10,000 critically ill people are waiting for a donor organ in Germany. Many die before they receive the saving transplant. Researchers hope to remedy this deficiency through animal organs. But on the way there are numerous hurdles. At least one could now overcome an international research team according to their own information.
The team led by Luhan Yang of the private US company eGenesis has used genetic engineering methods to create pigs that are free from active so-called endogenous retroviruses. In the journal "Science" they report on their work, involved was also the well-known genetic researcher George Church.
The special viruses (PERVs) are integrated into the genome of the pigs and are therefore difficult to combat. When transmitting a pig heart, there is a risk that these viruses in the human genome nest and cause immune deficiencies and cancer, writes the team.
The researchers around Yang could deactivate the viruses now however. For this they used the Gen scissors Crispr-Cas9. The scientists were thus able to turn off the PERVs in the genome of pig cells. From appropriately modified cells, they produced embryos that were free of active PERVs. In each case, 200 to 300 such embryos were transferred to 17 mother sows. As a result, 37 piglets were born in which the PERVs were inactivated. The oldest animals were four months old at the time of publication.
"This is really a very good development," said Joachim Denner, who did not participate in the study. He leads a working group at the Robert Koch Institute, which deals with the transmission of viruses in xenotransplantations.
Xeno-transplants, the transmission of animal organs to humans, have been researched for some time. There are studies in which pig hearts or kidneys have been transmitted to primates such as baboons. In further promising studies, diabetic islet cells have been transmitted from pigs, said Denner. These cells play an essential role in sugar metabolism. A real step further would be, however, only if the other problems of xenotransplantations were solved.
Many challenges remain
The most serious problem is the rejection reactions that cause animal organs in humans, explains Jan Gummert, heart transplant surgeon at the Heart and Diabetes Center North Rhine-Westphalia. To suppress these reactions, patients would need to take significantly more drugs with significant side effects than if they got a human organ. In addition, there is the problem with pig hearts, for example, that their right-hand chamber pumps somewhat less than in humans.
Therefore, Gummert is cautious about the new study: "This is an interesting story." However, it had to be shown if the results were reproducible and the piglets survived for a longer time. Because it is still unclear whether pigs need the distant viruses to survive.
In addition, so only one problem is solved. Pigs are needed, however, whose organs are not only free of PERVs, but also cause only minor rejection reactions in humans, so that the patients get along with a tolerable drug administration.
Artificial hearts could make pig hearts redundant
So far, there have been few attempts to transfer pig hearts to people who have all failed. "The transmission of animal organs to humans is a cherished dream for a long time," says Gummert. In medical practice, however, the application is so far unthinkable.
"I think it's more likely that the development of artificial hearts will progress faster than solving xenotransplantation problems." So far, artificial hearts are intended as a temporary solution to a transplant, said Gummert. In addition, there are technical systems for circulatory support that help many patients permanently.