Inflammation-induced Id2 promotes plasticity in regulatory T cells

T(H)17 cells originating from regulatory T (T-reg) cells upon loss of the T-reg-specific transcription factor Foxp3 accumulate in sites of inflammation and aggravate autoimmune diseases. Whether an active mechanism drives the generation of these pathogenic 'ex-Foxp3 T(H)17' cells, remains unclear. Here we show that pro-inflammatory cytokines enhance the expression of transcription regulator Id2, which mediates cellular plasticity of T-reg into 'ex-Foxp3' T(H)17 cells. Expression of Id2 in in vitro differentiated iT(reg) cells reduces the expression of Foxp3 by sequestration of the transcription activator E2A, leading to the induction of T(H)17-related cytokines. T-reg-specific ectopic expression of Id2 in mice significantly reduces the T-reg compartment and causes immune dysregulation. Cellular fate-mapping experiments reveal enhanced T-reg plasticity compared to wild-type, resulting in exacerbated experimental autoimmune encephalomyelitis pathogenesis or enhanced anti-tumor immunity. Our findings suggest that controlling Id2 expression may provide a novel approach for effective T-reg cell immunotherapies for both autoimmunity and cancer.