Treatment of chronic hepatitis B

Identification of hepatitis B virus A1762T/G1764A double mutant strain in patients in Southern Brazil

Infection by hepatitis B virus (HBV) is a worldwide public health problem. Chronic HBV infection with high viral replication may lead to cirrhosis and/or hepatocellular carcinoma. Mutant HBV strains, such as the HBV A1762T/G1764A double mutant, have been associated with poor prognosis and higher risk of the patient for developing cirrhosis and/or hepatocellular carcinoma. This study analyzed the presence of the HBV A1762T/G1764A double mutant in patients with chronic HBV and its association with clinical parameters such as viral load, aminotransferases, and HBV antigens. A total of 49 patients with chronic hepatitis B were included in the study, and the HBV A1762T/G1764A double mutant strain was detected in four samples (8.16%) by polymerase chain reaction followed by restriction fragment length analysis (PCR-RFLP). The viral load was not significantly different between patients with or without the double mutant strain (p=0.43). On the other hand, carriers of the HBV A1762T/G1764A double mutant had higher levels of ALT (p=0.0028), while AST levels did not differ between groups (p=0.051). In this study, 75% of the samples with the HBV A1762T/G1764A double mutation were HBeAg negative and anti-HBe positive, reflecting seroconversion even though they still displayed high viral loads. Our study has shown that the HBV A1762T/G1764A double mutant strain circulates in Brazilian patients, and is associated with elevated levels of ALT and HBeAg seroconversion.

Hepatitis B: New Approaches for Antiviral Chemotherapy

Progress in the development of effective therapeutic regimes for chronic hepatitis B has been slow, mainly due to the lack of promising lead compounds and useful assays for high throughput in-vitro screening. Nucleoside analogue chemotherapy has targeted the inhibition of the hepatitis B virus (HBV) polymerase and achieved inhibition of this unique viral enzyme. The persistence and resistance of HBV covalently closed circular (or supercoiled) DNA, the key replicative intermediate and sole transcriptional template, to existing treatments also poses challenges for the effective development of antiviral chemotherapy. In spite of these difficulties, the process of viral DNA replication, as well as supercoiled DNA generation and processing, is now being elucidated at the molecular level, presenting unique opportunities for new drug targeting and design. This review attempts to highlight these new approaches to the development of treatment regimes for this important disease.

Hepatitis B: Treatment for the 21st Century

Hepatitis B virus (HBV) infection constitutes a worldwide public health problem, causing both acute and chronic liver infections. Although a vaccine has been developed that is effective in preventing HBV infection, this is of no benefit to the estimated 350 million carriers of the virus. Chronic hepatitis B infection may lead to cirrhosis of the liver and hepatocellular carcinoma. Therefore, there is a clear need for antiviral therapy. Alpha interferon was the first therapeutic agent used against HBV infection. However, its lack of efficacy in many patients and significant adverse event profile has prompted the development of alternative therapies. Nucleoside analogues are currently being investigated as potential anti-HBV agents, with two compounds, famciclovir and lamivudine, undergoing Phase III clinical trials of long-term use. In preclinical studies using the Pekin duck model for hepatitis B, both compounds have been found to reduce the amount of serum duck HBV DNA to sub-detectable levels during therapy. However, once therapy was stopped, the virus returned to pretreatment levels, making long-term treatment necessary. In clinical studies in chronic hepatis B patients, treatment with these agents also resulted in a significant reduction of HBV DNA levels but, again, the return of HBV DNA after discontinuing treatment indicates the need for long-term therapy. The need for long-term treatment means that the virus may develop resistance to the antiviral agents. Resistance mutations to both famciclovir and lamivudine are now being reported after treatment of chronic HBV infection with these agents. Combination therapy may be a strategy to overcome the development of resistance. Therapeutic vaccines and new antiviral agents are also being developed.

Screening and identification of compounds with antiviral activity against hepatitis B virus using a safe compound library and novel real-time immune-absorbance PCR-based high throughput system

There are now seven nucleoside/tide analogues, along with interferon-α, that are approved by the FDA for the management of chronic hepatitis B virus (HBV) infection, a disease affecting hundreds of millions of people worldwide. These medications, however, are limited in usefulness, and significant side effects and the emergence of viral escape mutants make the development of novel and updated therapeutics a pressing need in the treatment of HBV. With this in mind, a library containing 2000 compounds already known to be safe in both humans and mice with known mechanisms of action in mammalian cells were tested for the possibility of either antiviral activity against HBV or selective toxicity in HBV producing cell lines. A modified real-time immune-absorbance-polymerase chain reaction (IA-PCR) assay was developed for this screen, utilizing cells that produce and secrete intact HBV virions. In this procedure, viral particles are first captured by an anti-HBs antibody immobilized on a plate. The viral load is subsequently assessed by real-time PCR directly on captured particles. Using this assay, eight compounds were shown to consistently reduce the amount of secreted HBV viral particles in the culture medium under conditions that had no detectable impact on cell viability. Two compounds, proparacaine and chlorophyllide, were shown to reduce HBV levels 4- to 6-fold with an IC₅₀ of 1 and 1.5 μM, respectively, and were selected for further study. The identification of these compounds as promising antiviral drug candidates against HBV, despite a lack of previous recognition of HBV antiviral activity, supports the validity and utility of testing known compounds for "off-pathogen target" activity against HBV, and also validates this IA-PCR assay as an important tool for the detection of anti-viral activity against enveloped viruses.

Evaluation of single and combination therapies with tenofovir disoproxil fumarate and emtricitabine in vitro and in a robust mouse model supporting high levels of hepatitis B virus replication

Next-generation therapies for chronic hepatitis B virus (HBV) infection will involve combinations of established and/or experimental drugs. The current study investigated the in vitro and in vivo efficacy of tenofovir disoproxil fumarate (TDF) and/or emtricitabine [(-)-FTC] alone and in combination therapy for HBV infection utilizing the HepAD38 system (human hepatoblastoma cells transfected with HBV). Cellular pharmacology studies demonstrated increased levels of (-)-FTC triphosphate with coincubation of increasing concentrations of TDF, while (-)-FTC had no effect on intracellular tenofovir (TFV) diphosphate levels. Quantification of extracellular HBV by real-time PCR from hepatocytes demonstrated the anti-HBV activity with TDF, (-)-FTC, and their combination. Combination of (-)-FTC with TDF or TFV (ratio, 1:1) had a weighted average combination index of 0.7 for both combination sets, indicating synergistic antiviral effects. No cytotoxic effects were observed with any regimens. Using an in vivo murine model which develops robust HBV viremia in nude mice subcutaneously injected with HepAD38 cells, TDF (33 to 300 mg/kg of body weight/day) suppressed virus replication for up to 10 days posttreatment. At 300 mg/kg/day, (-)-FTC strongly suppressed virus titers to up to 14 days posttreatment. Combination therapy (33 mg/kg/day each drug) sustained suppression of virus titer/ml serum (<1 log(10) unit from pretreatment levels) at 14 days posttreatment, while single-drug treatments yielded virus titers 1.5 to 2 log units above the initial virus titers. There was no difference in mean alanine aminotransferase values or mean wet tumor weights for any of the groups, suggesting a lack of drug toxicity. TDF-(-)-FTC combination therapy provides more effective HBV suppression than therapy with each drug alone.

