company’s behalf. The Company also estimates manufacturing costs based on services performed pursuant to contracts with contract manufacturing organizations that develop and manufacture product on the Company’s behalf. In accruing service fees, the Company estimates the period over which services will be performed and the level of effort to be expended in each period. These estimates are based on the Company’s communications with the third-party service providers and on information available at each balance sheet date. If the actual timing of the performance of services or the level of effort varies significantly from the estimate, the Company will adjust
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based compensation arrangements with employees and non-employee directors and consultants using a fair value method which requires the recognition of compensation expense for costs related to all stock-based payments, including stock options and restricted stock units, or RSUs. The fair value method requires the Company to estimate the fair value of stock options to employees and non-employees on the date of grant using the Black-Scholes option pricing model. The fair value of RSU awards are based on the fair value of the underlying common stock as of the grant date. The Company grants certain employees performance-based stock options. For awards that include performance conditions, no compensation cost is recognized until the performance goals are probable of being met, at which time the cumulative compensation expense from the service inception date would be recognized. Stock-based compensation costs are based on the fair value of the underlying option calculated using the Black-Scholes option pricing model and recognized as expense on a straight-line basis (for all but performance-based awards for which the accelerated method is used) over the requisite service period, which is the vesting period. Determining the appropriate fair value model and related assumptions requires judgment, including estimating expected term, expected stock price volatility, risk-free interest rate and dividend yield. The Company accounts for forfeitures
Accounting for Non-Recurring Grant Income	Accounting for Non-Recurring Grant Income Non-recurring grant income is recognized when the research and development activities have been undertaken and the Company has completed its assessment of whether such activities meet the relevant qualifying criteria. Grants received from government and other agencies in advance of the specific research and development costs to which they relate are deferred and recognized in the consolidated statement of operations in the period they are earned and when the related research and development costs are incurred. Non-recurring grant income recognized in interest and other income (expense), net was $135,000 for the year ended December 31, 2021. No non-recurring grant income was recognized during 2020.
Net Loss Per Share Attributable to Common Stockholders	Net Loss Per Share Attributable Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period, without consideration for potential dilutive shares of common stock. As the Company was in a loss position for all periods presented, basic net loss per share attributable to common stockholders is the same as diluted net loss per share attributable to common stockholders because the effects of potentially dilutive securities are antidilutive.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash and cash equivalents and short-term investments. The Company’s cash and Management
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In August 2018, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (Topic 350) The standard requires implementation costs incurred by customers in cloud computing arrangements to be deferred over the noncancelable term of the cloud computing arrangements plus any optional renewal periods (1) that are reasonably certain to be exercised by the customer or (2) for which exercise of the renewal option is controlled by the cloud service provider. The effective date of this pronouncement is for fiscal years beginning after December 15, 2020 and early adoption is permitted. The standard can be adopted either using the prospective or retrospective transition approach. The Company adopted ASU No. 2018-15 on January 1, 2021 and the adoption did not have a material impact on its consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), , Leases In the second quarter of 2021, the Company adopted ASU No. 2016-02 The adoption of Topic 842 as of January 1, 2021 resulted in the recognition of ROU assets of $0.5 million, corresponding lease liabilities of $0.6 million, the derecognition of Commitments and Contingencies T As part of the Topic 842 adoption, the Company elected certain practical expedients outlined in the guidance. The Company has chosen to apply the package of practical expedients for existing leases, which provides relief from reassessing: (i) whether a contract is or contains a lease, (ii) lease classification, and (iii) whether initial direct costs can be capitalized. The Company did not elect the hindsight practical expedient to reassess the lease term for existing leases. The Company elected the short-term lease exemption, under which any lease less than 12 months is excluded from recognition on the balance sheet. Additionally, the Company elected the non-separation of lease and non-lease components. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments Codification Improvements to Topic 326, Financial Instrument s —Credit Losses . This ASU does not change the core principle of the guidance in ASU 2016-13, instead these amendments are intended to clarify and improve operability of certain topics included within the credit losses guidance. The FASB also subsequently issued ASU No. 2019-04, Codification Improvements to Topic 326, Financial Instruments—Credit Losses, Derivatives and Hedging (Topic 815), and Financial Instruments (Topic 825), which did not change the core principle of the guidance in ASU 2016-13 but clarified that expected recoveries of amounts previously written off and expected to be written off should be included in the valuation account and should not exceed amounts previously written off and expected to be written off. In March 2020, the FASB issued ASU No. 2020-3, Codification Improvements to Financial Instruments which makes narrow-scope improvements to various financial instruments topics, including the new credit losses standard and clarifies the following areas ( i ) the contractual term of a net investment in a lease should be the contractual term used to measure expected credit losses; (ii) when an entity regains control of financial assets sold, an allowance for credit losses should be recorded. The guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2019 for public business entities, excluding smaller reporting companies. The Company adopted this guidance on a modified-retrospective basis effective January 1, 2021 and noted no material impact to the Company’s consolidated financial statements.
Recently Issued Accounting Pronouncements	Recently The Company has reviewed the FASB issued ASU accounting pronouncements and interpretations thereof that have effectiveness dates during the periods reported and in future periods. The Company has carefully considered the new pronouncements that alter previous generally accepted accounting principles and do not believe that any new or modified principles will have a material impact on the Company’s reported financial position or operations in the near term. The applicability of any standard is subject to the formal review of the Company’s financial management.

