0000950170-24-122328 | 10-Q | XBRL Viewer

Stock-based Compensation

9 Months Ended

Sep. 30, 2024

Share-Based Payment Arrangement [Abstract]

6. Stock-based Compensation

The Company recognized stock-based compensation as follows (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2024		2023		2024		2023
Research and development	$	4,488	$	5,300	$	14,873	$	16,269
General and administrative		4,547		4,759		14,378		14,987
Total stock-based compensation	$	9,035	$	10,059	$	29,251	$	31,256

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2023
Credit losses on marketable securities		$ 0
Impairment charges		$ 2,205	$ 0
General and Administrative Expense [Member]
Impairment charges	$ 2,200

Condensed Consolidated Statement of Stockholders' Equity (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
Statement of Stockholders' Equity [Abstract]
Issuance cost of common stock	$ 3,892

Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2024

Share-Based Payment Arrangement [Abstract]

Summary of Recognized Stock-Based Compensation

The Company recognized stock-based compensation as follows (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2024		2023		2024		2023
Research and development	$	4,488	$	5,300	$	14,873	$	16,269
General and administrative		4,547		4,759		14,378		14,987
Total stock-based compensation	$	9,035	$	10,059	$	29,251	$	31,256

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2024

Accounting Policies [Abstract]

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, 2023, 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 27, 2024.

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 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 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:


	Nine Months Ended September 30,
	2024		2023
	(In thousands)
Cash and cash equivalents	$	37,159	$	101,964
Restricted cash		1,546		1,546
Total cash, cash equivalents, and restricted cash	$	38,705	$	103,510

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, corporate bonds, certificates of deposit, and commercial paper. 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, current and noncurrent prepaid expenses, accounts payable, payable to collaboration partner, and accrued liabilities. The Company's investments in marketable securities are measured at fair value. The Company’s other financial instruments approximate fair value due to their relatively short maturities.

For investments in marketable securities, 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.

Leases

The Company determines whether an arrangement is or contains a lease at the inception of the arrangement. 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.

In August 2024, the Company approved a plan to transition operations from its laboratory and office space in Newark, California to its South San Francisco headquarters. The Company's intention is to sublease the Newark facility. The Company recorded an impairment charge of $2.2 million in general and administrative expenses to write-down the right-of-use asset and the leasehold improvements for the three months ended September 30, 2024.

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 contractual 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 performance obligation is estimated using externally sourced evidence if it is available. If externally sourced evidence is not available, the Company uses its best estimate of the SSP for the performance obligation.

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.

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.

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 on marketable securities.

