A historic medical accomplishment that ended in tragedy may yet have a silver lining. Doctors say that Richard Slayman, the world’s first living person to have received a genetically modified pig kidney, did not die as a result of the transplanted organ itself.
The 62-year-old Slayman died just two months after he underwent the experimental procedure at Massachusetts General Hospital in April 2024. Soon after, his doctors reported there was no immediate indication that Slayman’s death was caused by a rejection of the kidney. At a panel discussion hosted this week by the Boston Globe, Tatsuo Kawai, the chair of transplant surgery at Mass General, confirmed his probable cause of death: “an unexpected cardiac event.” The news is a positive sign that animal-to-human transplantation (also called xenotransplantation) can still be a viable way to help solve the longstanding shortage of human donor organs.
While the concept of xenotransplantion has been studied for decades, recent innovations in gene-editing technology have made it a much more feasible possibility. Scientists are now able to remove or even add genes to create pigs that are more compatible with human biology. Pigs and other mammals normally produce the sugar alpha gal, while humans don’t, for instance—a crucial difference taken out in the modified pigs.
Early experiments using these organs have largely been performed on animals and people declared brain-dead. Health regulators have begun allowing researchers to perform these experimental transplants on living patients who have few other options. Slayman qualified, having a long history of type 2 diabetes that had been increasingly difficult to manage with existing treatments (years earlier, he received a traditional donated kidney that had failed by 2023).
Doctors knew that Slayman also had a history of heart issues, but they believed that his health was stable enough for the procedure to go ahead. He was successfully discharged from the hospital two weeks after the transplant and even recovered enough to visit a local shopping mall twice before his death. An autopsy of Slayman’s body found no signs that his body had rejected the donated kidney or any other related oddities, Kawai said.
These procedures, groundbreaking as they are, have yet to yield a clear success story. In 2022, for instance, David Bennett—the world’s first living person to have received a genetically modified pig heart—died two months after his transplant. Unlike Slayman, the transplanted organ probably did help kill Bennett, since it was found to contain an unnoticed pig virus that likely contributed to the organ’s failure. That said, even these failures can provide important lessons (Bennett’s case prompted doctors in the field to better screen for hidden microbes, for example). And this technology will continue to be tested more extensively in humans.
At the same panel discussion, Mike Curtis, president and CEO of eGenesis, the company primarily responsible for creating the modified pigs used in this research, revealed the company’s immediate future. Starting as early as next year, eGenesis will reportedly test kidneys, hearts, and liver sourced from their pigs in formal clinical trials. The kidney and heart trials will involve a typical transplantation, while the liver trial will test if these organs can be used outside the body in people with end stage liver disease, similar to how a dialysis machine takes over a damaged kidney’s function.
It will take time to see if these early steps and stumbles will lead to a genuine breakthrough in transplant medicine. But given that over 100,000 people in the U.S. alone are on the waiting list for an organ today, it’s certainly a goal worth reaching for.
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