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

[Adjuvant effect of dispersed fullerene C60 on the immune response to constructs harboring amino acid and nucleotide sequences of hepatitis C virus nonstructural NS5B protein]

INTRODUCTION

A vaccine against hepatitis C has not yet been developed. Recombinant proteins and plasmids encoding hepatitis C virus (HCV) proteins, the components of candidate vaccines, induce a weak immune response and require the use of adjuvants. The aim of the work was to study the adjuvant action of an aqueous solution of fullerene C60 during immunization of mice with HCV recombinant protein NS5B (rNS5B) that is an RNA-dependent RNA polymerase, or with NS5B-encoding pcNS5B plasmid.

MATERIALS AND METHODS

An aqueous solution of dispersed fullerene (dnC60) was obtained by ultrafiltration. C57BL/6 mice were immunized with rNS5B subcutaneously, pcNS5B intramuscularly mixed with different doses of dnC60 three times, then the humoral and cellular response to HCV was evaluated.

RESULTS

Mice immunization with rNS5B in a mixture with dnC60 at doses of 250 g/mouse significantly induced humoral response: a dose-dependent increase in IgG1 antibody titers was 720 times higher than in the absence of fullerene. There was no increase in the cellular response to rNS5B when administered with dnC60. The humoral response to DNA immunization was weak in mice of all groups receiving pcNS5B. The cellular response was suppressed when the plasmid was injected in a mixture with dnC60.

CONCLUSIONS

Dispersed fullerene dnC60 is a promising adjuvant for increasing the immunostimulating activity of weakly immunogenic proteins including surface and other HCV proteins, important for a protective response. Further research is needed to enhance the ability of dnC60 to boost the cellular immune response to the components of the candidate vaccine.

Advancing our understanding of HIV co-infections and neurological disease using the humanized mouse

Humanized mice have become an important workhorse model for HIV research. Advances that enabled development of a human immune system in immune deficient mouse strains have aided new basic research in HIV pathogenesis and immune dysfunction. The small animal features facilitate development of clinical interventions that are difficult to study in clinical cohorts, and avoid the high cost and regulatory burdens of using non-human primates. The model also overcomes the host restriction of HIV for human immune cells which limits discovery and translational research related to important co-infections of people living with HIV. In this review we emphasize recent advances in modeling bacterial and viral co-infections in the setting of HIV in humanized mice, especially neurological disease, and Mycobacterium tuberculosis and HIV co-infections. Applications of current and future co-infection models to address important clinical and research questions are further discussed.

Advances in Transgenic Mouse Models to Study Infections by Human Pathogenic Viruses

Medical research is changing into direction of precision therapy, thus, sophisticated preclinical models are urgently needed. In human pathogenic virus research, the major technical hurdle is not only to translate discoveries from animals to treatments of humans, but also to overcome the problem of interspecies differences with regard to productive infections and comparable disease development. Transgenic mice provide a basis for research of disease pathogenesis after infection with human-specific viruses. Today, humanized mice can be found at the very heart of this forefront of medical research allowing for recapitulation of disease pathogenesis and drug mechanisms in humans. This review discusses progress in the development and use of transgenic mice for the study of virus-induced human diseases towards identification of new drug innovations to treat and control human pathogenic infectious diseases.

Generation of human MHC (HLA-A11/DR1) transgenic mice for vaccine evaluation

The rapid occurrence of emerging infectious diseases demonstrates an urgent need for a new preclinical experimental model that reliably replicates human immune responses. Here, a new homozygous humanized human leukocyte antigen (HLA)-A11/DR1 transgenic mouse (HLA-A11(+/+)/DR01(+/+)/H-2-β2m(-/-)/IAβ(-/-)) was generated by crossing HLA-A11 transgenic (Tg) mice with HLA-A2(+/+)/DR01(+/+)/H-2-β2m(-/-)/IAβ(-/-) mice. The HLA-A11-restricted immune response of this mouse model was then examined. HLA-A11 Tg mice expressing a chimeric major histocompatibility complex (MHC) molecule comprising the α1, α2, and β2m domains of human HLA-A11 and the α3 transmembrane and cytoplasmic domains of murine H-2D(b) were generated. The correct integration of HLA-A11 and HLA-DR1 into the genome of the HLA-A11/DR1 Tg mice (which lacked the expression of endogenous H-2-I/II molecules) was then confirmed. Immunizing mice with a recombinant HBV vaccine or a recombinant HIV-1 protein resulted in the generation of IFN-γ-producing cytotoxic T lymphocyte (CTL) and antigen-specific antibodies. The HLA-A11-restricted CTL response was directed at HLA immunodominant epitopes. These mice represent a versatile animal model for studying the immunogenicity of HLA CTL epitopes in the absence of a murine MHC response. The established animal model will also be useful for evaluating and optimizing T cell-based vaccines and for studying differences in antigen processing between mice and humans.

