Turning Pigs Into Organ Donors

That’s the goal of geneticist George Church, and last week he announced that his team at Harvard Medical School had succeeded. Currently, the demand for donor organs outstrips the supply by a factor of ten. Pigs could help to meet this demand, but their genomes contain hidden viruses called porcine endogenous retroviruses (PERVs), which could conceivably pop out of the transplanted organs and cause unexpected diseases.

Church’s team solved this problem by using CRISPR, a powerful gene-editing technique, to remove 62 of these hidden viruses from pig cells. Their methods, described today in a paper published in the journal Science.

But I’m not sure whether this will make it easier to use pig organs for transplants.

When I reported on such transplants for a feature in 2012, some immunologists mentioned to be that PERVs were a somewhat hypothetical concern. They’ve never been reactivated in studies where pig organs were transplanted into baboons, even when the monkeys had suppressed immune systems.

And Church’s study, as presented, doesn’t solve the other incompatibilities between pigs and primates. Differences in our proteins mean that pig organs, when transplanted into monkey hosts, are rejected by the immune system or plagued by clots. Despite decades of research, these whole-organ transplants rarely last for more than a few weeks or months (see my 2012 piece for more details). And without even short-term successes, no one knows how they would fare in the long-term.

Also, while this line of research is struggling, other scientists have made significant strides in creating lab-grown organs from a patient’s own cells, an approach that gets around all the species differences inherent in pig transplants.

My sense is that the PERV-less pigs are remarkable less as a source of organs and more as testament to the power of CRISPR, which has already allowed scientists to edit genes with unprecedented ease and precision. Church’s work, which increases the record for number of simultaneous edits from 6 to 62, shows just how quickly this technique is developing. And according to Nature News, he is also trying to edit other pig genes that might solve the cross-species incompatibilities that have stymied such transplants so far.