Tregitope 289 is a peptide derived from the Fc region of immunoglobulin G (IgG) and serves as a highly conserved T cell epitope that promotes the expansion of natural regulatory T cells. When co-delivered with type 1 diabetes (T1D) antigens, it can delay the onset of hyperglycemia and reduce the incidence of diabetes in NOD mouse models. Tregitope 289 is applicable for research in T1D and other autoimmune diseases.