CCR5 and HIV-1 infection: One such study by Perez et al. nullified M-tropic strain HIV-1 recognition of CCR5 co-receptors in CD4+ human T cells by introducing NHEJ in the endogenous CCR5 through the employment of ZFNs, effectively mimicking the naturally occurring homozygous Δ32 mutation that normally protects an individual from certain HIV-1 infections [83].