Detection of insulin mRNA in the peripheral blood after human islet transplantion predicts deterioration of metabolic control

Allo Beta Cell transplantation: specific features, unanswered questions, and immunological challenge

Type 1 diabetes (T1D) presents a persistent medical challenge, demanding innovative strategies for sustained glycemic control and enhanced patient well-being. Beta cells are specialized cells in the pancreas that produce insulin, a hormone that regulates blood sugar levels. When beta cells are damaged or destroyed, insulin production decreases, which leads to T1D. Allo Beta Cell Transplantation has emerged as a promising therapeutic avenue, with the goal of reinstating glucose regulation and insulin production in T1D patients. However, the path to success in this approach is fraught with complex immunological hurdles that demand rigorous exploration and resolution for enduring therapeutic efficacy. This exploration focuses on the distinct immunological characteristics inherent to Allo Beta Cell Transplantation. An understanding of these unique challenges is pivotal for the development of effective therapeutic interventions. The critical role of glucose regulation and insulin in immune activation is emphasized, with an emphasis on the intricate interplay between beta cells and immune cells. The transplantation site, particularly the liver, is examined in depth, highlighting its relevance in the context of complex immunological issues. Scrutiny extends to recipient and donor matching, including the utilization of multiple islet donors, while also considering the potential risk of autoimmune recurrence. Moreover, unanswered questions and persistent gaps in knowledge within the field are identified. These include the absence of robust evidence supporting immunosuppression treatments, the need for reliable methods to assess rejection and treatment protocols, the lack of validated biomarkers for monitoring beta cell loss, and the imperative need for improved beta cell imaging techniques. In addition, attention is drawn to emerging directions and transformative strategies in the field. This encompasses alternative immunosuppressive regimens and calcineurin-free immunoprotocols, as well as a reevaluation of induction therapy and recipient preconditioning methods. Innovative approaches targeting autoimmune recurrence, such as CAR Tregs and TCR Tregs, are explored, along with the potential of stem stealth cells, tissue engineering, and encapsulation to overcome the risk of graft rejection. In summary, this review provides a comprehensive overview of the inherent immunological obstacles associated with Allo Beta Cell Transplantation. It offers valuable insights into emerging strategies and directions that hold great promise for advancing the field and ultimately improving outcomes for individuals living with diabetes.

Assessment of plasma microvesicles to monitor pancreatic islet graft dysfunction: Beta cell- and leukocyte-derived microvesicles as specific features in a pilot longitudinal study

Markers of early pancreatic islet graft dysfunction and its causes are lacking. We monitored 19 type 1 diabetes islet-transplanted patients for up to 36 months following last islet injection. Patients were categorized as Partial (PS) or complete (S) Success, or Graft Failure (F), using the β-score as an indicator of graft function. F was the subset reference of maximum worsened graft outcome. To identify the immune, pancreatic, and liver contribution to the graft dysfunction, the cell origin and concentration of circulating microvesicles (MVs) were assessed, including MVs from insulin-secreting β-cells typified by polysialic acid of neural cell adhesion molecule (PSA-NCAM), and data were compared with values of the β-score. Similar ranges of PSA-NCAM⁺ -MVs were found in healthy volunteers and S patients, indicating minimal cell damage. In PS, a 2-fold elevation in PSA-NCAM⁺ -MVs preceded each β-score drop along with a concomitant rise in insulin needs, suggesting β-cell damage or altered function. Significant elevation of liver asialoglycoprotein receptor (ASGPR)⁺ -MVs, endothelial CD105⁺ -MVs, neutrophil CD66b⁺ -MVs, monocyte CD 14⁺ -MVs, and T4 lymphocyte CD4⁺ -MVs occurred before each β-score drop, CD8⁺ -MVs increased only in F, and B lymphocyte CD19⁺ -MVs remained undetectable. In conclusion, PSA-NCAM⁺ -MVs are noninvasive early markers of transplant dysfunction, while ASGPR⁺ -MVs signal host tissue remodeling. Leukocyte MVs could identify the cause of graft dysfunction.

