DNA vaccination in combination or not with lamivudine treatment breaks humoral immune tolerance and enhances cccDNA clearance in the duck model of chronic hepatitis B virus infection

Nucleic acid vaccines: A taboo broken and prospect for a hepatitis B virus cure

Although a prophylactic vaccine is available, hepatitis B virus (HBV) remains a major cause of liver-related morbidity and mortality. Current treatment options are improving clinical outcomes in chronic hepatitis B; however, true functional cure is currently the exception rather than the rule. Nucleic acid vaccines are among the emerging immunotherapies that aim to restore weakened immune function in chronically infected hosts. DNA vaccines in particular have shown promising results in vivo by reducing viral replication, breaking immune tolerance in a sustained manner, or even decimating the intranuclear covalently closed circular DNA reservoir, the hallmark of HBV treatment. Although DNA vaccines encoding surface antigens administered by conventional injection elicit HBV-specific T cell responses in humans, initial clinical trials failed to demonstrate additional therapeutic benefit when administered with nucleos(t)ide analogs. In an attempt to improve vaccine immunogenicity, several techniques have been used, including codon/promoter optimization, coadministration of cytokine adjuvants, plasmids engineered to express multiple HBV epitopes, or combinations with other immunomodulators. DNA vaccine delivery by electroporation is among the most efficient strategies to enhance the production of plasmid-derived antigens to stimulate a potent cellular and humoral anti-HBV response. Preliminary results suggest that DNA vaccination via electroporation efficiently invigorates both arms of adaptive immunity and suppresses serum HBV DNA. In contrast, the study of mRNA-based vaccines is limited to a few in vitro experiments in this area. Further studies are needed to clarify the prospects of nucleic acid vaccines for HBV cure.

Nucleic acid polymer REP 2139 and nucleos(T)ide analogues act synergistically against chronic hepadnaviral infection in vivo in Pekin ducks

Nucleic acid polymer (NAP) REP 2139 treatment was shown to block the release of viral surface antigen in duck HBV (DHBV)-infected ducks and in patients with chronic HBV or HBV/hepatitis D virus infection. In this preclinical study, a combination therapy consisting of REP 2139 with tenofovir disoproxil fumarate (TDF) and entecavir (ETV) was evaluated in vivo in the chronic DHBV infection model. DHBV-infected duck groups were treated as follows: normal saline (control); REP 2139 TDF; REP 2139 + TDF; and REP 2139 + TDF + ETV. After 4 weeks of treatment, all animals were followed for 8 weeks. Serum DHBsAg and anti-DHBsAg antibodies were monitored by enzyme-linked immunosorbent assay and viremia by qPCR. Total viral DNA and covalently closed circular DNA (cccDNA) were quantified in autopsy liver samples by qPCR. Intrahepatic DHBsAg was assessed at the end of follow-up by immunohistochemistry. On-treatment reduction of serum DHBsAg and viremia was more rapid when REP 2139 was combined with TDF or TDF and ETV, and, in contrast to TDF monotherapy, no viral rebound was observed after treatment cessation. Importantly, combination therapy resulted in a significant decrease in intrahepatic viral DNA (>3 log) and cccDNA (>2 log), which were tightly correlated with the clearance of DHBsAg in the liver.

CONCLUSION

Synergistic antiviral effects were observed when REP 2139 was combined with TDF or TDF + ETV leading to control of infection in blood and liver, associated with intrahepatic viral surface antigen elimination that persisted after treatment withdrawal. Our findings suggest the potential of developing such combination therapy for treatment of chronically infected patients in the absence of pegylated interferon. (Hepatology 2018;67:2127-2140).

Immune therapy for hepatitis B

Although several antiviral drugs are now available for treatment of patients with chronic hepatitis B (CHB), sustained off-treatment clinical responses and containment of CHB-related complications are not achieved in majority of CHB patients by antiviral therapy. In addition, use of these drugs is endowed with substantial long term risk of viral resistance and drug toxicity. The infinite treatment regimens of antiviral drugs for CHB patients are also costly and usually unbearable by most patients of developing and resource-constrained countries. Taken together, there is a pressing need to develop new and innovative therapeutic approaches for CHB patients. Immune therapy seems to be an alternate therapeutic approach for CHB patients because impaired or distorted or diminished immune responses have been detected in most of these patients. Also, investigators have shown that restoration or induction of proper types of immune responses may have therapeutic implications in CHB. Various immunomodulatory agents have been used to treat patients with CHB around the world and the outcomes of these clinical trials show that the properties of immune modulators and nature and designing of immune therapeutic regimens seem to be highly relevant in the context of treatment of CHB patients. In this review, the general properties and specific features of immune therapy for CHB have been discussed for developing the guidelines of effective regimens of immune therapy for CHB.

