Avian influenza A H5N1 is rapidly gaining the potential to be the next influenza pandemic threat. Human cases of H5N1 have proven to be approximately 60% fatal with a growing number of strains becoming resistant to antiviral treatments. Therefore, there is a strong need for new research to develop a pandemic H5N1 avian influenza vaccine. In this work, a synthetic polyanhydride nanoparticle-based vaccine (or nanovaccine) platform for respiratory pathogens such as H5N1 was designed. In particular, the work focused on the design of a subunit vaccine based on antigens specific to H5N1 avian influenza.

Intranasal administration of vaccines can increase the availability of antigens due to the large, permeable surface area of the lung and can avoid the harsh environments of the gastrointestinal tract. Despite these advantages, antigen delivered alone is often not immunogenic and requires the use of an adjuvant. Polyanhydride nanoparticles have been shown to be a promising platform for intranasal immunization with many beneficial properties including sustained release, cell internalization, and immunomodulation, which may be suitable for vaccines against respiratory pathogens such as H5N1 avian influenza.

The deposition and persistence of intranasally delivered nanovaccines at early time points was investigated with an eye towards examining the role of the initial fate of these particles on the induction of long-lasting memory responses and protective immunity. Polyanhydride nanoparticles were found to prolong the presence of antigen up to 63 days post-immunization leading to an enhancement of antibody titer, avidity, and epitope specificity. Furthermore, the long-lasting memory responses of particle-based vaccines were examined by utilizing an adoptive transfer model of antigen-specific CD8⁺ T cells and a model antigen (ovalbumin). Polyanhydride nanovaccines were shown to enhance the development of memory T cells capable of responding to challenge.

Next, the stability and release kinetics of a nanoparticle-encapsulated H5 hemagglutinin trimer (H5₃) were investigated to rationally determine the optimal polyanhydride chemistries suitable for protein stabilization. Results suggested that while several polyanhydride chemistries preserved the antigenicity of H5₃ upon release, formulations that provided a mildly acidic microenvironment enhanced structural stability. The insights gained from these studies were utilized to identify a lead candidate nanovaccine based on H5₃. The lead candidate nanovaccine was tested using in vivo experiments in a rodent model to define the immune response and it was observed that the nanovaccine formulation induced virus neutralizing titers as well as enhanced CD4⁺ T cell responses. Finally, the efficacy of the nanovaccine was evaluated with live viral challenge and demonstrated full protection. Together, the studies described herein indicate that polyanhydride nanovaccines represent a promising platform for a next generation vaccine against H5N1 avian influenza.