Behind the headlines: Could chicken eggs cure cancer?

Transgenic hens appear to have a major role in the production of future life-saving drugs. Rachel Liddle reports

What is the story?

Chickens have been genetically modified to lay eggs containing life-saving drugs, according to media reports.

The breakthrough could help fight cancer and become a cheap and quick way of producing drugs, say the papers.

A 500-strong flock of the birds has been bred at the Roslin Institute, near Edinburgh, which created Dolly the cloned sheep.

The chickens’ DNA was altered to enable them to produce proteins in their egg white which can then be extracted and used to make medicines.

It is the first time scientists have been able to produce chickens that can pass the altered DNA down to subsequent generations of offspring.

The scientists have engineered chickens to produce two proteins: human interferon beta-1a, which resembles a drug used to treat multiple sclerosis, and miR24, a monoclonal antibody.

These drugs are currently manufactured in vats of bacteria or other cells that have been genetically modified. If used as an alternative, designer chickens could help slash drug production costs.

Drugs produced through transgenic chickens could be in clinical trials within five years.

What is the research?

This is the latest step in the development of genetically modified, or transgenic, animals and birds that carry genes for human proteins. The idea is that farming these animals to produce therapeutic proteins in milk or eggs would be a novel way of producing drugs.

This could be cheaper and quicker than the industrial bioreactors currently used. It also provides a way of producing proteins, such as antibodies, with a similar composition and markers to those produced in the human body.

Chickens that express key proteins in their eggs could prove a more feasible drug source than transgenic mammals that produce human proteins in their milk. It is thought to be easier to create a flock of chickens than a herd of goats, for example, and they would also be cheaper to keep.

Proteins produced in this way are known as recombinant proteins because they are generated from sections of DNA that have been joined together.

In 2004, a team from the Roslin Institute in Midlothian reported that the lentivirus is a good way of inserting foreign genes into chickens to make them transgenic.

For the latest study, DNA from a lentivirus was joined to a piece of human DNA that encoded the desired protein to make a vector.

In this experiment, the scientists inserted genes encoding a humanised version of a mouse monoclonal antibody known as miR24 or human interferon beta-1a into the vector.

This vector was then injected into chick embryos and the gene for the recombinant protein was inserted into the ovalbumin gene of the chicken. Ovalbumin makes up 54 per cent of the protein in the white of a laid egg.

Cockerels carrying the vector in their semen were then crossed with wild-type hens. Their offspring produced eggs containing the proteins in the white, but no other tissues expressed the genes.

What do the researchers say?

Lead researcher from the Roslin Institute Dr Helen Sang said it is important that the recombinant proteins are only expressed in the egg white.

Otherwise, the proteins may have adverse health effects during the chickens’ life span.

Creating transgenic animals that can be used as a drug production platform has been a goal since the first transgenic mice were developed in the 1980s.

One key benefit of using transgenic chickens is their ability to add sugar molecules, or glycosylate, to proteins in the same way that the human body does, said Dr Sang. Glycosylation signals produced by animals can differ and bacteria do not carry out this process.

‘There are a particular class of proteins that need glycosylation,’ she said.

Antibodies and cytokines, for example, need to be glycosylated to have the same functional potency that they have when generated in the body. However, realisation of transgenic chickens as a drug source is a long way off, added Dr Sang.

‘They’ve got to purify these proteins out to show they’re very pure and there’s no egg white.’

The proteins will then have to be characterised before the clinical trial process begins, she said.

Recombinant proteins are likely to be too different from proteins already used in medicines to allow them to ‘leap frog’ the clinical trial process, added Dr Sang. ‘It’s something that’s got a lot of potential but it will be a long time before a GP will be seeing these drugs.’

If they do reach the surgery, patients should not be concerned about the transgenic source of the medicines, she continued.

‘By the time somebody was prescribed them, they wouldn’t be any different to a drug produced another way.’

What do other experts say?

Surrey GP Dr Imran Rafi, who is on the executive committee of the Primary Care Genetics Society, said: ‘It’s clearly going to be the way forward.

‘This may give drug companies a much quicker turnaround time in drug development.’ It could also allow novel therapeutics to be developed, he said.

‘But from the point of view of primary care, it’s early days yet to translating the research into general practice,’ added Dr Rafi.

‘They still need to go through clinical trials to [determine] efficacy and to make sure that the side effects of these drugs are properly recognised.

‘It is important to have the knowledge to be able to communicate that to patients.’

A spokesman for the Association of the British Pharmaceutical Industry said: ‘It’s quite an exciting possibility, but it isn’t the end of the story. There would be a lot more work needed with extracting the proteins and processing that needs to be done.’

Informing patients

  • Transgenic hens have been created to express therapeutic proteins in egg white.
  • Scientists have been working to create transgenic animals to produce drugs for over 20 years.
  • It could result in more potent versions of medications such as antibodies.
  • There is still much work to be done before proteins produced by animals reach clinical trial. 

What the papers said 

“GM hens lay eggs to fight cancer” the times 

“Anti-cancer chicken eggs produced” bbc online 

“Designer chickens with eggs that could save lives” daily mail

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