Antibody and Vaccine Group, Cancer Sciences Unit, University of Southampton, Faculty of Medicine, General Hospital, Southampton, United Kingdom;
Blood. 2014 Jan 30;123(5):669-77. doi: 10.1182/blood-2013-04-490821. Epub 2013 Nov 13.
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.
一种将类型 I 与类型 II 抗 CD20 单克隆抗体 (mAb) 区分开来的主要特征是从细胞表面内化的趋势,这降低了它们的治疗效果。我们之前已经表明,内化的程度与 I 型 mAb 同时结合 CD20 和抑制性 Fcγ 受体 FcγRIIb 的能力相关,形成双极构象。在这里,我们研究了针对其他 B 细胞表面受体的 mAb 是否也与 FcγRIIb 结合,以及这种相互作用是否促进内化。大多数 mAb 与 FcγRIIb 结合并激活,激活的强度与结合到细胞表面的 mAb 水平相关。然而,除了 CD19 和 CD38 之外,在细胞系或原发性慢性淋巴细胞白血病细胞中,大多数 mAb 结合的受体的内化既不受结合的影响,也不受激活的影响。此外,在高细胞浓度/密度下,细胞表面结合的 mAb 与 FcγRIIb 之间的顺式和反式相互作用都很明显,但反式相互作用不会抑制 I 型抗 CD20 mAb 介导的内化。这些数据表明,FcγRIIb 以顺式和反式两种构型被许多 mAb 结合,触发其激活,但只有一部分通过 FcγRIIb 内化。这些发现对设计新的基于抗体的治疗方法具有重要意义。