The present disclosure provides isolated preproinsulin-derived peptides of 8 or 9 amino acids, comprising the amino acid sequence WGPDPAA (SEQ ID NO: 1), isolated Class I peptide-HLA complexes presenting said peptides and isolated molecules having binding affinity for said peptides and/or said peptide-HLA complexes. Such compositions are useful in the treatment of type 1 diabetes mellitus (T1DM). Such isolated molecules can include a T cell receptor (TCR) having specific binding affinity for a peptide-MHC complex wherein the MHC is an HLA Class I molecule and the peptide is a preproinsulin-derived peptide of 8 to 10 amino acids, comprising the amino acid sequence WGPDPAA (SEQ ID NO: 1).
