Current situation of clinical islet transplantation from allogeneic toward xenogeneic

Scaffold-free endocrine tissue engineering: role of islet organization and implications in type 1 diabetes

Type 1 diabetes (T1D) is a chronic hyperglycemia disorder emerging from beta-cell (insulin secreting cells of the pancreas) targeted autoimmunity. As the blood glucose levels significantly increase and the insulin secretion is gradually lost, the entire body suffers from the complications. Although various advances in the insulin analogs, blood glucose monitoring and insulin application practices have been achieved in the last few decades, a cure for the disease is not obtained. Alternatively, pancreas/islet transplantation is an attractive therapeutic approach based on the patient prognosis, yet this treatment is also limited mainly by donor shortage, life-long use of immunosuppressive drugs and risk of disease transmission. In research and clinics, such drawbacks are addressed by the endocrine tissue engineering of the pancreas. One arm of this engineering is scaffold-free models which often utilize highly developed cell-cell junctions, soluble factors and 3D arrangement of islets with the cellular heterogeneity to prepare the transplant formulations. In this review, taking T1D as a model autoimmune disease, techniques to produce so-called pseudoislets and their applications are studied in detail with the aim of understanding the role of mimicry and pointing out the promising efforts which can be translated from benchside to bedside to achieve exogenous insulin-free patient treatment. Likewise, these developments in the pseudoislet formation are tools for the research to elucidate underlying mechanisms in pancreas (patho)biology, as platforms to screen drugs and to introduce immunoisolation barrier-based hybrid strategies.

Epigenetic memory as crucial contributing factor in directing the differentiation of human iPSC into pancreatic β-cells in vitro

Impaired insulin secretion contributes to the pathogenesis of type 1 diabetes mellitus through autoimmune destruction of pancreatic β-cells and the pathogenesis of severe forms of type 2 diabetes mellitus through β-cell dedifferentiation and other mechanisms. Replenishment of malfunctioning β-cells via islet transplantation has the potential to induce long-term glycemic control in the body. However, this treatment option cannot widely be implemented in clinical due to healthy islet donor shortage. Emerging β-cell replacement with human-induced pluripotent stem cell (iPSC) provides high remedial therapy hopes. Thus, tremendous progress has been made in developing β-cell differentiation protocols in vitro; however, most of the differentiated iPSC-derived β-cells showed immature phenotypes associated with low efficiency depending on the iPSC lines used, creating a crucial barrier for their clinical implementation. Multiple mechanisms including differences in genetic, cell cycle patterns, and mitochondrial dysfunction underlie the defective differentiation propensity of iPSC into insulin-producing β-cells. Accumulating evidence recently indicated that, following the reprogramming, epigenetic memory inherited from parental cells substantially affects the differentiation capacity of many iPSC lines. Therefore, differences in epigenetic signature are likely to be essential contributing factors influencing the propensity of iPSC differentiation. In this review, we will document the impact of the epigenome on the reprogramming efficacy and differentiation potential of iPSCs and how targeting the epigenetic residual memory could be an additional strategy to improve the differentiation efficiency of existing protocols to generate fully functional hPSC-derived pancreatic β-cells for diabetes therapy and drug screening.

Clinical Islet Xenotransplantation: Development of Isolation Protocol, Anti-Rejection Strategies, and Clinical Outcomes

Allogeneic islet transplantation has become a standard therapy for unstable type 1 diabetes. However, considering the large number of type 1 diabetic patients, the shortage of donors is a serious issue. To address this issue, clinical islet xenotransplantation is conducted. The first clinical islet xenotransplantation was performed by a Swedish team using fetal pancreatic tissue. Thereafter, clinical trials of islet xenotransplantation were conducted in New Zealand, Russia, Mexico, Argentina, and China using neonatal pig islets. In clinical trials, fetal or neonatal pancreata are used because of the established reliable islet isolation methods. These trials demonstrate the method's safety and efficacy. Currently, the limited number of source animal facilities is a problem in terms of promoting islet xenotransplantation. This limitation is due to the high cost of source animal facilities and the uncertain future of xenotransplantation. In the United States, the first xenogeneic heart transplantation has been performed, which could promote xenotransplantation. In Japan, to enhance xenotransplantation, the 'Medical Porcine Development Association' has been established. We hope that xenogeneic transplantation will become a clinical reality, serving to address the shortage of donors.

