Correlation between the infectivity of hepatitis C virus in vivo and its infectivity in vitro

Authentic Patient-Derived Hepatitis C Virus Infects and Productively Replicates in Primary CD4+ and CD8+ T Lymphocytes In Vitro

Accumulated evidence indicates that immune cells can support the replication of hepatitis C virus (HCV) in infected patients and in culture. However, there is a scarcity of data on the degree to which individual immune cell types support HCV propagation and on characteristics of virus assembly. We investigated the ability of authentic, patient-derived HCV to infect in vitro two closely related but functionally distinct immune cell types, CD4⁺ and CD8⁺ T lymphocytes, and assessed the properties of the virus produced by these cells. The HCV replication system in intermittently mitogen-stimulated T cells was adapted to infect primary human CD4⁺ or CD8⁺ T lymphocytes. HCV replicated in both cell types although at significantly higher levels in CD4⁺ than in CD8⁺ T cells. Thus, the HCV RNA replicative (negative) strand was detected in CD4⁺ and CD8⁺ cells at estimated mean levels ± standard errors of the means of 6.7 × 10² ± 3.8 × 10² and 1.2 × 10² ± 0.8 × 10² copies/μg RNA, respectively (P < 0.0001). Intracellular HCV NS5a and/or core proteins were identified in 0.9% of CD4⁺ and in 1.2% of CD8⁺ T cells. Double staining for NS5a and T cell type-specific markers confirmed that transcriptionally competent virus replicated in both cell types. Furthermore, an HCV-specific protease inhibitor, telaprevir, inhibited infection in both CD4⁺ and CD8⁺ cells. The emergence of unique HCV variants and the release of HCV RNA-reactive particles with biophysical properties different from those of virions in plasma inocula suggested that distinct viral particles were assembled, and therefore, they may contribute to the pool of circulating virus in infected patients.IMPORTANCE Although the liver is the main site of HCV replication, infection of the immune system is an intrinsic characteristic of this virus independent of whether infection is symptomatic or clinically silent. Many fundamental aspects of HCV lymphotropism remain uncertain, including the degree to which different immune cells support infection and contribute to virus diversity. We show that authentic, patient-derived HCV productively replicates in vitro in two closely related but functionally distinct types of T lymphocytes, CD4⁺ and CD8⁺ cells. The display of viral proteins and unique variants, the production of virions with biophysical properties distinct from those in plasma serving as inocula, and inhibition of replication by an antiviral agent led us to ascertain that both T cell subtypes supported virus propagation. Infection of CD4⁺ and CD8⁺ T cells, which are central to adaptive antiviral immune responses, can directly affect HCV clearance, favor virus persistence, and decisively influence the development and progression of hepatitis C.

The paradox of highly effective sofosbuvir-based combination therapy despite slow viral decline: can we still rely on viral kinetics?

High sustained virologic response (SVR) rates have been observed after 6 weeks of anti-HCV treatment using sofosbuvir, ledipasvir and a non-nucleoside polymerase-inhibitor (GS-9669) or a protease-inhibitor (GS-9451) and after 12 weeks with sofosbuvir + ledipasvir. Here we analyze the viral kinetics observed during these treatments to decipher the origin of the rapid cure and to evaluate the possibility of further reducing treatment duration. We found that viral kinetics were surprisingly slow in all treatment groups and could not reproduce the high SVR rates observed. Based on experimental results suggesting that NS5A- or protease-inhibitors can generate non-infectious virus, we incorporated this effect into a mathematical model. We found that to predict observed SVR rates it was necessary to assume that ledipasvir, GS-9669 and GS-9451 rapidly reduce virus infectivity. We predicted with this model that 4 weeks of triple therapy could be sufficient to achieve SVR in patients with undetectable viremia at week 1, but would be suboptimal in general. In conclusion, the rapid cure rate achieved with these combinations is largely disconnected from viral loads measured during treatment. A model assuming that rapid cure is due to a drug effect of generating non-infectious virus could be a basis for future response guided therapy.

Modelling hepatitis C therapy--predicting effects of treatment

Mathematically modelling changes in HCV RNA levels measured in patients who receive antiviral therapy has yielded many insights into the pathogenesis and effects of treatment on the virus. By determining how rapidly HCV is cleared when viral replication is interrupted by a therapy, one can deduce how rapidly the virus is produced in patients before treatment. This knowledge, coupled with estimates of the HCV mutation rate, enables one to estimate the frequency with which drug resistant variants arise. Modelling HCV also permits the deduction of the effectiveness of an antiviral agent at blocking HCV replication from the magnitude of the initial viral decline. One can also estimate the lifespan of an HCV-infected cell from the slope of the subsequent viral decline and determine the duration of therapy needed to cure infection. The original understanding of HCV RNA decline under interferon-based therapies obtained by modelling needed to be revised in order to interpret the HCV RNA decline kinetics seen when using direct-acting antiviral agents (DAAs). There also exist unresolved issues involving understanding therapies with combinations of DAAs, such as the presence of detectable HCV RNA at the end of therapy in patients who nonetheless have a sustained virologic response.

Current and emerging therapeutic approaches to hepatitis C infection

Hepatitis C virus is a frequent disease infecting an estimated 3% of the worlds population. It represents a major health problem and must be combated by all means. The aim of this review is to discuss the current treatment methods, including interferon-alpha, either standard or pegylated, and ribavirin. Emerging treatments will also be discussed for this potentially curable disease.

[The molecular biology of hepatitis C virus]

Since the discovery of the hepatitis C virus (HCV), a plethora of experimental models have evolved, allowing the virus's life cycle and the pathogenesis of associated liver diseases to be investigated. These models range from inoculation of cultured cells with serum from patients with hepatitis C to the use of surrogate models for the study of specific stages of the HCV life cycle: retroviral pseudoparticles for the study of HCV entry, replicons for the study of HCV replication, and the HCV cell culture model, which reproduces the entire life cycle (replication and production of infectious particles). The use of these tools has been and remains crucial to identify potential therapeutic targets in the different stages of the virus's life cycle and to screen new antiviral drugs. A clear example is the recent approval of two viral protease inhibitors (boceprevir and telaprevir) in combination with pegylated interferon and ribavirin for the treatment of chronic hepatitis C. This review analyzes the advances made in the molecular biology of HCV and highlights possible candidates as therapeutic targets for the treatment of HCV infection.

Isolation of human monoclonal antibodies to the envelope e2 protein of hepatitis C virus and their characterization

We isolated and characterized two human monoclonal antibodies to the envelope E2 protein of hepatitis C virus (HCV). Lymphoblastoid cell lines stably producing antibodies were obtained by immortalizing peripheral blood mononuclear cells of a patient with chronic hepatitis C using Epstein-Barr virus. Screening for antibody-positive clones was carried out by immunofluorescence with Huh7 cells expressing the E2 protein of HCV strain H (genotype 1a) isolated from the same patient. Isotype of resulting antibodies, #37 and #55, was IgG1/kappa and IgG1/lambda, respectively. Epitope mapping revealed that #37 and #55 recognize conformational epitopes spanning amino acids 429 to 652 and 508 to 607, respectively. By immunofluorescence using virus-infected Huh7.5 cells as targets both antibodies were reactive with all of the nine different HCV genotypes/subtypes tested. The antibodies showed a different pattern of immuno-staining; while #37 gave granular reactions mostly located in the periphery of the nucleus, #55 gave diffuse staining throughout the cytoplasm. Both antibodies were shown by immuno-gold electron microscopy to bind to intact viral particles. In a neutralization assay (focus-forming unit reduction using chimeric infectious HCV containing structural proteins derived from genotypes 1a, 1b, 2a, 2b, 3a, 4a, 5a, 6a, and 7a), #55 inhibited the infection of all HCV genotypes tested but genotype 7a to a lesser extent. #37 did not neutralize any of these viruses. As a broadly cross-neutralizing human antibody, #55 may be useful for passive immunotherapy of HCV infection.

