X4 Pharmaceuticals, Inc. (Nasdaq: XFOR) held a virtual investor day on Oct. 29, 2026, outlining its clinical development timeline for mavorixafor, an investigational oral CXCR4 antagonist being studied in primary chronic neutropenia (PCN).

According to the company, claims data identified approximately 15,000 symptomatic U.S. patients aged 12 and older with an absolute neutrophil count below 1,000 cells/µL and two or more infections in 2025, representing the base-case market. A potential expansion population of approximately 30,000 patients with one or more infections was also identified, subject to FDA labeling.

X4 said it remains on track to complete target enrollment of 126 participants in its 4WARD Phase 3 trial by the end of 2026. Blinded, pooled baseline data as of September 2026 show a median absolute neutrophil count of 483 cells/µL, with 68% of participants reporting three or more infections at baseline.

The company also introduced a planned Phase 2b trial called 4STEPS, designed to evaluate whether G-CSF dosage can be safely reduced after initiating mavorixafor. The first participant is expected to be enrolled in the first quarter of 2027.

Topline data from both the 4WARD and 4STEPS trials are expected in the first quarter of 2028. If 4WARD results are positive, X4 said a regulatory submission could follow, with potential FDA approval in late 2028 or early 2029.

"PCN is a serious, chronic disease with no new therapy approved in more than 30 years," said Adam Craig, M.D., Ph.D., Executive Chair of X4 Pharmaceuticals. "Our 4WARD Phase 3 trial is designed to clearly measure the clinical benefit of mavorixafor, and we remain on track to fully enroll the study by year end."

Mavorixafor is already approved in the U.S. and the European Union as XOLREMDI for patients aged 12 and older with WHIM syndrome. The FDA has granted Fast Track designation to the drug for the treatment of chronic neutropenia. Current PCN treatment options are limited to G-CSF injections and antibiotics, with no approved oral therapy available.