The future bearer of hope for transplant physicians (Image: ddp)
Speaking pigs could help in the future to meet the great need for donor organs for transplants. But before the transplantation of animal organs to humans works safely, scientists still have a number of hurdles to overcome. With pigs, many mud and dirt - in spite of the popular characters like the movie stars Rudi Rüssel, Piglet Babe and Miss Piggy. Hardly any other group of animals arouses as many associations as the pig, but who would have thought that just the transplantation medicine will once join this list. But it is in this area, which is more associated with sterile operating theaters than with pigsties, that bristle animals play an increasingly important role. The area on which the pigs make merit, scientists call xenotransplantation. It involves the transfer of cells, tissues or organs from one species to another, in this case from pigs to humans.

At first, science came to the pig for purely practical reasons: pigs are cheap everywhere to breed. However, the organs of the four-legged friends show in tests a higher microbiological safety, so a lower risk of transmitting diseases via the transplantation, such as the organs of monkeys. In the long term, the technology should provide a real alternative to classical organ transplantation and thus compensate for the ever-increasing shortage of human donor organs.

However, research must overcome several hurdles on the path of xenotransplantation to clinical practice. Thus, the rejection reaction is much stronger due to the low degree of relatedness than in the so-called allograft, the transmission of organs within a species. In the case of alien grafts, in addition to the usual "simple" rejection, a so-called hyperacute rejection occurs minutes after the transfer, triggered by special sugar residues on the cell surfaces of the grafts.

The microbiological safety also remains an issue: Most microorganisms can be eliminated by appropriate husbandry and breeding selection, but like any animal genome contains the pigs so-called retroviruses. These are pathogens that permanently incorporate their genetic material in an infection in the genetic material of the host. The xenotransplantation now carries the risk that such exciters in the pig called PERV in the human body trigger previously unknown infections, which can lead to tumors and immunodeficiencies. Finally, transplantation must take into account the different life expectancies of pigs and humans and the anatomical differences. display

Especially with regard to the first two points, research has made great progress in recent times, explain scientists of the German Working Group Xenotransplantation (DAX) at the Robert Koch Institute in Berlin. Already last year, American and British scientists reported successful breeding of genetically modified pigs lacking the described sugar residues on their cell surfaces. "In the meantime, cells and organs from these transgenic animals have been successfully analyzed in primate trials, " explains virologist and DAX leader Joachim Denner to ddp. The elimination of hyperacute rejection marks an important step toward clinical testing.

Denner's research group at the Robert Koch Institute is also concerned with virus safety. The researchers have succeeded in decisively improving the detection methods for various swine viruses. This facilitates the selection of animals that are free of infectious viruses. By the detection method the success rate of the genetic manipulations can be controlled. In addition, Denner reports on strategies to prevent the transmission of porcine retroviruses after transplantation. "We have succeeded in obtaining antibodies as the basis for a vaccine against PERVs, " says the virologist.

Despite the clearly positive signals, the researchers do not want to spread false hopes or even engage in time information. There is still a lot of research needed to minimize the described risks to humans in xenotransplantation.

The process will be implemented in stages, as the scientists agree: first, diabetics will probably be treated with porcine pancreatic islet cells. Based on these experiences, then the transplantation of other tissues and finally of the first organs would have to be examined, explains Denner. As the life expectancy of experimental animals in xenotransplantation tests increases, the knowledge about how to transplant more complex organs such as the kidney will increase in the near future.

If the breakthrough succeeds in a few years, and the xenotransplantation will reach clinical practice, the phrase "pig" will be given a whole new meaning to many people. Then "simple" laboratory pigs will come as lifesavers to new honors.

ddp / bdw Dirk Gilson

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