Two distinct durable human switched memory B cell populations are induced by vaccination and infection

The traditional definition of memory lymphocytes encompasses antigen-experienced, durable subsets that persist in the absence of antigen and are capable of responding to the antigen on subsequent encounters. We examined the relative durability of eight different non-overlapping class-switched human B cell sub-populations (excluding plasmablasts) that together encompass 100% of all human class switched B cells and identified only two long-lived B cell populations that persist after vaccination in the relative absence of their cognate antigen. In addition to canonical switched memory B cells (SWM) with an IgD- CD27+ CXCR5+ phenotype, a second, non-canonical but distinct memory population of IgD- CD27- CXCR5+ (double negative 1, DN1) B cells is also durable. Beyond surface phenotyping, DN1 memory B cells intriguingly exhibit lower levels of replacement mutations in complementarity determining as well as framework regions of their B cell receptors and have longer CDRH3 sequences relative to canonical SWM B cells. This non-canonical, human memory B cell subset is distinguished by a distinct TP63 driven transcriptional signature that has been linked to extended cell survival and these B cells persist in the circulation at least as long as canonical SWM B cells. Non-canonical human DN1 memory B cells therefore represent a second, distinct, durable, less somatically hypermutated, class-switched human memory B cell subset defined by a unique transcriptomic signature, that likely arises outside germinal centers and may have evolved to preserve immunological breadth. RNA-seq data of 18 samples, comprised of three groups, N, S, and D, representing three types of cells, i.e., "Naive B", "Switched Memory B", and "DN1 B" cells. Each group has 6 biological replicates.