CXCR4 and HIV-1 infection: CXCL12 and CXCR4 knockout mice are embryonic lethal [5], [6] and signaling through the CXCL12/CXCR4 axis has been implicated in organogenesis [7], [8], autoimmunity [9], [10], WHIM syndrome (Warts, Hypogammaglobulinemia, Infections, and Myelokathexis) [11], and human immunodeficiency virus -1 (HIV-1) infection [12], [13], [14].