PDCD1 and cancer: Like cancer cells' highly/over-expressed inhibitory molecules (e.g., PD-L1), some activated T cells also over-express corresponding inhibitory molecules 112, 113, such as programmed cell death protein 1 (PD-1), cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and mucin-containing protein 3 (TIM-3).