Demonstration of a hepatitis C virus-specific antigen predicted from the putative core gene in the circulation of infected hosts

Resistant-Associated Substitutions Do Not Affect HCV RNA and HCV Core Antigen Clearance During Direct-Acting Antiviral Agent Treatment in a Real-World Setting

Background

Since oral direct-acting antiviral agents (DAAs) became available, the global hepatitis C treatment situation has undergone tremendous changes. However there are still many issues worthy of attention in treatment.

Methods

We selected 53 HCV-infected patients who were treated and followed up in the Peking University First Hospital from December 2017 to January 2021 to detect the RASs in HCV. Pearson correlation analysis was used to analyze HCV RNA and HCV cAg, the Fisher exact test and chi-square test was used to compare the effects of RASs on the rate of decline of HCV RNA and HCV core antigen (cAg) during DAA treatment.

Results

The RASs and its prevalence on the NS3 are mainly Y56F 2.56% (1/39), Q80K 23.08% (9/39), S122G 71.79% (28/39), and V170I 38.46% (15/39). On the NS5A were R30Q 10.53% (4/38), P32A 5.26% (2/38), P58S 2.63% (1/39), and Y93H 21.05% (8/38). On NS5B were C316N 71.05% (27/38), C451H 2.63% (1/38), and I585C 2.63% (1/38). There was no significant correlation between the RASs (Y93H, V179I, Q80K, S122G, C316N) and HCV genotype (p > 0.05). The baseline serum HCV RNA and HCV cAg had a significant medium-degree correlation (r = 0.601, p = 0.002). After 1 week of DAA treatment was weak correlation (r = 0.413, p = 0.032). Q80K, S122G, V170I, Y93H, and C316N had no effect on the clearance of HCV RNA and HCV cAg within the first week of DAA treatment (p>0.05).

Conclusion

The HCV genotype may have a limited impact on the presence of the five RASs (Y93H, V179I, Q80K, S122G, and C316N) as shown in this study. HCV RNA and HCV cAg have a correlation, especially at baseline is the highest; the appearance of some RASs has no effect on DAA treatment in most chronic hepatitis C patients.

Correlation analysis of hepatitis C virus core antigen and low viral loads: Can core antigen replace nucleic acid test?

Value of hepatitis C virus (HCV) core antigen (cAg) test has been controversy in patients with low HCV loads for its lower sensitivity. We assessed correlation between HCV-cAg and HCV RNA in serum samples with low viral loads and analyzed the performance of HCV-cAg assay in determining diagnosis and treatment outcomes in chronic hepatitis C patients. Both HCV RNA and HCV-cAg were detected for 2298 serum samples. Correlation analysis was performed between the two tests. Receiver operating characteristics (ROC) curve was used to assess value of HCV-cAg test in determining diagnosis and response outcomes at the different HCV RNA thresholds. The two tests were correlated very well, and moreover, correlation in the low viral load group was higher than that in the high viral load group (r value: 0.901 and 0.517). Positive agreement of HCV-cAg ≥ 3 fmol/L was as high as 97.0% for HCV RNA ≥ 1000 IU/mL, and its negative agreement for HCV RNA < 15 IU/mL was up to 98.9% in all samples. Area under ROCs ranged from 0.939 to 0.992, regardless of HCV RNA thresholds. When lower limit of detection of HCV RNA was 15, 100 or 1000 IU/mL, positive predictive value of HCV-cAg was 96.8%, 98.8% or 92.4%, and its negative predictive value was 87.0%, 89.9% or 98.3%, respectively, on the basis of different cutoff values. High-sensitivity HCV-cAg detection may likely replace HCV RNA to confirm the existence of HCV and to guide the treatment of chronic HCV infection.

Hepatitis C virus core antigen: A simplified treatment monitoring tool, including for post-treatment relapse

BACKGROUND

Simple, affordable diagnostic tools are essential to facilitate global hepatitis C virus (HCV) elimination efforts.

OBJECTIVES

This study evaluated the clinical performance of core antigen (HCVcAg) assay from plasma samples to monitor HCV treatment efficacy and HCV viral recurrence.

STUDY DESIGN

Plasma samples from a study of response-guided pegylated-interferon/ribavirin therapy for people who inject drugs with chronic HCV genotype 2/3 infection were assessed for HCV RNA (AmpliPrep/COBAS Taqman assay, Roche) and HCVcAg (ARCHITECT HCV Ag, Abbott Diagnostics) during and after therapy. The sensitivity and specificity of the HCVcAg assay was compared to the HCV RNA assay (gold standard).

RESULTS

A total of 335 samples from 92 enrolled participants were assessed (mean 4 time-points per participant). At baseline, end of treatment response (ETR) and sustained virological response (SVR) visits, the sensitivity of the HCVcAg assay with quantifiable HCV RNA threshold was 94% (95% CI: 88%, 98%), 56% (21%, 86%) and 100%, respectively. The specificity was between 98 to 100% for all time-points assessed. HCVcAg accurately detected all six participants with viral recurrence, demonstrating 100% sensitivity and specificity. One participant with detectable (non-quantifiable) HCV RNA and non-reactive HCVcAg at SVR12 subsequently cleared HCV RNA at SVR24.

