From viral pathobiology to the treatment of hepatitis B virus infection EASL Monothematic Conference (Istanbul, Turkey, October 6–8, 2005)
Article Outline
- 1. Introduction
- 2. Pathobiology
- 3. Heterogeneity
- 4. Coinfection with other viruses
- 5. Immune pathogenesis of disease
- 6. Factors affecting the course of infection
- 7. Hepatitis B infection with low level viraemia
- 8. Treatment targets
- 9. Treatment of HBeAg positive chronic hepatitis B
- 10. Treatment of HBeAg negative chronic hepatitis B
- 11. Special populations
- 12. Treatments to come
- 13. (*) Faculty of the EASL Istanbul HBV Monothematic
- Copyright
1. Introduction
Hepatitis B virus infection, which was for over a decade put aside by the rising star of hepatitis C, has seen over the last years a resurgence of interest. This stemmed from a better knowledge of the virus itself, from the availability of new drugs and combinations, and from the realization that far from being eradicated by mass immunization programs HBV is still on a worldwide basis the major cause of cirrhosis and hepatocellular carcinoma, alone or in combinations with other viruses, alcohol and metabolic cofactors. This prompted the EASL Scientific Committee to organize a Monothematic Conference on HBV. Experts from Europe, USA, Canada, Australia, the Far East and other parts of the world convened in Istanbul on October 6–8, 2005 to review pathobiology and management of HBV-induced disease. The report, drafted by the meeting's organizers, attempts to summarize the achievements of the last years. A full audiovisual of all lectures given by the Faculty, whose members contributed to this report and are listed below (*), can be accessed on the EASL website at http://www.easl.ch/
2. Pathobiology
2.1. HBV replication and its regulation:
Following infection of the hepatocyte, the viral genomic DNA is transported to the nucleus and converted from a relaxed circular form to a covalently closed circular (CCC) DNA molecule. This is the major transcriptional template from which the viral pregenomic RNA is made and then transported to the cytosol where it is packaged with the viral polymerase into the nucleocapsid. Reverse transcription generates viral genomic DNA. At this stage in the viral life-cycle nucleos(t)ide analogues can inhibit HBV replication. Antiviral drug-resistance results from a process of adaptive mutations under therapy due to: high replication rates, low fidelity of viral polymerase, selective pressure of drug, replication space (new uninfected hepatocytes) in the liver, and fitness of each mutant. The emergence of drug-resistant mutants is replication-dependant. At least nine patterns of lamivudine resistance have been described whilst three patterns have been identified for adefovir and entecavir. The major concern is emergence of particular mutations, such as rtQ215S/rtV214A, which are cross-resistant across the class. Prevention of resistance can be achieved by maximising antiviral activity (appropriate, non-toxic dosing), maximising the genetic barriers to resistance (avoid sequential therapy) and increase pharmacological barriers (ensure patient compliance).
2.2. Mechanısms and consequences of vıral persıstence:
HBV replication is non cytopathic, HBV clearance and liver damage being due to cellular and humoral immune responses. Viral persistence results from interaction of a defective immune response, of the long half-life of infected hepatocytes and cccDNA and of viral genome variability. Nucleos(t)ide analogs select resistant virus strains, while the action of antiviral CTLs is affected both by selection of cells that do not support virus replication and antigen expression and by selection of virus strains with altered CTL epitopes. Viral persistence causes rebound of viral replication after treatment cessation, relapse under immunosuppression, selection of drug resistant and immune escape mutants and ultimately integration of viral into host genome. Viral persistence may require combination therapy to prevent and/or delay drug resistance.
3. Heterogeneity
3.1. HBV genotypes:
Eight HBV genotypes, A–H, differ in terms of replication and of expression and recognizability of immune epitopes, and may cause different disease patterns. Genotypes A, B, C and D are mainly found in northern and central Europe and in the USA, while genotypes B and C are prevalent in Asia and genotype D is found in Mediterranean region and India. Genotypes A prevails in Africa, together with E, while F–H are found in Central and South America. Genotypes A and F segregate into two subgenotypes, and genotypes B, C and D into four. Recombinations between genotypes due to coinfections can be found in the pre-core and core regions of HBV. Genotype shift is occurring in some area due to changing patterns of infection. HBV genotype may influence HBeAg seroconversion, presence of HBV variants and the natural history of liver disease. In HBeAg positive patients, genotype A and B are more sensitive to interferon than C and D. HBV genotype has no relevance in determining sensitivity tonucleos(t)ide analogs.
Genomics and proteomics of HBV mutants: 1010–1011 point mutations appear daily due in HBV carriers. Mutations within the ‘a’ determinant of HBsAg ORF are selected by vaccination and upon HBIg treatment of OLT recipients. Stop codon mutations in the precore region prevent HBeAg secretion and increase the stability of the epsilon encapsidation signal sequence, allowing immune escape and increasing the effectiveness of HBV replication. Some mutations in polymerase ORF change the secondary and tertiary structure of HBV-DNA polymerase and decrease the sensitivity to nucleos(t)ide analogs. Genomic changes do not strictly reflect functional changes, which are instead related to proteins. Proteomic studies are showing protein expression changes in HBV infection with different strains, which may affect therapeutic targets.
