SecProbe.io

CORRESP
 1
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 Document X4 Pharmaceuticals, Inc. 61 North Beacon Street, 4 th Floor Boston, MA 02134 September 15, 2025 VIA EDGAR U.S. Securities and Exchange Commission Division of Corporation Finance 100 F Street, N.E. Washington, DC 20549 Attention: Jessica Dickerson   Re: X4 Pharmaceuticals, Inc. Registration Statement on Form S-3 (File No. 333-290158) Ladies and Gentlemen: X4 Pharmaceuticals, Inc. hereby respectfully requests that, pursuant to Rule 461 promulgated under the Securities Act of 1933, as amended, the effectiveness of the above-referenced Registration Statement on Form S-3 be accelerated so that it will become effective on September 17, 2025, at 4:15 p.m., Eastern Time, or as soon as practicable thereafter, unless we or our outside counsel, Gibson, Dunn & Crutcher LLP, request by telephone that such Registration Statement be declared effective at some other time. We request that we be notified of such effectiveness by a telephone call to Melanie E. Neary of Gibson, Dunn & Crutcher at (415) 393-8243.   Sincerely, X4 PHARMACEUTICALS, INC. By: /s/ David Kirske David Kirske Chief Financial Officer and Treasurer   cc: Adam R. Craig, M.D., Ph.D., X4 Pharmaceuticals, Inc. Natasha Thoren, X4 Pharmaceuticals, Inc. Melanie E. Neary, Dunn & Crutcher LLP

<DOCUMENT>
<TYPE>TEXT-EXTRACT
<SEQUENCE>2
<FILENAME>filename2.txt
<TEXT>
 September 15, 2025

Adam Craig
Executive Chairman
X4 Pharmaceuticals, Inc.
61 North Beacon Street, 4th Floor
Boston, MA 02134

 Re: X4 Pharmaceuticals, Inc.
 Registration Statement on Form S-3
 Filed September 10, 2025
 File No. 333-290158
Dear Adam Craig:

 This is to advise you that we have not reviewed and will not review your
registration
statement.

 Please refer to Rules 460 and 461 regarding requests for acceleration.
We remind you
that the company and its management are responsible for the accuracy and
adequacy of their
disclosures, notwithstanding any review, comments, action or absence of action
by the staff.

 Please contact Jessica Dickerson at 202-551-8013 with any questions.

 Sincerely,

 Division of
Corporation Finance
 Office of Life
Sciences
cc: Ryan A. Murr, Esq.
</TEXT>
</DOCUMENT>

January 7, 2025
Adam Mostafa
Chief Financial Officer
X4 Pharmaceuticals, Inc
61 North Beacon Street, 4th Floor
Boston, MA 02134
Re:X4 Pharmaceuticals, Inc
Form 10-K for fiscal year ended December 31, 2023
Form 10-Q for the quarterly period ended September 30, 2024
File No. 001-38295
Dear Adam Mostafa:
            We have completed our review of your filings. We remind you that the company and
its management are responsible for the accuracy and adequacy of their disclosures,
notwithstanding any review, comments, action or absence of action by the staff.
Sincerely,
Division of Corporation Finance
Office of Life Sciences

CORRESP
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x4-secresponseletterfina

  December 23, 2024  U.S. Securities and Exchange Commission   Division of Corporation Finance  Office of Life Sciences   100 F Street, N.E.   Washington, D.C. 20549  Attention: Vanessa Robertson/Daniel Gordon  Re: X4 Pharmaceuticals, Inc.  Form 10-K for the fiscal year ended December 31, 2023  Form 10-Q for the quarterly period ended September 30, 2024  File No. 001-38295  Ladies and Gentlemen:  This letter sets forth responses of X4 Pharmaceuticals, Inc. (the “Company” or “we”) to the comments of the  staff of the Division of Corporation Finance (the “Staff”) of the U.S. Securities and Exchange Commission (the  “Commission”) set forth in your letter dated December 13, 2024, with respect to the Form 10-K for the fiscal year  ended December 31, 2023 (the “Form 10-K”) and the Form 10-Q for the quarterly period ended September 30, 2024  (the “Form 10-Q”).   The text of the Staff’s comments have been included in this letter for your convenience, and the Company’s  responses to the comments have been provided immediately thereafter.  Form 10-Q for the quarterly period ended September 30, 2024  Management’s Discussion and Analysis of Financial Condition and Results of Operations Results of Operations  Research and Development Expenses, page 30  1. Staff’s comment: We note that you did not break out research and development expense between direct and unallocated for all periods presented similar to your disclosure in the 10-K for the year ended December 31, 2023. Please confirm that you will break out research and development expense in future filings similar to the format of the 10-K. Alternatively, provide us with other quantitative or qualitative disclosure to be included in future filings that provides more transparency as to the type of research and development expenses incurred (i.e. by nature or type of expense) which should reconcile to total research and development expense on the Statements of Operations. Response:  The Company acknowledges the Staff’s comment. In its SEC filings, commencing with the Form 10-K for the year  period ending December 31, 2024 and continuing with the Form 10-Q for the quarterly period ending March 31,  2025 and onward, the Company will break out research and development expense between direct and unallocated  for all periods presented similar to our disclosure in the 10-K for the year ended December 31, 2023, which will  reconcile to total research and development expense on our Statements of Operations. We plan to disclose the direct  research and development expenses by product candidates that are in or have entered into clinical development. For  our Form 10-K for the year period ending December 31, 2024, our direct research and development expenses are  expected to include the following product candidates: X4P-001 (Mavorixafor), X4P-002 and X4P-003.

  We hope that the foregoing has been responsive to the Staff’s comments. If you have any questions related to  this letter, please contact me at 1-857-529-6333 (Ext: 8820).   Sincerely,  /s/ Adam S. Mostafa  Adam S. Mostafa  Chief Financial Officer  Via E-mail:  cc: Gabriela Morales-Rivera  Goodwin Procter LLP  61 North Beacon Street, 4th Floor, Boston, MA 02134 | (857) 529-8300| https://www.x4pharma.com/

December 13, 2024
Adam Mostafa
Chief Financial Officer
X4 Pharmaceuticals, Inc
61 North Beacon Street, 4th Floor
Boston, MA 02134
Re:X4 Pharmaceuticals, Inc
Form 10-K for fiscal year ended December 31, 2023
Form 10-Q for the quarterly period ended September 30, 2024
File No. 001-38295
Dear Adam Mostafa:
            We have limited our review of your filing to the financial statements and related
disclosures and have the following comment.
            Please respond to this letter within ten business days by providing the requested
information or advise us as soon as possible when you will respond. If you do not believe a
comment applies to your facts and circumstances, please tell us why in your response.
            After reviewing your response to this letter, we may have additional comments.
Form 10-Q for the quarterly period ended September 30, 2024
Management's Discussion and Analysis of Financial Condition and Results of Operations
Results of Operations
Research and Development Expenses, page 30
1.We note that you did not break out research and development expense between direct
and unallocated for all periods presented similar to your disclosure in the 10-K for the
year ended December 31, 2023. Please confirm that you will break out research and
development expense in future filings similar to the format of the 10-K.
Alternatively, provide us with other quantitative or qualitative disclosure to be
included in future filings that provides more transparency as to the type of research
and development expenses incurred (i.e. by nature or type of expense) which should
reconcile to total research and development expense on the Statements of Operations.
            In closing, we remind you that the company and its management are responsible for
the accuracy and adequacy of their disclosures, notwithstanding any review, comments,

December 13, 2024
Page 2
action or absence of action by the staff.
            Please contact Vanessa Robertson at 202-551-3649 or Daniel Gordon at 202-551-
3486 with any questions.
Sincerely,
Division of Corporation Finance
Office of Life Sciences

CORRESP
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Document

X4 Pharmaceuticals, Inc.

61 North Beacon Street, 4th Floor

Boston, MA 02134

August 22, 2023

Via Edgar

United States Securities and Exchange Commission

Division of Corporation Finance

100 F Street, N.E.

Washington, D.C. 20549

Attn:    Doris Stacey Gama

RE:    X4 Pharmaceuticals, Inc.

    Registration Statement on Form S-3

    File No. 333-273961

    Acceleration Request

        Requested Date:    August 24, 2023

        Requested Time:    4:00 p.m. Eastern Time

Ladies and Gentlemen:

Pursuant to Rule 461 under the Securities Exchange Act of 1933, as amended, the undersigned registrant hereby requests that the Securities and Exchange Commission take appropriate action to cause the above-referenced Registration Statement on Form S-3 (File No. 333-273961) (the “Registration Statement”) to become effective at 4:00 p.m. Eastern Time on Thursday, August 24, 2023, or as soon thereafter as is practicable.

