Main features of DNA-based immunization vectors

DNA-based immunization has initiated a new era of vaccine research. One of the main goals of gene vaccine development is the control of the levels of expression in vivo for efficient immunization. Modifying the vector to modu late expression or immunogenicity is of critical importance for the improve ment of DNA vaccines. The most frequently used vectors for genetic immuniza tion are plasmids, In this article, we review some of the main elements rel evant to their design such as strong promoter/enhancer region, introns, gen es encoding antigens of interest from the pathogen (how to choose and modif y them), polyadenylation termination sequence, origin of replication for pl asmid production in Escherichia coli, antibiotic resistance gene as selecta ble marker, convenient cloning sites, and the presence of immunostimulatory sequences (ISS) that can be added to the plasmid to enhance adjuvanticity and to activate the immune system. In this review, the specific modificatio ns that can increase overall expression as well as the potential of DNA-bas ed vaccination are also discussed.