Development of a novel mouse model to evaluate drug candidates against hepatitis B virus

Woodchuck hepatitis virus (WHV)-infected woodchucks have been used for preclinical development of drugs against hepatitis B virus (HBV). However, there is no simple in vivo model to evaluate small amounts of compounds against HBV. To develop such a model, HepAD38 cells, in which HBV replication is regulated by tetracycline (tet), were grown as subcutaneous tumours in nude mice. Mice developing viraemia were then left untreated or given tet in the drinking water. In some of the mice given tet, it was removed and the mice were injected intraperitoneally with phosphate buffer saline (PBS), lamivudine (3TC), clevudine (CLV) or tenofovir dipivoxil fumarate (TDF). Virus DNA titres were measured by real-time PCR during and after drug treatment. In water-fed and PBS-injected mice, virus titres reached approximately 10(9) copies/ml serum within 35 days of HepAD38 injection, whereas in tet-treated mice, virus titres remained at 10(4)-10(5) copies/ml. HBV DNA levels were suppressed by 3TC, TDF and CLV, with the latter two drugs showing more sustained virus suppression compared with 3TC. Combination therapy with CLV plus TDF was much more effective than either drug alone in suppressing virus titre for at least 3 weeks after the end of treatment. There was no demonstrable toxicity to HepAD38 cells in drug-treated mice. Hence, a robust tet-controlled system for HBV replication in vivo was demonstrated, validated with monotherapies against HBV and shown to be useful in assessing combination therapy. This system will be useful for preclinical assessment of small amounts of single or multiple compounds against HBV in vivo.

Three-phase sequential combined treatment with lamivudine and interferon in young patients with chronic hepatitis B

Alpha-interferon (IFN) or lamivudine monotherapy are ineffective in treating chronic HBeAg positive patients with high viral load and low alanine aminotransferase (ALT) levels. We investigated whether priming lamivudine treatment might enhance the antiviral and immunostimulant action of lamivudine/IFN combination in young tolerant patients. Eleven chronic HBeAg positive patients received: 100 mg/day lamivudine for 3 months followed by IFN 5 MU/m2/tiw with lamivudine 100 mg/day for 6 months and then lamivudine alone 100 mg/day for 9 months. Quantitative hepatitis B virus (HBV)-DNA was evaluated during treatment and core-promoter, precore and polymerase HBV mutants were detected by direct sequencing at the end of therapy. Serum HBV-DNA levels dropped during lamivudine monotherapy and in combination with IFN. After IFN withdrawal, viraemia transiently increased to high levels in five of 11 (45%) patients who showed rt M204V/I lamivudine mutant resistant. Two patients cleared HBeAg without anti-HBe seroconversion. One patient presented core-promoter (A1762T/G1764A) and precore stop codon mutations. Hence, three-phase sequential combined lamivudine/IFN treatment reduced HBV-DNA serum level, but did not lead to HBeAg and HBV-DNA clearance in these highly viraemic, normal ALT patients. Lamivudine/IFN combination did not prevent the emergence of YMDD lamivudine resistance. New schedules of antiviral treatments must be evaluated in this population at risk of disease progression.

A randomized, controlled, clinical study of thymosin alpha-1 versus interferon-alpha in [corrected] patients with chronic hepatitis B lacking HBeAg in China [corrected]

BACKGROUND

This study was designed to compare the efficacy and safety of thymosin-alphal (T-alpha1) with that of interferon-alpha (IFN-alpha) in patients with chronic hepatitis B who were positive for hepatitis B virus (HBV) DNA and hepatitis B envelope antibody (anti-HBe).

METHODS

Fifty-six patients were randomly divided into groups A and B. Both groups were comparable (p > 0.05) at baseline regarding age, sex, and alanine aminotransferase (ALT) levels. Group A patients received T-alpha1 1.6 mg subcutaneously twice weekly, while group B patients received IFN-alpha 5 million IU daily for 15 days, then thrice weekly for 6 months. Results from the 2 groups were compared with data from a group of 30 patients never treated with IFN-alpha and who were followed-up for 12 months (historical control [HC] group); the 3 groups were comparable (p > 0.05).

RESULTS

After treatment, a complete response (ALT normalization and HBV DNA loss) occurred in 8 of 26 patients in group A (30.8%) and 14 of 30 in group B (46.7%; chi2 = 1.476, p = 0.224). After a follow-up period of 6 months, a complete response was observed in 11 of 26 patients in group A (42.3%) and 7 of 30 in group B (23.3%; chi2 = 2.299, p = 0.129). The rate of complete response was significantly greater in the IFN-alpha than HC group at the end of therapy (46.7% vs 3.3%; chi2 = 15.022, p = 0.0001), and in the T-alphal than HC group at the end of follow-up (42.3% vs 3.3%; chi2 = 12.566, p = 0.0001). Ten of the 12 T-alphal responders (i.e. partial responders; 83.3%) experienced sustained, non-detectable HBV DNA after 6 months' treatment; 6 of the 14 T-alphal non-responders (42.9%) showed a delayed response of non-detectable HBV DNA during the follow-up period. Corresponding values for group B patients were 50% (9/18) and 0% (0/12). The rate of delayed response was significantly higher in group A than the other 2 groups (chi2 = 6.686, p = 0.010; chi2 = 4.964, p = 0.038), whereas the rate of flare was higher in group B than in the other 2 groups (chi2 = 3.445, p = 0.063; chi2 = 7.668, p = 0.006), during the follow-up period. Unlike IFN-alpha, T-alphal was well tolerated, i.e. no adverse effects were noted in group A.

CONCLUSION

These results suggest that a 6-month course of T-alpha1 therapy is effective and safe in patients with anti-HBe-positive chronic hepatitis B; T-alpha1 can reduce HBV replication in such patients. Compared with IFN-alpha, T-alpha1 is better tolerated and seems to induce a gradual and more sustained normalization of ALT and loss of HBV DNA. Combination therapy with T-alpha1 and IFN-alpha or nucleoside analogs for hepatitis B warrants further study.

