Date Full Report Received11/26/2012
Date Abstract Report Received11/26/2012
Funded ByNational Pork Board
PRRS is recognized by the pig industry worldwide as one of the most important swine diseases, and it is estimated to cost the US Swine Industry $ 560 million per year. The disease is caused by a PRRS virus (PRRSV).
Vaccination against PRRS is the best way to protect animals and reduce the economic burden for producers. Now, modified live vaccines for PRRS are in use in USA and Canada. However, these vaccines cannot protect against all diverse PRRSV strains. In addition, there is a risk of reversion to virulence under farm conditions. Therefore, a new generation of vaccines with higher safety and protective efficacy is required to control PRRS. Also, the availability of a DIVA (differentiating infected from vaccinated animals) vaccine would be of significant value for infected herds monitoring and eventual eradication of the disease. Here, we suggest developing a novel vaccine candidate based on plasmid DNA. The DNA vaccine is safe, relatively inexpensive, easy to produce and can elicit cellular immune responses that necessary for heterologous protection. In addition, DNA vaccine has a DIVA potential. Therefore, the main goal of this project is to develop a new improved vaccine for PRRSV with increased protection against heterologous PRRSV strains.
The project has three objectives: (1) to construct plasmids expressing synthetic genes for GP5 and M; (2) to characterize the expression of GP5 and M in cell culture; (3) to test the immunogenicity and protective efficacy of the vaccine in pigs.
Under the first objective, synthetic PRRSV genes encoding major structural proteins GP5 and M were constructed and cloned into two plasmid vectors for expression in pig cells. The sequences of the genes were optimized to achieve maximal levels of the proteins expression. In addition, sequence encoding a novel intramolecular adjuvant (polyQ) was added to the M gene to increase cell-mediated immune responses against M. Under the second objective, expression of GP5, M and M-polyQ genes were studied after transfection of cultured swine cells with DNA of the plasmids. Unfortunately, we could not detect the protein expression using several immunological methods. Therefore, more work is needed to achieve abundant PRRSV antigens expression in swine cells. Under the third objective, group of pigs were vaccinated with the mixture of the plasmid DNAs. However, PRRSV-specific immune responses were not detected.