CONCLUSIONS

HCVcAg demonstrated high sensitivity and specificity for detection of pre-treatment and post-treatment viraemia. This study indicates that confirmation of active HCV infection, including recurrent viraemia, by HCVcAg is possible. Reduced on-treatment sensitivity of HCVcAg may be a clinical advantage given the moves toward simplification of monitoring schedules.

Hepatitis C virus screening to reveal a better picture of infection

Antiviral therapy for hepatitis C virus (HCV) infection will be the next revolution in clinical virology. Sensible planning for treatment is needed, starting with population-screening policies ideally using the HCV core antigen. This will result in a more defined picture of the silent spread of HCV.

Recombinant expression of the alternate reading frame protein (ARFP) of hepatitis C virus genotype 4a (HCV-4a) and detection of ARFP and anti-ARFP antibodies in HCV-infected patients

HCV is a single-stranded RNA virus with a single open reading frame (ORF) that is translated into a polyprotein that is then processed to form 10 viral proteins. An additional eleventh viral protein, the alternative reading frame protein (ARFP), was discovered relatively recently. This protein results from a translational frameshift in the core region during the expression of the viral proteins. Recombinant expression of different forms of ARFP was previously done for HCV genotypes 1 and 2, and more recently, genotype 3. However, none of the previous studies addressed the expression of ARFP of HCV genotype 4a, which is responsible for 80 % of HCV infections in the Middle East and Africa. Moreover, the direct detection of the ARFP antigen in HCV-infected patients was never studied before for any HCV genotype. In the present study, recombinant ARFP derived from HCV genotype 4a was successfully expressed in E. coli and purified using metal affinity chromatography. The recombinant ARFP protein and anti-ARFP antibodies were used for detection of ARFP antigen in patients' sera, employing competitive enzyme-linked immunosorbent assay (ELISA) procedures. Furthermore, the recombinant antigen was also used to detect and quantify anti-ARFP antibodies in HCV-infected Egyptian patients at different stages of pegylated interferon/ribavirin therapy, using an ELISA assay. The ARFP antigen was detectable in 69.4 % of RNA-positive sera, indicating that ARFP antigen is produced during the natural course of HCV infection. In addition, significant levels of anti-ARFP antibodies were present in 41 % of the serum samples tested. The important diagnostic value of the recombinant ARFP antigen was also demonstrated.

Therapy-induced clearance of HCV core antigen from plasma predicts an end of treatment viral response

During viral assembly, viral proteins are released into plasma and can be used to infer viral load. The Architect hepatitis C virus (HCV) core antigen (Ag) assay is a potential alternative to HCV RNA quantification for measuring response to therapy and predicting an end of treatment viral response (EOTR). The HCVp22Ag assay was used to infer viral load in 68 window RNA-containing samples and in 284 samples from baseline to week 14 of ribavirin/interferon treatment in 23 patients with EOTR including three who relapsed, 20 not achieving EOTR and 11 controls. HCV Ag and RNA correlated well (r = 0.86) with linear dose responses on dilution. In patients on therapy and control patients, plasma HCV antigen was detected in 51 of 54 with an interpolated LOD cut off between 10(3) and 10(4) RNA IU/mL. Plasma HCV antigenaemia and plasma RNA levels were significantly different in EOTR from non-EOTR patients at 3 days after treatment start and all times thereafter. Positive and negative EOTR predictive values for HCV RNA >2 log drop and HCV Ag loss at 12 weeks were 70% and 74%, 85% and 93% respectively. HCV Ag reactivity has a linear dose response independent of genotype and correlates well with HCV RNA. The failure to clear HCV Ag is as accurate as the failure to clear HCV RNA at twelve weeks into therapy in predicting the likelihood of failure to achieve EOTR. HCV Ag potentially offers a convenient alternative to RNA measurement for defining a futility flag in HCV therapy.

Hepatitis C virus core antigen: analytical performances, correlation with viremia and potential applications of a quantitative, automated immunoassay

BACKGROUND

Testing for hepatitis C virus core antigen (HCV Ag) may represent a complementary tool to anti-HCV and HCV-RNA in the diagnosis and monitoring of HCV infection.

OBJECTIVE

To evaluate the performance characteristics of the automated Abbott ARCHITECT HCV Ag assay.

STUDY DESIGN

Five sites analyzed over 3000 routine serum samples from populations at different risk, comparing HCV Ag results with anti-HCV screening and supplemental assay results and with HCV-RNA.

RESULTS

The HCV Ag assay showed a specificity of 100%, a good precision (CV<10%) and excellent dilution linearity (r>0.999). The sensitivity (3 fmol/L) corresponds to 700-1100 IU/mL of HCV-RNA. A non-linear correlation with HCV-RNA was found: r=0.713 vs. Siemens bDNA (523 specimens), r=0.736 vs. Roche Cobas TaqMan (356 specimens) and r=0.870 vs. Abbott Real-Time PCR (273 specimens). HCV Ag quantitation was equally effective on different HCV genoypes (239 for genotype 1/1a/1b/1c, 108 for genotype 2/2a/2c, 86 for genotype 3/3a, 50 for genotype 4/4a/4c/4d). Testing of subjects at high risk for HCV and with potential or actual impairment of the immune system identified 2 cases negative for anti-HCV and positive for HCV Ag on 361 hemodialyzed (0.6%) and 7 cases on 97 (7.2%) among transplant recipients. HCV Ag positivity anticipated anti-HCV seroconversion in all three cases of acute hepatitis C.

