A, B WT and SKAP55−/− mice were s.c. injected with MO5 melanoma cells followed by two injection at day 7 and day 14 of OVA257-264-pulsed DCs or the PBS control respectively (n ≥ 5). The growth of tumors under skin was measured every three days according to tumor diameter (mean ± SEM, n ≥ 5 mice per group) (A). Surface expression levels of PD-1 were checked on OVA257-264-specific Vα2high/Vβ5+ CD8+ effector cells at day 30 (mean ± SD, n ≥ 5 mice) (B). 