Not Just a Sum? Identifying Different Types of Interplay between Constituents in Combined Interventions

Cellular and molecular synergy in AS01-adjuvanted vaccines results in an early IFNγ response promoting vaccine immunogenicity

Combining immunostimulants in adjuvants can improve the quality of the immune response to vaccines. Here, we report a unique mechanism of molecular and cellular synergy between a TLR4 ligand, 3-O-desacyl-4’-monophosphoryl lipid A (MPL), and a saponin, QS-21, the constituents of the Adjuvant System AS01. AS01 is part of the malaria and herpes zoster vaccine candidates that have demonstrated efficacy in phase III studies. Hours after injection of AS01-adjuvanted vaccine, resident cells, such as NK cells and CD8⁺ T cells, release IFNγ in the lymph node draining the injection site. This effect results from MPL and QS-21 synergy and is controlled by macrophages, IL-12 and IL-18. Depletion strategies showed that this early IFNγ production was essential for the activation of dendritic cells and the development of Th1 immunity by AS01-adjuvanted vaccine. A similar activation was observed in the lymph node of AS01-injected macaques as well as in the blood of individuals receiving the malaria RTS,S vaccine. This mechanism, previously described for infections, illustrates how adjuvants trigger naturally occurring pathways to improve the efficacy of vaccines.

A mechanism is revealed by which vaccine components co-operate to stimulate the immune system and improve vaccine efficacy. Some vaccines are formulated with adjuvants—compounds that induce a greater immune response to the vaccine and help to elicit greater protection against future infections. Arnaud Didierlaurent and his team of researchers at GSK Vaccines, Belgium, demonstrate that the two immunostimulants in the adjuvant AS01, used in several recently developed vaccines, works in tandem to trigger the activation of important immune system moderators. The synergistic effect of the immunostimulants modulate specific immune cells at the site of the vaccination to better prepare the body against future infection. Studies such as this allow us to better understand how vaccines work and lay the foundation for more informed research into future vaccine development.