Natural selection of adaptive mutations in non-structural genes increases trans-encapsidation of hepatitis C virus replicons lacking envelope protein genes

Hepatitis C Virus Resistance to Carbohydrate-Binding Agents

Carbohydrate binding agents (CBAs), including natural lectins, are more and more considered as broad-spectrum antivirals. These molecules are able to directly inhibit many viruses such as Human Immunodeficiency Virus (HIV), Hepatitis C Virus (HCV), Dengue Virus, Ebola Virus or Severe Acute Respiratory Syndrome Coronavirus through binding to envelope protein N-glycans. In the case of HIV, it has been shown that CBAs select for mutant viruses with N-glycosylation site deletions which are more sensitive to neutralizing antibodies. In this study we aimed at evaluating the HCV resistance to CBAs in vitro. HCV was cultivated in the presence of increasing Galanthus nivalis agglutinin (GNA), Cyanovirin-N, Concanavalin-A or Griffithsin concentrations, during more than eight weeks. At the end of lectin exposure, the genome of the isolated strains was sequenced and several potential resistance mutations in the E1E2 envelope glycoproteins were identified. The effect of these mutations on viral fitness as well as on sensitivity to inhibition by lectins, soluble CD81 or the 3/11 neutralizing antibody was assessed. Surprisingly, none of these mutations, alone or in combination, conferred resistance to CBAs. In contrast, we observed that some mutants were more sensitive to 3/11 or CD81-LEL inhibition. Additionally, several mutations were identified in the Core and the non-structural proteins. Thus, our results suggest that in contrast to HIV, HCV resistance to CBAs is not directly conferred by mutations in the envelope protein genes but could occur through an indirect mechanism involving mutations in other viral proteins. Further investigations are needed to completely elucidate the underlying mechanisms.

Genetic Diversity Underlying the Envelope Glycoproteins of Hepatitis C Virus: Structural and Functional Consequences and the Implications for Vaccine Design

In the 26 years since the discovery of Hepatitis C virus (HCV) a major global research effort has illuminated many aspects of the viral life cycle, facilitating the development of targeted antivirals. Recently, effective direct-acting antiviral (DAA) regimens with >90% cure rates have become available for treatment of chronic HCV infection in developed nations, representing a significant advance towards global eradication. However, the high cost of these treatments results in highly restricted access in developing nations, where the disease burden is greatest. Additionally, the largely asymptomatic nature of infection facilitates continued transmission in at risk groups and resource constrained settings due to limited surveillance. Consequently a prophylactic vaccine is much needed. The HCV envelope glycoproteins E1 and E2 are located on the surface of viral lipid envelope, facilitate viral entry and are the targets for host immunity, in addition to other functions. Unfortunately, the extreme global genetic and antigenic diversity exhibited by the HCV glycoproteins represents a significant obstacle to vaccine development. Here we review current knowledge of HCV envelope protein structure, integrating knowledge of genetic, antigenic and functional diversity to inform rational immunogen design.

The kinase-inhibitor sorafenib inhibits multiple steps of the Hepatitis C Virus infectious cycle in vitro

Hepatitis C Virus (HCV) chronic infection is a major cause of hepatocellular carcinoma. Sorafenib is the only medical treatment that has been approved for the treatment of this cancer. It is a multikinase inhibitor with anti-tumor activity against a wide variety of cancers. Sorafenib blocks angiogenesis and tumor cell proliferation through inhibition of kinases, such as VEGFR2, PDGFR, or the serine/threonine kinases RAF. Previous studies have reported an anti-HCV effect of sorafenib in vitro, but various mechanisms of action have been described. The aim of this study was to clarify the action of sorafenib on the complete HCV infectious cycle. In order to examine the action of sorafenib on all steps of the HCV infectious cycle, we used a combination of validated cell culture models, based on the HuH-7 reference cell line and primary human hepatocytes. We found that sorafenib blocks HCV infection by altering the viral entry step and the production of viral particles. Moreover, we observed that treatment with sorafenib lead to a modification of Claudin-1 expression and localization, which could partly be responsible for the anti-HCV effect. Collectively, our findings confirm the anti-HCV effect of sorafenib in vitro, while highlighting the complexity of the action of sorafenib on the HCV infectious cycle.

