Tamir Ben-Hur, M.D., Ph.D.
Department of Neurology, Hadassah - Hebrew University Hospital, Jerusalem, Israel

The adult brain, afflicted by degenerative and traumatic diseases, often fails to regenerate neurons or to rebuild myelin sheaths around naked axons. Cell transplantation is an experimental therapy that has recently ignited enthusiastic expectations to renew neural tissue. The potential application of stem cell transplantation in neurologic patients will be briefly reviewed, with special reference to demyelinating disorders, and some problematic issues that still face this therapeutic approach. Transplanting various precursor cell populations has proven effective in remyelinating focal lesions in adult CNS and in the developing CNS of animals with genetic dysmyelinating disorders. In the striata of animals with experimental Parkinson's disease, transplanted cells generated dopaminergic neurons, and improved their functional status. Stem cell transplantation to the spinal cord partially recovered motor function in animals with traumatic spinal cord injury. The limited survival and migration of transplanted cells in the brain are still crucial issues to deal with in order to bring this therapeutic approach closer to clinical reality in chronic and multifocal diseases like multiple sclerosis. Choice considerations in designing a transplantation strategy will include cell preparations that are expandable in large quantities, able to survive through remissions and relapses and be recruited upon call, to migrate into different demyelinating lesions for repair. Our experimental data in an animal model of multiple sclerosis suggest that intraventricular transplantation of precursor cell spheres may supply the brain with a stable reservoir of cells that react to inflammatory stimuli by migration into active lesions and attenuate clinical disease.