HIV-1 escapes from the 2nd generation combination shRNAs. (A) Stable cell lines (SupT1) expressing the shRNA-wt or shRNA-combi (wt+G8A+G15A) were infected with wt HIV-1 (1 ng CA-p24). Virus replication was monitored over time. SupT1 cells with the empty lentiviral vector JS1 served as positive control. (B) Control SupT1 cells and cells expressing shRNA-combi (wt+G8A+G15A) were infected with the escape variant (1 ng CA-p24) and wt HIV-1.