Article Commentary: Islet Xenotransplantation

Effects of Simulated Microgravity on the Morphology and Function of Neonatal Porcine Cell Clusters Cultured with and without Sertoli Cells

Human islet allografts are well known to induce full and sustained remission of hyperglycemia, with complete normalization of key metabolic parameters. Nevertheless, acquiring human islets, even from cadaveric human donor pancreases, remains a significant impediment to successful transplantation therapy for diabetes. To overcome this difficulty, neonatal porcine cell clusters (NPCCs) have been considered for human islet substitutes because they are easily obtained by collagenase digestion of the neonatal piglet pancreas. Currently, the major hurdle in using NPCCs for xenograft is the delay (time lag) in achieving the posttransplant normalization of blood glucose levels in animal diabetic recipients. The present work is the first attempt to evaluate whether incubation of NPCCs in simulated microgravity, in the presence or absence of Sertoli cells (SC), may reduce the maturation time lag of β-cells by differentiation acceleration in vitro, thereby expediting production, viability, and acquisition of functional competence of pretransplantation β-cell-enriched islets. Following a 3-day incubation period, NPCCs maintained in conventional culture, NPCCs incubated in simulated microgravity in the HARV biochamber, and NPCCs plus co-incubated SC in simulated microgravity were examined for viability, morphology, and insulin secretion. Results show that NPCCs grown alone in the HARV biochamber are superior in quality, both in terms of viability and functional competence, when compared to other culture pretreatment protocols. This finding strongly suggests that NPCC pretreatment in simulated microgravity may enhance the transplantation success of NPCCs in the diabetic recipient.

Mizoribine as sole immunosuppressive agent in islet xenotransplantation models: a candidate immunosuppressant causing no adverse effects on islets

Mizoribine (MZ) inhibits the differentiation and proliferation of helper T and B cells after antigen recognition by suppressing the purine biosynthesis pathway and nucleic acid synthesis. MZ has been used in kidney transplantation, but distinct data are unavailable for islet transplantation. The present study investigated the efficacy of MZ for islet xenotransplantation. Immunosuppressive effects of MZ were determined by mixed lymphocyte reaction (MLR) assay in vitro. Toxicities for Wistar rat islets were determined by adenosine triphosphate (ATP) contents of islets during 3-day culture and stimulation index in response to glucose after culture. Immunosuppressive effects in vivo were tested in a Wistar-to-B6 islet xenotransplantation model. MZ was administered continuously for 28 days subcutaneously or intramuscularly. MZ inhibited MLR response by approximately 50% at 0.1 μg/ml. ATP contents decreased with MZ >100 μg/ml, while stimulation index was maintained. Continuous infusion of MZ at 10 mg/kg maintained blood concentrations at 0.13-0.19 μg/ml, while intramuscular injection of MZ at 100 mg/kg/day (peak 520 μg/ml at 1 h postinjection) resulted in below measurable levels (<0.03 μg/ml) within 24 h. Graft survival was significantly prolonged following continuous infusion of 10 mg/kg/day compared to controls (31.0 ± 9.5 vs. 13.2 ± 5.2 days; p = 0.002). Furthermore, animals with intramuscular injection at doses of 3.2, 10, or 100 mg/kg/day showed significantly longer graft survival (20.0 ± 7.5, 22.0 ± 7.31, and 24.5 ± 8.1 days, respectively; p < 0.05 each). Histological examination showed significant suppression of lymphocyte infiltration by MZ administration. MZ showed immunosuppressive effects in an experimental islet xenotransplantation model without adverse effects on endocrine function of islet grafts.

Current status of islet cell transplantation

Despite substantial advances in islet isolation methods and immunosuppressive protocol, pancreatic islet cell transplantation remains an experimental procedure currently limited to the most severe cases of type 1 diabetes mellitus. The objectives of this treatment are to prevent severe hypoglycemic episodes in patients with hypoglycemia unawareness and to achieve a more physiological metabolic control. Insulin independence and long term-graft function with improvement of quality of life have been obtained in several international islet transplant centers. However, experimental trials of islet transplantation clearly highlighted several obstacles that remain to be overcome before the procedure could be proposed to a much larger patient population. This review provides a brief historical perspective of islet transplantation, islet isolation techniques, the transplant procedure, immunosuppressive therapy, and outlines current challenges and future directions in clinical islet transplantation.

