Low frequency of GITR+ T cells in ex vivo and in vitro expanded Treg cells from type 1 diabetic patients

Reported alterations in T reg cells from type 1 diabetes (T1D) patients led us to a revision of their phenotypical features compared with controls. A fine cytometric analysis was designed for their characterization, using a panel of markers including FOXP3, CTLA4, glucocorticoid-induced TNFR family related (GITR) and CD127. The frequency of peripheral CD4 + CD25 hi T reg cells was similar between samples. However, the yield of sorted T reg cells was significantly lower in patients than in controls. When comparing the T reg -cell phenotype between samples, the only difference concerned the expression of GITR. A significant decrease of GITR + cells and GITR mean fluorescence intensity within the T reg -cell population, and to a lesser extent in the effector population, was observed in T1D compared with controls. Moreover, GITR expression was analyzed in several conditions of T-cell activation and differences were only observed in T1D T reg cells versus controls when responding to sub-optimal stimulation, that is, soluble anti-CD3 or medium alone but not in the presence of anti-CD3-/anti-CD28-coated beads. However, expanded T1D T reg -cell-mediated suppression was as efficient as that mediated by their control counterparts, showing no association between their regulatory capacity and the reduced GITR. Our results show a higher susceptibility to apoptosis in patients’ versus controls’ T reg cells, suggesting that GITR is a T reg -cell marker that would be primarily involved in T reg -cell survival rather than in their suppressor function.