Investors holding StemCells Inc. ( STEM) were celebrating Friday after the company reported progress with experimental cells it hopes can help in the regeneration of damaged tissue. The Palo Alto, Calif., biotech said mice who were implanted with the company's human neural stem cells showed improved motor function in tests designed to measure recovery from complete hind limb paralysis. It said a link was also observed between the amount of functional recovery and the amount of cells implanted. "This data suggests that human neural stem cells could contribute to repairing the nervous system after injury," the company said, while conceding that the sample size in the test was small. Investors bid the shares up to $1.77, a nearly 140% gain.