New therapies for chronic hepatitis B

Targeting TLR9 agonists to secondary lymphoid organs induces potent immune responses against HBV infection

Despite the existence of a prophylactic vaccine against hepatitis B virus (HBV), chronic hepatitis B virus (CHB) infection remains the leading cause of cirrhosis and liver cancer in developing countries. Because HBV persistence is associated with insufficient host immune responses to the infection, development of an immunomodulator as a component of therapeutic vaccination may become an important strategy for treatment CHB. In the present study, we aimed to design a novel immunomodulator with the capacity to subvert immune tolerance to HBV. We developed a lymphoid organ-targeting immunomodulator by conjugating a naturally occurring, lipophilic molecule, α-tocopherol, to a potent CpG oligonucleotide adjuvant pharmacophore. This approach resulted in preferential trafficking of the α-tocopherol-conjugated oligonucleotide to lymphoid organs where it was internalized by antigen-presenting cells (APCs). Moreover, we show that conjugation of the oligonucleotides to α-tocopherol results in micelle-like structure formation, which improved cellular internalization and enhanced immunomodulatory properties of the conjugates. In a mouse model of chronic HBV infection, targeting CpG oligonucleotide to lymphoid organs induced strong cellular and humoral immune responses that resulted in sustained control of the virus. Given the potency and tolerability of an α-tocopherol-conjugated CpG oligonucleotide, this modality could potentially be broadly applied for therapeutic vaccine development.

RNA interference technologies and therapeutics: from basic research to products

RNA interference (RNAi) is a natural cellular process that regulates gene expression by a highly precise mechanism of sequence-directed gene silencing at the stage of translation by degrading specific messenger RNAs or blocking translation. In recent years, the use of RNAi for therapeutic applications has gained considerable momentum. It has been suggested that most of the novel disease-associated targets that have been identified are not ‘druggable’ with conventional approaches. However, any disease-causing gene and any cell type or tissue can potentially be targeted with RNAi.

This review focuses on the current knowledge of RNAi mechanisms and the safety issues associated with its potential use in a therapeutic setting. Some of the most important aspects to consider when working towards the application of RNAi-based products in a clinical setting have been related to achieving high efficacies and enhanced stability profiles through a careful design of the nucleic acid sequence and the introduction of chemical modifications, but most of all, to developing improved delivery systems, both viral and non-viral. These new delivery systems allow for these products to reach the desired target cells, tissues or organs in a highly specific manner and after administration of the lowest possible doses. Various routes of application and target locations are currently being addressed in order to develop effective delivery systems for different targets and pathologies, including infectious pathologies, genetic pathologies and diseases associated with dysregulation of endogenous microRNAs. As with any new technology, several challenges and important aspects to be considered have risen on the road to clinical intervention, e.g. correct design of preclinical toxicology studies, regulatory concerns, and intellectual property protection. The main advantages related to the use of RNAi-based products in a clinical setting, and the latest clinical and preclinical studies using these compounds, are reviewed.

Use of hepatitis B vaccine for the treatment of chronic hepatitis B

Current therapeutic approaches to control chronic hepatitis B (CH-B), such as administrations of interferon or nucleoside analogs, are still unsatisfactory. Vaccination with conventional hepatitis B (HB) vaccine is another therapeutic approach with lower cost and potentially long-lasting beneficial effect. However, a response rate to vaccination therapy is not necessarily high. Therefore, combination therapy of interferon, nucleoside analogs and vaccination, would be the promising therapeutic approach that improves therapeutic effect and solves the problems of individual therapies. Herein, we report the results of the clinical trial, the combination therapy of lamivudine (LAM) and HB vaccine in patientswith B-CH as one of the candidates for the combination therapies. The results indicate that the combination therapy of LAM and HB vaccine was more effective in regulating viral replication than the LAM monotherapy was. In addition, no adverse effect was observed in the patients given HB vaccine. This novel therapy should be further examined for the improvement of its efficacy and achievement of continuous suppression of HB virus replication.

Medex test, a novel modality for liver disease diagnosis: a pilot study

BACKGROUND AND AIMS

Liver diseases are associated with significant morbidity and health- related expenditure. Although cost-effective treatments are available, the disease is often asymptomatic until late in its course. "Medex Test," is the noninvasive detection of liver abnormalities by the measurement of changes in electrical impedance of dermal zones. This method is based on neuroreflexology, a branch of complementary medicine. This study addressed 2 questions: can Medex Test detect liver disease, and can it measure the severity of a known liver disease.

