1. Department of Neurosurgery, University of Minnesota Medical School, Minneapolis, MN 55455.
2. Department of Neurosurgery, First Hospital of China Medical University, Liaoning, P.R. China 110001.
3. Cancer Center, University of Minnesota Medical School, Minneapolis, MN 55455.
4. Stem Cell Institute, University of Minnesota Medical School, Minneapolis, MN 55455.
5. Department of Pediatrics, University of Minnesota Medical School, Minneapolis, MN 55455.