CXCR4 and immunodeficiency disease: For the CXCL12–CXCR4 axis, the CXCR4 antagonist mavorixafor, which mobilizes stem and endothelial progenitor cells, is under investigation for harnessing this reparative potential; however, only in patients with WHIM syndrome, a rare immunodeficiency caused by gain-of-function of CXCR4 gene [7].