0000950170-21-000725 | 10-Q | XBRL Viewer

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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2021	Jul. 30, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Trading Symbol	ALEC
Entity File Number	001-38792
Entity Tax Identification Number	82-2933343
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 Quarterly 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
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		80,875,423
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	DE

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 125,713	$ 49,969
Marketable securities	193,857	363,339
Prepaid expenses and other current assets	9,760	8,203
Total current assets	329,330	421,511
Property and equipment, net	28,701	30,181
Operating lease right-of-use assets	31,617	32,470
Restricted cash	1,472	1,472
Other assets	5,993	2,617
Total assets	397,113	488,251
Current liabilities:
Accounts payable	11,942	3,004
Accrued clinical supply costs	7,174	11,148
Accrued liabilities	22,100	22,538
Deferred revenue, current portion	25,417	23,886
Operating lease liabilities, current portion	7,760	7,512
Total current liabilities	74,393	68,088
Deferred revenue, long-term portion	96,208	108,417
Operating lease liabilities, long-term portion	41,839	43,744
Other long-term liabilities	158	472
Total liabilities	212,598	220,721
Stockholders' equity:
Common stock, $0.0001 par value; 200,000,000 shares authorized; 80,005,162 and 79,316,261 shares issued and outstanding as of June 30, 2021 and December 31, 2020	8	8
Additional paid-in capital	701,670	676,956
Accumulated other comprehensive income	203	614
Accumulated deficit	(517,366)	(410,048)
Total stockholders' equity	184,515	267,530
Total liabilities and stockholders’ equity	$ 397,113	$ 488,251

Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited) - $ / shares	Jun. 30, 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	80,005,162	79,316,261
Common stock, shares outstanding	80,005,162	79,316,261

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Total revenue	$ 6,568	$ 3,170	$ 10,678	$ 10,341
Type of Revenue [Extensible List]	alec:CollaborationRevenueMember	alec:CollaborationRevenueMember	alec:CollaborationRevenueMember	alec:CollaborationRevenueMember
Operating expenses:
Research and development	$ 47,818	$ 34,062	$ 93,551	$ 68,667
General and administrative	14,075	15,697	25,087	30,341
Total operating expenses	61,893	49,759	118,638	99,008
Loss from operations	(55,325)	(46,589)	(107,960)	(88,667)
Other income, net	178	1,263	642	3,322
Net loss	(55,147)	(45,326)	(107,318)	(85,345)
Unrealized gain (loss) on marketable securities	(207)	(936)	(411)	1,704
Comprehensive loss	$ (55,354)	$ (46,262)	$ (107,729)	$ (83,641)
Net loss per share, basic and diluted	$ (0.69)	$ (0.58)	$ (1.35)	$ (1.11)
Shares used in computing net loss per share, basic and diluted		78,415,195		76,617,938

