BackgroundIn 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 FindingsT-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.ConclusionsThere 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.

SummaryBecause type 1 diabetes (T1D) is a chronic, autoimmune, T cell-mediated disease, interventions affecting T cells are expected to modulate the immune cascade and lead to disease remission. We propose that increased CD4 + CD25 +high T cell apoptosis, a trait we discovered in recent-onset T1D subjects, reflects T1D partial remission within the first 6 months after diagnosis. Apoptosis of forkhead box P3 (FoxP3) + CD4 + CD25 +high T cells, in addition to total daily doses of insulin (TDD), blood glucose, HbA1c and age, were measured in 45 subjects with T1D at various times after diagnosis. Sixteen healthy control subjects were also recruited to the study. Higher CD4 + CD25 +high T cell apoptosis levels were detected within the first 6 months of diagnosis (odds ratio = 1·39, P = 0·009), after adjustment for age, TDD and HbA1c. A proportional hazards model confirmed that the decline of apoptosis after diagnosis of T1D was related significantly to survival time (hazards ratio = 1·08, P = 0·014), with TDD and age also contributing to survival. During this time there was an inverse relationship between CD4+ CD25 +high T cell apoptosis with TDD (r = -0·39, P = 0·008). The CD4 + CD25 +high T cell apoptosis levels decline significantly after the first 6 months from diagnosis of T1D and may help in the close monitoring of autoimmunity. In parallel, there is an increase in TDD during this time. We also propose that CD4 + CD25 +high T cell apoptosis assay can be used to gauge the efficacy of the several immune tolerance induction protocols, now under way.