Indeed, combined with the results of a retrospective cohort study conducted in HCC patients, we found that tissues from HCC patients with diabetes undergoing sitagliptin treatment had a higher level of CD8+ T lymphocyte infiltration than tissues from HCC patients with diabetes without sitagliptin treatment, which further supported that sitagliptin could elevate the efficacy of anti-PD1 antibody therapy. This evidence concerns the gene CD8A and diabetes mellitus.