Maraviroc is a CCR5 antagonist with potent anti-HIV-1 activity, demonstrated in both treatment naïve and experienced settings. Binding of maraviroc to CCR5 leads to the loss of receptor function. Individuals with non-functioning CCR5 due to a 32 base pair deletion in the encoding gene are observed at a 1% frequency in the northern European Caucasian population. These individuals have near normal immune function, although differential response to renal transplant and West Nile virus have been reported relative to individuals with functional CCR5. The modest impact on immune function is indicative of a functional overlap between CCR5 and other CC chemokine receptors. While the precise role of CCR5 has not been established, data suggest a role in chemotaxis and inflammation.