Inactivation of viruses in platelet and plasma products using a riboflavin-and-UV-based photochemical treatment

BACKGROUND

Multilayered blood safety programs reduce the risk of transfusion-transmitted diseases; however, there remains a risk of window period transmission of screened viruses and transmission of unscreened and emerging viruses from asymptomatic donors. To reduce this risk, a riboflavin-and-UV-light-based pathogen reduction process was evaluated against eight viral agents.

STUDY DESIGN AND METHODS

Riboflavin and UV light was evaluated against the following eight viral agents: encephalomyocarditis virus (EMC), hepatitis A virus (HAV), hepatitis C virus (HCV), influenza A (FLUAV), La Crosse virus (LACV), pseudorabies virus (PRV), sindbis virus (SINV), and vesicular stomatitis virus (VSV). Before treatment, a sample was removed to determine the product's initial viral load. After treatment the product's viral load was reevaluated and the log reduction was calculated.

RESULTS

Virus reduction after treatment with riboflavin and UV light is equivalent in platelet (PLT) and plasma units, as demonstrated by a 3.2-log reduction of EMC in plasma, PLTs, and PLT additive solution containing 35% plasma. Additionally, the following viral reductions values were observed: HAV 1.8 log, HCV at least 4.1 log, FLUAV at least 5.0 log, LACV at least 3.5 log, PRV 2.5 log, SINV 3.2 log, and VSV at least 6.3 log.

CONCLUSIONS

The results observed in this study suggest that treating PLT and plasma products with a riboflavin-and-UV-light-based pathogen reduction process could potentially eliminate window period transmission of screened viruses and greatly reduce the risk of transfusion transmission of unscreened viruses.

Nanoparticle encapsidation of Flock house virus by auto assembly of Tobacco mosaic virus coat protein

Tobacco Mosaic virus (TMV) coat protein is well known for its ability to self-assemble into supramolecular nanoparticles, either as protein discs or as rods originating from the ~300 bp genomic RNA origin-of-assembly (OA). We have utilized TMV self-assembly characteristics to create a novel Flock House virus (FHV) RNA nanoparticle. FHV encodes a viral polymerase supporting autonomous replication of the FHV genome, which makes it an attractive candidate for viral transgene expression studies and targeted RNA delivery into host cells. However, FHV viral genome size is strictly limited by native FHV capsid. To determine if this packaging restriction could be eliminated, FHV was adapted to express enhanced green fluorescent protein (GFP), to allow for monitoring of functional FHV RNA activity. Then TMV OA was introduced in six 3' insertion sites, with only site one supporting functional FHV GFP expression. To create nanoparticles, FHV GFP-OA modified genomic RNA was mixed in vitro with TMV coat protein and monitored for encapsidation by agarose electrophoresis and electron microscopy. The production of TMV-like rod shaped nanoparticles indicated that modified FHV RNA can be encapsidated by purified TMV coat protein by self-assembly. This is the first demonstration of replication-independent packaging of the FHV genome by protein self-assembly.

Incorporation of hepatitis C virus E1 and E2 glycoproteins: the keystones on a peculiar virion

Hepatitis C virus (HCV) encodes two envelope glycoproteins, E1 and E2. Their structure and mode of fusion remain unknown, and so does the virion architecture. The organization of the HCV envelope shell in particular is subject to discussion as it incorporates or associates with host-derived lipoproteins, to an extent that the biophysical properties of the virion resemble more very-low-density lipoproteins than of any virus known so far. The recent development of novel cell culture systems for HCV has provided new insights on the assembly of this atypical viral particle. Hence, the extensive E1E2 characterization accomplished for the last two decades in heterologous expression systems can now be brought into the context of a productive HCV infection. This review describes the biogenesis and maturation of HCV envelope glycoproteins, as well as the interplay between viral and host factors required for their incorporation in the viral envelope, in a way that allows efficient entry into target cells and evasion of the host immune response.

