New discussion about human-animal-hybridism

Two new Chim ren projects are causing a stir and criticism

Two research groups want to create human-animal hybrids by injecting human stem cells into early embryos of pigs or monkeys. © wildpixel / iStock
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Ethically acceptable or questionable? Currently, two research teams have rekindled the discussion about human-animal hybridism. Because both teams want to create such chimeras in unprecedented form. A Japanese team wants to breed long-term human organs in pigs, a Spanish-Chinese team has introduced human stem cells in monkey embryos.

Chimeras are hybrid beings consisting of cells and tissues of two different species. The "foreign" cells can be scattered randomly or concentrated in the form of specific organs. In 1984, for example, the first chimera of sheep and goat was produced in the laboratory. Shortly afterwards, researchers produced the first mice with a human immune system - a chimera variant that has been widely used in research ever since. There are also chimeras from different monkey species.

Human in the animal

But just hybrid creatures of humans and animals have been causing heated discussions for years. On the one hand, they are considered a promising way to gain medical knowledge and perhaps even to create human replacement organs in animals. At the same time, however, such chimeras raise the question of where the boundary between human and animal is - especially if human cells are also found in the brains of these animals.

As early as 2013, researchers generated mice with human cells in the brain - and these chimeras proved to be more adaptive than their untreated counterparts. Meerkats have also been injected into the brain by human stem cells. However, these chimeras did not originate from manipulation of early embryos.

Mixture already in the early embryo

This is different with the two currently discussed chimera projects. Because in these human stem cells are injected into their animal recipients in the early embryonic stage. As a result, not only is the human proportion of such chimeras higher, in theory, human cells can also be found in all tissues and organs, including the brain and germ cells. display

The latter, however, means that the descendants of such chimeras could also carry human shares - this would be a prohibited interference with the germline. So far, therefore, the production of human-animal embryos is allowed in many countries. The resulting hybrids must be killed on the 14th day after fertilization. In China, however, this restriction does not exist and Japan has also relaxed this restriction a few days ago.

What is the current Chim ren projects about?

In concrete terms, the team led by the Japanese researcher Hiromitsu Nakauchi is said to have already produced hybrids of chimpanzees and macaques by injecting stem cells into embryos. In 2010, they also produced mice that had a pancreatic pancreas made of rat cells. Such a breeding of a "foreign organ" in a chimera is possible if the genes needed for the development of this organ are specifically eliminated in the initial embryo. However, the long-term goal of the researchers is to use this method to breed pigs with human organs in the future.

A similar goal is pursued by Spanish researcher Juan Carlos Izpisua Belmonte and his team. They have put their own data on macaque embryos with pluripotent human stem cells. According to the researchers, this resulted in monkey-human chimps, which were then killed shortly before birth. However, so far this experiment is not published in any journal, so no further details are known. In addition, it took place in China, because there may be bred man-animal Chim ren beyond the 14th day.

Monkey Chim ren in the criticism

The reports on these two Chim ren projects have received worldwide attention as well as criticism. However, the approaches of the two teams are assessed quite differently also because Chim ren from monkey and human ethically are particularly controversial. Because of their great biological similarity, the non-human primates would be ideal for many research approaches, including organzucht. At the same time their close relationship makes the experimentation with monkeys in the opinion of many ethically questionable. The German Ethics Council therefore rejects monkey-human-Mischwesen fundamentally ab.

Similarly, R diger Behr of the German Primate Center: "Monkey-human-mixed beings according to the methods that are discussed here, I think is unethical, " he comments. "In monkey-human hybrids, I see a greater danger of a true Mischwesen-emergence: That not only a clearly demarcated organ of human cells in an animal arises, but a more thorough mixing of human and animal cells in the nascent organism done knnte. "

How regulated is the procedure?

By contrast, Behr considers the Japanese approach of targeted organ breeding in pigs to be less worrying. On the one hand, there is a lower risk of unregulated proliferation of human cells in such a chimera, and on the other hand, its overall share is rather low: "In a pig-human hybrid, it would produce a spare pancreatic pancreas The proportion of human cells is probably less than one percent of the total animal, "said Behr.

And there's something else to add, as Peter Dabrock, chairman of the German Ethics Council, commented in a commentary: "The Japanese have announced they will move forward step by step, want to be monitored externally and have marked a red line and are looking to talk to the public. "However, this is different with the Spanish-Chinese project:" Belmonte goes all out and wants to produce embryos from primate and human right away, "says Dabrock. It is to be expected that the mixing also takes place in the brain of the produced organism. This has a completely different quality than just the production of demarcated organs.

For both projects, however, it remains to be seen how achievable the goals of the two research teams actually are, and whether it is possible to specifically breed human organs in animals.

Source: Stanford University, El Pais, Science Media Center

- Nadja Podbregar