Vaccines are urgently needed to control the ongoing pandemic COVID-19 and previously emerging MERS/SARS caused by coronavirus (CoV) infections. The CoV spike receptor-binding domain (RBD) is an attractive vaccine target but is undermined by limited immunogenicity. We describe a dimeric form of MERS-CoV RBD that overcomes this limitation. The RBD-dimer significantly increased neutralizing antibody (NAb) titers compared to conventional monomeric form and protected mice against MERS-CoV infection. Crystal structure showed RBD-dimer fully exposed dual receptor-binding motifs, the major target for NAbs. Structure-guided design further yielded a stable version of RBD-dimer as a tandem repeat single-chain (RBD-sc-dimer) which retained the vaccine potency. We generalized this strategy to design vaccines against COVID-19 and SARS, achieving 10- to 100-fold enhancement of NAb titers. RBD-sc-dimers in pilot scale production yielded high yields, supporting their scalability for further clinical development. The framework of immunogen design can be universally applied to other beta-CoV vaccines to counter emerging threats.

迫切需要疫苗来控制正在流行的新冠肺炎 (COVID-19) 疫情以及之前出现的由冠状病毒 (CoV) 感染引起的中东呼吸综合征 (MERS)/非典型肺炎 (SARS)。冠状病毒刺突受体结合域（RBD）是一个有吸引力的疫苗靶点，但由于免疫原性有限而受到削弱。我们描述了一种二聚体形式的 MERS-CoV RBD，它克服了这一限制。与传统单体形式相比，RBD二聚体显着增加了中和抗体（NAb）滴度，并保护小鼠免受中东呼吸综合征冠状病毒感染。晶体结构显示 RBD-二聚体完全暴露双受体结合基序，这是 NAb 的主要靶标。结构引导设计进一步产生了稳定版本的 RBD-二聚体，作为串联重复单链 (RBD-sc-二聚体)，保留了疫苗效力。我们将这一策略推广到设计针对 COVID-19 和 SARS 的疫苗，实现 NAB 滴度提高 10 至 100 倍。 RBD-sc-二聚体在中试规模生产中产生了高产量，支持其进一步临床开发的可扩展性。免疫原设计框架可以普遍应用于其他 β-CoV 疫苗，以应对新出现的威胁。