Abstract 2001: Delta-24-RGDOX oncolytic adenovirus improves the survival by modulating the immune system in DMG models

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Abstract Purpose of Study: Diffuse Midline Gliomas (DMG) are aggressive pediatric brain tumors that arise in the brainstem of children, with a peak of incidence between 5-10 years old. The median survival of DMG patients is only 9 months, being the leading cause of pediatric death caused by a brain tumor. On this project we set to characterize the efficacy of Delta-24-RGDOX, an oncolytic adenovirus based on Delta-24-RGD platform, which has demonstrated safety and a therapeutic benefit in different pediatric tumors, armed with the ligand of OX40. The binding of OX40 to OX40L leads to the co-stimulation of CD4 and CD8 cells, generating effector and memory T cells. Therefore, the aim of this project is to improve the antitumor effect of the virus, providing a greater co-stimulation in the tumor. Experimental Procedures: Murine and human DMG cell lines were used. Viral protein expression was measured by western blot, viral replication was analyzed using a method based on hexon detection and the oncolytic effect by MTS assay. OX40L expression was measured by flow cytometry and qPCR. For in vivo experiments, cells were injected in the pons of mice using a screw-guided system. The adenovirus was administered once into the tumor using the same procedure. Tumor immune populations were analyzed by flow cytometry. Results: We first confirmed the oncolytic effect of Delta-24-RGDOX in DMG murine and human cell lines in vitro. The virus was able to infect the cells, produce viral proteins, and to cause cell death in a dose-dependent manner. In addition, we observed effective viral replication in human cell lines but not in mouse cells, as previously described. We then measured OX40L expression in infected cells both at protein and mRNA level, observing that at 50 PFU/cell almost 100% of cells expressed the ligand on their membrane. More importantly, the OX40L was functional as it activated CD8 lymphocytes in vitro. Once we confirmed that the viral administration in vivo was safe, we assess the efficacy of the virus in murine DMG models. We observed a significant survival benefit in mice bearing NP53 tumor treated with Delta-24-RGDOX, which lead to 30% of long-term survivors (P=0.003, median OS PBS 25.5 days vs 35.5 days for treated mice). More importantly, we administered the virus in an already stablished tumor model using XFM cells and also obtained a significant improve of survival (P=0.018, median OS PBS 9 days vs 12.5 treated mice). Finally, we analyzed the immune mechanisms underlying the survival benefit, both in the tumor and in spleen. We observed a significant increase of activated immune cells in the tumor microenvironment 7 days after the viral administration. In addition, splenocytes from virus-treated mice were also significantly more activated. Conclusions: These data show that Delta-24-RGDOX adenovirus expresses a functional OX40L that can modulate the immune response, leading to a significantly improved survival outcome in DMG models. Citation Format: Virginia Laspidea, Sara Labiano, Sumit Gupta, Hong Jiang, Iker Ausejo-Mauleon, Daniel de la Nava, Marc García-Moure, Javier Marco-Sanz, Reyes Hernández-Osuna, Oren J Becher, Juan Fueyo, Ana Patiño-García, Candelaria Gomez-Manzano, Marta M Alonso. Delta-24-RGDOX oncolytic adenovirus improves the survival by modulating the immune system in DMG models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2001.