Collaboration Agreements	9 Months Ended
Sep. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaboration Agreements	5. 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 collaborate on the global development and commercialization of progranulin-elevating monoclonal antibodies, including latozinemab and AL101 (GSK Agreement). The GSK Agreement became 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 received in January 2022. In addition, based on the development and commercialization plan for latozinemab 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 latozinemab and AL101. Outside of the United States, the Company will be eligible for double-digit tiered royalties. The Company and GSK will jointly develop latozinemab and AL101 with GSK conducting Phase 3 clinical trials for Alzheimer’s disease, Parkinson’s disease and other non-orphan indications. GSK will also conduct the initial Phase 2 trial for AL101 in Alzheimer’s disease. The Company and GSK will share development costs, 60% by GSK and 40% by the Company, except that subject to the GSK Amendment (defined below), 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 May 2023, the Company and GSK amended the GSK Agreement (GSK Amendment). Under the terms of the GSK Amendment, the Company is responsible for funding and sharing in GSK’s and the Company’s development costs up to $140.5 million for the conduct of the initial Phase 2 trial for AL101 in Alzheimer’s disease. The Company assessed the GSK Amendment in accordance with ASC 606 and concluded that the GSK Amendment was a contract modification to the GSK Agreement. Accordingly, the transaction price as of May 2023, was updated from $700 million to $571.6 million and the difference of $128.4 million was recorded as refund liability to collaboration partner for the expected cost reimbursement to GSK. The refund liability is an estimate of variable consideration calculated as the difference between the Company’s maximum funding of $140.5 million and the Company’s cost budget estimated using the expected value method. The Company determined that the modified performance obligation for the AL101 Alzheimer’s disease program is performing development activities to support the initial Phase 2 trial, including license rights and know-how. The Company updated the cost-based input measure of progress for the modified performance obligation and recorded a cumulative catch-up adjustment to revenue of $26.9 million on the modification date relating to performance obligation which was satisfied in prior periods. During the three months ended September 30, 2023, as a result of the planned closure of the latozinemab Phase 2 trial and concurrent agreement by the Company to cost-share additional R&D, the Company determined there was a modification of the GSK Agreement, resulting in a decrease of the scope of the performance obligation associated with the latozinemab FTD-C9orf72 Phase 2 trial and an increase in the amount of R&D cost-shared by the Company in future periods. The impact of this additional cost share was accounted for as a refund liability, which reduced the transaction price for the GSK Agreement by $4.2 million. The refund liability is an estimate of variable consideration. The Company determined that the modified performance obligation for the latozinemab FTD-C9orf72 indication is performing the first Phase 2 development activities, including license rights and know-how. The Company updated the cost-based input measure of progress for the modified performance obligation and recorded a cumulative catch-up adjustment to revenue of $4.9 million on the modification date relating to the performance obligation that was satisfied in prior periods. The transaction price at inception included fixed consideration consisting of the upfront payments of $700 million. The transaction price as of September 30, 2024 was decreased to $569.7 million due to the estimated refund liabilities created from the contract modifications. The Company reassessed the estimated refund liabilities to collaboration partner as of September 30, 2024 to be $72.2 million. Collaboration revenue under the GSK Agreement during the three and nine months ended September 30, 2024 was $8.0 million and $28.8 million, respectively, the entire amount of which was included in deferred revenue at the beginning of the respective period. For the three and nine months ended September 30, 2023 collaboration revenue under the GSK agreement was $7.5 million and $56.8 million, respectively. The deferred revenue related to the GSK Agreement was $219.3 million and $247.4 million as of September 30, 2024 and December 31, 2023, respectively. 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 condensed consolidated statements of operations, with any reimbursement of costs by GSK reflected as a reduction of such expenses. For the three and nine months ended September 30, 2024, the Company recognized a reduction of research and development expense of $5.5 million and $15.8 million, respectively, under the GSK Agreement. For the three and nine months ended September 30, 2023, the Company recognized a reduction of research and development expense of $7.8 million and $18.8 million, respectively, 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 was to perform research and development services for the two programs through the end of Phase 2 clinical trials, which were each considered to be separate performance obligations. AbbVie decided to terminate one of the two collaboration programs, the CD33 collaboration program, after AbbVie and Alector concluded that further development of AL003, the asset being developed under that program, was not warranted. AbbVie provided written notice to terminate the CD33 collaboration program on June 30, 2022. Accordingly, the Company is no longer developing that program and will not be eligible for any future milestones related to that program from AbbVie. The Company continues to develop the AL002 program under the AbbVie Agreement. AbbVie has the exclusive right to exercise an option under the AbbVie Agreement with the Company for $250.0 million. If AbbVie exercises its option for the AL002 program, AbbVie would take over development of the product candidate, and the program costs will be split between the parties. The Company would also share in profits and losses upon commercialization of any products. Alternatively, following AbbVie’s exercise of its option for the AL002 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 $225.0 million in milestone payments related to the regulatory approval for up to three indications. The Company assessed its collaboration agreement with AbbVie in the context of the delivery of the research and development services. In February 2023, the Company and AbbVie amended the AbbVie Agreement (AbbVie Amendment), which resulted in the Company receiving a $17.8 million milestone payment in March 2023 for the dosing of the first patient in a long-term extension (LTE) trial. In addition, under the terms of the AbbVie Amendment, the Company was eligible to earn up to an additional $12.5 million to support the enrollment of additional patients to replace discontinuations, and the Company received the total $12.5 million in 2023. The performance obligations to conduct the LTE trial and enroll additional patients are not considered distinct from the AL002 program performance obligation. The transaction price as of September 30, 2024 included fixed consideration consisting of the upfront payments of $205.0 million, the $17.8 million LTE milestone payment, and the $12.5 million payment for enrollment of additional patients. Collaboration revenue under the AbbVie Agreement during the three and nine months ended September 30, 2024 was $7.3 million and $17.5 million, respectively, the entire amount of which was included in deferred revenue at the beginning of the period. Collaboration revenue for the three and nine months ended September 30, 2023 was $1.6 million and $25.0 million, respectively. The deferred revenue related to the AbbVie Agreement was $28.9 million and $46.4 million as of September 30, 2024 and December 31, 2023, respectively. The deferred revenue is expected to be recognized over the research and development period of the AL002 program through the completion of the ongoing Phase 2 and Phase 2 LTE clinical trials.

Collaboration Agreements

9 Months Ended

Sep. 30, 2024

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Collaboration Agreements

5. 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 collaborate on the global development and commercialization of progranulin-elevating monoclonal antibodies, including latozinemab and AL101 (GSK Agreement). The GSK Agreement became 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 received in January 2022. In addition, based on the development and commercialization plan for latozinemab 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 latozinemab and AL101. Outside of the United States, the Company will be eligible for double-digit tiered royalties.

The Company and GSK will jointly develop latozinemab and AL101 with GSK conducting Phase 3 clinical trials for Alzheimer’s disease, Parkinson’s disease and other non-orphan indications. GSK will also conduct the initial Phase 2 trial for AL101 in Alzheimer’s disease. The Company and GSK will share development costs, 60% by GSK and 40% by the Company, except that subject to the GSK Amendment (defined below), 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 May 2023, the Company and GSK amended the GSK Agreement (GSK Amendment). Under the terms of the GSK Amendment, the Company is responsible for funding and sharing in GSK’s and the Company’s development costs up to $140.5 million for the conduct of the initial Phase 2 trial for AL101 in Alzheimer’s disease. The Company assessed the GSK Amendment in accordance with ASC 606 and concluded that the GSK Amendment was a contract modification to the GSK Agreement. Accordingly, the transaction price as of May 2023, was updated from $700 million to $571.6 million and the difference of $128.4 million was recorded as refund liability to collaboration partner for the expected cost reimbursement to GSK. The refund liability is an estimate of variable consideration calculated as the difference between the Company’s maximum funding of $140.5 million and the Company’s cost budget estimated using the expected value method. The Company determined that the modified performance obligation for the AL101 Alzheimer’s disease program is performing development activities to support the initial Phase 2 trial, including license rights and know-how. The Company updated the cost-based input measure of progress for the modified performance obligation and recorded a cumulative catch-up adjustment to revenue of $26.9 million on the modification date relating to performance obligation which was satisfied in prior periods.

