Monday, the University of Maryland School of Medicine announcement that his staff had done the first human pig heart transplant. The patient who received it had end-stage heart disease and was too ill to qualify for the standard transplant list. Three days after the operation, the patient was still alive.
The idea of using non-human organs to replace damaged human organs – called xenotransplantation – has a long history, inspired by the fact that there are more people on organ waiting lists than donors. . And, in recent years, our ability to make targeted genetic modifications has prompted people to start genetically modifying pigs to make them better donors. But the recent surgery was not part of a clinical trial, so it shouldn’t be taken as an indication that this approach is ready for large-scale safety and efficacy testing.
Instead, the surgery was cleared by the FDA under its “compassionate use“Access program. This allows people with life-threatening illnesses to receive experimental treatments that have not yet undergone rigorous clinical testing.
The heart used for this transplant came from a genetically modified line specially designed to reduce the risk of rejection by the human immune system. There are a number of lines that have been designed with this in mind (there are a review some of the competing ideas on what to change). This line was developed by a company called Revivicor (now part of United Therapeutics), but the company does not provide any details. on his website specific changes made. Revivicor’s search on ClinicalTrials.gov returns only one result involving a completely different pig line.
It is therefore difficult to know exactly which genes were changed in these pigs. The University of Maryland press release says there were three genes in pig that were inactivated to lower its immune profile and prevent rejection, and a fourth to block “excessive growth” of pig cells. In addition, six human genes have been inserted into pigs to improve the tolerance of the human immune system to foreign cells. While it’s easy to speculate on what these genes might be, the potential target list is much longer than what’s actually been edited.
Given the efforts made to generate the pig lines, it was clearly only a matter of time before this type of transplant was attempted. But the lack of details on the commercially developed heart donor means it’s difficult to judge this first effort scientifically. And the fact that the transplant took place without a transparent plan to assess the safety of the transplant raises the question of how informative the first effort will be.
From a human perspective, however, someone who has been hospitalized for months for lack of a properly functioning heart now has one. And its ability to stay functional will probably tell us something.
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- Scientists Transplanted Genetically Modified Pig Heart Into Human
- Kidneys from a genetically modified pig implanted in a brain-dead patient
- The genetic engineering behind pig-to-human transplants
- The xenotransplant patient who died received a heart infected with a pig virus