Immunization with a recombinant vaccinia virus that encodes nonstructural proteins of the hepatitis C virus suppresses viral protein levels in mouse liver

Chronic hepatitis C, which is caused by infection with the hepatitis C virus (HCV), is a global health problem. Using a mouse model of hepatitis C, we examined the therapeutic effects of a recombinant vaccinia virus (rVV) that encodes an HCV protein. We generated immunocompetent mice that each expressed multiple HCV proteins via a Cre/loxP switching system and established several distinct attenuated rVV strains. The HCV core protein was expressed consistently in the liver after polyinosinic acid–polycytidylic acid injection, and these mice showed chronic hepatitis C-related pathological findings (hepatocyte abnormalities, accumulation of glycogen, steatosis), liver fibrosis, and hepatocellular carcinoma. Immunization with one rVV strain (rVV-N25), which encoded nonstructural HCV proteins, suppressed serum inflammatory cytokine levels and alleviated the symptoms of pathological chronic hepatitis C within 7 days after injection. Furthermore, HCV protein levels in liver tissue also decreased in a CD4 and CD8 T-cell-dependent manner. Consistent with these results, we showed that rVV-N25 immunization induced a robust CD8 T-cell immune response that was specific to the HCV nonstructural protein 2. We also demonstrated that the onset of chronic hepatitis in CN2-29^(+/−)/MxCre^(+/−) mice was mainly attributable to inflammatory cytokines, (tumor necrosis factor) TNF-α and (interleukin) IL-6. Thus, our generated mice model should be useful for further investigation of the immunological processes associated with persistent expression of HCV proteins because these mice had not developed immune tolerance to the HCV antigen. In addition, we propose that rVV-N25 could be developed as an effective therapeutic vaccine.

Biological significance of HCV in various kinds of lymphoid cells

It has been reported that HCV can infect not only hepatocytes but also various kinds of lymphoid cells. Although many reports have described the biological significance of lymphotropic HCV, the issue remains controversial since the target lymphoid cells might have various kinds of functions in the immune system. One of the important roles of lymphoid cells in HCV replication is being a reservoir of HCV. Several groups described the detection of HCV-RNA in lymphoid cells after HCV eradication in plasma. Another important role of lymphotropic HCV is that it acts as a carcinogenic agent and induces immune dysfunction. In this paper, we summarize the reports regarding the biological significance of lymphotropic HCV in representative lymphoid cells.

An overview: in vitro models of HCV replication in different cell cultures

Although much of productive research has been conducted in the field of molecular virology of Hepatitis C virus (HCV) regarding its genes, gene functions and proteins, development of an efficient cell culture model for its replication remained a focused area. Focus has been directed to establish HCV in vitro replication system. This replication system should mimic its intrahepatic pathogenesis so that antivirals should be screened and in vitro gene profiling of HCV induced pathogenesis should be worked out. Since 1990 various experimental approaches and strategies have been utilized in phase of development of a robust replication model for HCV, and success has been reported for a few genotypes. Still the work is going on to have more success in availing such robust replication models for all the genotypes. This will help to have a common antiviral strategy against HCV induced pathogenesis involving any genotype or subtype.

An Assessment of the Use of Chimpanzees in Hepatitis C Research Past, Present and Future: 2. Alternative Replacement Methods

The use of chimpanzees in hepatitis C virus (HCV) research was examined in the report associated with this paper ( 1: Validity of the Chimpanzee Model), in which it was concluded that claims of past necessity of chimpanzee use were exaggerated, and that claims of current and future indispensability were unjustifiable. Furthermore, given the serious scientific and ethical issues surrounding chimpanzee experimentation, it was proposed that it must now be considered redundant — particularly in light of the demonstrable contribution of alternative methods to past and current scientific progress, and the future promise that these methods hold. This paper builds on this evidence, by examining the development of alternative approaches to the investigation of HCV, and by reviewing examples of how these methods have contributed, and are continuing to contribute substantially, to progress in this field. It augments the argument against chimpanzee use by demonstrating the comprehensive nature of these methods and the valuable data they deliver. The entire life-cycle of HCV can now be investigated in a human (and much more relevant) context, without recourse to chimpanzee use. This also includes the testing of new therapies and vaccines. Consequently, there is no sound argument against the changes in public policy that propose a move away from chimpanzee use in US laboratories.

Hepatitis C virus cell-cell transmission in hepatoma cells in the presence of neutralizing antibodies

Hepatitis C virus (HCV) infection of Huh-7.5 hepatoma cells results in focal areas of infection where transmission is potentiated by cell-cell contact. To define route(s) of transmission, HCV was allowed to infect hepatoma cells in the presence or absence of antibodies that neutralize cell-free virus infectivity. Neutralizing antibodies (nAbs) reduced cell-free virus infectivity by >95% and had minimal effect(s) on the frequency of infected cells in the culture. To assess whether cell-cell transfer of viral infectivity occurs, HCV-infected cells were cocultured with fluorescently labeled naïve cells in the presence or absence of nAbs. Enumeration by flow cytometry demonstrated cell-cell transfer of infectivity in the presence or absence of nAbs and immunoglobulins from HCV(+) patients. The host cell molecule CD81 and the tight junction protein Claudin 1 (CLDN1) are critical factors defining HCV entry. Soluble CD81 and anti-CD81 abrogated cell-free infection of Huh-7.5 and partially inhibited cell-cell transfer of infection. CD81-negative HepG2 hepatoma cells were resistant to cell-free virus infection but became infected after coculturing with JFH-infected cells in the presence of nAb, confirming that CD81-independent routes of cell-cell transmission exist. Further experiments with 293T and 293T-CLDN1 targets suggested that cell-cell transmission is dependent on CLDN1 expression.

CONCLUSION

These data suggest that HCV can transmit in vitro by at least two routes, cell-free virus infection and direct transfer between cells, with the latter offering a novel route for evading nAbs.

Hepatitis C virus lymphotropism: lessons from a decade of studies

The possibility that HCV infects lymphoid cells has been widely discussed. Evidence in favor of HCV tropism for lymphoid cells derives from a series of data including: (1) the higher sensitivity of testing HCVRNA in PBMC than in serum or plasma samples, with possible detection of HCV RNA-positive PBMC in the absence of HCV viremia; (2) short-term cultures of PBMC which yield a significant increase in the amount of viral RNA on stimulation by mitogens; (3) results of "in situ" methods (i.e. in situ hybridization, immunofluorescence); (4) efficient infection of lymphoid cell lines or PBMC from normal individuals; (5) the persistence of HCV RNA in PBMC obtained from HCV-positive subjects and injected into SCID mice; (6) the long-term persistence of HCV RNA in PBMC in spite of HCV RNA negativity of serum and liver in sustained responder patients after therapy. The principal criticisms concerning effective HCV infection of lymphoid cells arise from technical difficulty in identifying HCV RNA replicative intermediate in these elements. Conflicting data may also result from differences in PBMC infection by different genotypes, samples taken at different stages in the disease process and differences in the sensitivity of detection methods, as well as low replication levels and/or proportion of infected PBMC. Interesting available data about HCV lymphotropism, which is possibly important in influencing the natural history of infection, include: (1) possible preferential viral tropism for specific PBMC subsets; (2) different lymphotropism of different viral strains; (3) selection of distinctive viral strains; (4) identification of putative HCV cell receptors; (5) association between determination of HCV lymphatic infection and t(14; 18) translocation. The clinical correlates of HCV lymphotropism are potentially very numerous, including, first, its role in determining HCV-related lymphoproliferative disorders.

