SPATIAL ANALYSIS IDENTIFIES CD147 AS A NOVEL MARKER OF HIGH-GRADE CHILDHOOD POSTERIOR FOSSA EPENDYMOMA

: Ependymoma (EPN) is the third most common malignant tumor of the central nervous system in children. The spatial and temporal heterogeneity of cancer cell populations can impact the ability of EPN to overcome microenvironmental constraints. Data set analysis revealed that CD147 expression is increased in glioma, and its expression correlates with detrimental survival and higher mutational burden. We performed spatial phenotyping of tumor microenvironment in childhood posterior fossa type A EPN (PFA-EPN) central nervous system World Health Organization grade 2 (G2; n = 5) and grade 3 (G3; n = 7). Tumors were comprehensively assessed using multiplex immunofluorescence panels to detect immune, microglial, endothelial, and tumor cells. We observed significant differences in immune cell populations according to grading: a high number of T cells and cytotoxic T cell infiltration were features of G2 when compared with G3 cancers. The distance between CD4+ and CD8+ cells was lower in G3 tumors, highlighting an increase in cell interactions between T-cell populations in more aggressive tumors. Two tumor-associated macrophage subsets with distinct functional phenotypes (CD68+MCP1+ and CD68+CD44+), associated with tumor progression, were previously identified by single-cell RNA sequencing analyses in spinal EPN. We demonstrated that the CD68+CD44+ population was higher in G3 compared with G2 PFA. CD147+ microglia cells were closer to CD8+ cells and CD147+ tumor-proliferating cells in G3 than G2 counterparts. In G3 tumors, CD4+ cells were more distant from CD147+ microglial cells and from CD8+ lymphocytes and were closer to CD147+ tumor-proliferating cells. We provided evidence that CD147+ microglial cells could be playing a key role in PFA-EPN progression, promoting CD8+ T cells' exclusion. These findings highlight grading-related differences in PFA-EPN tumor microenvironment.