Modeling host interactions with hepatitis B virus using primary and induced pluripotent stem cell-derived hepatocellular systems. Proc Natl Acad Sci U S A. 2014;111:12193-12198. [PMID: 25092305 DOI: 10.1073/pnas.1412631111]

Recapitulation of hepatitis B virus-host interactions in liver organoids from human induced pluripotent stem cells

Therapies against hepatitis B virus (HBV) have improved in recent decades; however, the development of individualized treatments has been limited by the lack of individualized infection models. In this study, we used human induced pluripotent stem cell (hiPSC) to generate a functional liver organoid (LO) that inherited the genetic background of the donor, and evaluated its application in modeling HBV infection and exploring virus–host interactions. To establish a functional hiPSC-LO, we cultured hiPSC-derived endodermal, mesenchymal, and endothelial cells with a chemically defined medium in a three-dimensional microwell culture system. Based on cell-cell interactions, these cells could organize themselves and gradually differentiate into a functional organoid, which exhibited stronger hepatic functions than hiPSC derived hepatic like cell (HLC). Moreover, the functional LO demonstrated more susceptibility to HBV infection than hiPSC-HLC, and could maintain HBV propagation and produce infectious virus for a prolonged duration. Furthermore, we found that virus infection could cause hepatic dysfunction of hiPSC-LOs, with down-regulation of hepatic gene expression, induced release of early acute liver failure markers, and altered hepatic ultrastructure. Therefore, our study demonstrated that HBV infection in hiPSC-LOs could recapitulate virus life cycle and virus induced hepatic dysfunction, suggesting that hiPSC-LOs may provide a promising individualized infection model for the development of individualized treatment for hepatitis.

When Hepatitis B Virus Meets Interferons

Chronic hepatitis B virus (HBV) infection imposes a severe burden on global public health. Currently, there are no curative therapies for millions of chronic HBV-infected patients (Lok et al., 2017). Interferon (IFN; including pegylated IFN) is an approved anti-HBV drug that not only exerts direct antiviral activity, but also augments immunity against HBV infection. Through a systematic review of the literature, here we summarize and present recent progress in research regarding the interactions between IFN and HBV as well as dissect the antiviral mechanisms of IFN. We focus on inhibition of HBV replication by IFN-stimulated genes (ISGs) as well as inhibition of IFN signaling by HBV and viral proteins. Finally, we briefly discuss current IFN-based HBV treatment strategies. This review may help to better understand the mechanisms involved in the therapeutic action of IFN as well as the crosstalk between IFN and HBV, and facilitate the development of both direct-acting and immunology-based new HBV drugs.

A Chimeric Humanized Mouse Model by Engrafting the Human Induced Pluripotent Stem Cell-Derived Hepatocyte-Like Cell for the Chronic Hepatitis B Virus Infection

Humanized mouse model generated by grafting primary human hepatocytes (PHHs) to immunodeficient mouse has contributed invaluably to understanding the pathogenesis of hepatitis B virus (HBV). However, the source of PHHs is limited, which necessitates the search for alternatives. Recently, hepatocyte-like cells (HLCs) generated from human induced pluripotent stem cells (hiPSCs) have been used for in vitro HBV infection. Herein, we developed a robust human liver chimeric animal model to study in vivo HBV infection by engrafting the hiPSC-HLCs to Fah-/-Rag2-/-IL-2Rγc-/-SCID (FRGS) mice. After being optimized by a small molecule, XMU-MP-1, the hiPSC-HLCs engrafted FRGS (hHLC-FRGS) mice displayed approximately 40% liver chimerism at week 6 after engraftment and maintained at this level for at least 14 weeks. Viremia and HBV infection markers include antigens, RNA, DNA, and covalently closed circular DNA were detectable in HBV infected hHLC-FRGS mice. Furthermore, hiPSC-HLCs and hHLC-FRGS mice were successfully used to evaluate different antivirals. Therefore, we established a humanized mouse model for not only investigating HBV pathogenesis but also testing the effects of the anti-HBV drugs. Highlights:    (1) The implanted hiPSC-HLCs established a long-term chimerism in FRGS mice liver.    (2) hHLC-FRGS mice are adequate to support chronic HBV infection with a full viral life cycle.    (3) hiPSC-HLCs and hHLC-FRGS mice are useful tools for evaluation of antivirals against HBV infection in vitro and in vivo. Research in Context  To overcome the disadvantages of using primary human hepatocytes, we induced human pluripotent stem cells to hepatocyte-like cells (hiPSC-HLCs) that developed the capability to express important liver functional markers and critical host factors for HBV infection. The hiPSC-HLCs were permissive for the HBV infection and supported a full HBV replication. The hiPSC-HLCs were then engrafted to immunodeficient mouse to establish a chimeric liver mouse model, which was capable of supporting HBV infection in vivo and evaluating the effects of antiviral drugs. Our results shed light into improving the cellular and animal models for studying HBV and other hepatotropic viruses.

Microengineered cultures containing human hepatic stellate cells and hepatocytes for drug development

In non-alcoholic steatohepatitis (NASH), hepatic stellate cells (HSC) differentiate into myofibroblast-like cells that cause fibrosis, which predisposes patients to cirrhosis and hepatocellular carcinoma. Thus, modeling interactions between activated HSCs and hepatocytes in vitro can aid in the development of anti-NASH/fibrosis therapeutics and lead to a better understanding of disease progression. Species-specific differences in drug metabolism and disease pathways now necessitate the supplementation of animal studies with data acquired using human liver models; however, current models do not adequately model the negative effects of primary human activated HSCs on the phenotype of otherwise well-differentiated primary human hepatocytes (PHHs) as in vivo. Therefore, here we first determined the long-term effects of primary human activated HSCs on PHH phenotype in a micropatterned co-culture (MPCC) platform while using 3T3-J2 murine embryonic fibroblasts as the control cell type since it has been shown previously to stabilize PHH functions for 4-6 weeks. We found that HSCs were not able to stabilize the PHH phenotype to the same magnitude and longevity as the fibroblasts, which subsequently inspired the development of a micropatterned tri-culture (MPTC) platform in which (a) micropatterned PHHs were functionally stabilized using fibroblasts, and (b) the PHH phenotype was modulated by culturing HSCs within the fibroblast monolayer at physiologically-relevant ratios with PHHs. Transwell inserts containing HSCs were placed atop MPCCs containing fibroblasts to confirm the effects of paracrine signaling between PHHs and HSCs. We found that while albumin and urea secretions were relatively similar in MPTCs and MPCCs (suggesting well-differentiated PHHs), increasing HSC numbers within MPTCs downregulated hepatic cytochrome-P450 (2A6, 3A4) and transporter activities, and caused steatosis over 2 weeks. Furthermore, MPTCs secreted higher levels of pro-inflammatory interleukin-6 (IL-6) cytokine and C-reactive protein (CRP) than MPCCs. Treatment of MPCCs with HSC-conditioned culture medium confirmed that HSC secretions mediate the altered phenotype of PHHs observed in MPTCs, partly via IL-6 signaling. Lastly, we found that NADPH oxidase (NOX) inhibition and farnesoid X receptor (FXR) activation using clinically relevant drugs alleviated hepatic dysfunctions in MPTCs. In conclusion, MPTCs recapitulate symptoms of NASH- and early fibrosis-like dysfunctions in PHHs and have utility for drug discovery in this space.

HBV Bypasses the Innate Immune Response and Does Not Protect HCV From Antiviral Activity of Interferon

BACKGROUND & AIMS

Hepatitis C virus (HCV) infection is sensitive to interferon (IFN)-based therapy, whereas hepatitis B virus (HBV) infection is not. It is unclear whether HBV escapes detection by the IFN-mediated immune response or actively suppresses it. Moreover, little is known on how HBV and HCV influence each other in coinfected cells. We investigated interactions between HBV and the IFN-mediated immune response using HepaRG cells and primary human hepatocytes (PHHs). We analyzed the effects of HBV on HCV replication, and vice versa, at the single-cell level.

