BACR1
Homotypic adhesion and lysosome-mediated cell death evoked by anti-CD20 (Tositumomab) and HLA DR monoclonal antibodies
Andrey Ivanov1, Stephen Beers2, Claire Walshe2, Jamie Honeychurch2, Waleed Alduaij1, Kerry Cox2, Kathleen Potter2, Stephen Murray1, Claude Chan2, Tetyana Klymenko1, Katrina Erenpreisa3, Martin Glennie2, Tim Illidge1, Mark Cragg2
1Paterson Institute for Cancer Research, Manchester, UK, 2University of Southampton, UK, 3Biomedical Research and Study Centre, Riga, Latvia
Monoclonal antibodies (mAb) are becoming increasingly utilized in the treatment of lymphoid disorders. Although Fc-FcγR interactions are thought to explain much of their therapeutic effect, this does not explain why certain mAb specificities are more potent than others. Previously, we demonstrated that Type II anti-CD20 mAb were able to evoke a non-apoptotic cell death that appeared linked with the induction of homotypic adhesion (HA).
Here, we reveal that peripheral re-localization of actin is critical for the HA and cell death induced by both Type II anti-CD20 mAb and HLA DR Class II mAb in both lymphoma cell lines and primary CLL cells. Interactions between cells undergoing HA resulted in mutual exchange of plasma membrane components and the formation of cytoplasmic bridges between cells. Subsequent experiments involving FRAP revealed that actin dynamics are rapidly altered after mAb stimulation and that cell-cell contact is critical for efficient cell-death. The mode of cell death engaged is non-apoptotic, non-autophagic and dependent on both the integrity of plasma membrane cholesterol and activation of the V-type ATPase. This cytoplasmic cell death involves lysosomes which swell and then disperse their contents, including cathepsin B, into the cytoplasm and surrounding environment. The resulting loss of plasma membrane integrity occurs in the absence of DNA fragmentation and is independent of caspase and Bcl-2 control.
These experiments provide new insights into how two clinically relevant mAb elicit cell death and show for the first time that this occurs through a previously unrecognized lysosome-dependent pathway.
