Virus isolate-specific antibodies against hypervariable region 1 of the hepatitis C virus second envelope protein, gp70

Spouse-to-Spouse Transmission and Evolution of Hypervariable Region 1 and 5' Untranslated Region of Hepatitis C Virus Analyzed by Next-Generation Sequencing

Hepatitis C virus (HCV) transmission between spouses remains poorly characterized, largely due to the limited availability of samples from the early stage of infection, as well as methodological constraints. A fifty-eight year-old male developed acute hepatitis C infection and his 53-year old spouse has been HCV-positive for over 10 years. Serum samples were collected from both at the time of acute hepatitis C diagnosis in male (baseline) and then at 9 and 13 months. Hypervariable region 1 (HVR1) and 5’ untranslated region (5’UTR) sequences were amplified and subjected to next generation sequencing (NGS) using a pyrosequencing platform. Genetic variants were inferred by Shorah reconstruction method and compared by phylogenetic and sequence diversity analysis. As the sequencing error of the procedure was previously determined to be ≤ 1.5%, the analysis was conducted with and without the 1.5% cut-off with regard to the frequency of variants. No identical HVR1 variants were identified in spouses at baseline and follow-up samples regardless whether the cut-off was applied or not. However, there was high similarity (98.3%) between a minor baseline donor variant (1.7% frequency) and the most abundant baseline recipient variant (62.5% frequency). Furthermore, donor and recipient strains clustered together when compared to 10 control subjects from the same area and infected with the same HCV subtype. There was an increase in HVR1 complexity (number of genetic variants) over time in both spouses. In contrast, the 5'UTR region was stable and of low complexity throughout the study. In conclusion, intrafamilial HCV transmission may be established by a very minor variant and investigation of this phenomenon requires high-sensitivity assays, such as NGS.

Challenges to the development of vaccines to hepatitis C virus that elicit neutralizing antibodies

Despite 20 years of research, a vaccine to prevent hepatitis C virus (HCV) infection has not been developed. A vaccine to prevent HCV will need to induce broadly reactive immunity able to prevent infection by the 7 genetically and antigenically distinct genotypes circulating world-wide. HCV encodes two surface exposed glycoproteins, E1 and E2 that function as a heterodimer to mediate viral entry. Neutralizing antibodies (NAbs) to both E1 and E2 have been described with the major NAb target being E2. The function of E2 is to attach virions to host cells via cell surface receptors that include, but is not limited to, the tetraspanin CD81 and scavenger receptor class B type 1. However, E2 has developed a number of immune evasion strategies to limit the effectiveness of the NAb response and possibly limit the ability of the immune system to generate potent NAbs in natural infection. Hypervariable regions that shield the underlying core domain, subdominant neutralization epitopes and glycan shielding combine to make E2 a difficult target for the immune system. This review summarizes recent information on the role of NAbs to prevent HCV infection, the targets of the NAb response and structural information on glycoprotein E2 in complex with neutralizing antibodies. This new information should provide a framework for the rational design of new vaccine candidates that elicit highly potent broadly reactive NAbs to prevent HCV infection.

An heteroduplex mobility analysis assay based on capillary electrophoresis for the study of HCV quasispecies

The quasispecies nature of the hepatitis C virus (HCV) genome is central to the transmission, persistence and pathogenesis of the infection. Heteroduplex mobility analysis (HMA) is a simple and an inexpensive technique for the qualitative and quantitative analysis of genetic variation of viral quasispecies. An original HMA for the HVR1 region of HCV was developed, based on a semi-automated, non-radioactive capillary electrophoresis system, which allows the processing of large numbers of samples in short times, the accurate measure of mobility shifts and the quantitation of heteroduplexes. A set of 120 HVR1 clones of known sequence was used to develop the assay, which was tested on HVR1 sequences amplified directly from sera of 17 HCV-infected patients. HVR1 sequence divergence directly correlated with the heteroduplex mobility ratio (HMR) of hybrid molecules between six and 40 mismatches. Heteroduplexes between one and six mismatches were resolved, although HMRs were not proportional to base changes, likely due to an effect of type and position of the substitutions. The assay sensitivity was 1% of the total sample size. This assay may allow the application of quasispecies analysis to a wider range of clinical and basic investigations.