T- and B-cell responses to multivalent prime-boost DNA and viral vectored vaccine combinations against hepatitis C virus in non-human primates

Immune responses against multiple epitopes are required for the prevention of hepatitis C virus (HCV) infection, and the progression to phase I trials of candidates may be guided by comparative immunogenicity studies in non-human primates. Four vectors, DNA, SFV, human serotype 5 adenovirus (HuAd5) and Modified Vaccinia Ankara (MVA) poxvirus, all expressing hepatitis C virus Core, E1, E2 and NS3, were combined in three prime-boost regimen, and their ability to elicit immune responses against HCV antigens in rhesus macaques was explored and compared. All combinations induced specific T-cell immune responses, including high IFN-γ production. The group immunized with the SFV+MVA regimen elicited higher E2-specific responses as compared with the two other modalities, while animals receiving HuAd5 injections elicited lower IL-4 responses as compared with those receiving MVA. The IFN-γ responses to NS3 were remarkably similar between groups. Only the adenovirus induced envelope-specific antibody responses, but these failed to show neutralizing activity. Therefore, the two novel regimens failed to induce superior responses as compared with already existing HCV vaccine candidates. Differences were found in response to envelope proteins, but the relevance of these remain uncertain given the surprisingly poor correlation with immunogenicity data in chimpanzees, underlining the difficulty to predict efficacy from immunology studies.

Identification and retrospective validation of T-cell epitopes in the hepatitis C virus genotype 4 proteome: an accelerated approach toward epitope-driven vaccine development

With over 150 million people chronically infected worldwide and millions more infected annually, hepatitis C continues to pose a burden on the global healthcare system. The standard therapy of hepatitis C remains expensive, with severe associated side effects and inconsistent cure rates. Vaccine development against the hepatitis C virus has been hampered by practical and biological challenges posed by viral evasion mechanisms. Despite these challenges, HCV vaccine research has presented a number of candidate vaccines that progressed to phase II trials. However, those efforts focused mainly on HCV genotypes 1 and 2 as vaccine targets and barely enough attention was given to genotype 4, the variant most prevalent in the Middle East and central Africa. We describe herein the in silico identification of highly conserved and immunogenic T-cell epitopes from the HCV genotype 4 proteome, using the iVAX immunoinformatics toolkit, as targets for an epitope-driven vaccine. We also describe a fast and inexpensive approach for results validation using the empirical data on the Immune Epitope Database (IEDB) as a reference. Our analysis identified 90 HLA class I epitopes of which 20 were found to be novel and 19 more had their binding predictions retrospectively validated; empirical data for the remaining 51 epitopes was insufficient to validate their binding predictions. Our analysis also identified 14 HLA class II epitopes, of which 8 had most of their binding predictions validated. Further investigation is required regarding the efficacy of the identified epitopes as vaccine targets in populations where HCV genotype 4 is most prevalent.

Prediction of T-cell epitopes of hepatitis C virus genotype 5a

Background

Hepatitis C virus (HCV) is a public health problem with almost 185 million people estimated to be infected worldwide and is one of the leading causes of hepatocellular carcinoma. Currently, there is no vaccine for HCV infection and the current treatment does not clear the infection in all patients. Because of the high diversity of HCV, protective vaccines will have to overcome significant viral antigenic diversities. The objective of this study was to predict T-cell epitopes from HCV genotype 5a sequences.

Methods

HCV near full-length protein sequences were analyzed to predict T-cell epitopes that bind human leukocyte antigen (HLA) class I and HLA class II in HCV genotype 5a using Propred I and Propred, respectively. The Antigenicity score of all the predicted epitopes were analysed using VaxiJen v2.0. All antigenic predicted epitopes were analysed for conservation using the IEDB database in comparison with 406, 221, 98, 33, 45, 45 randomly selected sequences from each of the HCV genotypes 1a, 1b, 2, 3, 4 and 6 respectively, downloaded from the GenBank. For epitope prediction binding to common HLA alleles found in South Africa, the IEDB epitope analysis tool was used.

Results

A total of 24 and 77 antigenic epitopes that bind HLA class I and HLA class II respectively were predicted. The highest number of HLA class I binding epitopes were predicted within the NS3 (63%), followed by NS5B (21%). For the HLA class II, the highest number of epitopes were predicted in the NS3 (30%) followed by the NS4B (23%) proteins. For conservation analysis, 8 and 31 predicted epitopes were conserved in different genotypes for HLA class I and HLA class II alleles respectively. Several epitopes bind with high affinity for both HLA class I alleles and HLA class II common in South Africa.

Conclusion

The predicted conserved T-cell epitopes analysed in this study will contribute towards the future design of HCV vaccine candidates which will avoid variation in genotypes, which in turn will be capable of inducing broad HCV specific immune responses.

