Lead Sponsor: Boston Children's Hospital

Collaborators: National Institutes of Health (NIH), National Heart, Lung, and Blood Institute (NHLBI), Blood and Marrow Transplant Clinical Trials Network, Center for International Blood and Marrow Transplant Research, North American Pediatric Aplastic Anemia Consortium, Pediatric Transplantation and Cellular Therapy Consortium

Intervention / Treatment: DRUG: Cyclophosphamide, DRUG: Methotrexate, DRUG: cyclosporine, DRUG: Fludarabine, PROCEDURE: Immunosuppressive Therapy (IST), RADIATION: low-dose total body irradiation (TBI), DRUG: horse anti-thymocyte globulin (ATG), DRUG: rabbit anti-thymocyte globulin (ATG), PROCEDURE: Matched Unrelated Donor Hematopoetic Stem Cell Transplant

Lead Sponsor: Center for International Blood and Marrow Transplant Research

Intervention / Treatment: DRUG: Busulfan, DEVICE: Cell processing for TCRαβ+/CD19+ depletion

Lead Sponsor: North American Consortium for Histiocytosis

Collaborators: Histiocyte Society

Intervention / Treatment: DRUG: Prednisone, DRUG: Methotrexate, DRUG: 2-chlorodeoxyadenosine, PROCEDURE: hematopoietic stem cell transplantation (RIC-HSCT), BIOLOGICAL: Intravenous immunoglobulin, DRUG: Vinblastine, DRUG: mercaptopurine, DRUG: INDOMETHACIN, DRUG: Cytosine Arabinoside