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.