EXTH-62. EXAMINATION OF THE TUMOR MICROENVIRONMENT OF GLIOMAS TREATED WITH VIROIMMUNOTHERAPY REVEALS THE PRODUCTION OF ONCOMETABOLITES LEADING TO IMPROVED THERAPEUTIC STRATEGIES

Abstract

Abstract Oncolytic viruses are considered part of immunotherapy and have shown promise in preclinical experiments and clinical trials in a small fraction of patients. To improve the response rate, it is necessary to reshape the tumor microenvironment that shields the tumor from the immune system of the patient. We engineered Delta-24-RGDOX (DNX-2440), an oncolytic adenovirus to express the T-cell activator OX40L, which triggered, in murine glioblastoma models, a dramatic reshaping of the tumor microenvironment dominated by changes in immune processes in an RNA-seq analysis of ingenuity pathways. Paradoxically, network analyses also revealed that Delta-24-RGDOX induced robust activation of the cytokine-driven immunosuppressive IDO-Kynurenine-AhR circuitry, indicating a potential mechanism of resistance of gliomas to oncolytic virotherapy. To reverse this immunosuppression, we combined Delta-24-RGDOX with clinically relevant IDO inhibitors to treat glioma-bearing mice. The combined therapy decreased the activation of the IDO network without affecting viral activity. Flow cytometry assays revealed a decrease in the presence of the immunosuppressive cell populations, MDSCs and Tregs, which presence was higher in Delta-24-RGDOX-treated tumors. These data were further confirmed in gene set enrichment analyses. Functional co-culture studies showed that the combined therapy activated splenocytes against tumor antigens and that this activation was reversed by Kynurenine. Importantly, the combination treatment eradicated the tumors in a CD4-dependent manner and significantly prolonged the survival of glioma-bearing mice. Altogether, these studies indicate that the combination treatment promotes an adaptive immune response while decreasing the immunosuppression caused by the virus-induced IDO activation. Furthermore, our data identified the striking role of immunosuppressive pathways in the resistance of gliomas to oncolytic virotherapy. Specifically, the activity of the tumor microenvironment IDO circuitry was responsible, at least partially, for the remodeling of local immunosuppression after tumor infection. Combining molecular and immune-related therapies may improve outcomes in human gliomas treated with virotherapy.