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Summary

Using a library of recombinant VSV for coronavirus spike proteins, this study demonstrates that SARS-CoV2 uses the human ACE2 receptor and the synergistic processing by endosomal cathepsins B/L and TMPRSS2 proteinases for productive infection of cell lines. The latter is the major endosomal protein involved in the priming of the spike protein, as evidenced by significant inhibition of infection by the TMPRSS2 inhibitor, camostat mesylate, which affects both SARS-CoV-1 and -2 entry. Finally, sera of patients recovered from SARS-CoV show cross-neutralization of SARS-CoV2 suggesting that 76% amino acid identity is sufficient to promote heterologous immunity.

Does the study add to current knowledge?

ACE2 and TMPRSS2 are major cellular components promoting SARS-2-S driven infection of cell lines.

Does it challenge existing paradgims?

No

Research highlights

  1. VSV bearing SARS-Cov-2 S protein (SARS-2-S) shows SARS-2-S binds to ACE2 and utilises host TMPRSS2 and cathepsin B/L for S protein priming
  2. TMPRSS2 inhibitor camostat mesylate inhibited viral entry by VSV particles bearing SARS-2-S (with no unwanted cytotoxic effects) and camostat mesylate in conjunction with the CatB/L inhibitor E-64d fully abrogated viral entry into human lung cell line
  3. Sera obtained from SARS patients and rabbit sera raised against SARS-S reduced SARS-2-S driven entry of recombinant VSV-S particles into cells

Research Impact

For serological detection of SARS-COV-2: NO

For inhibition of COVID19 transmission: Potentially.

For treatment of SARS-COV-2 positive individuals: Potentially.

Methodology

Recombinant VSV library for screening of cell types, susceptible, receptors and serine and cysteine proteases involved in infection.

Strengths and weaknesses of the paper

Novelty: Shows how SARS-CoV-2 uses similar infection strategy to SARS-CoV-1 exploiting host ACE2 as receptor and TMPRSS2/cathepsin for activating the fusion mechanism of the spike protein. This work further describes camostat mesylate, which prevents virus entry by inhibiting TMPRSS2, as a potential antiviral. The cathepsin B/L inhibitors E-64d further shows an additive inhibitory effect with camostat mesylate.

Reproducibility: All in vitro experiments using human cell lines. No animal models.

Appropriate statistics Yes. Very simple study.

Low numbers

Using model coronavirus and not SARS-COV-2: Use of a recombinant non-related virus. No SARS-CoV2 viral particles used for corroboration of the phenotype. Important as other viral proteins might fine tune attachment and membrane fusion to the limiting membrane of the endosome.

Comparable incorporation of SARS-S and SARS-2-S into VSV particles has not been formally demonstrated experimentally (although both proteins are incorporated robustly)

Findings easily translated: No.