In preclinical studies, DC-derived exosomes administered as prophylactic 9 or therapeutic 5 cancer vaccines demonstrated their value as potent immune-activating agents, often more so than did live DCs. Based on this premise, some phase I trials of DC-exosomes have been conducted, showing promising results in very testing clinical scenarios, such as advanced non-small-cell lung cancer 10. Why DC-exosomes are more effective than live DCs in such therapeutic settings remains unclear. It may be that DC-exosomes can spontaneously activate host DCs or other immune cells to boost the antitumour response. Alternatively, these effects may simply be a result of the acellular nature of exosomes, capable of performing their activator functions while resisting the complex immune suppressive factors present in tumour-bearing hosts.