TMIC-54. RADIOTHERAPY-INDUCED REMODELING OF THE GLIOBLASTOMA MICROENVIRONMENT

Abstract

Abstract Radiotherapy (RT) is included in the standard of care for glioblastoma (GBM), and while primary tumors generally respond to RT, GBMs invariably recur as incurable lesions. We have previously demonstrated that RT generates a net tumor-supportive tumor microenvironment (TME), in part by inducing remodeling of the extracellular matrix, suggesting that there are therapeutic opportunities in targeting the altered TME of recurrent GBM. Here, we have used highly multiplexed immunohistochemistry in combination with single cell RNA sequencing to characterize the cellular composition and molecular alterations to the GBM TME as tumors progress from primary to irradiated to recurrent tumors, using a genetically engineered GBM mouse model. RT resulted in a phenotypic shift suggestive of a proneural-to-mesenchymal switch of lineage-traced tumor cells immediately after treatment, but proportions of tumor cell phenotypes were largely restored at the time of recurrence. Recurrent tumors displayed an altered immune landscape, as demonstrated e.g. by an increase in the proportion of CD8+ lymphocytes coupled to a decrease in the proportion of CD4+ cells. Together, our data suggest that RT remodels the GBM TME as well as alters the phenotype of bona fide glioma cells. Ongoing studies are aimed at understanding heterotypic cell-cell interactions unique to the irradiated and recurrent GBM TME.