Complex sentence: Dendritic cell-derived exosomes express MHC I, MHC II, and costimulatory molecules and have been proven to be able to induce and enhance antigen-specific T cell responses in vivo.
Split into simpler sentences: Dendritic cell-derived exosomes express MHC I, MHC II, and costimulatory molecules. Exosomes derived from dendritic cells have proven to be able to induce and enhance antigen-specific T cell responses in vivo.