ABSTRACT The 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.
【저자키워드】 COVID-19, SARS-CoV-2, immunogenicity, spike, insect cell expression system, 【초록키워드】 coronavirus disease, Vaccine, coronavirus, pandemic, S protein, glycosylation, neutralization, Transmission, immunization, ELISA, Receptor binding domain, Protein, mice, RBD, sera, Microscopy, therapeutic, S-2P, antigenicity, convalescent, non-human primate, expression, S-protein, S1 subunit, dose, COVID-19 patient, regimen, acute respiratory syndrome, candidate, recombinant COVID-19 vaccine, titre, trimer, wild-type, ectodomain, monomer, prefusion, offer, highly pathogenic, mammalian cell, Inclusion, enzyme-linked immunosorbent, lowest, evaluated, reduced, appear, subjects, expressed, suggested, analysis, elicit, induce, reactivity, insect cell, the mean, aluminium adjuvant, homotrimer, 【제목키워드】 neutralization, non-human primate, SARS-CoV-2 spike, titre, produced, elicit, insect cell,