CD4⁺ T cells from HICs have low susceptibility to HIV-1 infection. (A) PHA-activated CD4⁺ T cells from HICs and HDs were challenged with replicative HIV-1 BaL, using a protocol optimized to detect viral replication in vitro (left). HIV-1 replication in anti–CD3-activated CD4⁺ T cells from HICs and HDs (including all those depicted in the left panel) and HIV-1 viremic patients (VIR), after challenge with HIV-1 BaL, using a suboptimal in vitro infection protocol (right). Symbols represent the average (n = 3 independent infections) p24 values detected on day 7 after infection in culture supernatants for each donor. Horizontal lines indicate median values. (B) HIV-1 (BaL [R5], left), NL4.3 ([X4], center), and SIVmac251 (right) replication after infection, in suboptimal conditions, of CD4⁺ T cells from one representative HD and one HIC whose cells were resistant to infection. Means ± SDs of 3 independent infections are shown.