Lamivudine treatment can restore T cell responsiveness in chronic hepatitis B

Mutations of the woodchuck hepatitis virus polymerase gene that confer resistance to lamivudine and 2'-fluoro-5-methyl-beta-L-arabinofuranosyluracil

Administration of either lamivudine (2'-deoxy-3'-thiacytidine) or L-FMAU (2'-fluoro-5-methyl-beta-L-arabinofuranosyluracil) to woodchucks chronically infected with woodchuck hepatitis virus (WHV) induces a transient decline in virus titers. However, within 6 to 12 months, virus titers begin to increase towards pretreatment levels. This is associated with the emergence of virus strains with mutations of the B and C regions of the viral DNA polymerase (T. Zhou et al., Antimicrob. Agents Chemother. 43:1947-1954, 1999; Y. Zhu et al., J. Virol. 75:311-322, 2001). The present study was carried out to determine which of the mutants that we have identified conferred resistance to lamivudine and/or to L-FMAU. When inserted into a laboratory strain of WHV, each of the mutations, or combinations of mutations, of regions B and C produced a DNA replication-competent virus and typically conferred resistance to both nucleoside analogs in cell culture. Sequencing of the polymerase active site also occasionally revealed other mutations, but these did not appear to contribute to drug resistance. Moreover, in transfected cells, most of the mutants synthesized viral DNA nearly as efficiently as wild-type WHV. Computational models suggested that persistence of several of the WHV mutants as prevalent species in the serum and, by inference, liver for up to 6 months following drug withdrawal required a replication efficiency of at least 10 to 30% of that of the wild type. However, their delayed emergence during therapy suggested replication efficiency in the presence of the drug that was still well below that of wild-type WHV in the absence of the drug.

Therapeutic vaccination in chronic hepatitis B

AIMS

The aim was to test the efficacy of a pre-S2-containing vaccine (Genhevac-B) in chronic hepatitis B (CHB). Twenty-five naive patients (22 male, three female; median age 35; range: 6-69 years) with CHB were recruited. The inclusion criteria were: hepatitis B e antigen (HBeAg) positive or HBV-DNA detectable with liquid hybridization; alanine aminotransferase (ALT) is at least 1.5-fold the upper normal limit and histological evidence of chronic hepatitis.

METHODS

In the first period, all patients received monthly injections of 20, 40 and 60 microg of the vaccine. One month after the last injection, patients who still had HBV-DNA were divided into two randomly assigned groups. While the patients in the first group and the patients who lost HBV-DNA in the first period continued to receive monthly injections of 20 microg vaccine for a further 6 months, the patients in the second group received 9 MU interferon alpha-2b (Roferon-A), three times per week using the same method as for the first group. Patients were followed up after 12 months without treatment. Response was defined as the loss of HBV-DNA and normalization of ALT.

RESULTS

Six of the 25 patients lost HBV-DNA after 3 months. Nine of the remainder were randomly placed in the first group (vaccine-only) and 10 were placed in the second group (vaccine + interferon). End-of-treatment response was achieved, overall, 8/15 from the vaccine group and 6/10 from the combination. One patient from each group relapsed during the follow up. Overall, the sustained response (SR) rate was 46% (7/15) in the vaccine group, and 50% (5/10) in the combination group. Histological improvement was achieved in 6/7 SR with vaccine-only and all five with combination treatment, while 1/8 of failures of vaccine and 2/5 of failures of combination improved.

CONCLUSIONS

It was concluded that Genhevac-B decreases serum HBV-DNA levels in the majority of patients with CHB and sustained clearance was achieved in some patients. Combination of interferon-alpha with Genhevac-B is effective for the vaccine failures and may increase sustained response compared to interferon-alpha alone. However, the mechanism of action is yet to be explained.

The role of hepatitis B virus-specific memory CD8 T cells in the control of viral replication

BACKGROUND/AIMS

The aim of this study is to clarify the differences of host immune responses between acute self-limited and chronic persistent hepatitis B virus (HBV) infections by quantitative and qualitative analysis of HLA-A*2402-restricted HBV-specific CD8+ T cells.

METHODS

HBV-specific CD8+ T cells in peripheral blood mononuclear cells (PBMCs) from patients infected with HBV were analyzed by flow cytometry using two HLA-A*2402-HBV peptide tetrameric complexes.

RESULTS

High numbers of HBV-specific CD8+ T cells were detected in acute phase PBMCs from most individuals with acute HBV infection while the number of these cells was greatly reduced in recovery phase PBMCs. HBV-specific CD8+ T cells were not detected in PBMCs from individuals with chronic HBV infection except for one patient during acute exacerbation. HBV-specific CD8+ T cells were induced by in vitro peptide stimulation in PBMCs from chronic HBV carriers with a low level of serum HBV-DNA but not from those with a high level of serum HBV-DNA. CD28CD45RA phenotype analysis showed that HBV-specific CD8+ T cells in acute phase PBMCs predominantly express a memory T cell phenotype.

CONCLUSIONS

HBV-specific memory CD8+ T cells may play a crucial role in complete clearance of HBV from patients with acute HBV hepatitis.

