Reduced PD-1 expression on circulating CXCR5+ and CXCR5- FOXP3+ Treg cells marks type 1 diabetes initiation in children

Autoantibodies (AAbs) are a hallmark of Type 1 diabetes (T1D). Alterations in the frequency and phenotype of follicular helper (Tfh) T cells have been previously documented in patients with type 1 diabetes (T1D), but the contribution of follicular Treg cells, which are responsible for suppressing AAb development, is less clear. Here, we investigated the frequency and activation status of follicular (CXCR5+) and CXCR5- Treg cells in the blood of children with new onset T1D and children with risk for developing T1D (AAb-positive) and compared them to AAb-negative controls. Blood CXCR5+ and CXCR5- Treg cells were higher in frequency children with new onset T1D and expressed reduced amounts of PD-1 as compared to controls. Interestingly, the proportion of circulating FOXP3+ Tregs expressing PD-1 was also reduced in AAb-positive at-risk children as compared to controls, suggesting its potential use as a biomarker of disease initiation.