Abstracts

Rationale: Adult human neural progenitor cells (AHNPs) have been identified in brain specimens from elective surgery performed for the treatment of epilepsy (Walton et al. 2006). These cells could potentially be used to treat variety of neurological diseases by replenishing populations of neurons lost due to injury or degenerative processes. Cortical dysplasia (CD) is a common cause of intractable epilepsy and loss of inhibitory interneurons may contribute seizure susceptibility in some types of human CD. We investigated the survival and development of AHNPs transplanted into an animal model of CD, in utero irradiation in rats. This model is appropriate for this purpose because of a demonstrated loss of cortical interneurons in these animals. Methods: Timed-pregnant rats were obtained and exposed to 225 cGy of external radiation on embryonic day (E17). AHNPs were obtained from hippocampal specimens from patients with intractable epilepsy. AHNPs were expanded for multiple passages in vitro before being transduced with a lentiviral vector encoding recombinant human GFP. GFP-positive AHNPs were FACS sorted and expanded until transplantation. On post-natal day 1 (P1), 50,000 cells were grafted into the lateral ventricle or neocortex of control (N=26) and irradiated (N=22) rat pups using a Hamilton syringe. Animals were sacrificed for histology and immunohistochemistry on P14-35. Results: After intraventricular injections, AHNPs spread throughout both hemispheres of the brain and developed into mature-appearing neurons. They were seen more frequently in the hippocampus and less frequently in the neocortex. Direct intracortical injections resulted in more localized accumulations of AHNP-derived neurons. Survival and dispersion of transplanted neurons did not appear to be impaired in irradiated rats. By P35, neurons with both pyramidal and non-pyramidal morphologies could be seen in all subfields of the hippocampus and dentate gyrus. They were also seen throughout all layers of the neocortex. The morphology of the AHNP-derived neurons was appropriate to the location of the cells. GFP-labeled puncta that appeared to be pre-synaptic terminals could be seen surrounding the somata of adjacent host neurons; this raises the possibility of functional communication between transplanted and host neurons. Some neurons co-expressed pavalbumin and others co-expressed somatostatin. This suggests that some neurons differentiated into specific subtypes of inhibitory interneurons. Conclusions: AHNPs are capable of dispersing, migrating and surviving when transplanted into immature rat brain. They can also develop morphological characteristics of mature neurons of various sub-types that appear appropriate for the host structures in which they reside. Transplantation of AHNPs appears to work as well in irradiated rats as in controls. This provides encouraging preliminary data regarding the potential of these cells for neurorestorative therapy in human CD.