However, it is unclear whether CIK cell activity is boosted in the periphery by anti-PD-1 antibodies, and then they migrate into the tumor and kill tumor cells; or if the cells are already infiltrating the tumors but become exhausted or inhibited by PD-1 signaling, and their activity is subsequently restored by the PD-1 blockade. The gene discussed is PDCD1; the disease is neoplasm.