0000950170-23-005111 | 10-K | XBRL Viewer

Related Party Transactions	12 Months Ended
Dec. 31, 2022
Related Party Transactions [Abstract]
Related Party Transactions	9. Related Party Transactions In 2014, the Company entered into a collaboration agreement with Adimab, LLC (Adimab) under which the Company is developing antibodies discovered by Adimab in its latozinemab and AL101 programs and is developing antibodies optimized by Adimab in its AL002 program (2014 Adimab Agreement). The 2014 Adimab Agreement also provided for the Company’s development of antibodies optimized by Adimab in its AL003 program. However, AbbVie decided to terminate the CD33 collaboration program, after AbbVie and Alector collaboratively reviewed next steps for AL003, the asset being developed under that program, and concluded that further development of AL003 was not warranted. In August 2019, the Company signed a collaboration agreement with Adimab for research and development of additional antibodies (2019 Adimab Agreement). In December 2021, the Company signed another collaboration agreement with Adimab for antibody engineering research programs (2021 Adimab Agreement). The 2021 Adimab agreement expired at the end of the option period for the research program that was conducted under the agreement. The former Chief Executive Officer of Adimab through May 2022 is a Co-founder and Chairperson of the board of directors of Alector. For the years ended December 31, 2022, 2021, and 2020, Alector incurred expenses of $0.2 million, $1.0 million, and zero for milestone payments for progress of programs through clinical trials and other expenses. The Company had no accrued liabilities due to Adimab as of December 31, 2022 and 2021. Under the 2014 Adimab Agreement, the Company has made milestone payments and will owe low- to mid- single-digit royalty payments for commercial sales of the product candidate. Under the 2019 Adimab Agreements, the Company will owe certain milestone payments and low single-digit royalty payments for commercial sales of covered product candidates.

Related Party Transactions

12 Months Ended

Dec. 31, 2022

In 2014, the Company entered into a collaboration agreement with Adimab, LLC (Adimab) under which the Company is developing antibodies discovered by Adimab in its latozinemab and AL101 programs and is developing antibodies optimized by Adimab in its AL002 program (2014 Adimab Agreement). The 2014 Adimab Agreement also provided for the Company’s development of antibodies optimized by Adimab in its AL003 program. However, AbbVie decided to terminate the CD33 collaboration program, after AbbVie and Alector collaboratively reviewed next steps for AL003, the asset being developed under that program, and concluded that further development of AL003 was not warranted. In August 2019, the Company signed a collaboration agreement with Adimab for research and development of additional antibodies (2019 Adimab Agreement). In December 2021, the Company signed another collaboration agreement with Adimab for antibody engineering research programs (2021 Adimab Agreement). The 2021 Adimab agreement expired at the end of the option period for the research program that was conducted under the agreement. The former Chief Executive Officer of Adimab through May 2022 is a Co-founder and Chairperson of the board of directors of Alector. For the years ended December 31, 2022, 2021, and 2020, Alector incurred expenses of

$0.2 million, $1.0 million, and zero for milestone payments for progress of programs through clinical trials and other expenses. The Company had no accrued liabilities due to Adimab as of December 31, 2022 and 2021. Under the 2014 Adimab Agreement, the Company has made milestone payments and will owe low- to mid- single-digit royalty payments for commercial sales of the product candidate. Under the 2019 Adimab Agreements, the Company will owe certain milestone payments and low single-digit royalty payments for commercial sales of covered product candidates.

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Schedule of Federal and State Income Tax Provision

The federal and state income tax provision for the year ended December 31, 2022, 2021 and 2020 are summarized as follows (in thousands):


	Year Ended December 31,
	2022		2021		2020
Current:
Federal	$	2,209	$	—	$	—
State		1,045		—		—
Income tax provision	$	3,254	$	—	$	—

Schedule of Effective Income Tax Rate Reconciliation

A reconciliation of the federal statutory rate to the Company’s effective tax rate is as follows for the years ended December 31, 2022, 2021, and 2020 (in thousands):


	Year Ended December 31,
	2022			2021			2020
Tax benefit at federal statutory rate	$	(27,205	)	$	(7,627	)	$	(39,948	)
State income taxes		(344	)		398			(16,570	)
Tax credits		(20,184	)		(9,389	)		(8,010	)
Uncertain tax positions		7,733			2,347			2,003
Stock-based compensation		4,919			(2,368	)		353
Change in valuation allowance		38,421			16,800			62,280
Other		(86	)		(161	)		(108	)
Income tax provision	$	3,254		$	—		$	—

Schedule of Deferred Tax Assets and Liabilities

The tax effects of temporary differences that give rise to significant components of the Company’s deferred tax assets and liabilities consist of (in thousands):


	December 31,
	2022			2021
Deferred tax assets:
Net operating loss	$	20,963		$	63,868
Accrued bonus		806			1,811
Tax credits		26,319			19,614
Stock-based compensation		13,351			9,656
Deferred revenue		67,673			27,849
Lease liability		10,055			11,296
Section 174 R&D capitalization		35,150			—
Other		1,608			694
Gross deferred tax assets		175,925			134,788
Less valuation allowance		(164,316	)		(122,046	)
Total deferred tax assets	$	11,609		$	12,742
Deferred tax liabilities:
Depreciation and amortization	$	(5,155	)	$	(5,488	)
Right-of-use assets		(6,454	)		(7,254	)
Gross deferred tax liabilities		(11,609	)		(12,742	)
Deferred tax assets, net	$	—		$	—

Schedule of Unrecognized Tax Benefits

The following table summarizes the activity related to the Company’s unrecognized tax benefits for the years ended December 31, 2022, 2021, and 2020 (in thousands):


Balance as of December 31, 2020	$	4,592
Decreases related to tax positions taken during the prior year		(59	)
Increases related to tax positions taken during the current year		2,406
Balance as of December 31, 2021		6,939
Increases related to tax positions taken during the current year		8,199
Balance as of December 31, 2022	$	15,138

Income Taxes

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Income Taxes

The federal and state income tax provision for the year ended December 31, 2022, 2021 and 2020 are summarized as follows (in thousands):


	Year Ended December 31,
	2022		2021		2020
Current:
Federal	$	2,209	$	—	$	—
State		1,045		—		—
Income tax provision	$	3,254	$	—	$	—

A reconciliation of the federal statutory rate to the Company’s effective tax rate is as follows for the years ended December 31, 2022, 2021, and 2020 (in thousands):


	Year Ended December 31,
	2022			2021			2020
Tax benefit at federal statutory rate	$	(27,205	)	$	(7,627	)	$	(39,948	)
State income taxes		(344	)		398			(16,570	)
Tax credits		(20,184	)		(9,389	)		(8,010	)
Uncertain tax positions		7,733			2,347			2,003
Stock-based compensation		4,919			(2,368	)		353
Change in valuation allowance		38,421			16,800			62,280
Other		(86	)		(161	)		(108	)
Income tax provision	$	3,254		$	—		$	—

The tax effects of temporary differences that give rise to significant components of the Company’s deferred tax assets and liabilities consist of (in thousands):


	December 31,
	2022			2021
Deferred tax assets:
Net operating loss	$	20,963		$	63,868
Accrued bonus		806			1,811
Tax credits		26,319			19,614
Stock-based compensation		13,351			9,656
Deferred revenue		67,673			27,849
Lease liability		10,055			11,296
Section 174 R&D capitalization		35,150			—
Other		1,608			694
Gross deferred tax assets		175,925			134,788
Less valuation allowance		(164,316	)		(122,046	)
Total deferred tax assets	$	11,609		$	12,742
Deferred tax liabilities:
Depreciation and amortization	$	(5,155	)	$	(5,488	)
Right-of-use assets		(6,454	)		(7,254	)
Gross deferred tax liabilities		(11,609	)		(12,742	)
Deferred tax assets, net	$	—		$	—

In assessing the realization of deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred assets will be realized. The ultimate realization of the deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. Evaluating the need for a valuation allowance for deferred tax assets often requires judgment and analysis of all the positive and negative evidence available, including cumulative losses in recent years and projected future taxable income, to determine whether all or some portion of the deferred tax assets will not be realized. As of December 31, 2022, the Company has utilized a full valuation allowance to offset the net deferred tax assets as the Company believes it is not more likely than not that the net deferred tax assets will be fully realizable. The valuation allowance for deferred tax assets increased by $42.3 million during the year ended December 31, 2022.

As of December 31, 2022, the Company had federal and state net operating loss (NOL) carryforwards of approximately $40.3 million and $203.5 million, respectively. Federal NOL carryforwards have an indefinite life and deductions cannot exceed 80% of taxable income. State NOL carryforwards will begin to expire as early as 2030, if not utilized, or have an indefinite life. As of December 31, 2022, the Company also had federal and California tax credit carryforward of approximately $28.4 million and $11.6 million, respectively. The federal tax credits will begin to expire in 2036 while the California tax credits have no expiration date.

Generally, utilization of the NOL carryforwards and credits may be subject to an annual limitation due to the ownership change limitations provided by Section 382, which provides for limitations on NOL carryforwards and certain built-in losses following ownership changes, and Section 383, which provides for special limitations on certain excess credits, etc., of the Code, and similar state provisions. Accordingly, the Company’s ability to utilize NOL carryforwards may be limited as the result of such an “ownership change.” The carryforwards could be subject to an annual limitation, resulting in a reduction in the gross deferred tax assets before considering the valuation allowance. Further, a portion of the carryforwards may expire before being applied to reduce future earnings. The Company is not aware of any changes in ownership that would result in material limitations under Section 382 at this time.

