GDNF and amyotrophic lateral sclerosis: For instance, a phase 1/2a trial in a small cohort of ALS patients (NCT02943850) has shown that a single injection of human NPCs engineered to produce glial cell line-derived neurotrophic factor (GDNF) into the spinal cord is safe, and viable grafts differentiated into astrocytes that may be neuroprotective through increased GDNF production (Baloh et al., 2022).