Evolution of β-Cell Replacement Therapy in Diabetes Mellitus: Pancreas Transplantation

Bio nanocomposites of graphene oxide with carboxymethyl guargum: fabrication and characterization and application for type 1 diabetes

Islet cells transplantation has limitations like low survivability, which can be overcome by using extracellular matrix mimicking three-dimensional (3D) scaffolds, which supports the growth and proliferation of seeded cells. This study was aimed to investigate the role of novel 3D carboxymethyl guargum (CMGG) nanocomposite with reduced graphene oxide (rGO) for proliferation of pancreatic islet cells (RIN-5F) and rate of insulin secretion of RIN-5F cells. Scanning electron microscope and Fourier transform infrared results have demonstrated good porosity and the chemical interactions between CMGG and rGO. Mechanical testing and thermogravimetric analysis of nanofibers have shown good tensile strength and thermal stability with rGO in the nanocomposite. These scaffolds demonstratedin vitrobiocompatibility with acceptable ranges of biodegradability and hemocompatibility. Thein vitrocell proliferation and viability of RIN-5F cells on 3D CMGG nanofibers have significantly increased compared to two-dimensional (2D) cell control. Moreover, the glucose dependent insulin secretion of RIN-5F cells on CMGG nanocomposite has significantly increased upto 4-5 folds than cells on 2D cell control. The biomaterials used in this 3D nanofiber scaffold have shown to be biodegradable and hemocompatible and can be a promising platform for the proliferation and secretion of insulin from beta cells and can be effectively used in transplantation type-1 diabetes.

Small Molecule Differentiate PDX1-Expressing Cells Derived from Human Endometrial Stem Cells on PAN Electrospun Nanofibrous Scaffold: Applications for the Treatment of Diabetes in Rat

In this study, we designed an engineered tissue and transplanted it to an animal model, trying to take an effective step toward meeting the needs of diabetic patients. Here, human endometrial cells were differentiated into PDX1-expressing cells using a small molecule of Y-27632 on polyacrylonitrile (PAN) electrospun scaffolds and transplanted into diabetic rats. PAN nanofibers were made by electrospinning. RT-PCR and immunocytochemical analysis were performed to express pancreatic precursor (PP) genes. The differentiated cells were then transplanted into the abdominal cavity of diabetic rats with Streptozotocin. In another group of rats, differentiated cells were injected through the tail. Blood glucose was measured 7, 14, and 28 days after transplantation, and rat weight was also measured. The results showed that the expression of PP markers including Sox-17, Ngn3, Pdx1, and NKx2.2 genes was significantly increased in differentiated cells compared to the control group. In diabetic rats receiving differentiated cells, both transplanted and injected, glucose concentration as well as body weight improved compared to the control group. Rats receiving transplants in the peritoneum had a lower blood glucose concentration than those in the cell receiving group by injection, and the cell receiving group in the form of injections was more effective in increasing the body weight of rats than in the other groups. According to the results of the study, the transplantation of PP from endometrium using PAN scaffolding at the site of peritoneum could be recommended for the treatment of diabetes, although further studies are needed to provide a complete cure.

Stem Cell Therapy and Type 1 Diabetes Mellitus: Treatment Strategies and Future Perspectives

Type 1 diabetes mellitus (T1DM) is classified as an autoimmune disease which progressively results in the depletion of insulin-secreting β-cells. Consequently, the insulin secretion stops leading to hyperglycemic situations within the body. Under severe conditions, it also causes multi-organ diabetes-associated dysfunctionalities notably hypercoagulability, neuropathy, nephropathy, retinopathy, and sometimes organ failures. The prevalence of this disease has been noticed about 3% that has highlighted the serious concerns for healthcare professionals around the globe. For the treatment of this disease, the cell therapy is considered as an important therapeutic approach for the replacement of damaged β-cells. However, the development of autoantibodies unfortunately reduces their effectiveness with the passage of time and finally with the recurrence of diabetes mellitus. The development of new techniques for extraction and transplantation of islets failed to support this approach due to the issues related to major surgery and lifelong dependence on immunosuppression. For T1DM, such cells are supposed to produce, store, and supply insulin to maintain glucose homeostasis. The urgent need of much-anticipated substitute for insulin-secreting β-cells directed the researchers to focus on stem cells (SCs) to produce insulin-secreting β-cells. For being more specific and targeted therapeutic approaches, SC-based strategies opened up the new horizons to cure T1DM. This cell-based therapy aimed to produce functional insulin-secreting β-cells to cure diabetes on forever basis. The intrinsic regenerative potential along with immunomodulatory abilities of SCs highlights the therapeutic potential of SC-based strategies. In this article, we have comprehensively highlighted the role of SCs to treat diabetes mellitus.