The following table summarizes the activity related to the Company’s unrecognized tax benefits for the years ended December 31, 2022, 2021, and 2020 (in thousands):


Balance as of December 31, 2020	$	4,592
Decreases related to tax positions taken during the prior year		(59	)
Increases related to tax positions taken during the current year		2,406
Balance as of December 31, 2021		6,939
Increases related to tax positions taken during the current year		8,199
Balance as of December 31, 2022	$	15,138

If the unrecognized tax benefits for uncertain tax positions as of December 31, 2022, is recognized, there will be no impact to the effective tax rate as the tax benefit would increase the net deferred tax assets, which is currently offset with a full valuation allowance. The Company’s policy is to include interest and penalties related to unrecognized tax benefits, if any, within the provision for taxes in the consolidated statements of operations. The Company did not accrue any interest or penalties and does not have any tax positions for interest or penalties for the year ended December 31, 2022. The Company does not have any tax positions for which it is reasonably possible that the total amount of gross unrecognized tax benefits will significantly change within 12 months of December 31, 2022.

The Company recognizes the tax benefit of an uncertain tax position only if it is more likely than not that the position is sustainable upon examination by the taxing authority, based on the technical merits. During the years ended December 31, 2022 and 2021, the Company recorded an uncertain tax position of $8.2 million and $2.4 million, respectively. The income tax provision for the years ended December 31, 2022 and 2021, included a reversal of reserves on uncertain tax provisions of zero and $0.1 million. The Company’s income tax returns generally remain subject to examination by federal and most state tax authorities. The Company is currently not subject to any income tax audits by federal or state taxing authorities. The statute of limitations for tax liabilities for all years remains open.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

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+ Details

Collaboration Agreements	12 Months Ended
Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaboration Agreements	4. 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 (also referred to as AL001), and AL101 (GSK Agreement). The GSK Agreement was made effective on August 17, 2021. Under the terms of the GSK Agreement, the Company received $700 million in upfront payments, of which $500 million was received in August 2021 and $200 million was 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 and Parkinson’s disease and other non-orphan indications. The Company and GSK will share development costs 60% by GSK and 40% by the Company, except that the Company will solely bear the development costs of the initial Phase 2 clinical trials under the development plan, and the parties will share manufacturing development costs equally. The Company concluded that the GSK Agreement is within the scope of ASC 808, Collaborative Arrangements, as both parties are active participants in the activities and are exposed to significant risks and rewards dependent on the success of the commercialization of AL001 and AL101. Certain elements are required to be accounted for under ASC 606, Revenue From Contracts With Customers, where the counterparty is a customer for a good or service that is a distinct unit of account. The Company determined that the distinct performance obligations under ASC 606 consisted of: (i) license and know-how to AL001 FTD-GRN, which is currently in Phase 3 clinical development and (ii) the research and development activities, including license rights and know-how, relating to products in Phase 2 or earlier stages of development. The transaction price at inception and as of December 31, 2022, included fixed consideration consisting of the upfront payments of $700 million. All potential future milestones and other payments were considered constrained at the inception of the GSK Agreement and as of December 31, 2022, since the Company could not conclude it was probable that a significant reversal in the amount of revenue recognized would not occur. The respective standalone value for each of the performance obligations was allocated to the transaction price. The estimated SSP of each performance obligation was determined using discounted cash flows from the expected commercialization of AL001 and AL101 and estimated research and development costs to be incurred by the Company in the initial Phase 2 clinical trials. The estimate of SSP for each performance obligation reflects management's assumptions, which may include forecasted revenues, development timelines, discount rates, and probabilities of technical and regulatory success. For the license for FTD-GRN, the Company determined that GSK could benefit from the license at the time the license was granted and therefore, the related performance obligation was satisfied at a point in time. For the product candidates in Phase 2 or earlier stages of development, the Company determined that GSK could not benefit from the licenses without the corresponding development services that the Company has committed to perform due the earlier stage of development for these licenses. Except where agreed to otherwise, the Company will perform research and development activities through the end of the initial Phase 2 clinical trials. Revenue will be recognized over time as the research and development activities are performed. The Company will measure progress based on actual costs incurred to date compared to the overall total expected costs to satisfy the performance obligations. The research and development activities for products in Phase 3 clinical development were determined to be within the scope of ASC 808. Both parties will be active participants in the development, manufacturing, and commercialization of the product and are exposed to significant risks and rewards that are dependent on the commercial success of the products. The Company and GSK participate in profit and loss sharing for each program commensurate with each party's cost-sharing responsibilities during research and development. ASC 808 does not provide recognition and measurement guidance. As such, the Company determined that ASC 730, Research and Development, was appropriate to analogize to based on the nature of the cost-sharing provision of the agreement. The Company has concluded that payments to or reimbursements from GSK related to these services will be accounted for as an increase to or reduction of research and development expenses, respectively. Collaboration revenue under the GSK Agreement during the year ended December 31, 2022 and 2021, was $62.9 million and $192.1 million, respectively. The deferred revenue related to the GSK Agreement was $444.9 million and $307.9 million as of December 31, 2022 and 2021. The deferred revenue is expected to be recognized over the research and development period of the programs through the completion of initial Phase 2 clinical trials. Costs associated with co-development activities performed under the agreement are included in research and development expenses in the consolidated statements of operations, with any reimbursement of costs by GSK reflected as a reduction of such expenses. For the year ended December 31, 2022 and 2021, the Company recognized a reduction of research and development expense of $14.7 million and $8.8 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 collaboratively reviewed next steps for AL003, the asset being developed under that program, and concluded that further development of AL003 was not warranted. AbbVie provided written notice to terminate the CD33 collaboration program on June 30, 2022. The Company will no longer continue development of this 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 the development beginning with Phase 3 clinical trials, and the product candidates program costs will be split between the parties. The Company would also share in profits and losses upon commercialization of any products. However, 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. In February 2023, the Company and AbbVie amended the AbbVie agreement, which will result in the Company receiving a $17.8 million milestone payment for the dosing of the first patient in a long-term extension study. 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. The transaction price at inception and as of December 31, 2022, included fixed consideration consisting of the upfront payments of $205 million. All potential future milestones and other payments were considered constrained at the inception of the AbbVie Agreement and as of December 31, 2022, since the Company could not conclude it was probable that a significant reversal in the amount of revenue recognized would not occur. Collaboration revenue under the AbbVie Agreement during the years ended December 31, 2022, 2021, and 2020 was $70.7 million, $14.9 million, and $21.1 million, respectively. The deferred revenue related to the AbbVie Agreement was $46.7 million and $117.4 million as of December 31, 2022 and 2021, respectively. The deferred revenue is expected to be recognized over the research and development period of the programs through the AL002 program through the completion of Phase 2 clinical trials. For the year ended December 31, 2022, we recorded a net increase to collaboration revenue under the AbbVie Agreement due to changes in estimated costs to satisfy the performance obligations resulting from the termination of the AL003 program, partially offset by increases in total expected costs for the AL002 program. Innovent The Company entered into an agreement in March 2020 with Innovent Biologics (Innovent) to license, develop, and commercialize AL008 in China (Innovent Agreement). AL008 is the Company’s novel antibody targeting the CD47-SIRP-alpha pathway, a potent survival pathway co-opted by tumors to evade the innate immune system. Under the terms of the Innovent Agreement, Innovent would pay the Company up to $11.5 million in development milestones, $112.5 million in sales milestones, and future royalties on sales and the Company would retain the rights to develop and commercialize AL008 outside of China. The Company 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 were not included in the transaction price, as all these amounts were fully constrained as of December 31, 2022. As of December 31, 2022, no revenue has been recognized and no payments have been received under the Innovent Agreement.

Collaboration Agreements

12 Months Ended

Dec. 31, 2022

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Collaboration Agreements

4. 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 (also referred to as AL001), and AL101 (GSK Agreement). The GSK Agreement was made effective on August 17, 2021.

Under the terms of the GSK Agreement, the Company received $700 million in upfront payments, of which $500 million was received in August 2021 and $200 million was 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 and Parkinson’s disease and other non-orphan indications. The Company and GSK will share development costs 60% by GSK and 40% by the Company, except that the Company will solely bear the development costs of the initial Phase 2 clinical trials under the development plan, and the parties will share manufacturing development costs equally.

The Company concluded that the GSK Agreement is within the scope of ASC 808, Collaborative Arrangements, as both parties are active participants in the activities and are exposed to significant risks and rewards dependent on the success of the commercialization of AL001 and AL101. Certain elements are required to be accounted for under ASC 606, Revenue From Contracts With Customers, where the counterparty is a customer for a good or service that is a distinct unit of account.

The Company determined that the distinct performance obligations under ASC 606 consisted of: (i) license and know-how to AL001 FTD-GRN, which is currently in Phase 3 clinical development and (ii) the research and development activities, including license rights and know-how, relating to products in Phase 2 or earlier stages of development.

The transaction price at inception and as of December 31, 2022, included fixed consideration consisting of the upfront payments of $700 million. All potential future milestones and other payments were considered constrained at the inception of the GSK Agreement and as of December 31, 2022, since the Company could not conclude it was probable that a significant reversal in the amount of revenue recognized would not occur.

