X0508 4 2023-08-22 0 0001653087 Alector, Inc. ALEC 0001117003 MCGUIRE TERRANCE C/O POLARIS VENTURE PARTNERS LP ONE MARINA PARK DRIVE, 8TH FLOOR BOSTON MA 02210 1 0 1 0 0 Common Stock 2023-08-22 4 J 0 500000 0.00 D 11353817 I See footnote Common Stock 2023-08-22 4 J 0 6429 0.00 A 54996 D Common Stock 2023-08-22 4 J 0 98533 0.00 A 98553 I See footnote Common Stock 2023-08-22 4 J 0 98533 0.00 D 0 I See footnote Common Stock 2023-08-22 4 J 0 13133 0.00 A 39399 I See footnote Represents a pro-rata distribution, and not a purchase or sale, without additional consideration by Polaris Venture Partners Founders' Fund VI, L.P. ("PVPFF VI"), Polaris Venture Partners VI (AIV), L.P. ("PVP VI AIV") and Polaris Venture Partners VI (AIV-B), L.P. (p/k/a PVP VI (AIV) Feeder Corp. Holding Partnership, L.P., "PVP VI AIV-B" and, together with PVPFF VI, PVP VI AIV and Polaris Venture Partners VI, L.P. ("PVP VI"), the "Polaris Funds"). 27,606 shares were distributed by PVPFF VI, 379,180 shares were distributed by PVP VI AIV and 93,214 shares were distributed by PVP VI AIV-B. The general partner of each of the Polaris Funds is Polaris Venture Management Co. VI, L.L.C. ("PVM"). Each of Amir Nashat, Brian Chee, David Barrett, Bryce Youngren, Jonathan Flint, and the Reporting Person, a member of the Issuer's board of directors, are managing members of PVM (collectively, the "Managing Members") and may be deemed to have shared power to vote and dispose of the shares held by the Polaris Funds. (Continued from footnote 2) Each of the Managing Members and PVM disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that any of them is the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their respective pecuniary interest therein. 626,857 shares are held by PVPFF VI, 8,210,184 shares are held by PVP VI AIV, 2,018,308 shares are held by PVP VI AIV-B and 498,468 shares are held by PVP VI. Each of the Managing Members and PVM disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that any of them is the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their respective pecuniary interest therein. Represents a change in the form of ownership of the Reporting Person by virtue of the receipt of shares in the pro-rata in-kind distribution of common stock of the Issuer for no consideration by PVPFF VI. 26,250 of such shares are represented by restricted stock units, or RSUs, which vest on the earlier of (i) June 14, 2024 or (ii) the date of the Issuer's next annual meeting of stockholders. Represents a change in the form of ownership of PVM by virtue of the receipt of shares in the pro-rata in-kind distribution of common stock of the Issuer for no consideration by the Polaris Funds. Shares held by PVM. 276 shares received from PVPFF VI, 78,869 shares received from PVP VI AIV and 19,388 shares received from PVP VI AIV-B. The Managing Members, including the Reporting Person who is a member of the Issuer's board of directors, are managing members of PVM and may be deemed to have shared power to vote and dispose of the shares held by the Polaris Funds. (Continued from footnote 8) Each of the Managing Members disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that any of them is the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their respective pecuniary interest therein. Represents a pro-rata distribution, and not a purchase or sale, without additional consideration by PVM to its members. Represents a change in the form of ownership of McGuire Family 2008 GST Non-Exempt Irrevocable Trust ("McGuire Family Trust") by virtue of the receipt of shares in the pro-rata in-kind distribution of common stock of the Issuer for no consideration by PVM. Shares held by McGuire Family Trust. The Reporting Person, a member of the Issuer's board of directors, is the donor of McGuire Family Trust and may be deemed to have shared power to vote and dispose of the shares held by McGuire Family Trust. /s/ Lauren Crockett, as attorney in fact for Terrance G. McGuire 2023-08-24