The iscom structure as an immune-enhancing moiety: experience with viral systems.

The “ideal” vaccine should meet the following requirements: the induction of a long-lasting antibody response of biologically active antibodies, which should be elicited even in the presence of maternal antibodies ; functional T-cell responses which comprise both major histocompatibility complex (MHC) class-Iand class-II-restricted cytotoxic T cells (CTL) and helper T cells ; long-lasting protection against infection with the pathogen. Furthermore, the production procedures must be suitable for large-scale production and the product must be stable during prolonged periods of storage and transport. Last but not least, it has to be safe and devoid of any undesirable side effects. New generations of vaccines will probably be composed of relevant antigen subunits either derived from the pathogen itself or prepared via molecular biological or synthetic techniques. However, vaccine formulations based on individual antigens or subunits bearing one or more Band T-cell epitopes in a monomeric form have a major disadvantage : they are usually poorly immunogenic as compared to the original inactivated or attenuated pathogen. Therefore adjuvants or immune enhancers are needed to elicit the desired immune response. In general, adjuvants should contribute to the requirements stated above for the “ideal” vaccine. Most adjuvants however, only contribute to some of these, and concerns about undesirable side effects have largely prohibited their use in registered vaccines for humans.