Phenotypic cure 6 years after bone marrow transplantation in a β-thalassemia patient

A β-thalassemia major (TM) male patient underwent bone marrow transplantation from a fully matched carrier sister at age three. He continued to be transfusion dependent although chimerism evaluation, using analysis of the β-globin gene mutation, showed 90-98% donor cells in peripheral leukocytes after 3 months and 82-90% donor cells in the bone marrow after 26 and 30 months. Clinical improvement occurred gradually, and the patient became transfusion free 6 years posttransplant. We reason that an exceptional slow displacement of host red-blood-cell lineage took place that was not evident from the high level of chimerism found in peripheral leukocytes and bone marrow.