CONCLUSIONS

HCV Ag may be used as reflex testing on anti-HCV positive individuals to confirm or exclude an active infection, and on subjects with acute hepatitis or belonging to high risk groups.

A new sensitive and automated chemiluminescent microparticle immunoassay for quantitative determination of hepatitis C virus core antigen

A new sensitive and automated chemiluminescent assay was developed for the quantitative determination of hepatitis C virus (HCV) core antigen (Ag) in human sera or plasma: the Abbott ARCHITECT HCV Ag test. The assay sensitivity was determined by testing 10 commercial HCV seroconversion panels. Without exception, a positive result for HCV core Ag was observed before anti-HCV detection, resulting in an average reduction in the period between exposure and detection of 35.8 days. Both HCV core Ag and HCV RNA were detected in the panels at the same time, indicating equivalent sensitivity and detectability. A total of 197 HCV specimens comprising genotypes 1a, 1b, 2a, 2b, 3a, 3k, 4a, 5a and 6a were evaluated. Among these, 196 (99.5%), 191 (97%) and 193 (98%) were reactive using the HCV Ag, the immunoradiometric HCV Ag and the Amplicor HCV Monitor 2 assays, respectively. A comparison with the Amplicor HCV Monitor 2 showed a correlation coefficient (r) of 0.74. The specificity of the assay was established at 99.8% by testing 5403 specimens from US volunteer blood donors, hospitalized patients and individuals with medical conditions unrelated to HCV infection, in addition to specimens containing potentially interfering substances.

The role of core antigen detection in management of hepatitis C: a critical review

Several assays in research format and two commercial assays for the detection of hepatitis C virus (HCV) core protein or HCV core antigen have been developed in recent years. In order to elucidate the role and significance of HCV core antigen detection in the diagnosis and management of hepatitis C, we reviewed 56 studies published in peer-reviewed journals until September 2004. Evaluations in transfusion settings showed that the HCV core antigen assay detects HCV infection, similarly as nucleic acid techniques (NAT), between 40 and 50 days earlier than the current third generation HCV antibody screening assays. HCV core antigen levels closely track HCV RNA dynamics, and allow clinical monitoring of a patient's therapy, independently of HCV genotype, however, mainly in the samples with HCV RNA levels above 20,000 IU/ml. Considering the lower sensitivity of HCV core antigen detection in comparison to NAT, the HCV core antigen assay is not practical for the determination of the end of treatment response and sustained viral response, but could be useful for the determination of early viral response in the pegylated interferon-alpha and ribavirin treated patients infected with HCV genotype 1. The HCV core antigen detection is a viable tool for study of hepatitis C pathogenesis. The HCV core antigen can be used as a marker of HCV replication in anti-HCV positive individuals in the areas of the world that cannot afford NAT and/or in the settings that are not equipped or competent to perform HCV RNA testing. Because the manufacturer of HCV core antigen assays recently stopped an active marketing of these assays in several countries, it will, unfortunately and probably, never be possible to determine the actual potential and usefulness of HCV core antigen testing in the management of hepatitis C.

Benefit of hepatitis C virus core antigen assay in prediction of therapeutic response to interferon and ribavirin combination therapy

A highly sensitive second-generation hepatitis C virus (HCV) core antigen assay has recently been developed. We compared viral disappearance and first-phase kinetics between commercially available core antigen (Ag) assays, Lumipulse Ortho HCV Ag (Lumipulse-Ag), and a quantitative HCV RNA PCR assay, Cobas Amplicor HCV Monitor test, version 2 (Amplicor M), to estimate the predictive benefit of a sustained viral response (SVR) and non-SVR in 44 genotype 1b patients treated with interferon (IFN) and ribavirin. HCV core Ag negativity could predict SVR on day 1 (sensitivity = 100%, specificity = 85.0%, accuracy = 86.4%), whereas RNA negativity could predict SVR on day 7 (sensitivity = 100%, specificity = 87.2%, accuracy = 88.6%). None of the patients who had detectable serum core Ag or RNA on day 14 achieved SVR (specificity = 100%). The predictive accuracy on day 14 was higher by RNA negativity (93.2%) than that by core Ag negativity (75.0%). The combined predictive criterion of both viral load decline during the first 24 h and basal viral load was also predictive for SVR; the sensitivities of Lumipulse-Ag and Amplicor-M were 45.5 and 47.6%, respectively, and the specificity was 100%. Amplicor-M had better predictive accuracy than Lumipulse-Ag in 2-week disappearance tests because it had better sensitivity. On the other hand, estimates of kinetic parameters were similar regardless of the detection method. Although the correlations between Lumipulse-Ag and Amplicor-M were good both before and 24 h after IFN administration, HCV core Ag seemed to be relatively lower 24 h after IFN administration than before administration. Lumipulse-Ag seems to be useful for detecting the HCV concentration during IFN therapy; however, we still need to understand the characteristics of the assay.

