The objective of the proposed work is to develop a vaccine that provides broad protection against group 1 influenza A viruses – a group that includes the 1918, 1957-1958, and 2009 pandemic viruses, as well as avian influenza “viruses of concern” – by eliciting a robust and durable immune response targeting the highly conserved membrane-proximal stalk domain of hemagglutinin (HA). The project will test the hypothesis that the combination of shielding the variable head domain of HA, refocusing the immune response to the highly conserved stalk domain by controlling the orientation of HA, and multivalent presentation, will provide broad, durable, and robust protection against group 1 influenza A viruses. Influenza represents a serious global health problem, with seasonal influenza virus infections imposing significant health and economic burdens, and pandemics caused by novel influenza viruses representing an even more serious threat. Licensed vaccines induce an immune response that primarily targets the head domain of HA, which is highly variable in sequence. As a result, the immune response to influenza vaccination is narrow and strain-specific and would provide little protection against potential pandemic influenza viruses. While “broadly neutralizing” antibodies targeting the highly conserved stalk domain of HA are prophylactically and therapeutically protective against influenza virus challenges in vivo, such antibodies are not elicited effectively in natural infections or by licensed influenza vaccines. The immunosubdominance of the HA stalk domain may result from its membrane-proximal location, with interactions of B-cell receptors with conserved stalk epitopes being blocked by steric hindrance on virions which are densely packed with glycoproteins. Indeed, we have recently shown that tuning the orientation of HA to enhance the accessibility of stalk epitopes results in an enhanced protective stalk-directed immune response. Furthermore, we have demonstrated an approach (tethered antigenic suppression) for suppressing the immune response to the head domain of HA and refocusing the immune response on desired epitopes (such as the stalk). We have also designed vaccines that elicit a robust protective antibody response against a variety of antigens, including HA, by displaying them multivalently from virus-like particles. The first aim of the proposed work is to engineer and test novel HA antigen designs to provide an enhanced stalk- directed immune response. We will shield the head domain of HA to suppress its immunogenicity and will tune the orientation of the head-shielded HA to increase the accessibility of the stalk domain and enhance its immunogenicity. We will also investigate the ability to further increase the breadth of protection by using engineered HA antigens that incorporate stalk domains from different viral subtypes. The second aim is to characterize the breadth and the longevity of the anti-stalk response induced by vaccination in mice. The third aim is to characterize immunogenicity and vaccine efficacy in naïve and pre-immunized, male and female ferrets.

Project narrative The objective of the proposed work is to develop a broadly protective influenza vaccine by engineering the protein hemagglutinin and its multivalent presentation from nanoscale scaffolds. The research is relevant to public health because it could lead to the development of new and effective vaccines that provide robust, durable, and broad protection against influenza viruses.