1. From the Department of Hematology and Oncology, Hannover Medical School, Hannover, Germany; the Division of Experimental Hematology, Cincinnati Children's Research Foundation, Cincinnati, OH; the Departments of Neuroanatomy and Bone Marrow Transplantation, University Hospital Eppendorf, Hamburg, Germany; and the Department of Cell and Virus Genetics, Heinrich Pette Institute, Hamburg, Germany.