Possible misinterpretation of the mode of action of therapeutic antibodies in vitro: homotypic adhesion and flow cytometry result in artefactual direct cell death

To the editor: Two groups have recently proposed that type II anti-CD20 monoclonal antibodies (mAbs) B1 (tositumomab) and GA101, as well as anti–HLA-DR antibody (L243), induce strong homotypic adhesion and direct cell death. They claim, on the basis of annexin V, propidium iodide (PI), and flow