During the three months ended September 30, 2023, as a result of the planned closure of the latozinemab Phase 2 trial and concurrent agreement by the Company to cost-share additional R&D, the Company determined there was a modification of the GSK Agreement, resulting in a decrease of the scope of the performance obligation associated with the latozinemab FTD-C9orf72 Phase 2 trial and an increase in the amount of R&D cost-shared by the Company in future periods. The impact of this additional cost share was accounted for as a refund liability, which reduced the transaction price for the GSK Agreement by $4.2 million. The refund liability is an estimate of variable consideration. The Company determined that the modified performance obligation for the latozinemab FTD-C9orf72 indication is performing the first Phase 2 development activities, including license rights and know-how. The Company updated the cost-based input measure of progress for the modified performance obligation and recorded a cumulative catch-up adjustment to revenue of $4.9 million on the modification date relating to the performance obligation that was satisfied in prior periods.

The transaction price at inception included fixed consideration consisting of the upfront payments of $700 million. The transaction price as of September 30, 2024 was decreased to $569.7 million due to the estimated refund liabilities created from the contract modifications. The Company reassessed the estimated refund liabilities to collaboration partner as of September 30, 2024 to be $72.2 million.

Collaboration revenue under the GSK Agreement during the three and nine months ended September 30, 2024 was $8.0 million and $28.8 million, respectively, the entire amount of which was included in deferred revenue at the beginning of the respective period. For the three and nine months ended September 30, 2023 collaboration revenue under the GSK agreement was $7.5 million and $56.8 million, respectively. The deferred revenue related to the GSK Agreement was $219.3 million and $247.4 million as of September 30, 2024 and December 31, 2023, respectively. 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 condensed consolidated statements of operations, with any reimbursement of costs by GSK reflected as a reduction of such expenses. For the three and nine months ended September 30, 2024, the Company recognized a reduction of research and development expense of $5.5 million and $15.8 million, respectively, under the GSK Agreement. For the three and nine months ended September 30, 2023, the Company recognized a reduction of research and development expense of $7.8 million and $18.8 million, respectively, 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 was to perform research and development services for the two programs through the end of Phase 2 clinical trials, which were each considered to be separate performance obligations. AbbVie decided to terminate one of the two collaboration programs, the CD33 collaboration program, after AbbVie and Alector concluded that further development of AL003, the asset being developed under that program, was not warranted. AbbVie provided written notice to terminate the CD33 collaboration program on June 30, 2022. Accordingly, the Company is no longer developing that program and will not be eligible for any future milestones related to that program from AbbVie. The Company continues to develop the AL002 program under the AbbVie Agreement. AbbVie has the exclusive right to exercise an option under the AbbVie Agreement with the Company for $250.0 million. If AbbVie exercises its option for the AL002 program, AbbVie would take over development of the product candidate, and the program costs will be split between the parties. The Company would also share in profits and losses upon commercialization of any products. Alternatively, following AbbVie’s exercise of its option for the AL002 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 $225.0 million in milestone payments related to the regulatory approval for up to three indications. The Company assessed its collaboration agreement with AbbVie in the context of the delivery of the research and development services.

In February 2023, the Company and AbbVie amended the AbbVie Agreement (AbbVie Amendment), which resulted in the Company receiving a $17.8 million milestone payment in March 2023 for the dosing of the first patient in a long-term extension (LTE) trial. In addition, under the terms of the AbbVie Amendment, the Company was eligible to earn up to an additional $12.5 million to support the enrollment of additional patients to replace discontinuations, and the Company received the total $12.5 million in 2023. The performance obligations to conduct the LTE trial and enroll additional patients are not considered distinct from the AL002 program performance obligation. The transaction price as of September 30, 2024 included fixed consideration consisting of the upfront payments of $205.0 million, the $17.8 million LTE milestone payment, and the $12.5 million payment for enrollment of additional patients.

Collaboration revenue under the AbbVie Agreement during the three and nine months ended September 30, 2024 was $7.3 million and $17.5 million, respectively, the entire amount of which was included in deferred revenue at the beginning of the period. Collaboration revenue for the three and nine months ended September 30, 2023 was $1.6 million and $25.0 million, respectively. The deferred revenue related to the AbbVie Agreement was $28.9 million and $46.4 million as of September 30, 2024 and December 31, 2023, respectively. The deferred revenue is expected to be recognized over the research and development period of the AL002 program through the completion of the ongoing Phase 2 and Phase 2 LTE clinical trials.

