Blockade of CD62L inhibits CLL cell interaction with vascular endothelium
Dr. Chris Pepper
Brighton & Sussex Medical School
CD62L (L-selectin) is a key adhesion molecule that promotes cell tethering and rolling along the vascular endothelium in the context of trafficking of lymphocytes into lymph nodes, Chronic lymphocytic leukemia (CLL) cells are highly dependent on the lymphoid microenvironment, which makes CD62L a potential therapeutic target in this disease. Here we developed an assay to measure CLL cell interactions with endothelium under shear force using a Bioflux 200 and blocked CD62L using the anti-CD62L antibody DREG-56. CLL cell interactions with endothelium were visualized by time-lapse microscopy and CLL cell movement was tracked and quantified. DREG-56 reduced CLL cell adherence to, and rolling along, the endothelial layer (mean 41.01±23.41 cell tracks vs 26.13±33.32 respectively; P=0.02). This resulted in increased CLL cell velocity (P=0.03) and total distance rolled (P=0.04). DREG-56-treated CLL cells showed a 50% reduction in their ability to arrest on the endothelium compared with untreated controls (P=0.001). Studies using our circulating model of CLL showed that DREG-56 (1g/mL cells) reduced CLL cell migration (P=0.05). We confirmed that ibrutinib reduced CD62L expression on CLL cells (P=0.007) which was not a result of reduced transcription or surface shedding. This reduced the ability of CLL cells to adhere to endothelium (P=0.05); an effect that was significantly enhanced when DREG-56 and ibrutinib were combined (P=0.04). In conclusion, targeting CD62L inhibits CLL cell/endothelial cell interactions and is accentuated by co-administration with ibrutinib. These data imply that some of the clinical effects caused by ibrutinib are due to a reduced capacity of CLL cells to engage endothelium and extravasate.