Clinical evaluation (phase I) of a combination of two human monoclonal antibodies to HBV: safety and antiviral properties

Current and future use of antibody-based passive immunity to prevent or control HBV/HDV infections

With the increasing momentum and success of monoclonal antibody therapy in conventional medical practices, there is a revived emphasis on the development of monoclonal antibodies targeting the hepatitis B surface antigen (anti-HBs) for the treatment of chronic hepatitis B (HBV) and hepatitis D (HDV). Combination therapies of anti-HBs monoclonal antibodies, and novel anti-HBV compounds and immunomodulatory drugs presenting a promising avenue to enhanced therapeutic outcomes in HBV/HDV cure regimens. In this review, we will cover the role of antibodies in the protection and clearance of HBV infection, the association of anti-HBV surface antigen antibodies (anti-HBs) in protection against HBV and how antibody effector functions, beyond neutralization, are likely necessary. Lastly, we will review clinical data from previous and ongoing clinical trials of passive antibody therapy to provide a state-of-the-are perspective on passive antibody therapies in combinations with additional novel agents.

Classifying hepatitis B therapies with insights from covalently closed circular DNA dynamics

The achievement of a functional cure for chronic hepatitis B (CHB) remains limited to a minority of patients treated with currently approved drugs. The primary objective in developing new anti-HBV drugs is to enhance the functional cure rates for CHB. A critical prerequisite for the functional cure of CHB is a substantial reduction, or even eradication of covalently closed circular DNA (cccDNA). Within this context, the changes in cccDNA levels during treatment become as a pivotal concern. We have previously analyzed the factors influencing cccDNA dynamics and introduced a preliminary classification of hepatitis B treatment strategies based on these dynamics. In this review, we employ a systems thinking perspective to elucidate the fundamental aspects of the HBV replication cycle and to rationalize the classification of treatment strategies according to their impact on the dynamic equilibrium of cccDNA. Building upon this foundation, we categorize current anti-HBV strategies into two distinct groups and advocate for their combined use to significantly reduce cccDNA levels within a well-defined timeframe.

Potent broadly neutralizing antibody VIR-3434 controls hepatitis B and D virus infection and reduces HBsAg in humanized mice

BACKGROUND & AIMS

Chronic hepatitis B is a global public health problem, and coinfection with hepatitis delta virus (HDV) worsens disease outcome. Here, we describe a hepatitis B virus (HBV) surface antigen (HBsAg)-targeting monoclonal antibody (mAb) with the potential to treat chronic hepatitis B and chronic hepatitis D.

METHODS

HBsAg-specific mAbs were isolated from memory B cells of HBV vaccinated individuals. In vitro neutralization was determined against HBV and HDV enveloped with HBsAg representing eight HBV genotypes. Human liver-chimeric mice were treated twice weekly with a candidate mAb starting 3 weeks post HBV inoculation (spreading phase) or during stable HBV or HBV/HDV coinfection (chronic phase).

RESULTS

From a panel of human anti-HBs mAbs, VIR-3434 was selected and engineered for pre-clinical development. VIR-3434 targets a conserved, conformational epitope within the antigenic loop of HBsAg and neutralized HBV and HDV infection with higher potency than hepatitis B immunoglobulins in vitro. Neutralization was pan-genotypic against strains representative of HBV genotypes A-H. In the spreading phase of HBV infection in human liver-chimeric mice, a parental mAb of VIR-3434 (HBC34) prevented HBV dissemination and the increase in intrahepatic HBV RNA and covalently closed circular DNA. In the chronic phase of HBV infection or co-infection with HDV, HBC34 treatment decreased circulating HBsAg by >1 log and HDV RNA by >2 logs.

CONCLUSIONS

The potently neutralizing anti-HBs mAb VIR-3434 reduces circulating HBsAg and HBV/HDV viremia in human liver-chimeric mice. VIR-3434 is currently in clinical development for treatment of patients with chronic hepatitis B or D.

IMPACT AND IMPLICATIONS

Chronic infection with hepatitis B virus and co-infection with hepatitis D virus place approximately 290 million individuals worldwide at risk of severe liver disease and cancer. Available treatments result in low rates of functional cure or require lifelong therapy that does not eliminate the risk of liver disease. We isolated and characterized a potent human antibody that neutralizes hepatitis B and D viruses and reduces infection in a mouse model. This antibody could provide a new treatment for patients with chronic hepatitis B and D.

A human monoclonal antibody against HBsAg for the prevention and treatment of chronic HBV and HDV infection

Background & Aims

Elimination of chronic HBV/HDV infection remains a major global health challenge. Targeting excessive hepatitis B surface antigen (HBsAg) release may provide an interesting window of opportunity to break immune tolerance and to achieve a functional cure using additional antivirals.

Methods

We evaluated a HBsAg-specific human monoclonal antibody, as part of either a prophylactic or therapeutic strategy, against HBV/HDV infection in cell culture models and in human-liver chimeric mice. To assess prophylactic efficacy, mice were passively immunized prior to infection with HBV or HBV/HDV (coinfection and superinfection setting). Therapeutic efficacy was assessed in HBV and HBV/HDV-coinfected mice receiving 4 weeks of treatment. Viral parameters (HBV DNA, HDV RNA and HBsAg) were assessed in mouse plasma.

Results

The antibody could effectively prevent HBV/HDV infection in a dose-dependent manner with IC50 values of ∼3.5 ng/ml. Passive immunization showed complete protection of mice from both HBV and HBV/HDV coinfection. Moreover, HDV superinfection was either completely prevented or at least attenuated in HBV-infected mice. Finally, antibody treatment in mice with established HBV/HDV infection resulted in a significant decline in viremia and a concomitant drop in on-treatment HBsAg, with a moderate viral rebound following treatment cessation.

Conclusion

We present data on a valuable antibody candidate that could complement other antivirals in strategies aimed at achieving functional cure of chronic HBV and HDV infection.

Impact and implications

Patients chronically infected with HBV may eventually develop liver cancer and are at great risk of being superinfected with HDV, which worsens and accelerates disease progression. Unfortunately, current treatments can rarely eliminate both viruses from chronically infected patients. In this study, we present data on a novel antibody that is able to prevent chronic HBV/HDV infection in a mouse model with a humanized liver. Moreover, antibody treatment of HBV/HDV-infected mice strongly diminishes viral loads during therapy. This antibody is a valuable candidate for further clinical development.

A Single Dose of Anti-HBsAg Antibody-Encoding mRNA-LNPs Suppressed HBsAg Expression: a Potential Cure of Chronic Hepatitis B Virus Infection

It is the first time that mRNA-LNPs have been used to express anti-HBsAg antibodies (G12-scFv, G12-scFv-Fc, and G12-IgG). G12-scFv-Fc- and G12-IgG-encoding mRNA-LNPs exerted a sustained effect on HBsAg serum clearance in the adeno-associated virus (AAV)/HBV mouse model with persistent HBsAg expression.

