Pigs organs may offer potential for human transplants in the future, according to a story that recently appeared on CNN. But a few obstacles still stand in the way,
While pig organs are similar in size and function to human organs, they can carry what’s known as porcine endogenous retroviruses (PERVs).
Retroviruses, like those found in pig organs, carry their genetic blueprint in the form of ribonucleic acid (RNA) and transcribe it into deoxyribonucleic acid (DNA). This reverse of the typical cell transcription process from DNA to RNA allows a retrovirus to infect a cell and become permanently incorporated into that cell’s genome.
Researchers George Church of MIT’s Broad Institute and Harvard, Dong Niu of Zhejiang University and their colleagues successfully deactivated the family of retroviruses within the pig genome using the genome-editing technology CRISPR.
This new success overcomes a hurdle in the path of xenotransplantation—transplantation from one species to another.
First and foremost, the presence of PERVs in the pig cell genome needed to be proven contagious to human cells. The researchers did just that, showing that PERVs can be transmitted to human cells, even when fresh human cells had no prior exposure to pig cells.
Next, a map of the PERVs in the genome of pig connective tissue cells was created. Using CRISPR, the scientists deactivated all 25 gene sites identified as PERVs. With the help of growth factors and growth inhibitors added during the gene modification process, the researchers were able to grow cells that had 100% of the PERVs deactivated.
What’s more, PERV-inactivated embryos were implanted into sows and the resulting piglets showed no signs of PERVs.
A chimera is a single organism containing cells and DNA from two or more organisms. In 2009, the US National Institutes of Health introduced a policy that suspended funding for chimera-based research due to ethical concerns. Worries included the possibility of human cells populating the brain of an animal, therefore humanizing it, and human cells populating the germline of an animal, enabling human genes to pass onto offspring.
In August 2016, the US National Institutes of Health announced that it was considering a revision to the 2009 policy.
Though more research is needed, this new discovery supports the possibility of pig organs being safe and effective organ and tissue resources for human transplantation.
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