Structural Basis for Potent Cross-Neutralizing Human Monoclonal Antibody Protection against Lethal Human and Zoonotic Severe Acute Respiratory Syndrome Coronavirus Challenge

Abstract

Severe acute respiratory syndrome coronavirus (SARS-CoV) emerged in 2002, and detailed phylogenetic and epidemiological analyses have suggested that it originated from animals. The spike (S) glycoprotein has been identified as a major component of protective immunity, and 23 different amino acid changes were noted during the expanding epidemic. Using a panel of SARS-CoV recombinants bearing the S glycoproteins from isolates representing the zoonotic and human early, middle, and late phases of the epidemic, we identified 23 monoclonal antibodies (MAbs) with neutralizing activity against one or multiple SARS-CoV spike variants and determined the presence of at least six distinct neutralizing profiles in the SARS-CoV S glycoprotein. Four of these MAbs showed cross-neutralizing activity against all human and zoonotic S variants in vitro, and at least three of these were mapped in distinct epitopes using escape mutants, structure analyses, and competition assays. These three MAbs (S109.8, S227.14, and S230.15) were tested for use in passive vaccination studies using lethal SARS-CoV challenge models for young and senescent mice with four different homologous and heterologous SARS-CoV S variants. Both S227.14 and S230.15 completely protected young and old mice from weight loss and virus replication in the lungs for all viruses tested, while S109.8 completely protected mice from weight loss and clinical signs in the presence of viral titers. We conclude that a single human MAb can confer broad protection against lethal challenge with multiple zoonotic and human SARS-CoV isolates, and we identify a robust cocktail formulation that targets distinct epitopes and minimizes the likely generation of escape mutants.

Synthetic recombinant bat SARS-like coronavirus is infectious in cultured cells and in mice

“…We have identified several hmAbs that bind distinct, conserved locations in the SARS-CoV RBD and neutralize strains that originate from animal and human hosts (31). These hmAbs did efficiently neutralize Bat-SRBD, an important finding as it was not previously clear that mAbs targeting the SARS-CoV RBD would neutralize virus in the context of a different Spike backbone.…”

“…However, Bat-SRBD replicated poorly in vivo, calling for additional modifications to facilitate studies in mouse models. Robust structural information exists on the RBD-ACE2 interaction (29), mutations affecting this interaction have been identified (22,31), and Rosetta-modeling of short range RBD-mACE2 receptor interfaces can identify key residues essential for retargeting the host specificity of Bat-SRBD (Fig. S3) (48).…”

“…In parallel, these sera did not neutralize SARS-CoV infectivity, suggesting that the antibodies recognize epitopes in Spike outside the RBD in Bat-SRBD. Because the RBD appears to be the minimal motif required to alter host range of the Bat-SCoV precursor, we also tested whether Bat-SRBD could be neutralized with human monoclonal antibodies (hmAbs S109.8, S227.14, and S230.15), which recognize unique epitopes within the SARS-CoV RBD and cross-neutralize human and zoonotic SARS-CoV isolates in vitro and in vivo (31). The hmAbs neutralized Bat-SRBD, demonstrating the accessibility of the neutralizing epitopes of SRBD in the background of the Bat-SCoV Spike (Fig.…”

“…Murine pAbs specific for the Bat-SCoV Spike were generated as previously described (33). Neutralizing titers for mpAbs and hmAbs S109.8, S227.14, and S230.15 were determined by plaque reduction neutralization titer assay (PRNT50%) (31). The percentage of neutralization was calculated as follows: 1-(number of plaques in the presence of antibody/number of plaques in the absence of antibody) x 100%.…”

Progress Towards Recombinant Anti-Infective Antibodies

“…Antibodies with broad serotype specificity The use of a single therapeutic to treat disease caused by multiple sertoypes, akin to broad spectrum antibiotics, As discussed above, this can be achieved through recognition of a conserved epitope, as has been observed for SARS and influenza viruses [10, 37, 112] or engineering, as for BoNT/A1 and 2 subtypes [113]. …”