Abstract
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.