Immunization with plasmid DNA encoding hepatitis C virus envelope E2 antigenic domains induces antibodies whose immune reactivity is linked to the injection mode

A trivalent HCV vaccine elicits broad and synergistic polyclonal antibody response in mice and rhesus monkey

OBJECTIVE

Despite the development of highly effective direct-acting antivirals, a prophylactic vaccine is needed for eradicating HCV. A major hurdle of HCV vaccine development is to induce immunity against HCV with high genome diversity. We previously demonstrated that a soluble E2 (sE2) expressed from insect cells induces broadly neutralising antibodies (NAbs) and prevents HCV infection. The objective of this study is to develop a multivalent HCV vaccine to increase the antigenic coverage.

DESIGN

We designed a trivalent vaccine containing sE2 from genotype 1a, 1b and 3a. Mice and rhesus macaques were immunised with monovalent or trivalent sE2 vaccine, and sera or purified immunoglobulin were assessed for neutralisation against a panel of cell culture-derived virion (HCVcc) of genotype 1-7 in cell culture. Splenocytes from the vaccinated macaques were assessed for HCV-specific T cell response.

RESULTS

We showed that the trivalent vaccine elicited pangenotypic NAbs in mice, which neutralised HCVcc of all the seven genotypes more potently than the monovalent vaccine. Further analyses demonstrated that each sE2 component of this trivalent vaccine elicited unique spectrum of NAbs which acted synergistically to inhibit HCV infection. Finally, the trivalent vaccine triggered stronger and more uniform multigenotypic neutralising antibody response than the monovalent vaccine in rhesus macaques.

CONCLUSIONS

In summary, we developed a trivalent HCV vaccine that induces broad and synergistic-acting neutralising antibodies in mice and non-human primates.

Vaccination with dendritic cells pulsed with hepatitis C pseudo particles induces specific immune responses in mice

AIM

To explore dendritic cells (DCs) multiple functions in immune modulation.

METHODS

We used bone-marrow derived dendritic cells from BALB/c mice pulsed with pseudo particles from the hepatitis C virus to vaccinate naive BALB/c mice. Hepatitis C virus (HCV) pseudo particles consist of the genotype 1b derived envelope proteins E1 and E2, covering a non-HCV core structure. Thus, not a single epitope, but the whole "viral surface" induces immunogenicity. For vaccination, mature and activated DC were injected subcutaneously twice.

RESULTS

Humoral and cellular immune responses measured by enzyme-linked immunosorbent assay and interferon-gamma enzyme-linked immunosorbent spot test showed antibody production as well as T-cells directed against HCV. Furthermore, T-cell responses confirmed two highly immunogenic regions in E1 and E2 outside the hypervariable region 1.

CONCLUSION

Our results indicate dendritic cells as a promising vaccination model for HCV infection that should be evaluated further.

Towards a Brucella vaccine for humans

There is currently no licensed vaccine for brucellosis in humans. Available animal vaccines may cause disease and are considered unsuitable for use in humans. However, the causative pathogen, Brucella, is among the most common causes of laboratory-acquired infections and is a Center for Disease Control category B select agent. Thus, human vaccines for brucellosis are required. This review highlights the considerations that are needed in the journey to develop a human vaccine, including animal models, and includes an assessment of the current status of novel vaccine candidates.

DNA vaccine therapy for chronic hepatitis C virus (HCV) infection: immune control of a moving target

The use of DNA plasmids for DNA vaccination was first described in the early 1990 s. DNA vaccinations were successful in small animal models but in larger animals and humans problems appeared. One major obstacle, effective delivery, has been partly overcome by new delivery techniques, such as transdermal delivery with the gene gun, and in vivo electroporation. We are entering a new era of DNA vaccination, where such techniques can be tested in humans. DNA vaccination may be a useful therapy for chronic hepatitis C virus (HCV) infections. Patients with these infections have a reduced T cell response to the invading virus. The genetic variability of HCV, its immunomodulatory properties and high replication rate contribute to chronicity. By providing the correct stimulus T cells may be activated to clear the infection. The vaccination is intended to induce a coordinated immune-based attack on the continuously moving HCV target. If effective, this should help in clearing the infection.

Specific antibodies induced by DNA vaccination with extracellular domain of CD25 gene protect against ConA-induced autoimmune hepatitis

Antibodies to CD25 (anti-CD25) were used clinically to achieve immunosuppression in autoimmune disease, while the possibility of anti-antibodies generation influenced its efficiency. Here we reported that DNA vaccine encoding the extracellular domain of murine CD25 gene (pCD25-ECD) elicited anti-CD25 antibody production in BALB/c mice and subsequently prevents the host against ConA-induced autoimmune hepatitis. We found that serum CD25-specific antibodies were generated after vaccination with pCD25-ECD. Moreover, high levels of IL-4, IL-10 and anti-CD25 antibody were produced by splenocytes of vaccinated mice after CD25 protein restimulation in vitro. Furthermore, we demonstrated that the vaccinated mice suffered less from liver injury induced by ConA, accompanied by the reduction of pathogenic CD4+ T cells. Finally, we showed that the immunized serum could cause cytolysis of activated CD4+ T cells in vitro, depending on complements activation. Our study showed pCD25-ECD induced self anti-CD25 antibodies which executed immunosuppression in autoimmune hepatitis via antibody-complement pathway.

