Waves of SARS-CoV-2 infection have resulted from the emergence of viral variants with neutralizing antibody resistance mutations. Simultaneously, repeated antigen exposure has generated affinity ...matured B cells, producing broadly neutralizing receptor binding domain (RBD)-specific antibodies with activity against emergent variants. To determine how SARS-CoV-2 might escape these antibodies, we subjected chimeric viruses encoding spike proteins from ancestral, BA.1 or BA.2 variants to selection by 40 broadly neutralizing antibodies. We identify numerous examples of epistasis, whereby in vitro selected and naturally occurring substitutions in RBD epitopes that do not confer antibody resistance in the Wuhan-Hu-1 spike, do so in BA.1 or BA.2 spikes. As few as 2 or 3 of these substitutions in the BA.5 spike, confer resistance to nearly all of the 40 broadly neutralizing antibodies, and substantial resistance to plasma from most individuals. Thus, epistasis facilitates the acquisition of resistance to antibodies that remained effective against early omicron variants.
Vaccination will likely be a key component of strategies to curtail or prevent future sarbecovirus pandemics and to reduce the prevalence of infection and disease by future SARS-CoV-2 variants. A ..."pan-sarbecovirus" vaccine, that provides maximum possible mitigation of human disease, should elicit neutralizing antibodies with maximum possible breadth. By positioning multiple different receptor binding domain (RBD) antigens in close proximity on a single immunogen, it is postulated that cross-reactive B cell receptors might be selectively engaged. Heteromultimeric vaccines could therefore elicit individual antibodies that neutralize a broad range of viral species. Here, we use model systems to investigate the ability of multimeric sarbecovirus RBD immunogens to expand cross-reactive B cells and elicit broadly reactive antibodies. Homomultimeric RBD immunogens generated higher serum neutralizing antibody titers than the equivalent monomeric immunogens, while heteromultimeric RBD immunogens generated neutralizing antibodies recognizing each RBD component. Moreover, RBD heterodimers elicited a greater fraction of cross-reactive germinal center B cells and cross-reactive RBD binding antibodies than did homodimers. However, when serum antibodies from RBD heterodimer-immunized mice were depleted using one RBD component, neutralization activity against the homologous viral pseudotype was removed, but neutralization activity against pseudotypes corresponding to the other RBD component was unaffected. Overall, simply combining divergent RBDs in a single immunogen generates largely separate sets of individual RBD-specific neutralizing serum antibodies that are mostly incapable of neutralizing viruses that diverge from the immunogen components.
Despite mRNA vaccination, elderly individuals remain especially vulnerable to severe consequences of SARS-CoV-2 infection. Here, we compare the memory B cell responses in a cohort of elderly and ...younger individuals who received mRNA booster vaccinations. Plasma neutralizing potency and breadth were similar between the two groups. By contrast, the absolute number of SARS-CoV-2-specific memory B cells was lower in the elderly. Antibody sequencing revealed that the SARS-CoV-2-specific elderly memory compartments were more clonal and less diverse. Notably, memory antibodies from the elderly preferentially targeted the ACE2-binding site on the RBD, while those from younger individuals targeted less accessible but more conserved epitopes. Nevertheless, individual memory antibodies elicited by booster vaccines in the elderly and younger individuals showed similar levels of neutralizing activity and breadth against SARS-CoV-2 variants. Thus, the relatively diminished protective effects of vaccination against serious disease in the elderly are associated with a smaller number of antigen-specific memory B cells that express altered antibody repertoires.
Human monoclonal antibodies (mAbs) that target the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein have been isolated from convalescent individuals and developed into ...therapeutics for SARS-CoV-2 infection. However, therapeutic mAbs for SARS-CoV-2 have been rendered obsolete by the emergence of mAb-resistant virus variants. Here we report the generation of a set of six human mAbs that bind the human angiotensin-converting enzyme-2 (hACE2) receptor, rather than the SARS-CoV-2 spike protein. We show that these antibodies block infection by all hACE2 binding sarbecoviruses tested, including SARS-CoV-2 ancestral, Delta and Omicron variants at concentrations of ~7-100 ng ml
. These antibodies target an hACE2 epitope that binds to the SARS-CoV-2 spike, but they do not inhibit hACE2 enzymatic activity nor do they induce cell-surface depletion of hACE2. They have favourable pharmacology, protect hACE2 knock-in mice against SARS-CoV-2 infection and should present a high genetic barrier to the acquisition of resistance. These antibodies should be useful prophylactic and treatment agents against any current or future SARS-CoV-2 variants and might be useful to treat infection with any hACE2-binding sarbecoviruses that emerge in the future.
