Editor’s Note: This is part of a series of dispatches from the Knight Science Journalism Program’s 2021-22 Project Fellows.
Belly. Loin. Ham. Hock. Head. Ribs. Shoulder. We already use many parts of the pig. Would it be a stretch then to also harvest their heart, kidney, and liver — not to eat, but to help people who need lifesaving organ transplants but currently can’t get one? Currently, more than 106,000 people in the United States are on the national organ transplant waiting list, and 17 people die every day waiting to get an organ. For decades scientists have imagined that animal organs could help address the growing organ shortage.
Just a few years ago, the possibility was still remote. But over the course of my Knight Science Journalism project fellowship, scientists have taken huge strides in the quest toward using pig organs in people. For the past few months, I’ve been researching the field of species-to-species organ transplants, also known as xenotransplantation, for a book proposal. Little did I know how prescient the topic would end up being.
From the 1960s through the 1990s, when human donor organs were scarce, scientists attempted several transplants of monkey and chimpanzee organs into people. None were successful. Most of them failed within weeks, if not days. Even nonhuman primates — our closest genetic ancestors — were not suitable organ donors for us.
Perhaps the most famous case was that of Baby Fae, who in 1984 became the first newborn recipient of a baboon heart. Born with a life-threatening heart defect, she wasn’t expected to live long. With the new heart, she lived just 21 days, ultimately dying from organ rejection.
Eventually, scientists turned to pigs as the preferred source of future xenotransplants. We already raise them for food, they grow faster than monkeys and their organs are roughly the same size as humans.
In recent months, the change in strategy has yielded a string of major achievements.
The first came without much fanfare. About a month into my fellowship, I came across a fascinating preprint on bioRxiv about a sea lion that had received a xenotransplant of brain cells from pig embryos. Poisoned from toxic algae blooms, the sea lion was experiencing similar symptoms as humans with epilepsy: confusion, disorientation, temporary loss of consciousness, and frequent seizures. His seizures had gotten so bad that his caretakers at a Six Flags in California were considering euthanizing him. Instead, they reached out to Scott Baraban at the University of California, San Francisco, who had been working on a cell therapy for epilepsy. It involved transferring a certain type of progenitor neuron from a healthy brain into a brain with epilepsy.
But Baraban’s team had only tried the technique in rodents. To treat a sea lion, they’d need early brain cells from a larger mammal. Naturally, they turned to pigs. After all, scientists have been using them for other xenotransplant studies for years.
The New York Times covered the groundbreaking surgery when it occurred in October 2020. But the preprint I’d come across in my research reported that the cell transplant appeared to have been a success. A year after his transplant, the sea lion — affectionately named Cronutt — was seizure-free.
As I learned in my reporting throughout the fall, the field of xenotransplantation is incredibly competitive. Everyone wants to be the first — the first to put a pig organ in a person, that is.
I knew I had to write about it. Although not technically an organ transplant, it was still an interspecies transplant, and an exciting one at that. My story made it into National Geographic in January.
Even bigger advances in xenotransplantation were happening behind the scenes. And yet, even after conducting interviews with several experts in the field, none let on to the groundbreaking experiments they were about to attempt. As I learned in my reporting throughout the fall, the field of xenotransplantation is incredibly competitive. Everyone wants to be the first — the first to put a pig organ in a person, that is.
In October, surgeons at a New York University hospital achieved one of those firsts.
Doctors at the hospital attached a pig kidney to a brain-dead person who was being kept alive on a ventilator, and the kidney survived for more than two days without immediate rejection. The pig the organ came from had been genetically engineered to lack a gene that would have caused swift rejection upon transplantation into a person. When attached to blood vessels outside the woman’s body, the kidney functioned normally. A month later, researchers there attempted the experiment again with another pig kidney and a second patient and found that, once again, it worked.
The results were exciting and suggested that a key first barrier had been overcome: Thanks to gene editing, scientists now have the ability to manipulate the genomes of pigs to make them more suitable organ donors for people.
Another major milestone came in January. Surgeons at the University of Maryland Medical Center in Baltimore announced that they had transplanted a heart from a genetically engineered pig into a man who desperately needed a donor heart but wasn’t a candidate for one. He was on life support and he didn’t have much longer to live.
The donor pig in the Maryland procedure was even more engineered than the one in the NYU experiment. It had been modified to lack three pig genes responsible for immune rejection. Scientists had also added six human genes in the hopes that the modifications would help the recipient’s immune system recognize the heart as a human.
I was stunned by the news. I knew scientists were getting closer to attempting such a surgery; I just didn’t realize how close.
I feel lucky to have been able to visit the University of Maryland in October to interview one of the surgeons involved in the procedure, Muhammad M. Mohiuddin. While I was there, I had the opportunity to tour a lab where dozens of pig-to-baboon heart transplants had taken place. Just a few months later, a similar operating room at the University of Maryland would be the site of the first pig-to-human heart transplant.
With so many exciting developments in a matter of months, I think it’s time for people to consider the possibility that in the near future, their loved one could receive a life-altering transplant of cells or an entire organ from a pig. Will we look at food differently then? Is it moral to sacrifice the life of a pig to save the life of a person? And what happens when pigs become more humanlike?
The conversation is just beginning.
Emily Mullin is an award-winning science journalist who writes about how biology is shaping our future.