Toll-like receptor 4 and NOD-like receptor protein 3 inflammasome (TLR4/NLRP3)

AS02A is a proprietary adjuvant system developed by GlaxoSmithKline (GSK) that consists of an oil-in-water emulsion containing two potent immunostimulants: 3-O-desacyl-4'-monophosphoryl lipid A (MPL) and QS-21 (Garçon & Van Mechelen, 2011). The innate immune receptors engaged by this system primarily include Toll-like receptor 4 (TLR4) and the NLRP3 inflammasome (Reed et al., 2013). MPL acts as a direct agonist of TLR4, triggering signaling pathways that lead to the production of pro-inflammatory cytokines and the maturation of dendritic cells (Didierlaurent et al., 2009). In contrast, QS-21 is believed to engage the NLRP3 inflammasome indirectly; upon endocytosis, it causes lysosomal destabilization and the release of cathepsins, which subsequently trigger inflammasome assembly and the processing of IL-1β and IL-18 (Den Broeck et al., 2014). This dual-pathway activation is crucial for the induction of strong, long-lasting adaptive immune responses, particularly Th1-type cellular immunity and high-titer antibody production. AS02A has been a key component in the development of vaccines against complex pathogens, most notably in early formulations of the RTS,S malaria vaccine (RTS,S Clinical Trials Partnership, 2015).

Other names

Innate immune receptors engaged by AS02ATLR4NLRP3Pattern recognition receptorsPRRs

Synergistic activation of innate immunity via direct TLR4 agonism and indirect NLRP3 inflammasome activation through lysosomal destabilization.