P02.26.A FAP+ PERICYTE-LIKE CELLS PROMOTE MONOCYTE RECRUITMENT AND DIFFERENTIATION INTO TUMOR-ASSOCIATED MACROPHAGES IN GLIOBLASTOMA

Abstract BACKGROUND Glioblastoma (GBM), the most aggressive primary brain tumor, is characterized by a profoundly immunosuppressive microenvironment. Fibroblast activation protein (FAP) is upregulated in GBM and predominantly expressed in pericyte-like cells, suggesting their potential involvement in shaping the tumor microenvironment. However, the precise role of FAP+ pericyte-like cells in modulating the immune landscape of GBM remains largely unclear. This study investigates the influence of FAP+ pericyte-like cells on the GBM immune microenvironment, focusing on their interaction with monocytes and macrophages. MATERIAL AND METHODS TCGA-GBM data was analyzed to assess the correlation between FAP expression and immune cell infiltration. Gene expression was quantified using qRT-PCR and immunohistochemistry in GBM tissue samples. Spatial relationships between FAP+ pericyte-like cells and monocytes/macrophages were examined via immunofluorescence and spatial transcriptomics. Single-cell RNA sequencing was utilized to characterize the transcriptional profile of FAP+ pericytes. Furthermore, in vitro functional assays, including monocyte migration and co-culture experiments with patient-derived FAP+ pericyte-like cells and healthy donor monocytes, were conducted to elucidate the mechanisms of interaction. RESULTS Analysis of TCGA-GBM data, qRT-PCR, and immunohistochemistry revealed a higher abundance of monocytes and tumor-associated macrophages (TAMs) in GBMs with high FAP expression. Immunofluorescence analysis further demonstrated the localization of CD163+ tumor-supporting macrophages in close proximity to FAP+ pericyte-like cells. Single-cell RNA sequencing identified FAP+ pericytes as a distinct subpopulation of stromal cells within the perivascular space, characterized by a unique expression pattern of extracellular matrix components and chemokines. Notably, spatial transcriptomics confirmed the preferential localization of monocytes and M2 macrophages near FAP+ pericytes. Functionally, patient-derived FAP+ pericyte-like cells attracted monocytes through soluble factors and induced their differentiation and polarization into TAMs in vitro. CONCLUSION In summary, FAP+ pericyte-like cells in GBM stimulate the recruitment of peripheral monocytes and promote their differentiation into TAMs. Our results suggest that FAP+ pericyte-like cells may contribute to the pro-tumorigenic inflammatory state and immunosuppressive milieu characteristic of the GBM microenvironment, thereby warranting further investigation of their therapeutic potential. ACKNOWLEDGMENT This work was supported by the National Institute for Cancer Research (LX22NPO5102), the Center for Tumor Ecology (CZ.02.1.01/0.0/0.0/16_019/0000785), Charles University project GAUK 365022 and Cooperatio Program,,Oncology and Haematology“.