The frequency of Treg subsets distinguishes disease activity in ANCA vasculitis

OBJECTIVES: T regulatory cells (Tregs) are a heterogeneous group of immunoregulatory cells that dampen self‐harming immune responses and prevent the development of autoimmune diseases. In anti‐neutrophil cytoplasmic autoantibody (ANCA) vasculitis, Tregs possess diminished suppressive capacity, which has been attributed to the expression of a FOXP3 splice‐variant lacking exon 2 in T cells (FOXP3Δ2 CD4(+) T cells). However, the suppressive capacity of Tregs varies between subsets. We evaluated the frequency of Treg subsets in ANCA vasculitis as a potential explanation for diminished suppressive capacity. METHODS: We developed a custom mass cytometry panel and performed deep immune profiling of Tregs in healthy controls, patients with active disease and in remission. Using these data, we performed multidimensional reduction and discriminant analysis to identify associations between Treg subsets and disease activity. RESULTS: Total Tregs were expanded in ANCA vasculitis, which was associated with remission and the administration of rituximab and/or prednisone. The frequency of FOXP3Δ2 CD4(+) T cells did not distinguish disease activity and this population had high expression levels of CD127 and lacked both CD25 and Helios, suggesting that they are not conventional Tregs. The frequency of CXCR3(+), CD103(+) and CCR7(+) Tregs distinguished disease activity, and the combination of the frequency of these three Treg subsets segregated active patients from patients in remission and healthy controls. From these three subsets, the frequency of CXCR3(+) Tregs distinguished patients with active disease with renal involvement. CONCLUSION: Treg heterogeneity can discriminate disease activity and should be explored as a biomarker of disease activity in ANCA vasculitis.