Stock-based Compensation - Summary of Recognized Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 9,035	$ 10,059	$ 29,251	$ 31,256
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	4,488	5,300	14,873	16,269
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 4,547	$ 4,759	$ 14,378	$ 14,987

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 1D
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480483/718-10-35-1D

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480483/718-10-35-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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+ Details

Fair Value Measurements - Additional Information (Details) $ in Millions	Sep. 30, 2024 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturities of investments were less than one year	$ 398.1
Remaining contractual maturities, one year through two years	$ 57.3

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Sep. 30, 2024 shares
Trading Arrangements, by Individual
Material Terms of Trading Arrangement	(c) During our last fiscal quarter, the following officers and directors adopted or terminated a “Rule 10b5-1 trading arrangement” as defined in Regulation S-K Item 408, as follows: On September 12, 2024, Marc Grasso, the Company’s Chief Financial Officer, terminated a Rule 10b5-1 trading plan that was originally adopted on August 28, 2023 and provided for (i) the exercise of vested stock options to purchase an aggregate of up to 75,501 shares of the Company’s common stock, and (ii) the sale from time to time of an aggregate of up to 89,362 shares of the Company’s common stock. The terminated plan would have expired on September 30, 2024 had it not been terminated. On September 13, 2024, Dr. Grasso adopted a Rule 10b5-1 trading plan. Dr. Grasso’s plan provides for (i) the exercise of vested stock options to purchase an aggregate of up to 75,501 shares of the Company's common stock, and (ii) the sale from time to time of an aggregate of up to 84,357 shares of the Company’s common stock. Sales of the shares of the Company’s common stock set forth in Dr. Grasso's trading plan, if any, will be made at or above specified market prices. The trading plan will expire on September 13, 2025, or earlier if all transactions under the trading plan are completed. Dr. Grasso’s trading plan was entered into during an open insider trading window and is intended to satisfy the affirmative defense in Rule 10b5-1(c) under the Exchange Act and the Company’s policies regarding insider transactions. Other than as disclosed above, during our last fiscal quarter, no other officer or director (as defined in Rule 16a-1(f) under the Exchange Act) adopted or terminated a “Rule 10b5-1 trading arrangement” or a "non-Rule 10b5-1 trading arrangement" (each as defined in Item 408 of Regulation S-K).
Marc Grasso [Member]
Trading Arrangements, by Individual
Name	Marc Grasso
Title	Chief Financial Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	August 28, 2023
Rule 10b5-1 Arrangement Terminated	true
Termination Date	September 12, 2024
Expiration Date	September 30, 2024
Arrangement Duration	399 days
Dr Grasso [Member]
Trading Arrangements, by Individual
Name	Dr. Grasso
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	September 13, 2024
Expiration Date	September 13, 2025
Arrangement Duration	365 days
Other Officer or Director [Member]
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false
Rule 10B5-1 Trading Plan [Member] \| Marc Grasso [Member]
Trading Arrangements, by Individual
Aggregate Available	75,501
Rule 10B5-1 Trading Plan [Member] \| Dr Grasso [Member]
Trading Arrangements, by Individual
Aggregate Available	75,501
Rule 10B51 Trading Plan One [Member] \| Marc Grasso [Member]
Trading Arrangements, by Individual
Aggregate Available	89,362
Rule 10B51 Trading Plan One [Member] \| Gary Romano [Member]
Trading Arrangements, by Individual
Aggregate Available	84,357

Commitment and Contingencies - Addtional Information (Details)	Sep. 30, 2024 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Indemnification agreement liability	$ 0

Fair Value Measurements

9 Months Ended

Sep. 30, 2024

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:


	September 30, 2024
	Fair Value Hierarchy	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Market Value
	(In thousands)
Money market funds	Level 1	$	33,862	$	—	$	—		$	33,862
U.S. government treasury securities	Level 1		84,220		77		(12	)		84,285
Certificates of deposit	Level 2		15,679		6		—			15,685
Commercial paper	Level 2		102,823		127		(3	)		102,947
Corporate bonds	Level 2		217,836		745		(9	)		218,572
Total cash equivalents and marketable securities		$	454,420	$	955	$	(24	)	$	455,351

	December 31, 2023
	Fair Value Hierarchy	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Market Value
	(In thousands)
Money market funds	Level 1	$	67,101	$	—	$	—		$	67,101
U.S. government treasury securities	Level 1		178,232		86		(112	)		178,206
Certificates of deposit	Level 2		29,086		63		—			29,149
Commercial paper	Level 2		140,082		85		(34	)		140,133
Corporate bonds	Level 2		129,474		173		(78	)		129,569
Total cash equivalents and marketable securities		$	543,975	$	407	$	(224	)	$	544,158

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 September 30, 2024, the remaining contractual maturities of $398.1 million of investments were less than one year and $57.3 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 at maturity.

- 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.

