Normalization of glucose post-transplantation of pig pancreatic anlagen into non-immunosuppressed diabetic rats depends on obtaining anlagen prior to embryonic day 35

Omentum a powerful biological source in regenerative surgery

The Omentum is a large flat adipose tissue layer nestling on the surface of the intra-peritoneal organs. Besides fat storage, omentum has key biological functions in immune-regulation and tissue regeneration.

Omentum biological properties include neovascularization, haemostasis, tissue healing and regeneration and as an in vivo incubator for cells and tissue cultivation. Some of these properties have long been noted in surgical practice and used empirically in several procedures.

In this review article, the author tries to highlight the omentum biological properties and their application in regenerative surgery procedures. Further, he has started a process of standardisation of basic biological principles to pave the way for future surgical practice.

Classic and current opinion in embryonic organ transplantation

PURPOSE OF REVIEW

Here, we review the rationale for the use of organs from embryonic donors, antecedent investigations and recent work from our own laboratory, exploring the utility for transplantation of embryonic kidney and pancreas as an organ replacement therapy.

RECENT FINDINGS

Ultrastructurally precise kidneys differentiate in situ in rats following xenotransplantation in mesentery of embryonic pig renal primordia. The developing organ attracts its blood supply from the host. Engraftment of pig renal primordia requires host immune suppression. However, beta cells originating from embryonic pig pancreas obtained very early following initiation of organogenesis [embryonic day 28 (E28)] engraft long term in nonimmune-suppressed diabetic rats or rhesus macaques. Engraftment of morphologically similar cells originating from adult porcine islets of Langerhans occurs in animals previously transplanted with E28 pig pancreatic primordia.

SUMMARY

Organ primordia engraft, attract a host vasculature and differentiate following transplantation to ectopic sites. Attempts have been made to exploit these characteristics to achieve clinically relevant endpoints for end-stage renal disease and diabetes mellitus using animal models. We and others have focused on use of the embryonic pig as a donor.

Fetal pancreas transplants are dependent on prolactin for their development and prevent type 1 diabetes in syngeneic but not allogeneic mice

Transplantation of adult pancreatic islets has been proposed to cure type 1 diabetes (T1D). However, it is rarely considered in the clinic because of its transient effect on disease, the paucity of donors, and the requirement for strong immunosuppressive treatment to prevent allogeneic graft rejection. Transplantation of fetal pancreases (FPs) may constitute an attractive alternative because of potential abundant donor sources, possible long-term effects due to the presence of stem cells maintaining tissue integrity, and their supposed low immunogenicity. In this work, we studied the capacity of early FPs from mouse embryos to develop into functional pancreatic islets producing insulin after transplantation in syngeneic and allogeneic recipients. We found that as few as two FPs were sufficient to control T1D in syngeneic mice. Surprisingly, their development into insulin-producing cells was significantly delayed in male compared with female recipients, which may be explained by lower levels of prolactin in males. Finally, allogeneic FPs were rapidly rejected, even in the context of minor histocompatibility disparities, with massive graft infiltration with T and myeloid cells. This work suggests that FP transplantation as a therapeutic option of T1D needs to be further assessed and would require immunosuppressive treatment.

Xenotransplantation of embryonic pig pancreas for treatment of diabetes mellitus in non-human primates

Transplantation therapy for diabetes in humans is limited by the low availability of human donor whole pancreas or islets. Outcomes are complicated by immunosuppressive drug toxicity. Xenotransplantation is a strategy to overcome supply problems. Implantation of tissue obtained early during embryogenesis is a way to reduce transplant immunogenicity. Pig insulin is biologically active in humans. In that regard the pig is an appropriate xenogeneic organ donor. Insulin-producing cells originating from embryonic pig pancreas obtained very early following pancreatic primordium formation [embryonic day 28 (E28)] engraft long-term in rhesus macaques. Endocrine cells originating from embryonic pig pancreas transplanted in host mesentery migrate to mesenteric lymph nodes, engraft, differentiate and improve glucose tolerance in rhesus macaques without the need for immune suppression. Transplantation of embryonic pig pancreas is a novel approach towards beta cell replacement therapy that could be applicable to humans.