METHODS

PHHs were isolated from liver resection tissues from HBV-, HCV-, and human immunodeficiency virus-negative patients. Differentiated HepaRG cells overexpressing the HBV receptor sodium taurocholate cotransporting polypeptide (dHepaRGNTCP) and PHHs were infected with HBV. Huh7.5 cells were transfected with circular HBV DNA genomes resembling viral covalently closed circular DNA (cccDNA), and subsequently infected with HCV; this served as a model of HBV and HCV coinfection. Cells were incubated with IFN inducers, or IFNs, and antiviral response and viral replication were analyzed by immune fluorescence, reverse-transcription quantitative polymerase chain reaction, enzyme-linked immunosorbent assays, and flow cytometry.

RESULTS

HBV infection of dHepaRGNTCP cells and PHHs neither activated nor inhibited signaling via pattern recognition receptors. Incubation of dHepaRGNTCP cells and PHHs with IFN had little effect on HBV replication or levels of cccDNA. HBV infection of these cells did not inhibit JAK-STAT signaling or up-regulation of IFN-stimulated genes. In coinfected cells, HBV did not prevent IFN-induced suppression of HCV replication.

CONCLUSIONS

In dHepaRGNTCP cells and PHHs, HBV evades the induction of IFN and IFN-induced antiviral effects. HBV infection does not rescue HCV from the IFN-mediated response.

The Heteroaryldihydropyrimidine Bay 38-7690 Induces Hepatitis B Virus Core Protein Aggregates Associated with Promyelocytic Leukemia Nuclear Bodies in Infected Cells

Heteroaryldihydropyrimidines (HAPs) are compounds that inhibit hepatitis B virus (HBV) replication by modulating viral capsid assembly. While their biophysical effects on capsid assembly in vitro have been previously studied, the effect of HAP treatment on capsid protein (Cp) in individual HBV-infected cells remains unknown. We report here that the HAP Bay 38-7690 promotes aggregation of recombinant Cp in vitro and causes a time- and dose-dependent decrease of Cp in infected cells, consistent with previously studied HAPs. Interestingly, immunofluorescence analysis showed Cp aggregating in nuclear foci of Bay 38-7690-treated infected cells in a time- and dose-dependent manner. We found these foci to be associated with promyelocytic leukemia (PML) nuclear bodies (NBs), which are structures that affect many cellular functions, including DNA damage response, transcription, apoptosis, and antiviral responses. Cp aggregation is not an artifact of the cell system used, as it is observed in HBV-expressing HepAD38 cells, in HepG2 cells transfected with an HBV-expressing plasmid, and in HepG2-NTCP cells infected with HBV. Use of a Cp overexpression vector without HBV sequences shows that aggregation is independent of viral replication, and use of an HBV-expressing plasmid harboring a HAP resistance mutation in Cp abrogated the aggregation, demonstrating that the effect is due to direct compound-Cp interactions. These studies provide novel insight into the effects of HAP-based treatment at a single-cell level.IMPORTANCE Despite the availability of effective vaccines and treatments, HBV remains a significant global health concern, with more than 240 million individuals chronically infected. Current treatments are highly effective at controlling viral replication and disease progression but rarely cure infections. Therefore, much emphasis is being placed on finding therapeutics with new drug targets, such as viral gene expression, covalently closed circular DNA formation and stability, capsid formation, and host immune modulators, with the ultimate goal of an HBV cure. Understanding the mechanisms by which novel antiviral agents act will be imperative for the development of curative HBV therapies.

Highly efficient and expedited hepatic differentiation from human pluripotent stem cells by pure small-molecule cocktails

Background

The advent of human-induced pluripotent stem cells holds great promise for producing ample individualized hepatocytes. Although previous efforts have succeeded in generating hepatocytes from human pluripotent stem cells in vitro by viral-based expression of transcription factors and/or addition of growth factors during the differentiation process, the safety issue of viral transduction and high cost of cytokines would hinder the downstream applications. Recently, the use of small molecules has emerged as a powerful tool to induce cell fate transition for their superior stability, safety, cell permeability, and cost-effectiveness.

Methods

In the present study, we established a novel efficient hepatocyte differentiation strategy of human pluripotent stem cells with pure small-molecule cocktails. This method induced hepatocyte differentiation in a stepwise manner, including definitive endoderm differentiation, hepatic specification, and hepatocyte maturation within only 13 days.

Results

The differentiated hepatic-like cells were morphologically similar to hepatocytes derived from growth factor-based methods and primary hepatocytes. These cells not only expressed specific hepatic markers at the transcriptional and protein levels, but also possessed main liver functions such as albumin production, glycogen storage, cytochrome P450 activity, and indocyanine green uptake and release.

Conclusions

Highly efficient and expedited hepatic differentiation from human pluripotent stem cells could be achieved by our present novel, pure, small-molecule cocktails strategy, which provides a cost-effective platform for in vitro studies of the molecular mechanisms of human liver development and holds significant potential for future clinical applications.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0794-4) contains supplementary material, which is available to authorized users.

Inhibition of pMAPK14 Overcomes Resistance to Sorafenib in Hepatoma Cells with Hepatitis B Virus

Hepatitis B virus (HBV) targets the liver and is a major driver for liver cancer. Clinical data suggest that HBV infection is associated with reduced response to treatment with the multi-kinase inhibitor sorafenib, the first available molecularly targeted anti-hepatocellular carcinoma (HCC) drug. Given that Raf is one of the major targets of sorafenib, we investigated the activation state of the Raf-Mek-Erk pathway in the presence of HBV and in response to sorafenib. Here we show that hepatoma cells with replicating HBV are less susceptible to sorafenib inhibitory effect as compared to cells in which HBV expression is suppressed. However, although HBV replication is associated with increased level of pErk, its blockade only modestly augments sorafenib effect. In contrast, the phosphorylated form of the pro-oncogenic Mitogen-Activated Protein Kinase 14 (pMAPK14), a protein kinase that was recently linked to sorafenib resistance, is induced in sorafenib-treated hepatoma cells in association with HBV X protein expression. Knocking down pMAPK14 results in augmentation of the therapeutic efficacy of sorafenib and largely alleviates resistance to sorafenib in the presence of HBV. Thus, this study suggests that HBV promotes HCC resistance to sorafenib. Combining pMAPK14 inhibitors with sorafenib may be beneficial in patients with HBV-associated HCC.

Improving Prediction of Metabolic Clearance Using Quantitative Extrapolation of Results Obtained From Human Hepatic Micropatterned Cocultures Model and by Considering the Impact of Albumin Binding

The objective was to compare, with the same data set, the predictive performance of 3 in vitro assays of hepatic clearance (CL), namely, micropatterned cocultures (also referring to HepatoPac^®) and suspension as well as monolayer hepatocytes to define which assay is the most accurate. Furthermore, existing in vitro-to-in vivo extrapolation (IVIVE) methods were challenged to verify which method is the most predictive (i.e., direct scaling method without binding correction, conventional method based either on the unbound fraction in plasma (fu_p) according to the free-drug hypothesis, or based on an fu_p value adjusted for the albumin [ALB]-facilitated hepatic uptake phenomenon). Accordingly, the role of ALB binding was specifically challenged, and consequently, the ALB production was monitored in parallel to the metabolic stability. The ALB concentration data were used to compare the in vitro assays and to adjust the value of fu_p of each drug to mimic the ALB-facilitated hepatic uptake phenomenon. The results confirmed that the direct and conventional IVIVE methods generally overpredicted and underpredicted the CL in vivo in humans, respectively. However, the underprediction of the conventional IVIVE method based on fu_p was significantly reduced from data generated with the HepatoPac^® system compared with the 2 other in vitro assays, which is possibly because that system is producing ALB at a rate much closer to the in vivo condition in liver. Hence, these observations suggest that the presence of more ALB molecules per hepatocyte in that HepatoPac^® system may have facilitated the hepatic uptake of several bound drugs because their intrinsic CL was increased instead of being decreased by the ALB binding effect. Accordingly, the IVIVE method based on the fu_p value adjusted for the ALB-facilitated uptake phenomenon gave the lowest prediction bias from the statistical analyses. This study indicated that the HepatoPac^® system combined with the adjusted value of fu_p was the most reliable IVIVE method and revealed the importance of quantifying the in vitro-to-in vivo variation of ALB concentration to improve the CL predictions, which would help any future physiologically based pharmacokinetics modeling exercise.