Therapeutic potential of human mesenchymal stem cells derived beta cell precursors on a nanofibrous scaffold: An approach to treat diabetes mellitus

Diabetes mellitus is an autoimmune and chronic disorder that is rapidly expanding worldwide due to increasing obesity. In the current study, we were able to design a reliable 3-dimensional differentiation process of human Wharton's jelly mesenchymal stem cells into pancreatic beta cell precursors (PBCPs) and detected that transplanted PBCPs could improve hyperglycemia in a diabetes-induced model in mice. Polylactic acid/chitosan nanofibrous scaffold was prepared using an electrospinning method. Quantitative real-time reverse transcription-polymerase chain reaction and immunocytochemistry analysis were carried out to assess pancreatic marker expression in the differentiated cells. PBCPs were transplanted under the kidney capsule of diabetic mice that induced streptozotocin injection 14 days before the transplantation. Moreover, an intraperitoneal glucose tolerance test (ipGTT) was carried out 2 and 4 weeks after the transplantation to measure the reaction to a sudden increase of the blood glucose level in the transplanted animals. The results indicated that the expression of SRY (sex determining region Y)-box (Sox17), forkhead box A2 (FoxA2), pancreatic and duodenal homeobox 1 (Pdx1), neurogenin 3 (Ngn3), hepatic nuclear factor 4, alpha (Hnf4α), and NK2 homeobox 2 (Nkx2.2) were increased significantly in the differentiated cells compared with that of the control group. In the current study, the diabetic disease was confirmed by measuring blood glucose and proved by conducting some other behavioral tests. After the PBCPs transplantation in a diabetic model, the ipGTT and hyperglycemia investigation during the determinant times confirmed the disease's significant improvement in the experimental models. In this study, some preclinical data suggested that the transplantation of PBCPs associated with appropriate nanofiber scaffold can be utilized for the treatment of diabetes models. In addition, studies are required to elucidate the molecular mechanism of PBCPs acting in diabetes models before being used for patients with diabetes.

The rat pancreatic body tail as a source of a novel extracellular matrix scaffold for endocrine pancreas bioengineering

Background

Regenerative medicine and tissue engineering are promising approaches for organ transplantation. Extracellular matrix (ECM) based scaffolds obtained through the decellularization of natural organs have become the preferred platform for organ bioengineering. In the field of pancreas bioengineering, acellular scaffolds from different animals approximate the biochemical, spatial and vascular relationships of the native extracellular matrix and have been proven to be a good platform for recellularization and in vitro culture. However, artificial endocrine pancreases based on these whole pancreatic scaffolds have a critical flaw, specifically their difficult in vivo transplantation, and connecting their vessels to the recipient is a major limitation in the development of pancreatic tissue engineering. In this study, we focus on preparing a novel acellular extracellular matrix scaffold derived from the rat pancreatic body tail (pan-body-tail ECM scaffold).

Results

Several analyses confirmed that our protocol effectively removes cellular material while preserving ECM proteins and the native vascular tree. DNA quantification demonstrated an obvious reduction of DNA compared with that of the natural organ (from 931.9 ± 267.8 to 11.7 ± 3.6 ng/mg, P < 0.001); the retention of the sGAG in the decellularized pancreas (0.878 ± 0.37) showed no significant difference from the natural pancreas (0.819 ± 0.1) (P > 0.05). After transplanted with the recellularized pancreas, fasting glucose levels declined to 9.08 ± 2.4 mmol/l within 2 h of the operation, and 8 h later, they had decreased to 4.7 ± 1.8 mmol/l (P < 0.05).

Conclusions

The current study describes a novel pancreatic ECM scaffold prepared from the rat pancreatic body tail via perfusion through the left gastric artery. We further showed the pioneering possibility of in vivo circulation-connected transplantation of a recellularized pancreas based on this novel scaffold. By providing such a promising pancreatic ECM scaffold, the present study might represent a key improvement and have a positive impact on endocrine pancreas bioengineering.

Encapsulated Islet Transplantation: Where Do We Stand?

