Immune responses to plasmid DNA encoding the hepatitis C virus core protein

The Immunogenicity in Mice of HCV Core Delivered as DNA Is Modulated by Its Capacity to Induce Oxidative Stress and Oxidative Stress Response

HCV core is an attractive HCV vaccine target, however, clinical or preclinical trials of core-based vaccines showed little success. We aimed to delineate what restricts its immunogenicity and improve immunogenic performance in mice. We designed plasmids encoding full-length HCV 1b core and its variants truncated after amino acids (aa) 60, 98, 152, 173, or up to aa 36 using virus-derived or synthetic polynucleotides (core191/60/98/152/173/36_191v or core152s DNA, respectively). We assessed their level of expression, route of degradation, ability to trigger the production of reactive oxygen species/ROS, and to activate the components of the Nrf2/ARE antioxidant defense pathway heme oxygenase 1/HO-1 and NAD(P)H: quinone oxidoreductase/Nqo-1. All core variants with the intact N-terminus induced production of ROS, and up-regulated expression of HO-1 and Nqo-1. The capacity of core variants to induce ROS and up-regulate HO-1 and Nqo-1 expression predetermined their immunogenicity in DNA-immunized BALB/c and C57BL/6 mice. The most immunogenic was core 152s, expressed at a modest level and inducing moderate oxidative stress and oxidative stress response. Thus, immunogenicity of HCV core is shaped by its ability to induce ROS and oxidative stress response. These considerations are important in understanding the mechanisms of viral suppression of cellular immune response and in HCV vaccine design.

Design and expression of fusion protein consists of HBsAg and Polyepitope of HCV as an HCV potential vaccine

BACKGROUND

Hepatitis C virus (HCV) infection is a serious public health threat worldwide. Cellular immune responses, especially cytotoxic T-lymphocytes (CTLs), play a critical role in immune response toward the HCV clearance. Since polytope vaccines have the ability to stimulate the cellular immunity, a recombinant fusion protein was developed in this study.

MATERIALS AND METHODS

The designed fusion protein is composed of hepatitis B surface antigen (HBsAg), as an immunocarrier, fused to an HCV polytope sequence. The polytope containing five immunogenic epitopes of HCV was designed to induce specific CTL responses. The construct was cloned into the pET-28a, and its expression was investigated in BL21 (DE3), BL21 pLysS, BL21 pLysE, and BL21 AI Escherichia coli strains using 12% gel sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Finally, the identity of expressed fusion protein was confirmed by Western blotting using anti-His monoclonal antibody and affinity chromatography was applied to purify the expressed protein.

RESULTS

The accuracy of the construct was confirmed by restriction map analysis and sequencing. The transformation of the construct into the BL21 (DE3), pLysS, and pLysE E. coli strains did not lead to any expression. The fusion protein was found to be toxic for E. coli DE3. By applying two steps inhibition, the fusion protein was successfully expressed in BL21 (AI) E. coli strain.

CONCLUSION

The HBsAg-polytope fusion protein expressed in this study can be further evaluated for its immunogenicity in animal models.

Evasion of TNF-α-mediated apoptosis by hepatitis C virus

Hepatitis C virus (HCV) often causes chronic infection in humans, although the mechanisms for viral chronicity are not clearly understood. Tumor necrosis factor-α (TNF-α)-mediated apoptosis is a key element in a host organism's defense inhibiting viral spread and persistence. HCV has evolved mechanisms that antagonize host cell death signals so that virus propagation can continue unabated in infected cells. HCV core protein blocks TNF-α-mediated apoptosis signaling and inhibits caspase-8 activation by sustaining the expression of cellular FADD-like interleukin-1β-converting enzyme (FLICE)-like inhibitory protein (c-FLIP). HCV core protein also blocks TNF-induced proteolytic cleavage of the death substrate poly (SDP-ribose) polymerase from its native 116-kDa protein to the characteristic 85-kDa polypeptide. A decrease in endogenous c-FLIP by specific small-interfering RNA induces TNF-α-mediated apoptotic cell death and caspase-8 activation. However, HCV core neither affects the association between TNF receptor 1 (TNFR1) and TNFR1-associated death domain protein (TRADD) nor TRADD-Fas-associated death domain protein (FADD) and procaspase-8. Thus, HCV core protein appears to play a role in the inhibition of TNF-α-mediated cell death. This chapter describes methods to identify inhibitory mechanism of HCV for TNF-α-mediated apoptosis.

DNA vaccine expressing the non-structural proteins of hepatitis C virus diminishes the expression of HCV proteins in a mouse model

Most of the people infected with hepatitis C virus (HCV) develop chronic hepatitis, which in some cases progresses to cirrhosis and ultimately to hepatocellular carcinoma. Although various immunotherapies against the progressive disease status of HCV infection have been studied, a preventive or therapeutic vaccine against this pathogen is still not available. In this study, we constructed a DNA vaccine expressing an HCV structural protein (CN2), non-structural protein (N25) or the empty plasmid DNA as a control and evaluated their efficacy as a candidate HCV vaccine in C57BL/6 and novel genetically modified HCV infection model (HCV-Tg) mice. Strong cellular immune responses to several HCV structural and non-structural proteins, characterized by cytotoxicity and interferon-gamma (IFN-γ) production, were observed in CN2 or N25 DNA vaccine-immunized C57BL/6 mice but not in empty plasmid DNA-administered mice. The therapeutic effects of these DNA vaccines were also examined in HCV-Tg mice that conditionally express HCV proteins in their liver. Though a reduction in cellular immune responses was observed in HCV-Tg mice, there was a significant decrease in the expression of HCV protein in mice administered the N25 DNA vaccine but not in mice administered the empty plasmid DNA. Moreover, both CD8(+) and CD4(+) T cells were required for the decrease of HCV protein in the liver. We found that the N25 DNA vaccine improved pathological changes in the liver compared to the empty plasmid DNA. Thus, these DNA vaccines, especially that expressing the non-structural protein gene, may be an alternative approach for treatment of individuals chronically infected with HCV.

