At-Risk and Recent-Onset Type 1 Diabetic Subjects Have Increased Apoptosis in the CD4+CD25+high T-Cell Fraction

Background. In experimental models, Type 1 diabetes (T1D) can be prevented by adoptive transfer of CD4+CD25+ (FoxP3+) suppressor or regulatory T cells. Recent studies have found a suppression defect of CD4+CD25+(high) T cells in human disease. In this study we measure apoptosis of CD4+CD25+(high) T cells to see if it could contribute to reduced suppressive activity of these cells. Methods and Findings. T-cell apoptosis was evaluated in children and adolescent (35 females/40 males) subjects comprising recent-onset and long-standing T1D subjects and their first-degree relatives, who are at variable risk to develop T1D. YOPRO1/7AAD and intracellular staining of the active form of caspase 3 were used to evaluate apoptosis. Isolated CD4+CD25+(high) and CD4+CD25- T cells were co-cultured in a suppression assay to assess the function of the former cells. We found that recent-onset T1D subjects show increased apoptosis of CD4+CD25+(high) T cells when compared to both control and long-standing T1D subjects (p<0.0001 for both groups). Subjects at high risk for developing T1D ( 2-3Ab+ve) show a similar trend (p<0.02 and p<0.01, respectively). On the contrary, in long-standing T1D and T2D subjects, CD4+CD25+(high) T cell apoptosis is at the same level as in control subjects (p = NS). Simultaneous intracellular staining of the active form of caspase 3 and FoxP3 confirmed recent-onset FoxP3+ve CD4+CD25+(high) T cells committed to apoptosis at a higher percentage (15.3 +/- 2.2) compared to FoxP3+ve CD4+CD25+(high) T cells in control subjects (6.1 +/- 1.7) (p<0.002). Compared to control subjects, both recent-onset T1D and high at-risk subjects had significantly decreased function of CD4+CD25+(high) T cells (p = 0.0007 and p = 0.007, respectively). Conclusions. There is a higher level of ongoing apoptosis in CD4+CD25+(high) T cells in recent-onset T1D subjects and in subjects at high risk for the disease. This high level of CD4+CD25+(high) T-cell apoptosis could be a contributing factor to markedly decreased suppressive potential of these cells in recent-onset T1D subjects.