Induction of antibodies against structural proteins of hepatitis C virus in mice using recombinant adenovirus

Vaccine development for zoonotic viral diseases caused by positive‑sense single‑stranded RNA viruses belonging to the Coronaviridae and Togaviridae families (Review)

Outbreaks of zoonotic viral diseases pose a severe threat to public health and economies worldwide, with this currently being more prominent than it previously was human history. These emergency zoonotic diseases that originated and transmitted from vertebrates to humans have been estimated to account for approximately one billion cases of illness and have caused millions of deaths worldwide annually. The recent emergence of severe acute respiratory syndrome coronavirus-2 (coronavirus disease 2019) is an excellent example of the unpredictable public health threat causing a pandemic. The present review summarizes the literature data regarding the main vaccine developments in human clinical phase I, II and III trials against the zoonotic positive-sense single-stranded RNA viruses belonging to the Coronavirus and Alphavirus genera, including severe acute respiratory syndrome, Middle east respiratory syndrome, Venezuelan equine encephalitis virus, Semliki Forest virus, Ross River virus, Chikungunya virus and O'nyong-nyong virus. That there are neither vaccines nor effective antiviral drugs available against most of these viruses is undeniable. Therefore, new explosive outbreaks of these zoonotic viruses may surely be expected. The present comprehensive review provides an update on the status of vaccine development in different clinical trials against these viruses, as well as an overview of the present results of these trials.

Understanding Post Entry Sorting of Adenovirus Capsids; A Chance to Change Vaccine Vector Properties

Adenovirus vector-based genetic vaccines have emerged as a powerful strategy against the SARS-CoV-2 health crisis. This success is not unexpected because adenoviruses combine many desirable features of a genetic vaccine. They are highly immunogenic and have a low and well characterized pathogenic profile paired with technological approachability. Ongoing efforts to improve adenovirus-vaccine vectors include the use of rare serotypes and non-human adenoviruses. In this review, we focus on the viral capsid and how the choice of genotypes influences the uptake and subsequent subcellular sorting. We describe how understanding capsid properties, such as stability during the entry process, can change the fate of the entering particles and how this translates into differences in immunity outcomes. We discuss in detail how mutating the membrane lytic capsid protein VI affects species C viruses' post-entry sorting and briefly discuss if such approaches could have a wider implication in vaccine and/or vector development.

Recent advances and future directions in the management of hepatitis C infections

Current estimates indicate that the hepatitis C virus is the leading cause of death in the United States with infection rates steadily increasing. Successful treatment is made difficult by the presence of various host, virus, and treatment-related factors, warranting the development of new approaches to combat the silent epidemic. The addition of telaprevir and boceprevir to the pharmacotherapeutic arsenal drastically improved success rates in genotype 1 infected patients, but rapid development of resistance mechanisms, increases in adverse effects, and a low spectrum activity proved to be barriers to efficacious treatment. In late 2013, two new agents were approved - sofosbuvir and simeprevir - that have higher barriers to resistance, favorable safety profiles, and profoundly improved success rates; however higher costs associated with the new medications could limit their wider utilization. Further strategies to combat the virus are under development, ranging from interferon-free regimens as well as prophylactic and therapeutic vaccines to applications of nanotechnology, helping us get closer to improved treatment of patients infected with hepatitis C.

An assessment of the use of chimpanzees in hepatitis C research past, present and future: 1. Validity of the chimpanzee model

The USA is the only significant user of chimpanzees in biomedical research in the world, since many countries have banned or limited the practice due to substantial ethical, economic and scientific concerns. Advocates of chimpanzee use cite hepatitis C research as a major reason for its necessity and continuation, in spite of supporting evidence that is scant and often anecdotal. This paper examines the scientific and ethical issues surrounding chimpanzee hepatitis C research, and concludes that claims of the necessity of chimpanzees in historical and future hepatitis C research are exaggerated and unjustifiable, respectively. The chimpanzee model has several major scientific, ethical, economic and practical caveats. It has made a relatively negligible contribution to knowledge of, and tangible progress against, the hepatitis C virus compared to non-chimpanzee research, and must be considered scientifically redundant, given the array of alternative methods of inquiry now available. The continuation of chimpanzee use in hepatitis C research adversely affects scientific progress, as well as chimpanzees and humans in need of treatment. Unfounded claims of its necessity should not discourage changes in public policy regarding the use of chimpanzees in US laboratories.

