Alector (ALEC) 10-K 24 Feb 22 2021 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Feb. 15, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Trading Symbol	ALEC
Entity File Number	001-38792
Entity Tax Identification Number	82-2933343
Entity Public Float			$ 1,192.5
Entity Address, Address Line One	131 Oyster Point Blvd
Entity Address, Address Line Two	Suite 600
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	415
Local Phone Number	231-5660
Document Transition Report	false
Document Annual Report	true
Entity Registrant Name	Alector, Inc.
Entity Central Index Key	0001653087
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Common Stock, Shares Outstanding		82,039,774
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock
Entity Interactive Data Current	Yes
Entity Well-known Seasoned Issuer	Yes
Entity Incorporation, State or Country Code	DE
Documents Incorporated by Reference	Portions of the registrant’s Definitive Proxy Statement relating to the registrant’s Annual Meeting of Shareholders are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such Definitive Proxy Statement will be filed with the Securities and Exchange Commission within 120 days after the end of the registrant’s 2021 fiscal year ended December 31, 2021.
Auditor Name	Ernst & Young LLP
Auditor Location	Redwood City, California
Auditor Firm ID	42

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 329,152	$ 49,969
Marketable securities	406,099	363,339
Receivable from Collaboration partner	7,391	0
Prepaid expenses and other current assets	7,071	8,203
Total current assets	749,713	421,511
Property and equipment, net	27,330	30,181
Operating lease right-of-use assets	30,569	32,470
Restricted cash	1,472	1,472
Other assets	5,574	2,617
Total assets	814,658	488,251
Current liabilities:
Accounts payable	4,749	3,004
Accrued clinical supply costs	8,748	11,148
Accrued liabilities	27,460	22,538
Deferred revenue, current portion	90,803	23,886
Operating lease liabilities, current portion	7,795	7,512
Total current liabilities	139,555	68,088
Deferred revenue, long-term portion	334,415	108,417
Operating lease liabilities, long-term portion	39,806	43,744
Other long-term liabilities	158	472
Total liabilities	513,934	220,721
Commitments and contingencies
Stockholders' equity:
Common stock, $0.0001 par value; 200,000,000 shares authorized; 81,986,192 and 79,316,261 shares issued and outstanding as of December 31, 2021 and 2020, respectively	8	8
Additional paid-in capital	748,036	676,956
Accumulated other comprehensive income (loss)	(943)	614
Accumulated deficit	(446,377)	(410,048)
Total stockholders' equity	300,724	267,530
Total liabilities and stockholders' equity	$ 814,658	$ 488,251

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	81,986,192	81,986,192
Common stock, shares outstanding	79,316,261	79,316,261

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue:
Total revenue	$ 207,085	$ 21,098	$ 21,219
Type of Revenue [Extensible List]	Collaboration Revenue [Member]	Collaboration Revenue [Member]	Collaboration Revenue [Member]
Operating expenses:
Research and development	$ 189,407	$ 156,869	$ 100,528
General and administrative	55,038	59,403	35,095
Total operating expenses	244,445	216,272	135,623
Loss from operations	(37,360)	(195,174)	(114,404)
Other income, net	1,031	4,946	9,019
Net loss	(36,329)	(190,228)	(105,385)
Unrealized gain (loss) on marketable securities	(1,557)	472	184
Comprehensive loss	$ (37,886)	$ (189,756)	$ (105,201)
Net loss per share, basic and diluted	$ (0.45)	$ (2.45)	$ (1.71)
Shares used in computing net loss per share, basic and diluted	80,416,936	77,758,806	61,734,492

Consolidated Statement of Conve

Consolidated Statement of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Convertible preferred stock, beginning balance (in shares) at Dec. 31, 2018		45,374,836
Convertible preferred stock, beginning balance at Dec. 31, 2018		$ 210,520
Beginning balance (in shares) at Dec. 31, 2018			13,764,829
Beginning Balance at Dec. 31, 2018	$ (97,398)		$ 1	$ 17,078	$ (42)	$ (114,435)
Conversion of convertible preferred stock into common stock (in shares)		45,374,836	(45,374,836)
Conversion of convertible preferred stock into common stock	(210,521)	$ 210,520	$ (5)	(210,516)
Issuance of common stock upon initial public offering, net of issuance costs (in shares)			9,739,541
Issuance of common stock upon initial public offering, net of issuance costs	168,223		$ 1	168,222
Exercise of stock options (in shares)			180,287
Exercise of stock options	1,519			1,519
Purchase of common stock under employee stock purchase plan (in shares)			50,353
Purchase of common stock under employee stock purchase plan	798			798
Forfeiture/Cancellation of restricted common stock			(56,973)
Stock-based compensation	16,281			16,281
Unrealized gain (loss) on marketable securities	184				184
Net loss	(105,385)					(105,385)
Ending balance (in shares) at Dec. 31, 2019			69,052,873
Ending Balance at Dec. 31, 2019	194,743		$ 7	414,414	142	(219,820)
Issuance of common stock upon initial public offering, net of issuance costs (in shares)			9,602,500
Issuance of common stock upon initial public offering, net of issuance costs	224,511		$ 1	224,510
Exercise of stock options (in shares)			655,772
Exercise of stock options	6,331			6,331
Purchase of common stock under employee stock purchase plan (in shares)			86,870
Purchase of common stock under employee stock purchase plan	1,179			1,179
Forfeiture/Cancellation of restricted common stock			81,754
Stock-based compensation	30,522			30,522
Unrealized gain (loss) on marketable securities	472				472
Net loss	$ (190,228)					(190,228)
Ending balance (in shares) at Dec. 31, 2020	79,316,261		79,316,261
Ending Balance at Dec. 31, 2020	$ 267,530		$ 8	676,956	614	(410,048)
Exercise of stock options (in shares)			2,395,223
Exercise of stock options	28,530			28,530
Vesting of restricted stock units			156,420
Purchase of common stock under employee stock purchase plan (in shares)			136,331
Purchase of common stock under employee stock purchase plan	1,765			1,765
Forfeiture/Cancellation of restricted common stock			(18,043)
Stock-based compensation	40,785			40,785
Unrealized gain (loss) on marketable securities	(1,557)				(1,557)
Net loss	$ (36,329)					(36,329)
Ending balance (in shares) at Dec. 31, 2021	79,316,261		81,986,192
Ending Balance at Dec. 31, 2021	$ 300,724		$ 8	$ 748,036	$ (943)	$ (446,377)

Consolidated Statement of Con_2

Consolidated Statement of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Issuance cost of common stock	$ 1,148	$ 3,874

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (36,329)	$ (190,228)	$ (105,385)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	6,329	5,870	3,775
Stock-based compensation	40,785	30,522	16,281
Amortization of premiums and accretion of discounts on marketable securities	2,099	584	(4,701)
Amortization of right-of-use assets	1,986	1,395	1,799
Impairment loss on right-of-use assets	0	238	1,158
Loss from disposal of property and equipment, net	0	107	(39)
Changes in operating assets and liabilities:
Receivable from collaboration partner	(7,391)	0	0
Prepaid expenses and other current assets	1,132	(3,839)	(1,596)
Other assets	(2,957)	(2,498)	(42)
Accounts payable	1,917	2,409	152
Accrued liabilities and accrued clinical supply costs	2,391	12,232	9,210
Deferred revenue	292,915	(21,098)	(21,219)
Lease liabilities	(4,012)	(2,407)	868
Other long-term liabilities	(314)	(21)	353
Net cash provided by (used in) operating activities	298,551	(166,734)	(99,308)
Cash flows from investing activities:
Purchase of property and equipment	(3,247)	(5,032)	(15,265)
Purchase of marketable securities	(343,402)	(506,809)	(529,609)
Sale of marketable securities	10,696	0	0
Maturities of marketable securities	286,290	406,790	496,000
Net cash used in investing activities	(49,663)	(105,051)	(48,874)
Cash flows from financing activities:
Proceeds from issuance of common stock upon initial public offering, net of issuance costs	0	224,603	170,036
Proceeds from the exercise of options to purchase common stock	28,530	6,331	1,519
Proceeds from issuance of stock from employee stock purchase plan	1,765	1,179	798
Net cash provided by financing activities	30,295	232,113	172,353
Net increase (decrease) in cash, cash equivalents, and restricted cash	279,183	(39,672)	24,171
Cash, cash equivalents, and restricted cash at beginning of period	51,441	91,113	66,942
Cash, cash equivalents, and restricted cash at end of period	330,624	51,441	91,113
Non-cash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued liabilities	705	428	3,471
Deferred offering costs in accrued liabilities	0	0	465
Tenant improvements paid by landlord	$ 0	$ 0	$ 8,286