Normalization of glucose post-transplantation into diabetic rats of pig pancreatic primordia preserved in vitro

Embryonic day (E) 28 (E28) pig pancreatic primordia transplanted into the mesentery of non-immunosuppresed steptozotocin (STZ)-diabetic Lewis rats normalize levels of circulating glucose within 2-4 weeks. Exocrine tissue does not differentiate after transplantation of pancreatic primordia. Rather individual endocrine (beta) cells engraft within the mesentery.To determine whether transplanted pig pancreatic primordia engraft, differentiate and function in rat hosts after preservation in vitro, we implanted pig pancreatic primordia into STZ-diabetic rats either directly or after 24 hours of suspension in ice-cold University of Wisconsin (UW) preservation solution with added growth factors. Here we show engraftment in mesentery and mesenteric lymph nodes and normalization of glucose levels in STZ-diabetic rat hosts following transplantation of preserved E28 pig pancreatic primordia comparable to glucose normalization after transplantation of non-preserved E28 pancreatic primordia.

Organogenesis of kidney and endocrine pancreas: the window opens

Growing new organs in situ by implanting developing animal organ primordia (organogenesis) represents a novel solution to the problem of limited supply for human donor organs that offers advantages relative to transplanting embryonic stem (ES) cells or xenotransplantation of developed organs. Successful transplantation of organ primordia depends on obtaining them at defined windows during embryonic development within which the risk of teratogenicity is eliminated, growth potential is maximized, and immunogenicity is reduced. We and others have shown that renal primordia transplanted into the mesentery undergo differentiation and growth, become vascularized by blood vessels of host origin, exhibit excretory function and support life in otherwise anephric hosts. Renal primordia can be transplanted across isogeneic, allogeneic or xenogeneic barriers. Pancreatic primordia can be transplanted across the same barriers undergo growth, and differentiation of endocrine components only and secrete insulin in a physiological manner following mesenteric placement. Insulin-secreting cells originating from embryonic day (E) 28 (E28) pig pancreatic primordia transplanted into the mesentery of streptozotocin-diabetic (type 1) Lewis rats or ZDF diabetic (type 2) rats or STZ-diabetic rhesus macaques engraft without the need for host immune-suppression. Our findings in diabetic macaques represent the first steps in the opening of a window for a novel treatment of diabetes in humans.

Development of a novel xenotransplantation strategy for treatment of diabetes mellitus in rat hosts and translation to non-human primates

Transplantation therapy for diabetes is limited by unavailability of donor organs and outcomes complicated by immunosuppressive drug toxicity. Xenotransplantation is a strategy to overcome supply problems. Implantation of tissue obtained early during embryogenesis is a way to reduce transplant immunogenicity. Insulin-producing cells originating from embryonic pig pancreas obtained very early following pancreatic primordium formation [embryonic day 28 (E28)] engraft long-term in inbred diabetic Lewis or Zucker Diabetic Fatty (ZDF) rats or rhesus macaques. Endocrine cells originating from embryonic pig pancreas transplanted in host mesentery migrate to mesenteric lymph nodes, engraft, normalize glucose tolerance in rats and improve glucose tolerance in rhesus macaques without the need for immune suppression. Engraftment of primordia is permissive for engraftment of an insulin-expressing cell component from porcine islets implanted subsequently without immune suppression. Similarities between findings in inbred rat and non-human primate hosts bode well for successful translation to humans of what could be a novel xenotransplantation strategy for the treatment of diabetes.

