X0306 4 2020-10-01 0 0001653087 Alector, Inc. ALEC 0001757770 Rosenthal Arnon C/O ALECTOR, INC. 131 OYSTER POINT BLVD, SUITE 600 SOUTH SAN FRANCISCO CA 94080 1 1 0 0 Chief Executive Officer Stock Option (right to buy) 10.24 2020-10-01 4 A 0 457038 0.00 A 2030-09-30 Common Stock 457038 457038 D One forty-eighth (1/48th) of the shares subject to the option shall vest on the one month anniversary of October 1, 2020 (the "Vesting Commencement Date"), and one forty-eighth (1/48th) of the shares shall vest each month thereafter on the same day of the month as the Vesting Commencement Date (and if there is no corresponding day, on the last day of the month), subject to the Reporting Person continuing to be a service provider to the Issuer through each such date. /s/ Calvin Yu, attorney-in-fact 2020-10-05