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Reference 1: http://www.xbrl.org/2003/role/exampleRef
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+ Details

Income Taxes - Additional Information (Details)	3 Months Ended		9 Months Ended
Income Taxes - Additional Information (Details)	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21.00%			21.00%
Effective tax rate	0.00%	(2.90%)	(0.10%)	(4.20%)

Net Loss Per Share (Tables)

9 Months Ended

Sep. 30, 2024

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 Months Ended September 30,				Nine Months Ended September 30,
	2024		2023		2024		2023
Restricted stock units subject to future vesting		4,765,073		3,288,671		4,765,073		3,288,671
Options to purchase common stock		11,195,905		11,848,595		11,195,905		11,848,595
Shares committed under 2019 ESPP		171,412		173,878		171,412		173,878
Total		16,132,390		15,311,144		16,132,390		15,311,144

Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited) - $ / shares	Sep. 30, 2024	Dec. 31, 2023
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	97,929,897	84,879,693
Common stock, shares outstanding	97,929,897	84,879,693

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Collaboration revenue	$ 15,342	$ 9,109	$ 46,318	$ 81,872
Operating expenses:
Research and development	47,998	46,328	139,479	144,392
General and administrative	15,778	13,364	44,587	41,767
Total operating expenses	63,776	59,692	184,066	186,159
Loss from operations	(48,434)	(50,583)	(137,748)	(104,287)
Other income, net	6,214	7,360	20,853	18,876
Loss before income taxes	(42,220)	(43,223)	(116,895)	(85,411)
Income tax expense	0	1,252	80	3,546
Net loss	(42,220)	(44,475)	(116,975)	(88,957)
Unrealized gain on marketable securities	1,551	665	747	3,854
Comprehensive loss	$ (40,669)	$ (43,810)	$ (116,228)	$ (85,103)
Net loss per share, basic	$ (0.43)	$ (0.53)	$ (1.22)	$ (1.07)
Net loss per share, diluted	$ (0.43)	$ (0.53)	$ (1.22)	$ (1.07)
Shares used in computing net loss per share, basic	97,519,595	83,927,961	96,007,105	83,513,954
Shares used in computing net loss per share, diluted	97,519,595	83,927,961	96,007,105	83,513,954

Net Loss Per Share - Schedule of Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	16,132,390	15,311,144	16,132,390	15,311,144
Restricted Stock Units Subject to Future Vesting
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	4,765,073	3,288,671	4,765,073	3,288,671
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	11,195,905	11,848,595	11,195,905	11,848,595
Shares Committed Under 2019 ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	171,412	173,878	171,412	173,878

Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2024	Nov. 01, 2024
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3
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	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		97,932,605
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	DE

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2024

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:


	September 30, 2024
	Fair Value Hierarchy	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Market Value
	(In thousands)
Money market funds	Level 1	$	33,862	$	—	$	—		$	33,862
U.S. government treasury securities	Level 1		84,220		77		(12	)		84,285
Certificates of deposit	Level 2		15,679		6		—			15,685
Commercial paper	Level 2		102,823		127		(3	)		102,947
Corporate bonds	Level 2		217,836		745		(9	)		218,572
Total cash equivalents and marketable securities		$	454,420	$	955	$	(24	)	$	455,351

	December 31, 2023
	Fair Value Hierarchy	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Market Value
	(In thousands)
Money market funds	Level 1	$	67,101	$	—	$	—		$	67,101
U.S. government treasury securities	Level 1		178,232		86		(112	)		178,206
Certificates of deposit	Level 2		29,086		63		—			29,149
Commercial paper	Level 2		140,082		85		(34	)		140,133
Corporate bonds	Level 2		129,474		173		(78	)		129,569
Total cash equivalents and marketable securities		$	543,975	$	407	$	(224	)	$	544,158

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2024
Income Tax Disclosure [Abstract]
Income Taxes	7. Income Taxes For the three and nine months ended September 30, 2024, the Company's effective tax rate was 0% and (0.1)%, respectively. For the three and nine months ended September 30, 2023, the Company's effective tax rate was (2.9)% and (4.2)%, respectively. The difference between the effective tax rate for the three and nine months ended September 30, 2024, and the U.S. federal statutory rate of 21% was primarily due to the Company recording a full valuation allowance to its net deferred tax asset. The difference between the effective tax rate as of September 30, 2023, and the U.S. federal statutory rate of 21% was primarily due to the recognition of a certain amount of current year income tax as a result of the capitalization of research and development expenses under Section 174 of the Internal Revenue Code, effective beginning in 2022.

- Definition

The entire disclosure for income tax.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org/1943274/2147479360/740-10-S99-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480990/946-20-50-13

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
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-Paragraph 1
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-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org/740/tableOfContent

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-14

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-21

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-17

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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-Section S99
-Paragraph 2
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-Publisher FASB
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482603/740-30-50-2

+ Details

The Company and Liquidity - Additional Information (Details) - Over-Allotment Option [Member] $ / shares in Units, $ in Millions	Jan. 19, 2024 USD ($) $ / shares shares
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Public offerings \| shares	10,869,566
Share price \| $ / shares	$ 6.57
Aggregate net proceeds \| $	$ 71.1