Immunology of hepatitis B infection

The immune response initiated by the T-cell response to viral antigens is thought to be fundamental for viral clearance and disease pathogenesis in hepatitis B virus (HBV) infection. The T-cell response during acute self-limited hepatitis B in people is characterised by a vigorous, polyclonal, and multispecific cytotoxic and helper-T-cell response. By contrast, the immune response in chronic carriers, not able to eliminate the virus, is weak or undetectable. Thus a dominant cause of viral persistence could be the existence of a weak antiviral immune response. Methodological progress in animal models allows more precise investigation of the mechanisms by which the immune system resolves viral infection or develops chronic infection. Although clearance of most virus infections is widely thought to indicate the killing of infected cells by virus-specific T cells, data suggest that non-cytolytic intracellular viral inactivation by cytokines released by virus-inactivated lymphomononuclear cells could have an important role in the clearance of this virus without killing the infected cell. Additional factors that could contribute to viral persistence, which have been partly proven in animal models, are viral inhibition of antigen processing or presentation, modulation of the response to cytotoxic mediators, immunological tolerance to viral antigens, viral mutations, and infection of immunologically privileged sites. In view of the central role of cellular immunity in disease pathogenesis, strategies have been proposed to manipulate this cellular immune response in favour of protection from disease.

Failure of a reinforced triple course of hepatitis B vaccination in patients transplanted for HBV-related cirrhosis

Long-term immunoprophylaxis with anti-HBs immunoglobulins (HBIg) is used to prevent hepatitis B (HBV) reinfection after liver transplantation for HBV-related cirrhosis. This approach is highly expensive. A recent report proposed posttransplant HBV vaccination with a reinforced schedule as an alternative strategy to allow HBIg discontinuation. We investigated the efficacy of a reinforced triple course of HBV vaccination in 17 patients transplanted for HBsAg-positive cirrhosis 2 to 7 years earlier. The first cycle consisted of 3 double intramuscular doses (40 microg) of recombinant vaccine at month 0, 1, and 2, respectively. This was followed, in nonresponders, by a second cycle of 6 intradermal 10 microg doses every 15 days. All nonresponders then received a third cycle identical to the first one. Vaccination started 4.5 months after HBIg discontinuation, and lamivudine (100 mg/day) was given throughout the study. All patients were seronegative for HBsAg and HBV-DNA (by PCR) and positive for anti-HBe, and 7 were positive for anti-HDV. After the first cycle one patient (#5, 53 years old, male) developed an anti-HBs titer of 154 IU/L, another (#12) reached a titer of 20 IU/L and the remainder had titers <10 IU/L. At month 7, patient #5 reached a titer of 687 IU/L. After the second cycle only one additional patient (#9) had a slight response (an anti-HBs titer of 37 IU/L). After the third cycle patient #9 rose to an anti-HBs titer of 280 IU/L, patient #12 dropped to 10 IU/L, and no other patient responded. In conclusion, a highly reinforced HBV vaccination program is effective only in a few patients who had liver transplants for HBV-related cirrhosis.

Correlation of hepatitis B virus load with loss of e antigen and emerging drug-resistant variants during lamivudine therapy

It remains unclear whether sequential assessment of hepatitis B virus (HBV) load during lamivudine therapy can predict the loss of hepatitis B e antigen or emergence of drug-resistant variants. Therefore, a longitudinal study was carried out in 28 consecutive patients with chronic hepatitis B who started lamivudine therapy for a median of 12 months (range, 6-31). HBV DNA copy numbers were determined at 3-month intervals. From month 6 onward, HBV viral load below the detection limit of the PCR was predictive of the loss of envelope antigen (P = 0.043). Continuously detectable HBV DNA during the first 12 months of treatment indicated emergence of drug-resistant variants (P = 0.034). These data suggest that the goal of lamivudine therapy should be complete suppression of serum HBV DNA.

Quantity and quality of virus-specific CD8 cell response: relevance to the design of a therapeutic vaccine for chronic HBV infection

Chronic hepatitis B virus (HBV) infection is a major cause of morbidity and mortality worldwide, yet currently available therapies fail to provide long-term control of viral replication in most patients. Strategies to boost the weak virus-specific T-cell response typically found in patients with chronic hepatitis B have been proposed as a means of terminating persistent HBV infection. The potential problems arising from the stimulation of virus-specific immunity in a disease caused by a non-cytopathic virus, where viral control and liver injury are mediated by the immune system, are discussed. Furthermore, the concept of augmenting the HBV-specific T-cell response, which has previously been focused solely on quantitative issues, is expanded in the light of new findings of qualitative differences in the HBV-specific CD8 cell response.

High-level HIV-1 viremia suppresses viral antigen-specific CD4(+) T cell proliferation

In chronic viral infections of humans and experimental animals, virus-specific CD4(+) T cell function is believed to be critical for induction and maintenance of host immunity that mediates effective restriction of viral replication. Because in vitro proliferation of HIV-specific memory CD4(+) T cells is only rarely demonstrable in HIV-infected individuals, it is presumed that HIV-specific CD4(+) T cells are killed upon encountering the virus, and maintenance of CD4(+) T cell responses in some patients causes the restriction of virus replication. In this study, proliferative responses were absent in patients with poorly restricted virus replication although HIV-specific CD4(+) T cells capable of producing IFN-gamma were detected. In a separate cohort, interruption of antiretroviral therapy resulted in the rapid and complete abrogation of virus-specific proliferation although HIV-1-specific CD4(+) T cells were present. HIV-specific proliferation returned when therapy was resumed and virus replication was controlled. Further, HIV-specific CD4(+) T cells of viremic patients could be induced to proliferate in response to HIV antigens when costimulation was provided by anti-CD28 antibody in vitro. Thus, HIV-1-specific CD4(+) T cells persist but remain poorly responsive (produce IFN-gamma but do not proliferate) in viremic patients. Unrestricted virus replication causes diminished proliferation of virus-specific CD4(+) T cells. Suppression of proliferation of HIV-specific CD4(+) T cells in the context of high levels of antigen may be a mechanism by which HIV or other persistently replicating viruses limit the precursor frequency of virus-specific CD4(+) T cells and disrupt the development of effective virus-specific immune responses.