Once the Registration Statement has been declared effective, please orally confirm that event with Daniel I. Goldberg of Cooley LLP, counsel to the registrant, at (212) 479-6722.

[Signature page follows]

Sincerely,

X4 Pharmaceuticals, Inc.

By:     /s/ Adam S. Mostafa

    Adam S. Mostafa

Chief Financial Officer

cc:    Paula Ragan, Ph.D., Chief Executive Officer, X4 Pharmaceuticals, Inc.

    Daniel I. Goldberg, Cooley LLP

Eric Blanchard, Cooley LLP

            Courtney T. Thorne, Cooley LLP

United States securities and exchange commission logo
August 21, 2023
Adam Mostafa
Chief Financial Officer and Treasurer
X4 Pharmaceuticals, Inc
61 North Beacon Street, 4th Floor
Boston, MA 02134
Re:X4 Pharmaceuticals, Inc
Registration Statement on Form S-3
Filed August 14, 2023
File No. 333-273961
Dear Adam Mostafa:
            This is to advise you that we have not reviewed and will not review your registration
statement.
            Please refer to Rules 460 and 461 regarding requests for acceleration.  We remind you
that the company and its management are responsible for the accuracy and adequacy of their
disclosures, notwithstanding any review, comments, action or absence of action by the staff.
            Please contact Doris Stacey Gama at 202-551-3188 with any questions.
Sincerely,
Division of Corporation Finance
Office of Life Sciences
cc:       Daniel I. Goldberg, Esq.

CORRESP
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Document

X4 Pharmaceuticals, Inc.

61 North Beacon Street, 4th Floor

Boston, MA 02134

June 16, 2023

Via Edgar

United States Securities and Exchange Commission

Division of Corporation Finance

100 F Street, N.E.

Washington, D.C. 20549

Attn:    Jimmy McNamara

RE:    X4 Pharmaceuticals, Inc.

    Registration Statement on Form S-3

    File No. 333-272551

    Acceleration Request

        Requested Date:    June 20, 2023

        Requested Time:    4:00 p.m. Eastern Time

Ladies and Gentlemen:

Pursuant to Rule 461 under the Securities Exchange Act of 1933, as amended, the undersigned registrant hereby requests that the Securities and Exchange Commission take appropriate action to cause the above-referenced Registration Statement on Form S-3 (File No. 333-272551) (the “Registration Statement”) to become effective at 4:00 p.m. Eastern Time on Tuesday, June 20, 2023, or as soon thereafter as is practicable.

Once the Registration Statement has been declared effective, please orally confirm that event with Daniel I. Goldberg of Cooley LLP, counsel to the registrant, at (212) 479-6722.

[Signature page follows]

Sincerely,

X4 Pharmaceuticals, Inc.

By:     /s/ Adam S. Mostafa

    Adam S. Mostafa

Chief Financial Officer

cc:    Paula Ragan, Ph.D., Chief Executive Officer, X4 Pharmaceuticals, Inc.

    Daniel I. Goldberg, Cooley LLP

Eric Blanchard, Cooley LLP

            Courtney T. Thorne, Cooley LLP

United States securities and exchange commission logo
June 16, 2023
Adam Mostafa
Chief Financial Officer
X4 Pharmaceuticals, Inc
61 North Beacon Street, 4th Floor
Boston, Massachusetts 02134
Re:X4 Pharmaceuticals, Inc
Registration Statement on Form S-3
Filed June 9, 2023
File No. 333-272551
Dear Adam Mostafa:
            This is to advise you that we have not reviewed and will not review your registration
statement.
            Please refer to Rules 460 and 461 regarding requests for acceleration.  We remind you
that the company and its management are responsible for the accuracy and adequacy of their
disclosures, notwithstanding any review, comments, action or absence of action by the staff.
            Please contact Jimmy McNamara at 202-551-7349 with any questions.
Sincerely,
Division of Corporation Finance
Office of Life Sciences

CORRESP
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CORRESP

 X4 PHARMACEUTICALS, INC.

61 North Beacon Street, 4th Floor

Boston, MA 02134

 August 3, 2022

VIA EDGAR

 United
States Securities and Exchange Commission

 Division of Corporation Finance

100 F Street, N.E.

 Washington, D.C. 20549

Attn:
 Jason Drory

RE:
 X4 Pharmaceuticals, Inc.

Registration Statement on Form S-3

File No. 333-266410

Acceleration Request

            Requested Date:       August 5,
2022

             Requested Time:      4:00
p.m. Eastern Time

 Ladies and Gentlemen:

 Pursuant to
Rule 461 under the Securities Exchange Act of 1933, as amended, the undersigned registrant hereby requests that the Securities and Exchange Commission take appropriate action to cause the above-referenced Registration Statement on Form S-3 (File No. 333-266410) (the “Registration Statement”) to become effective at 4:00 p.m. Eastern Time on Friday, August 5, 2022, or as soon
thereafter as is practicable.

 Once the Registration Statement has been declared effective, please orally confirm that event with Daniel I. Goldberg of
Cooley LLP, counsel to the registrant, at (212) 479-6722.

 [Signature page follows]

 Sincerely,

X4 PHARMACEUTICALS, INC.

By:

 /s/ Adam S. Mostafa

Adam S. Mostafa

Chief Financial Officer

cc:
 Paula Ragan, Ph.D., Chief Executive Officer, X4 Pharmaceuticals, Inc.

Derek Meisner, Chief Legal Officer, X4 Pharmaceuticals, Inc.

Daniel I. Goldberg, Cooley LLP

Courtney T. Thorne, Cooley LLP

United States securities and exchange commission logo
August 2, 2022
Paula Ragan, Ph.D.
Chief Executive Officer
X4 Pharmaceuticals, Inc.
61 North Beacon Street, 4th Floor
Boston, MA 02134
Re:X4 Pharmaceuticals, Inc.
Registration Statement on Form S-3
Filed July 29, 2022
File No. 333-266410
Dear Dr. Ragan:
            This is to advise you that we have not reviewed and will not review your registration
statement.
            Please refer to Rules 460 and 461 regarding requests for acceleration.  We remind you
that the company and its management are responsible for the accuracy and adequacy of their
disclosures, notwithstanding any review, comments, action or absence of action by the staff.
            Please contact Jason Drory at 202-551-8342 with any questions.
Sincerely,
Division of Corporation Finance
Office of Life Sciences
cc:       Courtney Thorne

CORRESP
1
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CORRESP

 X4 PHARMACEUTICALS, INC.

61 North Beacon Street, 4th Floor

Boston, MA 02134

 May 12, 2022

VIA EDGAR

 United
States Securities and Exchange Commission

 Division of Corporation Finance

100 F Street, N.E.

 Washington, D.C. 20549

Attn: Tyler Howes

RE:
 X4 Pharmaceuticals, Inc.

Registration Statement on Form S-3

File No. 333-264459

Acceleration Request

    Requested Date:         May 13, 2022

    Requested Time:       4:00 p.m. Eastern Time

Ladies and Gentlemen:

 Pursuant to Rule 461 under the Securities
Exchange Act of 1933, as amended, the undersigned registrant hereby requests that the Securities and Exchange Commission take appropriate action to cause the above-referenced Registration Statement on Form S-3
(File No. 333-264459) (the “Registration Statement”) to become effective at 4:00 p.m. Eastern Time on Friday, May 13, 2022, or as soon thereafter as is practicable.

Once the Registration Statement has been declared effective, please orally confirm that event with Daniel I. Goldberg of Cooley LLP, counsel to the
registrant, at (212) 479-6722.

 [Signature page follows]

Sincerely,

X4 Pharmaceuticals, Inc.

By:

 /s/ Adam S. Mostafa

Adam S. Mostafa

Chief Financial Officer

cc:
 Paula Ragan, Ph.D., Chief Executive Officer, X4 Pharmaceuticals, Inc.

Derek Meisner, Chief Legal Officer, X4 Pharmaceuticals, Inc.

