Exhibit 4.2

NUMBER
ST
SERES
THERAPEUTICS™
Seres Therapeutics, Inc.
INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE
SHARES
SEE REVERSE FOR CERTAIN DEFINITIONS
CUSIP 81750R 10 2
This Certifies that
SPECIMEN
is the owner of
FULLY PAID AND NON-ASSESSABLE SHARES OF THE COMMON STOCK PAR VALUE $0.001 PER SHARE OF
Seres Therapeutics, Inc.
transferable on the books of the Corporation in person or by duly authorized attorney upon surrender of this certificate properly endorsed.
This certificate is not valid unless countersigned and registered by the Transfer Agent and Registrar. WITNESS the facsimile signatures of the duly authorized officers of the Corporation.
CERTIFICATE OF STOCK
DATED
COUNTERSIGNED AND REGISTERED:
AMERICAN STOCK TRANSFER & TRUST COMPANY, LLC
(Brooklyn, NY)
TRANSFER AGENT AND REGISTRAR BY:
AUTHORIZED SIGNATURE
CHIEF FINANCIAL OFFICER AND TREASURER
PRESIDENT AND CHIEF EXECUTIVE OFFICER
SECURITY COLUMBIAN UNITED STATES BANKNOTE COMPANY 1960

SERES THERAPEUTICS, INC.

THE CORPORATION IS AUTHORIZED TO ISSUE TWO CLASSES OF STOCK, COMMON STOCK AND PREFERRED STOCK. THE COMPANY WILL FURNISH WITHOUT CHARGE TO EACH SHAREHOLDER WHO SO REQUESTS, A SUMMARY OF THE POWERS, DESIGNATIONS, PREFERENCES AND RELATIVE, PARTICIPATING, OPTIONAL, OR OTHER SPECIAL RIGHTS OF EACH CLASS OF STOCK OF THE COMPANY AND THE QUALIFICATIONS, LIMITATIONS OR RESTRICTIONS OF SUCH PREFERENCES AND/OR RIGHTS, AND THE VARIATIONS IN RIGHTS, PREFERENCES AND LIMITATIONS DETERMINED FOR EACH SERIES WHICH ARE FIXED BY THE CERTIFICATE OF INCORPORATION OF THE COMPANY AND THE AUTHORITY OF THE BOARD OF DIRECTORS TO DETERMINE VARIATIONS FOR FUTURE SERIES. SUCH REQUEST MAY BE MADE TO THE OFFICE OF THE SECRETARY OF THE COMPANY OR TO THE TRANSFER AGENT.

The following abbreviations, when used in the inscription on the face of this certificate, shall be construed as though they were written out in full according to applicable laws or regulations:

TEN COM	—	as tenants in common	UNIF GIFT MIN ACT	—			Custodian
TEN ENT	—	as tenants by the entireties			(Cust)			(Minor)
JT TEN	—	as joint tenants with right of survivorship and not as tenants in common			under Uniform Gifts to Minors
					Act
						(State)

Additional abbreviations may also be used though not in the above list.

For value received,                                          hereby sells, assigns and transfers unto

PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER OF ASSIGNEE

(PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING ZIP CODE, OF ASSIGNEE)

	shares
represented by the within Certificate, and does hereby irrevocably constitute and appoint

	, attorney
to transfer the said shares on the books of the within named Corporation with full power of substitution in the premises.

Dated

NOTICE: THE SIGNATURE TO THIS ASSIGNMENT MUST CORRESPOND WITH THE NAME AS WRITTEN UPON THE FACE OF THE CERTIFICATE IN EVERY PARTICULAR, WITHOUT ALTERATION OR ENLARGEMENT OR ANY CHANGE WHATEVER.

Signature(s) Guaranteed:

THE SIGNATURE(S) MUST BE GUARANTEED BY AN ELIGIBLE GUARANTOR INSTITUTION (BANKS, STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS AND CREDIT UNIONS WITH MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM), PURSUANT TO S.E.C. RULE 17Ad-15.