CD40 Ligand and GMCSF Coexpression Enhance the Immune Responses and Protective Efficacy of PCV2 Adenovirus Vaccine

Porcine circovirus 2 (PCV2) capsid protein (Cap) is the major structural protein that is responsible for neutralizing antibodies development and protective immunity, thus it is usually used to develop vaccines against porcine circovirus-associated disease (PCVAD). Porcine CD40 ligand (CD40L) and granulocyte-macrophage colony-stimulating factor (GMCSF) have positive immunostimulatory effects on immunocytes and have been applied in vaccine efficacy improvement as attractive adjuvant cytokines, respectively. However, whether these two cytokines can produce synergistic effect in vaccines still need to be further studied. In this study, porcine CD40L and GMCSF were inserted into recombinant adenoviruses to test the immunogenicity of PCV2 adenovirus vaccine in mice. Western blot and indirect immunofluorescence assay showed that Ad-Cap, Ad-CD40L-Cap, Ad-Cap-GMCSF, and Ad-CD40L-Cap-GMCSF were successfully constructed. Indirect ELISA and virus neutralizing assay showed that CD40L and GMCSF could enhance humoral immune responses, and PCV2 Cap-specific antibody titer and neutralizing activities were significantly higher in Ad-CD40L-Cap-GMCSF group than that in the other groups that just inserted either porcine CD40L or GMCSF in recombinant adenoviruses. Moreover, lymphocyte proliferation assay and cytokine release assay showed that CD40L and GMCSF enhanced the cellular immune responses of Ad-Cap, and had synergistic effects in lymphocyte proliferative activities and Th1-type cytokine production. Following PCV2 challenge, the viral loads in lungs of Ad-CD40L-Cap-GMCSF group were significantly lower compared with Ad-Cap, Ad-CD40L-Cap, and Ad-Cap-GMCSF group. Taken together, the results of this study demonstrated that CD40L and GMCSF could synergistically enhance the protective immune responses of PCV2 adenovirus vaccine, which would be used as a potent vaccine for the prevention and control of PCVAD.