Japan, like some other countries, is struggling with the issue of human organ donation, but another solution is being pursued by university researchers here whose sheep, named “Saru”, may hold the key to the future of organ transplants.

Saru, which means “monkey” in Japanese, is part sheep and part monkey. 

Saru is not the only sheep in the barn to be genetically engineered, as others have been designed to produce partial human blood. However, Saru is a bit different.

If one reaches down on Saru’s shaved side, there’s a lump that feels a bit out of place.

It’s then that the leader of the team who created Saru, Professor Yutaka Hanazono, who has been working with sheep for over 10 years, leans in to explain.

The lump is monkey tissues, which have grown inside the sheep. Hanazono’s team has managed to take stem cells and implant them into monkey embryos, then used the sheep’s body to help grow the cells as if they were Saru’s own.

Using stem cells has many advantages but also a few disadavantages, chief among them being the inability to control what the stem cells become.

“If you put embryonic stem cells directly into an embryo, it creates a very wide variety of different tissues. So at the moment we are not yet able to make just a liver or just a nerve cell,” Hanazono told me.

If that can be overcome, the cells produced will be genetically identical to the patient’s cells.

“If we can create a sheep that has the patient’s tissues or cells, it would help solve the severe donor shortage problem. If you then transplant those cells or tissues, as it’s technically the patient’s own tissues, there is no immune system rejection. This is our eventual goal.”

Human stem cell research, especially involving embryonic stem cells, has been quite controversial, but this method manages to avoid much of that by using adult stem cells. Normal cells are taken from adult donors and then coerced into becoming stem cells, then used to create the donor’s tissues in the animal. Since the cells grown are genetically identical to the original donors, they can be used without any risk of the body rejecting them.

Organ transplants from humans are extremely rare in Japan, and even in the U.S. over 100,000 are on waiting lists and may die before receiving needed organs. 

Much still needs to be done at Utsunomiya and Jichi Medical University. In building up to creating human tissues and organs, experiments will first be done with mice, then pigs and sheep, and finally monkeys before scientists make the jump to humans.