From IRCCS Ospedale Pediatrico Bambino Gesù, Sapienza, University of Rome, Rome (F.L., M. Algeri); Ann and Robert H. Lurie Children's Hospital of Chicago, Northwestern University, Chicago (A.A.T., J.S.); Children's Hospital of Philadelphia and Perelman School of Medicine at the University of Pennsylvania, Philadelphia (J.L.K., T.S.O.); University College London Hospital (J.B.P., B.C.) and University College London Great Ormond Street Institute of Child Health and Great Ormond Street Hospital NHS Trust (A.J.T., P.J.A.) - all in London; Ramathibodi Hospital, Mahidol University, Bangkok, Thailand (S.H., U.A.); the Department of Pediatric Hematology, Oncology, and Stem Cell Transplantation in Children (M.G.S.) and the Institute of Experimental Hematology (A.S.), Hannover Medical School, Hannover, and GeneWerk, Heidelberg (M.S., I.L.) - both in Germany; Hôpital de la Timone (I.T.) and Institut Paoli-Calmettes Comprehensive Cancer Center (C.C.) - both in Marseille, France; the University of California, San Francisco, Benioff Children's Hospital, Oakland (A.L., M.C.W.); and the Division of Hematology-Oncology, Boston Children's Hospital, Harvard Medical School, Boston (A.S.), and Bluebird Bio, Cambridge (H.E., R.G., M. Asmal, R.A.C.) - all in Massachusetts.