Functionalized extracellular vesicles as advanced therapeutic nanodelivery systems

Extracellular vesicles (EVs) are membrane enclosed vesicles that are shed by almost all cell types, and play a fundamental role in cell-to-cell communication. The discovery that EVs are capable of functionally transporting nucleic acid- and protein-based cargoes between cells, rapidly promotes the idea of employing them as drug delivery systems. These endogenous vesicles indeed hold tremendous promise for therapeutic delivery. However, issues associated with exogenously administered EVs, including rapid clearance by the immune system, apparent lack of targeting cell specificity, and insufficient cytoplasmic delivery efficiency, may limit their therapeutic applicability. In this review, we discuss recent research avenues in EV-based therapeutic nanodelivery systems. Furthermore, we narrow our focus on the development of modification strategies to enhance the delivery properties of EVs, and elaborate on how to rationally harness these functionalized vesicles for therapeutic delivery.