UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

o

Rule 13d-1(b)

x

Rule 13d-1(c)

o

Rule 13d-1(d)

CUSIP No. 869367102

1

Name of Reporting Persons.

I.R.S. Identification Nos. of Above Persons (Entities Only).
Merck & Co., Inc.

2

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3

SEC Use Only

4

Citizenship or Place of Organization
New Jersey

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With:

5

Sole Voting Power
2,723,509

6

Shared Voting Power
0

7

Sole Dispositive Power
2,723,509

8

Shared Dispositive Power
0

9

Aggregate Amount Beneficially Owned by Each Reporting Person
2,723,509

10

Check Box if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11

Percent of Class Represented by Amount in Row (9)
11.9%*

12

Type of Reporting Person (See Instructions)
CO

CUSIP No. 869367102

1

Name of Reporting Persons.

I.R.S. Identification Nos. of Above Persons (Entities Only).
Merck Sharp & Dohme Corp.

2

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3

SEC Use Only

4

Citizenship or Place of Organization
New Jersey

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With:

5

Sole Voting Power
2,723,509

6

Shared Voting Power
0

7

Sole Dispositive Power
2,723,509

8

Shared Dispositive Power
0

9

Aggregate Amount Beneficially Owned by Each Reporting Person
2,723,509

10

Check Box if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11

Percent of Class Represented by Amount in Row (9)
11.9%*

12

Type of Reporting Person (See Instructions)
CO

Item 1.

(a)

Name of Issuer
Sutro Biopharma, Inc.

(b)

Address of Issuer’s Principal Executive Offices
310 Utah Avenue, Suite 150

South San Francisco, CA 94080

Item 2.

(a)

Name of Person Filing
(1) Merck & Co., Inc.

(2) Merck Sharp & Dohme Corp.

(b)

Address of Principal Business Office or, if none, Residence
(1) Merck & Co., Inc.: 2000 Galloping Hill Road, Kenilworth, NJ 07033

(2) Merck Sharp & Dohme Corp.: One Merck Drive, Whitehouse Station, NJ 08889

(c)

Citizenship
(1) Merck & Co., Inc.: New Jersey

(2) Merck Sharp & Dohme Corp.: New Jersey

(d)

Title of Class of Securities
Common Stock

(e)

CUSIP Number
869367102

Item 3.

If this statement is filed pursuant to Rule 13d-1(b), or 13d-2(b) or (c), check whether the person filing is a:

Not applicable.

Item 4.

Ownership.

(a)

Amount beneficially owned: 

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

(a)

Amount beneficially owned:    2,723,509

The reported securities are owned directly by Merck Sharp & Dohme Corp. (“MSD”), which is a direct, wholly owned subsidiary of Merck & Co., Inc. (“Merck”). Merck is an indirect beneficial owner of the reported securities.

(b)

Percent of class:    11.9%

Based on 22,823,630 shares of the Issuer’s common stock outstanding immediately following the Issuer’s public offering, which includes the full exercise of the underwriters’ over-allotment option, as reported in the Issuer’s Prospectus filed pursuant to Rule 424(b)(4) with the Securities and Exchange Commission on September 27, 2018, which is part of the Issuer’s Registration Statement.

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote:   

See Cover Pages Items 5-9

(ii)

Shared power to vote or to direct the vote:    

See Cover Pages Items 5-9

(iii)

Sole power to dispose or to direct the disposition of:   

See Cover Pages Items 5-9

(iv)

Shared power to dispose or to direct the disposition of:   

See Cover Pages Items 5-9.

Item 5.

Ownership of Five Percent or Less of a Class.

Not applicable.

Item 6.

Ownership of More than Five Percent on Behalf of Another Person.

Not applicable.

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company.

Not applicable.

Item 8.

Identification and Classification of Members of the Group.

Not applicable.

Item 9.

Notice of Dissolution of Group.

Not applicable.

Item 10.

Certification.

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

Date: October 4, 2018

MERCK & CO., INC.

By:

/s/ Faye C. Brown

Name: Faye C. Brown

Title: Senior Assistant Secretary

MERCK SHARP & DOHME CORP.

By:

/s/ Faye C. Brown

Name: Faye C. Brown

Title: Assistant Secretary

MERCK & CO., INC.

By:

/s/ Faye C. Brown

Name: Faye C. Brown

Title: Senior Assistant Secretary

MERCK SHARP & DOHME CORP.

By:

/s/ Faye C. Brown

Name: Faye C. Brown

Title: Assistant Secretary