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheets that sum to the total of the same amounts shown in the consolidated statements of cash flows: December 31, 2021 2020 Cash $ 734 $ 597 Cash equivalents 74,109 267,968 Cash and cash equivalents 74,843 268,565 Restricted cash 1,166 — Cash, cash equivalents and restricted cash $ 76,009 $ 268,565
Schedule of Useful Lives of Property and Equipment	The useful Laboratory equipment 5 years Office and computer equipment 3 years Leasehold improvements Shorter of remaining lease term or estimated useful life

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following tables summarize the fair value of the Company’s financial assets and liabilities measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): December 31, 2021 Valuation Hierarchy Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Assets: Cash equivalents: Money market funds Level 1 $ 74,109 $ — $ — $ 74,109 Short-term investments: Commercial paper Level 2 85,352 — (27 ) 85,325 Corporate debt Level 2 48,814 — (24 ) 48,790 Government bonds Level 2 33,809 — (52 ) 33,757 Total assets $ 242,084 $ — $ (103 ) $ 241,981 December 31, 2020 Valuation Hierarchy Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Assets: Cash equivalents: Money market funds Level 1 $ 267,968 $ — $ — $ 267,968 Short-term investments: Commercial paper Level 2 59,930 — — 59,930 Corporate bonds Level 2 22,717 1 (7 ) 22,711 Total assets $ 350,615 $ 1 $ (7 ) $ 350,609

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2021
Disclosure Of Balance Sheet Components [Abstract]
Summary of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2021 2020 Prepaid insurance $ 1,282 $ 1,236 Prepaid research and development costs 3,002 1,039 Other prepaid expenses 231 527 Other receivables — 3 Other current assets 463 — Total prepaid expenses and other current assets $ 4,978 $ 2,805
Summary of Property and Equipment, Net	Property and equipment, net consisted of the following (in thousands): December 31, 2021 2020 Leasehold improvements $ 16,594 $ 3,061 Laboratory equipment 1,353 555 Furniture and fixtures 649 263 Computer equipment and software 41 27 Total property and equipment, gross $ 18,637 $ 3,906 Less: accumulated depreciation (789 ) (1,971 ) Total property and equipment, net $ 17,848 $ 1,935
Summary of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): December 31, 2021 2020 Accrued research and development expenses $ 2,404 $ 3,260 Accrued compensation 3,573 2,543 Accrued professional services 1,274 524 Accrued construction costs 1,917 — Other accrued expenses 82 170 Total accrued liabilities $ 9,250 $ 6,497

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Future Minimum Lease Payments and Related Lease Liabilities	Future minimum lease payments and related lease liabilities as of December 31, 2021, were as follows: As of December 31: (in thousands) 2022 $ 4,203 2023 4,742 2024 4,907 2025 5,079 2026 and thereafter 32,833 Total undiscounted lease payments 51,764 Less: Imputed interest (17,175 ) Total 34,589
Future Undiscounted Lease Payments Under Non-cancellable Operating Leases	The Company’s future undiscounted lease payments under non-cancellable operating leases (as defined by prior guidance) as of December 31, 2020 were as follows: As of December 31: (in thousands) 2021 $ 618 2022 4,189 2023 4,756 2024 5,035 2025 and thereafter 38,332 Total 52,930

Stockholder's Equity (Tables)

