ARS | Publication request: THE EFFECT OF EUKARYOTIC EXPRESSION VECTORS AND ADJUVANTS ON DNA VACCINES IN CHICKENS USING AN AVIAN INFLUENZA MODEL

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 8, 2000
Publication Date: October 19, 2000

Interpretive Summary: Avian influenza in chickens and turkeys can cause a range of disease from mild respiratory infections to serious disease with high death losses. Because of the serious disease losses, efforts to develop better and cheaper vaccines to prevent the disease have been actively pursued. This research report describes a new type of vaccine that is currently being evaluated in humans and animals, called DNA vaccines. This vaccine uses a special piece of DNA, produced in bacteria, that includes a gene of the disease organism you're trying to vaccinate for. When the vaccine is injected into the chicken, the vaccine can elicit the production of protective antibody and stimulate other parts of the chicken immune system. We tested several different types of DNA pieces using influenza in chickens as our model. We found large differences in which DNA pieces gave a good response. We used the best DNA piece to also test whether we could improve ethe immune response with different adjuvants, chemicals commonly used to enhance the vaccine response. Only two of the six adjuvants tried improved the immune response. DNA vaccines in poultry show considerable promise, but continued efforts to improve the vaccines are necessary before they can be used commercially.

Technical Abstract: Many different methods can conceivably enhance the efficacy of DNA vaccines, including the use of different eukaryotic expression vectors with different promoters and different adjuvants. Four different promoters in five different plasmids were used to express the hemagglutinin protein of an H5 avian influenza virus, including two different immediate early cytomegalovirus (CMV), Rous sarcoma virus (RSV), chicken actin, and simian virus 40 (SV 40) promoters. All five constructs were shown to express detectable hemagglutinin protein in cell culture, but the pCI-neo HA plasmid with the CMV promoter provided the best response in chickens based on antibody titer and survivability after virulent influenza challenge. Using the pCI-neo construct, the effects of different adjuvants designed to increase the uptake of plasmid DNA were examined, including 25% sucrose, DEAE dextran, calcium phosphate, polybrene, and two different cationic liposomes. Both liposomes tested enhanced antibody titers as compared to the positive controls, but the other chemical adjuvants decreased the antibody response as compared to the control chickens that received just the plasmid alone. The results observed are promising for continued studies, but continued improvements in vaccine response and reduced costs are necessary before the technology can be commercially developed.