Bioprinted 3D Bionic Scaffolds with Pancreatic Islets as a New Therapy for Type 1 Diabetes-Analysis of the Results of Preclinical Studies on a Mouse Model

Recently, tissue engineering, including 3D bioprinting of the pancreas, has acquired clinical significance and has become an outstanding potential method of customized treatment for type 1 diabetes mellitus. The study aimed to evaluate the function of 3D-bioprinted pancreatic petals with pancreatic islets in the murine model. A total of 60 NOD-SCID (Nonobese diabetic/severe combined immunodeficiency) mice were used in the study and divided into three groups: control group; IsletTx (porcine islets transplanted under the renal capsule); and 3D bioprint (3D-bioprinted pancreatic petals with islets transplanted under the skin, on dorsal muscles). Glucose, C-peptide concentrations, and histological analyses were performed. In the obtained results, significantly lower mean fasting glucose levels (mg/dL) were observed both in a 3D-bioprint group and in a group with islets transplanted under the renal capsule when compared with untreated animals. Differences were observed in all control points: 7th, 14th, and 28th days post-transplantation (129, 119, 118 vs. 140, 139, 140; p < 0.001). Glucose levels were lower on the 14th and 28th days in a group with bioprinted petals compared to the group with islets transplanted under the renal capsule. Immunohistochemical staining indicated the presence of secreted insulin-living pancreatic islets and neovascularization within 3D-bioprinted pancreatic petals after transplantation. In conclusion, bioprinted bionic petals significantly lowered plasma glucose concentration in studied model species.

Islets in the body are never flat: transitioning from two-dimensional (2D) monolayer culture to three-dimensional (3D) spheroid for better efficiency in the generation of functional hPSC-derived pancreatic β cells in vitro

Diabetes mellitus (DM), currently affecting more than 537 million people worldwide is a chronic disease characterized by impaired glucose metabolism resulting from a defect in insulin secretion, action, or both due to the loss or dysfunction of pancreatic β cells. Since cadaveric islet transplantation using Edmonton protocol has served as an effective intervention to restore normoglycaemia in T1D patients for months, stem cell-derived β cells have been explored for cell replacement therapy for diabetes. Thus, great effort has been concentrated by scientists on developing in vitro differentiation protocols to realize the therapeutic potential of hPSC-derived β cells. However, most of the 2D traditional monolayer culture could mainly generate insulin-producing β cells with immature phenotype. In the body, pancreatic islets are 3D cell arrangements with complex cell-cell and cell-ECM interactions. Therefore, it is important to consider the spatial organization of the cell in the culture environment. More recently, 3D cell culture platforms have emerged as powerful tools with huge translational potential, particularly for stem cell research. 3D protocols provide a better model to recapitulate not only the in vivo morphology, but also the cell connectivity, polarity, and gene expression mimicking more physiologically the in vivo cell niche. Therefore, the 3D culture constitutes a more relevant model that may help to fill the gap between in vitro and in vivo models. Interestingly, most of the 2D planar methodologies that successfully generated functional hPSC-derived β cells have switched to a 3D arrangement of cells from pancreatic progenitor stage either as suspension clusters or as aggregates, suggesting the effect of 3D on β cell functionality. In this review we highlight the role of dimensionality (2D vs 3D) on the differentiation efficiency for generation of hPSC-derived insulin-producing β cells in vitro. Consequently, how transitioning from 2D monolayer culture to 3D spheroid would provide a better model for an efficient generation of fully functional hPSC-derived β cells mimicking in vivo islet niche for diabetes therapy or drug screening. Video Abstract.

Implantation underneath the abdominal anterior rectus sheath enables effective and functional engraftment of stem-cell-derived islets

