Replication of a hepatitis C virus replicon clone in mouse cells

BACKGROUND: Hepatitis C Virus (HCV) is a significant public health burden and small animal models are needed to study the pathology and immunobiology of the virus. In effort to develop experimental HCV mouse models, we screened a panel of HCV replicons to identify clones capable of replicating in mouse hepatocytes. RESULTS: We report the establishment of stable HCV replication in mouse hepatocyte and fibroblast cell lines using replicons derived from the JFH-1 genotype 2a consensus sequence. Viral RNA replication efficiency in mouse cells was comparable to that observed in human Huh-7 replicon cells, with negative-strand HCV RNA and the viral NS5A protein being readily detected by Northern and Western Blot analysis, respectively. Although HCV replication was established in the absence of adaptive mutations that might otherwise compromise the in vitro infectivity of the JFH-1 clone, no infectious virus was detected when the culture medium from full length HCV RNA replicating mouse cells was titrated on Huh-7 cells, suggesting that the mouse cells were unable to support production of infectious progeny viral particles. Consistent with an additional block in viral entry, infectious JFH-1 particles produced in Huh-7 cells were not able to establish detectable HCV RNA replication in naïve mouse cells. CONCLUSION: Thus, this report expands the repertoire of HCV replication systems and possibly represents a step toward developing mouse models of HCV replication, but it also highlights that other species restrictions might continue to make the development of a purely murine HCV infectious model challenging

Persistent hepatitis C virus infection in vitro: coevolution of virus and host.

The virological and cellular consequences of persistent hepatitis C virus (HCV) infection have been elusive due to the absence of the requisite experimental systems. Here, we report the establishment and the characteristics of persistent in vitro infection of human hepatoma-derived cells by a recently described HCV genotype 2a infectious molecular clone. Persistent in vitro infection was characterized by the selection of viral variants that displayed accelerated expansion kinetics, higher peak titers, and increased buoyant densities. Sequencing analysis revealed the selection of a single adaptive mutation in the HCV E2 envelope protein that was largely responsible for the variant phenotype. In parallel, as the virus became more aggressive, cells that were resistant to infection emerged, displaying escape mechanisms operative at the level of viral entry, HCV RNA replication, or both. Collectively, these results reveal the existence of coevolutionary events during persistent HCV infection that favor survival of both virus and host

Hydrodynamic injection of viral DNA: A mouse model of acute hepatitis B virus infection

Hepatitis B virus (HBV) is a prototype for liver-specific pathogens in which the failure of the immune system to mount an effective response leads to chronic infection. Our understanding of the immune response to HBV is incomplete, largely due to the narrow host restriction of this pathogen and the limitations of existing experimental models. We have developed a murine model for studying human HBV replication, immunogenicity, and control. After transfection of hepatocytes in vivo with a replication-competent, over-length, linear HBV genome, viral antigens and replicative intermediates were synthesized and virus was secreted into the blood. Viral antigens disappeared from the blood as early as 7 days after transfection, coincident with the appearance of antiviral antibodies. HBV transcripts and replicative intermediates disappeared from the liver by day 15, after the appearance of antiviral CD8 + T cells. In contrast, the virus persisted for at least 81 days after transfection of NOD/Scid mice, which lack functional T cells, B cells, and natural killer (NK) cells. Thus, the outcome of hydrodynamic transfection of HBV depends on the host immune response, as it is during a natural infection. The methods we describe will allow the examination of viral dynamics in a tightly controlled in vivo system, the application of mutagenesis methods to the study of the HBV life cycle in vivo, and the dissection of the immune response to HBV using genetically modified mice whose immunoregulatory and immune effector functions have been deleted or overexpressed. In addition, this methodology represents a prototype for the study of other known and to-be-discovered liver-specific pathogens

Immunogenicity and Tolerogenicity of Hepatitis B Virus Structural and Nonstructural Proteins: Implications for Immunotherapy of Persistent Viral Infections

