A Bacterially Expressed SARS-CoV-2 Receptor Binding Domain Fused With Cross-Reacting Material 197 A-Domain Elicits High Level of Neutralizing Antibodies in Mice

Liqin Liu; Tingting Chen; Lizhi Zhou; Jie Sun; Yuqian Li; Meifeng Nie; Hualong Xiong; Yuhe Zhu; Wenhui Xue; Yangtao Wu; Tingting Li; Tianying Zhang; Zhibo Kong; Hai Yu; Jun Zhang; Ying Gu; Qingbing Zheng; Qinjian Zhao; Ningshao Xia; Shaowei Li

doi:10.3389/fmicb.2022.854630

A Bacterially Expressed SARS-CoV-2 Receptor Binding Domain Fused With Cross-Reacting Material 197 A-Domain Elicits High Level of Neutralizing Antibodies in Mice

Front Microbiol. 2022 Apr 26:13:854630. doi: 10.3389/fmicb.2022.854630. eCollection 2022.

Authors

Liqin Liu^{1

2}, Tingting Chen^{1

2}, Lizhi Zhou^{1

2}, Jie Sun^{1

2}, Yuqian Li^{1

2}, Meifeng Nie^{1

2}, Hualong Xiong^{1

2}, Yuhe Zhu^{1

2}, Wenhui Xue^{1

2}, Yangtao Wu^{1

2}, Tingting Li^{1

2}, Tianying Zhang^{1

2}, Zhibo Kong^{1

2}, Hai Yu^{1

2}, Jun Zhang^{1

2}, Ying Gu^{1

2}, Qingbing Zheng^{1

2}, Qinjian Zhao^{1

2}, Ningshao Xia^{1

2}, Shaowei Li^{1

2}

Affiliations

¹ State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, School of Life Sciences, School of Public Health, Xiamen University, Xiamen, China.
² National Institute of Diagnostics and Vaccine Development in Infectious Diseases, Xiamen University, Xiamen, China.

Abstract

The Coronavirus disease 2019 (COVID-19) pandemic presents an unprecedented public health crisis worldwide. Although several vaccines are available, the global supply of vaccines, particularly within developing countries, is inadequate, and this necessitates a need for the development of less expensive, accessible vaccine options. To this end, here, we used the Escherichia coli expression system to produce a recombinant fusion protein comprising the receptor binding domain (RBD) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; residues 319-541) and the fragment A domain of Cross-Reacting Material 197 (CRM197); hereafter, CRMA-RBD. We show that this CRMA-RBD fusion protein has excellent physicochemical properties and strong reactivity with COVID-19 convalescent sera and representative neutralizing antibodies (nAbs). Furthermore, compared with the use of a traditional aluminum adjuvant, we find that combining the CRMA-RBD protein with a nitrogen bisphosphonate-modified zinc-aluminum hybrid adjuvant (FH-002C-Ac) leads to stronger humoral immune responses in mice, with 4-log neutralizing antibody titers. Overall, our study highlights the value of this E. coli-expressed fusion protein as an alternative vaccine candidate strategy against COVID-19.

Keywords: CRM197 A domain; Escherichia coli expression system; SARS-CoV-2; adjuvant; receptor binding domain; vaccine.