GATA-1–induced CCR5 down-regulation inhibits R5-tropic HIV infection. (A) T cells expressing HDV (▵), HDV.GATA-3 (□), or HDV.GATA-1 (•) were prepared as described in the caption of Figure 2 and superinfected with replication-competent CCR5-tropic HIV-1 (R5.HIV), at an MOI of 1 either in the absence (top left) or presence (top right) of HIV protease inhibitors and AZT, which were added at day 2 after infection. Infections were determined based on GFP expression as indicated. T cells expressing GATA-3 or GATA-1 were also infected with either VSV-G.HIV (bottom left) or X4.HIV (bottom right) at 1 MOI. All infection data are shown as the percentage of GFP⁺ T cells at the indicated times. (B) Culture supernatants were also collected from T cells infected with R5.HIV at the indicated times after infection, and viral replication was quantified via p24 ELISA. These data are representative of 3 independent experiments performed using T cells isolated from individual donors. Error bars indicate standard deviation of duplicate samples.