Blockade of PD-1 and its ligands at the time of antigen recognition renders self-antigen-specific T cells competent to produce effector cytokines. (A) Thy1.1-marked clone 4 cells were adoptively transferred into indicated hosts and harvested on day 4. Intracellular cytokine staining for IFN-γ was performed after 5-hour in vitro stimulation with the HA class I peptide in the presence of a blocking antibody cocktail (α-PD-1, α-B7-H1, and α-B7-DC, 30 μg/mL each, middle row) or isotype antibodies (top row). Gated on Thy1.1, 5 animals per group. (B,C) Clone 4 cells were adoptively transferred into C3-HA^low animals as above and PD-1, B7-H1 or B7-DC were blocked in vivo with 100 μg of indicated antibody administered at the time of adoptive transfer. Intracellular staining for IFN-γ was performed on day 4 after transfer. (B) Representative FACS plots, gated on CD8⁺ Thy1.1⁺ clone 4 lymphocytes. (C) Summary data of panel B, mean ± SEM n = 5, representative of 2 experiments.