AS01B adjuvant system (AS01B)

The AS01B adjuvant system is a proprietary liposome-based vaccine adjuvant comprised of two immunostimulatory components: 3-O-desacyl-4'-monophosphoryl lipid A (MPL), a detoxified Toll-like receptor 4 agonist, and QS-21, a purified saponin derived from Quillaja saponaria. These components are formulated in liposomes composed of dioleoylphosphatidylcholine and cholesterol. AS01B is designed to strengthen both innate and adaptive immune responses to coadministered vaccine antigens by promoting the activation and maturation of antigen-presenting cells, stimulating cytokine release, and enhancing Th1 CD4+ T cell as well as antibody responses. AS01B is a critical component in the efficacy of several modern vaccines, including those for herpes zoster, malaria, and respiratory syncytial virus, and is under evaluation in vaccines for other infectious diseases. Its design maximizes immunogenicity while maintaining a favorable safety and tolerability profile.

Other names

AS01BAS01 family (includes AS01B, AS01E, etc.)Adjuvant system AS01BShingrix adjuvant (contextual, as used in Shingrix)

AS01B contains two primary immunostimulants: 3-O-desacyl-4'-monophosphoryl lipid A (MPL) (a Toll-like receptor 4 agonist) and QS-21 (a saponin derived from Quillaja saponaria), formulated together in liposomes with cholesterol and dioleoylphosphatidylcholine. MPL activates antigen-presenting cells via TLR4, leading to cytokine production (e.g., IL-12, IL-18), innate immune activation, and Th1 polarization. QS-21 acts on antigen-presenting cells, can activate the NLRP3 inflammasome, and stimulate both antibody and T cell responses, especially promoting CD8+ T cell activation. The synergy of MPL and QS-21 effectively enhances both antibody-mediated and cell-mediated immunity following vaccination.