Engraftment of insulin-producing cells from porcine islets in non-immune-suppressed rats or nonhuman primates transplanted previously with embryonic pig pancreas

Transplantation therapy for diabetes is limited by unavailability of donor organs and outcomes complicated by immunosuppressive drug toxicity. Xenotransplantation is a strategy to overcome supply problems. Implantation of tissue obtained early during embryogenesis is a way to reduce transplant immunogenicity. Insulin-producing cells originating from embryonic pig pancreas obtained very early following pancreatic primordium formation (embryonic day 28 (E28)) engraft long-term in non-immune, suppressed diabetic rats or rhesus macaques. Morphologically, similar cells originating from adult porcine islets of Langerhans (islets) engraft in non-immune-suppressed rats or rhesus macaques previously transplanted with E28 pig pancreatic primordia. Our data are consistent with induction of tolerance to an endocrine cell component of porcine islets induced by previous transplantation of embryonic pig pancreas, a novel finding we designate organogenetic tolerance. The potential exists for its use to enable the use of pigs as islet cell donors for humans with no immune suppression requirement.

Engraftment of cells from porcine islets of Langerhans following transplantation of pig pancreatic primordia in non-immunosuppressed diabetic rhesus macaques

Transplantation therapy for human diabetes is limited by the toxicity of immunosuppressive drugs. If toxicity can be minimized, there will still be a shortage of human donor organs. Xenotransplantation of porcine islets is a strategy to overcome supply problems. Xenotransplantation in mesentery of pig pancreatic primordia obtained very early during organogenesis [embryonic day 28 (E28)] is a way to obviate the need for immunosuppression in rats or rhesus macaques and to enable engraftment of a cell component originating from porcine islets implanted beneath the renal capsule of rats. Here, we show engraftment in the kidney of insulin and porcine proinsulin mRNA-expressing cells following implantation of porcine islets beneath the renal capsule of diabetic rhesus macaques transplanted previously with E28 pig pancreatic primordia in mesentery. Donor cell engraftment is confirmed using fluorescent in situ hybridization (FISH) for the porcine X chromosome and is supported by glucose-stimulated insulin release in vitro. Cells from islets do not engraft in the kidney without prior transplantation of E28 pig pancreatic primordia in mesentery. This is the first report of engraftment following transplantation of porcine islets in non-immunosuppressed, immune-competent non-human primates. The data are consistent with tolerance to a cell component of porcine islets induced by previous transplantation of E28 pig pancreatic primordia.

Organogenetic tolerance

Transplantation therapy for humans is limited by insufficient availability of donor organs and outcomes are complicated by the toxicity of immunosuppressive drugs. Xenotransplantation is a strategy to overcome supply problems. Implantation of tissue obtained early during embryogenesis is a way to reduce immunogenicity of transplants. Insulin-producing cells originating from embryonic pig pancreas obtained very early following initiation of organogenesis [embryonic day 28 (E28)] engraft long-term in non-immune suppressed diabetic rats or rhesus macaques. Recently, we demonstrated engraftment of morphologically similar cells originating from adult porcine islets of Langerhans (islets) in rats previously transplanted with E28 pig pancreatic primordia. Our findings are consistent with induction of tolerance to a cell component of porcine islets induced by previous transplantation of embryonic pig pancreas, a phenomenon we designate organogenetic tolerance. Induction of organogenetic tolerance to porcine islets in humans with diabetes mellitus would enable the use of pigs as islet donors with no host immune suppression requirement. Adaptation of methodology for transplanting embryonic organs other than pancreas so as to induce organogenetic tolerance would revolutionize transplantation therapy.

Inhibition of gamma-secretase activity promotes differentiation of embryonic pancreatic precursor cells into functional islet-like clusters in poly(ethylene glycol) hydrogel culture

