Designed Nanoparticles Elicit Cross-Reactive Antibody Responses To Conserved Influenza Virus Hemagglutinin Stem Epitopes
Despite the availability of seasonal vaccines and antiviral medications, influenza virus continues to be a major health concern and pandemic threat due to the continually changing antigenic regions of the major surface glycoprotein, hemagglutinin (HA). One emerging strategy for the development of more efficacious seasonal and universal influenza vaccines is structure-guided design of nanoparticles that display conserved regions of HA, such as the stem. Using the H1 HA subtype to establish proof of concept, we found that an alpha-helical fragment (helix-A) from the conserved stem region can be displayed on nanoparticles. The stem region of HA on these nanoparticles is immunogenic and the nanoparticles are biochemically robust in that heat exposure did not destroy the particles and immunogenicity was retained. Furthermore, H1-nanoparticles protected mice from lethal challenge with H1N1 influenza virus. Importantly, antibodies elicited by these nanoparticles demonstrated homosubtypic and heterosubtypic cross-reactivity. The helix-A stem nanoparticle design represents a novel approach to display several hundred copies of non-trimeric conserved HA stem epitopes on vaccine nanoparticles. This design concept provides a new approach to universal influenza vaccine development strategies and opens up opportunities for the development of nanoparticles with broad coverage over many antigenically diverse influenza HA subtypes.