The researchers believe they isolated and nurtured adult stem cells from the patient's brain, cells that they re-injected to restore normal function.
"We definitely need to do more studies," said Dr. Michel Levesque of the Cedars-Sinai Medical Center in Los Angeles, who led the study. "This is the first case that shows a promising technique may work. It is an experimental procedure and has to be investigated further before it becomes accepted procedure."
More than two years after the experimental treatment, the man has no symptoms of Parkinson's, an incurable and fatal brain disease that starts with tremors and ends up incapacitating its victims.
Parkinson's is caused when brain cells that produce dopamine die off. Dopamine is a key neurotransmitter or message-carrying chemical that is involved in movement.
Many different groups of researchers are experimenting to see if these brain cells can be regenerated using stem cells, the so-called master cells that give rise to the various different tissues in the body.
Some stem cells come from very early embryos, some from aborted or miscarried fetuses and some can be found in a person's own tissues, but they are elusive.
The study is sure to be used in the debate over the use of embryonic stem cells. Some groups say adult stem cells can be as useful as those taken from embryos. Many scientists disagree and say both adult and embryonic stem cells should be studied.
Levesque said the patient, a nuclear engineer and jet pilot, developed Parkinson's in his 40s. He had tremors and stiffness in his muscles and the drugs used to treat the disease had, as they always do, stopped working.
His team drilled into the patient's skull and removed a piece of his brain. "We took a tiny piece of cortex measuring probably less than the size of a pea," Levesque said in a telephone interview. "What we extracted were neural stem cells or progenitor cells."
It is hard to tell whether a cell is a stem cell, but they grew the cells in special media, a kind of nurturing soup.
They checked to make sure at least some of the cells were producing dopamine, and then injected them back into the patient's brain, researchers told a meeting in Chicago of the American Association of Neurological Surgeons.
PET scans of the man's brain, which show brain function, showed that dopamine was being produced and used. "At three months there was a 58 percent increase," Levesque said.
But now the man's dopamine production, as measured by PET scans, is back to where it was when he was first treated, which puzzles Levesque, as the symptoms of Parkinson's have not returned.
He said it is possible that it takes a while for the symptoms to show after dopamine production dies down. Or perhaps PET scans do not show everything that is going on.
Other cells may also be involved in the processes that underlie Parkinson's, Levesque said.
It is also possible that the animals used to study Parkinson's do not accurately mimic the human disease, so that humans may react differently to treatment, he said.
Although the Phase I safety study was done using only the single patient, Levesque said the U.S. Food and Drug Administration had given his team the go-ahead to start a Phase II trial, which will include more patients and test for safety and whether the treatment works.
Levesque and colleagues formed a company to develop the technique, called Neurogeneration. It has been bought out by California-based CelMed Bioscience, a subsidiary of Canada-based Theratechnologies.