HCV Core Antigen Detection Research Articles

Using silver nanoparticle and thiol graphene quantum dots nanocomposite as a substratum to load antibody for detection of hepatitis C virus core antigen: Electrochemical oxidation of riboflavin was used as redox probe

In this study a facile green approach to employ silver nanoparticle (AgNPs) and thiol graphene quantum dots (GQD-SH) as the nanomaterial for ultrasensitive and selective detection of hepatitis C virus core antigen (HCV) have been investigated. AgNPs/GQD-SH was utilized as a substratum to load antibody for detection of hepatitis C virus core antigen. AgNPs have been immobilized on SH groups of GQDs via bonding formation of Ag-S and anti-HCV have been loaded on the electrode surface via the interaction between –NH2 group of antibody and AgNPs. Using the proposed nanocomposite provides a specific platform with increased surface which is capable of loading more antibodies to entrap the antigen. The decreasing of the electrochemical signal can be achieved after the specific recognition between antibodies and antigens. Riboflavin was used as a biological molecule with inherent properties, for the first time, as the redox probe in the development of HCV core antigen electrochemical immunosensor.Compared to the other redox probes, riboflavin is superior in its oxidization in negative potential range, where the number of interfering species for riboflavin is much fewer. The proposed immunosensor showed wide linear range from 0.05pgmL−1 to 60ngmL−1 with limit of detection of 3fgmL−1. This novel immunosensor was used to analyze the serum sample. The immunosensor provides a convenient, low-cost and simple method for HCV core antigen detection and proposes new horizons for quantitative detection of antigen in the clinical diagnosis.

Prevalence of Occult Hepatitis C Virus in Blood Donors in Zagazig City Blood Banks

Background: Egypt is reported as the country of highest incidence of HCV worldwide. The high rate of new cases reported require investigating uncommon sources of infection. Objectives: The study aimed to investigate the prevalence of occult hepatitis C infection (OCI) among blood donors from Zagazig city blood banks as a probable hidden source of transmission; and to evaluate HCV core Ag detection as a method for diagnosis of occult hepatitis C infection. Methodology: One hundred and forty blood donors from Zagazig university blood bank were incorporated into this study. Reverse transcription nested polymerase chain reaction from Peripheral Blood Monocyte (PBMC) and plasma obtained from subjects was done using HCV specific primers and HCV core antigen was detected using commercial ELISA kit. Results & Conclusion: HCV RNA was detected in PBMC extracted from 10 subjects (7.1 %). Two of them were also positive in plasma (1.4%). The overall incidence of OCI was 8/140 (5.7%). Out of them only one was also identified by ELISA HCV core antigen detection kit. The Comparison between ELISA technique for detection of HCV core antigen and nested PCR revealed sensitivity 30%, specificity 99.2% in PBMC and sensitivity 100%, specificity 98.6% in Plasma.

Dried Blood Spots: A Tool to Ensure Broad Access to Hepatitis C Screening, Diagnosis, and Treatment Monitoring.

With the advent of highly efficient antiviral therapies for hepatitis C virus (HCV) infection, providing broad access to diagnosis and care is needed. The dried blood spot (DBS) technique can be used to collect, store, and ship whole-blood specimens. Our goal was to assess the performance of standardized HCV diagnostic and monitoring tools in the analysis of DBS. Serum specimens and whole-blood specimens collected using the DBS technique from >500 patients were tested for virological markers used to diagnose and monitor HCV infection. Enzyme immunoassay detection of anti-HCV antibodies in specimens from DBS was reliable after establishment of a new signal-to-cutoff ratio. HCV RNA was detected DBS from the vast majority of patients with active replication, but HCV RNA levels were substantially lower than in serum specimens, implying that only the presence or absence of HCV RNA or changes in the HCV RNA level should be taken into consideration for therapy. Detection of HCV core antigen in specimens from DBS was not a sensitive marker of chronic HCV infection. HCV genotype determination was possible in the vast majority of DBS. This study shows that whole-blood specimens collected using the DBS technique can be confidently used to diagnose and monitor HCV infection. DBS could help improve access to care for HCV infection because they are suitable for use in large-scale screening programs, diagnosis, and therapeutic monitoring.

