Toll-like receptor-mediated adjuvanticity and immunomodulation in dendritic cells: Implications for peptide vaccines

Considerable success has been made with many peptide antigen formulations and it appears that peptide-based vaccines are emerging as the next generation of prophylactic and remedial immunotherapy. However, peptides are typically poorly immunogenic and rely on delivery with potent immunostimulatory adjuvants that activate the innate and adaptive arms of the immune system. Our research aims to develop novel peptide antigen delivery systems that incorporate multiple pattern-recognition receptor (PRR) agonists and is focused on those designed to stimulate Toll-like receptors (TLRs) on dendritic cells (DCs). The cytokine (IL-4, IL-6, IL-10, IL-12 and IL-23) profiles of DCs induced by individual TLR agonists have been evaluated. From this data we predicted which TLR agonists may influence a particular T helper cell (Th) response. Using purified DCs that were derived from precursor cells in murine bone marrow and then stimulated simultaneously with multiple TLR agonists, we have shown synergy between various TLR agonist pairs leading to enhanced cytokine production. Using various mitogen-activated protein kinase (MAPK) inhibitors (c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK) and p38 MAPK) we have demonstrated the importance of p38 MAPK and ERK signaling pathways in IL-12p70 and IL-12p40 production in DCs induced by TLR stimulation, whereas the JNK pathway appeared to have a negative regulatory role on cytokine production in DCs stimulated with certain TLR agonists. An important role for nuclear factorkappaB and phosphoinositol-3-kinase as positive regulators of TLR signaling in DCs leading to cytokine production was also demonstrated. The significance of this research lies not only in improving potency, but by understanding the immunological mechanisms of adjuvanticity, in being able to tailor peptide vaccines to generate specific types of Th responses required for immunity against various types of pathogens.