X0306 4 2016-04-01 0 0001609809 Seres Therapeutics, Inc. MCRB 0001233684 COOK DAVID N C/O SERES THERAPEUTICS, INC. 215 FIRST STREET CAMBRIDGE MA 02142 0 1 0 0 Chief Scientific Officer & EVP Common Stock 2016-04-01 4 S 0 46650 25.74 D 183023 D Common Stock 2016-04-01 4 S 0 6350 26.90 D 176673 D Common Stock 2016-04-04 4 S 0 8000 28.00 D 168673 D The transactions reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person. The price reported is a weighted average price. These shares were sold in multiple transactions at per share prices ranging from $25.27 to $26.21. 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 price reported is a weighted average price. These shares were sold in multiple transactions at per share prices ranging from $26.32 to $27.15. 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. /s/ Roger J. Pomerantz, Attorney-in-Fact 2016-04-05