Fully automated, internally controlled quantification of hepatitis B Virus DNA by real-time PCR by use of the MagNA Pure LC and LightCycler instruments

We report on the development of a fully automated real-time PCR assay for the quantitative detection of hepatitis B virus (HBV) DNA in plasma with EDTA (EDTA plasma). The MagNA Pure LC instrument was used for automated DNA purification and automated preparation of PCR mixtures. Real-time PCR was performed on the LightCycler instrument. An internal amplification control was devised as a PCR competitor and was introduced into the assay at the stage of DNA purification to permit monitoring for sample adequacy. The detection limit of the assay was found to be 200 HBV DNA copies/ml, with a linear dynamic range of 8 orders of magnitude. When samples from the European Union Quality Control Concerted Action HBV Proficiency Panel 1999 were examined, the results were found to be in acceptable agreement with the HBV DNA concentrations of the panel members. In a clinical laboratory evaluation of 123 EDTA plasma samples, a significant correlation was found with the results obtained by the Roche HBV Monitor test on the Cobas Amplicor analyzer within the dynamic range of that system. In conclusion, the newly developed assay has a markedly reduced hands-on time, permits monitoring for sample adequacy, and is suitable for the quantitative detection of HBV DNA in plasma in a routine clinical laboratory.

[Nucleoside analogues resistance in the treatment of chronic hepatitis B virus infection]

SUBJECT

Chronic hepatitis B virus (HBV) infection is usually treated by interferon alpha. However, a sustained response after stopping treatment is only obtained in 30% of patients.

ACTUALITY

New therapeutic nucleoside analogs have been developed, i.e. lamivudine, famciclovir, adefovir, entecavir, clevudine. However, as in HIV infection, clearance of the original hepatitis B virus with emergence of distinct resistant mutants have been observed during or after treatment with most nucleoside analogs. In this review, the underlying mechanisms of resistance and the characterisation of HBV mutants are described to optimize the best therapeutic regimen.

PERSPECTIVES

Treatment of chronic HBV infection, as most of other chronic viral infection, should be based on combination therapy with a special search for the appearance of HBV mutant resistant.

Treatment of chronic hepatitis B: current challenges and future directions

The clinical management of chronic hepatitis B infection has entered a new era with the introduction and widespread use of oral nucleoside analogues such as lamivudine and nucleotides such as adefovir dipivoxil. From this, new challenges have now emerged in terms of preventing antiviral drug resistance, promoting viral clearance and improving long-term survival. For example, the natural history of nucleoside or nucleotide analogue-associated hepatitis B virus resistant mutants has yet to be determined. Furthermore, the increasing prevalence of HBeAg negative disease with its reduced response to current therapies represents an ongoing challenge to attempts to improve standard of care. There is increasing recognition of the pivotal role that viral load and genotype, and their complex interactions with the host immune response, play in determining the outcome of these treatment interventions. The purpose of this paper is to highlight several key factors that should be considered in the context of future clinical research and management of chronic hepatitis B.

[Role of interferons in the treatment of hepatitis B and hepatitis C virus infections]

BACKGROUND

Since the discovery of hepatitis C (HCV), the efficacy of treatment has significantly progressed using standard mono-therapy: with Interferon alpha (IFN) during six months we obtained approximately 10% sustained response and currently with the association of pegylated IFN and Ribavirin a 55% sustained response was achieved.

CURRENT POSITION AND MAJOR POINTS

HCV infection continues to present therapeutic problems which have not entirely been solved, mainly related to clinical and biological tolerance, and non-responders. Moreover, the care of patients with extra-hepatic localization, cirrhotic patients, as well as therapeutic problems of co-infected HIV-HCV patients. As regards hepatitis B (HBV) new effective treatments against this virus have appeared, IFN then nucleoside analogs, some of which are available in France (i.e. lamivudine, adefovir, dipovoxil). The main objective of chronic hepatitis B treatment is to obtain the complete inhibition of the HBV virus by Hbe-antigen antibody seroconversion which would therefore significantly increase patient survival. In this article the advantages and disadvantages of the different treatments are assessed.

FUTURE PERSPECTIVES

Despite the considerable and rapid progress obtained in the therapeutic treatment of infection due to HCV and HBV a number of unknown factors remain, which warrants further trials, in particular to evaluate the efficacy as well as the tolerance of the antiviral agent association.

Comparison of treatments of chronic hepatitis B in children with lamivudine and alpha-interferon combination and alpha-interferon alone

BACKGROUND

The aim of this study was to compare the efficacy of the alpha-interferon treatment with treatment using alpha-interferon and lamivudine in combination for cases of childhood chronic hepatitis B infection.

METHODS

Patients were evaluated in two groups retrospectively. In group 1, 27 patients were simultaneously given alpha-interferon 2b 10 MU/m2, 3 days a week by s.c. injection plus lamivudine 4 mg/kg a day (maximum 100 mg) for 12 months. In group 2, there were 13 patients who only received the same dosage of alpha-interferon and no lamivudine over the same period of time.

RESULTS

In group 1 the initial mean value of alanine aminotransferase (ALT) was 121 +/- 66 IU/L and decreased to 27.8 +/- 11.5 IU/L; in group 2, initial mean values of ALT was 129 +/- 46 IU/L and decreased to 60 +/- 6 IU/L at the end of the twelfth month of the therapy (P < 0.05). Hepatitis B virus DNA (HBV-DNA) clearance was obtained in all group 1 patients and six of 13 patients in group 2 at the end of the therapy (P < 0.001). The rates of hepatitis B early (HBe) antigen clearance and anti-HBe seroconversion were 59 and 37% in group 1 and 46 and 30.7% in group 2 (P > 0.05). The number of patients with complete response was found to be 10 out of 27 (37%) in group 1 and four out of 13 cases (30.7%) in group 2, 6 months after the end of the therapy. There was no statistically significant difference between both groups (P > 0.05).

CONCLUSION

alpha-Interferon and lamivudine combination therapy had a more beneficial effect than alpha-interferon monotherapy in normalization of ALT and clearance of HBV-DNA; however, the complete response rate at 6 months after the end of the therapy was not statistically significantly different between both groups.

