Uptake and adjuvant activity of orally delivered saponin and ISCOM vaccines

Saponins are a highly heterogenous group of glycosides which are common in plants and have been known to have adjuvant properties since the 1920s. The immunostimulating complex or ISCOM is a particulate adjuvant/antigen delivery system. ISCOMs are open cage-like complexes typically with a diameter of about 40 nm which are built up by cholesterol, lipid, immunogen and saponins from the bark of Quillaia saponaria Molina (soap bark tree). ISCOMs and saponins are used as adjuvants in some commercial veterinary vaccines and have been examined as adjuvants in a large number of human experimental vaccines. This review describes the current status and potential of saponin and ISCOMs as adjuvants for orally-administered vaccines with special reference to the induction of local and systemic immune responses and interactions with the intestinal epithelium. The structure and composition of saponins and ISCOMs will also be reviewed.