November 9, 2018

Alison Lawton
Chief Executive Officer
Kaleido Biosciences, Inc.
65 Hayden Avenue
Lexington, MA 02421

       Re: Kaleido Biosciences, Inc.
           Amendment No. 1 to Draft Registration Statement on Form S-1
           Submitted October 26, 2018
           CIK No. 0001751299

Dear Ms. Lawton:

      We have reviewed your amended draft registration statement and have the
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 registration statement or filed registration statement, we may
have additional

Amendment No. 1 to Draft Registration Statement on Form S-1 submitted October
26, 2018

Prospectus Summary
Overview, page 1

1.     Please revise the first sentence of the first paragraph to clarify that
you are a non-IND
       clinical stage healthcare company.
2.     We note your revised disclosure on page 4 that you are conducting
ongoing ex
       vivo screening and testing in multi-drug resistant bacteremia in high
risk patients but you
       have not yet identified the specific MMT candidate for this program.
Given this
 Alison Lawton
FirstName LastNameAlison Lawton
Kaleido Biosciences, Inc.
Comapany 9, 2018
November NameKaleido Biosciences, Inc.
November 9, 2018 Page 2
Page 2
FirstName LastName
         statement, please explain why your pipeline table indicates that you
have completed ex
         vivo screening and testing in this program, and revise your disclosure
3.       We note your response to our prior comment 4 that the company
identified a potential
         MMT candidate for drug or disease-induced diarrhea through ex vivo
screening and that
         you have commenced a non-IND human clinical study to support this
program and that
         you are continuing to evaluate further MMT product candidates and have
initiated ex
         vivo testing. Please expand footnote 3 to the pipeline table to
include such disclosure in
         your prospectus.
4.       Please include a legend explaining the significance of the symbols in
the "Mechanism of
         Action" column with the pipeline table on pages 3 and 111.
5.       We note your response to our prior comment 9 that you have discussed
with the FDA your
         plan to move directly to Phase 2 for KB195, and that you will have to
         evaluate each of your other product candidates with respect to
bypassing Phase 1. Given
         the uncertainty, please add a column for Phase 1 to your product
pipeline table here and in
         the Business section. We will not object to narrative disclosure
relating to your belief that
         you may be able to bypass the Phase 1 trial.
Our Approach to Non-IND Human Clinical Studies, page 121

6.       We note your response to our prior comment 10 that you do not believe
the details of five
         of your safety and tolerability studies is material. However, if there
were any serious
         adverse events observed in these five human clinical studies, please
provide disclosure
         regarding such events.
Future Pipeline Opportunities, page 140

7.       We note your response to our prior comment 24. However, your
disclosure relating to the
         Type 2 diabetes study suggests that it is a relatively advanced
non-IND clinical trial and
         does not explain how this study differs from your other non-IND
clinical trials. Please
         expand your disclosure on page 141 to explain that it is a pilot
study, including why it is
         considered a pilot study and what it is intended to show. Please also
state that you have
         not yet identified a MMT candidate for introduction into the study.
Further, although you
         have not decided at this point whether you will commercialize an MMT
candidate or
         advance the candidate down a drug pathway, please disclose the FDA
position that
         diabetes is not a condition for which medical food can be labeled or
marketed so that
         investors are aware that this is not a possible marketing path.
Certain Relationships and Related Party Transactions, page 185

8.       We note your response to our prior comment 17 and that the Midori
license agreement is
         now an agreement between you and a wholly-owned subsidiary. Please
clarify whether
 Alison Lawton
Kaleido Biosciences, Inc.
November 9, 2018
Page 3
       Cadena is now the owner of the technology covered by the Midori license
       Please also tell us whether there are any continuing obligations between
the company and
       Midori pursuant to the license agreement.
9.     We note your response to comment 28 that you believe your services
agreement with
       Flagship Management, your majority stockholder, is immaterial. However,
we note your
       revised disclosure that pursuant to this agreement you have obtained the
services of your
       Chief Innovation Officer, among other services. Please tell us the types
of services you
       currently contract for pursuant to the agreement, including whether you
currently contract
       for, or intend in the future to contract for, the services of any of
your executive officers or
       You may contact Keira Nakada at 202-551-3659 or Jim Rosenberg at
202-551-3679 if
you have questions regarding comments on the financial statements and related
matters. Please
contact Irene Paik at 202-551-6553 or Erin Jaskot at 202-551-3442 with any
other questions.

FirstName LastNameAlison Lawton
                                                               Division of
Corporation Finance
Comapany NameKaleido Biosciences, Inc.
                                                               Office of
Healthcare & Insurance
November 9, 2018 Page 3
cc:       Kingsley L. Taft - Goodwin Procter LLP
FirstName LastName