DMG-33. Locoregional Therapy with Immune Co-stimulator-armed Oncolytic Adenovirus for Diffuse Midline Glioma

Abstract Diffuse midline glioma (DMG) is the most lethal brain cancer in children. Despite being immunologically cold, a recent phase 1 trial demonstrated immune activation in the tumor microenvironment (TME) of diffuse intrinsic pontine glioma (DIPG) treated with oncolytic adenovirus Delta-24-RGD, resulting in improved survival outcomes. We reported that Delta-24-RGDOX, armed with OX40 ligand (OX40L), enhanced antitumor immune response. To further improve the efficacy of the virus-mediated antitumor immunity, we developed Delta-24-RGDOX-IL15, co-expressing OX40L and IL-15. The expression of the transgenes in Delta-24-RGDOX-IL15 was assessed with flow cytometry and ELISA. The potency of the virus in cancer cells was evaluated with replication and cell viability assays. The anti-glioma activity of the virus was examined in the syngeneic intracranial model derived from a mouse DMG cell line with H3K27M mutation and expression of GD2 and luciferase in C57BL/6 mice. Tumor growth was tracked using bioluminescent imaging. Survival was evaluated using Kaplan-Meier analysis. Immune cells from TME were profiled with flow cytometry. DMG cells were infected by Delta-24-RGDOX-IL15, resulting in effective co-expression of OX40L and IL-15. The efficacy of Delta-24-RGDOX-IL15 was comparable to that of viruses expressing either of the transgenes but significantly enhanced the anti-tumor effects of GD2 chimeric antigen receptor (CAR) T cells. In mice with intracranial DMG, intratumoral injections of Delta-24-RGDOX-IL15 reduced tumor burden as assessed by bioluminescent imaging and prolonged survival with no significant toxicity. Moreover, locoregional therapy with Delta-24-RGDOX-IL15 induced inflammatory response within the TME, characterized by an increased frequency of cytotoxic T cells and a reduction in myeloid cells. In conclusion, Delta-24-RGDOX-IL15 demonstrates potent oncolytic activity in DMG cells. Locoregional treatment with the virus activates the TME, leading to improved anti-DMG immunity. With its safe intratumoral delivery and T cell-stimulating activity, Delta-24-RGDOX-IL15 is a promising candidate for combination with cellular therapies in future DMG trials.