Isolation and functional characterization of hepatitis B virus-specific T-cell receptors as new tools for experimental and clinical use

Activating adaptive immunity by bispecific, T-cell engager antibodies bridging infected and immune-effector cells is a promising novel therapy for chronic hepatitis B

Bispecific antibodies (bsAbs) are engineered immunoglobulins that combine two different antigen-binding sites in one molecule. BsAbs can be divided into two molecular formats: IgG-like and non-IgG-like antibodies. Structural elements of each format have implications for engaging the immune system. T cell engager antibodies (TCEs) are bsAbs designed to engage T cells with target cells. TCEs can be applied not only in cancer but also in infectious disease therapy to activate T-cell responses. In this review, we focus on current literature on the design and use of bsAbs as an innovative strategy to enhance adaptive antiviral immune responses. We summarized the novel T cell-related immunotherapies with a focus on TCEs, that are developed for the treatment of chronic hepatitis B. Chronic infection with the hepatitis B virus (HBV) had a death toll of 1.1 million humans in 2022, mainly due to liver cirrhosis and hepatocellular carcinoma developing in the more than 250 million humans chronically infected. A curative treatment approach for chronic hepatitis B is lacking. Combining antiviral therapy with immune therapies activating T-cell responses is regarded as the most promising therapeutic approach to curing HBV and preventing the sequelae of chronic infection. Attracting functionally intact T cells that are not HBV-specific and, therefore, have not yet been exposed to regulatory mechanisms and activating those at the target site in the liver is a very interesting therapeutic approach that could be achieved by TCEs. Thus, TCEs redirecting T cells toward HBV-positive cells represent a promising strategy for treating chronic hepatitis B and HBV-associated hepatocellular carcinoma.

Vector-Mediated Delivery of Human Major Histocompatibility Complex-I into Hepatocytes Enables Investigation of T Cell Receptor-Redirected Hepatitis B Virus-Specific T Cells in Mice, and in Macaque Cell Cultures

Adoptive T cell therapy using natural T cell receptor (TCR) redirection is a promising approach to fight solid cancers and viral infections in liver and other organs. However, clinical efficacy of such TCR+-T cells has been limited so far. One reason is that syngeneic preclinical models to evaluate safety and efficacy of TCR+-T cells are missing. We, therefore, developed an efficient viral vector strategy mediating expression of human major histocompatibility complex (MHC)-I in hepatocytes, which allows evaluation of TCR-T cell therapies targeting diseased liver cells. We designed adeno-associated virus (AAV) and adenoviral vectors encoding either the human-mouse chimeric HLA-A*02-like molecule, or fully human HLA-A*02 and human β2 microglobulin (hβ2m). Upon transduction of murine hepatocytes, the HLA-A*02 construct proved superior in terms of expression levels, presentation of endogenously processed peptides and activation of murine TCR+-T cells grafted with HLA-A*02-restricted, hepatitis B virus (HBV)-specific TCRs. In vivo, these T cells elicited effector function, controlled HBV replication, and reduced HBV viral load and antigen expression in livers of those mice that had received AAV-HBV and AAV-HLA-A*02. We then demonstrated the broad utility of this approach by grafting macaque T cells with the HBV-specific TCRs and enabling them to recognize HBV-infected primary macaque hepatocytes expressing HLA-A*02 upon adenoviral transduction. In conclusion, AAV and adenovirus vectors are suitable for delivery of HLA-A*02 and hβ2m into mouse and macaque hepatocytes. When recognizing their cognate antigen in HLA-A*02-transduced mouse livers or on isolated macaque hepatocytes, HLA-A*02-restricted, HBV-specific TCR+-T cells become activated and exert antiviral effector functions. This approach is applicable to any MHC restriction and target disease, paving the way for safety and efficacy studies of human TCR-based therapies in physiologically relevant preclinical animal models.

Immune escape pathways from the HBV core18-27 CD8 T cell response are driven by individual HLA class I alleles

Background and aims

There is growing interest in T cell-based immune therapies for a functional cure of chronic HBV infection including check-point inhibition, T cell-targeted vaccines or TCR-grafted effector cells. All these approaches depend on recognition of HLA class I-presented viral peptides. The HBV core region 18-27 is an immunodominant target of CD8+ T cells and represents the prime target for T cell-based therapies. Here, a high-resolution analysis of the core18-27 specific CD8+ T cell and the selected escape pathways was performed.

