Abstract 2777: A unique sub-population of PDGFRB+ glioma-associated mesenchymal stem cells constitute the perivascular niche in murine glioblastoma
Authors: Zaman Mohammad F. , Singh Sanjay K. , Hossain Anwar , Phillips Lynette M. , Gumin Joy , Ledbetter Daniel , Milutinovic Bojana 
Published: March 2024

Abstract
Microvascular proliferation (MVP) and spatial heterogeneity are defining histological features of glioblastoma (GBM). Using ex vivo culture method to analyze human GBMs we have previously identified mesenchymal stem cell (MSC)-like cells, called glioma-associated-MSCs (GA-MSCs) in the heterogenous tumor-microenvironment (TME) of GBMs. Like pericytes, fibroblastic cells and smooth muscle cells (SMCs), these GA-MSCs reside in the perivascular niche (PVN) within GBM, and their presence correlates with MVP, decrease in immune cell counts, and poor prognosis. However, the impact of GA-MSCs on the TME remains correlative, and to date, a causative role of GA-MSCs in MVP and immune evasion has not been established in vivo. We hypothesize that recruited GA-MSCs promote MVP and enhance immune evasion in the GBM-TME. To begin to address this hypothesis, we first identified and characterized GA-MSCs at single-cell resolution in an immunocompetent murine GBM model. We sorted tumor, immune, and non-tumor-non-immune (NTNI) cells from GFP-labelled GSC005 tumors in C57Bl/6 mice and performed scRNA-seq. Tumor cells (GFP+ cells) clustered together into 13 distinct cell states. Of the immune cells (CD45+), the most abundant cell types were microglia (33.9%), macrophages (31.9%), T cells (10.3%), dendritic cells (7.5%) and B cells (1.4%), mimicking human GBM. In the NTNI compartment, we identified 17 clusters, which mapped to endothelial cells, oligodendrocytes, astrocytes and other cell types. Interestingly, there were 4 distinct cell clusters that exclusively expressed platelet-derived growth factor receptor beta (PDGFRB). Three of these clusters mapped to pericytes, SMCs and fibroblastic cells. The fourth cluster expressed both adipose tissue and bone marrow MSC markers, identifying for the first time, GA-MSCs in murine GBM. Next, to define the spatial organization of GA-MSCs and their relationship to immune cells in the GBM TME, we conducted spatial proteomics. GA-MSC counts were significantly higher in the PVN compared with the avascular niche (AN) (p= 0.009) and GA-MSCs were absent in contralateral non-tumor regions. Interestingly, GA-MSCs co-localized with SMCs, fibroblastic cells and pericytes as well as pro-tumorigenic macrophages/microglia (Iba1+/CD163+) in the PVN indicating potential interactions between these cell populations. In conclusion, we have identified for the first time, MSC-like cells in the PVN of murine GBM. Our results suggest that these GA-MSCs are recruited to the TME where they may promote MVP, a hallmark of GBM, and interact with immunosuppressive immune cells. Building on these observations, future experiments will investigate the extent to which GA-MSCs drive MVP formation and immune evasion in GBM.
Citation Format: Mohammad F. Zaman, Sanjay K. Singh, Anwar Hossain, Lynette M. Phillips, Joy Gumin, Daniel Ledbetter, Bojana Milutinovic. A unique sub-population of PDGFRB+ glioma-associated mesenchymal stem cells constitute the perivascular niche in murine glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2777.