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Unravelling the unconventional processing and presentation of preproinsulin to the immune system in human Type 1 Diabetes: the role of intramembrane-cleaving proteases

Final Report Summary - DIABICLIPS (Unravelling the unconventional processing and presentation of preproinsulin to the immune system in human Type 1 Diabetes: the role of intramembrane-cleaving proteases.)

Type 1 Diabetes (T1D) is an autoimmune disease in which the loss of self-tolerance drives a focused adaptive immune response directed specifically against β-cells, the insulin-secreting cells of the pancreas. During the last 60 years the incidence of T1D has been increasing by 3-5% per year in Western Europe, doubling the number of cases every 20 years, so it becomes urgent to understand the autoimmune processes that underlie the disease. Both autoreactive CD4 and CD8 T lymphocytes are involved in this pathogenic process.
Amongst the original aims of the project is the study of the molecular and cellular basis of processing of autoantigens in T1D. For this type of study, it is critical to have access to T cell receptor (TCR) reagents, whether as cloned cells or coded sequences that can be placed into reporter cells. These are the key laboratory probes needed to study antigen processing. In addition, analysis of TCR use and structure represents a relatively novel and unexplored area of autoimmunity and T1D research. The identification of these sequences will generate a novel and incisive dataset, as information about TCR use and diversity of autoreactive clonotypes in T1D is missing.
The first step of the project was to screen newly diagnosed Type 1 diabetes patients (T1D) and matched healthy donors (HD) for their reactivity against several relevant autoantigens. Interestingly, we found that a subset of antigen-specific CD4+ T cells was present in both HD and T1D patients. This prompted us to investigate what is different between these cells in T1D vs HD that makes them pathogenic, by means of surface staining, gene expression profiling and TCR clonotyping. We also aimed to analyse the TCR repertoire of ex vivo sorted CD4+ populations (true naïve-TN-, central memory-CM-, effector memory-EM-, regulatory T cells-Treg- and stem-cell like memory cells-Tscm-) by deep sequencing to compare the characteristics of these populations between T1D and HD and also to obtain a pool of TCRs with which we could track antigen-specific TCRs. By doing this we can develop new diagnostic/risk assessments in which antigen-specific T cells can be identified directly from blood by sequencing, without having to culture, isolate and test the antigen specificity in vitro.
We find that autoantigen-specific CD4+ T cells are present in both HD and T1D patients, but in the latter the frequency is higher, and the phenotype/gene expression profile is different. Regarding the deep sequencing of TCR repertoires we found differences in the TCR diversity of some of the populations tested, as well as several T1D-exclusive clonotypes; this information will be published soon.
The expected results will include a complete clonal and phenotypic picture of antigen-specific CD4+ T cells in T1D patients versus HD, including an in depth analysis of the TCR repertoire of several immune-relevant CD4+ populations in T1D and in HD; in the latter case we are also extending current knowledge on the nature of a healthy immune system. These results will shed light on disease mechanisms, opening the door to new, more specific and safer treatments for T1D, increasing EU excellence and ERA competitiveness in several ways. First, due to the innovative nature of the project, we expect the results to have a high impact in the T1D research field, increasing citation of European papers. This will help place the host group and Europe in the leading position of TCR and T1D research; such a leading position will attract researchers and funding, increasing European attractiveness and competitiveness in this field. Second, new collaborations created during the life of this project will produce long-term synergies as all groups share the same research field (T1D) but from different vantages, making cooperative research a promising possibility. And finally, one of the EU Policy Areas is Public Health, aimed to be fostered through research and innovation on health issues: here is where the expected results of this project are placed, because the results highlighted above would open doors to new T1D treatments. This could improve patient quality of life by translating basic discoveries into clinical applications through the BRC translational centre. Thus, the expected results completely fit with EU policies, and clearly enhance EU excellence.
In conclusion, regarding the EU policy, the ERA strategic view, the Europe 2020 strategy and the Horizon 2020 instrument, the project and the expected results will clearly increase EU excellence and competitiveness, helping to produce long-term synergies with other EU institutions, and increasing public health and the wellbeing of the Europeans.