The respective standalone value for each of the performance obligations was allocated to the transaction price. The estimated SSP of each performance obligation was determined using discounted cash flows from the expected commercialization of AL001 and AL101 and estimated research and development costs to be incurred by the Company in the initial Phase 2 clinical trials. The estimate of SSP for each performance obligation reflects management's assumptions, which may include forecasted revenues, development timelines, discount rates, and probabilities of technical and regulatory success. For the license for FTD-GRN, the Company determined that GSK could benefit from the license at the time the license was granted and therefore, the related performance obligation was satisfied at a point in time. For the product candidates in Phase 2 or earlier stages of development, the Company determined that GSK could not benefit from the licenses without the corresponding development services that the Company has committed to perform due the earlier stage of development for these licenses. Except where agreed to otherwise, the Company will perform research and development activities through the end of the initial Phase 2 clinical trials. Revenue will be recognized over time as the research and development activities are performed. The Company will measure progress based on actual costs incurred to date compared to the overall total expected costs to satisfy the performance obligations.

The research and development activities for products in Phase 3 clinical development were determined to be within the scope of ASC 808. Both parties will be active participants in the development, manufacturing, and commercialization of the product and are exposed to significant risks and rewards that are dependent on the commercial success of the products. The Company and GSK participate in profit and loss sharing for each program commensurate with each party's cost-sharing responsibilities during research and development. ASC 808 does not provide recognition and measurement guidance. As such, the Company determined that ASC 730, Research and Development, was appropriate to analogize to based on the nature of the cost-sharing provision of the agreement. The Company has concluded that payments to or reimbursements from GSK related to these services will be accounted for as an increase to or reduction of research and development expenses, respectively.

Collaboration revenue under the GSK Agreement during the year ended December 31, 2022 and 2021, was $62.9 million and $192.1 million, respectively. The deferred revenue related to the GSK Agreement was $444.9 million and $307.9 million as of December 31, 2022 and 2021. The deferred revenue is expected to be recognized over the research and development period of the programs through the completion of initial Phase 2 clinical trials.

Costs associated with co-development activities performed under the agreement are included in research and development expenses in the consolidated statements of operations, with any reimbursement of costs by GSK reflected as a reduction of such expenses. For the year ended December 31, 2022 and 2021, the Company recognized a reduction of research and development expense of $14.7 million and $8.8 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 collaboratively reviewed next steps for AL003, the asset being developed under that program, and concluded that further development of AL003 was not warranted. AbbVie provided written notice to terminate the CD33 collaboration program on June 30, 2022. The Company will no longer continue development of this 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 the development beginning with Phase 3 clinical trials, and the product candidates program costs will be split between the parties. The Company would also share in profits and losses upon commercialization of any products. However, 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. In February 2023, the Company and AbbVie amended the AbbVie agreement, which will result in the Company receiving a $17.8 million milestone payment for the dosing of the first patient in a long-term extension study. 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.

The transaction price at inception and as of December 31, 2022, included fixed consideration consisting of the upfront payments of $205 million. All potential future milestones and other payments were considered constrained at the inception of the AbbVie Agreement and as of December 31, 2022, since the Company could not conclude it was probable that a significant reversal in the amount of revenue recognized would not occur.

Collaboration revenue under the AbbVie Agreement during the years ended December 31, 2022, 2021, and 2020 was $70.7 million, $14.9 million, and $21.1 million, respectively. The deferred revenue related to the AbbVie Agreement was $46.7 million and $117.4 million as of December 31, 2022 and 2021, respectively. The deferred revenue is expected to be recognized over the research and development period of the programs through the AL002 program through the completion of Phase 2 clinical trials. For the year ended December 31, 2022, we recorded a net increase to collaboration revenue under the AbbVie Agreement due to changes in estimated costs to satisfy the performance obligations resulting from the termination of the AL003 program, partially offset by increases in total expected costs for the AL002 program.

Innovent

The Company entered into an agreement in March 2020 with Innovent Biologics (Innovent) to license, develop, and commercialize AL008 in China (Innovent Agreement). AL008 is the Company’s novel antibody targeting the CD47-SIRP-alpha pathway, a potent survival pathway co-opted by tumors to evade the innate immune system. Under the terms of the Innovent Agreement, Innovent would pay the Company up to $11.5 million in development milestones, $112.5 million in sales milestones, and future royalties on sales and the Company would retain the rights to develop and commercialize AL008 outside of China. The Company 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 were not included in the transaction price, as all these amounts were

fully constrained as of December 31, 2022. As of December 31, 2022, no revenue has been recognized and no payments have been received under the Innovent Agreement.

Leases

12 Months Ended

Dec. 31, 2022

Leases [Abstract]

Leases

In June 2018, the Company signed a lease agreement to lease approximately 105,000 square feet in office and laboratory space in South San Francisco which serves as the Company’s headquarters (the “Headquarters”). The lease expires in 2029 with an option to renew for a period of ten years. The landlord paid for $15.7 million of tenant improvements. In connection with the lease, the Company entered into a letter of credit arrangement in the amount of $1.5 million as collateral for the lease, which is classified as restricted cash on the consolidated balance sheets. In October 2020, the Company signed a lease agreement to lease approximately 18,700 square feet of office and laboratory space in Newark, California. The lease term ends on February 6, 2028 with an option to extend for an additional five years. The landlord is obligated to pay for up to $0.4 million of tenant improvements. The measurement of the lease liabilities for the leases excludes the options to extend the term of the lease as such extensions are not reasonably certain to occur. Variable lease costs for all of the Company’s leases consist of operating expenses for the spaces.

In May 2019, the Company entered into an agreement to sublease approximately 25,000 square feet of the Headquarters (the “Sublease”), which was amended to approximately 23,600 square feet in December 2020. The Sublease expired in November 2021. The sublessee pays its proportionate share of operating expenses for the space.

In November 2021, the Company entered into an agreement to sublease approximately 7,132 square feet of the Headquarters, which was amended in May 2022 to include an additional space of 13,150 square feet. The

7,132 square feet of space subleased expired in December 2022 and the additional space will expire in November 2023.

The components of lease expense were as follows:


				December 31,
	2022			2021			2020
	(In thousands)
Operating lease cost	$	6,638		$	6,204		$	5,589
Variable lease cost		2,785			3,046			2,255
Sublease income and reimbursement of variable lease cost		(1,872	)		(2,141	)		(2,288	)
Total	$	7,551		$	7,109		$	5,556

As of December 31, 2022, the weighted-average remaining lease term for operating leases was 6.2 years and the weighted-average discount rate was 8.5%. Cash paid for amounts included in the measurement of lease liabilities for the year ended December 31, 2022, 2021, and 2020 was $8.2 million, $7.9 million, and $6.9 million, respectively, was included in net cash used in operating activities in our consolidated statements of cash flows.

The following are the lease payments owed under the Company’s operating leases as of December 31, 2022:


	(In thousands)
2023	$	8,436
2024		8,732
2025		9,037
2026		9,353
2027		9,681
Thereafter		11,096
Total undiscounted lease payments		56,335
Less: Present value adjustment		(13,008	)
Total lease liability	$	43,327

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2022

Earnings Per Share [Abstract]

Schedule of Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share

The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect:


	Year Ended December 31,
	2022		2021		2020
Restricted stock subject to future vesting		3,044,618		1,373,874		186,425
Options to purchase common stock		13,713,272		11,644,070		12,654,998
Shares committed under 2019 ESPP		167,133		70,406		86,677
Total		16,925,023		13,088,350		12,928,100

Income Taxes - Schedule of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Unrecognized tax benefits, beginning balance	$ 6,939	$ 4,592
Decreases related to tax positions taken during the prior year		(59)
Increases related to tax positions taken during the current year	8,199	2,406
Unrecognized tax benefits, ending balance	$ 15,138	$ 6,939

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2022

Fair Value Disclosures [Abstract]

Summary of Financial Assets Measured at Fair Value on a Recurring Basis

The following tables summarize the Company’s financial assets measured at fair value on a recurring basis by level within the fair value hierarchy:


	December 31, 2022
	Fair Value Hierarchy	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Market Value
	(In thousands)
Money market funds	Level 1	$	74,848	$	—	$	—		$	74,848
U.S. government treasury securities	Level 1		506,372		7		(4,569	)		501,810
Commercial paper	Level 2		44,438		2		(8	)		44,432
Corporate bonds	Level 2		29,352		4		(10	)		29,346
Total cash equivalents and marketable securities		$	655,010	$	13	$	(4,587	)	$	650,436


	December 31, 2021
	Fair Value Hierarchy	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Market Value
	(In thousands)
Money market funds	Level 1	$	218,451	$	—	$	—		$	218,451
U.S. government treasury securities	Level 1		407,041		8		(950	)		406,099
Total cash equivalents and marketable securities		$	625,492	$	8	$	(950	)	$	624,550

Consolidated Statements of Stockholders' Equity (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Issuance cost of common stock	$ 1,148

Leases (Tables)

12 Months Ended

Dec. 31, 2022

Leases [Abstract]

Components of Lease Expense

The components of lease expense were as follows:


				December 31,
	2022			2021			2020
	(In thousands)
Operating lease cost	$	6,638		$	6,204		$	5,589
Variable lease cost		2,785			3,046			2,255
Sublease income and reimbursement of variable lease cost		(1,872	)		(2,141	)		(2,288	)
Total	$	7,551		$	7,109		$	5,556

