Human stem cell grafts as therapies for motor neuron disease.

Stem cell transplantation, a widely accepted therapeutic approach to diseases of modular organs such as the heart and the endocrine pancreas, remains a controversial option for the nervous system. However, historical advances in the 1990s on key aspects of neural plasticity and the appreciation of the selective vulnerability of nerve cells and systems in degenerative and traumatic diseases require a re-examination of this scepticism. The successes and failures with prior trophic factor therapies are particularly enlightening; many lessons from this era can be creatively absorbed as the early outcomes with stem cell grafts in animal models of disease are evaluated. Stem cell grafting into spinal cord, traditionally a doomed enterprise because of lack of neurogenicity in this region and multiple early failures, is becoming promising again with recent findings from the authors' laboratory and elsewhere that specific types of cells and methods of culture are associated with much improved biological and functional outcomes.