Elimination of malignant tumor cells from human bone marrow using monoclonal antibodies and immunomagnetic beads.

Conditions for depletion of malignant tumor cells from human bone marrow using monoclonal antibodies and immunomagnetic beads were studied. Human hepatoma HA22T/VGH cells labeled with the supravital DNA binding dye Hoechst 33342 were seeded into normal human bone marrow at a ratio of tumor cells to marrow cells of 1:9. The immunobeads used were M-450 magnetic microspheres coated with sheep anti-mouse immunoglobulin. The marrow-tumor cell mixtures were incubated with a panel of antihuman hepatoma cell monoclonal antibodies (9B2, E10A1, and C2E6) at 4 degrees C for 40 min, and then reacted with immunomagnetic beads for 60 min longer. After incubation, the bead-coated tumor cells were removed from the marrow with a magnetic particle concentrator. Tumor residual was measured in a limiting dilution test, and the recovery of marrow progenitor cells was assessed by CFU-GM assay. The efficiency of tumor depletion was closely related to the amount of monoclonal antibody bound to tumor cells and the immunobead/tumor cell ratio. Monoclonal antibodies used in combination were more effective than their individual use alone. Two cycles of purging with both monoclonal antibodies and immunomagnetic beads resulted in an apparent improvement in tumor depletion as compared with one cycle. Using a cocktail of three monoclonal antibodies and purging the marrow for two cycles, 4 to 5 logs of tumor cells could be removed with a sufficient recovery (70%) of CFU-GM. However, multiple purging treatments (> or = 3 cycles) would be apparently damaging to hematopoietic progenitor cells.