Exosomes may contain various DNA, RNA, proteins, lipids, carbohydrates, and other metabolites of their cell of origin and transfer their contents from one cell to another via membrane vesicle trafficking. For example, Exosomes present proteins/antigens that influence the immune system via Dendritic Cells (DCs), B-cells and via functions in adaptive immune responses to pathogens and/or tumors. DC-derived Exosomes express MHC I antigens, MHC II antigens, co-stimulatory molecules and induce and enhance antigen-specific T-cell responses in vivo. Exosome production and Exosome content is influenced by molecular signals from the cell of origin, for example hypoxic tumor cells secrete Exosomes with enhanced angiogenic and metastatic potential. Exosomes are being tested in cancer immunotherapy and other clinical trials.