Long-term survive of ex-thalassemic patients with persistent mixed chimerism after bone marrow transplantation

Twenty-six transplanted thalassemic patients out of 295 analyzed, showed th e presence of persistent mixed chimerism, over a period of time varying bet ween 2 and 11 years after BMT, Despite the presence of large numbers of res idual host cells, these transplanted thalassemic patients no longer require red blood cell transfusions and have a functional graft, producing suffici ent levels of hemoglobin A ranging from 8.3-14.7 g/dl, These ex-thalassemic patients with persistent mixed chimerism, although they did not achieve co mplete donor engraftment are no longer exposed to the risk of graft rejecti on. The mechanisms underlying this apparent state of tolerance or education in these patients are at the present time unknown. However, these observat ions may be useful for physicians involved in defining optimal strategies f or clinical gene therapy, in utero hematopoietic stem cell transplantation and adoption of less toxic conditioning regimens in mini-transplantation.