Usefulness of a new immuno-radiometric assay to detect hepatitis C core antigen in a community-based population

A new immuno-radiometric assay (IRMA) to detect hepatitis C virus (HCV) core antigen (HCVcAg) has been developed. The aim of the present study was to investigate the sensitivity and specificity of this IRMA to measure HCV antigenemia, based on the detection of HCV RNA as the gold standard, and to assess the utility of the IRMA in a community-based population. Anti-HCV positive residents in a hyperendemic area of HCV infection in Japan were studied. Serum levels of HCVcAg were measured using IRMA, and the presence of HCV RNA was determined by a qualitative reverse transcription-polymerase chain reaction (RT-PCR) assay. The sensitivity and the specificity of the IRMA were 96.4 and 100%, respectively. The sensitivity of the IRMA was similar between serological HCV group I (HCV genotypes 1a and 1b) (97.6%) and group II (HCV genotypes 2a and 2b) (94.0%). There was a strong correlation between serum HCVcAg level and HCV-RNA measured by a quantitative RT-PCR (r = 0.832, P < 0.0001). There also was a very strong correlation of HCVcAg level between IRMA measurements performed on serum and those performed on plasma (r = 0.984, P < 0.0001). In conclusion, this new IRMA is useful for the detection of HCV core antigen in a community-based population.

Differential activation of interferon-inducible genes by hepatitis C virus core protein mediated by the interferon stimulated response element

We previously found that hepatitis C virus (HCV) core protein, which possesses the consensus sequence of genotype 1b, transcriptionally activates the interferon (IFN)-inducible 2'-5'-oligoadenylate synthetase (2'-5'-OAS) gene in human hepatocyte cells. To clarify the mechanism of this activation, we further characterized the core protein as an activator of the 2'-5'-OAS gene. We demonstrated that the activation of the 2'-5'-OAS gene by the core protein is a general phenomenon, regardless of HCV genotype and strain. We showed that the 20 N-terminal amino acids (aa) of the core protein were important to the activation of the 2'-5'-OAS gene, although this N-terminal region did not have any effect on the subcellular localization of the core protein. We demonstrated that the core protein was able to activate all promoters possessing the IFN-stimulated response element (ISRE) examined. However, we found that the level of activation of the 2'-5'-OAS gene promoter possessing a particular variant type of ISRE was significantly higher than that of other IFN-inducible gene promoters. This phenomenon was confirmed using synthetic promoters possessing five repeats of the consensus or a 2'-5'-OAS-type ISRE. In addition, we showed that gene activation induced by the core protein is mediated by the ISRE. These results imply that the core protein prefers a subclass of IFN-inducible genes, the promoters of which possess the 2'-5'-OAS-type ISRE. Accordingly, we found that the IFN-inducible double-stranded RNA-specific adenosine deaminase gene promoter, possessing a 2'-5'-OAS-type ISRE sequence, was also efficiently activated by the core protein. The exact mechanism by which the core protein enhances gene expression was not determined, but we could find no effects of core protein on gene expression and phosphorylation status of the components of the JAK-STAT signaling transduction pathway.

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Nonenveloped nucleocapsids of hepatitis C virus in the serum of infected patients

One of the characteristics of hepatitis C virus (HCV) is the high incidence of persistent infection. HCV core protein, in addition to forming the viral nucleocapsid, has multiple regulatory functions in host-cell transcription, apoptosis, cell transformation, and lipid metabolism and may play a role in suppressing host immune response. This protein is thought to be present in the bloodstream of the infected host as the nucleocapsid of infectious, enveloped virions. This study provides evidence that viral particles with the physicochemical, morphological, and antigenic properties of nonenveloped HCV nucleocapsids are present in the plasma of HCV-infected individuals. These particles have a buoyant density of 1.32 to 1.34 g/ml in CsCl, are heterogeneous in size (with predominance of particles 38 to 43 or 54 to 62 nm in diameter on electron microscopy), and express on their surface epitopes located in amino acids 24 to 68 of the core protein. Similar nucleocapsid-like particles are also produced in insect cells infected with recombinant baculovirus bearing cDNA for structural HCV proteins. HCV core particles isolated from plasma were used to generate anti-core monoclonal antibodies (MAbs). These MAbs stained HCV core in the cytoplasm of hepatocytes from experimentally infected chimpanzees in the acute phase of the infection. These chimpanzees had concomitantly HCV core antigen in serum. These findings suggest that overproduction of nonenveloped nucleocapsids and their release into the bloodstream are properties of HCV morphogenesis. The presence of circulating cores in serum and accumulation of the core protein in liver cells during the early phase of infection may contribute to the persistence of HCV and its many immunopathological effects in the infected host.