Daniel I. Goldberg, Cooley LLP

Courtney T. Thorne, Cooley LLP

United States securities and exchange commission logo
April 28, 2022
Paula Ragan, Ph.D.
Chief Executive Officer
X4 Pharmaceuticals, Inc
61 North Beacon Street, 4th Floor
Boston, Massachusetts 02134
Re:X4 Pharmaceuticals, Inc
Registration Statement on Form S-3
Filed April 22, 2022
File No. 333-264459
Dear Dr. Ragan:
            This is to advise you that we have not reviewed and will not review your registration
statement.
            Please refer to Rules 460 and 461 regarding requests for acceleration.  We remind you
that the company and its management are responsible for the accuracy and adequacy of their
disclosures, notwithstanding any review, comments, action or absence of action by the staff.
            Please contact Tyler Howes at 202-551-3370 with any questions.
Sincerely,
Division of Corporation Finance
Office of Life Sciences
cc:       Courtney Thorne, Esq.

CORRESP
1
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CORRESP

 X4 PHARMACEUTICALS, INC.

61 North Beacon Street, 4th Floor

Boston, MA 02134

 December 30, 2021

VIA EDGAR

 United
States Securities and Exchange Commission

 Division of Corporation Finance

100 F Street, N.E.

 Washington, D.C. 20549

Attn:
 Jordan Nimitz

RE:
 X4 Pharmaceuticals, Inc.

 Registration Statement on Form S-3

 File No. 333-261871

 Acceleration Request

Requested Date:

January 3, 2022

Requested Time:

4:00 p.m. Eastern Time

 Ladies and Gentlemen:

 Pursuant
to Rule 461 under the Securities Exchange Act of 1933, as amended, the undersigned registrant hereby requests that the Securities and Exchange Commission take appropriate action to cause the above-referenced Registration Statement on Form S-3 (File No. 333-261871) (the “Registration Statement”) to become effective at 4:00 p.m. Eastern Time on Monday, January 3, 2022, or as soon
thereafter as is practicable.

 Once the Registration Statement has been declared effective, please orally confirm that event with Daniel I. Goldberg of
Cooley LLP, counsel to the registrant, at (212) 479-6722.

 [Signature page follows]

Sincerely,

X4 PHARMACEUTICALS, INC.

By:

 /s/ Adam S. Mostafa

Adam S. Mostafa

Chief Financial Officer

cc:
 Paula Ragan, Ph.D., Chief Executive Officer, X4 Pharmaceuticals, Inc.

 Derek Meisner, Chief Legal Officer, X4 Pharmaceuticals, Inc.

 Daniel I. Goldberg, Cooley LLP

 Courtney T. Thorne, Cooley LLP

United States securities and exchange commission logo
December 29, 2021
Paula Ragan
Chief Executive Officer
X4 Pharmaceuticals, Inc
61 North Beacon Street, 4th Floor
Boston, Massachusetts 02134
Re:X4 Pharmaceuticals, Inc
Registration Statement on Form S-3
Filed December 23, 2021
File No. 333-261871
Dear Dr. Ragan:
            This is to advise you that we have not reviewed and will not review your registration
statement.
            Please refer to Rules 460 and 461 regarding requests for acceleration.  We remind you
that the company and its management are responsible for the accuracy and adequacy of their
disclosures, notwithstanding any review, comments, action or absence of action by the staff.
            Please contact Jordan Nimitz at 202-551-5831 with any questions.
Sincerely,
Division of Corporation Finance
Office of Life Sciences

CORRESP
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X4 Pharmaceuticals, Inc.

61 North Beacon Street, 4th Floor

Boston, MA 02134

July 7, 2021

Via Edgar

United States Securities and Exchange Commission

Division of Corporation Finance

100 F Street, N.E.

Washington, D.C. 20549

Attn:    Jeffrey Gabor

RE:    X4 Pharmaceuticals, Inc.

    Registration Statement on Form S-3

    File No. 333-257422

    Acceleration Request

        Requested Date:    July 9, 2021

        Requested Time:    4:00 p.m. Eastern Time

Ladies and Gentlemen:

Pursuant to Rule 461 under the Securities Exchange Act of 1933, as amended, the undersigned registrant hereby requests that the Securities and Exchange Commission take appropriate action to cause the above-referenced Registration Statement on Form S-3 (File No. 333-257422) (the “Registration Statement”) to become effective at 4:00 p.m. Eastern Time on Friday, July 9, 2021, or as soon thereafter as is practicable.

Once the Registration Statement has been declared effective, please orally confirm that event with Daniel I. Goldberg of Cooley LLP, counsel to the registrant, at (212) 479-6722.

[Signature page follows]

Sincerely,

X4 Pharmaceuticals, Inc.

By: __    /s/Adam S. Mostafa

    Adam S. Mostafa

Chief Financial Officer

cc:    Paula Ragan, Ph.D., Chief Executive Officer, X4 Pharmaceuticals, Inc.

    Derek Meisner, General Counsel, X4 Pharmaceuticals, Inc.

Daniel I. Goldberg, Cooley LLP

            Courtney T. Thorne, Cooley LLP

United States securities and exchange commission logo
July 2, 2021
Paula Ragan, Ph.D.
Chief Executive Officer
X4 Pharmaceuticals, Inc
61 North Beacon Street, 4th Floor
Boston, MA 02134
Re:X4 Pharmaceuticals, Inc
Registration Statement on Form S-3
Filed June 25, 2021
File No. 333-257422
Dear Dr. Ragan:
            This is to advise you that we have not reviewed and will not review your registration
statement.
            Please refer to Rules 460 and 461 regarding requests for acceleration.  We remind you
that the company and its management are responsible for the accuracy and adequacy of their
disclosures, notwithstanding any review, comments, action or absence of action by the staff.
            Please contact Jeffrey Gabor at 202-551-2544 with any questions.
Sincerely,
Division of Corporation Finance
Office of Life Sciences
cc:       Daniel Goldberg, Esq.

CORRESP
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CORRESP

 X4 PHARMACEUTICALS, INC.

61 North Beacon Street, 4th Floor

Boston, MA 02134

 October 22, 2020

VIA EDGAR

 United
States Securities and Exchange Commission

 Division of Corporation Finance

100 F Street, N.E.

 Washington, D.C. 20549

Attn:
 Ada D. Sarmento

RE:
 X4 Pharmaceuticals, Inc.

Registration Statement on Form S-3

File No. 333-249544

Acceleration Request

Requested Date: October 26, 2020

Requested Time: 4:00 p.m. Eastern Time

Ladies and Gentlemen:

 Pursuant to Rule 461 under the
Securities Exchange Act of 1933, as amended, the undersigned registrant hereby requests that the Securities and Exchange Commission take appropriate action to cause the above-referenced Registration Statement on Form
S-3 (File No. 333-249544) (the “Registration Statement”) to become effective at 4:00 p.m. Eastern Time on Monday, October 26, 2020, or
as soon thereafter as is practicable.

 Once the Registration Statement has been declared effective, please orally confirm that event with Daniel I.
Goldberg of Cooley LLP, counsel to the registrant, at (212) 479-6722 or with Courtney T. Thorne of Cooley LLP at (617) 937-2318.

[Signature page follows]

 Sincerely,

X4 PHARMACEUTICALS, INC.

By:

/s/ Adam S. Mostafa

 Adam S. Mostafa

 Chief Financial
Officer

cc:
 Paula Ragan, Ph.D., Chief Executive Officer, X4 Pharmaceuticals, Inc.

Daniel I. Goldberg, Cooley LLP

Courtney T. Thorne, Cooley LLP

United States securities and exchange commission logo
October 21, 2020
Paula Ragan, Ph.D.
Chief Executive Officer
X4 Pharmaceuticals, Inc
61 North Beacon Street, 4th Floor
Boston, MA 02134
Re:X4 Pharmaceuticals, Inc
Registration Statement on Form S-3
Filed October 19, 2020
File No. 333-249544
Dear Dr. Ragan:
            This is to advise you that we have not reviewed and will not review your registration
statement.
            Please refer to Rules 460 and 461 regarding requests for acceleration.  We remind you
that the company and its management are responsible for the accuracy and adequacy of their
disclosures, notwithstanding any review, comments, action or absence of action by the staff.
            Please contact Ada D. Sarmento at 202-551-3798 with any questions.
Sincerely,
Division of Corporation Finance
Office of Life Sciences
cc:       Daniel I. Goldberg, Esq.

CORRESP
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CORRESP

 X4 PHARMACEUTICALS, INC.

955 Massachusetts Avenue, 4th Floor

Cambridge, MA 02139

 August 17, 2020

VIA EDGAR

 United
States Securities and Exchange Commission

 Division of Corporation Finance

100 F Street, N.E.

 Washington, D.C. 20549

Attn:    Tim Buchmiller

RE:
 X4 Pharmaceuticals, Inc.

