Resistance to complement activation, cell membrane hypersialylation and relapses in chronic lymphocytic leukemia patients treated with rituximab and chemotherapy

// Anne Bordron 1, * , Cristina Bagacean 1, 3, * , Audrey Mohr 1 , Adrian Tempescul 1, 2 , Boutahar Bendaoud 1, 3 , Stephanie Deshayes 1 , Florence Dalbies 2 , Caroline Buors 4 , Hussam Saad 2 , Christian Berthou 1, 2 , Jacques-Olivier Pers 1, ** and Yves Renaudineau 1, 3, ** 1 U1227 B Lymphocytes and Autoimmunity, Universite de Brest, INSERM, IBSAM, Labex IGO, Networks IC-CGO and REpiCGO from ‘Canceropole Grand Ouest, Brest, France 2 Department of Haematology, CHRU Brest, Hopital Morvan, Brest, France 3 Laboratory of Immunology and Immunotherapy, CHRU Brest, Hopital Morvan, Brest, France 4 Laboratory of Haematology, CHRU Brest, Hopital Morvan, Brest, France * These authors have contributed equally to this work ** The last two authors as senior authors Correspondence to: Anne Bordron, email: anne.bordron@univ-brest.fr Keywords: chronic lymphocytic leukemia; rituximab; complement-dependent cytotoxicity; sialylation; progression-free survival Received: December 28, 2017     Accepted: June 04, 2018     Published: August 03, 2018 ABSTRACT The anti-CD20-specific monoclonal antibody rituximab (RTX), in combination with chemotherapy, is commonly used for primary treatment in chronic lymphocytic leukemia (CLL). However, relapses remain important and activation of the complement pathway is one of the mechanisms by which RTX generates the destruction of B cells directly by complement-dependent cytotoxicity (CDC), or indirectly by antibody-dependent cellular phagocytosis. In this study, the RTX capacity to induce CDC was established in 69 untreated CLL patients, this cohort including 34 patients tested before the initiation of RTX-chemotherapy. In vitro CDC-resistance to RTX predicts lower response rates to RTX-chemotherapy and shorter treatment free survival. Furthermore, the predictive value of CDC-resistance was independent from the clinical, cytogenetic and FcγR3A V158F polymorphism status. In contrast, CLL cell resistance to CDC predominates in IGHV unmutated patients and was related to an important α2-6 sialyl transferase activity, which in turn increases cell surface α2-6 hypersialylation. Suspected factors associated with resistance to CDC (CD20, CD55, CD59, factor H, GM1, and sphingomyelin) were not differentially expressed or recruited between the two CLL groups. Altogether, results provide evidence that testing RTX capacity to induce CDC in vitro represents an independent predictive factor of therapeutic effects of RTX, and that α2-6 hypersialylation in CLL cells controls RTX response through the control of the complement pathway. At a time when CLL therapy is moving towards chemo-free treatments, further experiments are required to determine whether performing an initial in vitro assay to appreciate CLL CDC resistance might be useful to select patients.