METHODS

This blinded case-control study included 2 parts. First, 113 patients with a known liver disease (hepatitis C, hepatitis B, and nonalcoholic fatty liver disease) and 85 controls with no known liver disease were evaluated by the Medex Test device. Second, necroinflammatory grading of biopsy results of 60 patients with chronic hepatitis C were compared with grade determined by Medex Test.

RESULTS

Medex Test detected with high sensitivity (85%) and specificity (94.1%) the presence of liver disorders. The high rates were similar for the different disorders and were independent of age and sex. Additionally, Medex Test matched the biopsy pathologic grading of necroinflammation in 78% of patients. Positive predictive value was not affected by age and sex and was better for higher degree of necroinflammation.

CONCLUSIONS

This pilot study demonstrated that Medex Test detects with high accuracy the presence of liver disorders and the necroinflammatory grade. This noninvasive, low cost test may in the future become an important tool in the diagnosis and management of liver disorders. We believe the further study of this novel method is warranted.

Novel approaches towards conquering hepatitis B virus infection

Currently approved treatments for hepatitis B virus (HBV) infection include the immunomodulatory agent, IFN-α, and nucleos(t)ide analogues. Their efficacy is limited by their side effects, as well as the induction of viral mutations that render them less potent. It is thus necessary to develop drugs that target additional viral antigens. Chemicals and biomaterials by unique methods of preventing HBV replication are currently being developed, including novel nucleosides and newly synthesized compounds such as capsid assembling and mRNA transcription inhibitors. Molecular therapies that target different stages of the HBV life cycle will aid current methods to manage chronic hepatitis B (CHB) infection. The use of immunomodulators and gene therapy are also under consideration. This report summarizes the most recent treatment possibilities for CHB infection. Emerging therapies and their potential mechanisms, efficacy, and pitfalls are discussed.

Novel Approaches to New Therapies for Hepatitis B Virus Infection

Hepatitis B is one of the most prevalent viral diseases in the world. It leads to chronic liver disease in 10% of infected individuals, putting them at an increased risk for liver-related morbidity and mortality from complications of cirrhosis and hepatocellular carcinoma. Despite the success of universal hepatitis B vaccination in many countries, this disease remains a major public health problem, resulting in more than 500,000 deaths per year. Although the current therapy for chronic hepatitis B (CHB) is effective, it is not optimal; novel approaches to the management of CHB are needed. An improved understanding of virus-host interactions, advances in gene therapy, the development of molecular therapies targeted at different stages of the hepatitis B virus life cycle, and new insights into various approaches of immune modulation will lead to the development of better therapeutic agents for the management of CHB. These advances herald a new era of combination therapy. In this review, we will discuss emerging therapies and potential mechanisms, and highlight the promises and pitfalls of these new treatment strategies.

Impaired function of hepatic natural killer cells from murine chronic HBsAg carriers

In the present study, we demonstrated hepatic NK cells in murine chronic HBsAg carriers for the first time. It was found that the number of hepatic NK cells was decreased; natural activation of hepatic NK cells was declined; and cytotoxicity of hepatic NK cells was attenuated, which might relate to the down-regulated expression of TRAIL on hepatic NK cells. Additionally, the response of hepatic NK cells to the specific stimulation of Poly (I:C) in murine chronic HBsAg carriers was changed. The increase in anti-tumor cytotoxic activity of intrahepatic activated NK cells was markedly impaired in the transgenic mice. The transgenic mice used here had high incidence of hepatocellular carcinoma, which might result from the relative weak reactivity and impaired anti-tumor activity of NK cells in the liver. Furthermore, remarkable liver injury was observed after stimulation of Poly (I:C), demonstrating the hypersensitivity to Poly (I:C) of murine chronic HBsAg carriers which might be related to the accumulated NK cells in the liver. Why the murine chronic HBsAg carriers are characterized with impaired hepatic NK cells and the implication of the impaired hepatic NK cells in pathogenesis of HBV-related diseases, such as hepatocellular carcinoma and recrudescent hepatitis, is worth of further investigating. These results of the functions of hepatic NK cells in murine chronic HBsAg carriers would contribute to interpreting the immune responses of NK cells in the liver and the immunological mechanisms of liver diseases in human chronic HBsAg carriers.

