As of April 4, 2025, there are 103,223 people in the United States waiting for an organ transplant that could save or greatly improve their life. Of those 103,223 people, seventeen of them will be dead by the end of the day. Tomorrow, seventeen more. Every eight minutes, another person is added to the transplant list at the United Network for Organ Sharing (UNOS), the only organ procurement and transplantation network in the United States. Eighty-six percent of those on the list need a kidney, but livers, hearts, lungs, pancreases, and other organs are needed as well. While over 170 million people in the United States are registered donors, only three out of a thousand people will die in a way that allows for deceased organ donation. The simple truth is this: we do not have enough organs.
The need for organs has only grown in America, largely due to increased longevity and higher rates of obesity associated with organ failure. Both science and public policy changes have offered a variety of creative potential solutions. One concept adopted in parts of Europe is known as “presumed consent,” where citizens choose to opt out of being an organ donor upon death, as opposed to the American system of opting-in. Another idea is to broaden the pool of cadaver donors by expanding the brain death requirement to a “persistent vegetative state” or allowing a potential donor who is soon to die to choose to donate their organs and experience a “death by donation.” While these potential solutions are ripe for controversy and ethical concerns about consent, they only slightly expand the donor pool—and, still, very few people are likely to die in a manner conducive to organ transplantation. A newer idea offers a different set of questions and controversies while having the capacity to almost completely solve the organ shortage crisis: xenotransplantation.
Xenotransplantation is already progressing in the United States. On March 21, 2024, Mass General Hospital performed the first successful kidney xenotransplantation into a living recipient, done under compassionate use for the recipient with no other option, and extended his life by two months. Furthermore, just recently on February 3, 2025, the FDA approved a clinical trial for patients with end-stage renal disease and the first transplant is expected to take place mid-year 2025. So, what is it?
Xenotransplantation is a process that uses organs from genetically modified pigs rather than human organs. The genetic modification is done using CRISPR/Cas9, the leading gene editing technology. Pigs are an ideal candidate for xenotransplantation for multiple reasons, including the similarities between pig and human organs, their short gestation period, their large litter sizes, and the present common acceptance of pigs being used as meat animals. Furthermore, the widespread use of pigs for organ transplants would present numerous benefits, including providing a near-unlimited supply of organs, reducing illegal organ trafficking, and allowing “borderline” candidates who would otherwise be denied a transplant an opportunity to have a new organ.
All this being said, xenotransplantation certainly presents a slew of complications and concerns. On the medical side, there is a possibility of transmitting animal viruses to the recipient and loved ones near the recipient. Furthermore, while pig kidneys are similar to human ones and both filter waste from blood and make urine, human kidneys have many important roles and it is currently unclear if pig kidneys can fulfill these functions long-term (though the longest-living recipient of a pig kidney says she is currently doing very well, months after the transplant). As for the pigs, they must be raised in sterile conditions to reduce the likelihood of infection to the human recipient. The pigs are also genetically modified to make their organs more suitable for humans and reduce the likelihood of animal viruses being transmitted, which has presented a debate on the ethics of using animals in such a way.
With the FDA giving the green light to clinical trials and the purported success of recent kidney xenotransplants, xenotransplantation appears to be gaining speed. It may present a unique solution to the organ shortage crisis while posing interesting questions about the consequences of using such technology.