The clinical significance of HCV core antigen detection during Telaprevir/Peg-Interferon/Ribavirin therapy in patients with HCV 1 genotype infection

BackgroundDirect-acting antiviral drugs (DAA) regimen improve the SVR rate. However, adverse effects often lead to therapy interruption. This underlines the importance to find some predictive parameters of response in order to consider the possibility of a shorter time of antiviral treatment in the appearance of adverse effects without affecting the success of the therapy. ObjectivesWe aimed to examine the HCVAg kinetics in the early phase of treatment and its predictive value of SVR in patients undergoing TPV/Peg-IFN/RBV treatment. Study designTwenty-three patients infected by HCV genotype 1 (1a n=11; 1b n=12) were included in this prospective study. ResultsAt baseline the median Log of HCVAg concentration in RVR and EVR patients were 3.15fmol/L and 3.45fmol/L, respectively with no significant differences. The baseline median HCV-RNA to HCVAg ratio was 233.77, this ratio was significantly lower when measured on day 1 (27.52) and on day 6 (24.84) (p<0.001). The two-tailed Fisher’s exact test indicated that the SVR response is statistically significantly different in patients with detected HCVAg at week1 compared to patients with no detectable HCVAg (p=0.05). The sensitivity, specificity, and negative and positive predictive values (NPV, PPV) were 53.8, 87.5, 53.8 and 87.5%, respectively. The area under the ROC curve was 0.71 at day T6, the best cut-off of 3fmol/L when evaluated with the HCVAg plasma concentration at dayT6. ConclusionUndetectable HCVAg in the early phase of TPV/Peg-IFN/RBV treatment could represent an important parameter for predicting SVR.

Clinical utility of hepatitis C virus core antigen quantification in patients with chronic hepatitis C

BackgroundHepatitis C virus (HCV) core antigen has been proposed as a surrogate marker of HCV replication. HCV core antigen detection and quantification can thus theoretically be used instead of nucleic acid testing (NAT) to diagnose infection and manage antiviral therapy, with several advantages compared to HCV RNA assays. HCV core antigen can now be easily detected and quantified by means of a chemiluminescent microparticle immunoassay on the Abbott Architect device. ObjectiveThe aim of the present study was to evaluate the clinical performance of the Architect HCV Ag assay for the detection and quantification of HCV core antigen in patients with chronic HCV genotype 1–6 infections. ResultsThe Architect HCV Ag assay had a specificity of 100% (95%CI: 97.8–100%). HCV core antigen levels were not influenced by the HCV genotype. The lower limit of detection of 3fmol/L corresponded to approximately 1000IU/mL of HCV RNA, regardless of the real-time PCR assay used. HCV core antigen and HCV RNA levels correlated for HCV genotype 1–4 (r=0.89 and r=0.88 for the m2000 and the CAP/CTM v2.0 assay, respectively). ConclusionsThe Architect HCV Ag assay is highly specific and easy to perform. It represents a valuable screening, diagnostic and monitoring tool, especially in the era of new all-oral, interferon-free antiviral strategies that do not require high analytical sensitivity.

Hepatitis C virus core antigen test in monitoring of dialysis patients.

Hepatitis C virus infection is a persistent worldwide public health concern. The prevalence of HCV infection is much higher in patients on chronic haemodialysis (HD) than in the general population. HCV infection can detrimentally affect patients throughout the spectrum of chronic kidney disease. Despite the control of blood products, hepatitis C virus transmission is still being observed among patients undergoing dialysis. Detection systems for serum HCV antibodies are insensitive in the acute phase because of the long serological window. Direct detection of HCV depends on PCR test but this test is not suitable for routine screening. Recent studies have highlighted the importance of HCV core antigen detection as an alternative to PCR. Few studies exist about the efficacy of HCV core antigen test in dialysis population. We studied the utility of HCV core antigen test in routine monitoring of virological status of dialysis patients. We screened 92 patients on long-term dialysis both by PCR HCV-RNA and HCV core antigen test. The sensitivity of HCVcAg test was 90%, the specificity 100%, the positive predictive power 100%, the negative predictive power 97%, and the accuracy 97%. We think serological detection of HCV core antigen may be an alternative to NAT techniques for routine monitoring of patients on chronic dialysis.

