Abstract A009: Engineering a novel suite of somatic transgenic murine Egfr-mutant glioblastoma models that recapitulate molecular, immunologic, and functional features of human glioblastoma

Abstract Glioblastoma (GBM) is the most common and deadly primary brain tumor in adults, characterized by diffuse infiltrative lesions, distinct oncogenic alterations, and a suppressive tumor immune microenvironment (TIME). These traits, however, are not recapitulated in current syngeneic murine glioma models thereby limiting the pre-clinical development of novel therapies. Here we describe a molecular toolkit for developing murine GBM models with patient-specific mutations that share striking resemblance with human disease. Leveraging mosaic analysis with dual-recombinase mediated cassette exchange (MADR) and CRISPR-Cas9, we generated autochthonous tumor models with single-copy somatic transgenesis of murine epidermal growth factor receptor variant III (mEGFRvIII) and loss-of-function mutations commonly observed in GBM. We further characterized a model lacking PTEN and CDKN2A (mEGFRvIII-PC) via histopathologic analyses, functional assays, and single-cell RNA sequencing in comparison to existing glioma models. mEGFRvIII-PC tumors developed as diffuse, infiltrative lesions with ill-defined margins and a necrotic core. The TIME was primarily comprised of microglia with minimal lymphocyte infiltration, recapitulating patient tumors. Furthermore, these tumors displayed intrinsic resistance to immune checkpoint blockade, potentially due to poor myeloid cell antigen presentation and T cell priming. Additionally, mEGFRvIII-PC cells were the most resistant to antigen-specific T cell-induced cytotoxicity and simultaneously promoted T cell exhaustion, while murine interferon-γ (mIFN-γ) stimulation induced a greater response in vitro with enhanced upregulation of PD-L1 relative to MHC-I. In sum, these findings demonstrate the superior fidelity of the mEGFRvIII-PC model to patient tumors and support its use in developing and refining novel therapeutic paradigms for GBM. Citation Format: Joshua J. Breunig, Katie Grausam, Marisa Pioso, Julio Sanchez, David Rincon Fernandez Pacheco, Emily Hatanaka, Paul Linesch, David A. Nathanson, Rob M. Prins, Stephen Shiao. Engineering a novel suite of somatic transgenic murine Egfr-mutant glioblastoma models that recapitulate molecular, immunologic, and functional features of human glioblastoma abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Brain Cancer; 2026 Mar 23-25; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2026;86 (6Suppl): Abstract nr A009.