Novel Conditioning Regimen in Wiskott-Aldrich Syndrome 147 Exon 1 2 3 4 5 6 7 8 9 10-1 10-2 11 12 A B C Normal control Before BMT After BMT Fig. 1. A patient diagnosed as Wiskott-Aldrich syndrome with a large deletion in the exon 1 to 11 of the WAS gene (B), compared with a normal control (A) by polymerase chain reaction (PCR) method, received bone marrow transplantation with a reduced toxicity myeloablative conditioning regimen. Bone marrow examination at one month post-transplantation revealed normal PCR pattern for all exons of the WAS gene (C). TAG CT-3′, exon 10-2 forward 5′-CAG CTA CTG GAC GTT CTG GA-3′and exon 10-2 reverse 5′-CAG TAT CCT GAC TTA GAC GG-3′, exon 11 forward 5′-GAG AAA TGC TCC TTT CCC AG-3′and exon 11 reverse 5′-TAG CCC TGG GAG CCA GGT TT-3′, exon 12 forward 5′-CTC CCA GGG CAT CTT ATC TT-3′and exon 12 reverse 5′- AGC ACA GGG CAG CAA GTA AC-3′. He received trans- plantation from an HLA-A, B, C, DR, and DQ-matched unre- lated male donor confirmed by a high-resolution molecular method, after the conditioning regimen composed of fludara- bine (40 mg/m2 on days -8, -7, -6, -5, -4, -3), busulfan (0.8 mg/kg i.v. q 6 hr on days -6, -5, -4, -3), and thymoglobulin (2.5 mg/kg on days -4, -3, -2). Written informed consent was obtained from parents of the patient before transplanta- tion. Graft versus host disease (GVHD) prophylaxis was com- posed of cyclosporin, methotrexate (15 mg/kg on day 1, 10 mg/kg on days 3 and 6), and thymoglobulin (1.25 mg/kg on days 7, 9, 11). Other supportive care was performed accord- ing to the guideline for stem cell transplantation of our cen- ter (6). The number of infused nucleated cells and CD34-pos- itive cells were 7.6×108/kg and 6.2×106/kg, respectively. He received G-CSF from 7 days after stem cell infusion and the nadir of white blood cells (0.09×109/L) occurred 12 days after transplantation. The number of days required for abso- lute neutrophil count of more than 0.5×109/L and 1.0× 109/L were 14 days and 15 days, respectively, and sponta- neous platelet recovery to more than 20×109/L and 100× 109/L required 16 days and 43 days, respectively. Grade I hematuria, grade II proteinuria, and grade II hepatic toxici- ty occurred during the transplantation but recovered spon- taneously. No other serious complications occurred during transplantation. Grade II acute GVHD occurred 17 days after transplantation but resolved after the treatment with steroid. Bone marrow examination performed at one month post-transplantation revealed the donor type chimerism at 98.4% analyzed by short tandem repeat analysis and the nor- mal polymerase chain reaction pattern in exons of the WAS gene (Fig. 1). After 3 months of transplantation, complete donor type chimerism was achieved. Post-transplatation lym- phoproliferative disease occurred 4 months after BMT but completely resolved with rituximab therapy. Chronic GVHD did not occur, and he is alive at 16 months after transplan- tation without any disease characteristics of WAS. DISCUSSION Purine-analog, in particular, fludarabine, has an advantage over cyclophosphamide. It has an immunosuppressive prop- erty that allows the engraftment of hematopoietic stem cells with minimal extramudullary toxicities (3-5). However, flu- darabine-based non-myeloablative conditioning with a reduc- ed myeloablative activity by reduction in busulfan dosage than the conventional conditioning regimen was not so suc- cessful owing to the poor engraftment in congenital immune- deficiency syndromes (7, 8). Transplantation with fludara- bine-based reduced toxicity but fully myeloablative condi- tioning regimen using the conventional dose of busulfan resulted in good engraftment without serious complications in WAS. 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