Plasticity of Human Regulatory T Cells in Healthy Subjects and Patients with Type 1 Diabetes

Abstract

Regulatory T cells (Tregs) constitute an attractive therapeutic target given their essential role in controlling autoimmunity. However, recent animal studies provide evidence for functional heterogeneity and lineage plasticity within the Treg compartment. To understand better the plasticity of human Tregs in the context of type 1 diabetes, we characterized an IFN-γ–competent subset of human CD4+CD127lo/−CD25+ Tregs. We measured the frequency of Tregs in the peripheral blood of patients with type 1 diabetes by epigenetic analysis of the Treg-specific demethylated region (TSDR) and the frequency of the IFN-γ+ subset by flow cytometry. Purified IFN-γ+ Tregs were assessed for suppressive function, degree of TSDR demethylation, and expression of Treg lineage markers FOXP3 and Helios. The frequency of Tregs in peripheral blood was comparable but the FOXP3+IFN-γ+ fraction was significantly increased in patients with type 1 diabetes compared to healthy controls. Purified IFN-γ+ Tregs expressed FOXP3 and possessed suppressive activity but lacked Helios expression and were predominately methylated at the TSDR, characteristics of an adaptive Treg. Naive Tregs were capable of upregulating expression of Th1-associated T-bet, CXCR3, and IFN-γ in response to IL-12. Notably, naive, thymic-derived natural Tregs also demonstrated the capacity for Th1 differentiation without concomitant loss of Helios expression or TSDR demethylation.

Helios+ and Helios− Cells Coexist within the Natural FOXP3+ T Regulatory Cell Subset in Humans

“…We were unable to detect IL-17 in either subset of nTreg clones likely because they were sorted from naive CD25 hi T cells, which are known to lack the Th17 precursor population (6). The increased cytokine/chemokine production by Helios 2 nTreg clones is intriguing as there is growing evidence for the existence of IFN-gsecreting Tregs (36), although whether these cells are protective or pathogenic remains controversial (36)(37)(38). When exposed to a Th1-polarizing environment, however, both Helios + and Helios 2 nTreg clones could readily increase expression of T-BET and IFNg, indicating that high Helios expression does not preclude transdifferentiation of nTregs into Th1-like cells.…”

Interindividual variation in human T regulatory cells

“…Whether Tregs from T1D patients are dysfunctional is controversial (30,32,(34)(35)(36)(37), and it is possible that only one facet of their activity is altered (38). Recent results also suggest that, in T1D patients, effector T cells may be refractory to inhibition by Treg cells (39,40) although this point has also been debated (30,38).…”

Harnessing the plasticity of CD4+ T cells to treat immune-mediated disease

“…Conversely, the treatment of tT Reg cells from mice or humans with the T H 17 cellinducing cytokines IL-6, IL-1β and IL-23 (especially in combination) can destabilize FOXP3 expression and induce IL-17 production in vitro 17,18 , and STAT3 (which is activated in response to these cytokines) is required for reprogramming 45 . Expression of IFNγ and T-bet in FOXP3 + T Reg cells in response to IL-12 has been widely observed in mice and humans 14,[46][47][48] , and this may help T Reg cells to control T H 1 cell-based immunopathology 49 . However, IFNγ-expressing T Reg cells are also intermediates in the deviation towards an inflammatory T H 1 cell phenotype in which FOXP3 expression is lost 50,51 .…”