Surface protein profiling of milk and serum extracellular vesicles unveil body fluid and cell-type signatures and insights on vesicle biogenesis

The promise of extracellular vesicles (EVs)-based liquid biopsy resides in the identification of specific signatures of EVs of interest. Knowing the EV profile of a body fluid can facilitate the identification of EV-based biomarkers of diseases. To this end, we characterised purified EVs from paired human milk and serum by surface protein profiling of cellular markers in association with gold standard EV markers (tetraspanins CD9, CD63 and CD81). By using the MACSPlex bead-based flow-cytometry assay with pan-tetraspanin detection (i.e. simultaneous CD9, CD63 and CD81 detection), besides specific breast epithelial cell signatures in milk EVs and platelet signatures in serum EVs, we also identified body fluid-specific markers of immune cells and stem cells. Interestingly, comparison of pan-tetraspanin and single tetraspanin detection unveiled both body fluid-specific tetraspanin distributions and specific tetraspanin distributions associated with certain cellular markers, which were used to model the potential biogenesis route of different EV subsets and their cellular origin.