Thin Film Formulation of an Outer Membrane Vesicle Vaccine

Infectious diseases caused by mucosal pathogens continue to pose a threat to humans across the globe. Most recently, the respiratory infection SARS-CoV-2, more commonly known as COVID-19, demonstrated the dangers these pathogens pose to the human body. Lower respiratory infections are currently the fourth leading cause of death in the world. While vaccines are continually developed to combat these pathogens, major advances are primarily being made with injectable vaccinations. Mucosal vaccines provide distinct advantages over traditional injectable vaccinations, as they promote a heightened immune response at the mucosal membrane, which is the main site of pathogen infection. A subunit mucosal vaccine would be very beneficial, as it poses less risk to the patient while maintaining vaccine efficacy. Outer membrane vesicles (OMVs), shed from gram-negative bacteria, occur naturally at relatively low concentrations. Genetic engineering can be used to enable bacteria to present protein antigens on their outer membrane, which remain on the surface of the vesicle after exocytosis. Ultracentrifugation can then be used to isolate outer membrane vesicles at high concentrations from genetically engineered bacteria, enabling these vesicles to be viable antigen-presenting particles. The stability of OMVs remains a challenge in current vaccine design, as OMVs may begin to degrade at room temperature. Currently, most research largely focuses on increasing injectable vaccine stability instead of exploring other vaccine delivery mechanisms. Therefore, it would be useful to explore other delivery methods as they may promote better OMV stabilization compared to OMVs in solution. Thin films are a promising mucosal vaccine platform, as they can carry a variety of antigens in the form of microparticles or nanoparticles, such as OMVs. Additionally, the salivary environment is extremely effective at dissolving thin films due to a combination of an aqueous environment, temperature, and enzymes. Previous work demonstrated the ability of different thin film formulations to produce stable matrices at room temperature. The optimal formulation to maximize OMV recovery over a period of 8 weeks when stored at room temperature in a thin film was then determined. Additionally, enzymatic dissolution of thin films was also investigated to determine if current thin film formulations could dissolve in the salivary environment.