The Company and Liquidity

The Company and Liquidity	12 Months Ended
	Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
The Company and Liquidity	1. The Company and Liquidity Alector, Inc. (Alector or the Company) is a Delaware corporation headquartered in South San Francisco, California. Alector is a clinical stage biopharmaceutical company pioneering immuno-neurology, a novel therapeutic approach for the treatment of neurodegeneration. Initial Public and Follow-on Offerings On February 7, 2019, the Company completed an initial public offering (IPO) through issuing and selling 9,739,541 shares of common stock at a public offering price of $ 19.00 per share, including 489,541 shares sold pursuant to the underwriters’ partial exercise of their option to purchase additional shares, resulting in aggregate net proceeds of $ 168.2 million, after deducting underwriting discounts and commissions and offering costs. Upon the closing of the IPO, all of the outstanding shares of convertible preferred stock automatically converted into 45,374,836 shares of common stock. Subsequent to the closing of the IPO, there were no shares of convertible preferred stock outstanding. On January 30, 2020, the Company completed a follow-on offering through issuing and selling 9,602,500 shares of common stock at a public offering price of $ 25.00 per share, including 1,252,500 shares sold pursuant to the underwriters’ full exercise of their option to purchase additional shares, resulting in aggregate net proceeds of $ 224.5 million, after deducting underwriting discounts and commissions and estimated offering costs.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States (GAAP) as defined by the Financial Accounting Standards Board (FASB). The consolidated financial statements include the accounts of Alector, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expense during the reporting period. The Company evaluates its estimates, including those related to revenue recognition, manufacturing accruals, clinical accruals, fair value of assets and liabilities, income taxes uncertainties, stock-based compensation, and related 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 materially differ from those estimates . Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, and short-term marketable securities. Cash and cash equivalents are deposited in checking and sweep accounts at financial institutions. Such deposits may, at times, exceed federally insured limits. Cash, Cash Equivalents, and Restricted Cash The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash and cash equivalents. Cash equivalents, which consist of amounts invested in money market funds, are stated at fair value. Restricted cash as of December 31, 2021 relates to a letter of credit established for a lease entered into in June 2018. 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: Year Ended December 31, 2021 2020 2019 (In thousands) Cash and cash equivalents $ 329,152 $ 49,969 $ 89,641 Restricted cash 1,472 1,472 1,472 Total cash, cash equivalents, and restricted cash $ 330,624 $ 51,441 $ 91,113 Marketable Securities All marketable securities have been classified as “available-for-sale” and are carried at fair value, based upon quoted market prices. The Company considers its available-for-sale portfolio as available for use in current operations. Accordingly, the Company may classify certain investments as short-term marketable securities, even though the stated maturity date may be one year or more beyond the current balance sheet date. For available-for-sale debt securities, unrealized gains, net of any related tax effects, are excluded from earnings and are included in other comprehensive income and reported as a separate component of stockholders’ equity until realized. The Company assesses available-for-sale debt securities on a quarterly basis to see if any unrealized loss is due to credit-related factors. Factors considered in determining whether an impairment is credit-related include the extent to which the investment’s fair value is less than its cost basis, declines in published credit ratings, changes in interest rates, and any other adverse factors related to the security. If it is determined that a credit-related impairment exists, the Company will measure the credit loss based on a discounted cash flows model. Credit-related impairments on available-for-sale debt securities are recognized as an allowance for credit losses with a corresponding adjustment to other income, net in the Company’s consolidated statement of operations. The unrealized loss position that is not credit-related is recorded, net of any related tax effects, in other comprehensive income until realized. There were no credit-related losses recognized for the periods presented. The cost of securities sold is based on the specific-identification method. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity. In accordance with our investment policy, management invests in money market funds, U.S. treasury securities, and corporate bonds. The Company has not experienced any losses on its deposits of cash, cash equivalents, and marketable securities. Fair Value of Financial Instruments The Company’s financial instruments include cash and cash equivalents, marketable securities, receivable from collaboration partner, current and noncurrent prepaid expenses, accounts payable, and accrued liabilities. The Company’s financial instruments approximate fair value due to their relatively short maturities. 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 the fair value of its financial instruments 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 are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2 – Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and Level 3 – Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation and amortization. Depreciation and amortization is computed using the straight-line method over the estimated useful lives of the respective assets, generally three to five years . Leasehold improvements are amortized over the lesser of their useful lives or the remaining life of the lease. When assets are retired or otherwise disposed of, the cost and related accumulated depreciation and amortization are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statements of operations in the period realized. Maintenance and repairs are charged to the consolidated statements of operations as incurred. Leases The Company determines whether an arrangement is or contains a lease at the inception of the lease. Leases are recognized on the balance sheet as right-of-use assets and lease liabilities. Lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The Company utilizes the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received and any prepaid or accrued rent. Rent expense for the operating lease is recognized on a straight-line basis over the lease term and is included in operating expenses on the statements of operations and comprehensive loss. Variable lease payments include lease operating expenses. The Company excludes balance sheet recognition of operating leases having a term of 12 months or less (short-term leases) and does not separate lease components and non-lease components for its long-term leases. Impairment of Long-Lived Assets The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparing the carrying amount to the future net undiscounted cash flows which the assets are expected to generate. If the total of the undiscounted future cash flows is less than the carrying amount of the assets, an impairment loss is recognized for the amount by which the carrying amount of the assets exceeds is fair value. For the year ended December 31, 2021, the Company did not recognize an impairment loss on its right-of-use assets. For the year ended December 31, 2020 , the Company recognized a $ 0.2 million impairment loss related to its decision to no longer utilize certain property through the end of the lease term. For the year ended December 31, 2019, the Company recognized a $ 1.2 million impairment loss on its right of use assets related to the portion of its headquarters being subleased. Revenue Recognition The Company recognizes revenue when control of promised goods or services is transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under arrangements, the Company performs the following steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract, and (v) recognize revenue when (or as) the entity satisfies the performance obligation. If it is determined that multiple performance obligations exist, the transaction price is allocated at the inception of the agreement to all identified performance obligations based on the relative standalone selling price (SSP). The relative SSP for each deliverable is estimated using external sourced evidence if it is available. If external sourced evidence is not available, we use our best estimate of the SSP for the deliverable. The Company recognizes collaboration revenue at a point in time if control of the promised good or service has been transferred to the customer. The Company recognizes collaboration revenue over time by measuring the progress toward complete satisfaction of the performance obligation using an input measure. In order to recognize revenue over the research and development period, the Company measures actual costs incurred to date compared to the overall total expected costs to satisfy the performance obligation. Revenues are recognized as the program costs are incurred. The Company re-evaluates the estimate of expected costs to satisfy the performance obligation each reporting period. Research and Development Costs Research and development costs are expensed as incurred and consist primarily of new product development. Research and development costs include salaries and benefits, consultants’ fees, process development costs, stock-based compensation, and laboratory supplies, as well as fees paid to third parties that conduct certain research and development activities on the Company’s behalf. In addition, research and development costs include the reimbursable costs incurred for the grant agreements, which includes payroll costs for time incurred on projects, laboratory supplies, and third-party research and development activities. A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers. The Company records accrued expenses for estimated preclinical study and clinical trial expenses. Estimates are based on the services performed pursuant to contracts with research institutions, contract research organizations in connection with clinical studies, investigative sites in connection with clinical studies, vendors in connection with preclinical development activities, and contract manufacturing organizations in connection with the production of materials for clinical trials. Further, the Company accrues expenses related to clinical trials based on the level of patient enrollment and activity according to the related agreement. The Company monitors patient enrollment levels and related activity to the extent reasonably possible and make judgments and estimates in determining the accrued balance in each reporting period. If the Company underestimates or overestimates the level of services performed or the costs of these services, actual expenses could differ from estimates. To date, the Company has not experienced significant changes in its estimates of preclinical studies and clinical trial accruals. Stock-based Compensation Stock-based compensation is measured on the grant date based on the fair value of the awards. The fair value of options to purchase common stock is measured using the Black-Scholes option-pricing model. Stock-based compensation associated with restricted stock units (RSUs) is based on the fair value of the Company's common stock on the grant date, which equals the closing price of the Company's common stock on the grant date. The Company recognizes expense over the vesting period of the awards. Expense for options and RSUs that vest based only on a service condition is recognized on a straight-line basis. In 2021, the Company granted RSUs with market conditions to certain executives. The fair value of RSUs with market conditions is estimated using a Monte Carlo simulation model. Assumptions and estimates utilized in the model include the stock price on grant date, risk-free interest rate, dividend yield, expected stock volatility, and estimated period to achieve the market condition. The expense is recognized based on continued employment of the participants, regardless of achievement of the market condition. Expense related to the RSUs with market conditions is recognized using the accelerated attribution method. The Company accounts for forfeitures as they occur for all awards. Comprehensive Loss Comprehensive loss includes net loss and certain changes in stockholders’ equity that are the result of transactions and economic events other than those with stockholders. The Company’s only element of other comprehensive loss was net unrealized gain (loss) on marketable securities. Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial statement and tax bases of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. The deferred tax assets are recognized to the extent the Company believes that these assets are more likely than not to be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to the Company’s historical operating performance and the recorded cumulative net losses in prior periods, the net deferred tax assets have been fully offset by a valuation allowance. The Company records uncertain tax positions using a two-step process. First, the Company determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position. Second, for those tax positions that meet the more-likely-than-not recognition threshold, the Company recognizes the largest amount of tax benefit that is more than 50% likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits on the interest expense line and other expense line, respectively, in the accompanying statements of operations. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits. Employee 401(k) Plan The Company has a qualified contributory savings plan under Section 401(k) of the Internal Revenue Code (the “Code”) covering substantially all U.S. employees of Alector. The 401(k) plan is designed to provide tax-deferred retirement benefits in accordance with the provisions of Section 401(k) of the Code. Eligible employees may defer up to 100 % of their eligible compensation up to the annual maximum as determined by the Internal Revenue Service. The Company’s contributions to the plan are discretionary. For the years ended December 31, 2021 and 2020, the Company made matching contributions of $ 0.8 million and $ 0.7 million, respectively. The Company did no t make any matching contributions for the year ended December 31, 2019. Segments The Company operates in one segment. The Company’s chief operating decision maker, its Chief Executive Officer, manages the Company’s operations on a consolidated basis for purposes of allocating resources.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The following tables summarize the Company’s financial assets measured at fair value on a recurring basis by level within the fair value hierarchy: December 31, 2021 Fair Value Amortized Unrealized Unrealized Fair Market (In thousands) Money market funds Level 1 $ 218,451 $ — $ — $ 218,451 U.S. government treasury securities Level 1 407,041 8 ( 950 ) 406,099 Total cash equivalents and marketable $ 625,492 $ 8 $ ( 950 ) $ 624,550 December 31, 2020 Fair Value Amortized Unrealized Unrealized Fair Market (In thousands) Money market funds Level 1 $ 37,951 $ — $ — $ 37,951 U.S. government treasury securities Level 1 357,725 620 ( 6 ) 358,339 Corporate bonds Level 2 5,000 — — 5,000 Total cash equivalents and marketable $ 400,676 $ 620 $ ( 6 ) $ 401,290 The Company’s Level 2 securities are valued using third-party pricing sources. The pricing services utilize industry standard valuation models for which all significant inputs are observable. The Company classifies marketable securities available to fund current operations as current assets. As of December 31, 2021, the remaining contractual maturities of $ 488.2 million of investments were less than one year and of $ 136.4 million of investments were after one year through two years. The Company does not intend to sell the investments that are currently in an unrealized loss position, and it is highly unlikely that the Company will be required to sell the investments before recovery of their amortized cost basis, which may be maturity. As of December 31, 2021, the Company considered any unrealized losses on our marketable securities to be driven by factors other than credit risk. The Company sold marketable securities for total proceeds of $ 10.7 million for the year ended December 31, 2021, for an immaterial realized gain based on the specific identification method. The Company did no t sell any marketable securities for the years ended December 31, 2020 and 2019.