Thymosin-alpha1 and famciclovir combination therapy activates T-cell response in patients with chronic hepatitis B virus infection in immune-tolerant phase

We examined whether combination therapy with thymosin-alpha1 and famciclovir would induce hepatitis B e antigen seroconversion in patients with chronic hepatitis B infection in the immune-tolerant phase without inducing significant hepatic necro-inflammation. We studied 32 hepatitis B e antigen positive patients in the immune-tolerant phase of infection, treated with 26-weeks combination therapy of famciclovir and thymosin-alpha1 (group 1). Thirty-two patients who received 26-weeks famciclovir monotherapy (group 2) and another 32 patients who received no treatment (group 3), served as controls. Peripheral blood mononuclear cell proliferation and cytokine secretion in response to recombinant HBV core and surface antigen and serial serum HBV-DNA, were assayed. No significant difference in adverse events were observed among the three groups. By week 26, the median reduction in group 1 (0.94 log10 copies/mL) was greater than group 2 (0.70 log10 copies/mL, P < 0.001). Five (15.6%) patients in group 1 at 52 weeks (median range 13-78 weeks) and none in group 2 or 3 experienced hepatitis B e antigen seroconversion (P = 0.053). Sustained serological clearance of hepatitis B e antigen was associated with activation of CD4 positive HBV-specific T-cell reactivity and were of T-helper 1. Hence combination therapy with immunomodulatory agents and nucleoside analogues should be explored.

Different activities of type I interferons on hepatitis B virus core promoter regulated transcription

The type I interferons (IFNs) are a group of closely related cytokines which have different signal transduction pathways and different biological activities. Using transient transfection of human hepatoma cells with reporter plasmids containing the firefly/renilla luciferase genes under the control of the HBV-Enhancer (Enh) I, Enh II and core promoter we have investigated the biological activities of 10 recombinant (r) type I IFNs on transcription. Low concentrations of IFN (0.025 ng/ml) had a significant and specific inhibitory effect but the potencies of the different recombinant type I IFNs differed markedly with IFNalpha8 and IFNbeta being six-fold more potent than the least effective subtype (IFNalpha1). However, the addition of IFNalpha5-the subtype produced predominantly in the human liver-did not cause any synergistic effects.The non-natural consensus IFN displayed a more pronounced inhibition of HBV-regulated transcription than IFNalpha8 or IFNalpha2 but not IFNbeta. The INF-induced inhibitory effect was not dependent on the presence of the HBV-Enh1 and in particular of an interferon stimulated response element (ISRE)-like sequence. The characterization of different effects among type I interferons on HBV-regulatory elements may implicate an IFN-subtype-specific role for the pathogenesis and treatment of HBV-infection.

European proficiency testing program for molecular detection and quantitation of hepatitis B virus DNA

External quality control of hepatitis B virus (HBV) DNA detection remains an important issue. This study reports and compares the results obtained from two different proficiency panels for both the qualitative and quantitative assessment of HBV DNA. The panels were designed by the European Union Quality Control Concerted Action, prepared by Boston Biomedica, Inc., and distributed in May 1999 (panel 1) and February 2000 (panel 2). Each contained two negative samples and six positive samples with 10(3) to 10(7) copies/ml (panel 1) or 10(3) to 2 x 10(6) copies of HBV DNA per ml (panel 2). For panel 1, 42 laboratories submitted 20 qualitative (all in-house PCRs) and 37 quantitative (87% commercial assays) data sets. For panel 2, 51 laboratories submitted 25 qualitative (all in-house PCRs) and 47 quantitative (94% commercial assays) data sets. Five data sets (8.8%) in panel 1 and two data sets (2.8%) in panel 2 contained totals of six and two false-positives, respectively, corresponding to false-positive result rates of 5.3% for panel 1 and 1.4% for panel 2. The false-negative result rates of 10.5% for panel 1 and 17.4% for panel 2 were dependent on the detection levels of the assays employed as well as panel composition. In the qualitative analysis of all data sets, 47.4% (panel 1) and 51.4% (panel 2) had all samples correct. An adequate or better score (all correct or only the weak-positive sample missed) was obtained with 77.2% of the panel 1 samples and 68.1% of the panel 2 samples. In the quantitative analysis, 57.1% (panel 1) and 42.6% (panel 2) of the data sets achieved an adequate or better score (positive results within the acceptable range of the geometric mean +/- 0.5 log(10) of all positive results). These results demonstrate that while the qualitative performance of HBV detection has considerably improved compared to that of a previously published HBV proficiency study, the detection levels of many commercial quantitative assays are still too high to allow adequate quantitation of all relevant clinical samples.

Lamivudine and interferon-alpha combination treatment of childhood patients with chronic hepatitis B infection

BACKGROUND

The aim of our study was to compare the efficacy of combined interferon-alpha and lamivudine in children with chronic hepatitis B infection and two durations of treatment (6 and 12 months).

METHODS

Combination of interferon-alpha 2b (10 MU/m2 of body surface) and lamivudine 4 mg/kg (maximum, 100 mg) were given synchronously to 30 patients for 6 months (Group 1) and to 27 patients for 12 months (Group 2). Biochemical, virologic and serologic features were compared between two groups at the end of therapy and 6 months after therapy.

RESULTS

Hepatitis B e antigen clearances were 33 and 59% at the end of treatment and 37 and 56% 6 months after therapy in Groups 1 and 2, respectively (P > 0.05). Hepatitis B virus DNA clearances were 97 and 100% at the end of treatment and 97 and 96% 6 months after therapy in Groups 1 and 2, respectively (P > 0.05). In both groups normalization of alanine aminotransferase was maintained at the end of therapy and 6 months after therapy (P < 0.05). Sustained complete responses were obtained in 20 and 37% of patients at the end of therapy and 6 months after therapy, respectively (P = 0.07).

CONCLUSIONS

When the combination of large dosage interferon-alpha 2b and lamivudine therapy in children was compared at the end of therapy and 6 months after therapy, normalization of alanine aminotransferase and the clearances of hepatitis B e antigen and hepatitis B surface antigen in both groups were directly proportional to the duration of treatment. However, the higher complete response rate at 12 months of combination therapy was not statistically different from that at 6 months.

