EXTH-61. MODULATION OF THE IL-27 RECEPTOR SIGNALING PATHWAY IN GLIOBLASTOMA AND ONCOLYTIC VIROTHERAPY

Abstract

Abstract Glioblastoma (GBM) is the most common primary malignant brain tumor in adults with median overall survival of 14-16 months. Glioblastoma progression involves multiple immunosuppressive pathways hindering the success of cancer immunotherapy. Oncolytic virotherapy is a promising approach to reprogram the glioblastoma microenvironment and restore anti-tumor immunity. Interleukin (IL)-27 receptor signaling pathway regulates development of effector T cells, IL-10 producing T regulatory type 1 (Tr1) cells and induction of co-inhibitory receptors associated with T cell exhaustion in cancer. In this study, we sought to tackle local and systemic GBM-induced immunosuppression using the novel rQNestin34.5v2 oncolytic herpes simplex virus type-1 (HSV-1), engineered to selectively replicate in glioma cells together with genetic disruptions of the IL-27 receptor signaling pathway. The antitumor activity of HSV-1 rQNestin34.5v2 was evaluated in IL-27ra-/- and wild-type C57BL/6 mice harboring orthotopic CT-2A and GL261 glioblastoma and in athymic nude mice harboring orthotopic patient derived glioblastoma xenografts (PDXs) selected from patients that had been treated in a clinical trial of intratumoral administration of HSV-1 rQNestin34.5v2 (ClinicalTrials.gov: NCT03152318). HSV-1 rQNestin34.5v2 exhibited superior capacity to infect glioma cells in vitro triggering release of proinflammatory cytokines and inducing immunogenic cell death in infected cells. Immune phenotyping of GL261 and CT-2A gliomas revealed astrocytes and microglia express the highest levels of IL-27R. Lack of IL-27R signaling decreased expression of the co-inhibitory receptors PD-1 and Tim-3 on circulating CD4+ T cells suggesting altered CD4+ T cell responses. In the tumor microenvironment, lack of IL-27R signaling decreased immune suppression as evidenced by reduced interleukin (IL)-10 secretion by glioma cells. Despite positive functional modifications on CD4+ T cells, global lack of IL-27R signaling promoted tumor growth accompanied by increased circulating myeloid derived suppressor cells (MDSCs) in the GL261 model. Experiments to address the immunoregulatory role of IL-27R signaling during HSV-1 rQNestin34.5v2 virotherapy-induced glioma tissue destruction are ongoing.