Replacing the decoy epitope of PCV2b capsid protein with a protective epitope enhances efficacy of PCV2b vaccine.

Microbial pathogens may evolve decoy epitopes to evade host immune responses. In recent years, a decoy epitope has been identified in the capsid protein (CP) of porcine circovirus type 2b (PCV2b) to divert the immune response away from protective epitopes in pigs. To avoid the decoy effect, we designed and produced a recombinant PCV2b CP (ΔCP) by replacing the decoy epitope with a neutralizing B cell epitope derived from CP and tested the ability of ΔCP to induce protective antibody responses in mice and pigs. As expected, the ΔCP, unlike inactivated PCV2b vaccines, recombinant PCV2b CP, and natural PCV2b infection, did not induce anti-decoy epitope antibodies. Although unable to form typical virus-like particles (VLPs), the ΔCP could increase the production of the anti-PCV2b antibodies among which no antibody against the decoy epitopes, and therefore induces improved protective immune responses in pigs challenged with PCV2b. These results provide an alternative strategy for development of recombinant subunit vaccines against PCV2b, and possibly other viruses, by replacing the decoy epitope with a protective epitope.