Stockholder's Equity (Tables)	12 Months Ended
	Dec. 31, 2021
Stockholders Equity Note [Abstract]
Schedule of Common Stock Reserved for Future Issuance	The Company reserved the following shares of common stock for issuance as follows: December 31, 2021 2020 Options issued and outstanding 5,662,824 3,909,873 Reserve for 2020 Incentive Plan 2,039,951 2,707,947 Unvested restricted stock units outstanding 50,000 — Common stock reserved for 2021 ATM program 5,265,929 — Reserved for employee stock purchase plan 729,775 360,086 Total common stock reserved 13,748,479 6,977,906

Equity Incentive Plan (Tables)

Equity Incentive Plan (Tables)	12 Months Ended
	Dec. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Option Activity	Stock options Stock option activity under the 2011 Plan and the 2020 Plan was as follows: Number of Shares Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Balances as of December 31, 2020 3,909,873 $ 10.78 8.40 $ 56,128 Additional shares authorized Stock options granted 2,871,400 $ 25.54 Stock options exercised (391,349 ) $ 4.11 Stock options cancelled (727,100 ) $ 24.41 Balances as of December 31, 2021 5,662,824 $ 16.98 8.26 $ 10,186 Exercisable as of December 31, 2021 2,065,942 $ 11.34 7.08 $ 8,120
Summary of RSU Activity under Equity Incentive Plan	A summary of RSU activity under our equity incentive plan and related information is as follows: Number of Shares Weighted-Average Grant Date Fair Value Per Share Unvested as of December 31, 2020 — $ — Granted 50,000 12.84 Unvested as of December 31, 2021 50,000 $ 12.84
Summary of Stock-Based Compensation Expense	The total stock-based compensation expense recognized was as follows (in thousands): Year Ended December 31, 2021 2020 Research and development $ 8,610 $ 2,274 General and administrative 7,652 2,614 Total stock-based compensation expense $ 16,262 $ 4,888
Summary of Fair Value of Each Award Issued Estimated on the Date of Grant Using the Black-Scholes Option Pricing Model	The fair value of each award issued was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions: Year Ended December 31, 2021 2020 Expected term (in years) 4.33-6.08 5.00-6.08 Expected volatility 88%-91% 85%-93% Risk-free interest rate 0.35%-1.31% 0.33%-1.45% Dividend yield — —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Components of Loss Before Income Taxes	For financial reporting purposes, loss before provision for income taxes, includes the following components (in thousands): Year Ended December 31, 2021 2020 Domestic $ 130,313 $ 63,406 Foreign 10 6 Loss before income taxes $ 130,323 $ 63,412
Reconciliation of Income Tax Computed at Federal Statutory Rates to Provision for Income Taxes	Reconciliation of income tax computed at federal statutory rates to the reported provision for income taxes was as follows (in thousands): Year Ended December 31, 2021 2020 Tax provision at U.S. statutory rate $ (27,368 ) $ (13,316 ) Stock-based compensation 794 426 R&D tax credits (2,392 ) (1,031 ) Change in valuation allowance 25,911 13,906 Section 382 limitations 2,922 — Other 133 15 Provision for income taxes $ — $ —
Deferred Tax Assets and Liabilities	The tax effects of temporary differences that give rise to significant portions of the Company’s deferred tax assets and liabilities are as follows (in thousands): December 31, 2021 2020 Deferred Tax Assets: Net operating loss carryforwards $ 57,073 $ 36,922 Research and development credits 7,367 6,246 Other intangibles 5 5 Accruals and reserves 686 583 Stock-based compensation 3,041 995 Tenant improvement allowances — 257 Lease liabilities 7,340 — Unrealized gain/loss on investments 240 — Total gross deferred tax assets 75,752 45,008 Less: valuation allowance (69,147 ) (44,745 ) Total deferred tax assets, net $ 6,605 $ 263 Deferred Tax Liabilities: Fixed assets $ (2,290 ) $ (263 ) Right-of-use assets (4,315 ) — Total gross deferred tax liabilities (6,605 ) (263 ) Net deferred tax assets $ — $ —
Unrecognized Tax Benefits	The Company has the following activity relating to the gross amount of unrecognized tax benefits (in thousands): Year Ended December 31, 2021 2020 Beginning balance $ 1,576 $ 1,116 Decreases based on tax positions related to prior year (789 ) — Additions based on tax positions related to current year 1,007 460 Ending balance $ 1,794 $ 1,576

