Abstract
The novel coronavirus pneumonia (COVID-19) pandemic is a great threat to human society and now is still spreading. Although several vaccines have been authorized for emergency use, only one recombinant subunit vaccine has been permitted for widespread use. More subunit vaccines for COVID-19 should be developed in the future. The receptor binding domain (RBD), located at the S protein of SARS-CoV-2, contains most of the neutralizing epitopes. However, the immunogenicity of RBD monomers is not strong enough. In this study, we fused the RBD-monomer with a modified Fc fragment of human IgG1 to form an RBD-Fc fusion protein. The recombinant vaccine candidate based on the RBD-Fc protein could induce high levels of IgG and neutralizing antibody in mice, and these could last for at least three months. The secretion of IFN-γ, IL-2 and IL-10 in the RBD-stimulated splenocytes of immunized mice also increased significantly. Our results first showed that the RBD-Fc vaccine could induce both humoral and cellular immune responses and might be an optional strategy to control COVID-19.
Highlights
The novel coronavirus pneumonia (COVID-19) that broke out in Wuhan, Hubei Province, in December 2019, was induced by the SARS-CoV-2 virus [1]
The receptor binding domain (RBD), spanning from residues 330–583 of the spike protein of the SARS-CoV2 (Figure 2A), was fused with a modified Fc fragment of mouse IgG1 or human IgG1 (Figure 2B) to form RBD-hFc or RBD-mFc proteins (Figure 2C). These two types of SARSCoV-2 RBD recombinant protein were successfully harvested from culture supernatant of transfected HEK293T cells, and purified using a protein A/G chromatographic column and a Superdex 200 increase column (Figure 2D,E)
The RBD, spanning from residues 330–583 of the spike protein of the SARS-CoV-2 (Figure 2A), was fused with a modified Fc fragment of mouse IgG1 or human IgG1 (Figure 2B) to form RBD-hFc or RBD-mFc proteins (Figure 2C). These two types of SARS-CoV-2 RBD recombinant protein were successfully harvested from culture supernatant of transfected HEK293T cells, and purified using a protein A/G chromatographic column and a Superdex 200 increase column (Figure 2D,E)
Summary
The novel coronavirus pneumonia (COVID-19) that broke out in Wuhan, Hubei Province, in December 2019, was induced by the SARS-CoV-2 virus [1]. As for the recombinant subunit vaccine, only one product (ZF2001) based on the tandem-repeat dimeric RBD protein has been permitted for widespread use [9]. Most of the NAbs target RBD [14,15], and partial antigen epitopes in other domains of the S protein may even cause the antibody-dependent effects (ADEs) [16] Some vaccines, such as MERS and SARS subunit vaccines, were developed based on the RBD protein [17,18]. A recombinant vaccine based on the RBD-Fc fusion protein could induce good humoral immune response in both nonhuman primates and mice [21]. We measured the longitudinal dynamics of the IgG and neutralizing antibody responses for three months Both humoral and cellular immune responses were detected in recombinant RBD subunit vaccine-immunized mice. We demonstrated an effective subunit vaccine based on the RBD-Fc fusion protein
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