Expression of structural proteins of hepatitis C virus (HCV) in mammalian cells

The vaccinia viral vector containing T7 promoter was used to construct the expression plasmids carrying HCV structural genes of C, El and E2/NS1. These genes were transiently expressed in mammalian cells in the presence of the T7 RNA polymerase which was provided by the recombinant vaccinia virus vTT7. Expression of mature core protein, envelope protein El and E2 was detected by Western blot using HCV patient sera as the primary antibodies. It was found that the sera from different HCV patients reacted differently with the expressed products, so did the sera collected at different times from the same patient, from whom the HCV structural genes were isolated. Among six mammalian cell lines, Vero and HeLa were the most suitable for the expression of C, El and E2-The recombinant vaccinia viruses have been constructed to constantly produce the C, El and E2 proteins for further research.

Evidence for protection against chronic hepatitis C virus infection in chimpanzees by immunization with replicating recombinant vaccinia virus

Given the failures of nonreplicating vaccines against chronic hepatitis C virus (HCV) infection, we hypothesized that a replicating viral vector may provide protective immunity. Four chimpanzees were immunized transdermally twice with recombinant vaccinia viruses (rVV) expressing HCV genes. After challenge with 24 50% chimpanzee infective doses of homologous HCV, the two control animals that had received only the parental VV developed chronic HCV infection. All four immunized animals resolved HCV infection. The difference in the rate of chronicity between the immunized and the control animals was close to statistical significance (P = 0.067). Immunized animals developed vigorous gamma interferon enzyme-linked immunospot responses and moderate proliferative responses. To investigate cross-genotype protection, the immunized recovered chimpanzees were challenged with a pool of six major HCV genotypes. During the acute phase after the multigenotype challenge, all animals had high-titer viremia in which genotype 4 dominated (87%), followed by genotype 5 (13%). However, after fluctuating low-level viremia, the viremia finally turned negative or persisted at very low levels. This study suggests the potential efficacy of replicating recombinant vaccinia virus-based immunization against chronic HCV infection.

Expression of pIX Gene Induced by Transgene Promoter: Possible Cause of Host Immune Response in First-Generation Adenoviral Vectors

First-generation (FG) adenoviral vectors (AdVs) have been widely used not only for gene therapy but also for basic studies. Because vectors of this type lack the E1A gene that is essential for the expression of other viral genes, their expression levels in target cells have been considered low. However, we found that the viral pIX gene, located immediately downstream of the inserted expression unit of the transgene, was significantly coexpressed with the transgene in cells infected with FG AdV. Whereas CAG and SRalpha promoters activated the pIX promoter considerably through their enhancer effects, the EF1alpha promoter hardly did. Moreover, when the expression unit was inserted in the rightward orientation, not only the pIX protein but also a fusion protein consisting of the N-terminal part of transgene product and pIX were sometimes coexpressed with the transgene product through an aberrant splicing mechanism. In in vivo experiments, a LacZ-expressing AdV bearing the CAG promoter caused an elevation of alanine aminotransferase, but an AdV bearing the EF1alpha promoter produced no detectable levels. Whereas the FG AdV expressing human growth hormone under the control of the CAG promoter maintained a high hormone level for less than 1 month, the FG AdV under the control of the EF1alpha promoter maintained a high level for at least 6 months. These results suggest that pIX coexpression may be one of the main causes of AdV-induced immune responses, and that the EF1alpha promoter is probably valuable for the long-term expression of FG AdV. Thus, the in vivo utility of FG AdV should be reevaluated.