Extended follow-up of anti-HBe-positive patients with chronic hepatitis B retreated with ribavirin and interferon-alpha

In a pilot study of combination therapy with ribavirin and IFN alpha conducted in anti-HBe-positive individuals with chronic hepatitis B, 21% of patients achieved a sustained ALT normalization and clearance of hepatitis B virus (HBV) DNA as measured by PCR. The present work has assessed whether these sustained responses are lasting long-term. In addition, IFN gamma levels were tested serially in serum as a measure of the immune system activation during treatment. By extending the post-treatment follow-up period 2 years the occurrence of delayed HBV DNA relapses was observed. A low serum level of IFN gamma was detected during and after treatment. IFN gamma demonstrated a multiphasic time-course: the amount of IFN gamma increased in parallel with reductions in HBV DNA but also with ALT flare-ups. In conclusion, the extended follow-up study of anti-HBe-positive patients after combined treatment with ribavirin and IFN alpha has shown that sustained responses are lasting in 17% patients but also that a late onset HBV DNA relapse may occur.

Treatment of chronic hepatitis B

This review updates the treatment of chronic hepatitis B infection. Complete eradication of hepatitis B virus (HBV) is not possible, so the efficacy of treatment has to be assessed by whether it can limit long-term cirrhosis-related complications. We discuss two major groups of treatments--immunomodulators (interferon alfa, thymosin alpha1, therapeutic vaccines) and nucleoside analogues (lamivudine, adefovir, entecavir, emtricitabine, beta-L-2'-deoxythymidine). To date, interferon alfa and lamivudine are the only two agents approved for chronic hepatitis B. Interferon alfa achieves a short-term outcome of around 20-30% loss of HBeAg. The efficacy is lower in Chinese patients, who are immunotolerant to HBV because of acquisition of the disease during early childhood, than in white patients. This difference is further confirmed on long-term follow-up. Interferon alfa does not affect the development of cirrhosis-related complications in Chinese patients, whereas in white patients, the frequency of long-term complications is reduced if interferon alfa is successful in inducing loss of HBeAg. Lamivudine profoundly suppresses viral replication and achieves an HBeAg seroconversion rate similar to that of interferon alfa. It is equally effective in Chinese and white patients because the main antiviral mechanism is through inhibition of reverse transcription of HBV during viral replication. However, long-term lamivudine therapy is associated with emergence of HBV variants, YMDD variants. Newer nucleoside analogues are being extensively investigated by studies in vivo and in vitro. Combination therapy with two or three nucleoside analogues or immunomodulators plus nucleoside analogues will be the future direction of treatment of chronic hepatitis B.

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.

Hepatic decompensation associated with lamivudine: a case report and review of lamivudine-induced hepatotoxicity

We report a case of a 62-yr-old man with chronic hepatitis B virus (HBV)-related cirrhosis who developed hepatic decompensation after being started on lamivudine requiring liver transplantation. Decompensated liver disease while on lamivudine has been previously reported on two occasions, both HIV coinfected patients on a combination of nucleoside analogues. Our patient is alive and well nearly 2 yr after successful liver transplantation.

Current Options for the Therapy of Chronic Hepatitis B Infection

Until recently the only available treatment for chronic hepatitis B was interferon-alpha. Over the past few years a new class of antiviral has become available, the reverse transcriptase inhibitors. Lamivudine is a nucleoside analogue reverse transcriptase inhibitor that was recently approved in many countries for the treatment of hepatitis B. Despite the potent action of lamivudine, the development of new antivirals and new strategies to treat hepatitis B are still the major goal. We review the latest options for therapy of chronic hepatitis B, including combination strategies that could be an approach to improving the response rate of antivirals.

Lamivudine resistance in hepatitis B: mechanisms and clinical implications

Lamivudine (beta-L-(-)-2',3'-dideoxy-3'-thiacytidine) has been a major breakthrough in the care of patients with hepatitis B. With prolonged monotherapy the development of resistance is an increasingly recognized problem that limits the long term efficacy of this nucleoside analogue. The most common mutations associated with lamivudine resistance occur within the highly conserved YMDD motif in the C domain of the viral polymerase and are often associated with a compensatory mutation in the proximal B domain. The structural and functional relationship of resistance mutations is reflected in different in vitro sensitivities to lamivudine and changes in replication capacities. During prolonged lamivudine treatment there can be successive changes of different resistant mutants (genotypic succession) or a single mutant can remain the dominant viral species. In patients treated for chronic hepatitis B infection the cumulative incidence of viral resistance reaches over 50% after 3 years. Most patients will have lower serum HBV DNA levels after the emergence of resistance which is ascribed to the decreased replication capacity of these mutants. Although severe flares and ongoing HBe antigen seroconversion can occur in these patients with lamivudine-resistant HBV, the impact of continued therapy on the long-term outcome is still insufficiently studied. In the setting of liver transplantation for HBV-associated disease the clinical course after the emergence of viral resistance is variable but still may lead to disease progression and graft failure. Analogous to the success of combination therapies to delay the emergence of antiviral-resistant HIV, it will be important to combine anti-HBV agents with additive or synergistic antiviral properties and different resistance profiles for future de novo combination therapies for hepatitis B infection.