Immunological evaluation of Escherichia coli-derived hepatitis C virus second envelope protein (E2) variants

Two variants of the hepatitis C virus (HCV) E2 envelope protein, lacking the C-terminal domain and comprising amino acids 458-650 (E2A) and 382-605 (E2C), respectively, were efficiently produced in BL21 (DE3) Escherichia coli cells. E2A and E2C were used to immunize mice. The E2C variant induced the maximal mean antibody titer. Anti-E2C mouse sera reacted mainly with E2 synthetic peptides covering the 70 amino acid N-terminal region of the E2 protein. Moreover, a panel of anti-HCV positive human sera recognized only the E2C protein (28.2%) and the synthetic peptide covering the HVR-1 of the E2 protein (23.1%). These data indicate the existence of an immunologically relevant region in the HVR-1 of the HCV E2 protein.

Genome of human hepatitis C virus (HCV): gene organization, sequence diversity, and variation

Hepatitis C virus (HCV) is the major etiologic agent of non-A, non-B hepatitis. HCV infection frequently causes chronic hepatitis, which progresses to liver cirrhosis and hepatocellular carcinoma. Since the discovery of HCV in 1989, a large number of genetic analyses of HCV have been reported, and the viral genome structure has been elucidated. An enveloped virus, HCV belongs to the family Flaviviridae, whose genome consists of a positive-stranded RNA molecule of about 9.6 kilobases and encodes a large polyprotein precursor (about 3000 amino acids). This precursor protein is cleaved by the host and viral proteinase to generate at least 10 proteins: the core, envelope 1 (E1), E2, p7, nonstructural (NS) 2, NS3, NS4A, NS4B, NS5A, and NS5B. These HCV proteins not only function in viral replication but also affect a variety of cellular functions. HCV has been found to have remarkable genetic heterogeneity. To date, more than 30 HCV genotypes have been identified worldwide. Furthermore, HCV may show quasispecies distribution in an infected individual. These findings may have important implications in diagnosis, pathogenesis, treatment, and vaccine development. The hypervariable region 1 found within the envelope E2 protein was shown to be a major site for the genetic evolution of HCV after the onset of hepatitis, and might be involved in escape from the host immunesurveillance system.

Hepatitis C virus and interferon resistance

Interferon plays a critical role in the host's natural defense against viral infections and in their treatment. It is the only therapy for hepatitis C virus (HCV) infection; however, many virus isolates are resistant. Several HCV proteins have been shown to possess properties that enable the virus to evade the interferon-mediated cellular antiviral responses.

Characterization of the effects of hepatitis C virus nonstructural 5A protein expression in human cell lines and on interferon-sensitive virus replication

The hepatitis C virus (HCV) nonstructural 5A (NS5A) protein has been implicated in the inherent resistance of HCV to interferon (IFN) antiviral therapy in clinical studies. Biochemical studies have demonstrated that NS5A interacts in vitro with and inhibits the IFN-induced, RNA-dependent protein kinase, PKR, and that NS5A interacts with at least one other cellular kinase. The present study describes the establishment and characterization of various stable NS5A-expressing human cell lines, and the development of a cell culture-based assay for determining the inherent IFN resistance of clinical NS5A isolates. Human epithelioid (Hela) and osteosarcoma (U2-OS) cell lines were generated that express NS5A under tight regulation by the tetracycline-dependent promoter. Maximal expression of NS5A occurred at 48 hours following the removal of tetracycline from the culture medium. The half-life of NS5A in these cell lines was between 4 to 6 hours. NS5A protein expression was localized cytoplasmically, with a staining pattern consistent with the location of the Golgi apparatus and endoplasmic reticulum. In the majority of cell lines, no obvious phenotypic changes were observed. However, three genotype 1b NS5A-expressing osteosarcoma cell lines exhibited cytopathic effect and severely reduced proliferation as a result of high-level NS5A expression. Full-length NS5A protein isolated from a genotype 1b IFN-nonresponsive patient (NS5A-1b) was capable of rescuing encephalomyocardititis virus replication during IFN challenge up to 40-fold, whereas a full-length NS5A-1a and an interferon sensitivity determining region (ISDR) deletion mutant (NS5A-1a-triangle upISDR) isolated from a genotype 1a IFN-nonresponsive patient showed no rescue activity. The NS5A-1b and NS5A-1a proteins also rescued vesicular stomatitis virus replication during IFN treatment by two- to threefold. These data cummulatively suggest that NS5A expression alone can render cells partially resistant to the effects of IFN against IFN-sensitive viruses, and that in some systems, these effects may be independent of the putative ISDR. A scenario is discussed in which the NS5A protein may employ multiple strategies contributing to IFN resistance during HCV infection.

