Efficacy and Safety Study of Mavorixafor in Participants With Warts, Hypogammaglobulinemia, Infections, and Myelokathexis (WHIM) Syndrome

This study has a double-blind, Randomized Placebo-Controlled Period and an Open-Label Period. The primary objective of the Randomized Placebo-Controlled Period is to demonstrate the efficacy of mavorixafor in participants with WHIM syndrome as assessed by increasing levels of circulating neutrophils compared with placebo, and relative to a clinically meaningful threshold. The primary objective of the Open-Label Period is to evaluate the safety and tolerability of mavorixafor in participants with WHIM syndrome. Participants are allowed to continue treatment in the Open-Label Period, if regionally applicable, until mavorixafor becomes commercially available, or until the study is terminated by the Sponsor.

Inclusion Criteria for the Randomized Placebo-Controlled Period : * Have signed the current approved informed consent form. Participants under 18 years of age (in the Netherlands and other applicable regions, participants under 16 years of age) will sign an approved informed assent form and must also have a signed parental/legal guardian consent. * Have a genotype-confirmed mutation of chemokine (C-X-C motif) receptor 4 (CXCR4) consistent with WHIM phenotype. * Agree to use a highly effective form of contraception. * Be willing and able to comply with the protocol. * Have confirmed ANC ≤400 cells/µL during screening, obtained while participant has no clinical evidence of infection. Inclusion Criteria for the Open-Label Period: * Completed the Randomized Period; or * Granted Early Release from the Randomized Period. Exclusion Criteria: * Has known systemic hypersensitivity to the mavorixafor drug substance, its inactive ingredients, or the placebo. * Is pregnant or breastfeeding. * Has any medical or personal condition, which 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.