Registration Statement on Form S-3

File No. 333-242372

Acceleration Request

Requested Date: August 19, 2020

Requested Time: 4:00 p.m. Eastern Time

Ladies and Gentlemen:

 Pursuant to Rule 461 under the
Securities Exchange Act of 1933, as amended, the undersigned registrant hereby requests that the Securities and Exchange Commission take appropriate action to cause the above-referenced Registration Statement on Form
S-3 (File No. 333-242372) (the “Registration Statement”) to become effective at 4:00 p.m. Eastern Time on Wednesday, August 19, 2020,
or as soon thereafter as is practicable.

 Once the Registration Statement has been declared effective, please orally confirm that event with Daniel I.
Goldberg of Cooley LLP, counsel to the registrant, at (212) 479-6722 or with Courtney T. Thorne of Cooley LLP at (617) 937-2318.

[Signature page follows]

 Sincerely,

X4 PHARMACEUTICALS, INC.

By:

/s/ Adam S. Mostafa

 Adam S. Mostafa

 Chief Financial
Officer

cc:
 Paula Ragan, Ph.D., Chief Executive Officer, X4 Pharmaceuticals, Inc.

Daniel I. Goldberg, Cooley LLP

Courtney T. Thorne, Cooley LLP

United States securities and exchange commission logo
August 12, 2020
Paula Ragan, Ph.D.
Chief Executive Officer
X4 Pharmaceuticals, Inc
955 Massachusetts Avenue, 4th Floor
Cambridge, Massachusetts 02139
Re:X4 Pharmaceuticals, Inc
Registration Statement on Form S-3
Filed August 7, 2020
File No. 333-242372
Dear Dr. Ragan:
            This is to advise you that we have not reviewed and will not review your registration
statement.
            Please refer to Rules 460 and 461 regarding requests for acceleration.  We remind you
that the company and its management are responsible for the accuracy and adequacy of their
disclosures, notwithstanding any review, comments, action or absence of action by the staff.
            Please contact Tim Buchmiller at (202) 551-3635 with any questions.
Sincerely,
Division of Corporation Finance
Office of Life Sciences
cc:       Courtney T. Thorne, Esq.

CORRESP
1
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CORRESP

 X4 PHARMACEUTICALS, INC.

955 Massachusetts Avenue, 4th Floor

Cambridge, MA 02139

 August 27, 2019

VIA EDGAR

 United
States Securities and Exchange Commission

 Division of Corporation Finance

100 F Street, N.E.

 Washington, D.C. 20549

Attn:    Sonia Bednarowski

            Justin Dobbie

RE:
   X4 Pharmaceuticals, Inc.

  Registration Statement on Form S-3

  File No. 333-233161

  Acceleration Request

            Requested Date:
August 29, 2019

             Requested
Time:        4:00 p.m. Eastern Time

 Ladies and Gentlemen:

Pursuant to Rule 461 under the Securities Act of 1933, as amended, the undersigned registrant hereby requests that the Securities and Exchange Commission take
appropriate action to cause the above-referenced Registration Statement on Form S-3 (File No. 333-233161) (the “Registration
Statement”) to become effective at 4:00 p.m. Eastern Time on Thursday, August 29, 2019, or as soon thereafter as is practicable.

 Once
the Registration Statement has been declared effective, please orally confirm that event with Daniel I. Goldberg of Cooley LLP, counsel to the registrant, at (212) 479-6722.

[Signature page follows]

 Sincerely,

X4 PHARMACEUTICALS, INC.

By:

/s/ Adam S. Mostafa

Adam S. Mostafa

Chief Financial Officer

cc:
 Paula Ragan, Ph.D., Chief Executive Officer, X4 Pharmaceuticals, Inc.

Daniel I. Goldberg, Cooley LLP

Courtney T. Thorne, Cooley LLP

CORRESP
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CORRESP

 Daniel I. Goldberg

 +1 212 479 6722

dgoldberg@cooley.com

VIA EDGAR

 August 22, 2019

 U.S.
Securities and Exchange Commission

 Division of Corporation Finance

100 F Street, N.E.

 Washington, D.C. 20549

Attn:
 Sonia Bednarowski

 Justin Dobbie

RE:
 X4 Pharmaceuticals, Inc.

 Registration Statement on Form S-3

 Filed August 9, 2019

 File No. 333-233161

Ladies and Gentlemen:

 On behalf of our client,
X4 Pharmaceuticals, Inc. (the “Company”), we are submitting this letter in response to a comment (the “Comment”) from the staff (the “Staff”) of the U.S. Securities and Exchange
Commission (the “Commission”) contained in its letter dated August 14, 2019 (the “Comment Letter”) with respect to the Company’s registration statement on Form
S-3 filed with the Commission on August 9, 2019 (the “Registration Statement”). In connection with its response, the Company will also be filing, via EDGAR, Amendment No. 1 to
the Registration Statement (“Amendment No. 1”). For the Staff’s convenience, we have incorporated the Comment into this response letter in italics.

Registration Statement on Form S-3

Description of Capital Stock

 Anti-Takeover Provisions

 Exclusive Forum Selection, page 15

1.
 We note that your forum selection provision 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 Securities Act or Exchange Act. In that 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, and Section 22 of the Securities Act creates concurrent
jurisdiction for federal and state courts over all suits brought to enforce any duty or liability created by the Securities Act or the rules and regulations thereunder. If the provision applies to Securities Act claims, please also revise your
prospectus to state that there is uncertainty as to whether a court would enforce such provision and that investors cannot waive compliance with the federal securities laws and the rules and regulations thereunder. If this provision does not apply
to actions arising under the Securities Act or Exchange Act, please also tell us how you will inform investors in future filings that the provision does not apply to any actions arising under the Securities Act or Exchange Act.

 Cooley LLP    55 Hudson Yards    New York,
NY    10001-2157

 t: (212) 479-6000 f: (212)
479-6275 cooley.com

 August 22, 2019

Page Two

 RESPONSE: The Company
acknowledges the Staff’s comment. In response to the Staff’s comment, the Company has revised its disclosure on page 15 of Amendment No. 1 to clarify the intent of the Company’s forum selection provision. The Company currently
has a separate risk factor set forth in its periodic reports titled “Our certificate of incorporation provides that the Court of Chancery of the State of Delaware will be the exclusive forum for substantially all disputes between the Company
and our stockholders, which could limit our stockholders’ ability to obtain a favorable judicial forum for disputes with the Company or our directors, officers, employees or stockholders.” In future annual reports on Form 10-K and other future flings were applicable, the Company advises the Staff that it will revise this risk factor to clarify that its forum selection provision does not apply to actions arising under the Securities
Act or Exchange Act.

 ***

We hope that the revisions reflected in Amendment No. 1 will be acceptable to the Staff. Please contact me at (212) 479-6722 or Courtney Thorne of Cooley LLP at (617) 937-2318 with any questions or further comments regarding the Registration Statement or our response to the Comment.

Sincerely,

 /s/ Daniel I. Goldberg

Daniel I. Goldberg

 Enclosure

cc:
 Paula Ragan, Ph.D., Chief Executive Officer, X4 Pharmaceuticals, Inc.

Adam S. Mostafa, Chief Financial Officer, X4 Pharmaceuticals, Inc.

Courtney T. Thorne, Cooley LLP

August 14, 2019
Paula Ragan
Chief Executive Officer
X4 Pharmaceuticals, Inc.
955 Massachusetts Avenue, 4th Floor
Cambridge, MA 02139
Re:X4 Pharmaceuticals, Inc.
Registration Statement on Form S-3
Filed August 9, 2019
File No. 333-233161
Dear Dr. Ragan:
            We have limited our review of your registration statement to those issues we have
addressed in our 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 amending your registration statement and providing the
requested information.  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 any amendment to your registration statement and the information you
provide in response to these comments, we may have additional comments.
Registration Statement on Form S-3
Description of Capital Stock
Anti-Takeover Provisions
Exclusive Forum Selection, page 15
1.We note that your forum selection provision 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
Securities Act or Exchange Act. In that 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, and Section
22 of the Securities Act creates concurrent jurisdiction for federal and state courts over all
suits brought to enforce any duty or liability created by the Securities Act or the rules and

 FirstName LastNamePaula Ragan
 Comapany NameX4 Pharmaceuticals, Inc.
 August 14, 2019 Page 2
 FirstName LastName
Paula Ragan
X4 Pharmaceuticals, Inc.
August 14, 2019
Page 2
regulations thereunder. If the provision applies to Securities Act claims, please also revise
your prospectus to state that there is uncertainty as to whether a court would enforce such
provision and that investors cannot waive compliance with the federal securities laws and
the rules and regulations thereunder.  If this provision does not apply to actions arising
under the Securities Act or Exchange Act, please also tell us how you will inform
investors in future filings that the provision does not apply to any actions arising under the
Securities Act or Exchange Act.
            We remind you that the company and its management are responsible for the accuracy
and adequacy of their disclosures, notwithstanding any review, comments, action or absence of
action by the staff.
            Refer to Rules 460 and 461 regarding requests for acceleration.  Please allow adequate
time for us to review any amendment prior to the requested effective date of the registration
statement.
            Please contact Sonia Bednarowski at 202-551-3666 or Justin Dobbie, Legal Branch
Chief, at 202-551-3469 with any questions.
Sincerely,
Division of Corporation Finance
Office of Healthcare & Insurance

CORRESP
1
filename1.htm

CORRESP

 Arsanis, Inc.

