Preparation and immunological effects of a bivalent subunit candidate vaccine based on the PCV-Cap-2-3 gene engineered from baculovirus

Introduction: in the family Circoviridae, are prevalent worldwide and pose a serious threat to the pig industry. Although vaccines against PCV2 are available, PCV3 vaccine development, prevention strategies, and surveillance for co-infections remain limited, leading to delayed outbreak responses. Therefore, the aim of this study was to develop a bivalent subunit vaccine targeting the prevalent strains of PCV2 and PCV3. Methods: Recombinant baculoviruses, Baculovirus-PCV2-Cap and Baculovirus-PCV3-Cap, were constructed to express the PCV2-Cap and PCV3-Cap proteins, respectively. Additionally, a recombinant baculovirus, Baculovirus-PCV-Cap-2-3, was engineered to co-express both proteins. Using GEL02 as the subunit vaccine adjuvant, purified proteins were formulated at an antigen concentration of 30 μg/mL. PCV2-Cap, PCV3-Cap, and PCV-Cap-2-3 subunit vaccines were prepared and administered to 28-day-old piglets. Results: Serological analysis showed that all vaccines induced the production of PCV-specific and neutralizing antibodies in pigs. Lymphocyte proliferation assays demonstrated that the PCV-Cap-2-3 subunit vaccine successfully induced cellular immune responses. Post-vaccination challenge protection tests showed that, following PCV2 and PCV3 challenge, the PCV-Cap-2-3 subunit vaccine group exhibited reduced pathological damage in organs compared with the PBS control group. Discussion: Overall, these results indicate that the developed vaccine effectively protected against both PCV2 and PCV3. The protective performance of this vaccine was comparable to that of commercial PCV2 vaccines, inducing robust immune responses in vaccinated pigs and showing potential for further development.