ATLANTA, Georgia (CNN) -- For the first time in the United States, stem cells have been directly injected into the spinal cord of a patient, researchers announced Thursday.

Doctors injected stem cells from 8-week-old fetal tissue into the spine of a man in his early 60s who has advanced ALS, or amyotrophic lateral sclerosis. It was part of a clinical trial designed to determine whether it is safe to inject stem cells into the spinal cord and whether the cells themselves are safe.

ALS is a fatal neurodegenerative disease that causes the deterioration of specific