Reduced ability of convalescent sera to recognize RDB variants
To determine whether RBDWT -specific immune sera might have a reduced ability to bind to mutated RBDs we performed ELISA and Biolayer Interferometry using sera from convalescent patients (shown in Fig. 3). As expected RBDWT was well recognized by convalescent sera in ELISA experiments. In contrast, RBDK417N and RBDN501Y were recognized in a slightly impaired fashion (shown in Fig. 3A). In marked contrast, mutation at position 484 essentially abolished recognition of both RBDE484K and RBDTRIP. Corresponding results were obtained using Biolayer Interferometry (shown in Fig. 3B). RBD-specific neutralizing antibodies typically block interaction of RBD with the viral receptor ACE2. We therefore assessed whether reduced binding of convalescent sera to RBDTRIP was paralleled by reduced ability of these antibodies to block binding of ACE2 to the triple mutant (shown in Fig. 3C). These experiments demonstrate that human convalescent sera essentially failed to block binding of ACE2 to RBDTRIP, explaining why SARS-CoV-2- induced antibodies largely fail to neutralize the triple mutant variants.