In the present study, we have investigated the impact of chronic dosing of the orally bioavailable CXCR4 antagonist X4-185 on leukocyte trafficking and distribution in primary and secondary lymphoid organs in a mouse model of WHIM syndrome harboring the heterozygous Cxcr41013 mutation, which is frequently observed in patients with WHIM syndrome. The gene discussed is CXCR4; the disease is WHIM syndrome.