Note: Funding Information: 1Department of Clinical Chemistry and Haematology, University Medical Center Utrecht, Utrecht University, the Netherlands; 2Van CreveldKliniek, University Medical Center Utrecht, Utrecht University, the Netherlands; 3Pediatric Blood and Marrow Transplantation Program, Wilhelmina Children’s Hospital, University Medical Center Utrecht, Utrecht University, the Netherlands; 4Hematology Unit, Anemia Physiopathology Unit, Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Milan, Italy; 5Department of Pediatrics and Child Neurology, Oita University Faculty of Medicine, Hasama, Yufu, Japan; 6Department of Transfusion Medicine and Cell Processing, Faculty of Medicine, Tokyo Women's Medical University, Japan; 7Directora Unidad Pediátrica de Trasplante Hematopoyético, Hospital Santa Creu i Sant Pau, Barcelona, Spain; 8Department of Hematology and Oncology, Shanghai Children’s Medical Center. Shanghai Jiao Tong University School of Medicine, China; 9Van Creveldkliniek, Department of Internal Medicine, University Medical Center Utrecht, Utrecht University, the Netherlands; 10Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand; 11Division of Stem Cell Transplantation, University Children`s Hospital, Zurich, Switzerland; 12Department of Pediatric Oncology, VU University Medical Center, Amsterdam, the Netherlands; 13Department of Pediatric Haematology, Leiden University Hospital, the Netherlands; 14Department of Internal Medicine, University Medical Center Utrecht, Utrecht University, the Netherlands; 15Servicio de Hematología, Hospital Universitario Marqués de Valdecilla, Santander, Spain; 16Servicio Hemato-Oncología Pediatrica, Hospital Infantil Universitario Niño Jesús, Madrid, Spain; 17Differentiation and Cytometry Unit, Hematopoietic Innovative Therapies Division, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Centro de Investigaciones Biomédicas en Red de Enfermedades Raras (CIBER-ER), Madrid, Spain and 18Advance Therapies Mixed Unit, Instituto de Investigación Sanitaria-Fundación Jiménez Díaz (IIS-FJD), Madrid, Spain *SvS and MB contributed equally to this work Correspondence: r.vanwijk@umcutrecht.nl doi:10.3324/haematol.2017.177857 Information on authorship, contributions, and financial & other disclosures was provided by the authors and is available with the online version of this article at www.haematologica.org.