Review
The Role of cccDNA in HBV Maintenance
Lena Allweiss 1 and Maura Dandri 1,2,*
1
I. Department of Internal Medicine, Center for Internal Medicine, University Medical Center Hamburg-Eppendorf, Martinistr. 52, D-20246 Hamburg, Germany
2
German Center for Infection Research (DZIF), Hamburg-Lübeck-Borstel Site, Germany
Academic Editors: Ulrike Protzer and Michael Nassal
Received: 4 May 2017 / Accepted: 19 June 2017 / Published: 21 June 2017
Abstract: Chronic hepatitis B virus (HBV) infection continues to be a major health burden worldwide; it can cause various degrees of liver damage and is strongly associated with the development of liver cirrhosis and hepatocellular carcinoma. The molecular mechanisms determining HBV persistence are not fully understood, but these appear to be multifactorial and the unique replication strategy employed by HBV enables its maintenance in infected hepatocytes. Both the stability of the HBV genome, which forms a stable minichromosome, the covalently closed circular DNA (cccDNA) in the hepatocyte nucleus, and the inability of the immune system to resolve chronic HBV infection are believed to be key mechanisms of HBV chronicity. Since a true cure of HBV requires clearance of intranuclear cccDNA from infected hepatocytes, understanding the mechanisms involved in cccDNA biogenesis, regulation and stability is mandatory to achieve HBV eradication. This review will summarize the state of knowledge on these mechanisms including the impact of current treatments on the cccDNA stability and activity. We will focus on events challenging cccDNA persistence in dividing hepatocytes.
Keywords:
hepatitis B virus; cccDNA; animal models; human liver chimeric mice; cell proliferation
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Such findings point out the important role that immune modulating factors play in reducing cccDNA loads and activity. We speculate that both direct killing of infected cells and compensatory proliferation of HBV-infected hepatocytes play a key synergistic role in the process of resolving acute hepatitis. This process might have also been functional in chronically HBV infected patients, which were reported to achieve more beneficial treatment outcomes when the stopping of long-term NA therapy was accompanied with a transitory hepatic flare [50,51,80].
6. Conclusions
In sum, even if elimination of the cccDNA from the infected liver remains challenging and more research is needed to develop therapeutic approaches boosting HBV-specific immune responses or agents directly targeting the cccDNA, cell division appears to be a natural Achilles’ heel in HBV persistence. At the same time, key factors produced by immune cells, like IFNs and tumor necrosis factor α, can further promote non-cytolytic inhibition of HBV replication and contribute to cccDNA destabilization [56]. The fact that even after a resolved acute infection low amounts of cccDNA molecules are detected in the liver of patients [81], raises hope that not the entire intrahepatic cccDNA reservoir needs to be eliminated to gain immunological control and resolve the infection. We hypothesize that if a sufficient amount of HBV-infected cells will be eliminated and even more cccDNA will be degraded through compensatory proliferation and non-cytolytic immune factors, the immune system should be able to resolve chronic HBV infection." 作者: StephenW 时间: 2017-6-24 16:07