QS-21 Adjuvant

QS-21 is an immunological adjuvant derived from a natural source: the bark of the South American tree Quillaja saponaria Molina. Crude extracts of Quillaja saponaria bark were found to have adjuvant activity in foot-andmouth disease vaccines in cattle (1 ). These extracts consisted of a complex mixture of tannins, polyphenolics, and triterpene glycoside “saponins.” The adjuvant activity was determined to be in the saponin fraction (2 ). This was later fractionated by high-performance liquid chromatography (HPLC) into at least 23 different triterpene glycoside saponins with a varying range of biological activity for adjuvanticity, surfactant properties, and toxicity (3 ). QS-21 was identified as a saponin with potent adjuvant activity and low toxicity (3 ). It can be purified to near homogenity via preparative HPLC. The high level of purity and standardization of the QS-21 saponin adjuvant has enabled evaluation of this compound in clinical trials of experimental vaccines.