Expression and Purification of SARS-CoV-2 Antibodies

The variable region of the heavy and light chains of CR3022^{36 (link)}, S309^{37 (link)}, 0304–3H3^{38 (link)}, and S2P6^{39 (link)} were cloned into the TGEX-HC and TGEX-LC vectors (Antibody Design Labs), respectively, according to the manufacturer’s protocol. ACE2 (residues 1 – 615) was cloned into TGEX-HC. The plasmids were expressed in Expi293F cells (ThermoFisher Scientific) using the ExpiFectamine Transfection Kit (Thermo Fisher Scientific) and transfected according to the manufacturer’s protocol. After incubation for 6 days at 37 °C for, the cells were centrifuged at 6000 ×g for 15 minutes. The supernatant was diluted in MabSelect Binding Buffer (20 mM sodium phosphate, 150 mM NaCl, pH 7.2) and passed through a 1-mL MabSelect SuRe column (Cytiva) connected to an ÄKTA Start. The column was washed and the proteins were eluted according to the manufacturer’s protocol. Fractions containing the protein were collected and dialyzed into PBS, then the concentration of antibodies and ACE2-Fc was measured using the BCA assay.