In vivo hierarchy of immunodominant and subdominant HLA-A*0201-restricted T-cell epitopes of HBx antigen of hepatitis B virus

A polyepitopic CD8+ T-cell response is critical for the control of hepatitis B virus (HBV) infection. The HBV X protein (HBx) is a multifunctional protein that is important for the viral life cycle and for host-virus interactions. The aim of this study was to analyze the immunogenicity and dominance of various HLA-A*0201-restricted HBx-derived epitopes. For this purpose, we immunized HLA-A*0201-transgenic mice with HBx-derived peptides and DNA. This is a powerful model for studying the induction of HLA-A*0201-restricted immune responses in vivo, as these mice possess a cytotoxic T lymphocyte (CTL) repertoire representative of HLA-A2.1 individuals. We used cytotoxic tests and enzyme-linked immunosorbent spot (ELISPOT) assays to study the induction of specific cytotoxic and interferon (IFN)-gamma-secreting T cells. This allowed us to classify the HBx epitopes according to their T-cell activation capacity. After endogenous processing of the antigen synthesized in vivo after DNA-based immunization, we found that the HBx-specific T-cell response is targeted against one immunodominant epitope. Furthermore, following peptide immunization, we identified six additional novel subdominant T-cell epitopes. Inclusion of well-characterized epitopic sequences of HBx in a new vaccine for chronic HBV infections could help to broaden the T-cell response.

The prospects of hepatic drug delivery and gene therapy

Liver targeted therapy is designed to deliver a substance preferentially to the organ in order to increase the accumulation, improve the therapeutic effect and reduce toxicity to other organs. The aim of selective targeting is to deliver a substance to a specific cell type in the liver. A variety of vehicles have been designed and further modified for selective targeting of therapeutics to the liver. The targeting properties and strategies of commonly used agents, such as liposomes, microspheres and recombinant chylomicrons, are discussed. Viral and non-viral vectors, such as cationic liposomes, reconstituted chylomicron remnants, adenoviruses, adeno-associated viruses, retroviruses, and SV-40, are currently being evaluated for the delivery of DNA to the liver. New developments in improving the targeting efficiency of the available vectors while avoiding their disadvantages have made their use in clinical trials of various genetic disorders possible. For viral hepatitis, antisense and ribozyme techniques are being employed with selective targeting approaches. A commonly employed current strategy for targeting hepatocellular carcinoma cells is to make the tumour cells convert non-toxic 'prodrugs' to toxic metabolites in situ, achieving a high concentration of the toxic product in the local milieu, while avoiding systemic toxicity. Although gene therapy itself is in its infancy, some encouraging results have been developed in studies of familial hypercholesterolaemia, haemophilia, alpha1-antitrypsin deficiency and Crigler-Najjar syndrome. The potential strengths as well as the problems with these studies are discussed.

New options in the treatment of chronic hepatitis

The short-term aim of chronic hepatitis B treatment is the suppression of Hepatitis B Virus (HBV) replication, as shown by the loss of HBV DNA by DNA hybridization and the loss of Hepatitis B e Antigen (HBeAg). Loss of Hepatitis B s Antigen (HBsAg) and HBV DNA as assayed by Polymerase Chain Reaction (PCR) is very difficult to achieve. There are two important treatment approaches. The first is immunomodulation, comprising Interferon (IFN) and other cytokine treatment and therapeutic vaccination. The second is antiviral treatment, which mainly includes treatment with nucleoside analogs. There are many limitations to IFN treatment, because it has succeeded only in a small number of patients with a high level of transaminase and a low level of HBV DNA. The theoretical basis of therapeutic vaccination is the use of a vaccine that contains epitopes known to stimulate Human Leucocyte Antigen (HLA)-restricted cytotoxic T cell activity in order to lyse the HBV-infected hepatocytes. Several strategies of hepatitis vaccination are the incorporation of both pre-S and S antigen, the incorporation of a Cytotoxic T Lymphocyte (CTL)-specific antigen, the use of an HBV vaccine complexed to Hepatitis B Immune Globulin (HBIG), and DNA vaccination. One of the limitations of therapeutic vaccination is the short duration of immunity to the CTL antigen. Lamivudine is an oral nucleoside analog with potent antiviral action. It rapidly reduces the HBV DNA level, a level that soon returns to pretreatment level after drug administration is terminated. This drug does not affect the covalently bond closed circular (ccc)DNA of infected hepatocytes; it only inhibits the formation of new viruses. One-year of Lamivudine treatment significantly improved necroinflammation and reduced the progression of fibrosis and the histologic activity index. HBeAg seroconversion occurred after prolonged treatment. The emergence of a tyrosine-methionine asparagine aspargine YMDD mutant is one of the drawbacks of lamivudine treatment. Therefore a combination with other antiviral agents or immune modulators, such as therapeutic vaccination, is likely to be more effective.

