PDCD1 and neoplasm: To investigate the elements that might hamper the effectiveness of adoptive cell immunotherapy using CIK cells, and to achieve optimized destruction of malignancy within tumor microenvironment, several immune inhibitory checkpoints, CTLA-4, 2B4, LAG-3, and PD-L1/PD-1 presumably correlated with a severe exhausted phenotype of T cells [36-38], were documented on the CIK cells.