Elucidating the characteristics and clonal evolutionary trajectory of influenza neuraminidase broadly reactive B cell.

Influenza virus neuraminidase (NA) is receiving increasing attention as a target for universal flu vaccines. Several broad NA inhibition monoclonal antibodies (BImAbs) targeting the highly conserved enzymatic pocket have been previously described. However, the molecular characteristics, clonal evolutionary trajectory, and B cell sources of BImAbs remain poorly understood. Here, using NA-mutant probes, we comprehensively profiled the immune signatures of NA-specific memory B cells (MBCs) from a healthy individual with NA cross-inhibition activity. From the NA-specific MBC repertoires, we identified a series of NA BImAbs with molecular features characterized by long HCDR3 regions with an "xxxDRxxx" motif, which exhibited broad inhibition against diverse influenza NAs. Clonal lineage tracing revealed that BImAbs followed a clonal evolutionary trajectory encompassing classical MBC (cMBC) and atypical MBC (aMBC). Both cMBC- and aMBC-derived BImAbs displayed similar inhibition against influenza NA. These findings enhance our understanding of the development of NA BImAbs and provide a foundation for the rational design of NA-based universal flu vaccines.