Reinfusion of leukemic cells with the autologous marrow graft: preclinical studies on lodging and regrowth of leukemia.

To evaluate in quantitative terms the contribution of leukemic cells present in the autologous marrow graft to the occurrence of leukemia relapse after autologous bone marrow transplantation, preclinical studies were performed in a rat model for human acute myelocytic leukemia (BNML). Firstly, the number of leukemic cells which--after intravenous transfer--cause death from leukemia in 50% of the recipient rats proved to be 24.7 cells. Secondly, it appeared that the regrowth of leukemic cells in rats heavily pretreated with high-dose cyclophosphamide and total body irradiation was significantly hampered as compared with non-pretreated controls as judged by survival times (37 and 31 days, respectively after 10(3) BNML cells i.v.). The most likely explanation is treatment-induced damage to the microenvironment. Differences in patterns of lodging of infused leukemic cells were ruled out by comparing the uptake of 51Cr-labeled BNML cells in various organs. Finally, extrapolated from the available rat data on log leukemic cell kill induced by high-dose chemoradiotherapy, an hypothesis is presented relating the total tumor load in man to the clinical outcome of autologous bone marrow transplantation. From this hypothesis it is derived that the minimal number of leukemic cells that causes leukemia upon intravenous transfer varies between 10(4) and 10(6).