This was evident in our phase I/IIa clinical trial delivering CNS10-NPC-GDNF to the ALS patient spinal cord, in which dorsal grafts may have contributed to cell reflux, neuroma formation at the dorsal root ganglia, pain in some participants, and lack of overall effects on motor neurons and function (Baloh et al., 2022). Here, GDNF is linked to amyotrophic lateral sclerosis.