These initial studies in LCMV infection were later extended to HIV infection and IL-21-producing CD4 T cells were associated with improved control of HIV-1 infection and preserved CD8 T cell function in humans (Iannello et al., 2010; Yue et al., 2010; Chevalier et al., 2011; Williams et al., 2011). This evidence concerns the gene CD4 and HIV-1 infection.