Immunogenic variation between multiple HLA-A*0201-restricted, Hepatitis C Virus-derived epitopes for cytotoxic T lymphocytes

CD8+ cytotoxic T lymphocytes (CTLs) play a critical role in the immune control of Hepatitis C Virus (HCV) infection. In the current study, a number of HLA-A*0201-restricted CTL epitopes derived from HCV were evaluated by examining the peptide-binding affinity for major histocompatibility complex (MHC) class I molecules, the stability of peptide-MHC complexes, killing activities of peptide-induced CTLs, and frequencies of intracellular interferon (IFN)-gamma-positive CD8+ T cells. Among 24 peptides tested, 15 peptides induced high or medium killing activities of peptide-specific CTLs. Thirteen of the 15 peptides exhibited high or medium binding affinities for HLA-A*0201 molecules, indicating that the high binding affinity for MHC class I molecules is an important factor for immunogenicity. In contrast, the stability of peptide-MHC class I complexes was not correlated with killing activities of peptide-induced CTLs. Furthermore, only a limited number of peptides could induce high or medium frequencies of IFN-gamma-producing CD8+ T cells, which were generally considered to play a crucial role for the clearance of HCV. Analyses of the immunogenicity of CTL epitopes such as in the current study should provide important information about the design of an efficient HCV vaccine that induces vigorous, sustained, and broad HCV-specific CTL responses.

Gene therapy for viral hepatitis

Hepatitis B and C infections are two of the most prevalent viral diseases in the world. Existing therapies against chronic viral hepatitis are far from satisfactory due to low response rates, undesirable side effects and selection of resistant viral strains. Therefore, new therapeutic approaches are urgently needed. This review, after briefly summarising the in vitro and in vivo systems for the study of both diseases and the genetic vehicles commonly used for liver gene transfer, examines the existing status of gene therapy-based antiviral strategies that have been employed to prevent, eliminate or reduce viral infection. In particular, the authors focus on the results obtained in clinical trials and experimental clinically relevant animal models.

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.

Protective immunity against alpha-cobratoxin following a single administration of a genetic vaccine encoding a non-toxic cobratoxin variant

Venomous snakebites result in almost 125,000 deaths per year worldwide. We present a new paradigm for the development of vaccines to protect against snakebite, using knowledge of the structure and action of specific toxins combined with a gene-based strategy to deliver a toxin gene modified to render it non-toxic while maintaining its three-dimensional structure and hence its ability to function as an immunogen. As a model for this approach, we developed a genetic vaccine to protect against alpha-cobratoxin (CTX), a potent, post-synaptic neurotoxin that is the major toxic component of the venom of Naja kaouthia, the monocellate cobra. To develop the vaccine, substitutions in the CTX cDNA were introduced at two residues critical for binding to the nicotinic acetylcholine receptor (Asp27 to Arg, Arg33 to Gly). The mutated CTX expression cassette was delivered in the context of a replication deficient adenovirus vector (AdmCTX). To assess whether expression of the mutated CTX in vivo leads to the development of protective immunity, BALB/c mice were challenged by IV administration of 2 microg of alpha-cobratoxin protein 21 or 63 days after administration of AdmCTX or Ad- Null (as a control; both, 10(9) particle units). Animals receiving AdmCTX but no alpha-cobratoxin challenge suffered no ill effects, but > or =80% of naive animals or those receiving the AdNull control vector died within 10 min from the alpha-cobratoxin challenge. In contrast, 100% of animals receiving a single dose of AdmCTX 21 or 63 days prior to alpha-cobratoxin challenge survived. The data demonstrates that an adenovirus-based vaccine can be developed to protect against lethal challenge with a potent snake venom. The effectiveness of this approach might serve as a basis to consider the development of a global public health program to protect those at risk for death by snakebite.

Adenoviruses as vaccine vectors

Adenoviruses have transitioned from tools for gene replacement therapy to bona fide vaccine delivery vehicles. They are attractive vaccine vectors as they induce both innate and adaptive immune responses in mammalian hosts. Currently, adenovirus vectors are being tested as subunit vaccine systems for numerous infectious agents ranging from malaria to HIV-1. Additionally, they are being explored as vaccines against a multitude of tumor-associated antigens. In this review we describe the molecular biology of adenoviruses as well as ways the adenovirus vectors can be manipulated to enhance their efficacy as vaccine carriers. We describe methods of evaluating immune responses to transgene products expressed by adenoviral vectors and discuss data on adenoviral vaccines to a selected number of pathogens. Last, we comment on the limitations of using human adenoviral vectors and provide alternatives to circumvent these problems. This field is growing at an exciting and rapid pace, thus we have limited our scope to the use of adenoviral vectors as vaccines against viral pathogens.

