ABSTRACT Type 1 diabetes is a T cell‐mediated autoimmune disease that leads to the destruction of the insulin‐producing beta cells of the pancreas, yet the antigens that drive this response have been difficult to define. This review traces the identification of hybrid insulin peptides (HIPs), posttranslationally modified autoantigens formed when a fragment of insulin is joined through a peptide bond to a fragment of a second beta cell granule protein, creating a sequence not encoded by any single gene. Beginning with the search for the antigen of the diabetogenic BDC‐2.5 clone in the nonobese diabetic (NOD) mouse, we show that its natural ligand is a hybrid of an insulin C‐peptide fragment and a peptide derived from chromogranin A, and that subsequent mass spectrometry analyses defined a set of disease‐relevant HIPs supported by both T cell reactivity and detection of the endogenous peptide. We summarize the recognition of HIPs by CD4 T cells across several HLA class II alleles in human disease, the enzymatic and nonenzymatic routes of HIP formation within acidic secretory and crinophagic compartments, and genetic evidence that reducing HIP formation delays diabetes. Finally, we propose a multi‐trigger model linking a species difference in HIP formation to the focal, episodic islet pathology of human type 1 diabetes.
ABSTRACT Type 1 diabetes (T1D) is an organ‐specific autoimmune disease that destroys insulin‐producing beta‐cells. Insulin is a vital hormone for regulating glycemia that often undergoes post‐translational modifications during processing from pre‐proinsulin to biologically active insulin. While necessary for proper glucose homeostasis, insulin is also an autoantigen recognized by autoreactive T cells in T1D. Cellular stress pathways including endoplasmic reticulum stress and oxidative stress mediated by an increase in reactive oxygen species (ROS) synthesis and/or a concomitant decrease in antioxidant function can further drive post‐translational modifications of various autoantigens in T1D including insulin. Innate immune‐derived ROS generation is an essential frontline defense against microbial infections, but ROS can also function as signaling intermediates to properly stimulate T cell responses. Oxidative stress‐induced post‐translational modifications are thought to trigger autoreactive T cells in T1D by generating novel neoepitopes, eliciting epitope spreading, or enhancing autoantigen interactions with antigen‐presenting cells. With the current technology, detecting post‐translationally modified proteins is challenging. In this review, we will explore the role of ROS and other post‐translational modifications involved in T1D. We will also discuss islet transplantation strategies being used for patients with T1D including novel cell sources for beta‐cell replacement and management of oxidative stress after transplantation.
ABSTRACT The discovery of MHC restriction, the resolution of peptide–MHC structure, and the identification of the T cell receptor gene quickly centered epitope‐level specificity as a core concern of T cell biology. Epitope mapping culminated in functional peptide‐based stimulation assays and tetramer staining, which together provide exquisite resolution of individual responses. Despite these tools, quantitative assessment of epitope‐resolved responses in complex human infections and tumors has rarely been applied at scale. As a result, no epitope‐aware correlates of protection or risk have been established for major infections, and most human T cell profiling still occurs at the level of representative epitopes or bulk assays. In this review, I propose that variation in specificity, defined as distinct epitope‐level responses across individuals, represents a largely untested critical element in our assessment of anti‐pathogen and antitumor immunity. Advances in TCR repertoire profiling and reverse epitope discovery now make formal tests of this hypothesis tractable, and I discuss approaches to determine the extent to which epitope variation underlies the noise and variation of human immune phenotypes.
ABSTRACT Pancreatic beta cells are active participants in the loss of immune tolerance because their high secretory demand creates exceptional vulnerability to inflammatory exposure, endoplasmic reticulum (ER) stress, calcium dysregulation, and redox imbalance. These conditions can promote enzymatic and nonenzymatic changes in self‐proteins, generating post‐translationally modified (PTM) antigens and neoepitopes that were absent or poorly represented during immune tolerance. This review integrates the contributions with the broader type 1 diabetes (T1D) field to examine how beta cell stress, transglutaminase‐2 dependent reactions, peptidyl‐arginine deiminase mediated citrullination, oxidative modifications, and post‐translational peptide fusion reshape the antigenic landscape. We consider how these products alter antigen presentation and recognition by autoreactive T cells and how an evolving neoepitope repertoire may promote antigenic diversification and epitope spreading. Importantly, clonal recruitment of new determinants must be distinguished from apparent broadening caused by T cell receptor (TCR) cross‐reactivity, dual‐TCR expression, bystander activation, or tissue redistribution. Defining when modified epitopes arise, which are naturally presented, and which responses contribute to pathogenesis could improve biomarker development, patient stratification, and therapeutic strategies designed to reduce beta cell stress, thus enhancing survival and identity maintenance, while restoring immune tolerance.
T-cell receptor repertoires are commonly characterized through sequence diversity and antigen binding, while the cellular functions associated with individual receptors are often measured separately. In this review, I consider how functional information can be incorporated more directly into repertoire analysis by linking receptor identity with measurable effector outputs at single-cell resolution. I focus on Nanovial-based technologies that combine antigen-specific capture, stimulation, secretion measurement, viable-cell recovery, and downstream sequencing in workflows compatible with flow cytometry and single-cell sequencing platforms. Studies using conventional peptide-major histocompatibility complex ligands, the non-classical antigen-presenting molecules MR1 and CD1d, and secretion-encoded single-cell sequencing illustrate how these approaches can complement binding-based enrichment by adding information about secretory effector responses. I also discuss the extension of this framework from ligand-defined screening to dyad-resolved assays involving target cells, which can reveal how receptor identity relates to transcriptional and functional programs arising during direct cell-cell interactions. Together, these developments provide tools for studying relationships among TCR sequence, antigen recognition, and cellular response, with potential applications in therapeutic receptor discovery and in generating datasets for predictive models of T-cell function.
