UC-MSCs induced regulatory T cells expansion. T cells (1 × 106) isolated from RA patients were cocultured with UC-MSCs (5 × 104) in the absence or presence of PHA in 24-well plates. After three days, regulatory T cells expression was analyzed in the CD4+ T cell fraction by flow cytometry. Numbers represent the mean percentage of positive cells from different groups. All the data are expressed as mean c.p.m. ± S.D, * P < 0.05.