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Gene editing used to eliminate viruses in pigs

 
  • Porcine endogenous retroviruses are embedded in the pig genome
  • But research has shown they can infect human cells, posing a potential hazard
  • The virus has been a stumbling block to using pigs to grow organs for humans
  • Now, US scientists have successfully eliminated the virus from pigs in a trial 

Mia De Graaf For Dailymail.com

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Growing human transplant organs in pigs has become a more realistic prospect after scientists used advanced gene editing to remove threatening viruses from the animals’ DNA.

Porcine endogenous retroviruses are permanently embedded in the pig genome but research has shown they can infect human cells, posing a potential hazard.

The existence of the virus has been a major stumbling block preventing the development of genetically engineered pigs to provide kidneys and other organs for transplant into human patients.

That hurdle may now have been cleared away, according to new research reported in the journal Science.

Researchers at Harvard University and a private company used the precision gene editing tool Crispr-Cas9 combined with gene repair technology to deactivate 100 percent of the virus in a line of pig cells.

Porcine endogenous retroviruses are embedded in the pig genome but research has shown they can infect human cells. Now, US scientists have successfully removed it (file image)

Porcine endogenous retroviruses are embedded in the pig genome but research has shown they can infect human cells. Now, US scientists have successfully removed it (file image)

Porcine endogenous retroviruses are embedded in the pig genome but research has shown they can infect human cells. Now, US scientists have successfully removed it (file image)

Piglets cloned from the fibroblast (connective tissue) cells turned out to be virus-free.

Dr Luhan Yang, co-founder and chief scientific officer at the biotech company eGenesis, said: ‘This is the first publication to report on virus-free pig production.

‘We generated a protocol to enable multiplex genome editing, eradicated all Perv activity using Crispr technology in cloneable primary porcine fibroblasts and successfully produced virus-free piglets.

‘This research represents an important advance in addressing safety concerns about cross-species viral transmission.

‘Our team will further engineer the virus-free pig strain to deliver safe and effective xenotransplantation.’

BENEFITS OF USING PIG-GROWN ORGANS FOR HUMANS

Pigs and humans have all of the same abdominal and thoracic organs.

For example, the stomach, spleen, bile duct system, small intestines, kidneys, bladder, heart, and lungs are basically the same.

BENEFITS:

1) No shortage of organs for transplants

2) Could apply liberal age limits – including elderly patients who are currently not eligible

3) Avoid cultural taboo of removing human organs

4) Avoid duress of people to donate organs/human organ trafficking market

5) Ensures quality of the organ, since the pigs can be prepared in advance

6) Transplants can be prescheduled

OBSTACLES:

1) A powerful immune barrier

2) A potential risk of transmitting microorganisms such as endogenous retrovirus

3) Ethical issues 

The scientists first mapped the Pervs present in the pig genome, identifying 25 in total.

Tests demonstrated that pig cells could infect human cells with the virus in the laboratory. The viruses could then be transmitted to other cells not exposed to pig tissue.

Whether or not the virus would actually cause diseases in humans is unknown, but they are considered an unacceptable risk.

Other endogenous retroviruses (ERVs) in humans have been suggested to play a role in cancers and autoimmune disorders, although evidence for this is lacking. Their involvement in multiple sclerosis and motor neurone disease has also been proposed.

Professor Ian McConnell, an expert in the field from Cambridge University, said the research was a ‘promising first step’.

He added: ‘Successful transplantation of tissues and organs from animals to man, known as xenotransplantation, has been one of the goals of modern medicine for the last 20 years.

‘The safe use of pig organs such as kidneys in xenotransplantation has been seen as an approach which could be used to overcome the shortage of donor organs in human transplantation.

‘The problem is that all pig cells carry cancer viruses embedded in their DNA. These are known as endogenous retroviruses which, although normally silent, can be activated to become fully infectious for human cells when pig cells carrying these retroviruses are co-incubated with human cells.

‘Since xenotransplantation involves long-term intimate cell-to-cell contact the potential for the species jump of retroviruses for the entire life-time of the transplants is a very real one.’ 

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