Persistence of HBV in HBsAg negative patients: HBV genomes may persist in the liver (±serum) of HBsAg negative individuals (‘occult’ HBV), in 20% of cases without any serology of HBV infection. Occult infection is rarely related to mutant HBV producing a modified HBsAg undetectable by monoclonal-based assays. Occult HBV is mainly due to strong suppression of viral replication and of gene expression due to host immune surveillance and epigenetic factors still largely unknown. Suppression of HBV replication explains the low or undetectable serum HBV-DNA usually found in patients with occult infection. The molecular basis of occult HBV infection might be related to the lifelong persistence in the nuclei of the hepatocytes of the HBV cccDNA. Occult HBV infection:
4. Coinfection with other viruses
4.1. HIV+HBV coinfection:
Management of chronic hepatitis B in HIV patients is complex due to lack of controlled trials and activity of therapeutic agents on both viruses. HBeAg or HBsAg seroconversion under treatment are uncommon and permanent suppression of HBV may be necessary to reach therapeutic objectives. Beside standard anti-HBV drugs, tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) are approved for HIV and active against HBV. Studies with IFN are limited in HIV/HBV co-infected patients but suggest a decreased response compared with HBV mono-infected patients. Pegylated IFN has never been studied in HIV/HBV co-infected patients. Prolonged monotherapy with LAM or FTC is associated with a high rate of HBV resistance. ADV and TDF have efficacy against wild type and LAM-resistant HBV in HIV co-infected patients. No HBV-resistance mutations have been documented in patients receiving nucleotide analogues but TDF or ADV was added to LAM in almost all the reported patients. Combination therapy with a nucleoside and a nucleotide analogue may ideally prevent long term HBV resistance.
4.2. HCV+HBV coinfection:
From 7 to 15% HBsAg carriers harbour HCV coinfection. IV drugs use, transfusions, area of residence and age are hierarchical independent risks. Triple hepatitis (HDV coinfection) and HIV coinfection are common in drug addicts. Cross-sectional studies suggest a reciprocal inverse relation between HBV and HCV replication, HCV being mostly predominant. Over longer follow-up HBV and HCV replication fluctuate in 30% of cases, leading to possible misclassification. Pre-treatment work-up must include longitudinal virological monitoring. Cohort studies show that HBsAg clearance occurs more frequently in dual HBV/HCV infection. Dual HBV/HCV infection causes however more severe histological damage and is an additive risk for HCC. Coinfected patients are treated empirically for the infection prevailing at baseline. One hundred and fourteen patients have been treated in 14 studies with IFN±ribavirin, in one study plus lamivudine. SVR was obtained for HCV in 0–69%. Reactivation of HBV replication was occasionally recorded under IFN.
4.3. HDV infection:
The delta virus needs the helper function of HBV to cause disease. Seven genotypes of HDV are differentiated. The recent decades have disclosed a steadily decrease in the incidence of HDV. However, outbreaks of HDV continue to be reported in different parts of the world. HDV causes the most severe form of chronic viral hepatitis and is important in this context. Immune responses are important in the pathogenesis of delta hepatitis although limited knowledge exists. In the one study published so far, patients with inactive but not with active-HDV disease displayed HDV-specific proliferative CD4 responses to HDAg suggesting that cellular immune responses most likely were able to control HDV infection. Very recently, ex vivo HDV- and HBV-specific T cell responses were explored. HBV-specific T cell responses were more frequent in HDV-coinfected than in HBV-monoinfected individuals. Further, more frequent HDV- and HBV-specific interferon-gamma responses were found in patients with mild liver disease while IL-10 responses dominated in individuals with high ALT levels. Increased frequencies of markers of innate immunity such as perforin expression of lymphoid cells have also been described.
Exploring the HDV life cycle has revealed new potential treatment strategies. Thus, an essential step in the virus assembly process involves the post-translational lipid modification of a specific HDV protein, namely prenylation of large delta antigen. Preventing prenylation abolishes virus particle formation. Prenylation inhibitors have been developed for use in humans but so far have not been tested in patients with chronic delta hepatitis.
The only established therapy for chronic delta hepatitis is high dose interferon to be given for at least 1 year. Such treatment appears to affect favorably the natural history of disease. In patients, who relapse or have a partial response to 1 year of therapy extended treatment may be needed. Lamivudine is not effective and combination treatments of interferon with lamivudine or ribavirin do not appear to offer additional benefit.