High, broad, polyfunctional, and durable T cell immune responses induced in mice by a novel hepatitis C virus (HCV) vaccine candidate (MVA-HCV) based on modified vaccinia virus Ankara expressing the nearly full-length HCV genome

A major goal in the control of hepatitis C infection is the development of a vaccine. Here, we have developed a novel HCV vaccine candidate based on the highly attenuated poxvirus vector MVA (referred to as MVA-HCV) expressing the nearly full-length (7.9-kbp) HCV sequence, with the aim to target almost all of the T and B cell determinants described for HCV. In infected cells, MVA-HCV produces a polyprotein that is subsequently processed into the structural and nonstructural HCV proteins, triggering the cytoplasmic accumulation of dense membrane aggregates. In both C57BL/6 and transgenic HLA-A2-vaccinated mice, MVA-HCV induced high, broad, polyfunctional, and long-lasting HCV-specific T cell immune responses. The vaccine-induced T cell response was mainly mediated by CD8 T cells; however, although lower in magnitude, the CD4(+) T cells were highly polyfunctional. In homologous protocol (MVA-HCV/MVA-HCV) the main CD8(+) T cell target was p7+NS2, whereas in heterologous combination (DNA-HCV/MVA-HCV) the main target was NS3. Antigenic responses were also detected against other HCV proteins (Core, E1-E2, and NS4), but the magnitude of the responses was dependent on the protocol used. The majority of the HCV-induced CD8(+) T cells were triple or quadruple cytokine producers. The MVA-HCV vaccine induced memory CD8(+) T cell responses with an effector memory phenotype. Overall, our data showed that MVA-HCV induced broad, highly polyfunctional, and durable T cell responses of a magnitude and quality that might be associated with protective immunity and open the path for future considerations of MVA-HCV as a prophylactic and/or therapeutic vaccine candidate against HCV.

Polyfunctional CD8(+) T cells are associated with the vaccination-induced control of a novel recombinant influenza virus expressing an HCV epitope

In hepatitis C virus (HCV) infection, CD8(+) T cell responses have been shown to be important in viral clearance. Examining the efficacy of CD8(+) T cell vaccines against HCV has been limited by the lack of an HCV infectious model in mice and the differences between MHC restriction in humans and mice. Using HLA-A2 transgenic HHD mice, we demonstrate that intranasally delivered Pam2Cys-based lipopeptides containing HLA-A2-restricted HCV epitopes can induce polyfunctional CD8(+) T cell responses in several organs including the liver. To examine the activity of these responses in an infectious context, we developed a recombinant influenza virus that expresses the NS5B(2594-2602) epitope from non-structural protein 5B of hepatitis C virus (PR8-HCV(NS5B)). We showed that mice inoculated with a lipopeptide containing the NS5B epitope had reduced viral loads following challenge with the PR8-HCV(NS5B) virus. This reduction was associated with the induction of NS5B(2594-2602)-specific IFN-γ and TNF-α co-producing CD8(+) T cells. The T cell receptor usage in the NS5B(2594-2602) response was found to exhibit a Vβ8.1/8.2 bias that was characterized by a narrow repertoire and a common CDR3β motif. This work has identified CD8(+) T cell functions induced by lipopeptides that are associated with viral control and demonstrate the potential of lipopeptide-based vaccines as candidates for treatment of HCV infection.

Generation of T-cell receptors targeting a genetically stable and immunodominant cytotoxic T-lymphocyte epitope within hepatitis C virus non-structural protein 3

Hepatitis C virus (HCV) is a major cause of severe liver disease, and one major contributing factor is thought to involve a dysfunction of virus-specific T-cells. T-cell receptor (TCR) gene therapy with HCV-specific TCRs would increase the number of effector T-cells to promote virus clearance. We therefore took advantage of HLA-A2 transgenic mice to generate multiple TCR candidates against HCV using DNA vaccination followed by generation of stable T-cell–BW (T-BW) tumour hybrid cells. Using this approach, large numbers of non-structural protein 3 (NS3)-specific functional T-BW hybrids can be generated efficiently. These predominantly target the genetically stable HCV genotype 1 NS3_1073–1081 CTL epitope, frequently associated with clearance of HCV in humans. These T-BW hybrid clones recognized the NS3₁₀₇₃ peptide with a high avidity. The hybridoma effectively recognized virus variants and targeted cells with low HLA-A2 expression, which has not been reported previously. Importantly, high-avidity murine TCRs effectively redirected human non-HCV-specific T-lymphocytes to recognize human hepatoma cells with HCV RNA replication driven by a subgenomic HCV replicon. Taken together, TCR candidates with a range of functional avidities, which can be used to study immune recognition of HCV-positive targets, have been generated. This has implications for TCR-related immunotherapy against HCV.

