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Scientists have created sheep-human hybrid embryos

Embryo of a pig-human hybrid from previous research. Credits: Juan Carlos Izpisua Belmonte

A team of researchers have announced that they have created hybrid sheep-human embryos, which could one day be the future of organ donation. The results were presented during the AGM of the American Association for Advances in Science in Austin Texas. 

By introducing human stem cells into sheep embryos, the scientists recently succeeded in creating the first interspecies sheep-human organism. This is a hybrid made up of over 99% sheep and less than 1% human cells. “The contribution of human cells so far is very small”, notes Hiro Nakauchi, a biologist specialising in stem cells in Stanford University. He specifies that there is around 1 human cell for every 10,000 sheep cells in the sheep embryos.

The research developed on previous experiments carried out by part of the same team, which a few months ago successfully developed human cells in early-phase pig embryos, also creating pig-human hybrids which the researchers described as “interspecies chimeras”. These experiments, which still divide the scientific community, could one day offer a unique solution to the thousands of people on waiting list for organ transplants.

The approach here is different from xenotransplantation, in which an organ belonging to another species is transplanted into a human. Although this is presented as an alternative that tackles organ shortage, the problem of organ rejection still remains. “Even today the best matched organs, except if they come from identical twins, don’t last very long because with time the immune system continuously is attacking them”, explains biologist Pablo Ross from the University of California in Davis (US). The organs produced in the interspecies chimeras could be -in the future – a means of producing enough organs to respond to transplant needs, for example by transplanting a hybrid pancreas, made from a sheep or a pig, into a desperate patient.

In order for such transplants to work, researchers believe that at least 1% of the embryonic cells need to be human -showing that the first steps taken in sheep are still at the very preliminary stage. Naturally, increasing the ratio of human cells inevitably increases the ethical questions surrounding the type of creature that would be produced, with the sole objective of harvesting its essential organs. “All of these approaches are controversial, and none of them are perfect”, says Pablo Ross, “but they offer hope to people who are dying on a daily basis.” “We need to explore all possible alternatives to provide organs to ailing people.”


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