Elimination of Malignant Clonogenic Breast Cancer Cells from Human Bone Marrow1

Autologous bone marrow transplantation is a promising approach to the treatment of breast cancer but is at present limited to patients without bone marrow metastases. To eliminate malignant clonogenic breast cancer cells from normal human bone marrow, immunomagnetic separation has been combined with chemoseparation using 4-hydroperoxycyclophosphamide. Breast cancer cell lines have been mixed with a 10-fold excess of irradiated human bone marrow from normal donors. Mixtures have been incubated with a combination of five different monoclonal antibodies which bind to epithelial cell surface antigens of Mr42,000, 55,000, 72,000,200,000, and >200,000. Antiglobulin coated microspheres which contained magnetite were added, and tumor cells were trapped in a magnetic field. Elimination of tumor cells from the decanted marrow was measured in a limiting dilution assay. Two treatments with antibody and microspheres permitted elimination of 2-4 logs of clonogenic breast cancer cells, depending upon the cell line studied. Similar treatment of nonirradiated normal marrow failed to affect levels of colony forming units-granulocyte-macrophage significantly. Use of immunomagnetic purging in combination with 4-hydroperoxycyclophosphamide eliminated up to 5 logs of tumor cells but reduced the recovery of colony forming units-granulocyte-macrophage. If prompt engraftment is observed following reinfusion of similarly treated marrow in phase I trials, these techniques should permit extension of autologous bone marrow transplantation to a larger population of breast cancer patients.