Hepatitis B treatment: rational combination chemotherapy based on viral kinetic and animal model studies

Hepatitis B virus (HBV) causes a generally non-cytopathic infection in the liver. Even though HBV is a DNA virus, it replicates via reverse transcription which is coordinated within the viral nucleocapsid by the virus-specific polymerase. The major transcriptional template is the viral mimichromosome from which the viral DNA exists as a covalently closed circular (ccc) molcule. The virus infects hepatocytes but can also be found in non-hepatocyte reservoirs such as bile-duct epithelium, mesangial cells of the kidney, pancreatic islet cells and lymphoid cells. When patients infected with HBV are treated with either interferon alpha or lamivudine, responses are variable and unpredictable. Sophisticated mathematical models analysing the dynamics of viral clearance during antiviral therapy have recently been applied to chronic hepatitis B. Typically complex profiles, rather than the usual biphasic responses seen with other diseases have been observed, indicating that antiviral efficacy requires substantila improvement. This may be achieved with combination chemotherapy. However, chronic hepatitis B is a complex and heterogeneous disease entity, and the challenge for the future is to define measurable end-points of treatment and address key virological issues such as the role of cccDNA and extra-hepatocyte replication in treatment failure. Clearly, new therapies and effective combination therapy protocols are urgently required in order to improve the present poor response rates in patients undergoing treatment.

CpG oligodeoxynucleotides with hepatitis B surface antigen (HBsAg) for vaccination in HBsAg-transgenic mice

DNA motifs containing unmethylated CpG dinucleotides within the context of certain flanking sequences enhance both innate and antigen-specific immune responses, due in part to the enhanced production of Th1-type cytokines. Here we explored the ability of CpG-containing oligodeoxynucleotides combined with recombinant hepatitis B surface antigen (HBsAg) to induce Th1 responses in mice that are transgenic for this antigen and that represent a model for asymptomatic hepatitis B virus chronic carriers. This was compared to hepatitis B virus-specific DNA-mediated immunization, which we have previously shown to induce the clearance of the transgene expression product and the down-regulation of hepatitis B virus mRNA in this transgenic mouse lineage. In control nontransgenic C57BL/6 mice, three immunizations with HBsAg and CpG triggered the production of anti-HBs antibodies and of HBs-specific T cells that secrete gamma interferon but do not display any HBsAg-specific cytotoxic activity. In the HBsAg-transgenic mice, immunization with HBsAg and CpG oligodeoxynucleotides, but not with CpG alone, induced the clearance of HBsAg circulating in the sera, with a concomitant appearance of specific antibodies, and was able to regulate the hepatitis B virus mRNA constitutively expressed in the liver. Finally, adoptive transfer experiments with CD8(+) T cells primed in C57BL/6 mice with HBsAg and CpG oligodeoxynucleotide-based immunization show that these cells were able to partially control transgene expression in the liver and to clear the HBsAg from the sera of recipient transgenic mice without an antibody requirement. CpG oligodeoxynucleotides motifs combined with HBsAg could therefore represent a potential therapeutic approach with which to treat chronically infected patients.

Immunotherapy of chronic hepatitis B by anti HBV vaccine: from present to future

Chronic liver disease and hepatocellular carcinoma associated with chronic hepatitis B virus (HBV)-infection are among the most serious human health problems in highly endemic regions. Current therapeutic approaches to control chronic hepatitis such as interferon-alpha and lamivudine are unsatisfactory. Vaccination would be the therapeutic procedure with the lowest cost and the potentially greatest benefit. The immunogenicity of selected HBV envelope- or capsid-based vaccine formulations for the induction or the broadening of T and B cell responses, deficient in HBV chronic carriers, are currently under study in animal models and in clinical trials.

