Linear B-cell epitopes of the NS3-NS4-NS5 proteins of the hepatitis C virus as modeled with synthetic peptides

Significance of monoclonal antibodies against the conserved epitopes within non-structural protein 3 helicase of hepatitis C virus

Nonstructural protein 3 (NS3) of hepatitis C virus (HCV), codes for protease and helicase carrying NTPase enzymatic activities, plays a crucial role in viral replication and an ideal target for diagnosis, antiviral therapy and vaccine development. In this study, monoclonal antibodies (mAbs) to NS3 helicase were characterized by epitope mapping and biological function test. A total of 29 monoclonal antibodies were produced to the truncated NS3 helicase of HCV-1b (T1b-rNS3, aa1192–1459). Six mAbs recognized 8/29 16mer peptides, which contributed to identify 5 linear and 1 discontinuous putative epitope sequences. Seven mAbs reacted with HCV-2a JFH-1 infected Huh-7.5.1 cells by immunofluorescent staining, of which 2E12 and 3E5 strongly bound to the exposed linear epitope ¹²³¹PTGSGKSTK¹²³⁹ (EP05) or core motif ¹³⁷³IPFYGKAI¹³⁸⁰ (EP21), respectively. Five other mAbs recognized semi-conformational or conformational epitopes of HCV helicase. MAb 2E12 binds to epitope EP05 at the ATP binding site of motif I in domain 1, while mAb 3E5 reacts with epitope EP21 close to helicase nucleotide binding region of domain 2. Epitope EP05 is totally conserved and EP21 highly conserved across HCV genotypes. These two epitope peptides reacted strongly with 59–79% chronic and weakly with 30–58% resolved HCV infected blood donors, suggesting that these epitopes were dominant in HCV infection. MAb 2E12 inhibited 50% of unwinding activity of NS3 helicase in vitro. Novel monoclonal antibodies recognize highly conserved epitopes at crucial functional sites within NS3 helicase, which may become important antibodies for diagnosis and antiviral therapy in chronic HCV infection.

A synthetic codon-optimized hepatitis C virus nonstructural 5A DNA vaccine primes polyfunctional CD8+ T cell responses in wild-type and NS5A-transgenic mice

The hepatitis C virus (HCV) nonstructural (NS) 5A protein has been shown to promote viral persistence by interfering with both innate and adaptive immunity. At the same time, the HCV NS5A protein has been suggested as a target for antiviral therapy. In this study, we performed a detailed characterization of HCV NS5A immunogenicity in wild-type (wt) and immune tolerant HCV NS5A-transgenic (Tg) C57BL/6J mice. We evaluated how efficiently HCV NS5A-based genetic vaccines could activate strong T cell responses. Truncated and full-length wt and synthetic codon-optimized NS5A genotype 1b genes were cloned into eukaryotic expression plasmids, and the immunogenicity was determined after i.m. immunization in combination with in vivo electroporation. The NS5A-based genetic vaccines primed high Ab levels, with IgG titers of >10(4) postimmunization. With respect to CD8(+) T cell responses, the coNS5A gene primed more potent IFN-γ-producing and lytic cytotoxic T cells in wt mice compared with NS5A-Tg mice. In addition, high frequencies of NS5A-specific CD8(+) T cells were found in wt mice after a single immunization. To test the functionality of the CTL responses, the ability to inhibit growth of NS5A-expressing tumor cells in vivo was analyzed after immunization. A single dose of coNS5A primed tumor-inhibiting responses in both wt and NS5A-Tg mice. Finally, immunization with the coNS5A gene primed polyfunctional NS5A-specific CD8(+) T cell responses. Thus, the coNS5A gene is a promising therapeutic vaccine candidate for chronic HCV infections.

The use of epitope arrays in immunodiagnosis of infectious disease: hepatitis C virus, a case study

Serodiagnosis of infectious disease is often based on the detection of pathogen-specific antibodies in a patient's blood. For this, mixtures of pathogen-related antigens are used as bait to capture corresponding antibodies in solid phase immunoassays such as enzyme immunoassay (EIA). Western blots provide improved diagnostic power as compared with EIA due to the fact that the mixture of markers in the EIA well is resolved and tested as individual antigens on the Western blot. Hence, confirmation of EIA results is accomplished using the antigen arrays of Western blots. Here we took this approach one step further and tested the attributes of using epitope arrays in a diagnostic platform coined "combinatorial diagnostics." As a case in point, we tested a panel of phage-displayed epitope-based markers in the serodiagnosis of hepatitis C virus (HCV). The repertoire of HCV antigens was deconvoluted into panels of distinct linear and conformational epitopes and tested individually by quantitative EIA. Combinatorial diagnostics proved to be effective for the discrimination between positive and negative sera as well as serotyping of HCV.

