In vitro dedifferentiation of fetal porcine pancreatic tissue prior to transplantation as islet-like cell clusters

Comparison of Size, Viability, and Function of Fetal Pig Islet-Like Cell Clusters after Digestion Using Collagenase or Liberase

Liberase is a highly purified blend of collagenases that has been specifically developed to eliminate the numerous problems associated with the conventional use of crude collagenase when isolating islet-like cell clusters (ICCs) from pancreases of different species. The influence of Liberase on yield, size, viability, and function of ICCs has been documented when this enzyme was used to digest adult but not fetal pancreases. In this study, we compared the effects of collagenase and Liberase on fetal pig ICCs. A total of eight fetal pig pancreas digestions were analyzed. Fetuses were obtained from Large White Landrace pigs of gestational age 80 ± 2.1 days. The pancreases were digested with either 3 mg/ml collagenase P or 1.2 mg/ml Liberase HI. The time taken to digest the pancreas was shorter for collagenase when compared with Liberase (22 ± 2 vs. 31 ± 2 min). The size of ICCs was similar for both collagenase (83 ± 0.5 μm) and Liberase (79 ± 0.4 μm) as was the number of ICCs produced per pancreas (7653 ± 1297 vs. 8101 ± 1177). Viability, as assessed using fluorescent markers, was slightly greater for Liberase (79 ± 1% vs. 76 ± 1%, p < 0.05). Responsiveness to β-cell stimulus (20 mM KCl) was similar for both methods of isolation, as was the insulin content of the ICCs, both in vitro and at 1 month after transplantation of 1500 ICCs beneath the renal capsule of immunoincompetent mice. Despite the high content of endotoxins in collagenase, the above results show that this enzyme was equally as efficient as Liberase in isolating functional ICCs from fetal pig pancreas.

Comparison of Fetal Porcine Aggregates of Purified β-Cells versus Islet-Like Cell Clusters as a Treatment of Diabetes

Fetal pig islet-like cell clusters (ICCs) have the potential to reverse diabetes 1–5 months after transplantation. In a fetal ICC, however, β-cells constitute only 6–8% of the cells, in contrast to 65% in an adult pig islet. Attempts to purify fetal β-cells from cell clusters and compare their function to that of ICCs have not been shown previously. β-Cells were purified from ICCs isolated from the fetal pig pancreas. These were then aggregated and maintained in culture for 3 days. ICCs were isolated from fetal pig pancreas and allowed to round up in culture for 3 days. Transplantation of aggregates and ICCs (10,000 and 12,600, respectively) into diabetic immunoincompetent mice resulted in normoglycemia at 18 ± 2 and 8 ± 1 weeks, respectively (p = 0.0006). Removal of grafts after normalization of blood glucose levels resulted in rapid return of hyperglycemia in both groups. In conclusion, a purified population of immature β-cells can be produced from the fetal pig pancreas. The reason these cells take longer than ICCs to reverse diabetes when transplanted is postulated to be because of the relative lack of precursor cells from which β-cells differentiate. This finding may have implications for stem cell therapy, as other cell types, other than purified β-cells, may be necessary for appropriate function in vivo.

Pig-to-nonhuman primates pancreatic islet xenotransplantation: an overview

The therapy of type 1 diabetes is an open challenging problem. The restoration of normoglycemia and insulin independence in immunosuppressed type 1 diabetic recipients of islet allotransplantation has shown the potential of a cell-based diabetes therapy. Even if successful, this approach poses a problem of scarce tissue supply. Xenotransplantation can be the answer to this limited donor availability and, among possible candidate tissues for xenotransplantation, porcine islets are the closest to a future clinical application. Xenotransplantation, with pigs as donors, offers the possibility of using healthy, living, and genetically modified islets from pathogen-free animals available in unlimited number of islets. Several studies in the pig-to-nonhuman primate model demonstrated the feasibility of successful preclinical islet xenotransplantation and have provided insights into the critical events and possible mechanisms of immune recognition and rejection of xenogeneic islet grafts. Particularly promising results in the achievement of prolonged insulin independence were obtained with newly developed, genetically modified pigs islets able to produce immunoregulatory products, using different implantation sites, and new immunotherapeutic strategies. Nonetheless, further efforts are needed to generate additional safety and efficacy data in nonhuman primate models to safely translate these findings into the clinic.