A Cell Culture Platform to Maintain Long-term Phenotype of Primary Human Hepatocytes and Endothelial Cells

BACKGROUND AND AIMS

Modeling interactions between primary human hepatocytes (PHHs) and primary human liver sinusoidal endothelial cells (LSECs) in vitro can help elucidate human-specific mechanisms underlying liver physiology/disease and drug responses; however, existing hepatocyte/endothelial coculture models are suboptimal because of their use of rodent cells, cancerous cell lines, and/or nonliver endothelial cells. Hence, we sought to develop a platform that could maintain the long-term phenotype of PHHs and primary human LSECs.

METHODS

Primary human LSECs or human umbilical vein endothelial cells as the nonliver control were cocultivated with micropatterned PHH colonies (to control homotypic interactions) followed by an assessment of PHH morphology and functions (albumin and urea secretion, and cytochrome P-450 2A6 and 3A4 enzyme activities) over 3 weeks. Endothelial phenotype was assessed via gene expression patterns and scanning electron microscopy to visualize fenestrations. Hepatic responses in PHH/endothelial cocultures were benchmarked against responses in previously developed PHH/3T3-J2 fibroblast cocultures. Finally, PHH/fibroblast/endothelial cell tricultures were created and characterized as described previously.

RESULTS

LSECs, but not human umbilical vein endothelial cells, induced PHH albumin secretion for ∼11 days; however, neither endothelial cell type could maintain PHH morphology and functions to the same magnitude/longevity as the fibroblasts. In contrast, both PHHs and endothelial cells displayed stable phenotype for 3 weeks in PHH/fibroblast/endothelial cell tricultures; furthermore, layered tricultures in which PHHs and endothelial cells were separated by a protein gel to mimic the space of Disse displayed similar functional levels as the coplanar tricultures.

CONCLUSIONS

PHH/fibroblast/endothelial tricultures constitute a robust platform to elucidate reciprocal interactions between PHHs and endothelial cells in physiology, disease, and after drug exposure.

Functional innate immunity restricts Hepatitis C Virus infection in induced pluripotent stem cell-derived hepatocytes

Knowledge of activation and interplay between the hepatitis C virus (HCV) and the hosts’ innate immunity is essential to understanding the establishment of chronic HCV infection. Human hepatoma cell lines, widely used as HCV cell culture system, display numerous metabolic alterations and a defective innate immunity, hindering the detailed study of virus-host interactions. Here, we analysed the suitability of induced pluripotent stem cell (iPSC)-derived hepatocyte-like cells (iHLCs) as a physiologically relevant model to study HCV replication in vitro. Density gradients and triglyceride analysis revealed that iHLCs secreted very-low density lipoprotein (VLDL)-like lipoproteins, providing a putative platform for bona fide lipoviroparticles. iHLCs supported the full HCV life cycle, but in contrast to Huh7 and Huh7.5 cells, replication and viral RNA levels decreased continuously. Following HCV infection, interferon-stimulated gene (ISG)-expression significantly increased in iHLCs, whereas induction was almost absent in Huh7/7.5 cells. However, IFNα-stimulation equally induced ISGs in iHLCs and hepatoma cells. JAK-STAT pathway inhibition increased HCV replication in mature iHLCs, but not in Huh7 cells. Additionally, HCV replication levels where higher in STAT2-, but not STAT1-knockdown iHLCs. Our findings support iHLCs as a suitable model for HCV-host interaction regarding a functional innate immunity and lipoprotein synthesis.

Bioengineered Liver Models for Drug Testing and Cell Differentiation Studies

In vitro models of the human liver are important for the following: (1) mitigating the risk of drug-induced liver injury to human beings, (2) modeling human liver diseases, (3) elucidating the role of single and combinatorial microenvironmental cues on liver cell function, and (4) enabling cell-based therapies in the clinic. Methods to isolate and culture primary human hepatocytes (PHHs), the gold standard for building human liver models, were developed several decades ago; however, PHHs show a precipitous decline in phenotypic functions in 2-dimensional extracellular matrix-coated conventional culture formats, which does not allow chronic treatment with drugs and other stimuli. The development of several engineering tools, such as cellular microarrays, protein micropatterning, microfluidics, biomaterial scaffolds, and bioprinting, now allow precise control over the cellular microenvironment for enhancing the function of both PHHs and induced pluripotent stem cell-derived human hepatocyte-like cells; long-term (4+ weeks) stabilization of hepatocellular function typically requires co-cultivation with liver-derived or non-liver-derived nonparenchymal cell types. In addition, the recent development of liver organoid culture systems can provide a strategy for the enhanced expansion of therapeutically relevant cell types. Here, we discuss advances in engineering approaches for constructing in vitro human liver models that have utility in drug screening and for determining microenvironmental determinants of liver cell differentiation/function. Design features and validation data of representative models are presented to highlight major trends followed by the discussion of pending issues that need to be addressed. Overall, bioengineered liver models have significantly advanced our understanding of liver function and injury, which will prove useful for drug development and ultimately cell-based therapies.

Recent advances in lineage differentiation from stem cells: hurdles and opportunities?

Pluripotent stem cells have the property of long-term self-renewal and the potential to give rise to descendants of the three germ layers and hence all mature cells in the human body. Therefore, they hold the promise of offering insight not only into human development but also for human disease modeling and regenerative medicine. However, the generation of mature differentiated cells that closely resemble their in vivo counterparts remains challenging. Recent advances in single-cell transcriptomics and computational modeling of gene regulatory networks are revealing a better understanding of lineage commitment and are driving modern genome editing approaches. Additional modification of the chemical microenvironment, as well as the use of bioengineering tools to recreate the cellular, extracellular matrix, and physical characteristics of the niche wherein progenitors and mature cells reside, is now being used to further improve the maturation and functionality of stem cell progeny.

Simultaneous Assessment of Clearance, Metabolism, Induction, and Drug-Drug Interaction Potential Using a Long-Term In Vitro Liver Model for a Novel Hepatitis B Virus Inhibitor

Long-term in vitro liver models are now widely explored for human hepatic metabolic clearance prediction, enzyme phenotyping, cross-species metabolism, comparison of low clearance drugs, and induction studies. Here, we present studies using a long-term liver model, which show how metabolism and active transport, drug-drug interactions, and enzyme induction in healthy and diseased states, such as hepatitis B virus (HBV) infection, may be assessed in a single test system to enable effective data integration for physiologically based pharmacokinetic (PBPK) modeling. The approach is exemplified in the case of (3S)-4-[[(4R)-4-(2-Chloro-4-fluorophenyl)-5-methoxycarbonyl-2-thiazol-2-yl-1,4-dihydropyrimidin-6-yl]methyl]morpholine-3-carboxylic acid RO6889678, a novel inhibitor of HBV with a complex absorption, distribution, metabolism, and excretion (ADME) profile. RO6889678 showed an intracellular enrichment of 78-fold in hepatocytes, with an apparent intrinsic clearance of 5.2 µl/min per mg protein and uptake and biliary clearances of 2.6 and 1.6 µl/min per mg protein, respectively. When apparent intrinsic clearance was incorporated into a PBPK model, the simulated oral human profiles were in good agreement with observed data at low doses but were underestimated at high doses due to unexpected overproportional increases in exposure with dose. In addition, the induction potential of RO6889678 on cytochrome P450 (P450) enzymes and transporters at steady state was assessed and cotreatment with ritonavir revealed a complex drug-drug interaction with concurrent P450 inhibition and moderate UDP-glucuronosyltransferase induction. Furthermore, we report on the first evaluation of in vitro pharmacokinetics studies using HBV-infected HepatoPac cocultures. Thus, long-term liver models have great potential as translational research tools exploring pharmacokinetics of novel drugs in vitro in health and disease.

