Synthetic Toll Like Receptor-4 (TLR-4) Agonist Peptides as a Novel Class of Adjuvants

Abstract

BackgroundAdjuvants serve as catalysts of the innate immune response by initiating a localized site of inflammation that is mitigated by the interactions between antigens and toll like receptor (TLR) proteins. Currently, the majority of vaccines are formulated with aluminum based adjuvants, which are associated with various side effects. In an effort to develop a new class of adjuvants, agonists of TLR proteins, such as bacterial products, would be natural candidates. Lipopolysaccharide (LPS), a major structural component of gram negative bacteria cell walls, induces the systemic inflammation observed in septic shock by interacting with TLR-4. The use of synthetic peptides of LPS or TLR-4 agonists, which mimic the interaction between TLR-4 and LPS, can potentially regulate cellular signal transduction pathways such that a localized inflammatory response is achieved similar to that generated by adjuvants.Methodology/Principal FindingsWe report the identification and activity of several peptides isolated using phage display combinatorial peptide technology, which functionally mimicked LPS. The activity of the LPS-TLR-4 interaction was assessed by NF-κB nuclear translocation analyses in HEK-BLUE™-4 cells, a cell culture model that expresses only TLR-4, and the murine macrophage cell line, RAW264.7. Furthermore, the LPS peptide mimics were capable of inducing inflammatory cytokine secretion from RAW264.7 cells. Lastly, ELISA analysis of serum from vaccinated BALB/c mice revealed that the LPS peptide mimics act as a functional adjuvant.Conclusions/SignificanceOur data demonstrate the identification of synthetic peptides that mimic LPS by interacting with TLR-4. This LPS mimotope-TLR-4 interaction will allow for the development and use of these peptides as a new class of adjuvants, namely TLR-4 agonists.

Toll-like Receptor 4 (TLR4) Modulation by Synthetic and Natural Compounds: An Update

“…38 Peptide-based TLR4 agonists have also been developed recently, by screening a 7-mer phage-display peptide library. 39 The activity of the peptides in activating TLR4 signaling was assessed by NF-κB nuclear translocation analyses in HEK-blue™ cells. Furthermore, the peptides were capable of inducing inflammatory cytokine secretion from RAW264.7 cells.…”

Targeting Toll-like receptors with small molecule agents

“…Additionally, these mimics can act as TLR4 agonists and functional adjuvants for vaccine development. 26 …”

Directing the Immune System with Chemical Compounds

“…50,51 Recently, peptide agonists of TLR4 have been identified via phage display and antibody binding assays. 52 It has yet to be determined how these peptides activate TLR4 and whether MD2 is necessary for binding. Endogenous molecules, such as heat shock proteins 60 53 and 70 54 , fibrinogen 55 , fibronectin domain A 56 , extracellular DNA-binding proteins 57 , and other molecules activate TLR4, but the modes of binding are unclear.…”