A Plasmid Encoding Japanese Encephalitis Virus PrM and E Proteins Elicits Protective Immunity in Suckling Mice

A plasmid encoding Japanese encephalitis virus (JEV) prM and E proteins was constructed, and its efficacy as a candidate vaccine against JEV was evaluated in suckling mice. Groups of 10 BALB/c mice (5-7 days old) were immunized twice via muscular injection with this DNA vaccine, an empty vector or PBS at an interval of 3 weeks, and were challenged with a lethal dose of JEV 3 weeks after the second inoculation. Both cellular and humoral immune responses were examined before the challenge. Two animals from each group were sacrificed to detect the JEV-specific cytotoxic T lymphocyte activity. JEV-specific lactate dehydrogenase release in the DNA vaccine, empty vector and PBS groups was 37.5%, 18% and 8.5% respectively. JEV-specific antibody was detected in 8 of 10 animals in DNA vaccine group with a geometrical mean titer of 1: 28.3. The pooled serum from the same group also showed a neutralizing activity. Six of 8 mice in the DNA vaccine group survived the challenge, with a protection rate of 75%, but all the mice died in the two control groups. These results show that this JEV prM and E DNA vaccine is immunogenic and protective against JEV infection in the mouse model.

Biosafety of the plasmid pcDNA3-1E of Eimeria acervulina in chicken

To evaluate the biosafety of the plasmid pcDNA3-1E of Eimeria acervulina in chicken, two-week-old chickens were injected intramuscularly with the plasmid pcDNA3-1E at dose of 50 μg/chicken. At the 15 days post-injection, the tissue samples were collected, the total DNA was extracted, and the 3-1E gene was amplified by PCR. Genomic DNA was first purified away from free plasmid using gel electrophoresis, and then assayed for integrated plasmid using PCR amplification of the 3-1E gene. Simultaneously, the environmental dejection samples were collected, the total bacterial DNA was extracted and then transfer of the pcDNA3-1E gene was detected by PCR amplification of the 3-1E gene. Two-week-old chickens were injected intramuscularly with the plasmid pcDNA3-1E with three dosage groups of 100 μg, 500 μg and 2500 μg/chicken for 14 days respectively, and with physiological saline at dose of 2500 μL/chicken as control group for acute toxicity test. A target band of 583 bp was obtained by PCR with chicken genomic DNA as template. If the chicken genomic DNA was purified, no target band could be obtained. It showed that the recombinant plasmid pcDNA3-1E existed in tissues, and no genomic integration of DNA plasmid was detected in the immunized chickens. No target band was found by PCR with environmental dejection bacteria genomic DNA as template. It showed that integration and transfer phenomenon did not exist in environment. The acute toxicity results showed the typical clinical symptoms did not occur in the inoculated chickens, the blood biochemical indices and viscera configuration were not affected significantly in the inoculated group and control group (P>0.05). The results showed that the plasmid pcDNA3-1E was safe and suitable for chicken clinical trials.

Inhibition of the HCV core protein on the immune response to HBV surface antigen and on HBV gene expression and replication in vivo

The hepatitis C virus (HCV) core protein is a multifunctional protein that can interfere with the induction of an immune response. It has been reported that the HCV core protein inhibits HBV replication in vitro. In this study, we test the effect of the HCV core gene on the priming of the immune response to hepatitis B surface antigen (HBsAg) and on the replication of HBV in vivo. Our results showed that the full-length HCV core gene inhibits the induction of an immune response to the heterogeneous antigen, HBsAg, at the site of inoculation when HCV core (pC191) and HBsAg (pHBsAg) expression plasmids are co-administered as DNA vaccines into BALB/c mice. The observed interference effect of the HCV core occurs in the priming stage and is limited to the DNA form of the HBsAg antigen, but not to the protein form. The HCV core reduces the protective effect of the HBsAg when the HBsAg and the HCV core are co-administered as vaccines in an HBV hydrodynamic mouse model because the HCV core induces immune tolerance to the heterogeneous HBsAg DNA antigen. These results suggest that HCV core may play an important role in viral persistence by the attenuation of host immune responses to different antigens. We further tested whether the HCV core interfered with the priming of the immune response in hepatocytes via the hydrodynamic co-injection of an HBV replication-competent plasmid and an HCV core plasmid. The HCV core inhibited HBV replication and antigen expression in both BALB/c (H-2d) and C57BL/6 (H-2b) mice, the mouse models of acute and chronic hepatitis B virus infections. Thus, the HCV core inhibits the induction of a specific immune response to an HBsAg DNA vaccine. However, HCV C also interferes with HBV gene expression and replication in vivo, as observed in patients with coinfection.

Advances in hepatitis C virus vaccines, part two: advances in hepatitis C virus vaccine formulations and modalities

INTRODUCTION

Developing a vaccine against HCV is an important medical and global priority. Unavailability and potential dangers associated with using attenuated HCV viral particles for vaccine preparation have resulted in the use of HCV genes and proteins formulated in novel vaccine modalities.

AREAS COVERED

In part one of this review, advances in basic knowledge for HCV vaccine design were provided. Herein, a detailed and correlated patents (searched by Espacenet) and literatures (searched by Pubmed) review on HCV vaccine formulations and modalities is provided, including: subunit, DNA, epitopic-peptide/polytopic, live vector- and whole yeast-based vaccines. Less-touched areas in vaccine studies such as mucosal, plant-based, and chimeric HBV/HCV vaccines are also discussed. Furthermore, results of preclinical/clinical studies on selected HCV vaccines as well as pros and cons of different strategies are reviewed. Finally, potential strategies for creation and/or improvement of HCV vaccine formulations are discussed.

EXPERT OPINION

Promising outcomes of a few HCV vaccine modalities in phase I/II clinical trials predict the accessibility of at least partially effective vaccines to inhibit or treat the chronic state of HCV infection (specially in combination with standard antiviral therapy). ChronVac-C (plasmid DNA), TG4040 (MVA-based), and GI-5005 (whole yeast-based) might be the most obvious HCV vaccine candidates to be approved in the near future.

