Removal of cells from a malignant B-cell line from bone marrow with immunomagnetic beads and with complement and immunoglobulin switch variant mediated cytolysis.

In this report we describe the generation of complement (C') fixing IgG2b CD19 and CD22 monoclonal antibodies (mAbs) by the isolation of immunoglobulin (Ig) class switch variants using a simple and efficient method for the selection of spontaneously mutating hybridomas. The aim of this study was to compare the efficacy of C'-mediated cytolysis vs immunomagnetic (IB) depletion of tumor cells from mixtures of malignant B cells and normal bone marrow. In a clonogenic assay employing the B-cell lines Namalwa and OCI.LY1, we found that the use of immunomagnetic beads warranted a highly efficient tumor cell removal independent of the Ig isotype of the mAbs used. Elimination of up to 4 log was achieved using a cocktail consisting of CD19, CD20, CD22 and CD37 B-cell mAbs. A less efficient killing of 2 log was obtained by C' lysis using IgM mAbs, while only about 1 log tumor cell elimination was obtained using IgG2b mAbs. Immunomagnetic purging, besides being more effective than C'-mediated cytolysis, is easier to handle and more rapid.