VP2 (PTA motif) encoding DNA vaccine confers protection against lethal challenge with infectious pancreatic necrosis virus (IPNV) in trout

IPNV in Atlantic salmon is represented by various strains with different virulence and immunogenicity linked to various motifs of the VP2 capsid. IPNV variant with P217, T221, A247 (PTA) motif is found to be avirulent in Atlantic salmon, but virulent in rainbow trout, and other salmonid species. This study describes a DNA vaccine delivered intramuscularly encoding the VP2 protein of infectious pancreatic necrosis virus (IPNV) with PTA motif that confers high protection in rainbow trout (Oncorhynchus mykiss). Intramuscular injection of 2, 5 and 10 μg of DNA (pcDNA3.1-VP2) in rainbow trout fry (4-5 g), confers relative protection of 75-83% in the different vaccine groups at 30 days post vaccination (450° days). The VP2 gene is expressed in spleen, kidney, muscle and liver at day 30 post-vaccination (RT-PCR), and IFN-1 and Mx-1 mRNA are upregulated at early time post vaccination, and so also for IgM, IgT, CD4 and CD8 in the head kidney of vaccinated fish compared to controls, 15 and 30 days post vaccination. Significant increase of serum anti-IPNV antibodies was found 30-90 days post-vaccination that was correlated with protection levels. Mortality corresponded with viral VP4 gene expression were significantly decreased in vaccinated and challenged fish. This shows for the first time that a VP2-encoding DNA vaccine delivered intramuscularly elicits a high level of protection alongside with high levels of circulating antibodies in rainbow trout and a lowered viral replication.