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 (<i>N</i> = 89) were randomized to <i>1</i>) ATG and pegylated granulocyte colony-stimulating factor (GCSF), <i>2</i>) ATG alone, or <i>3</i>) 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 (<i>n</i> = 82) with significance defined as one-sided <i>P</i> < 0.025, was significantly higher in subjects treated with ATG versus placebo (<i>P</i> = 0.00005) but not ATG/GCSF versus placebo (<i>P</i> = 0.032). HbA_1c was significantly reduced at 2 years in subjects treated with ATG (<i>P</i> = 0.011) and ATG/GCSF (<i>P</i> = 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.