RNA-sensing pattern-recognition receptors synergize with TLR2 or dectin-1 to trigger high production of IL-12p70 by human dendritic cells
IL-12p70 is crucial for T helper 1 polarization and the generation of type 1 immunity that is required to fight cancer and intracellular pathogens. Therefore, strategies to optimize the production of IL-12p70 by dendritic cells (DCs) may significantly improve the efficacy of vaccines and immunotherapies for cancer. However, the rules governing the production of IL-12p70 remain obscure. Here, we stimulated pattern recognition receptors (PRRs) representing all five families of PRRs, to evaluate their ability to elicit high production of IL-12p70 by human DCs. We used ten well-characterized agonists and stimulated human monocyte-derived DCs in vitro with either single agonists or 26 different combinations. We found that poly(I:C), which engages the RNA-sensing PRRs TLR3 and/or MDA5, was the only agonist that could elicit IL-12p70 production when used alone. Combinations of agonists of cell surface and intracellular PRRs were found to synergize to induce high IL-12p70 production, given that the combination included poly(I:C) or resiquimod, which both are agonists of intracellular, RNA sensing PRRs (TLR3/MDA5 and TLR7/8, respectively). Our data show that production of high IL-12p70 is strictly controlled, which is different from what we observed for IFN{beta}, whose production could be elicited by several intracellular PRRs. In conclusion, we identified six different combinations of PRR ligands able to induce high IL-12p70 production by human DCs. The identified synergistic PRR ligand combinations may represent strong adjuvant candidates in particular for therapeutic cancer vaccines.