CSIG-07. HYPERCELLULAR NODULES IN OLIGODENDROGLIOMA REPRESENT POCKETS OF PROLIFERATIVE STEM-LIKE TUMOR CELLS

Abstract INTRODUCTION Oligodendrogliomas are a progressive, infiltrative glioma. By histology, a subset of oligodendrogliomas demonstrate hypercellular nodules (HCN), which often have increased anaplasia compared to surrounding tumor. However, the signals driving anaplasia are unknown. METHODS We first performed a GeoMX 89-protein Digital Spatial Profiling (DSP, Nanostring) panel on a cohort of ten oligodendrogliomas with HCN., followed by spatial whole RNA transcriptome analysis (10x Genomics Visium) on six oligodendrogliomas. For the latter, following unsupervised clustering, we performed Gene Ontology (GO) enrichment analysis and Ingenuity Pathway Analysis (IPA, Qiagen) on the differentially expressed genes between HCN and adjacent tumor. We performed paired single nucleus RNA sequencing for deconvolution of the spatial transcriptomic data. RESULTS AND CONCLUSIONS By protein DSP, we identified a marker of stemness (OLIG2) and a proliferation marker (Ki-67) as present at increased levels (p< 0.05) within HCN. We subsequently performed spatial whole transcriptome analysis. On unsupervised clustering of differentially expressed genes, the HCN spots cluster away from the remaining tumor spots, supporting a distinct niche. GO and IPA both identified increased activity in several central nervous system developmental pathways, providing further evidence for the “precursor-like” state of cells in HCN. We then annotated paired single nucleus RNA sequencing results to align tumor cells with astrocytic-like, oligodendroglial-like, and stem-like cell states. Using this to deconvolute the spatial transcriptomic data, we found that the vast majority of HCN are enriched for either stem-like or OC-like/stem-like tumor cells. Taken together, the findings support HCN as niches for the most precursor-like, proliferative oligodendroglial cells.