CD8A and cancer: Programmed death-ligand 1 (PD-L1) binds to its receptor PD-1 and CD80 to suppress T-cell-mediated cancer cell killing by restricting T-cell effector functions.31-33 Two mechanisms are proposed for the regulation of PD-L1 by tumour cells: adaptive immune resistance, in which PD-L1 is upregulated on tumour cells in response to interferon gamma signalling from CD8+ T cells, and intrinsic immune resistance whereby PD-L1 expression in tumour cells is elicited by oncogenic signalling.