GAD65 (524-543) is a biologically active peptide comprising amino acids 524 to 543 of glutamic acid decarboxylase 65 (GAD65). It represents an early islet antigen fragment that elicits proliferative T cell responses in the non-obese diabetic (NOD) mouse model, instrumental in spontaneous autoimmune diabetes research. The peptide serves as a specific, possibly low affinity stimulant for the diabetogenic T cell clone BDC2.5. Notably, immunization with GAD65 (524-543) heightens NOD mice's vulnerability to type 1 diabetes when subjected to the adoptive transfer of BDC2.5 T cells.