Methods

HLA class I typing and viral sequence analyses were performed for 464 patients with chronic HBV infection. HBV-specific CD8+ T-cell responses against the prototype and epitope variants were characterized by flow cytometry.

Results

Consistent with promiscuous presentation of the core18-27 epitope, antigen-specific T cells were detected in patients carrying HLA-A*02:01, HLA-B*35:01, HLA-B*35:03 or HLA-B*51:01. Sequence analysis confirmed reproducible selection pressure on the core18-27 epitope in the context of these alleles. Interestingly, the selected immune escape pathways depend on the presenting HLA-class I-molecule. Although cross-reactive T cells were observed, some epitope variants achieved functional escape by impaired TCR-interaction or disturbed antigen processing. Of note, selection of epitope variants was exclusively observed in HBeAg negative HBV infection and here, detection of variants associated with significantly greater magnitude of the CD8 T cell response compared to absence of variants.

Conclusion

The core18-27 epitope is highly variable and under heavy selection pressure in the context of different HLA class I-molecules. Some epitope variants showed evidence for impaired antigen processing and reduced presentation. Viruses carrying such escape substitutions will be less susceptible to CD8+ T cell responses and should be considered for T cell-based therapy strategies.

Activation of distinct antiviral T-cell immunity: A comparison of bi- and trispecific T-cell engager antibodies with a chimeric antigen receptor targeting HBV envelope proteins

Despite the availability of an effective prophylactic vaccine, 820,000 people die annually of hepatitis B virus (HBV)-related liver disease according to WHO. Since current antiviral therapies do not provide a curative treatment for the 296 million HBV carriers around the globe, novel strategies to cure HBV are urgently needed. A promising approach is the redirection of T cells towards HBV-infected hepatocytes employing chimeric antigen receptors or T-cell engager antibodies. We recently described the effective redirection of T cells employing a second-generation chimeric antigen receptor directed against the envelope protein of hepatitis B virus on the surface of infected cells (S-CAR) as well as bispecific antibodies that engage CD3 or CD28 on T cells employing the identical HBV envelope protein (HBVenv) binder. In this study, we added a trispecific antibody comprising all three moieties to the tool-box. Cytotoxic and non-cytolytic antiviral activities of these bi- and trispecific T-cell engager antibodies were assessed in co-cultures of human PBMC with HBV-positive hepatoma cells, and compared to that of S-CAR-grafted T cells. Activation of T cells via the S-CAR or by either a combination of the CD3- and CD28-targeting bispecific antibodies or the trispecific antibody allowed for specific elimination of HBV-positive target cells. While S-CAR-grafted effector T cells displayed faster killing kinetics, combinatory treatment with the bispecific antibodies or single treatment with the trispecific antibody was associated with a more pronounced cytokine release. Clearance of viral antigens and elimination of the HBV persistence form, the covalently closed circular (ccc) DNA, through cytolytic as well as cytokine-mediated activity was observed in all three settings with the combination of bispecific antibodies showing the strongest non-cytolytic, cytokine-mediated antiviral effect. Taken together, we demonstrate that bi- and trispecific T-cell engager antibodies can serve as a potent, off-the-shelf alternative to S-CAR-grafted T cells to cure HBV.

HBV-HCC treatment with mRNA electroporated HBV-TCR T cells

Hepatocellular carcinoma is a significant global health challenge with steadily increasing incidence in the East Asia region. While both Hepatitis C and B virus infections account for the majority of HCC cases, the advent of potent antivirals against HCV infection has biased the aetiology towards chronic HBV infection that at the moment remains without an effective cure. For this reason, HBV-HCC remains a persistent global problem. Treatment options for intermediate to advanced stages of HBV-HCC remain limited, hence novel therapeutic strategies are required to fulfil this medical need. Following the considerable success of adoptive T-cell immunotherapy against B-cell malignancies, it is conceivable to envision whether the same could be achieved against HBV-HCC. In this review, we describe the development of T-cell therapy strategies for HBV-HCC and discuss the safety and the efficacy of the strategies in terms of the direct killing of tumour cells and the other alterations possibly induced by the action of the T cells.

