Immune Responses Induced By The Suicidal DNA Vaccines Co-expressing The GP5 Protein Of Porcine Reproductive And Respiratory Syndrome Virus And The E2 Protein Of Classical Swine Fever Virus In Mice

The E2 glycoprotein of classical swine fever virus(CSFV) is the major antigen that induces neutralizing antibodies and protective immune response against CSFV.It is often used in developing new-type vaccines and clinical diagnostic reagents,the GP5 of porcine reproductive and respiratory syndrome virus(PRRSV) is one of the major protective antigens, which is responsible for inducing neutralizing antibodies and cell-mediated immunity.Therefore,GP5 is the first choice for developing genetic engineering vaccines against PRRSV.Suicidal DNA vaccines,a new generation of vaccines based on the self-replicating RNA vaccines and conventional DNA vaccines,have emerged in recent years.The suicidal DNA vaccines not only have the advantages of biosafety and enhanced immunogenicity of self-replicating RNA vaccines, but also combines the advantages of conventional DNA vaccines,much lower production,storage,and administration costs.It has been demonstrated the suicidal DNA vaccines could break through immunotolerance by activating innate antiviral pathways.All these indicate that suicidal DNA vaccines are attractive vaccines.Six recombinant plasmids co-expressing the wild-type GP5 or the codon-optimized GP5 protein(containing pan-DR epitope) of porcine reproductive and respiratory syndrome virus(PRRSV) and the E2 protein of classical swine fever virus(CSFV) or the E2 fused with the UL49 of pseudorabies virus(PrV) were constructed based on the suicidal DNA vaccine pSFV1CS-E2 described previously.Expression of GP5 and E2 was confirmed by indirect immunofluorescence assay.The immunogenicity of six plasmids was evaluated in BALB/c mouse model.For the six plasmids, low-level of E2 and GP5 protein specific antibodies could be detected in the sera of the immunized mice.Specific lymphoproliferative responses to the PRRSV or CSFV stimulation were induced in the splenocytes of the immunized mice as demonstrated by CFSE staining assay and WST-8 assay. Antigen specific IFN-γand IL-4 secretion was detected in the splenocytes of some immunized mice by cytokine ELSIA.Fusion with the PrV UL49 in the suicidal vaccines induced significantly higher lymphoproliferative responses and cytokine secretion.Taken together,the suicidal DNA vaccines co-expressing GP5 and E2 could induce PRRSV and CSFV specific humoral and cellular immune responses..