Microencapsulated islet-like microtissues with toroid geometry for enhanced cellular viability

Transplantation of immuno-isolated islets is a promising strategy to restore insulin-secreting function in patients with Type 1 diabetes. However, the clinical translation of this treatment approach remains elusive due to the loss of islet viability resulting from hypoxia at the avascular transplantation site. To address this challenge, we designed non-spherical islet-like microtissues and investigated the effect of their geometries on cellular viability. Insulin-secreting microtissues with different shapes were fabricated by assembly of monodispersed rat insulinoma beta cells on micromolded nonadhesive hydrogels. Our study quantitatively demonstrated that toroid microtissues exhibited enhanced cellular viability and metabolic activity compared to rod and spheroid microtissues with the same volume. At a similar level of cellular viability, toroid geometry facilitated efficient packing of more cells into each microtissue than rod and spheroid geometries. In addition, toroid microtissues maintained the characteristic glucose-responsive insulin secretion of rat insulinoma beta cells. Furthermore, toroid microtissues preserved their geometry and structural integrity following their microencapsulation in immuno-isolatory alginate hydrogel. Our study suggests that adopting toroid geometry in designing therapeutic microtissues potentially reduces mass loss of cellular grafts and thereby may improve the performance of transplanted islets towards a clinically viable cure for Type 1 diabetes. STATEMENT OF SIGNIFICANCE: Transplantation of therapeutic cells is a promising strategy for the treatment of a wide range of hormone or protein-deficiency diseases. However, the clinical application of this approach is hindered by the loss of cell viability and function at the avascular transplantation site. To address this challenge, we fabricated hydrogel-encapsulated islet-like microtissues with non-spheroidal geometry and optimal surface-to-volume ratio. This study demonstrated that the viability of therapeutic cells can be significantly increased solely by redesigning the microtissue configuration without requiring any additional biochemical or operational accessories. This study suggests that the adoption of toroid geometry provides a possible avenue to improve the long-term survival of transplanted therapeutic cells and expedite the translation of cell-based therapy towards clinical application.

Pancreatic Islet Transplantation in Humans: Recent Progress and Future Directions

Pancreatic islet transplantation has become an established approach to β-cell replacement therapy for the treatment of insulin-deficient diabetes. Recent progress in techniques for islet isolation, islet culture, and peritransplant management of the islet transplant recipient has resulted in substantial improvements in metabolic and safety outcomes for patients. For patients requiring total or subtotal pancreatectomy for benign disease of the pancreas, isolation of islets from the diseased pancreas with intrahepatic transplantation of autologous islets can prevent or ameliorate postsurgical diabetes, and for patients previously experiencing painful recurrent acute or chronic pancreatitis, quality of life is substantially improved. For patients with type 1 diabetes or insulin-deficient forms of pancreatogenic (type 3c) diabetes, isolation of islets from a deceased donor pancreas with intrahepatic transplantation of allogeneic islets can ameliorate problematic hypoglycemia, stabilize glycemic lability, and maintain on-target glycemic control, consequently with improved quality of life, and often without the requirement for insulin therapy. Because the metabolic benefits are dependent on the numbers of islets transplanted that survive engraftment, recipients of autoislets are limited to receive the number of islets isolated from their own pancreas, whereas recipients of alloislets may receive islets isolated from more than one donor pancreas. The development of alternative sources of islet cells for transplantation, whether from autologous, allogeneic, or xenogeneic tissues, is an active area of investigation that promises to expand access and indications for islet transplantation in the future treatment of diabetes.

Combined Analysis of GAD65, miR-375, and Unmethylated Insulin DNA Following Islet Transplantation in Patients With T1D

AIM

Several biomarkers have been proposed to detect pancreatic β cell destruction in vivo but so far have not been compared for sensitivity and significance.

METHODS

We used islet transplantation as a model to compare plasma concentrations of miR-375, 65-kDa subunit of glutamate decarboxylase (GAD65), and unmethylated insulin DNA, measured at subpicomolar sensitivity, and study their discharge kinetics, power for outcome prediction, and detection of graft loss during follow-up.

