The worldwide spread of COVID-19 highlights the need for an efficient approach to rapidly develop therapeutics and prophylactics against SARS-CoV-2. The SARS-CoV-2 spike protein, containing the receptor-binding domain (RBD) and S1 subunit involved in receptor engagement, is a potential therapeutic target. We describe the development of a phage-displayed single-domain antibody library by grafting naive complementarity-determining regions (CDRs) into framework regions of a human germline immunoglobulin heavy chain variable region (IGHV) allele. Panning this library against SARS-CoV-2 RBD and S1 subunit identified fully human single-domain antibodies targeting five distinct epitopes on SARS-CoV-2 RBD with subnanomolar to low nanomolar affinities. Some of these antibodies neutralize SARS-CoV-2 by targeting a cryptic epitope located in the spike trimeric interface. Collectively, this work presents a versatile platform for rapid antibody isolation and identifies promising therapeutic anti-SARS-CoV-2 antibodies as well as the diverse immogneic profile of the spike protein.

COVID-19在世界范围内的传播突显了对快速开发针对SARS-CoV-2的疗法和预防剂的有效方法的需求。包含受体结合域（RBD）和参与受体结合的S1亚基的SARS-CoV-2突突蛋白是潜在的治疗靶标。我们描述了通过将幼稚的互补决定区（CDRs）嫁接到人类种系免疫球蛋白重链可变区（IGHV）等位基因的框架区中的噬菌体展示单域抗体库的发展。针对该SARS-CoV-2 RBD和S1亚基淘选该文库，可以鉴定出靶向SARS-CoV-2 RBD上五个不同表位且具有纳摩尔至低纳摩尔亲和力的完全人单结构域抗体。这些抗体中的一些通过靶向位于刺突三聚体界面中的隐蔽表位来中和SARS-CoV-2。总的来说，这项工作为快速分离抗体提供了一个通用平台，并鉴定了有前途的治疗性抗SARS-CoV-2抗体以及刺突蛋白的多种免疫学特征。