SecProbe.io

Mail Stop 4628
June 29, 2018

William J. Newell
Chief Executive Officer
Sutro Biopharma , Inc.
310 Utah Avenue, Suite 150
South San Francisco, CA 94080

Re: Sutro Biopharma, Inc.
Draft Registration Statement on Form S -1
Submitted June 1, 2018
CIK No.  0001382101

Dear Mr. Newell :

We have reviewed your draft registration statement  and have the following comments.  In
some of our comments, we may ask you to provide us with information so we may better
understand your disclosure.

Please respond to this letter by providing the requested information and either submitting
an amended draft registration statement or publicly filing your registration statement on
EDGAR.  If you do  not believe our comments apply to your facts and circumstances or do not
believe an amendment is appropriate, please tell us why in your response.

After reviewing the information you provide in response to these  comments  and your
amended draft registra tion statement or filed registration statement,  we may have  additional
comments.

Prospectus Summary, page 1

1. We note your disclosure here and in the Business section that your preclinical models for
STRO -001 have demonstrated “potent anti -tumor activity ” and its properties “suggest a
low likelihood of off -target toxicity ” and potential for improved therapeutic index, and
for STRO -002 that your preclinical  models have demonstrated “superior inhibition of
tumor growth” and greater linker stability relative  to the benchmark molecule you
created.  Please revise your disclosure to eliminate any suggestion that your candidates
have been or will ultimately be determined to be safe or effective or to have demonstrated
efficacy for purposes of granting marketing a pproval by the FDA or comparable agency,
including comparisons to the current standard of care.

2. We note your statements in this section and throughout your filing that your product
candidates will be first -in-class and best-in-class , and that your platform allows you to

William J. Newell
Sutro Biopharma, Inc.
June 29 , 2018
Page 2

 accelerate the discovery of first -in-class and best -in-class molecules.  Since these
statements imply an expectation of regulatory approval, they are inappropriate given your
early stage of development and lack of cli nical trial data.  Please remove these statements
and similar statements from the descriptions of your platform and product candidates.

Our Pipeline, page 2

3. We note  your product pipeline table s here and in your Business section include  programs
that are in the discovery phase.  Because you have not identified a product candidate for
these programs , it appears  premature to include them in a product pipeline table.  Please
revise or ad vise.  Please also include in the table columns for Phases 2 and 3 and the
indications intended t o be pursued for each product candidate.

Corporate Information, page 5

4. Please explain the difference between XpressCF and XpressCF+ at an appropriate place
in your filing.

Use of Proceeds, page 68

5. We note your disclosure that the expected net proceeds  of the offering will not be
sufficient to fund any of your product candidates through regulatory approval, and you
will need to raise substantial additional capital to complete the development and
commercialization of your product candidates. Please clari fy the expected stage of
development you expect to achieve with your current assets and the proceeds from this
offering.

Management’s Discussion and Analysis of Financial Condition and Results of Operations, page
79

Critical Accounting Polices and Estimates , page 88

Stock -Based Compensation, page 90

6. Revise the disclosure regarding your estimates of the fair value of stock options granted
to your employees to specify the methods used to determine the fair value of the shares
underlying these award s and to provide additional detail regarding the nature of the
material assumptions involved in making those estimates.   Separately, p rovide us with an
analysis explaining the reasons for material differences between recent valuations of your
common stock and your estimated offering price, once it is available.

William J. Newell
Sutro Biopharma, Inc.
June 29 , 2018
Page 3

 Business, page 94

Our Product Candidates, page 104

7. We note that the studies discussed in this section provide data without providing proper
context for such data.  For each of the studies discusse d in this section, please disclose the
date(s) of the studies, the sponsor and the location; scope and size; dosage and duration;
and actual results observed, including any negative findings.  Please also state whether
you have published the data for any of your studies.

8. You disclose on pages 107 and 111 that the toxicology studies you conducted to
investigate the safety of STRO -001 and STRO -002, respectively, did not result in any
“unexpected toxicity findings. ”  Please revise your disclosure to explain what you mean
by this statement.

