Researchers announced Monday that they had injected stem cells into a patient with a spinal cord injury on Friday, kicking off the world's first clinical trial of a therapy derived from human embryonic stem cells.

The patient was treated at Shepherd Center, a spinal cord and brain injury center in Atlanta.

Though the trial, run by Geron Corp. of Menlo Park, Calif., is in its earliest stages — aimed primarily at testing the treatment for safety — the event stands as a landmark one for embryonic stem cell researchers, who for years have studied the cells' potential to treat spinal cord injuries, diabetes and a variety of neurodegenerative diseases.

"All of that work, all of that money sent to the ivory towers is manifesting something. It's a real shot in the arm for the field," said Hans Keirstead, a neurobiologist at the Reeve-Irvine Research Center at UC Irvine who led a team that pioneered the treatment in rats and licensed the technology to Geron.

Keirstead's team managed first to turn human embryonic stem cells into oligodendrocytes, the cells that insulate nerve fibers with coatings of fatty myelin. Growing the "tubing" that protects nerve cells could in many cases be enough to allow signals to travel up and down the spine again, Keirstead said. That's because, in the vast majority of spinal cord injuries, the cord is not completely severed — rather, the myelin sheath that protects the nerve cells is damaged or destroyed.