Antiviral activity of shRNAs against clade B primary viruses. Sorted GFP-positive CD4⁺ T cells expressing luc, gag, rev, or vif shRNAs were infected with the IIIB, 89.6, or BaL lab-adapted strains or with primary HIV isolates from donors 214, 216, and 307 and analyzed by flow cytometry for p24 expression 6 days later. (A) Representative flow cytometry analysis of lentivirus-transduced CD4 T cells infected with primary virus from donor 216. (B) The extent of viral inhibition in cells expressing each of the 3 shRNAs was calculated as the reduction in the percent of p24-positive cells in cultures selected for HIV shRNA expression compared with cultures expressing luc shRNA. Values represent averages of 2 independent experiments, with the range indicated. The target sequences of the various viruses used are depicted in Table 2.