Autologous transplantation of a bone marrow graft manipulated by chemoseparation to eliminate residual tumor cells

History and Development of Autologous Stem Cell Transplantation for Acute Myeloid Leukemia

This review describes the development of cryopreservation, the birth of autologous stem cell transplantation (ASCT) and its past and present use to consolidate adult patients with acute myelogenous leukemia (AML). It summarizes the first autografts in patients in relapse, the experience of autografting in complete remission (CR), using bone marrow unpurged or purged in vitro with cyclophosphamide-derivatives, and the important shift to peripheral blood stem cells. The review also discusses the results of recent studies in favor of the use of ASCT to consolidate good- and intermediate-risk patients who reach CR with no detectable minimal residual disease, and those which support the inclusion of maintenance therapy post autograft with hypomethylating agents, anti-BCL-2, and, possibly, in the future, anti AML chimeric antigen receptor-T cells. Carefully applied to well-selected patients, ASCT may regain interest, because of its simplicity, its reduced toxicity, lower non-relapse mortality and better quality of life.

4-Hydroperoxycyclophosphamide inhibits proliferation by human granulocyte-macrophage colony-forming cells (GM-CFC) but spares more primitive progenitor cells

Despite its considerable toxicity to haemopoietic colony-forming cells, 4-hydroperoxycyclophosphamide (4-HC) has successfully been used to purge marrow of leukaemic cells before it is used to rescue patients from high-dose chemoradiotherapy. These conflicting observations indicate that haemopoietic progenitor cells that are not detected by the established colony-forming assays survive exposure to 4-HC and repopulate the marrow. The recent finding that murine spleen colony-forming cells (CFU-S) are resistant to 4-HC [Porcellini A, et al. (1983) Expl Hemat. 11 (suppl 14) 331 (abstract)] [14] also indicates that sensitivity to 4-HC can be used to distinguish primitive progenitor cells from committed progenitor cells. As part of a study on the nature of a population of blast colony-forming cells in human bone marrow, we tested their sensitivity to 4-HC to see whether they also are spared by the drug. We found that 4-HC had much less effect on the blast colony-forming cells than on the granulocyte-macrophage colony-forming cells (GM-CFC). This result suggests that the blast-colony-forming cells may be early human haemopoietic progenitor cells.

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).

No preferential sensitivity of clonogenic AML cells to ASTA-Z-7557

ASTA-Z-7557, an in vitro active metabolite of cyclophosphamide, has recently been introduced to purge autologous bone marrow grafts of patients with AML. The rationale of this approach assumes a relatively higher sensitivity of leukemic cells to the drug as compared to that of normal marrow precursors. We have investigated in direct comparison the sensitivity to ASTA-Z-7557 of normal bone marrow progenitors (GM-CFC and BFU-E) and clonogenic leukemic cells (L-CFC). Normal bone marrow cells and purified leukemic blast cells were exposed to varying concentrations of the drug. Dose-response relationships did not indicate a selective cytotoxic susceptibility of L-CFC to ASTA-Z-7557. The recovery of bone marrow precursors following exposure to ASTA-Z-7557 depended on the cell concentration during exposure and was higher for 2 X 10(7) cells/ml than for 1 X 10(6)/ml. To mimic minimal residual leukemia cell mixtures of 95% irradiated normal bone marrow cells with 5% leukemic blast cells were exposed to ASTA-Z-7557. In this mixture killing of L-CFC was largely decreased. These data suggest that in vitro incubation of autologous bone marrow grafts of patients with minimal residual leukemia with ASTA-Z-7557 might not offer a therapeutic advantage.