PDCD1 and neoplasm: Programmed death-ligand 1 (PD-L1), found on tumor and immune cells, binds to programmed cell death protein 1 on T cells, inhibiting T cell activity and allowing tumors to evade immune detection.4 Anti-PD-L1 antibodies block this interaction, “releasing the brakes” on T cells and enabling them to effectively target and destroy tumor cells.