X0206 3 2019-06-18 0 0001609809 Seres Therapeutics, Inc. MCRB 0001400240 Flagship Pioneering Inc. 55 CAMBRIDGE PARKWAY CAMBRIDGE MA 02142 0 0 1 0 0001724957 Flagship Pioneering Fund VI General Partner LLC 55 CAMBRIDGE PARKWAY CAMBRIDGE MA 02142 0 0 1 0 0001716926 Flagship Pioneering Fund VI, L.P. 55 CAMBRIDGE PARKWAY CAMBRIDGE MA 02142 0 0 1 0 0001780951 Nutritional Health LTP Fund General Partner LLC 55 CAMBRIDGE PARKWAY CAMBRIDGE MA 02142 0 0 1 0 0001780956 Nutritional Health LTP Fund, L.P. 55 CAMBRIDGE PARKWAY CAMBRIDGE MA 02142 0 0 1 0 Common Stock 4444444 I See Footnote Common Stock 4444444 I See Footnote On June 18, 2019, Flagship Pioneering Fund VI, L.P. ("Flagship Fund VI") acquired 4,444,444 shares pursuant to an underwritten public offering of common stock by the issuer (the "Offering"). The shares are held by Flagship Fund VI. Flagship Pioneering Fund VI General Partner LLC ("Fund VI GP") is the general partner of Flagship Fund VI. Flagship Pioneering, Inc. ("Flagship Pioneering") is the manager of Fund VI GP. Noubar B. Afeyan Ph.D. is the CEO and sole shareholder of Flagship Pioneering and may be deemed to have sole voting and investment power with respect to all shares held by Flagship Fund VI. Each of the reporting persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein. On June 18, 2019, Nutritional Health LTP Fund, L.P. ("Nutritional LTP") acquired 4,444,444 shares pursuant to the Offering. The shares are held by Nutritional LTP. Nutritional Health LTP Fund General Partner LLC ("Nutritional LTP GP") is the general partner of Nutritional LTP. Noubar B. Afeyan Ph.D. is the sole member and manager of Nutritional LTP GP and may be deemed to have sole voting and investment power with respect to all shares held by Nutritional LTP. Each of the reporting persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein. Flagship Pioneering, Inc., By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: CEO 2019-06-28 Flagship Pioneering Fund VI General Partner LLC, By: Flagship Pioneering, Inc., its manager, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: CEO 2019-06-28 Flagship Pioneering Fund VI, L.P., By: Flagship Pioneering Fund VI General Partner LLC, its general partner, By: Flagship Pioneering, Inc., its manager, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: CEO 2019-06-28 Nutritional Health LTP Fund General Partner LLC, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager 2019-06-28 Nutritional Health LTP Fund, L.P., By: Nutritional Health LTP Fund General Partner LLC, its general partner, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager 2019-06-28