Condensed Consolidated Statement of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Beginning balance at Dec. 31, 2019	$ 194,743	$ 7	$ 414,414	$ 142	$ (219,820)
Beginning balance (in shares) at Dec. 31, 2019		69,052,873
Issuance of common stock upon follow-on public offering, net of issuance costs	224,511	$ 1	224,510
Issuance of common stock upon follow-on public offering, net of issuance costs (in shares)		9,602,500
Exercise of stock options	3,217		3,217
Exercise of stock options (in shares)		361,096
Stock-based compensation	6,642		6,642
Unrealized loss on marketable securities	2,640			2,640
Net loss	(40,019)				(40,019)
Ending balance at Mar. 31, 2020	391,734	$ 8	648,783	2,782	(259,839)
Ending balance (in shares) at Mar. 31, 2020		79,016,469
Beginning balance at Dec. 31, 2019	194,743	$ 7	414,414	142	(219,820)
Beginning balance (in shares) at Dec. 31, 2019		69,052,873
Net loss	(85,345)
Ending balance at Jun. 30, 2020	355,331	$ 8	658,642	1,846	(305,165)
Ending balance (in shares) at Jun. 30, 2020		79,252,395
Beginning balance at Mar. 31, 2020	391,734	$ 8	648,783	2,782	(259,839)
Beginning balance (in shares) at Mar. 31, 2020		79,016,469
Exercise of stock options	2,196		2,196
Exercise of stock options (in shares)		190,709
Purchase of common stock under employee stock purchase plan	715		715
Purchase of common stock under employee stock purchase plan (in shares)		45,217
Stock-based compensation	6,948		6,948
Unrealized loss on marketable securities	(936)			(936)
Net loss	(45,326)				(45,326)
Ending balance at Jun. 30, 2020	355,331	$ 8	658,642	1,846	(305,165)
Ending balance (in shares) at Jun. 30, 2020		79,252,395
Beginning balance at Dec. 31, 2020	$ 267,530	$ 8	676,956	614	(410,048)
Beginning balance (in shares) at Dec. 31, 2020	79,316,261	79,316,261
Exercise of stock options	$ 3,874		3,874
Exercise of stock options (in shares)		415,386
Stock-based compensation	8,800		8,800
Unrealized loss on marketable securities	(204)			(204)
Net loss	(52,171)				(52,171)
Ending balance at Mar. 31, 2021	227,829	$ 8	689,630	410	(462,219)
Ending balance (in shares) at Mar. 31, 2021		79,731,647
Beginning balance at Dec. 31, 2020	$ 267,530	$ 8	676,956	614	(410,048)
Beginning balance (in shares) at Dec. 31, 2020	79,316,261	79,316,261
Net loss	$ (107,318)
Ending balance at Jun. 30, 2021	$ 184,515	$ 8	701,670	203	(517,366)
Ending balance (in shares) at Jun. 30, 2021	80,005,162	80,005,162
Beginning balance at Mar. 31, 2021	$ 227,829	$ 8	689,630	410	(462,219)
Beginning balance (in shares) at Mar. 31, 2021		79,731,647
Exercise of stock options	1,993		1,993
Exercise of stock options (in shares)		207,453
Purchase of common stock under employee stock purchase plan	969		969
Purchase of common stock under employee stock purchase plan (in shares)		84,105
Forfeiture of restricted common stock		(18,043)
Stock-based compensation	9,078		9,078
Unrealized loss on marketable securities	(207)			(207)
Net loss	(55,147)			(55,147)
Ending balance at Jun. 30, 2021	$ 184,515	$ 8	$ 701,670	$ 203	$ (517,366)
Ending balance (in shares) at Jun. 30, 2021	80,005,162	80,005,162

Condensed Consolidated Statement of Stockholders' Equity (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Statement Of Stockholders Equity [Abstract]
Issuance cost of common stock	$ 1,148

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities:
Net loss	$ (107,318)	$ (85,345)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,130	2,903
Stock-based compensation	17,878	13,590
Amortization of premiums and accretion of discounts on marketable securities	1,152	(250)
Amortization of right-of-use assets	938	608
Loss from disposal of property and equipment, net		9
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,557)	(2,084)
Other assets	(3,376)	(967)
Accounts payable	9,148	4,431
Accrued liabilities and accrued clinical supply costs	(4,225)	519
Deferred revenue	(10,678)	(10,341)
Lease liabilities	(2,014)	(1,328)
Other long-term liabilities	(314)
Net cash used in operating activities	(97,236)	(78,255)
Cash flows from investing activities:
Purchase of property and equipment	(1,775)	(3,863)
Purchase of marketable securities	(5,081)	(307,388)
Maturities of marketable securities	173,000	161,635
Net cash provided by (used in) investing activities	166,144	(149,616)
Cash flows from financing activities:
Proceeds from issuance of common stock upon follow-on public offering, net of issuance costs		224,603
Proceeds from the exercise of options to purchase common stock	5,867	5,413
Purchase of common stock under employee stock option plan		715
Net cash provided by financing activities	6,836	230,731
Net increase in cash, cash equivalents, and restricted cash	75,744	2,860
Cash, cash equivalents, and restricted cash at beginning of period	51,441	91,113
Cash, cash equivalents, and restricted cash at end of period	127,185	93,973
Non-cash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued liabilities	$ 348	$ 184

The Company and Liquidity

6 Months Ended

Jun. 30, 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.