Analysis of the cell tropism of HCV by using in vitro HCV-infected human lymphocytes and hepatocytes

BACKGROUND/METHODS

We recently established two hepatitis C virus (HCV) replication systems, using MT-2, a human T-cell leukemia virus type I-infected human T-cell line, and PH5CH, a non-neoplastic human hepatocyte line immortalized with simian virus 40 large T antigen. These HCV replication systems were used to assess the infective potencies of seven sera containing more than 10(6) HCV genomes per ml obtained from HCV-positive blood donors.

RESULTS

The results showed that these sera had different infectivities for MT-2 and PH5CH cells. One of the seven sera, 1B-1, was more infective for MT-2 cells than PH5CH cells, whereas all the sera except serum 1B-1 were more infective for PH5CH cells than for MT-2 cells. Intracellular HCV RNA could be detected at least 30 days after inoculation with three of the sera. These findings suggested that the infective potency of each serum depends on the type of target cells. To further investigate HCV replication in these cells, we examined the hypervariable region 1 (HVR1) populations of HCV recovered from both MT-2 and PH5CH cells at 8 days postinoculation. The results revealed that the shift to limited HVR1 populations from the quasi-species of HVR1 populations in both cells usually occurred within 8 days after virus inoculation. Furthermore, in two of four sera, the predominant HVR1 populations in MT-2 and PH5CH cells appeared to be different.

CONCLUSION

These results suggest that HCV exhibits cell tropism.

Tracking hepatitis C virus quasispecies major and minor variants in symptomatic and asymptomatic liver transplant recipients

To evaluate the possibility that distinct viral quasispecies play a role in the pathogenesis of progressive hepatitis C virus (HCV) infection, we performed a detailed evaluation of HCV quasispecies before and after liver transplantation in five patients infected with HCV genotype 1, three of whom developed severe recurrent hepatitis C and two of whom developed asymptomatic posttransplant infections with high-titered viremia. HCV quasispecies were characterized by using a combination of nucleotide sequencing plus heteroduplex tracking assay of the second envelope gene hypervariable region (HVR). An average of 30 HVR clones were analyzed per specimen; an average of five specimens were analyzed per patient over a 6- to 24-month study period. The complexity of HCV quasispecies in pretransplant serum varied, ranging from one to nine genetically distinct variants for the five patients. However, in all five cases, relatively homogenous quasispecies variants emerged after liver transplantation. In the three patients who developed recurrent hepatitis, quasispecies major variants present in pretransplant serum were efficiently propagated immediately after liver transplantation and were propagated throughout the course of acute and chronic hepatitis. In contrast, in the two asymptomatic cases, we observed rapid depletion of pretransplant quasispecies major variants from posttransplant serum, followed by emergence of new quasispecies variants by posttransplant day 30. Genetic analysis suggested that in these cases, the new quasispecies variants were derived from minor variants present at relatively low clonal frequency (less than 5% of HVR clones) within the pretransplant quasispecies populations. These data demonstrate that quasispecies tracking patterns are associated with the rapidity and severity of HCV-associated liver disease after liver transplantation. Further characterization of HCV quasispecies in animal model systems is warranted.