Alzheimer’s disease patients given gene therapy seemed to regrow some damaged brain cells and seemed to experience a slower loss of their ability to think and remember, U.S. scientists reported Sunday.

The trial therapy was not without risk. However. “Two subjects abruptly moved while the injection needle was in the brain, causing subcortical hemorrhage,” they wrote journal Nature Medicine. One died later and one suffered brain damage. After that, the patients were rendered unconscious and immobile using general anesthesia.

The treatment did appear safe if performed under general anesthesia, the researchers reported, and said they will try it in a larger group of patients.

In this gene-therapy experiment, researchers took skin cells from eight patients with mild Alzheimer’s disease. The researchers genetically modified the cells to produce a protein called nerve growth factor, or NGF, which prevents cell death and stimulates cell function.

They then infused these genetically engineered cells back into the patients’ brains. “After mean follow-up of 22 months in six subjects, no long-term adverse effects of NGF occurred,” they wrote in their report.

The brain of the patient who died was full of the amyloid protein plaques and tangled brain cell fibers that mark the incurable, brain-destroying disease, researchers said.

But it seemed to have also grown new cells that were producing NGF, and some seemed to be growing new connections, they said.

“If validated in further clinical trials, this would represent a substantially more effective therapy than current treatments for Alzheimer’s disease,” said Dr. Mark Tuszynski, a neuroscience professor at UCSD who led the study.

“This would also represent the first therapy for a human neurological disease that acts by preventing cell death,” Tuszynski said in a statement.

Positron emission tomography or PET scans done in four living patients suggested they grew some new brain cells and had fresh brain activity, the researchers said.

Six patients had their cognitive function - their ability to think, orient themselves and remember - tested using a standard method.

Over the follow-up period of 22 months, the rate of cognitive decline was reduced by as much as 51 percent, the researchers said.

“By comparison, currently approved medications for Alzheimer’s disease have an estimated impact on these cognitive measures of 5 percent to 27 percent, and are not known to affect decline over prolonged periods,” the researchers pointed out.