Pallegar, Praveen N.

Abstract In many cancers, a major barrier to effective immunotherapy is the dominance of tumor-associated myeloid cells (TAMs), which establish a profoundly immunosuppressive tumor microenvironment (TME). This challenge is particularly pronounced in glioblastoma (GBM), where myeloid cells represent the predominant immune population and actively suppress antitumor immunity. Identifying targets that can reprogram TAMs from an immunosuppressive state toward a pro-inflammatory, antigen-presenting phenotype remains a critical unmet need. Here, we identify the voltage-gated proton channel Hv1 as an immune-restricted regulator of glioma-associated macrophage function. Hv1 is notable not only for its immune-specific expression but also for its established roles in central nervous system (CNS) pathologies, where Hv1 depletion alters microglial and macrophage polarization, reduces myeloid accumulation, dampens inflammatory cytokine production, and limits secondary tissue damage. However, Hv1’s role in shaping the GBM immune landscape—particularly in vivo—has remained poorly understood due to low Hvcn1 transcript abundance and the lack of reliable antibodies and genetic tools. Given the dominance of myeloid cells in GBM and their central role in tumor immune regulation, we sought to define Hv1 function within this highly immunosuppressive brain TME. Analysis of patient datasets revealed that elevated Hv1 expression correlates with poor clinical prognosis. Consistently, Hv1 loss significantly prolonged survival in multiple murine glioma models. Using in vivo two-photon imaging and spectral flow cytometry, we show that Hv1 depletion reprograms TAMs toward an anti-tumor phenotype characterized by enhanced tumor cell phagocytosis, improved antigen presentation, and increased T cell infiltration. By generating new Hv1 reporter and conditional mouse lines, we further demonstrate that tumor-associated microglia and infiltrating macrophages are the principal sources of Hv1 and markedly upregulate its expression in response to glioma. Notably, selective deletion of Hv1 in infiltrating macrophages phenocopied the survival benefit observed with global Hv1 loss. Mechanistically, using mass spectrometry and genetic models, we identify the Stimulator of Interferon Genes (STING) as a previously unrecognized binding partner of Hv1, placing Hv1 within the STING signaling pathway, a central regulator of innate and adaptive immune responses. Together, these findings fill a critical gap in understanding myeloid Hv1 function in GBM and identify Hv1 as a promising target for reprogramming the tumor immune microenvironment. Citation Format: Jiaying Zheng, Lingxiao Wang, Shunyi Zhao, Katayoun Ayasoufi, Meijie Wang, Praveen N. Pallegar, Peter R. Strege, Langni Liu, Yushan Wan, Wenjing Zhang, Emma N. Goddery, Manling Xie, Arthur Beyder, Aaron J. Johnson, Long-Jun Wu. Myeloid Hv1-STING axis tunes glioma immunity [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(6_Suppl):Abstract nr A016.

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.

Abstract In a great partnership, the Federation of European Neuroscience Societies (FENS) and the Hertie Foundation organized the FENS‐Hertie 2022 Winter School on ‘Neuro‐immune interactions in health and disease’. The school selected 27 PhD students and 13 postdoctoral fellows from 20 countries and involved 14 faculty members experts in the field. The Winter School focused on a rising field of research, the interactions between the nervous and both innate and adaptive immune systems under pathological and physiological conditions. A fine‐tuned neuro‐immune crosstalk is fundamental for healthy development, while disrupted neuro‐immune communication might play a role in neurodegeneration, neuroinflammation and aging. However, much is yet to be understood about the underlying mechanisms of these neuro‐immune interactions in the healthy brain and under pathological scenarios. In addition to new findings in this emerging field, novel methodologies and animal models were presented to foment research on neuro‐immunology. The FENS‐Hertie 2022 Winter School provided an insightful knowledge exchange between students and faculty focusing on the latest discoveries in the biology of neuro‐immune interactions while fostering great academic and professional opportunities for early‐career neuroscientists from around the world.