TMOD-42. TREM2 modulates glioma-associated microglia and macrophage function in a genetic driver dependent manner

Abstract Triggering receptor expressed on myeloid cells 2 (TREM2) is a critical modulator of phagocytosis, inflammation, and survival for microglia and other macrophages. In neurodegenerative disorders, microglia expressing TREM2 play a protective role at distinct phases of disease progression, enabling uptake of toxic protein aggregates and dead neurons. TREM2 is also highly expressed on tumor-associated macrophages in a variety of cancers, promoting an immunosuppressive microenvironment. We and others have previously investigated the role of TREM2 in gliomas with confounding results, suggesting TREM2 could be pro-tumorigenic or anti-tumorigenic depending on experimental context (Peshoff, et al. Neuro Oncol. and Zheng, et al. Neuro Oncol.) In this study, we aim to resolve these findings by investigating the role of TREM2 across progression of gliomas with unique genetic drivers using immunocompetent mouse models. We employ syngeneic glioma stem cell lines generated via retroviral vectors expressing a dominant negative p53 along with amplification of human PDGFB or oncogenic HRAS G12V to model proneural and mesenchymal glioblastomas, respectfully. In contrast to our previous results demonstrating enhanced GL261 and CT2A growth in Trem2-/- mice, we demonstrate that Trem2 deficiency results in decreased tumor volume and improved survival when mice are challenged with Ras-driven, but not PDGFB-driven, gliomas. Furthermore, Trem2-/- mice display a more immunostimulatory microenvironment with increased T cell infiltration to mesenchymal-like tumors. We employ an in vitro co-culture system of primary mouse microglia with glioma stem cells to understand how microglia sense and respond to different genetic subtypes. We find that TREM2-mediated processes including microglial phagocytosis, chemotaxis, and survival are impacted by glioma genetic drivers. Together, these results indicate discrepancies in the literature regarding the function of TREM2 in gliomas may be explained by tumor genetics behind the cell lines used, which can provide a framework for understanding subtypes of gliomas that could respond to TREM2-modulating therapy.