**1. Introduction**

DNA vaccines were hailed as long ago as the 1990s as the next best thing in vaccines: Plasmid-based DNA vaccines are relatively easy and affordable to produce, sharing a common production method for all vaccines; they are thermostable and safe with no risk of virulence or apparently of anti-vector immunity, can be administered to immunocompromised individuals, and multiple plasmids can be mixed and used as a broad spectrum combination vaccine. DNA vaccines elicit mainly cell-mediated immune responses due to presentation of expressed antigens via major histocompatibility complex class I (MHC-I) presentation, which is similar to viral pathogens and a desirable feature of a vaccine [1]. One important drawback to DNA vaccines, however, is their lack of immunogenicity compared to protein-based or whole virus vaccines: Humoral responses are generally weak if not lacking altogether, and high, repeated doses of DNA are needed in order to obtain reasonable response rates in animal models. Additionally, results in small experimental animals have not translated well into human clinical trial results, and there are concerns over the safety of injecting large amounts of DNA (milligrams) into humans [2].
