Similarly, neural stem cells have long been promoted as a therapeutic in a broad variety of conditions that effectively span the gamut of neurological disease. Yet while these cells may be effective for some conditions, for many others they may be suboptimal, or even inappropriate. Indeed, their intrinsic multilineage competence and phenotypic plasticity can prove counterproductive to their use in targeted cell replacement. For instance, NSCs can generate neurons that in a glial disorder might be heterotopic, potentially integrating into extant neural networks in problematic manners. The neuronal phenotypes generated by NSCs in vivo may be difficult to instruct, and evidence for their phenotype-appropriate functional integration in higher cortical networks in adults is scarce. By the same token, they may generate astrocytes in abundance and in an environmentally-modulated fashion, not necessarily producing the phenotypes of interest when cell-type specific replacement is the goal. Similarly, their migration competence in vivo is relatively restricted, compared to their glial progenitor progeny, which are considerably more effective at long-distance migration and dispersal. As a result, NSCs may not be as appropriate vectors for the
