Sensitivity Study for the Key Parameters in Heterospheroid Preparation with Insulin-Secreting β‑Cells and Mesenchymal Stem Cells

The outcome of islet transplantation in clinics has been determined by the success of tissue engraftment. The strong immune attack that occurs upon transplantation of β-cells plays a central role as this attack results in the failure of transplanted tissue. To improve tissue engraftment, deleterious effects of immune reactions should be minimized for β-cell function and survival. Here, we report a systematic analysis of the effect of insulin-secreting β-cell (MIN6) and mesenchymal stem cell (MSC) number and size on the function of β-cells and present immune protection potential of heterospheroid structures through MSCs and synthetic scaffolds. We prepared 3D heterospheroids with MSCs and MIN6 cells through a hanging-drop approach. To precisely estimate the influence of critical parameters on heterospheroid size and insulin secretion function of β-cells, we prepared heterospheroids using two independent input variables: (i) initial cell number in each droplet and (ii) MIN6:MSC ratio. We studied the influence of initial cell numbers of 200 and 500, and six different MIN6:MSC ratios (1:0, 0:1, 1:1, 2:1, 5:1, and 10:1) for the preparation of heterospheroids through the hanging drop. Next, we used PEG hydrogels as a semipermeable physical barrier to improve immune protection from cytokines. Through encapsulation of our heterospheroids within PEG hydrogel, we were able to observe sustained β-cell survival and insulin secretion despite exposure of heterospheroids with proinflammatory cytokines. Insulin secretion was further promoted with glucagon like peptide-1 (GLP-1) incorporation within PEG hydrogel structure. This study is significant to demonstrate the synergistic effects of MIN6-MSC and scaffold-MIN6 interactions and to improve therapeutic efficacy of islet transplantation. Overall, this study comprehensively presents the optimum conditions for the preparation of MIN6-MSC spheroids, utilizes MSCs and GLP-1 functional PEG hydrogels as a scaffold to retain insulin secretion function and further demonstrates protection of heterospheroids exposed to proinflammatory cytokines.