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Cash flows from operating activities:
Net loss	$ (116,975)	$ (88,957)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	4,165	4,288
Stock-based compensation	29,251	31,256
Amortization of premiums and accretion of discounts on marketable securities	(11,800)	(10,510)
Amortization of right-of-use assets	2,598	2,302
Impairment loss of right-of-use asset and leasehold improvements	2,205	0
Changes in operating assets and liabilities:
Receivable from collaboration partner	0	(7,878)
Prepaid expenses and other current assets	4,784	(2,824)
Other assets	1,330	(2,139)
Accounts payable	1,333	638
Accrued liabilities and accrued clinical supply costs	(6,465)	4,667
Payable to collaboration partner	(931)	0
Deferred revenue	(46,318)	(51,592)
Refund liability to collaboration partner	(33,636)	(13,832)
Lease liabilities	(4,279)	(3,650)
Other long-term liabilities	(139)	139
Net cash used in operating activities	(174,877)	(138,092)
Cash flows from investing activities:
Purchase of property and equipment	(1,082)	(2,148)
Purchase of marketable securities	(381,120)	(414,478)
Maturities of marketable securities	446,074	500,473
Sale of marketable secuirities	1,857	0
Net cash provided by investing activities	65,729	83,847
Cash flows from financing activities:
Proceeds from issuance of common stock upon public offering, net of issuance costs	71,108	0
Proceeds from the exercise of options to purchase common stock	0	1,079
Purchase of common stock under employee stock purchase plaan	644	881
Net cash provided by financing activities	71,752	1,960
Net decrease in cash, cash equivalents, and restricted cash	(37,396)	(52,285)
Cash, cash equivalents, and restricted cash at beginning of period	76,101	155,795
Cash, cash equivalents, and restricted cash at end of period	38,705	103,510
Non-cash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued liabilities	$ 27	$ 201

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 37,159	$ 74,555
Marketable securities	420,043	474,306
Prepaid expenses and other current assets	12,162	16,946
Total current assets	469,364	565,807
Property and equipment, net	18,216	21,861
Operating lease right-of-use assets	20,809	25,195
Restricted cash	1,546	1,546
Other assets	6,088	7,418
Total assets	516,023	621,827
Current liabilities:
Accounts payable	5,017	3,775
Accrued clinical supply costs	3,379	5,215
Accrued liabilities	25,696	30,378
Deferred revenue, current portion	55,427	82,975
Payable to collaboration partner	6,772	7,703
Refund liability to collaboration partner, current portion	37,554	39,440
Operating lease liabilities, current portion	8,680	8,462
Total current liabilities	142,525	177,948
Deferred revenue, long-term portion	192,775	210,845
Refund liability to collaboration partner, long-term portion	34,597	67,047
Operating lease liabilities, long-term portion	25,959	30,456
Other long-term liabilities	1,234	1,373
Total liabilities	397,090	487,669
Commitments and contingencies (Note 4)
Stockholders' equity:
Common stock, $0.0001 par value; 200,000,000 shares authorized; 97,929,897 and 84,879,693 shares issued and outstanding as of September 30, 2024 and December 31, 2023	9	8
Additional paid-in capital	945,046	844,044
Accumulated other comprehensive income	931	184
Accumulated deficit	(827,053)	(710,078)
Total stockholders' equity	118,933	134,158
Total liabilities and stockholders’ equity	$ 516,023	$ 621,827

Commitments and Contingencies

9 Months Ended

Sep. 30, 2024

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

4. Commitments and Contingencies

Contingencies

From time to time, the Company may be involved in litigation related to claims that arise in the ordinary course of its business activities. The Company accrues for these matters when it is probable that future expenditures will be made and these expenditures can be reasonably estimated. As of September 30, 2024, the Company does not believe that any such matters, individually or in the aggregate, will have a material adverse effect on the Company’s financial position, results of operations or cash flows.

Indemnification

The Company enters into customary indemnification arrangements in the ordinary course of business with vendors, clinical trial sites and other parties. Pursuant to these arrangements, the Company indemnifies, holds harmless and agrees to reimburse the indemnified parties for certain losses suffered or incurred by the indemnified party. The term of these indemnification agreements is generally perpetual any time after the execution of the agreement. The maximum potential amount of future payments the Company could be required to make under these arrangements is not determinable. The Company has never incurred costs to defend lawsuits or settle claims related to these indemnification agreements. As a result, the Company has not recorded a liability related to such indemnification agreements as of September 30, 2024. As permitted under Delaware law, the Company has entered into indemnification agreements with its directors and officers that requires it to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by law. The Company also has directors’ and officers’ insurance.

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
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	$ 33,862	$ 67,101
Cash equivalents and marketable securities, Unrealized Gains	0	0
Cash equivalents and marketable securities, Unrealized Losses	0	0
Cash equivalents and marketable securities, Fair Market Value	33,862	67,101
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	84,220	178,232
Cash equivalents and marketable securities, Unrealized Gains	77	86
Cash equivalents and marketable securities, Unrealized Losses	(12)	(112)
Cash equivalents and marketable securities, Fair Market Value	84,285	178,206
Certificates of Deposit \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents and marketable securities, Amortized Cost	15,679	29,086
Cash equivalents and marketable securities, Unrealized Gains	6	63
Cash equivalents and marketable securities, Unrealized Losses	0	0
Cash equivalents and marketable securities, Fair Market Value	15,685	29,149
Commercial Paper \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents and marketable securities, Amortized Cost	102,823	140,082
Cash equivalents and marketable securities, Unrealized Gains	127	85
Cash equivalents and marketable securities, Unrealized Losses	(3)	(34)
Cash equivalents and marketable securities, Fair Market Value	102,947	140,133
Corporate Bonds \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents and marketable securities, Amortized Cost	217,836	129,474
Cash equivalents and marketable securities, Unrealized Gains	745	173
Cash equivalents and marketable securities, Unrealized Losses	(9)	(78)
Cash equivalents and marketable securities, Fair Market Value	218,572	129,569
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	454,420	543,975
Cash equivalents and marketable securities, Unrealized Gains	955	407
Cash equivalents and marketable securities, Unrealized Losses	(24)	(224)
Cash equivalents and marketable securities, Fair Market Value	$ 455,351	$ 544,158

