Characterization of ectopic colonies that form in widespread areas of the nervous system with neural stem cell transplants into the site of a severe spinal cord injury

Abstract

We reported previously the formation of ectopic colonies in widespread areas of the nervous system after transplantation of fetal neural stem cells (NSCs) into spinal cord transection sites. Here, we characterize the incidence, distribution, and cellular composition of the colonies. NSCs harvested from E14 spinal cords from rats that express GFP were treated withagrowth factor cocktail and grafted into the site of a complete spinal cord transection. Two months after transplant, spinal cord and brain tissue were analyzed histologically. Ectopic colonies were found at long distances from the transplant in the central canal of the spinal cord, the surface of the brainstem and spinal cord, and in the fourth ventricle. Colonies were present in 50% of the rats, and most rats had multiple colonies. Axons extended from the colonies into the host CNS. Colonies were strongly positive for nestin,a marker for neural precursors, and contained NeuN-positive cells with processes resembling dendrites, GFAP-positive astrocytes, APC/CC1-positive oligodendrocytes, and Ki-67-positive cells, indicating ongoing proliferation. Stereological analyses revealed an estimated 21,818 cells in a colony in the fourth ventricle, of which 1005 (5%) were Ki-67 positive. Immunostaining for synaptic markers (synaptophysin and VGluT-1) revealed large numbers of synaptophysin-positive puncta withinthecolonies but fewerVGluT-1 puncta. Continuing expansionofNSC-derivedcell massesinconfined spacesinthe spinal cord and brain could produce symptoms attributable tocompression of nearby tissue. It remains to bedetermined whether other cell types with self-renewing potential can also form colonies.