Circulating CXCR5^-PD-1^hi peripheral T helper cells are associated with progression to type 1 diabetes

Type 1 diabetes is preceded by a period of asymptomatic autoimmunity characterised by positivity for islet autoantibodies. Therefore, T helper cell responses that induce B cell activation are likely to play a critical role in the disease process. Here, we aimed to evaluate the role of a recently described subset, C-X-C motif chemokine receptor type 5-negative, programmed cell death protein 1-positive (CXCR5^-PD-1^hi) peripheral T helper (Tph) cells, in human type 1 diabetes.

The phenotype of blood CXCR5^-PD-1^hi CD4⁺ T cells was analysed by multicolour flow cytometry. The frequencies of circulating CXCR5^-PD-1^hi T cells were analysed in a cohort of 44 children with newly diagnosed type 1 diabetes, 40 autoantibody-positive (AAb⁺) at-risk children and 84 autoantibody-negative healthy control children, and the findings were replicated in a separate cohort of 15 children with newly diagnosed type 1 diabetes and 15 healthy control children.

Circulating CXCR5^-PD-1^hi Tph cells share several features associated with B cell helper function with circulating CXCR5⁺PD-1^hi follicular T helper (Tfh) cells. Moreover, the frequency of circulating Tph cells was increased in children with newly diagnosed type 1 diabetes, especially in those who are positive for multiple autoantibodies. Importantly, circulating Tph cells were also increased in autoantibody-positive at-risk children who later progressed to type 1 diabetes.

Our results demonstrate that circulating CXCR5^-PD-1^hi Tph cells are associated with progression to clinical type 1 diabetes. Consequently, Tph cells could have potential both as a biomarker of disease progression and as a target for immunotherapy in type 1 diabetes.