Adjuvant activities of novel cytokines, interleukin-23 (IL-23) and IL-27, for induction of hepatitis C virus-specific cytotoxic T lymphocytes in HLA-A*0201 transgenic mice

Searching the sequence databases has revealed two novel cytokines: interleukin-23 (IL-23) and IL-27. These cytokines are quite similar to, but clearly distinct from IL-12 in their structures and T-cell stimulatory fashions. In contrast to IL-12, however, little is known about the roles of IL-23 and IL-27 in the immune regulation. Previously, we evaluated the prime-boost immunization consisting of priming and the first boosting with the hepatitis C virus (HCV)-core expression plasmid, followed by a second boosting with recombinant adenovirus expressing HCV core for induction of HCV core-specific cytotoxic T lymphocytes (CTLs) in BALB/c mice. The present study demonstrates that HCV-specific CTL induction was greatly enhanced by coinoculation of an IL-12 expression plasmid in the prime-boost immunization, indicating the potent adjuvant activity of IL-12. We investigated whether similar adjuvant effects could be exerted by either IL-23 or IL-27 in a prime-boost immunization with HLA-A*0201 transgenic mice. Coadministration of either an IL-23 or an IL-27 expression plasmid, as well as an IL-12 expression plasmid, in a prime-boost immunization enhanced induction of HCV-specific CTLs and led to dramatic increases in the numbers of gamma interferon (IFN-gamma)-producing, HCV-specific CD8+ cells. Further, preinjections of IL-12, IL-23, or IL-27 expression plasmids before immunization resulted in great increases in the number of IFN-gamma-producing, HCV-specific CD8+ cells in response to immunization with recombinant adenovirus. These data revealed that both IL-23 and IL-27, as well as IL-12, are potent adjuvants for epitope-specific CTL induction. The two novel cytokines might offer new prophylactic and therapeutic strategies against infectious pathogens such as HCV.

Progress on new vaccine strategies against chronic viral infections

Among the most cost-effective strategies for preventing viral infections, vaccines have proven effective primarily against viruses causing acute, self-limited infections. For these it has been sufficient for the vaccine to mimic the natural virus. However, viruses causing chronic infection do not elicit an immune response sufficient to clear the infection and, as a result, vaccines for these viruses must elicit more effective responses--quantitative and qualitative--than does the natural virus. Here we examine the immunologic and virologic basis for vaccines against three such viruses, HIV, hepatitis C virus, and human papillomavirus, and review progress in clinical trials to date. We also explore novel strategies for increasing the immunogenicity and efficacy of vaccines.

A candidate DNA vaccine elicits HCV specific humoral and cellular immune responses

AIM: To investigate the immunogenicity of candidate DNA vaccine against hepatitis C virus (HCV) delivered by two plasmids expressing HCV envelope protein 1 (E1) and envelope protein 2 (E2) antigens respectively and to study the effect of CpG adjuvant on this candidate vaccine.

METHODS: Recombinant plasmids expressing HCV E1 and E2 antigens respectively were used to simultaneously inoculate mice with or without CpG adjuvant. Antisera were then collected and titers of anti-HCV antibodies were analyzed by ELISA. One month after the last injection, animals were sacrificed to prepare single-cell suspension of splenocytes. These cells were subjected to HCV antigen specific proliferation assays and cytokine secretion assays to evaluate the cellular immune responses of the vaccinated animals.

RESULTS: Antibody responses to HCV E1 and E2 antigens were detected in vaccinated animals. Animals receiving CpG adjuvant had slightly lower titers of anti-HCV antibodies in the sera, while the splenocytes from these animals showed higher HCV-antigen specific proliferation. Analysis of cytokine secretion from the splenocytes was consistent with the above results. While no antigen-specific IL-4 secretion was detected for all vaccinated animals, HCV antigen-specific INF-γ secretion was detected for the splenocytes of vaccinated animals. CpG adjuvant enhanced the secretion of INF-γ but did not change the profile of IL-4 secretion.

