Every RNA virus — from stomach bugs and influenza to chickenpox and the common cold — has its own story to tell, with a unique combination of symptoms, rates of transmission, duration, and chemical blueprint.

Yet on a genetic level, RNA viruses share common structural elements. The RNA of their genomes has strings, folds, and knot-like features that interact with the human body and with medicines in potentially predictable ways. And according to a new Yale study, understanding these structures could open the door to a new way of developing vaccines and medicines to treat any emerging pathogen — beginning with norovirus, the world’s most common stomach bug.

The new research from the Yale labs of Anna Marie Pyle and Craig Wilen has resulted in a norovirus vaccine that has proven effective in mouse models and may be adaptable for other RNA viruses. Pyle is Sterling Professor of Molecular, Cellular and Developmental Biology and professor of chemistry in the Faculty of Arts and Sciences and Wilen is an associate professor of laboratory medicine and immunobiology at Yale School of Medicine (YSM).

“Norovirus was an ideal proof-of-concept for our approach,” said Pyle, who also is a Howard Hughes Medical Institute investigator. “Its structural attributes were not known before we started this and yet it’s a virus with major public health consequences.”

The findings appear in the journal Cell.

Globally, there are an estimated 685 million cases of norovirus each year, according to the World Health Organization. It is the leading cause of gastroenteritis, causing up to 200,000 deaths annually, including 50,000 child deaths, primarily in low-income countries. There is currently no approved vaccine or treatment for it.

“Norovirus causes an enormous amount of distress worldwide, yet we still don’t have a treatment or a vaccine for it, largely because we understand so little about its basic biology,” said Tanja Hann, a doctoral student in molecular biophysics and biochemistry in the Yale Graduate School of Arts and Sciences, a member of the Pyle Lab, and first author of the new study.

“We wanted to see if we could use what we learned about the virus’ RNA structure to build a weakened version of it, one that could serve as the starting point for a vaccine,” Hann said.

For the study, the researchers looked at RNA structures (genetic blueprints encoded in ribonucleic acid rather than DNA) within the norovirus genome of mice. The Pyle lab has had prior success unlocking the RNA structure patterns of hepatitis C virus, West Nile virus, and SARS-CoV-2, the virus that causes COVID-19.

The norovirus genome, the researchers found, is highly structured. It is small and compact — making it easier to replicate and harder to kill — with folds that create two- and three-dimensional structures.

As the researchers looked for a way to slow or stop the virus from growing, they identified structural “hotspots” to exploit. They used two approaches for this: “ironing out” structures to elicit effects and disrupting structures by making small changes to the genome sequence.

One of their attempts stood out, proving to be effective at stopping norovirus even in immunocompromised mice. It effectively “unzipped” structures in a part of the virus containing the genetic code for viral proteins. The lab-developed “mutant” virus not only introduced structural changes into the viral genome that limited infection, but it also triggered an immune response capable of neutralizing the “normal” virus.

Arya Ökten, a member of the Wilen lab who recently earned her Ph.D. at YSM and co-author of the new study, described the structural alteration as akin to “unzipping” a string that had folded back on itself.

“Coming up with new and inventive ways to combat these pathogens — which have been around for a long time but have evaded vaccination — could make a huge difference in people’s lives,” Ökten said. “Norovirus, as just one example, is a virus that kills so many children under the age of five in low-to-middle income countries.”

The Wilen lab, which has done highly innovative norovirus research, provided expertise throughout the testing and monitoring phase of the study.

Yet perhaps the most significant finding of all, the researchers said, is the potential for adapting the technique to fight other pathogens, as the approach is applicable to any virus with a known sequence.

Only in recent years have scientists been able to detect the functional structures within an RNA virus — led, in part, by Pyle’s lab at Yale. In 2021, for example, the Pyle lab mapped structures within the SARS-CoV-2 virus, showing that its genome condenses into a tightly folded assembly.

“This could be particularly useful in dealing with an emerging RNA virus,” Pyle said. “If you know its genomic sequence, you can map its structures and see its important features. It’s a way to develop a stable vaccine for viruses you actually know very little about.”

The researchers said the approach provides extra immunity against all proteins within a virus — unlike an mRNA vaccine, which stimulates immunity to only one protein, such as the spike protein in the case of COVID mRNA vaccines.
The researchers’ next goal is to take their mouse model norovirus vaccine approach and pursue a human norovirus vaccine.

Renata Filler, a lab manager in the Wilen lab, is a co-author of the new study. Support for the research came from the Howard Hughes Medical Institute and the National Institutes of Health.