Novel hepatotrophic prodrugs of the antiviral nucleoside 9-(2-phosphonylmethoxyethyl)adenine with improved pharmacokinetics and antiviral activity

The device of new hepatotrophic prodrugs of the antiviral nucleoside 9-(2-phosphonylmethoxyethyl)adenine (PMEA) with specificity for the asialoglycoprotein receptor on parenchymal liver cells is described. PMEA was conjugated to bi- and trivalent cluster glycosides (K(GN)(2) and K(2)(GN)(3), respectively) with nanomolar affinity for the asialoglycoprotein receptor. The liver uptake of the PMEA prodrugs was more than 10-fold higher than that of the parent drug (52+/-6% and 62+/-3% vs. 4.8+/-0.7% of the injected dose for PMEA) and could be attributed for 90% to parenchymal cells. Accumulation of the PMEA prodrugs in extrahepatic tissue (e.g., kidney, skin) was substantially reduced. The ratio of parenchymal liver cell-to-kidney uptake-a measure of the prodrugs therapeutic window-was increased from 0.058 +/- 0.01 for PMEA to 1.86 +/- 0.57 for K(GN)(2)-PMEA and even 2.69 +/- 0.24 for K(2)(GN)(3)-PMEA. Apparently both glycosides have a similar capacity to redirect (antiviral) drugs to the liver. After cellular uptake, both PMEA prodrugs were converted into the parent drug, PMEA, during acidification of the lysosomal milieu (t(1/2) approximately 100 min), and the released PMEA was rapidly translocated into the cytosol. The antiviral activity of the prodrugs in vitro was dramatically enhanced as compared to the parent drug (5- and 52-fold for K(GN)(2)-PMEA and K(2)(GN)(3)-PMEA, respectively). Given the 15-fold enhanced liver uptake of the prodrugs, we anticipate that the potency in vivo will be similarly increased. We conclude that PMEA prodrugs have been developed with greatly improved pharmacokinetics and therapeutic activity against viral infections that implicate the liver parenchyma (e.g., HBV). In addition, the significance of the above prodrug concept also extends to drugs that intervene in other liver disorders such as cholestasis and dyslipidemia.

Decrease of wild-type and precore mutant duck hepatitis B virus replication during lamivudine treatment in white Pekin ducks infected with the viruses

BACKGROUND/AIMS

Lamivudine, an antiviral agent, has been used in the treatment of chronic hepatitis B, but little is known about its effect on intrahepatic replication of hepatitis B virus. We investigated the effect of lamivudine on the replication of wild-type and precore mutant duck hepatitis B virus (DHBV) in the liver and serum of DHBV carrier ducks.

METHODS

Chronic carrier ducks with either wild-type or precore mutant DHBV were treated for 2 weeks with either low-dose (20 mg/kg, p.o., b.i.d.) or high-dose lamivudine (100 mg/kg, p.o., b.i.d.) or were untreated. Serum levels of DHBV DNA were examined serially by slot-blot hybridization. A second group of chronic carrier ducks was treated for 12 weeks with lamivudine (100 mg/kg, p.o., b.i.d.) or was untreated. The amount of DHBV DNA in serum and its various replicative intermediates in the liver were serially examined by slot-, Southern, and Northern blot methods.

RESULTS

In the 2-week treatment study, concentration of DHBV DNA in serum treated with low- and high-dose lamivudine was reduced to 10.8% and 1.1% of the control level in wild-type DHBV carriers, and to 2.3% and 0.48% in precore mutant DHBV carriers, respectively. In the 12-week treatment study, concentration of DHBV DNA in serum at the end of treatment was reduced to <0.65% and <5.36% in wild-type and precore mutant DHBV carriers, respectively. Southern and Northern blot analyses revealed that the various replicative forms of DHBV DNA in the liver were decreased in all treated ducks, but, covalently closed circular DNA and RNA intermediates tended to remain unchanged.

CONCLUSIONS

Our results showed that lamivudine could reduce both wild-type and precore mutant DHBV levels in the liver through inhibition of the reverse transcription step, but complete elimination of the viruses from liver is difficult even by relatively long-term lamivudine monotherapy, suggesting a need for some additional therapy to obtain complete clearance.

Liver transplantation. American Association for the Study of Liver Diseases

Liver transplantation has revolutionized the care of patients with end-stage liver disease. Liver transplantation is indicated for acute or chronic liver failure from any cause. Because there are no randomized controlled trials of liver transplantation versus no therapy, the efficacy of this surgery is best assessed by carefully comparing postoperative survival with the known natural history of the disease in question. The best examples of this are in primary biliary cirrhosis and primary sclerosing cholangitis, for which well-validated disease-specific models of natural history are available. There are currently relatively few absolute contraindications to liver transplantation. These include severe cardiopulmonary disease, uncontrolled systemic infection, extrahepatic malignancy, severe psychiatric or neurological disorders, and absence of a viable splanchnic venous inflow system. One of the most frequently encountered contraindications to transplantation is ongoing destructive behavior caused by drug and alcohol addiction. The timing of the surgery can have a profound impact on the mortality and morbidity of patients undergoing liver transplantation. Because of the long waiting lists for donor organs, the need to project far in advance when transplantation might be required has proven to be one of the greatest challenges to those treating patients with end-stage liver disease. Three important questions must be addressed in a patient being considered for liver transplantation: (1) when should the patient be referred for possible transplantation? (2) when should the patient be listed for transplantation? and (3) when is the patient too sick to have a reasonable chance of surviving the perioperative period?

