Abstract
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 (). 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 (). 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 (). QS-21 was identified as a saponin with potent adjuvant activity and low toxicity (). 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.
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