5. Immune pathogenesis of disease
5.1. Viral clearance in acute hepatitis:
The virological and immunologic events early after exposure to HBV influence the evolution of infection towards control or chronicity. Limited viral expansion is observed for some weeks after infection before active replication, which rapidly leads to infection of most hepatocytes and high level viraemia. In self-limited infections HBV-DNA is cleared before the ALT peak, suggesting non-cytolytic mechanisms in the initial containment of HBV. The exponential elevation of HBV-DNA is rapidly followed in self-limited infections by induction of vigorous, multispecific, Th1-oriented CD4 and CD8 responses. Successful control of infection is followed by generation of long-lived memory T cells, sustained by the persistence of occult intrahepatic HBV under tight control by the immune response. Although the behaviour of the acute immune response in patients evolving to chronicity is only partially defined, data from the woodchuck and in natural HBV infection indicate that HBV persistence is associated with early quantitative and qualitative defects of specific T cell responses. Thus, although the final outcome of infection is related to the type of immune response mounted by the host, the factors influencing the quality of the anti-viral immune response remain speculative. Type and quantity of the infecting virus as well as the genetic background of the host may be crucial.
5.2. Viral tolerance to chronic infection:
Chronic hepatitis B is characterized by a collapse of HBV specific immunity with tolerance/anergy and deletion of HBV-specific T cells, proportional to HBV replication. Circulating and intrahepatic HBV-specific CD8+cells are functionally active in patients with <107 HBV-DNA copies/millilitre, but are deleted and/or functionally impaired in patients with >107 HBV-DNA copies/millilitre, with no relation between HBV-specific CD8+T cell response and degree of necroinflammation. HBeAg and HBsAg in large amounts are tolerogenic on T cells and in the tolerogenic liver environment, which affects priming, proliferation and survival of T cells, generate HBV-specific T cell defects in chronic carriers. HBV-specific T cell defects are profound but might be reverted. A transient recovery of HBV-specific T cell immunity can be observed in patients experiencing rapid HBV fluctuations. New treatment strategies designed to modify the level of HBV antigens expression, combining the use of anti-viral drugs and vaccines, might lead to full recovery of HBV-specific immunity.
Reactivation as an immune-mediated mechanism: hepatitis B reactivation or exacerbation is defined as abrupt increase of ALT by two fold and to a level greater than 5×ULN, or greater then 300
IU/L, in the absence of other causes of damage. Acute exacerbations of CHB occur during the natural history or could be iatrogenic (post-chemotherapy, after stopping antivirals or due to the emergence of drug-resistant HBV). The ALT flare is preceded by a sharp increase of viraemia. Rarely, hepatitis exacerbation may occur early during treatment with antiviral agents, in association with decreased viraemia.
Several studies of HBV-specific T cell reactivity indicate that ALT flares do not necessarily reflect T cell mediated lysis of infected hepatocytes and may associate with CD4+T cells and/or non-HBV specific immune reactivity.
The vigour and quality of T cell reactivity to HBV differ between exacerbation episodes. T cell responses mimicking those in self-limited acute hepatitis B may control HBV replication. Ineffective immune reactivity, triggered by HBV reactivation, contributes to progression of HBV disease.
6. Factors affecting the course of infection
6.1. Genetic factors:
The innate and adaptive host immune response, determine the outcome of infection. The first component of the host innate response involves the opsonisation of pathogens prior to phagocytosis by polymorphonuclear and mononuclear cells. One system involves the binding of mannose binding lectins to the mannose, terminated residues on the preS2 region of the envelope. Several studies have indicated that deficiencies of these opsonins are associated with persistent HBV infection and severe disease. The second response involves production of type 1 interferons, which induce an antiviral state. Deficient production of type 1 interferon has been shown in around 40% of patients with chronic HBV infection. Polymorphisms in genes encoding the type 1, interferon receptors, resulting in diminished membrane display, are associated with persistent HBV infection.
6.2. Fat:
Obesity and diabetes are highly prevalent in adults and may promote steatosis in subjects with liver disease of any etiology. An important role of fatty liver as a cofactor in HCV disease has been demonstrated, but very few data have been reported in chronic hepatitis B. Steatosis is reported in 30–40% of HBV patients, being severe (>25%) in 4–12%, in association to higher BMI and to high cholesterol and triglycerides. The prevalence of steatosis is moderately higher in HBsAg carriers with the metabolic syndrome, suggesting that fatty liver is likely the result of metabolic factors of the host. No evidence of its effect on the course of HBV disease is available.
6.3. Alcohol:
Among alcohol abusers the risk of developing cirrhosis is 10%, and even less for HCC. Consumption of >50gm/day significantly increases the risk of cirrhosis in HCV carriers, but no clear additional risk is identifiable for those below 50 but above 20gm/day. It is conceivable that HBV infected patients are more likely to develop cirrhosis if they have a significant alcohol consumption. The mean age of HBV infected patients upon development of cirrhosis and HCC is younger in presence of alcohol abuse, supporting a negative effect of >50gm/day. Still an important questions remains, whether a lower alcohol consumption might be harmless, as studies only distinguish between high (>50gm/day) and low or none but not between high (>50gm/day), moderate (20–50) and low (<20) consumption.
