CD274 and neoplasm: Collectively, these findings provide evidence that PD-1 is an important checkpoint in NK cell activation acting upon NK cells via multiple direct and indirect mechanisms summarized in Figure 2 and that PD-1/PD-L1 immunotherapy not only revives NK cell-mediated lysis of tumor cells and cytokine production, but concurrently supports the NK cell-directed priming and recruitment of the adaptive immune response.