Highly pathogenic avian influenza H5N1 clade 2.3.4.4b hemagglutinin and/or neuraminidase elicit immunity in a recombinant nanoparticle vaccine

The widespread transmission of highly pathogenic avian H5N1 influenza, clade 2.3.4.4b, in wild and livestock mammals with isolated human cases has heightened concerns for zoonotic outbreak, necessitating vaccine readiness. Here, we assess whether recombinant H5 hemagglutinin and N1 neuraminidase proteins can confer protection from disease when antigens are presented as an adjuvanted nanoparticle vaccine. Multimeric recombinant H5 and N1 derived from H5N1 clade 2.3.4.4b were coupled to liposomes that incorporated cobalt-porphyrin-phospholipid (CoPoP; for liposome display), along with the immunostimulatory adjuvants QS-21 and synthetic monophosphoryl lipid A. H5 and N1 rapidly converted from a soluble to a liposome-bound format, while maintaining reactivity with monoclonal antibody probes. Upon immunization, H5 and N1 elicited antigen-specific cellular and functional antibody responses, and bivalent H5 + N1 presentation on liposomes resulted in immune responses against both antigens, reduced viral load in lungs of infected mice, and protected them against lethal challenge with a highly virulent 2.3.4.4b H5N1 strain.