CONCLUSION: Vaccination of mice with plasmids encoding HCV E1 and E2 antigens induces humoral and cellular immune responses. CpG adjuvant significantly enhances the cellular immune response.

Progress on new vaccine strategies against chronic viral infections

Among the most cost-effective strategies for preventing viral infections, vaccines have proven effective primarily against viruses causing acute, self-limited infections. For these it has been sufficient for the vaccine to mimic the natural virus. However, viruses causing chronic infection do not elicit an immune response sufficient to clear the infection and, as a result, vaccines for these viruses must elicit more effective responses--quantitative and qualitative--than does the natural virus. Here we examine the immunologic and virologic basis for vaccines against three such viruses, HIV, hepatitis C virus, and human papillomavirus, and review progress in clinical trials to date. We also explore novel strategies for increasing the immunogenicity and efficacy of vaccines.

Protective Immunity Evoked Against Anthrax Lethal Toxin After a Single Intramuscular Administration of an Adenovirus-Based Vaccine Encoding Humanized Protective Antigen

Because of the need to develop a vaccine to rapidly protect the civilian population in response to a bioterrorism attack with Bacillus anthracis, we designed AdsechPA, a replication-deficient human serotype 5 adenovirus encoding B. anthracis protective antigen (PA) with codons optimized for expression in mammalian cells. With a single intramuscular administration to mice of 10(9) particle units of AdsechPA, a dose that can be scaled to human use, anti-PA antibodies were evoked more rapidly and at a higher level than with a single administration of the new U.S. military recombinant PA/Alhydrogel vaccine. Importantly, AdsechPA afforded approximately 2.7-fold more protection than the recombinant PA vaccine against B. anthracis lethal toxin challenge 4 weeks after a single vaccination. Even at 11 days postvaccination, AdsechPA provided some survival benefit, whereas the rPA/Alhydrogel vaccine provided none. In the context that equivalent human doses of Ad vectors have already been demonstrated to be safe in humans, a single administration of AdsechPA may provide the means to rapidly protect the civilian population against B. anthracis in response to a bioterrorism attack.

Enhanced induction of hepatitis C virus-specific cytotoxic T lymphocytes and protective efficacy in mice by DNA vaccination followed by adenovirus boosting in combination with the interleukin-12 expression plasmid

We evaluated the prime-boost immunization consisting of hepatitis C virus (HCV)-core expression plasmid (pCEP4-core) and replication-defective adenovirus expressing HCV-core (Adex1SR3ST) for core-specific CTL induction in mice. Compared to a single booster, double boosters after priming enhance CTL induction. The prime-double boosts immunization involving pCEP4-core priming followed by pCEP4-core and Adex1SR3ST boostings (pC/pC/aC) can induce core-specific CTLs as well as other combinations: pC/aC/aC; aC/pC/pC; aC/aC/aC, whereas pC/pC/pC does not induce CTLs. Furthermore, co-administration of interleukin-12 (IL-12) expression plasmid leads to the highly efficient CTL induction and clearance of HCV-core expressing vaccinia virus challenged. Thus, the prime-double boosts immunization together with IL-12 may be promising for HCV vaccine.

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.

Induction of hepatitis C virus-specific cytotoxic T lymphocytes in mice by immunization with dendritic cells transduced with replication-defective recombinant adenovirus

We studied the potential of dendritic cells (DCs) in priming hepatitis C virus (HCV)-specific cytotoxic T lymphocytes (CTLs) in mice. Recombinant adenovirus expressing HCV core (Adex1SR3ST) was employed to express core in DCs. Core-specific CTLs are effectively elicited by injecting Adex1SR3ST-transduced DCs, whereas injection of Adex1SR3ST does not result in effective priming. Further, Adex1SR3ST-transduced DCs more efficiently prime core-specific CTLs than Adex1SR3ST-transduced macrophages, or DCs treated with an anthrax toxin fusion protein reported previously. Upon challenge with recombinant HCV-core-expressing vaccinia virus, vaccinia titers are significantly reduced in mice immunized with Adex1SR3ST-transduced DCs. Thus, adenovirus-transduced DCs may be a promising candidate for a CTL-based vaccine against HCV.