Advances in human monoclonal antibody therapy for HBV infection

HBV neutralizing antibodies target the viral envelope antigens (HBsAg) and confer long-term immune protection in vaccinees and infected humans who seroconvert. They recognize various HBsAg epitopes, and can be armed with Fc-dependent effector functions essential for eliminating infected cells and stimulating adaptive immunity. Hundreds of HBsAg-specific monoclonal antibodies (mAbs) were produced from the early 80's, but it is only recently that bona fide human anti-HBV mAbs were generated from vaccinees and seroconverters. Neutralizing HBV mAbs have in vivo prophylactic and therapeutic efficacy in animal models, and the capacity to decrease antigenemia and viremia in infected humans. Thus, polyfunctional, potent and broad human HBV neutralizing mAbs offer novel opportunities to develop effective interventions to prevent and treat HBV infection. Here, we summarize recent findings on the humoral immune response to HBV, and explore the potential of human HBV neutralizing mAbs as immunotherapeutics to help achieving a functional cure for HBV.

Establishment of monoclonal antibodies broadly neutralize infection of hepatitis B virus

Antibodies against hepatitis B virus S protein can protect against hepatitis B virus (HBV) infection. Therefore, hepatitis B immunoglobulin (HBIG), which contains HBsAb, is used clinically as a therapy for HBV infection. In this study, we obtained a series of monoclonal antibodies that recognize multiple HBV genotypes. All the antibodies recognized conformational epitopes of S protein, but not linear epitopes. Several antibodies neutralized HBV infection and exhibited strong affinities and neutralizing activities. Antigenic epitope analysis demonstrated that they recognized residue Ile152 of S protein_, which is localized outside the "a" determinant. Ile152 is highly conserved, and a mutation in this residue resulted in reduced expression of large hepatitis B surface proteins (L protein), suggesting that the amino acid at this position is involved in the expression of L protein. In addition, the antibodies neutralized the infection of hepatitis D virus possessing a Gly145 mutation to Arg in S protein, which is a well-known escape mutation against HBIG treatment. Using mouse monoclonal antibodies, we successfully established a humanized antibody possessing affinities and neutralizing activities similar to those of the original mouse antibody. The antibodies generated in this study may have potential for use in alternative antibody therapies for HBV infection. This article is protected by copyright. All rights reserved.

Toward a complete cure for chronic hepatitis B: Novel therapeutic targets for hepatitis B virus

Hepatitis B virus (HBV) affects approximately 250 million patients worldwide, resulting in the progression to cirrhosis and hepatocellular carcinoma, which are serious public health problems. Although universal vaccination programs exist, they are only prophylactic and not curative. In the HBV life cycle, HBV forms covalently closed circular DNA (cccDNA), which is the viral minichromosome, in the nuclei of human hepatocytes and makes it difficult to achieve a complete cure with the current nucleos(t)ide analogs and interferon therapies. Current antiviral therapies rarely eliminate cccDNA; therefore, lifelong antiviral treatment is necessary. Recent trials for antiviral treatment of chronic hepatitis B have been focused on establishing a functional cure, defined by either the loss of hepatitis B surface antigen, undetectable serum HBV DNA levels, and/or seroconversion to hepatitis B surface antibody. Novel therapeutic targets and molecules are in the pipeline for early clinical trials aiming to cure HBV infection. The ideal strategy for achieving a long-lasting functional or complete cure might be using combination therapies targeting different steps of the HBV life cycle and immunomodulators. This review summarizes the current knowledge about novel treatments and combination treatments for a complete HBV cure.

Immunobiology and pathogenesis of hepatitis B virus infection

Hepatitis B virus (HBV) is a non-cytopathic, hepatotropic virus with the potential to cause a persistent infection, ultimately leading to cirrhosis and hepatocellular carcinoma. Over the past four decades, the basic principles of HBV gene expression and replication as well as the viral and host determinants governing infection outcome have been largely uncovered. Whereas HBV appears to induce little or no innate immune activation, the adaptive immune response mediates both viral clearance as well as liver disease. Here, we review our current knowledge on the immunobiology and pathogenesis of HBV infection, focusing in particular on the role of CD8⁺ T cells and on several recent breakthroughs that challenge current dogmas. For example, we now trust that HBV integration into the host genome often serves as a relevant source of hepatitis B surface antigen (HBsAg) expression during chronic infection, possibly triggering dysfunctional T cell responses and favouring detrimental immunopathology. Further, the unique haemodynamics and anatomy of the liver - and the changes they frequently endure during disease progression to liver fibrosis and cirrhosis - profoundly influence T cell priming, differentiation and function. We also discuss why therapeutic approaches that limit the intrahepatic inflammatory processes triggered by HBV-specific T cells might be surprisingly beneficial for patients with chronic infection.

Shared immunotherapeutic approaches in HIV and hepatitis B virus: combine and conquer

PURPOSE OF REVIEW

The aim of this study was to identify similarities, differences and lessons to be shared from recent progress in HIV and hepatitis B virus (HBV) immunotherapeutic approaches.

RECENT FINDINGS

Immune dysregulation is a hallmark of both HIV and HBV infection, which have shared routes of transmission, with approximately 10% of HIV-positive patients worldwide being coinfected with HBV. Immune modulation therapies to orchestrate effective innate and adaptive immune responses are currently being sought as potential strategies towards a functional cure in both HIV and HBV infection. These are based on activating immunological mechanisms that would allow durable control by triggering innate immunity, reviving exhausted endogenous responses and/or generating new immune responses. Recent technological advances and increased appreciation of humoral responses in the control of HIV have generated renewed enthusiasm in the cure field.

SUMMARY

For both HIV and HBV infection, a primary consideration with immunomodulatory therapies continues to be a balance between generating highly effective immune responses and mitigating any significant toxicity. A large arsenal of new approaches and ongoing research offer the opportunity to define the pathways that underpin chronic infection and move closer to a functional cure.

Restoration of a functional antiviral immune response to chronic HBV infection by reducing viral antigen load: if not sufficient, is it necessary?

