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Meeting Information            

Date:    June 15, 2016

      Time:  8:00 AM EDT

Location:   Seres Therapeutics, Inc.

200 Sidney Street

            SERES THERAPEUTICS, INC.

            200 SIDNEY STREET

            CAMBRIDGE, MA 02139

Cambridge, MA 02139

You are receiving this communication because you hold shares in the company named above.

This is not a ballot. You cannot use this notice to vote these shares. This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. You may view the proxy materials online at www.proxyvote.com or easily request a paper copy (see reverse side).

We encourage you to access and review all of the important information contained in the proxy materials before voting.

See the reverse side of this notice to obtain proxy materials and voting instructions.

Before You Vote  

Proxy Materials Available to VIEW or RECEIVE:

NOTICE AND PROXY STATEMENT         ANNUAL REPORT        

How to View Online:

Have the information that is printed in the box marked by the arrow (located on the following page) and visit: www.proxyvote.com.

How to Request and Receive a PAPER or E-MAIL Copy:

If you want to receive a paper or e-mail copy of these documents, you must request one. There is NO charge for requesting a copy. Please choose one of the following methods to make your request:

                               1) BY INTERNET:         www.proxyvote.com

                               2) BY TELEPHONE:     1-800-579-1639

                               3) BY E-MAIL*:             sendmaterial@proxyvote.com

*  If requesting materials by e-mail, please send a blank e-mail with the information that is printed in the box marked by the arrow    (located on the following page) in the subject line.

Requests, instructions and other inquiries sent to this e-mail address will NOT be forwarded to your investment advisor. Please make the request as instructed above on or before June 1, 2016 to facilitate timely delivery.

How To Vote  

Vote In Person: Many stockholder meetings have attendance requirements including, but not limited to, the possession of an attendance ticket issued by the entity holding the meeting. Please check the meeting materials for any special requirements for meeting attendance. At the meeting, you will need to request a ballot to vote these shares.

Vote By Internet: To vote now by Internet, go to www.proxyvote.com. Have the information that is printed in the box marked by the arrow   available and follow the instructions.

Vote By Mail: You can vote by mail by requesting a paper copy of the materials, which will include a proxy card.

The Board of Directors recommends you vote FOR

the following:

1.     Election of Directors

        Nominees:

        01)    Dennis A. Ausiello, M.D.

        02)    Roger J. Pomerantz, M.D.         

The Board of Directors recommends you vote FOR the following proposal:

2.     Ratify the appointment of PricewaterhouseCoopers LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2016.

NOTE: To transact such other business as may properly come before the Annual Meeting or any continuation, postponement, or adjournment thereof.