UC Riverside

Emerging and reemerging viruses remain a significant threat to human health. Multiple viral outbreaks have occurred since the start of the twenty-first century. Particularly concerning is the emergence of novel pandemic viruses such as the 2009 H1N1 influenza virus and SARS-CoV-2 coronavirus. Adaptive immune responses to these viruses provide a major mode of protection against virus infection and disease. Antibodies against the hemagglutinin protein of influenza viruses and the Spike protein of SARS-CoV-2 play an essential role in providing protection, since they can block virus entry into host cells and neutralize virus infection. However, these responses are often suboptimal. This dissertation examines how different modifications to viral proteins effects anti-viral immune responses. We tested the effect of nitration of influenza virus proteins on virus infectivity and immunogenicity. In vitro nitration of influenza virus proteins was found to reduce infectivity of multiple strains of influenza viruses. Additionally, chemical in vitro nitration of influenza HA protein led to reduced antibody responses against unmodified HA protein. However, nitration of influenza HA protein in vivo was not observed. While overall nitration of the influenza HA protein reduced antibody responses to the HA protein, it was hypothesized that modifications of specific amino acids of the HA protein could increase antibody responses to HA. Mutants of HA incorporating the unnatural amino acid p-nitrophenylalanine were generated and used for vaccination. However, increased antibody responses to the HA protein were not observed in unnatural amino acid mutants. Finally, we examined the ability of pre-existing immunity to influenza viruses to boost antibody responses to a novel vaccine antigen: the SARS-CoV-2 Spike protein. We found that a fusion protein vaccine made of the receptor-binding domain of Spike and the influenza NP protein generated accelerated antibody responses against Spike in mice with pre-existing immunity to influenza virus. The knowledge gained in these studies will help guide the optimization of vaccine strategies for better immune responses against novel emerging viral pathogens.