Progress in the development of preventive and therapeutic vaccines for hepatitis C virus

Hepatitis C virus (HCV) is a blood borne disease estimated to chronically infect 3% of the worlds' population causing significant morbidity and mortality. Current medical therapy is curative in approximately 50% of patients. While recent treatment advances of genotype 1 infection using directly acting antiviral agents (DAAs) are encouraging, there is still a need to develop vaccine strategies capable of preventing infection. Moreover, vaccines may also be used in future in combination with DAAs enabling interferon-free treatment regimens. Viral and host specific factors contribute to viral evasion and present important impediments to vaccine development. Both, innate and adaptive immune responses are of major importance for the control of HCV infection. However, HCV has evolved ways of evading the host's immune response in order to establish persistent infection. For example, HCV inhibits intracellular interferon signalling pathways, impairs the activation of dendritic cells, CD8(+) and CD4(+) T cell responses, induces a state of T-cell exhaustion and selects escape variants with mutations CD8(+) T cell epitopes. An effective vaccine will need to produce strong and broadly cross-reactive CD4(+), CD8(+) T cell and neutralising antibody (NAb) responses to be successful in preventing or clearing HCV. Vaccines in clinical trials now include recombinant proteins, synthetic peptides, virosome based vaccines, tarmogens, modified vaccinia Ankara based vaccines, and DNA based vaccines. Several preclinical vaccine strategies are also under development and include recombinant adenoviral vaccines, virus like particles, and synthetic peptide vaccines. This paper will review the vaccines strategies employed, their success to date and future directions of vaccine design.

Evaluation of core and NS4B synthetic peptide-based immunoassays for the detection of hepatitis C virus antibodies in clinical samples from Cameroon, Central Africa

BACKGROUND

According to previous data, the antibodies produced during natural hepatitis C virus (HCV) infection frequently recognize amino acids 10-43 in the core protein and 1689-1740 or 1921-1940 in the non-structural 4B (NS4B) protein. The reactivity of these peptides with the corresponding antibodies has mainly been evaluated using serum samples from Western countries where HCV genotype 1 (HCV-1) is predominant, and no information is available concerning samples from sub-Saharan countries where high HCV variability has been reported. OBJECTIVE OF THIS STUDY: To evaluate the performance of HCV core and NS4B peptide-based immunoassays in the serodiagnosis of HCV infection in Cameroon subjects.

STUDY DESIGN

Three core and four NS4B-based synthetic peptides derived from HCV genotypes 1b and 2a were designed and tested against a panel of 151 serum samples from Cameroon (40 positive for HCV-1, 32 for HCV-2, 39 HCV-4, and 40 HCV-negative).

RESULTS

The three core peptides all demonstrated strong immunoreactivity, regardless of the HCV genotype from which they were derived, with greater than 90% and 92% sensitivity and specificity. In contrast, the NS4B-derived peptides exhibited lower sensitivities (24.3-65.8% depending on the HCV genotype) but higher specificities (100% for all four peptides tested).

CONCLUSIONS

Our findings indicate that an HCV core peptide could be used for the diagnosis of chronic HCV infection. Among the NS4B peptides tested, a chimeric NS4B peptide encompassing both N- and C-terminal portions of the NS4B protein gave a much better performance than the two component N- and C-terminal peptides used individually.

Serum levels of anti-NS4a and anti-NS5a predict treatment response of patients with chronic hepatitis C

In order to understand better the clinical significance and prognostic value of antibody responses to HCV proteins and in search for parameters that may allow the early identification of non-sustained responders to therapy, antibody levels were measured against NS3, NS4a and NS5a at baseline in the serum of 120 patients chronically infected with HCV of genotype 1 that were classified as sustained responders, relapsers, or non-responders to therapy. The capacity of these antibody tests to predict therapy-outcome was evaluated. While no differences were observed in the anti-NS3 responses in these different response groups, anti-NS4a and anti-NS5a antibodies were observed more frequently and at higher titres in sustained responders versus non-responders or non-sustained responders (=non-responders + relapsers). Based on this observation, a combination of test results consisting of 'the absence of NS4a (AA 1687-1718) antibody at baseline and the presence of HCV-RNA exceeding 10(5) IU/ml after 1 week of treatment' was identified which predicts non-sustained response to treatment with 100% certainty. Replacing the HCV-RNA decision limit by a HCV-core antigen level of >15 pg/ml resulted in the same predictive value. The proposed algorithm also holds for patients treated with peg-interferon and ribavirin. In conclusion, in patients with chronic HCV infection, the decision to continue or stop treatment can be made after 1 week of treatment with (peg)-interferon alpha and ribavirin.

