IMPS-20COMBINATION THERAPY WITH ANTI-PD-1, ANTI-TIM-3, AND FOCAL RADIATION RESULTS IN REGRESSION OF MURINE GLIOMAS

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INTRODUCTION: Checkpoint molecules like programmed death-1 (PD-1) and T cell immunoglobulin mucin-3 (TIM-3) act as negative regulators of the immune system and can be upregulated in the setting of glioblastoma multiforme (GBM). Combined PD-1 blockade and stereotactic radiosurgery (SRS) have been shown to improve antitumor immunity and produces long-term survivors in a murine glioma model.1 However, tumor infiltrating lymphocytes can express multiple checkpoints (including TIM-3), and expression of ≥2 checkpoints corresponds to a more exhausted T cell phenotype.2 It was therefore hypothesized that the addition of a second checkpoint-blocking antibody could achieve additive or synergistic antitumor effects. METHODS: C57BL/6 mice were implanted with mouse glioma cell line GL261 transfected with luciferase and randomized into 8 treatment arms: (1) control, (2) SRS, (3) anti-PD-1 antibody, (4) anti-TIM-3 antibody, (5) anti-PD-1 + SRS, (6) anti-TIM-3 + SRS, (7) anti-PD-1 + anti-TIM-3, and (8) anti-PD-1 + anti-TIM-3 + SRS. Overall survival was measured. Brain, cervical lymph nodes, and peripheral blood were harvested on day 21 to assess immune activation. RESULTS: Survival benefits were observed with combined anti-TIM-3 antibody + SRS compared to anti-TIM-3 antibody alone with a median survival (MS) of 69 vs. 25 days and overall survival (OS) of 50% vs. 0%, respectively (p < 0.001 by log-rank Mantel-Cox). Dual blockade with anti-TIM-3 + anti-PD-1 antibody also improved survival compared to TIM-3 blockade alone, (MS of 100 vs. 25 days, OS 60% vs. 0%, respectively, p < 0.05). Notably, OS in the triple therapy group (anti-PD-1 + anti-TIM-3 + SRS) was 100% by day 100 (p < 0.05), a significant improvement compared to all other treatment arms. Flow cytometry of organs harvested on day 21 showed that compared to the dual therapy groups, mice treated with triple therapy had increased tumor infiltration by interferon-gamma+ (IFNg) and tumor necrosis factor-alpha+ (TNFa)-producing CD4+ T cells, as well as IFNg+ CD8+ lymphocytes. CONCLUSIONS: Combining anti-TIM-3 with anti-PD-1 and radiation was synergistic and conferred a significant survival benefit.