ADJUVANTS AND THEIR MODES OF ACTION

The trend towards the use of peptides and subunit proteins in modern vaccine design has necessitated the use of immunological adjuvants to achieve effective immunity. Aluminium hydroxide, a component of the diphtheria, tetanus and hepatitis B vaccines, was first described as an adjuvant over 60 years ago and is the only adjuvant currently approved for use in humans. It is also a common component of many veterinary vaccines. While this adjuvant is effective at enhancing antibody titres to antigens, the effectiveness of aluminium hydroxide is limited due to its inability to promote cell mediated immunity. Freund's Complete Adjuvant (FCA) has been used experimentally and does stimulate cellular immunity, but is unsuitable for human and veterinary use as it promotes, amongst other toxic side effects, local inflammation and granuloma formation at the site of injection. Thus, in recent years there has been a great deal of interest in developing novel, cheap, effective and safe adjuvants which stimulate cellular, as well as humoral immunity to be used with medical and veterinary vaccines. In addition, the recent unravelling of numerous immunological pathways has facilitated the rational development of new adjuvants and allowed a better understanding of the modes of action of traditional adjuvants.