MODULATION OF THE B-CELL RECEPTOR SIGNALING BY LENALIDOMIDE AND OFATUMUMAB IN CHRONIC LYMPHOCYTIC LEUKEMIA

Introduction: Lenalidomide is an immunomodulatory agent with therapeutic activity in chronic lymphocytic leukemia (CLL). Ofatumumab is a fully human anti-CD20 monoclonal antibody with enhanced antibody dependent and complement dependent cytotoxicity. In CLL, the combination of lenalidomide and anti-CD20 monoclonal antibodies seems to increase the response rate. The aim of this study is evaluating the effects of lenalidomide and ofatumumab -as single agents or in combination (lenofa)- on the activation state of signaling proteins on the route of the B-cell receptor (BCR), which represents the most prominent pathogenic mechanism in CLL. Methods: BCR signaling proteins, i.e. SYK, ERK1/2, PLC-γ1, BTK, Akt, NF-κB were functionally characterized in leukemic cells from CLL patients in the presence of lenalidomide, ofatumumab or their combination using a multiparametric flow cytometry-based assay. This method allows to measure, simultaneously and quantitatively, at the single cell level, phosphorylation status of signaling proteins. Results. Lenalidomide reduced the basal phosphorylation of ERK1/2, PLC-γ1 whereas had no effect on SYK, BTK, Akt and NF-κB phospho-state. Treatment with ofatumumab alone induced reduction of SYK and ERK1/2 phosphorylation whilst had no effect on PLC-γ1 and NF-κB. In contrast, ofatumumab induced a significant increase of BTK and Akt phosphorylation. When used in combination, the presence of lenalidomide reduced the stimulatory effect of ofatumumab on Akt and BTK, whereas did not change the phosphorylation level of SYK, ERK1/2, PLC-γ1, NF-κB. Conclusions: We showed that lenalidomide and ofatumumab exhibit modulating properties acting on BCR signaling proteins involved in leukemia cell proliferation and survival.