Coordinated regulation of self-renewal and cell cycle during human lympho-myeloid lineage restriction

• Identification of phenotypes representing the earliest lymphoid and neutrophil/monocyte lineages emerging from shared bipotent progenitors.

• Cell cycle shortening precedes the restriction of lymphoid and myeloid potentials.

Recent studies indicate the human lympho-myeloid restriction process to be a different and more heterogeneous one than historically inferred. Here we describe the development of bulk and clonal culture systems that efficiently support early B-lymphoid differentiation and its use to elucidate the biological and molecular changes that accompany their initial restriction from subsets of CD34+ human cord blood cells with lympho-myeloid-limited potential. Analyses of these changes revealed that the acquisition of B-lymphoid- and neutrophil/monocyte (NM)-restricted properties are accompanied by a concomitantly accelerated and lineage-shared cell cycling activity and loss of self-renewal potential. Single-cell transcriptome analysis identified reduced expression of multiple self-renewal-associated genes and an accompanying heterogeneous activation of lineage-regulatory modules during the production of B, NM and dendritic cell precursors. By applying a novel culture system that supports early human lymphoid differentiation, we uncover a shared mechanism of proliferation control, along with persistent biological and transcriptional heterogeneity in cells undergoing B and NM lineage restriction.