A candidate DNA vaccine encoding a fusion protein of porcine complement C3d-P28 and ORF2 of porcine circovirus type 2 induces cross-protective immunity against PCV2b and PCV2d in pigs.

Background: Porcine circovirus type 2 (PCV2) is an economically important viral pathogen for swine industry worldwide. However, current PCV2 vaccines provide incomplete protection against the PCV2d, which has recently emerged as the predominant pathogenic form of PCV2.

Methods: To develop a novel DNA vaccine with high efficacy against PCV2d virus, we fused the ORF2 of PCV2d to three copies of the minimum-binding domain of the complement C3 cascade terminal component, C3d-P28. Expression of ORF2 alone (pVO) or fused C3d-P28 (pVOC3) were verified by immunofluorescent assay. Vaccine efficacy was tested by measured the DNA copy and T and B cell immune response.

Results: Vaccination with pVOC3 reduced the levels of PCV2 genomic DNA after pigs were infected with either PCV2b or PCV2d genotypes, produced potent antibodies against PCV2, and stimulated PCV2-specific interferon-γ secreting cells.

Conclusion: Results suggested pVOC3 would be a safe and effective DNA vaccine to confer cross-protection against both PCV2b and PCV2d genotypes in pigs.