Gene editing techniques were used to change parts of chicken DNA to limit the spread of bird flu in a world first.
Scientists in the UK have found they can partially protect chickens from bird flu infections by editing their genes.
This could signal a new strategy to reduce the spread of the deadly virus.
Highly pathogenic avian influenza, known as bird flu, has spread to new corners of the globe since 2022, wiping out millions of poultry birds and sending egg and turkey prices soaring.
Experts warn that mutations could potentially threaten a human pandemic, though the current strain has not caused significant disease in people.
In a world-first, researchers said they used the gene-editing tool CRISPR to make specific changes to a gene called ANP32 that is essential to support flu viruses inside chickens' cells. CRISPR is a type of molecular "scissor" technology that scientists can use to edit DNA.
Flu viruses hijack proteins like ANP32 inside cells to help themselves replicate, and the edits in chickens were designed to stop the growth of bird flu.
Cases tend to increase in the spring and autumn as wild birds migrate.
Between April and June 2023, there were 98 domestic outbreaks and 634 wild bird outbreaks of avian influenza across 25 countries in Europe, the European Centre for Disease Prevention and Control (ECDC) said.
Gene-edited chickens showed resistance to bird flu
Experiments showed that almost all of the gene-edited chickens showed resistance to lower doses of a less lethal form of bird flu than the H5N1 strain that has circulated the globe recently, said Wendy Barclay, a flu expert and professor at the Imperial College of London.
When birds were exposed to much higher levels of the virus, though, about half of the gene-edited chickens had breakthrough infections, she said.
"We can move toward making chickens resistant to the virus but we're not there yet," Barclay said. "We would need more edits - more robust edits - to really shut down the virus replication".
The findings were published in Nature Communications on Tuesday.
Researchers now think that making three specific genetic changes to chickens' cells will better protect birds. However, they have not bred chickens with three edits yet, said Helen Sang, who previously studied genetically modifying chickens against bird flu at the University of Edinburgh.
Sang said scientists found that genetic modification would not work well enough.
'Gene-editing offers a promising route'
Unlike genetic modification, which introduces foreign genes, gene editing alters existing genes. The technology is considered to be less controversial than genetic modification and is more lightly regulated in some countries.
"The way forwards here is not to rely on single edits but to use a combination of them," Barclay said.
In a statement, the study's principal investigator Mike McGrew from the University of Edinburgh said: "Bird flu is a great threat to bird populations. Vaccination against the virus poses a number of challenges, with significant practical and cost issues associated with vaccine deployment.
"Gene-editing offers a promising route towards permanent disease resistance, which could be passed down through generations, protecting poultry and reducing the risks to humans and wild birds. Our work shows that stopping the spread of avian influenza in chickens will need several simultaneous genetic changes".
France this month became the first country in the European Union to vaccinate poultry against the virus.
However, that strategy led the US to impose trade restrictions on French poultry imports, citing a risk of introducing the virus into the country because vaccinated birds may not show signs of infection.