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

A Phase 2, Open-Label, Multi-Center Trial of Mavorixafor in Patients With 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 may continue treatment in an Extension Phase, if regionally applicable, 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 for any reason.

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.