In 1992, the era of DNA vaccines began with the report of antibody production upon intradermal injection of mice with a plasmid vector expressing a foreign antigen (1 ). A rapid succession of subsequent manuscripts showed stimulation of immune responses, including cytolytic T cells, upon inoculation of expression-vectors specific for antigens derived from viruses, bacteria, protozoa and tumor-associated antigens (2 –7 ). Plasmid DNA can be applied through various routes of injection including: intradermal, intramuscular, subcutaneous, intravenous, or directly on mucosal membranes (1 ,2 ,8 ,9 ). The most commonly used methods of inoculation involve the use of DNA-coated gold beads propelled into the skin by a gene gun or intramuscular inoculation of the vector in saline solution.