Classical swine fever virus (CSFV) and porcine circovirus type 2 (PCV2) have caused severe diseases in swine populations worldwide. Here, a polycistronic baculovirus vector was developed to express a bivalent vaccine, consisting of the CSFV-E2 and PCV2-Cap protein, and an immunomodulator protein derived from the Flammulina velutipes, FVE-FIP, as well as the selection marker, green fluorescent protein. The simultaneous expression of the CSFV-E2 and PCV2-Cap protein was mediated by the 2A-like sequence derived from the Perina nuda virus (PnV), while the expression of the FVE-FIP was driven by the internal ribosome entry site (IRES) element derived from the Rhophalosipum padi virus (RhPV). The Western blot analysis result suggested that the CSFV-E2, PCV2-Cap, and FVE-FIP protein were successfully co-expressed by the infected Spodoptera frugiperda IPBL-Sf21 (Sf21) cell line. The extracted cell lysate containing all three recombinant proteins was administered to Balb/C mice with or without the supplementation of Freund's adjuvant. The ELISA analysis of the serum collected from all the immunized groups showed detectable antibodies against CSFV-E2 and PCV2-Cap. Furthermore, the immunized group without the adjuvant supplementation demonstrated a similar level of antibodies to the group with adjuvant supplementation, suggesting the efficiency of the FVE-FIP in enhancing the immune response. These results demonstrated the polycistronic baculovirus vector could be employed to develop bivalent vaccines for pigs.
