While PD-L1 expression allows cancer cells to evade immune surveillance by suppressing T-cell-mediated immunity [3], natural killer (NK) cells can also contribute to immunotherapy mediated by a PD-1/PD-L1 blockade; cancers with low major histocompatibility complex (MHC) expression are responsive to PD1 blockade via a strong NK cell response [12]. Here, PDCD1 is linked to cancer.