950 Winter Street, Suite 4500

 Waltham, MA 02451

February 12, 2019

 VIA EDGAR

Securities and Exchange Commission

 Division of Corporation
Finance

 100 F Street, N.E.

 Washington, D.C. 20549

Re:
 Arsanis, Inc.

Registration Statement on Form S-4

File No. 333-228929

Request for Acceleration

 Ladies and
Gentlemen:

 Pursuant to Rule 461 promulgated under the Securities Act of 1933, as amended, Arsanis, Inc. (the “Registrant”) hereby requests
acceleration of the effective date of its Registration Statement on Form S-4 (File No. 333-228929), as amended (the “Registration Statement”), so that it
may become effective at 4:00 p.m. Eastern time on February 14, 2019, or as soon thereafter as practicable.

 [Remainder of Page
Intentionally Left Blank]

Very truly yours,

ARSANIS, INC.

By:

/s/ Michael P. Gray

Name:

Michael P. Gray

Title:

 President and Chief Executive

 Officer, Chief
Financial Officer

 Signature Page to
Acceleration Request

CORRESP
1
filename1.htm

CORRESP

 Arsanis, Inc.

950 Winter Street, Suite 4500

 Waltham, MA 02451

February 12, 2019

 VIA EDGAR

Securities and Exchange Commission

 Division of Corporation
Finance

 100 F Street, N.E.

 Washington, D.C. 20549

Re:
 Arsanis, Inc.

 Registration Statement on Form S-3

 File No. 333-229377

 Request for Acceleration

Ladies and Gentlemen:

 Pursuant to Rule 461 promulgated under
the Securities Act of 1933, as amended, Arsanis, Inc. (the “Registrant”) hereby requests acceleration of the effective date of its Registration Statement on Form S-3 (File No. 333-229377), as amended (the “Registration Statement”), so that it may become effective at 4:00 p.m. Eastern time on February 14, 2019, or as soon thereafter as practicable.

[Remainder of Page Intentionally Left Blank]

Very truly yours,

ARSANIS, INC.

By:

/s/ Michael P. Gray

Name:

Michael P. Gray

Title:

 President and Chief Executive Officer,

 Chief
Financial Officer

 Signature Page to Acceleration Request

February 7, 2019
Michael Gray
President and Chief Executive Officer, Chief Financial Officer
Arsanis, Inc.
890 Winter Street, Suite 230
Waltham, MA 02451
Re:Arsanis, Inc.
Registration Statement on Form S-4
Filed December 20, 2018
File No. 333-228929
Dear Mr. Gray :
            This is to advise you that we have not reviewed and will not review your registration
statement.
            Please refer to Rules 460 and 461 regarding requests for acceleration.  We remind you
that the company and its management are responsible for the accuracy and adequacy of their
disclosures, notwithstanding any review, comments, action or absence of action by the staff.
            Please contact Todd Schiffman at 202-551-3491 with any questions.
Sincerely,
Division of Corporation Finance
Office of Healthcare & Insurance

CORRESP
1
filename1.htm

CORRESP

 November 13, 2017

VIA EDGAR

 U.S. Securities and Exchange Commission

Division of Corporation Finance

 100 F Street, N.E.

Washington, D.C. 20549

Attn:
Dorrie Yale

Re:
Arsanis, Inc.

Registration Statement on Form S-1

File No. 333-221050

 Acceleration
Request

 Requested Date: November 15, 2017

Requested Time: 4:00 p.m., Eastern Standard Time

Ladies and gentlemen:

 In accordance with Rule
461 under the Securities Act of 1933, as amended (the “Act”), Citigroup Global Markets Inc., Cowen and Company, LLC and Piper Jaffray & Co., as representatives of the several underwriters, hereby join Arsanis, Inc.
in requesting that the Securities and Exchange Commission take appropriate action to cause the Registration Statement on Form S-1 (File No. 333-221050) (the
“Registration Statement”) to become effective on Wednesday, November 15, 2017, at 4:00 p.m., Eastern Standard Time, or as soon as practicable thereafter.

Pursuant to Rule 460 under the Act, please be advised that we will take reasonable steps to secure adequate distribution of the preliminary
prospectus, to underwriters, dealers, institutions and others, prior to the requested effective time of the Registration Statement.

 We
have been informed by the participating underwriters that they will comply with the requirements of Rule 15c2-8 under the Securities Exchange Act of 1934, as amended, to the extent applicable.

[Signature Page Follows]

Very truly yours,

CITIGROUP GLOBAL MARKETS INC.

By:

/s/ Russell Chong

 Name:

 Russell Chong

 Title:

 Managing Director

COWEN AND COMPANY, LLC

By:

/s/ E. James Streator, III

 Name:

 E. James Streator, III

 Title:

 Managing Director

PIPER JAFFRAY & CO.

By:

/s/ Christie L. Christina

 Name:

 Christie L. Christina

 Title:

 Managing Director

Piper Jaffrey & Co.

cc:
René Russo, Pharm.D., BCPS, Arsanis, Inc.

Michael D. Maline, Goodwin Procter LLP

Edwin O’Connor, Goodwin Procter LLP

Seo Salimi, Goodwin Procter LLP

Steven D. Singer, Esq., Wilmer Cutler Pickering Hale and Dorr LLP

Cynthia T. Mazareas, Esq., Wilmer Cutler Pickering Hale and Dorr LLP

 [Signature Page to
Acceleration Request]

CORRESP
1
filename1.htm

CORRESP

 Arsanis, Inc.

890 Winter Street, Suite 230

Waltham, MA 02451

November 13, 2017

 VIA EDGAR

 Securities and Exchange Commission

 Division of
Corporation Finance

 100 F Street, N.E.

 Washington, D.C.
20549

Re:
Arsanis, Inc.

Registration Statement on Form S-1

File No. 333-221050

Request for Acceleration

 Ladies and Gentlemen:

Pursuant to Rule 461 promulgated under the Securities Act of 1933, as amended, Arsanis, Inc. (the “Registrant”) hereby requests
acceleration of the effective date of its Registration Statement on Form S-1 (File No. 333-221050), as amended (the “Registration Statement”), so that it may become effective at 4:00 p.m. Eastern time on November 15, 2017, or as
soon thereafter as practicable.

 [Remainder of Page Intentionally Left Blank]

Very truly yours,

ARSANIS, INC.

By:

/s/ René Russo

Name:

  René Russo

Title:

  President and Chief Executive Officer

 Signature Page to Acceleration Request

CORRESP
1
filename1.htm

CORRESP

 +1 617 526 6000(t)

+1 617 526 5000(f)

 wilmerhale.com

 FOIA CONFIDENTIAL TREATMENT REQUEST

 The
entity requesting confidential treatment is:

 Arsanis, Inc.

890 Winter Street, Suite 230

 Waltham, MA 02451

 Attn: René Russo

 President and Chief
Executive Officer

 (781) 819-5704

October 26, 2017

 VIA EDGAR SUBMISSION

Securities and Exchange Commission

 Division of Corporation
Finance

 100 F Street, NE

 Washington, DC 20549

Attention: Dorrie Yale

Re:
Arsanis, Inc.

