(A), Tumor measurements of C57/BL6 mice inoculated with B16 melanoma. Mice began receiving treatment on d5 as indicated, receiving 0.2mg anti-PD1 or its isotype control every 4 days, and either metformin or vehicle. Number of mice tumor-free of the total inoculated is reported. (B) Representative flow cytogram depicting IFNγ and TNFα production from CD8+ tumor infiltrating T cells from B16-bearing mice treated as in A. (C) Tabulated IFNγ staining from multiple mice; each dot represents one animal. (D) Ki67 expression in CD8+ T cells from mice treated as in a as indicated. (E) As in A, but mice were inoculated with MC38. * P < 0.05, ** P < 0.01, *** P < 0.001 by unpaired t-test. Results represent the mean (A, C, D, E) or are representative of (B) three to five independent experiments.