X0306 4 2019-01-25 0 0001609809 Seres Therapeutics, Inc. MCRB 0001435744 DesRosier Thomas C/O SERES THERAPEUTICS, INC. 200 SIDNEY STREET CAMBRIDGE MA 02139 0 1 0 0 Chief Legal Officer and EVP COMMON STOCK 2019-01-26 4 M 0 15000 A 21525 D COMMON STOCK 2019-01-28 4 S 0 5471 5.7536 D 16054 D STOCK OPTION (RIGHT TO BUY) 6.01 2019-01-25 4 A 0 84800 0.00 A 2029-01-24 Common Stock 84800 84800 D RESTRICTED STOCK UNITS 2019-01-26 4 M 0 15000 0.00 D Common Stock 15000 25000 D Each restricted stock unit represents a contingent right to receive one share of Issuer common stock. The price reported is a weighted average price. These shares were sold in multiple transactions at per share prices ranging from $5.75 to $5.8435. The Reporting Person undertakes to provide upon request to the SEC staff, the Issuer, or any stockholder of the Issuer, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The option will vest as to 25% of the shares on January 25, 2020. The remainder of the shares will vest in 12 equal quarterly installments thereafter. These restricted stock units have vested and settled or will vest and settle as to 20% of the restricted stock units on January 26, 2018, 30% on January 26, 2019, and 50% on January 26, 2020. /s/ Thomas J. DesRosier 2019-01-29