TMOD-05. Glioma Exosomes Mediate Systemic Immune Suppression Through Myeloid Cell Targeting and Recruitment

Abstract BACKGROUND Immune suppression in glioma is marked by systemic reprogramming of bone marrow-derived cells (BDMCs). Tumor-derived exosomes (TEX) exhibit the requisite biodistribution, genomic contents, and specificity for short and long-range reprogramming of BDMCs. However, in vivo studies have emerged as the major obstacle for discovery of TEX cell-specific glioma immunotherapy. We report a syngeneic murine glioma model capable of tracking endogenously released TEX in real-time. METHODS We used the RCAS retroviral system develop IDH-mutant and wild-type glioma mouse models with concurrent induction of spontaneous glioma and reporting of GFP-tagged TEX. Tumor and blood samples were analyzed using spectral flow cytometry, multi-plex immunofluorescence and scRNA sequencing to characterize specific TEX-targeted immune cells and their corresponding spatial topography. RESULTS Our multimodal analyses reveal unique genotype-specificity of TEX-targeted immune ontogenies. In IDHm gliomas, myeloid cells were ubiquitously endowed with TEX and exhibited central topography within the tumor. Conversely, IDHwt TEX-containing myeloid cells were over-represented along the tumor periphery. These cells exhibited a dichotomous and polarized pattern of TEX uptake with dorsal (CD68/F4/80) and ventral (CD11b/F480) localization. Over 90% of CD4 T cells engulfed TEX and were highly enriched within the medial leading edge of the tumor. CD8 T cells contained the fewest proportion of TEX and were restrained to the meninges and peri-tumoral white matter. Remarkably, TEX were identified in non-neoplastic contralateral hemispheres and the meninges of tumor-bearing mice. Finally, flow analyses of blood samples detected an increase of TEX in circulating myeloid cells of IDHm tumor-bearing mice, emerging at 2 weeks and peaking at 6 weeks after tumor injection. CONCLUSIONS We have developed a novel mouse model that allows unprecedented endogenous tracking of glioma tumor exosomes. Tumor exosomes engage peripheral macrophages and enable recruitment of these cells into the local tumor microenvironment. Our data supports engineering exosomes for glioma immunotherapy.