DNA vaccination of poultry: The current status in 2015

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Poultry DNA vaccination studies are regularly being published since 1993.

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These studies are mainly, but not only, concerned with vaccination against viruses.

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The different strategies of improving DNA vaccine efficacies are presented.

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The fate of the vaccine plasmid, immune properties and other applications are described.

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Despite the compiling preclinical reports, a poultry DNA vaccine is yet unavailable in the market.

DNA vaccination is a promising alternative strategy for developing new human and animal vaccines. The massive efforts made these past 25 years to increase the immunizing potential of this kind of vaccine are still ongoing. A relatively small number of studies concerning poultry have been published. Even though there is a need for new poultry vaccines, five parameters must nevertheless be taken into account for their development: the vaccine has to be very effective, safe, inexpensive, suitable for mass vaccination and able to induce immune responses in the presence of maternal antibodies (when appropriate). DNA vaccination should meet these requirements. This review describes studies in this field performed exclusively on birds (chickens, ducks and turkeys). No evaluations of avian DNA vaccine efficacy performed on mice as preliminary tests have been taken into consideration. The review first describes the state of the art for DNA vaccination in poultry: pathogens targeted, plasmids used and different routes of vaccine administration. Second, it presents strategies designed to improve DNA vaccine efficacy: influence of the route of administration, plasmid dose and age of birds on their first inoculation; increasing plasmid uptake by host cells; addition of immunomodulators; optimization of plasmid backbones and codon usage; association of vaccine antigens and finally, heterologous prime-boost regimens. The final part will indicate additional properties of DNA vaccines in poultry: fate of the plasmids upon inoculation, immunological considerations and the use of DNA vaccines for purposes other than preventing infectious diseases.

Induced immunity against hepatitis B virus

Prevention of hepatitis B virus (HBV) infection with its consequent development of HBV chronic liver disease and hepatocellular carcinoma is a global mandatory goal. Fortunately, safe and effective HBV vaccines are currently available. Universal hepatitis B surface antigen HBV vaccination coverage is almost done. Growing knowledge based upon monitoring and surveillance of HBV vaccination programs has accumulated and the policy of booster vaccination has been evaluated. This review article provides an overview of the natural history of HBV infection, immune responses and the future of HBV infection. It also summarizes the updated sources, types and uses of HBV vaccines, whether in the preclinical phase or in the post-field vaccination.

The Pekin duck programmed death-ligand 1: cDNA cloning, genomic structure, molecular characterization and mRNA expression analysis

Programmed death ligand-1 (PD-L1) plays an important role in the attenuation of adaptive immune responses in higher vertebrates. Here, we describe the identification of the Pekin duck PD-L1 orthologue (duPD-L1) and its gene structure. The duPD-L1 cDNA encodes a 311-amino acid protein that has an amino acid identity of 78% and 42% with chicken and human PD-L1, respectively. Mapping of the duPD-L1 cDNA with duck genomic sequences revealed an exonic structure of its coding sequence similar to those of other vertebrates but lacked a noncoding exon 1. Homology modelling of the duPD-L1 extracellular domain was compatible with the tandem IgV-like and IgC-like IgSF domain structure of human PD-L1 (PDB ID: 3BIS). Residues known to be important for receptor binding of human PD-L1 were mostly conserved in duPD-L1 within the N-terminus and the G sheet, and partially conserved within the F sheet but not within sheets C and C'. DuPD-L1 mRNA was constitutively expressed in all tissues examined with highest expression levels in lung and spleen and very low levels of expression in muscle, kidney and brain. Mitogen stimulation of duck peripheral blood mononuclear cells transiently increased duPD-L1 mRNA expression. Our observations demonstrate evolutionary conservation of the exonic structure of its coding sequence, the extracellular domain structure and residues implicated in receptor binding, but the role of the longer cytoplasmic tail in avian PD-L1 proteins remains to be determined.