End-point limiting-dilution real-time PCR assay for evaluation of hepatitis C virus quasispecies in serum: performance under optimal and suboptimal conditions

An approach for determination of hepatitis C virus (HCV) quasispecies by end-point limiting-dilution real-time PCR (EPLD-PCR) is described. It involves isolation of individual coexisting sequence variants of the hypervariable region 1 (HVR1) of the HCV genome from serum specimens using a limiting-dilution protocol. EPLD-PCR applied to an HCV outbreak study provided insights into the epidemiological relationships between incident and chronic cases. When applied to samples from a longitudinal study of infected patients, HVR1 sequences from each sampling time-point were observed to group as distinct phylogenetic clusters. Melting peak analysis conducted on EPLD-PCR products generated from these patients could be used for evaluation of HVR1 sequence heterogeneity without recourse to clonal sequencing. Further, to better understand the mechanism of single-molecule PCR, experiments were conducted under optimal and suboptimal annealing temperatures. Under all temperature conditions tested, HVR1 variants from the major phylogenetic clusters of quasispecies could be amplified, revealing that successful HVR1 quasispecies analysis is not contingent to dilution of starting cDNA preparations to a single-molecule state. It was found that EPLD-PCR conducted at suboptimal annealing temperatures generated distributions of unique-sequence variants slightly different from the distribution obtained by PCR conducted at the optimal temperature. Hence, EPLD-PCR conditions can be manipulated to access different subpopulations of HCV HVR1 quasispecies, thus, improving the range of the quasispecies detection. Although EPLD-PCR conducted at different conditions detect slightly different quasispecies populations, as was shown in this study, the resulted samples of quasispecies are completely suitable for molecular epidemiological investigation in different clinical and epidemiological settings.

Modulation of immune response induced by co-administration of DNA vaccine encoding HBV surface antigen and HCV envelope antigen in BALB/c mice

Plasmid DNA vaccines encoding the hepatitis B virus (HBV) surface and hepatitis C virus (HCV) envelope antigens, respectively, were constructed, and attempt were made to find the possibility of a divalent vaccine against HBV and HCV. The expression of each plasmid in Cos-1 cells was confirmed using immunocytochemistry. To measure the induced immune response by these plasmids in vivo, female BALB/c mice were immunized intramuscularly with 100 microg of either both or just one of the plasmids. Anti-HBV and HCV-specific antibodies and related cytokines were evaluated to investigate the generation of both humoral and cellular immune responses. As a result, specific anti-HBV and anti-HCV serum antibodies from mice immunized with these plasmids were observed using immunoblot. The levels of IL-2 and RANTES showing a Th1 immune response were significantly increased, but there was no change in the level of IL-4 (Th2 immune response) in any of the immunized groups. Compared with each plasmid DNA vaccine, the combined vaccine elicited similar immune responses in both humoral and cell-mediated immunities. These results suggest that the combined DNA vaccine can induce not only comparable immunity experimentally without antigenic interference, but also humoral and Th1 dominant cellular immune responses. Therefore, they could serve as candidates for a simultaneous bivalent vaccine against HBV and HCV infections.

Development of prophylactic and therapeutic vaccines against hepatitis C virus

The hepatitis C virus was discovered 15 years ago as the agent responsible for most cases of transfusion-associated hepatitis non-A, non-B. At present, 180 million people worldwide are estimated to be infected with the virus, producing severe and progressive liver disease in millions and representing the most common reason for liver transplantation in adults. Although the spread of the virus can be halted by the application of primary prevention strategies, such as routine testing of blood donations, inactivation of blood products and systematic use of disposable needles and syringes, the development of a prophylactic vaccine could facilitate the control of this infection and protect those at high risk of being infected with hepatitis C virus. As the present therapy of chronic hepatitis C virus infections, consisting of a combined administration of pegylated interferon-alpha and ribavirin, is only successful in 50% of patients infected with genotype 1, and is costly and associated with serious side effects, there is an urgent need for better tolerated and more effective treatment modalities, and a therapeutic vaccine may be the solution. This review first provides an overview of the present knowledge regarding the interaction between the virus and immune system of the infected host, with special attention given to the possible mechanisms responsible for chronic evolution of the infection. The numerous candidate vaccines that have been developed in the past 10 years are discussed, including the studies in which their immunogenicity has been examined in rodents and chimpanzees. Finally, the only studies of therapeutic vaccines performed in humans to date are considered.

DNA vaccines: progress and challenges

In the years following the publication of the initial in vivo demonstration of the ability of plasmid DNA to generate protective immune responses, DNA vaccines have entered into a variety of human clinical trials for vaccines against various infectious diseases and for therapies against cancer, and are in development for therapies against autoimmune diseases and allergy. They also have become a widely used laboratory tool for a variety of applications ranging from proteomics to understanding Ag presentation and cross-priming. Despite their rapid and widespread development and the commonplace usage of the term "DNA vaccines," however, the disappointing potency of the DNA vaccines in humans underscores the challenges encountered in the efforts to translate efficacy in preclinical models into clinical realities. This review will provide a brief background of DNA vaccines including the insights gained about the varied immunological mechanisms that play a role in their ability to generate immune responses.

