HLA-DRB1 and type 1 diabetes mellitus: The majority of research in T1D cellular autoimmunity has focused on CD4+ T cell responses, restricted to HLA-DR4 (particularly HLA-DRB1*04:01) and focused on the four autoantigens (preproinsulin, GAD65, islet antigen (IA)−2, and zinc transporter 8 (ZnT8)) [7].