Related Party Transactions	6 Months Ended
Jun. 30, 2022
Related Party Transactions [Abstract]
Related Party Transactions	7. 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 former Chief Executive Officer of Adimab through May 2022 is a Co-founder and Chairperson of the board of directors of Alector. For the three and six months ended June 30, 2022, the Company incurred expenses of less than $0.1 million and $0.2 million, respectively. For the three months ended June 30, 2021, the Company incurred expenses of zero and $1.0 million for milestone payments for progress of programs through clinical trials. The Company had zero accrued liabilities due to Adimab as of June 30, 2022 and December 31, 2021. Under the 2014 Adimab Agreement, the Company has made milestone payments and will also owe low- to mid- single-digit royalty payments for commercial sales of the product candidate. Under the 2019 and 2021 Adimab Agreements, the Company will owe certain milestone payments and low single-digit royalty payments for commercial sales of covered product candidates.

Related Party Transactions

6 Months Ended

Jun. 30, 2022

7. 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 former Chief Executive Officer of Adimab through May 2022 is a Co-founder and Chairperson of the board of directors of Alector. For the three and six months ended June 30, 2022, the Company incurred expenses of less than $0.1 million and $0.2 million, respectively. For the three months ended June 30, 2021, the Company incurred expenses of zero and $1.0 million for milestone payments for progress of programs through clinical trials. The Company had zero accrued liabilities due to Adimab as of June 30, 2022 and December 31, 2021. Under the 2014 Adimab Agreement, the Company has made milestone payments and will also owe low- to mid- single-digit royalty payments for commercial sales of the product

candidate. Under the 2019 and 2021 Adimab Agreements, the Company will owe certain milestone payments and low single-digit royalty payments for commercial sales of covered product candidates.