Identification and Characterization of Antigen-Specific CD8+ T Cells Using Surface-Trapped TNF-α and Single-Cell Sequencing

CD8+ T cells are key mediators of antiviral and antitumor immunity. The isolation and study of Ag-specific CD8+ T cells, as well as mapping of their MHC restriction, has practical importance to the study of disease and the development of therapeutics. Unfortunately, most experimental approaches are cumbersome, owing to the highly variable and donor-specific nature of MHC-bound peptide/TCR interactions. Here we present a novel system for rapid identification and characterization of Ag-specific CD8+ T cells, particularly well suited for samples with limited primary cells. Cells are stimulated ex vivo with Ag of interest, followed by live cell sorting based on surface-trapped TNF-α. We take advantage of major advances in single-cell sequencing to generate full-length sequence data from the paired TCR α- and β-chains from these Ag-specific cells. The paired TCR chains are cloned into retroviral vectors and used to transduce donor CD8+ T cells. These TCR transductants provide a virtually unlimited experimental reagent, which can be used for further characterization, such as minimal epitope mapping or identification of MHC restriction, without depleting primary cells. We validated this system using CMV-specific CD8+ T cells from rhesus macaques, characterizing an immunodominant Mamu-A1*002:01-restricted epitope. We further demonstrated the utility of this system by mapping a novel HLA-A*68:02-restricted HIV Gag epitope from an HIV-infected donor. Collectively, these data validate a new strategy to rapidly identify novel Ags and characterize Ag-specific CD8+ T cells, with applications ranging from the study of infectious disease to immunotherapeutics and precision medicine.

Characterization of a library of 20 HBV-specific MHC class II-restricted T cell receptors

CD4⁺ T cells play an important role in the immune response against cancer and infectious diseases. However, mechanistic details of their helper function in hepatitis B virus (HBV) infection in particular, or their advantage for adoptive T cell therapy remain poorly understood as experimental and therapeutic tools are missing. Therefore, we identified, cloned, and characterized a comprehensive library of 20 MHC class II-restricted HBV-specific T cell receptors (TCRs) from donors with acute or resolved HBV infection. The TCRs were restricted by nine different MHC II molecules and specific for eight different epitopes derived from intracellularly processed HBV envelope, core, and polymerase proteins. Retroviral transduction resulted in a robust expression of all TCRs on primary T cells. A high functional avidity was measured for all TCRs specific for epitopes S17, S21, S36, and P774 (half-maximal effective concentration [EC₅₀] <10 nM), or C61 and preS9 (EC₅₀ <100 nM). Eight TCRs recognized peptide variants of HBV genotypes A to D. Both CD4⁺ and CD8⁺ T cells transduced with the MHC II-restricted TCRs were polyfunctional, producing interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-2, and granzyme B (GrzB), and killed peptide-loaded target cells. Our set of MHC class II-restricted TCRs represents an important tool for elucidating CD4⁺ T cell help in viral infection with potential benefit for T cell therapy.

Hepatitis-D Virus Infection Is Not Impaired by Innate Immunity but Increases Cytotoxic T-Cell Activity

Approximately 70 million humans worldwide are affected by chronic hepatitis D, which rapidly leads to liver cirrhosis and hepatocellular carcinoma due to chronic inflammation. The triggers and consequences of this chronic inflammation, induced by co-infection with the hepatitis D virus (HDV) and the hepatitis B virus (HBV), are poorly understood. Using CRISPR technology, we characterized the recognition of HDV mono- and co-infection by intracellular innate immunity and determined its influence on the viral life cycle and effector T-cell responses using different HBV and HDV permissive hepatoma cell lines. We showed that HDV infection is detected by MDA5 and -after a lag phase -induces a profound type I interferon response in the infected cells. The type I interferon response, however, was not able to suppress HDV replication or spread, thus providing a persistent trigger. Using engineered T-cells directed against the envelope proteins commonly used by HBV and HDV, we found that HDV immune recognition enhanced T-cell cytotoxicity. Interestingly, the T-cell effector function was enhanced independently of antigen presentation. These findings help to explain immune mediated tissue damage in chronic hepatitis D patients and indicate that combining innate triggers with T-cell activating therapies might allow for a curative approach.

