At-risk and recent-onset type 1 diabetic subjects have increased apoptosis in the CD4+CD25+ 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.