PDCD1 and neoplasm: The reasoning behind combining CTLA-4 with PD-1/PD-L1 blockade lies in their complementary mechanisms of action: inhibition of CTLA-4 increases T-cell expansion during the initial immune priming phase, while PD-1/PD-L1 blockade re-invigorates effector T cells within the tumor microenvironment (TME).