Ex Vivo Chemopurging of Autologous Bone Marrow with 4-Hydroperoxycyclophosphamide to Eliminate Occult Leukemic Cells

Abstract

The application of autologous bone marrow transplantation (ABMT) in treating acute leukemias in children has been limited by the presence of residual occult viable leukemic cells in the marrow cell suspension. One approach to this problem is the ex vivo treatment ("purging") of the autograft to eradicate these tumor cells yet spare the normal lymphohematopoietic stem cells. Initial studies of acute myeloid leukemia (AML) in a rodent model demonstrated that incubation with 4-hydroperoxycyclophosphamide (4HC), a congener of cyclophosphamide and an active alkylating agent in aqueous solution, could effectively eliminate viable AML cells from marrow cell suspensions without apparent toxicity to normal stem cells. We have conducted clinical trials of ABMT with 4HC-treated marrow in children with acute leukemia in remission; marrow was collected, treated ex vivo with 4HC (100 micrograms/ml), and cryopreserved in liquid nitrogen until reinfusion. Children received pre-ABMT conditioning with either high-dose cyclophosphamide and total body irradiation (CY-TBI) for acute lymphocytic leukemia (ALL) or high-dose busulfan and cyclophosphamide (BU-CY) for AML. Of nine children who underwent ABMT with 4HC-treated marrow for ALL in second complete remission (CR2), all relapsed (eight in the marrow, one in the central nervous system) at a median of 5 months (range, 2-17) after ABMT and all have died with relapsed ALL or as a consequence of its treatment. Twenty-nine children with AML (five in CR1, 24 in CR2) received autografts with chemopurged marrow at a median remission duration of 3 months (range, 2-15). Three patients died from sepsis during aplasia; 10 children (one in CR1 and nine in CR2) relapsed with AML at a median of 7 months (range, 2-23) after ABMT, for an actuarial relapse rate of 47%. Sixteen patients with AML (four in CR1, 12 in CR2) are in unmaintained remission at a median of 16 months (range, 6-102) after ABMT, for an actuarial disease-free survival of 49%. Although ABMT with 4HC-treated marrow appears to have a limited role in the treatment of children with ALL who lack a suitable related donor, the results in AML are encouraging and compare favorably with both syngeneic and allogeneic BMT in similar groups of patients.