Injury and neurodegenerative conditions of the spinal cord can lead to paralysis and loss of sensation. Cell therapeutic approaches can restore sensory innervation of the spinal cord following injury and protect spinal cord cells from degeneration. This thesis primarily focuses on the restoration of deaffarented sensory fibres following injury to the dorsal root and spinal cord. These injuries lead to the formation of a non-permissive glial scar that prevents sensory axons from reinnervating spinal cord targets. It takes advantage of a dorsal root injury model that closely mimics spinal root avulsion injuries occurring in humans. In the first part of the thesis, three different neural progenitor types from human or murine sources are tested for their regenerative properties following their transplantation to the site of dorsal root avulsion injury. In the second part, the ability of murine neural progenitors to protect spinal motor neurons from a neurodegenerative process is tested.

In the first original research article, I show that human embryonic stem cell derived neural progenitors are able to restore sensorimotor functions, mediated by the formation of a tissue bridge that allows ingrowth of sensory axons into the spinal cord. In the second research article, I present that murine boundary cap neural crest stem cells, a special type of neural progenitor that governs the entry of sensory axons into the spinal cord during development, are unable to form a permissive tissue bridge. This is possibly caused by the contribution of transplant derived ingrowth non-permissive glial cells. In the third research article, I show that human neural progenitors derived from foetal sources are capable of stimulating sensory ingrowth and that they ameliorate the glial scar. When this approach is combined with the delivery of sensory outgrowth stimulating neurotrophic factors, these cells fail to form a permissive tissue bridge and fail to modify the glial scar. In the final research article, murine boundary cap neural crest stem cells are shown to protect motor neurons, which harbor an amyotrophic lateral sclerosis causing mutation, from oxidative stress. Oxidative stress is a pathological component of amyotrophic lateral sclerosis in human patients.

Taken together, this thesis provides first evidence that sensory regeneration following a spinal root avulsion injury can be achieved by transplantation of human neural progenitors. In addition, it introduces murine boundary cap neural crest stem cells as interesting candidates for the cell therapeutic treatment of amyotrophic lateral sclerosis.