Individuals who are homozygous in the CCR5 gene (CCR5Δ32) are highly resistant to infection by CCR5- (R5-) tropic HIV as demonstrated by individuals heterozygous for CCR5Δ32 who display partial resistance to infection and slower disease progression (Huang et al. 1996; Liu et al. 1996; van Rij et al. 1999). This evidence concerns the gene CCR5 and infection.