T cell development from expanded hematopoietic progenitors reveals initiation control by Lmo2 and Flt3L priming

These cells undergo normal T cell differentiation in vivo and in vitro, verified by gene expression trajectories from single-cell RNA sequencing. Their absolute differentiation speed is slower than that of fresh progenitors but is modulated with Flt3L priming.

Leveraging this system, the earliest T cell lineage-initiating events in response to Notch signaling included chromatin opening and transcriptional activation of the TCR-Cβ locus. Acute CRISPR knockouts revealed that some transcription factors normally inherited from bone marrow progenitors impede early T cell development, with differing effects on proliferation. Among 23 factors tested, Lmo2 knockout greatly accelerated the onset of germline TCR-Cβ locus transcription and expression of Tcf7, Gata3, and Runx1 and their targets.