Follow-on Offering

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 offering costs.

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The condensed 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). In the opinion of management, these unaudited condensed consolidated financial statements include all normal, recurring adjustments that are necessary to present fairly the results of the interim periods presented. The condensed consolidated financial statements include the accounts of Alector, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2020, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on February 25, 2021.

Use of Estimates

The preparation of condensed 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 condensed 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 a financial institution. 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. There are no significant unrealized gains or losses on the money market funds for the periods presented.

Restricted cash as of June 30, 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 condensed consolidated balance sheets that sum to the total of the same amounts shown in the condensed consolidated statements of cash flows:


	Six Months Ended June 30,
	2021		2020
	(In thousands)
Cash and cash equivalents	$	125,713	$	92,501
Restricted cash		1,472		1,472
Total cash, cash equivalents, and restricted cash	$	127,185	$	93,973

Fair Value of Financial Instruments

The Company’s financial instruments include cash and cash equivalents, marketable securities, 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.

Revenue Recognition

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 was received by the Company in October 2017 and January 2018, respectively. The Company will perform research and development services for the antibodies to the two programs through the end of Phase 2 clinical trials which the Company expects to conduct through 2023. AbbVie will then have the exclusive right to exercise an option to enter into a license and collaboration agreement with the Company for one or both of the programs for $250.0 million each. If AbbVie exercises its option for the programs, 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.

The Company recognizes collaboration revenue 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 and make adjustments for any significant changes. Clinical trials are expensive and can take many years to complete, and the outcome is inherently

uncertain. Changes in the Company’s forecasted costs are likely to occur over time based upon changes in clinical trial procedures set forth in protocols, changes in estimates of manufacturing costs, or feedback from regulators on the design or operation of clinical trials. The Company has had changes to the overall expected costs to satisfy the performance obligations from period to period. For the three months ended June 30, 2021, the Company had a 1% increase in the forecast of the total expected costs. For the three months ended June 30, 2021, the increase in the overall expected costs to satisfy the performance obligation resulted in an approximately $0.7 million reduction in revenue compared to if the expected costs had remained the same, as a result of the cumulative catch up for the change in estimate. Collaboration revenue under the Company’s collaboration agreement with AbbVie during the three and six months ended June 30, 2021was $6.6 million and $10.7 million, respectively, the entire amount of which was included in deferred revenue at the beginning of the period. The deferred revenue was $121.6 million as of June 30, 2021. 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 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 for any 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 June 30, 2021. As of June 30, 2021, no revenue has been recognized or payments received under the Innovent Agreement.

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 are 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 are recognized on a straight-line basis.

The Company also granted RSUs with market conditions to certain executives. The fair value of the RSUs with market conditions are 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 the 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.

Fair Value Measurements

6 Months Ended

Jun. 30, 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:


	June 30, 2021
	Fair Value Hierarchy	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Market Value
	(In thousands)
Money market funds	Level 1	$	96,434	$	—	$	—		$	96,434
U.S. government treasury securities	Level 1		193,654		207		(4	)		193,857
Total cash equivalents and marketable securities		$	290,088	$	207	$	(4	)	$	290,291

	December 31, 2020
	Fair Value Hierarchy	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Market Value
	(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 securities		$	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 June 30, 2021, the remaining contractual maturities of $261.0 million of investments were less than one year and $29.3 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 June 30, 2021, the Company considered any unrealized losses on our marketable securities to be driven by factors other than credit risk.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Stock-based Compensation

6 Months Ended

Jun. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

4. Stock-based Compensation

The Company recognized stock-based compensation as follows:


	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
	(In thousands)				(In thousands)
Research and development	$	5,051	$	3,462	$	9,488	$	6,573
General and administrative		4,027		3,486		8,390		7,017
Total stock-based compensation	$	9,078	$	6,948	$	17,878	$	13,590

2019 Equity Incentive Plan

On January 1, 2021, the Company added 3,965,813 shares to the shares reserved for issuance under the 2019 Equity Incentive Plan (2019 Plan). As of June 30, 2021, the Company had reserved 18,989,234 shares of common stock for issuance under the 2019 Plan, of which 5,514,946 shares were available for issuance.