Collaboration Agreements

Collaboration Agreements	12 Months Ended
	Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration Agreements	Collaboration Agreements GSK On July 1, 2021, the Company entered into a Collaboration and License Agreement with Glaxo Wellcome UK Limited, a subsidiary of GlaxoSmithKline plc (GSK), pursuant to which the Company and GSK will collaborate on the global development and commercialization of progranulin-elevating monoclonal antibodies, including AL001 and AL101 (GSK Agreement). The GSK Agreement was made effective on August 17, 2021 . Under the terms of the GSK Agreement, the Company received $ 700 million in upfront payments, of which $ 500 million was received in August 2021 and $ 200 million was invoiced to GSK and collected in January 2022. In addition, based on the development and commercialization plan for AL001 and AL101, the Company may be eligible to receive up to an additional $ 1.5 billion in clinical development, regulatory, and commercial launch-related milestone payments. In the United States, the Company and GSK will equally share profits and losses from commercialization of AL001 and AL101. Outside of the United States, the Company will be eligible for double-digit tiered royalties. The Company and GSK will jointly develop AL001 and AL101. The Company will lead the global clinical development of AL001 and AL101, other than with respect to Phase 3 clinical trials for Alzheimer’s disease and Parkinson’s disease and other non-orphan indications, which will be led by GSK. The Company and GSK will share development costs 60 % by GSK and 40 % by the Company, except that the Company will solely bear the development costs of the initial Phase 2 clinical trials under the development plan, and the parties will share manufacturing development costs equally. In the United States, the Company and GSK will be jointly responsible for commercialization of AL001 and AL101, with the Company leading the commercialization for orphan indications and GSK leading the commercialization for Alzheimer’s disease and Parkinson’s disease and other non-orphan indications. Outside of the United States, GSK will be solely responsible for commercialization of AL001 and AL101 for all indications. The Company may opt out of the sharing of development costs and of profit and losses from commercialization in the United States on a product-by-product basis. In such case, the Company will no longer conduct development or commercialization of that product and the Company will receive tiered royalties on net sales in the United States instead of a share of profits or losses. GSK may terminate the agreement at any time with 180 days' notice, but the Company does not need to repay any portion of the payments received. The Company concluded that the GSK Agreement is within the scope of ASC 808, Collaborative Arrangements, as both parties are active participants in the activities and are exposed to significant risks and rewards dependent on the success of the commercialization of AL001 and AL101. Certain elements are required to be accounted for under ASC 606, Revenue From Contracts With Customers, where the counterparty is a customer for a good or service that is a distinct unit of account. The Company concluded that the GSK Agreement contained the following units of account: (i) license and know-how for FTD- GRN in Phase 3 clinical development, (ii) research and development activities, including license rights and know-how, relating to products in Phase 2 or earlier stages of development, and (iii) research and development services under the co-development plan to be accounted for outside of ASC 606, including all products that move into Phase 3 clinical development. The Company determined that the distinct performance obligations under ASC 606 consisted of: (i) license and know-how to AL001 FTD- GRN , which is currently in Phase 3 clinical development and (ii) the research and development activities, including license rights and know-how, relating to products in Phase 2 or earlier stages of development. The transaction price at inception included fixed consideration consisting of the upfront payments of $ 700 million. All potential future milestones and other payments were considered constrained at the inception of the GSK Agreement since the Company could not conclude it was probable that a significant reversal in the amount of revenue recognized would not occur. The respective standalone value for each of the performance obligations was allocated to the transaction price. The estimated SSP of each performance obligation was determined using discounted cash flows from the expected commercialization of AL001 and AL101 and estimated research and development costs to be incurred by the Company in the initial Phase 2 clinical trials. The estimate of SSP for each performance obligation reflects management's assumptions, which may include forecasted revenues, development timelines, discount rates, and probabilities of technical and regulatory success. For the license for FTD- GRN , the Company determined that GSK could benefit from the license at the time the license was granted and therefore, the related performance obligation was satisfied at a point in time. For the product candidates in Phase 2 or earlier stages of development, the Company determined that GSK could not benefit from the licenses without the corresponding development services that the Company has committed to perform due the earlier stage of development for these licenses. The Company will perform research and development activities through the end of the initial Phase 2 clinical trials. Revenue will be recognized over time as the research and development activities are performed. The Company will measure progress based on actual costs incurred to date compared to the overall total expected costs to satisfy the performance obligations. The research and development activities for products in Phase 3 clinical development were determined to be within the scope of ASC 808. Both parties will be active participants in the development, manufacturing, and commercialization of the product and are exposed to significant risks and rewards that are dependent on the commercial success of the products. The Company and GSK participate in profit and loss sharing for each program commensurate with each party's cost-sharing responsibilities during research and development. ASC 808 does not provide recognition and measurement guidance. As such, the Company determined that ASC 730, Research and Development, was appropriate to analogize to based on the nature of the cost-sharing provision of the agreement. The Company has concluded that payments to or reimbursements from GSK related to these services will be accounted for as an increase to or reduction of research and development expenses, respectively. Collaboration revenue under the GSK Agreement during the year ended December 31, 2021 was $ 192.1 million, no ne of which was included in deferred revenue at the beginning of the period. $ 173.4 million was revenue from the Phase 3 license for FTD- GRN recognized when the license and know-how were delivered following the effective date of the agreement. The deferred revenue related to the GSK Agreement was $ 307.9 million as of December 31, 2021. The deferred revenue is expected to be recognized over the research and development period of the programs through the completion of initial Phase 2 clinical trials. Costs associated with co-development activities performed under the agreement are included in research and development expenses in the consolidated statements of operations, with any reimbursement of costs by GSK reflected as a reduction of such expenses. For the year ended December 31, 2021 , the Company recognized a reduction of research and development expense of $ 8.8 million under the GSK Agreement. AbbVie The Company entered into an agreement in October 2017 with AbbVie Biotechnology, Ltd. (AbbVie) to co-develop antibodies to two program targets in preclinical development (AbbVie Agreement). Under the terms of the AbbVie Agreement, AbbVie made $ 205.0 million in upfront payments, of which $ 5.0 million and $ 200.0 million were received by the Company in October 2017 and January 2018, respectively. The Company will perform research and development services for the two programs through the end of Phase 2 clinical trials. After completion of the Phase 2 clinical trial for each program, AbbVie will then have the exclusive right to exercise an option to enter into a license and collaboration agreement with the Company for that program for $ 250.0 million. If AbbVie exercises its option for a program, AbbVie will take over the development of the product candidates for such program and costs will be split between the parties. The Company will also share in profits and losses upon commercialization of any products from such program. However, following AbbVie’s exercise of its option for a program, the Company may opt out of sharing in development costs and profits or losses for that program and instead receive tiered royalties. Additionally, under the terms of the AbbVie Agreement, the Company will be eligible to earn up to an additional $ 242.8 million in milestone payments per program related to the initiation of certain clinical studies and regulatory approval for up to three indications per program. The Company assessed its collaboration agreement with AbbVie in the context of the delivery of the research and development services. Collaboration revenue under the Company’s collaboration agreement with AbbVie during the years ended December 31, 2021 , 2020, and 2019 was $ 14.9 million, $ 21.1 million, and $ 21.2 million, respectively, the entire amount of which was included in deferred revenue at the beginning of the period. The deferred revenue related to the AbbVie Agreement was $ 117.4 million and $ 132.3 as of December 31, 2021 and 2020, respectively. The deferred revenue is expected to be recognized over the research and development period of the programs through the completion of Phase 2 clinical trials. The Company has had changes to the overall expected costs to satisfy the performance obligations from period to period. For the year ended December 31, 2021, we had a 14 % increase in the forecast of the total expected costs. As a result of the cumulative catch up for the change in estimate, revenue was reduced by approximately $ 12.8 million compared to if the expected costs had remained the same. Innovent The Company entered into an agreement in March 2020 with Innovent Biologics (Innovent) to license, develop, and commercialize AL008 in China (Innovent Agreement). AL008 is the Company’s novel antibody targeting the CD47-SIRP-alpha pathway, a potent survival pathway co-opted by tumors to evade the innate immune system. Under the terms of the Innovent Agreement, Innovent may pay the Company up to $ 11.5 million in development milestones, $ 112.5 million in sales milestones, and future royalties on sales. The Company retains the rights to develop and commercialize AL008 outside of China. The Company has determined there is one performance obligation for the delivery of the license and will recognize revenue when it is probable that there will not be significant reversal of cumulative revenue. Development and sales milestones under the Innovent Agreement have not been included in the transaction price, as all these amounts were fully constrained as of December 31, 2021. As of December 31, 2021 , no revenue has been recognized and no payments have been received under the Innovent Agreement.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	5. Balance Sheet Components Property and Equipment, Net Property and equipment, net consists of the following: December 31, 2021 2020 (In thousands) Leasehold improvements $ 25,949 $ 25,542 Lab equipment 14,043 11,610 Furniture and fixtures 2,330 2,222 Computer equipment 2,294 1,764 Property and equipment, gross 44,616 41,138 Less accumulated depreciation and amortization ( 17,286 ) ( 10,957 ) Total property and equipment, net $ 27,330 $ 30,181 Accrued Liabilities Accrued liabilities consist of the following: December 31, 2021 2020 (In thousands) Accrued research and development costs $ 13,330 $ 13,375 Accrued employee compensation 11,664 7,288 Accrued professional services 1,588 1,094 Accrued property and equipment 560 428 Other 318 353 Total accrued liabilities $ 27,460 $ 22,538