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.

Molecular anatomy and pathophysiologic implications of drug resistance in hepatitis B virus infection

Synthesis of the hepatitis B virus (HBV) DNA genome occurs within the viral nucleocapsid in a mechanistically ordered fashion. The nucleocapsid contains small pores that permit influx of nucleotide triphosphates and metabolites of nucleoside analogues such as lamivudine for DNA synthesis. Lamivudine is a potent inhibitor of HBV and human immunodeficiency virus (HIV) reverse transcriptases, but substitutions of isoleucine or valine for methionine within the tyrosine-methionine-aspartate-aspartate (YMDD) motif are associated with virologic and clinical resistance to lamivudine therapy. Under lamivudine selection pressure, the high viral production rate and the low fidelity viral polymerase contribute to frequent development of the YMDD mutants. However, the pattern and dynamics of emergence of the mutant viruses over the wild-type virus are determined by multiple factors including replication efficiency, host immune response, and availability of replication space. Structural modeling of HIV reverse transcriptase has permitted key insights into the molecular basis of lamivudine resistance of HBV based on evolutionary relatedness of HIV and HBV. The side groups of isoleucine and valine of the YMDD mutants sterically prevent lamivudine from appropriately configuring into the nucleotide binding site of the reverse transcriptase. Aminotransferase flares are associated with lamivudine therapy and may signify clinical resistance with emergence of YMDD mutants. They may also herald the recovery phase with seroconversion and viral clearance. Reconstitution of the endogenous anti-HBV immune response may be equally important in the control of viral replication by lamivudine and other nucleoside analogues.

Fas-mediated apoptosis causes elimination of virus-specific cytotoxic T cells in the virus-infected liver

Immunity to allogeneic MHC Ags is weak in rodent livers, raising questions as to the mechanisms that might control responses in this organ. Infection with an adenovirus vector reveals that T cell-mediated immunity to nonself-Ags in the liver is self-limiting. Virus-induced liver injury decreases and coincides with disappearance of virus-specific CTL, concomitant to an increase of apoptotic T cells early after infection. But whereas death in CD4 cells is independent of Fas, perforin, and TNF-alpha, that of CD8 cells requires Fas and not perforin or TNF-alpha pathways. Fas ligand is expressed on liver-infiltrating cells, pointing to death by fratricide that causes almost complete disappearance of virus-specific CTL 4 wk after infection. CTL elimination is virus dose dependent, and high doses induced high alanine aminotransferase values, elevated expression of Fas ligand on CD8 cells, and increased CD8 cell migration into the infected liver.

Acute flares in chronic hepatitis B: the natural and unnatural history of an immunologically mediated liver disease

Acute flares in chronic hepatitis B are common and may be caused by a number of identifiable and potentially treatable factors. The common link for many of these exacerbation episodes is a change in the immunologic response to hepatitis B virus (HBV), and this may have no identifiable cause or be triggered by an increase in viral replication or genotypic change. It is important to keep in mind the clinical situations in which patients are at increased risk of reactivated infection and secondary exacerbations. Reactivation is frequently induced by medical treatments such as cancer chemotherapy, antirejection drugs used in organ transplantation, and corticosteroids. The immunologic flares that often result from sudden withdrawal of these medications can be life-threatening unless recognized and treated promptly with antivirals, and there is increasing experience that preemptive antiviral treatment can diminish their occurrence and improve the outcome. The experience with lamivudine and other nucleoside analogues has increased our understanding of the molecular events behind hepatitis flares that occur when chronic hepatitis B is treated with drugs that potently inhibit HBV DNA polymerase. However, not all flares are explainable by events related to HBV infection alone. Depending on the population studied, as many as 20%-30% of flares may be caused by infection with other hepatotropic viruses, and this situation may inhibit HBV replication. Proper understanding of the etiology and effective treatment of acute flares in chronic hepatitis B requires an appreciation of high-risk clinical situations, assessment of HBV replication status, and testing for other viruses when appropriate.

Suppression of hepatitis B virus replication mediated by hepatitis A-induced cytokine production

BACKGROUND

Acute hepatitis A virus (HAV) infection can cause severe hepatitis especially in patients with underlying chronic liver disease. In patients with pre-existing chronic hepatitis B (HBV) acute HAV infection can suppress HBV replication. The exact mechanism of HBV suppression during acute HAV infection is still a subject of debate. One mechanism may be the production of HAV infection-induced cytokines leading to suppression of HBV replication and viral clearance.

AIM

To evaluate cytokine production and HBV-specific lympho-proliferative responses (LPR) during acute HAV infection in a patient with chronic HBV infection-clearing markers of active HBV replication.

DESIGN

Early detection of a case of acute HAV infection in an HBeAg-positive, HBV DNA-positive chronic HBV patient treated with lamivudine.

RESULTS

At the time of HAV infection a sharp peak in the gamma-interferon (IFN-gamma) level occurred just before the rise in serum transaminase activity. This was subsequently followed by a decrease in HBV DNA and HBeAg below the limit of detection of the assay. However the HBV-specific T-cell response was not modified. After resolution of the acute HAV infection and withdrawal of antiviral therapy HBV replication relapsed.

CONCLUSION

The sharp rise in IFN-gamma production mediated by the acute HAV infection may be pivotal in the suppression of HBV replication in chronic hepatitis B.