7. Hepatitis B infection with low level viraemia
7.1. The ‘inactive’ HBV carrier:
The ‘inactive carrier’ state is characterized by absence of HBeAg, normal ALT and low HBV-DNA in serum (< 103–105copies/ml). The natural history of asymptomatic carriers is controversial, since informations are often limited to medium-term follow-up. Data from a cohort of HBsAg positive Italian blood donors prospectively evaluated over 30 years show ALTs were only slightly altered over time mainly in relation with alcohol abuse. HBV-DNA levels were always low and more than 30% of individuals spontaneously cleared HBsAg during follow up. Liver-related deaths were few and survival of HBsAg carriers was comparable to HBsAg negative controls. By converse, inactive cirrhosis has been found in 35% of American HBsAg ‘inactive’ carriers, suggesting that they suffered significant damage during the immune clearance phase. Among Oriental ‘inactive’ carriers, spontaneous HBV reactivation occurs in 20–30% of subjects and HBeAg negative chronic hepatitis B develops during follow-up in 25%. Repeated reactivations and HBeAg negative chronic hepatitis lead to disease progression. Up to 20–40% of patients with HBeAg negative hepatitis have intermittently normal ALT and low HBV-DNA and are misclassified as ‘inactive HBsAg carriers’. A single HBV-DNA excludes 30–45% of cases at a cut-off of 105copies/ml and 20% at a cut-off of 3×104. A substantial percentage of patients with HBV cirrhosis or HCC are HBeAg negative with normal ALT and low HBV-DNA at presentation. Periodic surveillance for HCC should be performed if cirrhosis is present.
7.2. Chronic hepatitis B with low level viraemia and abnormal ALT:
An HBV-DNA cut-off level of 104-5copies/ml is recommended to differentiate chronic hepatitis B from inactive carriers. Given the fluctuating course of infection, HBV-DNA can drop below such cut-off at several time points during the course of HBeAg negative chronic hepatitis. Some HBeAg negative patients with elevated ALT have HBV-DNA levels persistently below the detection limit of non-PCR assays in the absence of confounding factors such as alcohol, drug intake or high BMI, and cannot be differentiated from inactive carriers by repeated HBV-DNA tests. ALT and necroinflammation and fibrosis scores are on average lower than in classical chronic hepatitis B. During follow-up, ALT and HBV-DNA usually do not fluctuate and remain at low level. Less than half of them normalize ALT under lamivudine. Until more evidence on long-term course and response to antivirals appears, follow-up without treatment seems to be the best strategy.
8. Treatment targets
8.1. HBV-DNA kinetics under treatment:
Since, HBsAg/anti-HBs seroconversion is a rare event, HBeAg/anti-HBe seroconversion is the primary therapeutic endpoint in HBeAg positive patients. In HBeAg negative patients maintained viral suppression is the aim of therapy which is rarely sustained after discontinuation of nucleos(t)ides. In HBeAg negative patients treated with (peg)interferon alpha, the sustained virological response rate is around 25–30%. A careful definition of the treatment endpoint is mandatory to define what early HBV-DNA kinetics should predict and for which antiviral regimen (nucleos[t]ide, [peg]interferon) this may relate. Patients treated with a nucleos(t)ide analogs have a rapid decline of HBV-DNA to 4–6 logs below baseline after 48 weeks of treatment, with relapse once treatment is stopped. Patients receiving pegylated interferon have a slower decline in HBV-DNA, sustained in a larger fraction after the end of treatment. During treatment a number of distinct HBV-DNA pattern are observed: with nucleos(t)ides some have a flat partial response, while others have a rapid biphasic or a slow multiphasic decline of HBV-DNA and sometimes a staircase pattern of viral decay. In some patients, treated with pegylated interferon an immediate rapid HBV-DNA decline is observed while others either have a delayed response or no decline. Furthermore, several patients treated with pegylated interferon show a viral rebound during treatment, while others have a virological relapse at the end of therapy and yet others achieve SVR. Mathematical modeling does not yet consider potential HBV cccDNA dynamics, different quasispecies with different efficacies, possible replication of infected cells or non-cytolytic loss of the infected state, extrahepatic (latent?) reservoir, T-cell responses, etc. In contrast to HCV, early HBV-DNA kinetics may not become a clinically useful predictor of the long-term outcome of antiviral therapy. If at all successful, individual kinetic analyses including HBV-DNA, HBeAg, HBsAg, ALT, cellular and humoral immunologic parameters as well as baseline factors such as age at infection, age, fibrosis, genotype and others may be required to obtain predictive information from the early therapy on the long-term therapeutic outcome. To date, high ALT and low HBV-DNA are well, established baseline predictors for therapeutic outcome independent of treatment schedule. In patients treated with peg interferon alpha HBV genotype A provides a good positive predictive value (PPV) and a viral decline of less than 1log at week 12 a high negative predictive value (NPV) for HBeAg/anti-HBe seroconversion. In patients, treated with nucleos(t)ides HBV-DNA levels at week 12 provide a good PPV but a poor NPV for PCR negativity, HBeAg loss, and ALT normalization at week 48. The NPV improves at week 24 of therapy. HBV-DNA levels at week 24 (and thereafter) are highly predictive for the risk of emergence of resistant mutants. HBV-DNA levels above 103copies/mL at week 24 or 48 (for lamivudine and adefovir, respectively) may be a clinically useful indicator for treatment optimization.
