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Adjuvant Classification

From a chemical point of view, adjuvants are a highly heterogeneous group of compounds that share only one functional characteristic: that of being able to enhance immune responses. Although adjuvants can be classified according to the type of immunity they best stimulate, this becomes problematic because most adjuvants activate both humoral and cell-mediated immunity. Only the extent of stimulation varies with different adjuvants. Besides, the antigen with which the adjuvant is mixed may also influence the final outcome of the immunization. Finally adjuvants can be classified according to the Toll-like receptors they may interact with.

In the literature you also find the words adjuvant formulation and vehicles and delivery systems along with the word “adjuvant”.

Adjuvant: An adjuvant is a substance which is added to a vaccine with the aim of increasing the efficiency of that vaccine. The word adjuvant has its origin from the Latin ”ad juvare” which means “to help”. The most commonly used adjuvants are: aluminium hydroxide, aluminium phosphate, Freund’s adjuvants and Quil-A saponin.

Adjuvant formulation: A composite preparation of several components acting together, among which at least one is adjuvant active.

Vehicle: A “vehicle” can be described as a form in which the adjuvant/antigen mixture is administered.

Traditional vehicles and delivery systems include: oil-in-water emulsions, water-in-oil emulsions, composite emulsions, virosomes and liposomes.

Brenntag’s range of adjuvants is most easily categorized by chemically grouping the components used in the final product.

The three categories comprising Brenntag’s adjuvants are:

1. Mineral-based adjuvants.

The most common compounds used in mineral formulations are aluminium hydroxide (e.g. Alhydrogel®), aluminium phosphate (e.g. Adju-Phos®) and Calcium Phosphate.

2. Saponins.

Purified Quil-A® is a widely used saponin adjuvant. On its own or in combination with other adjuvants, it exhibits strong adjuvanticity. When combined with cholesterol, phosphatidylcholine and amphipathic antigen, Quil-A® forms ISCOMs. These stable, particulate complexes present cells with multimeric copies of antigen in optimal orientations.

3. Oil-based adjuvants

(includes water-in-oil and oil-in-water emulsions). Some examples are FCA and FIA. The most prevalent oils used in adjuvants are pharmaceutical grades of light mineral oils (f.inst. paraffin) with emulsifiers.