Low-Dose Anti-Thymocyte Globulin Preserves C-Peptide, Reduces HbA _1c, and Increases Regulatory to Conventional T-Cell Ratios in New-Onset Type 1 Diabetes: Two-Year Clinical Trial Data

Abstract

A three-arm, randomized, double-masked, placebo-controlled phase 2b trial performed by the Type 1 Diabetes TrialNet Study Group previously demonstrated that low-dose anti-thymocyte globulin (ATG) (2.5 mg/kg) preserved β-cell function and reduced HbA _1c for 1 year in new-onset type 1 diabetes. Subjects ( N = 89) were randomized to 1) ATG and pegylated granulocyte colony-stimulating factor (GCSF), 2) ATG alone, or 3) placebo. Herein, we report 2-year area under the curve (AUC) C-peptide and HbA _1c, prespecified secondary end points, and potential immunologic correlates. The 2-year mean mixed-meal tolerance test–stimulated AUC C-peptide, analyzed by ANCOVA adjusting for baseline C-peptide, age, and sex ( n = 82) with significance defined as one-sided P < 0.025, was significantly higher in subjects treated with ATG versus placebo ( P = 0.00005) but not ATG/GCSF versus placebo ( P = 0.032). HbA _1c was significantly reduced at 2 years in subjects treated with ATG ( P = 0.011) and ATG/GCSF ( P = 0.022) versus placebo. Flow cytometry analyses demonstrated reduced circulating CD4:CD8 ratio, increased regulatory T-cell:conventional CD4 T-cell ratios, and increased PD-1 ⁺CD4 ⁺ T cells following low-dose ATG and ATG/GCSF. Low-dose ATG partially preserved β-cell function and reduced HbA _1c 2 years after therapy in new-onset type 1 diabetes. Future studies should determine whether low-dose ATG might prevent or delay the onset of type 1 diabetes.