Type 1/Type 2 immunity in infectious diseases

T helper type 1 (Th1) lymphocytes secrete secrete interleukin (IL)-2, interferon-gamma, and lymphotoxin-alpha and stimulate type 1 immunity, which is characterized by intense phagocytic activity. Conversely, Th2 cells secrete IL-4, IL-5, IL-9, IL-10, and IL-13 and stimulate type 2 immunity, which is characterized by high antibody titers. Type 1 and type 2 immunity are not strictly synonymous with cell-mediated and humoral immunity, because Th1 cells also stimulate moderate levels of antibody production, whereas Th2 cells actively suppress phagocytosis. For most infections, save those caused by large eukaryotic pathogens, type 1 immunity is protective, whereas type 2 responses assist with the resolution of cell-mediated inflammation. Severe systemic stress, immunosuppression, or overwhelming microbial inoculation causes the immune system to mount a type 2 response to an infection normally controlled by type 1 immunity. In such cases, administration of antimicrobial chemotherapy and exogenous cytokines restores systemic balance, which allows successful immune responses to clear the infection.

Hepatitis B e antigen seroconversion after lamivudine therapy is not durable in patients with chronic hepatitis B in Korea

It has been suggested that hepatitis B e antigen (HBeAg) seroconversion after lamivudine therapy is durable in Caucasians with chronic hepatitis B (CHB). However, little is known whether it is also durable in endemic areas of hepatitis B virus (HBV) infection. We evaluated the posttreatment durability of lamivudine-induced HBeAg seroconversion and the predictive factors for relapse in Korean patients with CHB. We retrospectively analyzed 98 HBeAg-positive patients with CHB who were treated with lamivudine between August 1996 and December 1997. Lamivudine was given at a dose of 150 mg per day. After HBeAg seroconversion, lamivudine was continued for an additional 2 to 4 months, and posttreatment monitoring continued for up to 24 months. HBeAg seroconversion was achieved in 34 of the 98 patients (34.7%). The mean duration of treatment in these seroconverters was 9.3 +/- 3.0 months. During the follow-up period, the cumulative relapse rates at 1 year and 2 years posttreatment were 37.5% and 49.2%, respectively. Most relapses were accompanied by elevation of serum alanine transaminase (94%) and reappearance of HBeAg (81%). Pretreatment serum HBV DNA levels and the duration of additional lamivudine therapy after HBeAg seroconversion were 2 independent predictive factors for posttreatment relapse. In conclusion, lamivudine-induced HBeAg seroconversion was not durable in this endemic area. And the duration of additional lamivudine therapy after HBeAg seroconversion significantly affected the posttreatment relapse. Further studies are needed to determine the duration of lamivudine and to elucidate the cause of high relapse after HBeAg seroconversion in endemic areas of HBV.

Efficacy of long-term lamivudine monotherapy in patients with hepatitis B e antigen-negative chronic hepatitis B

We evaluated the safety and efficacy of long-term lamivudine monotherapy in a group of 25 patients with hepatitis B e antigen (HBeAg)-negative chronic hepatitis B. Lamivudine was administered in a daily dose of 150 mg for a mean of 26 +/- 7 months and was well tolerated. No patient lost hepatitis B surface antigen (HBsAg). The rate of initial biochemical response increased from 88% at 6 months to 96% at 12 months of therapy, but it progressively decreased thereafter; the biochemical remission rate was 68% at 18 months, 59. 5% at 24 months, and 42.5% at >/=30 months. Alanine transaminase (ALT) increased to higher than the baseline levels in 8 of the 11 patients with a biochemical breakthrough reaching acute hepatitis levels in 6 of them. Acute icteric hepatitis developed in one patient. The virologic remission rate assessed by a sensitive quantitative polymerase chain reaction (PCR) assay was 68% at both 6 and 12 months, decreasing thereafter to 52% at 18 months and to 41. 6% at both 24 and >/=30 months. Virologic breakthroughs were always persistent and preceded ALT elevations by a median of 4 (3-24) months. YMDD mutants were detected in all patients with a virologic breakthrough. In conclusion, in patients with HBeAg-negative chronic hepatitis B, long-term lamivudine therapy is safe and is associated with high biochemical and virologic response rates at the end of the first year. However, response rates tend to decrease with time and breakthroughs due to YMDD mutants accumulate. ALT activity during breakthroughs often exceeds the baseline and may reach even acute hepatitis levels.

