Jing W. Xiao

Broadly neutralizing antibodies abrogate established hepatitis C virus infection

HCV-specific neutralizing antibodies protect humanized mice from challenge and suppress established infections. Neutralizing Antibodies Take Down the HCV Establishment In most individuals infected with hepatitis C virus (HCV), the HCV sets up shop—establishing a long-term, chronic infection that damages the liver and can lead to cirrhosis or liver cancer. de Jong et al. now report that a trio of neutralizing antibodies not only can prevent infection but also can treat and maybe even cure already established infection in multiple animal models. The broadly neutralizing antibodies, which could block multiple genotypes of HCV, were delivered into the muscle by a virus—an adeno-associated vector that does not cause disease—resulting in prolonged expression of the antibodies. If these data hold true in people, this approach may provide a new tool for treating HCV infection. In most exposed individuals, hepatitis C virus (HCV) establishes a chronic infection; this long-term infection in turn contributes to the development of liver diseases such as cirrhosis and hepatocellular carcinoma. The role of antibodies directed against HCV in disease progression is poorly understood. Neutralizing antibodies (nAbs) can prevent HCV infection in vitro and in animal models. However, the effects of nAbs on an established HCV infection are unclear. We demonstrate that three broadly nAbs—AR3A, AR3B, and AR4A—delivered with adeno-associated viral vectors can confer protection against viral challenge in humanized mice. Furthermore, we provide evidence that nAbs can abrogate an ongoing HCV infection in primary hepatocyte cultures and in a human liver chimeric mouse model. These results showcase a therapeutic approach to interfere with HCV infection by exploiting a previously unappreciated need for HCV to continuously infect new hepatocytes to sustain a chronic infection.

Mouse models of acute and chronic hepacivirus infection

New York City rats provide a gift to virologists Despite the development of curative drugs for hepatitis C virus (HCV) infection, global eradication of HCV will likely require a prophylactic vaccine. Progress toward a vaccine has been impeded by the absence of mouse models suitable for studying the immune response to HCV. Billerbeck et al. found that a HCV-related virus isolated from New York City rats produces an infection in laboratory mice that shares several immunological features with human infections (see the Perspective by Klenerman and Barnes). Their initial analyses of the infected mice revealed that acute clearance of the virus was dependent on T cells but not on natural killer cells. Science, this issue p. 204; see also p. 129 A mouse model may provide mechanistic insights into the immune response to hepatitis C virus infection. An estimated 71 million people worldwide are infected with hepatitis C virus (HCV). The lack of small-animal models has impeded studies of antiviral immune mechanisms. Here we show that an HCV-related hepacivirus discovered in Norway rats can establish high-titer hepatotropic infections in laboratory mice with immunological features resembling those seen in human viral hepatitis. Whereas immune-compromised mice developed persistent infection, immune-competent mice cleared the virus within 3 to 5 weeks. Acute clearance was T cell dependent and associated with liver injury. Transient depletion of CD4+ T cells before infection resulted in chronic infection, characterized by high levels of intrahepatic regulatory T cells and expression of inhibitory molecules on intrahepatic CD8+ T cells. Natural killer cells controlled early infection but were not essential for viral clearance. This model may provide mechanistic insights into hepatic antiviral immunity, a prerequisite for the development of HCV vaccines.

In situ expansion of engineered human liver tissue in a mouse model of chronic liver disease

An engineered microenvironment supports expansion of adult human engineered liver tissue after implantation in a mouse model of liver injury. Tissue seeds blossom after transplant There is an enormous clinical need for liver transplant tissue. Bioengineered livers might ultimately be used as a bridge to or alternative for whole organ transplantation. In new work, Stevens et al. fabricated human artificial liver “seeds” in biomaterials that were able to grow and expand after implantation into mice in response to liver injury. After growth, the human artificial liver seeds were able to carry out normal liver functions such as production of human proteins like transferrin and albumin. This study suggests that implanted engineered tissue seeds should be able to expand in response to the body’s own repair signals. Control of both tissue architecture and scale is a fundamental translational roadblock in tissue engineering. An experimental framework that enables investigation into how architecture and scaling may be coupled is needed. We fabricated a structurally organized engineered tissue unit that expanded in response to regenerative cues after implantation into mice with liver injury. Specifically, we found that tissues containing patterned human primary hepatocytes, endothelial cells, and stromal cells in a degradable hydrogel expanded more than 50-fold over the course of 11 weeks in mice with injured livers. There was a concomitant increase in graft function as indicated by the production of multiple human liver proteins. Histologically, we observed the emergence of characteristic liver stereotypical microstructures mediated by coordinated growth of hepatocytes in close juxtaposition with a perfused vasculature. We demonstrated the utility of this system for probing the impact of multicellular geometric architecture on tissue expansion in response to liver injury. This approach is a hybrid strategy that harnesses both biology and engineering to more efficiently deploy a limited cell mass after implantation.

