Ownership Submission
FORM 4
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN 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
OMB APPROVAL
OMB Number: 3235-0287
Expires: January 31, 2005
Estimated average burden hours per response... 0.5

(Print or Type Responses)
1. Name and Address of Reporting Person *
DesRosier Thomas
   2. Issuer Name and Ticker or Trading Symbol
Seres Therapeutics, Inc. [MCRB] 		5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director _____ 10% Owner
__X__ Officer (give title below) _____ Other (specify below)
See Remarks
(Last)
(First)
(Middle)
C/O SERES THERAPEUTICS, INC., 200 SIDNEY STREET		 3. Date of Earliest Transaction (Month/Day/Year)
01/26/2018
(Street)

CAMBRIDGE, MA 02139		 4. If Amendment, Date Original Filed(Month/Day/Year)
 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 Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)		 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code
(Instr. 8)		 4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)		 5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)		 6. Ownership Form: Direct (D) or Indirect (I)
(Instr. 4)		 7. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V Amount (A) or (D) Price
COMMON STOCK 01/26/2018   M   10,000 A (1) 10,000 D  
COMMON STOCK 01/26/2018   S   3,475 D $ 11.02 6,525 D  

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number. SEC 1474 (9-02)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 3)		 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 4. Transaction Code
(Instr. 8)		 5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4, and 5)		 6. Date Exercisable and Expiration Date
(Month/Day/Year)		 7. Title and Amount of Underlying Securities
(Instr. 3 and 4)		 8. Price of Derivative Security
(Instr. 5)		 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 4)		 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 4)		 11. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
RESTRICTED STOCK UNITS (1) 01/26/2018   M     10,000   (2)   (2) COMMON STOCK 10,000 $ 0 40,000 D  
STOCK OPTION (RIGHT TO BUY) $ 10.42 01/30/2018   A     80,000   (3) 01/29/2028 COMMON STOCK 80,000 $ 0 80,000 D  
STOCK OPTION (RIGHT TO BUY) $ 10.42 01/30/2018   A     100,000   (4) 01/29/2028 COMMON STOCK 100,000 $ 0 100,000 D  

Reporting Owners

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

Signatures

 /s/ Thomas J. DesRosier   01/30/2018
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 4(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) Each restricted stock unit represents a contingent right to receive one share of Issuer common stock.
(2) These restricted stock units have vested and settled or will vest and settle as to 20% of the restricted stock units on January 26, 2018, 30% on January 26, 2019; and 50% on January 26, 2020.
(3) This Option will vest as to 25% of the shares on January 30, 2019. The remainder of the shares will vest in 12 equal quarterly installments thereafter.
(4) This Option will vest as to one third of the shares on January 30, 2019, one third on January 30, 2020 and one third on January 30, 2021.
 
Remarks:
Chief Legal Officer and EVP

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.

Potential persons who are to respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB number.