Schedule of Lease Payments Owed Under Company's Operating Leases

The following are the lease payments owed under the Company’s operating leases as of December 31, 2022:


	(In thousands)
2023	$	8,436
2024		8,732
2025		9,037
2026		9,353
2027		9,681
Thereafter		11,096
Total undiscounted lease payments		56,335
Less: Present value adjustment		(13,008	)
Total lease liability	$	43,327

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Contingency [Line Items]
Valuation allowance deferred tax asset change in amount	$ 42,300,000
Uncertain tax provision	8,199,000	$ 2,406,000
Reversal of reserves on uncertain tax provisions	0	$ 100,000
California Tax Authority
Income Tax Contingency [Line Items]
Tax Credit Carryforward, Amount	11,600,000
Federal Tax Authority
Income Tax Contingency [Line Items]
Operating loss carry forward, net	40,300,000
Tax Credit Carryforward, Amount	$ 28,400,000
Tax Credit Beginning Expiration Year	2036
Federal Tax Authority \| Maximum
Income Tax Contingency [Line Items]
Operating loss carry forward, deductions	80.00%
State Tax Authority
Income Tax Contingency [Line Items]
Operating loss carry forward, net	$ 203,500,000
Operating loss carry forward beginning expiration year	2030

Balance Sheet Components - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 48,133	$ 44,616
Less accumulated depreciation and amortization	(22,612)	(17,286)
Total property and equipment, net	25,521	27,330
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,310	2,294
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,430	2,330
Lab Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	17,165	14,043
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 26,228	$ 25,949

Leases - Schedule of Lease Payments Owed Under Company's Operating Leases (Detail) $ in Thousands	Dec. 31, 2022 USD ($)
Leases [Abstract]
2023	$ 8,436
2024	8,732
2025	9,037
2026	9,353
2027	9,681
Thereafter	11,096
Total undiscounted lease payments	56,335
Less: Present value adjustment	(13,008)
Total lease liability	$ 43,327

Stock-based Compensation - Summary of Share-based Payment Award, Stock Options, Valuation Assumptions (Details) - Share-based Payment Arrangement, Option	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend yield	0.00%	0.00%	0.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 3 months 18 days	5 years 2 months 12 days	5 years 3 months 18 days
Expected volatility	79.00%	78.00%	74.00%
Risk-free interest rate	1.50%	0.50%	0.30%
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days
Expected volatility	80.00%	81.00%	78.00%
Risk-free interest rate	4.30%	1.30%	1.80%

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2022
Subsequent Events [Abstract]
Subsequent Events	11. Subsequent Events In February 2023, the Company and AbbVie amended the AbbVie agreement, which will result in the Company receiving a $17.8 million milestone payment for the dosing of the first patient in a long-term extension study.

Fair Value Measurements

12 Months Ended

Dec. 31, 2022

Fair Value Disclosures [Abstract]

Fair Value Measurements

The following tables summarize the Company’s financial assets measured at fair value on a recurring basis by level within the fair value hierarchy:


	December 31, 2022
	Fair Value Hierarchy	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Market Value
	(In thousands)
Money market funds	Level 1	$	74,848	$	—	$	—		$	74,848
U.S. government treasury securities	Level 1		506,372		7		(4,569	)		501,810
Commercial paper	Level 2		44,438		2		(8	)		44,432
Corporate bonds	Level 2		29,352		4		(10	)		29,346
Total cash equivalents and marketable securities		$	655,010	$	13	$	(4,587	)	$	650,436


	December 31, 2021
	Fair Value Hierarchy	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Market Value
	(In thousands)
Money market funds	Level 1	$	218,451	$	—	$	—		$	218,451
U.S. government treasury securities	Level 1		407,041		8		(950	)		406,099
Total cash equivalents and marketable securities		$	625,492	$	8	$	(950	)	$	624,550

The Company’s Level 2 securities are valued using third-party pricing sources. The pricing services utilize industry standard valuation models for which all significant inputs are observable. The Company classifies marketable securities available to fund current operations as current assets. As of December 31, 2022, the remaining contractual maturities of $640.8 million of investments were less than one year and $9.6 million of investment were after one year through two years. As of December 31, 2022, fifteen U.S. government treasury securities with an aggregate fair value of $133.2 million and an aggregate unrealized loss of $3.1 million were in a loss position for more than twelve months. 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. The Company did not sell any marketable securities for the years ended December 31, 2022 and 2020. For the year ended December 31, 2021, the Company sold marketable securities for the total proceeds of $10.7 million for an immaterial realized gain based on the specific identification method.

- 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

Net Loss Per Share

12 Months Ended

Dec. 31, 2022

Earnings Per Share [Abstract]

Net Loss Per Share

10.

Net Loss Per Share

The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect:


	Year Ended December 31,
	2022		2021		2020
Restricted stock subject to future vesting		3,044,618		1,373,874		186,425
Options to purchase common stock		13,713,272		11,644,070		12,654,998
Shares committed under 2019 ESPP		167,133		70,406		86,677
Total		16,925,023		13,088,350		12,928,100

Balance Sheet Components - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Accrued Liabilities, Current [Abstract]
Accrued research and development costs	$ 12,321	$ 13,330
Accrued employee compensation	12,758	11,664
Accrued professional services	1,983	1,588
Accrued property and equipment	337	560
Other	372	318
Total accrued liabilities	$ 27,771	$ 27,460

Leases - Components of Lease Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Leases [Abstract]
Operating lease cost	$ 6,638	$ 6,204	$ 5,589
Variable lease cost	2,785	3,046	2,255
Sublease income and reimbursement of variable lease cost	(1,872)	(2,141)	(2,288)
Total	$ 7,551	$ 7,109	$ 5,556

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
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	$ 74,848	$ 218,451
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	74,848	218,451
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	506,372	407,041
Cash equivalents and marketable securities, Unrealized Gains	7	8
Cash equivalents and marketable securities, Unrealized Losses	(4,569)	(950)
Cash equivalents and marketable securities, Fair Market Value	501,810	406,099
Commercial Paper \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents and marketable securities, Amortized Cost	44,438
Cash equivalents and marketable securities, Unrealized Gains	2
Cash equivalents and marketable securities, Unrealized Losses	(8)
Cash equivalents and marketable securities, Fair Market Value	44,432
Corporate Bonds \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents and marketable securities, Amortized Cost	29,352
Cash equivalents and marketable securities, Unrealized Gains	4
Cash equivalents and marketable securities, Unrealized Losses	(10)
Cash equivalents and marketable securities, Fair Market Value	29,346
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	655,010	625,492
Cash equivalents and marketable securities, Unrealized Gains	13	8
Cash equivalents and marketable securities, Unrealized Losses	(4,587)	(950)
Cash equivalents and marketable securities, Fair Market Value	$ 650,436	$ 624,550

Balance Sheet Components

12 Months Ended

Dec. 31, 2022

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Components

Property and Equipment, Net

Property and equipment, net consists of the following:


	December 31,
	2022			2021
	(In thousands)
Computer equipment	$	2,310		$	2,294
Furniture and fixtures		2,430			2,330
Lab Equipment		17,165			14,043
Leasehold Improvements		26,228			25,949
Property and equipment, gross		48,133			44,616
Less accumulated depreciation and amortization		(22,612	)		(17,286	)
Total property and equipment, net	$	25,521		$	27,330

Accrued Liabilities

Accrued liabilities consist of the following:


	December 31,
	2022		2021
	(In thousands)
Accrued research and development costs	$	12,321	$	13,330
Accrued employee compensation		12,758		11,664
Accrued professional services		1,983		1,588
Accrued property and equipment		337		560
Other		372		318
Total accrued liabilities	$	27,771	$	27,460

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net loss	$ (133,310)	$ (36,329)	$ (190,228)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	5,714	6,329	5,870
Stock-based compensation	46,146	40,785	30,522
Amortization of premiums and accretion of discounts on marketable securities	(1,163)	2,099	584
Amortization of right-of-use assets	2,758	1,986	1,395
Impairment loss on right-of-use assets	0	0	238
Loss from disposal of property and equipment, net	0	0	107
Changes in operating assets and liabilities:
Receivable from collaboration partner	4,804	(7,391)	0
Prepaid expenses and other current assets	(3,926)	1,132	(3,839)
Other assets	(835)	(2,957)	(2,498)
Accounts payable	(572)	1,917	2,409
Accrued liabilities and accrued clinical supply costs	(2,655)	2,391	12,232
Deferred revenue	66,383	292,915	(21,098)
Lease liabilities	(4,274)	(4,012)	(2,407)
Other long-term liabilities	601	(314)	(21)
Net cash provided by (used in) operating activities	(20,329)	298,551	(166,734)
Cash flows from investing activities:
Purchase of property and equipment	(4,117)	(3,247)	(5,032)
Purchase of marketable securities	(556,898)	(343,402)	(506,809)
Sale of marketable securities	0	10,696	0
Maturities of marketable securities	402,001	286,290	406,790
Net cash used in investing activities	(159,014)	(49,663)	(105,051)
Cash flows from financing activities:
Proceeds from issuance of common stock upon public offerings, net of issuance costs	0	0	224,603
Proceeds from the exercise of options to purchase common stock	3,059	28,530	6,331
Proceeds from issuance of stock from employee stock purchase plan	1,455	1,765	1,179
Net cash provided by financing activities	4,514	30,295	232,113
Net increase (decrease) in cash, cash equivalents, and restricted cash	(174,829)	279,183	(39,672)
Cash, cash equivalents, and restricted cash at beginning of period	330,624	51,441	91,113
Cash, cash equivalents, and restricted cash at end of period	155,795	330,624	51,441
Non-cash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued liabilities	$ 493	$ 705	$ 428