We assessed the ability of a gamma-secretase inhibitor to promote the in vitro differentiation of induced embryonic pancreatic precursor cell aggregates into functional islet-like clusters when encapsulated within a three-dimensional hydrogel. Undifferentiated pancreatic precursor cells were isolated from E.15 rat embryos, dissociated into single cells, and aggregated in suspension-rotation culture. Aggregates were photoencapsulated into poly(ethylene glycol) hydrogels with entrapped collagen type 1 and cultured for 14 days with or without a gamma-secretase inhibitor. Gene expression, proinsulin content, and C-peptide release were measured to determine differentiation and maturation of encapsulated precursor cell aggregates. In the control medium, scattered breakthrough beta cell differentiation was observed; however, cells remained largely insulin negative. Upon addition of a gamma-secretase inhibitor the majority of cells in clusters became insulin positive, and insulin per DNA and glucose-stimulated insulin release measurements for these cultures were comparable with those for adult rat islets. Cluster counts after culture day 14 were 88% of those initially encapsulated, demonstrating excellent cluster survival in hydrogel culture. These results indicate that concerted differentiation of pancreatic precursor cell aggregates into functionally mature islet-like clusters can be achieved in poly(ethylene glycol)-based hydrogel cultures by blocking cell contact-mediated Notch signaling with a gamma-secretase inhibitor.

Xenotransplantation of embryonic pig kidney or pancreas to replace the function of mature organs

Lack of donor availability limits the number of human donor organs. The need for host immunosuppression complicates transplantation procedures. Ultrastructurally precise kidneys differentiate in situ following xenotransplantation in mesentery of embryonic pig renal primordia. The developing organ attracts its blood supply from the host, obviating humoral rejection. Engraftment of pig renal primordia transplanted directly into rats requires host immune suppression. However, insulin-producing cells originating from embryonic pig pancreas obtained very early following initiation of organogenesis [embryonic day 28 (E28)] engraft long term in nonimmune-suppressed diabetic rats or rhesus macaques. Engraftment of morphologically similar cells originating from adult porcine islets of Langerhans (islets) occurs in rats previously transplanted with E28 pig pancreatic primordia. Here, we review recent findings germane to xenotransplantation of pig renal or pancreatic primordia as a novel organ replacement strategy.

Engraftment of cells from porcine islets of Langerhans and normalization of glucose tolerance following transplantation of pig pancreatic primordia in nonimmune-suppressed diabetic rats

Transplantation therapy for human diabetes is limited by the toxicity of immunosuppressive drugs. However, even if toxicity can be minimalized, there will still be a shortage of human donor organs. Xenotransplantation of porcine islets may be a strategy to overcome these supply problems. Xenotransplantation in mesentery of pig pancreatic primordia obtained very early during organogenesis [embryonic day 28 (E28)] can obviate the need for immune suppression in rats or rhesus macaques. Here, in rats transplanted previously with E28 pig pancreatic primordia in the mesentery, we show normalization of glucose tolerance in nonimmune-suppressed streptozotocin-diabetic LEW rats and insulin and porcine proinsulin mRNA-expressing cell engraftment in the kidney following implantation of porcine islets beneath the renal capsule. Donor cell engraftment was confirmed using fluorescent in situ hybridization for the porcine X chromosome and electron microscopy. In contrast, cells from islets did not engraft in the kidney without prior transplantation of E28 pig pancreatic primordia in the mesentery. This is the first report of prolonged engraftment and sustained normalization of glucose tolerance following transplantation of porcine islets in nonimmune-suppressed, immune-competent rodents. The data are consistent with tolerance induction to a cell component of porcine islets induced by previous transplantation of E28 pig pancreatic primordia.

Use of rat segmental intestine for fetal pancreatic transplantation

It is thought that the small intestine may provide a scaffold for pancreas regeneration. Herein, we investigated whether fetal pancreatic tissue could be transplanted into the segmental intestine in rats. Fetal pancreases from firefly luciferase transgenic Lewis rat embryos (embryonic day 14.5 and 15.5) were transplanted into streptozotocin (STZ)-induced diabetic wild-type Lewis rats. As a scaffold for pancreatic development, rat small intestinal segments were utilized after the removal of mucosa, and fetal pancreases were grafted into the luminal surface through the stoma. We also transplanted fetal pancreases into the omentum. The survival of transplanted fetal pancreases was monitored by luciferase-derived photons and blood glucose levels. Transplanted fetal pancreas-derived photons were stable for 28 days, suggesting that transplanted fetal pancreatic tissues survived and that their intestinal blood supply was maintained.

