X0306 4 2021-05-17 0 0001609809 Seres Therapeutics, Inc. MCRB 0001780951 Nutritional Health LTP Fund General Partner LLC 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001780956 Nutritional Health LTP Fund, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001222012 AFEYAN NOUBAR 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 Common Stock 2021-05-17 4 J 0 295171 0.00 D 2962963 I See Footnote Common Stock 4434600 I See Footnote Common Stock 1283282 I See Footnote Common Stock 2962963 I See Footnote Common Stock 2734994 I See Footnote Common Stock 376018 I See Footnote On May 17, 2021, Nutritional Health LTP Fund, L.P. ("Nutritional LTP") distributed to its limited partner(s), pro rata and without consideration, 295,171 shares of the Issuer's common stock. The aforementioned distribution was made in accordance with the exemptions afforded by Rule 16a-13 and Rule 16a-9 of the Securities Exchange Act of 1934, as amended. Shares 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. Each of the reporting persons except for Nutritional LTP disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Shares held by Flagship Ventures Fund IV, L.P. ("Flagship Fund IV"). Flagship Ventures Fund IV General Partner LLC ("Flagship Fund IV GP") is the general partner of Flagship Fund IV. Noubar B. Afeyan, Ph.D. is the sole manager of Flagship Fund IV GP. Each of the reporting persons except for Flagship Fund IV disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Shares held by Flagship Ventures Fund IV-Rx, L.P. ("Flagship Fund IV-Rx"). Flagship Fund IV GP is the general partner of Flagship Fund IV-Rx. Noubar B. Afeyan, Ph.D. is the sole manager of Flagship Fund IV GP. Each of the reporting persons except for Flagship Fund IV-Rx disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Shares held by Flagship Pioneering Fund VI, L.P. ("Flagship Fund VI"). Flagship Pioneering Fund VI General Partner LLC ("Flagship Fund VI GP") is the general partner of Flagship Fund VI. Flagship Pioneering, Inc. ("Flagship Pioneering") is the manager of Flagship Fund VI GP. Noubar B. Afeyan Ph.D. is the CEO, sole shareholder and director of Flagship Pioneering. Each of the reporting persons except Flagship Fund VI disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Shares held by Flagship VentureLabs IV LLC ("VentureLabs IV"). Flagship Fund IV is a member of VentureLabs IV and also serves as its manager. Each of the reporting persons except VentureLabs IV disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Shares held by Noubar B. Afeyan, Ph.D. Each of the reporting persons except for Noubar B. Afeyan, Ph.D. disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Includes 12,853 shares held through a trust for the benefit of Dr. Afeyan's children. Dr. Afeyan disclaims Section 16 beneficial ownership of these shares except to the extent of his pecuniary interest therein, and this report shall not be deemed an admission that the reporting person is the beneficial owner of such shares for Section 16 or any other purpose. Nutritional Health LTP Fund General Partner LLC, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager 2021-05-19 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 2021-05-19 Noubar B. Afeyan, Ph.D., by: /s/ Noubar B. Afeyan 2021-05-19