EXTOD-Immune: a randomised controlled trial to investigate whether a remotely monitored, home-based exercise intervention can reduce disease activity in people with type 1 diabetes.

Type 1 diabetes (T1D) is a chronic autoimmune disease in which the adaptive immune system targets insulin-producing β-cells of pancreatic islets, leading to dependence on exogenous insulin therapy. Cytotoxic (CD8⁺) T-cells specific for islet antigens are major players in T1D autoimmunity. Data indicate that regular exercise may preserve β-cell function in people recently diagnosed with T1D, but the role of islet-reactive CD8⁺ T-cells is unclear. In a randomised crossover design, this study will determine the impact of a 12-week exercise programme on the frequency and proliferative state of islet-reactive CD8⁺ T-cells in the peripheral blood of 20 adults diagnosed with T1D within the past 3 years. The exercise intervention will consist of three high-intensity interval training sessions per week (6-10 1 min intervals >80% maximum heart rate, with 1 min rest), the duration of which will incrementally increase from 14 to 22 min. Habitual physical activity and diet will be maintained during control and washout periods. At weeks 0, 12, 24 and 36, a fasting blood sample will be collected to quantify the frequency, phenotype and proliferative activity of islet-reactive CD8⁺ T-cells (primary outcome) and various clinical parameters. Glycaemic control will also be evaluated using 14-day continuous glucose monitoring at the start and end of each study arm. Findings may provide a rationale for conducting large-scale trials to evaluate the implementation of exercise into routine clinical care, particularly for people recently diagnosed with T1D when maintenance of β-cell function is critical to counteract disease progression. Trial registration number: ISRCTN79006041.