SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person* Flagship Pioneering Inc. (Last) (First) (Middle) 55 CAMBRIDGE PARKWAY (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)	2. Date of Event Requiring Statement (Month/Day/Year) 06/18/2019	3. Issuer Name and Ticker or Trading Symbol Seres Therapeutics, Inc. [ MCRB ]
		4. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)	5. If Amendment, Date of Original Filed (Month/Day/Year)
			6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)
Common Stock	4,444,444(1)	I	See Footnote(2)
Common Stock	4,444,444(3)	I	See Footnote(4)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

1. Name and Address of Reporting Person* Flagship Pioneering Inc. (Last) (First) (Middle) 55 CAMBRIDGE PARKWAY (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)

1. Name and Address of Reporting Person* Flagship Pioneering Fund VI General Partner LLC (Last) (First) (Middle) 55 CAMBRIDGE PARKWAY (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)

1. Name and Address of Reporting Person* Flagship Pioneering Fund VI, L.P. (Last) (First) (Middle) 55 CAMBRIDGE PARKWAY (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)

1. Name and Address of Reporting Person* Nutritional Health LTP Fund General Partner LLC (Last) (First) (Middle) 55 CAMBRIDGE PARKWAY (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)

1. Name and Address of Reporting Person* Nutritional Health LTP Fund, L.P. (Last) (First) (Middle) 55 CAMBRIDGE PARKWAY (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)

Explanation of Responses:

1. 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").

2. 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.

3. On June 18, 2019, Nutritional Health LTP Fund, L.P. ("Nutritional LTP") acquired 4,444,444 shares pursuant to the Offering.

4. 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.

Remarks:

	Flagship Pioneering, Inc., By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: CEO	06/28/2019
	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	06/28/2019
	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	06/28/2019
	Nutritional Health LTP Fund General Partner LLC, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager	06/28/2019
	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	06/28/2019
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 5 (b)(v).
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