A novel alginate hollow fiber bioreactor process for cellular therapy applications

Gel-matrix culture environments provide tissue engineering scaffolds and cues that guide cell differentiation. For many cellular therapy applications such as for the production of islet-like clusters to treat Type 1 diabetes, the need for large-scale production can be anticipated. The throughput of the commonly used nozzle-based devices for cell encapsulation is limited by the rate of droplet formation to approximately 0.5 L/h. This work describes a novel process for larger-scale batch immobilization of mammalian cells in alginate-filled hollow fiber bioreactors (AHFBRs). A methodology was developed whereby (1) alginate obstruction of the intra-capillary space medium flow was negligible, (2) extra-capillary alginate gelling was complete and (3) 83 +/- 4% of the cells seeded and immobilized were recovered from the bioreactor. Chinese hamster ovary (CHO) cells were used as a model aggregate-forming cell line that grew from mostly single cells to pancreatic islet-sized spheroids in 8 days of AHFBR culture. CHO cell growth and metabolic rates in the AHFBR were comparable to small-scale alginate slab controls. Then, the process was applied successfully to the culture of primary neonatal pancreatic porcine cells, without significant differences in cell viability compared with slab controls. As expected, alginate-immobilized culture in the AHFBR increased the insulin content of these cells compared with suspension culture. The AHFBR process could be refined by adding matrix components or adapted to other reversible gels and cell types, providing a practical means for gel-matrix assisted cultures for cellular therapy.

Pig-to-nonhuman primate islet xenotransplantation: a review of current problems

Islet allotransplantation has been shown to have potential as a treatment for type 1 diabetic patients. Xenotransplantation, using the pig as a donor, offers the possibility of an unlimited number of islets. This comprehensive review focuses on experience obtained in pig-to-nonhuman primate models, particularly with regard to the different types of islets (fetal, neonatal, adult) and isolation procedures used, and the methods to determine islet viability. The advantages and disadvantages of the methods to induce diabetes (pancreatectomy, streptozotocin) are discussed. Experience in pig-to-nonhuman primate islet transplantation studies is reviewed, including discussion of the possible mechanisms of rejection and the immunosuppressive regimens used. The research carried out to date has led to workable animal models to study islet xenotransplantation, but several questions regarding methodology remain unanswered, and details of these practicalities require to be adequately addressed. The encouraging porcine islet survival reported recently provides an indicator for future immunosuppressive regimens.

In vitro cultivation of human fetal pancreatic ductal stem cells and their differentiation into insulin-producing cells

AIM: To isolate, culture and identify the human fetal pancreatic ductal stem cells in vitro, and to observe the potency of these multipotential cells differentiation into insulin-producing cells.

METHODS: The human fetal pancreas was digested by 1 g/L collagease type IV and then 2.5 g/L trypsin was used to isolate the pancreatic ductal stem cells, followed by culture in serum-free, glucose-free DMEM media with some additional chemical substrates in vitro (according to the different stage). The cells were induced by glucose-free (control), 5 mmol/L, 17.8 mmol/L and 25 mmol/L glucose, respectively. The cell types of differentiated cells were identified using immunocytochemical staining.

RESULTS: The shape of human fetal pancreatic ductal stem cells cultured in vitro was firstly fusiform in the first 2 wk, and became monolayer and cobblestone pattern after another 3 to 4 wk. After induced and differentiated by the glucose of different concentrations for another 1 to 2 wk, the cells formed the pancreatic islet-like structures. The identification and potency of these cells were then identified by using the pancreatic ductal stem cell marker, cytokeratin-19 (CK-19), pancreatic β cell marker, insulin and pancreatic α cell marker, glucagons with immunocytochemical staining. At the end of the second week, 95.2% of the cells were positive for CK-19 immunoreactivity. Up to 22.7% of the cells induced by glucose were positive for insulin immunoreactivity, and less than 3.8% of the cells were positive for glucagon immunoreactivity in pancreatic islet-like structures. The positive ratio of immunoreactive staining was dependent on the concentration of glucose, and it was observed that the 17.8 mmol/L glucose stimulated effectively to produce insulin- and glucagons-producing cells.