Hepatitis B Virus-Related Hepatocellular Carcinoma: Pathogenic Mechanisms and Novel Therapeutic Interventions

BACKGROUND

Infection with the hepatitis B virus (HBV) is one of most important risk factors for hepatocellular carcinoma (HCC). Indeed, HBV is considered a group 1 human carcinogen and is a highly oncogenic agent. HBV cannot be effectively controlled or completely eliminated, so chronic HBV infection is a public health challenge worldwide.

SUMMARY

It is now believed that HBV-induced HCC involves a complex interaction between multiple viral and host factors. Many factors contribute to HBV-associated HCC, including products of HBV, viral integration and mutation, and host susceptibility. This review outlines the main pathogenic mechanisms with a focus on those that suggest novel targets for the prevention and treatment of HCC.

KEY MESSAGE

HBV infection is an important risk factor for HCC. Understanding the interaction between viral and host factors in HBV-induced HCC will reveal potential targets for future therapies.

PRACTICAL IMPLICATIONS

The two main therapeutic strategies consist of antiviral agents and immunotherapy-based approaches. Dendritic cell-based immunotherapy is promising for restoring the T cell-mediated antiviral immune response. Another approach is the specific expansion of the host's pool of HBV-specific T cells. Stimulation of the Toll-like receptors (TLRs), particularly TLR9, provides another means of boosting the antiviral response. Combination therapy with cytokines (interferon gamma and tumor necrosis factor alpha) plus lamivudine is more effective than these agents used alone. Therapeutic vaccines are being developed as an alternative to long-term antiviral treatment or as an adjunct.

Immunotherapeutic interventions in chronic hepatitis B virus infection: a review

Chronic hepatitis B virus (HBV) infection is a public health challenge worldwide. Antiviral agents (nucleos(t)ide analogues, NAs) and immune-based therapies (IFN-α or Pegylated-IFN-α) are two therapeutic approaches available currently against chronic hepatitis B (CHB). However, these approaches are associated with the development of acquired drug resistance or poor response rates and are accompanied by numerous side effects. Furthermore, due to defective innate and adaptive immune responses, HBV cannot be effectively controlled or completely eliminated, which may ultimately result in liver decompensation and hepatocelluar carcinoma. The imperative for development of new approaches targeting CHB cannot be overstated. Various immunotherapeutic interventions have been tried as adjuvants to inhibit HBV replication. In this paper, we will review immunotherapeutic interventions in the treatment of CHB.

Nucleic acid polymers prevent the establishment of duck hepatitis B virus infection in vivo

Nucleic acid polymers (NAPs) are novel, broad-spectrum antiviral compounds that use the sequence-independent properties of phosphorothioate oligonucleotides (PS-ONs) as amphipathic polymers to block amphipathic interactions involved in viral entry. Using the duck hepatitis B virus (DHBV) model of human hepatitis B virus infection, NAPs have been shown to have both entry and postentry antiviral activity against DHBV infection in vitro in primary duck hepatocytes (PDH). In the current study, various NAPs were assessed for their prophylactic activity in vivo against DHBV infection in ducks. The degenerate NAP REP 2006 prevented the development of widespread and persistent DHBV infection in 14-day-old ducks, while the acidic-pH-sensitive NAP REP 2031 had little or no prophylactic effect. REP 2006 displayed significant toxicity in ducks, which was attributed to CpG-mediated proinflammation, while REP 2031 (which has no CpG motifs) displayed no toxicity. A third NAP, REP 2055, which was designed to retain amphipathic activity at acidic pH and contained no CpG motifs, was well tolerated and displayed prophylactic activity against DHBV infection at doses as low as 1 mg/kg of body weight/day. These studies suggest that NAPs can be easily and predictably tailored to retain anti-DHBV activity and to have minimal toxic effects in vivo. Future studies are planned to establish the therapeutic efficacy of NAPs against persistent DHBV infection.

HBsAg, HBcAg, and combined HBsAg/HBcAg-based therapeutic vaccines in treating chronic hepatitis B virus infection

BACKGROUND

As the host immunity is diminished in patients with chronic hepatitis B (CHB), different approaches have been used to up-regulate their immune responses to produce therapeutic effects. But, cytokines, growth factors and polyclonal immune modulators could not exhibit sufficient therapeutic effects in these patients. Immune therapy with HBV-related antigens (vaccine therapy) has been used in CHB patients. But there is a paucity of information about the design of HBV antigen-based immune therapy in these patients.

DATA SOURCE

Preclinical and clinical studies on immune therapy with HBsAg-based vaccine, HBcAg and combination of HBsAg/HBcAg-based vaccines have been discussed.