Transplantation of pancreatic islets encapsulated within immuno-protective microcapsules is a strategy that has the potential to overcome graft rejection without the need for toxic immunosuppressive medication. However, despite promising preclinical studies, clinical trials using encapsulated islets have lacked long-term efficacy, and although generally considered clinically safe, have not been encouraging overall. One of the major factors limiting the long-term function of encapsulated islets is the host's immunological reaction to the transplanted graft which is often manifested as pericapsular fibrotic overgrowth (PFO). PFO forms a barrier on the capsule surface that prevents the ingress of oxygen and nutrients leading to islet cell starvation, hypoxia and death. The mechanism of PFO formation is still not elucidated fully and studies using a pig model have tried to understand the host immune response to empty alginate microcapsules. In this review, the varied strategies to overcome or reduce PFO are discussed, including alginate purification, altering microcapsule geometry, modifying alginate chemical composition, co-encapsulation with immunomodulatory cells, administration of pharmacological agents, and alternative transplantation sites. Nanoencapsulation technologies, such as conformal and layer-by-layer coating technologies, as well as nanofiber, thin-film nanoporous devices, and silicone based NanoGland devices are also addressed. Finally, this review outlines recent progress in imaging technologies to track encapsulated cells, as well as promising perspectives concerning the production of insulin-producing cells from stem cells for encapsulation.

Stem cell therapy emerging as the key player in treating type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is an autoimmune disease causing progressive destruction of pancreatic β cells, ultimately resulting in loss of insulin secretion producing hyperglycemia usually affecting children. Replacement of damaged β cells by cell therapy can treat it. Currently available strategies are insulin replacement and islet/pancreas transplantation. Unfortunately these offer rescue for variable duration due to development of autoantibodies. For pancreas/islet transplantation a deceased donor is required and various shortfalls of treatment include quantum, cumbersome technique, immune rejection and limited availability of donors. Stem cell therapy with assistance of cellular reprogramming and β-cell regeneration can open up new therapeutic modalities. The present review describes the history and current knowledge of T1DM, evolution of cell therapies and different cellular therapies to cure this condition.

Effect of edaravone in diabetes mellitus-induced nephropathy in rats

Edaravone, a synthetic-free radical scavenger, has been reported to reduce ischemia-reperfusion-induced renal injury by improving tubular cell function, and lowering serum creatinine and renal vascular resistance. The present study investigated the effect of edaravone in diabetes mellitus-induced nephropathy in rats. A single administration of streptozotocin (STZ, 55 mg/kg, i.p.) was employed to induce diabetes mellitus in rats. The STZ-administered diabetic rats were allowed for 10 weeks to develop nephropathy. Mean body weight, lipid alteration, renal functional and histopathology were analysed. Diabetic rats developed nephropathy as evidenced by a significant increase in serum creatinine and urea, and marked renal histopathological abnormalities like glomerulosclerosis and tubular cell degeneration. The kidney weight to body weight ratio was increased. Moreover, diabetic rats showed lipid alteration as evidenced by a signifi cant increase in serum triglycerides and decrease in serum high-density lipoproteins. Edaravone (10 mg/kg, i.p., last 4-weeks) treatment markedly prevented the development of nephropathy in diabetic rats by reducing serum creatinine and urea and preventing renal structural abnormalities. In addition, its treatment, without significantly altering the elevated glucose level in diabetic rats, prevented diabetes mellitus-induced lipid alteration by reducing serum triglycerides and increasing serum high-density lipoproteins. Interestingly, the renoprotective effect of edaravone was comparable to that of lisinopril (5 mg/kg, p.o, 4 weeks, standard drug). Edaravone prevented renal structural and functional abnormalities and lipid alteration associated with experimental diabetes mellitus. Edaravone has a potential to prevent nephropathy without showing an anti-diabetic action, implicating its direct renoprotection in diabetic rats.

Endocrine pancreas engineered using porcine islets and partial pancreatic scaffolds

OBJECTIVES

Because therapeutic options for severe diabetes are currently limited, there is a continuing need for new therapeutic strategies, especially in the field of regenerative medicine. Collaborative efforts across the fields of tissue engineering technology and islet biology may be able to create functionally engineered islets capable of restoring endocrine function in patients with insulin-dependent diabetes.