Depletion of T cells via Inducible Caspase 9 Increases Safety of Adoptive T-Cell Therapy Against Chronic Hepatitis B

T-cell therapy with T cells that are re-directed to hepatitis B virus (HBV)-infected cells by virus-specific receptors is a promising therapeutic approach for treatment of chronic hepatitis B and HBV-associated cancer. Due to the high number of target cells, however, side effects such as cytokine release syndrome or hepatotoxicity may limit safety. A safeguard mechanism, which allows depletion of transferred T cells on demand, would thus be an interesting means to increase confidence in this approach. In this study, T cells were generated by retroviral transduction to express either an HBV-specific chimeric antigen receptor (S-CAR) or T-cell receptor (TCR), and in addition either inducible caspase 9 (iC9) or herpes simplex virus thymidine kinase (HSV-TK) as a safety switch. Real-time cytotoxicity assays using HBV-replicating hepatoma cells as targets revealed that activation of both safety switches stopped cytotoxicity of S-CAR- or TCR-transduced T cells within less than one hour. In vivo, induction of iC9 led to a strong and rapid reduction of transferred S-CAR T cells adoptively transferred into AAV-HBV-infected immune incompetent mice. One to six hours after injection of the iC9 dimerizer, over 90% reduction of S-CAR T cells in the blood and the spleen and of over 99% in the liver was observed, thereby limiting hepatotoxicity and stopping cytokine secretion. Simultaneously, however, the antiviral effect of S-CAR T cells was diminished because remaining S-CAR T cells were mostly non-functional and could not be restimulated with HBsAg. A second induction of iC9 was only able to deplete T cells in the liver. In conclusion, T cells co-expressing iC9 and HBV-specific receptors efficiently recognize and kill HBV-replicating cells. Induction of T-cell death via iC9 proved to be an efficient means to deplete transferred T cells in vitro and in vivo containing unwanted hepatotoxicity.

Next Generation Sequencing-Based Identification of T-Cell Receptors for Immunotherapy Against Hepatocellular Carcinoma

Hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) remains a global health concern, and HBV proteins may be ideal targets for T cell-based immunotherapy for HCC. There is a need for fast and efficient identification of HBV-specific T cell receptors (TCRs) for the development of TCR-transduced T (TCR-T) cell-based immunotherapy. Two widely employed TCR identification approaches, T cell clonal expansion and single-cell sequencing, involve a TCR singularization process for the direct identification of Vα and Vβ pairs of TCR chains. Clonal expansion of T cells is well known to have tedious time and effort requirements due to the use of T cell cultures, whereas single-cell sequencing is limited by the requirements of cell sorting and the preparation of a single-cell immune-transcriptome library as well as the massive cost of the whole procedure. Here, we present a next-generation sequencing (NGS)-based HBV-specific TCR identification that does not require the TCR singularization process. Conclusion: Two pairing strategies, ranking-based strategy and α-β chain mixture-based strategy, have proved to be useful for NGS-based TCR identification, particularly for polyclonal T cells purified by a peptide-major histocompatibility complex (pMHC) multimer-based approach. Functional evaluation confirmed the specificity and avidity of two identified HBV-specific TCRs, which may potentially be used to produce TCR-T cells to treat patients with HBV-related HCC.

Distinct T-cell receptor profiles associated with hepatitis B e antigen seroconversion during entecavir treatment

BACKGROUND & AIMS

T-cell receptor (TCR) repertoire is ambiguously changed in chronic hepatitis B (CHB) patients during antivirus therapy. We tried to assess TCR repertoire dynamics and its clinical significance upon HBeAg seroconversion in CHB patients.

METHODS

Twenty CHB patients undergoing 1-year entecavir (ETV) treatment were enrolled, including 10 complete response (CR) vs 10 non-complete response (NCR) patients based on HBeAg seroconversion at week 48. The TCRβ complementarity-determining region 3 (CDR3) of peripheral CD4⁺ and CD8⁺ T cells at weeks 0, 12 and 48 was analyzed by unbiased high-throughput sequencing. The TCR repertoire profiles and their correlations with serological parameters were analyzed.

RESULTS

The diversity of TCRβ repertoires was decreasing in CR patients but increasing in NCR patients. The distribution pattern of TCR repertoires stratified according to clonotype frequencies changed in the opposite direction between CR and NCR patients. Narrow amounts of newly appearing clonotypes in CR patients experienced a more intensive and robust expansion and this phenomenon could occur as early as week 12 for the CD4⁺ subset but later at week 48 for the CD8⁺ subset. There existed some CR-exclusive clonotypes with a relatively low but increasing frequency at week 48. The number of unique TCRβ clonotypes was positively correlated with the ALT or HBV DNA level in CR patients but showed no or negative correlation in NCR patients.

CONCLUSION

Distinct TCR profiles contribute to predicting HBeAg seroconversion in CHB patients during ETV treatment and certain TCRβ CDR3 motif may be utilized for CHB immunotherapy in the future.

