PDCD1 and malignant colon neoplasm: First, we subcutaneously inoculated 2 × 105 MC38 colon cancer cells, which are tumour cells that are sensitive to anti-PD-1 antibody treatment, into Rig-I+/+ and Rig-I−/− mice and intraperitoneally injected 250 μg of cIg or anti-PD-1 antibody into each mouse on days 4, 7, 10 and 13 (Fig. 7A).