The major obstacle of basic and antiviral research in hepatitis B virus (HBV) infection is the lack of readily accessible, physiological cell culture systems permissive for viral infection and replication. Here we describe a highly physiological HBV infection model by using human hepatocyte-like cells (HLCs) derived from embryonic stem cells or induced pluripotent stem cells. Differentiated HLCs present key features of mature hepatocytes. Notably, the expression of viral receptor sodium-taurocholate cotransporting polypeptide (NTCP) is more stable in HLCs than in primary human hepatocytes (PHHs). HLCs support a robust and productive HBV infection that can be manipulated either by siRNA down-regulation of certain host factors involved in HBV replication or antiviral treatment. Unlike other in vitro models, HLCs support HBV spreading. By using this model, we identified two host-targeting agents, Genistin and PA452, as novel antivirals against HBV infection. HLC is a superior model for antiviral testing than NTCP over-expressing hepatoma cell lines. Genistin shows antiviral activities only in HLCs and PHHs but not in HepG2-NTCP or Huh7-NTCP cells. This novel HBV infection HLCs model offers a unique opportunity to advance our understanding of molecular details of the HBV life cycle, to further characterize virus-host interactions and to define new targets for HBV curative treatment. While the innate immune responses are generally the first line of defense against invading pathogens, it is controversial whether HBV replicates without activating the innate immunity or actively inhibits the innate pathways in the hepatocytes. To address this question, we used various hepatocyte culture models including hepatoma cell lines expressing viral receptor-NTCP, stem cell-derived hepatocytes and primary human hepatocytes. Using either transfection of HBV genome-containing plasmids or infection by infectious cell culture-generated HBV or patient-derived virus in human hepatoma cell lines and primary or stem cell-derived human hepatocytes, we have established various cell culture models of HBV infection and replication. Despite a robust HBV replication, no interferons (IFNs) or IFN-stimulated genes were induced. Using primary human hepatocyte engrafted SCID mice, HBV infection was established in vivo. At the peak of viremia, no induction of human IFN could be detected in the liver. These observations indicated a lack of innate immunity in terms of interferon response in HBV infected hepatocytes. To study if HBV actively inhibits innate immune sensing, poly IC and Sendai virus, known to be a potent inducer of interferon response, were tested in hepatocyte culture that were infected with HBV. Both type I and III IFNs as well as IFN-stimulated genes were strongly induced by the poly IC or Sendai virus. But concurrent HBV infection did not affect the magnitude nor breadth of this response. Confocal microscopy at single cell level further confirmed that HBV infected hepatocytes exhibited strong nuclear IRF3 and STAT1 expression after Sendai virus infection, similar to that of non-infected cells. Since HCV is known to induce a robust interferon response in infected hepatocytes, we also examined the interferon response in the HBV/ HCV co-infection setting. We co-infected HBV and HCV in primary human hepatocytes and studied their replication and the interferon response. We observed that HBV did not alter HCV replication nor down-regulate the well-known induction of interferon response by HCV, as compared to the HCV mono-infection. This finding supports the notion that HBV does not actively interfere with the innate sensing mechanism of the hepatocytes. Taken together, our results indicate that HBV behaves like a stealth virus and is not sensed by the innate immunity of the infected hepatocytes, potentially explaining the propensity of HBV to chronic infection.
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