Anti-S2 antibodies responsible for the SARS-CoV-2 infection-induced serological cross-reactivity against MERS-CoV and MERS-related coronaviruses

Minxiang Xie ^1,2,3,4* Qiao Wang ^1* Lei Sun ^5* Siyuan Sun ⁶ Jiaying He ⁷ Luotian Liu ⁶ Yuzhen Zhu ⁸ Yuru Han ⁶ Song Xue ⁶ Xiaofang Peng ⁶ Yinong Qiu ⁵ Yiming Long ⁶ Tianyu Lu ⁶ Wei Wu ⁶ Anqi Xia ⁶ Yunjiao Zhou ^10,9 Yan Yan ⁶ Qingsong Zhang ⁶ Yidan Gao ⁶ Lu Lu ⁶

• ¹ Key Laboratory of Medical Molecular Virology, School of Basic Medical Sciences, Fudan University, Shanghai, Beijing Municipality, China
• ² Shanghai Institute of Infectious Diseases and Biosecurity, Fudan University, Shanghai, Shanghai Municipality, China
• ³ Shanghai Frontiers Science Center of Pathogenic Microbes and Infection, Shanghai, China
• ⁴ School of Basic Medical Sciences, Shanghai Medical College, Fudan University, Shanghai, China
• ⁵ Institute of Biomedical Sciences, Fudan University, Shanghai, Shanghai Municipality, China
• ⁶ Fudan University, Shanghai, China
• ⁷ Microbiological Testing Department，Baoshan District Center for Disease Control and Prevention, Shanghai, China
• ⁸ Department of gastroenterology, Jingan District Central Hospitals, Fudan University, Shanghai, China
• ⁹ School of Medicine, Tongji University, Shanghai, Shanghai Municipality, China
• ¹⁰ Fundamental Research Center, Shanghai Yangzhi Rehabilitation Hospital (Shanghai Sunshine Rehabilitation Center), School of Medicine, Tongji University, Shanghai, China

Sarbecoviruses, such as SARS-CoV-2, utilize angiotensin-converting enzyme 2 (ACE2) as the entry receptor; while merbecoviruses, such as MERS-CoV, use dipeptidyl peptidase 4 (DPP4) for viral entry. Recently, several MERS-related coronaviruses, NeoCoV and PDF-2180, were reported to use ACE2, the same receptor as SARS-CoV-2, to enter cells, raising the possibility of potential recombination between SARS-CoV-2 and MERS-related coronaviruses within the co-infected ACE2-expressing cells. However, facing this potential recombination risk, the serum and antibody cross-reactivity against MERS/MERS-related coronaviruses after SARS-CoV-2 vaccination and/or infection is still elusive. Here, in this study, we showed that the serological cross-reactivity against MERS/MERS-related S proteins could be induced by SARS-CoV-2 infection but not by inactivated SARS-CoV-2 vaccination. Further investigation revealed that this serum cross-reactivity is due to monoclonals recognizing relatively conserved S2 epitopes, such as fusion peptide and stem helix, but not by antibodies against the receptor-binding domain (RBD), N-terminal domain (NTD) or subdomain-1 (SD1). Some of these anti-S2 cross-reactive mAbs showed cross-neutralizing activity, while none of them exhibited antibody-dependent enhancement (ADE) effect of viral entry in vitro. Together, these results dissected the SARS-CoV-2 infection-induced serological cross-reactivity against MERS/MERS-related coronaviruses, and highlighted the significance of conserved S2 region for the design and development of pan-β-coronaviruses vaccines.