254-OR: Islet Autoimmunity Is Highly Prevalent and Associated with Diminished Beta-Cell Function in Patients with Type 2 Diabetes (T2D) in the GRADE Study

We hypothesized that islet autoimmunity, hitherto considered the pathophysiologic basis of type 1 diabetes (T1D) and latent autoimmune diabetes of adults (LADA), could contribute to ß cell dysfunction in patients with type 2 diabetes (T2D). To evaluate this question, the Glycemia Reduction Approaches in Diabetes: A Comparative Effectiveness (GRADE) Study - Beta Cell Ancillary Study Network measured humoral islet autoimmunity (autoantibodies against 65 kDa glutamic acid decarboxylase (GAD65-Ab), islet autoantigen-2 (IA2-Ab) and zinc transporter-8 (ZnT8-Ab)) in 392 participants (age 57.2 ± 10.1 y; BMI 33.5 ± 6.2 kg/m²; diabetes duration 4.0 ± 3.0 y; HbA1c 7.5 ± 0.5 %; on metformin as the sole glucose-lowering medication), and cellular islet autoimmunity (T cell autoreactivity against a broad range of islet antigens) in 322 of the same participants. 41.4% had evidence of cellular islet autoimmunity and 13.5% had evidence of humoral islet autoimmunity, but only 5.4% had both. T cell autoreactivity to islet antigens, but not autoantibody-positivity, was associated with diminished ß cell function, as assessed by the ratio of incremental area under the curve (iAUC) of C-peptide to iAUC of glucose during 0-120 min of an OGTT (ß = -0.1403; se = 0.0612; p = 0.0219) or ∆C-peptide/∆glucose during 0-30 min of an OGTT (ß = -0.2113; se = 0.0728; p = 0.0037), adjusted for insulin sensitivity. T cell positive participants also had higher fasting plasma glucose (p = 0.045) and HbA1c (p = 0.001) than T cell negative participants. These findings indicate that islet autoimmunity in T2D patients is far more prevalent than previously recognized; T cell mediated islet autoimmunity is associated with diminished ß cell function.