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Summary of Outstanding Potentially Dilutive Shares Excluded From Calculation of Diluted Net Loss Per Share	The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect: Year Ended December 31, 2021 2020 Stock options to purchase common stock 5,662,824 3,909,873 Shares subject to employee stock purchase plan 15,924 275 Unvested restricted stock units 50,000 — Total 5,728,748 3,910,148

Organization - Additional Infor

Organization - Additional Information (Detail) $ / shares in Units, $ in Thousands	Aug. 04, 2020shares	Jul. 24, 2020USD ($)$ / sharesshares	Jul. 17, 2020	Dec. 31, 2020USD ($)shares	Dec. 31, 2021USD ($)
Proceeds from issuance of common stock upon initial public offering, net of underwriting discounts and commissions		$ 262,400		$ 267,021
Payment of deferred offering costs				2,974
Redeemable convertible preferred stock, shares issued upon conversion | shares		20,824,938
Accumulated deficit				$ (165,992)	$ (296,315)
Cash and cash equivalents and short-term investments					$ 242,700
Common Stock [Member]
Shares issued during the period | shares				16,889,403
Description of reverse stock split			one-for-8.81 basis
Reverse stock split, conversion ratio			0.113507378
IPO [Member]
Shares issued during the period | shares		14,750,000
Shares issued price per share | $ / shares		$ 17
Payments for underwriting expense		$ 20,100
Payment of deferred offering costs		$ 4,600
Over-Allotment Option [Member]
Shares issued during the period | shares	2,139,403

Basis of Presentation and Sig_4

Basis of Presentation and Significant Accounting Policies - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2021USD ($)	Dec. 31, 2021USD ($)Segment	Dec. 31, 2020USD ($)	Jan. 01, 2021USD ($)
Basis Of Presentation And Significant Accounting Policies [Line Items]
Number of operating segment | Segment		1
Impairments of long-lived assets		$ 0
Interest or penalties charged in relation to unrecognized tax benefits		0
Foreign currency translation adjustment		(5,000)	$ 9,000
Operating lease right-of-use assets		20,333,000
Lease liabilities		$ 34,589,000
ASU 2018-15 [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Change in accounting principle, ASU adopted		true
Change in accounting principle, ASU, adoption date		Jan. 1, 2021
Change in accounting principle, ASU, Immaterial effect		true
ASU 2016-02 [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Change in accounting principle, ASU adopted		true
Change in accounting principle, ASU, adoption date		Jan. 1, 2021
Change in accounting principle, ASU, Immaterial effect		true
Operating lease right-of-use assets				$ 500,000
Lease liabilities				600,000
Derecognition of deferred rent liability				1,400,000
Recognition of liability related to reallocation of consideration of lease pending commencement of second lease component				$ 1,300,000
Operating lease additional rent expense	$ 100,000
ASU 2016-13 [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Change in accounting principle, ASU adopted		true
Change in accounting principle, ASU, adoption date		Jan. 1, 2021
Change in accounting principle, ASU, Immaterial effect		true
Interest and Other Income (Expense), Net [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Non-recurring grant income		$ 135,000	$ 0

Basis of Presentation and Sig_5

Basis of Presentation and Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]
Cash	$ 734	$ 597
Cash equivalents	74,109	267,968
Cash and cash equivalents	74,843	268,565
Restricted cash	1,166
Cash, cash equivalents and restricted cash	$ 76,009	$ 268,565

Basis of Presentation and Sig_6

Basis of Presentation and Significant Accounting Policies - Schedule of Useful Lives of Property and Equipment (Detail)	12 Months Ended
	Dec. 31, 2021
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	5 years
Office and Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	3 years
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	Shorter of remaining lease term or estimated useful life

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 242,084	$ 350,615
Gross Unrealized Holding Gains		1
Gross Unrealized Holding Losses	(103)	(7)
Aggregate Fair Value	241,981	350,609
Level 1 [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	74,109	267,968
Aggregate Fair Value	74,109	267,968
Level 2 [Member] | Commercial Paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	85,352	59,930
Gross Unrealized Holding Losses	(27)
Aggregate Fair Value	85,325	59,930
Level 2 [Member] | Corporate Debt [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	48,814
Gross Unrealized Holding Losses	(24)
Aggregate Fair Value	48,790
Level 2 [Member] | Government Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	33,809
Gross Unrealized Holding Losses	(52)
Aggregate Fair Value	$ 33,757
Level 2 [Member] | Corporate Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost		22,717
Gross Unrealized Holding Gains		1
Gross Unrealized Holding Losses		(7)
Aggregate Fair Value		$ 22,711

