Inhibitory Fc?RIIb (CD32b) becomes activated by therapeutic mAb in both cis and trans and drives internalization according to antibody specificity.
2014; 123 (5): 669-677
CHEMOTHERAPY Advanced Hodgkin lymphoma-balancing toxicity and cure
NATURE REVIEWS CLINICAL ONCOLOGY
2011; 8 (11): 634-636
Fc gamma receptor IIb on target B cells promotes rituximab internalization and reduces clinical efficacy
2011; 118 (9): 2530-2540
A major feature that distinguishes type I from type II anti-CD20 monoclonal antibodies (mAbs) and reduces their therapeutic efficacy is the tendency to internalize from the cell surface. We have shown previously that the extent of internalization correlates with the capacity of type I mAb to simultaneously engage both CD20 and the inhibitory Fcγ receptor, FcγRIIb, in a bipolar configuration. Here, we investigated whether mAbs directed at other B-cell surface receptors also engaged FcγRIIb and whether this interaction promoted internalization. Most mAbs engaged and activated FcγRIIb, with the strength of activation related to the level of mAb bound to the cell surface. However, engagement did not affect internalization of most mAb-ligated receptors, either in cell lines or primary chronic lymphocytic leukemia cells with the exception of CD19 and CD38. Furthermore, at high cell concentrations/density both cis and trans interactions between cell-surface bound mAb and FcγRIIb were evident, but trans interactions did not inhibit type I anti-CD20 mAb-mediated internalization. These data identify that FcγRIIb is engaged by many mAbs in both cis and trans configurations, triggering its activation, but that internalization via FcγRIIb occurs for only a select subset. These findings have implications when designing new antibody-based therapeutics.
View details for DOI 10.1182/blood-2013-04-490821
View details for PubMedID 24227819
Novel type II anti-CD20 monoclonal antibody (GA101) evokes homotypic adhesion and actin-dependent, lysosome-mediated cell death in B-cell malignancies
2011; 117 (17): 4519-4529
The anti-CD20 mAb rituximab is central to the treatment of B-cell malignancies, but resistance remains a significant problem. We recently reported that resistance could be explained, in part, by internalization of rituximab (type I anti-CD20) from the surface of certain B-cell malignancies, thus limiting engagement of natural effectors and increasing mAb consumption. Internalization of rituximab was most evident in chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL), but the extent of internalization was heterogeneous within each disease. Here, we show that the inhibitory FcγRIIb on target B cells promotes this process and is largely responsible for the observed heterogeneity across a range of B-cell malignancies. Internalization correlated strongly with FcγRIIb expression on normal and malignant B cells, and resulted in reduced macrophage phagocytosis of mAb-coated targets. Furthermore, transfection of FcγRIIb into FcγRIIb negative Ramos cells increased internalization of rituximab in a dose-dependent manner. Target-cell FcγRIIb promoted rituximab internalization in a cis fashion and was independent of FcγRIIb on neighboring cells. It became phosphorylated and internalized along with CD20:anti-CD20 complexes before lysosomal degradation. In MCL patients, high FcγRIIb expression predicted less durable responses after rituximab-containing regimens. Therefore, target-cell FcγRIIb provides a potential biomarker of response to type I anti-CD20 mAb.
View details for DOI 10.1182/blood-2011-01-330357
View details for Web of Science ID 000294476400025
View details for PubMedID 21768293
Antigenic modulation limits the efficacy of anti-CD20 antibodies: implications for antibody selection
2010; 115 (25): 5191-5201
The anti-CD20 mAb rituximab has substantially improved the clinical outcome of patients with a wide range of B-cell malignancies. However, many patients relapse or fail to respond to rituximab, and thus there is intense investigation into the development of novel anti-CD20 mAbs with improved therapeutic efficacy. Although Fc-FcγR interactions appear to underlie much of the therapeutic success with rituximab, certain type II anti-CD20 mAbs efficiently induce programmed cell death (PCD), whereas rituximab-like type I anti-CD20 mAbs do not. Here, we show that the humanized, glycoengineered anti-CD20 mAb GA101 and derivatives harboring non-glycoengineered Fc regions are type II mAb that trigger nonapoptotic PCD in a range of B-lymphoma cell lines and primary B-cell malignancies. We demonstrate that GA101-induced cell death is dependent on actin reorganization, can be abrogated by inhibitors of actin polymerization, and is independent of BCL-2 overexpression and caspase activation. GA101-induced PCD is executed by lysosomes which disperse their contents into the cytoplasm and surrounding environment. Taken together, these findings reveal that GA101 is able to potently elicit actin-dependent, lysosomal cell death, which may potentially lead to improved clearance of B-cell malignancies in vivo.