8.2. IgM anti-HBc in the management of HBV carriers:
Quantification HBV-DNA to identify HBV induced liver damage has several limitations: (1) viral replication is not directly linked to liver damage; (2) necroinflammation in HBV carriers may be caused by virus-unrelated factors; (3) viral replication and biochemical activity may be intermittent. A threshold for antibodies against HBcAg of IgM class (IgM anti-HBc) of 600Units discriminates between acute and chronic hepatitis B. Several studies have shown that IgM anti-HBc are detectable in active but not in inactive carriers and that their fluctuations parallel those of HBV-DNA and ALT with a different temporal and quantitative kinetics. The assays proved useful to discriminate the HBeAg positive carriers in an active phase of disease from those in the tolerance phase. IgM anti-HBc were thus used to identify patients more prone to respond to IFN treatment and for post-treatment monitoring of HBeAg negative patients treated with IFN to identify potential sustained responders. IgM anti-HBc has several limitations. Newer chemiluminescence technology gives different IgM anti-HBc scores compared to first and second, generation microparticle EIAs. Performance comparisons between them are not available so far to re-define the ‘gray zone’ limits between inactive carriers and chronic hepatitis set by the older technology. A positive IgM anti-HBc is most useful in the diagnosis of acute hepatitis B, but it is found in 20% of chronic hepatitis B patients with acute exacerbations. The IgM anti-HBc has limited usefulness in the follow-up of HBeAg positive chronic hepatitis B. As a semi-quantitative measurement, it is most useful in the follow-up of inactive carriers, where a moderately elevated value characterizes HBeAg negative chronic hepatitis B, even when simultaneous ALT and HBV-DNA suggest an inactive carrier state. In this setting however cross-sectional studies have shown that the performance characteristics of semi-quantitative IgM anti-HBc was lower compared to ALT and HBV-DNA.
8.3. Is CCC DNA clearance achievable?
Persistence of HBV in patients with chronic HBV infection is related to the long half-life of CCC DNA in the hepatocyte nucleus and to an intracellular pathway whereby, nucleocapsid particles are recycled from the cytoplasm back into the nucleus, maintaining infection of hepatocytes without need for entry of new virions. CCC DNA is normally cleared by host immune response via cytolytic or non-cytolytic mechanisms. Recent studies using by CCC DNA-specific PCRs showed that adefovir, lamivudine and PEG IFN decrease intrahepatic CCC DNA although its reduction is less than that of total HBV-DNA. Modeling based on data in the adefovir phase III trial in HBeAg positive patients suggests that approximately 14 years of treatment would be needed to clear CCC DNA if there is no drug resistance. Thus, clearance of CCC DNA using available antivirals can only rarely be achieved. The likelihood of success is higher using more potent therapies with a negligible rate of drug resistance, particularly if the host immune response can be activated. Probably long-term suppression of CCC DNA to ‘low’ concentrations without actual clearance is sufficient in preventing progressive liver disease, since CCC DNA at low levels is detected in inactive carriers and in subjects with resolved HBV infection.
8.4. ‘Combined’ treatment end-points:
Virological (HBeAg loss, anti-HBe seroconversion, HBV-DNA suppression, HBsAg loss and anti-HBs seroconversion), biochemical (ALT normalisation), histological (changes in activity and fibrosis scores) and clinical end-points are used to assess therapies for chronic HBV infection. Choice of the most adequate end-point(s) depends on a number of variables related to the virological and clinical characteristics of patients and on timing of assessment. Virological and histological end-points are used for chronic hepatitis and compensated cirrhosis while clinical endpoints are more suitable in advanced and decompensated liver disease. For HBeAg positive chronic hepatitis, the combination of a durable HBeAg loss followed by anti-HBe seroconversion with adequate HBV-DNA suppression (<105copies/mL) represents a valid end-point for assessing the efficacy of antiviral therapy. For HBeAg negative patients, HBV-DNA suppression to negativity by PCR combined with durable ALT normalisation represents the most realistic and validated end-point. Clinical and prognostic value of combined end-points depends on their long term durability, either after a finite course of interferon (off-therapy durability) or maintained during prolonged therapy with nucleos(t)ide analogs (on-therapy durability). A complete response is achieved when these end-points are combined also with HBsAg loss, but this is rarely achieved in HBeAg positive or HBeAg negative patients.
