Researchers at Oregon Health & Science University have developed the first transgenic nonhuman primate model — genetically modified to carry a human gene — for studying hepatitis B virus. The breakthrough could lead to the development of new treatments for the disease, which affects about 250 million people globally and results in nearly 1 million deaths annually.
The findings were published today in the Proceedings of the National Academy of Sciences.
Ben Burwitz, Ph.D., associate professor at OHSU's Oregon National Primate Research Center, said hepatitis B virus, or HBV, only infects humans and a few other non-rodent species, making it challenging to develop animal models that replicate the human immune response. Right now, nonhuman primate models are only attainable following temporary changes, like adding the HBV entry receptor, a human protein called NTCP, to liver cells with the help of viral vectors. However, these methods aren't very efficient, the effects don't last long, and the immune system can sometimes interfere with the process.
The breakthrough in Burwitz's lab came from inserting NTCP into the genetic material of rhesus macaques, making them naturally susceptible to the virus.
"We used a gene-editing system called Piggybac that's less precise than CRISPR but much more efficient, which is critical when working with embryos in expensive procedures like IVF," said Lauren Rust, Ph.D., an assistant staff scientist in Burwitz's lab and lead author of the study.
The researchers edited the genes of seven nonhuman primates and identified two that carried the transgene. Tests showed that while the transgene was present in all tissues, it was only expressed in the liver — a critical factor for future HBV infection studies.
"This means the nonhuman primates mimic the human liver-specific susceptibility to HBV," Rust said. "We've shown that liver cells from these models can be infected with HBV in lab tests without any additional modifications. It's a huge step forward."
The researchers plan to breed future generations with the same genetic trait and study whether offspring develop chronic HBV infections when exposed to the virus at birth, similar to how infections progress in humans.
Hepatitis B is a global health challenge despite the availability of a vaccine. The virus spreads through contact with infected blood or bodily fluids, with most chronic cases stemming from mother-to-child transmission at birth.
"Most babies infected at birth develop chronic infections," Rust said. "There's no cure for chronic HBV, only medications that manage the disease. Chronic infection can lead to complications like liver cancer. We're creating a model that lets us study chronic HBV and test potential treatments in a way we never could before."
Burwitz said that while HBV-associated disease progresses more slowly than other viruses like HIV, its global burden is enormous.
"The virus replicates quietly in the body for years before the immune system reacts and causes liver damage slowly over time," he said.
While some progress has been made on immunotherapies for HBV, those being pursued are costly and difficult to transport, requiring stable temperatures. Future research out of Burwitz's lab will focus on using the transgenic model to study chronic infections and test therapeutic approaches, including small-molecule drugs in a pill form that could provide a cure.
"We've seen success with treatments for hepatitis C that wipe out the virus, and that's the goal here," Burwitz said. "Developing a drug that's effective, easy to distribute and affordable for global populations is critical."
The team's model is applicable to other viruses beyond HBV. Due to their new gene-editing technologies, they could create new transgenic models to study many diseases that impact human organs.
"This system is easily editable," Rust said. "We can alter it to study other diseases, particularly those specific to certain organs. For example, many people with HBV also have HIV, which worsens outcomes for both diseases. Our model can help us explore those co-infections as well."
In addition to Rust and Burwitz, OHSU co-authors include: Sreya Biswas, Ph.D., Sofiya Yusova, M.S., Savannah Lutz, B.S., Spandana Naldiga, Ph.D., Brayden J. Hinrichs, B.S., Michelle N. Sullivan, D.V.M., Ph.D., DACLAM, Jeremy Smedley, D.V.M., M.S., DACLAM, Jonah B. Sacha, Ph.D., Carol B. Hanna, Ph.D., Junghyun Ryu, Ph.D., Nadine Piekarski, Ph.D., Jamie Lo, M.D., Benjamin N. Bimber, Ph.D., and Jon Hennebold, Ph.D.; and Ulrike Protzer, M.D. and Jochen Martin Wettengel, M.D., with the Technical University of Munich.
This research was supported by the National Institutes of Allergy and Infectious Disease, Drug Abuse, and the Office of the Director, of the National Institutes of Health, under Award Numbers R21AI133632, R01AI157612, DP1DA056493, and P51 OD011092. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
All research involving animal subjects at OHSU must be reviewed and approved by the university's Institutional Animal Care and Use Committee (IACUC). The IACUC's priority is to ensure the health and safety of animal research subjects. The IACUC also reviews procedures to ensure the health and safety of the people who work with the animals. The IACUC conducts a rigorous review of all animal research proposals to ensure they demonstrate scientific value and justify the use of live animals.
