Yeast expressed classical swine fever E2 subunit vaccine candidate provides complete protection against lethal challenge infection and prevents horizontal virus transmission

Classical swine fever (CSF) caused by the classical swine fever virus (CSFV) is a highly contagious swine disease resulting in large economical losses worldwide. The viral envelope glycoprotein Erns and E2 are major targets for eliciting antibodies against CSFV in infected animals. A Pichia pastoris yeast expressed E2 protein (yE2) has been shown to induce a protective immune response against CSFV challenge. The purpose of this study is to determine the optimal dose of yE2 and its efficacy on the prevention of virus horizontal transmission. A yeast-expressed Erns (yErns) protein was also included to evaluate its immunogenicity. The yErns vaccinated pigs seroconverted to CSFV-Erns-specific antibody but no neutralizing antibody was detected and none survived after challenge infection, suggesting yErns and yE2 retain correct immunogenicity but only the yE2 is able to induce a protective immune response. All three doses of yE2 (200, 300, and 400 μg) could elicit high titers of neutralizing antibodies and protective responses after challenge. The yE2/200 group demonstrated a mild fever response but recovered soon, and none of the yE2/300 and yE2/400 pigs became febrile. The optimal dose of yE2 was recommended to be 300 μg of the total amount of secreted proteins. In addition, the yE2 vaccine could cross-protect from all three genotypes of viruses. Further, the yE2 vaccine efficacy in preventing virus horizontal transmission was evaluated by cohabitation of unimmunized sentinels 3 days after challenge infection. All the sentinel pigs were alive and had no clinical symptoms confirming yE2 vaccine could confer a protective immune response and prevent horizontal transmission of CSFV.

► A yeast expressed CSFV E2 (yE2) can induce high neutralizing antibody titer in pig. ► The yE2-immunized pigs prevent lethal challenge and horizontal transmission. ► The yE2 vaccine is able to cross-protect from all three genotypes of viruses. ► Production of the yE2 subunit vaccine is easy and less expensive.