The investigator is examining the safety of transplanting cells that have been engineered to produce a growth factor into the spinal cord of patients with Amyotrophic Lateral Sclerosis (ALS). The cells are called neural progenitor cells, which are a type of stem cell that can become several different types of cells in the nervous system. These cells have been derived to specifically become astrocytes, which is a type of neuronal cell. The growth factor is called glial cell line-derived neurotrophic factor, or GDNF. GDNF is a protein that promotes the survival of many types of neuronal cells. Therefore, the cells are called "CNS10-NPC-GDNF." The investigational treatment has been tested in animals, but it has not yet been tested in people. In this study, we want to learn if CNS10-NPC-GDNF cells are safe to transplant into the spinal cords of people.