IRES complexity before IFN-alpha treatment and evolution of the viral load at the early stage of treatment in peripheral blood mononuclear cells from chronic hepatitis C patients

At the early stage of treatment, IFN alpha-2a induces inhibition of HCV replication. The viral load reflects mainly the degradation rate of the viruses. However, differences in the behavior of the viral population depend on changes, which occurred in the HCV-IRES genome. In this study, cloning and sequencing strategies permitted the generation of a large number of IRES sequences from the PBMCs of 18 patients (5 women, 13 men) with chronic hepatitis C. The HCV IRES appeared to be highly conserved structurally. However, some variability was found between the different isolates obtained: 467 substitutions with a median of 7 variants/patients. No relationship was observed between pre-treatment IRES complexity and the viral load at the beginning. However, on review of the evolution of viral load in the PBMCs during the first 3 days of IFN alpha-2a treatment, patients could be classified into two groups: Group 1, in which the viral population continued to replicate and Group 2, in which the viral load decreased significantly (P = 0.01727). Positioning of the mutations on the predicted IRES secondary structure showed that the distribution of the mutations and their apparition frequency were different between the two groups. At the early stage of treatment, IFN alpha-2a was efficient in reducing the viral replication in a significant number of patients; mechanisms of response might affect the virus directly. However, pre-treatment genomic variations observed in the 5'NCR of HCV were not a parameter of a later response to antiviral therapy in chronic hepatitis C patients. (244)

Cell culture systems for the hepatitis C virus

Since the discovery of HCV in 1989, the lack of a cell culture system has hampered research progress on this important human pathogen. No robust system has been obtained by empiric approaches, and HCV cell culture remained hypothetical until 2005. The construction of functional molecular clones has served as a starting point to reconstitute a consensus infectious cDNA that was able to transcribe infectious HCV RNAs as shown by intrahepatic inoculation in a chimpanzee. Other consensus clones have been selected and established in a human hepatoma cell line as replicons, i.e. self-replicating subgenomic or genomic viral RNAs. However, these replicons did not support production of infectious virus. Interestingly, some full-length replicons could be established without adaptive mutations and one of them was able to replicate at very high levels and to release virus particles that are infectious in cell culture and in vivo. This new cell culture system represents a major breakthrough in the HCV field and should enable a broad range of basic and applied studies to be achieved.

Use of new T-cell-based cell lines expressing two luciferase reporters for accurately evaluating susceptibility to anti-human immunodeficiency virus type 1 drugs

Two new T-cell-based reporter cell lines were established to measure human immunodeficiency virus type 1 (HIV-1) infectivity. One cell line naturally expresses CD4 and CXCR4, making it susceptible to X4-tropic viruses, and the other cell line, in which a CCR5 expression vector was introduced, is susceptible to both X4- and R5-tropic viruses. Reporter cells were constructed by transfecting the human T-cell line HPB-Ma, which demonstrates high susceptibility to HIV-1, with genomes expressing two different luciferase reporters, HIV-1 long terminal repeat-driven firefly luciferase and cytomegalovirus promoter-driven renilla luciferase. Upon HIV infection, the cells expressed firefly luciferase at levels that were highly correlated (r2=0.91 to 0.98) with the production of the capsid antigen p24. The cells also constitutively expressed renilla luciferase, which was used to monitor cell numbers and viability. The reliability of the cell lines for two in vitro applications, drug resistance phenotyping and drug screening, was confirmed. As HIV-1 efficiently replicated in these cells, they could be used for multiple-round replication assays as an alternative method to a single-cycle replication protocol. Coefficients of variation for drug susceptibility evaluated with the cell lines ranged from 17 to 41%. The new cell lines were beneficial for evaluating antiretroviral drug resistance. Firefly luciferase gave a wider dynamic range for evaluating virus infectivity, and the introduction of renilla luciferase improved assay reproducibility. The cell lines were also beneficial for screening new antiretroviral agents, as false inhibition caused by the cytotoxicity of test compounds was easily detected by monitoring renilla luciferase activity.

Transmission in vitro of hepatitis C virus from persistently infected human B-cells to hepatoma cells by cell-to-cell contact

Virus cell-to-cell spread has been reported for many different viruses and may contribute to pathogenesis of viral disease. The role played by cell-to-cell contact in hepatitis C virus (HCV) transmission was studied in vitro by cell co-cultivation experiments. A human lymphoblastoid B-cell line, infected persistently with HCV in vitro (TO.FE(HCV)), was used as HCV donor [Serafino et al., 2003]; recipient cells were the human hepatoma HepG2 cell line. Both cell types were co-cultured for 48 hr to allow the cell-to-cell contacts. The hepatoma HepG2 cells are not permissive to free-virus infection, but they were infected successfully using TO.FE(HCV) cells as source of virus. The kinetics of viral RNA synthesis and the percentage of infected cells were compared in cell-mediated-and cell-free-viral infection. After co-cultivation, a consistent proportion of hepatoma cells replicated HCV and stably expressed viral antigens. Virus produced was infectious as demonstrated by the ability to reinfect fresh B-cells. This cell model shows that permissiveness to HCV infection can be achieved in vitro in non-permissive hepatoma cells by direct cell-to-cell contacts with infected human B-cells. This mechanism of virus spread may also play a pathogenic role in vivo.

HCV-hepatocellular carcinoma: new findings and hope for effective treatment

We present here a comprehensive review of the current literature plus our own findings about in vivo and in vitro analysis of hepatitis C virus (HCV) infection, viral pathogenesis, mechanisms of interferon action, interferon resistance, and development of new therapeutics. Chronic HCV infection is a major risk factor for the development of human hepatocellular carcinoma. Standard therapy for chronic HCV infection is the combination of interferon alpha and ribavirin. A significant number of chronic HCV patients who cannot get rid of the virus infection by interferon therapy experience long-term inflammation of the liver and scarring of liver tissue. Patients who develop cirrhosis usually have increased risk of developing liver cancer. The molecular details of why some patients do not respond to standard interferon therapy are not known. Availability of HCV cell culture model has increased our understanding on the antiviral action of interferon alpha and mechanisms of interferon resistance. Interferons alpha, beta, and gamma each inhibit replication of HCV, and the antiviral action of interferon is targeted to the highly conserved 5'UTR used by the virus to translate protein by internal ribosome entry site mechanism. Studies from different laboratories including ours suggest that HCV replication in selected clones of cells can escape interferon action. Both viral and host factors appear to be involved in the mechanisms of interferon resistance against HCV. Since interferon therapy is not effective in all chronic hepatitis C patients, alternative therapeutic strategies are needed to treat chronic hepatitis C patients not responding to interferon therapy. We also reviewed the recent development of new alternative therapeutic strategies for chronic hepatitis C, which may be available in clinical use within the next decade. There is hope that these new agents along with interferon will prevent the occurrence of hepatocellular carcinoma due to chronic persistent hepatitis C virus infection. This review is not inclusive of all important scientific publications due to space limitation.

