Successes and disappointments with clinical islet transplantation

The MHC-characterized Miniature Swine: Lessons Learned From a 40-Year Experience in Transplantation

Over the last 40 y, a specialized herd of miniature swine has been intentionally bred to develop lines of animals homozygous for the swine major histocompatibility complex (MHC), which have facilitated transplantation studies across reproducible MHC and minor antigen mismatch barriers. These MHC-characterized miniature swine (Mc-MS) have been used for the study of novel surgical techniques, various approaches to tolerance induction of solid organ and vascularized composite allografts, as well as studies of the immunobiology of allografts and xenografts. Mc-MS possess characteristics that are highly advantageous to these studies, and their continued use will likely continue to play an important role in bridging "bench-to-cage-to bedside" therapies in the field of transplantation. In this review, we highlight the seminal contributions of the Mc-MS model to the field and analyze their role in the broader context of large animal models in transplantation research.

Selection of Implantation Sites for Transplantation of Encapsulated Pancreatic Islets

Pancreatic islet transplantation has been validated as a valuable therapy for type 1 diabetes mellitus patients with exhausted insulin treatment. However, this therapy remains limited by the shortage of donor and the requirement of lifelong immunosuppression. Islet encapsulation, as an available bioartificial pancreas (BAP), represents a promising approach to enable protecting islet grafts without or with minimal immunosuppression and possibly expanding the donor pool. To develop a clinically implantable BAP, some key aspects need to be taken into account: encapsulation material, capsule design, and implant site. Among them, the implant site exerts an important influence on the engraftment, stability, and biocompatibility of implanted BAP. Currently, an optimal site for encapsulated islet transplantation may include sufficient capacity to host large graft volumes, portal drainage, ease of access using safe and reproducible procedure, adequate blood/oxygen supply, minimal immune/inflammatory reaction, pliable for noninvasive imaging and biopsy, and potential of local microenvironment manipulation or bioengineering. Varying degrees of success have been confirmed with the utilization of liver or extrahepatic sites in an experimental or preclinical setting. However, the ideal implant site remains to be further engineered or selected for the widespread application of encapsulated islet transplantation.

Necessities for a Clinical Islet Program

For more than two decades we have been refining advances in islet cell transplantation as a clinical therapy for patients suffering from type 1 diabetes. A great deal of effort has gone to making this a viable therapy for a broader range of patients with type 1 diabetes. Clinical results have progressively improved, demonstrating clinical outcomes on par with other organ transplants, specifically in terms of insulin independence, graft and patient survival. We are now at the point where islet cell transplantation, in the form of allotransplantation, has become accepted as a clinical therapy in adult patients affected by type 1 diabetes, in particular those suffering from severe hypoglycaemic unawareness. This chapter provides an overview on how this has been undertaken over the years to provide outcomes on par with other organ transplantation results. In particular this chapter focuses on the processes and facilities that are required to establish a clinical islet isolation and transplantation program. It also outlines the very important underpinning processes of selection of the organ donor for islet isolation, the processes of organ donor operation and preservation of the pancreas by various means and the ideal ways to best improve outcomes for human islet cell isolation. Providing these more optimal conditions we can underpin the isolation processes to provide islets for transplantation and as such a safe, effective and feasible therapeutic option for an increasing number of patients suffering from type 1 diabetes with severe hypoglycaemic unawareness.

Implanted islets in the anterior chamber of the eye are prone to autoimmune attack in a mouse model of diabetes

AIMS/HYPOTHESIS

Type 1 diabetes is an autoimmune disease resulting from the destruction of insulin-producing beta cells. Along with advances in generating replacement beta cells for treating diabetes, there is also increasing demand for non-invasive tools to evaluate the recurrence of autoimmune attack on transplanted tissue. Here, we examined the anterior chamber of the eye as a potential islet transplant site, and also evaluated whether in vivo imaging of the islets transplanted in the eye could enable real-time visualisation of autoimmune processes underway in the pancreas.

