Author Affiliations: Department of Medical Sciences, Toshiba General Hospital, Tokyo, Japan (Akbar SMF); Department of Hepatology, Bangabandhu Sheikh Mujib Medical University, Dhaka, Bangladesh (Al-Mahtab M); Clinical Research Organization, Dhaka, Bangladesh (Uddin MH); Laboratory of Animal Production, Faculty of Agriculture, Ehime University, Matsuyama, Japan (Khan MSI)

Corresponding Author: Sheikh Mohammad Fazle Akbar, MD, PhD, Department of Medical Sciences, Toshiba General Hospital, Higashi Oi 6-3-22, Tokyo 140-8522, Japan (Tel: 81-3-3764-0511; Fax: 81-3-3764-8992; Email: sheikh.akbar@po.toshiba. co.jp)

 

© 2013, Hepatobiliary Pancreat Dis Int. All rights reserved.

doi: 10.1016/S1499-3872(13)60057-0

 

 

Acknowledgement: We thank Dr. Shiyi Chen (Ehime University Graduate School of Medicine, Toon, Ehime, Japan) for her help to study mechanism of action of different vaccines in HBV transgenic mice.

Contributors: ASMF designed the manuscript. AMM and UMH performed clinical trials with vaccine therapies in patients with chronic hepatitis B with HBsAg/HBcAg-based vaccine. KMSI analyzed data. ASMF is the guarantor.

Funding: None.

Ethical approval: Not needed.

Competing interest: No benefits in any form have been received or will be received form a commercial party related directly or indirectly to the subject of this article.

 

 

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

 

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

 

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

 

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

 

(Hepatobiliary Pancreat Dis Int 2013;12:363-369)

 

KEY WORDS: chronic hepatitis B; HBsAg vaccine; HBsAg/HBcAg vaccine immune therapy; therapeutic vaccines

Although considerable information about the life cycle, epidemiology, immunology, pathogenesis and prevention of HBV has been available during the last three decades, there has been no significant progress in treating patients with chronic hepatitis B (CHB). Despite the advent of new antiviral agents for the treatment of CHB patients, sustained off-treatment responses are rarely achieved. Moreover, the long-term risk of viral resistance and drug toxicity are related to maintenance antiviral therapy with presently-available antiviral agents for CHB patients.^[1,2] Prolonged treatment with antiviral agents leads to unsustainable cost that is unbearable to the majority of global HBV-infected patients in resource-constrained countries of Asia and Africa.^{[3, 4]} Hence, there is a pressing need to develop new therapeutic approaches for patients with chronic HBV infection to increase therapeutic efficacy and to limit the high cost and risk of toxicity or viral resistance associated with maintenance antiviral therapy.^[5] In this regard, attention has been focused on the development of immune therapy for these patients. It has been reported that host immune responses are impaired in CHB patients and they are unable to respond properly to invading HBV and HBV-related antigens.^{[6, 7]} In addition, the therapeutic efficacy of antiviral drugs in CHB patients has been found to be related to the restoration of host immunity.^{[8, 9]} But the immune modulatory capacity of antiviral drugs may not be objective-oriented.^[10] Also, polyclonal immune modulators can not induce the adequate level of HBV-specific immunity in patients with chronic HBV infection. To induce strong HBV-specific immunity in CHB patients, a new therapeutic approach has been used in the last two decades. Patients with CHB have been immunized with HBsAg-based vaccine to restore HBV-specific immune responses. Although the initial response of HBsAg-based vaccine therapy was inspiring in CHB patients in studies,^[11-13] this approach was limited.^[14] Several approaches were taken to improve the efficacy of HBsAg-based vaccine therapy in CHB patients,^[15-18] but a randomized-controlled trial showed that it is unlikely that a therapeutic vaccine containing HBsAg and an antiviral drug (combination therapy) may be an effective therapeutic option for CHB.^[19]

 

The study of the therapeutic efficacy of vaccine therapy in animal models of HBV carrier state showed that the restoration of HBcAg-specific immunity may be required for containment of HBV replication and control of liver damages after chronic HBV infection.^[20,21] HBcAg-based immune therapy for CHB patients is in its infancy and only few studies have been conducted in CHB patients undergoing such therapy. Recent studies^[22,23] have used a vaccine containing both HBsAg and HBcAg to treat CHB patients.

