Regulators have given a green light to the world's first approved experiment using embryonic stem cells to treat a human disease. In the phase I clinical trial, Geron Corp. will use stem cells to treat spinal cord injury. The Food and Drug Administration approved the trial in January 2009 but put it on hold last September because of safety concerns after lab animals injected with stem cells developed small cysts at the injury site. Today, Geron announced that FDA has lifted the hold. There's more background in this post on The New York Time's Prescriptions blog.