View details for DOI 10.1182/blood-2010-07-296913
View details for Web of Science ID 000289984800017
View details for PubMedID 21378274
Anti-CD20 monoclonal antibodies: historical and future perspectives
HAEMATOLOGICA-THE HEMATOLOGY JOURNAL
2010; 95 (1): 135-143
Rituximab, a monoclonal antibody that targets CD20 on B cells, is now central to the treatment of a variety of malignant and autoimmune disorders. Despite this success, a substantial proportion of B-cell lymphomas are unresponsive or develop resistance, hence more potent anti-CD20 monoclonal antibodies (mAbs) are continuously being sought. Here we demonstrate that type II (tositumomab-like) anti-CD20 mAbs are 5 times more potent than type I (rituximab-like) reagents in depleting human CD20 Tg B cells, despite both operating exclusively via activatory Fcgamma receptor-expressing macrophages. Much of this disparity in performance is attributable to type I mAb-mediated internalization of CD20 by B cells, leading to reduced macrophage recruitment and the degradation of CD20/mAb complexes, shortening mAb half-life. Importantly, human B cells from healthy donors and most cases of chronic lymphatic leukemia and mantle cell lymphoma, showed rapid CD20 internalization that paralleled that seen in the Tg mouse B cells, whereas most follicular lymphoma and diffuse large B-cell lymphoma cells were far more resistant to CD20 loss. We postulate that differences in CD20 modulation may play a central role in determining the relative efficacy of rituximab in treating these diseases and strengthen the case for focusing on type II anti-CD20 mAb in the clinic.
View details for DOI 10.1182/blood-2010-01-263533
View details for Web of Science ID 000279113100012
View details for PubMedID 20223920
Life-threatening bleeding in a patient with a lupus inhibitor and probable acquired factor VII deficiency
BLOOD COAGULATION & FIBRINOLYSIS
2006; 17 (8): 667-671
Antibodies to CD20 have confirmed the hypothesis that monoclonal reagents can be given in vivo to alleviate human diseases. The targeting of CD20 on normal, malignant and auto-immune B-lymphocytes by rituximab has demonstrated substantial benefits for patients with a variety of B-cell lymphomas, as well as some with autoimmune disorders. There has been a notable increase in the survival rates from B-cell lymphoma in the decade since anti-CD20 therapy was introduced.
View details for DOI 10.3324/haematol.2008.001628
View details for Web of Science ID 000273869800022
View details for PubMedID 19773256
We report the case of a 71-year-old man on warfarin for chronic atrial fibrillation presenting with a massive spontaneous soft tissue bleed. Despite reversing the effects of warfarin with large doses of intravenous vitamin K and fresh frozen plasma, bleeding continued, and his prothrombin time and activated partial thromboplastin time remained prolonged. The prothrombin time and activated partial thromboplastin time failed to correct with 50% normal plasma. Further investigations confirmed a lupus inhibitor with low levels of factors II, V, VII and XI. Factor II, V and XI levels normalized, however, when the patient's plasma was diluted 1:16 in buffer, suggesting the lupus inhibitor may have been interfering with these factor assays causing artefactual low results. Factor VII levels remained consistently low at all dilutions. The patient subsequently died following a massive left haemothorax despite surgical intervention and treatment with activated recombinant factor VII concentrate. We presumed the primary problem was bleeding from a local vascular lesion but the patient was never well enough to undergo confirmatory angiography. This case highlights the fact that patients with lupus inhibitors can develop severe haemorrhagic complications, and illustrates the complexities involved in both the investigation and treatment of abnormal bleeding in these patients.
View details for Web of Science ID 000242672700010
View details for PubMedID 17102654