COMMENTARY ON: Abstract: Modeling hepatitis C virus infection using human induced pluripotent stem cells. Schwartz RE, Trehan K, Andrus L, Sheahan TP, Ploss A, Duncan SA, Rice CM, Bhatia SN. Proc Natl Acad Sci USA. 2012 February 14;109(7):2544–8. Epub 2012 January 30. Copyright (2012). Abstract reprinted with the permission from the National Academy of Sciences of the United States of America. http://www.ncbi.nlm.nih.gov/pubmed/22308485 Human pathogens impact patient health through a complex interplay with the host, but models to study the role of host genetics in this process are limited. Human induced pluripotent stem cells (iPSCs) offer the ability to produce host-specific differentiated cells and thus have the potential to transform the study of infectious disease; however, no iPSC models of infectious disease have been described. Here we report that hepatocyte-like cells derived from iPSCs support the entire life cycle of hepatitis C virus, including inflammatory responses to infection, enabling studies of how host genetics impact viral pathogenesis. © European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved. HCV infection is a major health problem worldwide since at least 70% of infections persist and cause chronic hepatitis which may progress to liver cirrhosis and hepatocellular carcinoma [[1]Alter M.J. Epidemiology of hepatitis C virus infection.World J Gastroenterol. 2007; 13: 2436-2441Crossref PubMed Scopus (1029) Google Scholar]. The lack of robust cell culture and small animal models persists as stumbling blocks to HCV research. Fortunately, thanks to the development of cell culture systems that support HCV replication [[2]Boonstra A. van der Laan L.J.W. Vanwolleghem T. et al.Experimental models for hepatitis C virus infection.Hepatology. 2009; 50: 1646-1655Crossref PubMed Scopus (73) Google Scholar], the entire HCV life cycle is now accessible for investigation. However, despite its strong advantages, the HCVcc system cannot completely mimic the events that occur during a natural HCV infection in vivo. Recently, HepaRG progenitor cells were shown to be capable of differentiating into hepatocytes and biliary epithelial cells, depending on culture conditions [[3]Parent R. Marion M.J. Furio L. et al.Origin and characterization of a human bipotent liver progenitor cell line.Gastroenterology. 2004; 126: 1147-1156Abstract Full Text Full Text PDF PubMed Scopus (178) Google Scholar]. These progenitors were used as a surrogate for primary human hepatocytes [[4]Lübberstedt M. Müller-Vieira U.M. Mayer M. et al.HepaRG human hepatic cell line utility as a surrogate for primary human hepatocytes in drug metabolism assessment in vitro.J Pharmacol Toxicol Methods. 2011; 63: 59-68Crossref PubMed Scopus (171) Google Scholar], and showed to be susceptible to in vitro infection with serum-derived HCV (genotype 3) and able to support long-term production of infectious lipoprotein-associated enveloped HCV particles [[5]Ndongo-Thiam N. Berthillon P. Errazuriz E. Bordes I. De Sequeira S. Trépo C. et al.Long-term propagation of serum hepatitis C virus (HCV) with production of enveloped HCV particles in human HepaRG hepatocytes.Hepatology. 2011; 54: 406-417Crossref PubMed Scopus (27) Google Scholar]. Taking these findings a step further, the model described by Schwartz, Trehan et al. offers the possibility to study genetic defects that impact HCV infection of human iPS-derived hepatocyte-like cells (iHLCs) [[6]Schwartz R.E. Trehan K. Andrus L. Sheahan T.P. Ploss A. Duncan S.A. et al.Modeling hepatitis C virus infection using human induced pluripotent stem cells.Proc Natl Acad Sci USA. 2012; (January 30 [Epub ahead of print])Google Scholar]. The iHLC is an interesting and original cell system for HCV studies. It results from the efficient generation of highly differentiated hepatocyte-like cells from iPS cells that display key liver functions and can integrate into the hepatic parenchyma in vivo [[7]Si-Tayeb K. Noto F.K. Nagaoka M. Li J. Battle M.A. duris C. et al.Highly efficient generation of human hepatocyte-like cells from induced pluripotent stem cells.Hepatology. 