P02.29.B HYPOXIA SHAPES TUMOR IMMUNE MICROENVIRONMENT THROUGH CELL-TYPE DEPENDENT RESPONSES IN DIFFUSE ASTROCYTOMAS

Abstract BACKGROUND Hypoxia is a critical driver of tumor aggressiveness in high-grade gliomas, yet its cell-type-specific effects on immune cell populations within the tumor microenvironment (TME) remain poorly understood. MATERIAL AND METHODS We investigated how hypoxia shapes the spatial distribution and functional states of monocyte-derived macrophages (MDMs) and brain-resident microglia (MG) in diffuse astrocytomas and glioblastomas (GB) by using cyclic immunohistochemistry (cIHC), single-cell RNA sequencing, spatial transcriptomics, and in vitro cell culture models. RESULTS Hypoxia induces divergent responses in these myeloid subsets, driving spatial immune patterning. CD163⁻ MDMs dominate hypoxic niches in GB, while MG populations are excluded from these regions, correlating with hypoxia-induced TNF upregulation, stress response signatures, and dampened interferon responses. Conversely, MDMs exhibit a shift towards hypoxia-associated immunosuppressive traits and altered metabolism. GBs display elevated hypoxic intensity compared to diffuse astrocytomas, as supported by hypoxia-response gene expression in TCGA dataset. In vitro, MG show heightened sensitivity to hypoxia-associated acidity compared to MDMs, suggesting together with microglial hypoxia response genes that their exclusion from hypoxic zones results from intrinsic vulnerability. CONCLUSION Our findings reveal that hypoxia remodels the TME by promoting immunosuppressive MDM accumulation and depletion of MG, creating spatially distinct immune landscapes that may underlie glioma progression. These results highlight hypoxia-driven immune dysregulation as a therapeutic target and underscore the importance of cell-type-specific strategies to counteract TME-driven immunosuppression in malignant gliomas.