Reduced lymphoid lineage priming promotes human hematopoietic stem cell expansion

Hematopoietic stem cells (HSCs) must balance self-renewal and lineage differentiation to regenerate the hematopoietic system throughout life. HSCs exhibit lineage-associated gene expression that keeps them responsive to demands of mature blood production. However, it is not known whether this process, termed lineage priming, directly influences HSC self-renewal. We investigated the link between stemness and lineage priming by attenuating the early lymphoid transcription factor E47 through ID2 over-expression (OE). Transcriptional profiling of ID2 OE HSCs showed down regulation of B-cell factors including EBF1 and FOXO1 with a concomitant increase in stemness programs and myeloerythroid factors including CEBPA and GATA1. This resulted in myeloid commitment bias from the earliest stages of differentiation. HSC self-renewal was strongly affected by this lineage perturbation resulting in an 11-fold expansion of HSCs. Thus, early lymphoid transcription factors antagonize human HSC self-renewal, providing a direct link between differentiation program priming and the maintenance of stem cell self-renewal. Three independent lineage depleted CB samples were transduced with P-CTRL or P-ID2 and injected into 5 mice (30 mice total). From every group of 5 mice, human lin- cells were isolated and GFP+CD34+CD38-CD45RA- HSPCs were sorted by FACS.