PD-L1 blockade enhances cytokine secretion by PD-1^high as well as PD-1^intermediate HIV-specific CD4 T cells. CD8-depleted PBMCs from 3 chronically infected, untreated subjects were incubated with an HIV Gag peptide pool or left unstimulated for 16 hours in the presence of isotype control or PD-L1 blocking antibody. (A) CD4 T cells were then negatively selected by lineage exclusion on the lymphocyte gate and sorted according to their level of PD-1 expression into PD-1^low, PD-1^intermediate, and PD-1^high subsets and isolated by live cell sorting. (B-D) IL-2 and IFN-γ secretion in the different cell subsets in the presence or absence of PD-L1 blockade. No significant IL-2 secretion was detected in the first subject.