Development of a simple and highly sensitive enzyme immunoassay for hepatitis C virus core antigen

A highly sensitive enzyme immunoassay (EIA) for the hepatitis C virus (HCV) core antigen (HCVcAg) was developed, and its performance was compared with that of the AMPLICOR HCV test (Roche Molecular Systems). The developed one-step pretreatment method, 30-min incubation of the specimen with a solution containing three different types of detergents (Triton X-100, 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate [CHAPS], and sodium dodecyl sulfate), does not require any special device. Because the interfering anti-core antibody in the sample was sufficiently inactivated by the pretreatment, HCVcAg in the sample could be detected. The immunoreactivity on gel filtration was shifted from void fractions to those corresponding to the molecular mass range from 20 to 25 kDa, which is equal to the estimated molecular mass of HCVcAg, after the pretreatment. By the recovery test with HCVcAg-positive serum, the recovery rate was 93.5 to 106. 5%. There was no interference with the EIA by anticoagulants or blood components in the serum. When the cutoff value was tentatively set at 0.5 mU/ml based on the distribution of healthy subjects' sera, the sera of all healthy subjects (n = 125) and patients with hepatitis B (n = 50) were negative. HCVcAg was detected in sera from 57 of 73 individuals (78.1%) with anti-HCV antibody. Similarly, HCV RNA was detected in sera from 59 individuals (80.8%) with the AMPLICOR HCV as the qualitative test (AMPLICOR HCV test) and in sera from 54 individuals (74.0%) by the AMPLICOR HCV Monitor as the quantitative test (AMPLICOR Monitor test). Concentrations of HCVcAg and HCV RNA (measured by the AMPLICOR Monitor test) correlated significantly (r = 0.8, P < 0.001). On seroconversion panels, HCVcAg was detected during the early stage of infection, when anti-HCV antibodies had not been produced. This assay for HCVcAg is simpler than assays for HCV RNA based on gene technology and shows specificity and sensitivity equivalent to those of the AMPLICOR HCV test.

HCV core immunodominant region analysis using mouse monoclonal antibodies and human sera: characterization of major epitopes useful for antigen detection

Monoclonal antibodies (MAbs) were generated by immunizing mice with a truncated recombinant protein corresponding to the immunodominant region (residues 1-120) of hepatitis C virus (HCV) nucleocapsid protein. The specific recognition by either human sera or mouse monoclonal antibodies of overlapping peptides spanning the core region 1-120 as well as the comparison with epitopes described earlier allowed the fine mapping of HCV core. Within the region 1-120, the major antigenic domain could be restricted to the first 45 amino acids. Indeed, the peptide S42G (residues 2-45) allowed the detection of an anti-HCV core response by all anticore-positive human sera examined. According to their epitope localization, three groups of mouse MABs could be evidenced that were directed against different regions of core. Group II MAbs recognized a strictly linear epitope (QDVKF, residues 20-24), whereas group I MABs were directed against a conformational epitope mainly located at the amino acid residues (QIVGG, 29-33). The epitope of group III MABs was also conformational (PRGRRQPI, residues 58-65). These three epitopes appeared close but different from the three major human epitopes RKTKRNTN, VYLLPR, and GRTWAQPGYPWPLY (residues 7-17, 34-39, and 73-86, respectively). Group II MAB 7G12A8 and group I MAB 19D9D6 were used in a sandwich ELISA for the capture and the detection, respectively, of viral core antigen in sera of patients with chronic HCV infection. After treatment of sera with triton x 100 in acidic conditions, amounts of viral antigen as low as 20 pg/ml of sera could be detected.

Detection of hepatitis C virus core protein circulating within different virus particle populations

Progress in studying pathogenesis and increasing the reliability of hepatitis C diagnosis can be achieved by analysis of different forms of virus particles circulating in blood of both patients and infected persons. Detection of hepatitis C virus (HCV) proteins faces two basic difficulties: low concentration of HCV proteins, and their blocking by antibodies. The aim of this work was to develop a method for the detection of nucleocapsid (core) protein in the plasma of HCV-infected persons using monoclonal antibodies (MABs). Twenty-seven anti-HCV-positive donor plasmas were studied of which 21 contained HCV RNA and 6 were negative. The plasmas were centrifuged for 3 hr at 143,000 g and the antigenic activity of core-protein was studied in the pellets by EIA using four MABs able to recognize four nonoverlapping determinants, two at N-terminus and two at C-terminus of recombinant core (1-150 aa). The determinants detected were present in the natural core protein of at least two genotypes (1b and 3a). Maximal efficiency of recombinant protein detection was achieved with 2 MABs, whereas a combination of 4 MABs was necessary for optimal detection of natural core protein. This is indicative of different conformational structures of natural protein and its gene-engineered analog. The sensitivity of core detection by monoclonal sandwich assay was 1 ng/ml in the pellet or 5 pg/ml after normalization to the initial plasma volume. To dissociate immune complexes, the pellet was treated with 2.5 M KBr after first treating the pellet with the nonionic detergent Tween 80 to remove the virus lipid envelope. Using this treatment protocol, core protein was found in 19 of 21 RNA positive plasmas.

