About Us

Developing novel therapeutics to treat people with rare immune system disorders

X4 Pharmaceuticals is a late-stage clinical biopharmaceutical company and a leader in the discovery and development of novel therapies for the treatment of diseases of the immune system via antagonism of the CXCR4 pathway, with a focus on rare diseases and those with limited treatment options. We believe that inhibition of the CXCR4 receptor creates the potential to provide therapeutic benefit across a wide variety of diseases, including primary immunodeficiencies and certain types of cancer.

Our lead clinical candidate, mavorixafor, is a first-in-class, small molecule antagonist of chemokine receptor CXCR4 being developed as a once-daily oral therapy. We are currently evaluating the safety and efficacy of mavorixafor in a Phase 3 clinical trial for the treatment of patients with WHIM syndrome, a rare, inherited, primary immunodeficiency disease caused by genetic mutations in the CXCR4 receptor gene. To date, mavorixafor has demonstrated proof-of-concept in WHIM syndrome in a Phase 2 clinical trial, including clinically meaningful increases in neutrophil and lymphocyte biomarker counts, as well as a trend of reduction in infection rates and wart burden, and has been generally well tolerated. Enrollment in the Phase 3 WHIM clinical trial is now complete and top-line clinical results are expected in the fourth quarter of 2022. For the WHIM indication, mavorixafor has been granted Breakthrough Therapy Designation, Fast Track Designation, and Rare Pediatric Designation in the U.S., and Orphan Drug Status in both the U.S. and European Union.

We are also studying mavorixafor in two Phase 1b clinical trials – one in combination with ibrutinib in patients with a rare B-cell lymphoma called Waldenstrom macroglobulinemia, and the other as a monotherapy in patients with Severe Congenital Neutropenia (SCN) and other chronic neutropenia disorders.

X4 is a global company headquartered in Boston, Massachusetts with research offices based in Vienna, Austria.


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