Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly transmissible coronavirus responsible for the global COVID-19 pandemic. Herein, we provide evidence that SARS-CoV-2 spreads through cell-cell contact in cultures, mediated by the spike glycoprotein. SARS-CoV-2 spike is more efficient in facilitating cell-to-cell transmission than is SARS-CoV spike, which reflects, in part, their differential cell-cell fusion activity. Interestingly, treatment of cocultured cells with endosomal entry inhibitors impairs cell-to-cell transmission, implicating endosomal membrane fusion as an underlying mechanism. Compared with cell-free infection, cell-to-cell transmission of SARS-CoV-2 is refractory to inhibition by neutralizing antibody or convalescent sera of COVID-19 patients. While angiotensin-converting enzyme 2 enhances cell-to-cell transmission, we find that it is not absolutely required. Notably, despite differences in cell-free infectivity, the authentic variants of concern (VOCs) B.1.1.7 (alpha) and B.1.351 (beta) have similar cell-to-cell transmission capability. Moreover, B.1.351 is more resistant to neutralization by vaccinee sera in cell-free infection, whereas B.1.1.7 is more resistant to inhibition by vaccinee sera in cell-to-cell transmission. Overall, our study reveals critical features of SARS-CoV-2 spike-mediated cell-to-cell transmission, with important implications for a better understanding of SARS-CoV-2 spread and pathogenesis.

Highlights

  • SARS-CoV-2 j cell-to-cell transmission j cell–cell fusion j neutralization j variants of concern transfer of virus to neighboring cells [24]

  • We evaluated whether the spike protein of SARS-CoV-2 is critical for viral spread through cell–cell contact

  • Very little is currently known about their mode of spread between cells or its efficiency compared with cell-free infection

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Summary

Introduction

SARS-CoV-2 j cell-to-cell transmission j cell–cell fusion j neutralization j variants of concern transfer of virus to neighboring cells [24]. Cellto-cell transmission has the ability to evade antibody neutralization, accounting for efficient virus spread and pathogenesis, as has been shown for HIV and hepatitis C virus (HCV) [28,29,30,31,32]. We evaluated cell-to-cell transmission of SARSCoV-2 in the context of cell-free infection and in comparison with SARS-CoV. Results from this in vitro study reveal the heretofore unrecognized role of cell-to-cell transmission that potentially impacts SARS-CoV-2 spread, pathogenesis, and shielding from antibodies in vivo

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