DIPG-13. TIM-3 TARGETED APTAMER IN COMBINATION WITH LOCO-REGIONAL RADIOTHERAPY IMPROVES SURVIVAL BY MODULATING THE IMMUNE INFILTRATION IN DIFFUSE MIDLINE GLIOMA MODELS Open Access

Diffuse midline gliomas (DMG) are the most aggressive pediatric brain tumors. Their meager survival has not changed in the last decades emphasizing the urgent need for effective treatments. TIM-3 has emerged as a new target expressed in multiple immune cell types, regulating adaptive and innate immunity. In this work, we used an aptamer against TIM-3 to modify the tumor microenvironment and enhance the antitumor effect.

For in vivo experiments, DMG murine cells were injected orthotopically into the pons of mice using a screw-guided system. The aptamer was administered intracranially (380pmol) on day 5 with the same system and three times intravenous (320pmol/mouse) 8-11-14 days after tumor implantation. In the radiotherapy experiments, 6Gy was given on day 7. Tumor and immune populations were analyzed by flow cytometry.

TIM-3 aptamer as monotherapy increases immune infiltration and elicits a specific immune response with a modest tendency to improve overall survival. Interestingly, we observed that radiotherapy, DMG standard of care, significantly induced TIM-3 expression in tumor and immune cells in the tumor microenvironment (TME). The combination of TIM-3 aptamer with radiotherapy increased the overall survival (3-fold), led to long-term survivors (30-50%), and generated immune memory in three different glioma models. Importantly, combination treatment significantly increases the infiltration of immune cells (3-fold) in the TME compared with the control groups. Radiotherapy and TIM-3 Apt treatment significantly increased the number and proliferative state of microglia, dendritic, NK, CD4, and CD8 T-cells. Interestingly, TIM-3 aptamer decreased the number and proliferative state of Tregs increasing the pro-inflammatory ratio of CD8: Tregs in the TME compared to non-treated groups after radiotherapy.

In conclusion, we provide evidence that combining radiotherapy with a TIM-3 aptamer increases overall survival, leads to the expansion of myeloid and T-cells in the TME, and generates immune memory in DMG models.