Immunomagnetic depletion of malignant cells from autologous bone marrow graft: from experimental models to clinical trials.

Using experimental modes with normal allogeneic bone marrow (BM) contaminated with Burkitt or neuroblastoma cell lines, and a liquid culture assay, we demonstrated that, when used in optimal conditions, the immunomagnetic depletion technique permitted a reproducible elimination of 3-4 log malignant cells. Results were very similar to those obtained with the complement lysis procedure in Burkitt lymphoma. This immunomagnetic procedure was used in 123 cases of autologous bone marrow transplantation (ABMT) in children with neuroblastoma. The analysis of the cases demonstrated, first, that the procedure induced a significant loss of mononuclear cells but was not toxic for BM precursors. Delays to engraftment observed in a few patients were probably due to the combination of pejorative factors, especially the damage caused to the micro-environment by previous heavy and prolonged chemotherapy or the double ABMT programme. Second, patients presented with profound T-cell defect with undetectable IL2 secretion up to 1 year post-graft but they all had normal NK functions from the first month post-graft, these functions exceeding normal values on the second and third months post-graft. Finally, in 20 cases, dual-immunofluorescence staining permitted the demonstration that the autograft contained malignant cells before purging that were eliminated by the immunomagnetic depletion.