Leases

Leases	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Leases	6. Leases In June 2018, the Company signed a lease agreement to lease approximately 105,000 square feet in office and laboratory space in South San Francisco which serves as the Company’s headquarters (the “Headquarters”). The lease expires in 2029 with an option to renew for a period of ten years . The landlord paid for $ 15.7 million of tenant improvements. In connection with the lease, the Company entered into a letter of credit arrangement in the amount of $ 1.5 million as collateral for the lease, which is classified as restricted cash on the consolidated balance sheets. In October 2020, the Company signed a lease agreement to lease approximately 18,700 square feet of office and laboratory space in Newark, California. The lease term ends on February 6, 2028 with an option to extend for an additional five years . The landlord is obligated to pay for up to $ 0.4 million of tenant improvements. The measurement of the lease liabilities for the leases excludes the options to extend the term of the lease as such extensions are not reasonably certain to occur. Variable lease costs for all of the Company’s leases consist of operating expenses for the spaces. In May 2019, the Company entered into an agreement to sublease approximately 25,000 square feet of the Headquarters (the “Sublease”), which was amended to approximately 23,600 square feet in December 2020. The Sublease expired in November 2021 . The sublessee pays its proportionate share of operating expenses for the space. In June 2019, in connection with the Sublease, the Company evaluated the related right-of-use asset for impairment. The lease costs plus amortization expense of the leasehold improvements in the subleased space exceeded the sublease income over the remaining sublease term. As such, the Company recorded an impairment charge of $ 1.2 million in general and administrative expenses to write-down the right-of-use asset such that no loss is expected to be recognized over the sublease period. The components of lease expense were as follows: December 31, 2021 2020 2019 (In thousands) Operating lease cost $ 6,204 $ 5,589 $ 5,875 Variable lease cost 3,046 2,255 1,328 Short-term lease cost — — 68 Sublease income and reimbursement of variable lease cost ( 2,141 ) ( 2,288 ) ( 1,263 ) Total $ 7,109 $ 5,556 $ 6,008 As of December 31, 2021 , the weighted-average remaining lease term for operating leases was 7.2 years and the weighted-average discount rate was 8.5 %. Cash paid for amounts included in the measurement of lease liabilities for the year ended December 31, 2021 , 2020, and 2019 was $ 7.9 million, $ 6.9 million, and $ 3.2 million, respectively, was included in net cash used in operating activities in our consolidated statements of cash flows. The following are the lease payments owed under the Company’s operating leases as of December 31, 2021: (In thousands) 2022 $ 8,171 2023 8,436 2024 8,732 2025 9,037 2026 9,353 Thereafter 20,777 Total undiscounted lease payments 64,506 Less: Present value adjustment ( 16,905 ) Total lease liability $ 47,601

