Vaccine adjuvants: role and mechanisms of action in vaccine immunogenicity

Inactivated vaccines require adjuvants to stimulate an immune response. The choice of adjuvant or immune enhancer determines whether the immune response is effective, ineffective or damaging. Accordingly, there is a need for new adjuvants that stimulate the appropriate immunity, for example, T cell immunity for intracellular pathogens and cancer vaccines. In several adjuvants, the identification of chemical groups that interact with specific cell toll-like receptors (innate immunity) or receptors for co-stimulatory ligands (adaptive immunity), has enabled the establishment of structure–function relationships that are useful in the design of new adjuvants. Because of the crucial immunomodulating role of adjuvants, sub-unit vaccine development will remain dependent on new adjuvants.