A novel recombinant multiepitope protein as a hepatitis C diagnostic intermediate of high sensitivity and specificity

A novel recombinant multiepitope protein has been designed that consists of six linear, immunodominant, and phylogenetically conserved epitopes from hepatitis C virus. Five of these antigens (core, NS3, NS4I, NS4II, and NS5) are being used in many of the third-generation kits while sixth epitope (core3g) is an additional sequence from a newly identified Indian isolate. The genes for these epitopes have been joined together to code for a single multiepitope protein that has been evaluated for its diagnostic potential for the detection of anti-HCV antibodies in human plasma. Two separate synthetic genes have been designed, both encoding the same six epitopes in a single open reading frame along with spacers having additional amino acids to function as flexible (r-HCV-F-MEP) or rigid (r-HCV-R-MEP) linkers. High-level expression of hepatitis C multiepitope protein in Escherichia coli has been achieved. The protein has been purified using a single affinity step yielding >25 mg pure protein/liter culture and used as the coating antigen in anti-HCV EIA. The use of this multiepitope protein eliminates the requirement for multiple diagnostic intermediates for the development of anti-HCV diagnostic kit. The sensitivity and specificity of the HCV multiepitope protein was evaluated by Boston Biomedica Worldwide Performance Panels, HCV Seroconversion Panels and Viral Co-infection Panels, and was found to be comparable with commercially available anti-HCV EIA kits. This analysis indicated its unequivocal performance as capture antigen in anti-HCV EIA. The high epitope density, careful choice of epitopes and use of E. coli system for expression, coupled with simple purification protocol provides the potential for the development of an inexpensive diagnostic test with high degree of sensitivity and specificity.

DNA immunization efficiently targets conserved functional domains of protease and ATPase/helicase of nonstructural 3 protein (NS3) of human hepatitis C virus

Nonstructural protein 3 (NS3) of human hepatitis C virus (HCV) is a conserved multi-functional protein essential for replication and translation of viral RNA and polyprotein processing. Early T-cell response against NS3 is capable of restricting viremia. We aimed at characterizing the immunogenicity in gene immunization of the conserved regions of NS3 critical for protein folding and activity. C57BL/6 mice were injected with NS3 gene of Russian HCV 1b isolate 274933RU. Immunization did not exert any overt histological changes and had no long-term effects on the immune status of NS3 gene-recipients. The immune response in NS3 gene-recipients was screened by antibody ELISA, T-cell proliferation test and immune assays for specific cytokine production. T-lymphocytes of NS3 gene-recipients proliferated in response to peptides representing conserved regions of protease and ATPase/helicase. Stimulated T-lymphocytes produced IL-2, and in response to protease-derived peptides, also IFN-gamma. Potent and long-lasting antibody response was raised against conserved NS3 regions including "Greek-key" motif of protease, motifs II, V and polynucleotide-binding domains of ATPase/helicase. Thus, gene immunization effectively targeted conserved regions critical for NS3 protease and helicase function. In type and specificity, immune response of NS3 gene-immunized mice mimicked immunity achieved in the acute self-limiting HCV infection of human and primates and in virus-exposed healthy individuals, indicating promiscuity of NS3 as immunogen.

Characterization of monoclonal antibodies and epitope mapping of the NS4 protein of hepatitis C virus

Recombinant DNA containing sequences of HCV NS4 protein was expressed in Escherichia coli cells. Six hybridoma clones producing monoclonal antibodies (MAB) to recombinant NS4 protein (rNS4), aa 1677-1756, were developed. Mapping with a panel of 33 peptides and reciprocal competitive EIA have shown that MAB obtained revealed five antigen determinants, not described earlier: MAB 3F11 and 3F12-one genotype-independent epitope of NS4A (aa 1700-1707) common for genotypes 1, 2 and 3; MAB 1D11-genotype-independent epitope (aa 1713-1728) and MAB 1D3-genotype (subtype 1b)-specific epitope of NS4B (aa 1711-1731); MAB 6B11 and C1-two conformation-dependent determinants in 5-1-1 region. These data indicate that the 5-1-1 region of NS4 protein has a complex antigenic structure and contains at least eight epitopes, including five, revealed in the present work. MAB obtained recognized native viral protein in the cytoplasm of liver cells of patients with chronic hepatitis C. The positive rates of the immunostaining for NS4 antigen using MAB 6B11, 1D11 and 3F12 were 64, 59 and 50%, respectively. It was found that 6B11 MAB to a conformation-dependent epitope much more actively interacts with native NS4 than with the recombinant protein to which MAB was developed. The epitope recognized by 6B11 MAB is highly immunogenic since it induces the B-cell response in all patients investigated with identified anti-NS4 antibodies in blood serum. The MAB panel obtained in this study may become a useful tool for the diagnostic purposes, for the investigation of NS4B function and for the host-viral interactions at the cell level.

