(550c) Stabilization of Pneumoccoccal Surface Protein A in Polyanhydride Nanoparticles: Consequences for the Design of a Pneumonia Vaccine

Pneumoccoccal surface protein A (PspA) is a choline-binding protein found on the surface of all pneumococcal strains and has been shown to be critical to the virulence of infections with Streptococcus pneumoniae.  PspA plays two different roles in invasive infection and nasopharyngeal carriage.  In invasive, systemic infections with S. pneumoniae, PspA prevents the deposition of complement, an immune protein that assists antibodies and phagocytic cells.  PspA also plays a role in carriage by binding the bactericidal glycoprotein, apolactoferrin.  Vaccination with PspA has been shown to be protective against a lethal challenge with S. pneumoniae making it a promising candidate for use in vaccines. Nanoparticles and microparticles made from polyanhydrides have been shown to successfully preserve antigenicity of proteins throughout the manufacture, storage, and release steps. These polymers have excellent biocompatibility and have been shown to have non-toxic, non-mutagenic degradation products. Another important benefit that leads to increased stabilization of protein is the use of a non-aqueous particle fabrication process, which not only prevents protein degradation during exposure to water, but also the loss of encapsulation efficiency observed in aqueous fabrication processes. Amphiphilic polyanhydrides are ideal candidates for vaccine delivery because of their ability to: stabilize and protect fragile antigens; provide a sustained release of antigen; and modulate the immune response.  The encapsulation and release of pneumococcal surface protein A from four polyanhydride chemistries based on sebacic acid (SA), 1,6-bis-(p-carboxyphenoxy)hexane (CPH) and 1,8-bis-(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG) demonstrated sustained drug delivery over a month.  The protein released from amphiphilic chemistries was shown to retain its structure through a combination of SDS-PAGE and circular dicroism.  The antigenicity of protein released from amphiphilic polyanhydride nanoparticles was preserved as confirmed with ELISA.  We also assessed the preservation of the biological functionality of PspA through a functional assay which takes advantage of the ability of secretory PspA to bind to apolactoferrin and prevent its bactericidal effects.  In these studies, we used a PspA deficient strain of streptococcus pneumoniae and demonstrated that PspA released from amphiphilic polyanhydride nanoparticles retained the ability to bind to apolactoferrin and prevent the killing of PspA deficient S. pneumoniae. Together, these studies provide a framework for the rational design of a pneumonia vaccine based on amphiphilic polyanhydride nanoparticles.