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

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(Print or Type Responses)

1. Name and Address of Reporting Person * Merck & Co., Inc.   2. Issuer Name and Ticker or Trading Symbol SUTRO BIOPHARMA INC [STRO] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 2000 GALLOPING HILL ROAD 3. Date of Earliest Transaction (Month/Day/Year) 10/01/2018 (Street) KENILWORTH, NJ 07033 4. If Amendment, Date Original Filed(Month/Day/Year) 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 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 10/01/2018   C   2,056,843 A (1) 2,056,843 I See Footnote (2) Common Stock 10/01/2018   P   666,666 A $ 15 2,723,509 I See Footnote (2)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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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

Series E Redeemable Convertible Preferred Stock

(1)

10/01/2018

C

74,794,315

(1)

(1)

Common Stock

2,056,843

$ 0

0

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		X
Merck Sharp & Dohme Corp. ONE MERCK DRIVE WHITEHOUSE STATION, NJ 08889		X

Signatures

Merck & Co., Inc. /s/ Faye C. Brown, Senior Assistant Secretary		10/02/2018
**Signature of Reporting Person		Date
Merck Sharp & Dohme Corp. /s/ Faye C. Brown, Assistant Secretary		10/02/2018
**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 share of Series E redeemable convertible preferred stock (the "Series E Preferred") automatically converted into 0.0275 shares of the Issuer's common stock 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. The Series E Preferred had no expiration date.
(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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