Fig. 5: The M1 virus induces local and systemic CD8⁺ T cell-dependent antitumor immunity.

A Tumor-infiltrating lymphocytes (TILs) were isolated from B16F10 tumor tissue samples and cocultured with the B16F10 cell line for 48 h; phase-contrast images are shown. The images are representative of six biological repetitions. Scale bars: 50 μm. B–D Lymphocytes isolated from B16F10 tumor tissue samples (TILs), tumor-draining lymph nodes (TDLN), and the spleen were cocultured with B16F10 cells for 48 h to evaluate lymphocytotoxicity. n = 7. The P value was determined by a two-tailed Student’s t test. E, F Granzyme B (E) and IFN-γ (F) were analyzed in supernatants of splenic lymphocytes cocultured with or without B16F10 cells. n = 6. The P value was determined by one-way ANOVA with Dunnett’s test. G C57BL/6 mice were implanted subcutaneously in the right flank with B16F10 cells on day 0 and treated intravenously with ctrl (n = 6) or M1 (n = 6) (1 × 10⁷ pfu) once per day on days 6–10. An anti-CD4 depletion antibody, anti-CD8 depletion antibody, or isotype control antibody was injected intraperitoneally on days 4, 7, 10, and 13. B16F10 tumor growth (left) and Kaplan–Meier survival (right) curves for the mice in each group are shown. ctrl, n = 9; M1, n = 10; M1 + isotype, n = 9; M1 + CD4 depletion, n = 9; M1 + CD8 depletion, n = 9. P values were determined by one-way ANOVA of the final time point as indicated in the graphs and by the log-rank test. Data are shown as the mean ± SD. n.s., not significant; *P < 0.05; **P < 0.01; ***P < 0.001. ****P < 0.0001. See also Supplementary Figs. S5 and S6.