Chronic infection with hepatitis B virus (HBV) is a major cause of chronic liver disease, cirrhosis and hepatocellular carcinoma (HCC) worldwide. Globally there are an estimated 400 million persons infected with HBV. In the United States, there are 1.25 million affected individuals and the epidemiology of the infection is changing with immigration of persons from endemic regions. The natural history of CHB also appears to be changing with an increasing prevalence of HBeAg negative chronic hepatitis B. Knowledge of the rate of progression between individuals with HBeAg positive and negative CHB is unknown. An equally important and related issue is the clinical assessment of disease severity. Unfortunately, there are no good laboratory markers of disease severity. Liver biopsy is the accepted gold standard for assessing disease severity and cirrhosis but is costly, invasive, and associated with complications, which often limits patient acceptability as well as being subject to sampling error ranging from 15-25%. Non-invasive methods to assess disease severity are highly desirable for practioners caring for patients with CHB. Despite the recent licensing of several new agents for treatment of CHB, therapy remains problematic due to the high rate of anti-viral drug resistance with nucleos(t)ide analogues and relatively poor response to interferon. Identifying the optimal regimen and defining the best parameters to monitor patients both on and off therapy are major unresolved issues. Given the number of chronically infected persons and the requirement for long-term therapy in many of these patients, newer agents with different therapeutic targets are needed, as well as cheaper, more effective regimens. Hypotheses/problems addressed: 1) Define the host, viral and environmental factors that determine the natural history and outcome of HBV infection. To study this problem, we have created a large database of untreated patients with chronic HBV (n350), which will be analyzed to identify factors that affect the natural history of chronic HBeAg positive and negative infections. This data will be used to develop a non-invasive model to predict fibrosis progression, in patients with CHB. We also plan to evaluate the role of transient ultrasound elastography (Fibroscan) to assess fibrosis stage in persons with CHB. These results will be compared to liver biopsy, MRI elastography and plasma will be stored for future proteomic analysis. The goal is to develop a series of blood and imaging tests that will obviate the need for liver biopsy in most patients with CHB. 2) Develop and evaluate novel, safer and more effective therapies for chronic viral hepatitis. Current therapy of CHB remains less than optimal. After one year of therapy, only 17-33% of HBeAg positive patients achieve HBeAg loss, a serologic marker of viral replication and 25-70% completely suppress viral replication. Consequently, relapse rates range from 30-50% if therapy is stopped after 48-52 weeks in HBeAg positive patients and approach 90% in HBeAg negative patients. There is limited information on the safety and efficacy of long-term therapy. In an effort to gain insight into the long-term benefit and more importantly safety of this agent, we conducted a long-term trial of lamivudine 100 mg daily for up to 10 years in patients who were able to maintain a normal alanine aminotransferase (ALT) level and complete viral suppression for a period of 4 years. In order to obtain data on long-term histologic outcome, patients underwent liver biopsy at baseline, 1, 4 and 8 years. Twenty-two of forty-three (6 HBeAg positive and 14 HBeAg negative) patients continue on therapy. This study revealed significant histologic improvement at 8 years including reversion of advanced fibrosis to normal findings. In addition, at 8-10 years clearance of HBsAg was observed in 25% of patients (rate at one year ranges from 0-2%) and no cases of hepatocellular carcinoma were observed. This data is important for advising patients on long-term prognosis with lamivudine therapy. Borrowing on the HIV paradigm that multiple agents that act at different sites of viral replication or have different resistant profiles may be more effective than monotherapy, we have conducted a randomized trial of lamivudine and adefovir versus adefovir monotherapy in patients with HBeAg positive and negative CHB with and without resistance to lamivudine. To date 42 patients have been enrolled into this trial. We have performed an analysis of the HBeAg positive, treatment nave cohort who have completed one year of therapy n=22. At last follow up, all 12 patients receiving combination therapy had normal ALT levels and 9 (75%) had lost HBeAg and had undetectable HBV DNA. In contrast, only 5 (50%) of the adefovir treated patients had normal ALT levels and only 4 (40%) lost HBeAg and had undetectable HBV DNA. One additional adefovir treated patient had viral rebound (&#8805;1 log increase in HBV DNA from nadir) and was considered a treatment failure. No viral rebound, suggesting development of viral resistance was observed in the combination arm. Neither the combination of lamivudine and adefovir nor adefovir monotherapy were associated with significant side effects. These results suggest that combination therapy may be more appropriate for long-term use but the results need to be validated in larger study. These promising results have led us to evaluate the combination of tenofovir and emtricitabine compared to tenofovir for patients with CHB. Tenofovir is a nucleotide analogue that is very effective at suppressing HBV DNA and has an excellent resistance profile. This study will examine the long-term efficacy and safety of tenofovir and emtricitabine versus tenofovir alone in patients with HBeAg positive and negative CHB with the goals of maintaining long-term viral suppression ands preventing the emergence of viral resistance. Enrollment is planned to begin in September, 2007. Elucidate the viral pathogenesis of HBV infection and mechanisms of action of anti-viral therapy The course of CHB following the development of anti-viral resistance is highly variable with some patients showing continued viral suppression, some with an accelerated course and others who lie in-between. The reasons for this wide variation in outcome are unknown. We hypothesized that following initial viral breakthrough, compensatory mutations that do not alter sensitivity to lamivudine but instead affect viral replication may account for the different phenotypic presentations observed. To investigate this issue, we sequenced the entire polymerase region of HBV at three time points, (baseline, at time of viral breakthrough and last available follow-up from patients enrolled in our long-term lamivudine trial) in 18 patients with HBeAg positive CHB, genotypes A or C who developed lamivudine resistance. Additional mutations other than the rt M204V/I that confers resistance to lamivudine were found. Several interesting findings emerged from this study. First, whether a patient develops rtM204V/I, conferring resistance to lamivudine, appears to be HBV genotype dependent. Thus patients with genotype A were found to have predominantly rtM204V whilst patients with genotype C were more likely to have rtM204I. Second, compensatory mutations were observed more frequently in patients who progressed to cirrhosis compared to those who did not. We are now investigating the effects of these mutations on viral replication in genotype A and C replicative constructs. Furthermore, we are developing in-vitro assays to evaluate drug resistance using virus cloned from patients serum. This will permit cross-resistance monitoring to other antiviral agents and aid in managing patients with resistant HBV.