Diagnosis and management of pre-core mutant chronic hepatitis B

Chronic hepatitis due to pre-core hepatitis B virus (HBV) mutants presents as hepatitis B e antigen (HBeAg)-negative chronic hepatitis B (CHB). HBeAg-negative CHB represents a late phase in the natural course of chronic HBV infection that develops after HBeAg loss and seroconversion to anti-HBe. It is usually associated with pre-core stop codon mutation at nucleotide 1896 (mainly selected in non-A HBV genotypes), but also with other pre-core changes or with mutations in the basic core promoter region (mainly in HBV genotype A). In chronic HBV infections, pre-core mutants can be detected both in patients with HBeAg-negative CHB and in inactive hepatitis B surface antigen (HBsAg) carriers. The diagnosis of HBeAg-negative CHB is based on HBsAg positivity, HBeAg negativity, and mainly on increased alanine aminotransferase (ALT) and serum HBV-DNA levels and exclusion of other causes of liver disease. The differential diagnosis between patients with CHB and inactive HBsAg carriers can be made only by close follow-up of aminotransferase activity and viraemia levels, although the cut-off level of serum HBV DNA has not been definitely determined. IgM anti-HBc levels have also been suggested as an index that increases the diagnostic accuracy for transient hepatitis flares, while liver biopsy confirms the diagnosis and evaluates the severity of the liver disease. Interferon-alpha (IFN-alpha) and lamivudine are the two drugs that have been tried, mainly in the management of HBeAg-negative CHB. A 12-month course of IFN-alpha achieves sustained biochemical remission in about 20% of patients, which has been associated with improvement in the long-term outcome of this subset. A 12-month course of lamivudine is rather ineffective, maintaining remission in less than 15% of patients after cessation of therapy. Long-term lamivudine is associated with progressively increasing rate of virological and subsequent biochemical breakthroughs due to YMDD mutants, with approximately 30% of patients remaining in remission in the third year of therapy. Several other antiviral agents are currently being evaluated in this setting with combined regimens being the most reasonable step for the near future.

Individualizing care of hepatitis B in older adults and Asians

PURPOSE

To review the pathophysiology of hepatitis B virus (HBV) as it relates to special groups such as older adults and Asian populations and to stratify preventive services relative to these particular populations.

DATA SOURCES

Selected scientific literature and practice guidelines.

CONCLUSIONS

The HBV is one of the most common causes of viral hepatitis. Acute infection is mostly self-limiting with nonspecific symptoms. Chronic infection is characterized by persistent serum levels of Hepatitis B surface antigen (HBsAg) for more than six months.

IMPLICATIONS FOR PRACTICE

Chronic HBV is a major risk factor for hepatocellular carcinoma. Special populations, such as older adults with decreased immune response and Asians from places with high endemic HBV infection, are at particularly high risk for progression of HBV infection to chronic states and serious liver damage.

Hepatitis B infection in China

Chronic HBV infection is a serious health threat in the Asian-Pacific region. The introduction of lamivudine has greatly improved the hope of these patients and is undoubtly a milestone in the management of chronic HBV infection. The combination of lamivudine with another nucleotide or nucleoside analogue or immunomodulatory agent to improve its therapeutic efficacy further must be investigated. Also, the use of lamivudine to prevent HBV reactivation on withdrawal of immunosuppressive therapy should be explored.

[Diagnosis and treatment of hepatitis B]

Hepatitis B constitutes a serious public health problem. It has been estimated that 350 million people--approximately 5% of the world population--have been infected by this virus. Of the people infected, in 90% to 95% of them there will be a spontaneous resolution of the disease. In 5% to 10% of the cases, though, the infection will persist and a chronic hepatitis will develop that may evolve leading, in the end, to liver cirrhosis, liver failure and/or carcinoma of the liver. The diagnosis of the different stages of the disease (i.e., acute, chronic infection) is performed using modern serologic techniques. Physicians, more recently, are having access to a series of laboratory tests which permit them to evaluate the viral load, replication of the virus and to testing of the efficacy of new anti-viral drugs. For the treatment of chronic hepatitis B new agents have been tested and some are being used with different degrees of success, such as, alfa-interferon, lamivudine, famciclovir, and adefovir dipivoxil, among others. Active immunization, using modern recombinant vaccines, are lately, the most important instrument of control of the infection caused by the hepatitis B virus.

Evaluation of quantitative PCR and branched-chain DNA assay for detection of hepatitis B virus DNA in sera from hepatocellular carcinoma and liver transplant patients

This study evaluated the applicability of quantitative PCR (Q-PCR) and branched-chain DNA assays for detection of hepatitis B virus (HBV) DNA in sera. For 42 samples, the detection rates were 81 and 41%, respectively, with a correlation coefficient of 0.633. The Q-PCR is useful for early monitoring of HBV load in high-risk patients.

Use of immunomodulatory therapy (other than interferon) for the treatment of chronic hepatitis B virus infection

Chronic hepatitis B virus (HBV) infection is a major health threat in Asia. In order to design a better therapeutic regimen, the underlying mechanism of HBV viral persistence must be understood. Immunological studies have found that impaired HBV virus-specific T cell reactivity is the major cause of chronic infection, whereas strong and multispecific T cell responses to HBV are associated with long-term control, but not elimination of the virus. Furthermore, in the serological clearance of hepatitis B surface antigen (HBsAg) in allogeneic haematopoietic cell transplantation, HBsAg seroconversion is associated with activation of the donor's hepatitis B core antigen-specific CD4+ T lymphocytes. This suggests that the donor's hepatitis B core antigen-specific CD4+ T cells provide 'intermolecular T cell help' for the HBsAg seroconversion. These findings are relevant to the future development of therapeutic vaccines or DNA vaccine as immunotherapy for chronic hepatitis B. Apart from interferon-alpha, thymosin alpha1 (Talpha1) has been investigated for treatment of chronic hepatitis B. Meta-analysis of 4 randomized controlled studies investigating the safety and efficacy of Talpha1 monotherapy for the treatment of chronic hepatitis B showed that 6 months treatment with Talpha1 (1.6 mg twice weekly) almost doubles the sustained response rate (36%) compared with controls (19%; P=0.04). However, more specific immunological approaches are being developed; notably, hepatitis B core antigen-based therapeutic vaccine was found to induce T cell proliferative responses in chronically infected hepatitis B patients to the T helper epitope included in the construct. However, the cytokine profile observed suggested the induction of a T helper 0/T helper 2 CD4+ T cell response rather than T helper 1 response. Thus, its combination with interferon-gamma or interleukin-12, which might reverse the CD4+T cell response, should be considered. In the future, it is likely that different types of combination therapy may have to be tailor-made for chronic HBV infection with different virological and immunological profiles and different degrees of liver damage.

Sensitive and accurate quantitation of hepatitis B virus DNA using a kinetic fluorescence detection system (TaqMan PCR)

The laboratory diagnosis of hepatitis B virus (HBV) infection is based mainly on serological assays. Yet the detection and quantitation of viral DNA is necessary when addressing directly the question of infectivity or when monitoring the viral load during therapy. Standard hybridization assays allow for exact quantitation, but their sensitivity is limited to 10(5)-10(6) viral genomes per ml of serum. The most sensitive tests for HBV DNA are nested PCR systems, which recognize virtually one molecule of the target DNA per reaction. However, these assays only provide very coarse quantitative statements. To take advantage of both methods, a new assay for HBV DNA is described based on the commercial TaqMan system. This assay is capable of quantifying HBV DNA from the theoretical lower limit up to 10(10) genome equivalents per ml of serum and, thus, covers the complete range of naturally occurring states of infections. The method was calibrated on the basis of serial plasmid dilutions and compared with a well-established nested PCR system. More than 100 HBV positive sera and serial dilutions of the Eurohep standard for both ad and ay subtypes were analyzed. The assay reliably detected all HBV positive samples. It shows minimal run-to-run deviations, allows for quantitation that covers eight orders of magnitude, and finally, completely avoids the risk of cross-contamination by PCR products. Thus, this technique combines the sensitivity of PCR amplification and the quantitation potential of hybridization tests and it is time efficient and safer.

