Allogeneic stem cell transplantation for inherited metabolic disorders: 35 years’ experience at a single institution

Hematopoietic stem cell transplants for inherited metabolic disorders performed at Tokai University Hospital between June 5, 1986, and May 28, 2021, were analyzed and compared between the period before 2007 and the period from 2007 onward based on availability of medical resources. Transplants were performed for 38 patients with mucopolysaccharidosis, 33 with adrenoleukodystrophy, and 16 with another disorder. Before 2007, oral busulfan-based regimens were mainly used. From 2007 onward, intravenous busulfan-based regimens or 4 Gy of thoracoabdominal irradiation (TAI), fludarabine, and melphalan (Mel)/treosulfan were adopted. Between 2002 and 2010, adrenoleukodystrophy was treated with 12 Gy of TAI and Mel. HLA-identical sibling bone marrow was used in 43% of cases before 2007 and 15% from 2007 onward, while alternative donors were selected for other transplants. Overall survival and event-free survival (EFS) before 2007 and from 2007 onward were 76% and 62%, and 97% and 85%, respectively (P = 0.006 and 0.017). Transplant era predicted superior overall survival and EFS, while myeloablative conditioning also predicted EFS. The incidence of primary graft failure decreased from 2007 onward, especially in cord blood transplant when 4 Gy of TAI with 150 mg/m² fludarabine and 180 mg/m² Mel or 42 g/m² treosulfan were used as conditioning.