PDCD1 and neoplasm: Recent results indicate that high-dose ascorbate treatment overcomes distinct resistance mechanisms against checkpoint inhibitors, and ascorbate enhances tumor recognition by the host immune system, yielding increased infiltration of macrophages and cytotoxic T cells into the tumor compared with anti-PD1 monotherapy, suggesting synergistic antitumoral mechanisms of the combined therapy in a murine lymphoma model and further in colorectal, breast, and pancreatic cancer mouse models [35,36].