Extracellular vesicles (EVs) secreted from probiotics, defined as live microorganisms with beneficial effects on the host, are expected to be new nanomaterials for EV-based therapy. To clarify the usability of probiotic-derived EVs in terms of EV-based therapy, we systematically evaluated their characteristics, including the yield, physicochemical properties, the cellular uptake mechanism, and biological functions, using three different types of probiotics: Bifidobacterium longum, Clostridium butyricum, and Lactobacillus plantarum WCFS1. C. butyricum secreted the largest amounts of EVs, whereas all the EVs showed comparable particle sizes and zeta potentials, ranging from 100 to 150 nm and -8 to -10 mV, respectively. The silkworm larvae plasma assay indicated that these EVs contain peptidoglycan that activates the host's immune response. Moreover, a cellular uptake study of probiotic-derived EVs in RAW264.7 cells (mouse macrophage-like cells) and DC2.4 cells (mouse dendritic cells) in the presence of inhibitors (cytochalasin B, chlorpromazine, and methyl-β-cyclodextrin) revealed that probiotic-derived EVs were mainly taken up by these immune cells via clathrin-mediated endocytosis and macropinocytosis. Furthermore, all the probiotic-derived EVs stimulated the innate immune system through the production of inflammatory cytokines (TNF-α and IL-6) from these immune cells, clarifying their utility as a novel adjuvant formulation. These findings on probiotic-derived EVs are valuable for understanding the biological significance of probiotic-derived EVs and the development of EV-based immunotherapy.
Keywords: adjuvant; extracellular vesicles; immune cells; immunotherapy; probiotics.