Identification of B cell epitopes of hepatitis C virus RNA dependent RNA polymerase

The aim of this study was to identify the B cell epitopes of hepatitis C virus (HCV) NS5B RNA dependent RNA polymerase (RdRp). The truncated HCV NS5B protein NS5B-dc21 was expressed in Escherichia coli and its antigenicity was confirmed by Enzyme-Linked Immunosorbent Assay (ELISA) using 130 HCV-positive human sera and 15 negative sera. Antibodies specific to NS5B-dc21 protein were purified by affinity chromatography using sepharose-4B coupled with the recombinant protein. A 12-mer phage displayed random peptide library was screened four rounds with the purified antibodies. Three epitopes were identified from the phage library, which correspond to amino acids 2444-2452, 2521-2528, and 2915-2925 of HCV RdRp. These epitopes were then expressed in E. coli as fusion proteins with phage M13 pIII protein. ELISA demonstrated that two of these epitopes (P4 and P34, corresponding to amino acids 2443-2452 and amino acids 2512-2528, respectively) have good reactivity and sensitivity. Mutagenesis study of P4 peptide showed that this epitope, which is derived from a phage displayed library, exhibited higher affinity with HCV serum than the corresponding original HCV sequences.

Antigenic heterogeneity of the hepatitis C virus NS5A protein

The effect of sequence variability between different types of hepatitis C virus (HCV) on the antigenic properties of the NS5 protein was studied by using recombinant proteins. A strong antigenic region was identified within the HCV NS5A protein at amino acids 2212 to 2313. Forty-five unique sequences encompassing this region were selected from GenBank and were compared to each other. The results of this analysis showed that the primary structure of this strong antigenic region is highly variable. Percent homology between different genotype sequences varied from 40.4 to 72.5%. Thirteen representative sequences from all six HCV genotypes were selected to design synthetic genes coding for this antigenic region. These genes were assembled by PCR from synthetic oligonucleotides and expressed in Escherichia coli as hybrid proteins with glutathione S-transferase. All 13 fusion proteins were purified from bacterial lysates and used to test a panel of anti-HCV positive sera (n = 91) obtained from patients infected with HCV genotypes 1 through 6. All but two proteins immunoreacted with 62 to 93% of HCV anti-NS5-positive serum samples. Although a variable degree of genotype-specific antigenic reactivity was detected, only one protein demonstrated a noticeable preference to immunoreact with antibodies against the homologous HCV genotype. On the other hand, closely related proteins derived from the same subtype or genotype immunoreacted with significantly different efficiency with HCV antibodies. Thus, sequence variability has a profound effect on the antigenic properties of the NS5A immunodominant regions. This observation should be taken into consideration in the development of diagnostic tests for the efficient detection of anti-HCV activity in serum specimens.

ADAM-HCV, a new-concept diagnostic assay for antibodies to hepatitis C virus in serum

We screened phage libraries using sera from noninfected individuals and patients infected by hepatitis C virus (HCV). By applying different selection and maturation strategies, we identified a wide collection of efficient phage-borne ligands for HCV-specific antibodies. The selected ligands retained their antigenic properties when expressed as multimeric synthetic peptides. Peptides that mimic several immunodominant epitopes of the virus were used to develop a novel type of diagnostic assay which efficiently detects antibodies to HCV in serum. This type of analysis provides a conclusive diagnosis for many patients identified as indeterminate according to presently available serological assays.

"Affinity maturation" of ligands for HCV-specific serum antibodies

We have previously screened a phage-displayed random peptide library using sera from patients and identified ligands binding to antibodies specifically associated with the hepatitis C virus infection. The ability of these peptides to detect HCV-specific antibodies was improved through an in vitro procedure which mimics the natural process of antibody affinity maturation operating in secondary immune response. Libraries were generated by mutating the sequence of the original peptide through a protocol that efficiently introduced substitution, insertion and deletion mutations on a single or population of clones. Screening these libraries isolated mutants that displayed increased specific reactivity with a broader range of sera from HCV-infected patients. Several variants of the original peptide were identified which discriminate between the various components of the specific polyclonal response. This methodology to select artificial ligands from RPL using sera and to enhance their diagnostic properties by affinity maturation makes the development of a diagnostic assay to detect disease-associated antibodies feasible, without requiring the natural antigen.

