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Key Points• Phagocytosis of CLL targets by neutrophils is a novel mechanism of action of the glycoengineered anti-CD20 antibody obinutuzumab.• This mechanism takes place in physiological conditions and requires CD16B and CD32A.Obinutuzumab (GA101) is a glycoengineered type 2 CD20 antibody with enhanced CD16A-binding and natural killer-mediated cytotoxicity. CD16B is highly homologous to CD16A and a major FcgR on human polymorphonuclear neutrophils (PMNs). We show here that glycoengineered obinutuzumab or rituximab bound CD16B with approximately sevenfold higher affinity, compared with nonglycoengineered wild-type parental antibodies. Furthermore, glycoengineered obinutuzumab activated PMNs, either purified or in chronic lymphoblastic leukemia whole blood, more efficiently than wild-type rituximab. Activation resulted in a 50% increase in CD11b expression and 70% down-modulation of CD62L on neutrophils and in release of tumor necrosis factor alpha, IL-6, and IL-8. Activation was not accompanied by generation of reactive oxygen species or antibody-dependent cellular cytotoxicity activity, but led to up to 47% phagocytosis of glycoengineered anti-CD20 opsonized chronic lymphoblastic leukemia targets by purified PMNs. Significant phagocytosis was observed in whole blood, but only in the presence of glycoengineered antibodies, and was followed by up to 50% PMN death. Finally we show, using anti-CD16B and anti-CD32A Fab and F(ab') 2 fragments, that both of these receptors are involved in PMN activation, phagocytosis, and cell death induced by glycoengineered antibodies. We conclude that phagocytosis by PMNs is an additional mechanism of action of obinutuzumab mediated through its higher binding affinity for CD16B. (Blood. 2013;122(20):3482-3491) IntroductionThe chimeric unmodified, wild-type CD20 IgG1 monoclonal antibody rituximab (MabThera and Rituxan) has shown significant therapeutic activity in B-non-Hodgkin lymphoma (B-NHL) and chronic lymphocytic leukemia (CLL).1,2 Rituximab is thought to act largely through immune-mediated mechanisms: complement-dependent cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC), and/or antibody-dependent phagocytosis (ADCP) by macrophages/monocytes.3,4 CD20 IgG1 antibodies can differ in their functional properties according to their binding mode to CD20. They are classified as type 1 when they show high CDC such as rituximab or as type 2 when they show high homotypic adhesion and direct cell death, respectively. 5,6 Improved versions of rituximab have been developed with the scope of enhancing response rates and reducing relapse or resistance. 7,8 One modification applied for CD20 and other therapeutic antibodies is termed "glycoengineering" and results in the decreased fucosylation of the carbohydrate attached to the Asn-297 glycosylation site of the Fc portion of the antibody. [9][10][11][12][13][14][15] Obinutuzumab (GA101) is a glycoengineered CD20 antibody derived from the murine Bly-1 antibody and is currently in pivotal clinical trials for the treatment of...

Ofatumumab (OFA) is a human anti-CD20 Ab approved for treatment of fludarabine-refractory B chronic lymphocytic leukemia (B-CLL). The efficacy of different immunotherapeutic strategies is best investigated in conditions that are as physiologic as possible. We have therefore compared the activity OFA and rituximab (RTX), alone or in combination with chemotherapeutic agents in unmanipulated whole blood assays, using flow cytometry. OFA (10–100 μg/ml) lysed B-CLL targets in whole blood more efficiently and with faster kinetics than RTX, with a mean 56% lysis at 24 h compared with 16%. This activity of OFA was fully complement dependent, as shown by >99% inhibition by anti-C5 Ab eculizumab and a lack of NK cell activation in whole blood. OFA-mediated NK cell activation was blocked by complement. OFA-mediated lysis could be increased an additional 15% by blocking CD55 and CD59 complement inhibitors. Interestingly, OFA-mediated lysis correlated significantly with CD20 expression levels (r2 = 0.79). OFA showed overlapping dose response curves similar to those for RTX in phagocytosis assays using either human macrophages or neutrophils. However, phagocytosis was inhibited in the presence of serum or whole blood. Finally, combined treatment with mafosfamide and fludarabine showed that these therapeutic drugs are synergistic in B-CLL whole blood assays and show superior activity when combined with OFA compared with RTX. These results confirm in B-CLL samples and in physiologic conditions the superior complement mediated cytotoxicity induced by OFA alone compared with RTX, the lack of NK cell activation, and phagocytosis in these conditions and suggest effective chemoimmunotherapy strategies using this new generation anti-CD20 Ab.

Background Obinutuzumab (GA101) is a third generation, glycoengineered defucosylated anti-CD20 antibody which shows higher binding affinity for CD16A than fully glycosylated rituximab (RTX). This higher binding leads to stronger NK mediated antibody dependent cellular cytotoxicity activity (ADCC) by obinutuzumab compared to that induced by RTX. The GPI-anchored CD16B molecule is highly homologous to CD16A and is the major FcγR on polymorphonuclear neutrophils (PMN). We have therefore investigated the binding of obinutuzumab to CD16B and its functional activity on human PMN compared to parent rituximab (RTX) or to defucosylated rituximab (G2 antibody). Methods Binding to CD16B of glycoengineered or fully glycosylated anti-CD20 antibodies was measured by surface plasmon resonance (Biacore). For PMN activation and phagocytosis, we have used either purified PMN or analyzed PMN function in unmanipulated whole blood assays from normal donors or CLL patients. PMN activation was measured as CD11b upregulation and CD62L downmodulation by flow cytometry. Phagocytosis by PMN of chronic lymphocytic leukemia (CLL) cells was measured by triple fluorescence (PKH26, CD15-FITC and CD19-APC) and flow cytometry. Results Obinutuzumab or glycoengineered defucosylated rituximab (called G2) bound CD16B with about 7 fold higher affinity, compared to non-glycoengineered wild type parental antibodies. This was true either using surface plasmon resonance or measuring antibody binding to live PMN. Furthermore obinutuzumab activated PMN, either purified or in whole blood, more efficiently than RTX. Activation resulted in a 50% increase in CD11b expression and 70% down-modulation of CD62L on PMN and in release of TNFα, IL-6 and IL-8. Activation was not accompanied by generation of reactive oxygen species or ADCC, but led to phagocytosis of anti-CD20 antibody opsonized CLL targets by purified PMN. Indeed up to 50% phagocytic PMN could be observed in presence of obinutuzumab or G2 antibodies after 6-24 hours incubation of purified PMN with CLL targets. Significant phagocytosis (15%) was also observed in whole blood, but only in presence of glycoengineered antibodies, and was followed by up to 50% PMN death. Finally we show, using blocking F(ab) and F(ab’)2 fragments specific for CD16B and CD32A, that both these receptors are involved in PMN activation, phagocytosis and cell death induced by glycoengineered anti-CD20 antibodies. The possible effect of NA1 and NA2 polymorphisms of CD16B on obinutuzumab binding and phagocytosis is under further investigation. Conclusions We conclude that phagocytosis by PMN is an additional mechanism of action of obinutuzumab, mediated through its higher binding affinity for CD16B compared to RTX. Phagocytosis takes place in whole blood and is followed by PMN death. This effect may in part explain the neutropenia observed after treatment of B-CLL patients with GA101. Disclosures: Golay: Roche Glycart AG: Research Funding. Ferrara Koller:Roche Glycart AG: Employment. Rambaldi:Roche Italia: Consultancy, Honoraria. Klein:Roche Glycart AG: Employment. Introna:Roche Glycart AG: Research Funding.

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