Xenotransplantation: One of the biggest achievements in xenotransplantation (transplantation of organs from animals to humans) is leading us closer to a time when patients suffering from kidney failure will no longer have to wait for several years to get an organ from a human. A patient in the United States at Massachusetts General Hospital survived for 271 days with a genetically engineered pig kidney, which prevented him from using dialysis until he got a human kidney.
The unique case of 66-year-old Tim Andrews demonstrates an achievement: the pig’s kidney wasn’t just an experimental substitute but served as a bridge until the patient could receive a human organ. This is the first case in which a person received a kidney from a pig, stopped dialysis for an extended period, and later succeeded with a human organ.
What is xenotransplantation?
Xenotransplantation involves the transplantation of organs, tissues, or cells from one animal species to another. Researchers have shown interest in the practice since well over a century ago due to the persistent problem of the shortage of organs among humans.
This approach has a long history. In 1906, the French surgeon Mathieu Jaboulay tried to transplant a kidney of a pig to a person. The blood started flowing inside, and the organ began functioning – producing urine- but then the human body immediately rejected it. For many years, great biological differences between people and animals made xenotransplantation seem nearly unattainable.
Nowadays, though, progress in genetic engineering has changed the situation.
How scientists modified the pig kidney
The latest kidney used in the operation was genetically altered to increase compatibility with the human immune system. This was achieved through the use of CRISPR-Cas9 technology for editing genes, where changes were made to the genome of the pigs.
Among these were the removal of pig genes that might lead to a strong reaction from the human immune system, the addition of human genes that would increase compatibility, and the deactivation of the porcine endogenous retroviruses found in pig DNA that could potentially infect humans. The kidney used in the earlier Mass General operation had 69 gene edits.
A nine-month bridge
The genetically modified pig kidney was transplanted in Andrews in January 2025. The organ started working straight away, and for 271 days he needed no dialysis – quite an achievement for a patient with terminal renal disease.
His kidneys’ performance was constantly observed for signs of immune rejection and possible transfer of any infectious agent carried by the animal to the recipient. Indeed, there were initial symptoms of T-cell mediated rejection, which were treated successfully. However, the research has found no trace of infection transmitted by a pig to Andrews.
In due time, Andrews experienced microscopic damage and inflammation of blood vessels, resulting in kidney failure. However, the treatment was not over yet, and this failure has revealed another use for xenotransplantation: maintaining the patients’ life until a human donor kidney is ready to be used.
In January 2026, Andrews got a donor human kidney. The new kidney functioned straight away, and there were no signs that his previous pig transplantation sensitized him to a human kidney.
Why the development matters
The shortage of donor organs becomes a critical problem in the area of kidney failure. Dialysis helps sustain people’s lives in such situations; however, this method is stressful, exhausting, and imposes many difficulties on patients’ health condition. Kidney transplants are usually considered to be more efficient, yet suitable human organs are not available for all patients who need them.
This issue motivates scientists to consider xenotransplantation as one of the potential solutions to the problem of organ shortage. Xenotransplantation means that the patient receives an organ from an animal rather than from a human.
According to Dr. Leonardo Riella of Massachusetts General Hospital, the future perspective in this sphere implies the utilization of xenotransplantation first of all to get rid of dialysis until a donor human organ is available, and then to utilize animal organs instead of human organs.
Challenges remain
Despite the optimism, scientists stress that xenotransplantation is still experimental. One successful patient does not prove that genetically modified pig kidneys can safely and reliably function in large numbers of people.
Researchers must determine how long the organs can survive, how immune rejection can be controlled, whether infections can be prevented over many years and which genetic modifications provide the greatest benefit.
The recent results are nevertheless encouraging. According to the Financial Times, several patients at Massachusetts General Hospital have now received genetically engineered pig kidneys, with some organs functioning for many months. The company developing the organs is preparing for a larger clinical program that could involve patients at multiple U.S. transplant centers.
The field has already come a long way from the first failed attempts at animal-to-human transplantation. The first genetically modified pig kidney transplant into a living human was performed at Massachusetts General Hospital in March 2024. Although that patient later died from causes unrelated to the transplant, the procedure demonstrated that a gene-edited pig kidney could function in a human body.
The latest case takes that achievement further. A pig kidney did not merely function temporarily—it kept a patient alive without dialysis for nine months and helped him reach a successful human transplant.
For millions of people affected by kidney failure, xenotransplantation could eventually transform transplantation from a race for scarce human organs into a system where organs are more readily available. The science is not yet ready for routine treatment, but the 271-day milestone suggests that the once-unthinkable idea of animal organs becoming part of mainstream medicine is moving closer to reality.
