Recombinant SARS-CoV-2 RBD with a built in T helper epitope induces strong neutralization antibody response

Su, Qiu-dong; Zou, Ye-ning; Yi, Yao; Shen, Li-ping; Ye, Xiang-zhong; Zhang, Yang; Wang, Hui; Ke, Hong; Song, Jing-dong; Hu, Ke-ping; Cheng, Bo-lin; Qiu, Feng; Yu, Peng-cheng; Zhou, Wen-ting; Zhao, Ran; Cao, Lei; Dong, Gao-feng; Bi, Sheng-li; Wu, Gui-zhen; Fu Gao, George; Zheng, Jerry

Without approved vaccines and specific treatments, COVID-19 is spreading around the world with above 26 million cases and approximately 864 thousand deaths until now. An efficacious and affordable vaccine is urgently needed. The Val308 – Gly548 of spike protein of SARS-CoV-2 linked with Gln830 – Glu843 of Tetanus toxoid (TT peptide) (designated as S1-4) and without TT peptide (designated as S1-5) were expressed and renatured. The antigenicity and immunogenicity of S1-4 were evaluated by Western Blotting (WB) in vitro and immune responses in mice, respectively. The protective efficiency was measured preliminarily by microneutralization assay (MN50). The soluble S1-4 and S1-5 protein was prepared to high homogeneity and purity. Adjuvanted with Alum, S1-4 protein stimulated a strong antibody response in immunized mice and caused a major Th2-type cellular immunity supplemented with Th1-type immunity. Furthermore, the immunized sera could protect the Vero E6 cells from SARS-CoV-2 infection with neutralizing antibody titer 256. Recombinant SARS-CoV-2 RBD with a built in T helper epitope could stimulate both strong humoral immunity supplemented with cellular immunity in mice, demonstrating that it could be a promising subunit vaccine candidate.