Scientists create a sheep that's 15% human (3/30/2007)

Scientists have created the world's first human-sheep hybrid with the body of a sheep and containing organs that are human.

The sheep have 15 per cent human cells and 85 per cent animal cells and brings the possibility of animal organs being transplanted into human's one step closer.

Professor Esmail Zanjani, with the University of Nevada, has spent seven years and $2.5 million perfecting the technique, which involves injecting human cells into a sheep's fetus.

He has created a sheep liver which is mostly human and eventually hopes to precisely match a sheep to a transplant patient, using their own stem cells to create their own flock of organ generating sheep.

Perfecting the process would involve extracting stem cells from the donor's bone marrow and injecting them into the peritoneum of a sheep's fetus. When the lamb is born, two months later, it would have a liver, heart, lungs and brain that are partly human and available for transplant without the risk of organ rejection.

As of March 2007 14,749 patients are waiting for an organ transplant in the US alone, and two thirds of them are expected to die before an organ becomes available.

The concept of transplanting animal organs into humans, called xenotransplantation, isn't new, and has been a goal of scientists for many years. However, it wasn't until the 1960's that they moved from simple trial and error to a systematic scientific study. Ultimately the early studies were unsuccessful, but much was learned in the process.

It wasn't until 1972 with the introduction of drug called cyclosporin, which minimizes the rejection of foreign tissue, that the research was re-ignited. Though the technique still wasn't successful, the reason for the initial failures (rejection), were starting to be understood.

In 1992 a pig liver was used to help a patient survive while a human liver donor was found. Though the organs couldn't be left in people indefinitely, they could be used as a temporary replacement until a donor could be found. Though still not fully successful it did show that the research was starting to bear fruit.

In 1995, the first genetically-altered animal organs were created and tested on humans. The genetically engineered pig livers were designed to be less prone to attack by the human body and were attached to patient's circulation but kept outside their body.

To date no animal to human transplant of a whole organ has been considered fully successful.

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