RESULTS

At 60 minutes after transplantation, GAD65 and miR-375 consistently showed near-equimolar and correlated increases proportional to the number of implanted β cells. GAD65 and miR-375 showed comparable power to predict poor graft outcome at 2 months, with areas under the curve of 0.833 and 0.771, respectively (P = 0.53). Using receiver operating characteristic analysis, we defined likelihood ratios (LRs) for rationally selected result intervals. In GADA-negative recipients (n = 28), GAD65 <4.5 pmol/L (LR = 0.15) and >12.2 pmol/L (LR = ∞) predicted good and poor outcomes, respectively. miR-375 could be used in all recipients irrespective of GAD65 autoantibody status (n = 46), with levels <1.4 pmol/L (LR = 0.14) or >7.6 pmol/L (LR = 9.53) as dual thresholds. The posttransplant surge of unmethylated insulin DNA was inconsistent and unrelated to outcome. Combined measurement of these three biomarkers was also tested as liquid biopsy for β cell death during 2-month follow-up; incidental surges of GAD65, miR-375, and (un)methylated insulin DNA, alone or combined, were confidently detected but could not be related to outcome.

CONCLUSIONS

GAD65 and miR-375 performed equally well in quantifying early graft destruction and predicting graft outcome, outperforming unmethylated insulin DNA.

Bioengineering the Endocrine Pancreas: Intraomental Islet Transplantation Within a Biologic Resorbable Scaffold

Transplantation of pancreatic islets is a therapeutic option to preserve or restore β-cell function. Our study was aimed at developing a clinically applicable protocol for extrahepatic transplantation of pancreatic islets. The potency of islets implanted onto the omentum, using an in situ-generated adherent, resorbable plasma-thrombin biologic scaffold, was evaluated in diabetic rat and nonhuman primate (NHP) models. Intraomental islet engraftment in the biologic scaffold was confirmed by achievement of improved metabolic function and preservation of islet cytoarchitecture, with reconstitution of rich intrainsular vascular networks in both species. Long-term nonfasting normoglycemia and adequate glucose clearance (tolerance tests) were achieved in both intrahepatic and intraomental sites in rats. Intraomental graft recipients displayed lower levels of serum biomarkers of islet distress (e.g., acute serum insulin) and inflammation (e.g., leptin and α2-macroglobulin). Importantly, low-purity (30:70% endocrine:exocrine) syngeneic rat islet preparations displayed function equivalent to that of pure (>95% endocrine) preparations after intraomental biologic scaffold implantation. Moreover, the biologic scaffold sustained allogeneic islet engraftment in immunosuppressed recipients. Collectively, our feasibility/efficacy data, along with the simplicity of the procedure and the safety of the biologic scaffold components, represented sufficient preclinical testing to proceed to a pilot phase I/II clinical trial.

Life and death of β cells in Type 1 diabetes: A comprehensive review

Type 1 diabetes (T1D) is an autoimmune disorder characterized by the destruction of insulin-producing pancreatic β cells. Immune modulators have achieved some success in modifying the course of disease progression in T1D. However, there are parallel declines in C-peptide levels in treated and control groups after initial responses. In this review, we discuss mechanisms of β cell death in T1D that involve necrosis and apoptosis. New technologies are being developed to enable visualization of insulitis and β cell mass involving positron emission transmission that identifies β cell ligands and magnetic resonance imaging that can identify vascular leakage. Molecular signatures that identify β cell derived insulin DNA that is released from dying cells have been described and applied to clinical settings. We also consider changes in β cells that occur during disease progression including the induction of DNA methyltransferases that may affect the function and differentiation of β cells. Our findings from newer data suggest that the model of chronic long standing β cell killing should be reconsidered. These studies indicate that the pathophysiology is accelerated in the peridiagnosis period and manifest by increased rates of β cell killing and insulin secretory impairments over a shorter period than previously thought. Finally, we consider cellular explanations to account for the ongoing loss of insulin production despite continued immune therapy that may identify potential targets for treatment. The progressive decline in β cell function raises the question as to whether β cell failure that is independent of immune attack may be involved.

