A Single-Cell Atlas of Transcriptional and Immunoglobulin Repertoire Evolution in Early B Cell Development.

The development of human B cells in the bone marrow can be separated into functionally and transcriptionally distinct subsets, which while canonically described have yet to be profiled deeply and individually and with NGS and bioinformatic techniques. In this study, single-cell RNA sequencing was performed on 65,110 B cells from six healthy donors to observe the foundation of the diversity observed in mature immune repertoires. Following the established narrative of development, committed B cells undergo heavy and light chain recombination, which together form the functional BCR. However, a granular per-subset phenotypic analysis reveals proliferative bursts following each recombination event, an aspect of BCR recombination previously undescribed in the pro-B phase of development. Heavy and light chain pairing becomes more similar to that of mature, circulating B cells with progress through lymphopoiesis, deleting features associated with autoreactivity. Prominent among these repertoire alterations is a substantial shortening of heavy chain CDR3s, and changes in V, D, and J gene usage. This study provides a detailed snapshot of the transcriptomic and repertoire genetics landscape of developing B cells, providing a deeper understanding of the repertoire-shaping influence of early selection processes, and introducing new avenues for repertoire development research.