TMIC-09GLIOBLASTOMA STEM CELL-DERIVED EXOSOMES PROMOTE M2 POLARIZATION OF HUMAN MONOCYTES

INTRODUCTION: Exosomes secretedby cancer cells have pleiotropic functions, and can promote autocrine signalingto distant cells. Elucidating the mechanistic modulation of the immune system by these exosomesprovides insight into potential biomarkers for detection, recurrence, and response, and identifies potential new therapeutic targets. METHODS: Exosomeswere isolated from human glioblastoma stem cells (GSC) and fibroblasts (control) using differential centrifugation. Fluorescent-labeled exosomeswere co-cultured with human peripheral blood mononuclear cells (PBMCs). Flow cytometry and confocal microscopymethods were utilized to determine the ability of immune cells to uptake exosomesand to evaluate subsequent intracellular trafficking. The exosomalprotein and RNA content was analyzed by mass spectrometry and Nanostring Counter System, respectively. The phenotypic and functional skewing of the monocytelineage was analyzed after exposing these cells to exosomes. The cytokine array was used to analyze the cytokines generated following treatment of human normal monocyteswith exosomes. RESULTS: The GSC- secreted exosomeswere preferentially absorbed by CD14+ monocytesand Gr-1+ derived myeloid cells isolated from healthy volunteers and/or glioblastoma patients. When activated, CD4+ and CD8+ T cells could also uptake GSC- secreted exosomes. Confocal microscopyrevealed that only monocytescould internalize GSC- secreted exosomesbut not fibroblast- secreted exosomes. The exposure to GSC- secreted exosomesinduces a phenotypic change in monocytesand prevents them from undergoing apoptosis. GSC- secreted exosomes, but not the fibroblast- secreted exosomes, increased expression of CD163, CD206, and decreased expression of MHC class II. Monocytestreated with GSC- secreted exosomesrelease IL-6, IL-1RA, CCL3, and CCL4 when compared to cells exposed to fibroblast exosomes. GSC- secreted exosomescontained distinct protein composition in contrast to fibroblast- secreted exosomesthat may affect the anti-tumor function of monocyte-derived macrophages. CONCLUSIONS: Monocytesdemonstrated a preferential uptake of GSC- secreted exosomeswhich then induced a glioma-supportive M2 phenotype. GSC- secreted exosomescan be a contributing factor in the M2 skewing within glioma microenvironment.