CCR5 and HIV-1 infection: Following discovery of a homozygous 32-nucleotide deletion (Δ32) in a CCR5 allele which yielded a truncated protein not expressed on the cell surface in individuals with natural resistance to HIV-1 infection [37–39], early clinical trials investigated the potential for inhibiting HIV entry through CCR5 by blocking the HIV-CCR5 interaction using small molecule approaches [40].