X0306 4 2019-02-11 0 0001653087 Alector, Inc. ALEC 0001117003 MCGUIRE TERRANCE C/O POLARIS VENTURE PARTNERS LP ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON MA 02210 1 0 0 0 Common Stock 2019-02-11 4 C 0 500000 A 500000 I See footnote Common Stock 2019-02-11 4 C 0 5274725 A 5774725 I See footnotes Common Stock 2019-02-11 4 C 0 2500000 A 8274725 I See footnotes Common Stock 2019-02-11 4 C 0 2808989 A 11083714 I See footnotes Common Stock 2019-02-11 4 C 0 1246883 A 12330597 I See footnotes Common Stock 2019-02-11 4 C 0 527597 A 12858194 I See footnotes Series A-1 Preferred Stock 2019-02-11 4 C 0 500000 0.00 D Common Stock 500000 0 I See footnote Series A-2 Preferred Stock 2019-02-11 4 C 0 5274725 0.00 D Common Stock 5274725 0 I See footnote Series B Preferred Stock 2019-02-11 4 C 0 2500000 0.00 D Common Stock 2500000 0 I See footnote Series C Preferred Stock 2019-02-11 4 C 0 2808989 0.00 D Common Stock 2808989 0 I See footnote Series D Preferred Stock 2019-02-11 4 C 0 1246883 0.00 D Common Stock 1246883 0 I See footnote Series E Preferred Stock 2019-02-11 4 C 0 527597 0.00 D Common Stock 527597 0 I See footnote All of the reported securities are held directly by the Polaris Funds (as defined below). Each of the Series A-1 Preferred Stock, Series A-2 Preferred Stock, Series B Preferred Stock, Series C Preferred Stock, Series D Preferred Stock and Series E Preferred Stock converted into Common Stock on a one-for-one basis upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. 27,606 shares are held by Polaris Venture Partners Founders' Fund VI, L.P ("PVPFF VI"), 379,174 shares are held by Polaris Venture Partners VI (AIV), L.P. ("PVP VI AIV") and 93,220 shares are held by PVP VI (AIV) Feeder Corp. Holding Partnership, L.P. ("PVP VI Feeder" and, together with PVP VI AIV, PVPFF VI, and Polaris Venture Partners VI, L.P. ("PVP VI"), the "Polaris Funds"). The general partner of each of the Polaris Funds is Polaris Venture Management Co. VI, L.L.C. ("PVM"). PVM may be deemed to have sole power to vote and dispose of the shares held by the Polaris Funds. Amir Nashat, Brian Chee, David Barrett, Bryce Youngren, Jon Flint, and the reporting person are managing members of PVM. The reporting person disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that the reporting person is the beneficial owner of such securities, except to the extent of his pecuniary interest therein, if any. 291,223 shares are held by PVPFF VI, 4,000,075 shares are held by PVP VI AIV and 983,427 shares are held by PVP VI Feeder. The reporting person disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that the reporting person is the beneficial owner of such securities, except to the extent of his pecuniary interest therein, if any. 138,030 shares are held by PVPFF VI, 1,895,867 shares are held by PVP VI AIV and 466,103 shares are held by PVP VI Feeder. The reporting person disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that the reporting person is the beneficial owner of such securities, except to the extent of his pecuniary interest therein, if any. 155,087 shares are held by PVPFF VI, 2,130,190 shares are held by PVP VI AIV and 523,712 shares are held by PVP VI Feeder. The reporting person disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that the reporting person is the beneficial owner of such securities, except to the extent of his pecuniary interest therein, if any. 68,842 shares are held by PVPFF VI, 945,571 shares are held by PVP VI AIV and 232,470 shares are held by PVP VI Feeder. The reporting person disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that the reporting person is the beneficial owner of such securities, except to the extent of his pecuniary interest therein, if any. 29,129 shares are held by PVPFF VI and 498,468 shares are held by PVP VI. The reporting person disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that the reporting person is the beneficial owner of such securities, except to the extent of his pecuniary interest therein, if any. /s/ Terrance McGuire 2019-02-13