High proinsulin:C-peptide ratio identifies individuals with stage 2 type 1 diabetes at high risk for progression to clinical diagnosis and responses to teplizumab treatment

AIMS/HYPOTHESIS

Tractable precision biomarkers to identify immunotherapy responders are lacking in type 1 diabetes. We hypothesised that proinsulin:C-peptide (PI:C) ratios, a readout of beta cell stress, could provide insight into type 1 diabetes progression and responses to immunotherapy.

METHODS

In this post hoc analysis, proinsulin and C-peptide levels were determined in baseline serum samples from 63 participants with stage 2 type 1 diabetes in the longitudinal TrialNet Teplizumab Prevention Study (n=41 in the teplizumab arm; n=22 in the placebo arm). In addition, previously tested demographic, C-peptide, glucose and proinsulin data were used for the new data analyses. The ratio of intact (unprocessed) proinsulin to C-peptide was analysed and relationships with progression to stage 3 diabetes were investigated.

RESULTS

Elevated baseline PI:C was strongly associated with more rapid progression of diabetes in both the placebo and teplizumab treatment groups, but teplizumab abrogated the impact of high pre-treatment PI:C on type 1 diabetes progression. Differential responses of drug treatment in those with high vs low PI:C ratios were independent of treatment effects of teplizumab on the PI:C ratio or on relevant immune cells.

CONCLUSIONS/INTERPRETATION

High pre-treatment PI:C identified individuals with stage 2 type 1 diabetes who were exhibiting rapid progression to stage 3 disease and who displayed benefit from teplizumab treatment. These data suggest that readouts of active disease, such as PI:C ratio, could serve to identify optimal candidates or timing for type 1 diabetes disease-modifying therapies.

Novel autoantibodies to the β-cell surface epitopes of ZnT8 in patients progressing to type-1 diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease characterized by autoimmune destruction of insulin-producing β-cells in pancreatic islets. Seroconversions to islet autoantibodies (IAbs) precede the disease onset by many years, but the role of humoral autoimmunity in the disease initiation and progression are unclear. In the present study, we identified a new IAb directed to the extracellular epitopes of ZnT8 (ZnT8ec) in newly diagnosed patients with T1D, and demonstrated immunofluorescence staining of the surface of human β-cells by autoantibodies to ZnT8ec (ZnT8ecA). With the assay specificity set on 99th percentile of 336 healthy controls, the ZnT8ecA positivity rate was 23.6% (74/313) in patients with T1D. Moreover, 30 children in a longitudinal follow up of clinical T1D development were selected for sequential expression of four major IAbs (IAA, GADA, IA-2A and ZnT8icA). Among them, 10 children were ZnT8ecA positive. Remarkably, ZnT8ecA was the earliest IAb to appear in all 10 children. The identification of ZnT8ec as a cell surface target of humoral autoimmunity in the earliest phase of IAb responses opens a new avenue of investigation into the role of IAbs in the development of β-cell autoimmunity.

Evidence of stress in β cells obtained with laser capture microdissection from pancreases of brain dead donors

Isolated islets used for transplantation are known to be stressed, which can result from the circumstances of death, in particular brain death, the preservation of the pancreas with its warm and cold ischemia, from the trauma of the isolation process, and the complex events that occur during tissue culture. The current study focused upon the events that occur before the islet isolation procedure. Pancreases were obtained from brain dead donors (n = 7) with mean age 50 (11) and normal pancreatic tissue obtained at surgery done for pancreatic neoplasms (n = 7), mean age 69 (9). Frozen sections were subjected to laser capture microdissection (LCM) to obtain β-cell rich islet tissue, from which extracted RNA was analyzed with microarrays. Gene expression of the 2 groups was evaluated with differential expression analysis for genes and pathways. Marked changes were found in pathways concerned with endoplasmic reticulum stress with its unfolded protein response (UPR), apoptotic pathways and components of inflammation. In addition, there were changes in genes important for islet cell identity. These findings advance our understanding of why islets are stressed before transplantation, which may lead to strategies to reduce this stress and lead to better clinical outcomes.