United States securities and exchange commission logo

                             December 9, 2020

       John Celebi
       President and Chief Executive Officer
       Sensei Biotherapeutics, Inc.
       620 Professional Drive
       Gaithersburg, MD 20879

                                                        Re: Sensei
Biotherapeutics, Inc.
                                                            Draft Registration
Statement on Form S-1
                                                            Submitted November
12, 2020
                                                            CIK No. 0001829802

       Dear Mr. Celebi:

              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

             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 November 12, 2020

       Prospectus Summary
       Company Overview, page 1

   1.                                                   We note your statements
throughout the prospectus that SNS-301 has been "well-tolerated
                                                        and has shown promising
anti-tumor activity" and you characterize the results received to
                                                        date as positive.
However, given that only nine patients have been evaluated to date,
                                                        please revise your
disclosure in the Summary to present a balanced view of the ongoing
                                                        clinical trial and the
meaning of the results. In addition, please include a risk factor
                                                        discussing the limited
nature of the data received to date and the potential for diverging
                                                        data once the patient
population is expanded.
 John Celebi
Sensei Biotherapeutics, Inc.
December 9, 2020
Page 2
2.       Please remove all references to "Phase 1/2" and "Phase 2/3" clinical
trials throughout the
         prospectus and instead reference either phase 1, 2, or 3 distinctly or
tell us the basis for
         your belief that have been approved to conduct a Phase1/2 trial and
that you will be
         eligible to conduct a Phase 2/3 trials for your SNS3-1 product
candidates and revise your
         disclosure as appropriate. Our concern is that the references as
currently disclosed may be
         read to imply a shorter clinical trial process or further progress
than has actually been
         made, and may skew a potential investor's understanding of the process
applicable to the
         company's product candidates. Please ensure your references throughout
the document are
         consistent with your disclosure regarding Government Regulation
beginning on page 113.
3.       We note the following statements on pages 1, 89 and 94 : "ImmunoPhage
is not only
         capable of driving T cell responses, but also generates strong B cell
mediated antibody
         responses. We believe that the unique features of ImmunoPhage,
including the flexibility
         of antigen design, the ease of platform engineering, its large
antigenic capacity, the low
         cost of goods and the high speed of manufacturing, as well as the
enduring stability of our
         product candidates, have the potential to lead to a paradigm shift in
         immunotherapies." Given your early stage of development and limited
clinical data
         received to date it does not appear these claims are supported. Please
remove in each place
         in which they appear.
4.       Please remove all references to "positive FDA feedback" received, as
this may be read to
         imply approval by the FDA and assured progression in the clinical
trial process which is
         not known or within the company's control.
5.       We note your statement that you believe that the addition of SNS-301
has the "potential to
         generate and expand ASPH specific anti-tumor T cells and thereby
enhance the efficacy
         of PD-1 blockade." Please remove all references to efficacy in
relation to your product
         candidates, as the determination of both safety and efficacy is solely
within the purview of
         the FDA, which has not yet determined SNS-301 to be safe or effective.
Our Pipeline, page 3

6.       Please revise your pipeline table to include a column for the
discovery phase prior to the
         preclinical phase and separate the columns depicting clinical trials
to distinctly show
         phases 1, 2 and 3. In addition, adjust your bar graph for each
candidate to accurately show
         its progression in relation to each phase once the table has been
revised. In this regard we
         note the pipeline table shown on your website.
FirstName LastNameJohn Celebi
       Please also remove the rows relating to SNS-CoV2 and "multiple
pathogens", as it does
Comapany    NameSensei
       not appear       Biotherapeutics,
                  from your              Inc.
                            disclosure elsewhere that these categories are
material to the
December   9, 2020business
                   Page 2 at this time.
FirstName LastName
 John Celebi
FirstName  LastNameJohn
Sensei Biotherapeutics, Inc.Celebi
December   NameSensei
             2020        Biotherapeutics, Inc.
Page 3    9, 2020 Page 3
FirstName LastName
Management's Discussion and Analysis of Financial Condition and Results of
Critical Accounting Policies and Significant Judgments and Estimates
Stock-Based Compensation
Fair Value of Common Stock, page 86

