Researchers cured mice with a version of Parkinson's disease by treating them with brain cells made from clones of their own skin cells.

The researchers employed nuclear transfer, which involves swapping genetic material from one individual into an egg cell belonging to another. The same procedure was used to create Dolly the sheep, one of the first animals produced by cloning.

The findings, published Sunday in the journal Nature Medicine, offer a glimpse into how the cloning technique might one day be used to develop therapies, as opposed to making copies of an individual. There are still hurdles to clear before the technique could be used in people with Parkinson's, said Mark Tomashima, a stem cell researcher at Sloan-Kettering Institute in New York.

"This is the first proof of principle for therapeutic cloning," said Tomashima. "This is the first study where we've made individual nuclear transfer lines and used them to treat mice with disease."

Parkinson's disease is an incurable disorder that robs about 1.5 million people in the U.S. of the ability to control body movements. People with the condition gradually lose neurons that make the brain chemical dopamine.

Tomashima and his colleagues in the lab of cell biologist Lorenz Studer took bits of skin from the tails of mice, plucked out the nucleus of the skin cells, and inserted them into egg cells from other mice whose own nuclei had been removed. Each line of stem cells that resulted was genetically identical to the mouse whose skin cells were initially removed.

The researchers coaxed the stem cells to turn into neurons that produce dopamine. Those neurons were then injected back into the mice, which carried a form of Parkinson's disease.

Before they were treated with the stem cells, the mice acted out a number of behaviors linked to their condition. They moved their paws in certain unusual ways and, when placed in a bowl, moved only in one direction. Normal mice move equally in both directions.

After being injected with the cells, the behavior of the mice returned to normal. When the mice were later killed, Tomashima and his colleagues found that the neural cells they'd injected had grown and formed connections with other cells.

Because the cells used to treat the mice were made from their own skin cells, the mice's bodies didn't reject them. That's the key reason scientists have been excited by the idea of therapeutic cloning since Dolly was created in 1996.

Before such a treatment can be tried in humans, scientists must learn how to make the cloning procedure work with human cells, something they thus far have been unable to do. They must also figure out how to keep human neural cells alive once they're transplanted. Those things will take time, Tomashima said.