The United States Food and Drug Administration (US FDA) has granted Breakthrough Therapy Designation to United States-based X4 Pharmaceuticals (Nasdaq: XFOR) for mavorixafor (X4P-001) intended for the treatment of adult patients with WHIM (Warts, Hypogammaglobulinemia, Infections, and Myelokathexis) syndrome, a rare, inherited, primary immunodeficiency disease caused by genetic mutations in the CXCR4 receptor gene, it was reported yesterday.

The product is a potential first-in-class, once-daily, oral, small molecule antagonist of chemokine receptor CXCR4 that is presently being investigated in a pivotal Phase three global clinical trial, 4WHIM, for the treatment of WHIM syndrome.

The Breakthrough Therapy Designation granted to the product is based on data from the company's Phase two open-label, multi-centre trial of mavorixafor in adult patients with WHIM syndrome. In this trial, proof of concept was established based on clinically meaningful increases in absolute neutrophil counts, absolute lymphocyte counts, evidence indicating reductions in infection rates and wart burden, and a safety profile showing that mavorixafor is well-tolerated.

Mavorixafor was granted orphan drug status by the US FDA in 2018 and by the European Commission in 2019 for the treatment of WHIM syndrome and is also being developed by X4 to treat Severe Congenital Neutropenia (SCN), Waldenström's macroglobulinemia (WM) and clear cell renal cell carcinoma (ccRCC).