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 *   Merck & Co., Inc. 2. Date of Event Requiring Statement (Month/Day/Year) 09/26/2018 3. Issuer Name and Ticker or Trading Symbol SUTRO BIOPHARMA INC [STRO] (Last) (First) (Middle) 2000 GALLOPING HILL ROAD 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 Original Filed(Month/Day/Year) (Street) KENILWORTH, NJ 07033 6. Individual or Joint/Group Filing(Check Applicable Line) ___ Form filed by One Reporting Person _X_ 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
Series E Redeemable Convertible Preferred Stock	  (1)	  (1)	Common Stock	2,056,843	$ (1)	I	See Footnote (2)

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Merck & Co., Inc. 2000 GALLOPING HILL ROAD KENILWORTH, NJ 07033	Â	  X	Â	Â
Merck Sharp & Dohme Corp. ONE MERCK DRIVE WHITEHOUSE STATION, NJ 08889	Â	  X	Â	Â

Signatures

Merck & Co., Inc. /s/ Faye C. Brown, Senior Assistant Secretary		09/26/2018
**Signature of Reporting Person		Date
Merck Sharp & Dohme Corp. /s/ Faye C. Brown, Assistant Secretary		09/26/2018
**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)	At any time at the holder's election, each share of the Issuer's Series E redeemable convertible preferred stock (the "Series E Preferred") is convertible into 0.0275 shares of the Issuer's common stock without payment or consideration. Upon the closing of the Issuer's sale of its common stock in its firm commitment underwritten initial public offering pursuant to a registration statement on Form S-1 (File No. 333-227103) under the Securities Act of 1933, as amended, each share of the Series E Preferred will automatically convert into 0.0275 shares of the Issuer's common stock without payment or consideration. The Series E Preferred has no expiration date. The number of underlying shares of common stock reported in Column 3 reflects a 36.3-for-1 reverse stock split that became effective on September 14, 2018.
(2)	These securities are owned directly by Merck Sharp & Dohme Corp., which is a direct, wholly owned subsidiary of Merck & Co., Inc. ("Merck"). Merck is an indirect beneficial owner of the reported securities.

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