Human islet T cells are highly reactive to preproinsulin in type 1 diabetes.

Cytotoxic CD8 T lymphocytes play a central role in the tissue destruction of many autoimmune disorders. In type 1 diabetes (T1D), insulin and its precursor preproinsulin are major self-antigens targeted by T cells. We comprehensively examined preproinsulin specificity of CD8 T cells obtained from pancreatic islets of organ donors with and without T1D and identified epitopes throughout the entire preproinsulin protein and defective ribosomal products derived from preproinsulin messenger RNA. The frequency of preproinsulin-reactive T cells was significantly higher in T1D donors than nondiabetic donors and also differed by individual T1D donor, ranging from 3 to over 40%, with higher frequencies in T1D organ donors with HLA-A*02:01. Only T cells reactive to preproinsulin-related peptides isolated from T1D donors demonstrated potent autoreactivity. Reactivity to similar regions of preproinsulin was also observed in peripheral blood of a separate cohort of new-onset T1D patients. These findings have important implications for designing antigen-specific immunotherapies and identifying individuals that may benefit from such interventions.

Proinsulin-Reactive CD4 T Cells in the Islets of Type 1 Diabetes Organ Donors.

Proinsulin is an abundant protein that is selectively expressed by pancreatic beta cells and has been a focus for development of antigen-specific immunotherapies for type 1 diabetes (T1D). In this study, we sought to comprehensively evaluate reactivity to preproinsulin by CD4 T cells originally isolated from pancreatic islets of organ donors having T1D. We analyzed 187 T cell receptor (TCR) clonotypes expressed by CD4 T cells obtained from six T1D donors and determined their response to 99 truncated preproinsulin peptide pools, in the presence of autologous B cells. We identified 14 TCR clonotypes from four out of the six donors that responded to preproinsulin peptides. Epitopes were found across all of proinsulin (insulin B-chain, C-peptide, and A-chain) including four hot spot regions containing peptides commonly targeted by TCR clonotypes derived from multiple T1D donors. Of importance, these hot spots overlap with peptide regions to which CD4 T cell responses have previously been detected in the peripheral blood of T1D patients. The 14 TCR clonotypes recognized proinsulin peptides presented by various HLA class II molecules, but there was a trend for dominant restriction with HLA-DQ, especially T1D risk alleles DQ8, DQ2, and DQ8-trans. The characteristics of the tri-molecular complex including proinsulin peptide, HLA-DQ molecule, and TCR derived from CD4 T cells in islets, provides an essential basis for developing antigen-specific biomarkers as well as immunotherapies.

Multiplex T-cell Stimulation Assay Utilizing a T-cell Activation Reporter-based Detection System.

Immune tolerance and response are both largely driven by the interactions between the major histocompatibility complex (MHC) expressed by antigen presenting cells (APCs), T-cell receptors (TCRs) on T-cells, and their cognate antigens. Disordered interactions cause the pathogenesis of autoimmune diseases such as type 1 diabetes. Therefore, the identification of antigenic epitopes of autoreactive T-cells leads to important advances in therapeutics and biomarkers. Next-generation sequencing methods allow for the rapid identification of thousands of TCR clonotypes from single T-cells, and thus there is a need to determine cognate antigens for identified TCRs. This protocol describes a reporter system of T-cell activation where the fluorescent reporter protein ZsGreen-1 is driven by nuclear factor of activated T-cells (NFAT) signaling and read by flow cytometry. Reporter T-cells also constitutively express additional pairs of fluorescent proteins as identifiers, allowing for multiplexing of up to eight different reporter T-cell lines simultaneously, each expressing a different TCR of interest and distinguishable by flow cytometry. Once TCR expression cell lines are made they can be used indefinitely for making new T-cell lines with just one transduction step. This multiplexing system permits screening numbers of TCR-antigen interactions that would otherwise be impractical, can be used in a variety of contexts (i.e., screening individual antigens or antigen pools), and can be applied to study any T-cell-MHC-antigen trimolecular interaction.

Multiplex T Cell Stimulation Assay Utilizing a T Cell Activation Reporter-Based Detection System.

Recent advancements in single cell sequencing technologies allow for identification of numerous immune-receptors expressed by T cells such as tumor-specific and autoimmune T cells. Determining antigen specificity of those cells holds immense therapeutic promise. Therefore, the purpose of this study was to develop a method that can efficiently test antigen reactivity of multiple T cell receptors (TCRs) with limited cost, time, and labor. Nuclear factor of activated T cells (NFAT) is a transcription factor involved in producing cytokines and is often utilized as a reporter system for T cell activation. Using a NFAT-based fluorescent reporter system, we generated T-hybridoma cell lines that express intensely fluorescent proteins in response to antigen stimulation and constitutively express additional fluorescent proteins, which serve as identifiers of each T-hybridoma expressing a unique TCR. This allows for the combination of multiple T-hybridoma lines within a single reaction. Sensitivity to stimulation is not decreased by adding fluorescent proteins or multiplexing T cells. In multiplexed reactions, response by one cell line does not induce response in others, thus preserving specificity. This multiplex assay system will be a useful tool for antigen discovery research in a variety of contexts, including using combinatorial peptide libraries to determine T cell epitopes.