Immune cells (QS-21 modulated)

QS-21 is a highly purified triterpene saponin derived from the bark of the Quillaja saponaria tree, widely recognized as a potent vaccine adjuvant that enhances both humoral and cellular immunity [1, 12]. It modulates a diverse array of immune cells, primarily targeting antigen-presenting cells (APCs) such as dendritic cells and macrophages, as well as T cells and natural killer (NK) cells [1, 4]. The primary molecular mechanism of QS-21 involves the activation of the NLRP3 inflammasome in APCs, which triggers the secretion of pro-inflammatory cytokines like IL-1β and IL-18, driving a Th1-biased immune response [2, 6]. Additionally, QS-21 facilitates the cross-presentation of exogenous antigens to CD8+ T cells by inducing lysosomal membrane destabilization, allowing antigens to escape into the cytoplasm and enter the MHC class I pathway [4, 7]. It may also provide direct co-stimulatory signals to T cells through its aldehyde group, which can form Schiff bases with cell surface receptors like CD2 [1, 13]. Due to its inherent toxicity (e.g., hemolysis) and reactogenicity, QS-21 is typically formulated in lipid-based adjuvant systems like AS01 or Matrix-M to improve safety and stability [9, 12]. These systems are critical components of several licensed vaccines, including those for shingles (Shingrix), malaria (Mosquirix), and respiratory syncytial virus (Arexvy) [11, 12].

Other names

Antigen-presenting cellsDendritic cellsMacrophagesT lymphocytesNatural Killer cellsNLRP3 inflammasome

QS-21 modulates immune cells by facilitating antigen cross-presentation through lysosomal destabilization and escape into the cytosol, activating the NLRP3 inflammasome in antigen-presenting cells (APCs) to release IL-1β and IL-18, and potentially providing co-stimulatory signals to T cells via its aldehyde group [1, 2, 4].