Usefulness of HCV-RNA assays in efficacy evaluation of interferon treatment for chronic hepatitis C: Amplicor HCV assay and branched DNA probe assay

We investigated the usefulness of Amplicor HCV assay and branched DNA probe assay in efficacy evaluation of interferon therapies for chronic hepatitis C. Subjects were 164 HCV-RNA positive chronic hepatitis C patients who received interferon-alpha (IFN-alpha, HLBI) 3-6 MU per day for 14-24 weeks. Their HCV-RNA levels were examined five times by using reverse transcription-polymerase chain reaction (RT-PCR) assay, Amplicor HCV assay, and branched DNA probe assay. Complete response rate in the low virus level patients was significantly higher than in the high virus level patients (P < 0.001). In complete responders, the rate of HCV-RNA disappearance 2 weeks after the initiation of IFN therapy was higher than in non-responders (P < 0.001). The HCV-RNA positive rates in RT-PCR assay and Amplicor HCV assay agreed by 98% or more. The HCV-RNA negative patients 6 months later were still negative 12 months later by Amplicor HCV assay. Before starting interferon therapy for chronic hepatitis C, it is advisable to make a prediction of treatment efficacy by using branched DNA probe assay. In addition, disappearance of HCV-RNA after 2 weeks of treatment could be a useful predictor of the therapeutic efficacy of IFN. Amplicor HCV assay is useful in detecting HCV-RNA and for efficacy evaluation during and after a given interferon therapy.

Detection of hepatitis C virus specific core protein in serum of patients by a sensitive fluorescence enzyme immunoassay (FEIA)

A protein-capture fluorescence enzyme immunoassay (FEIA) was developed using monoclonal antibodies (mAbs) against recombinant hepatitis C virus (HCV) core protein. Four hybridoma cell lines (5E3, 5F11, 515S, 1080S) were established and characterized. These monoclonal antibodies (mAbs) each had IgG1 and OgG2 isotypes, and recognized major B cell epitopes within the immunodominant nucleoprotein amino terminal subregion. Using mAb 5F11 as the first antibody to the solid phase and beta-D-galactosidase-conjugated mAb 5E3 as the second antibody to the protein, we established a specific HCV core protein capturing FEIA capable of detecting as little as 20 pg/ml of recombinant HCV core protein. HCV core protein in serum was detectable after treatment with 4.0% polyethyleneglycol, 0.5 NaOH, and 5% Triton X-100. The results of a peptide inhibition assay indicated that this FEIA is specific for HCV RNA positive sera. The quantity of HCV core protein detected in serum was significantly correlated to the level of HCV RNA. The detection limit for HCV core proteins was an HCV RNA per titer of approximately 10(4)/ml. Using this FEIA system, the detection ratio of HCV core protein in patients with chronic HCV infection was 92.3% (70/76).

Characterization of three novel monoclonal antibodies against hepatitis C virus core protein

Three novel monoclonal antibodies (MAbs) were established against a recombinant hepatitis C virus (HCV) core protein derived from cloned genotype 1b HCV cDNA. MAbs C7-50 and C8-59 recognize a conserved linear epitope represented by amino acid residues 21 to 40 of the nucleocapsid protein. MAb C8-48 is directed against a strain-specific conformational epitope located within the first 82 amino acids. A sensitive two-site MAb-based immunoradiometric assay was established using antibodies directed against distinct epitopes on the nucleocapsid protein. Processed 21 kDa core protein was detected by immunoblotting in human hepatocellular carcinoma cell lines and primary adult rat hepatocytes transfected with a cytomegalovirus promoter-driven expression construct. Immunofluorescence microscopy studies revealed a granular and vesicular cytoplasmic staining pattern. MAb C7-50 was used successfully to detect HCV core antigen in chronically infected chimpanzee liver tissue. These MAbs represent important reagents for the study of HCV biology and for the development of immunodiagnostic assays.

Effective production of the hepatitis C virus core antigen having high purity in Escherichia coli

The amino-terminal half of putative nucleocapsid (core) protein (amino acids 1-115) of hepatitis C virus (HCV) was directly overproduced in Escherichia coli under the control of the tac promoter. Overproduction of core antigen was achieved by inserting several target genes and by optimizing the culture conditions, whereas a large amount of directly expressed and purified core antigen has not yet been reported. Although the level of expression was comparable to that of the conventional E. coli fused expression system, our recombinant proteins contain only HCV amino acid sequence. Using recombinant E. coli, overproduced large-scale culture system was achieved in jar-fermenter. A highly purified sample of the expressed protein was obtained by ion-exchange and gel permeation column chromatography in the presence of 8 M urea. From a 3.5 l culture, approximately 440 mg of recombinant core protein was obtained after a two-step purification procedure. An enzyme-linked immunosorbent assay developed using the highly purified antigen satisfactorily diagnosed hepatitis C.

