Endometrial mesenchymal stem/stromal cells: The Enigma to code messages for generation of functionally active regulatory T cells.

Background: Regulatory T cells (Tregs) play an important role in fine-tuning of immune responses and are pivotal for a successful pregnancy. Recently, the importance of mesenchymal stem cells in regulation of immune responses in general and Tregs in particular has been highlighted. Here, we hypothesized that menstrual stromal/stem cells (MenSCs) contribute to uterine immune system regulation through induction of functionally active Tregs.

Methods: MenSCs were collected from 18 apparently healthy women and characterized. Bone marrow mesenchymal stem cells (BMSCs) served as a control. The effect of MenSCs on proliferation of anti-CD3/CD28-stimulated T CD4 + cells and generation of Tregs with or without pre-treatment with mitomycin C, IFN-γ and IL-1β was evaluated by flow cytometry. The potential role of IDO, PGE2, IL-6, IL-10, and TGF-β on proliferation of T CD4 + cells and generation of Tregs was assessed using blocking antibodies or agents. IDO activity was evaluated in MenSCs and BMSCs culture supernatants by a colorimetric assay. IL-10 and IFN-γ production in MenSCs-primed T CD4 + was measured using intracellular staining. To investigate the functional properties of Tregs induced by MenSCs, Treg cells were isolated and their functional property to inhibit proliferation of anti-CD3/CD28-stimulated PBMCs was assessed by flow cytometry.

Results: According to the results, proliferation of T CD4 + lymphocytes was enhanced in the presence of MenSCs, while pre-treatment of MenSCs with pro-inflammatory cytokines reversed this effect. PGE2 and IDO were the major players in MenSCs-induced T cell proliferation. Non-treated MenSCs decreased the frequency of Tregs, whereas after pre-treatment with IFN-γ and IL-1β, they induced functional Tregs with ability to inhibit the proliferation of anti-CD3/CD28-stimulated PBMCs. This effect was mediated through IL-6, IL-10, TGF-β and IDO. IFN-γ/IL-1β-treated MenSCs induced IL-10 and IFN-γ production in CD4 + T cells.

Conclusion: Collectively, these findings indicate that immunomodulatory impact of menstrual blood stem cells (MenSCs) on generation of Tregs and inhibition of T cells proliferation is largely dependent on pre-treatment with IFN-γ and IL-1β. This is the first report on immunomodulatory impact of MenSCs on Tregs and highlights the pivotal role of endometrial stem cells in regulation of local endometrial immune responses.