The wild-type hepatitis C virus core inhibits initiation of antigen-specific T- and B-cell immune responses in BALB/c mice

In this study, the effects of wild-type and deletion mutant hepatitis C virus (HCV) core proteins on the induction of immune responses in BALB/c mice were assessed. p2HA-C145-S23, encoding a core protein with the C-terminal 46 amino acids truncated, significantly produced stronger antibody and cellular responses than p2HA-C191-S23. The induction of immune responses by p2HA-C145-S23 was dose dependent. However, increasing the doses or repeated administration did not enhance immune responses by the wild-type core protein. In addition, p2HA-C191-S23 was apparently able to interfere with the priming of specific immune responses by p2HA-C145-S23 when the two were coadministered. These results demonstrated that the wild-type HCV core protein itself could inhibit the priming of immune responses in the course of a DNA vaccination, whereas the truncated HCV core protein could provide potential applications for the development of DNA- and peptide-based HCV vaccines.

Construction and immunological evaluation of multivalent hepatitis B virus (HBV) core virus-like particles carrying HBV and HCV epitopes

A multivalent vaccine candidate against hepatitis B virus (HBV) and hepatitis C virus (HCV) infections was constructed on the basis of HBV core (HBc) virus-like particles (VLPs) as carriers. Chimeric VLPs that carried a virus-neutralizing HBV pre-S1 epitope corresponding to amino acids (aa) 20 to 47 in the major immunodominant region (MIR) and a highly conserved N-terminal HCV core epitope corresponding to aa 1 to 60 at the C terminus of the truncated HBcDelta protein (N-terminal aa 1 to 144 of full-length HBc) were produced in Escherichia coli cells and examined for their antigenicity and immunogenicity. The presence of two different foreign epitopes within the HBc molecule did not interfere with its VLP-forming ability, with the HBV pre-S1 epitope exposed on the surface and the HCV core epitope buried within the VLPs. After immunization of BALB/c mice, specific T-cell activation by both foreign epitopes and a high-titer antibody response against the pre-S1 epitope were found, whereas an antibody response against the HBc carrier was notably suppressed. Both inserted epitopes also induced a specific cytotoxic-T-lymphocyte (CTL) response, as shown by the gamma interferon (IFN-gamma) production profile.

Identification and structural definition of H5-specific CTL epitopes restricted by HLA-A*0201 derived from the H5N1 subtype of influenza A viruses

The haemagglutinin (HA) glycoprotein of influenza A virus is a major antigen that initiates humoral immunity against infection; however, the cellular immune response against HA is poorly understood. Furthermore, HA-derived cytotoxic T-lymphocyte (CTL) epitopes are relatively rare in comparison to other internal gene products. Here, CTL epitopes of the HA serotype H5 protein were screened. By using in silico prediction, in vitro refolding and a T2 cell-binding assay, followed by immunization of HLA-A2.1/K(b) transgenic mice, an HLA-A*0201-restricted decameric epitope, RI-10 (H5 HA205-214, RLYQNPTTYI), was shown to elicit a robust CTL epitope-specific response. In addition, RI-10 and its variant, KI-10 (KLYQNPTTYI), were also demonstrated to be able to induce a higher CTL epitope-specific response than the influenza A virus dominant CTL epitope GL-9 (GILGFVFTL) in peripheral blood mononuclear cells of HLA-A*0201-positive patients who had recovered from H5N1 virus infection. Furthermore, the crystal structures of RI-10-HLA-A*0201 and KI-10-HLA-A*0201 complexes were determined at 2.3 and 2.2 A resolution, respectively, showing typical HLA-A*0201-restricted epitopes. The conformations of RI-10 and KI-10 in the antigen-presenting grooves in crystal structures of the two complexes show significant differences, despite their nearly identical sequences. These results provide implications for the discovery of diagnostic markers and the design of novel influenza vaccines.

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.

Characterization of cytotoxic T-lymphocyte epitopes and immune responses to SARS coronavirus spike DNA vaccine expressing the RGD-integrin-binding motif

Integrins are critical for initiating T‐cell activation events. The integrin‐binding motif Arg‐Gly‐Asp (RGD) was incorporated into the pcDNA 3.1 mammalian expression vector expressing the codon‐optimized extracellular domain of SARS coronavirus (SARS‐CoV) spike protein, and tested by immunizing C57BL/6 mice. Significant cell‐mediated immune responses were characterized by cytotoxic T‐lymphocyte ⁵¹Cr release assay and interferon‐gamma secretion ELISPOT assay against RMA‐S target cells presenting predicted MHC class I H2‐Kb epitopes, including those spanning residues 884–891 and 1116–1123 within the S2 subunit of SARS‐CoV spike protein. DNA vaccines incorporating the Spike‐RGD/His motif or the Spike‐His construct generated robust cell‐mediated immune responses. Moreover, the Spike‐His DNA vaccine construct generated a significant antibody response. Immunization with these DNA vaccine constructs elicited significant cellular and humoral immune responses. Additional T‐cell epitopes within the SARS‐CoV spike protein that may contribute to cell‐mediated immunity in vivo were also identified. J. Med. Virol. 81:1131–1139, 2009. © 2009 Wiley‐Liss, Inc.

Enhancement of the expression of HCV core gene does not enhance core-specific immune response in DNA immunization: advantages of the heterologous DNA prime, protein boost immunization regimen

BACKGROUND

Hepatitis C core protein is an attractive target for HCV vaccine aimed to exterminate HCV infected cells. However, although highly immunogenic in natural infection, core appears to have low immunogenicity in experimental settings. We aimed to design an HCV vaccine prototype based on core, and devise immunization regimens that would lead to potent anti-core immune responses which circumvent the immunogenicity limitations earlier observed.

METHODS

Plasmids encoding core with no translation initiation signal (pCMVcore); with Kozak sequence (pCMVcoreKozak); and with HCV IRES (pCMVcoreIRES) were designed and expressed in a variety of eukaryotic cells. Polyproteins corresponding to HCV 1b amino acids (aa) 1-98 and 1-173 were expressed in E. coli. C57BL/6 mice were immunized with four 25-microg doses of pCMVcoreKozak, or pCMV (I). BALB/c mice were immunized with 100 microg of either pCMVcore, or pCMVcoreKozak, or pCMVcoreIRES, or empty pCMV (II). Lastly, BALB/c mice were immunized with 20 microg of core aa 1-98 in prime and boost, or with 100 microg of pCMVcoreKozak in prime and 20 microg of core aa 1-98 in boost (III). Antibody response, [3H]-T-incorporation, and cytokine secretion by core/core peptide-stimulated splenocytes were assessed after each immunization.

