NEW YORK (AP) — Shares of StemCells Inc. jumped Tuesday after the company said it finished treating the first group of patients in a clinical trial of its stem cell therapy.

THE SPARK: StemCells said it has completed treatment for three patients and is now observing their long-term health. All three had suffered a "complete" spinal cord injury at chest level, which means they had no nerve function or feeling below the area that was injured. The company said two of the patients had greater sensory function a year after treatment, and one had recovered to the point that the injury is now considered "incomplete."

StemCells said that as far as it knows, this is the first time a patient has experienced that kind of improvement after treatment with neural stem cells.

The study measured changes in the patients' sensitivity to touch, heat and electrical stimuli. StemCells said one of the patients didn't experience any improvement.

THE BIG PICTURE: The Newark, Calif., company is studying therapies based on purified adult neural stem cells. It had previously reported that two of the three patients had improved six months after they were treated. StemCells is also testing its treatment on patients with complete injuries, and said it hopes those patients will have similar or larger improvements because they still have some nerve function.

Stem cell therapies are still an experimental field, and StemCells is a small company without any approved products.

SHARE ACTION: StemCells shares climbed 38 cents, or 22.8 percent, to $2.02 in afternoon trading. The stock has doubled in value since-mid July, when the company reported positive preclinical data for an experimental Alzheimer's disease therapy.