Complement-dependent cytotoxicity (CDC) is a potent effector mechanism, engaging both innate and adaptive immunity. Although strategies to improve the CDC activity of antibody therapeutics have primarily focused on enhancing the interaction between the antibody crystallizable fragment (Fc) and the first subcomponent of the C1 complement complex (C1q), the relative importance of intrinsic affinity and binding valency of an antibody to the target antigen is poorly understood. Here we show that antibody binding affinity to a cell surface target antigen evidently affects the extent and efficacy of antibody-mediated complement activation. We further report the fundamental role of antibody binding valency in the capacity to recruit C1q and regulate CDC. More specifically, an array of affinity-modulated variants and functionally monovalent bispecific derivatives of high-affinity anti-epidermal growth factor receptor (EGFR) and anti-human epidermal growth factor receptor 2 (HER2) therapeutic immunoglobulin Gs (IgGs), previously reported to be deficient in mediating complement activation, were tested for their ability to bind C1q by biolayer interferometry using antigen-loaded biosensors and to exert CDC against a panel of EGFR and HER2 tumor cells of various histological origins. Significantly, affinity-reduced variants or monovalent derivatives, but not their high-affinity bivalent IgG counterparts, induced near-complete cell cytotoxicity in tumor cell lines that had formerly been shown to be resistant to complement-mediated attack. Our findings suggest that monovalent target engagement may contribute to an optimal geometrical positioning of the antibody Fc to engage C1q and deploy the complement pathway.

中文翻译：

---

通过调节IgG对靶抗原的固有亲和力和结合价来调节抗体介导的补体依赖性细胞毒性。

补体依赖性细胞毒性（CDC）是一种有效的效应器机制，具有先天免疫和适应性免疫功能。尽管提高抗体治疗剂CDC活性的策略主要集中在增强抗体可结晶片段（Fc）与C1补体复合物（C1q）的第一亚成分之间的相互作用，抗体的固有亲和力和结合价的相对重要性对靶抗原的了解很少。在这里，我们表明抗体对细胞表面靶抗原的结合亲和力明显影响抗体介导的补体激活的程度和功效。我们进一步报告了抗体结合价在招募C1q和调节CDC的能力中的基本作用。进一步来说，高亲和力抗表皮生长因子受体（EGFR）和抗人表皮生长因子受体2（HER2）治疗性免疫球蛋白Gs（IgG）的一系列亲和力调节变异体和功能单价双特异性衍生物，以前据报道缺乏通过使用抗原加载的生物传感器通过生物层干涉术测试介导补体激活的C1q结合C1q的能力，以及对各种组织学起源的一组EGFR和HER2肿瘤细胞施加CDC的能力。显着地，降低亲和力的变体或单价衍生物，而不是其高亲和力的二价IgG对应物，在肿瘤细胞系中诱导了近乎完全的细胞毒性，而先前已显示出它们对补体介导的攻击具有抵抗力。