| Summary: | Myelodysplatic Syndrome (MDS) is a group of premalignant diseases characterised by ineffective erythropoiesis and categorised into risk groups ranging from low/intermediate to high-risk, based on the risk of disease progression toward acute myeloid leukaemia (AML)1. Expansion of CD4+CD25hiCD127lowFOXP3+ (Tregs) is a characteristic feature of high-risk MDS2. Although the only curative treatment for high-risk MDS is bone marrow transplantation, this is not always available due to age or lack of a compatibile donor. Nevertheless, treatment with the hypomethylating agent 5-Azacytidine (5AzaC) can improve quality of life and enhance life expectancy3, 4. Although the hypomethylating activity of 5AzaC is well established, its mechanism of action remains unclear. It has been shown by our group that following treatment with 5AzaC, the absolute number of Tregs is reduced, they became non-suppressive and secrete IL-17 and IFN-γ. We have also shown increased FOXP3 expression in the conventional CD4+ T cells (Tcon) of healthy donors following in-vitro culture with 5AzaC, without significant immunosuppressive properties. This subpopulation is so-called “Treg-like” cells. The focus of the study was on the FOXP3+ “Treg-like” cells derived from 5AzaC treated Tcon (CD4+CD25-). Our data demonstrate: 1) “Treg-like” cells show an increase in secretion of IL-17 and expression of FOXP3 and have no significant immunosuppressive properties; 2) the Treg-specific-demethylated region (TSDR) within the FOXP3 gene in “Treg-like” cells is fully methylated compared with Tregs; 3) analyses of cell surface and intracellular protein expression by CyTOF strongly suggeste that cells with high FOXP3 expression following 5AzaC treatment are not-stable Tregs, therefore the FOXP3 marker is not an indication of Tregs. Also, 5AzaC polarised Tcon towards a T inflammatory profile and PBMCs towards a T helper profile rather then Tregs. The phenotype and the CyTOF analyses gave an improvement in understanding how these “Treg-like” cells develop, behave and their potential use in therapy.
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