The first attempt at gene therapy for Alzheimer's patients appeared to significantly delay worsening of the disease in a few people who have tested it so far, scientists reported Sunday.

Far more research is needed to see if the experimental treatment, which requires a form of brain surgery, really helps.

But if the approach pans out, researchers say delivering protective substances, called growth factors, into a diseased brain holds the potential to rescue some dying brain cells.

In one patient, the brain tissue showed new growth, which was a first, according to a study published in Sunday's edition of the journal Nature Medicine.

"It won't cure the disease," said the lead researcher, Dr. Mark Tuszynski of the University of California, San Diego. That is because Alzheimer's destroys different types of cells in different areas of the brain; the new gene therapy targets just one of those.

The preliminary success indicates that similar approaches might help other neurodegenerative diseases, such as Parkinson's, Tuszynski said. "This is in a sense proof of principle for the potential use of growth factors," he said.

Doctors at Chicago's Rush University Medical Center have begun a second small study of the approach in Alzheimer's patients. Tuszynski, who co-founded a biotechnology company that is funding the Chicago work, hopes larger studies will begin within another year.

Tuszynski and colleagues took skin cells from eight patients in the early stages of Alzheimer's and modified the genes to secrete a protein found in healthy brains called nerve growth factor, or NGF.

Earlier studies had shown that injecting NGF-producing tissue into the brains of aging monkeys could reverse deterioration. Simply injecting NGF into people would not work. If it goes into the wrong part of the brain, it can cause serious side effects.

So, doctors drilled holes into the patients' skulls and implanted the NGF-producing skin cells directly onto Alzheimer's-injured spots.

Six patients were tracked for almost two years. Tests involving memory and other skills found their rate of cognitive decline slowed by 36 percent to 51 percent, better than is usually seen with medication, Tuszynski reported.

The first two patients were awake and moved during the cell implantation, causing bleeding in their brains; one patient died five weeks later. Remaining patients received the implants under general anesthesia to keep them still, and the researchers reported no further problems.

The brain tissue of the study participant who died had new growth protruding from Alzheimer's-injured cells at the implant site, the first time that sort of recovery has been seen from a human brain treatment, Tuszynski said. Additionally, PET scans of the other participants showed a measurable increase in their brains' metabolic activity.

"These results need to be interpreted with cautious optimism," said William Thies of the Alzheimer's Association. With so few patients in the study, "it's really impossible to tell whether the benefit was due to the treatment or natural fluctuation in symptoms," he said.

Moreover, he said, it would never be practical to perform brain surgery on millions of patients. Already, 4.5 million Americans have Alzheimer's, and with the country's population aging, a staggering 14 million may have it by 2050.

But if the gene-therapy approach ultimately works, it could revive interest in finding easier methods, he said.

As for the next step, instead of genetically modifying skin cells, Dr. David Bennett of the Rush University Medical Center has begun injecting the brains of up to 12 Alzheimer's patients with an NGF-bearing virus.

Animal studies suggest the virus may penetrate injured brain cells better, producing more of the protective growth factor for longer periods, he said.

"It's cautious optimism with a big C," Bennett stressed. "It can't be a cure, obviously ... but maybe it'll do something."