Characterization of a monoclonal antibody and its single-chain antibody fragment recognizing the nucleoside Triphosphatase/Helicase domain of the hepatitis C virus nonstructural 3 protein

We have produced a murine monoclonal antibody (MAb), ZX10, recognizing the NTPase/helicase domain of the hepatitis C virus (HCV) nonstructural 3 protein (NS3), from which we designed a single-chain variable fragment (ScFv). The ZX10 MAb recognized a discontinuous epitope of the NTPase/helicase domain, of which the linear sequence GEIPFYGKAIPL at residues 1371 to 1382 constitutes one part. cDNAs from variable regions coding for the heavy and light chains were cloned, sequenced, and assembled into the NS3-ScFv, which was inserted into procaryotic and eucaryotic expression vectors. Escherichia coli-expressed NS3-ScFv inhibited the binding of the ZX10 MAb to NS3, confirming a retained specificity. However, the ability to bind the peptide 1371-1382 had been lost. In vitro-translated NS3-ScFv and HCV NS3/NS4A were coprecipitated by antibodies to HCV NS4A, confirming the in vitro activity of the NS3 ScFv. Thus, we have designed a functional NS3 NTPase/helicase domain-specific ScFv which should be evaluated further with respect to disturbing enzymatic functions of the NS3 protein.

Development of low cost peptide-based anti-hepatitis C virus screening and confirmatory assays: comparison with commercially available tests

Screening and confirmatory low cost reagent tests have been developed for detection of anti-hepatitis C virus (HCV). Assays are based on the use of specific synthetic peptides from several structural and non-structural viral proteins. The efficacy of the screening anti-HCV EIA-Spep assay was compared with both Abbott EIA 2.0 (Abbott Laboratories, North Chicago, IL) and Ortho EIA 2.0 (Ortho Diagnostic Systems, Raritan, NJ) anti-HCV detection kits and the confirmatory EIA-Cpep assay was compared with the Abbott Matrix anti-HCV confirmation test. In the EIA-Spep, a pool of 3 peptides was added to each well of a microtiter plate. In EIA-Cpep, each well was separately coated with 1 of 4 peptides and 1 recombinant protein. A total of 867 blood donor samples from Costa Rica tested simultaneously with the 3 screening assays yielded the same specificity and negative predictive values of > or =99.9% and 100%, respectively. A comparative study on voluntary blood donor samples from Honduras, Nicaragua, and El Salvador using the 2 anti-HCV confirmatory assays revealed different patterns that are 46% positive, 24% indeterminate, and 30% negative with the EIA-Cpep assay vs. 31% positive, 48% indeterminate, and 21% negative with the Matrix assay. A study of 71 patient samples from Costa Rica showed a higher correlation between initially reactive samples when analyzed by the Abbott and Ortho kits, than when the assay results were compared between the Abbott and EIA-Spep kits; the latter detected 7 and 15 non-reactive samples, respectively. These results could reflect the use of a similar antigen source for the 2 commercial assays. The presence of HCV RNA in a group of 29 samples analyzed was related to the simultaneous reactivity in all 3 screening assays. None of the discordant samples had detectable levels of HCV RNA. Economic difficulties for health care services in the developing countries of Central America have prevented implementation of routine anti-HCV blood donor screening tests. This is likely to be the primary reason for uncontrolled dissemination of HCV, and the lack of identification of potential high risk groups. Alternative low cost reagents developed locally as described in this article could be a useful tool in the control of HCV spread throughout the developing world.

Antigenic heterogeneity of the hepatitis C virus NS4 protein as modeled with synthetic peptides

The effect of sequence heterogeneity on the immunologic properties of two strong antigenic regions of the hepatitis C virus (HCV) NS4 protein was studied by using a set of 443 overlapping 20-mer synthetic peptides. One antigenic region comprising the cleavage site between NS4a and NS4b (region 5-1-1) was modeled with peptides derived from 73 different known sequences, representing HCV genotypes 1-6. The other antigenic region, designated region 59 and located at the C-terminus of the NS4b protein, was modeled with peptides from 7 known sequences representing genotypes 1-3. All peptides were tested for antigenic reactivity by enzyme immunoassay with a panel of anti-HCV-positive serum specimens representing genotypes 1-5. The data demonstrated that immunoreactive peptides fell into two groups. One group, represented by N-terminal peptides, demonstrated genotype-independent immunoreactivity; the other group, from the central part of region 5-1-1, showed strict genotype specificity. Nineteen peptides from the genotype-independent group strongly immunoreacted with a wide range of serum samples containing antibodies to all 5 HCV genotypes. Twenty-five peptides from the genotype-specific group were found to strongly react with serum containing antibodies only to the genotype from which the peptides were derived. Similar to the N-terminal part of region 5-1-1, peptides derived from region 59 did not show genotype-specific immunoreactivity. Some peptides derived from the central part of region 59 showed very strong and broad antigenic reactivity. Thus, after examining two antigenic regions of the NS4 protein, we identified short sequences that can be used for the efficient detection of either genotype-independent or genotype-specific HCV antibodies.

