Mobilization without immune depletion fails to restore immunological tolerance or preserve beta cell function in recent onset type 1 diabetes

Summary Granulocyte colony‐stimulating factor (G‐CSF) has been used to restore immune competence following chemoablative cancer therapy and to promote immunological tolerance in certain settings of autoimmunity. Therefore, we tested the potential of G‐CSF to impact type 1 diabetes (T1D) progression in patients with recent‐onset disease [n = 14; n = 7 (placebo)] and assessed safety, efficacy and mechanistic effects on the immune system. We hypothesized that pegylated G‐CSF (6 mg administered subcutaneously every 2 weeks for 12 weeks) would promote regulatory T cell (Treg) mobilization to a degree capable of restoring immunological tolerance, thus preventing further decline in C‐peptide production. Although treatment was well tolerated, G‐CSF monotherapy did not affect C‐peptide production, glycated haemoglobin (HbA1c) or insulin dose. Mechanistically, G‐CSF treatment increased circulating neutrophils during the 12‐week course of therapy (P