Generation and Efficacy of Two Chimeric Viruses Derived from GPE Vaccine Strain as Classical Swine Fever Vaccine Candidates.

A previous study proved that vGPE mainly maintains the properties of classical swine fever (CSF) virus, which is comparable to the GPE vaccine seed and is a potentially valuable backbone for developing a CSF marker vaccine. Chimeric viruses were constructed based on an infectious cDNA clone derived from the live attenuated GPE vaccine strain as novel CSF vaccine candidates that potentially meet the concept of differentiating infected from vaccinated animals (DIVA) by substituting the glycoprotein E of the GPE vaccine strain with the corresponding region of non-CSF pestiviruses, either pronghorn antelope pestivirus (PAPeV) or Phocoena pestivirus (PhoPeV). High viral growth and genetic stability after serial passages of the chimeric viruses, namely vGPE/PAPeV E and vGPE/PhoPeV E, were confirmed in vitro. In vivo investigation revealed that two chimeric viruses had comparable immunogenicity and safety profiles to the vGPE vaccine strain. Vaccination at a dose of 10 TCID with either vGPE/PAPeV E or vGPE/PhoPeV E conferred complete protection for pigs against the CSF virus challenge in the early stage of immunization. In conclusion, the characteristics of vGPE/PAPeV E and vGPE/PhoPeV E affirmed their properties, as the vGPE vaccine strain, positioning them as ideal candidates for future development of a CSF marker vaccine.