WJ-MSCs modulate Treg phenotypic and transcriptional profiles in T1DM: comparative insights into direct and indirect mechanisms

Background: This study aims to evaluate the immunomodulatory effect of human umbilical cord-derived mesenchymal stromal cells (WJ-MSCs) on T regulatory cells (Tregs) isolated from the blood of healthy individuals and patients with type 1 diabetes (T1DM) under direct and indirect coculture conditions. Methods: Treg cells were isolated from the blood of healthy individuals and T1DM patients, cultured alone as a control, and co-cultured with WJ-MSCs under both direct and indirect conditions for 7 days. Treg proliferation was assessed using flow cytometry. Gene expressions of FOXP3, IL-10, IL-4, and TGF-β were analyzed via RTPCR, while cytokine levels of IL-10, IL-2, TGF-β, and TNF-α, as well as CD4, IL-2, and TNF-α localization, were evaluated using ELISA and immunofluorescence staining. Results: Tregs from T1DM patients were found to be lower in number compared to those from healthy individuals, and proliferation induced by MSCs alone was insufficient. In the T1DM group, expressions of TGF-β and FOXP3 were increased, particularly in direct co-culture. Tregs, whereas indirect coculture predominantly enhanced IL-10 production. Notably, direct coculture in the T1DM group was also associated with increased TNF-α expression. Conclusion: WJ-MSCs act as functional “reprogrammers” rather than simple mitogens for T1DM-derived Tregs. Our findings suggest a dual mechanism of action: direct contact reinforces transcriptional stability through FOXP3 upregulation, while paracrine effects establish a potent anti-inflammatory microenvironment via IL-10. These results emphasize that MSC-mediated immunomodulation is not uniformly suppressive and should be interpreted as a nuanced, microenvironment-driven process rather than a purely anti-inflammatory effect.