Proinsulin is considered an important autoantigen in type 1 diabetes (T1D). Autoreactivity to Proinsulin is very common in T1D patients with the HLA-DRB1*0401 haplotype. The Proinsulin 73-90 peptide (GAGSLQPLALEGSLQKRG) has been identified as an immunodominant T cell epitope of HLA-DRB1*0401 subjects with beta-islet cell autoimmunity.