Mechanism of Adsorption of Three RecombinantStreptococcus pneumoniae(Sp) Vaccine Antigens by an Aluminum Adjuvant

Abstract

The adsorption of three Streptococcus pneumoniae (Sp) vaccine antigens by aluminumcontaining adjuvants was studied. The antigens showed high binding affinity isotherms with aluminum hydroxide adjuvant described by the Langmuir equation but virtually no binding to aluminum phosphate adjuvant. The effects of ionic strength and ethylene glycol were evaluated to determine whether electrostatic or hydrophobic interactions were responsible for the observed binding to aluminum hydroxide, but no significant change in the adsorptive capacity was observed at either high ionic strength nor high concentrations of ethylene glycol for any of the antigens. This indicates that neither electrostatic nor hydrophobic interactions appear to be responsible for the observed binding, which means that ligand exchange may be the primary mechanism for this interaction. Further studies to evaluate the ability to elute a Sp antigen from aluminum hydroxide using fibrinogen (adsorptive coefficient 2.2 mL/µg) as a competitive protein resulted in evidence that Sp antigen follows the trend that proteins with higher adsorptive coefficients are able to displace those with lower adsorptive coefficients. It was also noted that the Sp antigens and α-lactalbumin (adsorptive coefficient 1.8 mL/µg) have similar adsorptive coefficients indicative of high affinity binding isotherms but do not contain phosphate, which has previously been used to explain ligand exchange for such proteins as α-casein and hepatitis B surface antigen (HBsAg). Further investigations using α-lactalbumin as a model protein may elucidate the binding interaction between the antigens in this study and aluminum adjuvants.

Association Between Immunogenicity and Adsorption of a RecombinantStreptococcus pneumoniaeVaccine Antigen by an Aluminum Adjuvant

“…The isoelectric points of the Sp antigens under investigation anticipate favorable electrostatic binding conditions to AH at pH 7.2 and electrostatic repulsion to AP, and this prediction has been shown to be accurate. 26 Previous studies have adjusted the amount of antigen adsorbed to AH adjuvant by pretreatment of the adjuvant with varying amounts of phosphate. 1,17 While this effectively modifies the surface of the AH and thereby changes the adsorptive capacity via a presumed electrostatic interaction, the degree to which the surface modification occurs and the time required cannot easily be controlled, nor are multiple formulations produced in the same manner completely reproducible.…”

Quality by Design for Biopharmaceutical Drug Product Development

“…There are contradicting examples in the literature with different viewpoint regarding the importance of antigen binding to aluminum adjuvants and its impact on the immune response (Chang et al 2001;Hemand and HogenEsch 2007;Romero Mendez et al 2007;Clapp et al 2011). Adsorption between antigens and aluminum adjuvants has been attributed to electrostatic, hydrophobic, and ligand exchange mechanisms (of which ligand exchange is considered to be the strongest absorption) (Iyer et al 2004;Vogeland and Hem 2003;Levesque and Alwis 2005). While most interactions between the adjuvant and antigen are electrostatic in nature, ligand exchange with phosphodiesters can occur with an aluminum hydroxide adjuvant.…”

Analytical Insights into Protein–Alum Interactions and Their Impact on Conformational Epitope

“…At a neutral pH, it has a negative charge due to its PZC being between 4.5 and 5.5. These differences between alum and alum-P affect the adsorption properties and the behavior of antigens on its surface [ 6 , 7 ].…”