7.       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 IPO and the estimated offering price. This information will
help facilitate our
         review of your accounting for equity issuances including stock
compensation and
         beneficial conversion features. Please discuss with the staff how to
submit your response.
Business, page 89

8.       Where appropriate, please disclose any human capital measures or
objectives that the
         company focuses on in managing its business. See Item 101(c)(2)(ii) of
Regulation S-K.
9.       We note your discussion of collaborations with AstraZeneca for future
Phase 2 clinical
         trials for SNS-301 and the University of Washington for your SNS-401
program. As each
         of these product candidates appear material to the business, for each
collaboration please
         disclose the company's rights and/or obligations, termination
provisions and expiration
         terms, and quantify the amounts paid to date (including upfront
payments and milestone
         payments already paid), the aggregate potential milestone payments to
be paid or
         received, and any applicable royalty rates. Please also file each as
an exhibit. Please also
         revise to disclose that status of any collaboration with the
manufacturer of pembrolizumab
         or include risk factor disclosure as appropriate.
Our Approach to Immunotherapy, page 94

10.      Please revise your disclosure to provide support for the statements
under the above
         heading relating to the functionality of your ImmunoPhage platform and
its components.
         To the extent you have clinical data to support the statements please
include a summary
         thereof. If you have no clinical data to support the statements,
please clearly state this in
         the disclosure.
Targeting ASPH, page 101

11.      Please clarify the purpose of the graphics on page 101 entitled
"Tumors Stained Highly
         Positive for ASPH", namely what the four individual images are meant
to convey (i.e., a
         progression of ASPH over time, four separate patient samples, etc.).

Intellectual Property, page 109

12.      Please revise your intellectual property discussion to disclose on an
individual basis the
         jurisdiction of each foreign patent and pending patent application.
 John Celebi
Sensei Biotherapeutics, Inc.
December 9, 2020
Page 4
License Agreement with Fred Hutch, page 112

13.    Please revise your reference to the annual license maintenance fee due
under the Fred
       Hutch Agreement from the mid-single digit thousands to "low six figures"
to a more
       clearly defined range. Please also confirm that the 1,429,412 shares
issued by Alvaxa to
       Fred Hutch (and subsequently exchanged for 2,191,514 shares of the
company's stock) is
       the only payment that has been made to date under the agreement.
Principal Stockholders, page 151

14.    Please include footnotes to your table that disclose the natural persons
       have beneficial ownership of the shares held by the entities listed in
your table.

15.    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 copies of the communications.
16.    We note the statements on the company's website that SNS-301 has shown
       safety and clinical benefit in Phase 1 patient trials, and is currently
in Phase 2 at multiple
       clinical sites across the USA", that SNS-301 has "successfully completed
a Phase 1
       clinical study", that ImmunoPhage has been "proven" "safe and tolerable
in phase 1 and 2
       clinical trials", and that it may solicit a "complete" immune response.
Although we note
       that the information contained on your website is not incorporated by
reference into the
       prospectus, the information cited above appears to be different from the
disclosure in the
       prospectus. Please explain.
17.    We note your disclosure throughout the prospectus that you are a smaller
       company; however, you have not indicated this status by checking the box
on the cover
       page of the registration statement. Please address this in your next
        You may contact Christine Torney at 202-551-3652 or Angela Connell at
if you have questions regarding comments on the financial statements and
related matters.
Please contact Laura Crotty at 202-551-7614 or Tim Buchmiller at 202-551-3635
with any other

FirstName LastNameJohn Celebi
                                                              Division of
Corporation Finance
Comapany NameSensei Biotherapeutics, Inc.
                                                              Office of Life
December 9, 2020 Page 4
cc:       Michael E. Tenta, Esq.
FirstName LastName