Stock-based Compensation

Stock-based Compensation	12 Months Ended
	Dec. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	7. Stock-based Compensation The Company recognized stock-based compensation as follows: Year Ended December 31, 2021 2020 2019 (In thousands) Research and development $ 21,443 $ 14,980 $ 8,031 General and administrative 19,342 15,542 8,250 Total stock-based compensation $ 40,785 $ 30,522 $ 16,281 Determination of Fair Value The estimated grant-date fair value of all the Company’s options to purchase common stock was calculated using the Black-Scholes option pricing model, based on the following assumptions: Year Ended December 31, 2021 2020 2019 Expected term (in years) 5.2 – 6.1 5.3 – 6.1 5.3 – 6.1 Expected volatility 78 % – 81% 74 % – 78% 76 % – 82 % Risk free interest rate 0.5 % – 1.3 % 0.3 % – 1.8 % 1.4 % – 2.6 % Dividend yield — — — The fair value of each stock option was determined by the Company using the methods and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment and estimation by management. Expected Term— The expected term represents the period that stock-based awards are expected to be outstanding. The expected term was derived by using the simplified method which uses the midpoint between the average vesting term and the contractual expiration period of the stock-based award. Expected Volatility— The Company has limited information on the volatility of stock options as the shares were not actively traded on any public markets prior to February 7, 2019. The expected volatility was derived from the historical stock volatilities of comparable peer public companies within its industry. These companies are considered to be comparable to the Company’s business over a period equivalent to the expected term of the stock-based awards. In 2020, the Company began giving weight to in its own historical volatility in the determination of expected volatility. Risk-Free Interest Rate— The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the date of grant for zero-coupon U.S. Treasury notes with maturities approximately equal to the expected term. Expected Dividend Rate— The expected dividend is zero as the Company has not paid nor does it anticipate paying any dividends on its common stock underlying its stock options in the foreseeable future. 2019 Equity Incentive Plan On February 6, 2019, the Company adopted the 2019 Equity Incentive Plan (2019 Plan) under which the Board may issue incentive stock options, nonstatutory stock options, restricted stock, restricted stock units, stock appreciation rights, performance units, and performance shares to the Company’s employees, directors, and consultants. The Company’s 2017 Stock Option and Grant Plan (2017 Plan) was terminated; however, shares subject to awards granted under it will continue to be governed by the 2017 Plan. Shares reserved for issuance but not issued pursuant to, or not subject to, awards granted under the 2017 Plan were added to the available shares in the 2019 Plan. Shares subject to awards granted under the 2017 Plan that are repurchased by, or forfeited to, the Company will also be reserved for issuance under the 2019 Plan. The board of directors, or a committee appointed by the board of directors, has the authority to determine to whom options or shares will be granted, the number of shares, the term, and the exercise price. If an individual owns stock representing 10 % or more of the outstanding shares, the exercise price of each share shall be at least 110 % of the fair market value and the term of the award shall not exceed five years . All other options granted under the 2019 Plan must have an exercise price at least equal to the fair market value on the date of grant and have a term not to exceed ten years . The shares generally vest over a four-year period with straight-line vesting with a 25 % one-year cliff. On January 1, 2021, the Company added 3,965,813 shares to the shares reserved for issuance under the 2019 Equity Incentive Plan. As of December 31, 2021 , the Company had reserved 17,060,430 shares of common stock under the 2019 Plan, of which 4,042,486 shares were available for issuance of future awards. Option a ctivity is shown below: Number of Weighted Weighted Aggregate (In years) (In thousands) Outstanding as of December 31, 2019 8,442,824 $ 12.79 Granted 5,597,148 15.35 Exercised ( 655,772 ) 9.65 Forfeited ( 729,202 ) 14.96 Outstanding as of December 31, 2020 12,654,998 13.96 Granted 3,264,059 21.53 Exercised ( 2,395,223 ) 11.91 Forfeited ( 1,879,764 ) 14.55 Outstanding as of December 31, 2021 11,644,070 $ 16.41 8.30 $ 62,008 Exercisable as of December 31, 2021 4,710,208 $ 14.66 7.60 $ 31,997 Vested and expected to vest as of December 31, 11,644,070 $ 16.41 8.30 $ 62,008 The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying stock options and the fair value of the Company’s common stock for stock options that were in-the-money. The aggregate intrinsic value of options exercised was $ 37.1 million, $ 11.1 million, and $ 1.8 million for the years ended December 31, 2021 , 2020, and 2019, respectively. The weighted-average grant-date fair value per share of options granted was $ 14.70 , $ 10.14 , and $ 12.06 , for the years ended December 31, 2021, 2020 and 2019, respectively. As of December 31, 2021 , total unrecognized stock-based compensation related to unvested stock options was $ 78.5 million, which the Company expects to recognize over a remaining weighted-average period of 2.3 years. 2019 Employee Stock Purchase Plan On February 6, 2019, the Company adopted the 2019 Employee Stock Option Plan (2019 ESPP). The 2019 ESPP enables eligible employees of the Company to purchase shares of common stock at a discount. Each offering period is approximately six months long beginning on the first trading day on or after June 1 and December 1 each year. ESPP participants purchase shares of common stock at a price per share equal to 85 % of the lesser of (1) the fair market value per share of the common stock on the first trading day of the offering period or (2) the fair market value of the common stock on the purchase date. As of December 31, 2021 , there was $ 0.5 million in unrecognized compensation expense related to the 2019 ESPP to be recognized over five months. Restricted Stock Activity Activity for the restricted stock awards and RSUs is shown below. In May 2021, the Company issued RSUs with market conditions to certain executives, which are also included in the table below. The RSUs with market conditions are earned based on stock price performance and continued service by the employee. The RSUs with market conditions trigger vesting upon the company's stock price attaining a specified level over a specified period of time. The shares then vest quarterly over one year after attainment. The Company used a Monte Carlo simulation model to determine the fair value of the awards at the grant date. The Monte Carlo model uses the fair value inputs on the grant date to run simulations and take an average of possible outcomes. The total grant date fair value of the RSUs with market conditions was $ 5.6 million to be amortized over an estimated weighted average service period of 2.2 years. Compensation expense related to awards with market-based conditions is recognized regardless of whether the market condition is ultimately satisfied if the related service has been provided. Number of Weighted Unvested restricted stock awards and restricted stock units as of December 31, 2019 994,838 $ 6.95 Vested ( 726,659 ) 6.95 Forfeited ( 81,754 ) 6.95 Unvested restricted stock awards and restricted stock units as of December 31, 2020 186,425 6.95 Granted 1,822,295 17.33 Vested ( 324,802 ) 10.35 Forfeited ( 310,044 ) 13.85 Unvested restricted stock units as of 1,373,874 $ 18.35 As of December 31, 2021 , total unrecognized stock-based compensation related to unvested restricted common stock issued to employees was $ 22.6 million, which the Company expects to recognize over a remaining weighted-average period of 2.4 years.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	8. Income Taxes The Company incurred net operating losses for the years ended December 31, 2021, 2020, and 2019. The Company has not reflected a benefit of such net operating loss carryforwards in the accompanying financial statements. The Company has established a full valuation allowance against its net deferred tax assets due to the uncertainty surrounding realization of such assets. A reconciliation of the federal statutory rate to the Company’s effective tax rate is as follows for the years ended December 31, 2021, 2020, and 2019 (in thousands): Year Ended December 31, 2021 2020 2019 Tax benefit at federal statutory rate $ ( 7,627 ) $ ( 39,948 ) $ ( 22,081 ) State income taxes 398 ( 16,570 ) ( 4,694 ) Tax credits ( 9,389 ) ( 8,010 ) ( 6,530 ) Uncertain tax positions 2,347 2,003 2,044 Stock-based compensation ( 2,368 ) 353 1,493 Nondeductible expense 88 51 124 Tax benefit recognized on utilization of — — ( 13,582 ) Deferred adjustment from amended tax — — ( 1,073 ) Change in valuation allowance 16,800 62,280 44,748 Other ( 249 ) ( 159 ) ( 449 ) Income tax provision $ — $ — $ — The tax effects of temporary differences that give rise to significant components of the Company’s deferred tax assets and liabilities consist of (in thousands): December 31, 2021 2020 Deferred tax assets: Net operating loss $ 63,868 $ 54,382 Accrued bonus 1,811 1,201 Tax credits 19,614 13,000 Stock-based compensation 9,656 6,493 Deferred revenue 27,849 32,129 Lease liability 11,296 12,457 Other 694 463 Gross deferred tax assets 134,788 120,125 Less valuation allowance ( 122,046 ) ( 105,226 ) Total deferred tax assets $ 12,742 $ 14,899 Deferred tax liabilities: Depreciation and amortization $ ( 5,488 ) $ ( 6,815 ) Right-of-use assets ( 7,254 ) ( 7,934 ) Other — ( 150 ) Gross deferred tax liabilities ( 12,742 ) ( 14,899 ) Deferred tax assets, net $ — $ — In assessing the realization of deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred assets will be realized. The ultimate realization of the deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. Evaluating the need for a valuation allowance for deferred tax assets often requires judgment and analysis of all the positive and negative evidence available, including cumulative losses in recent years and projected future taxable income, to determine whether all or some portion of the deferred tax assets will not be realized. As of December 31, 2021 , the Company has utilized a full valuation allowance to offset the net deferred tax assets as the Company believes it is not more likely than not that the net deferred tax assets will be fully realizable. The valuation allowance for deferred tax assets increased by $ 16.8 million during the year ended December 31, 2021. As of December 31, 2021 , the Company had federal and state net operating loss (NOL) carryforwards of approximately $ 236.6 million and $ 204.4 million, respectively. Federal NOL carryforwards have an indefinite life and deductions cannot exceed 80 % of taxable income. State NOL carryforwards will begin to expire as early as 2030 , if not utilized, or have an indefinite life. As of December 31, 2021 , the Company also had federal and California tax credit carryforward of approximately $ 21.1 million and $ 6.5 million, respectively. The federal tax credits will begin to expire in 2036 while the California tax credits have no expiration date. Generally, utilization of the NOL carryforwards and credits may be subject to an annual limitation due to the ownership change limitations provided by Section 382, which provides for limitations on NOL carryforwards and certain built-in losses following ownership changes, and Section 383, which provides for special limitations on certain excess credits, etc., of the Code, and similar state provisions. Accordingly, the Company’s ability to utilize NOL carryforwards may be limited as the result of such an “ownership change.” The carryforwards could be subject to an annual limitation, resulting in a reduction in the gross deferred tax assets before considering the valuation allowance. Further, a portion of the carryforwards may expire before being applied to reduce future earnings. The Company is not aware of any changes in ownership that would result in material limitations under Section 382 at this time. The following table summarizes the activity related to the Company’s unrecognized tax benefits for the years ended December 31, 2021, 2020, and 2019 (in thousands): Balance as of December 31, 2019 $ 3,035 Decreases related to tax positions taken during the ( 446 ) Increases related to tax positions taken during the 2,003 Balance as of December 31, 2020 4,592 Decreases related to tax positions taken during the ( 59 ) Increases related to tax positions taken during the 2,406 Balance as of December 31, 2021 $ 6,939 If the unrecognized tax benefits for uncertain tax positions as of December 31, 2021, is recognized, there will be no impact to the effective tax rate as the tax benefit would increase the net deferred tax assets, which is currently offset with a full valuation allowance. The Company’s policy is to include interest and penalties related to unrecognized tax benefits, if any, within the provision for taxes in the consolidated statements of operations. The Company did not accrue any interest or penalties and does not have any tax positions for interest or penalties for the year ended December 31, 2021. The Company does not have any tax positions for which it is reasonably possible that the total amount of gross unrecognized tax benefits will significantly change within 12 months of December 31, 2021. The Company recognizes the tax benefit of an uncertain tax position only if it is more likely than not that the position is sustainable upon examination by the taxing authority, based on the technical merits. During the year ended December 31, 2021 , the Company recorded a tax reserve of $ 2.4 million in relation to the tax credit carryover. The income tax provision for the year ended December 31, 2021, included a reversal of reserves on uncertain tax provisions of $ 0.1 million. The Company’s income tax returns generally remain subject to examination by federal and most state tax authorities. The Company is currently not subject to any income tax audits by federal or state taxing authorities. The statute of limitations for tax liabilities for all years remains open.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2021
Related Party Transactions [Abstract]
Related Party Transactions	9. Related Party Transactions The Company has a collaboration agreement with Adimab, LLC (Adimab) under which the Company is developing antibodies discovered by Adimab in its AL001 and AL101 programs, and the Company is developing antibodies optimized by Adimab in its AL002 and AL003 programs (2014 Adimab Agreement). In August 2019, the Company signed a collaboration agreement with Adimab for research and development of additional antibodies (2019 Adimab Agreement). In December 2021, the Company signed another collaboration agreement with Adimab for research and development of additional antibodies (2021 Adimab Agreement). The Chief Executive Officer of Adimab is a Co-founder and Chairperson of the board of directors of Alector. For the years ended December 31, 2021 , 2020, and 2019, Alector incurred expenses of $ 1.0 million, zero , and $ 2.8 million for milestone payments for progress of programs through clinical trials. The Company had no accrued liabilities due to Adimab as of December 31, 2021 and 2020. Under the 2014 Adimab Agreement, the Company will owe up to $ 3.5 million in milestone payments per program to Adimab for its product candidates. The Company will also owe low- to mid- single-digit royalty payments for commercial sales of such product candidates. Under the 2019 and 2021 Adimab Agreements, the Company will owe certain milestone payments and low single-digit royalty payments for commercial sales of covered product candidates. On January 30, 2020, in connection with the Company’s follow-on offering, a member of the Company’s board of directors purchased 20,000 shares of the Company’s common stock at the public offering price of $ 25.00 per share.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	10. Net Loss Per Share The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect : Year Ended December 31, 2021 2020 2019 Restricted stock subject to future vesting 1,373,874 186,425 994,838 Options to purchase common stock 11,644,070 12,654,998 8,442,824 Shares committed under 2019 ESPP 70,406 86,677 44,464 Total 13,088,350 12,928,100 9,482,126

