Biologists at Harvard have achieved a critical step in making pig-to-human transplants possible. By tweaking 62 gene points in the pigs' DNA, the researchers were able to turn off retroviruses in their genetic code—natural viruses that are safe for pigs, but can sicken and even kill humans.

Pigs have been studied as potential organ donors for many years. They are genetically similar to humans, which brings benefits and drawbacks. While their DNA is a lot like ours, making their bodies function in similar ways, they are also vulnerable to many of the same illnesses, one reason that disease outbreaks on factory farms cause so many health hazards for humans.

Still, if you haven't noticed, pigs are not 100 percent identical to humans. One of those differences is at the genetic level, where the RNA in a pig's organ may contain retroviruses that are safe (and beneficial) for pigs, but can turn a human's body into a boxing ring of host versus transplant.

The Harvard researchers used a highly specialized gene-editing system called "CRISPR" to get into the RNA and make 62 distinct "edits" in the pigs' genes. Those edits effectively kill the retroviruses by making them inactive.

Until now, researchers had only been able to make "edits" in 6 genes at a time, so this record of 62 is a giant leap forward. Once researchers overcome other genetic dissimilarities between pigs and humans, scientists can begin cloning pigs who would specifically be available for organ harvesting. All of their potentially harmful retroviruses would be inactivated.

"The real value and potential impact is in the number of lives that could be saved if we can one day use xenotransplants [transplants from other species] to close the huge gap between the number of available functional organs and the number of people who desperately need them," said Harvard's Wyss Institute Founding Director Donald Ingber.

According to the U.S. Department of Health and Human Services, 22 Americans die every day, waiting for an organ.

The Harvard study was published in the journal Science.

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