RESULTS

HBsAg-based prophylactic vaccine was used as an immune therapeutic agent in CHB patients; however, monotherapy with HBsAg-based immune therapy could not lead to sustained control of HBV replication and/or liver damages. HBsAg-based vaccine was used as a combination therapy with cytokines, growth factors, and antiviral drugs. HBsAg-based vaccine was also used for cell-based therapy. However, satisfactory therapeutic effects of HBsAg-based vaccine could not be documented in CHB patients. In the mean time, evidences have supported that HBcAg-specific immunity is endowed with antiviral and liver protecting capacities in CHB patients. Recent data concentrate on the clinical use of combined HBsAg- and HBcAg-based vaccines in CHB patients.

CONCLUSION

Antigen-based immune therapy with HBV-related antigens may be an alternative method for the treatment of CHB patients but proper designs of antigens, types of adjuvants, dose of vaccinations, and routes of administration need further analyses for the development of an effective regimen of immune therapy against HBV.

Non-antigen-specific and antigen-specific immune therapies for chronic hepatitis B: evidences from laboratory benches and patient's bedsides

INTRODUCTION

Due to unsatisfactory therapeutic efficacy and considerable side effects of antiviral drugs in patients with chronic hepatitis B (CHB), immunotherapy has emerged as an alternative approach. CHB immunotherapy may be categorized into two main types: i) non-antigen-specific immune therapy and ii) hepatitis B virus (HBV) antigen-specific immune therapy. Although different immune modulators have been used in CHB patients for the last two to three decades, the nature and design of ongoing regimens of immunotherapeutic approaches need considerable modifications.

AREAS COVERED

In this review, the authors have outlined the relevant immunotherapies for CHB patients that have been used for the last two to three decades. The mechanisms underlying the limited therapeutic efficacy of available therapeutic agents for CHB patients have been discussed to aid in the development of an effective therapeutic approach for these patients.

EXPERT OPINION

Circumstantial evidence indicates that a better regimen of immunotherapy may be developed using different HBV-related antigens or combinations of two or more HBV-related antigens, or combinations of HBV-related antigens and antiviral drugs. However, the capacity of 'inducible immunity' by immune modulators to cure or block progression of liver diseases in CHB patients needs to be addressed.

Immune responses and protection against H5N1 highly pathogenic avian influenza virus induced by the Newcastle disease virus H5 vaccine in ducks

Ducks play an important role in the epidemiology of avian influenza, and there is a need for new avian influenza vaccines that are suitable for mass vaccination in ducks. The immune responses as well as highly pathogenic avian influenza (HPAI) H5N1 protection induced by a Newcastle disease virus (NDV) vector expressing an H5N1 hemagglutinin (rNDV-H5) were investigated in mule ducks, a hybrid between Muscovy (Cairina moschata domesticus) males and Pekin (Anas platyrhynchos domesticus) females. Immunological tools to measure NDV and H5-specific serum antibody, mucosal, and cell-mediated immune (CMI) responses in ducks have been validated after infection with the vector NDV and an H5N1 low pathogenic avian influenza virus. The effect of maternally-derived antibodies (MDAs) to NDV on the humoral and CMI responses after NDV-H5 vaccination was also investigated. Our results showed the rNDV-H5 vaccine elicits satisfactory humoral and cellular responses in 11-day-old ducks correlating with a complete clinical and virological protection against the H5N1 strain. However, vaccination with rNDV-H5 in the presence of NDV MDA induced lower NDV-specific serum antibody, mucosal, and CMI responses than in ducks with no MDA, while interestingly the H5-specific serum antibody and duodenal IgY response were higher in ducks with NDV MDA. To our knowledge, this is the first report of the use of an NDV vector in ducks and of an HPAI H5N1 challenge in mule ducks, which appeared to be as resistant as Pekin ducks.