Toward maximizing the success rates of human islet isolation: influence of donor and isolation factors

In order to make islet transplantation a therapeutic option for patients with diabetes there is an urgent need for more efficient islet cell processing to maximize islet recovery. Improved donor management, organ recovery techniques, implementation of more stringent donor criteria, and improved islet cell processing techniques may contribute to enhance organ utilization for transplantation. We have analyzed the effects of donor and islet processing factors on the success rate of human islet cell processing for transplantation performed at a single islet cell processing center. Islet isolation outcomes improved when vasopressors, and in particular pitressin, and steroids were used for the management of multiorgan donors. Higher islet yields were obtained from adult male donors, BMI >25 kg/m2, adequate glycemic control during hospital stay, and when the pancreas was retrieved by a local surgical team. Successful isolations were obtained in 58% of the cases when > or = 4 donor criteria were met, and even higher success rates (69%) were observed when considering > or = 5 criteria. Our data suggest that a sequential, integrated approach is highly desirable to improve the success rate of islet cell processing.

Allogeneic islet transplantation

Significant progress has been made in the field of beta-cell replacement therapies by islet transplantation in patients with unstable Type 1 diabetes mellitus (T1DM). Recent clinical trials have shown that islet transplantation can reproducibly lead to insulin independence when adequate islet numbers are implanted. Benefits include improvement of glycemic control, prevention of severe hypoglycemia and amelioration of quality of life. Numerous challenges still limit this therapeutic option from becoming the treatment of choice for T1DM. The limitations are primarily associated with the low islet yield of human pancreas isolations and the need for chronic immunosuppressive therapies. Herein the authors present an overview of the historical progress of islet transplantation and outline the recent advances of the field. Cellular therapies offer the potential for a cure for patients with T1DM. The progress in beta-cell replacement treatment by islet transplantation as well as those of emerging immune interventions for the restoration of self tolerance justify great optimism for years to come.

Resolution of severe atopic dermatitis after tacrolimus withdrawal

Tacrolimus is an immunosuppressive agent used in solid organ and islet transplantation. Its topical form has shown benefit in the treatment of inflammatory skin conditions. Although tacrolimus has a wide spectrum of side effects, dermatological complications related to systemic tacrolimus therapy are limited in the literature. Atopic dermatitis (AD) is a chronic pruritic cutaneous condition that usually begins in infancy and is characterized by an increased Th2 response. We report the case of a patient with type 1 diabetes mellitus (T1DM) and history of AD latent for 10 years who developed severe dermatitis and alopecia 5 months after undergoing allogeneic islet transplantation and initiating a steroid-free immunosuppressive regimen with sirolimus and tacrolimus maintenance. After exclusion of other possible causes for the progression and exacerbation of the clinical presentation of AD, discontinuation of tacrolimus and introduction of mycophenolate mofetil resulted in full remission of the symptoms. The beneficial effects of tacrolimus withdrawal suggest a cause-effect relationship between this adverse event and the utilization of the drug. Islet graft function remained stable after modification of the therapeutic regimen (stable glycemic control and unchanged C-peptide).

Isolation outcome and functional characteristics of young and adult pig pancreatic islets for transplantation studies

INTRODUCTION

Pig islets have been proposed as an alternative to human islets for clinical use, but their use is limited by rejection. The availability of genetically modified pigs devoid of alpha1,3-galactosyltransferase might provide islets more suitable for xenotransplantation. To limit the costs involved in the logistics and health care of pigs for clinical xenotransplantation, we have studied whether younger, rather than older, pigs that are typically preferred can be used as islet donors.

METHODS

We utilized pancreases from Yorkshire and White Landrace wild-type pigs and alpha1,3-galactosyltransferase gene-knockout pigs of three main different age and size groups: (i) <6 months, (ii) 6 to 12 months, and (iii) >2 yr of age, inclusive of retired breeders. We compared isolation yield and in vitro and in vivo function of islet cells obtained from these groups.

RESULTS

Islets from adult pigs (>2 yr) offered not only higher islet yields, but retained the ability to preserve intact morphology during the isolation process and culture, in association with high functional properties after transplantation. Following isolation, islet cells from young (<6 m) and young-adult (6 to 12 m) pigs dissociated into small aggregates and single cells, and exhibited inferior functional properties than adult islets both in vitro and in vivo.

CONCLUSIONS

These data support the conclusion that, in view of the large number of islets needed to maintain normoglycemia after xenotransplantation, organ-source pigs need to reach adult age (>2 yr) before being considered optimal islet donors, in spite of the higher costs involved.

