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...