METHODS

Syngeneic islet equivalents were transplanted into the eye or kidney capsule of streptozotocin-induced diabetic C57BL/6 mice to compare islet dose (25-125 islet equivalents) and function across transplant sites. Autoimmune attack of syngeneic islets was evaluated in the pancreas and eye tissues of NOD and NOD-severe combined immunodeficient (SCID) mice given diabetogenic splenocytes.

RESULTS

Islet transplantation in the eye decreased fasting plasma glucose levels and increased weight gain and survival in an islet-dose-dependent manner. Even 50 islets in the eye reduced blood glucose levels, whereas ≥ 200 islets were required in the kidney for a similar effect. Autoimmune destruction of pancreatic islets in the eye mirrored that in the pancreas and could be visualised in real time by non-invasive imaging.

CONCLUSIONS/INTERPRETATION

We found that far fewer islets were required to restore normoglycaemia when transplanted into the anterior chamber of the eye vs the kidney capsule. However, our results suggest that islets are not protected against autoimmune attack in the eye, making this a suitable site for visualising autoimmune processes against transplanted tissue.

Allogeneic bone marrow cocultured with human islets significantly improves islet survival and function in vivo

BACKGROUND

A significant barrier to islet transplantation is the rapid loss of human islet function in vivo. The present study evaluates whether bone marrow (BM) could be used to support human islet survival and function in vivo.

METHODS

We cocultured human islets and BM for 3 weeks before transplantation into the left subrenal capsule of diabetic severe combined immunodeficient mice.

RESULTS

The cocultured human islets before transplantation demonstrated improved viability, increased size, and migration capacity in vitro. After 4 months, animals transplanted with precultured BM/islets exhibited euglycemia and detectable human insulin levels (157 μU/mL), whereas no human insulin was detected in the islet-only transplantation group. Furthermore, the removal of the transplants on day 126 resulted in hyperglycemia, indicating that the reduction of blood glucose was dependent on the transplants. Diabetic mice transplanted with BM/islets demonstrated the longest survival period (130 vs. 40 days for those with islet-only transplants). The transplanted BM/islets showed signs of vascularization and migration from the renal capsule into medulla.

CONCLUSIONS

Our results suggest that BM precultured with human islets may enhance the survival and function of transplanted islets, thus significantly improving the therapeutic efficacy of islet transplantation for type 1 diabetes.

The broad clinical phenotype of Type 1 diabetes at presentation

Immune-mediated (auto-immune) Type 1 diabetes mellitus is not a homogenous entity, but nonetheless has distinctive characteristics. In children, it may present with classical insulin deficiency and ketoacidosis at disease onset, whereas autoimmune diabetes in adults may not always be insulin dependent. Indeed, as the adult-onset form of autoimmune diabetes may resemble Type 2 diabetes, it is imperative to test for diabetes-associated autoantibodies to establish the correct diagnosis. The therapeutic response can be predicted by measuring the levels of autoantibodies to various islet cell autoantigens, such as islet cell antibodies (ICA), glutamate decarboxylase 65 (GAD65), insulin, tyrosine phosphatase (IA-2) and IA-2β, and zinc transporter 8 (ZnT8) and evaluating β-cell function. A high risk of progression to insulin dependency is associated with particular genetic constellations, such as human leukocyte antigen risk alleles, young age at onset, the presence of multiple autoantibodies, including high titres of anti-GAD antibodies; such patients should be offered early insulin replacement therapy, as they respond poorly to diet and oral hypoglycaemic drug therapy. Hence, considering the broad spectrum of phenotypes seen in adult-onset diabetes, treatment targets can only be reached by identification of immune-mediated cases, as their management differs from those with classical Type 2 diabetes.

