Exosomes are endosome-derived membrane vesicles, which are released by cells of diverse origin including dendritic cells, cancer cells [5] and EBV-infected B cells [6] . Exosomes bud from endosomal membranes and accumulate in multivesicular bodies, which eventually fuse with the cellular membrane and release the contained vesicles. Exosomes are rich in lipids and membrane proteins like MHC molecules, TNF-R and tetraspanins [5] but their specific composition depends on the cell of origin. Exosomes either fuse to the recipient cell membrane or are engulfed by phagocytic cells in such a way that exosome proteins are degraded and loaded onto MHC class II molecules [7] . Obviously, exosomes can deliver proteins as cargo in a very immunogenic manner so that they efficiently reactivate specific CD4+ T cell clones [8] . Hence, exosomes can induce strong and epitope-specific immune responses [9, 10] and can be used as an alternative to transfer strategies using gene vectors and as promising vaccines [11, 12] .