IMMUNOGENICITY OF A DNA VACCINE DERIVED FROM THE PASTEURELLA MULTOCIDA TOXIN GENE

Authors: Register, Karen

Submitted to: UJNR Food & Agricultural Panel Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/15/2004
Publication Date: 11/22/2004
Citation: Register, K.B. 2004. Immunogenicity of a dna vaccine derived from the pasteurella multocida toxin gene. UJNR Food & Agricultural Panel Proceedings. P. 8.

Interpretive Summary:

Technical Abstract: Pasteurella multocida is a widespread and costly pathogen responsible for both atrophic rhinitis and pneumonia in swine. The P. multocida toxin (PMT) is a primary virulence factor in atrophic rhinitis and a major protective immunogen. Technical difficulties and expense prevent the purification of PMT in amounts suitable for widespread use as a stand-alone vaccine or as an additive to existing vaccines. DNA vaccine technology may overcome these limitations and provide a practical solution for improving vaccine efficacy. In the present study vaccines were constructed comprising the entire PMT coding region, but containing a single point mutation demonstrated to eliminate enzymatic activity. The modified coding region was cloned into eukaryotic expression vectors VR1020 or VR1028 (Vical, Inc.); recombinants were designated either pMM4 or pMM5, respectively, and used to vaccinate mice. Groups of 15 mice each were injected in the right hind quadriceps with 50ug of either pMM4 or pMM5. Additional groups of mice injected with either VR1020 or VR1028 served as negative controls. Three weeks later mice were boosted with 50ug of DNA. A second boost was administered 4 weeks later. Five mice from each group were euthanized prior to the first and second boosts, and 4 weeks after the second boost. Blood and spleen cells were collected from all injected mice and from nonimmunized mice euthanized prior to the first injection. Pooled sera were tested by ELISA to assess the anti-PMT response. PMT-specific secretion of IFN-gamma measured with a sandwich ELISA, was used a marker for cellular immune responses. A single injection of pMM4, but not pMM5, elicited a detectable antibody response in mice. Antibody responses increased significantly after additional booster injections with pMM4, but not with pMM5. Endpoint titers have yet to be determined, but are all >103. Cell-mediated responses are currently being evaluated. These results suggest that DNA vaccine technology may be a feasible approach for improving the efficacy of vaccines for atrophic rhinitis in swine.