QS-21 saponin adjuvant (QS-21)

QS‑21 is a purified mixture of two closely related triterpene glycoside saponins derived from the bark of the soap bark tree (*Quillaja saponaria*). It serves as a potent immunological adjuvant in human vaccines by stimulating both humoral (antibody) and cellular (T-cell) immune responses. Its mechanism involves facilitating antigen uptake by dendritic cells through cholesterol-dependent pathways and promoting cross-presentation to cytotoxic T lymphocytes. While highly effective at boosting vaccine efficacy against infectious diseases like malaria and shingles as well as certain cancers and degenerative diseases, its use requires careful formulation due to inherent instability in aqueous solution and potential toxicity when administered directly. Encapsulation within liposomes or nanoparticles mitigates these issues while targeting delivery to phagocytic cells[1][2][3][4][5].

Other names

Saponin-based immune stimulationQuillaja saponaria saponin fraction 21Quillaja bark saponin (QS-21)Saponin adjuvant QS-21

QS‑21 acts as an immunological adjuvant by enhancing both antibody-mediated and cell-mediated immune responses. It facilitates antigen uptake by antigen-presenting cells via cholesterol-dependent endocytosis and disrupts endosomal membranes to promote cross-presentation of antigens on MHC I molecules. It can also activate the NLRP3 inflammasome pathway for cytokine release[2][4][5].