An in vitro model of human hematopoiesis identifies a regulatory role for the aryl hydrocarbon receptor.

In vitro models to study simultaneous development of different human immune cells and hematopoietic lineages are lacking. We identified and characterized, using single-cell methods, an in vitro stromal-cell free culture system of human hematopoietic stem and progenitor cell (HSPC) differentiation that allows concurrent development of multiple immune cell lineages. The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor influencing many biological processes in diverse cell types. Using this in vitro model, we found that AHR activation by the highly specific AHR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), drives differentiation of human umbilical cord-blood derived CD34+ HSPCs towards monocytes and granulocytes with a significant decrease in lymphoid and megakaryocyte lineage specification that may lead to reduced immunocompetence. Through use of single-cell modalities, we also discovered for the first time, that AHR activation decreased in progenitor cells, at both transcriptomic and protein levels, the expression of BCL11A and IRF8 which are critical genes involved in hematopoietic lineage specification processes. Our in vitro model of hematopoiesis, coupled with single cell tools, therefore allows for a better understanding of the role played by AHR in modulating hematopoietic differentiation.