Pig islets for clinical islet xenotransplantation. Curr Opin Nephrol Hypertens. 2009;18:495-500. [PMID: 19726985 DOI: 10.1097/MNH.0b013e328331a8e3]

Differentiation of Microencapsulated Neonatal Porcine Pancreatic Cell Clusters in Vitro Improves Transplant Efficacy in Type 1 Diabetes Mellitus Mice

BACKGROUND

Neonatal porcine pancreatic cell clusters (NPCCs) have been proposed as an alternative source of β cells for islet transplantation because of their low cost and growth potential after transplantation. However, the delayed glucose lowering effect due to the immaturity of NPCCs and immunologic rejection remain as a barrier to NPCC's clinical application. Here, we demonstrate accelerated differentiation and immune-tolerant NPCCs by in vitro chemical treatment and microencapsulation.

METHODS

NPCCs isolated from 3-day-old piglets were cultured in F-10 media and then microencapsulated with alginate on day 5. Differentiation of NPCCs is facilitated by media supplemented with activin receptor-like kinase 5 inhibitor II, triiodothyronine and exendin-4 for 2 weeks. Marginal number of microencapsulated NPCCs to cure diabetes with and without differentiation were transplanted into diabetic mice and observed for 8 weeks.

RESULTS

The proportion of insulin-positive cells and insulin mRNA levels of NPCCs were significantly increased in vitro in the differentiated group compared with the undifferentiated group. Blood glucose levels decreased eventually after transplantation of microencapsulated NPCCs in diabetic mice and normalized after 7 weeks in the differentiated group. In addition, the differentiated group showed nearly normal glucose tolerance at 8 weeks after transplantation. In contrast, neither blood glucose levels nor glucose tolerance were improved in the undifferentiated group. Retrieved graft in the differentiated group showed greater insulin response to high glucose compared with the undifferentiated group.

CONCLUSION

in vitro differentiation of microencapsulated immature NPCCs increased the proportion of insulin-positive cells and improved transplant efficacy in diabetic mice without immune rejection.

Islet encapsulation

Review of emerging advances and persisting challenges in the engineering and translation of islet encapsulation technologies.

Islet Microencapsulation: Strategies and Clinical Status in Diabetes

PURPOSE OF REVIEW

Type 1 diabetes mellitus (T1DM) is an autoimmune disease that results from the destruction of insulin-producing pancreatic β cells in the islets of Langerhans. Islet cell transplantation has become a successful therapy for specific patients with T1DM with hypoglycemic unawareness. The reversal of T1DM by islet transplantation is now performed at many major medical facilities throughout the world. However, many challenges must still be overcome in order to achieve continuous, long-term successful transplant outcomes. Two major obstacles to this therapy are a lack of islet cells for transplantation and the need for life-long immunosuppressive treatment. Microencapsulation is seen as a technology that can overcome both these limitations of islet cell transplantation. This review depicts the present state of microencapsulated islet transplantation.

RECENT FINDINGS

Microencapsulation can play a significant role in overcoming the need for immunosuppression and lack of donor islet cells. This review focuses on microencapsulation and the clinical status of the technology in combating T1DM.

Engraftment and reversal of diabetes after intramuscular transplantation of neonatal porcine islet-like clusters

BACKGROUND

Intraportal infusion is currently the method of choice for clinical islet cell transplantation but suffers from poor efficacy. As the liver may not represent an optimal transplantation site for Langerhans islets, we examined the potential of neonatal porcine islet-like clusters (NPICCs) to engraft in skeletal muscle as an alternative transplantation site.

METHODS

Neonatal porcine islet-like clusters were isolated from 2- to 5-day-old piglets and either transplanted under the kidney capsule (s.k.) or injected into the lower hindlimb muscle (i.m.) of streptozotocin-diabetic NOD-SCID IL2rγ(-/-) (NSG) mice. Survival, vascularization, maturation, and functional activity were analyzed by intraperitoneal glucose tolerance testing and immunohistochemical analyses.

RESULTS

Intramuscular transplantation of NPICCs resulted in development of normoglycemia and restored glucose homeostasis. Time to reversal of diabetes and glucose tolerance (AUC glucose and AUC insulin) did not significantly differ as compared to s.k. transplantation. Intramuscular grafts exhibited rapid neovascularization and graft composition with cytokeratin-positive ductal cells and beta cells at post-transplant weeks 2 and 8 and after establishment of normoglycemia was comparable in both groups.

CONCLUSIONS

Intramuscular injection represents a minimally invasive but efficient alternative for transplantation of NPICCs and, thus, offers an attractive alternative site for xenotransplantation approaches. These findings may have important implications for improving the outcome and the monitoring of pig islet xenotransplantation.

Optimal pig donor selection in islet xenotransplantation: current status and future perspectives

Islet transplantation is an attractive treatment of type 1 diabetes mellitus. Xenotransplantation, using the pig as a donor, offers the possibility of an unlimited supply of islet grafts. Published studies demonstrated that pig islets could function in diabetic primates for a long time (>6 months). However, pig-islet xenotransplantation must overcome the selection of an optimal pig donor to obtain an adequate supply of islets with high-quality, to reduce xeno-antigenicity of islet and prolong xenograft survival, and to translate experimental findings into clinical application. This review discusses the suitable pig donor for islet xenotransplantation in terms of pig age, strain, structure/function of islet, and genetically modified pig.

