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10 milestones in the quest to transplant animal organs to humans

It’s not just a marvel of modern medicine.

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In September, a team of surgeons successfully attached a genetically engineered pig kidney to a human body.

The kidney filtered waste (just like it was supposed to) and showed no signs of rejection after two days.


This marks a new milestone in the quest to make animal-to-human organ transplants a commonplace procedure.

Over 100,000 Americans are on the list for an organ transplant — and 17 people die every day while waiting.

Using organs from other species could offer a readily available solution to a deadly problem.

We’ve used heart valves from cows and pigs since the 1960s, but have yet to transplant entire organs to live humans without rejection.

And while it might seem constrained to the ambitions of modern medicine, the history of this process of cross-species organ swapping — known as xenotransplantation — is actually centuries in the making.



Here are 10 milestones in the history of cross-species transplants that got us to where we are today:


French doctor Jean Baptiste Denys conducted the first documented human blood transfusion — using blood from either a dog or lamb that he injected into a young man’s body.

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The patient lived — and Denys continued his transfusion experiments.

He was later tried for murder when one of his patients died. Blood transfusions were outlawed in Europe for decades afterward.


Doctors completed the first transplantation of a cornea from a pig to a human. However, the procedure was unsuccessful in the long term.


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In the 1800s, surgeons also experimented with skin grafts from animals, such as frogs, to humans.


Surgeon Alexis Carrel won the Nobel Prize for developing a technique to “sew” blood vessels together, paving the way for modern-day surgeries and organ transplants.

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Carrel also had an interest in transplanting organs across species.

In 1907, he wrote:


“The ideal method would be to transplant in man, organs of animals easy to secure and operate on, such as hogs, for instance.”


Surgeon James Hardy conducted the first modern heart transplant in the world, using a heart from a chimpanzee.



The recipient, who was dying of a cardiovascular disease that caused both his legs to be previously amputated, only lived a few hours after the transplant.


One of the most famous modern-day xenotransplant attempts was the case of Baby Fae, an infant girl with life-threatening congenital heart disease who received a baboon heart.

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Unfortunately, her body rejected the heart — in part because the baboon’s blood type was not compatible with hers. She died 20 days after the procedure.


A group of doctors from Sweden transplanted pig pancreas cells into human patients with diabetes, in an attempt to remedy the condition.



However, the transplants did not appear to have any long-term clinical benefit.


An international team of researchers reported they used CRISPR gene editing to inactivate pig viruses that cause immune reactions in humans.

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These viruses, called PERVs — porcine endogenous retroviruses — cause one of the biggest obstacles to xenotransplants because of their ability to jump from pig to human cells.


Two baboons living with transplanted pig hearts survived for over six months — the longest of any recorded xenotransplant in history.



This Nature study marked an important milestone — demonstrating the ability of one species to survive with a transplanted organ from another.


The FDA approved the use of genetically modified pigs for food and therapeutic use, paving the way for future applications.



However, the FDA does note that the pigs are not evaluated for xenotransplants, and individual approval must be obtained before medical companies can start using their organs in humans.

2021 and beyond

We saw the first transplant of a living, gene-edited pig kidney into a human body this year — what’s next?



Several biotech companies like eGenesis and Revivicor are funding research into modified pig organs, and aim for a future where they’re regularly used in human transplants.


Hurdles remain, but some researchers are optimistic that successful xenotransplants are right around the corner.

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