Optimizing delivery in a multivalent subunit influenza vaccine using mixed polymeric microparticle degradation rates.

The influenza virus continues to impose a significant yearly burden on society due to the variable efficacy of seasonal vaccines. Further strains like H5N1, that are not included in the seasonal influenza vaccine, may spill over from animal reservoirs and more significantly impact human health. A broadly acting subunit vaccine can offer protection across multiple strains but would have low immunogenicity without an adjuvant, which are currently limited and require delivery systems to mitigate side effects. Further, antigen delivery can be enhanced with carrier systems to provide dose sparing, and thermostability. This study explores acetalated dextran microparticles (Ace-DEX MPs) encapsulating cGAMP and computational optimized broadly reactive antigen (COBRA) hemagglutinin (HA) proteins, to form a multivalent influenza vaccine. Previous research has shown that Ace-DEX cGAMP MPs with varying degradation kinetics can modulate the immune response. Here, we investigate the effects of mixing MPs with different degradation rates to optimize the immune response. Mice vaccinated with slower-degrading cGAMP MPs exhibited higher IgG2a titers and IL-2 producing splenocytes, while those vaccinated with a mix of fast and slow-degrading cGAMP MPs had the highest IFN-γ producing splenocytes. The protection afforded in mice was also shown in ferrets with a H1, H3 and H5 trivalent COBRA formulation adjuvanted by slow degrading cGAMP MPs. Furthermore, using Ace-DEX MPs encapsulating two broadly reactive COBRA H1 and H3 immunogens in particles with fast and slow degradation rates, co-delivered with cGAMP MPs, resulted in less single antigen dominance when the more dominant antigen was encapsulated in the slowest degrading MP. This work underscores the utility of Ace-DEX MPs as a vaccine delivery platform and the impact of MP degradation kinetics on vaccine efficacy.