Persistent hepatitis B virus (HBV) infection is characterized by a weak and narrowly focused CD8(+) T-cell response to HBV that is thought to reflect the induction of central and/or peripheral tolerance to HBV proteins in neonatal and adult onset infections, respectively. Immunotherapeutic strategies that overcome tolerance and boost these suboptimal responses may lead to viral clearance in chronically infected individuals. The present study was performed to compare the relative immunogenicities and tolerogenicities of HBV structural (envelope [ENV]) and nonstructural (polymerase [POL]) proteins at the CD8(+) cytotoxic T lymphocyte (CTL) level in transgenic mice that replicate HBV in the liver and secrete infectious virus into the blood, thus representing an excellent model of persistent HBV infection. Interestingly, the mice were tolerant to the ENV but not to the POL proteins at the CTL level. Furthermore, the POL-specific CTLs had no impact on HBV replication or liver function in vivo, even though they were readily induced and reached the liver after DNA immunization, reflecting their relatively low avidity and the low level at which the POL protein is expressed by the hepatocyte. Collectively, these results suggest that the factors that make POL less tolerogenic also make POL-specific CTLs relatively inefficient effector cells when they reach the target organ. Immunotherapeutic strategies to control HBV infection by inducing virus-specific CTL responses in chronically infected subjects should be evaluated in light of this observation

Correction: CD40 Activation Rescues Antiviral CD8+ T Cells from PD-1-Mediated Exhaustion.

[This corrects the article DOI: 10.1371/journal.ppat.1003490.]

CD40 activation rescues antiviral CD8⁺ T cells from PD-1-mediated exhaustion.

The intrahepatic immune environment is normally biased towards tolerance. Nonetheless, effective antiviral immune responses can be induced against hepatotropic pathogens. To examine the immunological basis of this paradox we studied the ability of hepatocellularly expressed hepatitis B virus (HBV) to activate immunologically naïve HBV-specific CD8⁺ T cell receptor (TCR) transgenic T cells after adoptive transfer to HBV transgenic mice. Intrahepatic priming triggered vigorous in situ T cell proliferation but failed to induce interferon gamma production or cytolytic effector function. In contrast, the same T cells differentiated into cytolytic effector T cells in HBV transgenic mice if Programmed Death 1 (PD-1) expression was genetically ablated, suggesting that intrahepatic antigen presentation per se triggers negative regulatory signals that prevent the functional differentiation of naïve CD8⁺ T cells. Surprisingly, coadministration of an agonistic anti-CD40 antibody (αCD40) inhibited PD-1 induction and restored T cell effector function, thereby inhibiting viral gene expression and causing a necroinflammatory liver disease. Importantly, the depletion of myeloid dendritic cells (mDCs) strongly diminished the αCD40 mediated functional differentiation of HBV-specific CD8⁺ T cells, suggesting that activation of mDCs was responsible for the functional differentiation of HBV-specific CD8⁺ T cells in αCD40 treated animals. These results demonstrate that antigen-specific, PD-1-mediated CD8⁺ T cell exhaustion can be rescued by CD40-mediated mDC-activation

A single point mutation in E2 enhances hepatitis C virus infectivity and alters lipoprotein association of viral particles.

International audienceHepatitis C virus (HCV) infection is a major worldwide health problem. Our previous results showed that HCV evolved to gain the enhanced infectivity and altered buoyant density distribution during persistent infections in vitro. Here we showed that a point mutation I414T in HCV E2 was mainly responsible for these phenotypic changes. While the I414T mutation had no significant effect on HCV RNA replication and viral entry, it enhanced the production of infectious viral particles and decreased the dependency of viral entry on the levels of HCV receptors. Furthermore, we showed that the I414T mutation reduced the association of viral particles with low-density lipoprotein or very low-density lipoproteins during the virus secretion process, and the infection of the delipidated virus was more sensitive to the blockade by an anti-E2 neutralizing antibody and recombinant CD81 proteins. Our results provided more insights into understanding the roles of lipoprotein associations in HCV life cycle

A single point mutation in E2 enhances hepatitis C virus infectivity and alters lipoprotein association of viral particles.

International audienceHepatitis C virus (HCV) infection is a major worldwide health problem. Our previous results showed that HCV evolved to gain the enhanced infectivity and altered buoyant density distribution during persistent infections in vitro. Here we showed that a point mutation I414T in HCV E2 was mainly responsible for these phenotypic changes. While the I414T mutation had no significant effect on HCV RNA replication and viral entry, it enhanced the production of infectious viral particles and decreased the dependency of viral entry on the levels of HCV receptors. Furthermore, we showed that the I414T mutation reduced the association of viral particles with low-density lipoprotein or very low-density lipoproteins during the virus secretion process, and the infection of the delipidated virus was more sensitive to the blockade by an anti-E2 neutralizing antibody and recombinant CD81 proteins. Our results provided more insights into understanding the roles of lipoprotein associations in HCV life cycle