Nucleic acid vaccines: veterinary applications

Current status of aquatic species biologics

No vaccine is a substitute for good management and diligent biosecurity in an aquaculture facility. It is always important to ensure the best water quality possible, provide quality nutrition, avoid overcrowding of tanks and raceways, remove dead fish to prevent pathogen buildup and spread, and reduce or eliminate unnecessary stress on fish. Use of a preventive medicine vaccine program and improved management can help ensure good health in a fish population and reduce the industries' use of therapeutic agents.

DNA vaccination in the avian

Inoculation of naked DNA represents a novel approach to vaccine and immune therapeutic development. DNA vaccines or genetic immunization offers several advantages over the conventional vaccines for specific immune activation. Although a large number of vaccines have been made and are being used in the poultry industry, there have been no major advances in vaccine technology for this animal industry sector for decades. The potential advantages of DNA vaccines, such as over coming maternal immunity, in ovo delivery and absence of requirement for a cold-chain, combined with immunological efficacy make this new vaccine technology very attractive for the poultry industry. This review lists all of the published reports of experimental DNA vaccines developed for use in poultry and focuses on the trends, potentials and remaining barriers in the development of this new revolution in poultry vaccinology.

The application of nucleic acid vaccines in veterinary medicine

Nucleic acid immunisation entails the delivery of DNA (or RNA) encoding a vaccine antigen to the recipient. The DNA is taken up by host cells and transcribed to mRNA, from which the vaccine proteins are then translated. The expressed proteins are recognised as foreign by the host immune system and elicit an immune response, which may have both cell-mediated and humoral components. DNA vaccines offer a number of advantages over conventional vaccines, including ease of production, stability and cost. They also allow the production of vaccines against organisms which are difficult or dangerous to culture in the laboratory. This review describes the principles of DNA vaccination and the application of DNA vaccines to veterinary species. Although a great deal of developmental work is required before the technology can give rise to commercial vaccines in domestic animals, there is ongoing research in many fields and it is expected that a number of exciting developments will arise in the next decade.

Genetic immunization: what's in a name?

The concept and demonstration of genetic immunization (GI) was first introduced in 1992. At the time it appeared to be a revolutionary new approach in vaccinology. Since then, genetic immunization has been applied with much success in a wide variety of model and natural systems. It has also been used in several human clinical trials. Currently there is a general impression that genetic immunization has limitations inhibiting its broad use. The technique is thought to be poor at antibody production and more importantly not to work well in primates and humans (simian barrier). However, recent reports addressing these issues (poor antibody production and the simian barrier) showed improvements of GI to produce protective immune responses in humans. We propose that the apparent limitations of gene vaccines may arise from not using the technologies' potential to manipulate the immune system. This dearth of imaginative use is manifested in the tendency by some to term the technique DNA immunization. The apparent limitations of DNA vaccines may not be limitations for gene vaccines.

Enhanced protective response and immuno-adjuvant effects of porcine GM-CSF on DNA vaccination of pigs against Aujeszky's disease virus

This study was conducted to investigate whether the co-delivery of DNA encoding porcine cytokines would enhance a protective immune response in pigs to a Pseudorabies virus (PRV; or Aujeszky's disease virus) DNA vaccine. Aujeszky's disease in pigs results in respiratory and nervous symptoms with important economic losses. To evaluate cytokine effects, eukaryotic expression vectors were constructed for porcine GM-CSF, IL-2 and IFN-gamma. cDNA for each of these cytokines was inserted under the control of a CMV promoter in the pcDNA3 plasmid and cytokine expression was confirmed after DNA transfection in various mammalian cell cultures by bioassays (GM-CSF and IL2) and ELISA (IFN-gamma). Pigs were vaccinated by single intramuscular injection with plasmid DNA encoding PRV gB and gD along with various combinations of cytokine plasmid constructs. Pig serum was tested for the production of antibody by isotype specific anti-PRV ELISA. Pigs were then challenged with the highly virulent PRV strain NIA3 on day 21 after vaccination. The survival and growth rate of pigs were monitored for seven days after the viral challenge. The co-administration of GM-CSF plasmid increased the immune response induced by gB and gD PRV DNA vaccine. This immune response was characterized by an earlier appearance of anti-PRV IgG2, a significantly enhanced anti-PRV IgG1 and IgG2 antibody response, a significantly decreased and shortened viral excretion in nasal swabs and an improved protection to the viral challenge. In contrast, the co-administration of porcine IL-2 or IFN-gamma had no adjuvant effects. Our results thus demonstrate for the first time that the application of porcine GM-CSF gene in a DNA vaccine formulation can exert immuno-adjuvant and protective effects with single vaccination in the natural host pig against Aujeszky's disease.