A Dose Determination and Safety Study of X4P-001 (Mavorixafor) in Participants With Warts, Hypogammaglobulinemia, Infections, and Myelokathexis (WHIM) Syndrome


This is a Phase 2 study with an initial 24-week Treatment Period and an Extension Phase. The primary objectives of this Phase 2 study are to determine the safety, tolerability, and dose selection of mavorixafor in participants with WHIM syndrome. Participants are allowed to continue treatment in an Extension Phase, if regionally applicable, until it becomes commercially available or until the study is terminated by the Sponsor.

Full Title of Study: “A Phase 2, Open-Label, Multi-Center Trial of Mavorixafor in Patients With WHIM Syndrome”

Study Type

  • Study Type: Interventional
  • Study Design
    • Allocation: N/A
    • Intervention Model: Single Group Assignment
    • Primary Purpose: Treatment
    • Masking: None (Open Label)
  • Study Primary Completion Date: December 2022


  • Drug: X4P-001
    • Mavorixafor will be provided as either 25 mg or 100 mg capsules.

Arms, Groups and Cohorts

  • Experimental: X4P-001
    • Initial Treatment Phase: Participants will initiate treatment with mavorixafor at 50 milligrams (mg) once daily (QD) orally or a higher dose, with potential escalation based on area under the curve for absolute neutrophil count and absolute leukocyte count (AUCANC/ALC) values to a maximum total daily dose of 400 mg. Participants are expected to receive treatment for 24 weeks in the initial Treatment Period or until development of a treatment-limiting toxicity (TLT). Extension Phase: All participants will receive mavorixafor; the dose will not exceed 400 mg. In the Extension Phase, treatment may continue until mavorixafor becomes available via an alternative mechanism (for example, drug is commercially available, an expanded access program, etc.) or until the study is terminated by the sponsor.

Clinical Trial Outcome Measures

Primary Measures

  • Mean AUCANC and/or AUCALC
    • Time Frame: Time 0 (-15 minutes [min] pre-dose), 30, 60, and 90 min (each ± 5 min) and 2, 3, 4, 8, 12, 16, and 24 hours (each ±15 min) at Weeks 5, 13, and 21

Participating in This Clinical Trial

Inclusion Criteria

Participants with a clinical diagnosis of WHIM syndrome must meet all of the following criteria to be eligible for study participation: 1. Be at least 18 years of age. 2. Has signed the current approved informed consent form. 3. Has a genotype-confirmed mutation of chemokine receptor type 4 (CXCR4) consistent with WHIM syndrome. 4. Agree to use effective contraception. 5. Be willing and able to comply with this protocol. 6. Has confirmed ANC less than or equal to (≤) 400/µL or ALC ≤650/µL or both. Exclusion Criteria:

Participants with any of the following will be excluded from participation in the study: 1. Has known systemic hypersensitivity to the mavorixafor drug substance or its inactive ingredients. 2. Is pregnant or nursing. 3. Has a known history of a positive serology or viral load for human immunodeficiency virus (HIV) or a known history of acquired immunodeficiency syndrome (AIDS). 4. Has, at Screening, laboratory tests meeting one or more of the following criteria:

  • A positive antibody test for hepatitis C virus (HCV), unless documented to have no detectable viral load on 2 independent samples. – A positive test for hepatitis B surface antigen (HBsAg). 5. Has any medical or personal condition that, in the opinion of the Investigator, may potentially compromise the safety or compliance of the participant, or may preclude the participant's successful completion of the clinical study.
  • Gender Eligibility: All

    Minimum Age: 18 Years

    Maximum Age: N/A

    Are Healthy Volunteers Accepted: No

    Investigator Details

    • Lead Sponsor
      • X4 Pharmaceuticals
    • Provider of Information About this Clinical Study
      • Sponsor
    • Overall Official(s)
      • Chief Medical Officer, Study Director, X4 Pharmaceuticals

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