9. Treatment of HBeAg positive chronic hepatitis B
The current management of chronic hepatitis B (CHB) consists of two different approaches: (i) finite curative treatment and (ii) indefinite suppressive treatment. The former strategy is used with interferons while the latter is used with nucleos(t)ide analogs. In HBeAg (+) CHB, HBeAg loss and/or HBeAg seroconversion to anti HBe antigen are the most widely used primary efficacy parameters.
9.1. Treatment with interferons:
In three randomized, controlled clinical trials treatment with pegylated interferon alfa 2a or 2b was associated with a HBeAg seroconversion rate of around 30% and HBsAg seroconversion rate of 3% at 6 months after treatment free follow-up. Patients with high baseline ALT and low HBV-DNA are more likely to have sustained response. Addition of nucleos(t)ide analogs do not offer additional benefit over interferon monotherapy despite a more robust decline of HBV-DNA levels during combination treatment.
9.2. Treatment with nucleos(t)ide analogs:
Nucleos(t)ide analogs (NAs) are potent antiviral agents affecting the reverse transcription step of HBV replication. These drugs are generally well tolerated and are considered safe although with newer NAs long-term safety data still need to be generated. Thus, on long-term use as monotherapy, drug resistance and safety remains a concern. The effects of various NAs on serum HBV-DNA levels may not be directly comparable because of different assays used. Further, data on development of resistance to a particular NA need also be interpreted with caution not only since sensitivities of HBV-DNA assays differ but also since different definitions of resistance were used.log decline of HBV-DNA, undetectable HBV-DNA (<400copies/mL) in 21% of patients, a 12% seroconversion rate and histological improvement. After 3 years treatment, seroconversion increases to 45% but genotypic resistance is reported as 6%. Durability of HBeAg seroconversion may be around 90%, which needs confirmation by other studies. No serious adverse event attributable to adefovir has been reported, specifically in none of the patients has an increase of serum creatinine >0.5mg/dL, been reported.mg/day) and lamivudine-resistant CHB (dose 1g/day). In treatment-naïve patients, one year of entecavir leads to a more effective decline in HBV-DNA than lamivudine (7 vs. 5.5log); however, this does not translate to increased HBeAg seroconversion (21 vs. 18%, respectively). Entecavir is less effective in lamivudine resistant CHB, one year of treatment leads to a 5.1log decline in HBV-DNA and 8% of HBeAg seroconversion. Resistance to entecavir has so far been reported exclusively in lamivudine-resistant patients, reaching 10% after one year of treatment.
Telbivudine (Ldt) compared to lamivudine results in more effective decline of HBV-DNA after 52 weeks of treatment, however HBeAg loss is not increased. Resistance to telbivudine as defined as genotypically confirmed viral breakthrough is less than to lamivudine (3 vs. 8%).
Emtricitabine (FTC) is a cytosine analog with structural similarity to lamivudine; it is active against both HBV and HIV. One year of treatment is associated with PCR negative HBV-DNA in 56% of cases; HBeAg seroconversion rate is 12.1% and genotypic resistance occurs in12.6%.
Clevudine is a thymidine analog with in vitro activity against HBV and Epstein–Barr virus but not against HIV. This drug possesses a long half life (more than 40h). Six months clevudine treatment led to a 4.9log decrease in HBV-DNA; undetectable HBV-DNA was seen in 57% and HBeAg seroconversion in 9.5% of patients.
Tenofovir disoproxil fumarate (TDF) is the bioavailable prodrug of tenofovir, an adenosine nucleotide analogue with close structural similarity to adefovir. It has potent activity against HBV and HIV. Three hundredmg/daily TDF appears to be more effective than adefovir in lamivudine-resistant CHB. After 48 weeks of treatment with tenofovir vs. adefovir, 100 vs. 44% of patients, respectively, were PCR negative.
Resistance to the pyrimidine analog lamivudine confers resistance to other pyrimidine analogs such as emtricitabine, clevudine, telbivudine and elvucitabine. The purine analogs adefovir, tenofovir are effective against lamivudine resistant CHB, the other purine analog entecavir is partially effective. Most NAs are effective against adefovir resistant HBV strains. So far, combination treatments with adevofir and lamivudine, or telbivudine and lamivudine for 1 year were not superior to lamivudine monotherapy, but they decreased viral breakthrough due to lamivudine resistant strains. Ideally one would like to have drugs that express different mechanisms of action, have no cross resistance and are not competitive in their metabolic activation.
Treatment with interferons has been mentioned already. Lamivudine-pegylated interferon combination leads to a more profound on-treatment decrease in HBV-DNA than either drug alone but not to increased sustained efficacy. Variable timing and length of use of each drug and alternative combinations need to be further tested. Interleukin 2 was ineffective in several clinical trials whereas interleukin-12 led to dose dependent decline in HBV-DNA in one study. Thymosin α1 is an immune modifier with T-cell function augmenting properties. In several trials, thymosin was superior to placebo. Active immunotherapy with HBV vaccine led to a higher percentage of HBV-DNA negativation during treatment compared to an unvaccinated group. This effect was lost however, on vaccine-free follow-up.
