B, C WT and SKAP55−/−OT-ICD8+CTLs were generated from WT or SKAP55−/−OT-I Tg mice, then incubated with 10 nM OVA257-264-pulsed EL4 targets for 4 h to assess the in vitro cytotoxicity at different Effector:Target ratios (B; mean of triplicates ± SD); surface expression and the mRNA levels of PD-1 (C). Graphs are representative of at least three independent experiments. 