Quantitative antibody responses to structural (Core) and nonstructural (NS3, NS4, and NS5) hepatitis C virus proteins among seroconverting injecting drug users: impact of epitope variation and relationship to detection of HCV RNA in blood

To gain insight into the natural history of hepatitis C virus (HCV), 13 human immunodeficiency virus (HIV)-seronegative injecting drug users were studied who seroconverted for HCV as determined by third-generation enzyme-linked immunosorbent assay, showed an ensuing antibody response to HCV, and were not treated with any antiviral drugs during follow-up. Subjects included 13 untreated HIV-negative individuals, of whom 5 (38.5%) apparently cleared HCV and were polymerase chain reaction (PCR)-negative in at least 3 consecutive samples, 3 (23.1%) showed transient viremia and were PCR-negative in 1 sample during the study period, and the other 5 (38.5%) showed persistent viremia. Viremia was determined longitudinally by reverse-transcription PCR (RT-PCR) and quantified by branched DNA (bDNA). HCV genotypes were determined on serial samples during follow-up. Quantitative antibody levels to core, NS3, NS4, and NS5 were determined using the Chiron RIBA HCV-titering Strip Immunoblot Assay, which is based on HCV genotype 1. The antibody responses to core, NS3, NS4, and NS5 were erratic. In individuals infected with HCV genotype 1, significantly higher median antibody responses to core (P =.02) and to NS4 (P =.04) were found as compared with those infected with other genotypes, showing a significant impact of HCV genotype specificity of the assay. In groups infected with HCV genotype 1, significantly higher median NS3 antibody titers (2.61 relative intensity [RI] vs. 0.38 RI; P =.003) were found in the individuals with persistent viremia than in those with apparent resolution of HCV RNA in blood. In groups infected with genotypes other than genotype 1, significantly higher median NS3 antibody titers (0.89 RI vs. 0.03 RI; P =.0004) and NS5 antibody titers (1.86 RI vs. 0.01 RI; P =.006) were found in the individuals with persistent viremia than in those with apparent resolution of HCV RNA in blood. Individuals with viral persistence had higher HCV-RNA loads with higher antibody responses as compared with individuals with apparent viral clearance from blood. Apparent viral clearance from blood was observed in an unexpectedly high percentage (38.5%), associated with a significant decrease of antibodies to NS3, independent of HCV genotype, as compared with individuals with persistent viremia (P <.005). Apparent viral clearance from blood with gradual loss of antibodies to various HCV proteins, independent of HCV genotype, was observed in 4 of the 5 individuals within approximately 1 year after HCV seroconversion, whereas 1 of these individuals apparently cleared the virus from blood, with complete seroreversion.

Enhanced cellular immunity to hepatitis C virus nonstructural proteins by codelivery of granulocyte macrophage-colony stimulating factor gene in intramuscular DNA immunization

Hepatitis C virus (HCV) nonstructural (NS) proteins appeared to be important targets for HCV vaccine development, since NS-specific T-helper-cell responses are associated with clearance from acute HCV infection. In this report, we have constructed a plasmid, pTV-NS345, that encodes the HCV NS3, NS4 and NS5 proteins (NS345) and a bicistronic plasmid, PTV-NS345/GMCSF, in which the HCV NS345 polyprotein and GMCSF are translated independently. Intramuscular inoculation with pTV-NS345 plasmid DNA into the Buffalo rats generated both antibody and T-cell proliferative responses to each NS protein. The expression of GMCSF, together with HCV NS345 proteins, appeared to significantly increase T-cell proliferative responses. In particular, the inoculation of a bicistronic plasmid generated higher T-cell proliferative responses to each NS protein than did the coinjection of two separate plasmids, pTV-NS345 and pTV-GMCSF. These results demonstrate that the codelivery of GMCSF augmented HCV NS345-specific cellular immunity and that the intensity of the immunity was differed depending on how GMCSF gene is codelivered.

Restricted isotypic antibody reactivity to hepatitis C virus synthetic peptides in immunocompromised patients

An enzyme immunoassay based on three synthetic peptides from the core, NS4, and NS5 regions of hepatitis C virus allowed the detection of antibodies in 100% of immunocompetent infected patients and in 91% of immunocompromised patients (hemodialysis and hemophiliac patients). Immune impairment seemed to restrict the spectrum of antibody isotypes reacting to the core peptide.

DNA-based selection and screening of peptide ligands

Phage display selection strategies rely on the physical link between the displayed heterologous protein ligand and the DNA encoding it. Thus, genes expressing a ligand with a specific binding affinity can be selected rapidly. To improve the specificity and sensitivity of this technology for potential use in identifying ligands to a specific antibody present in a complex mixture, we incorporated a DNA selection step along with the phage display technology. Ligands for hepatitis C virus (HCV) antibodies present in serum were identified by panning a phage-displayed random peptide library against pools of serum HCV antibodies. An additional DNA hybridization screening step using single-stranded DNA isolated from one of the pools increased the specificity and sensitivity, resulting in the selection of an HCV antibody ligand with diagnostic potential.

