Early studies showed that DNA delivery method affected the cell types that were transfected. Gene Gun (bombardment of the epidermis with plasmid coated onto gold microbeads) tended to directly transfect epidermal keratinocytes and also Langerhans cells, which were shown to migrate rapidly to regional lymph nodes [25] . In this case, professional APCs were transfected directly and behave as the source of Ag presentation.