In vitro-generation of surrogate islets from adult stem cells

Type 1 diabetes is one of the more costly chronic diseases of children and adolescents throughout North America and Europe, exhibiting an average estimated prevalence rate of nearly 0.2%. It occurs in genetically predisposed individuals when the immune system attacks and destroys specifically the insulin-producing beta cells of the pancreatic islets of Langerhans. While routine insulin therapy can provide diabetic patients with their daily insulin requirements, non-compliance and undetected hyperglycemic excursions often lead to subsequent long-term microvascular and macrovascular complications. The only real cure for type 1 diabetes is replacement of the beta cell mass, currently being accomplished through ecto-pancreatic transplantation and islet implantation. Both of these procedures suffer from a chronic shortage of available donor tissue in comparison to the number of potential recipients. To circumvent this need, three alternative approaches are being intensively investigated: (1) the production of surrogate cells by genetically modifying non-endocrine cells to secrete insulin in response to glucose challenge; (2) the trans-differentiation of non-endocrine stem/progenitor cells or mature cells to glucose-responsive adult tissue; and (3) the regulated differentiation of islet stem/progenitor cells to produce large numbers of mature, functional islets. In recent years, each of these approaches has made impressive advances, leading to the most important question, 'how soon will this new science be available to the patient?' In the present review, we discuss some of the recent advances, focusing primarily on the differentiation of islet stem cells to functional endocrine pancreas that may form the basis for future treatment.

Evidence that tilapia islets do not express alpha-(1,3)gal: implications for islet xenotransplantation

BACKGROUND

Cell therapy for diabetes using teleost fish islet tissue has emerged as an intriguing alternative to the use of islet tissue from mammalian pancreases. The islet tissue, called Brockman bodies (BBs), is anatomically distinct from the pancreatic exocrine tissue and can be easily identified and isolated. Islets harvested from Nile tilapia (Oreochromis niloticus), when transplanted into streptozotocin-diabetic nude mice, produce long-term normoglycemia and achieve mammalian-like glucose tolerance profiles. We asked whether tilapia express the alpha-(1,3)gal epitope, the immunodominant target of human xenogeneic responses.

METHODS AND RESULTS

Immunostaining with the alpha-(1,3)gal-specific IB4 lectin on tilapia BB, liver, heart, spleen, and head kidney was negative, as was staining with murine anti-alpha-gal-specific monoclonal antibodies. Absence of alpha-gal-specific binding of IB4 or murine anti-gal mAbs to dispersed BBs was confirmed by fluorescent-activated cell sorter analysis. Tilapia BB cell membranes failed to reduce binding of anti-alpha-(1,3)gal-specific mAb in an enzyme-linked immunosorbent assay (ELISA) inhibition assay, while porcine and murine tissue lysates did. Tilapia BB cell lysates were shown to be devoid of alpha-1,3 galactosyltransferase activity by ELISA. Transplantation of tilapia BBs into diabetic alpha-gal knockout (gal KO) mice was not associated with accelerated xenograft rejection when compared with wild type control recipients (mean survival time 6.5 days vs. 7.2 days). Tilapia BBs failed to induce a rise in anti-gal IgG and IgM titers in gal KO mice, while the transplant of wild type mouse islets into gal KO mice caused a significant rise in anti-gal IgG and IgM antibodies.

CONCLUSIONS

We conclude that tilapia BBs are devoid of alpha-gal expression, and may offer an alternative to swine as a donor species for islet xenotransplantation.

PROLONGED SURVIVAL OF NEONATAL PORCINE ISLET XENOGRAFTS IN MICE TREATED WITH A DONOR-SPECIFIC TRANSFUSION AND ANTI-CD154 ANTIBODY1

BACKGROUND

Combined treatment with a single donor-specific transfusion (DST) and a brief course of anti-mouse CD154 monoclonal antibody (mAb) to induce co-stimulation blockade leads to long-term murine islet allograft survival. The authors hypothesized that this protocol could also induce long-term survival of neonatal porcine islet cell clusters (NPCC) in chemically diabetic immunocompetent mice and allow their differentiation into functional insulin-producing cells.

METHODS

Pancreata from 1- to 3-day-old pigs were collagenase digested and cultured for 8 days. NPCC were recovered and transplanted into the renal subcapsular space. Recipients included chemically diabetic nonobese diabetic (NOD)-scid and C57BL/6 mice that were otherwise untreated, treated with anti-CD154 mAb alone, or treated with DST plus anti-CD154 mAb. Plasma glucose concentration and body weight were measured, and xenografts were examined histologically.

RESULTS

NPCC fully differentiated and restored normoglycemia in four of five diabetic NOD-scid recipients but were uniformly rejected by diabetic C57BL/6 recipients. Anti-CD154 mAb monotherapy restored normoglycemia in 4 of 10 (40%) NPCC-engrafted, chemically diabetic C57BL/6 mice, but combined treatment with DST and anti-CD154 mAb restored normoglycemia in 12 of 13 (92%) recipients. Reversal of diabetes required 5 to 12 weeks. Surviving grafts were essentially free of inflammatory infiltrates 15 weeks after transplantation.

CONCLUSIONS

Combination therapy with a single DST and a brief course of anti-mouse CD154 mAb without maintenance immunosuppression permits survival and differentiation of NPCC in diabetic C57BL/6 mice. Successful grafts were associated with durable restoration of normoglycemia and the absence of graft inflammation.