A synthetic multi-epitope antigen enhances hepatitis C virus-specific B- and T-cell responses

Combining results from previous studies, a multi-epitope antigen PCXZ against the hepatitis C virus was synthesized in this study. The antigenic specificity of PCXZ was determined by recognizing antibodies in serum samples from hepatitis C virus patients, but not from healthy subjects or subjects who had the hepatitis B virus. The characteristics of PCXZ immunogenicity were evaluated in BALB/c mice. Strong antibody responses were generated in mice immunized with either naked PCXZ or PCXZ in Freund's adjuvant. As for the T-cell responses, Freund's adjuvant significantly increased interferon-γ secretion and enhanced the lytic activity of cytotoxic T lymphocytes. The epitope Pa, one component of PCXZ, made the most significant contribution to specific CTL lysis; this epitope was also a B-cell epitope and was able to induce high IgG titers. In summary, PCXZ was found to be highly immunogenic, and elicited both humoral and cellular immune responses in mice.

Estimating design space available for polyepitopes through consideration of major histocompatibility complex binding motifs

Major histocompatibility complex (MHC ) epitope presentation is needed for robust adaptive immune responses. Core peptide binding motifs for class I and class II MHC are 8-10 amino acids long, containing two or more "anchor" residues. These binding motifs define epitope anchor amino acid content and spacing, and knowledge of them has facilitated emergence of polyepitope vaccines. However, polyepitopes can exhibit "junctional epitopes" (neoepitopes interfering with vaccine function) resulting from juxtaposition of authentic epitopes. We have developed an algorithm for consideration of polyepitope sequence in light of MHC motifs to exhaustively identify all junctional-free polyepitope designs for any given set of authentic epitopes, and in so doing discovered that the number of such variants of any given polyepitope can be astronomically high. Our approach designs polyepitopes of any length, considers multiple MHC class I or class II motifs simultaneously and can be adapted to design variants of existing proteins with pre-selected epitope contents. We have also implemented the algorithm as a computer-based tool (CANVAC II), which we make available to interested parties. The vast diversity of junctional-free polyepitopes suggests that the number of potential T-helper epitope free protein variants may also be large, which may have implications for discovery of bioactive but non-immunogenic therapeutics.

Mucosally delivered peptides prime strong immunity in HLA-A2.1 transgenic rabbits

DNA vaccines delivered subcutaneously by gene-gun have generated strong protective and therapeutic immunity in rabbits. Recent studies have shown that peptides delivered by the mucosal routes also stimulate local and systemic immune responses. Since mucosal delivery is easier to administer and more cost-effective when compared to gene-gun delivery, we were interested to learn whether mucosally delivered peptides would prime protective immunity comparable to that of gene-gun-delivered DNA in rabbits. Our newly developed HLA-A2.1 transgenic rabbit model was used to test the hypothesis. We chose an HLA-A2.1 restricted cottontail rabbit papillomavirus (CRPV) E1 epitope (E1/303-311, MLQEKPFQL) for the peptide immunization studies because it provided complete protection when used as a DNA vaccine. Adjuvant has been widely used to boost immunity for vaccines. In this study, three adjuvants reported to be effective for rabbits (TT helper motif, PADRE and CpG2007) were tested with the peptide vaccine. Peptide alone or fused to TT helper or PADRE to create chimeric peptides was delivered by two mucosal routes (ocular and intranasal) together. Partial protection was found in HLA-A2.1 transgenic rabbits when peptide was delivered mucosally in the presence of adjuvant. When a subsequent booster of a half-dose of the corresponding DNA vaccine was delivered, complete protections were achieved. We conclude that mucosal peptide immunization can be combined with a single DNA vaccination to provide strong protective immunity in rabbits.

Using HLA-A2.1 Transgenic Rabbit Model to Screen and Characterize New HLA-A2.1 Restricted Epitope DNA Vaccines

We have established an HLA-A2.1 transgenic rabbit /cottontail rabbit papillomavirus (CRPV) infection model. Using this novel transgenic animal model, we reported earlier that a multivalent epitope DNA vaccine (CRPVE1ep1-5) containing five HLA-A2.1 restricted epitopes from CRPVE1 (42-50, 149-157, 161-169, 245-253 and 303-311) was successful in providing strong and specific protective and therapeutic immunity. Among these five epitopes, two (161-169 and 303-311) have been proven to stimulate strong immunity in both HLA-A2.1 transgenic mouse and rabbit models. In the current study, we further identified the remaining three epitopes (CRPVE1/42-50,149-157, 245-253) in both animal models. CRPVE1/149-157 was able to induce specific CTL responses in HLA-A2.1 transgenic mice by DNA immunization but undetectable by peptide immunization. CRPVE1/42-50 and 245-253 failed to respond in HLA-A2.1 transgenic mice either by peptide or DNA immunization. All the three epitopes when administrated as DNA vaccines, however, were able to stimulate strong protective immunity in HLA-A2.1 transgenic rabbits in a dose dependent manner. Among the five epitopes, two (CRPVE1/ 303-311and CRPVE1/149-157) DNA vaccines also showed specific therapeutic effects in CRPV-infected HLA-A2.1 transgenic rabbits. Taken together, the HLA-A2.1 transgenic rabbit model recognized more epitopes than did the HLA-A2.1 transgenic mouse model. Our data demonstrate that the HLA-A2.1 transgenic rabbit model can complement the HLA-A2.1 transgenic mouse model for the development and testing of new HLA-A2.1 restricted prophylactic and therapeutic T cell based DNA vaccines.

