These years, exosome as vehicle has been widly used in Bilology. Exosome is the signal communication between cells. It usually has size of 30-200 nm. Its just like the "Virus cell" which contain the membrane and DNA, RNA, etc.
Exosomes appear to have potent immunostimulatory roles. Therefore, one of the most important roles, I would think, would be the stimulation of anti-tunor immunity through the administration of exosomes derived from tumor cells or cell lines.