QS-21

QS-21 is a purified natural saponin fraction derived from the bark of the soapbark tree (Quillaja saponaria Molina), native to South America. It functions as a potent immunological adjuvant and is used in vaccines and immunotherapies to enhance both humoral and cell-mediated immune responses to co-administered antigens. Mechanistically, it forms complexes with cholesterol that intercalate into cell membrane lipids of antigen-presenting cells; this creates pores in the membrane that accelerate antigen uptake and presentation. This results in increased vaccine-specific antibody production and cytotoxic T-cell responses. QS-21 has been evaluated as an adjuvant in clinical trials for vaccines targeting infectious diseases (such as COVID-19, malaria, RSV) and cancer immunotherapies[1][2][3][4][5]. It is not itself an approved pharmaceutical but has been included in several globally approved vaccines.

Brand names

Stimulon

Other names

Quillaja saponin (QS-21)Saponin QA 21V1QA-21V1QA21V1QA 21V1QS-21-apiose isomerQS21-apiose isomerQS 21-apiose isomer