We found the MM.1S cells in the PD-1 KO co-culture have more cleaved form of caspase-3, caspase-7, caspase-8, caspase-9 and PARP than the control (Figure 3B), showing that PD-1 KO CTLs lead to an elevated caspase activation in tumor cells. This evidence concerns the gene PDCD1 and neoplasm.