Preparation and evaluation of immune effect of recombinant S1 protein based on SARS-CoV-2 beta variant
The codon sequence of the S1 protein of the SARS-CoV-2 Beta variant was optimized ac-cording to the preference of CHO cells and cloned into pSN expression vector to construct the re-combinant plasmid pSN-Beta-sl.Recombinant protein was expressed in CHO cells,identified using SDS-PAGE and Western blot,and purified through affinity chromatography.BALB/c mice were immunized with purified recombinant protein Beta-S1 combined with aluminum hydroxide adju-vant.Specific IgG antibody and its subtypes in serum and the cross-neutralization antibody activity against SARS-CoV-2 variants were evaluated.The results showed that the recombinant plasmid pSN-Beta-S1 was successfully constructed,and the recombinant protein Beta-S1 was produced u-sing the CHO cell expression system.The purified recombinant protein had a single band of about 120 kDa with the purity exceeding 85％and can bind to RBD pAb and strep-tag mAb.The recom-binant S1 protein showed good immunogenicity in BALB/c mice.The titers of specific IgG antibodies against RBD protein and S1 protein reached 1∶66 260 and 1∶133 120 on average 21 d after the third immunization,the antibody subtypes were mainly inclined to IgG1.Serum neutrali-zing antibody titer was 1∶629 for wild type,1∶1 720 for Beta,1∶374 for Delta,1∶77 for Omi-cron BA1 and 1∶101 for Omicron BA2.In this study,S1 recombinant protein of SARS-CoV-2 Beta variant was successfully expressed in CHO cell expression system and produced good immunoge-nicity and cross-neutralizing activity in BALB/c mice.These results provide a reference for the fur-ther development of broad-spectrum SARS-CoV-2 vaccine.
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