Pig-islet xenotransplantation: recent progress and current perspectives

Islet xenotransplantation is one prospective treatment to bridge the gap between available human cells and needs of patients with diabetes. Pig represents an ideal candidate for obtaining such available cells. However, potential clinical application of pig islet still faces obstacles including inadequate yield of high-quality functional islets and xenorejection of the transplants. Adequate amounts of available islets can be obtained by selection of a suitable pathogen-free source herd and the development of isolation and purification method. Several studies demonstrated the feasibility of successful preclinical pig-islet xenotransplantation and provided insights and possible mechanisms of xenogeneic immune recognition and rejection. Particularly promising is the achievement of long-term insulin independence in diabetic models by means of distinct islet products and novel immunotherapeutic strategies. Nonetheless, further efforts are needed to obtain much more safety and efficacy data to translate these findings into clinic.

Treatment of diabetic rats using islets from a herd of outbred Wuzhishan miniature pigs

AIM: To assess the efficacy of Wuzhishan miniature pig islets in the treatment of diabetic rats.

METHODS: Adult male miniatures pigs and market pigs were used as donors. After collagenase digestion, the islets were purified and intraportally transplanted into diabetic SPF rats, with cyclosporine (20 mg/kg) intramuscularly injected as an immunosuppressive agent. Islet graft survival was monitored by the detection of changes in blood sugar and liver histology in diabetic rats.

RESULTS: Islet yield was 4 608 IEQ/g ± 593 IEQ/g in the miniature pig group and 3 820 IEQ/g ± 718 IEQ/g in the market pig group. On day 1 after transplantation, the blood glucose decreased to normal in 84.6% of diabetic rats in both groups. Islet survival time was 3-5 d (median: 4.5 d) in the miniature pig group and 2-4 d (median: 3.7 d) in the market pig group. Kaplan-Meier analysis showed no significant difference between the two groups.

CONCLUSION: The Wuzhishan miniature pigs are an ideal donor species for islet xenotransplantation due to high islet yield and good islet function.

Advances in research of pig islet xenotransplantation for diabetes

Pig islet xenotransplantation is effective in treating diabetes. Nowadays, the research of islet xenotransplantation is still in the research phase, and its clinical use is mainly restricted by the shortage of functional islets and graft rejection. In recent years, several studies have demonstrated the feasibility of successful preclinical pig islet xenotransplantation. Moreover, promising results concerning prolonged insulin independence were achieved with the improvement of islet isolation technologies, application of novel immunotherapeutic strategies, and the development of transplantation surgery. This review aims to elucidate the advances in the separation and preparation of transplanted pig islet, immunological rejection and treatments, potential safety problems, and clinical studies.

Induction of protective genes leads to islet survival and function

Islet transplantation is the most valid approach to the treatment of type 1 diabetes. However, the function of transplanted islets is often compromised since a large number of β cells undergo apoptosis induced by stress and the immune rejection response elicited by the recipient after transplantation. Conventional treatment for islet transplantation is to administer immunosuppressive drugs to the recipient to suppress the immune rejection response mounted against transplanted islets. Induction of protective genes in the recipient (e.g., heme oxygenase-1 (HO-1), A20/tumor necrosis factor alpha inducible protein3 (tnfaip3), biliverdin reductase (BVR), Bcl2, and others) or administration of one or more of the products of HO-1 to the donor, the islets themselves, and/or the recipient offers an alternative or synergistic approach to improve islet graft survival and function. In this perspective, we summarize studies describing the protective effects of these genes on islet survival and function in rodent allogeneic and xenogeneic transplantation models and the prevention of onset of diabetes, with emphasis on HO-1, A20, and BVR. Such approaches are also appealing to islet autotransplantation in patients with chronic pancreatitis after total pancreatectomy, a procedure that currently only leads to 1/3 of transplanted patients being diabetes-free.

Controlling coagulation dysregulation in xenotransplantation

PURPOSE OF REVIEW

Deletion of the α1,3-galactosyltransferase (GalT) gene in pigs has removed a major xenoantigen but has not eliminated the problem of dysregulated coagulation and vascular injury. Rejecting GalT knockout organ xenografts almost invariably show evidence of thrombosis and platelet sequestration, and primate recipients frequently develop consumptive coagulopathy. This review examines recent findings that illuminate potential mechanisms of this current barrier to successful xenotransplantation.

RECENT FINDINGS

The coagulation response to xenotransplantation differs depending on the type of organ and quite likely the distinct vasculatures. Renal xenografts appear more likely to initiate consumptive coagulopathy than cardiac xenografts, possibly reflecting differential transcriptional responses. Liver xenografts induce rapid and profound thrombocytopenia resulting in recipient death within days due to bleeding; ex-vivo data suggest that liver endothelial cells and hepatocytes are responsible for platelet consumption by a coagulation-independent process.It has been proposed that expression of recipient tissue factor on platelets and monocytes is an important trigger of consumptive coagulopathy. Finally, pigs transgenic for human anticoagulants and antithrombotics are slowly but surely coming on line, but have not yet been rigorously tested to date.

SUMMARY

Successful control of coagulation dysregulation in xenotransplantation may require different combinatorial pharmacological and genetic strategies for different organs.