Understanding the molecular basis for immune recognition of SARS-CoV-2 spike glycoprotein antigenic sites will inform the development of improved therapeutics. We determined the structures of two human monoclonal antibodies–AZD8895 and AZD1061–which form the basis of the investigational antibody cocktail AZD7442, in complex with the receptor-binding domain (RBD) of SARS-CoV-2 to define the genetic and structural basis of neutralization. AZD8895 forms an ‘aromatic cage’ at the heavy/light chain interface using germ line-encoded residues in complementarity-determining regions (CDRs) 2 and 3 of the heavy chain and CDRs 1 and 3 of the light chain. These structural features explain why highly similar antibodies (public clonotypes) have been isolated from multiple individuals. AZD1061 has an unusually long LCDR1; the HCDR3 makes interactions with the opposite face of the RBD from that of AZD8895. Using deep mutational scanning and neutralization escape selection experiments, we comprehensively mapped the crucial binding residues of both antibodies and identified positions of concern with regards to virus escape from antibody-mediated neutralization. Both AZD8895 and AZD1061 have strong neutralizing activity against SARS-CoV-2 and variants of concern with antigenic substitutions in the RBD. We conclude that germ line-encoded antibody features enable recognition of the SARS-CoV-2 spike RBD and demonstrate the utility of the cocktail AZD7442 in neutralizing emerging variant viruses.

了解 SARS-CoV-2 刺突糖蛋白抗原位点免疫识别的分子基础将为开发改进的治疗方法提供信息。我们确定了两种人单克隆抗体 AZD8895 和 AZD1061 的结构，它们构成了研究抗体混合物 AZD7442 的基础，与 SARS-CoV-2 的受体结合域 (RBD) 复合，以定义 SARS-CoV-2 的遗传和结构基础中和。AZD8895 使用重链互补决定区 (CDR) 2 和 3 以及轻链 CDR 1 和 3 中种系编码的残基在重/轻链界面形成“芳香笼”。这些结构特征解释了为什么从多个个体中分离出高度相似的抗体（公共克隆型）。AZD1061具有异常长的LCDR1；HCDR3 与 RBD 的相对于 AZD8895 的面进行相互作用。通过深度突变扫描和中和逃逸选择实验，我们全面绘制了两种抗体的关键结合残基图，并确定了与病毒从抗体介导的中和中逃逸有关的位置。AZD8895 和 AZD1061 均具有针对 SARS-CoV-2 和与 RBD 中抗原取代相关的变体的强中和活性。我们得出的结论是，种系编码的抗体特征能够识别 SARS-CoV-2 刺突 RBD，并证明了鸡尾酒 AZD7442 在中和新出现的变异病毒方面的效用。