 Registration Statement on Form S-1

 Filed October 20, 2017

File No. 333-221050

 Ladies and
Gentlemen:

 On behalf of Arsanis, Inc. (the “Company”), set forth below is additional information to supplement
the Company’s prior response to comment 12 contained in the letter dated September 6, 2017 from the staff (the “Staff”) of the Office of Healthcare & Insurance of the Division of Corporate Finance of the
Securities and Exchange Commission (the “Commission”) relating to the Draft Registration Statement on Form S-1 (File No. 377-01662), submitted by
the Company to the Commission on August 10, 2017. Such Draft Registration Statement has been updated by the Company as reflected in the registration statement referenced above (File No. 333-221050), which was publicly filed by the Company
on October 20, 2017 (the “Registration Statement”). The supplemental response set forth below is based upon information provided to Wilmer Cutler Pickering Hale and Dorr LLP by the Company.

*        *        *

 Wilmer Cutler Pickering
Hale and Dorr LLP, 60 State Street, Boston, Massachusetts 02109

 Beijing     Berlin
    Boston     Brussels     Denver     Frankfurt     London     Los Angeles     New York
    Oxford     Palo Alto     Washington

 Securities and Exchange Commission

October 26, 2017

  Page
 2

 The Company respectfully submits the below additional information to assist the Staff in its review of the
Company’s position with respect to its determination of the fair value of its common stock underlying its outstanding equity awards and the reasons for the differences between the recent valuation of its common stock and the estimated offering
price for its initial public offering (“IPO”).

 Rule 83 Confidential Treatment Request by Arsanis, Inc.

Request #1

 Preliminary IPO Price Range

The Company advises the Staff that it preliminarily estimates a price range of approximately $[**] to $[**] per share (the “Preliminary Price
Range”) for its IPO, before giving effect to a reverse stock split that the Company plans to implement prior to effectiveness of the Registration Statement. The actual price range to be included in a subsequent amendment to the Registration
Statement (which will comply with the Staff’s interpretation regarding the parameters of a bona fide price range) has not yet been determined and remains subject to adjustment based on factors outside of the Company’s control.
However, the Company believes that the foregoing indicative price range will not be subject to significant change.

 Arsanis, Inc. respectfully requests
that the information contained in the response be treated as confidential information and that the Commission provide timely notice to René Russo, President and Chief Executive Officer, Arsanis, Inc., 890 Winter Street, Suite 230, Waltham,
Massachusetts 02451, (781) 819-5704, before it permits any disclosure of the bracketed information in Request #1.

Determining the Fair Value of Common Stock Prior to the IPO

As there has been no public market for the Company’s common stock to date, the estimated fair value of its common stock has been determined by the
Company’s board of directors (the “Board”) as of the date of each option grant, with input from management, considering the Company’s most recent third-party valuations of its common stock and the Board’s assessment
of additional objective and subjective factors that it believed were relevant and which may have changed from the date of the most recent third-party valuation through the date of the grant. As disclosed in the Registration Statement, the Company
obtained third-party valuations of its common stock as of December 31, 2015, April 22, 2016, December 31, 2016 and April 24, 2017 that were prepared using the option-pricing method. These third-party valuations were performed in
accordance with the guidance outlined in the American Institute of Certified Public Accountants’ Accounting and Valuation Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation.

 Securities and Exchange Commission

October 26, 2017

  Page
 3

 The Company advises the Staff that the only equity awards it has granted during last twelve months
consisted of the grant of stock options on June 19, 2017, when the Company granted options to purchase an aggregate of 2,245,450 shares of common stock at an exercise price of $1.17 per share, which the Board determined to be the fair value per
share of its common stock on that date. The Board’s determination of this fair value was based, in part, on the results of a third-party valuation of the Company’s common stock as of April 24, 2017 (the “April 2017
Valuation”). The April 2017 Valuation was prepared taking into account the sale of shares of the Company’s Series D preferred stock on April 24, 2017 at a price of $3.2457 per share. In particular, the April 2017 Valuation
determined the Company’s equity value using an option-pricing model backsolve approach that was based on the actual price paid for its Series D preferred stock in this contemporaneous, arm’s-length
transaction with new and existing investors. The April 2017 Valuation then applied a discount for lack of marketability to arrive at an indication of value of the Company’s common stock and resulted in a valuation of the Company’s common
stock of $1.17 per share. From April 24, 2017 to June 19, 2017, the Company continued to operate its business in the ordinary course and there were no significant developments in its business. The Board considered the results of the April
2017 Valuation, input from management and the objective and subjective factors listed on page 88 of the Registration Statement and determined that the fair value of the Company’s common stock was $1.17 per share at the time of the June 19,
2017 option grants.

 Comparison of Most Recent Valuation and the Preliminary Price Range

As is typical in IPOs, the Preliminary Price Range was not derived using a formal determination of fair value, but was determined based on discussions between
the Company and the underwriters. Prior to October 24, 2017, the Company and underwriters had not had any specific discussions regarding the Preliminary Price Range. Among the factors that were considered in setting the Preliminary Price Range
were the following:

•

the general conditions of the securities market and the recent market prices of, and the demand for, publicly traded common stock of comparable companies;

•

the Company’s financial condition and prospects;

•

estimates of business potential and earnings prospects for the Company and the industry in which it operates;

•

recent performance of IPOs of companies in the biotechnology sector; and

•

progress and stage of development of the Company’s development programs.

 Securities and Exchange Commission

October 26, 2017

  Page
 4

 Rule 83 Confidential Treatment Request by Arsanis, Inc.

Request #2

 The Company believes that the difference
between the fair value of its common stock as of June 19, 2017 of $1.17 per share and the Preliminary Price Range of $[**] to $[**] per share is the result of the factors above and the following factors and positive developments with respect to
the Company’s business that occurred subsequent to June 19, 2017:

•

The Preliminary Price Range necessarily assumes that the Company’s IPO has occurred and a public market for the Company’s common stock has been created, and therefore excludes any discount for lack of
marketability of the Company’s common stock. In contrast, a discount for lack of marketability of [**]% was applied to arrive at the fair value of common stock determined in the April 2017 Valuation.

Arsanis, Inc. respectfully requests that the information contained in the response be treated as confidential information and that the Commission provide
timely notice to René Russo, President and Chief Executive Officer, Arsanis, Inc., 890 Winter Street, Suite 230, Waltham, Massachusetts 02451, (781) 819-5704, before it permits any disclosure of the
bracketed information in Request #2.

•

The Preliminary Price Range necessarily assumes that all of the Company’s preferred stock has converted into common stock in connection with this IPO. The Company’s preferred stock currently has substantial
economic rights and preferences over the Company’s common stock. Upon the closing of this IPO, all outstanding shares of the Company’s preferred stock will convert into common stock, thus eliminating the superior rights and preferences of
the preferred stock as compared to the common stock.

•

Since the June 19, 2017 date of the Company’s most recent determination of the value of its common stock, the Company has taken several steps towards the completion of an IPO, including:

•

in mid-July, the Company held its IPO organizational meeting;

•

in September and October 2017, the Company held “testing-the-waters” meetings at which the Company received positive feedback
from potential investors; and

•

on October 20, 2017, the Company publicly filed the Registration Statement with the Commission.

 Securities and Exchange Commission

October 26, 2017

  Page
 5

•

Since the June 19, 2017 date of the Company’s most recent determination of the value of its common stock, the Company also made further progress in the advancement of its lead development programs and the
execution of its business strategies, including:

•

continued successful enrollment of its leading Phase 2 clinical trial of ASN100 for the prevention of S. aureus pneumonia in high-risk, mechanically ventilated patients;

•

initiation of activities to support a study of ASN100 for the treatment of S. aureus pneumonia in mechanically ventilated patients who do not meet the enrollment criteria for the ongoing Phase 2 trial due to
having already developed pneumonia;

•

the advancement of multiple development candidates into in vitro assays and in vivo models of RSV in the Company’s ASN500 program; and

•

the addition of two new members to the Company’s Board who possess relevant strategic, financial, fundraising and biotechnology and pharmaceutical industry experience.

•

The proceeds of a successful IPO would substantially strengthen the Company’s balance sheet by increasing its cash resources. In addition, the completion of this IPO would provide the Company with more ready access
to the public company equity and debt markets.

 The Company respectfully submits that the difference between the latest valuation and the
Preliminary Price Range is reasonable. The Company will continue to update its disclosure for all equity related transactions through the effective date of the Registration Statement.

The Company respectfully requests that the Staff return to the undersigned this letter pursuant to Rule 418 of the Securities Act of 1933, as amended, once
the Staff has completed its review. For the convenience of the Staff, we have provided a self-addressed stamped envelope for this purpose. We respectfully reserve the right to request that this letter be returned to us at an earlier date.

