Cooperative intracellular interactions between MyD88 and TRIF are required for CD4 T cell TH1 polarization with a synthetic TLR4 agonist adjuvant

GLA-SE is a synthetic adjuvant agonist of TLR4 that promotes potent poly-functional TH1 responses. Different TLR4 agonists may preferentially signal via MyD88 or TRIF to exert adjuvant effects. However the contribution of MyD88 and TRIF signaling to the induction of polyclonal TH1 responses by TLR4 agonist adjuvants has not been studied in vivo. To determine whether GLA-SE preferentially signals through MyD88 or TRIF, we evaluated the immune responses against a candidate tuberculosis vaccine antigen following immunization of mice lacking either signaling adapter compared to intact mice. We find that both MyD88 and TRIF are necessary for GLA-SE to induce a poly-functional TH1 immune response characterized by CD4 T cells producing IFN-γ, TNF and IL-2, as well as IgG2c class switching, when paired with the tuberculosis vaccine antigen ID93. Accordingly, the protective efficacy of ID93/GLA-SE immunization against aerosolized Mycobacterium tuberculosis was lost when either signaling molecule was ablated. We demonstrate that MyD88 and TRIF must be expressed in the same cell for the in vivo TH1-skewing adjuvant activity indicating that these two signaling pathways cooperate on an intracellular level. Thus engagement of both the MyD88 and TRIF signaling pathways are essential for the effective adjuvant activity of this TLR4 agonist.