10. Treatment of HBeAg negative chronic hepatitis B
The primary end-points in HBeAg negative CHB are ALT normalisation and loss of HBV-DNA. However, HBV-DNA measurements are not standardized and hence studies are not directly comparable.
10.1. Treatment with interferons:
Studies with conventional interferons in HBeAg negative chronic hepatitis B have shown end-of treatment responses of over 50% and high relapse rates ranging from 25 to 89%. Sustained response increases with treatment duration and HBsAg may be lost in 32–67% of patients during 6–7 years of treatment-free follow-up. One year pegylated interferon treatment leads to combined (biochemical and virological) response rate of around 35%, 6 months after treatment discontinuation. Combination of pegylated interferon and lamivudine leads to more profound end of treatment response than either drug alone, but this effect is lost 6 months after treatment cessation. High baseline ALT, low baseline HBV-DNA, female gender and younger age appear to independently predict sustained response.
10.2. Treatment with nucleos(t)ide analogs
Telbivudine is more effective than lamivudine; after one year of treatment, HBV-DNA was undetectable by PCR in 88 and 71% and genotypically confirmed viral breakthrough in 2 and 7% of patients taking telbivudine and lamivudine, respectively. Clevudine led to HBV-DNA decline by 4.2log after 24 weeks of treatment.
Tenofovir is currently being tested in a large phase III study. Development of virological breakthrough during TDF has not been reported so far. However, in HIV-HBV co-infected patients, a novel mutation, rtA194T, conferring reduced susceptibility to TDF, has been described.
Data on interleukin-2 and 12 are similar to reports in HBeAg(+) CHB.
Thymosin-α1 (or thymalfasin) has been used as a single agent in 3 randomized controlled trials and in two of these, performed better than placebo or interferon α. Thymalfasin was also used in combination with interferon-α with promising results.
Preliminary data of the use of therapeutic vaccines as traditional recombinant HBsAg vaccines, T-cell or DNA-based genetic vaccines are not encouraging. These studies should be redesigned to obtain stronger CTL stimulation using specific adjuvants or lysosomotropic agents.
11. Special populations
11.1. Acute and fulminant hepatitis B:
Recent studies using sensitive HBV-DNA assays revealed high HBV-DNA titres at presentation and thus imply a possible role for antivirals. In two open label studies, lamivudine was tested in 32 patients with acute severe hepatitis B. 27 patients survived without liver transplantation and had HBsAg clearance within 4–6 months. Treatment for 3–6 months was safe and resistance to lamivudine was not observed. However, not all of these patients had fulminant hepatitis by definition.
11.2. Advanced cirrhosis-pre liver transplantation:
lamivudine is safe and effective in decompensated liver cirrhosis, a condition with a 5 year survival rate of only 15% without treatment. High serum levels of bilirubin, creatinine and HBV-DNA were associated with early death, which occurred mainly in the first 6 months. In a placebo controlled randomized study, after a median duration of 32 months, disease progression decreased significantly in patients on lamivudine compared to placebo. In patients, with genotypic resistance the beneficial effect declines. Adefovir led to normal ALT and undetectable HBV-DNA leading to decreases in Child Pugh and MELD scores in more than 70% of lamivudine resistant patients. Data on newer nucleoside analogs do not exist currently.
11.3. Prophylaxis and treatment of HBV infection after liver transplantation:
Introduction of hepatitis B immunoglobulin (HBIg) therapy after transplantation and to pre- and post-transplant management with nucleoside analogs led to major improvement in survival of patients transplanted for HBV related end-stage liver disease. Optimal management consist of combined use of HBIg and lamivudine, which leads to HBV recurrence rates of only 10% in the high risk HBV-DNA-positive patient group. Patients with high HBV-DNA should start NAs before transplantation. Strategies to avoid long-term use of HBIg including HBV vaccination after discontinuation of HBIg or adoptive transfer of immunity (from HBsAb-positive donors), should be considered experimental. The latter approach appears to be a temporary phenomenon and data on the former approach are thus far conflicting.
11.4. End stage renal failure and renal transplants:
HBV infection remains frequent in dialysis patients and kidney recipients despite anti-HBV vaccination. HBV-infected cirrhotic dialysis patients have lower survival rates than those without dialysis. Kidney transplantation significantly increases HBV replication leading to more severe liver disease including cholestatic hepatic fibrosis and more rapid evolution to cirrhosis and hepatocellular carcinoma. Survival in kidney transplant recipients with HBV infection is less than in non-infected kidney transplant recipients (55 vs. 80%, respectively, at 10 years). Patients with significant liver disease (fibrosis >1) will require treatment. Interferons are deleterious and inefficient in kidney recipients and their use in dialysis patients is limited; thus, nucleos(t)ides analogues are the main therapy. Their doses need to be tampered according to renal function. Adefovir is efficient and nephrotoxicity is probably prevented when dose adjusted according to renal function. In patients who undergo kidney transplantation, pre-emptive treatment with nucleos(t)ide analogs should probably be preferred to salvage therapy at time of hepatitis reactivation. Combined kidney and liver transplantation should be considered for patients with liver cirrhosis.
