CD8+T Cells granzyme fori Inactive Actived procaspase caspase Dead Tumor cell tumo r cell CTL细胞释放穿孔素和颗粒酶杀伤肿瘤细胞机制T cell Tumor cell perforin Inactive procaspase Actived caspase Dead tumo r cell CTL 细胞释放穿孔素和颗粒酶杀伤肿瘤细胞机制 granzyme CD8+ T Cells