The extract contains water-soluble triterpene glycosides, which are members of a family of plant-based compounds called saponins. It is currently[when?] being tested as an adjuvant in various vaccines in attempts to improve their efficacy. It is believed to enhance both humoral and cell-mediated immunity.
Isolation of QS-21 destroys the soap bark tree, which has resulted in regulation of the tree by the governments where it is grown. A semi-synthesis strategy relies on purifying the prosapogenin (triterpene and branched trisaccharide) part of the molecule and adding the rest of QS-21 synthetically; this is reported to increase the yield by 2 orders of magnitude. This semi-synthetic approach has also facilitated experimentation with alternative acyl chain compositions.
QS-21 is currently[when?] under clinical evaluation as an additive for various trial vaccines, including those for HIV, malaria and cancer. As of 2002[update], it had been tested in more than 3000 patients in 60 clinical trials. It is a component of the Shingrix vaccine.
- Ragupathi G, Gardner JR, Livingston PO, Gin DY (2013). "Natural and synthetic saponin adjuvant QS-21 for vaccines against cancer". Expert Rev Vaccines. 10: 463–70. doi:10.1586/erv.11.18. PMC 3658151. PMID 21506644.
- Chea EK, Fernández-Tejada A, Damani P, Adams MM, Gardner JR, Livingston PO, Ragupathi G, Gin DY (2013). "Synthesis and preclinical evaluation of QS-21 variants leading to simplified vaccine adjuvants and mechanistic probes". J Am Chem Soc. 134: 13448–57. doi:10.1021/ja305121q. PMC 3436428. PMID 22866694.
- "SHINGRIX package insert" (PDF). Food and Drug Administration. Retrieved 7 April 2019.