Escape from Human Monoclonal Antibody Neutralization Affects In Vitro and In Vivo Fitness of Severe Acute Respiratory Syndrome Coronavirus

Rockx, Barry; Donaldson, Eric; Frieman, Matthew; Sheahan, Timothy; Corti, Davide; Lanzavecchia, Antonio; Baric, Ralph S.

BACKGROUND: Severe Acute Respiratory Syndrome (SARS) emerged as a human disease in 2002 and detailed phylogenetic analysis and epidemiological studies have suggested that the SARS-Coronavirus (SARS-CoV) originated from animals. The Spike (S) glycoprotein has been identified as a major target of protective immunity and contains at least three regions that are targeted by neutralizing antibodies in the S1 and S2 domains. We previously characterized a panel of neutralizing human monoclonal antibodies (MAbs) but the majority of epitopes recognized by the MAbs remained unknown. METHODS: In this study we generated neutralization escape mutants and studied the effect of these neutralization escape mutations on human and animal receptor usage as well as in vitro and in vivo fitness. RESULTS: Distinct but partially overlapping sets of amino acids were identified that are critical to the binding of MAbs with differential neutralization profiles. We also identified possible interactions between the S1 and S2 domains of the SARS-CoV S glycoprotein. Finally, we showed that escape from neutralization usually attenuates SARS-CoV infection. CONCLUSIONS: These data provide a mechanism to overcome neutralization escape by using broadly cross reactive cocktails of cross-neutralizing MAbs that recognize residues within the receptor binding domain, critical for virus replication and virulence.