RESULTS

Plasmids differed in core-expression capacity: mouse fibroblasts transfected with pCMVcore, pCMVcoreIRES and pCMVcoreKozak expressed 0.22 +/- 0.18, 0.83 +/- 0.5, and 13 +/- 5 ng core per cell, respectively. Single immunization with highly expressing pCMVcoreKozak induced specific IFN-gamma and IL-2, and weak antibody response. Single immunization with plasmids directing low levels of core expression induced similar levels of cytokines, strong T-cell proliferation (pCMVcoreIRES), and antibodies in titer 103(pCMVcore). Boosting with pCMVcoreKozak induced low antibody response, core-specific T-cell proliferation and IFN-gamma secretion that subsided after the 3rd plasmid injection. The latter also led to a decrease in specific IL-2 secretion. The best was the heterologous pCMVcoreKozak prime/protein boost regiment that generated mixed Th1/Th2-cellular response with core-specific antibodies in titer >or= 3 x 10(3).

CONCLUSION

Thus, administration of highly expressed HCV core gene, as one large dose or repeated injections of smaller doses, may suppress core-specific immune response. Instead, the latter is induced by a heterologous DNA prime/protein boost regiment that circumvents the negative effects of intracellular core expression.

Molecular therapy and prevention of liver diseases

Molecular analyses have become an integral part of biomedical research as well as clinical medicine. The definition of the molecular and genetic basis of many human diseases has led to a better understanding of their pathogenesis and has in addition offered new perspectives for their diagnosis, therapy and prevention. Genetically, liver diseases can be classified as hereditary monogenic, acquired monogenic, complex genetic and diseases. Based on this classification, gene therapy is based on six concepts: gene repair, gene substitution, cell therapy, block of gene expression or function, DNA vaccination as well as gene augmentation. While recent developments are promising, various delivery, targeting and safety issues need to be addressed before gene therapy will enter clinical practice. In the future, molecular diagnosis and therapy liver diseases will be part of our patient management and complement existing diagnostic, therapeutic and preventive strategies.

Hepatitis B virus precore protein augments genetic immunizations of the truncated hepatitis C virus core in BALB/c mice

DNA immunization has been used to induce either humoral or cellular immune responses against many antigens, including hepatitis C virus (HCV). In addition, DNA immunizations can be enhanced or modulated at the nucleotide level. Genetic immunizations were examined in BALB/c mice through the use of plasmids and chimeric DNA constructs encoding HCV core proteins and hepatitis B virus (HBV) precore (preC) regions. Plasmids encoding the truncated HCV core induced potent humoral and cellular responses to HCV; pcDNA3.0A-C154 produced a stronger antibody response than pcDNA3.0A-C191 (P < 0.01) and pcDNA3.0A-C69 (P < 0.05). HBV preC enhanced the humoral and cellular immune responses of BALB/c mice to HCV; however, pcDNA3.0A-C69preC resulted in a weak cytotoxic T lymphocyte (CTL) response. In addition, the humoral and cellular immune responses to HCV of groups immunized with pcDNA3.0A-C154preC and pcDNA3.0A-C191preC plasmids were higher than those of groups immunized with pcDNA3.0A-C154 and pcDNA3.0A-C191. In vivo CTL responses verified that mice immunized with preC core fused DNAs showed significantly high specific lysis compared with mice immunized with HCV cores only (P < 0.01). In our study, pcDNA3.0A-C154preC led to the highest immune response among all DNA constructs.

CONCLUSION

DNA that encodes truncated HCV core proteins may lead to increased immune responses in vivo, and these responses may be enhanced by HBV preC.

Cancerogenic effect of different fragments of the hepatitis C virus core protein

The hepatitis C virus core protein plays an extremely important role in the hepatocarcinogenesis of hepatitis C virus. Little, however, is known about the oncogenic potency of fragments. Thus, the purpose of the present study is to investigate the cancerogenic effects of the different core protein fragments. Two series of recombinant plasmids containing hepatitis C virus core gene fragments encoding the different-length core protein were constructed using plasmid enhanced green fluorescent protein (pEGFP)-C1 and pcDNA3.1(+), respectively. Human hepatocyte L02 cells transiently transfected with pEGFP-C1-based plasmids were subjected to confocal laser scanning microscopy analysis to determine the localization of the different core protein fragments. The stably transfected L02 cells with the pcDNA3.1(+)-based core protein plasmids were used to investigate the ultrastructural effects of the core protein and the tumorigenicity of L02 cells expressing core protein fragments in athymic nude mice. The full-length core protein and Core130-191 were completely localized in the cytoplasm, while Core1-59 existed exclusively in the nucleus. On the other hand, Core50-140 and Core1-140 were observed in both the nucleus and the cytoplasm. Ultrastructural changes of L02 cells expressing the full-length core protein were comprehensive and included, for example, irregular nuclear, increased nuclear/cytoplasmic ratio and mitochondria swelling. The slight changes were observed in the cells expressing Core50-140 and Core130-191, whereas the ultrastructure of the cells expressing Core1-59 remained normal. All the L02 cells stably expressing different fragments of the core protein, with the exception of the C-terminal truncated fragment Core1-59, could induce the occurrence of tumor in the nude mice. The N-terminal fragment of the core protein, Core1-59, was not oncogenic, while the intermediate and posterior segments of the hepatitis C virus core protein had the cancerogenic potency. In view of the existence of many important immunogenic epitopes in it, the core protein anterior segment might be a safer candidate for the development of hepatitis C virus vaccine.

