Modeling treatment responses to HBV
Text by Ben Winer, Jenna Gaska and Alexander Ploss
At least 250 million patients worldwide are persistently infected with hepatitis B virus (HBV). Chronic carriers are at risk of developing severe liver disease including fibrosis, cirrhosis and liver cancer (hepatocellular carcinoma, HCC). A vaccine exists to protect against HBV infection, and established infections can be treated with a variety of regimens. However, these treatments rarely cure and patients usually have to remain on antiviral therapy for life. Unfortunately, even when viremia is suppressed, patients remain at an elevated risk of developing HCC.
Study of HBV and development of more effective, curative regimens is notoriously difficult because of the scarcity of adequate experimental systems. HBV exhibits a highly restricted tissue and host tropism almost exclusively limited to human and chimpanzee hepatocytes. In primary hepatocytes and some hepatic cell lines, viremia is usually only maintained for a few days to weeks, inadequately reflecting the persistent phase of the infection. Restrictions on research in chimpanzees have made humanized mice the next best alternative for in vivo studies of HBV. Persistent HBV infection was first observed in human liver chimeric mice, which are engrafted with human hepatocytes, in the early 2000s but models at that time were rather frail and low in throughput, limiting their widespread use.
To address this challenge, we aimed to construct a new human liver chimeric mouse that could be infected with HBV. We teamed up with Michael Wiles and Benjamin Low, our colleagues at the Jackson Laboratory (Bar Harbor, ME), who employed a site-specific zinc-finger nuclease to knock-out the murine fumaryl acetoacetate hydrolase (FAH) gene in an immunodeficient background, yielding FNRG mice (now archived at JAX.org ref # 018454).
We demonstrate that these animals can be efficiently engrafted at high levels with human hepatocytes. Importantly, these FNRhuman liver chimeric G mice are susceptible to HBV infection. To establish utility for antiviral drug testing, we treated animals with entecavir (ETV), an inhibitor of the HBV reverse transcriptase already in clinical use. ETV administration efficiently suppressed viremia and when animals were weaned off this drug, HBV rebounded which mimics closely the treatment response patterns observed in patients.
Undoubtedly, additional refinements of this model will be needed to improve its utility for studying HBV infection but our study further highlights humanized mice as an enabling technology to bridge the gap between conventional (cell culture) models and the often highly complex situations observed in patients.
Schematic depiction of the experimental workflow. Figure by Florian Douam and Alexander Ploss.
Introducing the authors
Pictured: Benjamin Winer (right), graduate student, Department of Molecular Biology, Princeton University; Alexander Ploss (left), Ph.D., Assistant Professor, Department of Molecular Biology, Princeton University.
About the research
Benjamin Y. Winer, Tiffany Huang, Benjamin E. Low, Cindy Avery, Mihai-Alexandru Pais, Gabriela Hrebikova, Evelyn Siu, Luis Chiriboga, Michael V. Wiles, Alexander Ploss
Virology, Volume 502, February 2017, Pages 63–72