In vitro models for studying the simultaneous development of various human immune cells and hematopoietic lineages are currently lacking. Through the utilization of single-cell techniques, we have identified and characterized a stromal-cell-free in vitro culture system for the differentiation of human hematopoietic stem and progenitor cells (HSPCs). This system enables the concurrent development of multiple immune cell lineages.The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that influences various biological processes in different cell types. Employing our in vitro model, we observed that the activation of AHR by the persistent environmental contaminant and high affinity ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), directs the differentiation of CD34+ HSPCs derived from human umbilical cord blood toward monocytes and granulocytes. This is accompanied by a significant reduction in lymphoid and megakaryocyte lineage specification, which may lead to diminished immunocompetence. Furthermore, using single-cell techniques, we discovered that TCDD reduces the expression of key lineage specification genes, BCL11A and IRF8, at both transcriptomic and protein levels in progenitor cells. We also identified previously unreported transcriptomic and pathway level changes in early progenitor cells and in committed hematopoietic populations at the single cell level. In summary, our in vitro hematopoiesis model, combined with single-cell tools, provides valuable insights into the role of AHR and TCDD in modulating hematopoietic differentiation.
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