CD8A and melanoma: Consistent with our results that sitagliptin increased the number of tumoral infiltrated CD8+ T cells and improved the therapeutic effect of anti-PD1 on colorectal tumors and melanoma in this study, recent study shows that sitagliptin upregulates CXCL10 to increase CD8+ T lymphocyte infiltration and acts synergistically with anti-PD1 treatment for HCC and melanoma in mouse model [44, 45].