Viral Determinants of Chronic Hepacivirus Infection

Abstract The ability of the hepatitis C virus (HCV) to establish life-long chronic infection in most infected individuals makes it unique among RNA viruses. The molecular properties of the HCV genome and proteins are extensively characterized, but how they contribute to HCV persistence and immunopathogenesis remains poorly understood. This project seeks to identify the regions of the HCV genome that evolved to evade or modulate immunity to establish chronic infection. We isolated a rodent HCV-like virus (RHV) from a brown rat (Rattus norvegicus), RHV-rn1 (Rn-1), to develop surrogate animal models for HCV since Rn-1 established life-long chronic infection in rats and showed the potential for adaptation in lab mice. However, so far, Rn-1 studies have revealed two significant limitations. First, immunocompetent mice do not develop HCV-like prolonged or chronic infections. Second, although lab rats develop chronic infections, the lack of immunological and genetic resources limits their usefulness. A recent study described chronic Rn-1 infection in the collaborative cross (CC)- 071 mice; however, this CC strain is more susceptible to many Flaviviruses, and its mutated IRF3 gene, suppressed IFN signaling and T cell immunity, and diverse MHC haplotype limits its usefulness. Thus, an informative animal model to study the mechanism underlying spontaneous chronic HCV-like infections remains elusive and is critical for advancing this field. Finally, we identified a mouse-adapted variant Rn-2m that can establish prolonged or chronic viremia in normal lab mice. Subsequently, we identified the parent rat isolate Rn- 2 and its infection cleared within 3-4 weeks in mice, like Rn-1 infection. We also determined that chronic Rn-2m infection in mice leads to suppression of liver infiltrating leukocytes and virus-specific CD8 T cells, indicating that the mechanisms underlying the persistence of Rn-2m resemble that of HCV. Thus, there is a solid rationale for using Rn-2m as a surrogate for HCV to achieve the following two specific aims: Specific Aim 1 is to identify the genomic regions and mutations that allow Rn-2m to establish chronic infection. Specific Aim 2 is to compare the nature of infection and biological properties of Rn-2 and Rn-2m. We expect to identify the mutations (Aim- 1) that determine the unique biological properties of Rn-2m (Aim-2). This knowledge will gain new insights into the mechanism of HCV immune evasion. Additionally, proposed studies are critical for the informative use of this new animal model that develops spontaneous long-term chronic infection of a hepatotropic RNA virus.