CONCLUSION: The human fetal pancreatic ductal stem cells are capable of proliferation in vitro. These cells have multidifferentiation potential and can be induced by glucose and differentiated into insulin-producing cells in vitro.

Effect of adhesion or collagen molecules on cell attachment, insulin secretion, and glucose responsiveness in the cultured adult porcine endocrine pancreas: a preliminary study

The effect of either adhesion or collagen molecules on cell attachment, insulin secretion, and glucose responsiveness was investigated in adult porcine pancreatic endocrine (PE) cells that were cultured for a longer term in vitro. Six different types of molecules--laminin, fibronectin, poly-L-lysine (PLL), type I collagen, gelatin, and Matrigel--were used. Approximately 2.0 x 10(5) cells per dish of each molecule type were cultured for 4 weeks. In the laminin group, the insulin accumulation was maintained at a significantly higher level than in the control group at 4 weeks of culture, and glucose-stimulated insulin secretion and the insulin-positive rate were also higher than in the control group. In the Matrigel group, islet-like cell clusters were formed, but insulin accumulation rapidly decreased at 3-4 weeks of culture. A large number of PE cells attached tightly and spread in the fibronectin group until the fourth week of culture, but their function was not better than those in the control group. In the PLL and gelatin groups, the PE cell function was not significantly different from that of the control group. In the type I collagen group, insulin secretion was inferior to that of the other groups. The results of this study suggest that laminin is the most suitable extracellular matrix for the long-term culture preservation of PE cells.

Lowering of blood glucose to nondiabetic levels in a hyperglycemic pig by allografting of fetal pig isletlike cell clusters

BACKGROUND

Fetal pig isletlike cell clusters (ICCs) will differentiate when grafted into the thymus gland of outbred immunosuppressed nondiabetic pigs for up to 3 months. Whether these cells will survive for a similar period in a diabetic recipient and will mature with secretion of insulin to ameliorate the hyperglycemia is unknown.

METHODS

Between 40,000 and 125,000 ICCs (7,000 to 11,400 ICCs/kg) were injected into the thymus gland of five juvenile pigs immunosuppressed with cyclosporine and deoxyspergualin, and the animals were subsequently made diabetic by the injection of streptozotocin. Insulin was administered subcutaneously, with one pig dying from hypoglycemia. The animal with the least number of ICCs transplanted was killed 81 days later, and the graft was analyzed histologically. Blood glucose levels and porcine C-peptide in the remaining animals were monitored for a median of 101 days.

RESULTS

Histological analysis of the graft showed numerous epithelial cell clusters; the percentage of cells that contained insulin, glucagon, somatostatin, and pancreatic polypeptide were 61%, 64%, 25%, and 18%, respectively. Some cells contained more than one hormone. Porcine C-peptide was detected from 21 days after induction of diabetes but not before. In the pig receiving the most ICCs, blood glucose levels were lowered to nondiabetic levels 109 days after transplantation. Plasma C-peptide levels in response to glucagon in this pig steadily increased after grafting; peak levels were 0, 0.21, 0.45, and 0.52 ng/ml at 4, 21, 49, and 80 days after induction of diabetes compared to 0.09 ng/ml in control diabetic pigs. The secretion of C-peptide in response to oral and intravenous glucose and arginine also was greater than in untransplanted diabetic pigs, the pattern of secretion being consistent with developing fetal beta cells as the source of the C-peptide. Pancreatic insulin content was 0.1 mU/mg, 4% of that in nondiabetic pigs, and the number of beta cells per islet was 3 to 6 compared to 90 in nondiabetic controls.

CONCLUSIONS

ICCs will differentiate and function for up to 111 days when transplanted into outbred immunosuppressed pigs rendered diabetic. Blood glucose levels can be lowered to nondiabetic levels when sufficient numbers of ICCs are grafted.