Not so long ago adjuvants were characterised by a world-leading immunologist as the "immunologist‘s dirty little secret" (quote: Charles A. Janeway, 1989). In the last decades, however, the secrets have, at least to some extent been unveiled. Insight into how the immune response can be biased towards a cell-mediated (Th1) or antibody-mediated (Th2) profile by selective choice of adjuvants and later the discovery of the Toll-like receptors as mediators of adjuvant-induced immunostimulation are important milestones on this path.
Our range of adjuvants is most easily categorised by chemically grouping the components used in the final product.
Aluminium adjuvants have been used in practical vaccination for more than half a century to induce early, high-titre, long-lasting protective immunity. Billions of doses of aluminium-adjuvanted vaccines have been administered over the years and they are, at present, the most widely used adjuvants in both veterinary and human vaccines. In general, aluminium adjuvants are regarded as safe when used in accordance with current vaccination schedules.
The most common compounds used in mineral formulations are aluminium hydroxide and aluminium phosphate. These adjuvants are generally prepared by exposing aqueous solutions of aluminium ions, typically as sulphates and chlorides, to alkaline conditions in a well-defined and controlled chemical environment. Various soluble aluminium salts can be used for the production of aluminium hydroxide, but the experimental conditions, temperature, concentration and even the rate of the addition of the reagents, strongly influence the results.
Anions present at the time of preparation may coprecipitate and change the characteristics away from those of a “pure” aluminium hydroxide. Aluminium phosphate gel can be seen as an example of such a preparation, where the soluble aluminium salts are exposed to alkaline conditions in the presence of phosphate ions.
Purified quillaja saponin is a widely used saponin adjuvant. The product was originally developed by Professor Dr. Pharm. Kristian Dalsgaard in 1974 and adapted for commercial scale production in close cooperation with Croda. On its own or in combination with other adjuvants, it exhibits strong adjuvanticity. When combined under a specific circumstances, saponin may form stable immune stimulating complexes (ISCOMs) with cholesterol, phosphatidylcholine and amphipathic antigen. These complexes are spherical open cage-like structures of typically 40 nm in diameter. The complex displays immune stimulating properties and is used in order to induce a stronger immune response and longer protection.
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