Long-lasting B cell convergence to distinct broadly reactive epitopes following vaccination with chimeric influenza virus hemagglutinins II

In a phase I clinical trial, a chimeric hemagglutinin (cHA) immunogen induced antibody responses against the conserved HA stalk domain as designed. Here, we determined the specificity, function, and subsets of B cells induced by cHA vaccination by pairing single cell RNA-sequencing and B cell receptor repertoire sequencing. We have shown that the cHA inactivated vaccine with a squalene-based adjuvant induced a robust activated B cell and memory B cell (MBC) phenotype against two broadly neutralizing epitopes in the stalk domain. The overall specificities of the acute plasmablast (PB) and MBC responses clonally overlapped, suggesting B cell convergence to these broadly protective epitopes. At one-year post-immunization, we identified that cHA vaccination reshaped the HA-specific MBC pool to enrich for stalk-binding B cells. Altogether, these data indicate the cHA vaccine induced robust and durable B cell responses against broadly protective epitopes of the HA stalk domain, in line with serological data. MBCs (CD19+IgD-Probe+) from cHA vaccine and seasonal influenza vaccine recipients were sort purified for analysis of transcriptome and V(D)J gene usage