About Us

Developing novel therapeutics to treat people with chronic neutropenic 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 chronic neutropenic disorders 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. Results from this pivotal trial are expected in the fourth quarter of 2022, and we anticipate filing a U.S. New Drug Application for mavorixafor in WHIM early in the second half of 2023, if the Phase 3 results are positive.
  • We have also evaluated mavorixafor in two Phase 1b clinical trials:
    • One in patients with chronic neutropenic disorders, including idiopathic, cyclic, and congenital neutropenia: results from the first part of this trial (n=25) demonstrated mavorixafor’s ability to raise neutrophil counts in 100% of patients dosed and across all patient populations studied, both as monotherapy and in combination with standard of care, injectable G-CSF (granulocyte colony-stimulating factor). Further study of mavorixafor in these chronic neutropenic disorders is ongoing.
    • One in combination with the BTK inhibitor ibrutinib in patients with a rare B-cell lymphoma called Waldenström’s macroglobulinemia: results from this trial (n=16) demonstrated that 91% of evaluable patients achieved a major response to therapy, with 100% of relapsed/refractory patients having achieved a major response. Further studies of mavorixafor in oncology indications will be subject to completing a strategic partnership.

We believe that commercializing mavorixafor and providing a new therapeutic option to the estimated 50,000 individuals (U.S.) diagnosed with chronic neutropenic disorders has the potential to revolutionize the treatment landscape, which is currently only served by injectable therapies with significant limitations.

X4 is a global company headquartered in Boston, Massachusetts with a research center of excellence in Vienna, Austria.


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