Purification of MVs from ATP-treated cell supernatants was achieved by a standardized protocol based on differential centrifugations of conditioned cell media (Figure S2A in Supplementary Material): floating cells and membrane remnants were removed by a brief low-speed centrifugation and filtration, followed by a step of ultracentrifugation (10,000 g for 30 min). For electron microscopy analyses, the resulting pellet was resuspended in PBS and contrasted by uranyl acetate; several particles with a mean diameter of 200 nm appeared in this fraction (Figure S2B in Supplementary Material). Analogous indications came from the analyses of the pellets performed with dynamic light scattering and TRPS measurements (Figures S2C,D in Supplementary Material). The content of MVs with respect to that of exosomes and parental cells was analyzed by western blotting (Figure S2E in Supplementary Material). Flotillin-1 was equally present in both particle fractions at variance with Alix, more abundant in the exosomal rather than the MV fraction, as expected (16). The mitochondrial-resident protein COX-IV was absent from both exosomes and MVs, further confirming that the preparation was devoid of cells.