Immune Biomarkers of Residual Beta-cell Mass in Type 1 Diabetes

Overview

There is currently no imaging technique allowing to directly visualize and measure pancreatic beta-cell mass. Consequently, the best parameter to estimate this mass is the insulin (and its C-peptide byproduct) that residual beta cells are able to produce. This insulin secretion is measured during a meal test, before and at different times after drinking a standardized quantity of nutrients. However, this test is cumbersome (lasting 3 h, with blood samples taken every 30 minutes) and it holds poor sensitivity, probably insufficient to detect very few residual beta cells. Nevertheless, these few residual cells can improve glycemic control and can be instrumental for the clinical efficacy of immune and/or regenerative therapies. We hypothesize that residual beta cells may not only represent the remaining insulin secretory capacity, but also the antigenic load capable of stimulating beta-cell-reactive T lymphocytes. The disappearance of these T lymphocytes from circulating blood over time may thus be correlated with beta-cell loss. Measuring beta-cell-reactive T-cell responses may therefore provide simple and sensitive immune surrogate markers of residual insulin secretion. Other surrogate markers may be obtained by measuring urinary C peptide or residual secretion of the counter-regulatory hormone glucagon. The main objectives of this study are: 1. To evaluate the correlation between beta-cell-reactive T-cell responses and residual insulin secretion. 2. To evaluate the correlation between the residual insulin secretion measured by serum C peptide and by urinary C peptide. 3. To evaluate the correlation between the residual insulin and glucagon secretion.

Type 1 Diabetes (T1D) displays an average 4% annual increase in incidence in most Western countries, particularly in children and young adults. As it requires life-long treatments and it carries significant risks of hypoglycemic and long-term micro- and macrovascular complications, it is a leading cause of disability and public health expenditure. T1D is an autoimmune disease which comprises humoral responses (antibody-producing B lymphocytes) and cellular responses (T lymphocytes). However, antibodies are merely disease markers and do not play any major pathogenic role. Rather, T1D is caused by an abnormal recognition of beta-cell epitopes by T lymphocytes. This recognition leads to destruction of pancreatic insulin-secreting beta cells, hence the need for lifelong insulin treatment. However, beta-cell destruction is rarely complete at the time of T1D onset. The hypothesis under testing is that the residual beta-cell mass may represent not only the endogenous insulin secretory capacity, but also the antigenic load capable of maintaining activation of autoreactive T lymphocytes. In other words, the disappearance of beta-cell-reactive T-cell responses over time may be correlated with beta-cell loss. Measurement of these T-cell responses may thus provide surrogate immune markers of residual beta cells. The primary objective is to evaluate the correlation between residual insulin secretion and T-cell responses directed against beta-cell antigens. The secondary objectives are to evaluate the correlation between residual insulin secretion estimated by serum and urine C-peptide measurement; and to evaluate the correlation between residual insulin and glucagon secretion. The ImMaDiab study is a cohort-based investigation with blood sample collection. Both new-onset T1D children and adults will be recruited. Insulin secretion will be stimulated by a standardized meal test. Following T1D diagnosis, blood and urine samples will be collected every 6 months during 30 months in order to measure serum and urine C peptide, glucagon and T-lymphocyte responses against selected beta-cell antigens.