Diseases of the CNS are especially attractive targets for human stem and progenitor cell-based therapy, given the limited tissue regeneration manifested by the adult brain and spinal cord. A number of disorders, including diseases of myelin, retinal disease, Huntington Disease, Parkinson disease, and other neurodegenerative states manifested by the loss of one or more discrete phenotypes, may now be targeted for cell replacement therapy using hESC and hiPSC derivatives, in some cases with curative intent. However, other neurological disorders may not be readily amenable to cell replacement-based treatment, whether by virtue of an inhospitable disease environment, poor risk profiles of the donor cells, or a poor convergence of donor cell capabilities with host needs. Some may well be medically feasible targets, but may not be practicable, in light of already available alternative therapies, poor risk-benefit and cost-benefit profiles. In all cases, the suitability of cell therapy for any given clinical disorder - and indeed for any individual patient - will depend upon the pathogenesis of the host disorder, the homogeneity of the deficient host cell phenotype, the phenotype of the