Modulation of cellular immune response against hepatitis C virus nonstructural protein 3 by cationic liposome encapsulated DNA immunization

A vaccine strategy directed to increase Th1 cellular immune responses, particularly to hepatitis C virus (HCV) nonstructural protein 3 (NS3), has considerable potential to overcome the infection with HCV. DNA vaccination can induce both humoral and cellular immune responses, but it became apparent that the cellular uptake of naked DNA injected into muscle was not very efficient, as much of the DNA is degraded by interstitial nucleases before it reaches the nucleus for transcription. In this paper, cationic liposomes composed of different cationic lipids, such as dimethyl-dioctadecylammonium bromide (DDAB), 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), or 1,2-dioleoyl-sn-glycerol-3-ethylphosphocholine (DOEPC), were used to improve DNA immunization in mice, and their efficiencies were compared. It was found that cationic liposome-mediated DNA immunization induced stronger HCV NS3-specific immune responses than immunization with naked DNA alone. Cationic liposomes composed of DDAB and equimolar of a neutral lipid, egg yolk phosphatidylcholine (EPC), induced the strongest antigen-specific Th1 type immune responses among the cationic liposome investigated, whereas the liposomes composed of 2 cationic lipids, DDAB and DOEPC, induced an antigen-specific Th2 type immune response. All cationic liposomes used in this study triggered high-level, nonspecific IL-12 production in mice, a feature important for the development of maximum Th1 immune responses. In conclusion, the cationic liposome-mediated gene delivery is a viable HCV vaccine strategy that should be further tested in the chimpanzee model.

Development of a hepatitis C virus vaccine

Any program aimed at the development of a vaccine should consider several important issues because they may greatly influence the choice of immunogen used in the vaccine, the delivery system selected for its application, the population to be vaccinated, and the type of vaccine to be developed (ie, preventive or therapeutic). These issues concern the epidemiology of the infectious disease targeted, the actual routes of transmission, the antigenic diversity of the infectious agent, the existing therapies, and their rate of success. In the case of hepatitis C virus, a viral agent whose clinical existence was recognized in the 1970s but which was only identified by the use of molecular cloning technology in the late 1980s, some of these issues are particularly relevant.

Comparative vaccine studies in HLA-A2.1-transgenic mice reveal a clustered organization of epitopes presented in hepatitis C virus natural infection

A polyepitopic CD8(+)-T-cell response is thought to be critical for control of hepatitis C virus (HCV) infection. Using transgenic mice, we analyzed the immunogenicity and dominance of most known HLA-A2.1 epitopes presented during infection by using vaccines that carry the potential to enter clinical trials: peptides, DNA, and recombinant adenoviruses. The vaccines capacity to induce specific cytotoxic T lymphocytes and interferon gamma-producing cells revealed that immunogenic epitopes are clustered in specific antigens. For two key antigens, flanking regions were shown to greatly enhance the scope of epitope recognition, whereas a DNA-adenovirus prime-boost vaccination strategy augmented epitope immunogenicity, even that of subdominant ones. The present study reveals a clustered organization of HCV immunogenic HLA.A2.1 epitopes and strategies to modulate their dominance.

DNA-based immunotherapy: potential for treatment of chronic viral hepatitis?

Persistent HBV and HCV infection represent major causes of chronic liver disease with a high risk of progression to liver cirrhosis and hepatocellular carcinoma (HCC). Conventional protein-based vaccines are highly efficacious in preventing HBV infection; whereas in therapeutic settings with chronically infected patients, results have been disappointing. Prophylactic vaccination against HCV infection has not yet been achieved due to many impediments including frequent spontaneous mutations of the virus with escape from immune system control. Using animal models it has been demonstrated that DNA-based immunisation strategies may overcome this problem because of their potential to induce immunity against multiple viral epitopes. DNA-based vaccines mimic the effect of live attenuated viral vaccines, eliciting cell mediated immunity in addition to inducing humoral responses. Efficacy may further be improved by addition of DNA encoding immunomodulatory cytokines and more recently, direct genetic modulation of antigen-presenting cells, such as dendritic cells (DC), has been shown to increase antigen-specific immune responses. This review focuses on immunological aspects of chronic HBV and HCV infection and on the potential of DNA- and DC-based vaccines for the treatment of chronic viral hepatitis.

DNA immunization with fusion genes encoding different regions of hepatitis C virus E2 fused to the gene for hepatitis B surface antigen elicits immune responses to both HCV and HBV

AIM

Both Hepatitis B virus (HBV) and Hepatitis C virus (HCV) are major causative agents of transfusion-associated and community-acquired hepatitis worldwide. Development of a HCV vaccine as well as more effective HBV vaccines is an urgent task. DNA immunization provides a promising approach to elicit protective humoral and cellular immune responses against viral infection. The aim of this study is to achieve immune responses against both HCV and HBV by DNA immunization with fusion constructs comprising various HCV E2 gene fragments fused to HBsAg gene of HBV.

METHODS

C57BL/6 mice were immunized with plasmid DNA expressing five fragments of HCV E2 fused to the gene for HBsAg respectively. After one primary and one boosting immunizations, antibodies against HCV E2 and HBsAg were tested and subtyped in ELISA. Splenic cytokine expression of IFN-gamma and IL-10 was analyzed using an RT-PCR assay. Post-immune mouse antisera also were tested for their ability to capture HCV viruses in the serum of a hepatitis C patient in vitro.

RESULTS

After immunization, antibodies against both HBsAg and HCV E2 were detected in mouse sera, with IgG2a being the dominant immunoglobulin sub-class. High-level expression of INF-gamma was detected in cultured splenic cells. Mouse antisera against three of the five fusion constructs were able to capture HCV viruses in an in vitro assay.