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States (GAAP) as defined by the Financial Accounting Standards Board (FASB). The consolidated financial statements include the accounts of Alector, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expense during the reporting period. The Company evaluates its estimates, including those related to revenue recognition, manufacturing accruals, clinical accruals, fair value of assets and liabilities, income taxes uncertainties, stock-based compensation, and related 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 materially differ from those estimates .
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, and short-term marketable securities. Cash and cash equivalents are deposited in checking and sweep accounts at financial institutions. Such deposits may, at times, exceed federally insured limits.
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents, and Restricted Cash The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash and cash equivalents. Cash equivalents, which consist of amounts invested in money market funds, are stated at fair value. Restricted cash as of December 31, 2021 relates to a letter of credit established for a lease entered into in June 2018. 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: Year Ended December 31, 2021 2020 2019 (In thousands) Cash and cash equivalents $ 329,152 $ 49,969 $ 89,641 Restricted cash 1,472 1,472 1,472 Total cash, cash equivalents, and restricted cash $ 330,624 $ 51,441 $ 91,113
Marketable Securities	Marketable Securities All marketable securities have been classified as “available-for-sale” and are carried at fair value, based upon quoted market prices. The Company considers its available-for-sale portfolio as available for use in current operations. Accordingly, the Company may classify certain investments as short-term marketable securities, even though the stated maturity date may be one year or more beyond the current balance sheet date. For available-for-sale debt securities, unrealized gains, net of any related tax effects, are excluded from earnings and are included in other comprehensive income and reported as a separate component of stockholders’ equity until realized. The Company assesses available-for-sale debt securities on a quarterly basis to see if any unrealized loss is due to credit-related factors. Factors considered in determining whether an impairment is credit-related include the extent to which the investment’s fair value is less than its cost basis, declines in published credit ratings, changes in interest rates, and any other adverse factors related to the security. If it is determined that a credit-related impairment exists, the Company will measure the credit loss based on a discounted cash flows model. Credit-related impairments on available-for-sale debt securities are recognized as an allowance for credit losses with a corresponding adjustment to other income, net in the Company’s consolidated statement of operations. The unrealized loss position that is not credit-related is recorded, net of any related tax effects, in other comprehensive income until realized. There were no credit-related losses recognized for the periods presented. The cost of securities sold is based on the specific-identification method. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity. In accordance with our investment policy, management invests in money market funds, U.S. treasury securities, and corporate bonds. The Company has not experienced any losses on its deposits of cash, cash equivalents, and marketable securities.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company’s financial instruments include cash and cash equivalents, marketable securities, receivable from collaboration partner, current and noncurrent prepaid expenses, accounts payable, and accrued liabilities. The Company’s financial instruments approximate fair value due to their relatively short maturities. 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 the fair value of its financial instruments 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 are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2 – Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and Level 3 – Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data.
Property, Plant and Equipment	Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation and amortization. Depreciation and amortization is computed using the straight-line method over the estimated useful lives of the respective assets, generally three to five years . Leasehold improvements are amortized over the lesser of their useful lives or the remaining life of the lease. When assets are retired or otherwise disposed of, the cost and related accumulated depreciation and amortization are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statements of operations in the period realized. Maintenance and repairs are charged to the consolidated statements of operations as incurred.
Leases	Leases The Company determines whether an arrangement is or contains a lease at the inception of the lease. Leases are recognized on the balance sheet as right-of-use assets and lease liabilities. Lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The Company utilizes the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received and any prepaid or accrued rent. Rent expense for the operating lease is recognized on a straight-line basis over the lease term and is included in operating expenses on the statements of operations and comprehensive loss. Variable lease payments include lease operating expenses. The Company excludes balance sheet recognition of operating leases having a term of 12 months or less (short-term leases) and does not separate lease components and non-lease components for its long-term leases.
Impairment or Disposal of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparing the carrying amount to the future net undiscounted cash flows which the assets are expected to generate. If the total of the undiscounted future cash flows is less than the carrying amount of the assets, an impairment loss is recognized for the amount by which the carrying amount of the assets exceeds is fair value. For the year ended December 31, 2021, the Company did not recognize an impairment loss on its right-of-use assets. For the year ended December 31, 2020 , the Company recognized a $ 0.2 million impairment loss related to its decision to no longer utilize certain property through the end of the lease term. For the year ended December 31, 2019, the Company recognized a $ 1.2 million impairment loss on its right of use assets related to the portion of its headquarters being subleased.
Revenue Recognition	Revenue Recognition The Company recognizes revenue when control of promised goods or services is transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under arrangements, the Company performs the following steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract, and (v) recognize revenue when (or as) the entity satisfies the performance obligation. If it is determined that multiple performance obligations exist, the transaction price is allocated at the inception of the agreement to all identified performance obligations based on the relative standalone selling price (SSP). The relative SSP for each deliverable is estimated using external sourced evidence if it is available. If external sourced evidence is not available, we use our best estimate of the SSP for the deliverable. The Company recognizes collaboration revenue at a point in time if control of the promised good or service has been transferred to the customer. The Company recognizes collaboration revenue over time by measuring the progress toward complete satisfaction of the performance obligation using an input measure. In order to recognize revenue over the research and development period, the Company measures actual costs incurred to date compared to the overall total expected costs to satisfy the performance obligation. Revenues are recognized as the program costs are incurred. The Company re-evaluates the estimate of expected costs to satisfy the performance obligation each reporting period.
Research and Development Expense	Research and Development Costs Research and development costs are expensed as incurred and consist primarily of new product development. Research and development costs include salaries and benefits, consultants’ fees, process development costs, stock-based compensation, and laboratory supplies, as well as fees paid to third parties that conduct certain research and development activities on the Company’s behalf. In addition, research and development costs include the reimbursable costs incurred for the grant agreements, which includes payroll costs for time incurred on projects, laboratory supplies, and third-party research and development activities. A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers. The Company records accrued expenses for estimated preclinical study and clinical trial expenses. Estimates are based on the services performed pursuant to contracts with research institutions, contract research organizations in connection with clinical studies, investigative sites in connection with clinical studies, vendors in connection with preclinical development activities, and contract manufacturing organizations in connection with the production of materials for clinical trials. Further, the Company accrues expenses related to clinical trials based on the level of patient enrollment and activity according to the related agreement. The Company monitors patient enrollment levels and related activity to the extent reasonably possible and make judgments and estimates in determining the accrued balance in each reporting period. If the Company underestimates or overestimates the level of services performed or the costs of these services, actual expenses could differ from estimates. To date, the Company has not experienced significant changes in its estimates of preclinical studies and clinical trial accruals.
Stock-based Compensation	Stock-based Compensation Stock-based compensation is measured on the grant date based on the fair value of the awards. The fair value of options to purchase common stock is measured using the Black-Scholes option-pricing model. Stock-based compensation associated with restricted stock units (RSUs) is based on the fair value of the Company's common stock on the grant date, which equals the closing price of the Company's common stock on the grant date. The Company recognizes expense over the vesting period of the awards. Expense for options and RSUs that vest based only on a service condition is recognized on a straight-line basis. In 2021, the Company granted RSUs with market conditions to certain executives. The fair value of RSUs with market conditions is estimated using a Monte Carlo simulation model. Assumptions and estimates utilized in the model include the stock price on grant date, risk-free interest rate, dividend yield, expected stock volatility, and estimated period to achieve the market condition. The expense is recognized based on continued employment of the participants, regardless of achievement of the market condition. Expense related to the RSUs with market conditions is recognized using the accelerated attribution method. The Company accounts for forfeitures as they occur for all awards.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss and certain changes in stockholders’ equity that are the result of transactions and economic events other than those with stockholders. The Company’s only element of other comprehensive loss was net unrealized gain (loss) on marketable securities.
Income Tax	Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial statement and tax bases of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. The deferred tax assets are recognized to the extent the Company believes that these assets are more likely than not to be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to the Company’s historical operating performance and the recorded cumulative net losses in prior periods, the net deferred tax assets have been fully offset by a valuation allowance. The Company records uncertain tax positions using a two-step process. First, the Company determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position. Second, for those tax positions that meet the more-likely-than-not recognition threshold, the Company recognizes the largest amount of tax benefit that is more than 50% likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits on the interest expense line and other expense line, respectively, in the accompanying statements of operations. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits.
Employee 401 (K) Plan	Employee 401(k) Plan The Company has a qualified contributory savings plan under Section 401(k) of the Internal Revenue Code (the “Code”) covering substantially all U.S. employees of Alector. The 401(k) plan is designed to provide tax-deferred retirement benefits in accordance with the provisions of Section 401(k) of the Code. Eligible employees may defer up to 100 % of their eligible compensation up to the annual maximum as determined by the Internal Revenue Service. The Company’s contributions to the plan are discretionary. For the years ended December 31, 2021 and 2020, the Company made matching contributions of $ 0.8 million and $ 0.7 million, respectively. The Company did no t make any matching contributions for the year ended December 31, 2019.
Segment	Segments The Company operates in one segment. The Company’s chief operating decision maker, its Chief Executive Officer, manages the Company’s operations on a consolidated basis for purposes of allocating resources.

Summary of Significant Accoun_3

Summary of 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: Year Ended December 31, 2021 2020 2019 (In thousands) Cash and cash equivalents $ 329,152 $ 49,969 $ 89,641 Restricted cash 1,472 1,472 1,472 Total cash, cash equivalents, and restricted cash $ 330,624 $ 51,441 $ 91,113

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Summary of Financial Assets Measured at Fair Value on a Recurring Basis	The following tables summarize the Company’s financial assets measured at fair value on a recurring basis by level within the fair value hierarchy: December 31, 2021 Fair Value Amortized Unrealized Unrealized Fair Market (In thousands) Money market funds Level 1 $ 218,451 $ — $ — $ 218,451 U.S. government treasury securities Level 1 407,041 8 ( 950 ) 406,099 Total cash equivalents and marketable $ 625,492 $ 8 $ ( 950 ) $ 624,550 December 31, 2020 Fair Value Amortized Unrealized Unrealized Fair Market (In thousands) Money market funds Level 1 $ 37,951 $ — $ — $ 37,951 U.S. government treasury securities Level 1 357,725 620 ( 6 ) 358,339 Corporate bonds Level 2 5,000 — — 5,000 Total cash equivalents and marketable $ 400,676 $ 620 $ ( 6 ) $ 401,290

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net consists of the following: December 31, 2021 2020 (In thousands) Leasehold improvements $ 25,949 $ 25,542 Lab equipment 14,043 11,610 Furniture and fixtures 2,330 2,222 Computer equipment 2,294 1,764 Property and equipment, gross 44,616 41,138 Less accumulated depreciation and amortization ( 17,286 ) ( 10,957 ) Total property and equipment, net $ 27,330 $ 30,181
Summary of Accrued Liabilities	Accrued liabilities consist of the following: December 31, 2021 2020 (In thousands) Accrued research and development costs $ 13,330 $ 13,375 Accrued employee compensation 11,664 7,288 Accrued professional services 1,588 1,094 Accrued property and equipment 560 428 Other 318 353 Total accrued liabilities $ 27,460 $ 22,538

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Components of Lease Expense	The components of lease expense were as follows: December 31, 2021 2020 2019 (In thousands) Operating lease cost $ 6,204 $ 5,589 $ 5,875 Variable lease cost 3,046 2,255 1,328 Short-term lease cost — — 68 Sublease income and reimbursement of variable lease cost ( 2,141 ) ( 2,288 ) ( 1,263 ) Total $ 7,109 $ 5,556 $ 6,008
Schedule of Lease Payments Owed Under Company's Operating Leases	The following are the lease payments owed under the Company’s operating leases as of December 31, 2021: (In thousands) 2022 $ 8,171 2023 8,436 2024 8,732 2025 9,037 2026 9,353 Thereafter 20,777 Total undiscounted lease payments 64,506 Less: Present value adjustment ( 16,905 ) Total lease liability $ 47,601

