1. From the Stem Cell Biology Program, University of Louisville, Louisville, KY; the Protein Chemistry Laboratory, Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA; the Joint Program in Transfusion Medicine, Harvard Medical School, Boston, MA; Department of Transplantology, Children's Hospital, Jagiellonian University, Cracow, Poland; and the Department of Medicine, University of Alberta and Canadian Blood Services (CBS), Edmonton, AB, Canada.