A Higher Correlation of HCV Core Antigen with CD4+ T Cell Counts Compared with HCV RNA in HCV/HIV-1 Coinfected Patients

Development of HCV infection is typically followed by chronic hepatitis C (CHC) in most patients, while spontaneous HCV viral clearance (SVC) occurs in only a minority of subjects. Compared with the widespread application of HCV RNA testing by quantitative RT-PCR technique, HCV core antigen detection may be an alternative indicator in the diagnosis of hepatitis C virus infections and in monitoring the status of infectious individuals. However, the correlation and differences between these two indicators in HCV infection need more investigation, especially in patients coinfected by HIV-1. In this study, a total of 354 anti-HCV and/or anti-HIV serum positive residents from a village of central China were enrolled. Besides HCV-related hepatopathic variables including clinical status, ALT, AST, anti-HCV Abs, as well as the altered CD4+/CD8+ T cell counts, HCV core antigen and HCV viral load were also measured. The concentration of serum HCV core antigen was highly correlated with level of HCV RNA in CHC patients with or without HIV-1 coinfection. Of note, HCV core antigen concentration was negatively correlated with CD4+ T cell count, while no correlation was found between HCV RNA level and CD4+ T cell count. Our findings suggested that quantitative detection of plasma HCV core antigen may be an alternative indicator of HCV RNA qPCR assay when evaluating the association between HCV replication and host immune status in HCV/HIV-1 coinfected patients.

Utility of a commercial quantitative hepatitis C virus core antigen assay in a diagnostic laboratory setting

In this study, the utility and impact of hepatitis C virus (HCV) core antigen (Cag) detection via a commercial assay have been evaluated in diagnostic laboratory conditions. In a total of 272 samples from 226 individuals, HCV RNA was detected in 81.3% and anti-HCV antibody prevalence was 86.4%. HCV Cag reactivity was identified in 59.9% of the samples and in 75.8% with detectable RNA. The sensitivity and specificity of HCV Cag assay have been calculated as 75.8% and 95.1%, respectively, and agreement between HCV RNA and HCV Cag was moderate (κ = 0.554). HCV Cag and RNA levels were highly correlated (r = 0.915 and 0.937). A viral load threshold of 103 IU/mL has been recognized, above which the correlation with RNA became statistically significant and sensitivity increased to 90.9%. Detection and quantification of HCV core antigen have been observed as a strong alternative to nucleic acid testing for HCV monitorization.

Diagnostic performance of an immunoassay for simultaneous detection of HCV core antigen and antibodies among haemodialysis patients

Nosocomial transmission of HCV is a concern in haemodialysis (HD) units worldwide. Diagnosis of HCV infection among dialysis patients is currently based on the detection of anti HCV antibodies by ELISA, and is confirmed by HCV RNA. The average window period between HCV infection and seroconversion with new generations of HCV antibody tests remains approximately 70 days with more prolonged period among dialysis patients. In this study we assessed the diagnostic performance of an immunoassay designed for simultaneous detection of anti HCV antibodies and core antigen in one step in comparison to qualitative RT-PCR and anti HCV antibodies detection test among Egyptian haemodialysis patients. The studied patients were 39 chronic renal failure patients on maintenance haemodialysis. The results obtained in the present study revealed HCV infection of 56.4%. Combined Ag/Ab test detected 3 out of the 4 anti-HCV negative viraemic patients who were in the window period. The sensitivity, specificity and accuracy of the test were higher than that of anti HCV antibodies detection test (95.45%, 94.1% and 94.87% versus 81.8%, 88.23% and 84.6%) and they were raised to 100% on combining its positivity with liver enzymes elevation results. Therefore, this simple combined Ag/Ab test can be applied for early detection of HCV infection during window period among HD patients as an alternative to HCV RNA detection.

