Exosomes for targeted siRNA delivery across biological barriers

Using oligonucleotide-based drugs to modulate gene expression has opened a new avenue for drug discovery. In particular small interfering RNAs (siRNAs) are being rapidly recognized as promising therapeutic tools, but their poor bioavailability limits the full realization of their clinical potential. In recent years, cumulating evidence has emerged for the role of membrane vesicles, secreted by most cells and found in all body fluids, as key mediators of information transmission between cells. Importantly, a sub-group of these termed exosomes, have recently been shown to contain various RNA species and to mediate their horizontal transfer to neighbouring- or distant recipient cells. Here, we provide a brief overview on membrane vesicles and their role in exchange of genetic information. We also describe how these natural carriers of genetic material can be harnessed to overcome the obstacle of poor delivery and allow efficient systemic delivery of exogenous siRNA across biological barriers such as the blood–brain barrier.