X4 is focused on improving healthy immune system function by developing novel therapeutics for the treatment of rare diseases ... . Our first-in-class, oral, small molecule therapeutics are antagonists of chemokine receptor CXCR4, which have the potential to treat a broad range of rare diseases, including primary immunodeficiencies (PIs) and cancer. A number of PIs are attributed to the improper trafficking of immune cells related to increasing signaling on the CXCR4 receptor by its ligand CXCL12. X4 Pharmaceutical’s lead product candidate, mavorixafor (X4P-001), is a potentially first-in-class, once-daily, oral inhibitor of CXCR4, currently in a Phase 3 clinical trial for the treatment of WHIM syndrome, a rare, inherited, primary immunodeficiency disease caused by gain of function mutations in the CXCR4 receptor gene. Mavorixafor has demonstrated proof-of-concept in WHIM syndrome in a Phase 2 trial, including clinically meaningful increases in neutrophil and lymphocyte biomarker counts, as well as reduction in infection rates and wart burden, and a favorable safety and tolerability profile. Mavorixafor has been granted Breakthrough Therapy Designation by the U.S. Food and Drug Administration (FDA) for the treatment of adult patients with WHIM syndrome, and was granted orphan drug status by the FDA and by the European Commission for the treatment of WHIM syndrome, and rare pediatric disease designation by the FDA. Mavorixafor is also being developed by X4 to treat Severe Congenital and Idioipathic Neutropenia (SCN), CXCR4 mutant Waldenström’s macroglobulinemia (WM), clear cell renal cell carcinoma (ccRCC), and other solid tumors. X4 is a public biopharmaceutical company headquartered in Boston, Massachusetts with research offices in Vienna, Austria. read more