SARS-CoV-2 Variant Propagation in VeroE6TMPRSS2 Cells

VeroE6_TMPRSS2 cells^{21 (link)} were obtained from Japanese Collection of Research Bioresources (JCRB) Cell Bank (Osaka, Japan). VeroE6TMPRSS2 cells were maintained in DMEM supplemented with 10% FCS, 100 μg/ml of penicillin, 100 μg/ml of streptomycin, and 1 mg/mL of G418. SARS-CoV-2 NCGM-05–2N strain (SARS-CoV-2_05–2N) was isolated from nasopharyngeal swabs of a patient with COVID-19, who was admitted to the NCGM hospital^{22 (link),23} . Five clinically isolated SARS-CoV-2 mutant strains were used in the current study: two B.1.1.7 (alpha) strains [hCoV-19/Japan/QHN001/2020 (SARS-CoV-2QHN001, GISAID Accession ID; EPI_ISL_804007) and hCoV-19/Japan/QK002/2020 (SARS-CoV-2QK002, G ISAID Accession ID; EPI_ISL_768526)] and a B.1.351 (beta) strain [hCoV-19/Japan/TY8–612-P0/2021 (SARS-CoV-2_TY8–612)] were obtained from National Institute of Infectious Diseases, Tokyo, Japan. A B.1.617.1 (kappa) strain [TKYTK5356_2021 (SARS-CoV-2₅₃₅₆, DDBJ Accession ID; LC633761)] and a B.1.617.1 (beta) strain [hCoV-19/Japan/TKYK01734/2021 (SARS-CoV-2₁₇₃₄, GISAID Accession ID; EPI_ISL_2080609)] were provided from Tokyo Metropolitan Institute of public Health, Tokyo, Japan. Each variant was confirmed to contain each VOC-specific amino acid substitutions before the assays conducted in the present study (vide infra).