Current antiviral agents can control but not eliminate hepatitis B virus (HBV), because HBV establishes a stable nuclear covalently closed circular DNA (cccDNA). Interferon-α treatment can clear HBV but is limited by systemic side effects. We describe how interferon-α can induce specific degradation of the nuclear viral DNA without hepatotoxicity and propose lymphotoxin-β receptor activation as a therapeutic alternative. Interferon-α and lymphotoxin-β receptor activation up-regulated APOBEC3A and APOBEC3B cytidine deaminases, respectively, in HBV-infected cells, primary hepatocytes, and human liver needle biopsies. HBV core protein mediated the interaction with nuclear cccDNA, resulting in cytidine deamination, apurinic/apyrimidinic site formation, and finally cccDNA degradation that prevented HBV reactivation. Genomic DNA was not affected. Thus, inducing nuclear deaminases-for example, by lymphotoxin-β receptor activation-allows the development of new therapeutics that, in combination with existing antivirals, may cure hepatitis B.

HBV infection remains a leading cause of death worldwide. IFN-α inhibits viral replication in vitro and IntroductionHepatitis B Virus (HBV) infection remains a major health problem worldwide despite the availability of a highly effective preventive vaccine. HBV is a noncytopathic hepatotropic DNA virus that belongs to the family Hepadnaviridae, whose members share a distinctive strategy for replication. HBV replication occurs in the cytoplasm within viral capsids (core particles), where a genomesized RNA replicative intermediate, termed the pregenome (pgRNA), is converted by the virally encoded RNA-dependent and DNA-dependent reverse transcriptase/polymerase into a specific open circular (OC) duplex DNA (1). Transcription in the nucleus of the pgRNA from the covalently closed circular DNA (cccDNA) is the critical step for genome amplification and ultimately determines the rate of HBV replication (2). The cccDNA, which also serves as the template for the transcription of all viral messenger RNAs, is organized into a minichromosome in the nuclei of infected hepatocytes by histone and nonhistone proteins, and its function is regulated, similarly to cellular chromatin, by the activity of nuclear transcription factors, transcriptional coactivators and corepressors, and chromatin-modifying enzymes (2-4).Current antiviral therapies involve the use of nucleoside analogs and pegylated IFN-α (5). IFN-α, a type I IFN, engages the IFN-α/β receptor complex to activate the intracellular Jak/Stat signaling pathway, which modulates the transcription of a diverse set of target genes, referred to as IFN-stimulated genes (ISGs) (6). ISG

I nfection with hepatitis B virus (HBV) causes acute and chronic hepatitis and is strongly associated with the development of cirrhosis and hepatocellular carcinoma. Immediately after infection of hepatocytes, the viral DNA is transferred to the nucleus, where the viral polymerase is removed, and the double-stranded, open circular DNA is converted to a covalently closed circular DNA molecule (cccDNA). During chronic HBV infection (CH-B), cccDNA accumulates in hepatocyte nuclei, apparently at a level of about 5-50 copies per cell, where it persists as a minichromosome and functions as the template for the transcription of viral genes. 1 The RNA pregenome, in addition to producing capsid and polymerase proteins, becomes encapsidated and is reverse-transcribed. A particularity of the hepadnavirus life cycle is that DNA-containing nucleocapsids can either recycle back to the nucleus to amplify and maintain the pool of cccDNA or become enveloped and secreted into the blood, where new viral particles can spread to other hepatocytes. 2,3 Because cccDNA is the transcriptional template of the virus, it is required for maintenance of HBV infection.Evidence from the woodchuck hepatitis virus system indicated that the pool of cccDNA persisted even when viral production was strongly reduced by the presence of nucleoside analogues. 4,5 Woodchuck studies 6,7 and recent

360 million people are chronically infected with the human hepatitis B virus (HBV) and are consequently prone to develop liver cirrhosis and hepatocellular carcinoma. As approved therapeutic regimens-which modulate patients' antiviral defenses or inhibit the viral reverse transcriptase-are generally noncurative, strategies interfering with other HBV replication steps are required. Expanding on our demonstration that acylated peptides derived from the large HBV envelope protein block virus entry in vitro, we show their applicability to prevent HBV or woolly monkey hepatitis B virus infection in vivo, using immunodeficient urokinase-type plasminogen activator (uPA) mice repopulated with primary human or Tupaia belangeri hepatocytes. Accumulation of the peptides in the liver, their extraordinary inhibitory potency and specific mode of action permit subcutaneous delivery at very low doses. Inhibition of hepadnavirus entry thus constitutes a therapeutic approach to prevent primary HBV infection, such as after liver transplantation, and might also restrain virus spread in chronically infected patients.

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We simultaneously transduced cells with three lentiviral gene ontology (LeGO) vectors encoding red, green or blue fluorescent proteins. Individual cells were thereby marked by different combinations of inserted vectors, resulting in the generation of numerous mixed colors, a principle we named red-green-blue (RGB) marking. We show that lentiviral vector-mediated RGB marking remained stable after cell division, thus facilitating the analysis of clonal cell fates in vitro and in vivo. Particularly, we provide evidence that RGB marking allows assessment of clonality after regeneration of injured livers by transplanted primary hepatocytes. We also used RGB vectors to mark hematopoietic stem/progenitor cells that generated colored spleen colonies. Finally, based on limiting-dilution and serial transplantation assays with tumor cells, we found that clonal tumor cells retained their specific color-code over extensive periods of time. We conclude that RGB marking represents a useful tool for cell clonality studies in tissue regeneration and pathology.

We demonstrate that human hepatocyte division even without involvement of cytolytic mechanisms triggers substantial cccDNA loss. This process may be fundamental to resolve self-limiting acute infection and should be considered in future therapeutic interventions along with entry inhibition strategies.