 

This review addresses the current status of HBsAg-based immune therapy in CHB patients and provides an outline about the scope and limitations of HBcAg-based and HBsAg/HBcAg-based therapeutic vaccines in the management of chronic HBV infection.

 

 

Interferon, a drug with both antiviral and immune modulatory capacities, has been used in CHB patients from the early 1980s.^[24] Subsequently, nucleoside analogs with potent antiviral effects have been used in these patients from the 1990s.^[25] These drugs, especially nucleoside analogs, have shown potent antiviral capacities in most CHB patients. Evidences proved that these drugs are able to delay complications like liver cirrhosis and hepatocellular carcinoma.^{[26, 27]} The use of recently-developed nucleoside analogs in treating patients with CHB has also been described. Woo et al^[28] have shown that tenofovir and entecavir are the most effective antiviral agents for the treatment of patients with CHB. The two drugs have been found to induce undetectable HBV DNA and cause normalization of alanine aminotransferase in more than two thirds of treated patients. Entecavir was found to be a potent drug that improved liver histology in addition to their potent antiviral capacity.^[28] These drugs have shown sustained therapeutic effects in CHB patients.^{[26, 27]} However, other studies have provided evidences for limitations of antiviral drugs in CHB patients and their analyses have shown that these drugs may not be able to improve the clinical outcome or all intermediate parameters of CHB patients.^[29-31] Although it is difficult to address the causes for the different outcomes of antiviral drugs in CHB patients, antiviral drugs seem to be endowed with limited long-term therapeutic efficacy and some adverse effects. In addition, some of these drugs should be used for a prolonged time or even for a life-long time. Finally, antiviral drugs may not be a completely evidence-based therapeutic approach for CHB patients.^[6-9] These drugs are not able to eradicate all forms of HBV including cccDNA, and they cannot restore host immunity properly so that HBV replication and liver damages can be contained in off-treatment periods. In short, there is a need to develop evidence-based and novel therapeutic approaches for the treatment of CHB patients.

 

 

The rationale for the immune therapy of HBV infection has been shown by various evidences. Scientific and experimental evidences supported that patients with CHB exhibited impaired and distorted immunity to HBV.^{[6, 7, 32]} The natural course of HBV infection also showed that recovery from HBV infection is associated with restoration of HBV-specific immune responses.^[33] In fact, natural immune responses are capable of controlling HBV replication in most cases. And control of HBV by antiviral drug seems to be mediated at least in part by restoration of host immunity.^{[8, 9]} In addition, bone marrow transplantation from an HBV immune donor can mediate resolution of chronic HBV infection in a CHB recipient.^[34]

 

Hence, the concept of immune therapy for the treatment of patients with CHB is on a scientific basis. HBV-specific immunity could be induced by non HBV-specific agents like cytokines, growth factors and other modulators.^[35] Although some therapeutic effects of these agents were shown in CHB patients, sustained control of HBV replication and containment of liver damages could not be demonstrated by antigen non-specific immune modulators in randomized-controlled trials. The therapeutic efficacy of these immune modulators was insignificant, and adequate amounts of these agents could not be used for fear of adverse effects. With the advent of new immunological techniques, control of HBV replication and containment of liver damages can be mediated by HBV-specific immune responses, not by non HBV-specific immunity, in CHB patients.^{[6, 7]} Thus, application of HBV-related antigens (vaccine therapy) received scientific authenticity as an innovative therapy in HBV infection.

