[1] Inst Biomed Res, Frankfurt, Germany
[2] Univ Med Sch, Dept Hematol Oncol, Frankfurt, Germany
[3] Natl Ctr Tumor Dis, Heidelberg, Germany
[4] Inst Child Hlth, London, England
[5] Univ Zurich, Childrens Hosp, Div Hematol Immunol, Zurich, Switzerland