Identification of antigenic sites on three hepatitis C virus proteins using phage-displayed peptide libraries

A novel approach to screening phage-displayed peptide libraries has been used to identify hepatitis C virus (HCV) core, NS4 and NS5 sequences, which are antigenic in humans. Two random peptide libraries were used for screening using a mixture of HCV-positive sera or individual antibodies to core, NS3, NS4, and NS5 HCV proteins affinity-purified from this mixture. Sequencing of 56 selected phage clones resulted in 28 different peptide sequences and identification of seven antigenic regions, three in the core protein (19-26, 34-49, and 73-83), three in the NS4 (1681-1693, 1712-1718, and 1726-1736) and one in the NS5 protein (2251-2260). No NS3-specific peptides were identified. The immune response to core, NS4 and NS5 proteins includes a variety of linear determinants whereas epitopes on the investigated part of NS3 protein appear to be conformation-dependent.

Efficient display of an HCV cDNA expression library as C-terminal fusion to the capsid protein D of bacteriophage lambda

We describe the construction and characterization of a hepatitis C virus (HCV) cDNA expression library displayed as a fusion to the carboxy terminus of the capsid protein D of bacteriophage lambda. cDNA inserts were obtained by tagged random-priming of the HCV genome and cloned into a lambda vector from which chimeric phage bearing both wild-type D protein and D fusion products on the capsid surface were produced. The resulting library was affinity-selected with anti-HCV human monoclonal antibodies recognizing linear or conformational epitopes, and human sera from HCV-infected patients. Selection was monitored by immuno-screening experiments, ELISA, and sequence analysis of positive clones. The performance of this library was compared with two additional HCV cDNA display libraries generated as N-terminal fusions to the III and VIII capsid proteins of filamentous phage M13. The results obtained demonstrate the great potential of the lambda display system for constructing complex cDNA libraries for natural ligand discovery.

Human and murine antibody recognition is focused on the ATPase/helicase, but not the protease domain of the hepatitis C virus nonstructural 3 protein

The hepatitis C virus (HCV) nonstructural (NS) 3 protein has been shown to possess at least two enzymatic domains. The amino terminal third contains a serine-protease domain, whereas the carboxy terminal two thirds is comprised of an adenosine triphosphatase (ATPase)/helicase domain. These domains are essential for the maturation of the carboxy-terminal portion of the HCV polyprotein and catalyze the cap synthesis of the RNA genome. In this report, human and murine antibody responses induced by NS3 were characterized using a recombinant full-length NS3 (NS3-FL) protein, or the isolated protease or ATPase/ helicase domains, expressed and purified from Escherichia coli. Sera from 40 patients with chronic HCV infection were assayed in enzyme-linked immunoassays (EIAs) for antibody binding to the panel of NS3 proteins. Virtually all patient sera contained antibodies specific for NS3-FL and the ATPase/helicase domain, whereas only 10% of sera reacted with the protease domain of NS3. Human antibodies reactive with NS3-FL were highly restricted to the immunoglobulin G1 (IgG1) isotype and were inhibited by soluble ATPase/helicase, but not by the protease domain. The anti-NS3 (ATPase/helicase) reactivity decreased on denaturation by sodium dodecyl sulfate (SDS) and beta-mercaptoethanol (2ME), suggesting the recognition of nonlinear or conformational B-cell determinants. Similar to infected humans, mice immunized with NS3-FL developed high-titered primary antibody responses to the NS3 ATPase/ helicase domain, whereas an anti-NS3 protease response was not observed after primary or secondary immunizations. Thus, the human and murine humoral immune responses to the HCV NS3 protein are focused on the ATPase/helicase domain, are restricted to the IgG1 isotype in humans, and are conformationally dependent. Unexpectedly, in both species, the NS3 protease domain, present in the context of the full-length NS3, appears to possess low intrinsic immunogenicity in terms of antibody production.

Characterization of a linear epitope in the nonstructural region 4 of hepatitis C virus with reactivity to seroconversion antibodies

Mapping and possible diagnostic meaning of a highly conserved, linear NS4 epitope (NS4/3), located outside the C100-3 antigen within the carboxyl terminal proportion of the NS4 region, with major immunoreactivity with specimens of patients with HCV infection from various geographic origins is described. Transient, acute-phase IgM anti-HCV NS4/3 was detected coincidentally or earlier than active IgG anti-HCV NS4/3 response with four well-characterized seroconversion panels. GenBank alignment studies identified patch homologies between the NS4/3 sequence and a number of non-HCV proteins, which may explain part of the cross-reactivity of the NS4/3 epitope. Some of the "false positive reactivities" of the NS4/3 epitope with asymptomatic blood donors, not being confirmed with FDA-approved anti-HCV assays without the NS4/3 epitope, may be explained by recognition of very early seroconversion antibodies.

