Influenza vaccines and antivirals that target the conserved hemagglutinin stem
Koday, Merika Treants
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Influenza is a major public health threat, and pandemics, such as the 2009 H1N1 outbreak, are inevitable. Due to low efficacy of seasonal flu vaccines and the increase in drug-resistant strains of influenza viruses, there is a crucial need to develop new antivirals and vaccines to protect from seasonal and pandemic influenza. Recently, several broadly neutralizing antibodies have been characterized that bind to a highly conserved site on the viral hemagglutinin (HA) stem region. These antibodies are protective against a wide range of diverse influenza viruses indicating that the HA stem may be an excellent target for vaccines and antivirals. This thesis describes the development of a novel antiviral that effectively targets the HA stem, examines the ability of a conventional HA-based vaccine to elicit stem-specific antibodies, and explores the potential of stem-based vaccines to induce broadly neutralizing antibodies. Here I show that a small engineered protein computationally designed to bind to the same region of the HA stem as broadly neutralizing antibodies mediated protection against diverse strains of influenza in mice by a distinct mechanism that is independent of a host immune response. Since an antiviral targeting the conserved stem results in broad protection, I next investigated immunogenicity and protective efficacy of an E. coli heat-labile enterotoxin (LT) adjuvanted multigenic (LT-MA) universal influenza DNA vaccine consisting of four HA antigens, nucleoprotein (NP), and the ectodomain of the matrix protein (M2e) in nonhuman primates. Though the LT-MA DNA vaccine induced robust serum and mucosal antibody responses, it failed to induce broadly neutralizing antibodies. These results demonstrate that vaccination with full-length HA immunogen does not elicit stem-specific broadly neutralizing antibodies and further advancements in immunogen design are needed. In order to overcome this hurdle, I investigated a computationally designed DNA vaccine, based on the conserved HA stem, for the ability to induce antibody and T cell responses that provide protection from lethal influenza infection. Although these computationally designed headless HA immunogens were immunogenic and provided protection in vivo, they failed to elicit neutralizing antibodies. My results highlight the need for a vaccine immunogen that limits the immune response to the immunodominant head while directing the immune response to the stem and demonstrate that future vaccines will need to maintain the structural integrity of the fusion region in order to be successful. Together, these results have significant implications for the use of computational modeling to design new antivirals and vaccines against influenza and other viral diseases.
- Microbiology