Infection of HepG2 cells with recombinant adenovirus encoding the HCV core protein induces p21(WAF1) down-regulation -- effect of transforming growth factor beta

BACKGROUND/AIMS

Chronic infection with hepatitis C virus leads to liver cirrhosis and hepatocellular carcinoma. Hepatocellular carcinoma is sometimes associated with p53 dysfunction and decreased p21(WAF1) expression. The p21(WAF1) gene is a major target of p53, and p21(WAF1) protein regulates the activities of cyclin/CDK complexes involved in cell cycle control and tumor formation. Because core protein has oncogenic properties, we investigated the expression of p21(WAF1) following core expression.

METHODS

We analyzed by Western blot, Northern blot and transfection the expression of p21(WAF1) in HepG2 cell line under transient expression of Hepatitis C core protein by recombinant-adenoviral infection.

RESULTS AND DISCUSSION

Infection of HepG2 with core-encoding viruses induced the down-regulation of p21(WAF1) expression. This effect is due to a decrease in the p21(WAF1) gene transcription and of the p21(WAF1) protein half-life. These results support a role for Hepatitis C virus core protein in cell transformation. We also found also that the transforming growth factor beta can counteract the core-induced p21(WAF1) down-regulation. The antagonist effect of TGF beta, or of other molecules, on p21(WAF1) expression may be of particular interest for the treatment of HCV-positive hepatocellular carcinoma.

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.

Live and killed rhabdovirus-based vectors as potential hepatitis C vaccines

A highly attenuated, recombinant rabies virus (RV) vaccine strain-based vector was utilized as a new immunization strategy to induce humoral and cellular responses against hepatitis C (HCV) glycoprotein E2. We showed previously that RV-based vectors are able to induce strong immune responses against human immunodeficiency virus type I (HIV-1) antigens. Here we constructed and characterized three replication-competent RV-based vectors expressing either both HCV envelope proteins E1 and E2 or a modified version of E2 which lacks 85 amino acids of its carboxy terminus and contains the human CD4 transmembrane domain and the CD4 or RV glycoprotein cytoplasmic domain. All three constructs stably expressed the respective protein(s) as indicated by Western blotting and immunostaining. Moreover, surface expression of HCV E2 resulted in efficient incorporation of the HCV envelope protein regardless of the presence of the RV G cytoplasmic domain, which was described previously as a requirement for incorporation of foreign glycoproteins into RV particles. Killed and purified RV virions containing HCV E2 were highly immunogenic in mice and also proved useful as a diagnostic tool, as indicated by a specific reaction with sera from HCV-infected patients. In addition, RV vaccine vehicles were able to induce cellular responses against HCV E2. These results further suggest that recombinant RVs are potentially useful vaccine vectors against important human viral diseases.

Immunogenicity of the E1E2 proteins of hepatitis C virus expressed by recombinant adenoviruses

The E1 and E2 proteins of hepatitis C virus (HCV) are believed to be the viral envelope glycoproteins that are major candidate antigens for HCV vaccine development. We reported previously that the replication-competent recombinant adenovirus encoding core-E1-E2 genes of HCV (Ad/HCV) produces serologically reactive E1 and E2 proteins forming a heterodimer in substantial amounts. Here, we examined immunogenicity of the E1E2 proteins copurified from HeLa cells infected with Ad/HCV virus in mice. Furthermore, we constructed a replication-defective recombinant adenovirus encoding the core-E1-E2 genes of HCV (Ad.CMV.HCV) and examined immunogenicity of the virus in mice. The mice immunized intraperitoneally with the copurified E1E2 proteins induced mainly antibodies to E2, but not to E1 by Western blot analysis. The sera of mice immunized with the E1E2 inhibited the binding of E2 protein to the major extracellular loop of human CD81. E2-specific cytotoxic T cells (CTLs), but not antibodies to the E1E2 antigens were induced in the mice intramuscularly immunized with Ad.CMV.HCV virus. When immunized with both Ad.CMV.HCV virus and the E1E2, mice elicited E2-specific CTLs and antibodies to the E1E2 antigens. The results suggest that immunization of Ad.CMV.HCV virus combined with E2 protein is an effective modality to induce humoral as well as cellular immune response to E2 antigen.

