Activity of the CD20-directed monoclonal antibody GA101 relative to rituximab in Waldenstrom's macroglobulinemia (WM), and applicability to patients expressing FcγRIIIA-158 F/F.

Abstract

8112 Background: Rituximab alone and in combination is an important mainstay of therapy in WM. Rituximab interacts with Fcγ receptors whose binding is largely influenced by polymorphisms in FcγRIIIA-158. Polymorphisms in FcγRIIIA-158 predict overall response to rituximab alone, as well as attainment of VGPR or CR with rituximab combination therapy in WM. Patients expressing V/V or V/F at FcγRIIIA-158 show improved outcomes versus F/F. We therefore have sought novel antibodies which can improve outcomes for patients expressing FcγRIIIA-158-F/F. GA101 is a novel humanized anti-CD20 antibody with a glyco-engineered Fc receptor domain that exhibits increased FcγRIIIA binding. Methods: We examined ADCC activity for GA101 versus rituximab using 1) healthy donor derived NK cells which were genotyped for polymorphic expression at FcγRIIIA-158 against BCWM.1 cells; as well as autologous NK cells which were genotyped against WM patient LPCs. Results: These studies showed a 2.88, 1.88, and 1.22 fold increase in ADCC activity by healthy donor NK cells expressing FcγRIIIA-158 F/F, V/F, and V/V, respectively, against BCWM.1 WM cells for GA101 versus rituximab. Moreover, ADCC activity was enhanced by 1.98, 1.37 and 1.38 fold for autologous NK cells expressing FcγRIIIA-158 F/F, V/F, and V/V, respectively against WM LPCs. In addition, we also observed direct cytotoxicity against BCWM.1 and primary WM patient LPCs by GA101; in comparison, little or no direct apoptotic activity was observed by rituximab. Western blot analysis showed no activation of caspases 3, 6, 7, 9 in GA101 treated BCWM.1 cells, though nuclear translocation of apoptosis inducing factor (AIF) was observed by immunofluorescence microscopy. Conclusions: GA101 is associated with enhanced ADCC activity relative to rituximab by NK cells, particularly those expressing FcγRIIIA-158 F/F. In addition, GA101 initiates direct cell death in WM LPCs through a caspase independent manner. These studies provide the framework for the investigation of GA101 in WM, and suggest potential benefit for those patients who express FcγRIIIA-158 F/F. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Biogen Idec, Celgene, Genetic Technologies, Millennium Biogen Idec, Celgene, Millennium Celgene, Millennium