Animal Model to study heterogeneous outcomes of HCV Infection and Pathogenesis - Abstract Approximately 30% of hepatitis C virus-infected persons spontaneously clear the virus within six months. The remaining 70% develop chronic infection. Of those with chronic HCV infection, the risk of cirrhosis ranges from 15% to 30% within 20 years. The viral and immune correlates of these different outcomes of infection and pathogenesis remain poorly studied, mainly due to the lack of an informative animal model. We developed surrogate animal models for HCV using a rodent HCV-like virus isolated from feral brown rats (Rattus norvegicus), RHV-rn1 (Rn-1). So far, studies of Rn-1 infection and immunity in lab mice have revealed that normal immunocompetent mice do not develop prolonged or chronic HCV-like infections. Notably, chronic HCV and RHV infections can be studied in their natural host, humans and rats, respectively. However, how HCV evades immunity during the acute phase, a prerequisite for developing chronic infection, requires animal models that allow comparative analyses of HCV-like clearance and persistence and mechanistic analysis of innate and adaptive immune responses. To create such models, we isolated several new RHV variants from feral rats and used these as a pool for serial passaging and adaptation in mice. After several passages, we identified a mouse- adapted variant (Rn-2m) that produced delayed clearance or chronic infection in normal lab mice. Subsequently, we identified the parent rat virus Rn-2, and its infection cleared within 3-4 weeks in mice. The project seeks to identify the viral and immune determinants of heterogenous outcomes of HCV infection and pathogenesis. Considering the strengths and weaknesses of the rat and mouse models, we propose a comparative biology approach where the new Rn-2m infection in the mouse model, due to the availability of vast resources, will be used to develop and test hypotheses, and the rat model will be used for validation of key findings. Specific Aim 1 is to identify the viral correlates of spontaneous clearance and chronic infection. Our new data indicate that Rn-2m constantly evolves and modulates innate immune cells in the liver of infected mice to establish a prolonged or chronic infection. We will compare the nature of infection, evolution, and immunogenicity of clone- rescued Rn-2 and Rn-2m to identify viral correlates of acute clearance, delayed clearance, and chronic infection in mice and subsequently in rats. Specific Aim 2 is to identify the immune correlates of chronic infection and liver diseases. We will use RHV-specific mouse and rat MHC tetramers and E2 protein tetramers, ex vivo antigen stimulation, passive antibody, and in vivo T and B cell transfer, and cell depletion experiments to define the role of T and B cells in determining different outcomes of RHV infection and pathogenesis. We expect that the solid rationale behind our approach will yield a biologically relevant and widely accessible lab mouse model for HCV and gain novel and mechanistic insights into HCV immune evasion and pathogenesis. This knowledge is crucial for developing new strategies to prevent chronic HCV infections and associated liver diseases.