CONCLUSION

The results indicate that these fusion constructs could efficiently elicit humoral and Th1 dominant cellular immune responses against both HBV S and HCV E2 antigens in DNA-immunized mice. They thus could serve as candidates for a bivalent vaccine against HBV and HCV infection. In addition, the capacity of mouse antisera against three of the five fusion constructs to capture HCV viruses in vitro suggested that neutralizing epitopes may be present in other regions of E2 besides the hypervariable region 1.

Hepatitis C virus non-structural protein 3-specific cellular immune responses following single or combined immunization with DNA or recombinant Semliki Forest virus particles

The capacity of recombinant Semliki Forest virus particles (rSFV) expressing the hepatitis C virus non-structural protein 3 (NS3) to induce, in comparison or in combination with an NS3-expressing plasmid, specific cellular and humoral immune responses in murine models was evaluated. In vitro studies indicated that both types of vaccine expressed the expected size protein, albeit with different efficacies. The use of mice transgenic for the human HLA-A2.1 molecule indicated that the rSFV-expressed NS3 protein induces, as shown previously for an NS3 DNA vaccine, NS3-specific cytotoxic lymphocytes (CTLs) targeted at one dominant HLA-A2 epitope described in infected patients. All DNA/rSFV vaccine combinations evaluated induced specific CTLs, which were detectable for up to 31 weeks after the first injection. Overall, less than 1 log difference was observed in terms of the vigour of the bulk CTL response induced and the CTL precursor frequency between all vaccines (ranging from 1:2.6x10(5) to 1:1x10(6)). Anti-NS3 antibodies could only be detected following a combined vaccine regimen in non-transgenic BALB/c mice. In conclusion, rSFV particles expressing NS3 are capable of inducing NS3-specific cellular immune responses targeted at a major HLA-A2 epitope. Such responses were comparable to those obtained with a DNA-based NS3 vaccine, whether in the context of single or combined regimens.

Immunoprophylaxis of hepatitis C virus infection

Because hepatitis C virus is etiologically involved in about half the cases of the world's most common cancer, hepatocellular carcinoma, and because this virus is likely to continue to spread in most of the developing world for many years, the authors believe that development of a prophylactic vaccine is imperative. Numerous approaches are available to overcome the many impediments which make the development of an HCV vaccine difficult. Such impediments include the many viral genotypes and quasispecies of HCV and the association of virions with host lipids. It is likely that overcoming these impediments will require a vaccine which induces a strong cell-mediated response. The most promising approach seems to be DNA-based immunization or a prime-boost regimen with DNA priming and boosting with a viral vector. Potentiation of responses with adjuvant strategies will probably be necessary. Hepatitis C virus immunization is in an early stage of development. Given the explosive growth in the understanding of immunology, progress should be rapid.

Immunological evaluation of Escherichia coli-derived hepatitis C virus second envelope protein (E2) variants

Two variants of the hepatitis C virus (HCV) E2 envelope protein, lacking the C-terminal domain and comprising amino acids 458-650 (E2A) and 382-605 (E2C), respectively, were efficiently produced in BL21 (DE3) Escherichia coli cells. E2A and E2C were used to immunize mice. The E2C variant induced the maximal mean antibody titer. Anti-E2C mouse sera reacted mainly with E2 synthetic peptides covering the 70 amino acid N-terminal region of the E2 protein. Moreover, a panel of anti-HCV positive human sera recognized only the E2C protein (28.2%) and the synthetic peptide covering the HVR-1 of the E2 protein (23.1%). These data indicate the existence of an immunologically relevant region in the HVR-1 of the HCV E2 protein.

DNA vaccination: a potential weapon against infection and cancer

DNA vaccination is a novel approach for inducing immunity against target antigens. It provides a direct link between identification of genes encoding these antigens and incorporation of the gene sequences into a vaccine vehicle. Identification of candidate genes is proceeding very rapidly both for infectious organisms and for cancer cells. One advantage is that DNA appears to activate all pathways of immunity, especially cytotoxic T-cell responses, which have been difficult to induce with protein vaccines. For viruses, including those which have caused problems for blood transfusion, DNA vaccination could be used for prevention. However, for chronic infection, or for cancer, vaccination will be performed in a therapeutic setting. For this situation, it is probable that immune-activating sequences will have to be included in the vaccine. The ease of manipulation of gene sequences, together with the increasing knowledge of the operation of the immune system, means that we now have the tools to take vaccines into the next exciting stage of development.

Biolistic-mediated gene transfer using the bovine herpesvirus-1 glycoprotein D is an effective delivery system to induce neutralizing antibodies in its natural host

A genetic vaccine consisting of the bovine herpesvirus-1 (BHV-1) glycoprotein D (gD) gene was constructed and administered to cattle using the biolistic (gene-gun) process. Results were compared to standard intramuscular injection of an inactivated whole BHV-1 commercial vaccine. Cattle genetically immunized by the gene-gun-delivered gD subunit vaccine developed high titers of IgG antibodies specific to gD demonstrating that this immunization method is a potent humoral response inducer. Further, gene-gun vaccinated cattle produced high neutralizing antibody titers to BHV-1 similar to levels induced in the commercial vaccine immunized animals. Additionally, cellular immunity was measured by an increased level of IFN-gamma mRNA detected in PBMC of cattle immunized with the gD gene or with the commercial vaccine, whereas augmented levels of IL-4 were not detected following vaccination. Because of its simplicity and effectiveness in inducing an immune response in cattle similar to a commercial vaccine, gene-gun delivery of a subunit BHV-1 gD vaccine would be a viable alternative to current immunization protocols.

