Neural stem cells: properties and therapeutic potentials for hypoxic-ischemic brain injury in newborn infants.

Neural stem cells (NSCs) are defined by their ability to self-renew, to differentiate into cells of all glial and neuronal lineages throughout the neuraxis, and to populate developing or degenerating central nervous system (CNS) regions. The recognition that NSCs propagated in culture could be reimplanted into the mammalian brain, where they might integrate appropriately throughout the mammalian CNS and stably express foreign genes, has unveiled a new role for neural transplantation and gene therapy and a possible strategy for addressing the CNS manifestations of diseases that hitherto had been refractory to intervention. An intriguing phenomenon with possible therapeutic potentials has begun to emerge from our observations of the behavior of NSCs in animal models of neonatal hypoxic-ischemic (HI) brain injury. During phases of active neurodegeneration, factors seem to be transiently elaborated to which NSCs may respond by migrating to degenerating regions and differentiating specifically towards replacement of dying neural cells. NSCs may attempt to repopulate and reconstitute ablated regions. These 'repair mechanisms' may actually reflect the reexpression of basic developmental principles that may be harnessed for therapeutic ends. In addition, NSCs may serve as vehicles for gene delivery and appear capable of simultaneous neural cell replacement and gene therapy (e.g. with factors that might enhance neuronal differentiation, neurites outgrowth, proper connectivity, and/or neuroprotection). When combined with certain synthetic biomaterials, NSCs may be even more effective in 'engineering' the damaged CNS towards reconstitution. We have also cultured human NSCs or progenitors as neurospheres which were derived from fetal cadavers at 13 weeks of gestation, and transplanted them into HI-injured immature brains to investigate their therapeutic potentials in this type of model.