PP-137 Isolation of Ag_AB complex for detection of HCV Core antigen using ELISA method

PP-137 Isolation of Ag_AB complex for detection of HCV Core antigen using ELISA method

Development of a rapid one-step immunochromatographic assay for HCV core antigen detection

The hepatitis C virus (HCV) core protein possesses amino acid sequences highly conserved among HCV isolates and has proved useful for various diagnostic tests. To date, no information has been published regarding the development of an immunochromatographic test for HCV core antigen detection. Therefore, the aim of this research was to develop a rapid, easily performed, highly sensitive and specific test for detection of the HCV core antigen, based on the immunochromatographic strip. The genomic region encoding the core protein (amino acids 1–136) of the hepatitis C virus was expressed in Escherichia coli as a recombinant fusion protein with glutathione S-transferase (GST) cloned into the prokaryotic expression vector pET42a and was confirmed by immunological detection with HCV positive serum. Positive reactions were detected weakly at a 1:15 dilution of the serum and more strongly in 1:10, 1:5, 1:2 and 1:1 dilutions, by the immunochromatographic test. In addition, the test was capable of detecting 0.25–12.0 μg of the recombinant protein. This immunochromatographic technique opens new perspectives for the diagnosis of hepatitis C during the early seroconversion phase and for a rapid core antigen detection.

Production of Infectious Hepatitis C Virus of Various Genotypes in Cell Cultures

A unique hepatitis C virus (HCV) strain JFH-1 has been shown to replicate efficiently in cell culture with production of infectious HCV. We previously developed a DNA expression system containing HCV cDNA flanked by two self-cleaving ribozymes to generate HCV particles in cell culture. In this study, we produced HCV particles of various genotypes, including 1a (H77), 1b (CG1b), and 2a (J6 and JFH-1), in the HCV-ribozyme system. The constructs also contain the secreted alkaline phosphatase gene to control for transfection efficiency and the effects of culture conditions. After transfection into the Huh7-derived cell line Huh7.5.1, continuous HCV replication and secretion were confirmed by the detection of HCV RNA and core antigen in the culture medium. HCV replication levels of strains H77, CG1b, and J6 were comparable, whereas the JFH-1 strain replicates at a substantially higher level than the other strains. To evaluate the infectivity in vitro, the culture medium of JFH-1-transfected cells was inoculated into naive Huh7.5.1 cells. HCV proteins were detected by immunofluorescence 3 days after inoculation. To evaluate the infectivity in vivo, the culture medium from HCV genotype 1b-transfected cells was inoculated into a chimpanzee and caused a typical course of HCV infection. The HCV 1b propagated in vitro and in vivo had sequences identical to those of the HCV genomic cDNA used for cell culture transfection. The development of culture systems for production of various HCV genotypes provides a valuable tool not only to study the replication and pathogenesis of HCV but also to screen for antivirals.

Detection of hepatitis C virus core antigen for early diagnosis of hepatitis C virus infection in plasma donor in China

To evaluate the efficacy of a new hepatitis C virus (HCV) core antigen assay developed in China. After the determination of HCV infection, 49 serial samples were selected from 11 regular plasma donors in 5 different plasma stations. To compare the performance of HCV core antigen detection and HCV PCR, these samples were genotyped, and each specimen was analyzed by ELISA for the detection of HCV core antigen and by qualitative HCV PCR. Among all of the sequential samples, the original 13 specimens were HCV RNA-negative, and 36 samples were HCV RNA-positive. Twenty-seven samples (75%) were HCV core antigen-positive from these HCV RNA-positive specimens. Conversely, 27 samples (93.1%) were found HCV RNA-positive in HCV core antigen-positive samples. Intervals between HCV RNA and HCV core antigen-positive, as well as between HCV core antigen-positive and HCV antibody-positive were 36.0 and 32.8 d, respectively. This HCV core antigen assay, developed in China, is able to detect much of anti-HCV-negative, HCV RNA-positive preseroconversion window period (PWP) plasma donations.