Use of conventional or replicating nucleic acid-based vaccines and recombinant Semliki forest virus-derived particles for the induction of immune responses against hepatitis C virus core and E2 antigens

Replicating and nonreplicating nucleic acid-based vaccines as well as Semliki Forest-recombinant Viruses (rSFVs) were evaluated for the development of a vaccine against hepatitis C virus (HCV). Replicating SFV-DNA vaccines (pSFV) and rSFVs expressing HCV core or E2 antigens were compared with classical CMV-driven plasmids (pCMV) in single or bimodal vaccine protocols. In vitro experiments indicated that all vaccine vectors produced the HCV antigens but to different levels depending on the antigen expressed. Both replicating and nonreplicating core-expressing plasmids induced, upon injection in mice, specific comparable CTL responses ranging from 10 to 50% lysis (E:T ratio 100:1). Comparison of different injection modes (intramuscular versus intraepidermal) and the use of descalating doses of DNA (1-100 microgram) did not show an increased efficacy of the core-SFV plasmid compared with the CMV-driven one. Surprisingly, rSFVs yielded either no detectable anticore CTL or very low anti-E2 antibody titers following either single or bimodal administration together with CMV-expressing counterparts. Prime-boost experiments revealed, in all cases, the superiority of DNA-based only vaccines. The anti-E2 antibody response was evaluated using three different assays which indicated that all generated anti-E2 antibodies were targeted at similar determinants. This study emphasizes the potential of DNA-based vaccines for induction of anti-HCV immune responses and reveals an unexpected and limited benefit of SFV-based vaccinal approaches in the case of HCV core and E2.

Vaccination of chimpanzees with plasmid DNA encoding the hepatitis C virus (HCV) envelope E2 protein modified the infection after challenge with homologous monoclonal HCV

Hepatitis C virus (HCV) is an important cause of chronic liver disease worldwide. Development of vaccines to prevent HCV infection, or at least prevent progression to chronicity, is a major goal. In mice and rhesus macaques, a DNA vaccine encoding cell-surface HCV-envelope 2 (E2) glycoprotein stimulated stronger immune responses than a vaccine encoding intracellular E2. Therefore, we used DNA encoding surface-expressed E2 to immunize chimpanzees 2768 and 3001. Chimpanzee 3001 developed anti-E2 after the second immunization and antibodies to hypervariable region 1 (HVR1) after the third immunization. Although chimpanzee 2768 had only low levels of anti-E2 after the third immunization, an anamnestic response occurred after HCV challenge. CTL responses to E2 were not detected before challenge, but a strong response was detected after HCV challenge in chimpanzee 2768. An E2-specific CD4+ response was detected in chimpanzee 2768 before challenge and in both chimpanzees postchallenge. Three weeks after the last immunization, animals were challenged with 100 50% chimpanzee-infectious doses (CID(50)) of homologous monoclonal HCV. As a control, a naive chimpanzee was inoculated with 3 CID(50) of the challenge virus. The vaccine did not generate sterilizing immunity because both vaccinated chimpanzees were infected. However, both vaccinated chimpanzees resolved the infection early whereas the control animal became chronically infected. Compared with the control animal, hepatitis appeared earlier in the course of the infection in both vaccinated chimpanzees. Therefore, DNA vaccine encoding cell surface-expressed E2 did not elicit sterilizing immunity in chimpanzees against challenge with a monoclonal homologous virus, but did appear to modify the infection and might have prevented progression to chronicity.

Evaluation of hepatitis C virus glycoprotein E2 for vaccine design: an endoplasmic reticulum-retained recombinant protein is superior to secreted recombinant protein and DNA-based vaccine candidates

Hepatitis C virus (HCV) is the leading causative agent of blood-borne chronic hepatitis and is the target of intensive vaccine research. The virus genome encodes a number of structural and nonstructural antigens which could be used in a subunit vaccine. The HCV envelope glycoprotein E2 has recently been shown to bind CD81 on human cells and therefore is a prime candidate for inclusion in any such vaccine. The experiments presented here assessed the optimal form of HCV E2 antigen from the perspective of antibody generation. The quality of recombinant E2 protein was evaluated by both the capacity to bind its putative receptor CD81 on human cells and the ability to elicit antibodies that inhibited this binding (NOB antibodies). We show that truncated E2 proteins expressed in mammalian cells bind with high efficiency to human cells and elicit NOB antibodies in guinea pigs only when purified from the core-glycosylated intracellular fraction, whereas the complex-glycosylated secreted fraction does not bind and elicits no NOB antibodies. We also show that carbohydrate moieties are not necessary for E2 binding to human cells and that only the monomeric nonaggregated fraction can bind to CD81. Moreover, comparing recombinant intracellular E2 protein to several E2-encoding DNA vaccines in mice, we found that protein immunization is superior to DNA in both the quantity and quality of the antibody response elicited. Together, our data suggest that to elicit antibodies aimed at blocking HCV binding to CD81 on human cells, the antigen of choice is a mammalian cell-expressed, monomeric E2 protein purified from the intracellular fraction.