The prolonged viral antigen stimulation is the driving force for the development of immune tolerance to chronic hepatitis B virus (HBV) infection. The sustained reduction of viral proteins may allow for the recovery and efficient activation of HBV-specific T and B cells by immune-stimulating agents, checkpoint blockades and/or therapeutic vaccinations. Recently, several therapeutic approaches have been shown to significantly reduce intrahepatic viral proteins and/or circulating HBV surface antigen (HBsAg) with variable impacts on the host antiviral immune responses in animal models or human clinical trials. It remains to be further investigated whether reduction of viral protein expression or induction of intrahepatic viral protein degradation is more efficacious to break the immune tolerance to chronic HBV infection. It is also of great interest to know if the accelerated clearance of circulating HBsAg by antibodies has a long-term immunological impact on HBV infection and disease progression. Although it is clear that removal of antigen stimulation alone is not sufficient to induce the functional recovery of exhausted T and B cells, accumulating evidence suggests that the reduction of viral antigen load appears to facilitate the therapeutic activation of functional antiviral immunity in chronic HBV carriers. Based on a systematic review of the findings in animal models and clinical studies, the research directions toward discovery and development of more efficacious therapeutic approaches to reinvigorate HBV-specific adaptive immune function and achieve the durable control of chronic HBV infection, i.e. a functional cure, in the vast majority of treated patients are discussed.

Recent Advances in Hepatitis B Treatment

Hepatitis B virus infection affects over 250 million chronic carriers, causing more than 800,000 deaths annually, although a safe and effective vaccine is available. Currently used antiviral agents, pegylated interferon and nucleos(t)ide analogues, have major drawbacks and fail to completely eradicate the virus from infected cells. Thus, achieving a "functional cure" of the infection remains a real challenge. Recent findings concerning the viral replication cycle have led to development of novel therapeutic approaches including viral entry inhibitors, epigenetic control of cccDNA, immune modulators, RNA interference techniques, ribonuclease H inhibitors, and capsid assembly modulators. Promising preclinical results have been obtained, and the leading molecules under development have entered clinical evaluation. This review summarizes the key steps of the HBV life cycle, examines the currently approved anti-HBV drugs, and analyzes novel HBV treatment regimens.

Potent human broadly neutralizing antibodies to hepatitis B virus from natural controllers

Rare individuals can naturally clear chronic hepatitis B virus (HBV) infection and acquire protection from reinfection as conferred by vaccination. To examine the protective humoral response against HBV, we cloned and characterized human antibodies specific to the viral surface glycoproteins (HBsAg) from memory B cells of HBV vaccinees and controllers. We found that human HBV antibodies are encoded by a diverse set of immunoglobulin genes and recognize various conformational HBsAg epitopes. Strikingly, HBsAg-specific memory B cells from natural controllers mainly produced neutralizing antibodies able to cross-react with several viral genotypes. Furthermore, monotherapy with the potent broadly neutralizing antibody Bc1.187 suppressed viremia in vivo in HBV mouse models and led to post-therapy control of the infection in a fraction of animals. Thus, human neutralizing HBsAg antibodies appear to play a key role in the spontaneous control of HBV and represent promising immunotherapeutic tools for achieving HBV functional cure in chronically infected humans.

Serum HBsAg clearance has minimal impact on CD8+ T cell responses in mouse models of HBV infection

Antibody-mediated clearance of hepatitis B surface antigen (HBsAg) from the circulation of chronically infected patients (i.e., seroconversion) is usually associated with increased HBV-specific T cell responsiveness. However, a causative link between serum HBsAg levels and impairment of intrahepatic CD8⁺ T cells has not been established. Here we addressed this issue by using HBV replication-competent transgenic mice that are depleted of circulating HBsAg, via either spontaneous seroconversion or therapeutic monoclonal antibodies, as recipients of HBV-specific CD8⁺ T cells. Surprisingly, we found that serum HBsAg clearance has only a minimal effect on the expansion of HBV-specific naive CD8⁺ T cells undergoing intrahepatic priming. It does not alter their propensity to become dysfunctional, nor does it enhance the capacity of IL-2–based immunotherapeutic strategies to increase their antiviral function. In summary, our results reveal that circulating HBsAg clearance does not improve HBV-specific CD8⁺ T cell responses in vivo and may have important implications for the treatment of chronic HBV infection.

A Combination of Human Broadly Neutralizing Antibodies against Hepatitis B Virus HBsAg with Distinct Epitopes Suppresses Escape Mutations

Although there is no effective cure for chronic hepatitis B virus (HBV) infection, antibodies are protective and correlate with recovery from infection. To examine the human antibody response to HBV, we screened 124 vaccinated and 20 infected, spontaneously recovered individuals. The selected individuals produced shared clones of broadly neutralizing antibodies (bNAbs) that targeted 3 non-overlapping epitopes on the HBV S antigen (HBsAg). Single bNAbs protected humanized mice against infection but selected for resistance mutations in mice with prior established infection. In contrast, infection was controlled by a combination of bNAbs targeting non-overlapping epitopes with complementary sensitivity to mutations that commonly emerge during human infection. The co-crystal structure of one of the bNAbs with an HBsAg peptide epitope revealed a stabilized hairpin loop. This structure, which contains residues frequently mutated in clinical immune escape variants, provides a molecular explanation for why immunotherapy for HBV infection may require combinations of complementary bNAbs.

Hepatitis B: Current Status of Therapy and Future Therapies

Despite the availability of a protective vaccine for over 3 decades, the number of persons with chronic hepatitis B virus (HBV) infection remains high. These persons are at risk for cirrhosis and hepatocellular carcinoma. Current treatment is effective at inhibiting viral replication and reducing complications of chronic HBV infection, but is not curative. There is a need for novel, finite therapy that can cure chronic HBV infection. Several agents are in early-phase development and can be broadly viewed as agents that target the virus directly or indirectly or the host immune response. This article highlights key developments in antiviral/immunomodulatory therapy, the rationale for these approaches, and possible therapeutic regimens.

Recent Progress on Neutralizing Antibodies against Hepatitis B Virus and its Implications

BACKGROUND

Hepatitis B virus (HBV) infection remains a global health problem. As "cure" for chronic hepatitis B is of current priority, hepatitis B immunoglobulin (HBIG) has been utilized for several decades to provide post-exposure prophylaxis. In recent years, a number of monoclonal antibodies (mAbs) targeting HBV have been developed and demonstrated with high affinity, specificity, and neutralizing potency.

OBJECTIVE

HBV neutralizing antibodies may play a potentially significant role in the search for an HBV cure. In this review, we will summarize the recent progress in developing HBV-neutralizing antibodies, describing their characteristics and potential clinical applications.

RESULTS AND CONCLUSION

HBV neutralizing antibodies could be a promising alternative in the prevention and treatment of HBV infection. More importantly, global collaboration and coordinated approaches are thus needed to facilitate the development of novel therapies for HBV infection.

