AS01B adjuvant system (AS01B)

Molecular Classification

Other (Vaccine adjuvant system), Liposome-based adjuvant formulation

Other Names

AS01B, AS01 family (includes AS01B, AS01E, etc.), Adjuvant system AS01B, Shingrix adjuvant (contextual, as used in Shingrix)

Disease Roles

InfectionOther (Facilitating prophylaxis through immunization against infectious diseases such as herpes zoster, malaria, tuberculosis, RSV)

AS01B adjuvant system Overview

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.

Mechanism of Action

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.

Biological Functions

Immune response enhancement

Antigen presentation facilitation

Induction of innate and adaptive immunity

Promotion of Th1-type immunity and CD4+ T cell activation

Disease Associations

Infection

Other (Facilitating prophylaxis through immunization against infectious diseases such as herpes zoster, malaria, tuberculosis, RSV)

Safety Considerations

Generally well tolerated with a good safety record in large clinical trials and postmarketing experience
Some local and systemic reactogenicity, typically mild to moderate, such as injection site pain, redness, fever, myalgia
QS-21 can be associated with toxicity in other settings, but liposomal formulation with cholesterol in AS01B minimizes this risk

Interacting Drugs

Herpes zoster vaccine antigen (gE, in Shingrix)

Malaria vaccine antigen (RTS,S)

Tuberculosis vaccine antigen (M72)

RSV vaccine antigens

Associated Biomarkers

Biomarker
There are no specific biomarkers for patient selection or monitoring of AS01B itself. General immune activation markers (e.g., cytokine production, B cell and T cell responses) are used in vaccine evaluation.