3D microfluidic liver cultures as a physiological preclinical tool for hepatitis B virus infection

With more than 240 million people infected, hepatitis B virus (HBV) is a major health concern. The inability to mimic the complexity of the liver using cell lines and regular primary human hepatocyte (PHH) cultures pose significant limitations for studying host/pathogen interactions. Here, we describe a 3D microfluidic PHH system permissive to HBV infection, which can be maintained for at least 40 days. This system enables the recapitulation of all steps of the HBV life cycle, including the replication of patient-derived HBV and the maintenance of HBV cccDNA. We show that innate immune and cytokine responses following infection with HBV mimic those observed in HBV-infected patients, thus allowing the dissection of pathways important for immune evasion and validation of biomarkers. Additionally, we demonstrate that the co-culture of PHH with other non-parenchymal cells enables the identification of the cellular origin of immune effectors, thus providing a valuable preclinical platform for HBV research.

Pan-Genotype Hepatitis E Virus Replication in Stem Cell-Derived Hepatocellular Systems

BACKGROUND & AIMS

The 4 genotypes of hepatitis E virus (HEV) that infect humans (genotypes 1-4) vary in geographical distribution, transmission, and pathogenesis. Little is known about the properties of HEV or its hosts that contribute to these variations. Primary isolates grow poorly in cell culture; most studies have relied on variants adapted to cancer cell lines, which likely alter virus biology. We investigated the infection and replication of primary isolates of HEV in hepatocyte-like cells (HLCs) derived from human embryonic and induced pluripotent stem cells.

METHODS

Using a cell culture-adapted genotype 3 strain and primary isolates of genotypes 1 to 4, we compared viral replication kinetics, sensitivity to drugs, and ability of HEV to activate the innate immune response. We studied HLCs using quantitative reverse-transcriptase polymerase chain reaction and immunofluorescence assay and enzyme-linked immunosorbent assays. We used an embryonic stem cell line that can be induced to express the CRISPR-Cas9 machinery to disrupt the peptidylprolyl isomerase A gene, encoding cyclophilin A (CYPA), a protein reported to inhibit replication of cell culture-adapted HEV. We further modified this line to rescue expression of CYPA before terminal differentiation to HLCs and performed HEV infection studies.

RESULTS

HLCs were permissive for infection by nonadapted, primary isolates of HEV genotypes 1 to 4. HEV infection of HLCs induced a replication-dependent type III interferon response. Replication of primary HEV isolates, unlike the cell culture-adapted strain, was not affected by disruption of the peptidylprolyl isomerase A gene or exposure to the CYPA inhibitor cyclosporine A.

CONCLUSIONS

Cell culture adaptations alter the replicative capacities of HEV. HLCs offer an improved, physiologically relevant, and genetically tractable system for studying the replication of primary HEV isolates. HLCs could provide a model to aid development of HEV drugs and a system to guide personalized regimens, especially for patients with chronic hepatitis E who have developed resistance to ribavirin.

Hepatitis E virus: advances and challenges

At least 20 million hepatitis E virus (HEV) infections occur annually, with >3 million symptomatic cases and ∼60,000 fatalities. Hepatitis E is generally self-limiting, with a case fatality rate of 0.5-3% in young adults. However, it can cause up to 30% mortality in pregnant women in the third trimester and can become chronic in immunocompromised individuals, such as those receiving organ transplants or chemotherapy and individuals with HIV infection. HEV is transmitted primarily via the faecal-oral route and was previously thought to be a public health concern only in developing countries. It is now also being frequently reported in industrialized countries, where it is transmitted zoonotically or through organ transplantation or blood transfusions. Although a vaccine for HEV has been developed, it is only licensed in China. Additionally, no effective, non-teratogenic and specific treatments against HEV infections are currently available. Although progress has been made in characterizing HEV biology, the scarcity of adequate experimental platforms has hampered further research. In this Review, we focus on providing an update on the HEV life cycle. We will further discuss existing cell culture and animal models and highlight platforms that have proven to be useful and/or are emerging for studying other hepatotropic (viral) pathogens.

Interaction between Hepatitis B Virus and Toll-Like Receptors: Current Status and Potential Therapeutic Use for Chronic Hepatitis B

Immune defense against infection with the hepatitis B virus (HBV) is complex and involves both host innate and adaptive immune systems. It is well accepted that the development of sufficient HBV-specific T cell and B cell responses are required for controlling an HBV infection. However, the contribution of innate immunity to removing HBV has been explored in recent years. Toll-like receptors (TLRs) are recognized as the first line of antiviral immunity because they initiate intracellular signaling pathways to induce antiviral mediators such as interferons (IFNs) and other cytokines. Recent studies show that the activation of TLR-mediated signaling pathways results in a suppression of HBV replication in vitro and in vivo. However, HBV has also evolved strategies to counter TLR responses including the suppression of TLR expression and the blockage of downstream signaling pathways. Antiviral treatment in chronic HBV-infected patients leads to an upregulation of TLR expression and the restoration of its innate antiviral functions. Thus, TLR activation may serve as an additional immunotherapeutic option for treating chronic HBV infection in combination with antiviral treatment.

A polyelectrolyte multilayer platform for investigating growth factor delivery modes in human liver cultures

Polyelectrolyte multilayers (PEMs) of chitosan and heparin are useful for mimicking growth factor (GF) binding to extracellular matrix (ECM) as in vivo. Here, we developed a PEM platform for delivering bound/adsorbed GFs to monocultures of primary human hepatocytes (PHHs) and PHH/non-parenchymal cell (NPC) co-cultures, which are useful for drug development and regenerative medicine. The effects of ECM protein coating (collagen I, fibronectin, and Matrigel®) and terminal PEM layer on PHH attachment/functions were determined. Then, heparin-terminated/fibronectin-coated PEMs were used to deliver varying concentrations of an adsorbed model GF, transforming growth factor β (TGFβ), to PHH monocultures while using soluble TGFβ delivery via culture medium as the conventional control. Soluble TGFβ delivery caused a severe, monotonic, and sustained downregulation of all PHH functions measured (albumin and urea secretions, cytochrome-P450 2A6 and 3A4 enzyme activities), whereas adsorbed TGFβ delivery caused transient upregulation of 3 out of 4 functions. Finally, functionally stable co-cultures of PHHs and 3T3-J2 murine embryonic fibroblasts were created on the heparin-terminated/fibronectin-coated PEMs modified with adsorbed TGFβ to elucidate similarities and differences in functional response relative to the monocultures. In conclusion, chitosan-heparin PEMs constitute a robust platform for investigating the effects of GF delivery modes on PHH monocultures and PHH/NPC co-cultures. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 971-984, 2018.

Hepatitis B virus evades innate immunity of hepatocytes but activates cytokine production by macrophages

Hepatitis B virus (HBV) infects hepatocytes specifically and causes immune-mediated liver damage. How HBV interacts with the innate immunity at the early phase of infection, either with hepatocytes or other cells in the liver, remains controversial. To address this question, we utilized various human cell-culture models and humanized Alb-uPA/SCID mice. All these models were unable to mount an interferon (IFN) response despite robust HBV replication. To elucidate the mechanisms involved in the lack of IFN response, we examined whether HBV actively inhibits innate immune functions of hepatocytes. By treating HBV-infected cells with known inducers of the IFN signaling pathway, we observed no alteration of either sensing or downstream IFN response by HBV. We showed that the DNA innate sensing pathways are poorly active in hepatocytes, consistent with muted innate immune recognition of HBV. Upon exposure to high-level HBV, human macrophages could be activated with increased inflammatory cytokine expressions.

