CD4 and HIV-1 infection: Sang-Kyung Lee et al. showed that three anti-HIV shRNAs targeting rev, gag, and vif reduced the p24 level by more than 90%, demonstrating their ability to protect primary CD4+ T cells, which are the major targets of HIV-1 infection in vivo, from homologous virus as they did for HeLa-CD4 cells [37].