Malignant leukemic cell separation by iron colloid immunomagnetic adsorption

We describe an immunomagnetic assay applicable to bone marrow purging of leukemic patients before an autologous bone marrow transplantation. An iron colloidal suspension with a CD10 monoclonal antibody (MoAb) against the common acute lymphoblastic leukemia antigen (CALLA) covalently bound to the surface of the particles has been used. NALM-6 cells, a pre-B leukemic cell line expressing the CALLA, were labeled with supravital DNA dye (Hoechst 33342), mixed with peripheral blood, and incubated with the MoAb coated to iron particles. Using this reagent, at a cell concentration of 2000/microliters, a purging effect greater than 3.5 logs is observed with 0.1 mg of coated particles. Three successive rounds of treatment with the same coated particles at the same dose showed approximately the same depletion after each treatment. The recovery of clonogenic myeloid progenitors (granulocyte-macrophage colony-forming units; CFU-GM) is around 75%. No depletion was observed when the iron particles were not attached to the CD10 MoAb, or when they were attached to a MoAb not recognizing CD10+ cells. A comparison with another commercially available magnetic support was also performed in order to evaluate the performance of our assay, which appears simple, efficient, cheap, and capable of handling large volumes of cells in sterile conditions and minimal time.