Mechanisms of GII.4 norovirus antigenic variation and evolution

Noroviruses infect an estimated 21 million people annually in the United States, resulting in ~70,000 hospitalizations and ~800 deaths. These viruses are easily transmitted among people in close proximity, including healthcare and educational settings, cruise ships, military environments, and restaurants. Norovirus symptoms include vomiting and diarrhea over a period of 24-72 hours, but life-threatening or chronic infections can develop in infants and very young children, the elderly and immunocompromised individuals. Unfortunately, there are no licensed norovirus therapeutics or vaccines currently available. One factor complicating vaccine and therapeutic design for noroviruses is antigenic variation in GII.4 norovirus, which account for over 70% of all outbreaks. Every 2-4 years the predominant circulating GII.4 strain is replaced by a new emergent strain. In predominant GII.4 strains, genetic changes are most prevalent in continuously evolving areas of the capsid P2 domain and correlate with antigenic changes. This suggests that GII.4 norovirus strain emergence is driven by changes in neutralization epitopes as a result of escaping herd immunity to the previous strain. Therefore, effectively designed therapeutics and vaccines must be broadly active or easily reformulated to account for the antigenic properties of emergent viruses. Our work aims to define the mechanisms that drive genetic changes leading to antigenic changes in GII.4 noroviruses. In Chapter 2, we use structure-guided approaches to map epitope A, the immunodominant GII.4 blockade (potential neutralizaton) epitope. Chapter 3 characterizes antigenic changes between two successive GII.4 strains, GII.4-2009 New Orleans and GII.4-2012 Sydney. In Chapter 4, we investigate the antigenic change that occurs within an individual chronically infected with norovirus over time, map the varying epitopes and compare the degree of change with population-wide changes. We also propose that broadly-blocking GII.4 human monoclonal antibody 71.4 is a potential treatment for chronic norovirus infection. Chapter 5 proposes a VLP-based vaccine platform that utilizes chimeric particles to induce a broadly-blocking immune response against multiple GII.4 strains. These GII.4 norovirus studies have allowed us to identify major determinants of antigenic change in GII.4 noroviruses that will allow for rapid diagnostic identification of new epidemic strains and direct the rational development of norovirus therapeutics and vaccines.Doctor of Philosoph