PDCD1 and neoplasm: However, this study also presented a contradictory result: as there was no significant change in CD8 + T cell frequency or activity (using IFN-γ and granzyme B as activity indicators) between anti–PD-1–treated Tyro3-OE 4T1 tumors and 4T1-P tumors, it was suggested that the decrease in ferroptosis could be regulated by the intrinsic mechanisms of tumor cells.