Adjuvants are used in vaccine production to stimulate the immune system to raise an early, a long-lasting and an efficient immune response to the vaccine and thereby increase vaccine efficacy and provide a high degree of protection against the disease you wish to vaccinate against.
By using adjuvants you may reach the same level of immune protection using fewer injections than when vaccinating with the non-adjuvanted antigen alone.
This is essential in many relations. In developing countries with long geographical distances between the vaccinating physician and the population it saves valuable resources if protection can be achieved using two injections instead of three. In case you are vaccinating cattle that you have to bring in from the pampas, or other animals being kept in the open over large distances, just the resources needed for bringing the animals in for a second vaccination may be cost prohibitive.
In case the production of the vaccine antigens themselves is a cost essential factor, the use of adjuvants may offer the opportunity of reducing the antigen content in the vaccine without decreasing the vaccine efficacy - if compared to non-adjuvanted vaccine preparations.
When vaccinating e.g. breeding animals eliciting a high immune response in the mother animal may help the survival of the off-springs, as they receive maternal antibodies from weaning, at a time when their own immune response is not yet fully developed.
Classification of adjuvants
Not so long ago adjuvants were characterized 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 Th-1 or Th-2 profile by a 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.
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, oil-emulsions and purified quillaja 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:
- 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.
- Saponins. Purified quillaja saponin (e.g. 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, saponin forms ISCOMs. These stable, particulate complexes present cells with multimeric copies of antigen in optimal orientations.
- 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.