Identification of different states of hepatitis B virus infection with a quantitative PCR assay

The level of hepatitis B virus (HBV) DNA in serum reflects the replicative activity of HBV. To compare serum HBV DNA levels in different states of hepatitis B, 47 sera of patients with HBeAg-positive chronic hepatitis B, 4 sera of patients with HBeAg-negative chronic hepatitis B, 40 samples of patients after HBeAg seroconversion during alpha interferon treatment, 57 sera of inactive HBsAg carriers, and 42 sera of patients who had recovered from chronic hepatitis B more than 12 months prior to blood collection were checked for the presence of HBV DNA with the Amplicor HBV Monitor Test. In patients with HBeAg-positive chronic hepatitis B, the median of serum HBV DNA levels (8.3 x 10(8) copies/ml) was significantly higher than that for patients after HBeAg seroconversion (6.2 x 10(3) copies/ml) and than that for inactive HBsAg carriers (5.6 x 10(3) copies/ml). None of the patients who had recovered from hepatitis B had detectable HBV DNA in serum. Quantitative PCR proved to be a valuable tool for identification of different states of HBV infection. This technique was found to be a good method for determination of serum HBV DNA levels both for patients with HBeAg seroconversion and for inactive carriers who showed low viremia not detectable by conventional hybridization assays.

Antiviral chemotherapy for the treatment of hepatitis B virus infections

Approximately 5% of the world's human population have an increased risk for developing liver cancer and cirrhosis as a direct consequence of chronic infection with the hepatitis B virus (HBV). Antiviral chemotherapy remains the only option for controlling infection in these individuals, for whom the current licensed hepatitis B vaccines provide no benefit. Interferon (IFN)-alpha has proven benefit in a well-defined group of those with hepatitis B but has made little impact on the global burden of chronic liver disease. The development of more effective chemotherapy for treatment of chronic hepatitis B infection has proven to be extremely challenging, the result of both virus- and host-dependent factors, which will be reviewed in this article. Past attempts to treat chronic hepatitis B infection using nucleoside analogues were disappointing, but more recently, several nucleoside (or nucleotide) analogues have been identified that are potent and selective inhibitors of HBV replication. These agents fall into two broad categories: (1) nucleoside/nucleotides that have modified sugar residues in either cyclic or acyclic configurations and (2) stereoisomers of nucleosides in the "unnatural" L-configuration. Of the analogues that have been used clinically, representatives of the first category are purine derivatives, e.g., adefovir dipivoxil and famciclovir, whereas representatives of the second category are pyrimidine derivatives, such as lamivudine.

Thymosin alpha1 treatment of chronic hepatitis B: results of a phase III multicentre, randomized, double-blind and placebo-controlled study

Previous clinical trials have suggested that thymosin alpha1 (Talpha1), an immunomodulatory peptide, may be effective in the treatment of chronic hepatitis B (CHB). The aim of this study was to determine the efficacy of Talpha1 in a multicentre, placebo-controlled and double-blind study of 97 patients with serum hepatitis B virus (HBV) DNA- and hepatitis B e antigen (HBeAg)-positive CHB. Patients who had been hepatitis B surface antigen (HBsAg) positive for at least 12 months entered a 3-month screening period prior to randomization. Forty-nine patients received Talpha1 (1.6 mg) and 48 patients received placebo, twice weekly for 6 months, and were followed-up for an additional 6 months. At inclusion, both groups were comparable for age, gender, histological grading, and aminotransferase and HBV DNA levels. A complete response to treatment, defined as a sustained serum HBV DNA-negative status (two negative results at least 3 months apart) during the 12-month study, with negative HBV DNA and HBeAg values at month 12, was seen in seven (14%) patients given Talpha1 and in two (4%) patients treated with placebo (P = 0.084). Five (10%) patients given Talpha1 and four (8%) patients given placebo exhibited a delayed response (defined as sustained serum HBV DNA negativity achieved after the 12-month study period with negative HBV DNA and HBeAg values at the last assessment). A total of 12 (25%) patients given Talpha1 and six (13%) patients given placebo showed a sustained loss of HBV DNA with a negative HBeAg value during or following the 12-month study period (P < 0.11). These results do not confirm observations of treatment efficacy reported in other clinical studies.

Treatment of chronic hepatitis B virus infection: an Asia-Pacific perspective

Chronic hepatitis B infection is a serious health threat in the Asia-Pacific area. A consensus meeting on the treatment of chronic hepatitis B infection was conducted in Hong Kong, in August 1997. It was generally agreed that treatment of chronic hepatitis B infection should be based on the understanding of the natural history of chronic hepatitis B infection. To date, interferon alpha is the only Food and Drug Administration (FDA)-approved form of therapy for chronic hepatitis B infection. The overall response in Asian patients is unsatisfactory: approximately 15-20% will clear hepatitis B e antigen, but less than 5% will clear hepatitis B surface antigen. Newer immunomodulatory therapies are under trial. In contrast, nucleoside analogues, such as lamivudine (pending FDA approval) and famciclovir, have been shown to be potent suppressors of hepatitis B viral replication; however, their role as monotherapy in the treatment of chronic hepatitis B infection remains to be defined. Also, the issues of resistance to nucleoside analogues and withdrawal rebound need to be carefully studied. The future direction of therapy in chronic hepatitis B infection is probably a combination of nucleoside analogues or nucleoside analogues with immunomodulatory therapy.

Long-term therapy with the guanine nucleoside analog penciclovir controls chronic duck hepatitis B virus infection in vivo

Ducks congenitally infected with duck hepatitis B virus (DHBV) were treated with the antiviral guanine nucleoside analog penciclovir for 12 or 24 weeks at a dosage of 10 mg/kg of body weight per day. By the completion of both 12 and 24 weeks of therapy, molecular hybridization studies of the liver tissue revealed that the viral DNA, RNA, and protein levels were significantly reduced compared to those in the placebo-treated controls. Penciclovir treatment for 12 or 24 weeks was not associated with any toxicity, establishing the efficacy and safety of long-term penciclovir therapy in chronic DHBV infection.