METHODS

This engineered scaffold was seeded with isolated primary porcine islets via the pancreatic duct using a multi-step infusion technique. Endocrine function of perfusion-cultured islets in the native scaffold was analyzed by immunohistochemical staining of insulin and glucagon as well as by the insulin stimulation test.

RESULTS

The pancreas in this large animal could be uniformly decellularized by perfusion with trypsin and TritonX-100 via the pancreatic duct, as shown by positive staining of extracellular matrix (ECM) components. These scaffolds derived from porcine pancreas were able to maintain the cellular integrity of islets that had repopulated the parenchymal space, which is fundamental for the restoration of endocrine function. Insulin release up to four days after islet infusion was maintained.

CONCLUSIONS

This scaffold from a large animal maintained islet survival and function in the short-term, retaining the cells as a solid organ in the parenchymal space after infusion through the pancreatic duct. These results suggest that this scaffold is suitable for further fabrication of fully functional bioengineered endocrine pancreases when implanted in vivo. Therefore, it may represent a key improvement in the field of beta-cell replacement therapy. Nonetheless, the facilitation of longer-term islet survival and studies of implantation in vivo is required for successful clinical translation.

Advances in management of type 1 diabetes mellitus

Treatment of type 1 diabetes mellitus has always posed a challenge to balance hyperglycemia control with hypoglycemia episodes. The quest for newer therapies is continuing and this review attempts to outline the recent developments. The insulin molecule itself has got moulded into different analogues by minor changes in its structure to ensure well controlled delivery, stable half-lives and lesser side effects. Insulin delivery systems have also consistently undergone advances from subcutaneous injections to continuous infusion to trials of inhalational delivery. Continuous glucose monitoring systems are also becoming more accurate and user friendly. Smartphones have also made their entry into therapy of diabetes by integrating blood glucose levels and food intake with calculated adequate insulin required. Artificial pancreas has enabled to a certain extent to close the loop between blood glucose level and insulin delivery with devices armed with meal and exercise announcements, dual hormone delivery and pramlintide infusion. Islet, pancreas-kidney and stem cells transplants are also being attempted though complete success is still a far way off. Incorporating insulin gene and secretary apparatus is another ambitious leap to achieve insulin independence though the search for the ideal vector and target cell is still continuing. Finally to stand up to the statement, prevention is better than cure, immunological methods are being investigated to be used as vaccine to prevent the onset of diabetes mellitus.

Potential for pancreatic maturation of differentiating human embryonic stem cells is sensitive to the specific pathway of definitive endoderm commitment

This study provides a detailed experimental and mathematical analysis of the impact of the initial pathway of definitive endoderm (DE) induction on later stages of pancreatic maturation. Human embryonic stem cells (hESCs) were induced to insulin-producing cells following a directed-differentiation approach. DE was induced following four alternative pathway modulations. DE derivatives obtained from these alternate pathways were subjected to pancreatic progenitor (PP) induction and maturation and analyzed at each stage. Results indicate that late stage maturation is influenced by the initial pathway of DE commitment. Detailed quantitative analysis revealed WNT3A and FGF2 induced DE cells showed highest expression of insulin, are closely aligned in gene expression patterning and have a closer resemblance to pancreatic organogenesis. Conversely, BMP4 at DE induction gave most divergent differentiation dynamics with lowest insulin upregulation, but highest glucagon upregulation. Additionally, we have concluded that early analysis of PP markers is indicative of its potential for pancreatic maturation.

Transplantation of Encapsulated Pancreatic Islets as a Treatment for Patients with Type 1 Diabetes Mellitus

Encapsulation of pancreatic islets has been proposed and investigated for over three decades to improve islet transplantation outcomes and to eliminate the side effects of immunosuppressive medications. Of the numerous encapsulation systems developed in the past, microencapsulation have been studied most extensively so far. A wide variety of materials has been tested for microencapsulation in various animal models (including nonhuman primates or NHPs) and some materials were shown to induce immunoprotection to islet grafts without the need for chronic immunosuppression. Despite the initial success of microcapsules in NHP models, the combined use of islet transplantation (allograft) and microencapsulation has not yet been successful in clinical trials. This review consists of three sections: introduction to islet transplantation, transplantation of encapsulated pancreatic islets as a treatment for patients with type 1 diabetes mellitus (T1DM), and present challenges and future perspectives.