Increased Body Weight Via Injecting Myogenic Expression Growth Hormone-Releasing Hormone (GHRH) Plasmid DNA into Sheep

The ectopic expression of a sheep growth hormone-releasing hormone (GHRH) from muscle tissues, using a myogenic plasmid expression vector pM-GHRH, has been shown to result in enhanced animal growth. Animal injected with pM-GHRH alone exhibited a daily weight gain rate of 0.84+/-0.02%/d (p < 0.05), while that of the control animal was only 0.73+/-0.04%/d. A more significant growth enhancement was observed in the group treated with pM-GHRH plus 0.25% bupivacaine. The animal displayed a daily weight gain rate of 0.87+/-0.03%/d (p<0.01). In addition, the group treated by pM-GHRH and bupivacaine had higher levels of growth hormone (GH) in their blood (1.18+/-0.33 ng/mL) compared with the group treated by pM-GHRH vector alone (p < 0.05). Evaluation of body composition by dissection and histochemical analysis indicated a significant increase in bulk with no organomegaly or associated pathology. PCR analysis demonstrated that there was little plasmid residue detected in the pM-GHRH treated sheep.

Immunologic Analysis Induced by DNA Vaccine Encoding E Protein of Beijing-1 Strain Derived from Japanese Encephalitis Virus

OBJECTIVE

We have compared the gene expression and DNA immunization efficacy encoding prME and E proteins of a different strain (JaGAr-01) derived from Japanese encephalitis virus. This study aimed to construct a recombinant encoding E protein of the Beijing-1 strain derived from Japanese encephalitis virus and analyze the humoral, cellular and protective immunity induced by the above recombinant.

METHODS

The recombinant pJBE containing E (1,500 bps) gene from the Beijing-1 strain of Japanese encephalitis virus was constructed and then transfected into the HepG2 cell line by liposome fusion. The expression of E (about 53 kD) protein in transfected cells was analyzed by Western blot using a specific anti-JEV-E antibody. BALB/c mice were vaccinated with 3 microg of pJBE by the gene-gun technique. JaGAr-01 and Beijing-1 strains (10(5) PFU/100 microl) of Japanese encephalitis virus were given to BALB/c mice by intraperitoneal injection 3 weeks after double DNA immunization with a lethal virus challenge. BALB/c mice were observed for 21 days after challenge. An 80% plaque reduction neutralization test was performed to titrate the neutralization antibody before and after viral challenge. A lactate dehydrogenase activity release test was used to examine cytotoxic T lymphocyte activity after double DNA immunization.

RESULTS

The expression of about 53 kD protein associated with pJBE was determined in transfected HepG2 cells with specific anti-JEV-E antibody. A higher level of neutralization antibodies and the cytotoxicity effect were induced with pJBE immunization using the gene-gun technique, and were similar to those induced with inactivated vaccine derive from the Beijing-1 strain of Japanese encephalitis virus. Balb/c mice immunized with pJBE survived the challenge with the different strains of Japanese encephalitis virus; however, Balb/c mice immunized with inactivated vaccine did not survive the challenge with the JaGAr-01 strain of Japanese encephalitis virus at all.

CONCLUSIONS

DNA vaccine containing the E protein gene derived from Japanese encephalitis virus can provide not only better efficacy including humoral and cellular immunity, but also cross-protection against infection with homologous and heterologous Japanese encephalitis virus.

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.

Screening and identification of severe acute respiratory syndrome-associated coronavirus-specific CTL epitopes

Severe acute respiratory syndrome (SARS) is a highly contagious and life-threatening disease that emerged in China in November 2002. A novel SARS-associated coronavirus was identified as its principal etiologic agent; however, the immunopathogenesis of SARS and the role of special CTLs in virus clearance are still largely uncharacterized. In this study, potential HLA-A*0201-restricted spike (S) and nucleocapsid protein-derived peptides were selected from an online database and screened for potential CTL epitopes by in vitro refolding and T2 cell-stabilization assays. The antigenicity of nine peptides which could refold with HLA-A*0201 molecules was assessed with an IFN-gamma ELISPOT assay to determine the capacity to stimulate CTLs from PBMCs of HLA-A2(+) SARS-recovered donors. A novel HLA-A*0201-restricted decameric epitope P15 (S411-420, KLPDDFMGCV) derived from the S protein was identified and found to localize within the angiotensin-converting enzyme 2 receptor-binding region of the S1 domain. P15 could significantly enhance the expression of HLA-A*0201 molecules on the T2 cell surface, stimulate IFN-gamma-producing CTLs from the PBMCs of former SARS patients, and induce specific CTLs from P15-immunized HLA-A2.1 transgenic mice in vivo. Furthermore, significant P15-specific CTLs were induced from HLA-A2.1-transgenic mice immunized by a DNA vaccine encoding the S protein; suggesting that P15 was a naturally processed epitope. Thus, P15 may be a novel SARS-associated coronavirus-specific CTL epitope and a potential target for characterization of virus control mechanisms and evaluation of candidate SARS vaccines.

Comparison of antibody- and cell-mediated immune responses after intramuscular hepatitis C immunizations of BALB/c mice

Current treatments for hepatitis C infection have limited efficacy, and there is no vaccine available. The goal of this study was to compare the immune response to several immunization combinations against hepatitis C virus (HCV). Six groups of mice were immunized at weeks 0, 4, and 8 with different combinations of a candidate HCV vaccine consisting of 100 microg recombinant HCV core/E1/E2 (rHCV) DNA plasmid and/or 25 microg rHCV polyprotein and 50 microL Montanide ISA- 51. Four weeks after the last injection, all groups of mice were sacrificed and blood samples and spleens were collected for measuring the levels of specific HCV antibodies (total IgG, IgG1, and IgG2a). Cell proliferation and intracellular interferon-gamma were also measured. Among the groups of immunized mice, only the mice immunized with rHCV DNA plasmid, rHCV polyprotein, and montanide (group D) and mice immunized with rHCV polyprotein and montanide (group F) demonstrated a significant increase in the total IgG titer after immunization. IgG1 was the predominant antibody detected in both groups D and F. No IgG2a was detected in any of the groups. Proliferation assays demonstrated that splenocytes from group D and group C (rHCV DNA primed/rHCV polyprotein boost) developed significant anti-HCV proliferative responses. The combination of an rHCV DNA plasmid, rHCV polyprotein, and montanide induced a high antibody titer with a predominance of IgG1 antibodies and recognized the major neutralization epitopes in HVR1. In contrast, group C did not show an increase in anti-HCV antibodies, but did show a proliferative response.

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.

