X0306 4 2020-07-28 1 0001528115 Annexon, Inc. ANNX 0001597143 Clarus Lifesciences III, L.P. 101 MAIN STREET, SUITE 1210 CAMBRIDGE MA 02142 0 0 1 0 0001620148 Clarus Ventures III GP, L.P. 101 MAIN STREET, SUITE 1210 CAMBRIDGE MA 02142 0 0 1 0 0001762202 Blackstone Clarus III L.L.C. C/O THE BLACKSTONE GROUP INC. 345 PARK AVENUE NEW YORK NY 10154 0 0 1 0 0001484870 Blackstone Holdings II L.P. C/O THE BLACKSTONE GROUP INC. 345 PARK AVENUE NEW YORK NY 10154 0 0 1 0 0001464695 Blackstone Holdings I/II GP L.L.C. C/O THE BLACKSTONE GROUP INC. 345 PARK AVENUE NEW YORK NY 10154 0 0 1 0 0001393818 Blackstone Group Inc 345 PARK AVENUE NEW YORK NY 10154 0 0 1 0 0001404071 Blackstone Group Management L.L.C. C/O THE BLACKSTONE GROUP INC. 345 PARK AVENUE NEW YORK NY 10154 0 0 1 0 0001070844 SCHWARZMAN STEPHEN A C/O THE BLACKSTONE GROUP INC. 345 PARK AVENUE NEW YORK NY 10154 0 0 1 0 Common Stock 2020-07-28 4 C 0 643208 A 643208 I See Footnotes Common Stock 2020-07-28 4 C 0 950134 A 1593342 I See Footnotes Common Stock 2020-07-28 4 C 0 697860 A 2291202 I See Footnotes Common Stock 2020-07-28 4 C 0 239433 A 2530635 I See Footnotes Common Stock 2020-07-28 4 P 0 200000 17.00 A 2730635 I See Footnotes Series A-1 Redeemable Convertible Preferred Stock 2020-07-28 4 C 0 5666667 D Common Stock 643208 0 I See Footnotes Series B Redeemable Convertible Preferred Stock 2020-07-28 4 C 0 8370685 D Common Stock 950134 0 I See Footnotes Series C Redeemable Convertible Preferred Stock 2020-07-28 4 C 0 6148147 D Common Stock 697860 0 I See Footnotes Series D Redeemable Convertible Preferred Stock 2020-07-28 4 C 0 2109407 D Common Stock 239433 0 I See Footnotes The shares of Series A-1 Redeemable Convertible Preferred Stock of the Issuer were automatically converted on a 1-for-8.81 basis into common stock of the Issuer ("Common Stock") immediately prior to the closing of the Issuer's initial public offering. The shares of Series B Redeemable Convertible Preferred Stock of the Issuer were automatically converted on a 1-for-8.81 basis into Common Stock immediately prior to the closing of the Issuer's initial public offering. The shares of Series C Redeemable Convertible Preferred Stock of the Issuer were automatically converted on a 1-for-8.81 basis into Common Stock immediately prior to the closing of the Issuer's initial public offering. The shares of Series D Redeemable Convertible Preferred Stock of the Issuer were automatically converted on a 1-for-8.81 basis into Common Stock immediately prior to the closing of the Issuer's initial public offering. Reflects securities held directly by Clarus Lifesciences III, L.P. Clarus Ventures III GP, L.P. is the general partner of Clarus Lifesciences III, L.P. Blackstone Clarus III L.L.C. is the general partner of Clarus Ventures III GP, L.P. The sole member of Blackstone Clarus III L.L.C. is Blackstone Holdings II L.P. The general partner of Blackstone Holdings II L.P. is Blackstone Holdings I/II GP L.L.C. The sole member of Blackstone Holdings I/II GP L.L.C. is The Blackstone Group Inc. The sole holder of the Class C common stock of The Blackstone Group Inc. is Blackstone Group Management L.L.C. Blackstone Group Management L.L.C. is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person. Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934, each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the reported securities for purposes of Section 16 or for any other purpose. CLARUS LIFESCIENCES III, L.P., By: Clarus Ventures III GP, L.P., its GP, By: Blackstone Clarus III L.L.C., its GP, By: Blackstone Holdings II L.P., its managing member, By: Blackstone Holdings I/II GP L.L.C., its GP, By /s/ John G. Finley, Title: CLO 2020-07-30 CLARUS VENTURES III GP, L.P., By: Blackstone Clarus III L.L.C., its GP, By: Blackstone Holdings II L.P., its managing member, By: Blackstone Holdings I/II GP L.L.C., its GP, By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 2020-07-30 BLACKSTONE CLARUS III L.L.C., By: Blackstone Holdings II L.P., its managing member, By: Blackstone Holdings I/II GP L.L.C., its general partner, By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 2020-07-30 BLACKSTONE HOLDINGS II L.P., By: Blackstone Holdings I/II GP L.L.C., its general partner, By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 2020-07-30 BLACKSTONE HOLDINGS I/II GP L.L.C., By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 2020-07-30 THE BLACKSTONE GROUP INC., By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 2020-07-30 BLACKSTONE GROUP MANAGEMENT L.L.C., By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 2020-07-30 /s/ Stephen A. Schwarzman 2020-07-30