The functions of CXCR4 have not yet been fully understood, but it appears that it mediates a large variety of functions including leukocyte development and trafficking, HIV-infection, correct foetal vascularisation and CNS development and possibly cell division, tumourigenesis and growth (Tachibana et al, 1998; Zou et al, 1998; Gabuzda and Wang, 1999). The gene discussed is CXCR4; the disease is HIV infectious disease.