QS21

QS21 is a plant extract that may improve the ability of the immune system to respond to disease. It is derived from the Soap bark tree (Quillaja saponaria) found in the South American country of Chile.

The extract is a water soluble triterpene glucoside compound. It forms part of a family of plant-based compounds called saponins.

It is currently 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.

QS21 is currently under clinical evaluation as an additive for various trial vaccines, including those for HIV, malaria and cancer. As of 2002, it had been tested in more than 3000 patients in 60 clinical trials.