 

Different types of HBV-related antigens have been used as therapeutic vaccines in animal models of HBV infections: ducks, woodchucks and HBV transgenic mice. Recombinant surface proteins, DNA vaccines, and combination of DNA vaccines with antiviral drugs have been used in HBV-infected ducks to assess the potentials of these therapeutic approaches. The approaches have induced reduction or clearance of duck HBV DNA and clearance of duck surface antigen.^[36-38] Moreover, the use of vaccines against HBV has been evaluated in HBV-infected woodchucks. Immunizations of woodchucks with vaccines or combination of vaccine and antiviral agents have also shown HBsAb response and significant reduction of viral load and antigenemia.^[39-41]

 

Therapeutic vaccines have also shown favorable outcome in HBV transgenic mice, an animal model of chronic HBV carrier state that is prepared by microinjecting HBV genome into fertilized eggs of mice. Treatment of HBV transgenic mice with HBsAg-based vaccine or cell-based vaccine caused reduction or clearance of HBsAg from sera and HBV DNA negativity.^[42-44] These preclinical studies provided considerable insights into the possible therapeutic effects of vaccine therapy in chronic HBV infection.

 

Although HBV has different antigens, HBsAg-based vaccine is used first to treat CHB patients. There are several reasons to use HBsAg as a therapeutic vaccine in the treatment of HBV infection. HBsAg is the representative antigen of HBV infection. The presence of HBsAg in the sera indicates HBV infection. Moreover, disappearance of HBsAg and development of antibody to HBsAg (anti-HBs) are usually regarded as signs of recovery from HBV infection. HBsAg-based vaccines which are commercially available have been used preventively for more than three decades. Its safety has been confirmed in large population-based studies. The first report on vaccine therapy with HBsAg-based vaccine for CHB patients was published by Pol et al in 1994,^[11] although HBsAg-based vaccine has been used in CHB patients as early as 1982 to assess its immunogenecity in patients with chronic HBV-infection.^[45] The early studies inspired considerable optimism about HBsAg-based vaccine therapy in CHB patients because vaccine therapy causes reduction of HBV DNA, HBeAg seronegativity, and anti-HBe production.^[12-18] These studies suggested different protocols of vaccine therapy for CHB patients. Since the nature of vaccines was different, some investigators used HBsAg-based vaccine, but others used vaccines containing pres1 and pres2 antigens. In these studies, the doses of vaccines were different. The duration of vaccine therapy was also different in clinical trials using varied criteria for evaluation. Some studies checked only the HBV replication status, whereas others checked HBeAg negativity or anti-HBe seroconversion.^{[11, 12, 15-19]} The effects of vaccination on alanine aminotransferase levels were checked in some of the studies. However, the follow-up data of clinical trials with HBsAg-based vaccine therapy were almost non-existing. Again, it was elusive if vaccine therapy with HBsAg could show sustained antiviral response or not. In addition, limited or no therapeutic potentials of HBsAg-based vaccine therapy were reported.^{[46, 47]} Thus, both optimisms and frustrations prevailed about HBsAg-based vaccine therapy for CHB patients.

 

To improve the therapeutic potentials of HBsAg-based vaccine in CHB patients, alterations were made in the design of vaccine therapy. The nature of antigen, nature of adjuvant, dose of vaccine, and duration of vaccine were substantially changed. Wen et al^[12] used an antigen-antibody complex vaccine. Horiike et al^[15] used vaccine for 12 times. Strong adjuvants were also used.^{[19, 48]} Others used HBsAg-based vaccine as a part of combination therapy with antiviral drug or cytokines.^{[15, 49]} DNA vaccine expressing HBsAg was also used in CHB patients.^[50] With the advent of cell-based therapy for chronic infection and cancer, some investigators loaded HBsAg on dendritic cells, the most potent antigen-presenting cells. HBsAg-pulsed dendritic cells were used as a therapeutic vaccine in CHB patients in clinical trials.^{[51, 52]} Some of these trials showed encouraging results of HBsAg-based vaccine therapy, but a well-planned randomized-controlled trial of HBsAg-based vaccine therapy with an antiviral drug failed to show the increased therapeutic potential of combined vaccine and antiviral drug in contrast to antiviral drug monotherapy.^[19] Hence it is difficult to draw a conclusion about the therapeutic efficacy of HBsAg-based vaccine in CHB patients because there are ample opportunities to improve the design of HBsAg-based vaccine therapy for CHB patients (Fig. 1).

