Detection of a 5' UTR variation in the HCV genome after a long-term in vitro infection

Heterogeneity and coexistence of oncogenic mechanisms involved in HCV-associated B-cell lymphomas

The association of HCV-infection with B-lymphomas is supported by the regression of most indolent/low-grade lymphomas following anti-viral therapy. Studies on direct and indirect oncogenic mechanisms have elucidated the pathogenesis of HCV-associated B-lymphoma subtypes. These include B-lymphocyte proliferation and sustained clonal expansion by HCV-envelope protein stimulation of B-cell receptors, and prolonged HCV-infected B-cell growth by overexpression of an anti-apoptotic BCL-2 oncogene caused by the increased frequency of t(14;18) chromosomal translocations in follicular lymphomas. HCV has been implicated in lymphomagenesis by a "hit-and-run" mechanism, inducing enhanced mutation rate in immunoglobulins and anti-oncogenes favoring immune escape, due to permanent genetic damage by double-strand DNA-breaks. More direct oncogenic mechanisms have been identified in cytokines and chemokines in relation to NS3 and Core expression, particularly in diffuse large B-cell lymphoma. By reviewing genetic alterations and disrupted signaling pathways, we intend to highlight how mutually non-contrasting mechanisms cooperate with environmental factors toward progression of HCV-lymphoma.

Human cell types important for hepatitis C virus replication in vivo and in vitro: old assertions and current evidence

Hepatitis C Virus (HCV) is a single stranded RNA virus which produces negative strand RNA as a replicative intermediate. We analyzed 75 RT-PCR studies that tested for negative strand HCV RNA in liver and other human tissues. 85% of the studies that investigated extrahepatic replication of HCV found one or more samples positive for replicative RNA. Studies using in situ hybridization, immunofluorescence, immunohistochemistry, and quasispecies analysis also demonstrated the presence of replicating HCV in various extrahepatic human tissues, and provide evidence that HCV replicates in macrophages, B cells, T cells, and other extrahepatic tissues. We also analyzed both short term and long term in vitro systems used to culture HCV. These systems vary in their purposes and methods, but long term culturing of HCV in B cells, T cells, and other cell types has been used to analyze replication. It is therefore now possible to study HIV-HCV co-infections and HCV replication in vitro.

Molecular and cellular determinants of cell-to-cell transmission of HCV in vitro

It was reported previously that HCV can be transmitted from persistently infected human bone-marrow-derived B-lymphoblastoid cells (TO.FE(HCV)) to human hepatoma cells by cell-to-cell contact. The present study confirms and characterize further such type of HCV infection in vitro. TO.FE(HCV) cells were co-cultured with 2.2.15 hepatoma cells, that are not susceptible to cell-free infection by sera containing HCV of 1b genotype. By this co-cultivation system it was demonstrated that HCV transmission to recipient cells requires de novo virus RNA replication. Several factors may favor HCV-transmission, evidence is provided that TO.FE(HCV) cells were able to select HCV-quasispecies. 5'-UTR and core sequence analysis revealed differences in the HCV-quasispecies composition in serum inoculum and in infected TO.FE B-cells at 4 months post-inoculation. It is considered that the latter may be more successful in replicating HCV in vitro and used to express surface molecules which may be involved in cell-to-cell contact. In TO.FE(HCV) cells replicate distinct, or few close related, HCV-variants correlated with those of serum inoculum. Comparative analysis of tetra-spans and integrins expression undertaken by cytofluorimetry displayed higher level of expression for TO.FE cells in comparison to other human bone-marrow-derived B-cell lines. Overall, the observed persistent in vitro HCV replication is mediated by a continuous cell-to-cell reinfection that may be favored by selection of viral variants and expression of molecules involved in cell adhesion. These observations may provide an explanation for the establishment of HCV infection, the occurrence of chronic infection and HCV-related lymphoproliferative diseases.

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.

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.

Suggested role of the Golgi apparatus and endoplasmic reticulum for crucial sites of hepatitis C virus replication in human lymphoblastoid cells infected in vitro

Iacovacci et al. [(1997a) Research in Virology 148:147-151] described that the euploid diploid cells, of the normal human bone marrow-derived lymphoblastoid B-cell line TO.FE., are susceptible to hepatitis C virus (HCV) infection and support long term virus production. Transmission electron microscopy described some steps of HCV replication cycle in this in vitro infected cellular system [Serafino et al. (1997) Research in Virology 148:153-159]. In the present study, in order to identify the intracellular sites involved in HCV replication, the ultrastructural changes associated with infection in TO.FE. cells were correlated with the subcellular localisation of structural and nonstructural viral proteins. Transmission electron microscopy and confocal microscopy data indicate that these viral proteins appeared located in the Golgi apparatus and endoplasmic reticulum, suggesting an active involvement of these compartments in viral assembly and morphogenesis. Furthermore, transmission and scanning electron microscopic observations on cultures infected chronically support the hypothesis that these cellular compartments may serve as starting sites of the morphological changes associated to viral infection and replication, leading to cell-cell fusion, syncytia formation, and finally lysis of infected cells and virus release.

