Equine influenza antigen-based particle vaccine protects mice against homologous and heterosubtypic viral challenges

Influenza virus is a common source of respiratory illness and poses a major public health burden globally. Significant efforts have been dedicated towards developing and deploying effective vaccines. However, since being licensed in 1945, influenza vaccines have made limited progress and still suffer from several limitations, including suboptimal efficacy against variants. In this work, we report on two influenza A polyanhydride particle- and pentablock copolymer-based vaccine formulations intended for intranasal or subcutaneous administration. These nanovaccines are based on a newly discovered equine influenza A H3N8 hemagglutinin antigen (A/equine/1/KY/91), A/HK/1/68 nucleoprotein antigen, and a small molecule adjuvant. When these nanovaccines were administered to naïve mice, both formulations induced robust humoral and cellular immune responses that were protective against lethal challenges with influenza A/HK/1/68 (H3N2) or A/PR/8/34 (H1N1). This protection was characterized by reduced viral load, reduced airway disruption, and preservation of weight post-infection. Further studies with immunization and challenge of CD8⁺T cell depleted mice and passive serum transfer into recipient mice reinforced that the observed protection was due to a combination of both vaccine-induced antibody responses and CD8⁺T cell immunity. These findings demonstrate that intranasal and subcutaneous polymeric particle-based vaccines based on potentially universal influenza antigens are effective and promising platforms for supra-seasonal influenza vaccines. STATEMENT OF SIGNIFICANCE: We designed two influenza virus vaccine formulations based on polyanhydride microparticles and pentablock copolymer micelles for intranasal and subcutaneous administration. The intranasal vaccine is based on polyanhydride microparticles while the subcutaneous vaccine contains both polyanhydride microparticles and pentablock copolymer micelles. Both vaccines contain a newly discovered equine influenza H3N8 hemagglutinin antigen, a nucleoprotein antigen, and an adjuvant. Both vaccines induced robust antibodies and cellular immune responses and protected mice upon lethal challenge. The use of CD8⁺T cell depleted mice and passive transfer of sera from vaccinated mice to recipient mice reinforced that the protection was driven by vaccine-induced antibody and CD8⁺T cell responses. These findings demonstrate that polymeric particle- and micelle-based vaccines are promising supra-seasonal influenza vaccines.