Pig embryonic pancreatic tissue as a source for transplantation in diabetes: transient treatment with anti-LFA1, anti-CD48, and FTY720 enables long-term graft maintenance in mice with only mild ongoing immunosuppression

OBJECTIVE

Defining an optimal costimulatory blockade-based immune suppression protocol enabling engraftment and functional development of E42 pig embryonic pancreatic tissue in mice.

RESEARCH DESIGN AND METHODS

Considering that anti-CD40L was found to be thrombotic in humans, we sought to test alternative costimulatory blockade agents already in clinical use, including CTLA4-Ig, anti-LFA1, and anti-CD48. These agents were tested in conjunction with T-cell debulking by anti-CD4 and anti-CD8 antibodies or with conventional immunosuppressive drugs. Engraftment and functional development of E42 pig pancreatic tissue was monitored by immunohistology and by measuring pig insulin blood levels.

RESULTS

Fetal pig pancreatic tissue harvested at E42, or even as early as at E28, was fiercely rejected in C57BL/6 mice and in Lewis rats. A novel immune suppression comprising anti-LFA1, anti-CD48, and FTY720 afforded optimal growth and functional development. Cessation of treatment with anti-LFA1 and anti-CD48 at 3 months posttransplant did not lead to graft rejection, and graft maintenance could be achieved for >8 months with twice-weekly low-dose FTY720 treatment. These grafts exhibited normal morphology and were functional, as revealed by the high pig insulin blood levels in the transplanted mice and by the ability of the recipients to resist alloxan induced diabetes.

CONCLUSIONS

This novel protocol, comprising agents that simulate those approved for clinical use, offer an attractive approach for embryonic xenogeneic transplantation. Further studies in nonhuman primates are warranted.

Xenotransplantation of pancreatic and kidney primordia-where do we stand?

Lack of donor availability limits the number of human donor organs. The need for host immunosuppression complicates transplantation procedures. It is possible to 'grow' new pancreatic tissue or kidneys in situ via xenotransplantation of organ primordia from animal embryos (organogenesis of the endocrine pancreas or kidney). The developing organ attracts its blood supply from the host, enabling the transplantation of pancreas or kidney in 'cellular' form obviating humoral rejection. In the case of pancreas, selective development of endocrine tissue takes place in post-transplantation. In the case of kidney, an anatomically-correct functional organ differentiates in situ. Glucose intolerance can be corrected in formerly diabetic rats and ameliorated in rhesus macaques on the basis of porcine insulin secreted in a glucose-dependent manner by beta cells originating from transplants. Primordia engraft and function after being stored in vitro prior to implantation. If obtained within a 'window' early during embryonic pancreas development, pig pancreatic primordia engraft in non immune suppressed diabetic rats or rhesus macaques. Engraftment of pig renal primordia transplanted directly into rats requires host immune suppression. However, embryonic rat kidneys into which human mesenchymal cells are incorporated into nephronic elements can be transplanted into non-immune suppressed rat hosts. Here we review recent findings germane to xenotransplantation of pancreatic or renal primordia as a novel organ replacement strategy.

Subcutaneous transplantation of embryonic pancreas for correction of type 1 diabetes

Islet transplantation is a promising therapeutic approach for type 1 diabetes. However, current success rates are low due to progressive graft failure in the long term and inability to monitor graft development in vivo. Other limitations include the necessity of initial invasive surgery and continued immunosuppressive therapy. We report an alternative transplantation strategy with the potential to overcome these problems. This technique involves transplantation of embryonic pancreatic tissue into recipients' subcutaneous space, eliminating the need for invasive surgery and associated risks. Current results in mouse models of type 1 diabetes show that embryonic pancreatic transplants in the subcutaneous space can normalize blood glucose homeostasis and achieve extensive endocrine differentiation and vascularization. Furthermore, modern imaging techniques such as two-photon excitation microscopy (TPEM) can be employed to monitor transplants through the intact skin in a completely noninvasive manner. Thus, this strategy is a convenient alternative to islet transplantation in diabetic mice and has the potential to be translated to human clinical applications with appropriate modifications.