Activity for the options to purchase common stock shown below (in thousands, except share and per share amounts):


	Number of Options			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (In years)		Aggregate Intrinsic Value
Outstanding as of December 31, 2020		12,654,998		$	13.96
Granted		986,213			18.06
Exercised		(622,839	)		9.44
Forfeited		(815,969	)		13.78
Outstanding as of June 30, 2021		12,202,403		$	14.54		8.4	$	85,009
Exercisable as of June 30, 2021		4,588,394		$	14.13		7.9	$	33,816
Vested and expected to vest as of June 30, 2021		12,202,403		$	14.54		8.4	$	85,009

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. As of June 30, 2021, total unrecognized stock-based compensation related to unvested stock options was $71.8 million, which the Company expects to recognize over a remaining weighted-average period of 2.1 years.

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 included in the table below. The RSUs with market conditions are earned based on stock price performance and continued service by the employee.


	Number of Awards and Units			Weighted Average Grant Date Fair Value per Share
Unvested restricted stock awards and restricted stock units as of December 31, 2020		186,425		$	6.95
Granted		1,305,345			14.80
Vested		(143,640	)		6.95
Forfeited		(51,503	)		13.06
Unvested restricted stock awards and restricted stock units as of June 30, 2021		1,296,627		$	14.61

As of June 30, 2021, total unrecognized stock-based compensation related to unvested restricted stock awards and restricted stock units was $18.0 million, which the Company expects to recognize over a remaining weighted-average period of 2.7 years.

2019 Employee Stock Purchase Plan

The 2019 Employee Stock Purchase Plan (2019 ESPP) enables eligible employees of the Company to purchase shares of common stock at a discount. As of June 30, 2021, the Company has reserved for issuance 2,439,958 shares of common stock pursuant to the 2019 ESPP. Each offering period is approximately six months long. 2019 ESPP participants will 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.

Related Party Transactions

6 Months Ended

Jun. 30, 2021

Related Party Transactions

5. 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 product candidates, and the Company is developing antibodies optimized by Adimab in its AL002 and AL003 product candidates (2014 Adimab Agreement). In August 2019, the Company signed a new collaboration agreement with Adimab for research and development of additional

antibodies (2019 Adimab Agreement). The Chief Executive Officer of Adimab is a Co-founder and Chairperson of the board of directors of Alector. For the three and six months ended June 30, 2021, the Company incurred expenses of zero and $1.0 million for a milestone payment for first patient dosed in the AL002 Phase 2 trial, respectively. For the three and six months ended June 30, 2020, the Company incurred no expenses under the Adimab Agreements. The Company had no accrued liabilities due to Adimab as of three months ended June 30, 2021 and December 31, 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 Adimab Agreement, the Company will owe certain milestone payments per program for its product candidates and low single-digit royalty payments for commercial sales of such product candidates.

Net Loss Per Share

6 Months Ended

Jun. 30, 2021

Earnings Per Share [Abstract]

Net Loss Per Share

6. 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:


	Three and Six Months Ended June 30,
	2021		2020
Restricted stock and restricted stock units subject to future vesting		1,296,627		606,670
Options to purchase common stock		12,202,403		9,440,785
Shares committed under 2019 ESPP		59,413		25,822
Total		13,558,443		10,073,277

Subsequent Event

6 Months Ended

Jun. 30, 2021

Subsequent Events [Abstract]

Subsequent Event

7. Subsequent Event

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 Alector and GSK will collaborate on the global development and commercialization of progranulin-elevating monoclonal antibodies, AL001 and AL101 (GSK Agreement).

The consummation of the GSK Agreement is subject to obtaining any necessary consents and approvals, including review by the appropriate regulatory agencies under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (HSR Act).

