Exploring Novel Influenza Vaccine Strategies in the Swine Model: Along With New Potential Come New Challenges
Type of DegreePhD Dissertation
General Veterinary Medicine
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Influenza A virus (IAV) is a highly contagious respiratory pathogen that constitutes a significant threat to global public and animal health. Unremitting antigenic variation of IAV strains not only results in immune evasion but also has implications on vaccine development and efficacy. Indeed, current influenza vaccine technologies often induce poor immune responses and protection against antigenically distinct IAVs as they primarily target the immunodominant yet highly variable head domain of the hemagglutinin (HA) protein. To overcome the ever-increasing antigenic diversity, there is a need for developing novel vaccine strategies that target conserved influenza immunogens. The objective of this dissertation was to assess the immunogenicity and protective efficacy of two novel vaccine strategies in the swine model, a neuraminidase-based and a hemagglutinin-based vaccine approach as candidate broadly-protective influenza vaccine strategies. Neuraminidase (NA), although commonly neglected in influenza vaccine formulations, is a major antigenic protein of influenza virions previously shown to confer broad heterologous protection. In Chapter II, we compared a novel NA2 virus-like particle (VLP) platform containing the NA protein from the human A/Perth/16/2009 H3N2 strain to a commercial quadrivalent whole inactivated virus (QWIV) influenza vaccine. The NA2 VLP construct was highly immunogenic in the swine model and performed in a similar fashion to the QWIV vaccine in reducing pulmonary virus replication and lung pathology scores following heterologous challenge with A/swine/NorthCarolina/KH1552516/2016, an H3N2 swine field isolate. Overall, our study demonstrated that while neither vaccine elicited complete protection, the NA2 VLP platform induced substantial protection against heterologous challenge. A novel vaccination strategy that deploys prime-boost immunization with antigenically mismatched whole inactivated virus (WIV) vaccines has been recently explored and has been shown to be highly effective in enhancing the immunogenicity of inactivated vaccines against antigenically divergent influenza viruses by presumably targeting conserved subdominant HA epitopes shared by the mismatched vaccine strains. In Chapter III, we investigated the immunogenic properties and protective efficacy of H1N1 heterologous prime-boost vaccination in the swine model compared to immunization with the corresponding mismatched monovalent and bivalent vaccines. Specifically, we prime immunized pigs with the A/California/07/2009 (CA09) H1N1 WIV and later boosted them with the heterologous A/sw/Minnesota/A02636116/2021 (MN21) H1N1 WIV. We demonstrated that heterologous boosting did not expand the scope of cross-reactive antibody responses against antigenically distinct swine and human IAVs compared to the corresponding monovalent and bivalent vaccination regimens. Furthermore, we observed that following challenge with the mismatched A/swine/Georgia/27480/2019 (GA19) H1N2 virus, heterologous prime-boosted pigs showed prolonged clinical disease, and increased pulmonary pathology scores compared to mock-vaccinated pigs. Our results showed that H1-specific heterologous prime-boost vaccination, rather than enhancing cross-protection, exacerbated the clinical outcome and pathology after challenge with the mismatched GA19 strain. Overall the work presented here highlights the untapped potential of NA-based vaccination in conferring broad heterologous immunity and protection and underscores the concern for the development of candidate broadly protective influenza vaccine platforms that target conserved subdominant epitopes on the HA protein.