X0306 4 2021-07-02 0 0001653087 Alector, Inc. ALEC 0001635264 King Robert C/O ALECTOR, INC. 131 OYSTER POINT BLVD, SUITE 600 SOUTH SAN FRANCISCO CA 94080 0 1 0 0 Chief Development Officer Common Stock 2021-07-02 4 M 0 30000 8.16 A 552317 D Common Stock 2021-07-02 4 M 0 30000 10.14 A 582317 D Common Stock 2021-07-02 4 S 0 60000 31.14 D 522317 D Employee Stock Option (right to buy) 8.16 2021-07-02 4 M 0 30000 0.00 D 2028-07-02 Common Stock 30000 120000 D Employee Stock Option (right to buy) 10.14 2021-07-02 4 M 0 30000 0.00 D 2028-11-06 Common Stock 30000 70000 D The sales reported by the Reporting Person were effected pursuant to a Rule 10b5-1 trading plan adopted on May 19, 2020. Shares subject to the option vest in 48 equal monthly installments beginning on August 2, 2018. One fourth (1/4th) of the shares subject to the option vested on November 1, 2019, and one forty-eighth (1/48th) of the shares subject to the option vest each month thereafter. /s/ David Oh, attorney in fact 2021-07-07