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (42,220)	$ (38,676)	$ (36,079)	$ (44,475)	$ 1,375	$ (45,857)	$ (116,975)	$ (88,957)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
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-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-9

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 805
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-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147476176/805-60-65-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 323
-Name Accounting Standards Codification
-Section 65
-Paragraph 2
-Subparagraph (g)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478666/740-323-65-2

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(20))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Subparagraph (SX 210.4-08(g)(1)(ii))
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org/1943274/2147482765/220-10-50-6

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org/1943274/2147483443/250-10-50-3

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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Reference 16: http://www.xbrl.org/2003/role/disclosureRef
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Reference 17: http://www.xbrl.org/2003/role/exampleRef
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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
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Reference 19: http://www.xbrl.org/2003/role/disclosureRef
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Reference 20: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 37,159	$ 74,555	$ 101,964
Restricted cash	1,546	1,546	1,546
Total cash, cash equivalents, and restricted cash	$ 38,705	$ 76,101	$ 103,510	$ 155,795

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2024

Accounting Policies [Abstract]

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


	Nine Months Ended September 30,
	2024		2023
	(In thousands)
Cash and cash equivalents	$	37,159	$	101,964
Restricted cash		1,546		1,546
Total cash, cash equivalents, and restricted cash	$	38,705	$	103,510

Collaboration Agreements - Additional Information (Details) $ in Thousands			1 Months Ended							3 Months Ended		9 Months Ended
	Aug. 17, 2021 USD ($)	Jul. 01, 2021 USD ($)	Dec. 31, 2023 USD ($)	May 31, 2023 USD ($)	Mar. 31, 2023 USD ($)	Feb. 28, 2023 USD ($)	Jan. 31, 2022 USD ($)	Jan. 31, 2018 USD ($)	Oct. 31, 2017 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense										$ 47,998	$ 46,328	$ 139,479	$ 144,392
GlaxoSmithKline plc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Effective date of agreement	Aug. 17, 2021
Upfront payments		$ 700,000										$ 700,000
Milestone payment received	$ 500,000						$ 200,000
Additional milestone payments to support the enrollment	$ 500,000						$ 200,000
Percentage of development cost												0.60
Collaboration revenue										8,000	7,500	$ 28,800	56,800
Deferred revenue			$ 247,400							219,300		219,300
Research and development expense										5,500	7,800	15,800	18,800
Reduction in transaction price											4,200		4,200
Transaction price										569,700		569,700
Contract with customer, refund liability				$ 128,400
Maximum funding				140,500
Cumulative adjustment to revenue				26,900							4,900
GlaxoSmithKline plc \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Additional milestone payments related to initiation of certain clinical studies and regulatory approval										1,500,000		1,500,000
Transaction price		$ 700,000
GlaxoSmithKline plc \| Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Transaction price				$ 571,600
GlaxoSmithKline plc \| Change in Estimate [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract with customer, refund liability										72,200		$ 72,200
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			$ 205,000
Milestone payment received			12,500		$ 17,800			$ 200,000	5,000			17,800
Exclusive option rights exercised for each program									250,000
Additional milestone payments to support the enrollment			12,500		$ 17,800			$ 200,000	5,000			17,800
Collaboration revenue										7,300	$ 1,600	17,500	$ 25,000
Deferred revenue			$ 46,400							28,900		28,900
Payment for enrollment of additional patients										$ 12,500		$ 12,500
AbbVie Biotechnology Limited \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payment received						$ 12,500
Additional milestone payments related to initiation of certain clinical studies and regulatory approval									$ 225,000
Additional milestone payments to support the enrollment						$ 12,500

