PDCD1 and neoplasm: To gain further insight into the anti-tumor and immunomodulatory effects as well as the underlying mechanisms of action, we investigated REG in combination with anti-PD1 (aPD1) in two murine CRC models—the subcutaneous MC38 hypermutated/MSI tumor model and the orthotopic CT26 non-hypermutated/MSS tumor model [24, 25].