1. From the Centre for Allogeneic Stem Cell Transplantation and Department of Clinical Immunology, Karolinska University Hospital, Stockholm, Sweden; the Department of Bone Marrow Transplantation, University Hospital Essen, Germany; the Clinic of BMT, Haematology and Oncology, Idar-Oberstein, Germany; and the Department of Paediatric Haematology, Oncology and Endocrinology, University Hospital Essen, Germany.