Stock-based Compensation - Summary of Recognized Stock-Based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 46,146	$ 40,785	$ 30,522
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	24,895	21,443	14,980
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 21,251	$ 19,342	$ 15,542

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2022	Dec. 31, 2021
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	82,895,718	82,895,718
Common stock, shares outstanding	81,986,192	81,986,192

Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2022

Balance Sheet Related Disclosures [Abstract]

Summary of Property and Equipment, Net

Property and equipment, net consists of the following:


	December 31,
	2022			2021
	(In thousands)
Computer equipment	$	2,310		$	2,294
Furniture and fixtures		2,430			2,330
Lab Equipment		17,165			14,043
Leasehold Improvements		26,228			25,949
Property and equipment, gross		48,133			44,616
Less accumulated depreciation and amortization		(22,612	)		(17,286	)
Total property and equipment, net	$	25,521		$	27,330

Summary of Accrued Liabilities

Accrued liabilities consist of the following:


	December 31,
	2022		2021
	(In thousands)
Accrued research and development costs	$	12,321	$	13,330
Accrued employee compensation		12,758		11,664
Accrued professional services		1,983		1,588
Accrued property and equipment		337		560
Other		372		318
Total accrued liabilities	$	27,771	$	27,460

Stock-based Compensation - Summary of Restricted Stock Awards and Restricted Stock Units (Details) - Restricted Stock Awards And Restricted Stock Units - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Shares
Number of Shares, Unvested, beginning balance	1,373,874	186,425
Number of Shares, Granted	2,539,014	1,822,295
Number of Shares, Vested	(414,577)	(324,802)
Number of Shares, Forfeited	(453,693)	(310,044)
Number of Shares, Unvested, ending balance	3,044,618	1,373,874
Weighted-average grant-date fair value
Weighted Average Grant Date Fair Value per Share, Unvested, beginning balance	$ 18.35	$ 6.95
Weighted Average Grant Date Fair Value per Share, Granted	10.02	17.33
Weighted Average Grant Date Fair Value per Share, Vested	18.63	10.35
Weighted Average Grant Date Fair Value per Share, Forfeited	16.21	13.85
Weighted Average Grant Date Fair Value per Share, Unvested, ending balance	$ 11.68	$ 18.35

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2022

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Basis of Presentation

The consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States (GAAP) as defined by the Financial Accounting Standards Board (FASB). The consolidated financial statements include the accounts of Alector, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expense during the reporting period. The Company evaluates its estimates, including those related to revenue recognition, manufacturing accruals, clinical accruals, fair value of assets and liabilities, income taxes uncertainties, stock-based compensation, and related assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, and short-term marketable securities. Cash and cash equivalents are deposited in checking and sweep accounts at financial institutions. Such deposits may, at times, exceed federally insured limits.

Cash, Cash Equivalents, and Restricted Cash

The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash and cash equivalents. Cash equivalents, which consist of amounts invested in money market funds, are stated at fair value.

Restricted cash as of December 31, 2022 relates to a letter of credit established for a lease entered into in June 2018.

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheets that sum to the total of the same amounts shown in the consolidated statements of cash flows:


	Year Ended December 31,
	2022		2021		2020
	(In thousands)
Cash and cash equivalents	$	154,323	$	329,152	$	49,969
Restricted cash		1,472		1,472		1,472
Total cash, cash equivalents, and restricted cash	$	155,795	$	330,624	$	51,441

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, 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, receivable from collaboration partner, current and noncurrent prepaid expenses, accounts payable, and accrued liabilities. The Company’s financial instruments approximate fair value due to their relatively short maturities.

The Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The Company determines the fair value of its financial instruments based on assumptions that market participants would use in pricing an asset or liability in the principal or most advantageous market. When considering market participant assumptions in fair value measurements, the following fair value hierarchy distinguishes between observable and unobservable inputs, which are categorized in one of the following levels:

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

Level 2 – Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and

Level 3 – Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data.

Property and Equipment

Property and equipment are stated at cost, net of accumulated depreciation and amortization. Depreciation and amortization is computed using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized over the lesser of their useful lives or the remaining life of the lease. When assets are retired or otherwise disposed of, the cost and related accumulated depreciation and amortization are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statements of operations in the period realized. Maintenance and repairs are charged to the consolidated statements of operations as incurred.

Leases

The Company determines whether an arrangement is or contains a lease at the inception of the lease. Leases are recognized on the balance sheet as right-of-use assets and lease liabilities. Lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The Company utilizes the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received and any prepaid or accrued rent. Rent expense for the operating lease is recognized on a straight-line basis over the lease term and is included in operating expenses on the statements of operations and comprehensive loss. Variable lease payments include lease operating expenses.

The Company excludes balance sheet recognition of operating leases having a term of 12 months or less (short-term leases) and does not separate lease components and non-lease components for its long-term leases.

Impairment of Long-Lived Assets

The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparing the carrying amount to the future net undiscounted cash flows which the assets are expected to generate. If the total of the undiscounted future cash flows is less than the carrying amount of the assets, an impairment loss is recognized for the amount by which the carrying amount of the assets exceeds its fair value. For the years ended December 31, 2022 and 2021, the Company did not recognize an impairment loss on its right-of-use assets. For the year ended December 31, 2020, the Company recognized a $0.2 million impairment loss related to its decision to no longer utilize certain property through the end of the lease term.

Revenue Recognition

The Company recognizes revenue when control of promised goods or services is transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under arrangements, the Company performs the following steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract, and (v) recognize revenue when (or as) the entity satisfies the performance obligation. If it is determined that multiple performance obligations exist, the transaction price is allocated at the inception of the agreement to all identified performance obligations based on the relative standalone selling price (SSP). The relative SSP for each deliverable is estimated using external sourced evidence if it is available. If external sourced evidence is not available, we use our best estimate of the SSP for the deliverable.

The Company recognizes collaboration revenue at a point in time if control of the promised good or service has been transferred to the customer. The Company recognizes collaboration revenue over time by measuring the progress toward complete satisfaction of the performance obligation using an input measure. In order to recognize revenue over the research and development period, the Company measures actual costs incurred to date compared to the overall total expected costs to satisfy the performance obligation. Revenues are recognized as the program costs are incurred. The Company re-evaluates the estimate of expected costs to satisfy the performance obligation each reporting period.

Research and Development Costs

Research and development costs are expensed as incurred and consist primarily of new product development. Research and development costs include salaries and benefits, consultants’ fees, process development costs, stock-based compensation, and laboratory supplies, as well as fees paid to third parties that conduct certain research and development activities on the Company’s behalf. In addition, research and development costs include the reimbursable costs incurred for the collaboration agreements, which includes payroll costs for time incurred on projects, laboratory supplies, and third-party research and development activities.

A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers. The Company records accrued expenses for estimated preclinical study and clinical trial expenses. Estimates are based on the services performed pursuant to contracts with research institutions, CROs in connection with clinical studies, investigative sites in connection with clinical studies, vendors in connection with preclinical development activities, and contract manufacturing organizations in connection with the production of materials for clinical trials. Further, the Company accrues expenses related to clinical trials based on the level of patient enrollment and activity according to the related agreement. The Company monitors patient enrollment levels and related activity to the extent reasonably possible and make judgments and estimates in determining the accrued balance in each reporting period. If the Company underestimates or overestimates the level of services performed or the costs of these services, actual expenses could differ from estimates. To date, the Company has not experienced significant changes in its estimates of preclinical studies and clinical trial accruals.

Stock-based Compensation

Stock-based compensation is measured on the grant date based on the fair value of the awards. The fair value of options to purchase common stock is measured using the Black-Scholes option-pricing model. Stock-based compensation associated with restricted stock units (RSUs) is based on the fair value of the Company's common stock on the grant date, which equals the closing price of the Company's common stock on the grant date. The Company recognizes expense over the vesting period of the awards. Expense for options and RSUs that vest based only on a service condition is recognized on a straight-line basis.

In 2021, the Company granted RSUs with market conditions to certain executives. The fair value of RSUs with market conditions is estimated using a Monte Carlo simulation model. Assumptions and estimates utilized in the model include the stock price on grant date, risk-free interest rate, dividend yield, expected stock volatility, and estimated period to achieve the market condition. The expense is recognized based on continued employment of the participants, regardless of achievement of the market condition. Expense related to the RSUs with market conditions is recognized using the accelerated attribution method.

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

Comprehensive Loss

Comprehensive loss includes net loss and certain changes in stockholders’ equity that are the result of transactions and economic events other than those with stockholders. The Company’s only element of other comprehensive loss was net unrealized gain (loss) on marketable securities.

Income Taxes

The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial statement and tax bases of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date.

The deferred tax assets are recognized to the extent the Company believes that these assets are more likely than not to be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to the Company’s historical operating performance and the

recorded cumulative net losses in prior periods, the net deferred tax assets have been fully offset by a valuation allowance.