Liver bioengineering: Current status and future perspectives

The present review aims to illustrate the strategies that are being implemented to regenerate or bioengineer livers for clinical purposes. There are two general pathways to liver bioengineering and regeneration. The first consists of creating a supporting scaffold, either synthetically or by decellularization of human or animal organs, and seeding cells on the scaffold, where they will mature either in bioreactors or in vivo. This strategy seems to offer the quickest route to clinical translation, as demonstrated by the development of liver organoids from rodent livers which were repopulated with organ specific cells of animal and/or human origin. Liver bioengineering has potential for transplantation and for toxicity testing during preclinical drug development. The second possibility is to induce liver regeneration of dead or resected tissue by manipulating cell pathways. In fact, it is well known that the liver has peculiar regenerative potential which allows hepatocyte hyperplasia after amputation of liver volume. Infusion of autologous bone marrow cells, which aids in liver regeneration, into patients was shown to be safe and to improve their clinical condition, but the specific cells responsible for liver regeneration have not yet been determined and the underlying mechanisms remain largely unknown. A complete understanding of the cell pathways and dynamics and of the functioning of liver stem cell niche is necessary for the clinical translation of regenerative medicine strategies. As well, it will be crucial to elucidate the mechanisms through which cells interact with the extracellular matrix, and how this latter supports and drives cell fate.

Association between local neuroretinal function and control of adolescent type 1 diabetes

PURPOSE

To evaluate associations between neuroretinal function measured with multifocal electroretinogram (mfERG) and disease variables in adolescents with type 1 diabetes and no retinopathy.

METHODS

Fundus photographs, blood glucose (BG) concentration, HbA1c, and monocular mfERG were performed on 115 adolescent patients (mean age ± SD; 15.7 ± 1.8 years) and 30 controls (18.0 ± 2.8 years). All subjects had best-corrected visual acuity ≥ 20/20. The 45° mfERG stimulus included 103 hexagons, reversing between dark and bright according to a pseudorandom m-sequence. Amplitudes (AMPs) and implicit times (ITs) were derived from local mfERG response waveforms, and Z-scores were calculated. Retinal maps of abnormality frequencies were generated. Differences between controls and patients were evaluated using t-tests. Associations between mfERG and age, duration, and diabetes control were examined using linear regression analysis.

RESULTS

Mean mfERG IT was significantly longer in the patients compared with that in the controls (P = 0.019), but AMP was not different (P > 0.05). In all, 26 eyes (23%) of the patients had abnormal IT and 3 eyes (3%) had abnormal AMP. IT abnormalities were essentially distributed randomly across the retina. There were too few AMP abnormalities to examine their retinal distribution. IT was positively correlated with HbA1c (P < 0.0002) but not correlated with diabetes duration, BG, or age.

CONCLUSIONS

Higher long-term blood glucose concentration is associated with degraded neuroretinal function in adolescents with type 1 diabetes and no retinopathy. Over 20% of these patients have abnormal neuroretinal function. It will be important to determine longitudinally whether the relationship between mfERG IT and diabetes control exists within individual adolescent patients.

Current status of immunomodulatory and cellular therapies in preclinical and clinical islet transplantation

Clinical islet transplantation is a β-cell replacement strategy that represents a possible definitive intervention for patients with type 1 diabetes, offering substantial benefits in terms of lowering daily insulin requirements and reducing incidences of debilitating hypoglycemic episodes and unawareness. Despite impressive advances in this field, a limiting supply of islets, inadequate means for preventing islet rejection, and the deleterious diabetogenic and nephrotoxic side effects associated with chronic immunosuppressive therapy preclude its wide-spread applicability. Islet transplantation however allows a window of opportunity for attempting various therapeutic manipulations of islets prior to transplantation aimed at achieving superior transplant outcomes. In this paper, we will focus on the current status of various immunosuppressive and cellular therapies that promote graft function and survival in preclinical and clinical islet transplantation with special emphasis on the tolerance-inducing capacity of regulatory T cells as well as the β-cells regenerative capacity of stem cells.

Role of heme oxygenase-1 in transplantation

Heme oxygenase-1 (HO-1) is the rate-limiting enzyme in heme catabolism that converts heme to Fe++, carbon monoxide and biliverdin. HO-1 acts anti-inflammatory and modulates apoptosis in many pathological conditions. In transplantation, HO-1 is overexpressed in organs during brain death, when undergoing ischemic damage and rejection. However, intentionally induced, it ameliorates pathological processes like ischemia reperfusion injury, allograft, xenograft or islet rejection, facilitates donor specific tolerance and alleviates chronic allograft changes. We herein consistently summarize the huge amount of data on HO-1 and transplantation that have been generated in multiple laboratories during the last 15years and suggest possible clinical implications and applications for the near future.