Combinatorial immune refocusing within the influenza hemagglutinin head elicits cross-neutralizing antibody responses

Abstract

The head domain of influenza hemagglutinin (HA) elicits potently neutralizing yet mostly strain-specific antibodies during infection and vaccination. Here we evaluated a series of immunogens that combined several immunofocusing techniques for their ability to enhance the functional breadth of vaccine-elicited immune responses. We designed a series of 'trihead' nanoparticle immunogens that display native-like closed trimeric heads from the HAs of several H1N1 influenza viruses, including hyperglycosylated variants and hypervariable variants that incorporate natural and designed sequence diversity at key positions in the periphery of the receptor binding site (RBS). Nanoparticle immunogens displaying triheads or hyperglycosylated triheads elicited higher HAI and neutralizing activity against vaccine-matched and -mismatched H1 viruses than corresponding immunogens lacking either trimer-stabilizing mutations or hyperglycosylation, indicating that both of these engineering strategies contributed to improved immunogenicity. By contrast, mosaic nanoparticle display and antigen hypervariation did not significantly alter the magnitude or breadth of vaccine-elicited antibodies. Serum competition assays and electron microscopy polyclonal epitope mapping revealed that the trihead immunogens, especially when hyperglycosylated, elicited a high proportion of antibodies targeting the RBS, as well as cross-reactive antibodies targeting a conserved epitope on the side of the head. Our results yield important insights into antibody responses against the HA head and the ability of several structure-based immunofocusing techniques to influence vaccine-elicited antibody responses.

A modular platform to display multiple hemagglutinin subtypes on a single immunogen

“…Further studies with different combinations of HAs could aid in understanding how length and composition influences epitope focusing. Combining the BOAS platform with other immune-focusing approaches 32 such as hyperglycosylation 14,31,61,62 or resurfacing 30,63 could enhance cross-reactive responses Additionally, modifying linker spacing and rigidity can also be used as a mechanism to enhance BCR cross-linking and thus enhance cross-reactive B cell activation and elicitation 64 .…”

“…Indeed, RBS-directed antibodies often are potently neutralizing, as they directly inhibit HA engagement with host cell sialic acid, while interface-and stem-directed antibodies generally protect via Fc-dependent mechanisms (e.g., ADCC, ADCP). Several rational immunogen design approaches 21 such as epitope removal 22,23 , domain chimeras 24 , computational sequence optimization (COBRAs) [25][26][27][28][29] , epitope resurfacing 30 and hyperglycosylation 14,31,32 attempt to focus to these epitopes.…”