Role of hepatitis C virus (HCV) viremia and HCV genotype in the immune recovery from highly active antiretroviral therapy in a cohort of antiretroviral-naive HIV-infected individuals

BACKGROUND

The roles of hepatitis C virus (HCV) viremia and HCV genotype in the immune response to highly active antiretroviral therapy (HAART) are poorly understood. Our aim was to assess the CD4+ cell count recovery after HAART in human immunodeficiency virus (HIV)-infected patients with HCV viremia and HIV-infected patients who tested negative for HCV antibody (HCV-Ab). We also aimed to assess whether the response to HAART in these patients varied according to HCV genotype.

METHODS

The analysis focused on 1219 HCV-Ab-negative patients and 284 HCV-viremic patients from a cohort of HIV-infected subjects that includes persons who were antiretroviral naive before initiating HAART after cohort enrollment. HCV RNA load and HCV genotype were determined in plasma specimens obtained and stored during the 6-month period preceding the initiation of HAART.

RESULTS

The chance of achieving a CD4+ cell count increase of > or = 100 cells/microL from the pre-HAART level tended to be poorer in HCV-viremic patients than in patients who tested negative for HCV-Ab (adjusted relative hazard [RH], 0.82; 95% confidence interval [CI], 0.66-1.01; P = .06). In contrast, a comparison of patients who had a HCV RNA load >1 x 10(6) IU/mL with patients who had a HCV RNA load of 5-1 x 10(6) IU/mL revealed no significant association between HCV RNA load and achievement of an increased CD4+ cell count (adjusted RH, 0.97; 95% CI, 0.75-1.27; P = .83). There was no clear association between HCV genotype and the probability of achieving a CD4+ cell count increase.

CONCLUSIONS

An association between the presence of HCV-Ab and immune reconstitution after HAART has been shown elsewhere. Results of our large, prospective study support a direct role of HCV viremia in the CD4+ cell count response to HAART. Moreover, our results underline the fact that, in individuals coinfected with HIV and HCV, the goal of treating HCV infection is to eradicate HCV, to both slow the rate of HCV progression and limit potential interference with the response to HAART.

Persistence of hepatitis C virus in patients successfully treated for chronic hepatitis C

It is unclear whether the current antiviral treatment for chronic hepatitis C virus (HCV) infection results in complete elimination of the virus, or whether small quantities of virus persist. Our study group comprised 17 patients with chronic HCV who had sustained virological response (SVR) after interferon/ribavirin treatment. Serum and peripheral blood mononudear cells were collected 2 to 3 times at 3- to 6-month intervals starting 40 to 109 months (mean, 64.2 +/- 18.5 months) after the end of therapy. In addition, lymphocyte and macrophage cultures were established at each point. In 11 patients, frozen liver tissue samples were available from follow-up biopsies performed 41 to 98 months (mean, 63.6 +/- 16.7 months) after therapy. Presence of HCV RNA was determined by sensitive reverse-transcriptase polymerase chain reaction, and concentration of positive and negative strands was determined by a novel quantitative real-time reverse transcriptase polymerase chain reaction. Only 2 of 17 patients remained consistently HCV RNA negative in all analyzed compartments. HCV RNA was detected in macrophages from 11 patients (65%) and in lymphocytes from 7 patients (41%). Viral sequences were also detected in 3 of 11 livers and in sera from 4 patients. Viral replicative forms were found in lymphocytes from 2 and in macrophages from 4 patients. In conclusion, our results suggest that in patients with SVR after therapy, small quantities of HCV RNA may persist in liver or macrophages and lymphocytes for up to 9 years. This continuous viral presence could result in persistence of humoral and cellular immunity for many years after therapy and could present a potential risk for infection reactivation.

Hepatitis C virus replication in stably transfected HepG2 cells promotes hepatocellular growth and tumorigenesis

HepG2 cells stably transfected with a full-length, infectious hepatitis C virus (HCV) cDNA demonstrated consistent replication of HCV for more than 3 years. Intracellular minus strand HCV RNA was present. Minus strand synthesis was NS5B dependent, and was sensitive to interferon alpha (IFN alpha) treatment. NS5B and HCV core protein were detectable. HCV stimulated HepG2 cell growth and survival in culture, in soft agar, and accelerated tumor growth in SCID mice. These mice became HCV RNA positive in blood, where the virus was also sensitive to IFN alpha. The RNA banded at the density of HCV, and was resistant to RNase prior to extraction. Hence, HCV stably replicates in HepG2 cells, stimulates hepatocellular growth and tumorigenesis, and is susceptible to IFN alpha both in vitro and in vivo.

Efficient formation of vesicular stomatitis virus pseudotypes bearing the native forms of hepatitis C virus envelope proteins detected after sonication

Hepatitis C virus (HCV) causes chronic hepatitis, liver cirrhosis and hepatocellular carcinoma in addition to acute hepatitis. The HCV genome encodes two envelope glycoproteins, E1 and E2. To investigate the role of E1 and E2 in HCV infection, we used a recombinant vesicular stomatitis virus (VSV), VSVdeltaG*, harboring the green fluorescent protein gene instead of the VSV G envelope protein gene. It was complemented with the native form of E1 and E2, or E1 or E2 alone, to make HCV pseudotypes VSVdeltaG*(HCV), VSVdeltaG*(E1), and VSVdeltaG*(E2). Neither E1 nor E2 expression was detected on the cell surface, as reported. Unlike previous reports, infectious activities of VSVdeltaG*(HCV), VSVdeltaG*(E1) and VSVdeltaG*(E2) pseudotypes were detected under conditions where VSV was completely neutralized by anti-VSV. We could enhance the infectious titers 100-fold by sonication upon virus harvest. Bovine lactoferrin efficiently inhibited infection by VSVdeltaG*(HCV) as well as VSVdeltaG*(E2), as the interaction between E2 and lactoferrin has been thought to contribute to the inhibition of HCV infectivity. VSVdeltaG*(HCV) infected many adherent cell lines, including hepatic cell lines, but not most hematopoietic cell lines. Treatment of cells with trypsin, tunicamycin, or sulfated polysaccharides before infection reduced the infectivity of VSVdeltaG*(HCV) by about 90%, suggesting that a cell surface protein(s) with sugar chains plays an important role in HCV infection. The VSV pseudotypes developed here would be useful for analyzing the early stages of HCV infection.

Effect of the 5′ non-translated region on self-assembly of hepatitis C virus genotype 1a structural proteins produced in insect cells

The effect of the 5' non-translated region (5'NTR) on hepatitis C virus (HCV) morphogenesis in insect cells is investigated in this study. Expression in baculovirus-infected cells of a sequence encoding the C and E1 structural proteins under the control of the very late promoter P10 (AcSLP10-C-E1) led to the synthesis of C and C-E1 complexes, essentially found in dense reticular material associated with the ER and sedimenting at a density of 1.24-1.26 g ml(-1). Addition of the 5'NTR upstream of the C-E1 sequence (AcSLP10-5'NTR-E1) prevents translation from the initiating codon, probably because of the presence of five AUG codons in this sequence. When cells were co-infected with these two viruses, virus-like particles (VLPs) were found in the cytoplasm. The size and shape of these VLPs were variable. Concomitantly, a shift in the sedimentation profile from 1.24-1.26 to 1.15-1.18 g ml(-1) was observed, suggesting an association of C/E1 with the ER membrane. A unique vector was then constructed bearing a mutated 5'NTR (mutation of the five AUGs) and the sequence encoding all of the structural proteins and part of NS2 (5'NTRm-C-E1-E2-p7-NS2Delta). Translation of structural proteins was restored and electron microscopic observation of a cytoplasmic extract showed the presence of icosahedral particles with a density of 1.15-1.18 g ml(-1).

