Convergent and clonotype-enriched mutations in the light chain drive affinity maturation of a public antibody

Public antibodies that recognize conserved epitopes are critical for vaccine development, and identifying somatic hypermutations (SHMs) that enhance antigen affinity in these public responses is key to guiding vaccine design for better protection. We propose that affinity-enhancing SHMs are selectively enriched in public antibody clonotypes, surpassing the background frequency seen in antibodies carrying the same V genes, but with different epitope specificities. Employing a human IGHV4-59/IGKV3-20 public antibody as a model, we compare SHM signatures in antibodies also using these V genes, but recognizing other epitopes. Critically, this comparison identified clonotype-enriched mutations in the light chain. Our analyses also show that these SHMs, in combination, enhance binding to a previously uncharacterized viral epitope, with antibody responses to it increasing after multiple vaccinations. Our findings offer a framework for identifying affinity-enhancing SHMs in public antibodies based on convergence and clonotype-enrichment and can help guide vaccine design aimed to elicit public antibodies. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=138 SRC="FIGDIR/small/642041v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@1c4559eorg.highwire.dtl.DTLVardef@d12202org.highwire.dtl.DTLVardef@fca57org.highwire.dtl.DTLVardef@ad5041_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIClonotype-enriched SHMs are identified in the light chain of a public antibody, M15 C_LIO_LIThese light chain SHMs enhance affinity of M15 C_LIO_LIM15 targets a previously undescribed, conserved viral epitope C_LIO_LISerum antibody levels targeting this epitope increase after repeated vaccinations C_LI