Abstract A078: Dissecting the myeloid lineage in human gliomas

The immune cell composition of the tumor microenvironment can be a decisive factor for tumor pathogenesis. Gliomas are tumors that develop from the glial cells of the brain and spinal cord and make up to 30% of all brain tumors. In gliomas, microglia and infiltrating macrophages can comprise up to 30 to 50% of total tumor-associated cells. Increased CD68 staining, a marker of microglia/macrophages, in adult gliomas is positively associated with histologic tumor grade. Despite the accumulated evidence substantiating a critical role for microglia and infiltrating macrophages in gliomagenesis, little is known is about the molecular mechanisms driving microglial contribution to tumor growth and whether microglia/macrophages are therapeutic targets in both low- and high-grade gliomas. Despite microglia sharing common properties with other tissue-resident macrophages, they express hundreds of genes at higher levels compared to other tissue-resident macrophages, many of which are influenced by the brain micro-environment. Additionally, engraftment of bone-marrow derived cells into the central nervous system fails to produce microglia identical to yolk sac-derived microglia at the transcriptional level. Hence, in any inflammatory context, including cancer, an interesting question arises: how does each population contribute to the pathogenesis and/or resolution of inflammation? To elucidate the role(s) of microglia/macrophages in gliomas, we isolated the myeloid fraction from primary pediatric and adult low-grade and high-grade gliomas using flow cytometry. By integrating bulk and single-cell transcriptome analysis, we find significant inter- and intratumoral heterogeneity within the myeloid population. Additionally, we find evidence for tumor environment-dependent gene change. In combination with ongoing comparative analysis of the corresponding epigenetic landscapes of the myeloid populations, we seek to decipher how the tumor microenvironment reprograms the transcription factor network in microglia/macrophages to generate tumor-promoting cells. Citation Format: Claudia Z. Han, Sascha H. Duttke, Zhengyu Ouyang, Sebastian Preissl, Johannes C.M. Schlachetzki, Alexander Nott, Conor Fitzpatrick, Carolyn O'Connor, Nicole G. Coufal, Mihir Gupta, David D. Gonda, Michael L. Levy, Ben-Haim Sharona, Barba David, Joseph D. Ciacci, Alexander A. Khalessi, Clark C. Chen, Bing Ren, Christopher K. Glass. Dissecting the myeloid lineage in human gliomas [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A078.