Human pluripotent stem cell-derived islets (hPSC islets) are a promising alternative to primary human islets for the treatment of insulin-deficient diabetes. We previously demonstrated the feasibility of this approach in nonhuman primates; however, the therapeutic effects of hPSC islets can be limited by the maladaptive processes at the transplantation site. Here, we demonstrate successful implantation of hPSC-derived islets in a new transplantation site in the abdomen, the subanterior rectus sheath, in eight nonhuman primates (five male and three female). In this proof-of-principle study, we find that hPSC islets survive and gradually mature after transplantation, leading to improved glycemic control in diabetic primates. Notably, C-peptide secretion responds to meal challenge from 6 weeks post-transplantation (wpt), with stimulation indices comparable to those of native islets. The average post-prandial C-peptide level reaches approximately 2.0 ng ml^-1 from 8 wpt, which is five times higher than the peak value we previously obtained after portal vein infusion of hPSC islets and was associated with a decrease of glycated hemoglobin levels by 44% at 12 wpt. Although additional studies in larger cohorts involving long-term follow-up of transplants are needed, our results indicate that the subanterior rectus sheath supports functional maturation and maintenance of hPSC islets, suggesting that it warrants further exploration as a transplantation target site in the context of for hPSC-based cell-replacement therapies.

Evaluation of equine xenogeneic mixed lymphocyte reactions using 5-ethynyl-2'-deoxyuridine (EdU)

Allogeneic solid organ transplantation is currently the only treatment option for end stage organ disease. The shortage of available donor organs has driven efforts to utilize xenogeneic organs for transplantation. In vitro methods for evaluating immune-compatibility are a quick and low cost means of screening novel tissue products prior to more involved, expensive, and invasive live animal studies. Recently, a new analog of the DNA base thymidine, 5-ethynyl-2'-deoxyuridine (EdU), was developed. It may be used in a fast, efficient and specific means of evaluating cell proliferation via flow cytometry. This study was designed to test and optimize this platform for assessing equine xenogeneic one-way mixed lymphocyte reaction (MLR) to porcine stimulator cells. Furthermore, it was hypothesized that an enriched T-lymphocyte (T-cell) population would generate a stronger proliferative response to stimulation, and higher levels of cytokine production when compared to unfractionated peripheral blood mononuclear cells (PBMCs). PBMCs and T-cells were isolated from 3 horses and 4 pigs. Equine xenogeneic MLRs were set up using porcine allogeneic MLRs as a reference for clinically acceptable levels of cell proliferation. Equine T-cells showed significantly greater EdU incorporation in one-way xenogeneic MLRs than equine PBMCs. However, there was no significant difference in cell proliferation between porcine T-cell and PBMC as responders in allogenic one-way MLRs. Given the results of this study, we consider that enriched equine T-cells should be used in preference to unfractionated PBMCs when attempting to evaluate the equine xenogeneic response using the EdU assay as an indicator of suitability for transplant in vivo.

β-cell mitochondria in diabetes mellitus: a missing puzzle piece in the generation of hPSC-derived pancreatic β-cells?

Diabetes mellitus (DM), currently affecting 463 million people worldwide is a chronic disease characterized by impaired glucose metabolism resulting from the loss or dysfunction of pancreatic β-cells with the former preponderating in type 1 diabetes (T1DM) and the latter in type 2 diabetes (T2DM). Because impaired insulin secretion due to dysfunction or loss of pancreatic β-cells underlies different types of diabetes, research has focused its effort towards the generation of pancreatic β-cells from human pluripotent stem cell (hPSC) as a potential source of cells to compensate for insulin deficiency. However, many protocols developed to differentiate hPSCs into insulin-expressing β-cells in vitro have generated hPSC-derived β-cells with either immature phenotype such as impaired glucose-stimulated insulin secretion (GSIS) or a weaker response to GSIS than cadaveric islets. In pancreatic β-cells, mitochondria play a central role in coupling glucose metabolism to insulin exocytosis, thereby ensuring refined control of GSIS. Defects in β-cell mitochondrial metabolism and function impair this metabolic coupling. In the present review, we highlight the role of mitochondria in metabolism secretion coupling in the β-cells and summarize the evidence accumulated for the implication of mitochondria in β-cell dysfunction in DM and consequently, how targeting mitochondria function might be a new and interesting strategy to further perfect the differentiation protocol for generation of mature and functional hPSC-derived β-cells with GSIS profile similar to human cadaveric islets for drug screening or potentially for cell therapy.