Construction of HCV-polytope vaccine candidates harbouring immune-enhancer sequences and primary evaluation of their immunogenicity in BALB/c mice

An efficient vaccine against hepatitis-C virus (HCV) infection requires vigorous and focused CD8(+) T-cell responses against viral antigens. Due to immunosuppressive effect of HCV antigens, polytope vaccines comprising the minimal CD8(+)CTL epitopes are of peculiar concern. Herein, to provide information for construction of efficient HCV polytope vaccine candidates, one H-2D(d) (E2(405-414):E(2)) and two HLA-A*0201 (E1(363-372):E(1) and Core(35-44):C)-restricted CD8(+) T-cell epitopes of HCV were selected. By employing number of in silico analyses, the E(2)E(1)C linear format was predicted as optimum epitope consecution and after amplification by SOEing-PCR, the corresponding DNA sequence was cloned in pcDNA3.1+ vector. To further evaluate the role of immune-enhancer elements, a universal T-helper epitope (PADRE), endoplasmic reticulum signal sequence (ERss) and hepatitis-B surface-antigen (HBsAg) gene were fused separately or in combination to the E(2)E(1)C minigene. In vitro analyses of polytopes by different DNA/protein-based assays demonstrated proper transcription/expression of constructs in transfected cells. Measurement of the HBsAg-mediated particle secretion by ELISA indicated lack of secretion in the related polytopes. Results of delayed-type hypersensitivity (DTH) as a preliminary in vivo analysis, and confirmatory ELISPOT assays showed the proper processing and presentation of H-2D(d)-restricted-E(2) epitope and approved the enhancing effect of PADRE and ERss sequences but not HBsAg for the immune responses against E(2) in immunized BALB/c mice. Our results pointed to the value of in silico predictions and application of immune-enhancer elements as well as DTH analysis for design and primary in vivo evaluation of HCV polytopes, prior to costly transgenic studies on immunogenicity of HLA-A*0201 epitopes.

A vector-based minigene vaccine approach results in strong induction of T-cell responses specific of hepatitis C virus

Multiepitope-based vaccines against hepatitis C virus (HCV) were designed in the form of three minigenes encompassing four domains of the NS3, NS4 and NS5B proteins that contain multiple class I/II restricted epitopes. The polyEp-WT minigene encodes all four domains in fusion, the polyEp-C minigene encodes the same fusion but optimised for mammalian translation and the polyEp-E3 minigene has an additional endoplasmic reticulum targeting sequence. Whereas the minigenes vectorised by DNA were poorly immunogenic, adenovirus vectorisation induced strong and broader IFNgamma-ELISpot and CTL responses in HLA-A2 transgenic mice. In addition, polyEp-WT and polyEp-E3 responses were found cross-reactive in a recombinant Listeria-NS3-based surrogate challenge. This study illustrates the potency of vectorised minigenes in the field of HCV vaccine development.

Development of anti-PAX3 immune responses; a target for cancer immunotherapy

PAX3 is overexpressed in several human cancers and is absent from normal adult human tissues. It is known to have an oncogenic function in human malignancy, and is therefore a promising target for cancer immunotherapy. We screened the murine and human PAX3 amino acid sequences for peptides that bind common MHC class I types, and identified murine GVFINGRPL and human KLTEARVQV sequences. Mice immunised with either a selected PAX3 peptide, or with a PAX3 expressing DNA vector, developed specific anti-PAX3 immune responses that inhibited tumour growth. The intensity of the immune response was significantly enhanced by pulsing of the peptide onto dendritic cells. Anti-PAX3 T cell lines were established from splenocytes of immunised mice. Intravenous administration of anti-PAX3 T cells caused regression of established tumours indicating a promising clinical application for anti-PAX3 immunotherapy. The human peptide stimulated growth of similar T cell lines from peripheral blood of three out of three normal human blood donors. These showed specific cytotoxicity against a range of human PAX3+ and HLA-A2+ cancer cell lines. Moreover, an anti-PAX3 response was detected as a component of the anti-tumour immune response in a patient treated with lysate pulsed dendritic cell vaccination. The ability to generate strong and specific anti PAX3 immune responses from the T cell repertoire in both mice and humans, provides evidence for PAX3 as a promising target for immunotherapy of cancer.