Bone marrow transplantation and haemato-oncologic patients: any patient with overt or occult HBV infection receiving systemic chemo- or radiotherapy, bone marrow or peripheric stem cell transplantation are at increased for HBV reactivation. Clinical reactivation occurs following withdrawal of chemotherapy and emergence of immune recovery and can be fatal. Risk of reactivation correlates with degree of viral load, use of corticosteroids, degree of immunosupression and male sex. Preemptive use of nucleoside analogs prevents HBV reactivation and is superior to deferred therapy at onset of reactivation. Optimal duration of preemptive therapy is not established but it is recommended to continue antiviral therapy for at least 6 months after completing chemotherapy. Immunosuppressed patients have reduced immunogenicity to HBV vaccines. Means of augmenting immunogenicity to HBV vaccines include dose doubling, use of intradermal injections or S, pre-S1 and pre-S2 vaccines.
12. Treatments to come
A new immune based therapy is oral immune regulation. In a preliminary human study, 42 chronic HBV subjects were treated orally with HBsAg+preS1+preS2 for 30 weeks. Oral immune regulation induced a significant decrease in viral load in 46% of subjects. Three out of eleven HBeAg positive subjects lost HBeAg. Oral immune regulation was associated with increased HBV-specific T-cell proliferation and cytotoxicity, IFN-γ production and natural killer T (NKT) cell activity. β-Glucosylceramide (GC) is a natural occurring glycolipid. GC inhibited NKT cell proliferation in vitro, and alleviated immune mediated damage in several animal models of immune mediated hepatitis.
Nucleic acid based antiviral strategies include use of antisense oligonucleotides, engineered ribozymes and short interfering RNAs. Antisense oligonucleotides act by interfering with RNA function. The main problems are lack of tissue specificity; short half, life and poor bioavailability. Ribozymes are catalytically active RNA molecules. Pre-clinical studies in HBV have demonstrated marked efficacy in cellular and animal models but low efficacy in phases I/II trials. RNA interference stands for sequence-specific inhibition of gene expression by double-stranded RNA molecules. Successful application has been shown in cell culture systems and animal models. Recent work describes promising results in liver-specific delivery of these molecules.
13. (*) Faculty of the EASL Istanbul HBV Monothematic
Ulus S. Akarca, Turkey; Alfredo Alberti, Italy; Yves Benhamou, France; Antonio Bertoletti, UK; Thomas Berg, Germany; Ferruccio Bonino, Italy; A. Mithat Bozdayi, Turkey; Hakan Bozkaya, Turkey; Maurizia Brunetto, Italy; Maria Buti, Spain; Hari Conjeevaram, USA; Miguel Angel Casado, Spain; Yilmaz Cakaloglu, Turkey; Antonio Craxì, Italy; Robert A. de Man, The Netherlands; Geoffrey Dusheiko, UK; Rafael Esteban, Spain; Patrizia Farci, Italy; Carlo Ferrari, Italy; Giovanni B. Gaeta, Italy; Jeffrey S. Glenn, USA; Stefanos Hadziyannis, Greece; Harry L.A. Janssen, The Netherlands; Yaron Ilan, Israel; George K.K. Lau, Hong Kong; Pietro Lampertico, Italy; Massimo Levrero, Italy; Stephen A. Locarnini, Australia; Anna S. Lok, USA; Emanuel K. Manesis, Greece; Michael Manns, Germany; Patrick Marcellin, France; Giulio Marchesini, Italy; Mario Mondelli, Italy; Ricardo Moreno-Otero, Spain; David J. Mutimer, UK; Nikolai V. Naoumov, UK; George Papatheodoridis, Greece; Jean-Michel Pawlotsky, France; Marion Peters, USA; Stanislas Pol, France; Giovanni Raimondo, Italy; Mario Rizzetto, Italy; Tania Roskams, Belgium; Didier Samuel, France; Eugene R. Schiff, USA; Raymond F. Schinazi, USA; Daniel Shouval, Israel; Joseph J.Y. Sung, Hong Kong; Howard C. Thomas, UK; Hans L. Tillman, Germany; Nurdan Tözün, Turkey; Christian Trepo, France; Erica Villa, Italy; Heiner Wedemeyer, Germany; Cihan Yurdaydın, Turkey; Stefan Zeuzem, Germany; Fabien Zoulim, France
PII: S0168-8278(06)00169-3
doi:10.1016/j.jhep.2006.03.004
© 2006 Published by Elsevier Inc.