Immune response to an epitope of the NS4 protein of hepatitis C virus in HCV-related disorders

NS4, a nonstructural protein of HCV, is a frequent target of antibodies in infected subjects. According to recent data, the antibodies frequently recognize the sequence 1921-40 of the NS4 protein. The aim of this work was to analyze antibody reactivity with the sequence 1921-40 in different HCV-related disorders. Although this sequence is located in a relatively invariant region of viral genome, two strain-specific sequences are described. Thus, three NS4 1921-1940 peptides were synthesized: the BK shared by most viral strains, the J6 (strain 2a), and the J8 (strain 2b). The peptides were used as antigens in the solid phase for measuring serum IgG antibodies in an ELISA assay. Antibodies reactive with the 1921-40 BK peptide were detected in 64% of sera from patients with autoimmune hepatitis (AIH), 51% from chronic hepatitis C (CHC), and 22% from mixed cryoglobulinemia (MC). The frequency of positive sera in MC was significatively lower than in AIH (P < 0.0001) or CHC (P < 0.0021). Similar results were obtained with the J6 and J8 peptides. All sera that did not react with the BK peptide were negative on J6 and J8 and conversely most sera reacting with the BK peptide also bound the J6 and the J8 peptides. No correlation was found between the genotype of the infecting virus and the presence of antibodies to any of the NS4 peptides. These results indicate that many HCV-infected subjects produce antibodies to the NS4 sequence 1921-40. The immune response to this sequence is not strain specific and varies with the different disorders associated with HCV infection.

Identification of antigenic regions in the GB hepatitis viruses GBV-A, GBV-B, and GBV-C

The genomes of two novel members of the Flaviviridae associated with GB agent hepatitis (GB viruses A and B) were cloned and sequenced recently. The genome of a third novel virus (GB virus C), related to but distinct from GB viruses A and B, has also been identified and characterized. Overlapping clones encompassing the large open reading frames of these three viruses have been expressed in E. coli as CTP:CMP-3-deoxy-D-manno-octulosonate cytidylyltransferase (CKS) fusion proteins. Bacterial lysates were subjected to Western blot analyses using sera from GB agent-infected tamarins and human sera from various individuals with or "at risk" for non-A, non-B, non-C, non-D, non-E hepatitis. Antigenic regions were identified in the putative NS3, NS4, and NS5 proteins from all three viruses. An antigenic region was also identified in the putative core protein of GB virus B. Many of the clones identified originally as encoding antigenic proteins were quite large. To map these regions more narrowly, smaller overlapping clones were generated by polymerase chain reaction (PCR), expressed as recombinant CKS fusion proteins and tested by Western blot. Additionally, a lambda gt11 expression library was generated from infectious tamarin sera and immunoscreened. These studies have identified at least three epitopes in GB virus A, five epitopes in GB virus B and four epitopes in GB virus C.

Characterization of the antibody reactivity to synthetic peptides from different parts of the hepatitis C virus genome

Infection by hepatitis C virus (HCV)*, the aetiologic agent responsible for the majority of non-A-non-B posttransfusion hepatitis, is detected by assaying for antibodies against structural and nonstructural recombinant proteins or synthetic peptides. The aim of this study was to characterize the antibody reactivity of selected sera against antigenic peptides spanning immunodominant regions of the core, NS4 and NS5 HCV proteins. Reactivity to synthetic peptides was determined by enzyme immunoassay (EIA) for 11 selected sera from blood donors (good responders), for 27 selected sera from hemodialysis patients (poor responders), all positive for HCV antibodies (tested by different second and third-generation assays), and for 7 negative sera. Some peptides from the core and the NS4 region were widely recognized by the tested sera. Sera not reactive with core, NS4, or NS5 region by some immunoblot assays exhibited reactivity against peptides from these proteins. Autoimmune reactivity associated with HCV infection was evaluated by using a synthetic peptide derived from the GOR peptide; 8/11 HCV-positive sera were found reactive against this peptide. No correlation was found between reactivity to any of the peptides tested and the presence of HCV RNA in the serum or with HCV genotype. The EIA reactivity of peptides from the core region suggested a multideterminant antigenic structure, where reactivity of each epitope may be differentially affected by neighboring amino acids depending on individual sera. This situation was particularly evidenced in selected sera from poor responder specimens where a more restricted antibody response to core peptides was observed. Reactivity of sera from HCV-infected patients with synthetic peptides from the core, NS4, and NS5 regions indicated the presence of multiple linear epitopes (particularly in the core region) that may be used in a mixture for immunodiagnosis; however, the length and exact position of the synthetic peptides must be chosen carefully.