 

Most of the clinical trials of HBsAg-based vaccine therapy for CHB patients were performed to assess its safety and efficacy in CHB patients. Thus, there is paucity of information about the mechanisms underlying limited efficacy of HBsAg-based vaccine therapy in CHB patients. Some insights into this have been retrieved from some clinical trials in CHB patients. However, deep insights into this could not be accumulated from CHB patients due to ethical and technical limitations. For example, the role of HBsAg-based vaccine on hepatic immune responses could not be elucidated in CHB patients because of unavailability of serial sections of liver tissues from CHB patients at different time points: 1) before commencement of therapy, 2) during vaccine therapy, 3) after completion of therapy, and 4) 6 or 12 months after the end of therapy. Some insights into this have been gained from analysis of the mechanism of vaccine therapy in HBV transgenic mice.

 

HBsAg-based vaccines in CHB patients and in HBV transgenic mice induced increased levels of proinflammatory cytokines, maturation of dendritic cells, increased frequencies of HBsAg-specific immunocytes in the sera, spleen and liver, HBsAg negativity and anti-HBs production.^[53-55] The studies in CHB patients were limited to assess these parameters in the sera, whereas investigations in HBV transgenic mice provided an opportunity to evaluate the cellular events in the liver. It was found that HBsAg-based vaccine induced HBsAg-specific immunity of various magnitudes in HBV transgenic mice, but it failed to induce HBcAg-specific immunity in HBV transgenic mice. HBsAg-based vaccine had almost no effect on induction of HBcAg-specific cytotoxic T lymphocytes (CTL) in the liver of HBV transgenic mice (Fig. 2).^[20,21] As HBcAg-specific CTL is regarded as a critical regulator related to the control of HBV replication and containment of liver damages in CHB, inability of induction of HBcAg-specific CTL by HBsAg-based vaccine may be one of the mechanisms underlying their limited therapeutic efficacy in CHB patients. In addition to HBV-specific CTL, little is known about the induction of anti-HBs by HBsAg-based vaccination in CHB patients. Some studies^{[16, 47, 51]} have reported transient induction of anti-HBs because of HBsAg-based immune therapy, but the sustained presence of anti-HBs after HBsAg-based vaccination has not been confirmed.^[51] In addition, the functional capacity of anti-HBs induced by HBsAg-based vaccination in CHB patients has not been assessed. It seems that both HBV-specific CTL and neutralizing anti-HBs would be required to attain the sustained control of HBV replication and containment of liver damages in CHB patients.

 

Maini et al^[56] reported that patients with CHB who could control HBV replication and contain liver damages have significantly higher levels of HBcAg-specific CTL compared with CHB patients who fail to control HBV replication and liver damages. Thus, evidences supporting a protective role of liver-derived HBcAg-specific CTL and a pathogenic role of antigen non-specific immunity in CHB patients were documented. Taken together, a rationale for applying HBcAg-based therapeutic intervention in CHB patients was shown. Heathcote et al^[57] used HBcAg-based epitope to treat CHB patients in the 1990s. Recently, we have used HBcAg-based cellular vaccine to assess their impact on hepatic immunity in HBV transgenic mice containing full HBV genome and all HBV-related antigens. Our study revealed interesting information about HBcAg-based vaccine in HBV transgenic mice. Immunization of HBcAg-based vaccine caused HBsAg-negativity and anti-HBs production in the sera. Moreover, both HBsAg-CTL and HBcAg-specific CTL were detected in the liver of HBV transgenic mice immunized with HBcAg-based vaccine.^[20] In addition, the role of HBcAg as a tentative therapeutic vaccine has been shown in duck and woodchuck models of HBV infection.^{[37, 41]} It is still unclear whether HBcAg-based vaccine would be able to induce both HBsAg-CTL and HBcAg-specific CTL in the liver of CHB patients, but preclinical studies provide a rationale to use HBcAg as a therapeutic vaccine in CHB patients. The major limitation of proceeding studies is the unavailability of human consumable HBcAg-based vaccine.