A single immunization with a plasmid encoding hepatitis C virus (HCV) structural proteins under the elongation factor 1-alpha promoter elicits HCV-specific cytotoxic T-lymphocytes (CTL)

Recent studies have raised the possibility that DNA-based vaccination may prove useful for generating virus-specific cytotoxic T-lymphocytes (CTL) responses. Recently, a plasmid containing the human elongation factor 1alpha(EF1-alpha) promoter, pEF321, was reported to be a versatile expression vector for gene expression in mammalian cells in vitro. In the present study, we assessed the capability of a novel plasmid, pEFCE1E2, encoding hepatitis C virus (HCV) structural proteins (core, E1 and E2) under the EF1-alpha promoter to generate CTL against HCV in vivo. BALB/c mice were immunized with the pEFCE1E2 but not with a plasmid possessing the same cDNA under the cytomegalovirus developed HCV-specific effector cells by a single immunization. These effector cells elicited by pEFCE1E2 immunization were CD8(+) and major histocompatibility complex class I restricted. These studies provided evidence for the potential utility of the EF1-alpha promoter for development of DNA vaccines against HCV infections.

Transcription map and expression of bovine herpesvirus-1 glycoprotein D in early region 4 of bovine adenovirus-3

Early region 4 (E4) of bovine adenovirus type 3 (BAV-3) was analyzed by Northern blotting, RT-PCR analysis, cDNA sequencing, and S1 nuclease protection assays. The transcriptional map of the E4 region of BAV-3 has marked dissimilarities from those of mouse adenovirus-1, ovine adenovirus-287, and human adenovirus-2, for which the transcriptional maps have been constructed. The E4 region of BAV-3, located between 98.6 and 89.8 MU transcribes seven distinct classes of bovine adenovirus type 3 mRNA. The seven mRNA species formed by the removal of one to three introns share both the 3' end and a short 5' leader (25 nucleotides). The E4 mRNAs can encode at least five unique polypeptides, namely, 143R1, 69R, 143R2, 268R, and 219R. Isolation of a replication-competent recombinant "BAV404" containing 1.9-kb insertion [glycoprotein (gD) of bovine herpesvirus 1, under the control of a SV40 early promoter and poly(A)] in the region between E4 and the right ITR suggested that this region is nonessential for BAV-3 replication. Expression of gD by BAV404 recombinant virus was confirmed by immunoprecipitation with gD-specific monoclonal antibodies. Analysis of the kinetics of protein expression indicated that gD is expressed at both early and late times postinfection. These results suggest that: (a) E4 produces seven 5'-3' coterminal mRNAs and (b) the right terminal region of BAV-3 can be used for the expression of vaccine antigens.

High titers of antibodies inhibiting the binding of envelope to human cells correlate with natural resolution of chronic hepatitis C

Most cases of hepatitis C virus (HCV) infection result in chronic disease; however, a very small fraction of patients naturally clear the virus and resolve chronic hepatitis. In an attempt to correlate immune response with chronic disease resolution, we compared the antibody response in patients with different outcomes of the infection. Antibody responses to HCV structural proteins were assessed in 34 patients originally diagnosed with acute hepatitis. Five cases resolved acute infection, 22 developed chronic hepatitis, and 7 naturally resolved chronic hepatitis C. To estimate HCV neutralizing antibodies we used the neutralization of binding (NOB) assay, which evaluates inhibition of the envelope-2 protein binding to human cells. Enzyme-linked immunosorbent assay was used for the quantitative assessment of serum antibodies. The presence of HCV RNA was ascertained by reverse transcription-polymerase chain reaction. In 6 of 7 patients naturally recovered from chronic hepatitis C, the emergence and the persistence (for more than 3 months) of high serum titers (>1/600) of NOB antibodies coincided with virus clearance and clinical resolution of hepatitis. NOB antibody activity was observed in only 2 of 5 patients recovered from acute hepatitis C. Chronic patients who did not show any resolution during the course of the study developed low or no NOB antibodies. Because of the correlation between prolonged high NOB titers and natural resolution of chronic hepatitis C, vaccination or passive immunization aimed at high titers of NOB antibodies may be valuable new therapeutic approaches for chronic hepatitis C.

