Virus-free and live-cell visualizing SARS-CoV-2 cell entry for studies of neutralizing antibodies and compound inhibitors

Zhang, Yali; Wang, Shaojuan; Wu, Yangtao; Hou, Wangheng; Yuan, Lunzhi; Sheng, Chenguang; Wang, Juan; Ye, Jianghui; Zheng, Qingbing; Ma, Jian; Xu, Jingjing; Wei, Min; Li, Zonglin; Nian, Sheng; Xiong, Hualong; Zhang, Liang; Shi, Yang; Fu, Baorong; Cao, Jiali; Yang, Chuanlai; Li, Zhiyong; Yang, Ting; Liu, Lei; Yu, Hai; Hu, Jianda; Ge, Shengxiang; Chen, Yixin; Zhang, Tianying; Zhang, Jun; Cheng, Tong; Yuan, Quan; Xia, Ningshao

The ongoing COVID-19 pandemic, caused by SARS-CoV-2 infection, has resulted in hundreds of thousands of deaths. Cellular entry of SARS-CoV-2, which is mediated by the viral spike protein and host ACE2 receptor, is an essential target for the development of vaccines, therapeutic antibodies, and drugs. Using a mammalian cell expression system, we generated a recombinant fluorescent protein (Gamillus)-fused SARS-CoV-2 spike trimer (STG) to probe the viral entry process. In ACE2-expressing cells, we found that the STG probe has excellent performance in the live-cell visualization of receptor binding, cellular uptake, and intracellular trafficking of SARS-CoV-2 under virus-free conditions. The new system allows quantitative analyses of the inhibition potentials and detailed influence of COVID-19-convalescent human plasmas, neutralizing antibodies and compounds, providing a versatile tool for high-throughput screening and phenotypic characterization of SARS-CoV-2 entry inhibitors. This approach may also be adapted to develop a viral entry visualization system for other viruses.