Influenza vaccine nanoparticle design and evaluation assisted by cryo-electron microscopy

Authors

• DM McCraw
• ML Myers
• MT Conlon
• NM Gulati
• JR Gallagher
• U Torian
• AK Harris

Abstract

Influenza virus is a major threat to public health due to the ability of the virus to rapidly mutate antigenic sites recognized by the immune system. There are 16 different avian hemagglutinin (HA) subtypes for influenza virus A (H1-H16). Commercial vaccines target currently-circulating subtypes H1 and H3. Subtypes H5, H7, and H9 circulate in animal populations, but human infection from animal contact has also occurred. Animal viruses able to infect humans pose a zoonotic and pandemic threat, whereby introducing novel influenza subtypes into the human population. Therefore, one broad question is how to design novel influenza vaccine platforms that that can (1) improve the efficacy of seasonal influenza vaccines, (2) improve pandemic preparedness from zoonotic influenza viruses, and (3) improve the breath of protection for universal influenza vaccine development. Here, we show proof-of-concept for a novel vaccine nanoplatform strategy aimed to integrate conserved epitopes for H1-H16 HA influenza subtypes into recombinant nanoparticles. We used the methods of cryo-electron microscopy with bioinformatics, protein design and expression, biochemistry and immunology for the development of a novel vaccine nanoplatform. A library of chimeric fusion proteins was designed to have conserved influenza epitopes from H1-H16 HA fused to a protein scaffolding that forms nanoparticles. We found that the library expressed in sufficient quantities for further structural, immunogenic, and challenge studies. Cryo-EM indicated that purified proteins formed symmetrical nanoparticles and the fused epitopes were on the particle surface. We found that nanoparticles were immunogenic in animals and ELISA and western blotting assays confirmed that the nanoparticles elicited antibodies that displayed heterosubtypic binding to different HA subtypes. Interestingly, the nanoparticles were immunogenic even after heating to 90 C, suggesting that they are thermogenically stable, which could allow for long-term vaccine storage and distribution without the need for a cold-chain. Furthermore, we found that mice immunized with H1 nanoparticles were protected from lethal challenge with the 2009 H1N1 pandemic virus. In summary, our nanoplatform is on a continuum of research to develop immunogens with increase effectiveness towards seasonal and pandemic influenza viruses—and aid in the development of a universal influenza vaccine.

Scientific Focus Area: Virology

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