February 15, 2019

William Hinshaw
Chief Executive Officer
Axcella Health Inc.
840 Memorial Drive
Cambridge, MA 02139

       Re: Axcella Health Inc.
           Draft Registration Statement on Form S-1
           Submitted January 28, 2019
           CIK No. 0001633070

Dear Mr. Hinshaw:

       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
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 registration statement or filed registration statement, we may
have additional

Draft Registration Statement on Form S-1 filed January 28, 2019

Prospectus Summary
Overview, page 1

1.     We note your disclosure on page 1 that, "We believe generating this rich
human dataset at
       this early stage of development eliminates translational uncertainty."
Please revise to
       clarify "translational uncertainty."
Our Pipeline, page 2

2.     Given the early stage of development of AXA4010, and limited disclosure
you have
       provided with respect to such product candidate, please provide uswith
an analysis as to
       why inclusion of AXA4010 in the pipeline table here and on page 111 is
appropriate. The
 William Hinshaw
FirstName LastNameWilliam Hinshaw
Axcella Health Inc.
Comapany NameAxcella Health Inc.
February 15, 2019
February 15, 2019 Page 2
Page 2
FirstName LastName
         table is intended to provide information about your product candidates
in development
         that are reasonably likely to result in an approved product in the
foreseeable future.
Implications of being an emerging growth company, page 6

3.       Please supplementally provide us with copies of all written
communications, as defined in
         Rule 405 under the Securities Act, that you, or anyone 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 copes of the communications.
Use of Proceeds, page 88

4.       Please describe with greater specificity how far the proceeds from the
offering will allow
         you to advance your various programs. If any material amounts of other
funds are
         necessary to accomplish the specified purposes, state the amounts and
sources of other
         funds needed for each specified purpose and the sources. Refer to
Instruction 3 to Item
         504 of Regulation S-K.
Management's Discussion and Analysis of Financial Condition and Results of
Stock-based Compensation, page 106

5.       Once you have an estimated offering price or range, please explain to
us how you
         determined the fair value of the common stock underlying your equity
issuances and the
         reasons for any differences between the recent valuations of your
common stock leading
         up to the initial public offering and the estimated offering price or
range. This
         information will help facilitate our review of your accounting for
equity issuances.
Our Human-Focused AXA Development Program, page 116

6.       We note your disclosure on page 117 that the EMM Safety Database
"synthesizes our own
         and third-party data on dose ranges for each EMM or combinations of
EMM previously
         studied in humans without any or significant safety issues" and your
disclosure on page
         120 that, "We did not observe any significant safety issues with
AXA1665 in this study
         ..." Please revise your disclosure throughout the prospectus that
present conclusions
         regarding the safety or efficacy of products to the extent that such
determinations have not
         been made by the FDA or comparable regulatory bodies.
AXA1665 Program, page 120

7.       To the extent possible, please discuss in greater detail the possible
non-drug pathways that
         the company could pursue. Please revise accordingly your related
disclosure on pages 135
         and 143.
 William Hinshaw
FirstName LastNameWilliam Hinshaw
Axcella Health Inc.
Comapany NameAxcella Health Inc.
February 15, 2019
Page 3
February 15, 2019 Page 3
FirstName LastName
AXA2678 Muscle Program, page 141

8.       We note the following disclosure on page 141: "The above clinical
observations prompted
         additional cell-based experiments in cultured muscle cells to gain
further mechanistic
         insights into AXA2678's effect on muscle mass and function." Please
disclose what these
         additional cell-based experiments revealed.
Certain Relationships and Related Party Transactions
Services agreement, page 193

9.       Please file the services agreement as an exhibit or advise us why such
agreement is not
         required to be filed. See Item 601(b)(10) of Regulation S-K.
Principal Stockholders, page 197

10.      To the extent known, please provide the information for the first two
columns of the
         beneficial ownership table on page 197.
Description of Capital Stock
Choice of forum, page 202

11.      We note that your disclosure identifies the Court of Chancery of the
State of Delaware as
         the exclusive forum for certain litigation, including any "derivative
action." Please
         disclose whether this provision applies to actions arising under the
federal securities laws.
         In this regard, we note that Section 27 of the Exchange Act creates
exclusive federal
         jurisdiction over all suits brought to enforce any duty or liability
created by the Exchange
         Act or the rules and regulations thereunder.

12.      Please explain the meaning of all abbreviations and defined terms the
first time they are
         used. For example, the abbreviation PCT, which first appears on page
145, is not
13.      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 Hinshaw
Axcella Health Inc.
February 15, 2019
Page 4

       You may contact Li Xiao at 202-551-4391 or Jeffrey Lewis at 202-551-6216
if you have
questions regarding comments on the financial statements and related matters.
Please contact
David Plattner at 202-551-8094 or Tom Kluck at 202-551-3233 with any other

FirstName LastNameWilliam Hinshaw
                                                         Division of
Corporation Finance
Comapany NameAxcella Health Inc.
                                                         Office of Healthcare &
February 15, 2019 Page 4
cc:       Laurie A. Burlingame, Esq.
FirstName LastName