PRF1 and neoplasm: As shown in Fig. 4b–d, treatment with PDL1 protein alone did not affect the release of Granzme M and perforin of NK cells, but PDL1 treatment in the presence of the tumour cells (i.e., HN30 and HN4) under the co-culture condition inhibited the release of Granzme M and perforin from NK cells.