Towards in vitro and in vivo model systems for Hepatitis B and Delta Viruses

Abstract

Hepatitis B virus (HBV) is one of the oldest viruses known to afflict humankind, having been discovered in the remains of ancient Egyptian and Korean mummies. Today, HBV remains a global scourge, infecting approximately 257 million individuals worldwide, of whom about 887,000 die of complications each year. Besides fundamental interest into the basic biology of this virus, a need to develop curative therapeutics motivates biomedical research. For the past several decades, study of this virus and development of therapies has been hampered by a severe lack of model systems, both in vitro and in vivo. While in vitro systems cannot support robust infection for more than a week, there exist few in vivo systems for the virus at all, save for the chimpanzee, research on which a recent NIH moratorium halted, and the transgenic mouse, which while certainly helpful is genetically dissimilar to humans. In this thesis, we make progress on both the in vitro and in vivo fronts. For an in vitro model, we employ the self-assembling primary human hepatocyte co-culture (SACC-PHH) model system, which takes advantage of non-parenchymal fibroblasts to allow primary human hepatocytes to support HBV infection for up to four weeks, far longer than current systems and without suppression of antiviral immunity. We utilize this model for several applications, including co-infection with the satellite hepatitis Delta virus, testing of antiviral therapeutics, RNA sequencing, and mathematical modeling of infection. For an in vivo model, we pursue a viral adaptation project. Here, we mutagenize residues of the HBV surface protein, preS1, to discover variants capable of utilizing a cynomolgus macaque hepatocyte receptor for entry. Altogether, we anticipate that our results will empower other researchers to pursue some of the most pressing questions in HBV biology today, whether they concern the host immune response to infection, transcriptomic changes undergone by infected hepatocytes, or the development of curative therapeutics.