Earlier this month, surgeons at Massachusetts General Hospital in Boston achieved a first in medicine when they successfully transplanted a genetically modified pig kidney into a 62-year-old man. This surgery in a living patient offers hope to millions of individuals on transplant waiting lists worldwide who are in critical need of a kidney.
Following the failure of a previous kidney transplant and life-threatening complications from dialysis, a pig kidney transplant now offers Richard “Rick” Slayman a solution that could potentially save his life.
Slayman had battled kidney disease for over ten years. Despite undergoing dialysis and kidney transplant in 2018, Rick’s condition had worsened significantly, leaving him in a state of despair. The team at Massachusetts General Hospital worked for a year to plan this surgery, which received special permission from US regulators on compassionate grounds.
Also, in March, a team at Xijing Hospital in Xi’an, China transplanted a pig liver into a human for the first time. This operation was performed on a 50-year-old man who was clinically dead, with his family’s consent. The pig liver, which came from a genetically modified miniature pig, was connected to the man’s blood vessels and worked for ten days (as indicated by bile production) before being removed.
Both experiments advance the field of xenotransplantation considerably. Xenotransplantation involves transferring live cells, tissues, or organs from animals to humans. This field has held promise for addressing the critical organ shortage faced by many patients worldwide for many years.
You might be asking yourself a question: Why do we need pig organs to replace human ones?
Ideally, advances in cell biology could eliminate the need for animal organs, allowing for the creation of tissues and organs in labs or through 3D printing. However, the reality is that the demand for transplants far exceeds available human donors, leading to the deaths of countless patients waiting for a match.
Pigs have a longstanding history in medical transplants, serving as sources for everything from corneal to heart valve transplants. Their anatomical and physiological similarities to humans make them ideal candidates for organ donation. They grow quickly, can be genetically modified, and their organs are a compatible size for human transplantation.
However, challenges have existed for many years. The 80-million-year evolutionary gap between pigs and humans means we are quite unlike each other. Pig organs are instantly identified as foreign by the human immune system, often leading to immediate rejection. Pig cells carry unique sugars not found in humans, triggering immune responses that can result in transplant failure. Additionally, differences in blood clotting and the presence of viruses in pig DNA pose risks for human recipients.
The xenotransplants this year will need to be followed up. However, the initial success can be attributed to monumental efforts to overcome these differences. Extensive modifications were made possible by gene-editing technologies like CRISPR-Cas9, which were employed to alter pig genomes in ways that reduce the risk of organ rejection and viral transmission.
Scientists made 69 changes to the pig’s DNA to prevent the human immune system from rejecting the kidney. This surgery also builds on past attempts, like the 2022 transplant of a pig kidney into a brain-dead patient and a pig heart into a critically ill patient.
Meanwhile, the operation in China employed a pig liver that had undergone six genetic modifications. Given the complexity of how the liver works, this approach will serve mainly as a temporary solution for liver failure, buying time for patients waiting for a human liver donor.
So, does that mean pig organs will become commonplace? No, at least, not yet.
As exciting as the initial successes are, there’s still a long way to go. Experts around the world will follow Slayman’s health and will examine the details of the surgery in China carefully. They are closely watching future developments, in anticipation of additional xenotransplantation results that will extend or save lives.
Anirban Mahapatra is a scientist and the author of COVID-19: Separating Fact From Fiction. His second popular science book, When The Drugs Don’t Work: The Hidden Pandemic That Could End Medicine, will be published this year. The views expressed are personal.