An accelerated vaccine schedule with a poly-antigenic hepatitis C virus MVA-based candidate vaccine induces potent, long lasting and in vivo cross-reactive T cell responses

We designed and evaluated in HLA-class I transgenic mouse models a hepatitis C virus (HCV) T cell-based MVA vectored vaccine expressing three viral antigens known to be targets of potent CD8+- and CD4+-mediated responses. An accelerated (3 week-based) vaccination induced specific CD8+ T cells harboring two effector functions (cytolytic activity - both in vitro and in vivo- and production of IFNgamma) as well as specific CD4+ T cells recognizing all three vaccine antigens. Responses were long lasting (6 months), boostable by a fourth MVA vaccination and in vivo cross-reactive as demonstrated in a surrogate Listeria-based challenge assay. This candidate vaccine has now moved into clinical trials.

Expression of the alternative reading frame protein of Hepatitis C virus induces cytokines involved in hepatic injuries

Hepatitis C virus (HCV) Core has been implicated in immune-mediated mechanisms associated with the development of chronic hepatic diseases. Discovery of different alternative reading frame proteins (ARFPs) expressed from the HCV Core coding sequence challenges properties assigned to Core. This study was designed to evaluate the immunomodulatory functions of Core and ARFPs in monocytes, dendritic cells (DCs), macrophages (Mphi) and hepatocytes, cells that are all capable of supporting HCV replication. THP-1 cells, monocyte-derived Mphi and DCs, and Huh7 cells were infected by using adenoviruses (Ad) encoding Core, CE1E2 and a Core sequence modified so that the Core protein is wild type, but no ARFPs are expressed (CDeltaARFP). THP-1 cells and DCs infected with Ad encoding Core or CE1E2 produced significant levels of interleukin-6 (IL-6), IL-8, MCP-1 and MIP-1beta, whereas production of these chemokines with AdCDeltaARFP was reduced or abolished. Similar effects on IL-8 production were observed in Huh7 cells and on IL-6 and MIP-1beta in Mphi. Wild-type Core sequence, but not CDeltaARFP, could trans-activate the IL-8 promoter and this activation was not associated with activation of p38/p42-44MAPK. This study illustrates, for the first time, the critical importance of ARFP expression in immunomodulatory functions attributed to Core expression and suggests a potential involvement of ARFP in mechanisms associated with HCV pathogenesis.

Establishment of a cottontail rabbit papillomavirus/HLA-A2.1 transgenic rabbit model

Three transgenic rabbit lines that express a well-characterized human major histocompatibility complex class I (MHC-I) gene (HLA-A2.1) have been established. All three lines carry the HLA-A2.1 heavy chain and are able to pass the transgene to their offspring with both the outbred and the inbred EIII/JC genetic background. HLA-A2.1 colocalizes exclusively with rabbit MHC-I on the cell surfaces. These HLA-A2.1 transgenic rabbits demonstrated infection patterns similar to those found after cottontail rabbit papillomavirus (CRPV) challenge when compared with results in normal rabbits, although higher regression rates were found in HLA-A2.1 transgenic rabbits. Because the CRPV genome can accommodate significant modifications, the CRPV/HLA-A2.1 rabbit model has the potential to be used to screen HLA-A2.1-restricted immunogenic epitopes from human papillomaviruses in the context of in vivo papillomavirus infection.

Vaccine-induced early control of hepatitis C virus infection in chimpanzees fails to impact on hepatic PD-1 and chronicity

Broad T cell and B cell responses to multiple HCV antigens are observed early in individuals who control or clear HCV infection. The prevailing hypothesis has been that similar immune responses induced by prophylactic immunization would reduce acute virus replication and protect exposed individuals from chronic infection. Here, we demonstrate that immunization of naïve chimpanzees with a multicomponent HCV vaccine induced robust HCV-specific immune responses, and that all vaccinees exposed to heterologous chimpanzee-adapted HCV 1b J4 significantly reduced viral RNA in serum by 84%, and in liver by 99% as compared to controls (P=0.024 and 0.028, respectively). However, despite control of HCV in plasma and liver in the acute period, in the chronic phase, 3 of 4 vaccinated animals developed persistent infection. Analysis of expression levels of proinflammatory cytokines in serial hepatic biopsies failed to reveal an association with vaccine outcome. However, expression of IDO, CTLA-4 [corrected] and PD-1 levels in liver correlated with clearance or chronicity.

CONCLUSION

Despite early control of virus load, a virus-associated tolerogenic-like state can develop in certain individuals independent of vaccination history.

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.

Relation between viral fitness and immune escape within the hepatitis C virus protease

BACKGROUND

The hepatitis C virus (HCV) mutates within human leucocyte antigen (HLA) class I restricted immunodominant epitopes of the non-structural (NS) 3/4A protease to escape cytotoxic T lymphocyte (CTL) recognition and promote viral persistence. However, variability is not unlimited, and sometimes almost absent, and factors that restrict viral variability have not been defined experimentally.

AIMS

We wished to explore whether the variability of the immunodominant CTL epitope at residues 1073-1081 of the NS3 protease was limited by viral fitness.

