A 57-year-old US man with terminal heart disease who received a transplant of a genetically modified pig heart, is still doing well three days later.

The surgery, which was the first of its kind to be carried out, was the only available option for the patient, David Bennett. He had been deemed ineligible for a conventional heart transplant at a number of leading transplant centers.

The procedure was carried out by the University of Maryland Medical Center (UMMC) in the US, where Mr Bennett is being carefully monitored in order to determine whether the transplant provides lifesaving benefits.

According to Dr Bartley Griffith, who surgically transplanted the pig heart into Mr Bennett, this is a “breakthrough surgery”.

“It brings us one step closer to solving the organ shortage crisis. There are simply not enough donor human hearts available to meet the long list of potential recipients,” he said.

The US Food and Drug Administration granted emergency authorisation for the surgery on New Year’s Eve through its expanded access (compassionate use) provision. This is used when an experimental medical product, in this case a genetically-modified pig heart, is the only option available for a patient faced with a serious or life-threatening medical condition.

“It was either die or do this transplant. I want to live. I know it’s a shot in the dark, but it’s my last choice. I look forward to getting out of bed after I recover,” Mr Bennett said the day before his surgery.

He had been hospitalised and bedridden for the past few months. 

The transplanting of animal organs is known as xenotransplantation. It has the potential to save thousands of lives, however there are serious risks involved, including the possibility of triggering a dangerous immune response which can cause immediate rejection of the organ.

Organs from genetically modified pigs have been the focus of much of the research in xenotransplantation, in part because of physiological similarities between pigs, human, and non-human primates. Pig heart valves have already been used successfully to replace valves in humans.

Prior to his surgery, Mr Bennett was fully informed of the risks involved. He was told that this procedure was experimental with unknown risks and benefits.

He had been admitted to the hospital more than six weeks earlier with life-threatening arrythmia and was connected to a heart-lung bypass machine (ECMO) in order to keep him alive. In addition to not qualifying for the heart transplant list, he was also deemed ineligible for an artificial heart pump due to his arrhythmia.

During the surgery, a new drug was used along with conventional anti-rejection drugs, which are designed to suppress the immune system and prevent the body from rejecting the foreign organ.

Three genes, which are responsible for rapid antibody-mediated rejection of pig organs by humans, were “knocked out” in the donor pig. Six human genes responsible for immune acceptance of the pig heart were inserted into the genome.

One additional gene in the pig was also knocked out to prevent excessive growth of the pig heart tissue, which totaled 10 unique gene edits made in the donor pig.

The president and CEO of UMMC, Dr Bert O’Malley, described the procedure as “truly a historic, monumental step forward”.

“While we have long been at the forefront of research driving progress toward the promise of xenotransplantation as a viable solution to the organ crisis, many believed this breakthrough would be well into the future,” he said.