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-indu cing (M-tropic/NSI) strains is associated with disease progression in infected individuals. HIV89.6 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 syn cytium inducing. We have shown that HIV89.6 can utilize both the M-tro pic and T-tropic cofactors CCR-5 and CXCR-4, respectively, in conjunct ion with CD4 for fusion and entry into otherwise nonpermissive nonhuma n cells. To better understand the nature of restricted HIV89.6 infecti on of transformed cells, we analyzed its interaction with CD4-expressi ng transformed human HeLaCD4-LTR/beta-Gal cells, which contain the bet a-galactosidase gene linked to the HIV-1 LTR. Here we show that HIV89. 6 enters these cells and undergoes reverse transcription and integrati on. Furthermore, HIV89.6 induces LTR-driven beta-galactosidase express ion, indicating Tat-dependent trans-activation, in a similar number of cells as the permissive T-tropic/SI isolate HIVHXB Acute infection wi th HIV89.6, however, produces markedly lower levels of p24 antigen and infectious virus per trans-activation-positive cell than HIVHXB In co ntrast, transfection results in high levels of expression for both vir uses but HIV89.6 still fails to establish spreading infection. HIV89.6 is also blocked after entry in two other nonpermissive cell lines, SU P-TI and U937. HIV89.6 arrest in HeLaCD4-LTR/beta-Gal cells at a stage subsequent to entry, reverse transcription, integration, and Tat expr ession is a novel level at which HIV-1 strain-and cell-specific restri ctions define host cell tropism. These studies emphasize that complex patterns of tropism are determined by the interplay of permissive or r estricted virus-cell interactions at multiple steps in the replication cycle.