African swine fever (ASF) is a deadly disease of swine currently causing a worldwide pandemic, leading to severe economic consequences for the porcine industry. The control of disease spread is hampered by the limitation of available effective vaccines. Live attenuated vaccines (LAVs) are currently the most advanced vaccine prototypes, providing strong protection against ASF. However, the significant advances achieved using LAVs must be complemented with further studies to analyze vaccine-induced immunity. Here, we characterized the onset of cross-protective immunity triggered by the LAV candidate BA71ΔCD2. Intranasally vaccinated pigs were challenged with the virulent Georgia 2007/1 strain at days 3, 7 and 12 postvaccination. Only the animals vaccinated 12 days before the challenge had effectively controlled infection progression, showing low virus loads, minor clinical signs and a lack of the unbalanced inflammatory response characteristic of severe disease. Contrarily, the animals vaccinated 3 or 7 days before the challenge just showed a minor delay in disease progression. An analysis of the humoral response and whole blood transcriptome signatures demonstrated that the control of infection was associated with the presence of virus-specific IgG and a cytotoxic response before the challenge. These results contribute to our understanding of protective immunity induced by LAV-based vaccines, encouraging their use in emergency responses in ASF-affected areas.

Porcine circovirus type 2 (PCV2) is the main causative agent of porcine circovirus-associated disease (PCVAD) that profoundly impacts the swine industry worldwide. While most of the commercial PCV vaccines are developed based on PCV genotype 2a (PCV2a), PCV genotype 2b (PCV2b) has become predominant since 2003. In this study, we developed and evaluated DNA-based bivalent vaccines covering both PCV2a and PCV2b. We generated a new immunogen, PCV2b-2a, by combining consensus sequences of the PCV2a and PCV2b capsid proteins (Cap2a and Cap2b) in a form of fusion protein. We also examined whether modifications of the PCV2b-2a fusion protein with a signal sequence (SS) and granulocyte macrophage-colony stimulating factor (GM-CSF) fusing with interleukine-4 (IL-4) (GI) could further improve the vaccine immunogenicity. An immunogenicity study of BALB/cAJcl mice revealed that the DNA vector pVAX1 co-expressing PCV2b-2a and GI (pVAX1.PCV2b-2a-GI) was most potent at inducing both antibody and cellular immune responses against Cap2a and Cap2b. Interestingly, the vaccines skewed the immune response towards Th1 phenotype (IgG2a > IgG1). By performing ELISA and ELISpot with predicted epitope peptides, the three most immunogenic B cell epitopes and five putative T cell epitopes were identified on Cap2a and Cap2b. Importantly, our DNA vaccines elicited broad immune responses recognizing both genotype-specific and PCV2-conserved epitopes. Sera from mice immunized with the DNAs expressing PCV2b-2a and PCV2b-2a-GI significantly inhibited PCV2a cell entry at serum dilution 1:8. All these results suggest a great potential of our PCV2b-2a-based vaccines, which can be further developed for use in other vaccine platforms to achieve both vaccine efficacy and economical production cost.