CONCLUSION

HBV behaves like a "stealth" virus and is not sensed by, nor actively interferes with, the intrinsic innate immunity of infected hepatocytes. Macrophages are capable of sensing HBV, but require exposure to high HBV titers, potentially explaining the long "window period" during acute infection and HBV's propensity to chronic infection. (Hepatology 2017;66:1779-1793).

A robust cell culture system supporting the complete life cycle of hepatitis B virus

The discovery of sodium taurocholate cotransporting polypeptide (NTCP) as the hepatitis B virus (HBV) receptor enabled researchers to create hepatoma cell lines susceptible to HBV infection. Infection in current systems, however, is inefficient and virus fails to spread. Infection efficiency is enhanced by treating cells with polyethylene glycol 8000 (PEG) during infection. However, this alone does not promote virus spread. Here we show that maintaining PEG in culture medium increases the rate of infection by at least one order of magnitude, and, most importantly, promotes virus spread. To demonstrate the utility of this system, we show that two interferon-stimulated genes (ISGs), ISG20 and tetherin, restrict HBV spread in NTCP-expressing hepatoma cells. Thus, this protocol can be easily applied to existing cell culture systems to study the complete HBV life cycle, including virus spread.

Engineered Livers for Infectious Diseases

Engineered liver systems come in a variety of platform models, from 2-dimensional cocultures of primary human hepatocytes and stem cell-derived progeny, to 3-dimensional organoids and humanized mice. Because of the species-specificity of many human hepatropic pathogens, these engineered systems have been essential tools for biologic discovery and therapeutic agent development in the context of liver-dependent infectious diseases. Although improvement of existing models is always beneficial, and the addition of a robust immune component is a particular need, at present, considerable progress has been made using this combination of research platforms. We highlight advances in the study of hepatitis B and C viruses and malaria-causing Plasmodium falciparum and Plasmodium vivax parasites, and underscore the importance of pairing the most appropriate model system and readout modality with the particular experimental question at hand, without always requiring a platform that recapitulates human physiology in its entirety.

Induced pluripotent stem cells: A new addition to the virologists armamentarium

A significant amount of our understanding of the molecular events occurring during viral replication has originated from studies utilizing cell lines. These cell lines are normally obtained by the culture of samples from spontaneously occurring tumors or are derived by genetic manipulation of primary cells. The genetic events inducing immortalization and/or transformation to allow continual passage in culture can have profound effects resulting in a marked loss of cell type fidelity. The development of induced pluripotent stem cells (iPSCs) has revolutionized the field of developmental biology and is ushering in an era of personalized medicine for a wide range of inherited genetic diseases. Previously, development of iPSCs required dedicated facilities as well as highly detailed technical knowledge. The pace of development in this field however has been so rapid, that iPSCs are moving into an era of "off the shelf" use, whereby the use and manipulation of these cells is well within the ability of the majority of laboratories with standard tissue culture facilities. The introduction of iPSCs to studies in the field of virology is still in its infancy, and so far has been largely confined to viruses that are difficult to propagate in other experimental systems, but it is likely that this technology will become a standard methodology in the virologists armamentarium.

Nicotinamide N-methyltransferase expression decreases in iron overload, exacerbating toxicity in mouse hepatocytes

Iron overload causes the generation of reactive oxygen species that can lead to lasting damage to the liver and other organs. The goal of this study was to identify genes that modify the toxicity of iron overload. We studied the effect of iron overload on the hepatic transcriptional and metabolomic profile in mouse models using a dietary model of iron overload and a genetic model, the hemojuvelin knockout mouse. We then evaluated the correlation of nicotinamide N-methyltransferase (NNMT) expression with body iron stores in human patients and the effect of NNMT knockdown on gene expression and viability in primary mouse hepatocytes. We found that iron overload induced significant changes in the expression of genes and metabolites involved in glucose and nicotinamide metabolism and that NNMT, an enzyme that methylates nicotinamide and regulates hepatic glucose and cholesterol metabolism, is one of the most strongly down-regulated genes in the liver in both genetic and dietary iron overload. We found that hepatic NNMT expression is inversely correlated with serum ferritin levels and serum transferrin saturation in patients who are obese, suggesting that body iron stores regulate human liver NNMT expression. Furthermore, we demonstrated that adenoviral knockdown of NNMT in primary mouse hepatocytes exacerbates iron-induced hepatocyte toxicity and increases expression of transcriptional markers of oxidative and endoplasmic reticulum stress, while overexpression of NNMT partially reversed these effects. Conclusion: Iron overload alters glucose and nicotinamide transcriptional and metabolic pathways in mouse hepatocytes and decreases NNMT expression, while NNMT deficiency worsens the toxic effect of iron overload. For these reasons, NNMT may be a drug target for the prevention of iron-induced hepatotoxicity. (Hepatology Communications 2017;1:803-815).

The IFN-λ-IFN-λR1-IL-10Rβ Complex Reveals Structural Features Underlying Type III IFN Functional Plasticity

Type III interferons (IFN-λs) signal through a heterodimeric receptor complex composed of the IFN-λR1 subunit, specific for IFN-λs, and interleukin-10Rβ (IL-10Rβ), which is shared by multiple cytokines in the IL-10 superfamily. Low affinity of IL-10Rβ for cytokines has impeded efforts aimed at crystallizing cytokine-receptor complexes. We used yeast surface display to engineer a higher-affinity IFN-λ variant, H11, which enabled crystallization of the ternary complex. The structure revealed that IL-10Rβ uses a network of tyrosine residues as hydrophobic anchor points to engage IL-10 family cytokines that present complementary hydrophobic binding patches, explaining its role as both a cross-reactive but cytokine-specific receptor. H11 elicited increased anti-proliferative and antiviral activities in vitro and in vivo. In contrast, engineered higher-affinity type I IFNs did not increase antiviral potency over wild-type type I IFNs. Our findings provide insight into cytokine recognition by the IL-10R family and highlight the plasticity of type III interferon signaling and its therapeutic potential.

Li-Fraumeni Syndrome Disease Model: A Platform to Develop Precision Cancer Therapy Targeting Oncogenic p53

Li-Fraumeni syndrome (LFS) is a rare hereditary autosomal dominant cancer disorder. Germline mutations in TP53, the gene encoding p53, are responsible for most cases of LFS. TP53 is also the most commonly mutated gene in human cancers. Because inhibition of mutant p53 is considered to be a promising therapeutic strategy to treat these diseases, LFS provides a perfect genetic model to study p53 mutation-associated malignancies as well as to screen potential compounds targeting oncogenic p53. In this review we briefly summarize the biology of LFS and current understanding of the oncogenic functions of mutant p53 in cancer development. We discuss the strengths and limitations of current LFS disease models, and touch on existing compounds targeting oncogenic p53 and in vitro clinical trials to develop new ones. Finally, we discuss how recently developed methodologies can be integrated into the LFS induced pluripotent stem cell (iPSC) platform to develop precision cancer therapy.

Long-term hepatitis B infection in a scalable hepatic co-culture system

Hepatitis B virus causes chronic infections in 250 million people worldwide. Chronic hepatitis B virus carriers are at risk of developing fibrosis, cirrhosis, and hepatocellular carcinoma. A prophylactic vaccine exists and currently available antivirals can suppress but rarely cure chronic infections. The study of hepatitis B virus and development of curative antivirals are hampered by a scarcity of models that mimic infection in a physiologically relevant, cellular context. Here, we show that cell-culture and patient-derived hepatitis B virus can establish persistent infection for over 30 days in a self-assembling, primary hepatocyte co-culture system. Importantly, infection can be established without antiviral immune suppression, and susceptibility is not donor dependent. The platform is scalable to microwell formats, and we provide proof-of-concept for its use in testing entry inhibitors and antiviral compounds.

The lack of models that mimic hepatitis B virus (HBV) infection in a physiologically relevant context has hampered drug development. Here, Winer et al. establish a self-assembling, primary hepatocyte co-culture system that can be infected with patient-derived HBV without further modifications.

