A new study published in Microbiology Spectrum reports the establishment of a liver-humanized NSG-PiZ mouse model that is fully permissive to hepatitis B virus (HBV) infection. In this model, HBV can persist for at least for 6 months and for this reason can be used to study disease progression as well as antiviral therapies during both acute and chronic HBV infections.
Dr. Keith Jerome, a professor in the Vaccine and Infectious Disease Division, and corresponding author of the study said, “We were shocked when we went to test our HBV therapy in vivo and found out that the previous liver-humanized mouse models were so complex that they can only be routinely done by commercial contract labs, and at a cost of several thousand dollars per mouse. We were able to do one experiment, but we couldn’t afford to follow up and optimize the therapy.” This led Dr. Jerome and his team to “develop a simpler model for liver humanization and HBV infection.” With this model “academic researchers would have an option that’s affordable, and that they can easily do in their own labs,” Dr. Jerome added.
One of the major obstacles to studying HBV pathogenesis is the difficulty of culturing the virus in the lab. In addition, there are no animal models to study HBV that fully recapitulate the human infections. “The study of HBV pathogenesis and validation of novel anti-HBV therapeutics in vivo has been extremely challenging,” said Dr. Daniel Stone, a senior staff scientist in Dr. Jerome’s lab and leader of the study, along with former Jerome lab postdoc Rossana Colon-Thillet and research technician Michelle Loprieno. Dr. Stone explained that “HBV is a highly species restricted virus that can only replicate in humans, great apes, and Asian tree shrews that are not commonly used in research." Dr. Jerome’s team tackled this problem with a winning idea: affordable liver-humanized NSG-PiZ mice. “They are relatively simple to establish, cost a fraction of commercially available mice such as FRG and PXB liver-humanized mice, and can be readily used as an alternative model for the study of HBV replication and new antiviral therapies” said Dr. Stone.
The Jerome team’s mouse model used immunodeficient NSG-PiZ mice whose genetic backgrounds provide a stable engraftment environment for primary human hepatocytes (PHH). Before PHH transplantation, NSG-PiZ mice were treated with hepatotoxic drugs to insult their hepatocytes. Excitingly, most NSG-PiZ mice tolerated PHH engraftment and the chimeric mouse liver was shown to be functional by detection of secreted serum human albumin (HUAlb). Then, liver-humanized NSG-PiZ mice were infected with HBV. The authors found that HBV replicates in liver-humanized NSG-PiZ mice for at least 169 days. Histological analysis of chimeric mouse livers showed that HBV replication was restricted to PHHs.
Next, the researchers showed that antiviral drugs, commonly used to treat patients with chronic hepatitis B, can restrict HBV replication in infected PHHs. The authors also demonstrated that infected PHHs can be transduced with AAV vectors, commonly used to deliver antiviral gene therapeutics to hepatocytes for HBV treatment. One particularly interesting feature of this new mouse model was a high correlation between covalently closed circular DNA (cccDNA)and total HBV DNA. cccDNA is incredibly difficult to get rid of and is the root of HBV chronicity in humans as well. These results make the liver-humanized NSG-PiZ mice model an ideal tool to study antivirals or gene-based therapies for HBV.
Around 300 million people worldwide live with HBV, and chronic infection is the most common risk factor for liver damage and cancer. “New curative therapies for HBV are desperately needed since chronic infections are largely incurable with existing therapies,” said Dr. Stone.
Going forward, Dr. Jerome’s team is using liver-humanized NSG-PiZ mice to “improve our gene editing approach to HBV infections” and for “testing new approaches with both academic and private sector partners,” said Dr. Jerome. “We are using gene therapy to deliver endonucleases including CRISPR-Cas9 and meganucleases that selectively cleave and eliminate persistent viral DNA within infected cells. Our new model of chronic HBV infection will allow us to validate this and other curative approaches for the treatment of HBV in vivo,” Dr. Stone added.
“I’m thrilled that Rossana, Dan and Michelle’s work is accelerating the search for an HBV cure,” Dr. Jerome concluded.
The spotlighted research was supported by grants from the National Institute of Health, the National Cancer Institute and the Washington Research Foundation postdoctoral fellowship.
Fred Hutch/University of Washington/Seattle Children's Cancer Consortium member Dr. Keith Jerome contributed to this work.
Colón-Thillet R, Stone D, Loprieno MA, Klouser L, Roychoudhury P, Santo TK, Xie H, Stensland L, Upham SL, Pepper G, Huang ML, Aubert M, Jerome KR. 2023. Liver-Humanized NSG-PiZ Mice Support the Study of Chronic Hepatitis B Virus Infection and Antiviral Therapies. Microbiol Spectr. e0517622. Available online ahead of print.