Transplantation of an indigenous neural stem cell population leading to hyperplasia and atypical integration.

Astrocytes exhibit neural stem cell characteristics in vitro by generating multipotent clones of cells. In order to see if normal cues are present in vivo that can direct these astrocytes to generate cells of neuronal lineage, the astrocytes were transplanted into the persistently neurogenic mouse subependymal zone/rostral migratory stream. Grafted astrocytes assumed migratory profiles, joined chains of indigenous neuroblasts, and migrated into the olfactory bulb. Additionally, however, some grafted astrocytes "homed" to the lateral ventricle where they became hyperplastic, forming spherical structures composed of cells of mixed phenotype that attached to the ventricular wall, and eventually penetrated and dispersed within surrounding brain parenchyma. It is proposed that, with an interest in the use of stem cell transplants for neurological disease, findings of hyperplasia and apparent atypical integration of a native population of multipotent astrocytic stem cells suggest the need for caution before beginning even autologous neural stem cell transplants.