The neutralizing antibody response to influenza virus is dominated by antibodies that bind to the globular head of haemagglutinin, which undergoes a continuous antigenic drift, necessitating the re-formulation of influenza vaccines on an annual basis. Recently, several laboratories have described a new class of rare influenza-neutralizing antibodies that target a conserved site in the haemagglutinin stem1,2,3,4,5,6. Most of these antibodies use the heavy-chain variable region VH1-69 gene, and structural data demonstrate that they bind to the haemagglutinin stem through conserved heavy-chain complementarity determining region (HCDR) residues. However, the VH1-69 antibodies are highly mutated and are produced by some but not all individuals6,7, suggesting that several somatic mutations may be required for their development8,9. To address this, here we characterize 197 anti-stem antibodies from a single donor, reconstruct the developmental pathways of several VH1-69 clones and identify two key elements that are required for the initial development of most VH1-69 antibodies: a polymorphic germline-encoded phenylalanine at position 54 and a conserved tyrosine at position 98 in HCDR3. Strikingly, in most cases a single proline to alanine mutation at position 52a in HCDR2 is sufficient to confer high affinity binding to the selecting H1 antigen, consistent with rapid affinity maturation. Surprisingly, additional favourable mutations continue to accumulate, increasing the breadth of reactivity and making both the initial mutations and phenylalanine at position 54 functionally redundant. These results define VH1-69 allele polymorphism, rearrangement of the VDJ gene segments and single somatic mutations as the three requirements for generating broadly neutralizing VH1-69 antibodies and reveal an unexpected redundancy in the affinity maturation process.

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This work was partly supported by the European Research Council (grant number 250348) IMMUNExplore, the Swiss National Science Foundation (grant number 141254), Fondazione Cariplo Vaccine Program (grant number 2009-3594), the Human Frontiers Science Program (grant number RGP0009/2007-C), the European Commission (grant number FP7-HEALTH-2011-280873) ADITEC and the National Institutes of Health (U19 grant number AI-057266). A.L. is supported by the Helmut Horten Foundation.

Author information

Author notes

    • Davide Corti
    •  & Antonio Lanzavecchia

    These authors contributed equally to this work.


  1. Insitute for Research in Biomedicine, Università della Svizzera Italiana, Via Vincenzo Vela 6, 6500 Bellinzona, Switzerland

    • Leontios Pappas
    • , Mathilde Foglierini
    • , Luca Piccoli
    • , Chiara Silacci
    • , Blanca Fernandez-Rodriguez
    • , Isabella Giacchetto-Sasselli
    • , Federica Sallusto
    • , Davide Corti
    •  & Antonio Lanzavecchia
  2. Department of Infectious Diseases and Vaccines MedImmune LLC, One MedImmune Way, Gaithersburg, Maryland 20878, USA

    • Nicole L. Kallewaard
    •  & Qing Zhu
  3. Viral Pathogens and Biosafety Unit, San Raffaele Scientific Institute, Via Olgettina 58, 20132 Milan, Italy

    • Filippo Turrini
    •  & Elisa Vicenzi
  4. Humabs BioMed SA, Via Mirasole 1, 6500 Bellinzona, Switzerland

    • Gloria Agatic
    •  & Davide Corti
  5. Unit of Preventive Medicine, San Raffaele Scientific Institute, Via Olgettina 58, 20132 Milan, Italy

    • Gabriele Pellicciotta
  6. Insitute for Microbiology, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland

    • Antonio Lanzavecchia


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L.Pa. designed and performed experiments, analysed the data and wrote the manuscript. L.Pa. and M.F. performed phylogenetic analysis. M.F. performed bioinformatic analysis. L.Pi. performed SPR and IF experiments. C.S., B.F.-R., G.A. and I.G.-S. provided technical support for antibody isolation and purification. F.T. and E.V. performed genotypic analysis. N.L.K. and Q.Z. designed, performed and analysed viral neutralization experiments. G.P. provided blood samples from healthy volunteers. F.S. wrote the manuscript. D.C. and A.L. designed the experiments, provided overall supervision and wrote the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Antonio Lanzavecchia.

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