Scientists have discovered a way to make chimeric animals that have organs belonging to another species by injecting stem cells into an embryo of the other species. The researchers injected rat stem cells into the embryos of mice that had been genetically modified so that they could not produce their own organs, creating mice with rat organs. The researchers say the technique could be used to grow human organs in pigs using patients’ own stem cells, for use as transplants. By using a patient’s own stem cells, it could help to lower the risk of the patient’s body rejecting the transplanted organ, while also providing a rich supply of donor organs.

Current organ shortages mean that patients must face long waiting lists for transplants. Professor Hiromitsu Nakauchi, of the University of Tokyo in Japan and who led the research, said:

“Our ultimate goal is to generate human organs from induced pluripotent stem cells. The technique, called blastocyst complementation, provides us with a novel approach for organ supply. We have successfully tried it between mice and rats. We are now rather confident in generating functional human organs using this approach.”

Professor Nakauchi and his team used a type of adult stem cell known as induced pluripotent stem cells, which can be taken from a tissue sample such as skin and encouraged to grow into any type of cell found in the body. With his colleagues, he injected these cells extracted from rats into the embryos of mice that were unable to develop their own pancreas, the organ that produces vital hormones such as insulin. When the mice grew to adulthood, they showed no signs of diabetes and had developed a pancreas that had been formed almost entirely from the injected rat stem cells.

The researchers claim that the rat stem cells grew in the space left by the missing mouse pancreas and so almost any organ could be grown in this manner. If developed for use with human stem cells, the technique could foster a way of treating diabetic patients by providing a way of replacing their pancreas. Professor Nakauchi said they hoped to further trial the technique by growing other organs and were also seeking approval to use human stem cells. They have, however, already produced pigs that were able to produce human blood by injecting human blood cells into pig foetuses.

He said:

“For ethical reasons we cannot make an organ deficient human embryo and use it for blastocyst complementation. So to make use of this system to generate human organs, we must use this technique using blastocysts of livestock animals such as pigs instead. Blastocyst complementation across species had never been tested before, but we have now shown that it can work.” ~ Independent, Jun 19