Economics of Pathogen Inactivation Technology for Platelet Concentrates in Japan

Residual risk of transmitting recognized and emerging blood-borne pathogens via blood transfusion in Japan persists despite advances in blood safety screening. The INTERCEPT Blood System (IBS) for platelets was developed to inactivate a broad spectrum of pathogens to reduce the risk of transfusion-transmitted infections. In this study we assessed the economic impact of the IBS on platelet transfusion costs. An economic analysis model was used to assess both net cost and cost-effectiveness of the IBS for the patient populations accounting for most of the platelet use in Japan. Pathogen exposure included viruses currently recognized to cause transfusion-transmitted infections and emerging pathogens of potential significance for transfusion-transmitted infections. Economic assessment of the full potential of the IBS revealed that only a small increase in net cost can be expected with implementation. The cost-effectiveness of the IBS for platelets is comparable with and potentially better than that of other blood safety interventions (eg, nucleic acid testing) and, in general, other recently implemented safety interventions (eg, chemical regulations and traffic safety measures) accepted as valuable in Japan. Thus a preventive approach using pathogen inactivation with the IBS may be considered a desirable strategy for improving the current safety of platelet transfusions in Japan.

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Transactivating effect of hepatitis C virus core protein: a suppression subtractive hybridization study

AIM

To investigate the transactivating effect of hepatitis C virus (HCV) core protein and to screen genes transactivated by HCV core protein.

METHODS

pcDNA3.1(-)-core containing full-length HCV core gene was constructed by insertion of HCV core gene into EcoRI/BamHI site. HepG2 cells were cotransfected with pcDNA3.1(-)-core and pSV-lacZ. After 48 h, cells were collected and detected for the expression of beta-gal by an enzyme-linked immunosorbent assay (ELISA) kit. HepG2 cells were transiently transfected with pcDNA3.1(-)-core using Lipofectamine reagent. Cells were collected and total mRNA was isolated. A subtracted cDNA library was generated and constructed into a pGEM-Teasy vector. The library was amplified with E. coli strain JM109. The cDNAs were sequenced and analyzed in GenBank with BLAST search after polymerase chain reaction (PCR).

RESULTS

The core mRNA and protein could be detected in HepG2 cell lysate which was transfected by the pcDNA3.1(-)-core. The activity of beta-galactosidase in HepG2 cells transfected by the pcDNA3.1(-)-core was 5.4 times higher than that of HepG2 cells transfected by control plasmid. The subtractive library of genes transactivated by HCV core protein was constructed successfully. The amplified library contained 233 positive clones. Colony PCR showed that 213 clones contained 100-1 000 bp inserts. Sequence analysis was performed in 63 clones. Six of the sequences were unknown genes. The full length sequences were obtained with bioinformatics method, accepted by GenBank. It was suggested that six novel cDNA sequences might be target genes transactivated by HCV core protein.

CONCLUSION

The core protein of HCV has transactivating effects on SV40 early promoter/enhancer. A total of 63 clones from cDNA library were randomly chosen and sequenced. Using the BLAST program at the National Center for Biotechnology Information, six of the sequences were unknown genes. The other 57 sequences were highly similar to known genes.

Interferon alpha-2b inhibits negative-strand RNA and protein expression from full-length HCV1a infectious clone

We have established a T7-based model system for hepatitis C virus (HCV) 1a strain, which involves the use of a replication-defective adenovirus that carries the gene for T7 RNA polymerase and a transcription plasmid containing full-length HCV cDNA clone. To facilitate high-level expression of HCV, sub-confluent Huh7 cells were first infected with adenovirus containing the gene for the T7 RNA polymerase and then transfected with the transcription plasmid. As a negative control, part of NS5B gene of this clone was deleted which abolishes the HCV RNA-dependent RNA polymerase and prevents replication of viral RNA. This model produces high levels of structural (core, E1, E2) and nonstructural proteins (NS5), which were detected by Western blot analysis and immunofluorescence assay. Negative-strand HCV RNA was detected only in the wild-type clone in the presence of actinomycin D, and no RNA was detected with the NS5B deleted mutant control. As a practical validation of this model, we showed that IFN alpha-2b selectively inhibits negative-strand RNA synthesis by blocking at the level of protein translation. The inhibitory effect of IFN alpha-2b is not due reduction of transcription by T7 polymerase or due to intracellular degradation of HCV RNA. This in vitro model provides an efficient and reliable means of assaying negative-strand RNA, protein processing, and testing the antiviral properties of interferon.

Development of a GB virus B marmoset model and its validation with a novel series of hepatitis C virus NS3 protease inhibitors

GB virus B (GBV-B), a flavivirus closely related to HCV, has previously been shown to infect and replicate to high titers in tamarins (Saguinus sp.). This study describes the use of GBV-B infection and replication in the common marmoset (Callithrix jacchus) for the successful development and validation of a surrogate animal model for hepatitis C virus (HCV). Infection of marmosets with GBV-B produced a viremia that peaked at 10(8) to 10(9) genome copies/ml for a period of 40 to 60 days followed by viral clearance at 60 to 80 days postinfection. Passage of the initial tamarin-derived GBV-B in marmosets produced an infectious stock that gave a more reproducible and consistent infection in the marmoset. Titration of the virus stocks in vivo indicated that they contained 1 infectious unit for every 1,000 genome copies. Cultures of primary marmoset hepatocytes were also successfully infected with GBV-B, with high levels of virus detected in supernatants and cells for up to 14 days postinfection. Treatment of GBV-B-infected hepatocyte cultures with a novel class of HCV protease inhibitor (pyrrolidine 5,5 trans-lactams) reduced viral levels by more than 2 logs. Treatment of GBV-B-infected marmosets with one such inhibitor resulted in a 3-log drop in serum viral titer over 4 days of therapy. These studies provide the first demonstration of the in vivo efficacy of a small-molecule inhibitor for HCV in an animal model and illustrate the utility of GBV-B as a surrogate animal model system for HCV.

Infection of primary human macrophages with hepatitis C virus in vitro: induction of tumour necrosis factor-alpha and interleukin 8

Hepatitis C virus (HCV) has been reported to replicate in monocytes/macrophages in infected patients. However, it is unclear whether macrophages are susceptible to infection in vitro and whether such an infection is consequential. Sera from 26 HCV-infected patients were incubated with primary human macrophages collected from healthy donors. Virus negative strand was detected by a Tth enzyme-based strand-specific assay and virus sequences were analysed by single strand conformation polymorphism (SSCP) and sequencing. Concentrations of the cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-1beta, IL-6, IL-8, IL-10 and IL-12p70 were measured in culture supernatants and respective mRNAs were analysed in cell extracts by quantitative RT-PCR. For 15 sera, HCV RNA was detectable in 2- and 3-week cultures from at least one donor. Virus negative strand was detected in 29 % of macrophage samples in this group. In four cases, HCV RNA sequences amplified from macrophages differed from those amplified from sera suggesting evolution during infection. Concentrations of TNF-alpha and IL-8 were found to be significantly higher in supernatants from HCV-infected cultures. In conclusion, these preliminary data suggest that primary human macrophages are susceptible to HCV infection in vitro and this infection is associated with the induction of cytokines TNF-alpha and IL-8.

