PDCD1 and neoplasm: The combination of CTLA-4 and PD-1 blockade has been shown to be able to improve antitumor responses; in this regard, it has been shown that the monoclonal anti-CTLA4 antibody ipilimumab is able to increase tumor-infiltrating T cells and up-regulate the PD-1/PD-L1 inhibitory pathway in a compensatory manner, highlighting how drug combination therapy applications may be very effective [41].