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DEVELOPMENT OF NOVEL BROADLY PROTECTIVE VACCINE CANDIDATES FOR SWINE INFLUENZA VIRUSES

Student Name: Gabriela Mansano Do Nascimento
Student Concentration: Immunology and Infectious Disease
Mansano Do Nascimento
Principal Investigator: Diego Diel
Degree Conferral Date: August 2023
Committee Member 1: Colin Parrish
Committee Member 2: Hector Aguilar-Carreno
Committee Member 3: Scott Coonrod
Abstract:

Influenza A viruses (IAVs) belonging to H1 and H3 subtype are a major cause of respiratory disease outbreaks in swine worldwide. Antigenic drift and shift lead to a wide genetic diversity, resulting in lack of protection by vaccine strains against divergent IAV-S. Here, we aimed at developing vaccine candidates able to elicit broad immune responses against divergent IAV-S viruses. Initially, we designed a consensus of HA based on the sequences of contemporary virus isolates for the H1 subtype (conH1), minimizing the average pairwise genetic distance between the generated consensus and the HA from circulating H1 viruses. Through homologous recombination with Orf virus (ORFV), we obtained a recombinant virus expressing the conH1 (ORFV∆121conH1) and assessed its immunogenicity in swine. Immunization with the recombinant ORFV∆121conH1 virus elicited cross reactive IgG levels as determined by an indirect ELISA using a panel of 12 divergent H1 viruses. Additionally, the frequency of T helper/memory cells secreting IL-17A and IFN-γ, and cytotoxic T lymphocytes (CTLs) secreting IFN-γ was increased in the blood of vaccinated piglets compared to unvaccinated animals considering the groups challenged with the Ca/09. Interestingly, the percentage of IL-17A induced T cells was higher in the bronchoalveolar lavage (BAL) of vaccinated animals challenged with the Oh/07. Reduced virus shedding was observed in immunized animals. We also wanted to test the idea of re-directing the immune responses towards conserved domains of HA could induce cross-protection and the effect of this on the breath of protection against IAV-S. To test this hypothesis, we generated two recombinant ORFVs expressing chimeric HAs encoding the stalk region of a contemporary H1N1 swine strain and exotic heads of either H6 or H8 subtypes, OV-cH6/1 and OV-cH8/1, respectively. The immunogenicity and cross-protection of these vaccine candidates were assessed in swine after intramuscular priming with OVcH6/1 and a booster with OV-cH8/1, followed by challenge with the same divergent strains of IAV-S used in the previous study. Levels and breadth of IAV-S specific IgG humoral responses were assessed in sera by using ELISA for 12 divergent IAV-S. The data showed that swine vaccinated with our ORFV recombinant vaccine candidates presented increasing IgG responses after the booster. In addition, the significant higher levels of IgG that reacted against whole-virus antigen from different clades and strains in vaccinated swine suggest cross-reactivity between IgG antibodies present in sera post-vaccination and a diverse range of contemporary H1N1 IAV-S. Shedding of infectious virus and viral RNA were reduced in nasal secretions from vaccinated piglets. Taken together, these results demonstrated that our ORFV-based IAV-S vaccine candidates induce protection in swine and pave the way for the potential use of consensus- and chimeric-HAs for influenza A prophylaxis in swine.