Following the consummation of the GSK Agreement, Alector will receive $700 million in upfront payments, $500 million expected to be paid in the third quarter of 2021 and $200 million expected to be paid in the first quarter of 2022. In addition, based on the development and commercialization plan for AL001 and AL101, Alector will 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, Alector and GSK will equally share profits and losses from commercialization of AL001 and AL101. Outside of the United States, Alector will be eligible for double-digit tiered royalties.

Alector and GSK will jointly develop AL001 and AL101. Alector will lead the global clinical development of AL001 and AL101, other than with respect to Phase 3 clinical studies for Alzheimer’s disease and Parkinson’s disease and other non-orphan indications, which will be led by GSK. Alector and GSK will share development costs 60% by GSK and 40% by Alector, except that Alector will solely bear the development costs of the initial Phase 2 clinical studies under the development plan, and the parties will share manufacturing development costs equally.

In the United States, Alector and GSK will be jointly responsible for commercialization of AL001 and AL101, with Alector 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 responsible for commercialization of AL001 and AL101 for all indications.

Alector 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, Alector will no longer conduct development or commercialization of that product and Alector will receive royalties on net sales in the United States instead of a share of profits.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2021

Accounting Policies [Abstract]

Basis of Presentation

Use of Estimates

Concentration of Credit Risk

Cash, Cash Equivalents, and Restricted Cash

Restricted cash as of June 30, 2021 relates to a letter of credit established for a lease entered into in June 2018.


	Six Months Ended June 30,
	2021		2020
	(In thousands)
Cash and cash equivalents	$	125,713	$	92,501
Restricted cash		1,472		1,472
Total cash, cash equivalents, and restricted cash	$	127,185	$	93,973

Fair Value of Financial Instruments

Level 1 – Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date;

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.

Revenue Recognition

Stock-based Compensation

Comprehensive Loss

- Definition

Disclosure of accounting policy for revenue from contract with customer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130561-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
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-Subparagraph (b)
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130563-203045

Reference 7: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
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-Paragraph 4
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18823-107790

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
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-Section 50
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130564-203045

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 20
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130566-203045

+ Details

Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2021

Accounting Policies [Abstract]

Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash


	Six Months Ended June 30,
	2021		2020
	(In thousands)
Cash and cash equivalents	$	125,713	$	92,501
Restricted cash		1,472		1,472
Total cash, cash equivalents, and restricted cash	$	127,185	$	93,973

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 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:


	June 30, 2021
	Fair Value Hierarchy	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Market Value
	(In thousands)
Money market funds	Level 1	$	96,434	$	—	$	—		$	96,434
U.S. government treasury securities	Level 1		193,654		207		(4	)		193,857
Total cash equivalents and marketable securities		$	290,088	$	207	$	(4	)	$	290,291

	December 31, 2020
	Fair Value Hierarchy	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Market Value
	(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 securities		$	400,676	$	620	$	(6	)	$	401,290

Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Recognized Stock-Based Compensation

The Company recognized stock-based compensation as follows:


	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
	(In thousands)				(In thousands)
Research and development	$	5,051	$	3,462	$	9,488	$	6,573
General and administrative		4,027		3,486		8,390		7,017
Total stock-based compensation	$	9,078	$	6,948	$	17,878	$	13,590

Summary of Options to Purchase Common Stock

Activity for the options to purchase common stock shown below (in thousands, except share and per share amounts):


	Number of Options			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (In years)		Aggregate Intrinsic Value
Outstanding as of December 31, 2020		12,654,998		$	13.96
Granted		986,213			18.06
Exercised		(622,839	)		9.44
Forfeited		(815,969	)		13.78
Outstanding as of June 30, 2021		12,202,403		$	14.54		8.4	$	85,009
Exercisable as of June 30, 2021		4,588,394		$	14.13		7.9	$	33,816
Vested and expected to vest as of June 30, 2021		12,202,403		$	14.54		8.4	$	85,009

Summary of Restricted Stock Awards and Restricted Stock Units

Activity for the restricted stock awards and RSUs is shown below


	Number of Awards and Units			Weighted Average Grant Date Fair Value per Share
Unvested restricted stock awards and restricted stock units as of December 31, 2020		186,425		$	6.95
Granted		1,305,345			14.80
Vested		(143,640	)		6.95
Forfeited		(51,503	)		13.06
Unvested restricted stock awards and restricted stock units as of June 30, 2021		1,296,627		$	14.61

