The treatment of diabetes mellitus by transplantation of isolated pancreatic islets is an approach that remains the subject of research by a large number of investigators throughout the world. A crucial requirement for the success of this enterprise is the ability to prepare viable isolated islets in adequate quantity. Over the years numerous descriptions of procedures for islet isolation from the pancreas of experimental animals and of man have been advanced; each claiming to be an improvement on previous methods. Indeed, there certainly have been advances, although few techniques live up to the claims that are made in their support Part of the problem is the generally poor methodology

OBJECTIVEAutoimmune diseases, including type 1 diabetes, are thought to have a Th17-cell bias and/or a T-regulatory cell (Treg) defect. Understanding whether this is a hallmark of patients with type 1 diabetes is a crucial question that is still unsolved, largely due to the difficulties of accessing tissues targeted by the disease.RESEARCH DESIGN AND METHODSWe phenotypically and functionally characterized Th17 cells and Tregs residing in the pancreatic-draining lymph nodes (PLNs) of 19 patients with type 1 diabetes and 63 nondiabetic donors and those circulating in the peripheral blood of 14 type 1 diabetic patients and 11 healthy subjects.RESULTSWe found upregulation of Th17 immunity and functional defects in CD4+CD25bright Tregs in the PLNs of type 1 diabetic subjects but not in their peripheral blood. In addition, the proinsulin-specific Treg-mediated control was altered in the PLNs of diabetic patients. The dysfunctional Tregs isolated from diabetic subjects did not contain contaminant effector T cells and were all epigenetically imprinted to be suppressive, as defined by analysis of the Treg-specific demethylated region within the forkhead box P3 (FOXP3) locus.CONCLUSIONSThese data provide evidence for an unbalanced immune status in the PLNs of type 1 diabetic subjects, and treatments restoring the immune homeostasis in the target organ of these patients represent a potential therapeutic strategy.

Aims/hypothesis: Efficient islet isolation is an important prerequisite for successful clinical islet transplantation. Although progressively improved, islet yield and quality are, however, unpredictable and variable and require standardisation. Methods: Since 1989 we have processed 437 pancreases using the automated method. The donor characteristics, pancreas procurement, and digestion and purification procedures including a wide enzyme characterisation of these pancreases were analysed and correlated with islet yield and transplant outcome. Results: By univariate analysis, islet yield was significantly associated with donor age (r=0.16; p=0.0009), BMI (r=0.19; p= 0.0004), good pancreas condition (p=0.0031) and weight (r=0.15; p=0.0056), total collagenase activity (r=0.22; p= 0.0001), adjusted collagenase activity/mg (r=0.18; p=0.0002), collagenase activity/solution volume (r=0.18; p=0.0002) and neutral protease activity/solution volume (r=0.14; p= 0.0029). A statistically significant contribution to the variability of islet yield in a multivariate analysis performed on donor variables was found for donor BMI (p=0.0008). In a multivariate analysis performed on pancreas variables a contribution was found for pancreas weight (p=0.0064), and for a multivariate analysis performed on digestion variables we found a contribution for digestion time (p= 0.0048) and total collagenase activity (p=0.0001). Twenty-four patients with type 1 diabetes received single islet preparations from single donors. In these patients, multivariate analyses showed that the reduction in insulin requirement was significantly associated with morphological aspects of islets (p= 0.0010) and that 1-month C-peptide values were associated with islet purity (p=0.0071). Conclusions/interpretation: These data provide baseline donor, digestion and purification selection criteria for islet isolation using the automated method and indicate that the morphological aspect may be a clinically relevant measure of islets on which the decision for transplant can be based.

In type 2 diabetes, chronic hyperglycemia has been suggested to be detrimental to beta-cell function, causing reduced glucose-stimulated insulin secretion and disproportionately elevated proinsulin. In the present study, we investigated the effect on several beta-cell functions of prolonged in vitro exposure of human pancreatic islet cultures to high glucose concentrations. Islets exposed to high glucose levels (33 mmol/l) for 4 and 9 days showed dramatic decreases in glucose-induced insulin release and in islet insulin content, with increased proportion of proinsulin-like peptides relative to insulin. The depletion in insulin stores correlated with the reduction in insulin mRNA levels and human insulin promoter transcriptional activity. We also demonstrated that high glucose dramatically lowered the binding activity of pancreatic duodenal homeobox 1 (the glucose-sensitive transcription factor), whereas the transcription factor rat insulin promoter element 3b1 activator was less influenced and insulin enhancer factor 1 remained unaffected. Most of these beta-cell impairments were partially reversible when islets first incubated for 6 days in high glucose were transferred to normal glucose (5.5 mmol/l) concentrations for 3 days. We conclude that cultured human islets are sensitive to the deleterious effect of high glucose concentrations at multiple functional levels, and that such mechanisms may play an important role in the decreased insulin production and secretion of type 2 diabetic patients.