1. Transplantation Research Center (P.F.), Nephrology Division, Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115;
2. San Raffaele Scientific Institute (P.F.), 20132 Milan, Italy;
3. Bone Marrow Transplantation Unit (J.V.), School of Medicine of Ribeirão Preto, University of São Paulo, São Paulo 01223-000, Brazil;
4. University of Iowa and VA Medical Center (N.Z.), Iowa City, Iowa 52242