# EDGAR Filing Document

**Accession Number:** 0001501697
**File Stem:** 0001501697-25-000019
**Filing Date:** 2025-9
**Character Count:** 2451
**Document Hash:** 5bef79c5ada24d2423b3cc4b71e3da05
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001501697-25-000019.hdr.sgml**: 20251121

**ACCESSION NUMBER**: 0001501697-25-000019

**CONFORMED SUBMISSION TYPE**: CORRESP

**PUBLIC DOCUMENT COUNT**: 1

**FILED AS OF DATE**: 20250915

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** X4 Pharmaceuticals, Inc
- **CENTRAL INDEX KEY:** 0001501697
- **STANDARD INDUSTRIAL CLASSIFICATION:** BIOLOGICAL PRODUCTS (NO DIAGNOSTIC SUBSTANCES) [2836]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 273181608
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** CORRESP

**BUSINESS ADDRESS:**
- **STREET 1:** 61 NORTH BEACON STREET
- **STREET 2:** 4TH FLOOR
- **CITY:** BOSTON
- **STATE:** MA
- **ZIP:** 02134
- **BUSINESS PHONE:** 857-529-8300

**MAIL ADDRESS:**
- **STREET 1:** 61 NORTH BEACON STREET
- **STREET 2:** 4TH FLOOR
- **CITY:** BOSTON
- **STATE:** MA
- **ZIP:** 02134

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Arsanis, Inc.
- **DATE OF NAME CHANGE:** 20100920

**X4 Pharmaceuticals, Inc.**

61 North Beacon Street, 4<sup>th</sup> Floor

Boston, MA 02134

September 15, 2025

<u>VIA EDGAR</u>

U.S. Securities and Exchange Commission

Division of Corporation Finance

100 F Street, N.E.

Washington, DC 20549

Attention: Jessica Dickerson

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| | |
|:---|:---|
| **Re:** | **X4 Pharmaceuticals, Inc.** |

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**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.

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| | |
|:---|:---|
| Sincerely, | Sincerely, |
| X4 PHARMACEUTICALS, INC. | X4 PHARMACEUTICALS, INC. |
| By: | /s/ David Kirske |
|  | David Kirske |
|  | Chief Financial Officer and Treasurer |

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cc: Adam R. Craig, M.D., Ph.D., X4 Pharmaceuticals, Inc.Natasha Thoren, X4 Pharmaceuticals, Inc.Melanie E. Neary, Dunn & Crutcher LLP

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