Hepatitis C virus core protein: an update on its molecular biology, cellular functions and clinical implications

The present review article is an update on various features of hepatitis C virus (HCV) core protein including its molecular biology, role in HCV replication, involvement in HCV pathogenesis, etiological role in hepatocellular carcinogenesis, significance in diagnosis and vaccination against HCV infection. Core protein is a structural protein of HCV virus and has only recently been characterized. It was found to play a major role in HCV-induced viral hepatitis. Although published information shows a lot about the clinical significance of HCV core protein, several studies are still needed to demonstrate its exact significance in viral biology and underlying HCV pathogenesis.

Skin targeted DNA vaccine delivery using electroporation in rabbits II. Safety

The Achilles heel of gene-based therapy is gene delivery into the target cells efficiently with minimal toxic effects. Viral vectors for gene/DNA vaccine delivery are limited by the safety and immunological problems. Recently, nonviral gene delivery mediated by electroporation has been shown to be efficient in different tissues including skin. There are no detailed reports about the effects of electroporation on skin tissue, when used for gene/DNA vaccine delivery. In a previous study we demonstrated the efficacy of skin targeted DNA vaccine delivery using electroporation in rabbits [Medi, B.M., Hoselton, S., Marepalli, B.R., Singh, J., 2005. Skin targeted DNA vaccine delivery using electroporation in rabbits. I. Efficacy. Int. J. Pharm. 294, 53-63]. In the present study, we investigated the safety aspects of the electroporation technique in vivo in rabbits. Different electroporation parameters (100-300 V) were tested for their effects on skin viability, macroscopic barrier property, irritation and microscopic changes in the skin. Skin viability was not affected by the electroporation protocols tested. The electroporation pulses induced skin barrier perturbation and irritation as indicated by elevated transepidermal water loss (TEWL) and erythema/edema, respectively. Microscopic studies revealed inflammatory responses in the epidermis following electroporation using 200 and 300 V pulses. However, these changes due to electroporation were reversible within a week. The results suggest that the electroporation does not induce any irreversible changes in the skin and can be a useful technique for skin targeted DNA vaccine delivery.

Skin targeted DNA vaccine delivery using electroporation in rabbits. I: efficacy

Genetic immunization through skin is highly desirable as skin has plenty of antigen presenting cells (APCs) and is easily accessible. The purpose of this study was to investigate the effects of electroporation pulse amplitude, pulse length and number of pulses on cutaneous plasmid DNA vaccine delivery and immune responses, following intradermal injection in vivo in rabbits. Expression of the delivered plasmid was studied using a reporter plasmid, coding for beta-galactosidase. The efficiency of DNA vaccine delivery was investigated using a DNA vaccine against Hepatitis B, coding for Hepatitis B surface antigen (HBsAg). Serum samples and peripheral blood mononuclear cells (PBMC) were analyzed for humoral and cellular immunity, respectively, following immunization. The expression of transgene in the skin was transient and reached its peak in 2 days post-delivery with 200 and 300 V pulses. The expression levels with 200 and 300 V pulses were 48- and 129-fold higher, respectively, compared with the passive on day 2. In situ histochemical staining of skin with X-gal demonstrated the localized expression of beta-galactosidase with electroporation pulses of 200 and 300 V. Electroporation mediated cutaneous DNA vaccine delivery significantly enhanced both humoral and cellular immune responses (p<0.05) to Hepatitis B compared to passive delivery. The present study demonstrates the enhanced DNA vaccine delivery to skin and immune responses by topical electroporation. Hence, electroporation mediated cutaneous DNA vaccine delivery could be developed as a potential alternative for DNA vaccine delivery.

Immune responses with DNA vaccines encoded different gene fragments of severe acute respiratory syndrome coronavirus in BALB/c mice

To analyze the immune responses of DNA vaccine encoded different gene fragments of severe acute respiratory syndrome coronavirus (SARS-Cov), SARS-Cov gene fragments of membrane (M), nucleocapsid (N), spike a (Sa), and spike b (Sb) proteins were cloned into pcDNA3.1 (Invitrogen) vector to form plasmids pcDNAM, pcDNAN, pcDNASa, and pcDNASb, respectively. After mice were immunized intramuscularly with pcDNAM, pcDNAN or pcDNASa-pcDNASb plasmid, blood was collected and serum was separated. Humoral immune response was detected with the enzyme-linked immunosorbent assay, and cellular immune response of SARS-Cov DNA vaccines was detected with lymphoproliferation assay and cytotoxic T lymphocyte assay. Results show that cellular and humoral immune responses can be detected after immunization with pcDNAM, pcDNAN or pcDNASa-pcDNASb plasmids in BALB/c mice. However, pcDNAM stimulated the highest cellular immune response than other plasmids, and pcDNASa-pcDNASb stimulated the highest humoral immune response in week 12. The present results not only suggest that DNA immunization with pcDNAM, pcDNAN or pcDNASa-pcDNASb could be used as potential DNA vaccination approaches to induce antibody in BALB/c mice, but also to illustrate that gene immunization with these SARS DNA vaccines different immune response characters.

Immunization with hepatitis C virus core gene triggers potent T-cell response, but affects CD4+ T-cells

Numerous attempts to induce immunity against HCV core (HCV-C) by DNA immunization met serious difficulties in optimizing T-helper cell and antibody responses. Immunomodulatory properties of HCV-C could be blamed that seem to be dependent on the genotype of HCV source. Here, we characterized HCV-C gene from HCV 1b isolate 274933RU. Eukaryotic expression of HCV-C was effectively driven by CMVIE, while human elongation factor 1 alpha promoter directed low levels of HCV-C expression. C57BL/6 mice were immunized with CMVIE-driven HCV-C gene, and assessed for specific antibody production, T-cell proliferation and cytokine secretion. The number and proportion of CD19+, CD3+, CD3+/CD4+, and CD3+/CD8+ splenocytes in HCV-C gene recipients was evaluated by flow cytometry. A significant mounting drop in CD3+/CD4+ T-cell counts occurred in HCV-C gene-recipients as compared to the controls. Despite that, 75% of mice exhibited core-specific cellular reactivity revealed as high proliferative responses to HCV-C and HCV-C peptides. Stimulated T-cells secreted predominantly IFN-gamma and IL-2. A shift of epitope specificity was observed with the early response being broad, and the late limited to the HCV-C C-terminus. Thus, we demonstrate both T-cell immunogenicity and T-cell modulation by core of HCV 1b. Immune modulation by HCV core may affect host ability to mount long-lasting cellular and antibody response and should be dealt with in designing core-based HCV vaccines.

