To prove that an enhancement of tumour-killing activity by NTP-GM-D17 was a result of reduced interaction of PD-1 and PD-L1, the effect of NTP-GM-D17 was examined on a subclone of SKOV-3/Luc cells, the PD-L1 gene of which was disrupted by the CRISPR/Cas9 system (KO-SKOV-3 cells) (Fig. 4d, right panel). Here, PDCD1 is linked to neoplasm.