Epigenetic signatures mark early peripheral human B lineage bifurcation and differential transcriptional profiles in mature populations.

Abstract

During human B cell maturation, immature transitional (T1) cells transit from bone marrow into the blood. At the subsequent immature T2 stage, a separation into IgM^hi (T2M^hi) and IgM^lo (T2M^lo) developmental trajectories has been proposed. Here, we isolate T1, T2M^hi and T2M^lo cells from human adult and cord blood for bulk and single-cell ATAC-seq, CUT&RUN, RNA-seq and CITE-seq to profile their transcriptomic and epigenetic differences. We identify accessible chromatin domains discriminating between T2M^hi and T2M^lo cells in peripheral B cell development, with signatures persisting during the differentiation of T2M^lo to naïve B cells. Similarly, memory and marginal zone B cells retain epigenetic hallmarks of their T2M^lo and T2M^hi precursors, coupled with transcriptional diversity. Imaging mass cytometry with RNAscope of spleen, appendix and tonsil further validates the spatial relationships of expressed genes. Our study thus provides insights into B lineage T2 bifurcation and describes epigenetic signatures of B cell developmental pathways.