“…For human IgG1 expression of S2P6 ( 17 ), variable region sequences of heavy and light chains were synthesized (Integrated DNA Technologies, Coralville, IA, USA) and cloned into pCEP-WPRE-hCH (hIgG1) and pCEP-WPRE-hCK for heavy and light chains, respectively, via the NEBuilder HiFi DNA Assembly system (New England Biolabs, Ipswich, MA, USA). Heavy and light chain constructs were cotransfected into ExpiCHO cells (Thermo Fisher Scientific, Waltham, MA, USA), and recombinant IgG molecules were produced and purified as previously described ( 18 ). The following antibodies were used: anti-S2 mAbs NBP2 (Novus Biologicals, Centennial, CO, USA, Cat#NBP2-90999) and MA5 (Thermo Fisher Scientific, Cat#MA5-35946), anti-RBD mAb MM43 (Sino Biological, Cat# 40591-MM43) and anti-SARS-CoV-2 NP mAb 1G6 ( 19 ).…”