title: Increasing the potency of an alhydrogel-formulated anthrax vaccine by minimizing antigen-adjuvant interactions.
abstract: Aluminum salts are the most widely used vaccine adjuvants, and phosphate is known to modulate antigen-adjuvant interactions. Here we report an unexpected role for phosphate buffer in an anthrax vaccine (SparVax) containing recombinant protective antigen (rPA) and aluminum oxyhydroxide (AlOH) adjuvant (Alhydrogel). Phosphate ions bind to AlOH to produce an aluminum phosphate surface with a reduced rPA adsorption coefficient and binding capacity. However, these effects continued to increase as the free phosphate concentration increased, and the binding of rPA changed from endothermic to exothermic. Crucially, phosphate restored the thermostability of bound rPA so that it resembled the soluble form, even though it remained tightly bound to the surface. Batches of vaccine with either 0.25 mM (subsaturated) or 4 mM (saturated) phosphate were tested in a disease model at batch release, which showed that the latter was significantly more potent. Both formulations retained their potency for 3 years. The strongest aluminum adjuvant effects are thus likely to be via weakly attached or easily released native-state antigen proteins.
authors.affiliation: PharmAthene UK Ltd., Billingham, United Kingdom.
authors.forename: Allan
authors.initials: A
authors.lastname: Watkinson
authors.forename: Andrei
authors.initials: A
authors.lastname: Soliakov
authors.forename: Ashok
authors.initials: A
authors.lastname: Ganesan
authors.forename: Karie
authors.initials: K
authors.lastname: Hirst
authors.forename: Chris
authors.initials: C
authors.lastname: Lebutt
authors.forename: Kelly
authors.initials: K
authors.lastname: Fleetwood
authors.forename: Peter C
authors.initials: PC
authors.lastname: Fusco
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Fuerst
authors.forename: Jeremy H
authors.initials: JH
authors.lastname: Lakey
mesh_terms: D000276:Adjuvants, Immunologic / Q000008:administration & dosage* / Q000378:metabolism; D000536:Aluminum Hydroxide / Q000008:administration & dosage* / Q000378:metabolism; D000818:Animals; D000881:Anthrax / Q000517:prevention & control*; D022122:Anthrax Vaccines / Q000008:administration & dosage* / Q000737:chemistry / Q000276:immunology*; D000942:Antigens, Bacterial / Q000378:metabolism; D002021:Buffers; D002626:Chemistry, Pharmaceutical; D004195:Disease Models, Animal; D004355:Drug Stability; D005260:Female; D051379:Mice; D010710:Phosphates / Q000378:metabolism; D011485:Protein Binding
chemical_list: D000276:Adjuvants, Immunologic; D022122:Anthrax Vaccines; D000942:Antigens, Bacterial; D002021:Buffers; D010710:Phosphates; D000536:Aluminum Hydroxide