Physical Characterization and Formulation Development of a Recombinant Pneumolysoid Protein-Based Pneumococcal Vaccine

Streptococcus pneumoniae is a major cause of death in children worldwide. There are more than 90 known pneumococcus serotypes that vary by geographical location. Pneumolysin is a protein toxin produced by virtually all invasive strains of S. pneumoniae and is considered an important virulence factor. Pneumolysin is immunogenic and has the potential to be a new vaccine antigen offering broad serotype-independent coverage. To develop a stable vaccine formulation, the conformational stability of a recombinant pneumolysin mutant (pneumolysoid L460D) was characterized by various techniques. Three data visualization diagrams were constructed to summarize the biophysical data of the L460D pneumolysoid; the protein is most stable in solution at pH 6-7, and loses conformational integrity above 48°C. Excipient screening assays were performed and sugars such as trehalose and sucrose stabilized the pneumolysin mutant with respect to improving thermal transition temperatures and minimizing aggregation. In addition, the protein antigen showed efficient binding to aluminum hydroxide adjuvant. The conformational stability of the L460D pneumolysoid on the surface of alhydrogel adjuvant was little affected by adsorption, either with or without excipients. These studies provide important preformulation characterization information useful for the development of a stable pneumolysin mutant-based vaccine.