Monoclonal antibodies (mAbs) have become an important class of therapeutics, particularly in the realm of anticancer immunotherapy. While the two antigen-binding fragments (Fabs) of an mAb allow for high-avidity binding to molecular targets, the crystallizable fragment (Fc) engages immune effector elements. mAbs of the IgG class are used for the treatment of autoimmune diseases and can elicit antitumor immune functions not only by several mechanisms including direct antigen engagement via their Fab arms but also by Fab binding to tumors combined with Fc engagement of complement component C1q and Fcγ receptors. Additionally, IgG binding to the neonatal Fc receptor (FcRn) allows for endosomal recycling and prolonged serum half-life. To augment the effector functions or half-life of an IgG1 mAb, we constructed a novel "2Fc" mAb containing two Fc domains in addition to the normal two Fab domains. Structural and functional characterization of this 2Fc mAb demonstrated that it exists in a tetrahedral-like geometry and retains binding capacity via the Fab domains. Furthermore, duplication of the Fc region significantly enhanced avidity for Fc receptors FcγRI, FcγRIIIa, and FcRn, which manifested as a decrease in complex dissociation rate that was more pronounced at higher densities of receptor. At intermediate receptor density, the dissociation rate for Fc receptors was decreased 6- to 130-fold, resulting in apparent affinity increases of 7- to 42-fold. Stoichiometric analysis confirmed that each 2Fc mAb may simultaneously bind two molecules of FcγRI or four molecules of FcRn, which is double the stoichiometry of a wild-type mAb. In summary, duplication of the IgG Fc region allows for increased avidity to Fc receptors that could translate into clinically relevant enhancement of effector functions or pharmacokinetics.

中文翻译：

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具有增强的Fc受体亲和力的新型双重Fc抗体的设计和表征。

单克隆抗体（mAb）已成为一类重要的疗法，尤其是在抗癌免疫疗法领域。尽管mAb的两个抗原结合片段（Fabs）允许与分子靶标高亲和力结合，但可结晶片段（Fc）与免疫效应元件结合。IgG类单克隆抗体可用于治疗自身免疫疾病，不仅可以通过几种机制（包括通过其Fab臂直接与抗原结合，而且可以通过Fab与肿瘤结合并结合补体成分C1q和Fcγ受体的Fc结合）引发抗肿瘤免疫功能。 。另外，与新生儿Fc受体（FcRn）结合的IgG可实现内体再循环和延长的血清半衰期。为了增加IgG1 mAb的效应子功能或半衰期，我们构建了新的“ 2Fc” 除了正常的两个Fab结构域外，mAb还包含两个Fc结构域。此2Fc mAb的结构和功能表征证明它以四面体状几何结构存在，并通过Fab结构域保留了结合能力。此外，Fc区的重复显着增强了对Fc受体FcγRI，FcγRIIIa和FcRn的亲和力，这表现为复合解离速率的降低，这在更高的受体密度下更为明显。在中等受体密度下，Fc受体的解离速率降低了6至130倍，导致表观亲和力增加了7至42倍。化学计量分析证实，每个2Fc mAb可以同时结合两个分子的FcγRI或四个分子的FcRn，这是野生型mAb的化学计量的两倍。总之，