Natural History, Therapy and Pathogenesis of Chronic Viral Hepatitis B

National Institute Of Diabetes And Digestive And Kidney Diseases

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Abstract

Summary: Globally there are an estimated 291 million persons infected with hepatitis B virus (HBV). In the United States, there are 1.25 million individuals with chronic HBV infection. Chronic HBV infection is a major cause of chronic liver disease, cirrhosis and hepatocellular carcinoma (HCC) worldwide. The natural history of chronic hepatitis B (CHB) appears to be changing with an increasing prevalence of HBeAg negative CHB and recognition of a group of patients with moderate levels of HBV DNA and ALT levels with undetermined natural history. Knowledge of the rate of disease progression among individuals with moderate levels of HBV DNA and ALT levels is unknown. Despite the availability of safe and effective oral nucleoside analogues for treatment of CHB, therapy remains problematic due to the need for prolonged therapy and limited effectiveness and tolerability of the alternate treatment, interferon. Clearance of hepatitis B surface antigen (HBsAg) is the desired surrogate endpoint of therapy but is rarely achieved with current therapy. Identifying the optimal regimen, defining when to treat, for how long and when to stop therapy to achieve this endpoint are major unresolved issues. In addition, defining the best parameters to monitor patients both on and off therapy are not clear. Hypotheses/problems addressed: 1) Define the host, viral and environmental factors that determine the natural history and outcome of HBV infection. Two forms of CHB are recognized based on hepatitis B e antigen (HBeAg) status either HBeAg positive or negative. We investigated two biomarkers, HBV RNA and HBV core-related antigen (HBcrAg), to determine if they would be useful in characterizing disease activity among patients with HBV-human immunodeficiency virus (HIV) coinfection. We first used the two markers to assess ongoing HBV transcription and their associations with hepatic HBsAg and HBcAg staining (immunohistochemical (IHC) staining in patients coinfected with HBV and HIV. We found that HBcAg, HBsAg levels and IHC staining persisted despite viral suppression, and IHC grades and staining patterns correlated with markers of transcription (HBV RNA) and translation (HBcrAg). We next evaluated the longitudinal dynamics of HBV RNA and HBcrAg and their association with classical HBV serum biomarkers and liver histology and viral staining among the same HBV-HIV cohort. Among HBV-HIV coinfected adults on suppressive dually active antiviral therapy, the use of novel HBV markers revealed continued improvement in suppression of HBV transcription and translation over time. Notably among HBeAg negative patients there was minimal improvement in HBV RNA and HBcrAg levels. Taken together, the two studies suggest that additional antiviral strategies directed to HBV protein expression may be necessary to ameliorate liver injury, particularly among the subset of HBV-HIV patients with HBeAg negative chronic hepatitis B. 2) Develop and evaluate novel, safer and more effective therapies for chronic viral hepatitis. Current therapy for CHB remains less than optimal. Only two classes of drugs are approved for use: nucleos(t)ide analogues and peginterferon. Relapse is common if nucleos(t)ides are discontinued after one year in the absence of HBsAg loss. Consequently, they must often be administered long-term or indefinitely. However, long-term use is associated with increased risk of side effects and higher costs. Therefore, the focus of current studies is to develop strategies to induce HBsAg loss (functional cure) to permit discontinuation of therapy and improve outcome of the infection. We are taking several approaches to this problem. The first approach is to combine the two available therapies, peginterferon alfa with tenofovir, compared to tenofovir alone. This is being conducted as part of the Hepatitis B Research Network- a multicenter trial that enrolled 200 subjects. After 192 weeks of therapy and 48 weeks of off-treatment observation, the rate of HBsAg loss was not significantly different in the group that received combination peginterferon alfa with tenofovir compared to the group that received tenofovir alone for 192 weeks. Clearance of HBsAg appeared to be more influenced by viral genotype. These data underscore the need for better approaches to treat CHB. A second approach is to employ siRNA technology to reduce HBsAg levels by decreasing HBsAg mRNA. This approach alone may be insufficient to clear HBsAg and therefore we plan to combine the siRNA with peginterferon as a therapeutic modality. The primary endpoint will be loss of HBsAg and secondary analyses will investigate the virological, histological, and immunological profiles following therapy with this regimen. The protocol is ready for submission to the FDA. 3) Elucidate the viral pathogenesis of HBV infection and assess novel markers of HBV disease activity. Better markers are needed to monitor untreated and treated patients with CHB. Two novel markers, HBV RNA and hepatitis B core-related antigen (HBcrAg) are strongly correlated with activity of covalently closed circular DNA (cccDNA), the transcriptional template for all viral proteins. Therefore, we hypothesized that they might be more useful than existing markers (HBV DNA, ALT, HBsAg levels) in predicting loss of HBeAg and HBsAg which are important milestones in CHB. We developed a series of logistic regression models incorporating each of these variables to a base model consisting of other host and viral factors to predict HBeAg and HBsAg loss. Incorporation of either marker alone or in combination did not significantly improve the predictive ability of the model. HBeAg and HBsAg levels were the best predictors of HBeAg and HBsAg loss, respectively. Hepatitis B core (HBcAg) and surface (HBsAg) antigen expression have been shown to correlate with disease activity in CHB. However, the effect of inhibition of viral replication and transcription on the expression of these two markers is unknown. We assessed the effect of inhibition of viral replication and transcription on HBcAg and HBsAg expression and explored whether HBcAg and HBsAg staining could predict HBsAg loss. There was a significant decline in HBcAg but not HBsAg staining after 4 years of nucleos(t)ide analogue treatment but their respective staining patterns remain unchanged. This result suggests that HBcAg but not HBsAg staining was closely associated with viral replication. Persistence of HBsAg after inhibition of viral replication and transcription particularly among HBeAg negative patients suggest that HBsAg is derived from integrated HBV DNA. Low HBsAg staining is predictive of HBsAg loss in serum. In chronic HBV infection, hepatitis B e antigen (HBeAg) and HBsAg clearance are important milestones toward immune control. A drop in HBV DNA is an established correlate of both HBeAg and HBsAg clearance. We evaluated changes in HBV RNA and HBcrAg levels, markers of transcriptional activity of covalently closed circular DNA (cccDNA), with HBeAg and HBsAg clearance, and compared them with changes in HBV DNA level among adult participants enrolled in the HBRN. The analysis demonstrated that HBeAg clearance resulted in greater relative declines in HBV RNA and HBcrAg compared with HBV DNA, suggesting that HBeAg clearance is associated with a greater inhibition of viral transcription than replication and HBsAg clearance resulted in further decline in HBV DNA but no observable change in HBV RNA or HBcrAg, likely because cccDNA was transcriptionally silent at baseline. The study highlights the value of monitoring cccDNA transcriptional activity via HBV RNA and HBcrAg as a predictor of HBeAg clearance. Additionally, it demonstrates that cccDNA transcriptional activity markedly declines after HBeAg clearance, and cccDNA transcriptional inactivity is a prerequisite for HBsAg clearance.