Genetic immunization: bacteria as DNA vaccine delivery vehicles.

The so-called DNA vaccination represents one of the most notable tools under development in the field of vaccinology. The concept of administering the gene coding for any given protective antigen and make responsible vaccinee's own cells to produce the protein appeals as too simple to be true. Indeed, the implementation of this approach for mass vaccination should overcome several bottlenecks, such as need of high dosages and poor immunogenicity. In this context, the use of live attenuated bacteria as delivery system for plasmid DNA has emerged as a promising alternative to overcome many of those pitfalls. In addition, this approach is not only amenable for mucosal administration, but allows to specifically target professional antigen presenting cells. This results in their transfection, as well as in their activation and maturation, due to their built-in adjuvant properties resulting from the stimulation of pattern recognition receptors. This chapter discusses the specific features that should be taken into consideration when designing a plasmid vector, current candidate bacterial carriers for DNA delivery and main safety issues.