Hepatitis B virus transgenic mouse model of chronic liver disease

A model for hepatitis B virus-associated chronic liver disease has been made using cloned hepatitis B virus DNA as a transgene in a severe combined immunodeficient host. These mice consistently support virus gene expression and replication. After adoptive transfer of unprimed, syngeneic splenocytes, these mice cleared virus from liver and serum, and developed chronic liver disease. This model will permit identification of the host and virus contributions to chronic liver disease in the absence of tolerance.

Treatment of chronic hepatitis B: new antiviral therapies

Chronic hepatitis B infection is the most important cause of cirrhosis and hepatocellular carcinoma worldwide. Interferon-alpha has been shown to be effective in approximately one third of patients, and response seems to be sustained in long-term follow-up studies in Western countries. New treatments using lamivudine and other nucleoside analogues such as famciclovir, lobucavir, and adfovir showed promising results although sustained suppression of viral replication is unusual after discontinuation of therapy. The results of recent clinical studies using these nucleoside analogues are discussed in detail in this review. Other important issues such as drug resistance and the role of combination therapy are also addressed.

Robustaflavone, a potential non-nucleoside anti-hepatitis B agent

Robustaflavone, a naturally occurring biflavanoid isolated from Rhus succedanea, was found to be a potent inhibitor of hepatitis B virus (HBV) replication in 2.2.15 cells, with an effective concentration (EC50) of 0.25 microM, and a selectivity index (SI, IC50/EC90) of 153. Robustaflavone hexaacetate inhibited HBV replication with an EC50 of 0.73 microM, but exhibited no cytotoxicity at concentrations up to 1000 microM. Combinations of robustaflavone with penciclovir and lamivudine displayed synergistic anti-HBV activity, having the most pronounced effects when the combination ratios were similar to the ratio of EC50 potencies. Thus, a 1:1 combination of robustaflavone and penciclovir exhibited an EC50 of 0.11 microM and an SI of 684, while a 10:1 combination of robustaflavone and lamivudine exhibited an EC50 of 0.054 microM and an SI of 894. Statistical analyses of the combination data using the Combostat program confirmed that robustaflavone exhibited synergism with both penciclovir and lamivudine.

Emergence and takeover of YMDD motif mutant hepatitis B virus during long-term lamivudine therapy and re-takeover by wild type after cessation of therapy

Treatment of hepatitis B virus (HBV) with lamivudine is effective in suppressing virus replication and results in reduced inflammatory activity. However, the emergence of lamivudine-resistant mutant virus, with amino acid substitution in the YMDD motif of DNA polymerase, has been reported. We report the emergence and takeover of YMDD mutant and re-takeover by wild type during and after long-term lamivudine therapy. YMDD mutants were detected in five patients who showed DNA breakthrough (HBV DNA becoming detectable after a period of DNA negativity), which occurred after 9 to 14 months of lamivudine therapy. Four of five mutants had amino acid sequence YIDD, and the remaining mutant had YVDD. Patients with high HBV-DNA titer and/or hepatitis B e antigen tended to develop breakthrough (P = .038). Using a sensitive and specific polymerase chain reaction (PCR)-based method developed in this study, the emergence of YMDD mutants was detected 1 to 4 months before DNA breakthrough, but not detected in any of the pretreatment sera. The mutants were predominant at breakthrough, but were replaced by wild-type virus 3 to 4 months after cessation of therapy in the two patients who discontinued therapy. One of these patients had a relapse of hepatitis. Mutant continued to replicate in the remaining three patients who continued to receive treatment, and relapse occurred in only one of these patients. Our results suggest that the replication of YMDD mutant viruses is less than wild type and is re-overtaken by wild type after cessation of therapy. Re-administration of lamivudine, possibly combined with other antiviral therapy, might be useful in some patients experiencing hepatitis with lamivudine-resistant variants.