Researchers at Baylor College of Medicine have reported a significant advancement in the study of human norovirus, a major cause of acute viral gastroenteritis globally. Norovirus particularly affects young children, the elderly, and individuals with weakened immune systems. There are currently no approved vaccines or antiviral treatments for this virus; management is limited to supportive care.
Historically, scientists have struggled to grow sufficient quantities of human norovirus (HuNoV) in laboratory settings, hindering research into prevention and treatment methods. The new study addresses this challenge by identifying factors that restrict viral replication and developing a method to support long-term cultivation of the virus.
"In 2016, a previous breakthrough occurred when scientists in our lab and collaborators successfully grew HuNoV in human intestinal enteroids (HIEs), or 'mini-guts'– miniature, lab grown versions of the human gut," said first author Gurpreet Kaur, graduate student in molecular virology and microbiology at Baylor working in Dr. Mary Estes' lab. "While this system allowed researchers to infect cells and study the virus, it still had a major shortcoming – the virus would not grow through repeated rounds, the way scientists can grow many other microorganisms. After just a few rounds, norovirus replication would stop, making it impossible to build up long lasting viral stocks."
Because of these limitations, researchers have relied on collecting viruses from patient stool samples—a process that is inconsistent and makes large-scale experiments difficult.
"Looking to overcome this obstacle, we studied several versions of HIEs to understand why norovirus growth usually stops," said co-author Dr. Sue Crawford, assistant professor of molecular virology and microbiology at Baylor. "Using RNA sequencing, a method that measures gene activity, we discovered that infected HIEs produced high levels of chemokines, molecules that help the body mount an immune response. Three chemokines stood out: CXCL10, CXCL11 and CCL5."
"We then investigated whether blocking signaling of these chemokines through their receptors would allow human norovirus to replicate better in HIEs," Kaur said. "We tested a drug called TAK 779, originally developed to block chemokine effects. When TAK 779 was added to the HIE cultures, norovirus replication increased dramatically – virus spread throughout the cells in the cultures, and we achieved replication for 10 to 15 consecutive passages."
"TAK 779 allowed us to generate consistent batches of infectious virus from lab cultures instead of human stool - something we and other researchers have been seeking for decades," Crawford said.
The research also found that not all strains respond similarly; while TAK-779 enhanced replication for certain strains such as GII.3 as well as GII.17 and GI.1 strains, it did not enhance growth for GII.4—the most common strain responsible for outbreaks.
"We observed that TAK 779 did not enhance replication of GII.4 strains, the most common cause of human outbreaks," said corresponding author Dr. Mary K. Estes, Distinguished Service Professor and Cullen Foundation Endowed Chair at Baylor College of Medicine’s Department of Molecular Virology and Microbiology."This difference appears to be because GII.4 viruses do not trigger chemokine secretion in HIEs... This suggests that a different process limits GII.4 growth in HIEs.We are currently optimizing our HIE culture conditions to enable efficient passaging of additional HuNoV strains including GII.4."
This development enables continuous laboratory growth and maintenance of norovirus strains without relying on patient samples—an advance expected to facilitate further studies into viral structure as well as antiviral drug screening and vaccine development.
