RUNX:CBFb complex constrains fetal-restricted innate T cell generation from adult lymphopoietic progenitors

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Summary During intrauterine development the immune system generates cell subsets that will colonize mucosal barriers. This process is restricted to a fetal/neonatal window as adult cells are unable to replenish mucosal lymphocytes. Despite this sharp temporal constraint, the molecular mechanisms underpinning adult versus fetal hematopoietic potential has not been fully elucidated. We propose that the expression of a specific set of fetal factors controlled by the dosage of the transcriptional complex RUNX:CBF2 is responsible for the acquisition of fetal developmental potential. We made the unexpected discovery that CBF2 haploinsufficiency confers adult hematopoietic stem cells the ability to reconstitute the prototypical type 3 cytokine producing T17 cells. Transcriptional analysis of adult hematopoietic progenitors in CBF2 heterozygous mice revealed the upregulation of genes usually active in embryos and likely controlled directly by RUNX:CBF2 complex. We propose that an ensemble of transcription factors (TFs) central to embryonic hematopoiesis can instruct adult progenitors to acquire fetal lymphopoietic potential. To test this hypothesis we will take advantage of the in utero transplantation assay that faithfully recapitulate the fetal niche. Developmental assays of conventional or genetically altered precursors in utero will help dissect the cellular and transcriptional requirements during the generation of mucosal innate-like lymphoid cells. We also propose to exploit the developmental plasticity imposed by CBF2 haploinsufficiency to rewire adult regulatory circuits in adult progenitors to adopt an embryonic developmental potential. Candidate fetal factors that are regulated by RUNX:CBF2 will be overexpressed in adult progenitors for their ability to generate immune subsets with a restricted fetal origin. In Aim 1, we will determine the overall chromatin landscape that characterizes CBF2 heterozygous adult progenitors and permit enhanced reconstitution of fetal-type innate lymphocytes. In Aim 2, we will identify the genes required for reprogramming adult hematopoietic progenitors towards fetal lymphopoietic potential. Our long term goal is to map with high granularity transcriptional changes that license hematopoietic progenitors to give rise to tissue resident fetal/neonatal-derived immune cells.