(738b) Polyanhydride Nanoparticle Adjuvants: Implications for a Single Dose Anthrax Vaccine

While vaccination has proven to be the most preventable method for eliminating infectious diseases over the past 200 years, infectious disease still remains a leading cause of death worldwide. Additionally, the rise in bioterrorism with biowarfare agents such as anthrax has demonstrated an urgent need for more effective vaccination strategies. In particular, the current anthrax vaccine, which is only available to military personnel, is administered in five doses and needs to be taken every year. Many problems associated with vaccine efficacy (i.e., the need for multiple administrations, poor immunogenicity and stability of vaccine antigens, undesirable side effects, and rapidly evolving/mutating pathogens) could be addressed with the use of polymeric adjuvants capable of controlling antigen delivery and enhancing immune activation. Polyanhydrides are a class of biomaterials with excellent biocompatibility and have shown much promise as vaccine delivery vehicles and adjuvants. Specifically, copolymers based upon poly(sebacic anhydride) (SA), 1,6-bis (p-carboxyphenoxy) hexane (CPH), and 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG) have been of particular interest as novel adjuvants. They have tunable antigen release kinetics, which would provide an antigen depot in vivo, allowing for long-term antigen exposure. Furthermore they have demonstrated antigen stabilization capabilities as well as immunomodulatory adjuvant properties to enhance antigen immunogenicity. In this study, the ability of CPTEG:CPH- and CPH:SA-based copolymer nanoparticles was assessed to control the release kinetics and preserve the fragile structure of the recombinant protective antigen (rPA) of Bacillus anthracis upon delivery in vitro. The rPA-loaded nanoparticles were then further investigated for their ability to induce humoral and cell-mediated immune responses against the rPA antigen in vivo using a single dose vaccine regimen. The results indicated a chemistry dependent trend of the polyanhydride nanoparticles on rPA release kinetics and on preservation of rPA antigenicity and structure (primary, secondary, and tertiary). The CPTEG-rich chemistries exhibited superior antigen preservation and rapid release, while the CPH-rich chemistries showed moderate antigen preservation and slow release, and SA-rich chemistries resulted in poor antigen preservation and moderate release. Interestingly, the results from the in vivo single dose immunizations of the nanoparticles also demonstrated chemistry-dependent trends. Antibody titers and avidity levels of mice immunized with rPA-loaded 50:50 CPH:SA nanoparticles were greater than or comparable to the alum-adjuvanted rPA positive control. However, B cells from draining lymph nodes of mice immunized with rPA-loaded 20:80 CPH:SA nanoparticles demonstrated enhanced antigen-specific proliferation in vitro. Finally, both CPH:SA chemistries induced significant expansion of CD19+ B cells in vivo comparable to that observed in mice immunized with alum-adjuvanted rPA. It is hypothesized based on the rPA stabilization results that future in vivo experiments with rPA-loaded CPTEG:CPH nanoparticles may be able to bridge this gap between achieving high antibody titers/avidity and antigen-specific proliferation because they encompass a more antigen-friendly environment and can be tailored to fit the desired release kinetics. The data demonstrate that polyanhydride nanoparticle formulations can be tailored to induce specific immune responses through their controlled release kinetics, antigen preservation and adjuvant capabilities, which are key strategies in developing a single dose anthrax vaccine.