P02.04.a Uncovering and Targeting Metabolic Regulators of Immunosuppressive Lipid-Laden Macrophages in Glioblastoma

BACKGROUND Glioblastoma tumors are characterized by a prominent infiltration of tumor-associated macrophages (TAMs), constituting up to 30-40% of the cellular make-up. These cells typically harbor immunosuppressive features which, in conjunction with T cell paucity, contribute to a tumor microenvironment (TME) uniquely refractory to immunotherapy response. Therefore, due to their critical role in tumor progression and therapy response, TAMs represent a promising therapeutic target within the brain TME. MATERIAL AND METHODS To address the challenge of macrophage heterogeneity in glioblastoma, we conducted comprehensive multi-omics analyses including scRNAseq, spatial transcriptomics, ATACseq and lipidomics, that identified distinct TAM subsets within tissue-resident microglia and infiltrating monocyte-derived macrophage (MDM) pools. RESULTS We discovered a pro-tumorigenic and immunosuppressive subset common in both cell lineages characterized by high lipid metabolic activity which we termed lipid-laden macrophages (LLMs). These cells engulf and recycle lipid-rich myelin debris to fuel cancer cell proliferation and thereby promote malignancy. Beyond these functions, LLMs also exhibit immunosuppressive features that are induced by myelin debris uptake. Next, we aim to investigate the relationship between myelin-induced metabolic pathways and the subsequent immunosuppressive phenotype of LLMs. To accomplish this, we will employ a genetic screen on primary murine macrophages using a CRISPR knockout library. This approach will target the cellular metabolome and surfaceome, with the goal of rewiring TAMs toward a more immunogenic phenotype. To enable selective targeting of LLMs, we developed lipid nanoparticle (LNP)-based approaches. Our findings demonstrate that LNPs efficiently deliver cargo to macrophages in the TME, with formulations that can be tailored for enhanced cell type-specific uptake. CONCLUSION We identified myelin as a key molecule fostering a tumor-permissive brain TME. We are currently harnessing genetic screening together with the development of cell type-specific LNPs which will enable interventions targeting the immuno-metabolic axis, potentially advancing new treatment strategies for glioblastoma.