Chickens made resistant to bird flu with CRISPR gene editing

Chickens have been gene-edited to acquire resistance to bird flu, suggesting a possible way to protect flocks from future outbreaks. But years of further testing and regulatory approval are needed before gene-edited birds can be farmed for consumption.

Since 2021, a record outbreak of avian flu has devastated poultry farms and wild birds worldwide, caused by the H5N1 subtype of the influenza A virus. The outbreak has also spread to some mammals and occasionally people – including two fatal cases in Cambodia in the past week.

As a result, countries including Mexico, France and Ecuador have recently joined China in vaccinating poultry against bird flu. But the US and UK have decided against this strategy, partly due to concerns that current vaccines don’t provide full protection against the circulating strains and would lead to resistant forms of the virus evolving.

Alewo Idoko-Akoh, then at the University of Edinburgh ,UK, and his colleagues have now tested whether gene editing can be used to protect chickens from the virus. All subtypes of the bird flu virus use a chicken protein called ANP32A to replicate inside chicken cells. By editing genes in chicken cells using CRISPR technology, the researchers found that changing two amino acids in ANP32A prevented the virus from being able to replicate in the cells.

They then edited chicken embryos to produce 10 chickens with the altered form of ANP32A, before exposing the birds to a natural dose of the H9N2 subtype of bird flu, which causes milder illness than H5N1. The team also exposed a group of 10 non-edited chickens to the virus and swabbed all the birds’ airways daily for seven days after exposure. All of the non-edited chickens became infected, but only one of the gene-edited chickens did.

Idoko-Akoh and his colleagues repeated the experiment with a viral dose 1000 times higher than the natural dose. This time, 5 out of 10 gene-edited birds became infected, but the virus levels in their airways were substantially lower than it was in non-edited chickens.

In these birds, the virus had acquired genetic mutations that enabled it to replicate with the help of two proteins similar to ANP32A, called ANP32B and ANP32E, reducing its reliance on ANP32A. This could explain why some of the gene-edited birds became infected.

The researchers then showed that editing the genes for all three proteins together completely prevents virus replication in chicken cells. “We are planning to genetically edit chickens to target all three genes, which we think will be needed to make birds completely resistant to bird flu,” says Idoko-Akoh. “We’re aiming for complete protection to avoid the emergence of viruses resistant to the gene edits.”

Despite the promising results, there are many barriers to overcome before bird flu-resistant chickens hit the market. “I’m thinking it’ll be 20 years from now before we might have gene-edited chickens in farms, says Idoko-Akoh. “You have to test for the health and welfare of the chickens, breed the chickens and distribute them.”

“Rolling out the technology will be pretty expensive, and that may create an issue in terms of access in places like Africa and Asia where some of the greatest risk for bird flu exists,” he says.

Culturally sensitive discussions about the technology will be necessary to find out what people find acceptable in terms of food production, says Idoko-Akoh.

“This is a really fantastic study at a time where we’re having a global crisis of avian influenza,” says Kirsty Short at the University of Queensland, Australia. “They really thoroughly investigated gene editing as a way to give birds resistance to influenza.”

“We may never achieve 100 per cent protection [against bird flu] using this approach alone, but a combination of genetic modification, widespread vaccination and improved farming practices, such as reducing contact between birds, could be really effective,” says Short.