[Mimicking polyclonal immune response in therapy: from combination of two monoclonal antibodies to oligoclonal antibody-based mixtures]

Monoclonal antibodies have revolutionized the treatment of many diseases, but their clinical effectiveness remains limited in some cases. Associations of antibodies binding to the same target (homo-combination) or to several different targets (hetero-combination), thereby mimicking a polyclonal humoral immune response, have demonstrated a therapeutic improvement in pre-clinical and clinical trials, mainly in the field of oncology and infectious diseases. The combinations increase the efficacy of the biological responses and override resistance mechanisms observed with antibody monotherapy. The most common method of formulating and administering antibody combinations is a separate formulation, with sequential injection of each antibody as individual drug substance. Alternatively, combined formulations are developed where the separately-produced antibodies are mixed before administration or produced simultaneously by a single cell line, or a mixture of cell lines as a polyclonal master cell bank. The regulation, the toxicity and the injection sequence of these oligoclonal antibody-based mixtures remain points to be clarified and optimized for a better therapeutic effect.

Restoring, releasing or replacing adaptive immunity in chronic hepatitis B

Multiple new therapeutic approaches are currently being developed to achieve sustained, off-treatment suppression of HBV, a persistent hepatotropic infection that kills ~2,000 people a day. A fundamental therapeutic goal is the restoration of robust HBV-specific adaptive immune responses that are able to maintain prolonged immunosurveillance of residual infection. Here, we provide insight into key components of successful T cell and B cell responses to HBV, discussing the importance of different specificities and effector functions, local intrahepatic immunity and pathogenic potential. We focus on the parallels and interactions between T cell and B cell responses, highlighting emerging areas for future investigation. We review the potential for different immunotherapies in development to restore or release endogenous adaptive immunity by direct or indirect approaches, including limitations and risks. Finally, we consider an alternative HBV treatment strategy of replacing failed endogenous immunity with infusions of highly targeted T cells or antibodies.

Toward a Functional Cure for Hepatitis B: The Rationale and Challenges for Therapeutic Targeting of the B Cell Immune Response

The central role of the cellular immune response in the control and clearance of the hepatitis B virus (HBV) infection has been well-established. The contribution of humoral immunity, including B cell and antibody responses against HBV, has been investigated for a long time but has attracted increasing attention again in recent years. The anti-HBs antibody was first recognized as a marker of protective immunity after the acute resolution of the HBV infection (or vaccination) and is now defined as a biomarker for the functional cure of chronic hepatitis B (CHB). In this way, therapies targeting HBV-specific B cells and the induction of an anti-HBs antibody response are essential elements of a rational strategy to terminate chronic HBV infection. However, a high load of HBsAg in the blood, which has been proposed to induce antigen-specific immune tolerance, represents a major obstacle to curing CHB. Long-term antiviral treatment by nucleoside analogs, by targeting viral translation by siRNA, by inhibiting HBsAg release via nucleic acid polymers, or by neutralizing HBsAg via specific antibodies could potentially reduce the HBsAg load in CHB patients. A combined strategy including a reduction of the HBsAg load via the above treatments and the therapeutic targeting of B cells by vaccination may induce the appearance of anti-HBs antibodies and lead to a functional cure of CHB.

Therapeutic strategies for hepatitis B virus infection: towards a cure

Chronic hepatitis B virus (HBV) infection is a common cause of liver disease globally, with a disproportionately high burden in South-East Asia. Vaccines and nucleoside or nucleotide drugs are available and reduce both new infection rates and the development of liver disease in HBV-positive persons who adhere to long-term suppressive treatment. Although there is still considerable value in optimizing access to virus-suppressing regimens, the scientific and medical communities have embarked on a concerted journey to identify new antiviral drugs and immune interventions aimed at curing infection. The mechanisms and drug targets being explored are diverse; however, the field universally recognizes the importance of addressing the persistence of episomal covalently closed circular DNA, the existence of integrated HBV DNA in the host genome and the large antigen load, particularly of hepatitis B surface antigen. Another major challenge is to reinvigorate the exhausted immune response within the liver microenvironment. Ultimately, combinations of new drugs will be required to cure infection. Here we critically review the recent literature that describes the rationale for curative therapies and the resulting compounds that are being tested in clinical trials for hepatitis B.

Viral envelope-specific antibodies in chronic hepatitis B virus infection

While the cellular immune response associated with acute and chronic HBV infection has been thoroughly studied, the B cell response in chronic hepatitis B and the role of antibodies raised against the HBV envelope antigens in controlling and prevention of infection requires further investigation. The detection of anti-HBs antibodies is considered as one of the biomarkers for functional cure of chronic hepatitis B virus infection, as well as for protective immunity. Indeed, vaccine-induced neutralizing anti-HBs antibodies have been shown to protect against HBV challenge. Yet, the therapeutic potential of viral envelope-specific antibodies and the mechanism involved in protection and prevention of cell-to-cell transmission warrants additional investigative efforts. In this review, we will provide a critical overview of the available preclinical and clinical literature supporting the putative role of active and passive vaccination and neutralizing envelope-specific antibodies for therapeutic intervention in combination regimens intended to cure persistent HBV infection.

HBsAg-redirected T cells exhibit antiviral activity in HBV-infected human liver chimeric mice

BACKGROUND

Chronic hepatitis B virus (HBV) infection remains incurable. Although HBsAg-specific chimeric antigen receptor (HBsAg-CAR) T cells have been generated, they have not been tested in animal models with authentic HBV infection.

METHODS

We generated a novel CAR targeting HBsAg and evaluated its ability to recognize HBV+ cell lines and HBsAg particles in vitro. In vivo, we tested whether human HBsAg-CAR T cells would have efficacy against HBV-infected hepatocytes in human liver chimeric mice.

RESULTS

HBsAg-CAR T cells recognized HBV-positive cell lines and HBsAg particles in vitro as judged by cytokine production. However, HBsAg-CAR T cells did not kill HBV-positive cell lines in cytotoxicity assays. Adoptive transfer of HBsAg-CAR T cells into HBV-infected humanized mice resulted in accumulation within the liver and a significant decrease in plasma HBsAg and HBV-DNA levels compared with control mice. Notably, the fraction of HBV core-positive hepatocytes among total human hepatocytes was greatly reduced after HBsAg-CAR T cell treatment, pointing to noncytopathic viral clearance. In agreement, changes in surrogate human plasma albumin levels were not significantly different between treatment and control groups.

CONCLUSIONS

HBsAg-CAR T cells have anti-HBV activity in an authentic preclinical HBV infection model. Our results warrant further preclinical exploration of HBsAg-CAR T cells as immunotherapy for HBV.

