TMIC-06. TUMOR ASSOCIATED MACROPHAGES DRIVE TUMOR PROGRESSION AND ARE TRANSCRIPTIONALLY SHAPED BY HISTONE MUTATIONS IN DIFFUSE MIDLINE GLIOMA

Abstract Little progress has been made to delineate the inflammatory microenvironment in pediatric high-grade glioma (pHGG) and diffuse midline glioma (DMG). We utilize molecularly defined human samples and immunocompetent mouse models to study how tumor location and genetic driver mutations influence the tumor microenvironment (TME). We first induced tumors of each pHGG/DMG molecular subtype (H3WT, H3G34R, H3.1K27M, H3.3K27M) into both the cortical hemisphere and midline of separate mice and performed survival studies and flow cytometry. The main driving factor shaping the immune landscape and survival is the driver mutation, not tumor location. Next, we performed single cell RNA sequencing on murine H3WT cortical pHGG, H3WT DMG, H3.1 and H3.3K27M DMGs, paired with multiplex flow cytometry. H3K27M DMGs have sparse T cell infiltration and limited T cell recruiting chemokine production. The main non-neoplastic cell type in all tumors was infiltrating myeloid cells and microglia. H3WT DMGs had the greatest myeloid cell and monocyte-derived macrophage (MDM) infiltration, while H3.3K27M DMGs were enriched for microglia. Disease associated gene signatures were found in tumor-associated macrophages (TAMs) that are found in other neurodegenerative diseases, marked by down-regulation of inflammatory signaling, interferon responses, and up-regulation of metabolism-related pathways. H3.3K27M DMGs were enriched for disease-associated TAMs. These gene signatures were then identified in human pHGG/DMG scRNA sequencing data. CD16 monocytes and microglia were enriched for diseased signatures, while CD14 monocytes were pro-inflammatory. We demonstrate that reprogramming this diseased signature in mice results in increased T cell infiltration and extension of survival in H3K27M DMG. Last, through pharmacologic inhibition of CCR1 and CCR5, we demonstrate preventing TAM infiltration in DMG results in enhanced survival, comparable to radiation therapy. Together, this work provides the foundation for developing immunotherapies targeted at specific subgroups of pHGG and DMGs, such as CAR-T-cell, oncolytic viral therapy, and checkpoint blockade.