Generation of high-affinity rabbit polyclonal antibodies to the murine urokinase receptor using DNA immunization

The urokinase receptor (uPAR) is a glycolipid anchored cell surface glycoprotein that plays a central role in extracellular proteolysis during tissue remodeling processes and cancer invasion. By intramuscular (i.m.) injection of rabbits with plasmid DNA coding for a carboxy-terminally truncated secreted form of the murine uPAR (muPAR), specific anti-sera with a titer of 64,000, as measured by ELISA, have been obtained. Rabbits received a total of 10 monthly injections of 1 mg DNA in phosphate-buffered saline. The antibody titer peaked between the 5th and 7th injection and slowly declined after the 8th injection. After the final immunization the immune response persisted for at least 6 months without further injections. The antibodies generated by DNA immunization were useful for immunohistochemistry and immunoblotting, recognizing the antigen both in its native and in its reduced and alkylated form. Using the antibodies in immunoblotting muPAR was identified in lysates of peritoneal macrophages, spleen and lung tissue. Both the intact and cleaved form of muPAR were identified in lysates of a murine monocyte cell line P388D.1. No cross-reaction with human uPAR was observed. In immunohistochemical analysis of normal mouse lung tissue uPAR immunoreactivity was located in the alveoli and pulmonary vessels, whereas the bronchial epithelium was negative. These results demonstrate that DNA immunization of rabbits using i.m. injection is a very effective and easy method to raise polyclonal antibodies which can be used for characterization and localization of muPAR in mouse tissue.

Hepatitis C virus-like particles synthesized in insect cells as a potential vaccine candidate

BACKGROUND & AIMS

Hepatitis C virus (HCV) is a leading cause of chronic hepatitis in the world. Successful vaccine development is crucial in controlling global HCV infection. We have previously described the generation of HCV-like particles (HCV-LPs) in insect cells using a recombinant baculovirus containing the complementary DNA of the HCV structural proteins. These HCV-LPs had similar morphological and biophysical properties as the putative virions. In this study, we analyzed the structural features, antigenic composition, seroreactivity, and immunogenicity of purified HCV-LPs.

METHODS

HCV-LPs were analyzed by electron microscopy and antibody immunolabeling and precipitation. An enzyme-linked immunosorbent assay (ELISA) using HCV-LPs was developed. The humoral response to HCV-LPs in mice was studies by core and envelope ELISAs, Western immunoblotting, and immunofluorescence.

RESULTS

Structural and antigenic compositions of HCV-LPs were shown to be similar to those of putative HCV virions. Using the HCV-LP ELISA, high-titer anti-HCV antibodies were detected in individuals infected with various HCV genotypes. In vivo, HCV-LPs elicited a humoral response broadly directed against HCV structural proteins.

CONCLUSIONS

HCV-LPs resemble HCV virions and are capable of inducing a humoral response targeted against various regions of HCV structural proteins, suggesting that HCV-LPs may be promising as a potential vaccine candidate.

The molecular biology of hepatitis C virus. Genotypes and quasispecies

Hepatitis C virus (HCV) is an important cause of chronic liver disease worldwide. HCV is a positive-strand genotype RNA virus with extensive genetic heterogeneity; HCV isolates define 6 major genotypes, and HCV circulates within an infected individual as a number of closely related but distinct species, termed a quasispecies. This article reviews characteristic aspects of HCV molecular biology and their implications for treatment and vaccine development.

Expression of noncovalent hepatitis C virus envelope E1-E2 complexes is not required for the induction of antibodies with neutralizing properties following DNA immunization

Interactive glycoproteins present on the surface of viral particles represent the main target of neutralizing antibodies. The ability of DNA vaccination to induce antibodies directed at such structures was investigated by using eight different expression plasmids engineered either to favor or to prevent interaction between the hepatitis C virus (HCV) envelope glycoproteins E1 and E2. Independently of the injection route (intramuscular or intraepidermal), plasmids expressing antigens capable of forming heterodimers presumed to be the prebudding form of the HCV envelope protein complex failed to induce any significant, stable antibodies following injection in mice. In sharp contrast, high titers of antibodies directed at both conformational and linear determinants were induced by using plasmids expressing severely truncated antigens that have lost the ability to form native complexes. In addition, only a truncated form of E2 induced antibodies reacting against the hypervariable region 1 of E2 (specifically with the C-terminal part of it) known to contain a neutralization site. When injected intraepidermally into small primates, the truncated E2-encoding plasmid induced antibodies able to neutralize in vitro the binding of a purified E2 protein onto susceptible cells. Because such antibodies have been associated with viral clearance in both humans and chimpanzees, these findings may have important implications for the development of protective immunity against HCV.

Characterization of the humoral and cellular immune responses against hepatitis C virus core induced by DNA-based immunization

Hepatitis C Virus (HCV) causes most cases of posttransfusion hepatitis. Chronic HCV infection is highly related to chronic hepatitis, cirrhosis and hepatocellular carcinoma. Current therapies are only minimally effective and no vaccine has been developed. DNA-based immunization could be of prophylactic and therapeutic value for HCV infection. By intramuscular inoculation in BALB/c mice with an HCV recombinant plasmid pCI-HCV-C, we found significant levels of IgM antibody, but no significant IgG rise. After boost the immunized mice with recombinant HCV-core protein (cp1-10; 1-164aa), the anticore IgG, verified by Western-blotting, rose rapidly, which was two weeks earlier than that with control plasmid. Spleen cells from pCI-HCV-C immunized mice gave higher proliferation index (PI) than control (P < 0.05). The PI of cp1-10 boosted mice was even higher. Proliferation blocking assay with mAb proved the responding cell to be of CD4+ CD8- phenotype, supporting specific priming of T helper cells. A 51Cr-releasing CTL assay specific for HCV-core was developed, and a specific CTL response against HCV-core was demonstrated in both pCI-HCV-C immunized mice and mice boosted with cp1-10. Strong cytotoxic activity against peptide-pulsed p815 cells (H-2d), but not EL-4 cells (H-2b), suggested MHC class I restriction of the CTL activity. Blocking of CTL with mAb proved the effector cells to be of CD4- CD8+. Three CTL epitopes in HCV-core protein were demonstrated. We failed to detect CTL when immunized only with core protein. The results suggested that vaccination with HCV-core derived DNA sequences could be an effective method to induce humoral and cellular immune responses to HCV.

