Cell surface CCR5 density determines the postentry efficiency of R5 HIV-1 infection

We have recently reported that the mean number of CCR5 coreceptors at the surface of CD4(+) T cells (CCR5 density) correlates with viral load and disease progression in HIV-1-infected persons. Here, we definitively establish that CCR5 density determines the level of virus production and identify the stages of HIV-1 replicative cycle modulated by this effect. We show, by transducing the CCR5 gene into CCR5(+) cells, that CCR5 overexpression resulted in an HIV-1 overinfectability. We sorted HOS-CD4(+)-CCR5(+) cells into two subpopulations, HODhigh and HOSlow, the former expressing seven times more cell surface CCR5 molecules than the latter. Virus production was 30-80 times higher in HOShigh cells than in HOSlow cells after a single round of infection. In contrast, only twice as many viral particles entered the cytosol of HOShigh cells as compared with the cytosol of HOSlow cells. Yet, seven times as many early, and 24 times as many late, reverse transcription products were found in HOShigh cells as compared with HOSlow cells. Moreover, a 24- to 30-fold difference in the number of copies of integrated HIV-1 DNA was observed. No difference in HIV-1 LTR activation between the two cell lines was evident. Finally, we show that the higher virus production observed in HOShigh cells is inhibited by pertussis toxin, a Galphai protein inhibitor. Thus, CCR5 density mainly modulates postentry steps of the virus life cycle, particularly the reverse transcription. These data explain why CCR5 density influences HIV-1 disease progression and underline the therapeutic interest of lowering CCR5 expression.