Influence of conditioning on the outcome of allogeneic bone marrow transplantation

Allogeneic bone marrow transplantation is widely used for the treatment of various hematologic disorders. The results are quite reproducible from center to center with a mean disease-free survival of 50%, which varies from 10% in patients transplanted in relapse to 70% in young patients transplanted in first complete remission or in the chronic phase of chronic myeloid leukemia. Relapse is one of the main complications, and its frequency increases with disease status and the use of T cell depletion and the subsequent loss of the graft versus leukemia effect of transplanted allogeneic cells. New agents such as high dose ARA-C, VP 16, Myleran, and Melphalan have been studied in Phase I-II studies. Different modalities of total body irradiation, that is, single dose or fractionated or hyperfractionated doses, have been used. None of these new modalities has modified significantly the long-term disease-free survival rate because of the toxicity of any attempt to diminish the rate of relapse with intensified regimens. Single dose total body irradiation of 10 Gy seems to reduce the risk of leukemic relapse when compared with 12 Gy fractionated total body irradiation, especially when the marrow is T depleted.