Stock-based Compensation (Table

Stock-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Recognized Stock-Based Compensation	The Company recognized stock-based compensation as follows: Year Ended December 31, 2021 2020 2019 (In thousands) Research and development $ 21,443 $ 14,980 $ 8,031 General and administrative 19,342 15,542 8,250 Total stock-based compensation $ 40,785 $ 30,522 $ 16,281
Summary of Share-based Payment Award, Stock Options, Valuation Assumptions	The estimated grant-date fair value of all the Company’s options to purchase common stock was calculated using the Black-Scholes option pricing model, based on the following assumptions: Year Ended December 31, 2021 2020 2019 Expected term (in years) 5.2 – 6.1 5.3 – 6.1 5.3 – 6.1 Expected volatility 78 % – 81% 74 % – 78% 76 % – 82 % Risk free interest rate 0.5 % – 1.3 % 0.3 % – 1.8 % 1.4 % – 2.6 % Dividend yield — — —
Summary of Options to Purchase Common Stock	ctivity is shown below: Number of Weighted Weighted Aggregate (In years) (In thousands) Outstanding as of December 31, 2019 8,442,824 $ 12.79 Granted 5,597,148 15.35 Exercised ( 655,772 ) 9.65 Forfeited ( 729,202 ) 14.96 Outstanding as of December 31, 2020 12,654,998 13.96 Granted 3,264,059 21.53 Exercised ( 2,395,223 ) 11.91 Forfeited ( 1,879,764 ) 14.55 Outstanding as of December 31, 2021 11,644,070 $ 16.41 8.30 $ 62,008 Exercisable as of December 31, 2021 4,710,208 $ 14.66 7.60 $ 31,997 Vested and expected to vest as of December 31, 11,644,070 $ 16.41 8.30 $ 62,008

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation of the federal statutory rate to the Company’s effective tax rate is as follows for the years ended December 31, 2021, 2020, and 2019 (in thousands): Year Ended December 31, 2021 2020 2019 Tax benefit at federal statutory rate $ ( 7,627 ) $ ( 39,948 ) $ ( 22,081 ) State income taxes 398 ( 16,570 ) ( 4,694 ) Tax credits ( 9,389 ) ( 8,010 ) ( 6,530 ) Uncertain tax positions 2,347 2,003 2,044 Stock-based compensation ( 2,368 ) 353 1,493 Nondeductible expense 88 51 124 Tax benefit recognized on utilization of — — ( 13,582 ) Deferred adjustment from amended tax — — ( 1,073 ) Change in valuation allowance 16,800 62,280 44,748 Other ( 249 ) ( 159 ) ( 449 ) Income tax provision $ — $ — $ —
Schedule of Deferred Tax Assets and Liabilities	The tax effects of temporary differences that give rise to significant components of the Company’s deferred tax assets and liabilities consist of (in thousands): December 31, 2021 2020 Deferred tax assets: Net operating loss $ 63,868 $ 54,382 Accrued bonus 1,811 1,201 Tax credits 19,614 13,000 Stock-based compensation 9,656 6,493 Deferred revenue 27,849 32,129 Lease liability 11,296 12,457 Other 694 463 Gross deferred tax assets 134,788 120,125 Less valuation allowance ( 122,046 ) ( 105,226 ) Total deferred tax assets $ 12,742 $ 14,899 Deferred tax liabilities: Depreciation and amortization $ ( 5,488 ) $ ( 6,815 ) Right-of-use assets ( 7,254 ) ( 7,934 ) Other — ( 150 ) Gross deferred tax liabilities ( 12,742 ) ( 14,899 ) Deferred tax assets, net $ — $ —
Schedule of Unrecognized Tax Benefits	The following table summarizes the activity related to the Company’s unrecognized tax benefits for the years ended December 31, 2021, 2020, and 2019 (in thousands): Balance as of December 31, 2019 $ 3,035 Decreases related to tax positions taken during the ( 446 ) Increases related to tax positions taken during the 2,003 Balance as of December 31, 2020 4,592 Decreases related to tax positions taken during the ( 59 ) Increases related to tax positions taken during the 2,406 Balance as of December 31, 2021 $ 6,939

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Schedule of Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share	The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect : Year Ended December 31, 2021 2020 2019 Restricted stock subject to future vesting 1,373,874 186,425 994,838 Options to purchase common stock 11,644,070 12,654,998 8,442,824 Shares committed under 2019 ESPP 70,406 86,677 44,464 Total 13,088,350 12,928,100 9,482,126

The Company and Liquidity - Add

The Company and Liquidity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 30, 2020	Feb. 07, 2019	Dec. 31, 2020	Dec. 31, 2019
Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Public offerings			9,602,500	9,739,541
Initial Public Offering
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Public offerings		9,739,541
Share price		$ 19
Proceeds from issuance of common stock, net of underwriting discounts and commissions and offering expenses		$ 168.2
Convertible preferred stock, shares outstanding		0
Initial Public Offering | Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Conversion of convertible preferred stock to common stock		45,374,836
Over-Allotment Option
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Public offerings	1,252,500	489,541
Follow-on-offering
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Public offerings	9,602,500
Share price	$ 25
Proceeds from issuance of common stock, net of underwriting discounts and commissions and offering expenses	$ 224.5

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Summary Of Significant Accounting Policies [Line Items]
Credit losses on marketable securities	$ 0	$ 0
Impairment loss on right-of-use assets	$ 0	238,000	$ 1,158,000
Defined contribution plan, maximum annual contributions per employee, percent	100.00%
Defined matching contribution plan	$ 800,000	$ 700,000	$ 0
Minimum
Summary Of Significant Accounting Policies [Line Items]
Property, plant, and equipment useful life	3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Property, plant, and equipment useful life	5 years

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 329,152	$ 49,969	$ 89,641
Restricted cash	1,472	1,472	1,472
Total cash, cash equivalents, and restricted cash	$ 330,624	$ 51,441	$ 91,113	$ 66,942

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents and marketable securities, Amortized Cost	$ 218,451	$ 37,951
Cash equivalents and marketable securities, Unrealized Gains	0
Cash equivalents and marketable securities, Unrealized Losses	0
Cash equivalents and marketable securities, Fair Market Value	218,451	37,951
U.S Government Treasury Securities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents and marketable securities, Amortized Cost	407,041	357,725
Cash equivalents and marketable securities, Unrealized Gains	8	620
Cash equivalents and marketable securities, Unrealized Losses	(950)	(6)
Cash equivalents and marketable securities, Fair Market Value	406,099	358,339
Corporate Bonds | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents and marketable securities, Amortized Cost		5,000
Cash equivalents and marketable securities, Fair Market Value		5,000
Cash Equivalents and Marketable Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents and marketable securities, Amortized Cost	625,492	400,676
Cash equivalents and marketable securities, Unrealized Gains	8	620
Cash equivalents and marketable securities, Unrealized Losses	(950)	(6)
Cash equivalents and marketable securities, Fair Market Value	$ 624,550	$ 401,290

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Remaining contractual maturities of investments were less than one year	$ 488,200
Remaining contractual maturities of investments were less than one year through two years	136,400
Sale of marketable securities	$ 10,696	$ 0	$ 0

Collaboration Agreements - Addi

Collaboration Agreements - Additional Information (Details) $ in Thousands	Aug. 17, 2021USD ($)	Jul. 01, 2021USD ($)	Jan. 31, 2022USD ($)	Oct. 31, 2017USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue		$ 0			$ 307,900
Research and development expense					$ 189,407	$ 156,869	$ 100,528
Increase in expected cost percentage					14.00%
Reduced revenue					$ 12,800
GlaxoSmithKline plc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Effective date of agreement	Aug. 17, 2021
Upfront payments		$ 700,000			$ 700,000
Upfront payment received	$ 500,000
Percentage Of Development Cost					0.60
Collaboration revenue					$ 192,100
Research and development expense					8,800
GlaxoSmithKline plc | Subsequent Event
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payment received			$ 200,000
GlaxoSmithKline plc | Phase 3 License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenue					173,400
GlaxoSmithKline plc | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Additional milestone payments per program related to initiation of certain clinical studies and regulatory approval					$ 1,500,000
Alector
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage Of Development Cost					0.40
AbbVie Biotechnology Limited
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payments				$ 205,000
Upfront payment received				5,000				$ 200,000
Collaboration revenue					$ 14,900	21,100	$ 21,200
Deferred revenue					117,400	$ 132,300
Exclusive option rights exercised for each program				250,000
AbbVie Biotechnology Limited | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Additional milestone payments per program related to initiation of certain clinical studies and regulatory approval				$ 242,800
Innovent
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenue					0
Development milestone					11,500
Sales milestone					$ 112,500

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 44,616	$ 41,138
Less accumulated depreciation and amortization	(17,286)	(10,957)
Total property and equipment, net	27,330	30,181
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	25,949	25,542
Lab Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	14,043	11,610
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,330	2,222
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 2,294	$ 1,764

Balance Sheet Components - Su_2

Balance Sheet Components - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Accrued Liabilities Current [Abstract]
Accrued research and development costs	$ 13,330	$ 13,375
Accrued employee compensation	11,664	7,288
Accrued professional services	1,588	1,094
Accrued property and equipment	560	428
Other	318	353
Total accrued liabilities	$ 27,460	$ 22,538