Human immunodeficiency virus facilitates infection/replication of hepatitis C virus in native human macrophages

Hepatitis C virus (HCV) was found to replicate in monocytes/macrophages particularly in patients with human immunodeficiency virus type 1 (HIV-1) infection. This study was undertaken to determine whether HIV facilitates HCV infection of native human macrophages in vitro. Monocytes/macrophages were collected from healthy donors, infected with HIV M-tropic molecular clone, and then exposed to HCV-positive sera. Presence of positive and negative HCV RNA strands was determined with a novel strand-specific quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR). Preceding as well as near-simultaneous infection with HIV made the macrophages more susceptible to infection with HCV; in particular, an HCV RNA-negative strand was detectable almost exclusively in the setting of concomitant HIV infection. Furthermore, HCV RNA load correlated with HIV replication level in the early stage of infection. The ratio of positive to negative strand in macrophages was lower than in control liver samples. HIV infection was also found to facilitate HCV replication in a Daudi B-cell line with engineered CD4 expression. It seems that HIV infection can facilitate replication of HCV in monocytes/macrophages either by rendering cells more susceptible to HCV infection or by increasing HCV replication. This could explain the presence of extrahepatic HCV replication in HIV-coinfected individuals.

Expression of a full-length hepatitis C virus cDNA up-regulates the expression of CC chemokines MCP-1 and RANTES

We had previously reported the cloning of the complete genome of an isolate of hepatitis C virus (HCV), HCV-S1, of genotype 1b. We have constructed a full-length complementary DNA (cDNA) clone of HCV-S1 using nine overlapping cDNA clones that encompassed its entire genome. HCV core, E1, E2, NS-3, -4B, -5A, and -5B proteins were detected in 293T cells by immunoblot analyses when expression of the full-length HCV-S1 was driven under a CMV promoter. Expression of full-length HCV-S1 led to induction of the CC chemokines RANTES and MCP-1 at both the mRNA and the protein levels in HeLa, Huh7, and HepG2 cells. Reporter gene assays showed that a minimal MCP-1 promoter construct containing 128 nucleotides upstream of its translational start site was sufficient for optimal HCV-mediated activation. HCV induced AP-1 binding activities to this region, as determined from electrophoretic mobility shift assays and supershifts with anti-AP-1 antibodies. Transfection of full-length HCV-S1 up-regulated both AP-1 binding activities as well as c-jun transcripts. A minimal promoter construct containing 181 nucleotides upstream of the RANTES translational start site was sufficient for maximal HCV-mediated induction. Gel mobility shift and supershift assays showed that HCV induced NF-kappaB and other unknown binding activities to the A/B-site within this region. In HeLa cells, HCV core and NS5A could separately augment promoter activities of both MCP-1 and RANTES. In Huh7 cells, only NS5A produced a similar effect, while rather surprisingly, HCV core induced a dramatic reduction in promoter activities of these two genes. This study provides the first direct evidence for the induction of CC chemokines in HCV infection and draws attention to their roles in affecting the progress and outcome of HCV-associated liver diseases.

Inducible system in human hepatoma cell lines for hepatitis C virus production

We cloned the complete complementary DNA of an isolate of the hepatitis C virus, HCV-S1, into a tetracycline-inducible expression vector and stably transfected it into two human hepatoma cell lines, Huh7 and HepG2. Twenty-six Huh7 and two HepG2-positive clones were obtained after preliminary screening. Two Huh7 (SH-7 and -9) and one HepG2 (G-19) clones were chosen for further characterisation. Expression of HCV proteins in these cells accumulated from 6 h to 4 days posttreatment. Full-length viral plus-strand RNA was detected by Northern analyses. Using RT-PCR and ribonuclease protection assay, we also detected the synthesis of minus-strand HCV RNA. Plus- and minus-strand viral RNA was still detected after treatment with actinomycin D. Indirect immunofluorescence staining with anti-E2, NS4B, and NS5A revealed that these proteins were mostly localised to the endoplasmic reticulum (ER). Culture media from tet-induced SH-9 cells was separated on sucrose density gradients and analysed for the presence of HCV RNA. Viral RNA levels peaked at two separate ranges, one with a buoyant density of 1.08 g/ml and another from 1.17 to 1.39 g/ml. Electron microscopy demonstrated the presence of subviral-like particles (approximately 20-25 nm in diameter) in the cytoplasm of SH-9 and G-19 cells, which were positively labelled by anti-HCV core antibodies. Anti-E2 antibodies strongly labelled cytoplasmic vesicular structures and some viral-like particles. Complete viral particles of about 50 nm which reacted with anti-E2 antibodies were observed in the culture media of tet-induced SH-9 cells following negative staining. Supernatant from tet-treated SH-9 cells was found to infect nai;ve Huh7 and stable Huh7-human CD81 cells.

Recombinant antibody Fab against the hypervariable region 1 of hepatitis C virus blocks the virus adsorption to susceptible cells in vitro

Antibodies against hypervariable region 1 (HVR1) of hepatitis C virus (HCV) are putatively considered to be neutralizing. We previously found that monoclonal antibodies (mAbs) (30F1 and 30F3) against the HVR1 of HCV neutralize HCV in vitro. To develop potentially therapeutic molecules against HCV, we cloned cDNAs of antibody Fab fragments from the mouse hybridoma cells secreting these two mAbs. Fab fragments produced in Escherichia coli were purified by a single step of nickel-chelate affinity chromatography via a hexa-histidine tag. The specificity of the Fabs was confirmed by competition ELISA, BIAcore analysis, and N-terminal amino acid sequencing. The binding constant for the interaction with HVR1 was 1.39 nM for Fab 30F1 and 3.96 nM for Fab 30F3. The HCV capture assay and inhibition of HCV adsorption test demonstrated that both Fabs had neutralizing activity. The data may be useful for designing immunological therapy of HCV.

In vivo and in vitro evidence that cross-reactive antibodies to C-terminus of hypervariable region 1 do not neutralize heterologous hepatitis C virus

The hypervariable region 1 (HVR1) of hepatitis C virus (HCV) may contain neutralizing epitopes. A chimpanzee in whom cross-reactive anti-HVR1 antibodies had been induced by immunization was challenged with heterologous HCV for clarifying whether cross-reactive anti-HVR1 antibodies can neutralize heterologous HCV. Acute hepatitis C occurred in this chimpanzee after the challenge. Rechallenge with mixtures of the highest titer cross-reactive immune serum and heterologous HCV, after the chimpanzee had cleared the viremia, again resulted in HCV infection. Virus capture assay and inhibition of virus adsorption to susceptible cells, by the immune sera from the chimpanzee and highly cross-reactive monoclonal antibodies (mAbs) against the C-terminus of HVR1 of the challenge virus, showed that cross-reactive anti-HVR1 had no cross-neutralizing activity. The data imply that the HVR1 component is insufficient to develop an effective HCV vaccine.

Hepatitis C virus nonstructural proteins are localized in a modified endoplasmic reticulum of cells expressing viral subgenomic replicons

For many years our knowledge on hepatitis C virus (HCV) replication has been based on in vitro experiments or transfection studies. Recently, the first reliable system for studying viral replication in tissue culture cells was developed. Taking advantage of this system, we examined in detail the localization of viral nonstructural (NS) proteins in cells containing functional replication complexes. By fractionation experiments and immunomicroscopy, we observed that all NS proteins were associated with the endoplasmic reticulum (ER) membranes, confirming the hypothesis that the ER is the site of membrane-associated HCV RNA replication. Interestingly, NS3 and NS4A were preferentially localized in endoplasmic reticulum cisternae surrounding mitochondria, suggesting additional subcellular compartment-related functions for these viral proteins. Furthermore, the immunoelectron microscopy revealed the loss of the organization and other morphological alterations of the ER (convoluted cisternae and paracrystalline structures), resembling alterations observed in liver biopsies of HCV-infected individuals and in flavivirus-infected cells.