PATIENTS

Venous blood was obtained from six patients (four HLA-A2+) with chronic HCV infection and from one HLA-A2+ patient with acute HCV infection.

METHODS

NS3/4A genes were amplified from serum, cloned in a eukaryotic expression plasmid, sequenced, and expressed. CTL recognition of naturally occurring and artificially introduced escape mutations in HLA-A2-restricted NS3 epitopes were determined using CTLs from human blood and genetically immunised HLA-A2-transgenic mice. HCV replicons were used to test the effect of escape mutations on HCV protease activity and RNA replication.

RESULTS

Sequence analysis of NS3/4A confirmed low genetic variability. The major viral species had functional proteases with 1073-1081 epitopes that were generally recognised by cross reactive human and murine HLA-A2 restricted CTLs. Introduction of mutations at five positions of the 1073-1081 epitope prevented CTL recognition but three of these reduced protease activity and RNA replication.

CONCLUSIONS

Viral fitness can indeed limit the variability of HCV within immunological epitopes. This helps to explain why certain immunological escape variants never appear as a major viral species in infected humans.

In vivo hierarchy of immunodominant and subdominant HLA-A*0201-restricted T-cell epitopes of HBx antigen of hepatitis B virus

A polyepitopic CD8+ T-cell response is critical for the control of hepatitis B virus (HBV) infection. The HBV X protein (HBx) is a multifunctional protein that is important for the viral life cycle and for host-virus interactions. The aim of this study was to analyze the immunogenicity and dominance of various HLA-A*0201-restricted HBx-derived epitopes. For this purpose, we immunized HLA-A*0201-transgenic mice with HBx-derived peptides and DNA. This is a powerful model for studying the induction of HLA-A*0201-restricted immune responses in vivo, as these mice possess a cytotoxic T lymphocyte (CTL) repertoire representative of HLA-A2.1 individuals. We used cytotoxic tests and enzyme-linked immunosorbent spot (ELISPOT) assays to study the induction of specific cytotoxic and interferon (IFN)-gamma-secreting T cells. This allowed us to classify the HBx epitopes according to their T-cell activation capacity. After endogenous processing of the antigen synthesized in vivo after DNA-based immunization, we found that the HBx-specific T-cell response is targeted against one immunodominant epitope. Furthermore, following peptide immunization, we identified six additional novel subdominant T-cell epitopes. Inclusion of well-characterized epitopic sequences of HBx in a new vaccine for chronic HBV infections could help to broaden the T-cell response.

Recognition of endogenously synthesized HLA-DR4 restricted HCV epitopes presented by autologous EBV transformed B-lymphoblastoid cell line

Hepatitis C virus (HCV) causes non-A, non-B hepatitis and infects an estimated 170 million people worldwide. The treatment for HCV infection is often unsuccessful with high costs and many side-effects. There is a great need for alternative therapies including preventive and therapeutic vaccination for HCV infection. The experiments in this study were carried out to elucidate whether endogenously expressed antigen can be presented to helper T-cells restricted by class II molecules and to determine whether responses to plasmid-derived antigen resemble those that we have reported for recombinant antigens or synthetic peptides. To address these issues, a multi-epitope minigene was expressed in 293T-cells and Epstein-Barr virus (EBV)-transformed B-lymphoblastoid cells (BLCL). The transfected BLCLs were employed as APCs to stimulate epitope-specific T-cell hybridomas (THC). The results demonstrated that the endogenously expressed minigene antigens could be processed and presented to T-cell hybridomas by HLA matched BLCL. Five out of seven incorporated epitopes were recognized. Blockade of HLA DR could abolish the release of IL-2, which demonstrated that the endogenously expressed minigene antigens were presented by MHC class II molecules. The presentation of endogenously expressed antigens was much more efficient than that of exogenous antigens, at least in the present study. The findings obtained here have important significance for the development of an HCV DNA vaccine.

Genetic immunization and comprehensive screening approaches in HLA-A2 transgenic mice lead to the identification of three novel epitopes in hepatitis C virus NS3 antigen

Interferon-gamma (IFN gamma)-producing CD8+ T cells have been shown to play a key role in the control or eradication of hepatitis C virus (HCV) infections. In particular, T cells specific of the non-structural protein 3 (NS3) are often associated with control of viremia. The aim of the study was to identify novel HLA-A2 restricted CD8+ T cell epitopes specific of NS3 using a combination of comprehensive approaches. HLA-A2.1 transgenic mice were immunized with a DNA vaccine optimized for NS3 specific epitope presentation and induced CD8+ T cell reactivity was screened using 42 algorithm-predicted peptides as well as a library of 78 overlapping 15-mer peptides spanning the whole protein. Three epitopes mapping within the NS3 protease (GLL: aa 1038-1047) or helicase (ATL: aa 1260-1268 and TLH: aa 1617-1625) were identified. These epitopes, which display similar and high in vitro binding capacities to soluble HLA-A2 molecules, are able to induce either cytotoxic T lymphocytes (CTL) and/or IFN gamma-producing T cells. Comparative in vitro target cell sensitization studies revealed a higher immunogenicity of the GLL peptide as compared with both ATL and TLH peptides. This peptide was capable to recall in vitro HCV-specific IFN gamma and IL-10-producing T cells from peripheral blood mononuclear cells (PBMC) of chronically infected patients. These data increase the pool of NS3-specific CD8+ T cell epitopes available to analyze HCV associated immunity and could contribute to the design and evaluation of candidate vaccines.

