144 0001895592 XXXXXXXX LIVE 0001653087 Alector, Inc. 001-38792 131 Oyster Point Blvd. Suite 600 South San Francisco CA 94080 (415)-231-5660 Sara Kenkare-Mitra Officer Common Stock Morgan Stanley Smith Barney LLC Executive Services

200 W Civic Center Dr. 4th Floor Sandy UT 84070

12519 69606 84136381 12/04/2023 Nasdaq Common Stock 12/01/2023 Vesting of Restricted Stock Units Issuer N 25246 12/01/2023 (1) N Sara Kenkare-Mitra

C/O Alector, Inc. 131 Oyster Point Blvd., Suite 600 South San Francisco CA 94080

Common Stock 09/05/2023 6214 32277 (1) The securities to be sold were received upon the settlement of vested restricted stock units, or RSUs. The reported shares will be sold to satisfy the reporting person's tax obligations in connection with the vesting of RSUs. 12/01/2023 /s/ Jordan Hochstrasser, by power of attorney