Plan-β: a bioengineering approach against type 1 diabetes

The restoration of euglycemia after intraportal islet transplantation remains short-lived, requires islets from multiple donors, and necessitates life-long immunosuppressive therapy. In this thesis we propose different bioengineering strategies to improve islet transplantation outcome. In chapter 2 and 3 we describe the development and characterization of a microwell scaffold platform for extrahepatic islet transplantation. In chapter 2 the concept of the microwell design is introduced. We have shown that human islets cultured in this platform for seven days exhibit an insulin secretion profile and insulin content comparable to those of free-floating control islets. Chapter 3 explores three different fabrication methods to introduce pores in the microwell scaffold platform: particulate leaching, solvent casting on pillared wafers, and laser drilling. Methods were evaluated for pore size and geometry, reproducibility and flexibility, and the form and stability of the final construct. Transplantation studies in the epididymal fat elucidate the potential of this porous scaffold platform to restore blood glucose levels in a diabetic mouse model. However, we do observe a significant decrease in beta-cell density and a changed vascularization pattern in scaffold-implanted islets compared to native pancreatic islets, which, we hypothesize, are indications for delayed revascularization. Therefore, we explore in chapter 4 the potential of composite islets with different proangiogenic cell types to improve islet revascularization after transplantation. Here, we demonstrate that composite islets with hMSCs and HUVECs exhibit a higher in vivo angiogenic potential compared with uncoated islets or islets combined with hMSCs or pre-conditioned hMSCs in EGM-2 medium. In chapter 5, we propose a method to monitor non-invasively beta-cell survival after islet transplantation. For this, we describe the use of radiolabelled exendin-3, which specifically targets pancreatic β-cells. We demonstrate that the uptake of 111In-exendin-3 in scaffold-implanted islets could be clearly visualized on ex vivo SPECT scans, with histology and autoradiography studies showing vascularized islets with specific tracer uptake in β-cell regions. Provided that tracer uptake can also be determined in vivo, this presents a viable method to monitor the influence of native and engineered transplantation sites on long-term β-cell survival.