Expression of human CD81 in transgenic mice does not confer susceptibility to hepatitis C virus infection

We previously demonstrated that hepatitis C virus (HCV) binds to human CD81 through the E2 glycoprotein. Therefore, expression of the human CD81 molecule in transgenic mice was expected to provide a new tool to study HCV infection in vivo, as the chimpanzee is the only species currently available as a laboratory animal model that can be infected with HCV. We produced transgenic mice expressing the human CD81 protein in a wide variety of tissues. We confirmed binding of recombinant E2 glycoprotein to the liver tissue as well as to thymocytes and splenic lymphocytes in the transgenic mice. We inoculated chimpanzee plasma infected with HCV into these animals. None of these transgenic animals showed evidence of viral replication. Furthermore, human CD81 transgenic mice that lack expression of endogenous mouse CD81 were also resistant to HCV infection. We conclude that expression of human CD81 alone is insufficient to confer susceptibility to HCV infection in the mouse. The presence of additional possible factors for HCV infection is discussed.

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.

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.

Replication of the hepatitis C virus

Infection with the hepatitis C virus (HCV) is a major cause of chronic liver disease. HCV is an enveloped plus-strand RNA virus closely related to flavi- and pestiviruses. The first cloning of the HCV genome, about 10 years ago, initiated research efforts leading to the elucidation of the genomic organization and the definition of the functions of most viral proteins. Despite this progress the lack of convenient animal models and appropriate in vitro propagation systems have hampered a full understanding of the way the virus multiplies. This review summarizes our current knowledge about HCV replication and describes attempts pursued in the last few years to establish efficient and reliable cell culture systems.

Susceptibility of human and non-human cell lines to HCV infection as determined by the centrifugation-facilitated method

The centrifugation-facilitated inoculation method was used to test 51 human and non-human cell lines for ability to support HCV replication. As determined by nested RT-PCR, one fifth of the cell lines tested were virus positive 15 days post inoculation suggesting that the centrifugation-facilitated inoculation is an efficient method for cell infection with HCV. However, virus production by infected cultures remained of low grade, thus showing that the unknown factors which limit HCV replication in vitro are not overcome by the procedure.

TOFE human-B-cell-line-based adsorption-inhibition assay to detect HCV neutralizing antibodies

We previously demonstrated that the human lymphoblastoid B-cell line (LCL) TOFE, derived from normal human bone marrow, is permissive to HCV infection. In this report we developed an in vitro HCV adsorption-inhibition assay based on TOFE cells, to reveal the presence of neutralizing antibodies in sera from acutely infected patients.

Morphological modifications induced by HCV infection in the TOFE human lymphoblastoid cell line

In this study, we analysed by transmission electron microscopy (TEM), sequential details of morphological modifications that accompanied viral morphogenesis in the lymphoblastoid cell line (LCL) TOFE infected in vitro with hepatitis C virus (HCV). As previously reported, we observed virus-like particles (VLPs) in cytoplasmic vesicles mainly located in the perinuclear region of infected cells. In this area, the Golgi apparatus and the endoplasmic reticulum (ER) appeared hyperplastic, remarkably enriched in vesicles and lysosomal structures. Furthermore, only in this perinuclear region, cytopathic-effect(CPE)-like changes seemed to originate, consisting in enlarged cytoplasmic vacuoles filled with degenerative amorphous material containing VLPs. Finally, the complete filling-up of the cytoplasm with these degenerative vacuoles, in addition to cellular lysis displayed by some cells, appeared as the possible terminal pattern of the infectious process. Our data suggest that in vitro HCV-infected TOFE cells undergo typical CPE-like changes that may be connected with virus replication.

Quantitation of hepatitis C virus RNA production in two human bone marrow-derived B-cell lines infected in vitro

The ability of hepatitis C virus (HCV) to replicate in two B-cell lines, CE and TOFE, derived from bone marrow of healthy subjects was compared using qualitative and quantitative molecular methods. The presence of intracellular negative-stranded HCV RNA (replicative intermediate) was investigated by nested polymerase chain reaction (PCR) in the infected cultures at different times after infection. The amounts of positive-stranded HCV RNA (genomic RNA copies) synthesized and released from cells one week after in vitro infection were determined by competitive PCR after reverse transcription of viral RNA for the 5' viral untranslated region. In both cell lines, HCV RNA replication took place, but the TOFE cell line appeared to be a more efficient virus producer than the CE cell line. The TOFE cell line could be a valuable and reliable tool for basic and clinical HCV studies.

Ultrastructural observations of viral particles within hepatitis C virus-infected human B lymphoblastoid cell line

Hepatitis C virus (HCV)-infected TOFE cells, a human bone marrow-derived B-cell line, were studied by transmission electron microscopy (TEM). We reported the presence of virus-like particles, (VLPs) having a diameter of 45 nm on average, within the cytoplasm of HCV-infected cells and their absence in uninfected cells. The VLPs were mostly seen in dilated cisternae of endoplasmic reticulum (ER) and consisted of an electron-dense core and a membrane envelope with surface projections. In the HCV-infected TOFE cells, examination by TEM revealed tubular structures similar to those observed in liver cells of chimpanzees and humans infected by the virus. In some instances, the outer membrane of the particles was connected to the ER membrane, indicating possible virus budding into the cisternae. Rarely, coated vesicles containing a particle were seen. In most of the infected cells, enlarged cytoplasmic vacuoles filled with degenerative amorphous material were observed. The data suggest a flavivirus-like pattern of HCV morphogenesis in infected non-hepatic cells and identify lymphoblastoid TOFE cells as a valuable system for the study of the sequential steps of the infection process and the morphological effects produced by HCV infection.