Protective efficacy of an orf virus-vector encoding the hemmagglutinin and the nucleoprotein of influenza A virus in swine

Abstract

Swine influenza is a highly contagious respiratory disease of pigs caused by influenza A viruses (IAV-S). IAV-S causes significant economic losses to the swine industry and poses constant challenges to public health due to its zoonotic potential. Thus effective IAV-S vaccines are highly desirable and would benefit both animal and human health. Here, we developed two recombinant orf viruses, expressing the hemagglutinin (HA) gene (OV-HA) or both the HA and the nucleoprotein (NP) genes of IAV-S (OV-HA-NP). The immunogenicity and protective efficacy of these two recombinant viruses were evaluated in pigs. Both OV-HA and OV-HA-NP recombinants elicited robust virus neutralizing antibody response in pigs. Notably, although both recombinant viruses elicited IAV-S-specific T-cell responses, the frequency of IAV-S specific proliferating T cells secreting IFN-γ upon re-stimulation was higher in OV-HA-NP-immunized animals than in the OV-HA group. Importantly, IgG1/IgG2 isotype ELISAs revealed that immunization with OV-HA induced Th2-biased immune responses, whereas immunization with OV-HA-NP virus resulted in a Th1-biased immune response. While pigs immunized with either OV-HA or OV-HA-NP were protected when compared to non-immunized controls, immunization with OV-HA-NP resulted in better protective efficacy as evidenced by reduced virus shedding in nasal secretions and reduced viral load in the lung. This study demonstrates the potential of ORFV-based vector for control of swine influenza virus in swine. Importance Effective influenza A virus (IAV-S) vaccines capable of providing robust protection to genetically diverse IAV-S in swine are lacking. Here, we explored the potential of orf virus based vectors expressing the hemagglutining (HA) or both the HA and the nucleoprotein (NP) genes of influena A virus (IAV-S) in eliciting protection against IAV-S in pigs. We observed that both recombinant viruses elicited IAV-S-specific humoral and cell-mediated immune responses in pigs. Addition of the NP and co-expression of this protein with HA, another major influenza protective antigen, resulted in higher T cell responses which presumably led to better protection in OV-HA-NP immunized animals, as evidenced by lower levels of virus shedding and viral load in lungs. This study highlights the the potential of ORFV as a vector platform for vaccine delivery against IAV-S. Results here provide the foundation for future development of broadly protective ORFV-based vectors for IAV-S for use in swine.