METHODS
Among 7 patients with RP-mutated DBA who received HCT in Kyushu University Hospital (n=6) and Kobe Children’s Hospital (n=1) from 2000 to 2020, the latest six patients received targeted BU and fludarabine (FLU) conditioning in the first HCT. BU was administered intravenously four times daily for four days. The cumulative area-under-the-curve (AUC) of BU was calculated by JMP Pro 11 (version 11.2.0 for Windows; JMP Inc., SAS Institute Japan) based on the results of a test-dose using the Dried Blood Spot method. Based on the transfusion-dependent periods and serum ferritin levels, the target of cumulative AUC was adjusted to 60–75 mg/L×h (65~80% of the conventional myeloablative cumulative AUC [85–95 mg/L×h]). FLU was administered at 180 mg/m2 in four to six divided doses. Rabbit anti-thymocyte globulin (rATG) (2.5–5.0 mg/kg Thymoglobulin, Genzyme, Boston, MA) was added in five patients. Tacrolimus and short-term methotrexate were used for acute GVHD prophylaxis in all patients. The date of engraftment was defined as the first of three consecutive days when the neutrophil count was >0.5×109/L. Donor chimerism was assessed by sex chromosome fluorescence in situ hybridization or short tandem repeats.