The Company records uncertain tax positions using a two-step process. First, the Company determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position. Second, for those tax positions that meet the more-likely-than-not recognition threshold, the Company recognizes the largest amount of tax benefit that is more than 50% likely to be realized upon ultimate settlement with the related tax authority.

The Company recognizes interest and penalties related to unrecognized tax benefits on the interest expense line and other expense line, respectively, in the accompanying statements of operations. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits.

Employee 401(k) Plan

The Company has a qualified contributory savings plan under Section 401(k) of the Internal Revenue Code (the “Code”) covering substantially all U.S. employees of Alector. The 401(k) plan is designed to provide tax-deferred retirement benefits in accordance with the provisions of Section 401(k) of the Code. Eligible employees may defer up to 100% of their eligible compensation up to the annual maximum as determined by the Internal Revenue Service. The Company’s contributions to the plan are discretionary. For the years ended December 31, 2022, 2021, and 2020, the Company made matching contributions of $1.2 million, $0.8 million, and $0.7 million, respectively.

Segments

The Company operates in one segment. The Company’s chief operating decision maker, its Chief Executive Officer, manages the Company’s operations on a consolidated basis for purposes of allocating resources.

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2022	Feb. 21, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Trading Symbol	ALEC
Entity File Number	001-38792
Entity Tax Identification Number	82-2933343
Entity Public Float			$ 627.1
Entity Address, Address Line One	131 Oyster Point Blvd
Entity Address, Address Line Two	Suite 600
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	415
Local Phone Number	231-5660
Document Transition Report	false
Document Annual Report	true
Entity Registrant Name	Alector, Inc.
Entity Central Index Key	0001653087
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Common Stock, Shares Outstanding		83,027,910
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock
Entity Interactive Data Current	Yes
Entity Well-known Seasoned Issuer	No
Entity Incorporation, State or Country Code	DE
Documents Incorporated by Reference	Portions of the registrant’s Definitive Proxy Statement relating to the registrant’s 2023 Annual Meeting of Stockholders are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such Definitive Proxy Statement will be filed with the Securities and Exchange Commission within 120 days after the end of the registrant’s 2022 fiscal year ended December 31, 2022.
Auditor Name	Ernst & Young LLP
Auditor Location	San Mateo, California
Auditor Firm ID	42

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2019		69,052,873
Beginning Balance at Dec. 31, 2019	$ 194,743	$ 7	$ 414,414	$ 142	$ (219,820)
Issuance of common stock upon follow-on public offering, net of issuance costs of $1,148 (in shares)		9,602,500
Issuance of common stock upon follow-on public offering, net of issuance costs	224,511	$ 1	224,510
Exercise of stock options (in shares)		655,772
Exercise of stock options	6,331		6,331
Purchase of common stock under employee stock purchase plan (in shares)		86,870
Purchase of common stock under employee stock purchase plan	1,179		1,179
Forfeiture of restricted common stock		(81,754)
Stock-based compensation	30,522		30,522
Unrealized gain (loss) on marketable securities	472			472
Net loss	(190,228)				(190,228)
Ending balance (in shares) at Dec. 31, 2020		79,316,261
Ending Balance at Dec. 31, 2020	267,530	$ 8	676,956	614	(410,048)
Exercise of stock options (in shares)		2,395,223
Exercise of stock options	28,530		28,530
Vesting of restricted stock units		156,420
Purchase of common stock under employee stock purchase plan (in shares)		136,331
Purchase of common stock under employee stock purchase plan	1,765		1,765
Forfeiture of restricted common stock		(18,043)
Stock-based compensation	40,785		40,785
Unrealized gain (loss) on marketable securities	(1,557)			(1,557)
Net loss	$ (36,329)				(36,329)
Ending balance (in shares) at Dec. 31, 2021	81,986,192	81,986,192
Ending Balance at Dec. 31, 2021	$ 300,724	$ 8	748,036	(943)	(446,377)
Exercise of stock options (in shares)		298,238
Exercise of stock options	3,059		3,059
Vesting of restricted stock units		414,578
Purchase of common stock under employee stock purchase plan (in shares)		196,710
Purchase of common stock under employee stock purchase plan	1,455		1,455
Stock-based compensation	46,146		46,146
Unrealized gain (loss) on marketable securities	(3,632)			(3,632)
Net loss	$ (133,310)				(133,310)
Ending balance (in shares) at Dec. 31, 2022	81,986,192	82,895,718
Ending Balance at Dec. 31, 2022	$ 214,442	$ 8	$ 798,696	$ (4,575)	$ (579,687)

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Net operating loss	$ 20,963	$ 63,868
Accrued bonus	806	1,811
Tax credits	26,319	19,614
Stock-based compensation	13,351	9,656
Deferred revenue	67,673	27,849
Lease liability	10,055	11,296
Section 174 R&D capitalization	35,150	0
Other	1,608	694
Gross deferred tax assets	175,925	134,788
Less valuation allowance	(164,316)	(122,046)
Total deferred tax assets	11,609	12,742
Deferred tax liabilities:
Depreciation and amortization	(5,155)	(5,488)
Right-of-use assets	(6,454)	(7,254)
Gross deferred tax liabilities	(11,609)	(12,742)
Deferred tax assets, net	$ 0	$ 0

Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Summary of Recognized Stock-Based Compensation

The Company recognized stock-based compensation as follows:


	Year Ended December 31,
	2022		2021		2020
	(In thousands)
Research and development	$	24,895	$	21,443	$	14,980
General and administrative		21,251		19,342		15,542
Total stock-based compensation	$	46,146	$	40,785	$	30,522

Summary of Share-based Payment Award, Stock Options, Valuation Assumptions

The estimated grant-date fair value of all the Company’s options to purchase common stock was calculated using the Black-Scholes option pricing model, based on the following assumptions:


	Year Ended December 31,
	2022	2021	2020
Expected term (in years)	5.3– 6.1	5.2 – 6.1	5.3 – 6.1
Expected volatility	79% – 80%	78% – 81%	74% – 78%
Risk free interest rate	1.5% – 4.3%	0.5% – 1.3%	0.3% – 1.8%
Dividend yield	—	—	—

Summary of Options to Purchase Common Stock

Option activity is shown below:


	Number of Options			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(In years)		(In thousands)
Outstanding as of December 31, 2020		12,654,998		$	13.96
Granted		3,264,059			21.53
Exercised		(2,395,223	)		11.91
Forfeited		(1,879,764	)		14.55
Outstanding as of December 31, 2021		11,644,070			16.41
Granted		4,996,366			12.11
Exercised		(298,239	)		10.26
Forfeited		(2,628,925	)		18.28
Outstanding as of December 31, 2022		13,713,272		$	14.62		8.0	$	1,583
Exercisable as of December 31, 2022		6,776,201		$	14.75		7.0	$	1,276
Vested and expected to vest as of December 31, 2022		13,713,272		$	14.62		8.0	$	1,583

Summary of Restricted Stock Awards and Restricted Stock Units

Activity for the restricted stock awards and RSUs is shown below.


	Number of Shares			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		1,822,295			17.33
Vested		(324,802	)		10.35
Forfeited		(310,044	)		13.85
Unvested restricted stock units as of December 31, 2021		1,373,874			18.35
Granted		2,539,014			10.02
Vested		(414,577	)		18.63
Forfeited		(453,693	)		16.21
Unvested restricted stock units as of December 31, 2022		3,044,618		$	11.68

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Tax benefit at federal statutory rate	$ (27,205)	$ (7,627)	$ (39,948)
State income taxes	(344)	(398)	(16,570)
Tax credits	(20,184)	(9,389)	(8,010)
Uncertain tax positions	7,733	2,347	2,003
Stock-based compensation	4,919	(2,368)	353
Change in valuation allowance	38,421	16,800	62,280
Other	(86)	(161)	(108)
Income tax provision	$ 3,254	$ 0	$ 0

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Leases - Additional Information (Detail) $ in Thousands		1 Months Ended				12 Months Ended
Leases - Additional Information (Detail) $ in Thousands	Jun. 30, 2018 ft²	Nov. 30, 2021 ft²	Dec. 31, 2020 USD ($) ft²	Oct. 31, 2020 USD ($) ft²	May 31, 2019 ft²	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	May 31, 2022 ft²
Lessee Lease Description [Line Items]
Tenant improvement allowance \| $						$ 15,700
Amount form letter of credit \| $			$ 1,472			$ 1,472	$ 1,472	$ 1,472
Lease expiration year						2029
Operating lease, renewal period						10 years
Operating lease term						The lease expires in 2029 with an option to renew for a period of ten years.
Weighted average remaining lease term for operating leases						6 years 2 months 12 days
Weighted average discount rate for operating leases						8.50%
Cash paid for amounts included In measurement of lease liabilities \| $						$ 8,200	$ 7,900	$ 6,900
Offices and Laboratory Facilities \| South San Francisco
Lessee Lease Description [Line Items]
Area under lease \| ft²	105,000		23,600
Area under sublease \| ft²		7,132			25,000
Sublease expiration month and year						2022-12	2021-11
Additional area sublease expiration month and year						2023-11
Operating sublease, existence of option to extend						true
Additional area of property in lease \| ft²									13,150
Offices and Laboratory Facilities \| South San Francisco
Lessee Lease Description [Line Items]
Tenant improvement allowance \| $				$ 400
Area of property \| ft²				18,700
Lease, description						In October 2020, the Company signed a lease agreement to lease approximately 18,700 square feet of office and laboratory space in Newark, California. The lease term ends on February 6, 2028 with an option to extend for an additional five years. The landlord is obligated to pay for up to $0.4 million of tenant improvements.
Lease expiration date				Feb. 06, 2028
Extend for an additional lease term				5 years

Stock-based Compensation

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

Stock-based Compensation

The Company recognized stock-based compensation as follows:


	Year Ended December 31,
	2022		2021		2020
	(In thousands)
Research and development	$	24,895	$	21,443	$	14,980
General and administrative		21,251		19,342		15,542
Total stock-based compensation	$	46,146	$	40,785	$	30,522

Determination of Fair Value

The estimated grant-date fair value of all the Company’s options to purchase common stock was calculated using the Black-Scholes option pricing model, based on the following assumptions:


	Year Ended December 31,
	2022	2021	2020
Expected term (in years)	5.3– 6.1	5.2 – 6.1	5.3 – 6.1
Expected volatility	79% – 80%	78% – 81%	74% – 78%
Risk free interest rate	1.5% – 4.3%	0.5% – 1.3%	0.3% – 1.8%
Dividend yield	—	—	—

The fair value of each stock option was determined by the Company using the methods and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment and estimation by management.

