Immunologic effects of the interferon lambda 3 genotype in chronic hepatitis C

Abstract

In 2009, ground breaking pharmacogenetic data emerged identifying single nucleotide polymorphisms (SNPs) in the region of the interferon lambda 3 (IFNL3) gene as predictors of response to the treatment of genotype 1 hepatitis C virus (HCV) infection. These robust, well replicated findings were delivered via genome-wide association studies (GWAS) and firmly established an association but not causation. The studies in this thesis were designed to enhance our understanding of the mechanism by which IFNL3 may exert its influence on HCV clearance. The major outcomes of the research were: 1. Through exploring the biology of IFNL3 we demonstrate the immune cells (including peripheral blood mononuclear cells (PBMCs), monocytes, and plasmacytoid dendritic cells (pDCs) are all responsive to IFNL3. We identified relatively more of the membrane-bound or functional form of IFNL receptor 1 (IFNLR1) on immune cells. In comparison with HCV infected liver biopsies un-stimulated immune cells expressed significantly higher levels of IFNL3 and comparable levels of IFNLR1. These data together suggest innate immune cells are likely to be the central players in elucidating the functional significance of the IFNL3 polymorphisms. 2. The haplotype effect on IFNL3 expression was explored across a variety of samples including: immune cells with and without IFN alpha stimulation (IFNA), liver biopsies and whole blood from HCV infected subjects undergoing treatment. We were not able to establish a significant association between IFNL3 expression levels and IFNL3-genotype in this body of work. 3. We examined for IFN stimulated gene (ISG) signatures according to IFNL3-genotype in liver biopsies and peripheral blood from HCV infected subjects. A dichotomy between immune cells and hepatic tissue is suggested by the finding of higher peripheral blood ISGs in the subjects with the IFNL3 favorable genotype. This is in contrast to the replicated data of lower hepatic ISGs in the IFNL3 favourable group. Heightening the complexity of the ISG narrative we identified a cluster of hepatic ISGs, the metallothioneins (MTs), which are significantly up-regulated in IFNL3 responders. The higher MT expression in the IFNL3 responders may contribute to their improved viral clearance and MT inducing agents may be useful adjuncts to therapy for HCV infection. 4. Finally, immunological parameters in the context of IFNL3-genotype, during the first four weeks of therapy in subjects with HCV, were explored. Evidence of an IFNL3-genotype effect on peripheral blood was identified with significantly lower pre-treatment white cell counts, monotypes, neutrophils and absolute lymphocyte counts established in subjects with the favorable genotype. Results suggest an association between immune-cell trafficking and IFNL3-genotype which may mediate viral clearance. Furthermore, data suggests a Th1 dominant effect in HCV subjects with the favourable IFNL3-genotype. The studies contained in this thesis augment our understanding of the immunologic effects of the IFNL3-genotype in the context of chronic HCV infection. They supplement the armamentarium of emerging data in this field and aid the quest to establish causality of the IFNL3 polymorphisms and HCV clearance.