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

Abstract - Vaccination of pigs with DNA constructs encoding Pseudorabies Viral glycoprotein C (PRV gC) was previously shown, by Gerdts et al., to provide only partial protection against Aujeszky's disease, after three immunisations (Gerdts et al., J. Gen. Virol. 78 (1997) 2139-2144). The aim of the present work was to evaluate the immuno-adjuvant and protective efficacy of porcine cytokines on anti-PRV DNA vaccination in pigs. Eukaryotic expression vectors were constructed for porcine GM-CSF, IL-2 and IFN- . cDNA for each of these cytokines was inserted under the control of a CMV promoter in the pcDNA3 plasmid using standard molecular biology techniques. The cytokine cDNA plasmid constructs were transfected in various mammalian cell cultures and tested for protein expression by bioassays (GM-CSF and IL-2) and ELISA (IFN- ). There was significant production of the three cytokines in the corresponding cell transfected supernatants. Pigs were then vaccinated by single i.m. injection with plasmid DNA coding for 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. Survival and growth rate of the pigs were monitored for seven days after viral challenge. When compared to the PRV DNA vaccine alone, the immune response induced by co-administration of the GM-CSF plasmid construct with the PRV gB and gD DNA vaccine, was characterised by an earlier appearance of anti-PRV IgG2, a significantly enhanced anti-PRV IgG1 and IgG2 antibody production and a significantly decreased viral replication in nasal swabs, which resulted in improved animal protection to the challenge, as evidenced by increased growth rates. In contrast, co-administration of porcine IL-2 or IFN- had no adjuvant effects. In conclusion, these results demonstrate for the first time that application of the porcine GM-CSF gene in a DNA vaccine formulation can exert immuno-adjuvant and protective effects with a single immunisation, in the natural host pig against Aujeszky's disease.