Ownership Submission
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, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
  Chapman Marcus
 2. Date of Event Requiring Statement (Month/Day/Year)
04/18/2019		 3. Issuer Name and Ticker or Trading Symbol
Seres Therapeutics, Inc. [MCRB]
(Last)
(First)
(Middle)
C/O SERES THERAPEUTICS, INC., 200 SIDNEY STREET		 4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director _____ 10% Owner
__X__ Officer (give title below) _____ Other (specify below)
See Remarks
 5. If Amendment, Date Original Filed(Month/Day/Year)
(Street)

CAMBRIDGE, MA 02139		 6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
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)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly. SEC 1473 (7-02)
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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 of Derivative Security: 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
Stock Option (Right to Buy)   (1) 03/24/2025 Common Stock 25,000 $ 15.77 D  
Stock Option (Right to Buy)   (2) 01/31/2026 Common Stock 12,500 $ 26.2 D  
Stock Option (Right to Buy)   (3) 01/25/2027 Common Stock 10,000 $ 9.89 D  
Stock Option (Right to Buy)   (4) 01/29/2028 Common Stock 18,000 $ 10.42 D  
Restricted Stock Units   (5)   (6) Common Stock 12,000 $ (7) D  
Stock Option (Right to Buy)   (8) 01/31/2029 Common Stock 23,000 $ 6.38 D  

Reporting Owners

Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
Chapman Marcus
C/O SERES THERAPEUTICS, INC.
200 SIDNEY STREET
CAMBRIDGE, MA 02139		       See Remarks  

Signatures

/s/ Thomas J. DesRosier, Attorney-in-fact for Marcus Chapman 04/24/2019
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 5(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1) The option is fully vested and exercisable.
(2) The option has vested as to 25% of the shares on February 1, 2017. The remainder of the shares will vest or have vested in 12 equal quarterly installments thereafter.
(3) The option has vested as to 25% of the shares on January 26, 2018. The remainder of the shares will vest or have vested in 12 equal quarterly installments thereafter.
(4) The option has vested as to 25% of the shares on January 30, 2019. The remainder of the shares will vest or have vested in 12 equal quarterly installments thereafter.
(5) These restricted stock units will vest in full on November 1, 2019.
(6) Not applicable.
(7) Each restricted stock unit represents a contingent right to receive one share of Issuer common stock.
(8) This option will vest as to 25% of the shares on February 1, 2020. The remainder of the shares will vest in 12 equal quarterly installments thereafter.
 
Remarks:
Exhibit List: Exhibit 24 - Power of Attorney

Principal Financial and Accounting Officer

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