HCV core antigen detection in seropositive samples

Detection of antibodies to HCV is typically the primary test utilized to identify HCV-infected individuals. Seropositive individuals may then be tested for HCV RNA by nucleic acid testing (NAT) to determine if the individual is actively infected with HCV. In addition, NAT assays that are based on quantitation of HCV RNA copies/ml, are utilized to determine the effectiveness of antiviral therapy. Over the last several years, HCV core antigen tests have been developed that have shown utility both for the identifying active HCV infection and for monitoring antiviral therapy. Although these assays are relatively simple and rapid, the HCV core antigen tests have not been widely accepted mostly due to their lack of sensitivity. Recently developed assays have shown improved sensitivity, and may represent an alternative or adjunct to HCV NAT both for identifying active HCV infection and for monitoring antiviral therapy. J. Med. Virol. 79:S52–S53, 2007. © 2007 Wiley-Liss, Inc.

Circulating viral core and E1 antigen levels as supplemental markers for HCV Chronic hepatitis

The performance of polyclonal monospecific rabbit anti-sera raised against synthetic peptides derived from conserved HCV sequences of genotype 4 was evaluated for efficient detection of viral core and E1 antigens in circulating immune complexes (ICs) precipitated from 65 serum samples of HCV patients. The infection was established in those patients by the presence of HCV RNA in their sera. A novel enzyme-linked immunosorbent assay (ELISA) was developed for the detection of HCV core and E1 antigen in serum samples. Western blot analyses were used to demonstrate the presence of the core and E1 target antigen in serum samples. The mean OD readings of both core and E1 antigens were significantly higher (P < 0.05) among the viremic patients when compared to controls. Also a significant positive correlation (P < 0.05, r = 0.98) between the values of both core and E1 was recorded. Western blot analysis based on monospecific antibodies against core and E1 recognized the 38-kDa and 88 -kDa bands respectively in the sera of all infected patients. No specific reaction was observed with the sera from uninfected individuals. Interestingly the results of core and E1 antigen levels displayed no positive correlation with the HCV copy number as measured by bDNA. Liver enzymes (ALT and AST) showed a moderate positive correlation (r = 0.44 and 0.47 respectively) with the viral core antigens level. The same trend holds true for E1 (r = 0.43 and 0.64 for ALT and AST respectively). HCV load in infected patients revealed extremely poor correlation with serum ALT and AST levels (r = 0.022 and 0.002 respectively). In conclusion we present a new combination of serological tools correlating with liver enzyme levels that could be utilized as supplemental tests to viral load testing. Also, a sensitive and specific immunoassay was developed for the detection of HCV core and E1 in human serum. This test can be applied for laboratory diagnosis of HCV infection.

A chemiluminescent, magnetic particle-based immunoassay for the detection of hepatitis C virus core antigen in human serum or plasma

Hepatitis C virus (HCV) exposure in blood donors is determined serologically by the detection of anti-HCV antibodies in serum or plasma. However, a "window" period of 30-70 days after exposure exists where specific antibodies to HCV antigens are not detected. The use of nucleic acid testing for the detection of HCV RNA or antigen testing for the detection of HCV core protein have resulted in dramatic reductions in the pre-seroconversion window period. In this study, an automated HCV core antigen detection test was developed. This magnetic microparticle-based assay utilizes anti-HCV core monoclonal antibody to capture antigen present in human serum or plasma. Captured antigen is then detected using an anti-HCV core monoclonal antibody conjugated with a chemiluminescent compound. The specificity of this assay was established at 99% upon testing a population of normal volunteer blood donors. Sensitivity was determined by testing 16 commercially available HCV seroconversion panels representing genotypes 1a, 1b, 2b, and 3a. In each panel tested, HCV core antigen was detected prior to anti-HCV antibody, resulting in a reduction of the window period by greater than 23 days on average, and greater than 34 days on panels initially NAT negative. In addition, HCV core antigen was detected in >97% of HCV RNA positive/antibody negative specimens, exhibiting sensitivity nearly equivalent to nucleic acid testing in the pre-seroconversion window period for the panels examined.