Immunotherapy of hepatocellular carcinoma with infection of hepatitis B or C virus

Hepatocellular carcinoma (HCC) has one of highest mortalities globally amongst cancers, but has limited therapeutic options once in the advanced stage. Hepatitis B or C virus infection are the most common drivers for HCC carcinogenesis, triggering chronic liver inflammation and adding to the complexity of the immune microecosystem of HCC. The emergence of immunotherapy has afforded a new avenue of therapeutic options for patients with advanced HCC with a history of hepatitis B or C virus infection. This article reviews the change of immunity elicited by hepatitis B or C virus infection, the immune feature of HCC, and the clinical evidence for immunotherapy in advanced HCC and discusses future directions in this field.

Chronic Viral Liver Diseases: Approaching the Liver Using T Cell Receptor-Mediated Gene Technologies

Chronic infection with viral hepatitis is a major risk factor for liver injury and hepatocellular carcinoma (HCC). One major contributing factor to the chronicity is the dysfunction of virus-specific T cell immunity. T cells engineered to express virus-specific T cell receptors (TCRs) may be a therapeutic option to improve host antiviral responses and have demonstrated clinical success against virus-associated tumours. This review aims to give an overview of TCRs identified from viral hepatitis research and discuss how translational lessons learned from cancer immunotherapy can be applied to the field. TCR isolation pipelines, liver homing signals, cell type options, as well as safety considerations will be discussed herein.

HBV-Induced Immune Imbalance in the Development of HCC

Chronic hepatitis B virus (HBV) infection is one of the high-risk factors for human HCC. Despite the integration of virus DNA and the oncoprotein HBx, chronic necroinflammation and hepatocellular regeneration account for hepatocarcinogenesis. As a non-cytopathic virus, HBV is extensively recognized to mediate chronic liver damage through abnormal immune attack. However, the mechanisms driving HBV infection to HCC are poorly understood. During chronic HBV infection in humans, the adaptive immunity changes from immune tolerance to progressive immune activation, inactivation, reactivation and exhaustion, all of which may be the immune pathogenic factors for the development of HCC. Recently, the immunopathogenic mechanisms were described in mouse HBV-induced HCC models, which is absolutely dependent on the presence of HBV-specific T cell response and NK cell-derived IFN-γ, findings which are consistent with the observations from CHB and HCC patients. In this review, we summarize recent research progression on the HBV-specific CD8⁺ T cells, and also CD4⁺ T cells, B cells and non-specific immune cells and molecules underlying chronic HBV infection and eventual HCC development to demonstrate the pathogenesis of HBV-induced immune imbalance. Based on the progression, we discussed the potential of immune-based therapies and their challenges in the treatment of HBV-related HCC, including the checkpoint inhibition, genetically modified T cell transfer, therapeutic vaccines and metabolic modulation.

T cell receptor grafting allows virological control of Hepatitis B virus infection

T cell therapy is a promising means to treat chronic HBV infection and HBV-associated hepatocellular carcinoma. T cells engineered to express an HBV-specific T cell receptor (TCR) may achieve cure of HBV infection upon adoptive transfer. We investigated the therapeutic potential and safety of T cells stably expressing high affinity HBV envelope- or core-specific TCRs recognizing European and Asian HLA-A2 subtypes. Both CD8+ and CD4+ T cells from healthy donors and from chronic hepatitis B patients became polyfunctional effector cells when grafted with HBV-specific TCRs and eliminated HBV from infected HepG2-NTCP cell cultures. A single transfer of TCR-grafted T cells into HBV-infected, humanized mice controlled HBV infection and virological markers declined 4-5 log or below detection limit. When - as in a typical clinical setting - only a minority of hepatocytes were infected, engineered T cells specifically cleared infected hepatocytes without damaging non-infected cells. Cell death was compensated by hepatocyte proliferation and alanine amino transferase levels peaking at day 5 to 7 normalized again thereafter. Co-treatment with the entry inhibitor Myrcludex B ensured long-term control of HBV infection. Thus, T cells stably transduced with highly functional TCRs have the potential to mediate clearance of HBV-infected cells causing limited liver injury.

Hepatitis B virus-specific effector CD8+ T cells are an important determinant of disease prognosis: A meta-analysis

BACKGROUND

Hepatitis B virus (HBV)-specific effector CD8⁺ T cells are critical for viral clearance. To determine the effects of HBV-specific effector CD8⁺ T cells on HBV infection, we performed a meta-analysis of the available literature.