Revascularization of transplanted pancreatic islets and role of the transplantation site

Since the initial reporting of the successful reversal of hyperglycemia through the transplantation of pancreatic islets, significant research efforts have been conducted in elucidating the process of revascularization and the influence of engraftment site on graft function and survival. During the isolation process the intrinsic islet vascular networks are destroyed, leading to impaired revascularization after transplant. As a result, in some cases a significant quantity of the beta cell mass transplanted dies acutely following the infusion into the portal vein, the most clinically used site of engraftment. Subsequently, despite the majority of patients achieving insulin independence after transplant, a proportion of them recommence small, supplemental exogenous insulin over time. Herein, this review considers the process of islet revascularization after transplant, its limiting factors, and potential strategies to improve this critical step. Furthermore, we provide a characterization of alternative transplant sites, analyzing the historical evolution and their role towards advancing transplant outcomes in both the experimental and clinical settings.

Naturally occurring immunoglobulin M (nIgM) autoantibodies prevent autoimmune diabetes and mitigate inflammation after transplantation

OBJECTIVE

To investigate whether polyclonal serum naturally occurring immunoglobulin M (nIgM) therapy prevents the onset and progression of autoimmune diabetes and promotes islet allograft survival.

BACKGROUND

nIgM deficiency is associated with an increased tendency toward autoimmune disease development. Elevated levels of nIgM anti-leukocyte autoantibodies are associated with fewer graft rejections.

METHODS

Four- to five-week-old female nonobese diabetic (NOD) littermates received intraperitoneal nIgM or phosphate-buffered saline/bovine serum albumin/immunoglobulin G (100 μg followed by 50-75 μg biweekly) until 18 weeks of age. C57BL/6 recipients of 300 BALB/c or 50 C57BL/6 islet grafts received saline or nIgM.

RESULTS

Eighty percent control mice (n = 30) receiving saline became diabetic by 18 to 20 weeks of age. In contrast, none of 33 of nIgM-treated mice became diabetic (P < 0.0001). Discontinuing therapy resulted in hyperglycemia in only 9 of 33 mice at 22 weeks postdiscontinuation, indicating development of β-cell unresponsiveness. nIgM therapy initiated at 11 weeks of age resulted in hyperglycemia in only 20% of treated animals (n = 20) compared with 80% of controls (P < 0.0001). Treatment of mildly diabetic mice with nIgM (75 μg 3× per week) restored normoglycemia (n = 5), whereas severely diabetic mice required minimal dose islet transplant with nIgM to restore normoglycemia (n = 4). The mean survival time of BALB/c islet allografts transplanted in streptozotocin-induced diabetic C57BL/6 mice was 41.2 ± 3.3 days for nIgM-treated recipients (n = 4, fifth recipient remains normoglycemic) versus 10.2 ± 2.6 days for controls (n = 5) (P < 0.001). Also, after syngeneic transplantation, time taken to return to normoglycemia was 15.4 ± 3.6 days for nIgM-treated recipients (n = 5) and more than 35 days for controls (n = 4).

CONCLUSIONS

nIgM therapy demonstrates potential in preventing the onset and progression of autoimmune diabetes and in promoting islet graft survival.

"Brittleness" in diabetes: easier spoken than broken

By definition, brittle diabetes (BD) is an unstable condition. Patients with BD suffer chronically from poor metabolic control, characterized by severe instability of glycemic values with frequent and unpredictable hypoglycemic and/or diabetic ketoacidosis episodes that cannot be attributed to failure in management. Quality of life is dramatically compromised because of very frequent acute complications leading to hospital admissions and because of premature chronic complications. It remains difficult to identify all patients with BD as diagnostic criteria are still not well defined. In practice, metabolic instability is manifested most obviously by chaotic glycemic profiles, which show greater and more unpredictable variation than in "stable" patients with diabetes. It is important that patients with BD are not adequately controlled, even by closely supervised, intensive insulin regimens, including continuous subcutaneous and/or intravenous insulin infusion. Their care is often very expensive in terms of time and resources, and their lives are constantly at risk for severe metabolic derangement. Management can also be frustrating and demoralizing for everyone involved, including the patient's family as well as the diabetes care team. Adopting a team approach, involving a broad range of disciplines, is essential in treating patients with BD and helping them to achieve and maintain both normoglycemia and quality of life.

