DNA Vaccination by Electrogene Transfer

Abstract

Vaccination: Traditional and new generation vaccines Vaccination is historically one of the most important methods for the prevention of infectious diseases in humans and animals. When Edward Jenner inoculated James Phipps with a bovine poxvirus to induce protection against the closely related human pathogen smallpox virus in 1796 and then, almost a century later, Pasteur developed a live attenuated vaccine against rabies, the basic principles for vaccine development were established (Fraser and Rappuoli 2005). Traditionally, a vaccine is known as a preparation of attenuated or killed microorganisms or of subunit vaccines (purified components of a pathogen including the protein-conjugated capsular polysaccharides, toxoids, cell-free extracts, recombinant proteins and stand-alone capsular polysaccharides) administered for inducing active immunity to a specific disease. Two types of immunization exist with intrinsic differences between them: prophylactic vaccination initiates a response against an antigen to which the immune response is naive, leading to a long-term memory cell maintenance and protective efficacy; therapeutic vaccination stimulates the immune system to a chronically displayed antigen, leading to a clearance of an established infection. Several infectious diseases can be prevented by vaccines produced with conventional approaches. These methods are based on the cultivation in laboratory conditions of the microorganism from which single components are isolated individually by using biochemical, microbiological and serological techniques. Each antigen is produced in pure form either directly from the bacterium or using the DNA recombinant technology, and finally tested for its ability to induce an immune response (Serruto and Rappuoli 2006). Conventional approaches provided the basis of vaccinology and led to great achievements such as the eradication of smallpox and the virtual disappearance of diseases like diphtheria, tetanus, poliomyelitis, pertussis, measles, mumps, rubella and invasive Haemophilus influenzae B, increasing the life quality and expectancy (Andre 2003). Nevertheless, they present major disadvantages such as to be time-consuming and, more important, to be impractical in some circumstances due to the difficulty in cultivating some microorganisms in vitro and to the fact that even attenuation may result in detrimental or unwanted immune responses (Purcell et al.