CXCR4, also called fusin, is an alpha-chemokine receptor specific for stromal-derived-factor-1 (SDF-1 also called CXCL12), a molecule endowed with potent chemotactic activity for lymphocytes. This receptor is one of several chemokine receptors that HIV isolates can use to infect CD4+ T cells. Traditionally, HIV isolates that use CXCR4 are known as T-cell tropic isolates. Typically these viruses are found late in infection. It is unclear whether the emergence of CXCR4-using HIV is a consequence or a cause of immunodeficiency.

Besides, CXCR4 is upregulated during the implantantion window in natural and HRT cycles in the endometrium, producing, in presence of a human blastocyst, a surface polarization of the CXCR4 receptors suggesting that this rececptor is implicated in the adhesion phase of human implantation.