Seth J. Zost
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Researcher at Vanderbilt University Medical Center
Cell Reports, 2019-12-24
Antibodies targeting the receptor binding site (RBS) of the influenza virus hemagglutinin (HA) protein are usually not broadly-reactive because their footprints are typically large and extend to nearby variable HA residues. Here, we identified several human H3N2 HA RBS-targeting monoclonal antibodies (mAbs) that were sensitive to substitutions in conventional antigenic sites and were not broadly-reactive. However, we also identified one H3N2 HA RBS-targeting mAb that was exceptionally broadly reactive despite being sensitive to substitutions in residues outside of the RBS. We determined that similar antibodies are present at measurable levels in the sera of some individuals but that they are inefficiently elicited by conventional vaccines. Our data indicate that some HA RBS-targeting antibodies can be surprisingly effective against variable viral strains even if they are somewhat sensitive to substitutions in HA residues adjacent to the RBS.
A longstanding question is how influenza evolves to escape human immunity, which is polyclonal and can target many distinct epitopes on the virus. Here we map how all amino-acid mutations to influenza's major surface protein affect viral neutralization by polyclonal human sera. The serum of some individuals is so focused that it selects single mutations that reduce viral neutralization by over an order of magnitude. However, different viral mutations escape the sera of different individuals. This individual-to-individual variation in viral escape mutations is not present among ferrets, which are frequently used as a model in influenza studies. Our results show how different single mutations help influenza escape the immunity of different members of the human population, a phenomenon that could shape viral evolution and disease susceptibility.
Influenza viruses grown in eggs for the purposes of vaccine generation often acquire mutations during egg adaptation or possess differential glycosylation patterns than viruses circulating amongst humans. Here, we report that seasonal influenza virus vaccines possess an egg-derived sulfated N-acetyllactosamine (LacNAc) that is an antigenic decoy. Half of subjects that received an egg-grown vaccine mounted an antibody response against this egg-derived antigen. Egg-binding monoclonal antibodies specifically bind viruses grown in eggs, but not viruses grown in other chicken derived cells, suggesting only egg-grown vaccines can induce anti-LacNAc antibodies. Notably, antibodies against the sulfated LacNAc utilized a restricted antibody repertoire and possessed features of natural antibodies, as most antibodies were IgM and have simple heavy chain complementarity determining region 3. By analyzing a public dataset of influenza virus vaccine induced plasmablasts, we discovered egg-binding public clonotypes that were shared across studies. Together, this study shows that egg-grown vaccines can induce antibodies against an egg-associated glycan, which may divert the host immune response away from protective epitopes.
The SARS-CoV-2 pandemic has led to an urgent need to understand the molecular basis for immune recognition of SARS-CoV-2 spike (S) glycoprotein antigenic sites. To define the genetic and structural basis for SARS-CoV-2 neutralization, we determined the structures of two human monoclonal antibodies COV2-2196 and COV2-21301, which form the basis of the investigational antibody cocktail AZD7442, in complex with the receptor binding domain (RBD) of SARS-CoV-2. COV2-2196 forms an "aromatic cage" at the heavy/light chain interface using germline-encoded residues in complementarity determining regions (CDRs) 2 and 3 of the heavy chain and CDRs 1 and 3 of the light chain. These structural features explain why highly similar antibodies (public clonotypes) have been isolated from multiple individuals1-4. The structure of COV2-2130 reveals that an unusually long LCDR1 and HCDR3 make interactions with the opposite face of the RBD from that of COV2-2196. Using deep mutational scanning and neutralization escape selection experiments, we comprehensively mapped the critical residues of both antibodies and identified positions of concern for possible viral escape. Nonetheless, both COV2-2196 and COV2-2130 showed strong neutralizing activity against SARS-CoV-2 strain with recent variations of concern including E484K, N501Y, and D614G substitutions. These studies reveal germline-encoded antibody features enabling recognition of the RBD and demonstrate the activity of a cocktail like AZD7442 in preventing escape from emerging variant viruses.
Cell Host & Microbe, 2020-11-20
Antibodies targeting the SARS-CoV-2 spike receptor-binding domain (RBD) are being developed as therapeutics and make a major contribution to the neutralizing antibody response elicited by infection. Here, we describe a deep mutational scanning method to map how all amino-acid mutations in the RBD affect antibody binding, and apply this method to 10 human monoclonal antibodies. The escape mutations cluster on several surfaces of the RBD that broadly correspond to structurally defined antibody epitopes. However, even antibodies targeting the same RBD surface often have distinct escape mutations. The complete escape maps predict which mutations are selected during viral growth in the presence of single antibodies, and enable us to design escape-resistant antibody cocktails–including cocktails of antibodies that compete for binding to the same surface of the RBD but have different escape mutations. Therefore, complete escape-mutation maps enable rational design of antibody therapeutics and assessment of the antigenic consequences of viral evolution. ### Competing Interest Statement J.E.C. has served as a consultant for Sanofi; is on the Scientific Advisory Boards of CompuVax and Meissa Vaccines; is a recipient of previous unrelated research grants from Moderna and Sanofi; and is a founder of IDBiologics. Vanderbilt University has applied for patents concerning SARS-CoV-2 antibodies analyzed in this work. S.P.J.W. and P.W.R. have filed a disclosure with Washington University for the recombinant VSV. The other authors declare no competing interests.
Adaptive immunity to influenza A virus is limited by frequent mutations in the immunodominant head of hemagglutinin (HA). Over the last century, the upward trend in HA-head glycosylation indicates glycan addition can increase fitness, but its role in viral evolution remains unclear. Here, we report glycan evolution follows a clock-like rhythm, pacing the timeline, trajectory, and replacement of HA. Following pandemic introduction, glycans are added to HA at 4- to 6-year intervals, until a functional glycan limit is reached, after which, at 9- to 12-year intervals, glycans are either swapped between different sites, or the HA is replaced by a novel pandemic virus. Using this, we predicted the appearance of the newest glycan on pH1N1 HA. Phylogeographic reconstruction suggests these highly fit strains originated in the Middle East, before rapidly replacing all strains globally. Going forward, we can use this simple algorithm to forecast future glycan evolution and identify seasons with higher pandemic potential.