Clinical potential of emerging new agents in hepatitis B

Treatment of chronic hepatitis B is directed at interrupting the natural history and clinical outcomes of the disease. It needs to take into account the virology and replication cycle of the hepatitis B virus (HBV), and the host immune response to HBV. Long term follow-up of patients treated with interferon supports the paradigm that a sustained, major suppression of HBV replication, particularly that associated with hepatitis B e antigen (HBeAg) seroconversion, interrupts the natural history of hepatitis B. The availability of potent but well tolerated and orally available HBV antivirals, of which lamivudine is the prototype, has allowed clearer treatment objectives to be formulated. These are: temporary or permanent reduction of hepatitis (necroinflammatory) activity, arrest of fibrotic progression, prevention of cirrhosis and liver failure, and prevention of recurrent HBV infection after liver transplantation. Lamivudine has good medium term efficacy in achieving each of these objectives. The only significant problem for the longer term is emergence of antiviral resistance conferred by mutations in the YMDD (tyrosine-methionine-aspartic acid-aspartic acid) motif of the HBV reverse transcriptase. As a result, contentious issues remain about defining when antiviral therapy is indicated, whether to treat for a defined interval or indefinitely, and when to stop treatment if HBeAg seroconversion is not achieved. Some personal views are expressed in this review. Among newer HBV antivirals in clinical studies, adefovir dipivoxil, entecavir and emtricitabine appear to be at least as potent as lamivudine in suppressing HBV replication. Famciclovir appears less potent. In vitro studies show that YMDD mutations confer cross-resistance between lamivudine, emtricitabine and beta-L-Fd4C (L-2',3'-didehydro-dideoxy-5-fluorocytidine). However, adefovir dipivoxil, lobucavir, entecavir, DAPD (beta-D-2,6-diaminopurine dioxolane) and possibly clevudine (L-FMAU) suppress replication of YMDD mutant HBV, as well as wildtype. Preliminary studies indicate clinical efficacy of adefovir dipivoxil once resistance to lamivudine has developed. Immunomodulatory approaches to treatment of chronic hepatitis B are conceptually attractive, but newer agents used to date (thymalfasin, interleukin-12, therapeutic vaccines) have not demonstrated sufficient efficacy for widespread use. The next challenge for HBV treatment is to use antivirals in combination and/or in cyclical therapy to reduce the emergence of drug resistance and increase efficacy, particularly to achieve sustainable post-treatment suppression of hepatitis B.

How can the cellular immune response control hepatitis B virus replication?

In this review we focus on aspects of the virus-specific cellular immune response, although we should point out that all the components of the innate and adaptive immune response are likely to play a role in successful control of hepatitis B virus (HBV) infection. We concentrate particularly on the relevance of the polyclonality and multispecificity of the HBV-specific cytotoxic T cell response to its antiviral activity. In this context, we discuss the possible role of viral escape mutations and highlight evidence from other models of the benefit of multispecificity in antiviral responses. We stress the contribution of CD4 help for effective CD8 responses and raise the possibility that HBV may produce factors inhibiting the antiviral response.

Beneficial effects of lamivudine in hepatitis B virus-related decompensated cirrhosis

BACKGROUND/AIMS

HBV-related chronic liver disease patients often present with hepatic decompensation and are not eligible for interferon therapy. Whether long-term lamivudine is effective in these patients was prospectively evaluated.

METHODS

Eighteen patients with HBV-related decompensated cirrhosis, all with quantitative DNA +ve and 10 HBeAg +ve, were given lamivudine 150 mg/d.

RESULTS

Each patient received at least 9 months (mean 17.9) of lamivudine. Three HBeAg+ve patients (30%) seroconverted to anti-HBe and one lost HBsAg during the follow-up. An improvement from baseline in the aspartate aminotransferase (130 vs. 72 IU/l, p<0.04); alanine aminotransferase (111 vs. 58 IU/l, p<0.01) and Child-Pugh score (8.3 vs 6.7, p<0.013) was seen. Lamivudine had no significant side-effects. HBV DNA became undetectable in all patients by 8 weeks of therapy. In three (17%) patients, HBV DNA again became positive at 9, 9 and 27 months. YMDD mutant was, however, detected in only one (6%). A significant reduction was noted in the morbidity and hospitalizations for complications of liver disease before and after starting lamivudine (1.5+/-0.7 vs. 0.6+/-0.7, p<0.002).

CONCLUSIONS

In decompensated HBV-related cirrhosis, lamivudine: i) is effective in suppressing HBV DNA and seroconversion to anti-HBe (30%), ii) can achieve significant improvement in clinical and biochemical status of liver functions.

Protection or damage: a dual role for the virus-specific cytotoxic T lymphocyte response in hepatitis B and C infection?

During infection with hepatitis B or C viruses, cytotoxic T lymphocytes (CTLs) have been implicated as both the mediators of protection and the principal effectors of liver pathology. Recent studies have allowed an investigation of the relationship between virus-specific CTL responses, liver damage and viral replication. In the presence of an efficient virus-specific CTL response, a scenario is emerging where inhibition of viral replication can be independent of liver pathology. We discuss the possibility that an inadequate CTL response--unable to control viral replication--may contribute to liver pathology not only directly but also via the recruitment of non-virus-specific T cells.

Combination therapy with lamivudine and famciclovir for chronic hepatitis B-infected Chinese patients: a viral dynamics study

In vitro studies have shown that lamivudine and penciclovir (the active metabolite of famciclovir) act synergistically to inhibit hepatitis B virus (HBV) replication. We compared the effectiveness of HBV viral suppression by lamivudine monotherapy versus lamivudine plus famciclovir combination therapy in Chinese patients with chronic HBV infection. Twenty-one Chinese hepatitis B e antigen (HBeAg)-positive patients, with detectable HBV DNA (Digene Hybrid Capture II), were randomized to receive either lamivudine 150 mg/d orally (group 1, 9 patients) or lamivudine 150 mg/d plus famciclovir 500 mg 3 times a day orally (group 2, 12 patients) for 12 weeks, with a follow-up period of at least 16 weeks. Serial serum HBV-DNA levels were determined and a mathematical model with provision for incomplete inhibition of virus production during therapy was applied to analyze the dynamics of viral clearance. The mean antiviral efficacy was significantly greater in group 2 than in group 1 (0.988 +/- 0.012 vs. 0.94 +/- 0.03, P =.0012). HBV DNA returned to pretreatment level within 16 weeks after the end of initial treatment in 4 patients (66.7%) in group 1 and none in group 2 (P =.08), who remained HBeAg positive and received no further treatment after week 12. Hence, in Chinese chronic HBeAg-positive patients, combination therapy using lamivudine and famciclovir was superior to lamivudine monotherapy in inhibiting HBV replication. Further studies of longer duration are needed to define whether combination therapy will increase the HBeAg seroconversion rate and decrease the rate of emergence of lamivudine-resistant variants.

