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August 10, 2017

Pig-to-human organ transplants advance with gene-editing experiment

Scientists create piglets cleansed of potentially harmful viruses in humans

Researchers say a "promising strategy" is developing that could lead someday to transplanting vital organs from pigs into humans.

The New York Times reported Thursday that scientists successfully created gene-edited piglets cleansed of viruses that could cause disease in humans. If the experiment proves safe and effective, it could make it possible to supplement human organ shortages by using livers, hearts and other organs transplanted from pigs.

"They could be a real game changer," Dr. David Klassen, chief medical officer at the nonprofit United Network for Organ Sharing, said in the report.

According to the UNOS web site, there were 33,611 organ transplants in 2016 and 116,800 patients on waiting lists.

Researchers first explored the idea of xenotransplantation in the 1990s, but in 1998 they discovered genes for viruses – known as retroviruses – in pigs that resembled leukemia-causing genes in monkeys. In an ensuing experiment, the retroviruses spread from pig cells to human cells, which in turn could infect other human cells.

But after using the gene-editing technology CRISPR, there is no evidence that any of the piglets were infected with porcine retroviruses, according to the report.

The New York Times reported the process of the procedure:

They took cells from pigs and snipped the viral DNA from their genomes. Then the scientists cloned the edited cells.

Each pig cell was brought back to its earliest developmental stage and then slipped into an egg, giving it the genetic material to allow the egg to develop into an embryo. The embryos were implanted in sows and grew into piglets that were genetically identical to the pig that supplied the initial cell.

Cloning often fails; most of the embryos and fetuses died before birth, and some piglets died soon after they were born. But Dr. [George] Church and his colleagues ended up with 15 living piglets, the oldest now 4 months old. None have the retroviruses.

Church, a Harvard University geneticist who led the experiments, said the first pig-to-human transplants could take place within two years, potentially moving toward closing the gap between organ supply and demand.

The experiment marks another breakthrough in a controversial field of study that has been regulated by the government and feared too dangerous for decades, according to a Newsweek report.

"Porcine organs are considered favorable resources for xenotransplantation since they are similar to human organs in size and function, and can be bred in large numbers," the researchers wrote in a study published Thursday in the journal Science.

But it may be years before enough is known about the technique's safety.

Scientists told the Times that the pigs grown for their organs would represent a small fraction of the 100 million pigs killed each year for food in the United States, and that they would be anesthetized and killed humanely.

The study can be found here.

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