What can the HLA transgenic mouse tell us about autoimmune diabetes?

Type 1 diabetes mellitus is a polygenic disease strongly associated with the class II molecules DR3, 4 and the linked DQ2, 8 alleles. These molecules play an important role in presentation of peptide antigens after intracellular processing to CD4 T lymphocytes. A number of in vitro approaches have been used to elucidate the molecular basis for the association of particular HLA alleles with susceptibility to or protection from Type 1 diabetes mellitus. These have focused on the structure of the antigen-presenting molecules, together with their peptides. Binding studies, peptide elution, molecular modelling and crystallisation of the peptide MHC complex have between them made it possible to define the peptide-binding regions and to examine the stability of binding of peptides from putative autoantigens. It is difficult to study the role of these molecules in vivo in humans, and HLA transgenic mice have been generated to overcome this problem. Studies of mice expressing the HLA class II alleles associated with diabetes have shown that the presence of HLA molecules alone does not cause disease except in the presence of an islet "insult", even when this "insult" would in itself be insufficient to precipitate disease in the absence of the HLA class II transgene. HLA transgenic mice offer a way to elucidate the in vivo role of these molecules, and could help the development of targeted immunotherapy.

Modifying Adenoviral Vectors for Use as Gene-Based Cancer Vaccines

The past decade has produced significant advances in our understanding of antigen-presenting cells, tumor antigens, and other components of the immune response to cancer. Gene-based vaccination is emerging as one of the more promising approaches for loading dendritic cells (DC) with tumor-associated antigens. In this respect, it is proposed that adenoviral (AdV) vectors can deliver high antigen concentrations, promote effective processing and MHC expression, and stimulate potent cell-mediated immunity. While AdV vectors have performed well in pre-clinical vaccine models, their application to patient care has limitations. The in vivo administration of AdV vectors is associated with both innate and adaptive host responses that result in tissue inflammation and injury, viral neutralization, and premature clearance of AdV-transduced cells. A variety of strategies have been developed to address these limitations. The ideal vaccine would avoid vector-related immune responses, have relative specificity for transducing DC, and induce high levels of transgene expression. This review describes the range of host responses to AdV vaccines, identifies strategies to reduce viral recognition and enhance transgene antigen expression, and suggests future approaches to vector development and administration. There is every reason to believe that safer and more effective forms of AdV-based vaccines can be developed and applied to patient therapy.

Efficient induction of T helper 1 CD4+ T-cell responses to hepatitis C virus core and E2 by a DNA prime-adenovirus boost

Hepatitis C virus (HCV) is an important causative agent of liver disease, but currently there is no available prophylactic vaccine against HCV infection. Here, we investigated the HCV E2- and core-specific T-cell responses induced by DNA (D) and/or recombinant adenovirus (A) vaccines. In single (D versus A) or double immunizations (D-D versus A-A), the recombinant adenovirus vaccines induced higher levels of IFN-gamma secreting T-cell response and cytotoxic T lymphocytes (CTL) response than the DNA vaccines. However, a heterologous (D-A) regimen elicited the highest level of T helper 1 (Th1) CD4(+) T-cell responses. Furthermore, three E2-specific CTL epitopes were mapped using a peptide pool spanning the E2 protein sequence (a.a. 384-713) in BALB/c mice, and one of these (E2 405-414: SGPSQKIQLV) was shown to be immunodominant. Interestingly, no significant differences were found in the repertoire of E2-specific T-cell responses or in the immunodominance hierarchy of the three epitopes induced by D-D, D-A, A-A, and A-D, indicating that the breadth and hierarchy of T-cell responses is independent of these different vaccination regimens. In conclusion, the heterologous DNA prime-recombinant adenovirus boost regimen described offers an efficient promising strategy for the development of an effective T-cell-based HCV vaccine.

Hepatitis C virus infection: when silence is deception

Hepatitis C virus (HCV) uses complex and unique mechanisms to prevent, evade or subvert innate and adaptive immune responses and to establish persistent infection and chronic hepatitis. Recently developed experimental systems have significantly facilitated the analysis of HCV replication, virus-host interaction and pathogenesis of chronic hepatitis and have provided new insights into the mechanisms of HCV clearance and persistence.

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.