X4 Pharmaceuticals is a biopharmaceutical company that researches, develops, and commercializes therapeutics for rare diseases. They're currently conducting Phase III clinical trials on their lead product, mavorixafor, to treat various rare diseases, including hypogammaglobulinemia and myelokathexis syndrome. The company is also developing two CXCR4 antagonists to treat brain cancers and primary immunodeficiencies.