The impact of TCR repertoire diversity on Treg-cell function is controversial. Regarding the prevention of autoimmune disease, previous studies on the effective suppression of EAE through Treg cells with

limited TCR repertoires came to divergent conclusions 47, 48. A recent study by Adeegbe et al. found that limited TCR diversity of transferred Treg cells was a risk factor for autoimmune disease in IL-2Rbeta−/− mice 49. Intriguingly, non-obese diabetic mice were recently shown to select a low diversity Treg-cell TCR repertoire 50. Understanding the parameters that govern Treg-cell homeostasis will be critical for the design of future Treg-cell-based intervention strategies. Sufficient availability of organ-specific antigen must be considered in translational attempts to manipulate organ-specific autoimmunity Casein Kinase inhibitor with engineered Treg cells of known self-peptide specificity. Otherwise, exogenous therapeutic Treg cells may be lost quickly after transfer. Previous studies suggested that organ-specific self-antigen preferentially drives the survival and/or expansion of organ-specific Treg-cell clones 11, 13, 21, 22. Our results also support the view that the antigen specificity of Treg cells changes by anatomical location, although

MLN8237 TCR sequences of recovered Treg cells from pLNs and mLNs were largely overlapping. This may be the result of two possible scenarios. Either Treg cells recirculate less than naïve T cells or differences are due to selective local survival. Importantly, our study infers that Treg-cell diversity is connected to diversity and availability of specific self- and foreign-antigen and thus the amount of DCs presenting it on MHC class II. In accord, it was recently shown that DC ablation Calpain reduced Treg-cell frequencies 51, 52, whereas an increase of DC numbers by FLT3L treatment led to expansion of peripheral naturally occurring Treg cells 52,

53. However, in the latter report, it was concluded that Treg-cell proliferation was mainly IL-2 dependent. In our study, we also recognized IL-2 as a master regulator that controls the absolute size of the Treg-cell pool. We propose that an optimal and maximally broad organ-specific Treg-cell TCR repertoire is continuously shaped by inter- and intraclonal competition for diverse antigen. Within a peripheral Treg-cell niche, sufficient population diversity seems to be crucial for proper Treg-cell function. Hence, in future studies, HT-sequencing analysis of Treg-cell diversity may be suitable to predict the relative risk of T-cell-mediated diseases. C57BL/6-Foxp3eGFP (here: WT) 54, C57BL/6-Foxp3.LuciDTR-4 36, and C57BL/6-Tg(TcraTcrb)425Cbn/J (here: OT-II/TCR-Tg) 55 mice have been described. The Thy1.