In search of hepatitis C virus receptor(s)

Since the genomic sequence of HCV was determined, significant progress has been made towards understanding the functions of the HCV-encoded proteins, despite the lack of an efficient in-vitro replication system or convenient small-animal model. The identity of the receptor for HCV remains elusive, however. Low-density lipoprotein receptor, CD81, and GAGs may all act as receptors for HCV, either sequentially or by different viral quasispecies. Recent work using pseudotypic VSV bearing E1 or E2 chimeric molecules showed that entry of the E1 pseudotype can be inhibited by recombinant LDLr, whereas the E2 pseudotype is more sensitive to inhibition by recombinant CD81 or heparin. These results suggest that E1 and E2 may be responsible for interactions with different cellular molecules. It is also conceivable that additional, yet unidentified, cellular proteins are involved in viral binding and entry. Intriguingly, the reports of HCV-RNA associated with PBMC suggest that HCV infection may not be restricted to hepatocytes. Thus, separate reservoirs of virus may exist, and HCV may use different receptors to access these different cell types.

Novel cell culture systems for the hepatitis C virus

Infections with the hepatitis C virus (HCV) are a major cause of acute and chronic liver disease. The high prevalence of the virus, the insidious course of the disease and the poor prognosis for long-term persistent infection make this pathogen a serious medical and socioeconomical problem. The identification of the viral genome approximately 10 years ago rapidly led to the delineation of the genomic organization and the structural and biochemical characterization of several virus proteins. However, studies of the viral life cycle as well as the development of antiviral drugs have been difficult because of the lack of a robust and reliable cell culture system. Numerous attempts have been undertaken in the past few years but only recently a highly efficient cell culture model could be developed. This system is based on the self replication of engineered HCV minigenomes (replicons) in a transfected human hepatoma cell line. A summary of the various HCV cell culture models with a focus on the replicon system and its use for drug development is described.

Study of the infection of human blood derived monocyte/macrophages with hepatitis C virus in vitro

Hepatitis C virus (HCV) is essentially hepatotropic, but clinical observations based on quasispecies composition in different compartments or on viral RNA detection in cells suggest that the virus is able to infect and persist in cells other than liver cells. It was shown previously that peripheral blood mononuclear cells (PBMCs) are permissive to HCV replication in vitro but at a very low rate. Since different viruses associated with chronic infections are known to persist in monocyte/macrophages, it is important to determine whether these mononuclear blood cells are susceptible preferentially to HCV. In order to study HCV interaction with monocytes/macrophages, these cells were isolated from the blood of healthy donors and incubated with HCV genotype 1b positive sera. The detection by RT-PCR of the positive- and negative-strand RNA in the cells at different times and the increase in the amount of intracellular viral RNA measured by the branched DNA assay suggest that monocyte/macrophages can support HCV RNA replication. The rate, however, is very low. The analysis of hypervariable region 1 (HVR-1) nucleotide sequences indicated that some minor variant present in the inoculum might display a specific tropism for the monocytes/macrophages. These results provide evidence that human monocytes/macrophages might represent a reservoir for HCV. This cell tropism may be a crucial factor in the pathogenesis of hepatitis C.

Ultrastructural observations in hepatitis C virus-infected lymphoid cells

It is currently unclear whether the hepatocellular damage in chronic hepatitis C virus (HCV) infection is produced through the intrahepatic action of the anti-HCV immune response or through a direct cytopathic effect. In order to investigate the features of HCV replication (morphogenesis and cytopathic effect), we studied the infection of a permissive lymphocytic B cell line, Daudi cells, which were infected with sera of HCV-positive patients, and were examined after various time points under electron microscope. Viral genomic RNA was detected by in situ hybridization, and apoptosis with the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method. The amount of viral genomic RNA was observed to increase during infection. HCV replicated rapidly, since characteristics of viral morphogenesis resembling those of yellow fever virus in a hepatoma cell line could be found 2 days after infection. These included the following: a) several viral particles identical in size (about 42 nm) and structure (a spherical 30-nm-sized electron-dense nucleocapsid surrounded by a membrane) to yellow fever virus were present in the cytoplasm of cells displaying already typical signs of the early stage of apoptosis; b) numerous membrane-bound organelles and in particular the endoplasmic reticulum and vacuoles were observed; c) proliferation of membranes was apparent; and d) intracytoplasmic electron-dense inclusion bodies which have been demonstrated to correspond to nucleocapsids for other flaviviruses were detected. Several cells presented electron-dense areas in the endoplasmic reticulum displaying 30-nm circular structures lying among an amorphous material. Striking cytopathic features with ballooning, extremely enlarged vacuoles and signs of apoptosis were found in cells often containing sequestered aggregates of virus-like particles. By in situ hybridization we found that such enlarged cells contained HCV RNA. Our results thus indicate that the ultrastructural features of HCV viral particles and their morphogenesis resemble that of yellow fever virus and dengue virus. In Daudi cells, HCV infection seems to rapidly trigger apoptotic cell death, and efficient release of viral particles does not seem to take place.

Preventing the spread of hepatitis B and C viruses: where are germicides relevant?

Hepatitis B virus (HBV) and hepatitis C virus (HCV) are the most prevalent bloodborne pathogens. Infections caused by these organisms can become chronic and may lead to liver cirrhosis and carcinoma. Limited chemotherapy is now available, but only HBV can be prevented through vaccination. Both viruses are enveloped and relatively sensitive to many physical and chemical agents; their ability to survive in the environment may not be as high as often believed. As a result, their spread occurs mainly through direct parenteral or percutaneous exposure to tainted body fluids and tissues. Careful screening of and avoiding contact with such materials remain the most effective means of protection. Nevertheless, the indirect spread of these viruses, although much less common, can occur when objects that are freshly contaminated with tainted blood enter the body or contact damaged skin. Germicidal chemicals are important in the prevention of HBV and HCV spread through shared injection devices, sharps used in personal services (such as tattooing and body piercing), and heat-sensitive medical/dental devices (such as flexible endoscopes) and in the cleanup of blood spills. Microbicides in vaginal gels may also interrupt their transmission. General-purpose environmental disinfection is unlikely to play a significant role in the prevention of the transmission of these viruses. Testing of low-level disinfectants and label claims for such products against HBV and HCV should be discouraged. Both viruses remain difficult to work with in the laboratory, but closely related animal viruses (such as the duck HBV) and the bovine viral diarrhea virus show considerable promise as surrogates for HBV and HCV, respectively. Although progress in the culturing of HBV and HCV is still underway, critical issues on virus survival and inactivation should be addressed with the use of these surrogates.

[Hepatitis C virus culture systems]

Hepatitis C virus pathogenesis and cycle are difficult to study because of the lack of culture system able to replicate efficiently the virus. Furthermore such a system will permit screen new antiviral drugs. Studies were realized to select cell culture system able to allow hepatitis C virus replication. Primary cell cultures and cell lines were used to performed HCV culture. Most of these works used lymphocyte and hepatocyte primary cultures or cell lines because of HCV tropism in these cells in vivo. Animals and arthropods cell lines were used as well for their capacity to bind and replicate HCV. The aim of this review is to present the different cell systems used to replicate HCV in culture and the results obtained.

