A combination of an anti-SLAMF6 antibody and ibrutinib efficiently abrogates expansion of chronic lymphocytic leukemia cells

// Burcu Yigit 1 , Peter J. Halibozek 1 , Shih-Shih Chen 2 , Michael S. O’Keeffe 1 , Jon Arnason 3 , David Avigan 3 , Valter Gattei 4 , Atul Bhan 5 , Osman Cen 6 , Richard Longnecker 6 , Nicholas Chiorazzi 2 , Ninghai Wang 1 , Pablo Engel 7 , Cox Terhorst 1 1 Division of Immunology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA 2 Karches Center for Chronic Lymphocytic Leukemia Research, The Feinstein Institute for Medical Research, Manhasset, NY, USA 3 Division of Hematology/Oncology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA 4 Clinical and Experimental Onco-Hematology Unit, Centro di Riferimento Oncologico, I.R.C.C.S., Aviano, Italy 5 Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA 6 Department of Microbiology and Immunology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA 7 Immunology Unit, Department of Cell Biology, Immunology and Neurosciences, Medical School, University of Barcelona, Barcelona, Spain Correspondence to: Burcu Yigit, email: byigit@bidmc.harvard.edu Cox Terhorst, email: cterhors@bidmc.harvard.edu Keywords: CLL, TCL1-192, SLAMF6, BCR, ibrutinib Received: January 29, 2016      Accepted: March 07, 2016      Published: March 25, 2016 ABSTRACT The signaling lymphocyte activation molecule family [SLAMF] of cell surface receptors partakes in both the development of several immunocyte lineages and innate and adaptive immune responses in humans and mice. For instance, the homophilic molecule SLAMF6 (CD352) is in part involved in natural killer T cell development, but also modulates T follicular helper cell and germinal B cell interactions. Here we report that upon transplantation of a well-defined aggressive murine B220 + CD5 + Chronic Lymphocytic Leukemia (CLL) cell clone, TCL1-192, into SCID mice one injection of a monoclonal antibody directed against SLAMF6 (αSlamf6) abrogates tumor progression in the spleen, bone marrow and blood. Similarly, progression of a murine B cell lymphoma, LMP2A/λMyc, was also eliminated by αSlamf6. But, surprisingly, αSLAMF6 neither eliminated TCL1-192 nor LMP2A/λMyc cells, which resided in the peritoneal cavity or omentum. This appeared to be dependent upon the tumor environment, which affected the frequency of sub-populations of the TCL1-192 clone or the inability of peritoneal macrophages to induce Antibody Dependent Cellular Cytotoxicity (ADCC). However, co-administering αSlamf6 with the Bruton tyrosine kinase (Btk) inhibitor, ibrutinib, synergized to efficiently eliminate the tumor cells in the spleen, bone marrow, liver and the peritoneal cavity. Because an anti-human SLAMF6 mAb efficiently killed human CLL cells in vitro and in vivo , we propose that a combination of αSlamf6 with ibrutinib should be considered as a novel therapeutic approach for CLL and other B cell tumors.