Leases - Additional Information

Leases - Additional Information (Detail)	Jun. 30, 2018ft²	Dec. 31, 2020USD ($)ft²	Oct. 31, 2020USD ($)ft²	May 31, 2019ft²	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Lessee Lease Description [Line Items]
Tenant improvement allowance					$ 15,700,000
Amount form letter of credit		$ 1,472,000			$ 1,472,000	$ 1,472,000	$ 1,472,000
Lease expiration year					2029
Operating lease, renewal period					10 years
Operating lease term					The lease expires in 2029 with an option to renew for a period of ten years.
Operating sublease, impairment charges					$ 0	238,000	1,158,000
Weighted average remaining lease term for operating leases					7 years 2 months 12 days
Weighted average discount rate for operating leases					8.50%
Cash paid for amounts included In measurement of lease liabilities					$ 7,900	$ 6,900	$ 3,200
Offices and Laboratory Facilities | South San Francisco
Lessee Lease Description [Line Items]
Area under lease | ft²	105,000	23,600
Area under sublease | ft²				25,000
Sublease expiration month and year					2021-11
Operating sublease, existence of option to extend					true
Ongoing loss over sublease period					$ 0
Offices and Laboratory Facilities | South San Francisco | General and Administrative Expense
Lessee Lease Description [Line Items]
Operating sublease, impairment charges					$ 1,200,000
Offices and Laboratory Facilities | South San Francisco
Lessee Lease Description [Line Items]
Tenant improvement allowance			$ 400,000
Area of property | ft²			18,700
Lease, description					In October 2020, the Company signed a lease agreement to lease approximately 18,700 square feet of office and laboratory space in Newark, California. The lease term ends on February 6, 2028 with an option to extend for an additional five years. The landlord is obligated to pay for up to $0.4 million of tenant improvements.
Lease expiration date			Feb. 6, 2028
Extend for an additional lease term			5 years

Leases - Components of Lease Ex

Leases - Components of Lease Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease cost	$ 6,204	$ 5,589	$ 5,875
Variable lease cost	3,046	2,255	1,328
Short-term lease cost		0	68
Sublease income and reimbursement of variable lease cost	(2,141)	(2,288)	(1,263)
Total	$ 7,109	$ 5,556	$ 6,008

Leases - Schedule of Lease Paym

Leases - Schedule of Lease Payments Owed Under Company's Operating Leases (Detail) $ in Thousands	Dec. 31, 2021USD ($)
Leases [Abstract]
2022	$ 8,171
2023	8,436
2024	8,732
2025	9,037
2026	9,353
Thereafter	20,777
Total undiscounted lease payments	64,506
Less: Present value adjustment	(16,905)
Total lease liability	$ 47,601

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Recognized Stock-Based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 40,785	$ 30,522	$ 16,281
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	21,443	14,980	8,031
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 19,342	$ 15,542	$ 8,250

Stock-based Compensation - Sche

Stock-based Compensation - Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions (Details) - Share-based Payment Arrangement, Option	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend yield	0.00%	0.00%	0.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 2 months 12 days	5 years 3 months 18 days	5 years 3 months 18 days
Expected volatility	78.00%	74.00%	76.00%
Risk-free interest rate	0.50%	0.30%	1.40%
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days
Expected volatility	78.00%	74.00%	82.00%
Risk-free interest rate	1.30%	1.80%	2.60%

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Feb. 06, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2021
Restricted Stock Awards And Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected weighted average period		2 years 4 months 24 days
Grant date fair value of units granted		$ 5.6
Share-based payment award requisite service period		2 years 2 months 12 days
Un-recognized compensation expense		$ 22.6
2019 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
Expected weighted average period		2 years 3 months 18 days
Common stock reserved for issuance		17,060,430			3,965,813
Percentage of stock owned by Individual	10.00%
Percentage of exercise price per share from fair market value	110.00%
Stock options, term	5 years
Cliff vesting percentage	25.00%
Cliff vesting period	1 year
Common stock, shares available for issuance		4,042,486
Aggregate intrinsic value of option exercised		$ 37.1	$ 11.1	$ 1.8
Weighted-average grant-date fair value per share of options granted		$ 14.70	$ 10.14	$ 12.06
Un-recognized compensation expense		$ 78.5
2019 Equity Incentive Plan | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options, term	10 years
2019 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price of common stock, percentage	85.00%
Subsequent offering period	6 months
Un-recognized compensation expense		$ 0.5

Stock-based Compensation - Su_2

Stock-based Compensation - Summary of Restricted Common Stock (Details) - Restricted Stock Awards And Restricted Stock Units - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Shares
Number of Shares, Unvested, beginning balance	186,425	994,838
Number of Shares, Granted	1,822,295
Number of Shares, Vested	(324,802)	(726,659)
Number of Shares, Forfeited	(310,044)	(81,754)
Number of Shares, Unvested, ending balance	1,373,874	186,425
Weighted-average grant-date fair value
Weighted Average Grant Date Fair Value per Share, Unvested, beginning balance	$ 6.95	$ 6.95
Weighted Average Grant Date Fair Value per Share, Granted	17.33
Weighted Average Grant Date Fair Value per Share, Vested	10.35	6.95
Weighted Average Grant Date Fair Value per Share, Forfeited	13.85	6.95
Weighted Average Grant Date Fair Value per Share, Unvested, ending balance	$ 18.35	$ 6.95

Stock-based Compensation - Su_3

Stock-based Compensation - Summary of Options to Purchase Common Stock (Details) - 2019 Equity Incentive Plan - 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]
Number of Options, Outstanding, beginning balance	12,654,998	8,442,824
Number of Options, Granted	3,264,059	5,597,148
Number of Options, Exercised	(2,395,223)	(655,772)
Number of Options, Forfeited	(1,879,764)	(729,202)
Number of Options, Outstanding, ending balance	11,644,070	12,654,998
Number of Options, Exercisable	4,710,208
Number of Options, Vested and expected to vest	11,644,070
Weighted average exercise price, Outstanding, beginning balance	$ 13.96	$ 12.79
Weighted average exercise price, Granted	21.53	15.35
Weighted average exercise price, Exercised	11.91	9.65
Weighted average exercise price, Forfeited	14.55	14.96
Weighted average exercise price, Outstanding, ending balance	16.41	$ 13.96
Weighted average exercise price, Exercisable	14.66
Weighted average exercise price, Vested and expected to vest	$ 16.41
Weighted Average Remaining Contractual Term, Outstanding	8 years 3 months 18 days
Weighted Average Remaining Contractual Term, Exercisable (In years)	7 years 7 months 6 days
Weighted Average Remaining Contractual Term, Vested and expected to vest (In years)	8 years 3 months 18 days
Aggregate Intrinsic Value, Outstanding	$ 62,008
Aggregate Intrinsic Value, Exercisable	31,997
Aggregate Intrinsic Value, Vested or expected to vest	$ 62,008

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Tax benefit at federal statutory rate	$ (7,627)	$ (39,948)	$ (22,081)
State income taxes	398	(16,570)	(4,694)
Tax credits	(9,389)	(8,010)	(6,530)
Uncertain tax positions	2,347	2,003	2,044
Stock-based compensation	(2,368)	353	1,493
Nondeductible expense	88	51	124
Tax benefit recognized on utilization of attributes previous reserved	0	0	(13,582)
Deferred adjustment from amended tax return	0	0	(1,073)
Change in valuation allowance	16,800	62,280	44,748
Other	(249)	(159)	(449)
Income tax provision	$ 0	$ 0	$ 0

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Net operating loss	$ 63,868	$ 54,382
Accrued bonus	1,811	1,201
Tax credits	19,614	13,000
Stock-based compensation	9,656	6,493
Deferred revenue	27,849	32,129
Lease liability	11,296	12,457
Other	694	463
Gross deferred tax assets	134,788	120,125
Less valuation allowance	(122,046)	(105,226)
Total deferred tax assets	12,742	14,899
Deferred tax liabilities:
Depreciation and amortization	(5,488)	(6,815)
Right-of-use assets	(7,254)	(7,934)
Others	0	150
Gross deferred tax liabilities	(12,742)	(14,899)
Deferred tax assets, net	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)
Income Tax Contingency [Line Items]
Valuation allowance deferred tax asset change in amount	$ 16.8
Tax reserve	2.4
Reversal of reserves on uncertain tax provisions	0.1
California Tax Authority
Income Tax Contingency [Line Items]
Tax Credit Carryforward, Amount	6.5
Federal Tax Authority
Income Tax Contingency [Line Items]
Operating loss carry forward, net	236.6
Tax Credit Carryforward, Amount	$ 21.1
Tax Credit Beginning Expiration Year	2036
Federal Tax Authority | Maximum
Income Tax Contingency [Line Items]
Operating loss carry forward, deductions	80.00%
State Tax Authority
Income Tax Contingency [Line Items]
Operating loss carry forward, net	$ 204.4
Operating loss carry forward beginning expiration year	2030

Income Taxes - Schedule of Unre

Income Taxes - Schedule of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Unrecognized tax benefits, beginning balance	$ 4,592	$ 3,035
Decreases related to tax positions taken during the prior year	(59)	(446)
Increases related to tax positions taken during the current year	2,406	2,003
Unrecognized tax benefits, ending balance	$ 6,939	$ 4,592

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	Jan. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Follow-on-offering
Related Party Transaction [Line Items]
Public offerings	9,602,500
Share price	$ 25
Follow-on-offering | Director
Related Party Transaction [Line Items]
Public offerings	20,000
Adimab
Related Party Transaction [Line Items]
Related party transaction expenses		$ 1,000,000	$ 0	$ 2,800,000
Accrued liabilities due to related parties		0	$ 0
Two Thousand Fourteen Adimab Agreement | Maximum
Related Party Transaction [Line Items]
Future milestone payments owed		$ 3,500,000

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	13,088,350	12,928,100	9,482,126
Restricted Stock Awards And Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	1,373,874	186,425	994,838
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	11,644,070	12,654,998	8,442,824
Shares Committed Under 2019 ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	70,406	86,677	44,464