Expected Term—The expected term represents the period that stock-based awards are expected to be outstanding. The expected term was derived by using the simplified method which uses the midpoint between the average vesting term and the contractual expiration period of the stock-based award.

Expected Volatility—The Company has limited information on the volatility of stock options as the shares were not actively traded on any public markets prior to February 7, 2019. The expected volatility was derived from the historical stock volatilities of comparable peer public companies within its industry. These companies are considered to be comparable to the Company’s business over a period equivalent to the expected term of the stock-based awards. In 2020, the Company began giving weight to in its own historical volatility in the determination of expected volatility.

Risk-Free Interest Rate—The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the date of grant for zero-coupon U.S. Treasury notes with maturities approximately equal to the expected term.

Expected Dividend Rate—The expected dividend is zero as the Company has not paid nor does it anticipate paying any dividends on its common stock underlying its stock options in the foreseeable future.

2019 Equity Incentive Plan and 2022 Inducement Plan

On February 6, 2019, the Company adopted the 2019 Equity Incentive Plan (2019 Plan) under which the Board may issue incentive stock options, nonstatutory stock options, restricted stock, restricted stock units, stock appreciation rights, performance units, and performance shares to the Company’s employees, directors, and consultants. The Company’s 2017 Stock Option and Grant Plan (2017 Plan) was terminated; however, shares subject to awards granted under it will continue to be governed by the 2017 Plan. Shares reserved for issuance but not issued pursuant to, or not subject to, awards granted under the 2017 Plan were added to the available shares in the 2019 Plan. Shares subject to awards granted under the 2017 Plan that are repurchased by, or forfeited to, the Company will also be reserved for issuance under the 2019 Plan. The board of directors, or a committee appointed by the board of directors, has the authority to determine to whom options or shares will be granted, the number of shares, the term, and the exercise price. If an individual owns stock representing 10% or more of the outstanding shares, the exercise price of each share shall be at least 110% of the fair market value and the term of the award shall not exceed five years. All other options granted under the 2019 Plan must have an exercise price at least equal to the fair market value on the date of grant and have a term not to exceed ten years. The stock options generally vest over a four-year period with one forty-eighth of the shares vesting each month or over a four-year period with 25% vesting at the one-year cliff and monthly thereafter. The RSUs generally vest over a period of three years with one-twelfth of the shares vesting quarterly. On January 1, 2022, the Company added 4,099,309 shares to the shares reserved for issuance under the 2019 Equity Incentive Plan. As of December 31, 2022, the Company had reserved 20,463,901 shares of the automatic conversion provision of common stock under the 2019 Plan, of which 5,587,550 shares were available for issuance of future awards.

On January 1, 2022, the Company adopted the 2022 Inducement Plan (Inducement Plan) and reserved 1,630,000 shares for issuance under the Inducement Plan for the grant of equity-based awards to individuals who were not previously employees or non-employee directors of the Company. On September 22, 2022, the Company increased the number of shares available for issuance under the 2022 Inducement Plan to a total of 3,300,000 shares. As of December 31, 2022, 1,401,483 shares were available for issuance of future awards under the Inducement Plan.

Option activity is shown below:


	Number of Options			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(In years)		(In thousands)
Outstanding as of December 31, 2020		12,654,998		$	13.96
Granted		3,264,059			21.53
Exercised		(2,395,223	)		11.91
Forfeited		(1,879,764	)		14.55
Outstanding as of December 31, 2021		11,644,070			16.41
Granted		4,996,366			12.11
Exercised		(298,239	)		10.26
Forfeited		(2,628,925	)		18.28
Outstanding as of December 31, 2022		13,713,272		$	14.62		8.0	$	1,583
Exercisable as of December 31, 2022		6,776,201		$	14.75		7.0	$	1,276
Vested and expected to vest as of December 31, 2022		13,713,272		$	14.62		8.0	$	1,583

The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying stock options and the fair value of the Company’s common stock for stock options that were in-the-money. The aggregate intrinsic value of options exercised was $1.2 million, $37.1 million, and $11.1 million for the years ended December 31, 2022, 2021, and 2020, respectively. The weighted-average grant-date fair value per share of options granted was $8.42, $14.70, and $10.14, for the years ended December 31, 2022, 2021, and 2020, respectively. As of December 31, 2022, total unrecognized stock-based compensation related to unvested stock options was $64.4 million, which the Company expects to recognize over a remaining weighted-average period of 2.7 years.

Restricted Stock Activity

Activity for the restricted stock awards and RSUs is shown below. In May 2021 and January 2022, the Company issued RSUs with market conditions to certain executives, which are also included in the table below. The RSUs with market conditions are earned based on stock price performance and continued service by the employee. The RSUs with market conditions trigger vesting upon the company's stock price attaining a specified level over a specified period of time. The shares then vest quarterly over one year after attainment. The Company used a Monte Carlo simulation model to determine the fair value of the awards at the grant date. The Monte Carlo model uses the fair value inputs on the grant date to run simulations and take an average of possible outcomes. The total grant date fair value of the RSUs with market condition was $6.6 million to be amortized over an estimated weighted average service period of 2.1 years. Compensation expense related to awards with market-based conditions is recognized regardless of whether the market condition is ultimately satisfied if the related service has been provided.


	Number of Shares			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		1,822,295			17.33
Vested		(324,802	)		10.35
Forfeited		(310,044	)		13.85
Unvested restricted stock units as of December 31, 2021		1,373,874			18.35
Granted		2,539,014			10.02
Vested		(414,577	)		18.63
Forfeited		(453,693	)		16.21
Unvested restricted stock units as of December 31, 2022		3,044,618		$	11.68

As of December 31, 2022, total unrecognized stock-based compensation related to unvested restricted common stock issued to employees was $30.2 million, which the Company expects to recognize over a remaining weighted-average period of 2.4 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. Each offering period is approximately six months long beginning on the first trading day on or after June 1 and December 1 each year. ESPP participants purchase shares of common stock at a price per share equal to 85% of the lesser of (1) the fair market value per share of the common stock on the first trading day of the offering period or (2) the fair market value of the common stock on the purchase date. On January 1, 2022, 591,397 shares were added to the shares reserved for issuance under the 2019 ESPP pursuant to the annual automatic increase. As of December 31, 2022, there was $0.4 million in unrecognized compensation expense related to the 2019 ESPP to be recognized over five months.

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 154,323	$ 329,152	$ 49,969
Restricted cash	1,472	1,472	1,472
Total cash, cash equivalents, and restricted cash	$ 155,795	$ 330,624	$ 51,441	$ 91,113

Stock-based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions			12 Months Ended
	Sep. 22, 2022	Feb. 06, 2019	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Jan. 01, 2022	Jan. 01, 2021
Restricted Stock Awards And Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected weighted average period			2 years 4 months 24 days
Grant date fair value of units granted			$ 6.6
Share-based payment award requisite service period			2 years 1 month 6 days
Un-recognized compensation expense			$ 30.2
2019 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period		4 years
Expected weighted average period			2 years 8 months 12 days
Automatic conversion provision of common stock reserved for issuance			20,463,901				4,099,309
Percentage of stock owned by Individual		10.00%
Percentage of exercise price per share from fair market value		110.00%
Stock options, term		5 years
Cliff vesting percentage		25.00%
Cliff vesting period		1 year
Common stock, shares available for issuance			5,587,550
Aggregate intrinsic value of option exercised			$ 1.2	$ 37.1	$ 11.1
Unrecognized stock-based compensation			$ 64.4
Weighted-average grant-date fair value per share of options granted			$ 8.42	$ 14.70	$ 10.14
2019 Equity Incentive Plan \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options, term		10 years
2019 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Automatic conversion provision of common stock reserved for issuance						591,397
Purchase price of common stock, percentage			85.00%
Subsequent offering period			6 months
Un-recognized compensation expense			$ 0.4
2022 Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Automatic conversion provision of common stock reserved for issuance						1,630,000
Common stock, shares available for issuance			1,401,483
Number of additional shares authorized (in shares)	3,300,000

The Company and Liquidity

12 Months Ended

Dec. 31, 2022

Organization, Consolidation and Presentation of Financial Statements [Abstract]

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 estimated offering costs.