Protection or damage: a dual role for the virus-specific cytotoxic T lymphocyte response in hepatitis B and C infection?

During infection with hepatitis B or C viruses, cytotoxic T lymphocytes (CTLs) have been implicated as both the mediators of protection and the principal effectors of liver pathology. Recent studies have allowed an investigation of the relationship between virus-specific CTL responses, liver damage and viral replication. In the presence of an efficient virus-specific CTL response, a scenario is emerging where inhibition of viral replication can be independent of liver pathology. We discuss the possibility that an inadequate CTL response--unable to control viral replication - may contribute to liver pathology not only directly but also via the recruitment of non-virus-specific T cells.

Hepatitis B e antigen seroconversion: effects of lamivudine alone or in combination with interferon alpha

Seroconversion of hepatitis B e antigen (HBeAg) is an important marker for resolution of active hepatitis B virus (HBV) infection and for a long-term positive response to treatment. Lamivudine, a nucleoside analogue, is the first effective oral treatment for chronic hepatitis B in patients with evidence of viral replication and liver disease. When appropriate patient groups are compared, treatment with lamivudine for 1 year leads to HBeAg seroconversion in a similar proportion of patients as a standard course of interferon (IFN) alpha therapy. Seroconversion increases during prolonged therapy (up to 3 years), and is sustained post-treatment in more than three-quarters of patients. Response rates are related to the pretreatment level of serum alanine aminotransferase (ALT) and reach 65% in those patients with serum ALT > 5 x upper limit of normal (ULN) after one year. For patients with pretreatment ALT > 2 x ULN, response was seen in 38% after one year, rising to 65% after 3 years. To date, combination with IFN and lamivudine has not been shown to confer additional benefit compared with lamivudine monotherapy. Lamivudine is effective and appropriate for use in a greater proportion of HBV infected patients than IFN alpha, particularly those infected at birth or in early childhood. Furthermore, because seroconversion after lamivudine is not normally associated with a severe flare of liver disease, as seen with IFN, it is more suitable for use in patients with active liver disease and cirrhosis. In conclusion, lamivudine is more suitable than IFN for a broad range of patients, including those with severe liver disease, recurrent flares, pre-core mutant HBV and those who have failed previously IFN treatment or are immunosuppressed. Lamivudine is also better tolerated than IFN.

Profound suppression of hepatitis B virus replication with lamivudine

The therapeutic goals in chronic hepatitis B are to prevent or decrease cirrhosis and hepatocellular carcinoma in patients with pre-cirrhotic or early cirrhotic disease and to stabilise patients with end-stage cirrhosis. Lamivudine is an oral nucleoside analogue that suppresses hepatitis B virus (HBV) replication, and so may achieve both these treatment objectives. The active 5'-triphosphate metabolite of lamivudine has two modes of viral suppression. First, it mimics deoxycytidine triphosphate and is incorporated into newly synthesised HBV DNA to cause chain termination. Second, it demonstrates competitive inhibition of viral DNA-dependent and RNA-dependent DNA polymerase activity (i.e., reverse transcriptase activity). Lamivudine may, therefore, act at four possible stages during HBV replication: reverse transcription of pre-genomic mRNA into nascent minus-strand DNA; formation of plus strand DNA from nascent minus-strand DNA; completion of double-stranded DNA; and formation of covalently closed circular DNA. In clinical studies, lamivudine therapy reduced serum HBV DNA and this was associated with significant improvements in liver histology and significant and sustained enhancement of the proliferative CD4-mediated response to HBeAg and hepatitis B core antigen (HBcAg), and an increased frequency of HBeAg-specific T cells. HBV DNA concentrations often returned to pre-treatment values when therapy ended prior to the loss of hepatitis B e antigen (HBeAg). Although the emergence of HBV variants with a mutation in the YMDD (tyrosine-methionine-aspartate-aspartate) motif has been observed, such variants show reduced susceptibility to lamivudine due to limited replication competence, and their emergence is not a signal to cease lamivudine therapy. In conclusion, viral suppression with lamivudine offers a means of disease improvement and immunological control in chronic hepatitis B.

Lamivudine for hepatitis B in clinical practice

Lamivudine is a potent, once-daily, oral antiviral therapy that is effective and well tolerated in most patient groups with chronic hepatitis B virus infection, including those with pre-core mutant infection. Studies to date show that lamivudine suppresses serum viral replication, causing reductions in serum hepatitis B virus (HBV) DNA and enhancing hepatitis B e antigen (HBeAg) seroconversion (loss of HBeAg plus presence of antibodies to HBeAg [anti-HBe]). Lamivudine also improves liver disease, as shown by normalisation of alanine transaminase (ALT) levels and reduced progression to cirrhosis. Lamivudine is effective in patients who are interferon (IFN) alpha naïve and in those who have failed to respond to IFN alpha, and it suppresses HBV in decompensated liver disease and in liver transplantation. Variants with mutations in the YMDD (tyrosine-methionine-aspartate-aspartate) motif may emerge with prolonged lamivudine therapy, but most patients maintain clinical control. Lamivudine has a safety profile similar to that of placebo and it is better tolerated than IFN alpha. In conclusion, lamivudine represents a major advance in the therapeutic options available for the management of patients with chronic hepatitis B and should now be considered the drug of choice for most patients who require treatment.

