Chronic lymphocytic leukaemia cells are efficiently killed by an anti‐CD20 monoclonal antibody selected for improved engagement of FcγRIIIA/CD16

Abstract

Summary Patients with chronic lymphocytic leukaemia (CLL) treated with a combination of fludarabine, cyclophosphamide and rituximab show a high response rate. However, only a poor response is observed following rituximab monotherapy. The use of chemo‐immunotherapy is often associated with haematological and infectious complications. Thus, an antibody with an enhanced ability to kill CLL cells could lead to better clinical responses to antibody monotherapy and the possibility of lowering drug doses during chemo‐immunotherapy. We generated a chimeric anti‐CD20 monoclonal antibody (mAb), EMAB‐6, which has a low fucose content. Apoptosis and complement activities for EMAB‐6 were similar to those seen for rituximab. By contrast, EMAB‐6 mAb showed improved Fcγ receptor IIIA (FcγRIIIA)/CD16 binding and FcγRIIIA‐dependent effector functions. It induced a higher in vitro antibody‐dependent cellular cytotoxicity against CLL cells and a higher FcγRIIIA‐mediated interleukin‐2 production by FcγRIIIA+ Jurkat cells in the presence of CLL cells at both low and maximally saturating concentrations. Comparative studies between CLL and lymphoma cells coated with EMAB‐6 or rituximab indicated that the difference of efficacy was more pronounced at low doses and when target cells expressed fewer CD20 molecules. Thus, EMAB‐6 mAb represents a promising drug candidate for the treatment of CLL by inducing a strong cytotoxicity against tumour cells that express low CD20 levels.

Single-Domain Antibody–Based and Linker-Free Bispecific Antibodies Targeting FcγRIII Induce Potent Antitumor Activity without Recruiting Regulatory T Cells

“…Our in vitro data showed a strong and specific NK cell-mediated lysis of CEA-expressing tumor cells (from pancreatic and colorectal cancers) at picomolar concentrations, that is, orders of magnitude lower than conventional mAbs (10,42). These results suggest that a high affinity for FcgRIIIa translates into improved cytotoxic activity of effector cells in vitro, a finding also described with mutated and glycoengineered antibodies (43,44).…”

“…The fact that about 80% of the Caucasian population is homozygous (F/F) or heterozygous (F/V) for low-affinity FcgRIIIa (F158) is likely an important issue for antibody-based immunotherapy. Moreover, the in vivo efficacy of therapeutic antibodies is hindered by the presence of fucose residues in the N-glycosylation motif (N297 residue) of the Fc region that markedly decreases their affinity for FcgRIIIa (8)(9)(10). Therapeutic antibodies also compete with serum IgG for binding to the high-affinity FcgRI and to the intermediate-affinity FcgRIIIa.…”

Analysis of CD16+CD56dim NK cells from CLL patients: evidence supporting a therapeutic strategy with optimized anti-CD20 monoclonal antibodies

“…This mAb has been granted an orphan-drug status in Europe and in the USA for CLL treatment (http://www.lfb.fr/en/home.html). A previous generation of this antibody, named EMAB-6, sharing the same specificity and a similar glycosylation pattern, was described in de Romeuf et al 9 …”

“…EMAB-6 shows improved FcgRIIIA binding, resulting in enhanced ADCC, mediated particularly by macrophages 8 and NK cells. 9 The NK cells constitute a unique component of the innate immune system, able to recognize various targets without specific sensitization. The NK cells are heterogeneous and differ in their proliferative potential, homing characteristics, functional capabilities and in responses to a wide range of cytokines.…”

Les anticorps EMABling®

“…Grâce à une stratégie analogue de criblage in vitro d'un Acm capable de fixer fortement le RFcγIII et d'induire une ADCC contre des cellules tumorales CD20 + , le LFB a produit et sélectionné l'Acm anti-CD20 LFB-R603. Dans différentes expériences d'ADCC (utilisant comme cellules effectrices des cellules mononucléées du sang périphérique, des cellules NK, ou des macrophages et comme cibles différentes cellules CD20 + ), cet Acm présente une capacité à lyser les cellules CD20 + supérieure à celle du rituximab, en particulier lorsque la densité de CD20 est faible, comme c'est le cas des cellules de patients souffrant de leucémie lymphoïde chronique (LLC) [7]. Des données in vivo obtenues chez le singe cynomolgus montrent que LFB-R603 induit une déplétion dose-dépendante, profonde et prolongée, des cellules CD20 + , non seulement dans le sang péri-phérique mais également dans les organes lymphoïdes, sans signe majeur de toxicité ou d'immunogénicité.…”