The idea is to turn back the clock inside cells to when they were newly formed and malleable - and then reprogram their genes to regrow tissues or switch off genes that spur disease.
"It's an area of tremendous interest," said Dr. Harold Varmus, director of the National Institutes of Health. He is pushing a Congress afraid of possible human cloning not to ban Dolly-spurred research with such medical promise.
Dolly's creation from a single reprogrammed udder cell gave a boost to companies already trying different methods to switch genes on and off, in a little-known field called developmental biology.
"I used to have the door slammed in my face," said Dr. Doros Platika, president of Ontogeny Inc. Just weeks after Dolly made headlines, the company raised $25 million from suddenly less-skeptical investors to try regrowing, among other things, brain cells destroyed by Parkinson's disease.
Dolly showed "this is not science fiction," added Platika, a neurologist who is preparing to publish data showing his treatment stimulated brain-cell regrowth in mice. "People now realize there's a lot more plasticity in the body than they thought."
Virtually every cell contains a person's entire genetic blueprint, all 80,000 to 100,000 genes.
During embryo development, cells become specialized - scientists call it "differentiation" - meaning only the genes responsible for each cell's function in life are turned on. The mix of genes that are awake and those that are in a deep sleep determines that a skin cell will forever be a skin cell, and not a brain cell or a pancreas cell.
Then Dolly creator Ian Wilmut shattered biology's dogma.
The Scottish researcher essentially took a sheep's udder cell and "undifferentiated" it, making it think it was still an early embryo cell with no special function. Then he awakened all the genes to spin off the cells needed for a sheep.
The medical interest in Wilmut's discovery "is not cloning per se," Varmus said in an interview. While he cautioned that years of research are needed, "There's a lot of potential for gene control."
One key to Wilmut's success was awakening the deprogrammed cell after it was placed inside a sheep's egg. Biologists already knew eggs and early embryos from different species contain gene-regulating molecules that switch genes on and off during different stages of life.
If doctors could control those gene-regulating substances, they might stimulate regrowth of nerve cells, which do not regenerate naturally after a spinal cord injury.
Or they might deprogram a skin cell and reawaken only genes that create bone marrow to grow cancer victims a customized transplant. Or they could fight sickle cell anemia by switching on a vital blood-producing gene.
Developmental biologists already were isolating gene-regulating molecules, but instead of working backwards from an adult cell, they cull the substances from human and animal embryos and try growing them up.
Ontogeny, based in Cambridge, Mass., has patented 30 molecules that activate genes responsible for, among other things, the embryonic development of brain, sperm and bone cells. These genes become dormant, so Platika's goal is to awaken them to redo their jobs in Parkinson's patients, men with low sperm counts or elderly women with broken hips.
"We have a long way to go," cautioned Harvard University's Dr. Stuart Orkin, who can grow new blood from mouse embryo cells but has found it doesn't work properly when transplanted into animals.
Dolly's method did raise the potential of customized treatments that patients' bodies wouldn't reject, by working backwards from a patient's own cells instead of using lab-grown cells, said Millennium Pharmaceuticals President Steve Holtzman. He is a member of the National Bioethics Advisory Commission that will advise President Clinton about cloning.
Said Ontogeny's Platika: "To me it's so exciting because it said you can ... unlock the body's capabilities to repair and regenerate."