Last updated April 18, 2018 at 9:21 am
Humans have taken another tiny step along the rocky road that may one day allow us to grow organs for medical transplant.
US scientists announced at the weekend that they have produced hybrid sheep-human embryos by introducing human stem cells into sheep embryos.
They were only a little bit human – around one in 10,000 cells – and were not allowed to develop past 28 days of age, but they were real and their existence will no doubt be controversial.
The research builds on previous experiments by some of the same team that saw human cells successfully grown inside early-stage pig embryos in the lab, creating pig-human hybrids that they described as interspecies chimeras.
The latest breakthrough was presented to the American Association for the Advancement of Science annual meeting in Austin, Texas, by reproductive biologist Associate Professor Pablo Ross from the University of California, Davis.
Organs produced in interspecies chimeras could be one way of generating enough supply to meet demand, by transplanting, say, a hybridised pancreas from a sheep or pig to a human patient.
To make chimeras, researchers isolate one animal’s stem cells, which can develop into any cell type in the body. They then inject some stem cells from one species into the embryo of another.
If the embryo’s DNA is hacked so that it does not grow a particular organ, the interloping cells would be the only ones that could fill in the gap. In this way, researchers could grow a human liver inside of a living pig, for example.
For transplants to work Ross and his colleagues think at least 1 per cent of the embryo’s cells would need to be human, meaning their work is still very preliminary.
Increasing the human ratio would, of course, raise ethical issues that they are only too aware of. “I have the same concerns,” Ross says.
“Let’s say that if our results indicate that the human cells all go to the brain of the animal, then we may never carry this forward.”
He believes we need to at least find out a little more, however.
“All of these approaches are controversial, and none of them are perfect, 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.”
Ross’s collaborator, stem cell biologist Dr Hiro Nakauchi from Stanford University, told the meeting that researchers were trying to target where human cells proliferate, to ensure that they didn’t set up shop in animals’ brains or sex organs.