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                                                           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.