Doctors are making progress in the transplantation of animal organs into humans – albeit in small steps. For the first time in the world, a US team has successfully inserted a pig kidney into a human. The 62-year-old man, who suffers from life-threatening kidney disease, received the genetically modified organ on Saturday, said the Massachusetts General Hospital (MGH) in Boston (US state of Massachusetts). The operation lasted four hours, the patient is recovering well and will probably be discharged soon.

“The real hero today is the patient,” said Joren Madsen, director of the MGH Transplant Center, according to the statement. The operation would not have been possible without his courage and willingness to embark on a journey into uncharted medical territory. He will become a “beacon of hope for countless people suffering from end-stage kidney disease,” said Madsen. In Germany alone, thousands of people are waiting for an organ transplant; human donor organs are rare.

So-called xenotransplantations – transfers of animal organs to humans – have been researched for decades. Pigs are particularly suitable as donors because their organs and metabolism are similar to those of humans. Most recently, pig hearts were implanted into two seriously ill patients in the USA; both patients died several weeks after the operation. In addition, a pig kidney was transferred to a brain-dead person.

A lot of research work is still needed

Christian Hagl, xenotransplantation expert and director of cardiac surgery at the University Hospital of Munich, considers the kidney transplant to have been a success. “It makes sense to continue working on the issue. But I am skeptical as to whether we will be transplanting pig kidneys on a large scale next year,” Hagl told the German Press Agency.

“I assume that in two to three years, selected patients for whom other procedures are not an option will be able to have a pig’s heart inserted.” For kidneys, it may take another five years, as the organ has much more complex tasks in the body. “But it will take significantly longer for these procedures to become standard therapies.”

According to the US statement, the patient who was now operated on had suffered from type 2 diabetes and high blood pressure for many years. He received a human donor kidney in 2018, but it caused severe problems about five years later. The patient therefore started dialysis again. “He repeatedly experienced complications with the dialysis vascular access, requiring hospital visits every two weeks for clot removal and surgical corrections. This significantly affected his quality of life,” the statement said.

Mini study planned in Germany

Scientists have been trying for some time to make pig organs usable for humans. In order for this to be possible, the genetic makeup of the donor animals must, among other things, be changed. Without genetic adaptation, transmission to humans would result in an immediate, severe rejection reaction. In this specific case, 69 genetic modifications were made, according to the clinic.

Hagl and colleagues want to start a kind of mini-study with pig hearts in Germany, the aim is for the beginning of 2027. Organs will be implanted in four people at once. “We believe we can do better,” says Hagl, referring to pig heart transplants in the USA. The pigs that are bred in Germany for this purpose are better suited, among other things because they have smaller hearts and are therefore more suitable for humans, explained Hagl. The local pigs are also better for kidney transplants.

Basically: “The kidney is actually more complex than the heart. Roughly speaking, the heart is primarily a muscle that pumps blood. Among other things, the kidney has to filter the blood and produce hormones.”

Other xenografts are islet cells from the pancreas of pigs. In clinical studies they are already being transferred to people with diabetes and are supposed to produce insulin there. It is already common practice to use modified pig heart valves in humans, says Hagl.