CD81 and cancer: In order to evaluate the feasibility of our tetraspanin-based cathepsin B-targeting strategy, as a first step we expressed CD9/CD63/CD81-RFP CS/NACS recombinant constructs in 5637 cancer cell line, characterized by high cathepsin B expression level, and compared the 3 resulting phenotypes in terms of fluorescence pattern, amount of protein produced with respect to basal, and amount of protein sorted into the EV fraction (Figure 2).