HLA-haploidentical hematopoietic stem cell transplantation in pediatric patients with hemoglobinopathies: current practice and new approaches.

We review current approaches in HLA-haploidentical hematopoietic stem cell transplantation (haplo-HSCT) for pediatric patients with hemoglobinopathies with a focus on recent developments using TCRα/β+/CD19+ depleted grafts in patients with β-thalassemia major (TM) or sickle cell disease (SCD) in two European transplant units. Eleven TM and three SCD patients (Roma cohort) received a preparative regimen consisting of busulfan/thiotepa/cyclophosphamide/ATG preceded by fludarabine/hydroxyurea/azathioprine. The preparative regimen for 5 SCD patients included treosulfan/thiotepa/fludarabine/ATG (Berlin pilot cohort). All grafts were PBSC engineered by TCR-α/β+/CD19+ depletion. In both cohorts, rates for graft failure, treatment related mortality (TRM) and GvHD were encouraging. Overall survival (OS) and disease-free survival (DFS) in the Roma cohort were 84 and 69%, respectively, while OS and DFS are 100% in the Berlin cohort. Immune reconstitution was satisfactory. Although asymptomatic viral reactivation was common, no severe viral infection occured. These data confirm that TCR-α/β+/CD19+ depletion is a well-suited haplo-HSCT strategy for children with hemoglobinopathies. We discuss the results in the context of additional optimization strategies and introduce our concepts for multicenter trial protocols in Germany.