The onset of metabolic dysregulation in type 1 diabetes (T1D) occurs after autoimmune destruction of the majority of pancreatic insulin-producing beta cells. We previously demonstrated that the DNA encoding the insulin gene is uniquely unmethylated in these cells and then developed a methylation-specific PCR (MSP) assay to identify circulating beta cell DNA in streptozotocin-treated mice prior to the rise in blood glucose. The current study extends to autoimmune non-obese diabetic (NOD) mice and humans, showing in NOD mice that beta cell death occurs six weeks before the rise in blood sugar and coincides with the onset of islet infiltration by immune cells, demonstrating the utility of MSP for monitoring T1D. We previously reported unique patterns of methylation of the human insulin gene, and now extend this to other human tissues. The methylation patterns of the human insulin promoter, intron 1, exon 2, and intron 2 were determined in several normal human tissues. Similar to our previous report, the human insulin promoter was unmethylated in beta cells, but methylated in all other tissues tested. In contrast, intron 1, exon 2 and intron 2 did not exhibit any tissue-specific DNA methylation pattern. Subsequently, a human MSP assay was developed based on the methylation pattern of the insulin promoter and human islet DNA was successfully detected in circulation of T1D patients after islet transplantation therapy. Signal levels of normal controls and pre-transplant samples were shown to be similar, but increased dramatically after islet transplantation. In plasma the signal declines with time but in whole blood remains elevated for at least two weeks, indicating that association of beta cell DNA with blood cells prolongs the signal. This assay provides an effective method to monitor beta cell destruction in early T1D and in islet transplantation therapy.

Islet allotransplantation in the United States (US) is facing an imminent demise. Despite nearly three decades of progress in the field, an archaic regulatory framework has stymied US clinical practice. Current regulations do not reflect the state‐of‐the‐art in clinical or technical practices. In the US, islets are considered biologic drugs and “more than minimally manipulated” human cell and tissue products (HCT/Ps). In contrast, across the world, human islets are appropriately defined as “minimally manipulated tissue” and not regulated as a drug, which has led to islet allotransplantation (allo‐ITx) becoming a standard‐of‐care procedure for selected patients with type 1 diabetes mellitus. This regulatory distinction impedes patient access to islets for transplantation in the US. As a result only 11 patients underwent allo‐ITx in the US between 2016 and 2019, and all as investigational procedures in the settings of a clinical trials. Herein, we describe the current regulations pertaining to islet transplantation in the United States. We explore the progress which has been made in the field and demonstrate why the regulatory framework must be updated to both better reflect our current clinical practice and to deal with upcoming challenges. We propose specific updates to current regulations which are required for the renaissance of ethical, safe, effective, and affordable allo‐ITx in the United States.

The Glucagon-like peptide 1 receptor (GLP-1R) has become an important target for imaging due to its elevated expression profile in pancreatic islets, insulinoma, and the cardiovascular system. Because native GLP-1 is degraded rapidly by dipeptidyl peptidase-IV (DPP-IV), several studies have conjugated different chelators to a more stable analog of GLP-1 (such as exendin-4) as PET or SPECT imaging agents with various advantages and disadvantages. Based on the recently developed Sarcophagin chelator, here, we describe the construction of GLP-1R targeted PET probes containing monomeric and dimeric exendin-4 subunit. The in vitro binding affinity of BarMalSar-exendin-4 and Mal₂Sar-(exendin-4)₂ was evaluated in INS-1 cells, which over-express GLP-1R. Mal₂Sar-(exendin-4)₂ demonstrated around 3 times higher binding affinity compared with BaMalSar-exendin-4. After ⁶⁴Cu labeling, microPET imaging of ⁶⁴Cu-BaMalSar-exendin-4 and ⁶⁴Cu-Mal₂Sar-(exendin-4)₂ were performed on subcutaneous INS-1 tumors, which were clearly visualized with both probes. The tumor uptake of ⁶⁴Cu-Mal₂Sar-(exendin-4)₂ was significantly higher than that of ⁶⁴Cu-BaMaSarl-exendin-4, which could be caused by polyvalency effect. The receptor specificity of these probes was confirmed by effective blocking of the uptake in both tumor and normal positive organs with 20-fold excess of unlabeled exendin-4. In conclusion, sarcophagine cage conjugated exendin-4 demonstrated persistent and specific uptake in INS-1 insulinoma model. Dimerization of exendin-4 could successfully lead to increased tumor uptake in vivo. Both ⁶⁴Cu-BaMalSar-exendin-4 and ⁶⁴Cu-Mal₂Sar-(exendin-4)₂ hold a great potential for GLP-1R targeted imaging.

Umbilical cord mesenchymal stem cell-derived extracellular vesicles (UC-MSC-EVs) have become an emerging strategy for treating various autoimmune and metabolic disorders, particularly diabetes. Delivery of UC-MSC-EVs is essential to ensure optimal efficacy of UC-MSC-EVs. To develop safe and superior EVs-based delivery strategies, we explored nuclear techniques including positron emission tomography (PET) to evaluate the delivery of UC-MSC-EVs in vivo. In this study, human UC-MSC-EVs were first successfully tagged with I-124 to permit PET determination. Intravenous (I.V.) and intra-arterial (I.A.) administration routes of [¹²⁴I]I-UC-MSC-EVs were compared and evaluated by in vivo PET-CT imaging and ex vivo biodistribution in a non-diabetic Lewis (LEW) rat model. For I.A. administration, [¹²⁴I]I-UC-MSC-EVs were directly infused into the pancreatic parenchyma via the celiac artery. PET imaging revealed that the predominant uptake occurred in the liver for both injection routes, and further imaging characterized clearance patterns of [¹²⁴I]I-UC-MSC-EVs. For biodistribution, the uptake (%ID/gram) in the spleen was significantly higher for I.V. administration compared to I.A. administration (1.95 ± 0.03 and 0.43 ± 0.07, respectively). Importantly, the pancreas displayed similar uptake levels between the two modalities (0.20 ± 0.06 for I.V. and 0.24 ± 0.03 for I.A.). Therefore, our initial data revealed that both routes had similar delivery efficiency for [¹²⁴I]I-UC-MSC-EVs except in the spleen and liver, considering that higher spleen uptake could enhance immunomodulatory application of UC-MSC-EVs. These findings could guide the development of safe and efficacious delivery strategies for UC-MSC-EVs in diabetes therapies, in which a minimally invasive I.V. approach would serve as a better delivery strategy. Further confirmation studies are ongoing.