Comparison of Omentum and Subcutis as Implant Sites for Device-Encapsulated Human iPSC-Derived Pancreatic Endoderm in Nude Rats.

Subcutaneous implants of device-encapsulated stem cell-derived pancreatic endoderm (PE) can establish a functional beta cell mass (FBM) with metabolic control in immune-compromised mice. In a study with human-induced pluripotent stem cell-PE, this outcome was favored by a preformed pouch which allowed lesion-free insertion of devices in a pre-vascularized site. This was not reproduced in nude rats, known to exhibit a higher innate reactivity than mice and therefore relevant as preclinical model: a dense fibrotic capsule formed around subcutis (SC) implants with virtually no FBM formation. Placement in omentum (OM) of nude rats provided a less fibrous, better vascularized environment than SC. It resulted in less donor cell loss (56% recovery at post-transplant-PT week 3 versus 16% in SC) allowing FBM-formation. At PT week 30, 6/13 OM-recipients exhibited glucose-induced plasma hu-C-peptide to 0.1-0.4 ng/ml, versus 0/8 in SC-recipients. These levels are more than 10-fold lower than in a state of metabolic control. This shortcoming is not caused by inadequate glucose responsiveness of the beta cells but by their insufficient number. The size of the formed beta cell mass (0.4 ± 0.2 µl) was lower than that reported in mice receiving the same cell product subcutaneously; the difference is attributed to a lower expansion of pancreatic progenitor cells and to their lower degree of differentiation to beta cells. This study in the nude rat model demonstrates that OM provides a better environment for formation of beta cells in device-encapsulated PE-implants than SC. It also identified targets for increasing their dose-efficacy.

Cell Mass Increase Associated with Formation of Glucose-Controlling ß-Cell Mass in Device-Encapsulated Implants of hiPS-Derived Pancreatic Endoderm.

Device-encapsulated human stem cell-derived pancreatic endoderm (PE) can generate functional ß-cell implants in the subcutis of mice, which has led to the start of clinical studies in type 1 diabetes. Assessment of the formed functional ß-cell mass (FBM) and its correlation with in vivo metabolic markers can guide clinical translation. We recently reported ex vivo characteristics of device-encapsulated human embryonic stem cell-derived (hES)-PE implants in mice that had established a metabolically adequate FBM during 50-week follow-up. Cell suspensions from retrieved implants indicated a correlation with the number of formed ß cells and their maturation to a functional state comparable to human pancreatic ß cells. Variability in metabolic outcome was attributed to differences in number of PE-generated ß cells. This variability hinders studies on processes involved in FBM-formation. This study reports modifications that reduce variability. It is undertaken with device-encapsulated human induced pluripotent stem cell-derived-PE subcutaneously implanted in mice. Cell mass of each cell type was determined on intact tissue inside the device to obtain more precise data than following isolation and dispersion. Implants in a preformed pouch generated a glucose-controlling ß-cell mass within 20 weeks in over 60% of recipients versus less than 20% in the absence of a pouch, whether the same or threefold higher cell dose had been inserted. In situ analysis of implants indicated a role for pancreatic progenitor cell expansion and endocrine differentiation in achieving the size of ß- and α-cell mass that correlated with in vivo markers of metabolic control. Stem Cells Translational Medicine 2019;8:1296&1305.

Increase Functional ß-Cell Mass in Subcutaneous Alginate Capsules With Porcine Prenatal Islet Cells but Loss With Human Adult Islet Cells.

Alginate (Alg)-encapsulated porcine islet cell grafts are developed to overcome limitations of human islet transplantation. They can generate functional implants in animals when prepared from fetal, perinatal, and adult pancreases. Implants have not yet been examined for efficacy to establish sustained, metabolically adequate functional ß-cell mass (FBM) in comparison with human islet cells. This study in immune-compromised mice demonstrates that subcutaneous implants of Alg-encapsulated porcine prenatal islet cells with 4 × 105 ß-cells form, over 10 weeks, a FBM that results in glucose-induced plasma C-peptide >2 ng/mL and metabolic control over the following 10 weeks, with higher efficiency than nonencapsulated, while failing in peritoneum. This intracapsular FBM formation involves ß-cell replication, increasing number fourfold, and maturation toward human adult ß-cells. Subcutaneous Alg-encapsulated human islet cells with similar ß-cell number establish implants with plasma C-peptide >2 ng/mL for the first 10 weeks, with nonencapsulated cells failing; their ß-cells do not replicate but progressively die (>70%), explaining C-peptide decline and insufficient metabolic control. An Alg matrix thus helps establish ß-cell functions in subcutis. It allows formation of sustained metabolically adequate FBM by immature porcine ß-cells with proliferative activity but not by human adult islet cells. These findings define conditions for evaluating its immune-protecting properties.

Functional Beta Cell Mass from Device-Encapsulated hESC-Derived Pancreatic Endoderm Achieving Metabolic Control.

Human stem cells represent a potential source for implants that replace the depleted functional beta cell mass (FBM) in diabetes patients. Human embryonic stem cell-derived pancreatic endoderm (hES-PE) can generate implants with glucose-responsive beta cells capable of reducing hyperglycemia in mice. This study with device-encapsulated hES-PE (4 × 106 cells/mouse) determines the biologic characteristics at which implants establish metabolic control during a 50-week follow-up. A metabolically adequate FBM was achieved by (1) formation of a sufficient beta cell number (>0.3 × 106/mouse) at >50% endocrine purity and (2) their maturation to a functional state comparable with human pancreatic beta cells, as judged by their secretory responses during perifusion, their content in typical secretory vesicles, and their nuclear NKX6.1-PDX1-MAFA co-expression. Assessment of FBM in implants and its correlation with in vivo metabolic markers will guide clinical translation of stem cell-derived grafts in diabetes.