Good things come in small packages: Overcoming challenges to harness extracellular vesicles for therapeutic delivery.

Extracellular vesicles (EVs) hold great promise as potential therapeutic carriers. EVs are biologically active, intrinsically transporting cargo between cells. Moreover, they can be loaded with specific cargo for distribution and/or engineered to achieve enhanced uptake. Although studies have already demonstrated therapeutic delivery using EVs, various challenges must be overcome before EV technology is ready for the clinic. Since the properties of EVs are dependent upon their cell of origin and the conditions of their formation, establishing clear characterization practices is essential to ensuring reproducibility and safety. Identifying methods for mass production of EVs is crucial for achieving high EV yields necessary for clinical trials. This review introduces current theory behind EV formation and function, describes the latest methods for characterization and mass production, and discusses future opportunities for extracellular vesicles in therapeutic delivery.