Prevention of hepatitis C virus infection

Despite the promising progress made in the development of experimental HCV hyperimmune globulin preparations and recombinant vaccines, prevention of HCV infection will continue to be an important research front for many years. Until effective and safe immunoprophylaxis is available, preventive efforts will require further understanding of risk factors associated with infection and implementation of strategies to reduce such exposures.

Recombinant viruses as vaccines and immunological tools

Recombinant viruses have been investigated as candidate vaccines, and have also been used extensively as immunological tools. Recent advances in this area include the following: the construction and testing of a recombinant simian immunodeficiency virus encoding human interferon-gamma; the development of new vectors such as recombinant poliovirus; and the generation of polyepitope vaccines. Basic immunological research has benefited from the use of recombinant viruses to further understand the role of molecules such as CD40 ligand, nitric oxide and interleukin-4.

Induction of cytotoxic T-cell response against hepatitis C virus structural antigens using a defective recombinant adenovirus

A replication-defective recombinant adenovirus (RAd), RAdCMV-CE1, containing core and E1 genes of hepatitis C virus (HCV) was constructed. RAdCMV-CE1 was able to express core and E1 proteins both in mice and human cells. Immunization of BALB/c mice with RAdCMV-CE1 induced a specific cytotoxic T-cell response against the two HCV proteins. This response was characterized using a panel of 60 synthetic 14- or 15-mer overlapping peptides (10 amino-acid overlap) spanning the entire sequence of these proteins. Five main epitopes were found in the core protein, four of which had been previously described either in mice or humans. One single novel epitope was found in E1. Fine mapping of this E1 determinant, showed that octamer GHRMAWDM is the minimal epitope recognized by cytotoxic T lymphocytes (CTL). The cytotoxic T-cell response was H-2d restricted, lasted for at least 100 days, and was mediated by T cells with the classic CD4-CD8+ phenotype. This work demonstrates that replication-defective recombinant adenoviruses can efficiently express HCV proteins and are able to induce an in vivo cytotoxic T-cell response against a diversity of epitopes from HCV antigens. These vectors should be taken into consideration in the design of vaccines and also as a means to stimulate specific T-cell responses in chronic HCV carriers.

Plasmid DNA expressing a secreted or a nonsecreted form of hepatitis C virus nucleocapsid: comparative studies of antibody and T-helper responses following genetic immunization

In a murine model, we have compared humoral and T-helper (Th) responses induced following genetic immunization with two hepatitis C virus (HCV) plasmid-derived immunogens: a plasmid expressing the full-length nucleocapsid (CAP) as a nonsecreted antigen (pCMVC2) and a plasmid expressing the amino-terminal part of CAP as a secreted antigen (pS2S.C2N). In BALB/c mice, intramuscular injection of either plasmid induced IgG2a antibodies associated with a Th1-like profile characterized by the in vitro splenic production of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma). The pS2S.C2N plasmid induced antibody titers three- to five-fold higher than those obtained with the pCMVC2 plasmid (maximal titers 1:1,500 versus 1:500). In control experiments, immunization using purified CAP antigen induced a predominant, but not exclusive, Th2-like profile as determined by the splenic production of IL-4 and IL-10. Six putative Th determinants were identified using a panoply of overlapping synthetic peptides in in vitro stimulation assays: amino acids 20-44, 39-63, 79-113, 89-113, 118-142, and 138-152. For all CAP immunogens, MHC haplotype of immunized mice was found to influence seroconversion rates but not the type of cytokines produced in vitro. H-2d mice were faster responders and displayed recall T-cell activation by a larger number of peptides than H-2b mice, whereas H-2s mice were overall very poor responders. Splenic stimulation by at least one determinant, amino acids 79-103, appeared to be highly specific of the H-2b background and of DNA immunization only. These data indicate that DNA immunogens expressing different forms of HCV-CAP are not associated with different Th profiles but rather different seroconversion rates and antibody titers and that collaboration of distinct T-help epitopes can be restricted by the MHC background.