PDCD1 and neoplasm: High-grade chronic viral infections, or persistent tumor antigen stimulation results in CD8+ T cell exhaustion, which mirrors decreased effector function and proliferative capacity.Tex manifest over-expression of inhibitory receptors, including CD279 (PD-1), a lymphoid cell surface protein of the Ig superfamily, and a member of the extended CD28/CTLA-4 family of Tcell regulators, which acts as a mature T cell checkpoint for the modulation of apoptosis.