Modulating the foreign body response of implants for diabetes treatment

Diabetes Mellitus is a group of diseases characterized by high blood glucose levels due to patients' inability to produce sufficient insulin. Current interventions often require implants that can detect and correct high blood glucose levels with minimal patient intervention. However, these implantable technologies have not reached their full potential in vivo due to the foreign body response and subsequent development of fibrosis. Therefore, for long-term function of implants, modulating the initial immune response is crucial in preventing the activation and progression of the immune cascade. This review discusses the different molecular mechanisms and cellular interactions involved in the activation and progression of foreign body response (FBR) and fibrosis, specifically for implants used in diabetes. We also highlight the various strategies and techniques that have been used for immunomodulation and prevention of fibrosis. We investigate how these general strategies have been applied to implants used for the treatment of diabetes, offering insights on how these devices can be further modified to circumvent FBR and fibrosis.

Pancreas transplantation for type 1 diabetes in Japan: past, present and future prospects

In Japan, the first pancreas transplantation was performed in 1984 from a brain-dead donor; subsequently, however, the concept of brain death became a social issue. Thereafter, the "Organ Transplant Act", which enables brain-dead transplantation, was enacted in 1997, and then revised in 2010 so that donation after brain death became possible only with the consent of the family. Under the recipient selection and registration system developed after the enactment of the "Organ Transplant Act", more than 400 pancreas transplants have been carried out at facilities certified for brain-dead pancreas transplantation in Japan. Of the 410 total cadaveric pancreas transplants performed by the end of 2019, the patient survival and pancreatic and kidney graft survival rates were considered to be comparable to those in the United States and Europe despite the high frequency of marginal donors. Minimally invasive allogenic islet transplantation came to be covered by national health insurance in 2020 following good outcomes of a recent trial. Furthermore, to overcome the serious donor shortage in Japan, development of xenogeneic islet transplantation and regenerative medicine using stem cells is in progress, with xenotransplantation using porcine islets appearing particularly promising.

Advances and complications of regenerative medicine in diabetes therapy

The rapid development of technologies in regenerative medicine indicates clearly that their common application is not a matter of if, but of when. However, the regeneration of beta-cells for diabetes patients remains a complex challenge due to the plurality of related problems. Indeed, the generation of beta-cells masses expressing marker genes is only a first step, with maintaining permanent insulin secretion, their protection from the immune system and avoiding pathological modifications in the genome being the necessary next developments. The prospects of regenerative medicine in diabetes therapy were promoted by the emergence of promising results with embryonic stem cells (ESCs). Their pluripotency and proliferation in an undifferentiated state during culture have ensured the success of ESCs in regenerative medicine. The discovery of induced pluripotent stem cells (iPSCs) derived from the patients’ own mesenchymal cells has provided further hope for diabetes treatment. Nonetheless, the use of stem cells has significant limitations related to the pluripotent stage, such as the risk of development of teratomas. Thus, the direct conversion of mature cells into beta-cells could address this issue. Recent studies have shown the possibility of such transdifferentiation and have set trends for regeneration medicine, directed at minimizing genome modifications and invasive procedures. In this review, we will discuss the published results of beta-cell regeneration and the advantages and disadvantages illustrated by these experiments.

Long-term follow-up for the microbiological safety of clinical microencapsulated neonatal porcine islet transplantation

Enrollment in three clinical trials for microencapsulated neonatal porcine islet xenotransplantation to treat unstable type 1 diabetic patients concluded in November 2014. In this study, we report a long-term follow-up assessment of microbiological safety for these trials. Thirty-eight type 1 diabetic patients received microencapsulated neonatal porcine islet transplants. Islets were isolated and prepared from the pancreata of New Zealand (NZ) based designated pathogen-free (DPF) pigs under GMP conditions. Blood samples of thirty-six patients were collected from 5 to 7 years post-first transplant and were tested by real-time PCR for porcine circovirus-1 (PCV1), porcine circovirus-2 (PCV2), porcine lymphotropic herpesvirus 1 (PLHV1), porcine lymphotropic herpesvirus 2 (PLHV2), and porcine cytomegalovirus (PCMV). To detect porcine endogenous retrovirus (PERV), specific real-time PCR and product enhanced reserve transcriptase (PERT) assays were performed. PCV1, PCV2, PLHV1, PLHV2, PCMV, PERV, and reverse transcriptase (RT) activity remained undetected in all tested samples indicating no viral transmission. Except for one patient that died due to complications unrelated to the transplant, there were no significant adverse events. Microbiological safety was demonstrated for microencapsulated neonatal porcine islet xenotransplantation from 5-7 years post-transplantation consistent with earlier reports.