Plerixafor, a CXCR4 antagonist originally developed for similar purposes, has been licensed for its ability to mobilize stem cells from the bone marrow, of use following administration of chemotherapeutics (Brave et al., 2010) and is also showing early promise as a treatment for patients with the immunosuppressive WHIM syndrome, resulting from dysregulation of CXCR4 function (McDermott et al., 2011). The gene discussed is CXCR4; the disease is WHIM syndrome.