CCR5Δ32 Protein Expression and Stability Are Critical for Resistance to Human Immunodeficiency Virus Type 1 In Vivo

Abstract

ABSTRACT Human immunodeficiency virus type 1 (HIV-1) infection of individuals carrying the two alleles of the CCR5Δ32 mutation (CCR5 −/− ) has rarely been reported, but how the virus overcomes the CCR5 Δ 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 CCR5Δ32 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 CCR5Δ32 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 CCR5Δ32 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 CCR5Δ32 protein conferred resistance to primary X4 but not to lab-adapted X4 virus. These data provide strong support for the hypothesis that the CCR5Δ32 protein actively confers resistance to HIV-1 in vivo and suggest that the loss or reduction of CCR5Δ32 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 CCR5Δ32 protein.