Interrogating immune niches in a murine GBM model under radiation therapy 2335073

Abstract

Adult glioblastoma (GBM) is the most aggressive primary brain tumor in adults, with a median survival of approximately 14 months. Standard of care, surgical resection followed by radiation therapy (RT) and temozolomide, has remained largely unchanged since 2005. A major barrier to therapeutic progress is limited understanding of how distinct immune populations within the tumor microenvironment (TME), particularly microglia and peripherally derived macrophages, respond to therapy. We developed an immunocompetent, autochthonous adult GBM mouse model driven by EGFRvIII expression with loss of PTEN and CDKN2A. Tumor-bearing mice received a single 8 Gy dose of whole-brain radiation. Immune profiling was performed seven days post-treatment using immunohistochemistry, single-cell RNA sequencing, and spatial transcriptomics to assess myeloid composition and treatment-induced changes within the TME. RT-treated tumors exhibited reduced tumor burden compared to untreated controls, along with increased accumulation of IBA1+ myeloid cells. Single-cell RNA sequencing identified brain-resident microglia and peripherally derived macrophages as the dominant immune populations in both treatment groups. RT induced a relative enrichment of CD49d+ peripheral macrophages. Transcriptomic analyses revealed ontogeny-specific responses to RT, with peripheral macrophages enriched for inflammatory, angiogenic, and lipid-associated gene programs consistent with a disease-associated phenotype. Ongoing spatial transcriptomic analysis using 10x Genomics Visium HD will spatially resolve microglia and peripheral macrophages within the TME and adjacent non-tumor brain regions. Together, this integrated approach defines myeloid heterogeneity in GBM and provides insight into how distinct immune populations respond to radiation therapy. CIRM Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)