Surface display technology is an emerging key player in presenting functional proteins for targeted drug delivery and therapy. Although a number of technologies exist, a desirable mammalian surface display system is lacking. Exosomes are extracellular vesicles that facilitate cell-cell communication and can be engineered as nano-shuttles for cell-specific delivery.
Researchers at Santa Clara University have developed a novel exosome surface display technology by exploiting mammalian cell secreted nano-vesicles and their trans-membrane protein tetraspanins. By constructing a set of fluorescent reporters for both the inner and outer surface display on exosomes at two selected sites of tetraspanins, they demonstrated the successful exosomal display via gene transfection and monitoring fluorescence in vivo. The researchers subsequently validated our system by demonstrating the expected intracellular partitioning of reporter protein into sub-cellular compartments and secretion of exosomes from human HEK293 cells. Lastly, they established the stable engineered cells to harness the ability of this robust system for continuous production, secretion, and uptake of displayed exosomes with minimal impact on human cell biology. In summary, this work has paved the way for potential applications of exosome, including exosome tracking and imaging, targeted drug delivery, as well as exosome-mediated vaccine and therapy.
System design of surface engineering of exosome
(a) Schematic of Surface engineering of exosome via tetraspanin proteins. CD63 is a “M” shape transmembrane protein with two termini and small middle loop on inner surface while two other loops exist on the outer surface of the exosome. Peptides can be fused with CD63 either at the second loop (outer surface display; red oval) or the C-terminus (inner surface display; green oval). (b) Delivery of CD63 fusion genes into living cells will partition the displayed fluorescent marker (green) on the surface of exosome via CD63 anchoring. (c & d)Engineered exosomes are released into the culture medium that can be recovered with polymer-based precipitation solution and centrifugation. (e) Enriched exosomes can be used for analysis or characterization. (f) A list of potential applications.