In vivo infectivity of liver extracts after resolution of hepadnaviral infection following therapy associating DNA vaccine and cytokine genes

DNA-based vaccination appears of promise for chronic hepatitis B immunotherapy, although there is an urgent need to increase its efficacy. In this preclinical study, we evaluated the therapeutic benefit of cytokine (IL-2, IFN-γ) genes co-delivery with DNA vaccine targeting hepadnaviral proteins in the chronic duck hepatitis B virus (DHBV) infection model. Then, we investigated the persistence of replication-competent virus in the livers of apparently resolved animals. DHBV carriers received four injections of plasmids encoding DHBV envelope and core alone or co-delivered with duck IL-2 (DuIL-2) or duck IFN-γ (DuIFN-γ) plasmids. After long-term (8 months) follow-up, viral covalently closed circular (ccc) DNA was analysed in duck necropsy liver samples. Liver homogenates were also tested for in vivo infectivity in neonatal ducklings. Co-delivery of DuIFN-γ resulted in significantly lower mean viremia starting from week 21. Viral cccDNA was undetectable by conventional methods in the livers of 25% and 57% of animals co-immunized with DuIL-2 and DuIFN-γ, respectively. Interestingly, inoculation of liver homogenates from 7 such apparently resolved animals, exhibiting cccDNA undetectable in Southern blotting and DHBV expression undetectable or restricted to few hepatocytes, revealed that three liver homogenates transmitted high-titre viremia (3-5×10(10) vge/mL) to naïve animals. In conclusion, our results indicate that IFN-γ gene co-delivery considerably enhances immunotherapeutic efficacy of DNA vaccine targeting hepadnaviral proteins. Importantly, we also showed that livers exhibiting only minute amounts of hepadnaviral cccDNA could induce extremely high-titre infection, highlighting the caution that should be taken in occult hepatitis B patients to prevent HBV transmission in liver transplantation context.

In vivo electroporation improves therapeutic potency of a DNA vaccine targeting hepadnaviral proteins

This preclinical study investigated the therapeutic efficacy of electroporation (EP)-based delivery of plasmid DNA (pDNA) encoding viral proteins (envelope, core) and IFN-γ in the duck model of chronic hepatitis B virus (DHBV) infection. Importantly, only DNA EP-therapy resulted in a significant decrease in mean viremia titers and in intrahepatic covalently closed circular DNA (cccDNA) levels in chronic DHBV-carrier animals, compared with standard needle pDNA injection (SI). In addition, DNA EP-therapy stimulated in all virus-carriers a humoral response to DHBV preS protein, recognizing a broader range of major antigenic regions, including neutralizing epitopes, compared with SI. DNA EP-therapy led also to significant higher intrahepatic IFN-γ RNA levels in DHBV-carriers compared to other groups, in the absence of adverse effects. We provide the first evidence on DNA EP-therapy benefit in terms of hepadnaviral infection clearance and break of immune tolerance in virus-carriers, supporting its clinical application for chronic hepatitis B.

T cell immunopathogenesis and immunotherapeutic strategies for chronic hepatitis B virus infection

Hepatitis B is caused by the host immune response and T cells play a major role in the immunopathogenesis. More importantly, T cells not only destroy hepatocytes infected by hepatitis B virus (HBV), but also control HBV replication or eradicate HBV in a noncytolytic manner. Therefore, analysis of T cell immune response during acute and chronic HBV infection is important to develop a strategy for successful viral control, which could lead to immunotherapy for terminating persistent HBV infection. There have been many attempts at immunotherapy for chronic HBV infection, and some have shown promising results. High viral load has been shown to suppress antiviral immune responses and immunoinhibitory signals have been recently elucidated, therefore, viral suppression by nucleos(t)ide analogs, stimulation of antiviral immune response, and suppression of the immunoinhibitory signals must be combined to achieve desirable antiviral effects.

Progress in DNA vaccination against HBV infection

Chronic HBV infection remains a leading cause of serious liver disease and hepatocellular carcinoma in spite of the existence of an effective preventive vaccine. Although the actual antiviral treatments have greatly improved, they only rarely clear viral infection. In this regard, therapeutic DNA vaccination appears to have great promise to stimulate and restore the impaired immune responses in chronic HBV carriers. This review examines preclinical studies of preventive and therapeutic DNA vaccines in different animal models (mouse, woodchuck and duck) and the first clinical studies in chronically infected patients. We also focused on different approaches aimed at enhancing the effectiveness of DNA vaccines such as combination therapy with antiviral drugs and in vivo DNA electroporation.

