The aryl hydrocarbon receptor (AHR) plays an important physiological role in hematopoiesis. AHR is highly expressed in hematopoietic stem and progenitor cells (HSPCs) and inhibition of AHR results in a marked expansion of human umbilical cord blood-derived HSPCs following cytokine stimulation. It is unknown whether AHR also contributes earlier in human hematopoietic development. To model hematopoiesis, human embryonic stem cells (hESCs) were allowed to differentiate in defined conditions in the presence of the AHR antagonist StemReginin-1 (SR-1) or the AHR agonist 2,3,7,8-tetrachlorodibenzo-dioxin (TCDD). We demonstrate a significant increase in CD34CD31 hematoendothelial cells in SR-1-treated hESCs, as well as a twofold expansion of CD34CD45 hematopoietic progenitor cells. Hematopoietic progenitor cells were also significantly increased by SR-1 as quantified by standard hematopoietic colony-forming assays. Using a clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9)-engineered hESC--tdTomato reporter cell line with deletion, we further demonstrate a marked enhancement of hematopoietic differentiation relative to wild-type hESCs. We also evaluated whether AHR antagonism could promote innate lymphoid cell differentiation from hESCs. SR-1 increased conventional natural killer (cNK) cell differentiation, whereas TCDD treatment blocked cNK development and supported group 3 innate lymphoid cell (ILC3) differentiation. Collectively, these results demonstrate that AHR regulates early human hematolymphoid cell development and may be targeted to enhance production of specific cell populations derived from human pluripotent stem cells.

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BackgroundMesenchymal stem cells (MSCs) are increasingly considered to be used as biological immunosuppressants in hematopoietic stem cell transplantation (HSCT). In the early reconstitution phase following HSCT, natural killer (NK) cells represent the major lymphocyte population in peripheral blood and display graft-vs-leukemia (GvL) effects. The functional interactions between NK cells and MSCs have the potential to influence the leukemia relapse rate after HSCT. Until date, MSC-NK cell interaction studies are largely focussed on bone marrow derived (BM)-MSCs. Umbilical cord derived (UC)-MSCs might be an alternative source of therapeutic MSCs. Thus, we studied the interaction of UC-MSCs with unstimulated allogeneic NK cells.ResultsUC-MSCs could potently suppress NK cell cytotoxicity in overnight cultures via soluble factors. The main soluble immunosuppressant was identified as prostaglandin (PG)-E2. Maximal PGE2 release involved IL-1β priming of MSCs after close contact between the NK cells and UC-MSCs. Interestingly, blocking gamma-secretase activation alleviated the immunosuppression by controlling PGE2 production. IL-1 receptor activation and subsequent downstream signalling events were found to require gamma-secretase activity.ConclusionAlthough the role of PGE2 in NK cell-MSC has been reported, the requirement of cell-cell contact for PGE2 induced immunosuppression remained unexplained. Our findings shed light on this puzzling observation and identify new players in the NK cell-MSC crosstalk.Electronic supplementary materialThe online version of this article (doi:10.1186/s12964-014-0063-9) contains supplementary material, which is available to authorized users.

Human blood NK cells exert strong cytotoxicity against transformed cells and produce different cytokines and chemokines with an important role in modulating immune responses. However, the nature of NK-cell function depends on NK-cell interaction with other immune cells. One type of immune cells that communicate with NK cells are 6-sulfo LacNAc DCs (slanDCs), which comprise a major subpopulation of proinflammatory human blood DCs. In this study, we investigated the molecular mechanisms by which slanDCs interact with NK cells. Our in vitro studies demonstrate that LPS-stimulated slanDCs enhance activation and function of NK cells essentially via membrane-bound TNF-α (mTNF-α). LPS stimulation upregulates expression of mTNF-α in slanDCs, and surface TNF receptor 2 (TNFR2) is upregulated on NK cells after coincubation with slanDCs. IL-12 secreted by slanDCs increases surface expression of TNFR2 in NK cells. TNFR2 signaling in NK cells leads to activation of NF-kB, a transcription factor for cytokines such as GM-CSF. GM-CSF provided by NK cells is responsible for enhancing IL-12 secretion in slanDCs. In conclusion, TNFR2 and IL-12 signaling, which support one another, enables slanDCs to enhance NK-cell function through mTNF-α, thereby regulating immune responses.Keywords: cell-cell contact r mTNF-α r NK-cell stimulation r slanDCs r TNFR2 upregulation Additional supporting information may be found in the online version of this article at the publisher's web-site Introduction NK cells are a group of innate lymphocytes defined by lack of CD3 and the surface expression of CD56 [1]. Based on the cell surface density of CD56 expression, human NK cells can be subdivided into two distinct subsets [2,3]. CD56 dim CD16 bright NK cells represent the majority (̴ ß90%) of peripheral blood NK cells and exert high cytotoxic capacity against tumor-or virus-infected cells without prior Ag sensitization [4,5]. CD56 bright CD16 dim/neg NK cells comCorrespondence: Dr. Roland Jacobs e-mail: jacobs.roland@mh-hannover.de prise approximately 10% of peripheral blood NK cells and produce high levels of cytokines and chemokines with an important role in modulating immune responses [4][5][6]. The function of NK cells is regulated by the balance of activating and inhibitory signals that are transmitted by different membrane receptors [3,6,7]. However, the overall nature of NK-cell cytotoxic and cytokine responses depends on the cytokine microenvironment as well as interactions with other cells of the immune system [6]. Among the immune cells that communicate with NK cells and modulate their function are different DC subsets either in peripheral blood or in lymph nodes [8][9][10][11]. DCs are a heterogeneous group of professional APCs that develop in the BM [12]. DCs have been subdivided into myeloid C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu 3718 Dejene M. Tufa et al. Eur. J. Immunol. 2014. 44: 3717-3728 DCs (mDCs) and plasmacytoid DCs based on the expression levels of CD11c and CD123. Under normal conditions, mDCs ...