Targeting of hepatitis C virus core protein for MHC I or MHC II presentation does not enhance induction of immune responses to DNA vaccination

We analyzed different vaccine approaches aimed at enhancing CD4(+)- and CD8(+)-dependent responses against hepatitis C virus (HCV) core antigen. Specific DNA vectors expressing various forms of the core in fusion with the ubiquitin or the lysosome-associated membrane protein (LAMP) were generated. These expressed the full-length wildtype core; the full-length core expressed as a covalent fusion with the ubiquitin; the full-length core expressed as a noncovalent fusion with the ubiquitin and containing a N-stabilizing or N-destabilizing residue; and the full-length core expressed as a fusion with the LAMP sequence. In vitro expression levels of the different plasmids differed by as much as tenfold. After injection into mice, none of the plasmids yielded a detectable antibody response, whereas core-specific cytotoxic T-lymphocyte (CTL) activity could be observed with all plasmids as long as 21 weeks postimmunization. No increase in CTL activity (ranging from 7% to 34% specific lysis) was observed with the ubiquitin-fusion-expressed core antigens compared with the wildtype core. The lowest CTL activity (< 5% specific lysis) was observed with the LAMP fusion. This vector was nonetheless unable to induce a detectable proliferative response. Screening of 10 different putative CTL peptide epitopes failed to reveal newly targeted epitopes when the core-fusion plasmids were used compared with the wildtype core-expressing plasmid. These data underline the difficulty in optimizing anti-core cellular immune response using molecular targeting strategies in DNA-based vaccination.

Genetic vaccines

In a few short years, genetic vaccine technology has moved rapidly from a novel concept to an important strategy for the development of human and veterinary vaccines, for numerous indications. This article discusses current areas in which further refinements in technology will influence a variety of infectious disease treatments, including intramuscular and intradermal inoculation, gene gun inoculation, the mechanism of antigen presentation, and the use of genetic adjuvants.

DNA-antiviral vaccines: new developments and approaches--a review

Current vaccines can be divided into "live," "recombinant" and "killed" vaccines. Live vaccines are traditionally composed of attenuated viruses or bacteria, selected for their reduced pathogenicity. Recombinant vaccines, driven by a viral or bacterial vector express foreign antigens, or only recombinant proteins injected as antigen. Killed vaccines consist of inactivated whole pathogens. But all these traditional vaccines have some disadvantages: Attenuated live vaccine are able to undergo mutation and as mutated viruses or bacteria can now provoke the diseases against which the vaccine should protect the organism. A further disadvantage of live vaccines is the possibility of shedding which is a real problem especially in veterinary medicine. Clearly, there is a need for better vaccines to protect against diseases without the disadvantages associated with vaccines presently in use. Modern vaccines might be characterized as safe, no risk of reversion to pathogenicity, and they should be stable without the necessity of a "cold chain." Production should be simple, standardized and inexpensive. Vaccine development has now been improved by the ability to use direct inoculations of plasmid DNA encoding viral or bacterial proteins. One of the major benefits of DNA-vaccines, variously termed "DNA-, genetic- or nucleic acid-immunization," is the endogenous synthesis of the encoded protein. Therefore DNA vaccines mimic natural infection and provoke both strong humoral and cellular immune response. This review summarizes new developments and approaches of DNA vaccination and explains the construction of expression plasmids as well as possible mechanisms of immune responses.

Identification of a domain containing B-cell epitopes in hepatitis C virus E2 glycoprotein by using mouse monoclonal antibodies

Evidence from clinical and experimental studies of human and chimpanzees suggests that hepatitis C virus (HCV) envelope glycoprotein E2 is a key antigen for developing a vaccine against HCV infection. To identify B-cell epitopes in HCV E2, six murine monoclonal antibodies (MAbs), CET-1 to -6, specific for HCV E2 protein were generated by using recombinant proteins containing E2t (a C-terminally truncated domain of HCV E2 [amino acids 386 to 693] fused to human growth hormone and glycoprotein D). We tested whether HCV-infected sera were able to inhibit the binding of CET MAbs to the former fusion protein. Inhibitory activity was observed in most sera tested, which indicated that CET-1 to -6 were similar to anti-E2 antibodies in human sera with respect to the epitope specificity. The spacial relationship of epitopes on E2 recognized by CET MAbs was determined by surface plasmon resonance analysis and competitive enzyme-linked immunosorbent assay. The data indicated that three overlapping epitopes were recognized by CET-1 to -6. For mapping the epitopes recognized by CET MAbs, we analyzed the reactivities of CET MAbs to six truncated forms and two chimeric forms of recombinant E2 proteins. The data suggest that the epitopes recognized by CET-1 to -6 are located in a small domain of E2 spanning amino acid residues 528 to 546.

