PROS1 and type 1 diabetes mellitus: Our data strongly support evidence that epitopes and neoepitopes are formed in the stressed β cells from hormone secretory proteins,13,14,16,52–56 and we show here that these are processed and presented in the MHC immunopeptidome to become islet-derived autoreactive T cell targets, which may be major targets early in the development of T1D in human subjects.