In a two-hour operation, surgeons connected the kidney of a genetically modified pig to the bloodstream of a brain-dead woman. The organ started working almost immediately, said Robert Montgomery of New York University, who led the team. The operation took place in September, the first on Tuesday was the American newspaper USA Today reported about it. After 54 hours, the research team ended the experiment and switched off the woman’s life-sustaining machines.
Relatives of the brain-dead woman had agreed to the experiment. The pig was specially bred to be an organ donor. The Revivicor company, a subsidiary of the US company United Therapeutics, had switched off a gene in the animal’s genome through a genetic procedure. Without this change, the human immune system reacts almost immediately and aggressively to the animal organ. Numerous research groups and companies around the world are working on so-called xenografts, organs that are to be transplanted from animals into humans, whose own tissue fails due to illness or injury. The aim is to remedy the global shortage of replacement organs. However, transplantation across species boundaries not only harbors difficult ethical problems, it is also anything but easy from a medical point of view.
The urine production started practically immediately, it is said
The surgeons connected the organ to blood vessels in the woman’s thigh and inserted a tube through which the urine that had formed could drain. According to Montgomery, the organ was transplanted onto the body rather than in for observation and regular samples to be taken. Urine production started practically immediately, Montgomery reported to American media. After the transplantation of human donor kidneys to organ recipients with kidney disease, the function does not start until days after the operation. To date, Montgomery’s work has not yet been published in a specialist journal.
Robert Montgomery is the director of the Langone Transplant Institute at New York University.
(Photo: HANDOUT / via REUTERS)
Experts have mixed reactions to the news. Some see this as an important advance in the direction of clinical studies with animal organs in living patients. For others, the procedure looks more like a publicity stunt. “Even if the functioning pig kidney was only observed for 54 hours, a time that is far too short to make any statements about immunological rejection, this is yet another step in xenotransplantation in the clinic,” says Joachim Denner, head of the working group Virus safety of xenotransplantation at the Institute of Virology at the Free University of Berlin. This experiment also hardly allows any statements to be made about the possible transmission of pig viruses to the brain-dead patient. Viruses integrated into the pig genome, which many experts consider to be a problem for xenotransplantations, were not removed from the genome of the donor animal.
The heart surgeon Bruno Reichart, who carried out the first heart transplant in Germany in 1981, rates the scientific value of the experiment in the USA as “not particularly high”. In terms of craftsmanship, the procedure is simple, and the gain in knowledge due to the short duration of the experiment is low. Because of the connection outside the body, it remains unclear whether the kidneys can actually provide the filtering performance that is so important for the organism. “The kidneys of the dead continued to function, but whether the pig kidney could really have replaced the function of a human kidney is beyond the scope of this investigation,” says Reichart, who himself works on xenotransplants. He plans to transplant pig hearts onto people. The transplantation of pig hearts to baboons, which he published three years ago with his team from the University of Munich, was considered to be groundbreaking in the field. This only succeeded by suppressing the baboon’s immune system with drugs, but then the pig hearts worked for many months.
Thanks to numerous advances in the control of the immune system, but also in the breeding of animal donor organs, many experts now consider the fundamentals to be solid enough to start initial clinical trials with animal organs in humans. Heart valves from cattle or pigs have been transplanted for years, and entire organs are to follow soon. Patients with severe kidney damage and too short a life expectancy to wait for a human replacement organ could already benefit from a pig kidney, wrote xenograft experts David Cooper and Hidetaka Hara from the University of Alabama in a recent journal. The patients would have a life without automatic blood purification by dialysis, and “the experience gained would drive progress much faster than if we continued research in the laboratory”.
However, Bruno Reichart warns against hasty action. “Xenotransplantation can only work if society is behind it.” He fears that questionable experiments could discredit the entire field of research.