Abstract Diffuse midline glioma (DMG) are aggressive pediatric brain tumors with limited treatment options and poor prognosis. Oncolytic virotherapy using Delta-24-RGD has emerged as a potential therapeutic strategy. However, resistance mechanisms, including those related to immune suppression, can limit its efficacy. To overcome these, we combined Delta-24-RGD with an anti-TIM-3 monoclonal antibody. TIM-3, a member of immune checkpoint inhibitors, is expressed on multiple immune cell types and regulates adaptive and innate immunity, contributing to the immunosuppressive tumor microenvironment. Furthermore, previous studies have shown that TIM-3 blockade, as a monotherapy, demonstrates promising efficacy in DMG preclinical models. In this study, we examine whether combining Delta-24-RGD with TIM-3 blockade enhances therapeutic outcomes in DMG. Our results demonstrate that Delta-24-RGD infection upregulates TIM-3 expression in DMG cell lines and orthotopic murine models. We observed increased TIM-3 levels in both tumor cells and the tumor microenvironment, indicating a potential mechanism of immune suppression and tumor escape. Detailed immune profiling revealed that while Delta-24-RGD activates T cells initially, it also increases regulatory T cell (Treg) proliferation and cytotoxic T lymphocyte exhaustion, impairing antitumor immunity. Moreover, TIM-3 inhibition reversed T cell exhaustion in vitro without affecting activation or proliferation markers. Notably, in immunocompetent DMG models, combining Delta-24-RGD with systemic anti-TIM-3 significantly improved median overall survival compared to monotherapies, resulting in 25% long-term survivors free of disease, without detectable toxicity. Finally, in an aggressive orthotopic DMG model (UC-BL6-C7, H3K27M) resistant to monotherapies, intratumoral co-injection of Delta-24-RGD and anti-TIM-3 significantly improved median overall survival compared to other treatments, including systemic. Overall, our findings suggest that TIM-3 blockade can mitigate virus-induced immune exhaustion, enhancing the therapeutic potential of oncolytic virotherapy in DMG.
Nuin et al. (Fri,) studied this question.