An insight into the diagnosis and pathogenesis of hepatitis C virus infection

This review focuses on research findings in the area of diagnosis and pathogenesis of hepatitis C virus (HCV) infection over the last few decades. The information based on published literature provides an update on these two aspects of HCV. HCV infection, previously called blood transmitted non-A, non-B infection, is prevalent globally and poses a serious public health problem worldwide. The diagnosis of HCV infection has evolved from serodetection of non-specific and low avidity anti-HCV antibodies to detection of viral nucleic acid in serum using the polymerase chain reaction (PCR) technique. Current PCR assays detect viral nucleic acid with high accuracy and the exact copy number of viral particles. Moreover, multiplex assays using real-time PCR are available for identification of HCV-genotypes and their isotypes. In contrast to previous methods, the newly developed assays are not only fast and economic, but also resolve the problem of the window period as well as differentiate present from past infection. HCV is a non-cytopathic virus, thus, its pathogenesis is regulated by host immunity and metabolic changes including oxidative stress, insulin resistance and hepatic steatosis. Both innate and adaptive immunity play an important role in HCV pathogenesis. Cytotoxic lymphocytes demonstrate crucial activity during viral eradication or viral persistence and are influenced by viral proteins, HCV-quasispecies and several metabolic factors regulating liver metabolism. HCV pathogenesis is a very complex phenomenon and requires further study to determine the other factors involved.

Evasion of superinfection exclusion and elimination of primary viral RNA by an adapted strain of hepatitis C virus

Cells that are productively infected by hepatitis C virus (HCV) are refractory to a second infection by HCV via a block in viral replication known as superinfection exclusion. The block occurs at a postentry step and likely involves translation or replication of the secondary viral RNA, but the mechanism is largely unknown. To characterize HCV superinfection exclusion, we selected for an HCV variant that could overcome the block. We produced a high-titer HC-J6/JFH1 (Jc1) viral genome with a fluorescent reporter inserted between NS5A and NS5B and used it to infect Huh7.5 cells containing a Jc1 replicon. With multiple passages of these infected cells, we isolated an HCV variant that can superinfect cells at high levels. Notably, the superinfectious virus rapidly cleared the primary replicon from superinfected cells. Viral competition experiments, using a novel strategy of sequence-barcoding viral strains, as well as superinfection of replicon cells demonstrated that mutations in E1, p7, NS5A, and the poly(U/UC) tract of the 3' untranslated region were important for superinfection. Furthermore, these mutations dramatically increased the infectivity of the virus in naive cells. Interestingly, viruses with a shorter poly(U/UC) and an NS5A domain II mutation were most effective in overcoming the postentry block. Neither of these changes affected viral RNA translation, indicating that the major barrier to postentry exclusion occurs at viral RNA replication. The evolution of the ability to superinfect after less than a month in culture and the concomitant exclusion of the primary replicon suggest that superinfection exclusion dramatically affects viral fitness and dynamics in vivo.

Permissivity of primary human hepatocytes and different hepatoma cell lines to cell culture adapted hepatitis C virus

Significant progress has been made in Hepatitis C virus (HCV) culture since the JFH1 strain cloning. However, developing efficient and physiologically relevant culture systems for all viral genotypes remains an important goal. In this work, we aimed at producing a high titer JFH1 derived virus to test different hepatic cells’ permissivity. To this end, we performed successive infections and obtained a JFH1 derived virus reaching high titers. Six potential adaptive mutations were identified (I599V in E2, R1373Q and M1611T in NS3, S2364P and C2441S in NS5A and R2523K in NS5B) and the effect of these mutations on HCV replication and infectious particle production was investigated. This cell culture adapted virus enabled us to efficiently infect primary human hepatocytes, as demonstrated using the RFP-NLS-IPS reporter protein and intracellular HCV RNA quantification. However, the induction of a strong type III interferon response in these cells was responsible for HCV inhibition. The disruption of this innate immune response led to a strong infection enhancement and permitted the detection of viral protein expression by western blotting as well as progeny virus production. This cell culture adapted virus also enabled us to easily compare the permissivity of seven hepatoma cell lines. In particular, we demonstrated that HuH-7, HepG2-CD81, PLC/PRF/5 and Hep3B cells were permissive to HCV entry, replication and secretion even if the efficiency was very low in PLC/PRF/5 and Hep3B cells. In contrast, we did not observe any infection of SNU-182, SNU-398 and SNU-449 hepatoma cells. Using iodixanol density gradients, we also demonstrated that the density profiles of HCV particles produced by PLC/PRF/5 and Hep3B cells were different from that of HuH-7 and HepG2-CD81 derived virions. These results will help the development of a physiologically relevant culture system for HCV patient isolates.