Mechanisms of Antigen Adsorption Onto an Aluminum-Hydroxide Adjuvant Evaluated by High-Throughput Screening

Abstract

The adsorption mechanism of antigen on aluminum adjuvant can affect antigen elution at the injection site and hence the immune response. Our aim was to evaluate adsorption onto aluminum hydroxide (AH) by ligand exchange and electrostatic interactions of model proteins and antigens, bovine serum albumin (BSA), β-casein, ovalbumin (OVA), hepatitis B surface antigen, and tetanus toxin (TT). A high-throughput screening platform was developed to measure adsorption isotherms in the presence of electrolytes and ligand exchange by a fluorescence-spectroscopy method that detects the catalysis of 6,8-difluoro-4-methylumbelliferyl phosphate by free hydroxyl groups on AH. BSA adsorption depended on predominant electrostatic interactions. Ligand exchange contributes to the adsorption of β-casein, OVA, hepatitis B surface antigen, and TT onto AH. Based on relative surface phosphophilicity and adsorption isotherms in the presence of phosphate and fluoride, the capacities of the proteins to interact with AH by ligand exchange followed the trend: OVA < β-casein < BSA < TT. This could be explained by both the content of ligands available in the protein structure for ligand exchange and the antigen's molecular weight. The high-throughput screening platform can be used to better understand the contributions of ligand exchange and electrostatic attractions governing the interactions between an antigen adsorbed onto aluminum-containing adjuvant.

Optimizing the utilization of aluminum adjuvants in vaccines: you might just get what you want

“…The decrease of hydrolysis (termed relative surface phosphophilicity) was inversely correlated with the affinity of the antigens. 47 The adsorptive strength is an important parameter because too tight adsorption can interfere with the antibody response, as illustrated by the model antigen alpha-casein, which has eight phosphate groups available for ligand exchange, resulting in strong adsorption to AH. 53 The strongly adsorbed casein did not induce T-cell activation possibly because adsorption interfered with antigen processing.…”

Inactivated alpha toxin from Clostridium novyi type B in nano-emulsion protect partially protects Swiss mice from lethal alpha toxin challenge

“…Critical reports regarding the use of aluminum hydroxide adjuvant for clostridial vaccines suggested that both size and conformational changes of toxoid affect surface-protein interactions with aluminum ligands during administration, thereby affecting the immune response 14 . New controlled release systems have been proposed as antigen delivery vehicles because of their utility as immunological adjuvants, with absence of toxicity, biodegradability, and slow release of encapsulated antigens 14 . Here, we observed that the nano-iCnB showed a high volume with 66.5% of the sample, suggesting improved encapsulation and controlled release of antigen (Fig.…”

Unraveling the enigma: elucidating the relationship between the physicochemical properties of aluminium-based adjuvants and their immunological mechanisms of action

“…The AH adjuvants used in clinical vaccines, for instance, are touted as having high adsorptive capacities for myriad proteins under isotonic conditions. Notable examples include the adsorptive capacity of Alhydrogel ® for bovine serum albumin (BSA), β-casein and hepatitis B surface antigen (HBsAg) in 0.15 M NaCl, all of which are substantial at 1.25, 3.43 and 1.43 mg/mg Al respectively [ 21 ]. Despite these considerable values, the quantity of adjuvant used within prophylactic vaccines often greatly exceeds that of the antigen and thus ensures that complete adsorption is consistently achieved.…”