Wolf's discovery demonstrating that a reporter gene is expressed in myocytes subsequent to injection of naked DNA, was exploited by immunologists and vaccinologists to develop a new generation of vaccines. This observation galvanized the research and in a short lapse of time, an oceanic volume of knowledge has been accumulated. The research carried out in a variety of animal models showed the efficacy of genetic immunization against viruses, bacteria, and some parasites by the ability to induce a strong priming effect resulting from long-lasting persistence of plasmid as episomes. Furthermore, it was demonstrated that newborn or infant immune unresponsiveness to classical vaccines can be corrected by genetic immunization. The applications of genetic immunization for prophylaxis of infections was extended to immunotherapy, namely, cancerous, auto immune, and allergic diseases. Immunologists have provided pertinent information on the cellular basis of the immune responses elicited by genetic immunization, and molecular biologists have established the molecular basis of intrinsic adjuvant properties of plasmids.

Genetic / DNA immunization represents a novel approach to vaccine and immune therapeutic development. The direct injec tion of nucleic acid expression cassettes into a living host results in a limited number of its cells becoming factories for production of the introduced gene products. This host-inappropriate gene expression has important immunological consequences, resulting in the specific immune activation of the host against the gene delivered antigen. The recent demonstration by a number of laboratories that the induced immune responses are functional in experimental models against both specific infectious diseases and cancers is likely to have dramatic consequences for the develop ment of a new generation of experimental vaccines and immune therapies. This technology has the potential to enable the pro duction of vaccines and immune-based therapies that are not only effective immunologically but are accessible to the entire world (rather than just to the most developed nations). Vaccine Development Vaccination against pathogenic microorganisms represents one of the most important advances in the history of medicine. Vaccines, including those against polio, measles, mumps, rubella, hepatitis A, hepatitis B, pertussis and other diseases, have dramatically improved and protected more human lives than any other avenue of modern medicine. The vaccine against smallpox, for example, has been so successful that it is now widely believed that this malicious killer, responsible for more deaths in the twentieth century than World Wars I and II combined, has been removed from the face of the earth.

By two years of age, healthy infants in the United States can receive up to 20 vaccinations to protect against 11 diseases. Although most people know that vaccines effectively protect against serious infectious diseases, approximately one-quarter of parents in a recent survey believe that infants get more vaccines than are good for them, and that too many immunizations could overwhelm an infant's immune system. The Immunization Safety Review Committee reviewed the evidence regarding the hypothesis that multiple immunizations increase the risk for immune dysfunction. Specifically, the committee looked at evidence of potential biological mechanisms and at epidemiological evidence for or against causality related to risk for infections, the autoimmune disease type 1 diabetes, and allergic disorders.

Vaccination has been established as an efficient procedure to prevent infections. Over the past few years, a new method of subunit vaccination has attracted the attention of immunologists. Despite its popularity, it is only recently that the basic mechanisms that drive the immune response to the encoded antigen have begun to unfold. The multidisciplinary approach of this book outlines the basic characteristics of gene (DNA) vaccination, the role of APCs or bone marrow derived cells in the induction of the immune response. It points out the potential applications for various infectious and allergic diseases and describes the multifaceted properties of DNA in initiating and determining the subsequent immune responses to the encoded antigen.

The induction of antigen-specific immune responses after in vivo transfection with expression plasmids has triggered a revolution of vaccine research. After a first hype, evoked by the fascinating options of this method, clinical studies did not reach the ambitious aims and a phase of disillusion ensued. It became obvious that Gene vaccines displayed a weaker immunogenicity in humans than had been observed in the mouse models. Meanwhile these hurdles have been overcome and gene vaccines undergo a renaissance. The present book gives an update of the “world of naked gene vaccines”, namely DNA and RNA vaccines. Its content ranges from general mechanisms, inherent immunostimulatory properties and the vast potential to modulate immune responses, to recent successful clinical studies and approved veterinary gene vaccines. Beyond the state-of-the-art of genetic immunization, the reader will be stimulated with a chapter addressing “burning questions”.

The field of DNA vaccines has undergone explosive growth in the last few years. As usual, some historical precursors of this approach can be d- cerned in the scientific literature of the last decades. However, the present state of affairs appears to date from observations made discreetly in 1988 by Wolff, Malone, Felgner, and colleagues, which were described in a 1989 patent and published in 1990. Quite surprisingly, they showed that genes carried by pure plasmid DNA and injected in a saline solution, hence the epithet “naked DNA,” could be taken up and expressed by skeletal muscle cells with a low but reproducible frequency. Such a simple methodology was sure to spawn many applications. In a separate and important line of experimentation, Tang, De Vit, and Johnston announced in 1992 that it was indeed possible to obtain humoral immune responses against proteins encoded by DNA delivered to the skin by a biolistic device, which has colloquially become known as the “gene gun. ” The year 1993 saw the publication of further improvements in the me- ods of naked DNA delivery and, above all, the first demonstrations by several groups of the induction of humoral and cytotoxic immune responses to viral antigens expressed from injected plasmid DNA. In some cases, protection against challenge with the pathogen was obtained. The latter result was - questionably the touchstone of a method of vaccination worthy of the name.

DNA Vaccines: An Introduction; M.R. Hilleman. Architecture of a DNA vaccine; G. Pavlakis. DNA vaccine delivery; S. Kaufmann. Adjuvanticity of DNA vaccines; A. Krieg. Immune responses to DNA vaccines: Antigen presentation; R. Steinman. Immune responses to DNA vaccines: Antigen processing; J. Yewdell. Immune responses to DNA vaccines: Induction of B cells; G. Kelsoe. Immune responses to DNA vaccines: Induction of CD4+ T cells; E. Shevach. Immune responses to DNA vaccines: Induction of CD8+ T cells; L. Whitton. Immune responses to DNA vaccines: Cytokines as immune mediators as part of the immune response and their potential as genetic adjuvants to DNA vaccines; H. Ertl. Immune responses to DNA vaccines: Chemokines as immune mediators as part of the immune response and their potential as genetic adjuvants to DNA vaccines; P. Murphy. DNA Vaccines to infectious agents: RNA viruses; J. Ulmer. DNA Vaccines to infectious agents: HIV/SIV; B. Wahren. DNA Vaccines to infectious agents: DNA viruses; B. Rouse. DNA Vaccines to infectious agents: Tumor-associated viruses (excluding HBV); R. Kennedy. DNA Vaccines to infectious agents: Bacteria; D. Lowrie. DNA Vaccines to infectious agents: Parasites; S. Hoffman. Use of DNA vaccines for neonatal/early childhood immunization; C.-A. Siegrist. The potential of DNA vaccines for developing countries; H. Wilde. DNA vaccines and their potential to counterbalance biological warfare/bioterrorism; A. Schmaljohn. DNA vaccines to cancer associated/specific antigens; DNA vaccines to autoimmune diseases; H. Wigzell. DNA vaccines to allergic diseases; Yan Chuah, P. Holt. DNA vaccines for gene therapy; K. High. Safety concerns for DNA; D. Klinman. DNA vaccines: Summary.