Hepatitis Delta Virus: Replication Strategy and Upcoming Therapeutic Options for a Neglected Human Pathogen

The human Hepatitis Delta Virus (HDV) is unique among all viral pathogens. Encoding only one protein (Hepatitis Delta Antigen; HDAg) within its viroid-like self-complementary RNA, HDV constitutes the smallest known virus in the animal kingdom. To disseminate in its host, HDV depends on a helper virus, the human Hepatitis B virus (HBV), which provides the envelope proteins required for HDV assembly. HDV affects an estimated 15-20 million out of the 240 million chronic HBV-carriers and disperses unequally in disparate geographical regions of the world. The disease it causes (chronic Hepatitis D) presents as the most severe form of viral hepatitis, leading to accelerated progression of liver dysfunction including cirrhosis and hepatocellular carcinoma and a high mortality rate. The lack of approved drugs interfering with specific steps of HDV replication poses a high burden for gaining insights into the molecular biology of the virus and, consequently, the development of specific novel medications that resiliently control HDV replication or, in the best case, functionally cure HDV infection or HBV/HDV co-infection. This review summarizes our current knowledge of HBV molecular biology, presents an update on novel cell culture and animal models to study the virus and provides updates on the clinical development of the three developmental drugs Lonafarnib, REP2139-Ca and Myrcludex B.

Daunting but Worthy Goal: Reducing the De Novo Cancer Incidence After Transplantation

Solid-organ transplant recipients are at increased risk of developing de novo malignancies compared with the general population, and malignancies become a major limitation in achieving optimal outcomes. The prevention and the management of posttransplant malignancies must be considered as a main goal in our transplant programs. For these patients, immunosuppression plays a major role in oncogenesis by both impairement of immunosurveillance, enhancement of chronic viral infection, and by direct prooncogenic effects. It is essential to manage the recipient with a long-term adapted screening program beginning before transplantation to use a prophylaxis to decrease infection-related cancer, to propose a viral monitoring, and to modulate the immunosuppression toward lower doses especially for calcineurin inhibitors. Indeed, strategies to induce tolerance or to allow a dramatic reduction of the immunosuppression burden are the more promising approaches for the reduction of the posttransplant malignancies.

Induced Pluripotent Stem Cells: Global Research Trends

The induced pluripotent stem cell (iPSC) was first described more than 10 years ago and is currently used in various basic science and clinical research fields. The aim of this report is to examine the trends in research using iPSCs over the last 10 years. The 2006-2016 PubMed database was searched using the MeSH term "induced pluripotent stem cells." Only original research articles were selected, with a total of 3323 articles. These were classified according to research theme into reprogramming, differentiation protocols for specific cells and/or tissues, pathophysiological research on diseases, and discovery of new drugs, and then the trends over the years were analyzed. We also focused on 232 research publications on the pathophysiological causes of diseases and drug discovery with impact factor (IF; Thomson Reuters) of six or more. The IF of each article was summed up by year, by main target disease, and by country, and the total IF score was expressed as trends of research. The trends of research activities of reprogramming and differentiation on specific cells and/or tissues reached maxima in 2013/2014. On the other hand, research on pathophysiology and drug discovery increased continuously. The 232 articles with IF ≥6 dealt with neurological, immunological/hematological, cardiovascular, and digestive tract diseases, in that order. The majority of articles were published from the United States, followed by Japan, Germany, and United Kingdom. In conclusion, iPSCs have become a general tool for pathophysiological research on disease and drug discovery.

A Role for the Host DNA Damage Response in Hepatitis B Virus cccDNA Formation-and Beyond?

Chronic hepatitis B virus (HBV) infection puts more than 250 million people at a greatly increased risk to develop end-stage liver disease. Like all hepadnaviruses, HBV replicates via protein-primed reverse transcription of a pregenomic (pg) RNA, yielding an unusually structured, viral polymerase-linked relaxed-circular (RC) DNA as genome in infectious particles. Upon infection, RC-DNA is converted into nuclear covalently closed circular (ccc) DNA. Associating with cellular proteins into an episomal minichromosome, cccDNA acts as template for new viral RNAs, ensuring formation of progeny virions. Hence, cccDNA represents the viral persistence reservoir that is not directly targeted by current anti-HBV therapeutics. Eliminating cccDNA will thus be at the heart of a cure for chronic hepatitis B. The low production of HBV cccDNA in most experimental models and the associated problems in reliable cccDNA quantitation have long hampered a deeper understanding of cccDNA molecular biology. Recent advancements including cccDNA-dependent cell culture systems have begun to identify select host DNA repair enzymes that HBV usurps for RC-DNA to cccDNA conversion. While this list is bound to grow, it may represent just one facet of a broader interaction with the cellular DNA damage response (DDR), a network of pathways that sense and repair aberrant DNA structures and in the process profoundly affect the cell cycle, up to inducing cell death if repair fails. Given the divergent interactions between other viruses and the DDR it will be intriguing to see how HBV copes with this multipronged host system.

Markov modeling in hepatitis B screening and linkage to care

Background

With up to 240 million people chronically infected with hepatitis B worldwide, including an estimated 2 million in the United States, widespread screening is needed to link the infected to care and decrease the possible consequences of untreated infection, including liver cancer, cirrhosis and death. Screening is currently fraught with challenges in both the developed and developing world. New point-of-care tests may have advantages over standard-of-care tests in terms of cost-effectiveness and linkage to care. Stochastic modeling is applied here for relative utility assessment of point-of-care tests and standard-of-care tests for screening.

Methods

We analyzed effects of point-of-care versus standard-of-care testing using Markov models for disease progression in individual patients. Simulations of large cohorts with distinctly quantified models permitted the assessment of particular screening schemes. The validity of the trends observed is supported by sensitivity analyses for the simulation parameters.

Results

Increased utilization of point-of-care screening was shown to decrease hepatitis B-related mortalities and increase life expectancy at low projected expense.

Conclusions

The results suggest that standard-of-care screening should be substituted by point-of-care tests resulting in improved linkage to care and decrease in long-term complications.

Micropatterned Co-Cultures of Human Hepatocytes and Stromal Cells for the Assessment of Drug Clearance and Drug-Drug Interactions

Drug clearance rates from the body can determine drug exposure that can affect efficacy or toxicity. Thus, accurate prediction of drug clearance during preclinical development can help guide dose selection in humans, but animal testing is not always predictive of human outcomes. Because hepatic drug metabolism is a rate-limiting step in the overall clearance of many drugs, primary human hepatocytes (PHHs) in suspension cultures or monolayers are used for drug clearance predictions. Yet, the precipitous decline in drug metabolism capacity can lead to significant underestimation of clearance rates, particularly for low turnover compounds that have desirable one-pill-a-day dosing regimens. In contrast, micropatterned co-cultures (MPCCs) of PHHs and fibroblasts display phenotypic stability for several weeks and can help mitigate the limitations of conventional cultures. Here, we describe protocols to create and use MPCCs for drug clearance predictions, and for modeling clinically-relevant drug-drug interactions that can affect drug clearance. © 2017 by John Wiley & Sons, Inc.

Interplay between the Hepatitis B Virus and Innate Immunity: From an Understanding to the Development of Therapeutic Concepts

The hepatitis B virus (HBV) infects hepatocytes, which are the main cell type composing a human liver. However, the liver is enriched with immune cells, particularly innate cells (e.g., myeloid cells, natural killer and natural killer T-cells (NK/NKT), dendritic cells (DCs)), in resting condition. Hence, the study of the interaction between HBV and innate immune cells is instrumental to: (1) better understand the conditions of establishment and maintenance of HBV infections in this secondary lymphoid organ; (2) define the role of these innate immune cells in treatment failure and pathogenesis; and (3) design novel immune-therapeutic concepts based on the activation/restoration of innate cell functions and/or innate effectors. This review will summarize and discuss the current knowledge we have on this interplay between HBV and liver innate immunity.

