Exosomes serve as a promising therapeutic nanoplatform. However, the exosomes produced by donor cells are a heterogeneous group, with only a small portion having high therapeutic efficacy. Specific isolation of the subpopulation with high efficacy is important for lowering the dose and minimizing toxicity. In this study, we loaded target mRNA and displayed specific Flag in engineered exosomes simultaneously. Briefly, the donor cells were transfected with plasmid expressing a fusion protein Flag-TCS-PTGFRN-CTSL-MCP, namely, exosome sorter. During biogenesis, the RNA-binding motif MCP can specifically bind with MS2-containing RNA and sort the target RNA into the lumen of exosomes. Anti-Flag magnetic beads can capture and thus purify the engineered exosomes via recognition of the Flag on the surface of exosomes. After purification, the Flag could be cleaved by thrombin treatment while MCP can be separated from the fusion protein by CTSL autocleavage upon exosome acidification, minimizing the side effects and augmenting the therapeutic effects. By the proof-of-concept experiment, the exosome sorter-based "all-in-one" strategy was confirmed effective in both the encapsulation of therapeutic mRNA (Ldlr-MS2) into exosomes and the subsequent purification. The purified Ldlr-MS2-containing exosomes had much higher efficacy in alleviating atherosclerosis, in comparison with the bulk exosomes, confirming the advantage of the proposed "all-in-one" strategy.
Keywords: encapsulation; engineering strategy; exosomes; familial hypercholesterolemia; heterogeneity; purification.