Germline-Encoded Affinity for Cognate Antigen Enables Vaccine Amplification of a Human Broadly Neutralizing Response...

Antibody paratopes are formed by hypervariable complementarity-determining regions (CDRH3s) and variable gene-encoded CDRs. The latter show biased usage in human broadly neutralizing antibodies (bnAbs) against both HIV and influenza virus, suggesting the existence of gene-endowed targeting solutions that may be amenable to pathway amplification. To test this, we generated transgenic mice with human CDRH3 diversity but simultaneously constrained to individual user-defined human immunoglobulin variable heavy-chain (V_H) genes, including IGHV1-69, which shows biased usage in human bnAbs targeting the hemagglutinin stalk of group 1 influenza A viruses. Sequential immunization with a stalk-only hemagglutinin nanoparticle elicited group 1 bnAbs, but only in IGHV1-69 mice. This V_H-endowed response required minimal affinity maturation, was elicited alongside pre-existing influenza immunity, and when IGHV1-69 B cells were diluted to match the frequency measured in humans. These results indicate that the human repertoire could, in principle, support germline-encoded bnAb elicitation using a single recombinant hemagglutinin immunogen.