Net Loss Per Share (Tables)

6 Months Ended

Jun. 30, 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:


	Three and Six Months Ended June 30,
	2021		2020
Restricted stock and restricted stock units subject to future vesting		1,296,627		606,670
Options to purchase common stock		12,202,403		9,440,785
Shares committed under 2019 ESPP		59,413		25,822
Total		13,558,443		10,073,277

The Company and Liquidity - Additional Information (Details) $ / shares in Units, $ in Millions	Jan. 30, 2020 USD ($) $ / shares shares
Follow-on-offering
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Public offerings	9,602,500
Share price \| $ / shares	$ 25.00
Proceeds from issuance of common stock, net of underwriting discounts and commissions and offering expenses \| $	$ 224.5
Over-Allotment Option
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Public offerings	1,252,500

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended	6 Months Ended
	Jan. 31, 2018	Oct. 31, 2017	Jun. 30, 2021	Jun. 30, 2021
Summary Of Significant Accounting Policies [Line Items]
Increase in expected cost percentage			1.00%
Reduced revenue			$ 700
Deferred revenue			121,600	$ 121,600
AbbVie Biotechnology Limited
Summary Of Significant Accounting Policies [Line Items]
Upfront payments		$ 205,000
Upfront payment received	$ 200,000	5,000
Exclusive option rights exercised for each program		250,000
Collaboration revenue			$ 6,600	10,700
AbbVie Biotechnology Limited \| Maximum
Summary Of Significant Accounting Policies [Line Items]
Additional milestone payments per program related to initiation of certain clinical studies and regulatory approval		$ 242,800
Innovent
Summary Of Significant Accounting Policies [Line Items]
Collaboration revenue				0
Development milestone				11,500
Sales milestone				112,500
Money Market Funds
Summary Of Significant Accounting Policies [Line Items]
Unrealized gains or loss on money market funds				$ 0

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 125,713	$ 49,969	$ 92,501
Restricted cash	1,472	1,472	1,472
Total cash, cash equivalents, and restricted cash	$ 127,185	$ 51,441	$ 93,973	$ 91,113

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 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	$ 96,434	$ 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	96,434	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	193,654	357,725
Cash equivalents and marketable securities, Unrealized Gains	207	620
Cash equivalents and marketable securities, Unrealized Losses	(4)	(6)
Cash equivalents and marketable securities, Fair Market Value	193,857	358,339
Corporate Bonds \| Fair Value, Inputs, 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	290,088	400,676
Cash equivalents and marketable securities, Unrealized Gains	207	620
Cash equivalents and marketable securities, Unrealized Losses	(4)	(6)
Cash equivalents and marketable securities, Fair Market Value	$ 290,291	$ 401,290

Fair Value Measurements - Additional Information (Details) $ in Millions	Jun. 30, 2021 USD ($)
Fair Value Disclosures [Abstract]
Remaining contractual maturities of investments were less than one year	$ 261.0
Remaining contractual maturities of investments were less than one year through two years	$ 29.3

Stock-based Compensation - Summary of Recognized Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 9,078	$ 6,948	$ 17,878	$ 13,590
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	5,051	3,462	9,488	6,573
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 4,027	$ 3,486	$ 8,390	$ 7,017

Stock-based Compensation - Additional Information (Details) - USD ($) $ in Millions		6 Months Ended
	Feb. 06, 2019	Jun. 30, 2021	Jan. 01, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected weighted average period		2 years 1 month 6 days
Unrecognized stock-based compensation		$ 71.8
2019 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance		18,989,234	3,965,813
Common stock, shares available for issuance		5,514,946
2019 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance		2,439,958
Purchase price of common stock, percentage	85.00%
Subsequent offering period	6 months
Restricted Stock Awards and Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation		$ 18.0
Expected weighted average period		2 years 8 months 12 days