In Situ Liver Expression of HBsAg/CD3-Bispecific Antibodies for HBV Immunotherapy

Current therapies against hepatitis B virus (HBV) do not reliably cure chronic infection, necessitating new therapeutic approaches. The T cell response can clear HBV during acute infection, and the adoptive transfer of antiviral T cells during bone marrow transplantation can cure patients of chronic HBV infection. To redirect T cells to HBV-infected hepatocytes, we delivered plasmids encoding bispecific antibodies directed against the viral surface antigen (HBsAg) and CD3, expressed on almost all T cells, directly into the liver using hydrodynamic tail vein injection. We found a significant reduction in HBV-driven reporter gene expression (184-fold) in a mouse model of acute infection, which was 30-fold lower than an antibody only recognizing HBsAg. While bispecific antibodies triggered, in part, antigen-independent T cell activation, antibody production within hepatocytes was non-cytotoxic. We next tested the bispecific antibodies in a different HBV mouse model, which closely mimics the transcriptional template for HBV, covalently closed circular DNA (cccDNA). We found that the antiviral effect was noncytopathic, mediating a 495-fold reduction in HBsAg levels at day 4. At day 33, bispecific antibody-treated mice exhibited 35-fold higher host HBsAg immunoglobulin G (IgG) antibody production versus untreated groups. Thus, gene therapy with HBsAg/CD3-bispecific antibodies represents a promising therapeutic strategy for patients with HBV.

Antibody-dependent and antibody-independent uptake of HBsAg across human leucocyte subsets is similar between individuals with chronic hepatitis B virus infection and healthy donors

Maintaining detectable levels of antibodies to hepatitis B surface antigen (HBsAg) in serum after HBsAg sero-conversion is the key clinical endpoint indicative of recovery from infection with hepatitis B virus (HBV). As HBV-infected hepatocytes secrete HBsAg subviral particles in vast excess over HBV virions, detectable hepatitis B surface antibody (anti-HBs) titres imply complete elimination of HBV virions as well as HBsAg particles. Although intrahepatic phagocytes, for example Kupffer cells, are thought to mediate clearance of HBsAg via antibody (Ab)-dependent and Ab-independent mechanisms, the relative contributions of circulating phagocytic cell types to HBsAg elimination are poorly characterized. Understanding the role of various immune cell subsets in the clearance of HBsAg is important because Ab-dependent or Ab-independent phagocytic HBsAg uptake may modulate presentation of HBsAg-derived epitopes to antigen-specific T cells and hence plays a critical role in adaptive immunity against HBV. This study aims to characterize phagocytic leucocyte subsets capable of internalizing HBsAg immune complexes (HBsAg:IC) or un-complexed HBsAg particles in whole blood directly ex vivo. The data show that uptake of HBsAg:IC occurs most prominently in monocytes, B cells, dendritic cells and in neutrophils. In contrast, B cells, and to a lesser degree also monocytes, seem to be effective phagocytes for un-complexed HBsAg. Importantly, a similar pattern of phagocytic HBsAg uptake was observed in blood from chronic hepatitis B (CHB) patients compared to healthy controls, suggesting that phagocytosis-related cellular functions are not altered in the context of CHB.

Antibody-mediated immunotherapy against chronic hepatitis B virus infection

The currently available drugs to treat hepatitis B virus (HBV) infection include interferons and nucleos(t)ide analogs, which can only induce disease remission and are inefficient for the functional cure of patients with chronic HBV infection (CHB). Since high titers of circulating hepatitis B surface antigen (HBsAg) may be essential to exhaust the host anti-HBV immune response and they cannot be significantly reduced by current drugs, new antiviral strategies aiming to suppress serum hepatitis B surface antigen (HBsAg) could help restore virus-specific immune responses and promote the eradication of the virus. As an alternative strategy, immunotherapy with HBsAg-specific antibodies has shown some direct HBsAg suppression effects in several preclinical and clinical trial studies. However, most described previously HBsAg-specific antibodies only had very short-term HBsAg suppression effects in CHB patients and animal models mimicking persistent HBV infection. More-potent antibodies with long-lasting HBsAg clearance effects are required for the development of the clinical application of antibody-mediated immunotherapy for CHB treatment. Our recent study described a novel mAb E6F6 that targets a unique epitope on HBsAg. It could durably suppress the levels of HBsAg and HBV DNA via Fcγ receptor-dependent phagocytosis in vivo. In this commentary, we summarize the current research progress, including the therapeutic roles and mechanisms of antibody-mediated HBV clearance as well as the epitope-determined therapeutic potency of the antibody. These insights may provide some clues and guidance to facilitate the development of therapeutic antibodies against persistent viral infection.

Challenges for the pharmaceutical technical development of protein coformulations

Objectives

This review discusses challenges to stability, analytics and manufacturing of protein coformulations. Furthermore, general considerations to be taken into account for the pharmaceutical development of coformulated protein drug products are highlighted.

Key findings

Coformulation of two or more active substances in one single dosage form has recently seen increasing use offering several advantages, such as increased efficacy and/or the overall reduction of adverse event incidents in patients. Most marketed coformulated drug products are composed of small molecules. As proteins are not only comparatively large but also complex molecules, the maintenance of their physicochemical integrity within a formulation throughout pharmaceutical processing, storage, transport, handling and patient administration to ensure proper pharmacokinetics and pharmacodynamics in vivo already represents various challenges for single-entity products. Thus, nowadays, only sparse biologics-based coformulations can be found, as additional complexity during development is given for these products.

Summary

The complexity of the dosage form and the protein molecules results into additional challenges to formulation, manufacture, storage, transport, handling and patient administration, stability and analytics during the pharmaceutical development of protein coformulations. Various points have to be considered during different stages of development in order to obtain a safe and efficacious product.

Present and future therapies of hepatitis B: From discovery to cure

Hepatitis B virus (HBV) is a significant global pathogen, infecting more than 240 million people worldwide. While treatment for HBV has improved, HBV patients often require lifelong therapies and cure is still a challenging goal. Recent advances in technologies and pharmaceutical sciences have heralded a new horizon of innovative therapeutic approaches that are bringing us closer to the possibility of a functional cure of chronic HBV infection. In this article, we review the current state of science in HBV therapy and highlight new and exciting therapeutic strategies spurred by recent scientific advances. Some of these therapies have already entered into clinical phase, and we will likely see more of them moving along the development pipeline.

CONCLUSION

With growing interest in developing and efforts to develop more effective therapies for HBV, the challenging goal of a cure may be well within reach in the near future.

A bispecific antibody against two different epitopes on hepatitis B surface antigen has potent hepatitis B virus neutralizing activity

Treatment of chronic hepatitis B virus (HBV) infection with interferon and viral reverse transcriptase inhibitor regimens results in poor viral clearance, loss of response, and emergence of drug-resistant mutant virus strains. These problems continue to drive the development of new therapeutic approaches to combat HBV. Here, we engineered a bispecific antibody using two monoclonal antibodies cloned from hepatitis B surface antigen (HBsAg)-specific memory B cells from recombinant HBsAg-vaccinated healthy volunteers. Next, we evaluated its efficacy in neutralizing HBV in HepaRG cells. This bispecific antibody, denoted as C4D2-BsAb, had superior HBV-neutralizing activity compared with the combination of both parental monoclonal antibodies, possibly through steric hindrance or induction of HBsAg conformational changes. Moreover, C4D2-BsAb has superior endocytotic characteristics into hepatocytes, which inhibits the secretion of HBsAg. These results suggest that the anti-HBsAg bispecific antibody may be an effective treatment method against HBV infection.

