Cell therapy in Huntington's disease

Huntington's disease is an autosomal dominant genetic disease, which results in progressive neuronal degeneration in the neostriatum and neocortex, and associated functional impairments in motor, cognitive, and psychiatric domains. Although the genetic mutation is identified, involving an abnormal CAG expansion within the htt gene on chromosome 4, the mechanism by which this leads to neuronal cell death and the question of why striatal neurones are targeted both remain unknown. Thus, in addition to the search for molecular and genetic strategies to inhibit development of the disease, we still need to identify effective strategies for cellular repair in affected individuals. Aspects of the human neuropathology can be well modeled by excitotoxic or metabolic lesions in experimental animals, and in transgenic mice carrying the htt mutation, providing the basis for testing alternative therapeutic strategies. The rationale and efficacy of alternative cell therapies are reviewed, including transplantation repair with embryonic striatal tissues, expansion and differentiation of striatal-like cells from stem cells, and in vivo and ex vivo gene therapy for delivery of neuroprotective growth factor molecules. Pilot and experimental clinical trials of several approaches are now also underway, and the alternative strategies are compared.