Hybrid Insulin Peptides are Autoantigens in Type 1 Diabetes

We recently established that hybrid insulin peptides (HIPs) are present in human islets and that T cells reactive to HIPs are found in the residual islets of type 1 diabetic (T1D) organ donors. Here we investigate whether HIP-reactive T cells are indicative of ongoing autoimmunity in human T1D patients. We used IFN-γ ELISPOT analyses on peripheral blood mononuclear cells (PBMCs) to determine if new onset T1D or control subjects displayed T cell reactivity to a panel of 16 HIPs. We observed that nearly half of the patients responded to one or more HIPs. Responses to 4 HIPs were significantly elevated in T1D patients but not in control subjects. To characterize the T cells reactive to HIPs, we used a CFSE-based assay to clone T cells from PBMCs. We isolated 6 non-redundant, antigen-specific T cell clones, most of which reacting to their target HIPs in the low nanomolar range. One T cell clone was isolated from the same patient on two different blood draws, indicating persistence of this T cell clone in the peripheral blood. This work suggests that HIPs are important target antigens in human T1D subjects and may play a critical role in disease.