Uses of flow cytometry in virology

This article reviews some of the published applications of flow cytometry for in vitro and in vivo detection and enumeration of virus-infected cells. Sample preparation, fixation, and permeabilization techniques for a number of virus-cell systems are evaluated. The use of flow cytometry for multiparameter analysis of virus-cell interactions for simian virus 40, herpes simplex viruses, human cytomegalovirus, and human immunodeficiency virus and its use for determining the effect of antiviral compounds on these virus-infected cells are reviewed. This is followed by a brief description of the use of flow cytometry for the analysis of several virus-infected cell systems, including blue tongue virus, hepatitis C virus, avian reticuloendotheliosis virus, African swine fever virus, woodchuck hepatitis virus, bovine viral diarrhea virus, feline leukemia virus, Epstein-Barr virus, Autographa californica nuclear polyhedrosis virus, and Friend murine leukemia virus. Finally, the use of flow cytometry for the rapid diagnosis of human cytomegalovirus and human immunodeficiency virus in peripheral blood cells of acutely infected patients and the use of this technology to monitor patients on antiviral therapy are reviewed. Future prospects for the rapid diagnosis of in vivo viral and bacterial infections by flow cytometry are discussed.

Transmission of hepatitis C virus from mothers to infants. The Vertical Transmission of Hepatitis C Virus Collaborative Study Group

BACKGROUND

Although there are case reports of vertical transmission of hepatitis C virus (HCV), it remains uncertain to what extent infected mothers transmit this virus to their infants.

METHODS

We investigated the transmission of HCV from infected mothers to their babies by analyzing HCV RNA in the blood. Three independent studies were performed. First, 7698 parturient women were tested for anti-HCV antibodies; 53 were positive. Their 54 infants (including one set of twins) were followed prospectively for at least six months and tested for HCV disease were prospectively studied. Third, the families of three HCV-infected infants were examined retrospectively.

RESULTS

Of the 53 antibody-positive mothers, 31 were also positive for serum HCV RNA: Three of the 54 babies born to these mothers (5.6 percent) became positive for HCV RNA during the follow-up period. None of the babies of the 22 women who were antibody-positive but HCV RNA-negative became positive for HCV RNA: In the second study, HCV RNA was detected in one of the six infants of infected mothers. In the third study, HCV RNA was detected in the mothers of the three HCV-infected infants. In each of the seven infected infants we studied, the genomic sequence of HCV was almost identical to that from the mother. These seven mothers had significantly higher titers of HCV RNA than did the mothers of infants with no evidence of infection (mean [+/- SD], 10(6.4 +/- 0.5) vs. 10(4.4 +/- 1.5) per milliliter; P < 0.001).

CONCLUSIONS

HCV is vertically transmitted from mother to infant, and the risk of transmission is correlated with the titer of HCV RNA in the mother.

Isolation and epitope characterization of human monoclonal antibodies to hepatitis C virus core antigen

In this study we describe the establishment of two hybridoma cell lines secreting human monoclonal antibodies to the 22-kD nucleocapsid protein (core, p22) of the hepatitis C virus (HCV). For this purpose we isolated B lymphocytes from an anti-HCV positive blood donor and infected them with Epstein-Barr (EBV). We obtained several lymphoblastoid cell clones secreting antibodies to the recombinant HCV core protein. The B-cell cultures were oligoclonally expanded and two of them were fused with the (mouse:human) heteromyeloma cell line K6H6/B5. The resulting stable hybridomas produce antibodies of the IgG1/kappa (U1/F10) and the IgM/kappa (Ul/F11) isotype reacting specifically with the recombinant core protein p22. To identify the epitopes recognized by these antibodies we synthesized overlapping peptides (13-mer and 6-mer) from the amino terminus of the core amino acid sequence. Antibody reactivity to these peptides was analyzed in an immunoblot assay. Finally, we were able to define a linear epitope recognized by the Ul/F10 antibody on the nucleocapsid protein. The antibody shows specificity to the sequence N-VYLLPR-C, which corresponds to the amino acids 34-39 of the core sequence.

Rapid detection of hepatitis C virus RNA by direct capture from blood

A new diagnostic assay for hepatitis C virus RNA detection is described. HCV genomic RNA is captured onto streptavidin-coated magnetic beads by solution hybridization with biotinylated complementary oligonucleotides. The specificity of the capture assay is confirmed using different capture oligonucleotides as well as sera representing different types of HCV. Sensitivity was determined by testing serial dilutions of a HCV infected plasma. A panel of 50 sera was tested for anti-HCV by a Line Immunoassay and for HCV-RNA by both a conventional guanidinium extraction method and the new capture assay. The specificity of the capture assay was 95.8% and the sensitivity was 92.3% compared to the standard protocol. This method provides a rapid and simple alternative for HCV-RNA detection in blood samples.