Activation of Th1 immunity is a common immune mechanism for the successful treatment of hepatitis B and C: tetramer assay and therapeutic implications

Both chronic hepatitis B and C virus (HBV and HCV) infections respond ineffectively to current antiviral therapies. Recent studies have suggested that treatment outcomes may depend on the development of type 1 T helper (Th1) and Th2 cell responses. Specifically, activation of Th1 immunity may play a major role in successfully treating hepatitis B and C. This model was revisited herein by evaluating immune responses in 36 HBV and 40 HCV patients with or without treatment, in an attempt to find a common immune mechanism for successful treatment. The immune responses in all examined cases were studied by peripheral blood mononuclear cell (PBMC) proliferation and cytokine responses to viral antigens, cytotoxic T lymphocyte (CTL) responses, enzyme-linked immunospot (ELISPOT) assay, and tetramer staining of virus-specific CD8+ T cells. The overall results revealed that all responders among both HBV- and HCV-infected cases displayed significantly higher PBMC proliferation to viral antigens with a predominant Th1 cytokine profile. Furthermore, the Th1-dominant responses were associated with significant enhancement of CTL activities and were correlated with ELISPOT data, while non-responders responded more weakly. During therapy, the numbers of tetramer-staining, virus-specific CD8+ T cells showed greater increases in responders than in non-responders (p = 0.001). The frequencies determined by the tetramer assay were approximately 200-fold higher than data estimated by limiting-dilution analysis. In conclusion, activation of Th1 immunity accompanied by enhancement of CTL activity during therapy is a common immune mechanism for successfully treating hepatitis B and C, and therefore may have important therapeutic implications.

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.

In vitro studies of core peptide-bearing immunopotentiating reconstituted influenza virosomes as a non-live prototype vaccine against hepatitis C virus

Evidence from both animal and human viral diseases indicate that cytotoxic T lymphocytes (CTL) are crucial in antiviral defense. However, a major problem to generate cytotoxic immunity is that in vivo exogenous antigens are usually presented via MHC class II pathway and normally fail to induce CTL. The aim of this study is to describe a novel non-live prototype vaccine based on immunopotentiating reconstituted influenza virosomes (IRIV) as vehicles to deliver HLA-A*0201-restricted hepatitis C virus (HCV) peptides (core 35-44 and 131-140) into the cytoplasm of at least three different target cell types [including T2, a transporter associated with antigen processing (TAP)-deficient cell line] resulting in MHC class I peptide presentation and lysis by peptide-specific CTL lines. Comparison of kinetics and analysis of the influence of peptide-stripping and Brefeldin A (BFA) reveal that there exists an endogenous, TAP-independent and BFA-sensitive pathway for virosomally delivered peptides. Moreover, virosomes containing influenza matrix peptide 58-66 can efficiently re-stimulate in vivo primed CTL and, importantly, IRIV containing HCV core peptides can even prime CTL from peripheral blood mononuclear cells of HCV(-) healthy blood donors in vitro. The fact that in vitro primed CTL are also able to specifically lyse target cells infected with recombinant vaccinia virus encoding the HCV core protein is of great importance for future studies based on in vivo mouse models. One of the most evident advantages of the virosomes in vivo will be their capability to protect the incorporated peptide from a large variety of degrading proteases.

Additives and protein-DNA combinations modulate the humoral immune response elicited by a hepatitis C virus core-encoding plasmid in mice

Humoral and cellular immune responses are currently induced against hepatitis C virus (HCV) core following vaccination with core-encoding plasmids. However, the anti-core antibody response is frequently weak or transient. In this paper, we evaluated the effect of different additives and DNA-protein combinations on the anti-core antibody response. BALB/c mice were intramuscularly injected with an expression plasmid (pIDKCo), encoding a C-terminal truncated variant of the HCV core protein, alone or combined with CaCl2, PEG 6000, Freund's adjuvant, sonicated calf thymus DNA and a recombinant core protein (Co. 120). Mixture of pIDKCo with PEG 6000 and Freund's adjuvant accelerated the development of the anti-core Ab response. Combination with PEG 6000 also induced a bias to IgG2a subclass predominance among anti-core antibodies. The kinetics, IgG2a/IgG1 ratio and epitope specificity of the anti-core antibody response elicited by Co. 120 alone or combined with pIDKCo was different regarding that induced by the pIDKCo alone. Our data indicate that the antibody response induced following DNA immunization can be modified by formulation strategies.

Hepatitis C virus core protein: intriguing properties and functional relevance

Hepatitis C virus (HCV) often causes a prolonged and persistent infection, and an association between hepatocellular carcinoma (HCC) and HCV infection has been noted. The pathogenesis of liver damage is at least in part related to virus-mediated factors. Understanding the molecular basis of pathogenesis is a major challenge in gaining insight into HCV-associated disease progression. Recent experimental evidence using HCV cloned genomic regions suggests that the core protein has numerous functional activities. These include its likely role in encapsidation of viral RNA, a regulatory effect on cellular and unrelated viral promoters, interactions with a number of cellular proteins, an modulatory role in programmed cell death or apoptosis under certain conditions, involvement in cell growth promotion and immortalization, induction of HCC in transgenic mice, and a possible immunoregulatory role. These intriguing properties suggest that the core protein, in concert with cellular factors, may contribute to pathogenesis during persistent HCV infection.

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.

Cytotoxic T cell responses against hepatitis B virus polymerase induced by genetic immunization

BACKGROUND/AIMS

Individuals with chronic hepatitis B may benefit from genetic (DNA-based) immunization through induction of viral clearance by enhancement of suboptimal cellular immune responses. While marked cellular immune responses to hepatitis B virus (HBV) nucleocapsid and envelope proteins occur after genetic immunization in mice, it is unknown whether genetic immunization is capable of eliciting such responses to HBV polymerase. We wished to develop assays for the determination of HBV polymerase specific immune responses in mice and investigate whether genetic immunization may elicit humoral and cellular immune responses to HBV polymerase.

