In the control group, the let-7i mimic still significantly decreased the HIV-1 infection-induced apoptosis of CD4+ T cells (Fig. 5C,D, left panel), but when IL-2 was knocked down, the apoptosis caused by HIV-1 infection was not rescued by let-7i overexpression (Fig. 5C,D, right panel). The gene discussed is CD4; the disease is HIV-1 infection.