Quantitation of tumor cell removal from bone marrow: a preclinical model

We have developed a multiassay system consisting of fluorescence microscopy, immunocytology and tumor colony assay to monitor the removal of tumor cells from bone marrow. This system was tested in preclinical purging experiments in which neuroblastoma cells were seeded into bovine marrow and purged by treatment with monoclonal antibodies and immunomagnetic beads. Eight experiments were performed on two different neuroblastoma cell lines seeded at 2% and/or 5% contamination. We consistently demonstrated greater than a 3 log removal with one cycle of antibody/bead treatment and greater than a 1 log further reduction by addition of a second cycle. We also demonstrated removal of all detectable tumor stem cells by this purging method. We feel that this system will prove valuable for monitoring ex vivo tumor removal in future clinical studies and should be considered for use in other purging trials.