Breaching the species barrier: Towards an immunocompetent HBV-susceptible mouse model

PROJECT SUMMARY Chronic hepatitis B virus (HBV) infection remains an enduring global public health challenge, affecting approximately 300 million individuals, despite prophylactic vaccines. The current FDA-approved anti-HBV drugs suppress viral replication but are unable to eliminate the viral covalently closed circular DNA (cccDNA) genome within infected hepatocytes. Restoring the immune response holds promise as a potential avenue toward a cure; however, T-cell exhaustion commonly observed in chronic HBV-infected patients impedes effective viral clearance. Regrettably, progress towards curative treatments has been stymied by the scarcity of appropriate immunocompetent animal models susceptible to HBV. HBV exhibits high species specificity, infecting only humans and chimpanzees. Mice, widely used for modeling human diseases due to their well-characterized immune system, high reproductive capability, and short gestation period, are not naturally susceptible to HBV infection, even after expressing human sodium taurocholate co-transporting polypeptide, the HBV entry receptor. The primary obstacle to HBV infection in murine hepatocytes is the inability to establish cccDNA, which is essential for HBV infection and persistence. Although HBV can infect mice xenotransplanted with human hepatocytes, these models are immunodeficient. Humanized mice engrafted with both human hepatocytes and human immune cells could surmount this deficiency, but their immune response tends to be weak and constrained. In this study, we aim to identify the host and viral determinants capable of breaching the species barrier for HBV infection in murine hepatocytes and thereby develop HBV-susceptible mouse models. In Aim 1, we will take a host-centric approach to determine if alterations in the murine hepatocyte cellular environment can lead to HBV cccDNA formation. Specifically, we will test whether genetic diversity across mouse strains or diversity induced by functional genomics approaches renders murine hepatocytes more permissive to HBV infection and replication. In Aim 2, we will take a virus-centric approach to determine the role of nucleocapsid uncoating in cccDNA formation within murine hepatocytes. We will also exploit the power of viral diversity to a degree never attempted with HBV to select viral variants capable of forming cccDNA in mouse hepatocytes. The proposed experiments have high reward potential. There is an inherent risk; however, the risks are more than justified because a simple mouse model would be accessible to scientists around the globe and accelerate research. We designed most experiments so that regardless of the outcome, the results will provide valuable novel insights into HBV host tropism and develop new technologies. We expect these efforts will ultimately lead to the creation of a fully HBV-susceptible immunocompetent mouse model that is suitable for developing therapeutic strategies, including immune perturbations, to promote a functional cure.