Quantitative detection of hepatitis B virus DNA with a new PCR assay

The Amplicor HBV Monitor Test for quantitative detection of serum hepatitis B virus (HBV) DNA has recently been introduced. This assay is based on PCR and a non-radioactive hybridization and detection system on microwell plates. Evaluation in a routine diagnostic laboratory showed excellent sensitivity and adequate reproducibility; however, a more automated format would be desirable. The Amplicor HBV Monitor Test is useful for recognizing those patients who might benefit from antiviral treatment and for evaluation of the efficacy of anti-hepatitis B virus treatment.

Evaluation of a new assay for HBV DNA quantitation in patients with chronic hepatitis B

BACKGROUND

The Amplicor HBV Monitor Test for quantitative determination of serum hepatitis B virus (HBV) DNA has recently been introduced. This assay is based on PCR and a non-radioactive hybridization and detection system on microwell plates.

OBJECTIVE

The performance of the Amplicor HBV Monitor Test was evaluated in a routine diagnostic laboratory. The Amplicor HBV Monoitor assay was compared to the Digene Hybrid Capture System HBV DNA assay for the quantitation of HBV in patient sera.

STUDY DESIGN

Sensitivity and reproducibility were determined with 10-fold dilution series of two Eurohep HBV reference plasma specimens. Furthermore, 196 sera from 14 children with chronic HBV infection and interferon therapy were tested with both assays.

RESULTS

The detection limit was found to be 10(3) copies/ml with the Amplicor PCR assay compared to 10(6) to 10(7) copies/ml with the Digene hybridization assay. Both assays were quasi-linear over the measurable ranges. The new PCR assay proved to be very reliable. With the Amplicor PCR assay, 26.2% of the HBV DNA-positive clinical samples were found between 10(3) and 10(7) copies/ml and all of them tested below the detection limit with the hybridization assay.

CONCLUSION

The Amplicor HBV Monitor Test shows excellent sensitivity and provides a valuable tool for the detection of HBV DNA in serum. It can be used for recognizing those patients who might benefit from antiviral therapy, for evaluation of the efficacy of anti-HBV therapy, and for validation of blood products.

Review: Present and future directions in the treatment of chronic hepatitis B infection

The last decade has witnessed substantial progress in the development of chemotherapeutic agents for chronic hepatitis B. However, the only currently licensed treatment in Australia, interferon-alpha, has low initial response rates and the adverse effects are often unacceptable. Of the newer agents in the class of nucleoside analogues, famciclovir and lamivudine are in phase III clinical trials with encouraging preliminary results, while other agents, such as bis-POM PMEA (Adefovir), are at phase I/II development. Future approaches to therapy will be governed by an understanding of the effects of nucleoside analogues on the natural history of the disease as well as on the hepatitis B virus hepatocyte interaction. Combination antiviral therapy should theoretically offer improved response rates, decrease the development of viral resistance, and provide the greatest reduction in viral load, but it has not yet been widely examined in the clinical setting. In this article, we review the currently available strategies, discuss potential problem areas, and speculate on promising approaches with combination chemotherapy and the features of agents soon to be trialed.

Hepatitis B virus replication--an update

Hepatitis B virus (HBV), the causative agent of type B hepatitis in humans, is the prototypic member of the hepadnaviridae, a family of small enveloped DNA-containing viruses with pronounced host and tissue specificity. This property has greatly hampered progress in understanding the initial events of infection, i.e. attachment, penetration and uncoating. After the discovery, originally made with the duck hepatitis B virus (DHBV), that hepadnaviruses replicate by reverse transcription, DNA transfection of cloned wild-type and mutant HBV genomes into cell lines supporting virion formation has revealed the molecular mechanisms of the late steps of the infectious cycle in some detail. During the last few years, such studies have emphasized the differences between hepadnaviral and retroviral replication. Very recent research, however, indicates that the border separating the two viral families may not be as strict as previously thought. In this article, we will briefly summarize the pertinent differences, and will then focus on the new data, with particular emphasis on the initiation of reverse transcription.

Chronic viral hepatitis in childhood

In endemic areas infection with hepatitis B virus is a common cause of chronic liver disease in childhood. High levels of viral replication and mild ALT abnormalities are the rule in children infected perinatally and many of them are likely to maintain viral replication through their youth. Conversely about 90% of children infected later in life clear HBeAg and achieve sustained remission of liver disease before reaching adulthood. The eventual outcome of infection and disease in these patients remains unpredictable as reactivation of liver damage and viral replication may occur after several years of sustained remission. Cirrhosis is a rare and early complication of chronic HBV infection in children, and a risk factor for hepatocellular carcinoma. IFN therapy can accelerate HBV DNA clearance, improving the spontaneous anti-HBe seroconversion rate in Caucasian children by two to three times. Hepatitis delta is the most severe form of chronic viral hepatitis in childhood. Cirrhosis can be diagnosed in up to 26% of patients at presentation, and few cases respond to IFN therapy. Hepatitis C is relatively rare in children. Before the discovery of HCV, blood transfusions were the most common source of infection. Hepatitis C is usually a mild, asymptomatic disease in otherwise healthy children, but has a poor propensity to spontaneous remission over the years. For this reason, and based on the experience in adults, IFN treatment is now being evaluated.

Combination low-dose lymphoblastoid interferon and thymosin alpha 1 therapy in the treatment of chronic hepatitis B

This open label study was initiated to assess the safety and efficacy of lymphoblastoid interferon-alpha (IFN-alpha) and thymosin alpha 1 (T alpha 1) in the treatment of 11 patients with chronic hepatitis B, who had failed to respond to standard IFN-alpha 2b therapy, and in four interferon naive patients. These fifteen hepatitis B surface antigen (HBsAg) positive and serum hepatitis B virus (HBV) DNA positive patients were given T alpha 1 (1 mg) subcutaneously (s.c.) on 4 consecutive days. Low-dose lymphoblastoid IFN-alpha (3 MU) was administered intramuscularly (i.m.) on the fourth day. Beginning with the second and for the subsequent 25 weeks, patients self-administered T alpha 1 twice weekly in the morning followed, 12 h later, by 3 million units (MU) lymphoblastoid IFN-alpha. Patients were followed-up for 12 months. Nine (60%) of the 15 patients, including six (55%) of the 11 patients previously treated with IFN-alpha 2b, responded by losing serum HBV DNA and normalizing alanine aminotransferase (ALT) values. Six of the nine responders seroconverted to HBsAg negativity. Significant improvements in the Knodell histological activity index were observed in the responders and no significant adverse effects were observed. Combination low-dose lymphoblastoid IFN-alpha and T alpha 1 treatment may provide a safe and potentially effective therapeutic approach in chronic hepatitis B. These results require confirmation in future randomized controlled studies.

