Dendritic cells (DCs) are the most potent antigen presenting cells and the only 
ones capable of inducing primary cytotoxic immune responses. We found that DCs 
secrete a population of membrane vesicles, called exosomes. Exosomes are 60-80 
nm vesicles of endocytic origin. The protein composition of exosomes was 
subjected to a systematic proteomic analysis. Besides MHC and co-stimulatory 
molecules, exosomes bear several adhesion proteins, most likely involved in 
their specific subjected to targeting. We also found that exosomes accumulate 
several cytosolic factors, probably involved in their endosomal biogenesis. Like 
DCs, exosomes induced immune responses in vivo. Indeed, a single injection of 
DC-derived exosomes sensitized with tumor peptides induced potent anti tumor 
immune responses in mice and the eradication of established tumors. 
Tumor-specific cytotoxic T lymphocytes were found in the spleen of 
exosome-treated mice, and the anti tumor effect of exosomes was sensitive to in 
vivo depletion of CD8+ T cells. These results show that exosomes induce potent 
anti tumor effects in vivo, and strongly support the implementation of human 
DC-derived exosomes for cancer immunotherapy.