Stock-based Compensation - Summary of Options to Purchase Common Stock (Details) - 2019 Equity Incentive Plan - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options, Outstanding, beginning balance	12,654,998
Number of Options, Granted	986,213
Number of Options, Exercised	(622,839)
Number of Options, Forfeited	(815,969)
Number of Options, Outstanding, ending balance	12,202,403
Number of Options, Exercisable	4,588,394
Number of Options, Vested and expected to vest	12,202,403
Weighted average exercise price, Outstanding, beginning balance	$ 13.96
Weighted average exercise price, Granted	18.06
Weighted average exercise price, Exercised	9.44
Weighted average exercise price, Forfeited	13.78
Weighted average exercise price, Outstanding, ending balance	14.54
Weighted average exercise price, Exercisable	14.13
Weighted average exercise price, Vested and expected to vest	$ 14.54
Weighted Average Remaining Contractual Term, Outstanding (in years)	8 years 4 months 24 days
Weighted Average Remaining Contractual Term, Exercisable (In years)	7 years 10 months 24 days
Weighted Average Remaining Contractual Term, Vested and expected to vest (In years)	8 years 4 months 24 days
Aggregate Intrinsic Value, Outstanding	$ 85,009
Aggregate Intrinsic Value, Exercisable	33,816
Aggregate Intrinsic Value, Vested or expected to vest	$ 85,009

Stock-based Compensation - Summary of Restricted Stock Awards and Restricted Stock Units (Details) - Restricted Stock Awards and Restricted Stock Units	6 Months Ended
	Jun. 30, 2021 $ / shares shares
Number of Shares
Number of Shares, Unvested, beginning balance \| shares	186,425
Number of Shares, Granted \| shares	1,305,345
Number of Shares, Vested \| shares	(143,640)
Number of Shares, Forfeited \| shares	(51,503)
Number of Shares, Unvested, ending balance \| shares	1,296,627
Weighted-average grant-date fair value
Weighted Average Grant Date Fair Value per Share, Unvested, beginning balance \| $ / shares	$ 6.95
Weighted Average Grant Date Fair Value per Share, Granted \| $ / shares	14.80
Weighted Average Grant Date Fair Value per Share, Vested \| $ / shares	6.95
Weighted Average Grant Date Fair Value per Share, Forfeited \| $ / shares	13.06
Weighted Average Grant Date Fair Value per Share, Unvested, ending balance \| $ / shares	$ 14.61

Related Party Transactions - Additional Information (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jan. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Future milestone payments owed		$ 3,500,000		$ 3,500,000
Follow-on-offering
Related Party Transaction [Line Items]
Public offerings	9,602,500
Share price	$ 25.00
Two Thousand Fourteen Adimab Agreement
Related Party Transaction [Line Items]
Related party transaction expenses		0	$ 0	1,000,000.0	$ 0
Adimab
Related Party Transaction [Line Items]
Accrued liabilities due to related parties		$ 0		$ 0		$ 0

Net Loss Per Share - Schedule of Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	13,558,443	10,073,277
Restricted Stock and Restricted Stock Units Subject to Future Vesting
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	1,296,627	606,670
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	12,202,403	9,440,785
Shares Committed Under 2019 ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	59,413	25,822

Subsequent Event (Additional Information) (Details) - USD ($) $ in Millions		3 Months Ended
	Jul. 01, 2021	Mar. 31, 2022	Sep. 30, 2021
Collaboration and License Agreement [Member] \| GSK [Member] \| Scenario Forecast [Member]
Subsequent Event [Line Items]
Upfront payments		$ 200	$ 500
Subsequent Event [Member]
Subsequent Event [Line Items]
Costs for global development to bear, percentage	40.00%
Subsequent Event [Member] \| Maximum [Member]
Subsequent Event [Line Items]
Additional milestone payment	$ 1,500
Subsequent Event [Member] \| GSK [Member]
Subsequent Event [Line Items]
Costs for global development to bear, percentage	60.00%
Subsequent Event [Member] \| Collaboration and License Agreement [Member] \| GSK [Member]
Subsequent Event [Line Items]
Upfront payments	$ 700