Figure 2.

Infectivity and co-receptor usage of envelope proteins expressed by clonal viruses. Recombinant reporter viruses were generated in which the env sequence (gp120 + the extracellular domain of gp41) was derived from clonal viruses isolated from plasma of patients chronically infected with HIV-1. The ability of these viruses, which express Renilla luciferase in the place of Nef, to infect U373 cells stably expressing CD4 and either CCR5 (panel A) or CXCR4 (panel B) co-receptors was measured by evaluating luciferase expression in target cells 44 hours after infection. For patient 2, clonal viruses were obtained from plasma samples obtained 8 months apart (26 and 34 months after initial diagnosis). The ability of all recombinant viruses to infect the two cell types was evaluated, but results are shown only for viruses that induced significant luciferase activity in the indicated target cell type [>2 (RLU/sec)/(ng p24/ml)]. Viruses could be classified as having strict R5 tropism (open symbols) strict X4 tropism (solid black symbols) and dual tropism (sold gray symbols). Results for viruses expressing env sequences amplified by RT-PCR from patient plasma is also shown (stars). Each symbol is the mean of at least 3 independent experiments; the mean coefficient of variation for these results is as follows: U373-R5 cells, 42% (range 3 – 83%); U373-X4 cells, 50% (range 10 – 78%). For each patient, significant differences were found comparing the viruses with the highest and lowest infectivity (p < 0.05 – 0.001 by t-test).