Inhibitors of hepatitis B virus attachment and entry

Inhibition of virus entry has become a major concept in the development of new antiviral drugs. Entry inhibitors can either neutralize activities of viral surface proteins or target essential host factors such as (co)receptors. Due to its distinct tissue tropism and the highly specific viral and cellular factors involved in its entry, hepatitis B virus (HBV) is an ideal candidate for entry inhibition. Hepatitis B immunoglobulins neutralize infection by binding to the S-domain of HBV surface proteins and are used to prevent reinfection of the graft after liver transplantation. Novel S or preS-specific monoclonal antibodies are currently in development. The identification of sodium-taurocholate cotransporting polypeptide (NTCP) as a bona fide receptor has revealed a suitable target for HBV entry inhibition. NTCP receptor function is blocked by a variety of different agents including Myrcludex B, a synthetic N-acylated preS1-derived lipopeptide that inhibits HBV entry in vitro and in vivo with high efficacy. Current antiviral treatment for chronic HBV-infected patients focuses on the inhibition of the viral polymerase via nucleos(t)ide analogues (NA). Entry inhibitors in combination with NAs could block reinfection and shield naive hepatocytes that emerge from natural liver turnover, opening up new therapeutic options.

Strategies to inhibit entry of HBV and HDV into hepatocytes

Although there has been much research into the pathogenesis and treatment of hepatitis B virus (HBV) and hepatitis D virus (HDV) infections, we still do not completely understand how these pathogens enter hepatocytes. This is because in vitro infection studies have only been performed in primary human hepatocytes. Development of a polarizable, HBV-susceptible human hepatoma cell line and studies of primary hepatocytes from Tupaia belangeri have provided important insights into the viral and cellular factors involved in virus binding and infection. The large envelope (L) protein on the surface of HBV and HDV particles has many different functions and is required for virus entry. The L protein mediates attachment of virions to heparan sulfate proteoglycans on the surface of hepatocytes. The myristoylated N-terminal preS1 domain of the L protein subsequently binds to the sodium taurocholate cotransporting polypeptide (NTCP, encoded by SLC10A1), the recently identified bona fide receptor for HBV and HDV. The receptor functions of NTCP and virus entry are blocked, in vitro and in vivo, by Myrcludex B, a synthetic N-acylated preS1 lipopeptide. Currently, the only agents available to treat chronic HBV infection target the viral polymerase, and no selective therapies are available for HDV infection. It is therefore important to study the therapeutic potential of virus entry inhibitors, especially when combined with strategies to induce immune-mediated killing of infected hepatocytes.

Back to the future: recombinant polyclonal antibody therapeutics

Antibody therapeutics are one of the fastest growing classes of pharmaceuticals, with an annual US market over $20 billion, developed to treat a variety of diseases including cancer, auto-immune and infectious diseases. Most are currently administered as a single molecule to treat a single disease, however there is mounting evidence that cocktails of multiple antibodies, each with a unique binding specificity and protective mechanism, may improve clinical efficacy. Here, we review progress in the development of oligoclonal combinations of antibodies to treat disease, focusing on identification of synergistic antibodies. We then discuss the application of modern antibody engineering technologies to produce highly potent antibody preparations, including oligoclonal antibody cocktails and truly recombinant polyclonal antibodies. Specific examples illustrating the synergy conferred by multiple antibodies will be provided for diseases caused by botulinum toxin, cancer and immune thrombocytopenia. The bioprocessing and regulatory options for these preparations will be discussed.

Compatibility and stability of pertuzumab and trastuzumab admixtures in i.v. infusion bags for coadministration

The physical/chemical stability and potential interactions after diluting two immunoglobulin G1 monoclonal antibodies (mAb), pertuzumab (Perjeta®) and trastuzumab (Herceptin®), in a single intravenous (i.v.) infusion bag containing 0.9% saline (NaCl) solution was evaluated. As commercial products, pertuzumab and trastuzumab are administered through i.v. infusion to patients sequentially, that is, one drug after the other. To increase convenience and minimize the in-clinic time for patients, the compatibility of coadministering pertuzumab (420 and 840 mg) mixed with either 420 or 720 mg trastuzumab, respectively, in a single 250 mL polyolefin or polyvinyl chloride i.v. bag stored for up to 24 h at 5°C or 30°C was determined. The controls (i.e., pertuzumab alone in an i.v. bag, trastuzumab alone in an i.v. bag) and the mAb mixture were assessed using color, appearance, and clarity, concentration and turbidity by ultraviolet spectroscopy, particulate analysis by light obscuration, size-exclusion chromatography, capillary electrophoresis-sodium dodecyl sulfate, analytical ultracentrifugation, and ion-exchange chromatography. Additionally, capillary zone electrophoresis, imaged capillary isoelectric focusing, and potency were utilized to measure the stability of the admixtures containing 1:1 mixtures of pertuzumab/trastuzumab and their respective controls (420 mg pertuzumab alone and 420 mg trastuzumab alone). No observable differences were detected by the above methods in the pertuzumab/trastuzumab mixtures stored up to 24 h at either 5°C or 30°C. The physicochemical methods as listed above were able to detect both molecules as well as the minor variants in the drug mixture, even though some overlap of mAb species were seen in the chromatograms and electropherograms. Furthermore, biophysical analysis also did not show any interactions between the two mAbs or any physical instability under these conditions. Additionally, the drug mixture tested by the pertuzumab-specific inhibition of cell proliferation bioassay showed comparable potency before and after storage. On the basis of these results, pertuzumab and trastuzumab admixture in a single i.v. bag is physically and chemically stable for up to 24 h at 5°C or 30°C and can be used for clinical administration.

Novel mechanism of antibodies to hepatitis B virus in blocking viral particle release from cells

Antibodies are thought to exert antiviral activities by blocking viral entry into cells and/or accelerating viral clearance from circulation. In particular, antibodies to hepatitis B virus (HBV) surface antigen (HBsAg) confer protection, by binding circulating virus. Here, we used mathematical modeling to gain information about viral dynamics during and after single or multiple infusions of a combination of two human monoclonal anti-HBs (HepeX-B) antibodies in patients with chronic hepatitis B. The antibody HBV-17 recognizes a conformational epitope, whereas antibody HBV-19 recognizes a linear epitope on the HBsAg. The kinetic profiles of the decline of serum HBV DNA and HBsAg revealed partial blocking of virion release from infected cells as a new antiviral mechanism, in addition to acceleration of HBV clearance from the circulation. We then replicated this approach in vitro, using cells secreting HBsAg, and compared the prediction of the mathematical modeling obtained from the in vivo kinetics. In vitro, HepeX-B treatment of HBsAg-producing cells showed cellular uptake of antibodies, resulting in intracellular accumulation of viral particles. Blocking of HBsAg secretion also continued after HepeX-B was removed from the cell culture supernatants.

