Alternatively, intramuscular injection of plasmid predominantly led to transfection of myocytes. Myocytes lack expression of major histocompatibility complex class (MHC) II and costimulatory molecules and thus would not be expected to prime T lymphocytes directly. Instead, immune priming likely occurs by dendritic cells (DCs) [26, 27] that presumably migrate to the site of DNA inoculation in response to inflammatory or chemotactic signals following vaccination [28, 29] . These DCs are thought to present antigen by cross-presentation of extracellular antigen or following direct transfection of plasmid DNA [26, 30] .