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(rns) 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(rns) and vGPE(−)/PhoPeV E(rns), 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(4.0) TCID(50) with either vGPE(−)/PAPeV E(rns) or vGPE(−)/PhoPeV E(rns) conferred complete protection for pigs against the CSF virus challenge in the early stage of immunization. In conclusion, the characteristics of vGPE(−)/PAPeV E(rns) and vGPE(−)/PhoPeV E(rns) affirmed their properties, as the vGPE(−) vaccine strain, positioning them as ideal candidates for future development of a CSF marker vaccine.