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2021
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]
Investment maturity period	2 years

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Prepaid Expense And Other Assets Current [Abstract]
Prepaid insurance	$ 1,282	$ 1,236
Prepaid research and development costs	3,002	1,039
Other prepaid expenses	231	527
Other receivables		3
Other current assets	463
Total prepaid expenses and other current assets	$ 4,978	$ 2,805

Balance Sheet Components - Su_2

Balance Sheet Components - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 18,637	$ 3,906
Less: accumulated depreciation	(789)	(1,971)
Total property and equipment, net	17,848	1,935
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	16,594	3,061
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	1,353	555
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	649	263
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 41	$ 27

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Prepaid Expense And Other Assets Current [Abstract]
Depreciation expense	$ 2.1	$ 0.7

Balance Sheet Components - Su_3

Balance Sheet Components - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Accrued Liabilities Current [Abstract]
Accrued research and development expenses	$ 2,404	$ 3,260
Accrued compensation	3,573	2,543
Accrued professional services	1,274	524
Accrued construction costs	1,917
Other accrued expenses	82	170
Total accrued liabilities	$ 9,250	$ 6,497

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Nov. 01, 2021USD ($)	Dec. 31, 2020USD ($)	Mar. 31, 2019USD ($)	Nov. 30, 2011USD ($)	Dec. 31, 2021USD ($)Claim	Dec. 31, 2020USD ($)	May 31, 2021USD ($)	Jan. 01, 2021USD ($)
Gain Contingencies [Line Items]
Sublease Income					$ 100,000
Aggregate sublease payment receivable	$ 3,400,000
Operating lease right-of-use assets					20,333,000
Lease liabilities					$ 34,589,000
Weighted average incremental borrowing rate					8.40%
Operating lease cost					$ 2,900,000
Variable lease payments					400,000
Rent expense						$ 400,000
Income (loss)					(130,323,000)	(63,412,000)
Loss contingency accrual					$ 0
Indemnification Agreement [Member]
Gain Contingencies [Line Items]
Loss contingency pending claims | Claim					0
Stanford Agreement [Member] | Research and Development Arrangement [Member]
Gain Contingencies [Line Items]
Sponsor research agreements, commitment amount				$ 500,000
Sponsored Research Agreement [Member]
Gain Contingencies [Line Items]
Maximum threshold period allowed for filing market authorization			15 years
Proceeds from funding					$ 135,000
Income (loss)						$ 0
Sponsored Research Agreement [Member] | Other Income [Member]
Gain Contingencies [Line Items]
Proceeds from funding					$ 590,000
Sponsored Research Agreement [Member] | Research and Development Arrangement [Member]
Gain Contingencies [Line Items]
Maximum expected research funding			$ 651,000
South San Francisco, California [Member]
Gain Contingencies [Line Items]
Operating lease, term of contract					7 years
Operating lease, expiration month and year					2024-06
Operating lease, renewal term					5 years
Brisbane, California [Member]
Gain Contingencies [Line Items]
Operating lease, term of contract		10 years				10 years
Operating lease, renewal term		10 years				10 years
Operating lease, expected to begin month and year		2021-11
Operating lease, option to extend [true false]		true
Operating lease, base rent abatement period		3 months
Tenant improvement allowance receivable		$ 10,800,000				$ 10,800,000
Letter of credit		$ 1,000,000				$ 1,000,000
Operating lease consideration allocated recorded as liability								$ 1,300,000
Operating lease right-of-use assets					$ 20,300,000		$ 21,000,000
Lease liabilities					$ 34,600,000		$ 22,200,000
Weighted average remaining lease term					9 years 10 months 24 days
Operating lease, commenced month and year		2021-05

Commitments and Contingencies_2

Commitments and Contingencies - Future Minimum Lease Payments and Related Lease Liabilities (Detail) $ in Thousands	Dec. 31, 2021USD ($)
Commitments And Contingencies Disclosure [Abstract]
2022	$ 4,203
2023	4,742
2024	4,907
2025	5,079
2026 and thereafter	32,833
Total undiscounted lease payments	51,764
Less: Imputed interest	(17,175)
Lease liabilities	$ 34,589