Long-term engraftment following transplantation of pig pancreatic primordia into non-immunosuppressed diabetic rhesus macaques

BACKGROUND

Transplantation therapy for human diabetes is limited by a shortage of donor organs, and transplant function diminished over time by cell death and limited potential for expansion of beta cells in pancreas or islets. Outcomes are complicated by immunosuppression. A way to overcome supply and expansion problems is to xenotransplant embryonic tissue. Previously, we have shown that beta cells originating from embryonic day (E) 28 (E28) pig pancreatic primordia transplanted into the mesentery of streptozotocin (STZ)-diabetic (type 1) Lewis rats or Zucker Diabetic Fatty (ZDF) diabetic (type 2) rats engraft and normalize glucose tolerance without the need for host immune-suppression.

METHODS

In this study, we transplant E28 pig pancreatic primordia in the mesentery of STZ-diabetic rhesus macaques.

RESULTS

Long-term engraftment of pig beta cells within liver, pancreas and mesenteric lymph nodes post-transplantation of E28 pig pancreatic primordia into STZ-diabetic rhesus macaques is demonstrated by electron microscopy, positive immune-histochemistry for insulin, and positive RT-PCR and in situ hybridization for porcine proinsulin mRNA. Insulin requirements were reduced in one macaque followed over 22 months post-transplantation and porcine insulin detected in plasma using sequential affinity chromatography, HPLC and mass spectrometry. Of potential importance for application of this transplantation technology to treatment of diabetes in humans and confirmatory of our previous findings in Lewis and ZDF rats, no host immunosuppression is required.

CONCLUSIONS

Under selected circumstances, pancreatic primordia elicit a muted immune response relative to more differentiated tissue, such that engraftment occurs in non-immunosuppressed hosts. Our findings that pig pancreatic primordia engraft long-term in non-immunosuppressed STZ-diabetic rhesus macaques establishes the potential for their use in human diabetics.

Reduced immunogenicity of first-trimester human fetal pancreas

OBJECTIVE

The use of human fetal pancreatic tissue may provide a potential source of transplantable beta-cells as a therapy for type 1 diabetes. Human fetal pancreas has a remarkable capacity to grow and differentiate in vivo and has been shown to reverse diabetes in rodents. However, it is known that human fetal pancreas obtained from the second trimester of gestation is immunogenic and is rejected after transplantation. Tissue obtained from earlier stages might prove to be immune privileged, as has been shown for other tissues.

RESEARCH DESIGN AND METHODS

In this study, we determined the immunogenicity of human fetal pancreatic tissue obtained from the first trimester of gestation in a humanized mouse model. A microarray study of immunoregulatory gene expression in first- and second-trimester human fetal pancreas was also undertaken.

RESULTS

The analysis of transplanted human fetal pancreata revealed a significantly decreased immunogenicity of the first-trimester tissue. The first-trimester grafts showed only limited cellular infiltration and contained numerous insulin-positive cells, whereas second-trimester tissue was completely infiltrated and rejected. Furthermore an analysis of immunoregulatory genes expressed in first- and second-trimester human fetal pancreas by microarray demonstrated the upregulation of several key immunoregulatory genes in the second-trimester tissue. This might account for the reduced immunogenicity of the younger tissue.

CONCLUSIONS

Our results provide the first indication that the use of first-trimester human fetal pancreas for transplantation might increase the survival of the grafts and might decrease the requirement for immunosuppressive drugs.

