CD274 and neoplasm: Bearing that in mind, we designed an experimental approach in which parental PD-L1 WT or PD-L1-deficient A20 leukemia cells were injected intravenously or intraperitoneally into semiallogeneic F1 recipients to study the role of PD-L1 expression on tumor cells in NK cell-mediated rejection and to assess the putative involvement of PD-1 co-inhibition in hybrid resistance to tumor implantation.