Genetic Immunization Generates Cellular and Humoral Immune Responses Against the Nonstructural Proteins of the Hepatitis C Virus in a Murine Model

Exposure to hepatitis C virus (HCV) is associated with a high prevalence of persistent viral infection and the development of chronic liver disease and hepatocellular carcinoma. Recovery from acute infection may depend upon the generation of broad-based cellular immune responses to viral structural and nonstructural proteins. We used the DNA-based immunization approach in BALB/c mice to determine whether the HCV nonstructural proteins NS3, NS4, and NS5 will induce Ab responses, CD4+ Th cell proliferation, and cytokine release in response to stimulation by recombinant proteins as well as generate CD8+ CTL activity both in vitro and in vivo. We found that the nonstructural proteins were particularly good immunogens and produced cellular immune responses when administered as a DNA construct. Indeed, a tumor model was established following inoculation of syngenic SP2/0 cells stably transfected with NS5. We observed protection against tumor formation and growth only in mice immunized with the NS5-encoding DNA construct, establishing the generation of significant CTL activity in vivo by this technique. The results indicate that genetic immunization may define the cellular immune response of the host to HCV nonstructural proteins and is a promising approach for vaccine development.

Optimal induction of hepatitis C virus envelope-specific immunity by bicistronic plasmid DNA inoculation with the granulocyte-macrophage colony-stimulating factor gene

In this study, we have constructed various DNA vaccine vectors that carried hepatitis C virus (HCV) envelope genes without and with the granulocyte-macrophage colony-stimulating factor (GM-CSF) gene in several different ways. In Buffalo rats that received plasmids carrying the HCV envelope genes, which encode envelope proteins E1 and E2, both antibody and lymphoproliferative responses against these proteins were induced. These responses were greatly enhanced by the codelivery of the GM-CSF gene. In particular, inoculation with a bicistronic plasmid that independently expressed the GM-CSF gene and the envelope genes in the same construct generated the highest antibody titers and significantly increased lymphoproliferative responses against these proteins. Moreover, strong antibody responses to homologous and heterologous hypervariable region 1 peptides were elicited in the immunized rats.

Characterization of human monoclonal antibodies specific to the hepatitis C virus glycoprotein E2 with in vitro binding neutralization properties

Both linear and conformational determinants of hepatitis C virus (HCV) are believed to be involved in viral neutralization. After immortalization of B cells from HCV chronically infected patients with Epstein-Barr virus, we obtained two polyclonal lymphoblastoid cell lines (LCL) secreting human monoclonal antibodies (HMabs). One clone was derived from a patient infected with a genotype 4 isolate while the second was isolated from a genotype 1b-infected patient. Immunoprecipitation studies, Western blot, and immunofluorescence analysis, peptide scanning, and ELISA studies indicated that the HMabs (1) recognized conformation-dependent determinant(s), (2) were capable of recognizing genotype 1a and 1b derived antigens, and (3) were able to precipitate noncovalently associated E1E2 complexes believed to exist on the surface of virion particles. The HMab derived from the genotype 4-infected patient was in addition shown to neutralize the in vitro binding of recombinant E2 protein onto susceptible cells suggesting a potential for in vivo neutralization. These data indicate that anti-E2 antibodies directed at conserved conformational-dependent determinant(s) exist in chronic HCV infection.

Modulation of immune responses to hepatitis C virus envelope E2 protein following injection of plasmid DNA using single or combined delivery routes

Different delivery routes of plasmid DNA may result in the induction of differential humoral and cellular immunity. We have studied the influence of two main routes of plasmid injection, performed intramuscularly and intraepidermally using a gene gun, for the induction of immune responses specific to hepatitis C virus (HCV) envelope protein E2. Three plasmids expressing different immunogenic domains of E2 (amino acids [aa] 384443, aa 504-555, and aa 384-746) were injected into BALB/c mice according to five different protocols using various combinations of intramuscular (i.m.) or intraepidermal (i.e.) primary and booster injections. Seroconversion rates, antibody titers and isotypes, epitope recognition, and T-helper (Th) release cytokine profiles were analyzed. Antibody titers and epitope recognition were linked to either or both the nature of the immunogen expressed and the delivery route chosen. In all cases, the lowest antibody titers were obtained using single i.m.-based protocols. Independently of the antibody titers generated, only some specific i.e.-combined delivery routes induced antibodies able to recognize determinants located in the N-terminal of E2 (aa 384411 and aa 411437) and mimicked by synthetic peptides. By contrast, the antibody isotypes and the splenic cytokine production identified were independent of the plasmids used and the delivery route implemented. All conditions resulted in Th-1 like responses suggested by the exclusive detection of IgG2a and 2b antibodies and the production of interferon gamma (INF-gamma) but no interleukin-4 (IL-4). Overall, our results suggest that the combination of i.m. and i.e. delivery routes provides the most efficient way to induce a broad immune response against HCV-E2.

Genetic vaccines: strategies for optimization

Vaccination with attenuated or killed microbes, purified or recombinant subunit proteins and synthetic peptides is often hampered by toxicity, the presence of infectious agents, weak immune responses and prohibiting costs, especially in the developing world. Such problems may be circumvented by genetic immunization which has recently emerged as an attractive alternative to conventional vaccines. Numerous studies have already shown that immunization of experimental animals with plasmid DNA encoding antigens from a wide spectrum of bacteria, viruses, protozoa and cancers leads to protective humoral and cell-mediated immunity. This review deals with the background and progress made so far with DNA vaccines and their theoretical and practical advantages as well as potential risks, discusses proposed mechanisms of DNA transfection of cells and induction of immune responses to the produced vaccine antigen, and evaluates strategies for the control and optimization of such responses.