Commitments and Contingencies_3

Commitments and Contingencies - Future Undiscounted Lease Payments Under Non-cancellable Operating Leases (Detail) $ in Thousands	Dec. 31, 2020USD ($)
Commitments And Contingencies Disclosure [Abstract]
2021	$ 618
2022	4,189
2023	4,756
2024	5,035
2025 and thereafter	38,332
Total	$ 52,930

Stockholder's Equity - Addition

Stockholder's Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Aug. 31, 2021	Dec. 31, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Common stock, voting rights		The holders of the Company’s common stock have one vote for each share of common stock.
Common stock, dividends declared		$ 0
Common stock		$ 39	$ 38
Common stock, shares issued		38,560,854	38,157,618
Sales Agreement with Cowen and Company LLC [Member] | 2021 ATM Program [Member]
Class Of Stock [Line Items]
Common stock	$ 100,000
Percentage of gross proceeds of common stock to be paid	3.00%
Common stock, shares issued		0

Stockholder's Equity - Schedule

Stockholder's Equity - Schedule of Common Stock Reserved for Future Issuance (Detail) - shares	Dec. 31, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Common stock reserved	5,662,824	3,909,873
Common stock reserved	13,748,479	6,977,906
Options Issued and Outstanding [Member]
Class Of Stock [Line Items]
Common stock reserved	5,662,824	3,909,873
Reserve for 2020 Incentive Plan [Member]
Class Of Stock [Line Items]
Common stock reserved	2,039,951	2,707,947
Unvested Restricted Stock Units Outstanding [Member]
Class Of Stock [Line Items]
Common stock reserved	50,000
Reserved for Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Common stock reserved	729,775	360,086
2021 ATM Program [Member]
Class Of Stock [Line Items]
Common stock reserved	5,265,929

Equity Incentive Plan - Additio

Equity Incentive Plan - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of number of shares of capital stock outstanding on last day of preceding year	4.00%
Stock option grants description	Awards granted under the 2020 Plan expire no later than ten years from the date of grant. For the Incentive Stock Options, or ISOs, and Nonstatutory Stock Options, or NSOs, the option price shall not be less than 100% of the estimated fair value on the date of grant. Options granted typically vest over a four-year period but may be granted with different vesting terms.
Option expiry period	10 years
Vesting Period	4 years
Options available for future grant	2,039,951
Intrinsic value of options exercised	$ 6,400	$ 200
Weighted- average exercise price per share, Stock options granted	$ 25.54
Common stock for future issuance	13,748,479	6,977,906
Total stock-based compensation expense	$ 16,262	$ 4,888
Employees [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted- average exercise price per share, Stock options granted	$ 18.83	$ 12.33
Incentive Stock Options, or ISOs, and Nonstatutory Stock Options, or NSOs [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase of Common stock at end of each offering period at price equal to percentage of fair market value of shares	100.00%
Options Issued and Outstanding [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation cost	$ 51,900
Unrecognized stock-based compensation cost expected period for recognition	3 years 10 days
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation cost expected period for recognition	2 years 11 months 23 days
Unrecognized stock-based compensation cost	$ 600
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase of Common stock at end of each offering period at price equal to percentage of fair market value of shares	85.00%
Share purchases funded through payroll deductions minimum percentage of employee?s eligible compensation	1.00%
Share purchases funded through payroll deductions maximum percentage of employee?s eligible compensation	15.00%
Common stock for future issuance	729,775	360,086
Percentage of shares of common stock outstanding on last day of immediately preceding fiscal year	1.00%
Total stock-based compensation expense	$ 100	$ 100

Equity Incentive Plan - Summary

Equity Incentive Plan - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of shares, Beginning balance	3,909,873
Number of shares, Stock options granted	2,871,400
Number of shares, Stock options exercised	(391,349)
Number of shares, Stock options cancelled	(727,100)
Number of shares, Ending balance	5,662,824	3,909,873
Shares available for grant, Exercisable	2,065,942
Weighted- average exercise price per share, Beginning balance	$ 10.78
Weighted- average exercise price per share, Stock options granted	25.54
Weighted- average exercise price per share, Stock options exercised	4.11
Weighted- average exercise price per share, Stock options cancelled	24.41
Weighted- average exercise price per share, Ending balance	16.98	$ 10.78
Weighted- average exercise price per share, Exercisable	$ 11.34
Weighted- average remaining contractual term	8 years 3 months 3 days	8 years 4 months 24 days
Weighted- average remaining contractual term, Exercisable	7 years 29 days
Aggregate intrinsic value	$ 10,186	$ 56,128
Aggregate intrinsic value, Exercisable	$ 8,120

