Longitudinal BCR repertoire dynamics reveal the evolution of broadly binding antibodies following heterologous SARS-CoV-2 vaccination and breakthrough infection: a single-donor case study.

Continued SARS-CoV-2 antigenic drift and the persistent risk of zoonotic sarbecovirus spillover highlight the need for broadly protective countermeasures. Here, we longitudinally profiled the B-cell receptor (BCR) repertoire of a single volunteer who received heterologous booster vaccination followed by Omicron BF.7 breakthrough infection, integrating bulk BCR sequencing with single B-cell culture and antibody binding analysis. Breakthrough infection was associated with broadened serum neutralization across SARS-CoV-2 variants and related sarbecoviruses, consistent with recall of antibodies targeting conserved epitopes. Repertoire analysis revealed stage-specific remodeling, with high-affinity binding antibodies shifting from an IGHV1-46-enriched profile after vaccination to preferential representation of IGHV3-30-3 after infection. Isolated monoclonal antibodies exhibited nanomolar-to-picomolar binding affinities to diverse animal-derived sarbecovirus spikes, with broad binding commonly, but not universally, associated with CDRH3 lengths of 14-16 amino acids. Phylogenetic and sequence analyses defined divergent evolutionary trajectories for IGHV1-46 and IGHV3-30-3 lineages, highlighting candidate genetic features that warrant validation in larger cohorts. Together, these findings describe how sequential heterologous antigen exposures can reshape the humoral repertoire in one individual and generate hypotheses for future pan-sarbecovirus antibody and vaccine studies.