Comparison of four methods for quantitative measurement of hepatitis B viral DNA

AIMS/METHODS

Four assays for measuring HBV-DNA quantitatively have been compared with regard to sensitivity, precision and linearity. The methods were 125I-labelled solution hybridisation assay (liquid hybridisation, Abbott), an ELISA-based chemiluminescent RNA-DNA hybrid assay (RNA-DNA, Digene), a chemiluminescent branching oligonucleotide assay (bDNA, Chiron) and a membrane hybridisation assay using slot-blot equipment (slot blot).

RESULTS

The bDNA assay was linear over three orders of magnitude and was the most sensitive assay, being approximately ten times more sensitive than the other assays, so that samples negative on RNA-DNA, liquid hybridisation and slot blot gave quantifiable results on bDNA. Furthermore, intra- and inter-assay variability showed that the bDNA and liquid hybridisation assays had the greatest precision, with coefficients of variation of 6.6% to 11.5% and 2.3% to 10.5%, respectively. However, the nominated amounts of HBV DNA in the standards (from all assays) were not reproducible in the other assays, such that amounts measured with bDNA would give values approximately twice that of RNA-DNA and 60 times that of liquid hybridisation.

CONCLUSIONS

The recently developed bDNA assay has advantages compared with the other assays in quantitating samples with low levels of virus present. In addition, since the assays vary considerably by a number of criteria, the method of measurement should always be reported.

The guanine nucleoside analog penciclovir is active against chronic duck hepatitis B virus infection in vivo

Ducks congenitally infected with duck hepatitis B virus (HBV) were treated with the antiviral guanine nucleoside analog penciclovir for 4 weeks at a dose of 10 mg/kg of body weight per day. The effects of treatment on viremia and intrahepatic viral genome replication, transcription, and translation were examined. In seven of eight penciclovir-treated ducks, viremia was barely detectable after a week of treatment. After 4 weeks of treatment, molecular hybridization studies showed that intrahepatic viral DNA, RNA, and protein levels were significantly reduced compared with those in placebo-treated controls. Synthesis of all viral replicative intermediates, including the normally persistent viral supercoiled DNA species, was inhibited by penciclovir treatment. Examination of liver tissue sections after in situ DNA hybridization or immunohistochemical staining confirmed that viral DNA and protein synthesis had been profoundly inhibited in most hepatic parenchymal cells. However, small subpopulations of cells, in particular the small bile duct epithelial cells, remained strongly positive for duck HBV antigens and DNA despite treatment. There was no evidence of toxicity associated with penciclovir therapy. This study confirms the safety and potent antihepadnaviral activity of penciclovir in vivo but indicates that further improvements in antiviral therapy will be required to completely eliminate HBV infection.

Efficient hammerhead ribozyme-mediated cleavage of the structured hepatitis B virus encapsidation signal in vitro and in cell extracts, but not in intact cells

Hepatitis B virus (HBV), the causative agent of B-type hepatitis in man, is a small enveloped DNA virus that replicates through reverse transcription of an RNA intermediate, the terminally redundant RNA pregenome. An essential highly conserved cis-element present twice on this RNA is the encapsidation signal epsilon, a stem-loop structure that is critical for pregenome packaging and reverse transcription. Epsilon is hence an attractive target for antiviral therapy. Its structure, however, is a potential obstacle to antivirals whose action depends on hybridization, e.g. ribozymes. Here we demonstrate effective in vitro cleavage inside epsilon by hammerhead ribozymes containing flanking sequences complementary to an adjacent less structured region. Upon co-transfection with a HBV expression construct corresponding ribozymes embedded in a U6 snRNA context led to a significant, though modest, reduction in the steady-state level of HBV pregenomes. Inactive ribozyme mutants revealed that antisense effects contributed substantially to this reduction, however, efficient epsilon cleavage by the intracellularly expressed ribozymes was observed in Mg(2+)-supplemented cell lysates. Artificial HBV pregenomes carrying the ribozymes in cis and model RNAs lacking all HBV sequences except epsilon exhibited essentially the same behaviour. Hence, neither the absence of co-localization of ribozyme and target nor a viral component, but rather a cellular factor(s), is responsible for the strikingly different ribozyme activities inside cells and in cellular extracts.

Distinct requirements for primary sequence in the 5'- and 3'-part of a bulge in the hepatitis B virus RNA encapsidation signal revealed by a combined in vivo selection/in vitro amplification system

Hepatitis B virus (HBV) is a small DNA virus that replicates by reverse transcription of a terminally redundant RNA, the pregenome. Specific packaging of this transcript into viral capsids is mediated by interaction of the reverse transcriptase, P protein, with the 5'-proximal encapsidation signal epsilon, epsilon-function is correlated with the formation of a hairpin structure containing a bulge and a loop, each consisting of 6 nt. To analyse the importance of primary sequence in these regions, we have combined selection of encapsidation competent individuals from pools of randomized epsilon-sequences in transfected cells with in vitro amplification, thus bypassing the current experimental limitations of the HBV system. While no alterations of the authentic loop sequence were detectable, many different sequences were tolerated in the 3'-part of the bulge. However, at the two 5'-proximal bulge positions the wt sequence was strongly selected for, indicating that for RNA packaging close contacts between protein and the 5'- but not the 3'-part of the bulge are important. Such a bipartite organisation provides a structural basis for the recently demonstrated special role of the 3'-part of the bulge as template for the first nucleotides of (-)-strand DNA in HBV reverse transcription.

Reversion of duck hepatitis B virus DNA replication in vivo following cessation of treatment with the nucleoside analogue ganciclovir

In order to define, in more detail, the virological events which occur after completion of antiviral chemotherapy, ducks congenitally infected with the duck hepatitis B virus (DHBV) were treated for 4 weeks with the nucleoside analogue ganciclovir and followed up over a 7-day period. Specimens of serum and liver were collected daily during follow-up for virological analysis. Treatment resulted in a substantial reduction in both viraemia and liver DHBV DNA replicative intermediates. However, after cessation of treatment, viraemia returned to detectable levels within 4 days. In the liver, the viral supercoiled DNA (SC DNA) was the form least affected by therapy and returned to near control levels by day 2 post-treatment. The other hepatic replicative intermediates reached pretreatment levels within 4 days of cessation of therapy. This study has defined the kinetics of relapse of viral replication after completion of antiviral therapy in the duck hepatitis B model. Of all viral replicative forms, the SC DNA appears to be the one which is most resistant to nucleoside analogue therapy and is presumably responsible for the relapse phenomenon observed post-treatment.