Human induced-pluripotent stem cell-derived hepatocyte-like cells as an in vitro model of human hepatitis B virus infection

In order to understand the life cycle of hepatitis B virus (HBV) and to develop efficient anti-HBV drugs, a useful in vitro cell culture system which allows HBV infection and recapitulates virus-host interactions is essential; however, pre-existing in vitro HBV infection models are often problematic. Here, we examined the potential of human induced-pluripotent stem (iPS) cell-derived hepatocyte-like cells (iPS-HLCs) as an in vitro HBV infection model. Expression levels of several genes involved in HBV infection, including the sodium taurocholate cotransporting polypeptide (NTCP) gene, were gradually elevated as the differentiation status of human iPS cells proceeded to iPS-HLCs. The mRNA levels of these genes were comparable between primary human hepatocytes (PHHs) and iPS-HLCs. Following inoculation with HBV, we found significant production of HBV proteins and viral RNAs in iPS-HLCs. The three major forms of the HBV genome were detected in iPS-HLCs by Southern blotting analysis. Anti-HBV agents entecavir and Myrcludex-B, which are a nucleoside analogue reverse transcriptase inhibitor and a synthetic pre-S1 peptide, respectively, significantly inhibited HBV infection in iPS-HLCs. These data demonstrate that iPS-HLCs can be used as a promising in vitro HBV infection model.

Intestinal organoid as an in vitro model in studying host-microbial interactions

Background

Organoid is an in vitro three-dimensional organ-bud that shows realistic microanatomy and physiologic relevance. The progress in generating organoids that faithfully recapitulate human in vivo tissue composition has extended organoid applications from being just a basic research tool to a translational platform with a wide range of uses. Study of host-microbial interactions relies on model systems to mimic the in vivo infection. Researchers have developed various experimental models in vitro and in vivo to examine the dynamic host-microbial interactions. For some infectious pathogens, model systems are lacking whereas some of the used systems are far from optimal.

Objective

In the present work, we will review the brief history and recent findings using organoids for studying host-microbial interactions.

Methods

A systematic literature search was performed using the PubMed search engine. We also shared our data and research contribution to the field.

Results

we summarize the brief history of 3D organoids. We discuss the feasibility of using organoids in studying host-microbial interactions, focusing on the development of intestinal organoids and gastric organoids. We highlight the advantage and challenges of the new experimental models. Further, we discuss the future direction in using organoids in studying host-microbial interactions and its potential application in biomedical studies.

Conclusion

In combination with genetic, transcriptome and proteomic profiling, both murine- and human-derived organoids have revealed crucial aspects of development, homeostasis and diseases. Specifically, human organoids from susceptible host will be used to test their responses to pathogens, probiotics, and drugs. Organoid system is an exciting tool for studying infectious disease, microbiome, and therapy.

Human stem cell-derived hepatocytes as a model for hepatitis B virus infection, spreading and virus-host interactions

BACKGROUND & AIMS

One major obstacle of hepatitis B virus (HBV) research is the lack of efficient cell culture system permissive for viral infection and replication. The aim of our study was to establish a robust HBV infection model by using hepatocyte-like cells (HLCs) derived from human pluripotent stem cells.

METHODS

HLCs were differentiated from human embryonic stem cells and induced pluripotent stem cells. Maturation of hepatocyte functions was determined. After HBV infection, total viral DNA, cccDNA, total viral RNA, pgRNA, HBeAg and HBsAg were measured.

RESULTS

More than 90% of the HLCs expressed strong signals of human hepatocyte markers, like albumin, as well as known host factors required for HBV infection, suggesting that these cells possessed key features of mature hepatocytes. Notably, HLCs expressed the viral receptor sodium-taurocholate cotransporting polypeptide more stably than primary human hepatocytes (PHHs). HLCs supported robust infection and some spreading of HBV. Finally, by using this model, we identified two host-targeting agents, genistin and PA452, as novel antivirals.

CONCLUSIONS

Stem cell-derived HLCs fully support HBV infection. This novel HLC HBV infection model offers a unique opportunity to advance our understanding of the molecular details of the HBV life cycle; to further characterize virus-host interactions and to define new targets for HBV curative treatment.

LAY SUMMARY

Our study used human pluripotent stem cells to develop hepatocyte-like cells (HLCs) capable of expressing hepatocyte markers and host factors important for HBV infection. These cells fully support HBV infection and virus-host interactions, allowing for the identification of two novel antiviral agents. Thus, stem cell-derived HLCs provide a highly physiologically relevant system to advance our understanding of viral life cycle and provide a new tool for antiviral drug screening and development.

Effects of amino acid substitutions in hepatitis B virus surface protein on virion secretion, antigenicity, HBsAg and viral DNA

BACKGROUND & AIMS

As important virological markers, serum hepatitis B surface antigen (HBsAg) and hepatitis B virus (HBV) DNA levels show large fluctuations among chronic hepatitis B patients. The aim of this study was to reveal the potential impact and mechanisms of amino acid substitutions in small hepatitis B surface proteins (SHBs) on serum HBsAg and HBV DNA levels.

METHODS

Serum samples from 230 untreated chronic hepatitis B patients with genotype C HBV were analyzed in terms of HBV DNA levels, serological markers of HBV infection and SHBs sequences. In vitro functional analysis of the identified SHBs mutants was performed.

RESULTS

Among 230 SHBs sequences, there were 39 (16.96%) sequences with no mutation detected (wild-type) and 191 (83.04%) with single or multiple mutations. SHBs consist of 226 amino acids, of which 104 (46.02%) had mutations in our study. Some mutations (e.g., sE2G, sL21S, sR24K, sT47A/K, sC69stop (sC69∗), sL95W, sL98V, and sG145R) negatively correlated with serum HBsAg levels. HBsAg and HBV DNA levels from this group of patients had a positive correlation (r=0.61, p<0.001). In vitro analysis showed that these mutations reduced extracellular HBsAg and HBV DNA levels by restricting virion secretion and antibody binding capacity. Virion secretion could be rescued for sE2G, sC69∗, and sG145R by co-expression of wild-type HBsAg.

CONCLUSION

The serum HBsAg levels were lower in untreated CHB patients with novel SHBs mutations outside the major antigenic region than those without mutations. Underlying mechanisms include impairment of virion secretion and lower binding affinity to antibodies used for HBsAg measurements.

LAY SUMMARY

The hepatitis B surface antigen (HBsAg) is a major viral protein of the hepatitis B virus (HBV) secreted into patient blood serum and its quantification value serves as an important marker for the evaluation of chronic HBV infection and antiviral response. We found a few new amino acid substitutions in HBsAg associated with lower serum HBsAg and HBV DNA levels. These different substitutions might impair virion secretion, change the ability of HBsAg to bind to antibodies, or impact HBV replication. These could all result in decreased detectable levels of serum HBsAg. The factors affecting circulating HBsAg level and HBsAg detection are varied and caution is needed when interpreting clinical significance of serum HBsAg levels. Clinical trial number: NCT01088009.

The Smc5/6 Complex Restricts HBV when Localized to ND10 without Inducing an Innate Immune Response and Is Counteracted by the HBV X Protein Shortly after Infection

The structural maintenance of chromosome 5/6 complex (Smc5/6) is a restriction factor that represses hepatitis B virus (HBV) transcription. HBV counters this restriction by expressing HBV X protein (HBx), which targets Smc5/6 for degradation. However, the mechanism by which Smc5/6 suppresses HBV transcription and how HBx is initially expressed is not known. In this study we characterized viral kinetics and the host response during HBV infection of primary human hepatocytes (PHH) to address these unresolved questions. We determined that Smc5/6 localizes with Nuclear Domain 10 (ND10) in PHH. Co-localization has functional implications since depletion of ND10 structural components alters the nuclear distribution of Smc6 and induces HBV gene expression in the absence of HBx. We also found that HBV infection and replication does not induce a prominent global host transcriptional response in PHH, either shortly after infection when Smc5/6 is present, or at later times post-infection when Smc5/6 has been degraded. Notably, HBV and an HBx-negative virus establish high level infection in PHH without inducing expression of interferon-stimulated genes or production of interferons or other cytokines. Our study also revealed that Smc5/6 is degraded in the majority of infected PHH by the time cccDNA transcription could be detected and that HBx RNA is present in cell culture-derived virus preparations as well as HBV patient plasma. Collectively, these data indicate that Smc5/6 is an intrinsic antiviral restriction factor that suppresses HBV transcription when localized to ND10 without inducing a detectable innate immune response. Our data also suggest that HBx protein may be initially expressed by delivery of extracellular HBx RNA into HBV-infected cells.