Additive Antiviral Effects of Lamivudine and α-Interferon in Chronic Hepatitis B Infection

α-Interferon has limited efficacy against chronic hepatitis B virus (HBV) infection. Nucleoside analogues may confer greater benefits, however, it is likely that combination therapies will be required for effective control of this infection. We investigated the antiviral effect of lamivudine and interferon therapy in eight patients with high HBV-DNA levels. Six patients received lamivudine/interferon combination therapy followed, after a 6-month drug-free period, with lamivudine monotherapy. Mean HBV viral load (copies/ml) reduction was significantly greater after 4 months of combination therapy (4.3x103) compared to an equivalent period of lamivudine monotherapy (2.9x102) ( P=0.03). Two patients were given 6 months of lamivudine/interferon combination therapy followed immediately by lamivudine monotherapy. Cessation of interferon in these patients led to a rapid 1–2 log10 increase in HBV viral load. These findings suggest that α-interferon has a direct antiviral effect on chronic HBV infection, which may be additive to, or synergistic with lamivudine.

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.

Nucleoside analogues in the treatment of chronic hepatitis B

Many nucleoside analogues have been investigated for the treatment of chronic hepatitis B. Some were withdrawn because of significant adverse effects and some are still in the early stage of clinical assessment. Lamivudine has been demonstrated to have consistent efficacy and safety in large-scale, phase III clinical trials. It has achieved a milestone in the treatment of chronic hepatitis B and is now commercially available in many countries. Being a potent inhibitor of hepatitis B viral replication, it achieved around 18% HBeAg seroconversion in HBeAg-positive patients after 1 year of therapy. HBeAg seroconversion is a good endpoint for therapy and has been shown to be 80% durable. The response was better among patients with raised pretreatment alanine aminotransferase levels. Liver necro-inflammation and fibrosis improved significantly after 1 year. Further improvement on extended therapy was observed together with an incremental increase in HBeAg seroconversion. Similar efficacy was demonstrated in HBeAg-negative viraemic patients. The main drawback is the emergence of drug-resistant variants starting from the sixth to ninth month of treatment. This can be associated with varying degrees of relapse of disease activity and may offset the benefit of therapy. With extended therapy, drug-resistant variants continue to emergence at a rate of around 20% per year. Adefovir dipivoxil and entacavir are nucleoside or nucleotide analogues shown to suppress both the wild-type and lamivudine-resistant virus. Combination of these nucleoside/nucleotide analogues with immune modulators may be the answer to eradicate the virus in short-term therapy and avoid the issue of drug resistance.

Vaccination to treat persistent viral infection

Persistent infections caused by such agents as the human immunodeficiency virus, hepatitis B virus, Epstein-Barr virus, etc., present formidable medical problems. A defining characteristic of these infections is that anti-viral cytotoxic T lymphocytes (CTL) may be lost or, if present, fail to clear the infection. Here we report a vaccination strategy which was successful in generating lytic CTL in persistently infected mice. Vaccination with an immunodominant CTL epitope derived from the nucleoprotein of lymphocytic choriomeningitis virus (LCMV) delivered in the form of a lipopeptide incorporating a universal CD4 helper epitope successfully induced lytic MHC-restricted CTL in mice persistently infected with LCMV since birth. However, induction of such CTL did not eliminate the virus, most likely because the CTL were generated at low frequencies and had 2 to 3 logs lower affinity than CTL generated in uninfected mice inoculated with the vaccine. Both CTL populations from either uninfected or persistently infected mice produced significant and similar amounts of interferon-gamma and IL-6. Vaccine-induced low-affinity CTL were still inadequate at complete removal of the virus when combined with LCMV-specific CD4 helper T lymphocytes. Thus, our results establish that CTL can be generated in persistently infected mice and that a crucial factor for clearing viral infection is the affinity of the CTL.

In vitro antihepadnaviral activities of combinations of penciclovir, lamivudine, and adefovir

Penciclovir (9-[2-hydroxy-1-(hydroxymethyl)-ethoxymethyl]guanine [PCV]), lamivudine ([-]-beta-L-2',3'-dideoxy-3'-thiacytidine [3TC]), and adefovir (9-[2-phosphonylmethoxyethyl]-adenine [PMEA]) are potent inhibitors of hepatitis B virus (HBV) replication. Lamivudine has recently received approval for clinical use against chronic human HBV infection, and both PCV and PMEA have undergone clinical trials against HBV in their respective prodrug forms (famciclovir and adefovir dipivoxil [bis-(POM)-PMEA]). Since multidrug combinations are likely to be used to control HBV infection, investigation of potential interactions between PCV, 3TC, and PMEA is important. Primary duck hepatocyte cultures which were either acutely or congenitally infected with the duck hepatitis B virus (DHBV) were used to investigate in vitro interactions between PCV, 3TC, and PMEA. Here we show that the anti-DHBV effects of all the combinations containing PCV, 3TC, and PMEA are greater than that of each of the individual components and that their combined activities are approximately additive or synergistic. These results may underestimate the potential in vivo usefulness of PMEA-containing combinations, since there is evidence that PMEA has immunomodulatory activity and, at least in the duck model of chronic HBV infection, is capable of inhibiting DHBV replication in cells other than hepatocytes, the latter being unaffected by treatment with either PCV or 3TC. Further investigation of the antiviral activities of these drug combinations is therefore required, particularly since each of the component drugs is already in clinical use.