2010; 51: 297-305Crossref PubMed Scopus (1013) Google Scholar]. Inhibition of HNF4α in this system was shown to perturb hepatocyte differentiation once the endoderm was specified, mimicking previous findings generated from mouse knockout models, suggesting the usefulness of this model to study hepatocyte development in a human context [[8]Delaforest A.M. Nagaoka M. Si-Tayeb K. Noto F.K. Konopka G. Battle M.A. et al.HNF4A is essential for specification of hepatic progenitors from human pluripotent stem cells.Development. 2011; 138: 4143-4153Crossref PubMed Scopus (159) Google Scholar]. The HLCs and iHLCs co-express alpha fetoprotein and albumin, as well as a repertoire of phase-1 and phase-2 drug metabolizing enzymes, which are known to be expressed in fetal but also adult hepatocytes. To date, studies using HLC were able to show their application in detoxification [[9]Funakoshi N. Duret C. Pascussi J.M. Blanc P. Maurel P. Daujat-Chavanieu M. et al.Comparison of hepatic-like cell production from human embryonic stem cells and adult liver progenitor cells: CAR transduction activates a battery of detoxification genes.Stem Cell Rev. 2011; 7: 518-531Crossref PubMed Scopus (32) Google Scholar] when differentiated from human ES cells and modeling metabolic inborn genetic disease (for review, see [[10]Rountree C.B. Mishra L. Willenbring H. Stem cells in liver diseases and cancer: recent advances on the path to new therapies.Hepatology. 2012; 55: 298-306Crossref PubMed Scopus (93) Google Scholar]) when differentiated from human iPS cells. This is the first time that HLCs were described as a model to study host–pathogen interactions [[6]Schwartz R.E. Trehan K. Andrus L. Sheahan T.P. Ploss A. Duncan S.A. et al.Modeling hepatitis C virus infection using human induced pluripotent stem cells.Proc Natl Acad Sci USA. 2012; (January 30 [Epub ahead of print])Google Scholar]. Schwartz, Trehan et al. reported that (1) iHLCs expressed known HCV host factors involved in HCV entry (CD81, SRBI, CLDN1, OCLN); (2) iHLCs supported the entire life cycle of genotype 2a HCV reporter virus expressing secreted Gaussia luciferase (GLuc), as previously described [[11]Marukian S. Andrus L. Sheahan T. Jones C.T. Charles E.D. Ploss A. et al.Hepatitis C virus induces interferon-λ and interferon-stimulated genes in primary liver cultures.Hepatology. 2011; 54: 1913-1923Crossref PubMed Scopus (161) Google Scholar], and incubation with antiviral drugs induced a significant decrease of viral production. Culture supernatants at 13 days post infection (dpi) were able to infect HuH-7.5 cells, which are highly permissive to HCV; (3) HCV infection induced an antiviral inflammatory response by the increasing mRNA expression of interferon gamma inducible protein 10 (CXCL-10) and IFN-inducible T cell α chemoattractant (CXCL-11). These two chemokines, expressed by hepatocytes during chronic hepatitis C, are in part responsible for the recruitment of inflammatory T cells into the liver (for review, see [[12]Larrubia J.R. Benito-Martínez S. Calvino M. Sanz-de-Villalobos E. Parra-Cid T. Role of chemokines and their receptors in viral persistence and liver damage during chronic hepatitis C virus infection.World J Gastroenterol. 2008; 14: 7149-7159Crossref PubMed Scopus (115) Google Scholar]). TNF-α secretion was detected in cell culture supernatants from 2 to 14 dpi, and IL-28B/IL-29 only in response to viral infection at 2 dpi. Several recent genome wide association studies (GWAS) report that single nucleotide polymorphisms (SNPs) adjacent to IL28B (which encodes IFN-λ3) predict spontaneous resolution of HCV infection and outcome of treatment among HCV genotype 1 infected patients [[13]Rauch A. Kutalik Z. Descombes P. Cai T. Di Iulio J. Mueller T. et al.Genetic variation in IL28B is associated with chronic hepatitis C and treatment failure: a genome-wide association study.Gastroenterology. 