Synthetic gene for the hepatitis C virus nucleocapsid protein

A synthetic gene encoding the hepatitis C virus (HCV) nucleocapsid protein was constructed and expressed in E. coli. To synthesize this gene, we developed a new method that results in the enzymatic synthesis of long polydeoxyribonucleotides from oligodeoxyribonucleotides. The method, designated as the 'Exchangeable Template Reaction' (ETR), uses oligonucleotides as templates for DNA polymerase. A special mechanism was designed to exchange the templates during the polymerase reaction. The mechanism relies on the formation of a single-stranded 3'-protrusion at the 'growing point' of the elongating DNA such that it can be subsequently annealed, in a sequence-specific manner, with the next synthetic oligonucleotide. When annealed to the 3'-protrusion, the added oligonucleotide becomes a template for DNA polymerase, and the protruding 3'-end of the double-stranded DNA is used as the primer. The HCV nucleocapsid gene was assembled with DNA ligase from three fragments synthesized by ETR. The data verify that this method is efficient. The main advantage of ETR is the ability to combine more than two oligonucleotides in one tube together with polymerase and an enzymatic activity that produces a 3'-protrusion (e.g., BstXI) rather than the sequential addition of each component. The data demonstrate that as many as five oligonucleotides can be used simultaneously, resulting in a synthesized DNA fragment of designed sequence. The synthetic gene expressed in E. coli produced a 27 kDa protein that specifically interacted with antibodies from sera obtained from HCV-infected individuals.

Correlation of serum antibody titers against hepatitis C virus core protein with clinical features by western blot (immunoblot) analysis using a recombinant vaccinia virus expression system

In order to study the relationships among the clinical features of hepatitis C patients, the presence of hepatitis C virus (HCV) RNA in their blood, and their serum antibody titers against the core protein of virus and to study the antibody levels in asymptomatic HCV carriers, a recombinant vaccinia virus containing a core protein gene was constructed. The recombinant virus expressed a protein with a molecular mass of 22 kDa in RK-13 cells as determined by Western blot (immunoblot) analysis. By using the cell lysate of virus-infected cells and serially diluted serum samples, core antibody titers in the groups of patients in the chronic hepatitis phase and in the convalescent phase as well as in asymptomatic carriers were determined by enhanced chemiluminescence Western blot analysis. Almost all patients in the chronic phase were shown to have high antibody titers of more than 1:500,000 and with no exception had of HCV RNA in their sera. On the other hand, patients who had recovered naturally and were in the convalescent phase were shown to have significantly lower antibody titers, and the antibody was not detected in the lowest serum dilution of 1:500 in 43% of these patients (three of seven total patients). Antibody levels of patients who showed a good response to interferon treatment decreased to intermediate levels between those of patients in the chronic phase and those of patients in convalescent phase. The antibody titers in asymptomatic carriers varied considerably from 1:500,000 to 1:500, and 41% (11 of 27 total individuals) of these carriers showed a high titer equivalent to that of those in the chronic phase. Core antibody was detected consistently in the individuals in whom HCV RNA was detected. This system for core antibody might be useful for identifying the stage of an apparent HCV infection.

Equilibrium centrifugation studies of hepatitis C virus: evidence for circulating immune complexes

The buoyant density of hepatitis C virus (HCV), with high in vivo infectivity (strain H) or low in vivo infectivity (strain F), was determined by sucrose gradient equilibrium centrifugation. Viral RNA of strain H was detected in fractions with densities of < or = 1.09 g/ml (principally approximately 1.06 g/ml), while that of strain F was found in fractions with densities of approximately 1.06 and approximately 1.17 g/ml. The observed difference was confirmed by differential flotation centrifugation; in NaCl solution with a density of 1.063 g/ml, most of the HCV RNA of strain H was detected in the top fraction, while that of strain F appeared in the bottom. The same relationship between buoyant density and infectivity was observed in flotation centrifugation experiments with other HCV strains. In immunoprecipitation experiments with anti-human immunoglobulin, HCV (as measured by HCV RNA) was precipitated from the samples with low infectivity and high density but not from those with high infectivity and low density. Examination of serial sera from a chimpanzee infected with HCV revealed parallel changes in the buoyant density and immunoprecipitability of HCV-associated RNA during the course of infection. These data suggest that HCV is bound to anti-HCV antibodies as antigen-antibody complexes in chronic hepatitis C.

p26 protein and 33-nm particle associated with nucleocapsid of hepatitis C virus recovered from the circulation of infected hosts

Hepatitis C virus (HCV) has not yet been cultured or visualized. We attempted to recover HCV-associated particles from plasma of infected humans to assess the natural properties of the virus. Starting with 720 ml of donor plasma containing high titer of HCV core antigen ELISA activities, we identified HCV core antigen activity and viral RNA enriched in a potassium bromide density gradient fraction with a density of 1.115 g/ml. Icosahedron-shaped particles with an average diameter of 33 nm were liberated by treatment of the fraction with the detergent Tween 80. These particles were selectively visualized with an electron microscope using a grid coated with a murine monoclonal antibody directed to HCV core peptide and were also observed in aggregated forms with an immune electron microscope (IEM) with use of the anti-core antibody. An ultracentrifugation pellet of the above fraction was treated with sodium dodecyl sulfate (SDS) and 2-mercaptoethanol (2ME) and run in SDS-PAGE. A protein that bound antibodies directed to the predicted core protein of HCV was found at a molecular size estimated as about 26,000 Da, significantly greater than the 191 amino acid residues predicted from the presumed core gene of HCV. It is possible that translation initiation and/or the COOH-terminal cleavage site for HCV core protein in vivo may differ from estimates derived from the amino acid sequence of the polyprotein precursor. The nucleocapsid could also be chemically altered in the infected cell, resulting in a gel mobility different from the native protein.