Pancreatic islet transplantation

Pancreatic islet transplantation is a minimally invasive treatment that has the potential to prevent diabetes after total pancreatectomy for benign disease (islet autotransplantation) and to reverse diabetes in those with type 1 diabetes (islet allotransplantation). In both scenarios, the treatment involves extracting sufficient numbers of pancreatic islets from the resected or donor pancreas and infusing these through the portal vein into the patient's liver. The results for both forms of this treatment have been encouraging over recent years, with up to 85% of adult patients remaining insulin independent for at least 1 year after transplantation. However, there are a number of challenges that need to be overcome before these treatments can be used routinely in children. The aim of this review is to outline the rationale, methodology, and current results of islet allotransplantation, and to discuss the potential new developments that could enable this important treatment to be widely applicable to children. Although islet autotransplantation is not discussed in detail, the overall rationale and methods are similar. However, as the procedure involves the transplantation of the patient's own islets, and the indication for the procedure is not for autoimmune disease, there are none of the difficult immune challenges of allotransplantation.

Alteration of purinergic neurotransmission in isolated atria of streptozotocin-induced diabetic rats

Cardiac dysfunctions are described in diabetes. However, the role of purinergic neurotransmission in diabetes-related cardiovascular diseases is unknown. The purpose of this study was to evaluate the purinergic neurotransmission in isolated atria from streptozotocin-induced diabetic rats. The animals were grouped as control and diabetic with 30 days (D30) and 60 days (D60) after streptozotocin-induced diabetes. The isolated left and right atria were used in functional experiments. The effects of adenosine triphosphate, uridine diphosphate, and adenosine were evaluated on atrial inotropism and chronotropism. The antagonists 8-cyclopentyl-1,3-dipropylxanthine and pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate were also used, as blockers of P1 and P2 receptors, respectively. A negative inotropic effect followed by a positive inotropic effect was induced by adenosine triphosphate in isolated atria. This negative inotropic effect was decreased by 25% in left atria of D30. Additionally, the apparent affinity for adenosine was diminished in left atria of D30, suggesting changes in P1 receptor function. No changes were found in the right atria of D30 stimulated by adenosine. The left atria and right atria stimulated by uridine diphosphate showed an increased inotropic effect of 92% and 17%, respectively. No changes were observed in left and right atria of D30 stimulated by uridine diphosphate. Our data showed the involvement of purinergic neurotransmission in diabetes-related cardiovascular changes.

Evolution of β-Cell Replacement Therapy in Diabetes Mellitus: Islet Cell Transplantation

Diabetes mellitus remains one of the leading causes of morbidity and mortality worldwide. According to the Centers for Disease Control and Prevention, approximately 23.6 million people in the United States are affected. Of these individuals, 5 to 10% have been diagnosed with Type 1 diabetes mellitus (T1DM), an autoimmune disease. Although it often appears in childhood, T1DM may manifest at any age, leading to significant morbidity and decreased quality of life. Since the 1960s, the surgical treatment for diabetes mellitus has evolved to become a viable alternative to insulin administration, beginning with pancreatic transplantation. While islet cell transplantation has emerged as another potential alternative, its role in the treatment of T1DM remains to be solidified as research continues to establish it as a truly viable alternative for achieving insulin independence. In this paper, the historical evolution, procurement, current status, benefits, risks, and ongoing research of islet cell transplantation are explored.

B7-H4 Pathway in Islet Transplantation and β-Cell Replacement Therapies

Type 1 diabetes (T1D) is a chronic autoimmune disease and characterized by absolute insulin deficiency. β-cell replacement by islet cell transplantation has been established as a feasible treatment option for T1D. The two main obstacles after islet transplantation are alloreactive T-cell-mediated graft rejection and recurrence of autoimmune diabetes mellitus in recipients. T cells play a central role in determining the outcome of both autoimmune responses and allograft survival. B7-H4, a newly identified B7 homolog, plays a key role in maintaining T-cell homeostasis by reducing T-cell proliferation and cytokine production. The relationship between B7-H4 and allograft survival/autoimmunity has been investigated recently in both islet transplantation and the nonobese diabetic (NOD) mouse models. B7-H4 protects allograft survival and generates donor-specific tolerance. It also prevents the development of autoimmune diabetes. More importantly, B7-H4 plays an indispensable role in alloimmunity in the absence of the classic CD28/CTLA-4 : B7 pathway, suggesting a synergistic/additive effect with other agents such as CTLA-4 on inhibition of unwanted immune responses.