In vivo proliferation of hepadnavirus-infected hepatocytes induces loss of covalently closed circular DNA in mice

Chronic hepatitis B virus (HBV) infection is maintained by the presence of covalently closed circular DNA (cccDNA), the template of viral transcription and replication. In quiescent hepatocytes, cccDNA is a stable molecule that can persist throughout the hepatocyte lifespan. However, in chronic HBV infection, immunomediated cell injury and compensatory hepatocyte proliferation may favor cccDNA decline and selection of cccDNA-free cells. To investigate the impact of liver regeneration on cccDNA stability and activity in vivo, we used the urokinase-type plasminogen activator (uPA)/severe combined immunodeficiency (SCID) mouse model. Primary tupaia hepatocytes (PTHs) chronically infected with woolly monkey HBV (WM-HBV) were isolated from one highly viremic uPA/SCID chimeric mouse and transplanted into 20 uPA recipients. Expansion of transplanted PTHs and viral load changes were determined by real-time polymerase chain reaction and immunohistochemistry. Transplantation of WM-HBV infected hepatocytes led to an average of 3.8 PTH doublings within 80 days, 75% reduction of virion productivity (relaxed circular DNA/cccDNA), and lower expression levels of pregenomic RNA and hepatitis B core antigen. Remarkably, a median 2-log decline of cccDNA per cell determined during PTH proliferation was due to both dilution of the cccDNA pool among daughter cells and a 0.5-log loss of intrahepatic cccDNA loads (P = 0.02). Intrahepatic viral DNA sequences persisting at the end of the study were mostly present as replicative intermediates and not as integrated virus.

CONCLUSION

Cell division in the setting of liver regeneration and without administration of antiviral drugs induced strong destabilization of the cccDNA reservoir, resulting in cccDNA clearance in the great majority of chronically infected hepatocytes.

Efficacy of pre-S-containing HBV vaccine combined with lamivudine in the treatment of chronic HBV infection

Treatment of chronic hepatitis B (CHB) is difficult. The response rate to interferon (IFN) as well as nucleoside analogs is not more than 30% in general. While interferon has many side effects, development of resistance in most of the nucleoside analogs precludes long-term use. Both groups of drugs are most efficacious in patients who already had or develop strong cellular immunity with treatment. A pre-S2-containing vaccine was shown to enhance cellular immunity and suppress hepatitis B virus (HBV)-DNA in subjects with chronic hepatitis B. We aimed to test the efficacy of short-term use of a nucleoside analog in combination with a pre-S2-containing vaccine in patients with CHB. In this open study, 48 consecutive patients (32 males and 16 females, mean age +/- SD: 33 +/- 12 years) with CHB without cirrhosis were treated with 100 mg/day lamivudine and four weekly intramuscular injections of Genhevac B 20 mcg (six doses) for 24 weeks. While 19 patients were hepatitis B e antigen (HBeAg) positive (+ve), 29 patients were Anti-HBe/HBV-DNA +ve at the outset. Response was defined as seroconversion to anti-HBe in HBeAg +ve subjects and normalization of alanine aminotransferase (ALT) with loss of HBV-DNA in anti-HBe/HBV-DNA +ve subjects. HBeAg seroconversion occurred in 5/19 subjects (26%). Eighteen of 29 anti-HBe/HBV-DNA +ves responded. In the follow-up, while relapse was not observed in any of the patients who seroconverted, 11/18 from the anti-HBe/HBV-DNA +ve group relapsed, resulting in a sustained response (SR) rate of 24% in this group. All the relapses happened in the first 48 weeks of follow-up, with no relapse thereafter. Pretreatment high serum HBV-DNA was a strong negative predictor of sustained response (SR) in HBeAg +ve group. Pretreatment serum ALT over 2 x upper limit of normal and HBV-DNA less than 200 pg/ml appeared positive predictors. None of HBeAg +ve previous interferon failures responded. Twenty-four weeks of lamivudine and hepatitis B vaccine treatment induces SR in around 1/4 of the patients with CHB. Most of the responders had high ALT and relatively low DNA.

[Treatment of hepatitis B: new perspectives]

Despite the development of new anitiviral agents, the treatment of chronic hepatitis B remains a major clinical challenge. Major achievements have been made with the rationale use of antivirals exhibiting a complementary cross resistance profile to prevent antiviral drug resistance. The current concept of modern antiviral therapy of chronic hepatitis B relies on a precise virologic monitoring and early treatment adaptation to prevent drug resistance. The difficulty of achieving viral clearance and the risk of drug resistance development are major arguments to continue research in the field of antivirals and to identify new targets for therapy. The development of true combination therapy is highly desirable to fulfil the objective of long-term viral suppression, clearance of viral cccDNA and infected cells and ultimately cure of the disease.