Equity Incentive Plan - Summa_2

Equity Incentive Plan - Summary of RSU Activity under Equity Incentive Plan (Detail)	12 Months Ended
	Dec. 31, 2021$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Granted | shares	50,000
Number of shares, Unvested as of December 31, 2021 | shares	50,000
Weighted-Average Grant Date Fair Value Per Share, Granted | $ / shares	$ 12.84
Weighted-Average Grant Date Fair Value Per Share, Granted Unvested as of December 31, 2021 | $ / shares	$ 12.84

Equity Incentive Plan - Summa_3

Equity Incentive Plan - Summary of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 16,262	$ 4,888
Research and Development [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	8,610	2,274
General and Administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 7,652	$ 2,614

Equity Incentive Plan - Summa_4

Equity Incentive Plan - Summary of Fair Value of Each Award Issued Estimated on the Date of Grant Using the Black-Scholes Option Pricing Model (Detail)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, Minimum	88.00%	85.00%
Expected volatility, Maximum	91.00%	93.00%
Risk-free interest rate, Minimum	0.35%	0.33%
Risk-free interest rate, Maximum	1.31%	1.45%
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	4 years 3 months 29 days	5 years
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 29 days	6 years 29 days

Income Taxes - Components of Lo

Income Taxes - Components of Loss Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Domestic	$ 130,313	$ 63,406
Foreign	10	6
Loss before income taxes	$ 130,323	$ 63,412

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Income Tax Computed at Federal Statutory Rates to Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Tax provision at U.S. statutory rate	$ (27,368)	$ (13,316)
Stock-based compensation	794	426
R&D tax credits	(2,392)	(1,031)
Change in valuation allowance	25,911	13,906
Section 382 limitations	2,922
Other	$ 133	$ 15

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 57,073	$ 36,922
Research and development credits	7,367	6,246
Other intangibles	5	5
Accruals and reserves	686	583
Stock-based compensation	3,041	995
Tenant improvement allowances		257
Lease liabilities	7,340
Unrealized gain/loss on investments	240
Total gross deferred tax assets	75,752	45,008
Less: valuation allowance	(69,147)	(44,745)
Total deferred tax assets, net	6,605	263
Fixed assets	(2,290)	(263)
Right-of-use assets	(4,315)
Total gross deferred tax liabilities	$ (6,605)	$ (263)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Jun. 30, 2021
Income Tax [Line Items]
Federal net operating loss carryforwards	$ 257,900,000
State net operating loss carryforwards	$ 70,700,000
Percentage of taxable income	80.00%
State carryforward losses expiration beginning year	2031
Increase in valuation allowance	$ 24,400,000	$ 14,800,000
Uncertain tax position	0
Unrecognized tax benefits, interest or penalty accruals	$ 0	$ 0
Earliest Tax Year [Member]
Income Tax [Line Items]
Open tax year examination	2011
Latest Tax Year [Member]
Income Tax [Line Items]
Open tax year examination	2021
Federal [Member]
Income Tax [Line Items]
NOLs do not expire	$ 197,100,000		$ 257,800,000
Tax credit carryforwards	$ 7,300,000
Federal carryforward losses expiration beginning year	2031
NOLs do not expire			100,000
Federal credits			3,700,000
State [Member]
Income Tax [Line Items]
NOLs do not expire			30,800,000
Tax credit carryforwards	$ 5,600,000
NOLs do not expire			$ 39,900,000

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Beginning balance	$ 1,576	$ 1,116
Decreases based on tax positions related to prior year	(789)
Additions based on tax positions related to current year	1,007	460
Ending balance	$ 1,794	$ 1,576

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Common Stockholders - Summary of Outstanding Potentially Dilutive Shares Excluded From Calculation of Diluted Net Loss Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	5,728,748	3,910,148
Shares Subject to Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	15,924	275
Stock Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	5,662,824	3,909,873
Unvested Restricted Stock Units [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	50,000