Expression of Interferon Effector Gene SART1 Correlates with Interferon Treatment Response against Hepatitis B Infection

Interferon-α (IFN-α) has limited response rate in the treatment of chronic hepatitis B (CHB). The underlying mechanism of differential responsiveness to IFN remains elusive. It has been recently reported that SART1 mediates antiviral effects of IFN-α in the hepatitis C virus (HCV) cell culture model. In this study, we investigated the role of SART1 in antiviral activity of IFN-α against hepatitis B virus (HBV) using blood and liver biopsy samples from chronic hepatitis B patients treated with pegylated IFN-α and HepG2 cells transfected with cloned HBV DNA. We observed that the basal SART1 expression in liver and PBMCs before IFN treatment was significantly higher in responders than in nonresponders. Furthermore, baseline SART1 expression level positively correlated with the degree of HBV DNA and HBeAg decline after IFN treatment. Mechanistically, silencing SART1 abrogated the antiviral activity of IFN-α, reduced the expression of IFN-stimulated genes (ISGs) Mx, OAS, and PKR, and attenuated JAK-STAT signaling in HepG2 cells, suggesting that SART1 regulates IFN-mediated antiviral activity through JAK-STAT signaling and ISG expression. Our study elucidates the important role of SART1 in IFN-mediated anti-HBV response and provides new insights into understanding variation of IFN treatment response in CHB patients.

Hepatitis B immunopathogenesis and immunotherapy

Worldwide there are over 248 million chronic carriers of HBV of whom about a third eventually develop severe HBV-related complications. Due to the major limitations of current therapeutic approaches, the development of more effective strategies to improve therapeutic outcomes in chronic hepatitis B (CHB) patients seems crucial. Immune activation plays a critical role in spontaneous viral control; therefore, new modalities based on stimulation of the innate and adaptive immune responses could result in the resolution of infection and are promising approaches. Here, we summarize the HBV immunopathogenesis, and discuss the encouraging results obtained from the promising immune-based innovations, such as therapeutic vaccination, cytokine therapy, cell-based therapies and blocking inhibitory receptors, as current and future immunotherapeutic interventions.

Clinical Trials in a Dish

Clinical trials 'in a dish' involve testing medical therapies for safety or effectiveness in the laboratory with human tissue. This has become possible owing to recent biotechnology advances including induced pluripotent stem cells, organs-on-a-chip, and whole-genome sequencing. We provide here an overview of the landscape and highlight steps the FDA is taking to advance the science of clinical trials in a dish and to support the development and validation of new regulatory paradigms to assess drug safety using these new technologies.

Activating the innate immune response to counter chronic hepatitis B virus infection

INTRODUCTION

Chronic infection with hepatitis B virus (HBV) is endemic to several populous parts of the world, where resulting complicating cirrhosis and hepatocellular carcinoma occur commonly. Licensed drugs to treat the infection have limited curative efficacy, and development of therapies that eliminate all replication intermediates of HBV is a priority. Areas covered: The recent demonstration that the activation of the innate immune response may eradicate HBV from infected hepatocytes has a promising therapeutic application. Small molecule stimulators of Toll-like receptors (TLRs) inhibit replication of woodchuck hepatitis virus in woodchucks and HBV in chimpanzees and mice. Early stage clinical trials using GS-9620, a TLR7 agonist, indicate that this candidate antiviral is well tolerated in humans. Using an alternative approach, triggering the innate immune response with agonists of lymphotoxin-β receptor caused efficient APOBEC-mediated deamination and degradation of viral covalently closed circular DNA. Expert opinion: Eliminating HBV cccDNA from infected individuals would constitute a cure, and has become the focus of intensive research that employs various therapeutic approaches, including gene therapy. Immunomodulation through innate immune activation shows promise for the treatment of chronic infection of HBV (CHB) and, used in combination with other therapeutics, may contribute to the global control of infections and ultimately to the eradication of HBV.

Cell Culture Models for the Investigation of Hepatitis B and D Virus Infection

Chronic hepatitis B virus (HBV) and hepatitis D virus (HDV) infections are major causes of liver disease and hepatocellular carcinoma worldwide. Despite the presence of an efficient preventive vaccine, more than 250 million patients are chronically infected with HBV. Current antivirals effectively control but only rarely cure chronic infection. While the molecular biology of the two viruses has been characterized in great detail, the absence of robust cell culture models for HBV and/or HDV infection has limited the investigation of virus-host interactions. Native hepatoma cell lines do not allow viral infection, and the culture of primary hepatocytes, the natural host cell for the viruses, implies a series of constraints restricting the possibilities of analyzing virus-host interactions. Recently, the discovery of the sodium taurocholate co-transporting polypeptide (NTCP) as a key HBV/HDV cell entry factor has opened the door to a new era of investigation, as NTCP-overexpressing hepatoma cells acquire susceptibility to HBV and HDV infections. In this review, we summarize the major cell culture models for HBV and HDV infection, discuss their advantages and limitations and highlight perspectives for future developments.

Chronic hepatitis B: immune pathogenesis and emerging immunotherapeutics

Hepatitis B virus (HBV) evades, subverts, activates and regulates host immune components, thereby impacting its natural history and disease pathogenesis. Recent advances in our understanding of immune interactions in chronic viral infection and tumor therapy are applicable to chronic hepatitis B (CHB). With recent successes of tumor immunotherapy, there is a renewed interest in exploring immunotherapeutics in achieving sustained and functional cure of chronic hepatitis B. In this review, we discuss aspects of host innate and adaptive immune regulatory and pathogenic responses relevant for HBV infection. We also highlight several immune modulatory approaches in clinical development to treat CHB.

Engineered Liver Platforms for Different Phases of Drug Development

Drug-induced liver injury (DILI) remains a leading cause of drug withdrawal from human clinical trials or the marketplace. Owing to species-specific differences in liver pathways, predicting human-relevant DILI using in vitro human liver models is crucial. Microfabrication tools allow precise control over the cellular microenvironment towards stabilizing liver functions for weeks. These tools are used to engineer human liver models with different complexities and throughput using cell lines, primary cells, and stem cell-derived hepatocytes. Including multiple human liver cell types can mimic cell-cell interactions in specific types of DILI. Finally, organ-on-a-chip models demonstrate how drug metabolism in the liver affects multi-organ toxicities. In this review we survey engineered human liver platforms within the needs of different phases of drug development.

Cell sources for in vitro human liver cell culture models

In vitro liver cell culture models are gaining increasing importance in pharmacological and toxicological research. The source of cells used is critical for the relevance and the predictive value of such models. Primary human hepatocytes (PHH) are currently considered to be the gold standard for hepatic in vitro culture models, since they directly reflect the specific metabolism and functionality of the human liver; however, the scarcity and difficult logistics of PHH have driven researchers to explore alternative cell sources, including liver cell lines and pluripotent stem cells. Liver cell lines generated from hepatomas or by genetic manipulation are widely used due to their good availability, but they are generally altered in certain metabolic functions. For the past few years, adult and pluripotent stem cells have been attracting increasing attention, due their ability to proliferate and to differentiate into hepatocyte-like cells in vitro However, controlling the differentiation of these cells is still a challenge. This review gives an overview of the major human cell sources under investigation for in vitro liver cell culture models, including primary human liver cells, liver cell lines, and stem cells. The promises and challenges of different cell types are discussed with a focus on the complex 2D and 3D culture approaches under investigation for improving liver cell functionality in vitro Finally, the specific application options of individual cell sources in pharmacological research or disease modeling are described.