Phase III 4WHIM trial of X4P-001-RD meets primary endpoint in WHIM syndrome

4WHIM met its primary endpoint, with mavorixafor achieving clinical and statistical superiority over placebo when measuring TATANC, or the length of time that participants’ absolute neutrophil counts (ANC) remained above a clinically meaningful threshold of 500 cells per microliter (severe neutropenia), over 24-hour periods at 4 time points throughout the 52-week trial.

Mean TATANC, was 15.04 hours in the treatment group versus 2.75 hours in the placebo group (P<0.0001). 4whim also met a key secondary endpoint, with mavorixafor achieving clinical and statistical superiority over placebo when measuring tatalc, or the length of time that participants’ absolute lymphocyte counts (alc) remained above a clinically meaningful threshold of 1,000 cells per microliter (lymphopenia), over 24-hour periods at 4 time points throughout the 52-week trial. mean tatalc was 15.80 hours in the treatment group versus 4.55 hours in the placebo group.

Increases in both TATANC and TATALC were maintained versus placebo and baseline across 52 weeks, demonstrating durability of treatment effect during the trial. Mavorixafor was generally well tolerated in the trial, with no treatment-related serious adverse events reported and no discontinuations for safety events. Following completion of the placebo-controlled portion of the trial, more than 90% of the eligible participants opted to receive treatment with mavorixafor in the open-label trial extension. Additional data review and analysis of the secondary and exploratory endpoints of the 4WHIM trial are ongoing, with plans to present detailed results at a future medical meeting.