Pig organ transplants open ethical can of worms
The transplant of pig organs into human patients made global headlines last week with two milestone achievements in the field, but ethical considerations such as virus transmission may still present a barrier to it becoming common practice.
The first feat involved Chinese doctors transplanting a pig’s liver into a patient who had suffered brain death. The surgery saw the organ function for 10 days before it was removed based on the family’s wishes. In China, brain death is not considered legal death.
The second milestone transplant took place in the United States, where a pig’s kidney was put into a patient with end-stage kidney failure. The procedure had previously been performed on clinically dead patients.
These surgeries, as well as others in recent years, have shown the life-saving potential of xenotransplantation – the transplantation of organs or tissues from one species into another.
“One of the potential benefits of xenotransplantation is the limitless graft supply that would help a lot of patients with urgent need for transplant,” said Albert Chan Chi-yan, a clinical professor at the University of Hong Kong and director of Queen Mary Hospital’s Liver Transplant Centre.
The limitless supply of organs could bring hope to hundreds of thousands of patients around the world waiting for their names to get to the top of transplant lists amid global shortages.
But ethical concerns could prove a fly in the ointment.
“[One concern is] the risk of disease transmission from animal species to humans,” Chan said.
Pigs used for human transplants are typically bred in specialised facilities to ensure they are pathogen-free. However, this has not always been successful.
In 2022, a transplant which saw the first pig heart placed into a patient with terminal heart disease ended in the patient’s death because of an undetected virus.
Although the “potential benefits are considerable”, the possibility of transmitting infectious agents is still a major concern, especially as some may not be detected before transplant, according to the US Food and Drug Administration (FDA).
“Tolerance to the new organ and risk of acute rejection are other problems to overcome in this field,” Chan said.
Animals used in xenotransplantation are genetically modified to reduce the risk of organ rejection. Pigs can also be genetically modified to add in human genes to ensure the organ is a better fit.
The kidney used in the US transplant last week came from a pig with a record 69 gene edits, according to a report by Nature.
Scientists in China have also pursued the humanisation of donor animals by inserting human stem cells into pig embryos, producing embryos with kidneys that are made up of mostly human cells.
In this study, the scientists acknowledged the major ethical concern that human cells could end up in the brain or genital ridge of the embryos, which could lead to differentiation into reproductive cells.
There might also be concerns about “the psychological impact to the organ recipient” after surgery, Chan said.
According to FDA guidelines, the transplant of animal organs into humans should be limited to patients with “serious or life-threatening diseases” for whom alternative therapies may not be available.
Despite the ethical concerns, a report on a 2018 meeting in China which included the World Health Organization stated that xenotransplantation “could bridge the gap between demand for, and supply of, human organs for transplantation”.
While xenotransplantation was in its infancy in practical terms, Chan said there was a lot more work to do.
“Future research should focus on how genetic editing could help to modify the animal organ to become entirely suitable and acceptable for human application,” he said.