Abortive Infection in HeLaCD4 Cells by a Primary HIV Type 1 Isolate: Implications for Differential Host Cell Tropism

The emergence of T cell-tropic, syncytium-inducing (T-tropic/SI) HIV-1 variants from the background of macrophage-tropic, non-syncytium-inducing (M-tropic/NSI) strains is associated with disease progression in infected individuals. HIV_89.6 is a primary isolate with a transitional phenotype: like M-tropic strains it replicates in primary macrophages and lymphocytes but not in most transformed cells, yet it is also syncytium inducing. We have shown that HIV_89.6 can utilize both the M-tropic and T-tropic cofactors CCR-5 and CXCR-4, respectively, in conjunction with CD4 for fusion and entry into otherwise nonpermissive nonhuman cells. To better understand the nature of restricted HIV_89.6 infection of transformed cells, we analyzed its interaction with CD4-expressing transformed human HeLaCD4-LTR//β-Gal cells, which contain the β-galactosidase gene linked to the HIV-1 LTR. Here we show that HIV_89.6 enters these cells and undergoes reverse transcription and integration. Furthermore, HIV_89.6 induces LTR-driven β-galactosidase expression, indicating Tat-dependent trans-activation, in a similar number of cells as the permissive T-tropic/SI isolate HIV_HXB. Acute infection with HIV_89.6, however, produces markedly lower levels of p24 antigen and infectious virus per trans-activation-positive cell than HIV_HXB. In contrast, transfection results in high levels of expression for both viruses but HlV_89.6 still fails to establish spreading infection. HIV_89.6 is also blocked after entry in two other nonpermissive cell lines, SUP-T1 and U937. HIV_89.6 arrest in HeLaCD4-LTR/β-Gal cells at a stage subsequent to entry, reverse transcription, integration, and Tat expression is a novel level at which HIV-1 strainand cell-specific restrictions define host cell tropism. These studies emphasize that complex patterns of tropism are determined by the interplay of permissive or restricted virus-cell interactions at multiple steps in the replication cycle.