CONCLUSION

These results identify a novel antiviral mechanism of antibodies to HBsAg (anti-HBs) involving prolonged blocking of the HBV and HBsAg subviral particles release from infected cells. This may have implications in designing new therapies for patients with chronic HBV infection and may also be relevant in other viral infections.

Analysis of the epitope and neutralizing capacity of human monoclonal antibodies induced by hepatitis B vaccine

Hepatitis B virus (HBV) is an infectious agent that is a significant worldwide public health issue. However, the mechanism by which vaccination-induced antibodies prevent HBV infection remains unclear. To investigate the mechanism by which antibodies induced by hepatitis B surface Ag (HBsAg)-vaccination prevent HBV infection in humans, we prepared human monoclonal antibodies (mAbs) against HBsAg using a novel cell-microarray system from peripheral blood B-lymphocytes from vaccinated individuals. We then characterized the IgG subclass, L-chain subtype, and V-gene repertoire of the H/L-chain, as well as affinities of each of these mAbs. We also determined the epitopes of the individual mAbs using synthesized peptides, and the HBV-neutralizing activities of mAbs using the hepatocyte cell line HepaRG. Consequently, IgG1 and kappa chain was mainly used as the mAbs for HBsAg. Seventy percent of the mAbs bound to the loop domain of the small-HBsAg and showed greater neutralizing activities. There were no relationships between their affinities and neutralization activities. A combination of mAbs recognizing the first loop domain showed a synergistic effect on HBV-neutralizing activity that surpassed conventional hepatitis B-Ig (HBIG) in the HepaRG cell line assay. These results may contribute to the development of effective mAb treatment against HBV infection replacing conventional HBIG administration.

Current prophylactic strategies against hepatitis B virus recurrence after liver transplantation

Prophylactic strategies against hepatitis B virus (HBV) recurrence after liver transplantation (LT) are essential for patients with HBV-related disease. Before LT, lamivudine (LAM) was proposed to be down-graded from first- to second-line therapy. In contrast, adefovir dipivoxil (ADV) has been approved not only as first-line therapy but also as rescue therapy for patients with LAM resistance. Furthermore, combination of ADV and LAM may result in lower risk of ADV resistance than ADV monotherapy. Other new drugs such as entecavir, telbivudine and tenofovir, are probably candidates for the treatment of hepatitis-B-surface-antigen-positive patients awaiting LT. After LT, low-dose intramuscular hepatitis B immunoglobulin (HBIG), in combination with LAM, has been regarded as the most cost-effective regimen for the prevention of post-transplant HBV recurrence in recipients without pretransplant LAM resistance and rapidly accepted in many transplant centers. With the introduction of new antiviral drugs, new hepatitis B vaccine and its new adjuvants, post-transplant HBIG-free therapeutic regimens with new oral antiviral drug combinations or active HBV vaccination combined with adjuvants will be promising, particularly in those patients with low risk of HBV recurrence.

Cell therapy for the diseased liver: from stem cell biology to novel models for hepatotropic human pathogens

It has long been known that hepatocytes possess the potential to replicate through many cell generations because regeneration can be achieved in rodents after serial two-thirds hepatectomy. It has taken considerable time and effort to harness this potential, with liver regeneration models involving hepatocyte transplantation developing over the past 15 years. This review will describe the experiments that have established the models and methodology for liver repopulation, and the use of cells other than adult hepatocytes in liver repopulation, including hepatic cell lines and hematopoietic, cord blood, hepatic and embryonic stem cells. Emphasis will be placed on the characteristics of the models and how they can influence the outcome of the experiments. Finally, an account of the development of murine models that are competent to accept human hepatocytes is provided. In these models, liver deficiencies are induced in immunodeficient mice, where healthy human cells have a selective advantage. These mice with humanized livers provide a powerful new experimental tool for the study of human hepatotropic pathogens.

Specific targeting of hepatitis C virus core protein by an intracellular single-chain antibody of human origin

The hepatitis C virus (HCV) core protein is essential for viral genome encapsidation and plays an important role in steatosis, immune evasion, and hepatocellular carcinoma. It may thus represent a promising therapeutic target to interfere with the HCV life-cycle and related pathogenesis. In this study, we used phage display to generate single-chain variable domain antibody fragments (scFv) to the core protein from bone marrow plasma cells of patients with chronic hepatitis C. An antibody with high-affinity binding (scFv42C) was thus identified, and the binding site was mapped to the PLXG motif (residues 84-87) of the core protein conserved among different genotypes. Whereas scFv42C displayed diffuse cytoplasmic fluorescence when expressed alone in the Huh7 human hepatoma cell line, cotransfection with the core gene shifted its subcellular distribution into that of core protein. The intracellular association of scFv42C with its target core protein was independently demonstrated by the fluorescence resonance energy transfer technique. Interestingly, expression of the single-chain antibody reduced core protein levels intracellularly, particularly in the context of full HCV replication. Moreover, cell proliferation as induced by the core protein could be reversed by scFv4C coexpression. Therefore, scFv42C may represent a novel anti-HCV agent, which acts by sequestering core protein and attenuating core protein-mediated pathogenesis.

In vivo hepatitis B virus-neutralizing activity of an anti-HBsAg humanized antibody in chimpanzees

Previously, we constructed a humanized antibody (HuS10) that binds to the common a antigenic determinant on the S protein of HBV. In this study, we evaluated its HBV-neutralizing activity in chimpanzees. A study chimpanzee was intravenously administered with a single dose of HuS10, followed by intravenous challenge with the adr subtype of HBV, while a control chimpanzee was only challenged with the virus. The result showed that the control chimpanzee was infected by the virus, and thus serum HBV surface antigen (HBsAg) became positive from the 14(th) to 20(th) week and actively acquired serum anti-HBc and anti-HBs antibodies appeared from the 19(th) and 23(rd) week, respectively. However, in the case of the study chimpanzee, serum HBsAg became positive from the 34(th) to 37(th) week, while actively acquired serum anti-HBc and anti-HBs antibodies appeared from the 37(th) and 40(th) week, respectively, indicating that HuS10 neutralized the virus in vivo and thus delayed the HBV infection. This novel humanized antibody will be useful in the immunoprophylaxis of HBV infection.

