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.