Exosomes and the emerging field of exosome-based gene therapy.

Exosomes are a subtype of membrane vesicle released from the endocytic compartment of live cells. They play an important role in endogenous cell-to-cell communication. Previously shown to be capable of traversing biological barriers and to naturally transport functional nucleic acids between cells, they potentially represent a novel and exciting drug delivery vehicle for the field of gene therapy. Existing delivery vehicles are limited by concerns regarding their safety, toxicity and efficacy. In contrast, exosomes, as a natural cell-derived nanocarrier, are immunologically inert if purified from a compatible cell source and possess an intrinsic ability to cross biological barriers. Already utilised in a number of clinical trials, exosomes appear to be well-tolerated, even following repeat administration. Recent studies have shown that exosomes may be used to encapsulate and protect exogenous oligonucleotides for delivery to target cells. They therefore may be valuable for the delivery of RNA interference and microRNA regulatory molecules in addition to other single-stranded oligonucleotides. Prior to clinical translation, this nanotechnology requires further development by refinement of isolation, purification, loading, delivery and targeting protocols. Thus, exosome-mediated nanodelivery is highly promising and may fill the void left by current delivery methods for systemic gene therapy.