World's first successful pig-to-human heart transplant

Surgeons have successfully transplanted a pig heart into a human recipient for the first time, enabled by genome editing.

In a world first, researchers have genetically engineered a pig heart to resist transplant immune rejection in a human patient. Although it is unclear how long the patient will benefit for, this could pave the way for trials of so-called xenotransplants from non-human species, and help reduce transplant waiting lists.

'This was a breakthrough surgery and brings us one step closer to solving the organ shortage crisis,' explained Professor Bartley Griffith, the surgeon who performed the procedure from the University of Maryland School of Medicine (UOMSM).

The recipient of the transplant, 57 year-old David Bennett, had advanced terminal heart failure but had been deemed ineligible for a human heart transplant. The experimental procedure, granted special authorisation by the Food and Drug Administration, used the heart from a genetically modified pig from US company Revivicor. In previous studies at the UOMSM, baboons who received a Revivicor pig heart transplant survived for up to two years.

In order to maximise the chances of transplant acceptance, ten genes were edited in the line of donor pigs. Three genes encoding pig-specific sugars were deleted, which would have provoked rapid immune attack in the recipient. Six human genes were added in order to control inflammatory responses, blood coagulation, and antibody responses. The final edit was the removal of a gene encoding a growth hormone receptor, to prevent excessive growth of the pig heart tissue.

Two other novel techniques were performed in parallel to make the operation a success. The patient was treated with an experimental immunosuppressive drug, and the pig heart itself was perfused with a solution containing hormones and even cocaine to keep the tissue viable while waiting for transplant.

Currently, the patient has shown no immediate signs of transplant rejection and is being monitored closely.

'This is a great step forward - you can compare it with the first landing on the moon,' commented Dr Joachim Denner to the New Scientist, a xenotransplant researcher at the Free University of Berlin, Germany.

However, experts have warned that there are a still many unanswered questions to address before the method can be scaled up for human trials. For instance, it is difficult to standardise genome editing between individual animals, which is necessary for regulatory approval. The approach also raises ethical questions, such as whether animals should be raised for the sole purpose of xenotransplantation.

A spokesperson for NHS Blood and Transplant commented on the research: 'We have been watching this particular field of research for many years. However, there is still some way to go before transplants of this kind become an everyday reality.'