Transplantation of renal primordia: renal organogenesis

Dialysis and allotransplantation of human kidneys represent effective therapies to replace kidney function, but the former replaces only a small component of renal function, and the latter is limited by lack of organ availability. Xenotransplantation of whole kidneys from nonprimate donors is complicated by humoral and severe cellular rejection. The use of individual cells or groups of cells to repair damaged tissue (cellular therapies) offers an alternative for renal tissue replacement. However, recapitulation of complex functions such glomerular filtration and reabsorption and secretion of solutes that are dependent on a three-dimensionally integrated kidney structure are beyond the scope of most cellular replacement therapies. The use of nonvascularized embryonic renal primordia for transplantation circumvents humoral rejection of xenogeneic tissue and ameliorates cellular rejection. Renal primordia are preprogrammed to attract a vasculature and differentiate into a kidney and in this manner undergo organogenesis after transplantation into the mesentery of hosts. Here we review a decade's progress in renal organogenesis.

Glucose tolerance normalization following transplantation of pig pancreatic primordia into non-immunosuppressed diabetic ZDF rats

Pancreas or pancreatic islet transplantation in humans is limited by organ availability, and success of the latter is negatively impacted upon by tissue loss post-transplantation and limited potential for expansion of beta cells. A way to overcome the supply and expansion problems is to xenotransplant embryonic tissue. Previously, we have shown that beta cells originating from embryonic day (E) 28 (E28) pig pancreatic primordia transplanted into the mesentery of streptozotocin-diabetic (type 1) Lewis rats engraft without the need for host immune-suppression and normalize glucose tolerance. Here we show long-term engraftment of pig beta cells within liver, pancreas and mesenteric lymph nodes post-transplantation of E28 pig pancreatic primordia into diabetic ZDF rats, a model for type 2 diabetes. Porcine insulin is present in circulation after an oral glucose load. Glucose tolerance is normalized in transplanted ZDF hosts and insulin sensitivity restored in formerly diabetic ZDF males. Release of porcine insulin in vitro from tissue originating in transplanted rats occurs within 1 min of glucose stimulation characteristic of first-phase secretion from beta cells. Of potential importance for application of this transplantation technology to treatment of type 2 diabetes in humans and confirmatory of our previous findings in Lewis rats, no host immunosuppression is required for engraftment of E28 pig pancreatic primordia.

Embryonic pig pancreatic tissue transplantation for the treatment of diabetes

BACKGROUND

Transplantation of embryonic pig pancreatic tissue as a source of insulin has been suggested for the cure of diabetes. However, previous limited clinical trials failed in their attempts to treat diabetic patients by transplantation of advanced gestational age porcine embryonic pancreas. In the present study we examined growth potential, functionality, and immunogenicity of pig embryonic pancreatic tissue harvested at different gestational ages.

METHODS AND FINDINGS

Implantation of embryonic pig pancreatic tissues of different gestational ages in SCID mice reveals that embryonic day 42 (E42) pig pancreas can enable a massive growth of pig islets for prolonged periods and restore normoglycemia in diabetic mice. Furthermore, both direct and indirect T cell rejection responses to the xenogeneic tissue demonstrated that E42 tissue, in comparison to E56 or later embryonic tissues, exhibits markedly reduced immunogenicity. Finally, fully immunocompetent diabetic mice grafted with the E42 pig pancreatic tissue and treated with an immunosuppression protocol comprising CTLA4-Ig and anti-CD40 ligand (anti-CD40L) attained normal blood glucose levels, eliminating the need for insulin.

CONCLUSIONS

These results emphasize the importance of selecting embryonic tissue of the correct gestational age for optimal growth and function and for reduced immunogenicity, and provide a proof of principle for the therapeutic potential of E42 embryonic pig pancreatic tissue transplantation in diabetes.

Growing new endocrine pancreas in situ

Type 1 diabetes mellitus is a major cause of endstage renal disease in young adults. Maintenance of normoglycemia in type 1 diabetics using exogenous insulin is difficult under the best of circumstances. Transplantation therapies are limited by the scarcity of human donor organs, rendering a priority the identification of an alternative source for replacing insulin-secreting cells. Embryonic pancreatic primordia transplanted into diabetic animal hosts undergo selective endocrine differentiation in situ and normalize glucose tolerance. Pancreatic primordia can be transplanted across isogeneic, allogeneic, and both concordant (rat-to-mouse) and highly disparate (pig-to-rodent) xenogeneic barriers. Successful transplantation of pancreatic primordia depends on obtaining them at defined windows during embryonic development within which the risk of teratogenicity is eliminated, growth potential is maximized, and immunogenicity is reduced. Here we review studies exploring the potential for pancreatic organogenesis post-transplantation of embryonic primordia as a therapy for type 1 diabetes.