Condensed Consolidated Statement of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2022	$ 214,442	$ 8	$ 798,696	$ (4,575)	$ (579,687)
Beginning balance (in shares) at Dec. 31, 2022		82,895,718
Exercise of stock options	1,079		1,079
Exercise of stock options (in shares)		132,191
Vesting of restricted stock units		323,869
Stock-based compensation	10,975		10,975
Unrealized gain (loss) on marketable securities	2,376			2,376
Net Income (Loss)	(45,857)				(45,857)
Ending balance at Mar. 31, 2023	183,015	$ 8	810,750	(2,199)	(625,544)
Ending balance (in shares) at Mar. 31, 2023		83,351,778
Beginning balance at Dec. 31, 2022	214,442	$ 8	798,696	(4,575)	(579,687)
Beginning balance (in shares) at Dec. 31, 2022		82,895,718
Net Income (Loss)	(88,957)
Ending balance at Sep. 30, 2023	162,555	$ 8	831,912	(721)	(668,644)
Ending balance (in shares) at Sep. 30, 2023		84,136,381
Beginning balance at Mar. 31, 2023	183,015	$ 8	810,750	(2,199)	(625,544)
Beginning balance (in shares) at Mar. 31, 2023		83,351,778
Purchase of common stock under employee stock purchase plan (in shares)		139,267
Purchase of common stock under employee stock purchase plan	881		881
Vesting of restricted stock units		339,255
Stock-based compensation	10,222		10,222
Unrealized gain (loss) on marketable securities	813			813
Net Income (Loss)	1,375				1,375
Ending balance at Jun. 30, 2023	196,306	$ 8	821,853	(1,386)	(624,169)
Ending balance (in shares) at Jun. 30, 2023		83,830,300
Vesting of restricted stock units		306,081
Stock-based compensation	10,059		10,059
Unrealized gain (loss) on marketable securities	665			665
Net Income (Loss)	(44,475)				(44,475)
Ending balance at Sep. 30, 2023	162,555	$ 8	831,912	(721)	(668,644)
Ending balance (in shares) at Sep. 30, 2023		84,136,381
Beginning balance at Dec. 31, 2023	$ 134,158	$ 8	844,044	184	(710,078)
Beginning balance (in shares) at Dec. 31, 2023	84,879,693	84,879,693
Issuance of common stock upon public offering, net of issuance cost $3,892	$ 71,108	$ 1	71,107
Issuance of common stock upon public offering, net of issuance cost $3,892(in shares)		10,869,566
Vesting of restricted stock units		635,303
Stock-based compensation	10,307		10,307
Unrealized gain (loss) on marketable securities	(587)			(587)
Net Income (Loss)	(36,079)				(36,079)
Ending balance at Mar. 31, 2024	178,907	$ 9	925,458	(403)	(746,157)
Ending balance (in shares) at Mar. 31, 2024		96,384,562
Beginning balance at Dec. 31, 2023	$ 134,158	$ 8	844,044	184	(710,078)
Beginning balance (in shares) at Dec. 31, 2023	84,879,693	84,879,693
Net Income (Loss)	$ (116,975)
Ending balance at Sep. 30, 2024	$ 118,933	$ 9	945,046	931	(827,053)
Ending balance (in shares) at Sep. 30, 2024	97,929,897	97,929,897
Beginning balance at Mar. 31, 2024	$ 178,907	$ 9	925,458	(403)	(746,157)
Beginning balance (in shares) at Mar. 31, 2024		96,384,562
Purchase of common stock under employee stock purchase plan (in shares)		154,113
Purchase of common stock under employee stock purchase plan	644		644
Vesting of restricted stock units		782,387
Stock-based compensation	9,909		9,909
Unrealized gain (loss) on marketable securities	(217)			(217)
Net Income (Loss)	(38,676)				(38,676)
Ending balance at Jun. 30, 2024	150,567	$ 9	936,011	(620)	(784,833)
Ending balance (in shares) at Jun. 30, 2024		97,321,062
Vesting of restricted stock units		608,835
Stock-based compensation	9,035		9,035
Unrealized gain (loss) on marketable securities	1,551			1,551
Net Income (Loss)	(42,220)				(42,220)
Ending balance at Sep. 30, 2024	$ 118,933	$ 9	$ 945,046	$ 931	$ (827,053)
Ending balance (in shares) at Sep. 30, 2024	97,929,897	97,929,897

The Company and Liquidity

9 Months Ended

Sep. 30, 2024

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 biotechnology company pioneering immuno-neurology, a novel therapeutic approach for the treatment of neurodegeneration.

Public Offering

On January 19, 2024, the Company completed a public offering through selling and issuing 10,869,566 shares of common stock at a price per share of $6.57, resulting in aggregate net proceeds of $71.1 million, after deducting underwriting discounts and commissions and offering costs.

Net Loss Per Share

9 Months Ended

Sep. 30, 2024

Earnings Per Share [Abstract]

Net Loss Per Share

8. 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 Months Ended September 30,				Nine Months Ended September 30,
	2024		2023		2024		2023
Restricted stock units subject to future vesting		4,765,073		3,288,671		4,765,073		3,288,671
Options to purchase common stock		11,195,905		11,848,595		11,195,905		11,848,595
Shares committed under 2019 ESPP		171,412		173,878		171,412		173,878
Total		16,132,390		15,311,144		16,132,390		15,311,144

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2024

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

Use of Estimates

Concentration of Credit Risk

Cash, Cash Equivalents, and Restricted Cash

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


	Nine Months Ended September 30,
	2024		2023
	(In thousands)
Cash and cash equivalents	$	37,159	$	101,964
Restricted cash		1,546		1,546
Total cash, cash equivalents, and restricted cash	$	38,705	$	103,510

Marketable Securities

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.

Leases

Revenue Recognition

Stock-based Compensation

The Company accounts for forfeitures as they occur for all awards.

Comprehensive Loss