METHODS

BALB/c (H-2d) mice were injected with a DNA expression construct for HBV polymerase. Humoral immune responses to HBV polymerase were analyzed with a newly established ELISA. Cellular immune responses were determined using recombinant vaccinia virus infected target cells expressing HBV polymerase at high levels.

RESULTS

Assays for the detection of HBV polymerase-specific immune responses were developed. Immunized animals exhibited substantial polymerase-specific cytotoxic T lymphocyte responses. However, no humoral immune responses to HBV polymerase were detectable.

CONCLUSIONS

Our study demonstrates that DNA-based immunization will generate substantial CTL responses to HBV polymerase and may be an important component of an immunotherapeutic strategy to combat chronic HBV infection.

A truncated variant of the hepatitis C virus core induces a slow but potent immune response in mice following DNA immunization

Vaccination of BALB/c mice with pIDKCo, a plasmid containing the coding sequence for the first 176 amino acids of the hepatitis C virus (HCV) core protein, induced both humoral and cellular specific immune responses. Particularly, the level of anti-core antibodies increased slowly with time up to a mean value above 1:8000 that was generally superior than that found in anti-HCV positive individuals. Six out of nine anti-HCV positive human sera were able to inhibit at different extent the binding of mouse anti-core sera to a recombinant capsid protein. Our results show that it is possible to elicit a potent humoral and cellular immune response against the HCV core antigen in mice following DNA immunization.

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.

Immunization of rabbits with cottontail rabbit papillomavirus E1 and E2 genes: protective immunity induced by gene gun-mediated intracutaneous delivery but not by intramuscular injection

We previously demonstrated that gene gun-based intracutaneous vaccination of rabbits with a combination of, but not with individual papillomavirus E1, E2, E6 and E7 genes provided complete protection against cottontail rabbit papillomavirus (CRPV) infection. In the present study, we tested whether vaccination of inbred and outbred rabbits with a combination of CRPV E1 and E2 genes could provide complete protection against virus infection. In the first experiment, gene gun-based intracutaneous vaccination with E1 and E2 genes prevented papilloma formation in the majority of inbred rabbits and promoted systemic papilloma regression in one non-protected rabbit. In contrast, needle-mediated intramuscular injection of E1 and E2 genes did not prevent papilloma formation nor promoted systemic papilloma regression, indicating an absence of strong protective immunity. In the second experiment, six outbred rabbits were immunized by gene gun-based intracutaneous administration of the E1 and E2 genes. Prevention of papilloma formation or systemic papilloma regression was observed in three vaccinated rabbits. Papillomas persisted on the remaining three rabbits, but were significantly smaller than that on control rabbits. These results suggested that gene gun-based intracutaneous vaccination with the combination of papillomavirus E1 and E2 genes induced strong protective antivirus immunity but may be insufficient for complete protection in an outbred population.

DNA-based vaccination induces humoral and cellular immune responses against hepatitis B virus surface antigen in mice without activation of C-myc

AIM: To develop a safe and effective DNA vaccine for inducing humoral and cellular immunological responses against hepatitis B virus surface antigen (HBsAg).

METHODS: BALB/c mice were inoculated with NV-HB/s, a recombinant plasmid that had been inserted S gene of hepatitis B virus genome and could express HBsAg in eukaryotes. HBsAg expression was measured by ABC immunohistochemical assay, generation of anti-HBs by ELISA and cytotoxic T lymphocyte (CTL), by MTT method, existence of vaccine DNA by Southern blot hybridization and activation of oncogene C-myc by in situ hybridization.

RESULTS: With NV-HB/s vaccination by intramuscular injection, anti-HBs was initially positive 2 wk after inoculation while all mice tested were HBsAg positive in the muscles. The titers and seroconversion rate of anti-HBs were steadily increasing as time went on and were dose-dependent. All the mice inoculated with 100 μg NV-HB/s were anti-Bs positive one month after inoculation, the titer was 1∶1024 or more. The humoral immune response was similar induced by either intramuscular or intradermal injection. CTL activities were much stronger (45.26%) in NV-HB/s DNA immunized mice as compared with those (only 6%) in plasma-derived HBsAg vaccine immunized mice. Two months after inoculation, all muscle samples were positive by Southern-blot hybridization for NV-HB/s DNA detection, but decreased to 25% and all were undetectable by in situ hybridization after 6 mo. No oncogene C-myc activation was found in the muscle of inoculation site.

CONCLUSION: NV-HB/s could generate humoral and cellular immunological responses against HBsAg that had been safely expressed in situ by NV-HB/s vaccination.

Immunogenicity and protective efficacy of DNA vaccines encoding secreted and non-secreted forms of Mycobacterium tuberculosis Ag85A

OBJECTIVE

To determine the efficacy of Ag85A-DNA against challenge with a highly virulent human clinical isolate of Mycobacterium tuberculosis (CSU37) and to compare the potencies of two types of Ag85A-DNA vaccines; those expressing secreted and non-secreted forms of the protein.

DESIGN

Ag85A-DNA vaccinated mice were challenged with a highly virulent clinical isolate of M. tuberculosis (CSU37) in order to compare the efficacy of these vaccines. In vitro studies were also performed.

RESULTS

Enhanced humoral and cellular responses were induced in mice vaccinated with the secreted Ag85A-DNA compared to the non-secreted Ag85A-DNA. In addition, secreted Ag85A-DNA conferred protective immunity against infection with M. tuberculosis (CSU37).

CONCLUSIONS

DNA vaccines encoding M. tuberculosis Ag85A have been shown to induce potent humoral and cellular immune responses leading to protection from M. tuberculosis (Erdman) challenge in mouse models. In this study we demonstrate that Ag85A can confer protection in a rigorous challenge model using a highly virulent human clinical isolate of M. tuberculosis (CSU37). This challenge model appears able to discriminate between DNA vaccines of differing potencies, as the more immunogenic DNA construct encoding a secreted form of Ag85A was protective, whereas the less immunogenic DNA construct encoding a non-secreted form of Ag85A was not.