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Summary Of Significant Accounting Policies [Line Items]
Credit losses on marketable securities	$ 0
Impairment loss on right-of-use assets	$ 0	$ 0	$ 238
Defined contribution plan, maximum annual contributions per employee, percent	100.00%
Defined matching contribution plan	$ 1,200	$ 800	$ 700
Minimum
Summary Of Significant Accounting Policies [Line Items]
Property, plant, and equipment useful life	3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Property, plant, and equipment useful life	5 years

Net Loss Per Share - Schedule of Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	16,925,023	13,088,350	12,928,100
Restricted Stock Awards And Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	3,044,618	1,373,874	186,425
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	13,713,272	11,644,070	12,654,998
Shares Committed Under 2019 ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	167,133	70,406	86,677

Collaboration Agreements - Additional Information (Details) $ in Thousands			1 Months Ended			12 Months Ended
	Aug. 17, 2021 USD ($)	Jul. 01, 2021 USD ($)	Jan. 31, 2022 USD ($)	Jan. 31, 2018 USD ($)	Oct. 31, 2017 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Feb. 28, 2023 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue						$ 444,900	$ 307,900
Research and development expense						210,418	189,407	$ 156,869
GlaxoSmithKline plc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Effective date of agreement	Aug. 17, 2021
Upfront payments		$ 700,000				$ 700,000
Upfront payment received	$ 500,000		$ 200,000
Percentage Of Development Cost						0.60
Collaboration revenue						$ 62,900	192,100
Research and development expense						14,700	8,800
GlaxoSmithKline plc \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Additional milestone payments per program related to initiation of certain clinical studies and regulatory approval						$ 1,500,000
Alector
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage Of Development Cost						0.40
AbbVie Biotechnology Limited
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payments					$ 205,000	$ 205,000
Upfront payment received				$ 200,000	5,000
Collaboration revenue						70,700	14,900	$ 21,100
Deferred revenue						46,700	$ 117,400
Exclusive option rights exercised for each program					250,000
AbbVie Biotechnology Limited \| Subsequent Event
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payments									$ 17,800
AbbVie Biotechnology Limited \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Additional milestone payments per program related to initiation of certain clinical studies and regulatory approval					$ 225,000
Innovent
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenue						0
Development milestone						11,500
Sales milestone						$ 112,500

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2022

Accounting Policies [Abstract]

Basis of Presentation

Use of Estimates

Concentration of Credit Risk

Cash, Cash Equivalents, and Restricted Cash

Restricted cash as of December 31, 2022 relates to a letter of credit established for a lease entered into in June 2018.


	Year Ended December 31,
	2022		2021		2020
	(In thousands)
Cash and cash equivalents	$	154,323	$	329,152	$	49,969
Restricted cash		1,472		1,472		1,472
Total cash, cash equivalents, and restricted cash	$	155,795	$	330,624	$	51,441

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.

Property and Equipment

Leases

Impairment of Long-Lived Assets

Revenue Recognition

Research and Development Costs

Stock-based Compensation

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

Comprehensive Loss

Income Taxes

recorded cumulative net losses in prior periods, the net deferred tax assets have been fully offset by a valuation allowance.

Employee 401 (K) Plan

Employee 401(k) Plan

Segments

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 154,323	$ 329,152
Marketable securities	558,528	406,099
Receivable from Collaboration partner	2,587	7,391
Prepaid expenses and other current assets	10,997	7,071
Total current assets	726,435	749,713
Property and equipment, net	25,521	27,330
Operating lease right-of-use assets	27,811	30,569
Restricted cash	1,472	1,472
Other assets	6,409	5,574
Total assets	787,648	814,658
Current liabilities:
Accounts payable	4,189	4,749
Accrued clinical supply costs	5,559	8,748
Accrued liabilities	27,771	27,460
Deferred revenue, current portion	48,231	90,803
Operating lease liabilities, current portion	8,059	7,795
Total current liabilities	93,809	139,555
Deferred revenue, long-term portion	443,370	334,415
Operating lease liabilities, long-term portion	35,268	39,806
Other long-term liabilities	759	158
Total liabilities	573,206	513,934
Commitments and contingencies
Stockholders' equity:
Common stock, $0.0001 par value; 200,000,000 shares authorized; 82,895,718 and 81,986,192 shares issued and outstanding as of December 31, 2022 and December 31, 2021, respectively	8	8
Additional paid-in capital	798,696	748,036
Accumulated other comprehensive loss	(4,575)	(943)
Accumulated deficit	(579,687)	(446,377)
Total stockholders' equity	214,442	300,724
Total liabilities and stockholders' equity	$ 787,648	$ 814,658

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturities of investments were less than one year	$ 640,800
Remaining contractual maturities of investments were less than one year through two years	9,600
Sale of marketable securities	0	$ 10,696	$ 0
US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of instruments in loss position	133,200
Unrealized loss	$ 3,100

Related Party Transactions - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Adimab
Related Party Transaction [Line Items]
Accrued liabilities due to related parties	$ 0	$ 0
Two Thousand Fourteen Adimab Agreement
Related Party Transaction [Line Items]
Related party transaction expenses	$ 200,000	$ 1,000,000.0	$ 0

- Definition

Carrying amount as of the balance sheet date of obligations due all related parties. For classified balance sheets, represents the current portion of such liabilities (due within one year or within the normal operating cycle if longer).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iii)(C))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442552-122756

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(5))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442552-122756

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iv))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442526-122756

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iii)(B))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442526-122756

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(5))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442526-122756

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(a))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(1))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iv))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442552-122756

+ Details

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2022

Accounting Policies [Abstract]

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


	Year Ended December 31,
	2022		2021		2020
	(In thousands)
Cash and cash equivalents	$	154,323	$	329,152	$	49,969
Restricted cash		1,472		1,472		1,472
Total cash, cash equivalents, and restricted cash	$	155,795	$	330,624	$	51,441

Income Taxes - Schedule of Federal and State Income Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Current:
Federal	$ 2,209	$ 0	$ 0
State	1,045	0	0
Income tax provision	$ 3,254	$ 0	$ 0

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

The Company and Liquidity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	Jan. 30, 2020	Dec. 31, 2020
Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Public offerings		9,602,500
Over-Allotment Option
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Public offerings	1,252,500
Follow-on-offering
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Public offerings	9,602,500
Share price	$ 25.00
Proceeds from issuance of common stock, net of underwriting discounts and commissions and offering expenses	$ 224.5

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Total revenue	$ 133,617	$ 207,085	$ 21,098
Type of Revenue [Extensible List]	Collaboration Revenue [Member]	Collaboration Revenue [Member]	Collaboration Revenue [Member]
Operating expenses:
Research and development	$ 210,418	$ 189,407	$ 156,869
General and administrative	61,033	55,038	59,403
Total operating expenses	271,451	244,445	216,272
Loss from operations	(137,834)	(37,360)	(195,174)
Other income, net	7,778	1,031	4,946
Loss before income taxes	(130,056)	(36,329)	(190,228)
Income tax expense	3,254	0	0
Net loss	(133,310)	(36,329)	(190,228)
Unrealized gain (loss) on marketable securities	(3,632)	(1,557)	472
Comprehensive loss	$ (136,942)	$ (37,886)	$ (189,756)
Net loss per share, basic	$ (1.62)	$ (0.45)	$ (2.45)
Net loss per share, diluted	$ (1.62)	$ (0.45)	$ (2.45)
Shares used in computing net loss per share, basic	82,467,587	80,416,936	77,758,806
Shares used in computing net loss per share, diluted	82,467,587	80,416,936	77,758,806

Subsequent Events - Additional Information (Details) $ in Millions	1 Months Ended
	Feb. 28, 2023 USD ($)
Subsequent Event \| AbbVie Biotechnology Limited
Subsequent Event [Line Items]
Milestone payment receivable	$ 17.8

Stock-based Compensation - Summary of Options to Purchase Common Stock (Details) - 2019 Equity Incentive Plan - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options, Outstanding, beginning balance	11,644,070	12,654,998
Number of Options, Granted	4,996,366	3,264,059
Number of Options, Exercised	(298,239)	(2,395,223)
Number of Options, Forfeited	(2,628,925)	(1,879,764)
Number of Options, Outstanding, ending balance	13,713,272	11,644,070
Number of Options, Exercisable	6,776,201
Number of Options, Vested and expected to vest	13,713,272
Weighted average exercise price, Outstanding, beginning balance	$ 16.41	$ 13.96
Weighted average exercise price, Granted	12.11	21.53
Weighted average exercise price, Exercised	10.26	11.91
Weighted average exercise price, Forfeited	18.28	14.55
Weighted average exercise price, Outstanding, ending balance	14.62	$ 16.41
Weighted average exercise price, Exercisable	14.75
Weighted average exercise price, Vested and expected to vest	$ 14.62
Weighted Average Remaining Contractual Term, Outstanding	8 years
Weighted Average Remaining Contractual Term, Exercisable (In years)	7 years
Weighted Average Remaining Contractual Term, Vested and expected to vest (In years)	8 years
Aggregate Intrinsic Value, Outstanding	$ 1,583
Aggregate Intrinsic Value, Exercisable	1,276
Aggregate Intrinsic Value, Vested or expected to vest	$ 1,583