Relationship between tightness of binding and immunogenicity in an aluminum-containing adjuvant-adsorbed hepatitis B vaccine

Phospholipid-containing antigens, such as Hepatitis B Surface Antigen (HBsAg), adsorb to aluminum-containing adjuvants by ligand exchange of a phosphate group for a hydroxyl group on the adjuvant surface. In this study, a tightness of binding (TOB) assay was developed to characterize the strength of binding between HBsAg and aluminum hydroxyphosphate sulfate adjuvant containing two levels of phosphate. Antigen desorption was induced using either fluoride or phosphate as a competing ion. HBsAg, formulated as a monovalent or combination vaccine, showed decreased tightness of binding when the amount of phosphate in the adjuvant composition increased, indicating that there was less ligand exchange between HBsAg and the adjuvant. Furthermore, the physicochemical property of TOB was related to enhanced immunogenicity in a murine model. These data show that tightness of binding can be a useful characterization tool, and potential predictor of immunogenicity, during development of vaccines that adsorb to aluminum adjuvants via ligand exchange.