In vivo priming by DNA injection occurs predominantly by antigen transfer

DNA vaccines can stimulate both humoral and cytolytic immune responses, Alt hough bone marrow-derived elements present the expressed rig, the mechanism s for acquiring immunogenic peptides have yet to be fully elucidated, APCs may become directly transfected by plasmid DNA or process extracellular pro teins produced by other transfected cells. Using a transactivating plasmid system and bone marrow chimeras, we show that both mechanisms appear to be involved however, the bulk of the immune response is dependent on expressio n of Ag by nonlymphoid tissues and transfer to APCs. These in vivo studies are the first to define the role of transfected nonlymphoid cells in genera ting Ag for presentation by bone marrow-derived APCs after needle injection with plasmid DNA.