Major step towards growing human organs in pigs
Scientists use gene editing to eliminate viruses in the animals
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 CrisprCas9 combined with gene repair technology to deactivate 100 percent of the virus in a line of pig cells. Piglets cloned from the fibroblast 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."
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. 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 an unacceptable risk.
Other endogenous retroviruses in humans have been suggested to play a role in cancers and autoimmune disorders, although evidence is lacking. Their involvement in multiple sclerosis and motor neurone disease has also been proposed.
Professor Ian McConnell 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. The safe use of pig organs such as kidneys 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.' (© Daily Mail, London)