Mosquito cells bind and replicate hepatitis C virus

Several studies have demonstrated some hepatitis C virus (HCV) replication in lymphocyte and hepatocyte cell lines such as in African green monkey Vero cells. The aim of the present study was to select other cell lines able to bind and replicate HCV. Human hepatoma PLC/PRF/5 cells, human lymphoma Namalwa cells, Vero and mosquito AP61 cells were inoculated with HCV-positive plasma, washed six times and examined for the presence of the viral genome at different times post infection, using an RT-PCR method. Binding of HCV to cells was estimated by HCV RNA detection in cells 2 hr after inoculation and in the last wash of these cells. Successive virus passages in cells were carried out. All the cells studied were able to bind HCV but only AP61 and Vero cells provided evidence of replication and production of infectious virus: virus RNA was detected during 28 days post-infection in four successive virus passages. CD81 molecules, a putative HCV receptor, were detected by cytofluorometric analysis. Vero cells express CD81 molecules whereas these molecules were not detected on AP61 cells. It is suggested that other receptors are involved in HCV binding to Vero and AP61 cells.

HVR1 quasispecies analysis from a long-term culture of hepatitis C virus in Hep G2 derived cells grown in a haemodialysis cartridge

Studies on the in vitro hepatitis C virus (HCV) infection are hampered by the lack of an appropriate system to culture permissive cells to be continuously infected with HCV. Trypsinization required for cell passage can lead to possible temporary loss of permissiveness for infection, whereas refreshment of the medium can result in loss of infectious particles necessary for perpetuation of the infection; it is therefore very difficult to maintain a continuous HCV infection in cell cultures. A new infection method was designed and evaluated in order to prevent these unfavourable circumstances. A cell line derived from the human hepatoblastoma cell line Hep G2 was grown in the extracapillary space of a haemodialysis cartridge, in the presence of a HCV-positive inoculum, while the culture medium was recirculated through the intracapillary space, supplying the cells with nutrients and oxygen. HCV RNA could continuously be detected in the cells up to 77 days of culture. Sequence analysis of the HCV hypervariable region 1 (HVR1) revealed that 56% and 75%, respectively, of the clones obtained from the cells at day 20 and 40 after start of the infection were different from the clones obtained from the original inoculum and that certain nucleotide positions in this region were more susceptible to mutations, leading to an alteration in amino acid sequence. As none of these sequences were present in the clones from the inoculum, it is suggested that new HCV quasispecies have emerged as a result of viral replication in the hepatocytes in vitro. This system seems a valuable tool for the in vitro evaluation of antiviral drugs.

Use of whole blood specimens for routine clinical quantitation of hepatitis C virus RNA does not increase assay sensitivity

The measurement of hepatitis C virus (HCV) RNA levels in the blood has, in the last few years, become a critical component in the therapy of patients with HCV infections. Initially, extraction methods for serum and plasma were used, but a newer method that uses Catrimox-14 as the extraction agent for whole blood has been reported. Because the whole blood extraction method may yield higher virus levels if significant levels of virus are present in the white blood cells (WBC), the method was evaluated for use in our clinical diagnostic laboratory despite its higher reagent costs and more time-consuming methodology. RNA was simultaneously extracted from 39 clinical samples by four different methods: Catrimox-14-Trizol extraction from whole blood, Trizol extraction from whole blood, Trizol extraction from serum, and a commercial serum extraction method, the EZNA total RNA kit. In addition, in an effort to quantitate the amount of HCV RNA virus in the WBC, Trizol extraction from isolated WBC was also performed. Quantitative results for samples from which RNA was extracted by all four methods were essentially the same; the Catrimox-14-Trizol method did not yield increased virus levels. Insignificant levels of virus were found in the WBC. The results did not demonstrate a clinical usefulness for the Catrimox-14-Trizol method.

Low cell binding ability of HCV is closely related to interferon treatment especially in patients with HCV genotype 2a/2b. A large series prospective study on Japanese patients with chronic hepatitis C

BACKGROUND/AIMS

We have previously shown that the quantity of antibody-free virion in the pre-treatment sera of the patients with chronic hepatitis C is a good predictive factor for the efficacy of interferon treatment. However, the biological significance of the free virion should be verified by a prospective study.

METHODS

We prospectively evaluated 152 consecutive patients with chronic hepatitis C who received a standardized interferon treatment, and analyzed the free virion and the binding titers, the ability of hepatitis C virus (HCV) to bind to the human lymphocytic cell line.

RESULTS

Sixty-five patients achieved a long-term sustained remission, 76 patients did not respond to the interferon therapy, and 11 patients dropped out. The sera from the patients with genotype 2a/2b had significantly lower free virion and cell binding titers than those with genotype 1b. A multivariate analysis showed three independent variables associated with the interferon response; cell binding titer <10(0.5)/ml, viral load <10(4.5) copies/50 microl, and genotype 2a/2b with odds ratios of 14.6, 11.8, and 9.8, respectively.

CONCLUSIONS

The low level of in vitro cell binding ability of HCV helped to clarify the good responsiveness to interferon observed in patients especially with a high viral load of genotype 2a/2b.

Inhibitory effects of sudanese medicinal plant extracts on hepatitis C virus (HCV) protease

One hundred fifty-two methanol and water extracts of different parts of 71 plants commonly used in Sudanese traditional medicine were screened for their inhibitory effects on hepatitis C virus (HCV) protease (PR) using in vitro assay methods. Thirty-four extracts showed significant inhibitory activity (>/=60% inhibition at 100 microg/mL). Of these, eight extracts, methanol extracts of Acacia nilotica, Boswellia carterii, Embelia schimperi, Quercus infectoria, Trachyspermum ammi and water extracts of Piper cubeba, Q. infectoria and Syzygium aromaticum, were the most active (>/=90% inhibition at 100 microg/mL). From the E. schimperi extract, two benzoquinones, embelin (I) and 5-O-methylembelin (II), were isolated and found as potent HCV-PR inhibitors with IC(50) values of 21 and 46 microM, respectively. Inhibitory activities of derivatives of I against HCV-PR as well as their effects on other serine proteases were also investigated.

Characterization of hepatitis C virus (HCV) and HCV E2 interactions with CD81 and the low-density lipoprotein receptor

Hepatitis C virus (HCV) or HCV-low-density lipoprotein (LDL) complexes interact with the LDL receptor (LDLr) and the HCV envelope glycoprotein E2 interacts with CD81 in vitro. However, E2 interactions with LDLr and HCV interactions with CD81 have not been clearly described. Using sucrose gradient-purified low-density particles (1.03 to 1.07 g/cm(3)), intermediate-density particles (1. 12 to 1.18 g/cm(3)), recombinant E2 protein, or control proteins, we assessed binding to MOLT-4 cells, foreskin fibroblasts, or LDLr-deficient foreskin fibroblasts at 4 degrees C by flow cytometry and confocal microscopy. Viral entry was determined by measuring the coentry of alpha-sarcin, a protein synthesis inhibitor. We found that low-density HCV particles, but not intermediate-density HCV or controls bound to MOLT-4 cells and fibroblasts expressing the LDLr. Binding correlated with the extent of cellular LDLr expression and was inhibited by LDL but not by soluble CD81. In contrast, E2 binding was independent of LDLr expression and was inhibited by human soluble CD81 but not mouse soluble CD81 or LDL. Based on confocal microscopy, we found that low-density HCV particles and LDL colocalized on the cell surface. The addition of low-density HCV but not intermediate-density HCV particles to MOLT-4 cells allowed coentry of alpha-sarcin, indicating viral entry. The amount of viral entry also correlated with LDLr expression and was independent of the CD81 expression. Using a solid-phase immunoassay, recombinant E2 protein did not interact with LDL. Our data indicate that E2 binds CD81; however, virus particles utilize LDLr for binding and entry. The specific mechanism by which HCV particles interact with LDL or the LDLr remains unclear.