Submitted to: American Society for Virology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: April 14, 2014
Publication Date: N/A
Technical Abstract: One of the leading causes of economic loss in the global pork industry is the swine pathogen porcine reproductive and respiratory syndrome virus (PRRSV). It is a positive sense single-stranded RNA virus which emerged in the late 1980’s in North America and Europe, with highly pathogenic strains emerging in Southeast Asia in 2006. PRRSV has proven to be one of the most rapidly evolving pathogens, and the catastrophic potential to the US pork industry of importation of highly pathogenic PRRSV underscores the need for more effective vaccination strategies. Although modified live virus (MLV) vaccines have been available for nearly 20 years, only modest success has been achieved in PRRSV control and prevention. This is likely due to high genetic diversity, rapid rate of viral evolution, and the lack of a broadly protective immune response to vaccination. Various adjuvants have been used to stimulate a more robust response to vaccination, and in some cases, purified cytokines have been used in this capacity. While the use of purified proteins would be cost prohibitive for PRRSV vaccination, genetic modification of a PRRSV MLV vaccine with a cytokine expression cassette would serve as a kind of genetic adjuvant. Insertion of foreign genes within the PRRSV genome has been previously shown to be unstable and these insertions are rapidly mutated or deleted. To avoid this, we engineered the cytokine expression cassettes into a unique class of subgenomic RNA termed heteroclite RNA. Cytokines examined include IL-7, IL-12p70, IL-15 and IL-18, which were all selected for their potential to enhance cell-mediated immune response to vaccination. Heteroclite RNAs are translation competent, replicate during viral infection and are packaged into viral particles. Expression of the exogenous cytokine gene, packaging of recombinant heteroclite RNA, and replication of the augmented PRRSV MLV was assessed in permissive cell culture.