Exosomes - small extracellular vesicles that are shed by cells - have long offered promise as drug delivery systems for small molecules, DNA, RNA and other biologic payloads. The first of these are now in the clinic. Exosomes - small extracellular vesicles that are shed by cells - have long offered promise as drug delivery systems for small molecules, DNA, RNA and other biologic payloads. The first of these are now in the clinic.