CCR5Δ32 protein expression and stability are critical for resistance to human immunodeficiency virus type 1 in vivo

Human immunodeficiency virus type 1 (HIV-1) infection of individuals carrying the two alleles of the CCR5 Delta 32 mutation (CCR5(-/-)) has rarely been reported, but how the virus overcomes the CCR5 Delta 32 protective effect in these cases has not been delineated. We have investigated this in 6 infected (HIV+) and 25 HIV(-)CCR5(-/-) individuals. CD4(+) T lymphocytes isolated from HIV(-)CCR5(-/-) peripheral blood mononuclear cells (PBMCs) showed lower levels of CXCR4 expression that correlated with lower X4 Env-mediated fusion. Endogenous CCR5 Delta 32 protein was detected in all HIV(-)CCR5(-/-) PBMC samples (n = 25) but not in four of six unrelated HIV(-)CCR5(-/-) PBMC samples. Low levels were detected in another two HIV(+)CCR5(-/-) PBMC samples. The expression of adenovirus 5 (Ad5)-encoded CCR5 Delta 32 protein restored the protective effect in PBMCs from three HIV+ CCR5(-/-) individuals but failed to restore the protective effect in PBMCs isolated from another three HIV(+)CCR5(-/-) individuals. In the latter samples, pulse-chase analyses demonstrated the disappearance of endogenous Ad5-encoded CCR5 Delta 32 protein and the accumulation of Ad5-encoded CCR5 during the chase periods. PBMCs isolated from CCR5(-/-) individuals showed resistance to primary X4 but were readily infected by a lab-adapted X4 strain. Low levels of Ad5-encoded CCR5 Delta 32 protein conferred resistance to primary X4 but not to lab-adapted X4 virus. These data provide strong support for the hypothesis that the CCR5 Delta 32 protein actively confers resistance to HIV-1 in vivo and suggest that the loss or reduction of CCR5 Delta 32 protein expression may account for HIV-1 infection of CCR5(-/-) individuals. The results also suggest that other cellular or virally induced factors may be involved in the stability of CCR5 Delta 32 protein.