Collaboration and License Agreements, page 112

Celgene Collaboration, page 112

9. We note that you are eligible to earn tiered royalties ranging from single -digit to low
double -digit percentages on worldwide sales of any commercial product that may result
from the 2017 Calgene Agreement. This disclosure is too broad and could imply that
your royalty rate is up to 49%.   Please revise your disclosure here and throughout the
prospectus to give investors a reasonable idea of  the amount of the royalty rate that does
not exceed 10 percentage points .

Merck KGaA, Darmstadt, Germany Collaboratio n, page 113

10. We note your disclosure that the MDA Agreement term expires on a product -by-product
and country -by-country basis, and that upon expiration, Merck KGaA, Darmstadt,
Germany will have a fully paid -up, royalty free, perpetual, and irrevocable non -exclusive
license, with the right to grant sublicenses, under certain of your intellectual property
rights.  Please disclose the years , or range of years if more appropriate, in which this
agreement will expire.

Intellectual Property, page 116

11. Please revise your dis closure to clearly identify your material patents or patent
applications, including the patents or patent applications relating to your Xpress CF
Platform, and your product  candidates, STRO -001 and STRO -002.  For each such
material patent or patent application, please disclose (1) whether the patents relate to
XpressCF Plaform or the specific product(s) to which such patents or patent applications
relate; (2) whether the pat ents are owned or licensed from  Stanford or other third parties
(3) the type of patent protection; (4) patent expiration dates and expected expiration dates

William J. Newell
Sutro Biopharma, Inc.
June 29 , 2018
Page 4

 for patent applications; and (5) the jurisdictions where such patents were issued and such
patent a pplications are pendi ng.

Management, page 131

12. We note that your website indicates that you have a scientific advisory board and a
clinical advisory board.  Please revise your disclosure to describe the role or function of
each of your scientific advisory board and clinical advisory board, and whether there are
any rul es of procedures governing these boards.  Please also disclose how members of
such boards are compensated.

Certain Relationships and Related Party Transactions, page 150

Letter Agre ement with Four Oaks, page 151

13. Please revise your disclosure to describe the compensation terms under you letter
agreement with Four Oaks.   In this regard, please clarify whether your future payments to
Four Oaks of amount s equal to 2% of any future payme nts received under your 2017
Celgene Agreement  are your only payment obligations under  the letter agreement .  Please
also file a copy of this agreement as an exhibit or explain why it is not required to be
filed.  Refer to 601(b)(1 0)(ii)(B) of Regulation S -K.

Principal Stockholders, page 153

14. Consistent with Item 403 of Regulation S -K and Exch ange Act Rule 13d -3, please
identify the person or persons who directly or indirectly exercise sole or shared voting
and/or dispositive power with respect to the shares held by Mutual Fund Series Trust, on
behalf of Eventide Healthcare & Life Sciences Fund.

General

15. Please supplementally provide us with copies of all written communications, as defined
in Rule 405 under the Securities Act, that you, or anyon e authorized to do so on your
behalf, present to potential investors in reliance on Section 5(d) of the Securities Act,
whether or not they retain copies of the communications.

16. Please provide us proofs of all graphics, visual, or photographic information you will
provide in the printed prospectus prior to its use, for example in a preliminary prospectus.
Please note that we may have comments regarding this material.

William J. Newell
Sutro Biopharma, Inc.
June 29 , 2018
Page 5

 You may contact  Wei Lu , Staff Accountant, at (202) 551 -3725  or Ethan Horowitz ,
Accounti ng Branch Chief, at 202 -551-3311 if you have questions regarding comments on the
financial s tatements and related matters.  Please contact Irene Barberena -Meissner, Staff
Attorney , at (202) 551 -6548 or Kevin Dougherty, Staff Attorney, at (202) 551 -3271  with any
other questions.

Sincerely,

 /s/ John Reynolds

John Reynolds
Assistant Director
Office of Natural Resources

cc: Rob Freedman , Esq.
Fenwick & West  LLP