In addition, the Company requests confidential treatment under 17 C.F.R. § 200.83 for the contents of this letter and has submitted a separate request
for confidential treatment in accordance therewith to the Commission’s Office of Freedom of Information and Privacy Act Operations.

*        *        *

 Securities and Exchange Commission

October 26, 2017

  Page
 6

 If you have any further questions or comments, or if you require any additional
information, please contact the undersigned by telephone at (617) 526-6393. Thank you for your assistance.

Very truly yours,

 /s/ Cynthia T. Mazareas

Cynthia T. Mazareas

cc:
René Russo, Arsanis, Inc.

 Office of Freedom of Information and Privacy Act Operations

 Securities and Exchange Commission

100 F Street N.E., Mail Stop 2736

Washington, D.C. 20549

CORRESP
1
filename1.htm

CORRESP

 +1 617 526 6000(t)

+1 617 526 5000(f)

 wilmerhale.com

 October 20, 2017

 By Electronic Submission

Securities and Exchange Commission

 Division of Corporation
Finance

 100 F Street, N.E.

 Washington, DC 20549

Attention: Dorrie Yale

Re:
Arsanis, Inc.

 Registration Statement on Form
S-1

 Ladies and Gentlemen:

Submitted herewith for filing on behalf of Arsanis, Inc. (the “Company”) is a Registration Statement on Form
S-1 (the “Registration Statement”) relating to the registration under the Securities Act of 1933, as amended (the “Securities Act”), of $57,500,000 of Common Stock of the
Company. The filing of the Registration Statement is being effected by direct transmission to the EDGAR System of the Securities and Exchange Commission (the “Commission”). On October 20, 2017, in anticipation of this filing, the
Company caused the filing fee of $7,158.75 to be wire transferred to the Commission’s account at US Bank. The Registration Statement relates to the Company’s initial public offering of securities. It is the intent of the Company and the
managing underwriters of the proposed offering to have the Registration Statement declared effective as early as possible. Acceleration requests may be made orally, and the Company and the managing underwriters of the proposed offering have
authorized us to represent on their behalf that they are aware of their obligations under the Securities Act with respect thereto.

 The Registration
Statement is also being filed in response to comments contained in the letter dated October 3, 2017 (the “Letter”) from the Staff (the “Staff”) of the Office of Healthcare & Insurance of the Division
of Corporate Finance of the Commission to René Russo, the Company’s President and Chief Executive Officer, relating to Amendment No. 1 to the Confidential Draft Registration Statement on Form
S-1 (File No. 377-01662) submitted by the Company to the Commission on September 20, 2017, and we are responding on behalf of the Company to the comments of
the Staff contained in the Letter.

 The responses set forth below are based upon information provided to us by representatives of the Company. The
responses are keyed to the numbering of the comments and the headings used in the Letter. Where appropriate, the Company has responded to the Staff’s comments by making changes to the disclosure in the Registration Statement. Page numbers
referred to in the responses reference the Registration Statement.

 Securities and Exchange Commission

Division of Corporation Finance

 October 20, 2017

Page 2

 On behalf of the Company, we advise you as follows:

Prospectus Summary

 Our Pipeline, page 1

1.
We refer to your revised disclosure on page 4 in response to prior comment 1 that you are currently conducting preclinical studies for your ASN300 program. However, we note that you state on your website that you are
“currently set to enter preclinical development” for this program. Please reconcile this discrepancy, and if the ASN300 program remains in the discovery phase, please revise your table here and in the Business section to remove this
program as it would be premature to include it.

Response:
In response to the Staff’s comment, the Company has updated its website to reflect that its ASN300 program is currently in preclinical development.

Key Advantages of ASN100, page 2

2.
We acknowledge your revised disclosure and response to prior comment 3. Your revised disclosure indicates that you expect to conduct an interim analysis to assess the probability that the trial will succeed as
currently designed. To balance your disclosure in the fourth bullet on page 2, please also include a brief reference in the bullet to this expected interim analysis.

Response:
In response to the Staff’s comment, the Company has revised the disclosure on pages 3 and 98 of the Registration Statement.

ASN300 and ASN200, page 4

3.
We refer to your revised disclosure that in early studies, you have observed “efficacy” and “potentiation of antibiotic efficacy.” As efficacy determinations are solely within the FDA’s
authority, please remove these statements here and elsewhere in your prospectus regarding these product candidates’ efficacy.

Response:
In response to the Staff’s comment, the Company has revised the disclosure on pages 4 and 103 of the Registration Statement.

Use of Proceeds, page 60

4.
We acknowledge your response to prior comment 10. Please also clarify that the proposed use described in the third bullet of the third paragraph is not expected to apply to the ASN500 program.

 Securities and Exchange Commission

Division of Corporation Finance

 October 20, 2017

Page 3

Response:
In response to the Staff’s comment, the Company has revised the disclosure on page 60 of the Registration Statement.

Business, Phase 2 Clinical Trial, page 99

5.
We acknowledge your revised disclosure, but we note that your discussion in the first paragraph on page 99 states that your trial is designed to detect a “statistically significant” reduction in the
occurrence of S. aureus pneumonia, and that you note the risk on page 43 that clinical trial results may not meet the level of statistical significance required for FDA approval. Please expand your discussion to explain the term and discuss how
statistical significance relates to the FDA’s evidentiary standards of efficacy. Refer to prior comment 13.

Response:
In response to the Staff’s comment, the Company has revised the disclosure on page 99 of the Registration Statement to delete the reference to statistical significance. The Company supplementally advises the
Staff that the Food and Drug Administration (the “FDA”) does not provide guidance on powering of Phase 2 clinical trials for statistical significance and, accordingly, any statistical significance of data from the Company’s
Phase 2 trial will not be dispositive with respect to the FDA’s evidentiary standards of efficacy. If the Company’s Phase 2 trial meets its primary endpoint, the FDA will review the totality of the evidence to determine the degree to which
the results of the trial support the potential for safety and efficacy of ASN100 and what additional clinical trials will be required to demonstrate safety and efficacy.

Collaboration and License Agreements, page 108

6.
We acknowledge your revised disclosure in response to prior comment 17. Please further revise your disclosure to provide investors with a sense of understanding of when the Adimab Option Agreement will expire if you
do not exercise the option. Additionally, with respect to both of the Adimab agreements, please revise your disclosure to clarify the expiration of the royalty terms.

Response:
In response to the Staff’s comment, the Company has revised the disclosure on pages 110, 111, F-23, F-24 and F-25 of the
Registration Statement.

 Transactions with Related Persons, page 159

7.
Please file as an exhibit the Stockholders´ Agreement discussed on page 162 or advise why you believe the agreement is not required to be filed.

Response:
In response to the Staff’s comment, the Company has filed the Stockholders’ Agreement as an exhibit to the Registration Statement.

 Securities and Exchange Commission

Division of Corporation Finance

 October 20, 2017

 Page
 4

 If you have any further questions or comments, or if you require any additional information,
please contact the undersigned by telephone at (617) 526-6393 or facsimile at (617) 526-5000. Thank you for your assistance.

Very truly yours,

 /s/ Cynthia T.
Mazareas

Cynthia T. Mazareas

 cc:     René
Russo, Arsanis, Inc.

October 3, 2017
Rene Russo
President and Chief Executive Officer
Arsanis, Inc.
890 Winter Street, Suite 230
Waltham, MA 02451
Arsanis, Inc.
Amendment No. 1 to Draft Registration Statement on Form S-1
Submitted September 20, 2017
CIK No. 0001501697Re:
Dear Dr. Russo:
We have reviewed your amended draft offering 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 offering statement or publicly filing your offering 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 any amendment
to your draft offering statement or filed offering statement and the information you provide in
response to these comments, we may have additional comments. Unless we note otherwise, our
references to prior comments are to comments in our September 6, 2017 letter.
Amendment No. 1 to Draft Registration Statement on Form S-1
Prospectus Summary
Our Pipeline, page 1
1. We refer to your revised disclosure on page 4 in response to prior comment 1 that you are
currently conducting preclinical studies for your ASN300 program.  However, we note
that you state on your website that you are "currently set to enter preclinical
development" for this program.  Please reconcile this discrepancy, and if the ASN300
program remains in the discovery phase, please revise your table here and in the Business
section to remove this program as it would be premature to include it.

