Surgeons transplanted a pig heart into a 57-year-old patient on Friday at the University of Maryland Medical Center. Professor Bartley Griffith, director of the Center's cardiac transplant program, described the patient as “awake, recovering and speaking to his caregivers,” in a video posted online on Monday.
Three years ago, Sir Terence English – who performed the first successful heart transplant in the UK – predicted humans would be receiving heart transplants from pigs within three years. Timelines for medical innovations usually have a way of blowing out far beyond such hopes, but it turns out English was spot on.
The eight-hour heart operation follows the first two transplants of pig kidneys into human recipients, performed last year. Both were proofs-of-concept to people unable to survive long-term for other reasons, such as a woman who had experienced brain death.
In each case, the donors were no ordinary pigs – if they could have been, we'd have been performing transplants like this for decades, saving tens of thousands of people who have died waiting for organs.
Instead, the pigs were genetically engineered to not produce a sugar molecule that induces powerful attacks from the human immune system. Although this was the most important, removal of the relevant gene was just one of ten genetic modifications required to make the pig a suitable donor: four pig genes were knocked out and six human genes were added. One of the removed genes would, if left unaltered, have meant the heart – taken from a not-fully-grown pig – would have continued growing after transplantation.
The process had previously been demonstrated through transplants from pigs to non-human primates.
There is already an insufficient supply of human organs, and the problem will worsen as an aging population increases demand. That leaves two options: create artificial organs from scratch (for example using stem cells), or transplant them from animals. The stem cell route may be less ethically fraught, particularly for vegans, but it's likely to have a long way to go, at least for complex organs like hearts.
Pigs are sufficiently biologically similar to humans that their organs are likely to do the job within the human body, provided they are not rejected by the recipient’s immune system. Preventing rejection has been the challenge, however – one that scientists have spent decades trying to overcome.
For David Bennett, being a pioneer was his only hope, as his prospects were not good enough to justify a human heart more likely to save someone else. “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,” Bennett said in a statement. However, the New York Times reports Bennett's first reaction to the idea was; “Will I oink?”
“The successful procedure provided valuable information to help the medical community improve this potentially life-saving method in future patients,”Dr Muhammad Mohiuddin, whose work on transplanting animal organs made the operation possible said.
“The driver for all this was to provide an opportunity for patients with end-stage heart disease who couldn't qualify, or just didn't get a heart in time, to treat their poor heart function with a transplant,” Griffith said. “What everybody wants is not to be limited simply by the supply of human organs for transplant."
"A number of the organs can be treated and used in this way from an animal [...] If that's true we will change the face of what is possible for people who now wait years for a transplant.”
Success may bring an end to the shortage of donor organs, but recipients will need to take drugs to prevent rejection all their lives, just as most of those who receive donated human organs do. These drugs weaken the immune system, making organ donors vulnerable to disease at any time, something that has been greatly exacerbated over the last two years.