"Don'T Eat Me": Cd47 And Lfa-1 Modulate Cll Response To Nurselike Cells-Mediated Antibody-Dependent Phagocytosis Induced By Rituximab And Obinutuzumab (Ga101)

Abstract Abstract 1762 INTRODUCTION AND AIMS: Efficacy of therapeutic monoclonal antibodies depends to a large extent on the induction of effective antibody dependent cell cytotoxicity and phagocytosis (ADCC/ADCP) by CD16A+ immune effector cells. Chao et al. have recently unraveled the role of antibody dependent cell cytotoxicity and phagocytosis (ADCP) in rituximab (RTX)-induced tumor cell clearance using murine models of NHL [Chao M, 2010]. Nurse-like cells (NLC) provide pro-survival signals by direct contact and/or secretion of soluble factors while remaining M2-macrophages by nature [Ysebaert L, 2011]. M2 macrophages rapidly clear multiple opsonized targets [Leidi M, 2009], infiltrate lymph nodes and bone marrow, and are resistant to chemotherapeutic drugs thereby acting as important mediators of anti-CD20 mediated ADCP in CLL. We used an in vitro culture system to assess NLC-mediated ADCP mediated by RTX and obinutuzumab (GA101), a type II, glyco-engineered CD20 antibody with enhanced ADCC/ADCP through improved CD16A binding. METHODS: Antibody-mediated B cell depletion was determined by flow cytometry after antibody treatment. PBMCs from CLL patients were cultured for 14 days to allow outgrowth of NLC [Tsukada N, 2002]. Cells were collected and either (i) put in 6-well plates in the same medium without NLC (w/o NLC), or (ii) seeded back onto NLC (CLL+NLC), before anti-CD20 antibodies were added at 10μg/ml for 7d. For CD47 blocking experiments, cells were incubated for 15 min with blocking antibodies before being seeded back onto NLC. An Affymetrix Uplus2.0 chip was used for gene expression profiling (GEP) of 19 NLC and 5 normal CD14+ monocytes samples. For phenotype studies, CLL cells in suspension were thoroughly harvested with medium, and remaining adherent CLL cells were discarded from NLC by vigorous pipetting, before staining with CD47-FITC/LFA-1-PE antibodies. RESULTS: CONCLUSIONS: Our results suggest that NLC may be therapeutically exploited through mediators of ADCP, especially in lymphoid organs. For that purpose, the combination of CD47 and CD20 antibodies may be considered. Due to its efficacy even in LFA-1hi patients, GA101 is considered a better mediator of NLC-ADCP. Exploring the regulation of CD47 in CLL cells is important because it may interfere with strategies targeting surface antigens through FcgammaR-dependent mechanisms. Disclosures: Ysebaert: Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding. Klein:Roche: Employment, Equity Ownership, Patents & Royalties.