Hepatitis C virus infects rhesus macaque hepatocytes and simianized mice.

At least 170 million people are chronically infected with hepatitis C virus (HCV). Owing to the narrow host range of HCV and restricted use of chimpanzees, there is currently no suitable animal model for HCV pathogenesis studies or the development of a HCV vaccine. To identify cellular determinants of interspecies transmission and establish a novel immunocompetent model system, we examined the ability of HCV to infect hepatocytes from a small nonhuman primate, the rhesus macaque (Macaca mulatta). We show that the rhesus orthologs of critical HCV entry factors support viral glycoprotein‐dependent virion uptake. Primary hepatocytes from rhesus macaques are also permissive for HCV‐RNA replication and particle production, which is enhanced when antiviral signaling is suppressed. We demonstrate that this may be owing to the diminished capacity of HCV to antagonize mitochondrial antiviral‐signaling protein–dependent innate cellular defenses. To test the ability of HCV to establish persistent replication in vivo, we engrafted primary rhesus macaque hepatocytes into immunocompromised xenorecipients. Inoculation of resulting simian liver chimeric mice with either HCV genotype 1a or 2a resulted in HCV serum viremia for up to 10 weeks. Conclusion: Together, these data indicate that rhesus macaques may be a viable model for HCV and implicate host immunity as a potential species‐specific barrier to HCV infection. We conclude that suppression of host immunity or further viral adaptation may allow robust HCV infection in rhesus macaques and creation of a new animal model for studies of HCV pathogenesis, lentivirus coinfection, and vaccine development. (Hepatology 2015;62:57‐67)

Insufficient interleukin-12 signalling favours differentiation of human CD4(+) and CD8(+) T cells into GATA-3(+) and GATA-3(+) T-bet(+) subsets in humanized mice.

Differentiation of CD4+ T cells into type 1 or type 2 subsets is mediated by the expression of the opposing lineage defining transcription factors T‐bet and GATA‐3. However, the existence of GATA‐3+ T‐bet+ CD4+ T cells in mice suggests functional plasticity of these subsets. Little is known about type 1 and type 2 plasticity of human T‐cell subsets in vivo. Here, we show that in the xenogeneic environment of humanized mice, which lacks a functional immune‐regulatory network, human CD4+ and, notably, CD8+ T cells preferentially differentiate into interleukin (IL)‐4+ GATA‐3+ and IL‐4+ interferon‐γ+ GATA‐3+ T‐bet+ subsets. Treatment with recombinant human IL‐12 or expansion of IL‐12‐producing human dendritic cells in vivo reverted this phenotype and led to the down‐regulation of GATA‐3 expression. These changes also correlated with improved antiviral immune responses in humanized mice. In conclusion, our study shows the capacity of human CD4+ and CD8+ T cells for stable co‐expression of GATA‐3 and T‐bet in humanized mice and reveals a critical role for IL‐12 in regulating this phenotype.

Interferon regulatory factor 2 protects mice from lethal viral neuroinvasion.

Li et al. describe a novel role for IRF2, previously known as a negative regulator of type I IFN signaling, in protection of mice from lethal viral neuroinvasion by facilitating the proper localization of B cells and antibodies to the central nervous system.

Analysis of Hepatitis C Virus Particle Heterogeneity in Immunodeficient Human Liver Chimeric fah-/- Mice

Background & Aims Hepatitis C virus (HCV) is a leading cause of chronic liver diseases and the most common indication for liver transplantation in the United States. HCV particles in the blood of infected patients are characterized by heterogeneous buoyant densities, likely owing to HCV association with lipoproteins. However, clinical isolates are not infectious in vitro and the relative infectivity of the particles with respect to their buoyant density therefore cannot be determined, pointing to the need for better in vivo model systems. Methods To analyze the evolution of the buoyant density of in vivo–derived infectious HCV particles over time, we infected immunodeficient human liver chimeric fumaryl acetoacetate hydrolase-/- mice with J6/JFH1 and performed ultracentrifugation of infectious mouse sera on isopicnic iodixanol gradients. We also evaluated the impact of a high sucrose diet, which has been shown to increase very-low-density lipoprotein secretion by the liver in rodents, on lipoprotein and HCV particle characteristics. Results Similar to the severe combined immunodeficiency disease/Albumin-urokinase plasminogen activator human liver chimeric mouse model, density fractionation of infectious mouse serum showed higher infectivity in the low-density fractions early after infection. However, over the course of the infection, viral particle heterogeneity increased and the overall in vitro infectivity diminished without loss of the human liver graft over time. In mice provided with a sucrose-rich diet we observed a minor shift in HCV infectivity toward lower density that correlated with a redistribution of triglycerides and cholesterol among lipoproteins. Conclusions Our work indicates that the heterogeneity in buoyant density of infectious HCV particles evolves over the course of infection and can be influenced by diet.