Cellular therapies for kidney failure

Dialysis and transplantation of human kidneys represent effective therapies to replace kidney function, but each has limitations. Xenotransplantation of whole kidneys from non-primate donors is complicated by humoral and severe cellular rejection. The use of individual cells or groups of cells to regenerate or repair damaged tissue (cellular therapies) offers an alternative for renal replacement. Cellular strategies include: incorporation of new nephrons into the kidney; growing new kidneys in situ/renal organogenesis; use of embryonic or adult stem cells; and nuclear transplantation/therapeutic cloning. These approaches circumvent humoral rejection of xenogeneic tissue. Cellular rejection is ameliorated if embryonic cells are transplanted. It is likely that replacement of renal function via one or more cellular approach will constitute a part of future mainstream medical practice.

Differential origin for endothelial and mesangial cells after transplantation of pig fetal renal primordia into rats

Xenotransplantation of renal primordia in lieu of human kidney allografts has been proposed as a solution for the lack of organ availability. We and others have shown that growth and development of pig renal primordia occur post-transplantation across a highly disparate xenogenic barrier to rat. The origins (donor versus host) of endothelial cells (ECs) and mesangial cells (MCs) in grafts are incompletely delineated. In the present study, we investigated using immunohistochemistry, the origin ECs and MCs of the metanephric xenografts originating from embryonic day 28 (E28) pig embryos transplanted into rats. We employed species-specific antibodies: anti-rat endothelial cell antigen-1 (RECA-1) and -CD31 to detect rat- and pig-derived ECs, respectively; and anti-Thy-1 and -vimentin to detect rat- and pig-derived MCs, respectively. Both intra- and extraglomerular ECs in the xenografts were stained exclusively with rat-specific anti-RECA-1 at 5, 7, or 8 weeks post-transplantation, whereas ECs were not stained with pig-specific anti-CD31. In contrast, MCs in the xenografts were stained predominantly using the pig specific anti-vimentin, although a few glomeruli were positive for rat-specific anti-Thy-1. We conclude that the predominant origin of ECs post-transplantation of embryonic pig metanephroi into rats is the host, whereas MCs originate mainly from the donor.

Organogenesis of the endocrine pancreas

Organogenesis of the endocrine pancreas. Embryonic pancreatic primordia transplanted into diabetic animal hosts undergo selective endocrine differentiation in situ and normalize glucose tolerance. Pancreatic primordia can be transplanted across isogeneic, allogeneic, and both concordant (rat to mouse) and highly disparate (pig to rodent) xenogeneic barriers. This review explores the therapeutic potential for pancreatic organogenesis posttransplantation of embryonic primordia.

Windows of opportunity for organogenesis

Growing new organs in situ by implanting developing animal organ anlagen/primordia represents a novel solution to the problem of limited supply for human donor organs that offers advantages relative to transplanting embryonic stem (ES) cells or xenotransplantation of developed organs. We and others have shown that renal anlagen transplanted into animal hosts undergo differentiation and growth, become vascularized by blood vessels of host origin, exhibit excretory function and support life in otherwise anephric hosts. Renal anlagen can be transplanted across both concordant (rat to mouse) and highly disparate (pig to rodent) xenogeneic barriers. Similarly, pancreatic anlagen can be transplanted across concordant and highly disparate barriers, and undergo growth, differentiation and secrete insulin in a physiological manner following intra-peritoneal placement. Successful transplantation of organ primordia depends on obtaining them at defined windows during embryonic development within which the risk of teratogenicity is eliminated, growth potential is maximized, and immunogenicity is reduced. Here we review studies that delineate such developmental windows of opportunity for kidney and pancreas.