Antiviral therapy with entecavir combined with post-exposure "prime-boost" vaccination eliminates duck hepatitis B virus-infected hepatocytes and prevents the development of persistent infection

Short-term antiviral therapy with the nucleoside analogue entecavir (ETV), given at an early stage of duck hepatitis B virus (DHBV) infection, restricts virus spread and leads to clearance of DHBV-infected hepatocytes in approximately 50% of ETV-treated ducks, whereas widespread and persistent DHBV infection develops in 100% of untreated ducks. To increase the treatment response rate, ETV treatment was combined in the current study with a post-exposure "prime-boost" vaccination protocol. Four groups of 14-day-old ducks were inoculated intravenously with a dose of DHBV previously shown to induce persistent DHBV infection. One hour post-infection (p.i.), ducks were primed with DNA vaccines that expressed DHBV core (DHBc) and surface (pre-S/S and S) antigens (Groups A, B) or the DNA vector alone (Groups C, D). ETV (Groups A, C) or water (Groups B, D) was simultaneously administered by gavage and continued for 14 days. Ducks were boosted 7 days p.i. with recombinant fowlpoxvirus (rFPV) strains also expressing DHBc and pre-S/S antigens (Groups A, B) or the FPV-M3 vector (Groups C, D). DHBV-infected hepatocytes were observed in the liver of all ducks at day 4 p.i. with reduced numbers in the ETV-treated ducks. Ducks treated with ETV plus the control vectors showed restricted spread of DHBV infection during ETV treatment, but in 60% of cases, infection became widespread after ETV was stopped. In contrast, at 14 and 67 days p.i., 100% of ducks treated with ETV and "prime-boost" vaccination had no detectable DHBV-infected hepatocytes and had cleared the DHBV infection. These findings suggest that ETV treatment combined with post-exposure "prime-boost" vaccination induced immune responses that eliminated DHBV-infected hepatocytes and prevented the development of persistent DHBV infection.

Monoclonal antibodies for prophylaxis and therapy of infectious diseases

Monoclonal antibodies (mAb) are attractive biologic drugs due to their exquisite specificity and well understood mechanisms of action, which results in a higher predictability and lower attrition rate compared with other drugs. Therefore, it may seem surprising that only a single mAb is presently marketed for an infectious disease indication. However, the antibiotic resistance crisis, emerging viral diseases and bioterroristic threats have recently spurred the development of anti-infective mAbs, of which more than a dozen are being tested in clinical trials. Conceptually, and validated in many preclinical models, mAbs will be most effective when used prophylactically against acute viral infections and bacterial toxins. The acute bacterial and chronic viral infections, which are medically and economically far more important, are much more difficult to control by antibodies, as the recent clinical failure of some polyclonal antibody products has shown. In these situations, the synergistic action of two or more mAbs together with a small molecule drug will most likely be required for therapeutic efficacy. This review aims to highlight the scientific and economic opportunities and obstacles that are encountered in the quest to add mAbs to the armament of anti-infective drugs.

Endogenous cytotoxic T-cell response contributes to the long-term antiretroviral protection induced by a short period of antibody-based immunotherapy of neonatally infected mice

Neutralizing monoclonal antibodies (MAbs) are increasingly being considered for blunting human viral infections. However, whether they can also exert indirect effects on endogenous antiviral immune responses has been essentially overlooked. We have recently shown that a short (several-day) period of immunotherapy with the neutralizing 667 MAb of mouse neonates shortly after infection with the lethal FrCas(E) retrovirus not only has an immediate effect on the viral load but also permits an endogenous antiviral immunity to emerge. Even though passive immunotherapy was administered during the particular period of immunocompetence acquisition, the endogenous response eventually arising was protective and persisted long (>1 year) after the MAb has disappeared. As very high levels of anti-FrCas(E) antibodies, predominantly of the immunoglobulin G2a (IgG2a) isotype and showing strong neutralization activity, were found in the sera of MAb-treated mice, it was necessary to address whether this humoral immunity was sufficient on its own to confer full protection against FrCas(E) or whether a cytotoxic T-lymphocyte (CTL) response was also necessary. Using a variety of in vivo assays in young and adult animals previously infected by FrCas(E) and treated by 667, we show here that transient 667 immunotherapy is associated with the emergence of a CTL response against virus-infected cells. This cytotoxic activity is indispensable for long-term antiviral protective immunity, as high neutralizing antibody titers, even enhanced in in vivo CD8(+) cell depletion experiments, cannot prevent the FrCas(E)-induced death of infected/treated mice. Our work may have important therapeutic consequences, as it indicates that a short period of MAb-based immunotherapy conducted at a stage where the immune system is still developing can be associated with the mounting of a functional Th1-type immune response characterized by both CTL and IgG2a-type humoral contributions, the cooperation of which is known to be essential for the containment of chronic infections by a variety of viruses.

New animal models for hepatitis C viral infection and pathogenesis studies

Hepatitis C virus (HCV) is a major cause of chronic liver disease, cirrhosis and hepatocellular carcinoma (HCC). In man, the pathobiological changes associated with HCV infection have been attributed to both the immune system and direct viral cytopathic effects. Until now, the lack of simple culture systems to infect and propagate the virus has hampered progress in understanding the viral life cycle and pathogenesis of HCV infection, including the molecular mechanisms implicated in HCV-induced HCC. This clearly demonstrates the need to develop small animal models for the study of HCV-associated pathogenesis. This review describes and discusses the development of new HCV animal models to study viral infection and investigate the direct effects of viral protein expression on liver disease.

Clinical evaluation (Phase I) of a human monoclonal antibody against hepatitis C virus: safety and antiviral activity

BACKGROUND/AIMS

HCV-AB68, a human monoclonal antibody against the envelope protein of hepatitis C virus (HCV), neutralizes HCV in cell-culture and in the HCV-Trimera mouse model. A Phase 1 clinical trial was designed to test safety, tolerability, and antiviral activity of HCV-AB68 in patients with chronic HCV-infection.

METHODS/RESULTS

Single doses of HCV-AB68, 0.25-40 mg, administered to 15 patients were well tolerated with no moderate or serious adverse events (SAEs) reported. In six patients, HCV-RNA levels transiently decreased by 2- to 100-fold immediately following infusion and rebound to baseline in 24-48 h. Multiple doses of HCV-AB68, 10-120 mg, were administered to 25 patients. Doses were given weekly for 3 weeks, then 3x a week during the fourth week, after which patients were followed for 3 months. No drug-related SAEs were reported and no specific pattern of adverse events was evident. Eight out of 25 patients had at least a 1-log reduction and 17 had at least a 0.75-log reduction in HCV-RNA levels from baseline at one or more time points following HCV-AB68 infusion.

CONCLUSIONS

These data support the investigation of HCV-AB68 in the prevention of recurrent HCV-infection in patients who had received hepatic allografts for end-stage liver disease.