Development of effective preventative interventions against SARS-CoV-2, the etiologic agent of COVID-19 is urgently needed. The viral surface spike (S) protein of SARS-CoV-2 is a key target for prophylactic measures as it is critical for the viral replication cycle and the primary target of neutralizing antibodies. We evaluated design elements previously shown for other coronavirus S protein-based vaccines to be successful, e.g. prefusion-stabilizing substitutions and heterologous signal peptides, for selection of a S-based SARS-CoV-2 vaccine candidate. In vitro characterization demonstrated that the introduction of stabilizing substitutions (i.e., furin cleavage site mutations and two consecutive prolines in the hinge region of S1) increased the ratio of neutralizing versus non-neutralizing antibody binding, suggestive for a prefusion conformation of the S protein. Furthermore, the wild type signal peptide was best suited for the correct cleavage needed for a natively-folded protein. These observations translated into superior immunogenicity in mice where the Ad26 vector encoding for a membrane-bound stabilized S protein with a wild type signal peptide elicited potent neutralizing humoral immunity and cellular immunity that was polarized towards Th1 IFN-γ. This optimized Ad26 vector-based vaccine for SARS-CoV-2, termed Ad26.COV2.S, is currently being evaluated in a phase I clinical trial (ClinicalTrials.gov Identifier: NCT04436276).

中文翻译：

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编码预融合稳定SARS-CoV-2 Spike免疫原的基于Ad26载体的COVID-19疫苗诱导有效的体液和细胞免疫应答

迫切需要开发针对SARS-CoV-2（COVID-19的病原体）的有效预防措施。SARS-CoV-2的病毒表面刺突（S）蛋白是预防措施的关键目标，因为它对病毒复制周期和中和抗体的主要目标至关重要。我们评估了先前显示的用于其他基于冠状病毒S蛋白的疫苗的设计元素是否成功，例如融合前稳定替代和异源信号肽，以选择基于S的SARS-CoV-2疫苗。体外表征表明，稳定取代的引入（即弗林蛋白酶切割位点突变和S1铰链区的两个连续脯氨酸）增加了中和性抗体结合与非中和性抗体结合的比率，提示S蛋白的融合前构象。此外，野生型信号肽最适合天然折叠蛋白所需的正确切割。这些观察结果转化为小鼠具有更高的免疫原性，其中编码带有野生型信号肽的膜结合的稳定S蛋白的Ad26载体引起有效的中和体液免疫和细胞免疫，对Th1IFN-γ呈极化作用。目前正在I期临床试验（ClinicalTrials.gov标识符：NCT04436276）中评估这种针对SARS-CoV-2的优化的基于Ad26载体的疫苗，称为Ad26.COV2.S。这些观察结果转化为小鼠具有更高的免疫原性，其中编码带有野生型信号肽的膜结合的稳定S蛋白的Ad26载体引起有效的中和体液免疫和细胞免疫，对Th1IFN-γ极化。目前正在I期临床试验（ClinicalTrials.gov标识符：NCT04436276）中评估这种针对SARS-CoV-2的优化的基于Ad26载体的疫苗，称为Ad26.COV2.S。这些观察结果转化为小鼠具有更高的免疫原性，其中编码带有野生型信号肽的膜结合的稳定S蛋白的Ad26载体引起有效的中和体液免疫和细胞免疫，对Th1IFN-γ呈极化作用。目前正在I期临床试验（ClinicalTrials.gov标识符：NCT04436276）中评估这种针对SARS-CoV-2的优化的基于Ad26载体的疫苗，称为Ad26.COV2.S。