• Tingting Li, Qingbing Zheng, Hai Yu, Dinghui Wu, Wenhui Xue, Hualong Xiong, Xiaofen Huang, Meifeng Nie, Mingxi Yue, Rui Rong, Sibo Zhang, Yuyun Zhang, Yangtao Wu, Shaojuan Wang, Zhenghui Zha, Tingting Chen, Tingting Deng, Yingbin Wang, Tianying Zhang, Yixin Chen, Quan Yuan, Qinjian Zhao, Jun Zhang, Ying Gu, Shaowei Li, and Ningshao Xia.
• State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, School of Life Sciences, School of Public Health, Xiamen University, Xiamen, People's Republic of China.
• Emerg Microbes Infect. 2020 Dec 1; 9 (1): 2076-2090.

AbstractThe current coronavirus disease 2019 (COVID-19) pandemic was the result of the rapid transmission of a highly pathogenic coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), for which there is no efficacious vaccine or therapeutic. Toward the development of a vaccine, here we expressed and evaluated as potential candidates four versions of the spike (S) protein using an insect cell expression system: receptor binding domain (RBD), S1 subunit, the wild-type S ectodomain (S-WT), and the prefusion trimer-stabilized form (S-2P). We showed that RBD appears as a monomer in solution, whereas S1, S-WT, and S-2P associate as homotrimers with substantial glycosylation. Cryo-electron microscopy analyses suggested that S-2P assumes an identical trimer conformation as the similarly engineered S protein expressed in 293 mammalian cells but with reduced glycosylation. Overall, the four proteins confer excellent antigenicity with convalescent COVID-19 patient sera in enzyme-linked immunosorbent assay (ELISA), yet show distinct reactivities in immunoblotting. RBD, S-WT and S-2P, but not S1, induce high neutralization titres (>3-log) in mice after a three-round immunization regimen. The high immunogenicity of S-2P could be maintained at the lowest dose (1 μg) with the inclusion of an aluminium adjuvant. Higher doses (20 μg) of S-2P can elicit high neutralization titres in non-human primates that exceed 40-times the mean titres measured in convalescent COVID-19 subjects. Our results suggest that the prefusion trimer-stabilized SARS-CoV-2 S-protein from insect cells may offer a potential candidate strategy for the development of a recombinant COVID-19 vaccine.

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