Clinical usefulness of total hepatitis C virus core antigen quantification to monitor the response to treatment with peginterferon alpha‐2a plus ribavirin*

Early virological response may predict outcome following treatment with peginterferon alpha-2a and ribavirin in patients chronically infected with hepatitis C virus (HCV). As total HCV core antigen may constitute an alternative direct marker to HCV RNA for assessing the levels of viraemia in such patients, we evaluated the correlation between HCV core antigen and HCV RNA, and whether HCV core antigen at baseline, 4 and 12 weeks after treatment could predict sustained virological response (SVR) to combined therapy, in comparison with HCV RNA. A total of 290 serum samples from 58 previously treatment naïve chronic HCV patients were examined for HCV core antigen and HCV-RNA by means of quantitative HCV RNA when receiving combination therapy for the first time. SVR was significantly associated with basal HCV core antigen but not with HCV RNA. There was a good correlation between HCV core antigen and HCV RNA (r(2) = 0.781). The negative predictive value of HCV core antigen testing in predicting nonresponse at weeks 4 and 12 were 75 and 100%, and for undetectable or a 2-log drop in HCV RNA were 69.6 and 75% respectively. HCV core antigen detection is quick, and easy to perform alternative to HCV RNA, and could be used as a marker of HCV viraemia for monitoring the progress of therapy.

Evaluation of a total core antigen assay for the diagnosis of hepatitis C virus infection in hemodialysis patients

Hemodialysis patients are recognized as a group at high risk of infection with hepatitis C virus (HCV). Therefore, such a population should be screened routinely for the presence of HCV viremia. Since nucleic acid techniques remain expensive and largely unavailable in many laboratories in the developing world, the present study assesses the clinical usefulness of the HCV core antigen enzyme immunoassay for the diagnosis of HCV infection in dialysis patients. One hundred seventy-five dialysis patients were screened for the presence of anti-HCV antibodies and HCV RNA in the serum. One hundred twenty-eight serum samples were collected from the 76 patients who were anti-HCV antibody- and/or HCV RNA-positive. These were evaluated for total HCV core antigen. Of these samples, 55 had sufficient volume to be further tested to quantify HCV RNA by reverse transcription polymerase chain reaction (RT-PCR). Genotyping of the HCV strains showed that the majority belonged to genotype 1b (77%). The HCV core antigen assay showed a sensitivity and specificity of 84% and 89%, respectively. The use of core antigen assay has enabled the early detection of three patients who developed an acute hepatitis C infection during the period of study. A correlation study was undertaken between the quantitative values of viral load, expressed as pg/ml of HCV core antigen in serum, and viral RNA in UI/ml. A significant correlation was observed (Pearson's correlation coefficient: 0.552; P<0.001). In conclusion, detection of HCV core antigen in serum is an inexpensive, reliable, and highly specific assay that can be useful in most laboratory settings to diagnose HCV infection, and especially in laboratories where nucleic acid technologies are not yet available.

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.

Diagnosis of hepatitis C: update 2004

Abstract Diagnosis of hepatitis C virus infection (HCV) is based on HCV antibody testing by standard serological tests and immunoblot assays for confirmation in special cases. Differentiation of past and ongoing hepatitis C is performed by detection of HCV core antigen and HCV RNA. Ongoing hepatitis C can be assigned to infection with one or multiple HCV sub‐ and genotypes by characteristic sequence differences. Infection with HCV genotype 2 or 3 is the best pretreatment parameter for prediction of sustained virologic response to interferon‐alfa based antiviral therapy. During antiviral therapy, the key to assess virologic treatment response is quantitative measurement of HCV RNA. A decline of HCV RNA concentration from baseline to week 12 of less than 2 log steps or an absolute viral load above 30.000 IU/mL in genotype 1 infected patients is strongly associated with viral non‐response. For estimation of early virologic response on the basis of HCV core antigen measurement positive detection of core antigen at week 12 was correlated with virologic non‐response. At week 24 of treatment, at the end‐of‐therapy and during follow‐up highly sensitive HCV RNA detection assays are critical for discontinuation of further therapy and correct estimation of virologic response. Mutational analysis of different HCV regions (hypervariable region 1, non‐structural protein 5A) may provide additional information about sensitivity/resistance to interferon‐based antiviral therapy but have not yet introduced into clinical practice.