2010; 138: 1338-1345Abstract Full Text Full Text PDF PubMed Scopus (1049) Google Scholar]. The strongest predictor of sustained virological response (SVR) is an SNP (rs12979860) and the CC genotype, which have SVR rates more than 2-fold higher than when the T variant is present. The effect of the IL28B haplotype status on treatment response might be attenuated for genotypes 2 and 3 (for review, see [[14]Balagopal A. Thomas D.L. Thio C.L. IL28B and the control of hepatitis C virus infection.Gastroenterology. 2010; 139: 1865-1876Abstract Full Text Full Text PDF PubMed Scopus (208) Google Scholar]). The mechanisms that mediate the association between different SNPs and HCV control are poorly understood. IFN-λ activates a transcriptional program resembling that of IFNα/β in liver cells and inhibits HCV replication in the JFH1 infection model [[15]Zhang L. Jilg N. Shao R.X. Lin W. Fusco D.N. Zhao H. et al.IL28B inhibits hepatitis C virus replication through the JAK–STAT pathway.J Hepatol. 2011; 55: 289-298Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar] as well as in human fetal liver cells [[11]Marukian S. Andrus L. Sheahan T. Jones C.T. Charles E.D. Ploss A. et al.Hepatitis C virus induces interferon-λ and interferon-stimulated genes in primary liver cultures.Hepatology. 2011; 54: 1913-1923Crossref PubMed Scopus (161) Google Scholar]. Otherwise, HCVcc induces expression of IFN-λ, CXCL-10, and CXCL-11. Both viral and host factors influence the level of gene induction. Concomitant assessment of pretreatment IP-10 or CXCL-10 and IL28B-related SNPs augments the prediction of the first phase decline in HCV RNA and the final therapeutic outcome [[16]Lagging M. Askarieh G. Negro F. Bibert S. Söderholm J. Westin J. et al.Response prediction in chronic hepatitis C by assessment of IP-10 and IL28B-related single nucleotide polymorphisms.PLoS One. 2011; 6: e17232Crossref PubMed Scopus (135) Google Scholar]. A better understanding of HCV/host interactions is urgently needed in order to develop improved therapies. This study demonstrates that HCVcc infection induces an antiviral inflammatory response, including chemokines and IL28B. Therefore, as suggested by the authors, we can speculate that iPSCs generated from identified patients with a genetic background that impact HCV infection could serve as a model for studying the influence of innate immunity on such infection, which should considerably impact our current knowledge on antiviral therapy. In order to efficiently identify new candidate genes and decrease the cost and time consumption of iPSCs generation, characterization and differentiation, next generation sequencing technology (NGS) could now be combined to GWAS as two-phase sampling designs for patients’ selection (Fig. 1) [[17]Chen Z. Craiu R.V. Bull S.B. Two-phase stratified sampling designs for regional sequencing.Genet Epidemiol. 2012; (March 28 [Epub ahead of print])https://doi.org/10.1002/gepi.2162Crossref Google Scholar]. Despite the undeniable strength of modeling HCV infection using cells from diverse genetic backgrounds, further maturation of iHLCs must be achieved in order to faithfully reflect HCV/host interactions. In addition, it will be important to learn how HCV isolates representing other HCV genotypes interact with IFN systems, especially IFN-λ (Fig. 1). The study of hepatitis C viral pathogenesis with patient-derived iPS cells will open new perspectives of research opportunities. The authors declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript.
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