The pig hearts had to be manipulated before the transplantation. (Photo: dpa)
Wednesday, December 05, 2018
As part of a study, a German research team transplanted pig hearts into the bodies of five baboons. With success: The monkeys tolerate the new organs. The experts speak of a milestone for the future of organ donation for humans.
Baboon transplanted pig hearts survived more than half a year in an experiment before the study was discontinued. Thus, the transfer of pig hearts to humans as a solution to the lack of donor organs has come a big step closer. A research team led by the Munich heart surgeon Bruno Reichart and the veterinarian Eckhard Wolf transplanted genetically modified pig hearts into baboons using a sophisticated technique. Two out of five animals were still in good health after 90 days when their attempt was terminated, as the researchers report in the journal "Nature". Two animals even lived 195 and 182 days, a good half a year before being killed. Heart and liver function were normal, rejection reactions did not exist. An animal died of thrombosis after 51 days. The overall result was a milestone on the way to a possible transplantation of pig hearts in humans, the scientists explained. In general, with a survival time of three months, the condition set by the International Transplantation Society for clinical trials is met. About three years would be further preparations before the first clinical trials on selected patients could be possible – "if all goes well," said Reichart. Independent experts see the study as an important step on the way to transplantation in humans. Four of the five baboons seemed to tolerate the transplant well without developing severe infections as a result of immunosuppression, emphasized the Berlin transplant expert Christoph Knosalla in a "Nature" commentary. Therefore, this developed technology can also work in humans, if the xenotransplantation – the exchange across species boundaries – far enough advanced to start initial clinical trials.Temporär SchweineherzThe Aachen physician Rene Tolba called the results "clinically highly relevant". "A first clinical indication for such a xenotransplantation could be the so-called" Bridge to Transplantation ", where a critically ill patient waiting for a donor organ would be offered a transplant of a pig heart as a bridge." Xenotransplantation has been under research since the 1980s , Pigs are particularly suitable as donors because their metabolism is similar to that of humans. Reichart, who had the first heart lung transplantation in Germany in 1983, has been dealing with the topic for a long time and was for many years head of the special research area for xenotransplantation of the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG). Until now, baboon transplantations had survived a maximum of 57 days. Above all, the team around Reichart changed the type of transplantation. Instead of cooling the heart as usual, it was connected to a circuit containing a plasma-containing fluid so that it was oxygenated before and during the operation. This may also be a possibility for conventional transplants to improve success, Reichart said. In addition, the researchers reduced the blood pressure of the baboons during surgery to that of pigs to protect the organ. "Obviously, pig hearts are worse at keeping alive than human hearts," said Reichart. Hope for pilot studiesThe researchers had to take another step in the attempt. Baboons are smaller than pigs – the pig heart grew and resulted in fatal liver damage. Therefore, the researchers gave a drug (temsirolimus, a derivative of rapamycin) to stem growth. That would be unnecessary in humans, since his heart corresponds in size to the pig's heart. The pigs had been genetically manipulated to reduce the rejection reaction. More such experiments would have to follow, Reichart said. According to the specifications for clinical trials, six out of ten animals should reach at least the three-month period. This can be achieved in half a year, said Reichart. "We hope to finish this in the spring." At the same time, it's about testing new immunosuppressants. "We need a humanized antibody, which we must use in the next two years," said Reichart. "We hope to get approval to do pilot studies." Not only pig hearts, but also kidneys should be transplanted. At the same time, however, it will take another year before the animal donor organs can be used as a standard method and animals could be specially produced for them. Better planning of transplants More about animal donor organs would have many advantages, Reichart said. The entire microbiology of the donor organ is known in contrast to donor hearts of dead people. This reduces the risk of infections. The recipient can be prepared in peace. "This is the elegant thing about xenotransplantation: in contrast to human transplantation, everything is known in advance." Recently, a big step had been taken a few years ago in the transplantation of genetically modified pig hearts into baboons. The hearts were used in the abdomen and beat there for two and a half years – but without replacing the heart of the baboon. The vision to save human life with animal organs goes back a long way. In the United States, in the 1980s, a doctor had even dared use a baboon heart for a dying newborn with an inoperative heart. The girl only survived for about two weeks. In clinical studies, porcine pancreatic islet cells have already been transplanted to help people with diabetes.