METHODS

Electronic database searches identified appropriately designed studies that detected specific CD8⁺ T cells in HBV-infected patients. Our main endpoints were the course of infection, seroconversion of HBV "e" antigen (HBeAg), the level of HBVDNA, and alanine aminotransferase (ALT) activity. We used a fixed/random model for analysis, according to the results of a heterogeneity test (P value of Q-squared, I²).

RESULTS

Our searches found five eligible articles. Pooled estimation of the reported results showed that levels of specific CD8⁺ T cells were significantly higher in patients with acute hepatitis B than in patients with chronic hepatitis B (odds ratio [OR] = 76.30, 95% confidence interval [CI]: 15.37-378.70). With respect to chronic hepatitis B, patients with <10⁷ copies/ml HBVDNA had higher levels of specific CD8⁺ T cells relative to patients with >10⁷ copies/ml HBVDNA, but the difference had no statistics significance (OR: 3.89, 95% CI: 0.71-21.33). Patients with negative HBeAg or positive anti-HBeAg antibody (anti-HBe) results had significantly higher levels of specific CD8⁺ T cells versus patients with positive HBeAg results (OR: 5.82, 95% CI: 1.41-24.13). There were no significant associations between the levels of specific CD8⁺ T cells and serum ALT activity (OR = 0.86, 95% CI: 0.01-74.15).

CONCLUSION

HBV-specific effector CD8⁺ T cells influence the disease activity in HBV-infected patients in various ways and determine prognosis by eliminating the virus. Therefore, efforts of studying HBV-specific effector CD8⁺ T cells focused vaccine are potentially needed.

Targeting Innate and Adaptive Immune Responses to Cure Chronic HBV Infection

Fewer than 1% of chronic hepatitis B virus infections per year are cured with antiviral treatment. This creates a need for long-term treatment, which poses challenges for patients and health systems. Because cure is accompanied by recovery of antiviral immunity, a combination of direct-acting antiviral agents and immunotherapy are likely to be required. Extensive efforts have been made to identify determinants of the failed immune response to hepatitis B virus in patients with chronic infection. We review mechanisms of immune dysfunction in patients with chronic hepatitis B virus infection, immunotherapy strategies in development, and the challenges associated with successful implementation of immunotherapy.

Hepatitis B Virus Adaptation to the CD8+ T Cell Response: Consequences for Host and Pathogen

Chronic viral hepatitis infections are a major public health concern, with an estimated 290 million individuals infected with hepatitis B virus (HBV) globally. This virus has been a passenger in human populations for >30,000 years, and remains highly prevalent in some settings. In order for this endemic pathogen to persist, viral adaptation to host immune responses is pre-requisite. Here, we focus on the interplay between HBV infection and the CD8+ T cell response. We present the evidence that CD8+ T cells play an important role in control of chronic HBV infection and that the selective pressure imposed on HBV through evasion of these immune responses can potentially influence viral diversity, chronicity, and the outcome of infection, and highlight where there are gaps in current knowledge. Understanding the nature and mechanisms of HBV evolution and persistence could shed light on differential disease outcomes, including cirrhosis and hepatocellular carcinoma, and help reach the goal of global HBV elimination by guiding the design of new strategies, including vaccines and therapeutics.

Gene Therapy for Chronic HBV-Can We Eliminate cccDNA?

Chronic infection with the hepatitis B virus (HBV) is a global health concern and accounts for approximately 1 million deaths annually. Amongst other limitations of current anti-HBV treatment, failure to eliminate the viral covalently closed circular DNA (cccDNA) and emergence of resistance remain the most worrisome. Viral rebound from latent episomal cccDNA reservoirs occurs following cessation of therapy, patient non-compliance, or the development of escape mutants. Simultaneous viral co-infections, such as by HIV-1, further complicate therapeutic interventions. These challenges have prompted development of novel targeted hepatitis B therapies. Given the ease with which highly specific and potent nucleic acid therapeutics can be rationally designed, gene therapy has generated interest for antiviral application. Gene therapy strategies developed for HBV include gene silencing by harnessing RNA interference, transcriptional inhibition through epigenetic modification of target DNA, genome editing by designer nucleases, and immune modulation with cytokines. DNA-binding domains and effectors based on the zinc finger (ZF), transcription activator-like effector (TALE), and clustered regularly interspaced short palindromic repeat (CRISPR) systems are remarkably well suited to targeting episomal cccDNA. This review discusses recent developments and challenges facing the field of anti-HBV gene therapy, its potential curative significance and the progress towards clinical application.