 

It is well-known that anti-HBs is a protective antibody for HBV and its presence in the sera is essential for blocking HBV replication. Moreover, the development of anti-HBs in CHB patients either by natural or therapeutic means usually indicates the recovery from chronic HBV infection. On the other hand, HBcAg-based vaccine is able to induce HBcAg-specific CTL in the liver of HBV transgenic mice without causing liver damages.^{[20, 21]} In short, an effective regimen of immune therapy may be developed for CHB patients if both of these antigens are used as immune therapeutic agents. There are few studies on HBsAg/HBcAg-based vaccine in CHB patients (Fig. 1). A study^[22] used epitopes of HBsAg and HBcAg to load on dendritic cells and used epitope-pulsed dendritic cells in CHB patients, and found the potent antiviral effects of dendritic cells vaccines that contain HBsAg and HBcAg epitopes. However, the data from these CHB patients after vaccine therapy were lacking. Thus it was not clear if the therapeutic effect of vaccines persisted after therapy. Recently, we have used a human consumable HBsAg/HBcAg vaccine in HBV transgenic mice and found that a vaccine containing both antigens represents a potent therapeutic agent.^[21] Subsequently, a phase I/II clinical trial was performed in CHB patients to evaluate the safety and efficacy of the vaccine.^[23] The outcome of this trial was inspiring because HBsAg/HBcAg-based immunization was safe for all patients and sustained HBV negativity was recorded in more than 50% of the patients. In addition, persistent normalization of alanine aminotransferase was recorded in the majority of the patients. At present, a phase III clinical trial has been undertaken with HBsAg/HBcAg-based combined vaccine through the nasal and subcutaneous route in CHB patients (ClinicalTrials.gov; Protocol Registration Receipt 06/12/2011). The outcome of this therapy is inspiring but off-treatment efficacy would provide more insights into the scope and limitation of this approach in CHB patients.

 

 

Management of chronic HBV infection and its complications represents major challenges to various branches of life sciences. HBV persists in the hosts for a long period and even life-long. HBV may remain in silent form for decades and become active because of alterations of the immune status of hosts. In millions of HBV-infected patients, HBV causes liver damages that are progressive in nature and result in serious complications like liver cirrhosis, liver decompensation, and hepatocellular carcinoma. The resultant public health burden related to chronic HBV infection and HBV-related liver diseases is enormous. Antiviral drugs that have been developed during the last three decades seem to be poorly effective in controlling HBV replication and liver damage as well as blocking HBV-related complications in most of CHB patients. Thus, there is a pressing need to develop new approaches for the control of chronic HBV infection. Immune therapy has been recognized as an alternative to treat CHB patients. Immune restoration for therapeutic purposes in CHB patients is valid, but controversies remain over its design. This is a tough challenge because immune therapy has not been optimized for most pathological conditions, although evidences have shown that it is evidence-based therapeutic approach for treating chronic infections and cancers. In the context of chronic HBV infection, this review mainly focused on the nature of antigens used to treat CHB patients. Other factors determining the therapeutic efficacy of an agent, such as the dose and duration of therapy as well as therapeutic strategy (monotherapy or combination therapy) need to be evaluated in future when data will be available on immune therapy with HBsAg-based vaccine, HBcAg-based vaccine and HBsAg/HBcAg-based vaccine in CHB patients. Although more studies are required to find the nature of appropriate vaccine for immune therapy of CHB patients, various therapeutic vaccines seem to be safe in humans and mice. Further studies on their efficacy should focus on relative use of HBsAg, HBcAg and HBsAg/HBcAg-based vaccine in CHB patients. The development of an effective vaccine against CHB would not only be a milestone for the treatment of HBV infection, but also will contribute to the development of therapeutic vaccines and immune therapeutic approaches for other chronic infections, cancers, etc.

 

 

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