But now, U.S. scientists have taken skin cells and used them to clone a human embryo -- not to make a cloned baby but to repair organs.
American scientists are one step closer to using stem cells to reverse paralysis or treat damaged hearts. But how the scientists in Oregon did it may raise some eyebrows.
"They cloned a human embryo. To this point, that had never been done before," Houston infertility expert Dr. Timothy Hickman said.
Hickman says these scientists from the Oregon Health & Science University were not trying to create a baby.
"I'll go on record saying there's no reputable physician or scientist that's doing anything like this that we know," Dr. Hickman said.
The Oregon research is about using stem cells to repair organs.
"Any type of disease where the cells die and they can't be regenerated currently would be the potential benefit of this," Dr. Hickman said.
The Oregon scientists used a skin cell to start their clone. When the skin cell was combined with an unfertilized human egg, it grew into a blastocyst. Stem cells from the blastocyst were removed, and in the lab, were transformed into pancreatic cells, which could help diabetics, blood cells, heart cells that could repair heart attack damage. It also could help liver cells and neurons which could repair spinal cord injuries and potentially reverse paralysis.
"There's a lot of hope. This is science fiction kind of stuff, but we're getting closer and closer," Dr. Hickman said.
But Dr. Hickman says using these stem cells to help patients is still a long way off. It will take years of additional research to make sure this is more science than fiction.
Using a patient's own skin cells to make stem cells means the patient could be his own "cell donor." There would be no risk of rejection. And the goal would be to use a patient's stem cells to repair his organs, and help patients avoid the need for organ transplants.