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Antimicrob. Agents Chemother. doi:10.1128/AAC.00268-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Investigating Toll-Like Receptor Agonists for Potential to Treat Hepatitis C Virus Infection

Discovery Biology, Pfizer Global Research & Development, Sandwich, Kent CT13 9NJ, UK

^* To whom correspondence should be addressed. Email: tanya.parkinson{at}pfizer.com.

	Abstract

Toll-like receptors (TLRs) are key mediators of innate immunity and their activation by microbial components leads to production of cytokines and interferons. Recombinant interferon alpha has been used to treat several viral diseases and is the current standard of care for hepatitis C virus (HCV) infection. Recently, agonists of TLR7 and TLR9 have been shown to have clinical efficacy in HCV patients and this is correlated with their ability to induce endogenous type I interferon production. We have carried out a comprehensive study of agonists of TLRs 1-9 to determine if any additional TLRs can induce antiviral molecules from human peripheral blood mononuclear cells (PBMCs). The agonists were incubated with PBMCs, then the supernatant was removed and added to HCV replicon cells to assess antiviral activity. Agonists of TLRs 3, 4, 7, 8 and 9 were found to be potent inducers of antiviral activity in PBMC supernatants and the activity correlated with induction of interferon alpha and the interferon-induced antiviral biomarker 2', 5' oligo adenylate synthase. Antiviral activity of TLR7 and 8 agonists was blocked by an antibody which binds to the type I interferon receptor, confirming that the antiviral activity results from type I interferon induction. TLR4 and TLR8 agonists were found to strongly induce the pro-inflammatory cytokines interleukin 1 beta and tumor necrosis factor alpha at concentrations similar to those inducing antiviral activity. This raises concerns about adverse side effects if these were to be used as antiviral agents. We therefore conclude that TLRs 3, 7 and 9 represent the most attractive targets for development of new HCV therapies.