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Abstract
Multiple subtypes of influenza viruses have circulated throughout human history and people are infected with more than one influenza virus during their lifetimes. H2N2 influenza viruses infected humans in the past, but have not circulated between people since 1968. One objective of this dissertation was to determine if people today had protective antibodies against historical or currently circulating H2 influenza viruses. Without protective immunity, the human population would be highly susceptible to another H2 influenza virus pandemic. A second objective was to develop a broadly-reacting HA-based vaccine to elicit protective immune responses against currently circulating H2 influenza viruses or viruses that evolve in the future.Using the computationally optimized broadly reactive antigen (COBRA) methodology, four H2 rHA vaccines were designed, produced, and purified. These H2 COBRA rHA vaccines were tested in pre-clinical mouse and ferret models. The overarching hypothesis of this project was that human participants born after 1964 would have low levels of immunity to H2 influenza viruses and that H2 COBRA rHA vaccines
would elicit neutralizing antibodies against multiple H2 influenza viruses in both naïve and pre-immune animal models.
Serum B cells and memory B cells specific to H2 influenza viruses were not present in individuals born after 1964. Also, there was no expansion of cross-reactive B cells to H2 influenza viruses after vaccination. DBA/2J mice were vaccinated with either COBRA or WT H2 rHAs. Viral challenges of vaccinated mice showed that COBRA H2 rHA vaccinated mice had survival and weight loss comparable to the homologous WT H2 rHA vaccinated mice for each of the viral challenges.
Fitch ferrets were infected with H1N1, H2N2, or H3N2 influenza viruses in different combinations. Ferrets infected with H2N2 influenza viruses alone, H1N1 influenza viruses alone, H1N1 influenza viruses then H3N2 influenza viruses and H3N2 influenza viruses then H1N1 influenza viruses had high H2 influenza virus specific antibody titers to the viral panel after vaccination with both the COBRA and WT H2 rHA vaccines. The viral titers in the ferret nasal washes were also significantly lower in the Z1 COBRA rHA vaccinated ferrets across all of the pre-immune groups.