Rene Russo
Arsanis, Inc.
October 3, 2017
Page 2

Key Advantages of ASN100, page 2
2. We acknowledge your revised disclosure and response to prior comment 3.  Your revised
disclosure indicates that you expect to conduct an interim analysis to assess the
probability that the trial will succeed as currently designed.  To balance your disclosure in
the fourth bullet on page 2, please also include a brief reference in the bullet to
this expected interim analysis.
ASN300 and ASN200, page 4
3. We refer to your revised disclosure that in early studies, you have observed "efficacy" and
"potentiation of antibiotic efficacy."  As efficacy determinations are solely within the
FDA’s authority, please remove these statements here and elsewhere in your prospectus
regarding these product candidates' efficacy.
Use of Proceeds, page 60
4. We acknowledge your response to prior comment 10.  Please also clarify that the
proposed use described in the third bullet of the third paragraph is not expected to apply
to the ASN500 program.
Business
Phase 2 Clinical Trial, page 99
5. We acknowledge your revised disclosure, but we note that your discussion in the first
paragraph on page 99 states that your trial is designed to detect a "statistically significant"
reduction in the occurrence of S. aureus pneumonia, and that you note the risk on page 43
that clinical trial results may not meet the level of statistical significance required for
FDA approval.  Please expand your discussion to explain the term and discuss how
statistical significance relates to the FDA’s evidentiary standards of efficacy.  Refer to
prior comment 13.
Collaboration and License Agreements, page 107
6. We acknowledge your revised disclosure in response to prior comment 17.  Please further
revise your disclosure to provide investors with a sense of understanding of when the
Adimab Option Agreement will expire if you do not exercise the option.  Additionally,
with respect to both of the Adimab agreements, please revise your disclosure to clarify
the expiration of the royalty terms.
Transactions with Related Persons, page 158
7. Please file as an exhibit the Stockholders´ Agreement discussed on page 161 or advise
why you believe the agreement is not required to be filed.

Rene Russo
Arsanis, Inc.
October 3, 2017
Page 3

You may contact Ibolya Ignat at 202-551-3636 or Sharon Blume at 202-551-3474 if you
have questions regarding comments on the financial statements and related matters.  Please
contact Dorrie Yale at 202-551-8776 or Christopher Edwards at 202-551-6761 with any other
questions.
Division of Corporation Finance
Office of Healthcare & Insurance
cc: Cynthia T. Mazareas

September 6, 2017
Rene Russo
President and Chief Executive Officer
Arsanis, Inc.
890 Winter Street, Suite 230
Waltham, MA 02451
Arsanis, Inc.
Draft Registration Statement on Form S-1
Submitted August 10, 2017
CIK No. 0001501697Re:
Dear Dr. Russo:
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 registration statement or filed registration statement, we may have additional
comments.
Form DRS filed August 10, 2017
Prospectus Summary
Our Pipeline, page 1
1. We note your inclusion in your pipeline table of ASN300 and ASN200, and your notation
that you need external funding for these two programs.  We also note your statement on
page 16 that you intend to focus your capital resources primarily on the development of
ASN100 and to rely primarily on external funding for the development of other product
candidates.  Since it does not appear that you are currently pursuing these programs, it is
premature to include them in a pipeline table.  Please revise your table to remove these
programs, or alternatively, please explain how you are pursuing them.

Rene Russo
Arsanis, Inc.
September 6, 2017
Page 2
Key Advantages of ASN100, page 2
2. Please revise the third bullet in this section to disclose the number of participants treated
with the ASN100 combination dose in the Phase 1 trial at doses equivalent to or higher
than the dosage being used in the Phase 2 trial. Please add similar disclosure in your
Business section in your discussion of the Phase 1 data.
3. We refer to your statement in the fourth bullet that your Phase 2 trial has been designed to
demonstrate superiority to placebo, and that you expect any Phase 3 trial will be similarly
designed.  We also note your statements in the first full paragraph on page 3 and in the
second paragraph on page 97 that an independent data monitoring committee will be
conducting an analysis of interim results to determine the power of the trial for statistical
significance.  Please balance your disclosure in this bullet to explain that you are still in
the early stages of this trial and to refer to this interim analysis.  In addition, in the first
full paragraph on page 3, please also disclose how many of the expected 354 patients in
the Phase 2 trial have been enrolled as of a recent date.
Risks Associated with Our Business, page 4
4. Please disclose the accumulated deficit in the first bullet, and expand your second bullet
to explain that you do not expect this offering to provide sufficient proceeds to allow you
to complete a Phase 3 trial for ASN100 (assuming a successful completion of the Phase 2
trial).
5. Please add a bullet to discuss the continued concentration of ownership by management
and your principal stockholders after the offering.  Please include in this bullet and in the
corresponding risk factor beginning on page 50 a discussion of the number of your
directors who are affiliated with your principal stockholders.
Implications of Being an Emerging Growth Company, page 5
6. 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.
The Offering, page 6
7. Please disclose what percentage of your total share capital will be held by the public
immediately after the offering.
Risk Factors, page 10
8. Please add a risk factor to discuss potential conflicts that exist because the chairman of
your board is also the co-founder and CEO of Adimab, the counterparty to your license

Rene Russo
Arsanis, Inc.
September 6, 2017
Page 3

agreement for your lead product candidate.
Our existing and any future indebtedness . . ., page 14
9. Please expand your discussion in this risk factor to disclose that borrowings under your
loan agreement with SVB are collateralized by a pledge of 65% of the capital stock of
your Austrian subsidiary.
Use of Proceeds, page 59
10. Please revise the third bullet in the third paragraph to discuss how much of the proceeds
will be used to advance your preclinical program ASN500 for the treatment of RSV.
11. We refer to your statement that you expect you will need additional funding to complete
the clinical development of ASN100.  Please clarify the amount of such additional
funding you will need.  Refer to Instruction 3 of Item 504 of Regulation S-K.
Management's Discussion And Analysis of Financial Condition and Results of Operations
Stock-Based Compensation, page 85
12. Please disclose the dates and fair values for the third-party valuations of your common
stock during the periods presented.  Clarify the estimated common stock price at the time
of the June 19, 2017 options issuance and explain to us how it relates to the share price in
the April 2017 Series D convertible preferred stock financing. Once you have an
estimated offering price or range, please explain to us 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.
Business, page 90
13. We note your reference to statistical significance in the last paragraph on this page.
 Please expand your discussion to explain the term and discuss how statistical
significance relates to the FDA’s evidentiary standards of efficacy.
Our Lead Product Candidate: ASN100, page 93
14. We note your statement in the penultimate paragraph on page 98 that preclinical assays
for anti-infective products are generally predictive of clinical efficacy.  Please revise your
disclosure to explain your rationale of this statement.

Rene Russo
Arsanis, Inc.
September 6, 2017
Page 4

Intellectual Property, page 103
15. Please expand your disclosure regarding your patent portfolio to disclose the type of
patent protection provided by the patents or patent applications (e.g., composition of
matter, method of use).  Please also disclose the foreign jurisdictions where you have
issued patents or pending applications.
16. We refer to your statement that you co-own two patent families with Max Planck
Gesellschaft.  Please revise your disclosure to explain whether there is an agreement
between you covering the use of these patents.
Collaboration and License Agreements, page 105
17. Please revise your disclosure to discuss the term of each of these agreements.
18. Please revise your description of the Adimab Collaboration Agreement to also discuss the
payment terms if you elect to pay through the revenue election method within a ten-point
range.
Scientific and Clinical Advisory Boards, page 129
19. Please explain how members of the scientific and clinical advisory boards are
compensated.
Management
Board Composition, page 136
20. Please revise your disclosure to explain how your current directors were elected pursuant
to the terms of your charter documents currently in place.
Consolidated Financial Statements
Notes to Consolidated Financial Statements
20.  Subsequent Events, page F-50
21. You disclose that because the price per share of the Series D preferred stock was lower
than the Conversion Price of your Series A-2, Series B and Series C preferred stock, the
conversion price of each of these series was amended to $3.7172 per share for Series A-2,
$4.7510 per share for Series B and $5.6739 per share for Series C preferred stock. In light
of these amendments, please explain in more detail how you accounted for the original
instruments from the date of their issuance through the date you amended the conversion
terms.

Rene Russo
Arsanis, Inc.
September 6, 2017
Page 5
You may contact Ibolya Ignat at 202-551-3636 or Sharon Blume at 202-551-3474 if you
have questions regarding comments on the financial statements and related matters.  Please
contact Dorrie Yale at 202-551-8776 or Christopher Edwards at 202-551-6761 with any other
questions.
Division of Corporation Finance
Office of Healthcare & Insurance
cc: Cynthia T. Mazareas