Studies of circulating microparticle release in peripheral blood after pancreatic islet transplantation

The loss of graft function after intraportal islet transplantation is likely multifactorial involving allogeneic rejection, recurrent autoimmunity, graft exhaustion due to a marginally implanted islet mass, immunosuppressant toxicity, and impaired β-cell regeneration. Because early markers of the loss of β-cell mass or function are lacking, monitoring of islet function remains a challenging issue. We have reported herein monitoring of membrane procoagulant microparticles (MPs) as markers of cell stress in the plasma of three recipients with various clinical histories. Early kinetics of C-peptide and MPs followed identical patterns during the first weeks after transplantation; a major increase probably reflected processes related to cell infusion and islet engraftment. Importantly in the case of rejection, MPs and C-peptide showed opposite patterns. A fall in C-peptide was associated with enhanced insulin needs. Our results suggested that a peak in MP levels might indicate rejection with prognotic value. Treatment of the loss of islet function by a new islet infusion or steroid therapy returned MP and C-peptide levels to their baselines with concomitant restoration of islet function. In the patient with suspected acute cellular rejection, MPs also appeared to be sensors of immunosuppressive steroid therapy.

Caspase inhibitor IDN6556 facilitates marginal mass islet engraftment in a porcine islet autotransplant model

BACKGROUND

Large numbers of islets are lost in the early phase after clinical islet transplantation, through apoptosis, necrosis, or innate inflammatory injury. We previously demonstrated the efficacy of a series of caspase inhibitors in mouse models on islet engraftment through reduction in early posttransplant apoptosis. We studied IDN6556, a caspase inhibitor with a first-pass effect, in a large animal (pig) intraportal marginal mass islet autotransplant model.

METHODS

Total pancreatectomy and marginal mass islet autotransplantation were carried out in Yucatan miniature swine to explore the effects of IDN6556 on islet engraftment. Pigs were treated with IDN6556 at a dose of 20 mg/kg orally twice daily (n=7) or phosphate-buffered saline control (n=6) orally for 7 days, and blood glucose was monitored for 1 month. Glucose tolerance and acute insulin release were determined at 1 month.

RESULTS

There were no differences in islet procurement, isolation, or islet functional parameters between the two groups. Pigs receiving IDN6556 had lower fasting blood glucose level after transplantation and a higher percentage (100% vs. 33.3%) showed fasting blood glucose levels less than 11 mM. This translated into an enhanced metabolic reserve and acute insulin release for pigs in the treatment group.

CONCLUSIONS

IDN6556 led to enhanced islet engraftment in this large animal islet transplant model. Although this study has limitations including a short interval of study (1 month) and the use of unpurified islets, the results justify early clinical trials of IDN6556 in islet transplantation.

Immunologic and metabolic biomarkers of β-cell destruction in the diagnosis of type 1 diabetes

Type 1 diabetes (T1D), also known as insulin-dependent diabetes mellitus, is a chronic disorder that results from autoimmune destruction of insulin-producing β cells in the islets of Langerhans within the pancreas ( Atkinson and Maclaren 1994). This disease becomes clinically apparent only after significant destruction of the β-cell mass, which reduces the ability to maintain glycemic control and metabolic function. In addition, it continues for years after clinical onset until, generally, there is complete destruction of insulin secretory capacity. Because prevention and therapy strategies are targeted to this pathologic process, it becomes imperative to have methods with which it can be monitored. This work discusses current research-based approaches to monitor the autoimmunity and metabolic function in T1D patients and their potential for widespread clinical application.

Characterization of the transcriptome in isolated and transplanted mouse pancreatic islets: associations with engraftment and dysfunction

The transplantation of pancreatic islets is an option for therapeutic management of hypoglycemia unawareness in select patients with type 1 diabetes mellitus. Characteristics of the transcriptome of freshly isolated islets, islet allografts, and islet isograft are reported in the literature. However, no single experiment has undertaken a comparison of the islet allograft to isograft. Potential implications of the latter are the use in diagnosis of rejection and to discover the molecular pathways in islet allograft dysfunction after transplant. Here, the mouse model of islet transplant is used to characterize the transcriptome of freshly isolated islets and compare islet graft in an isogeneic vs. allogeneic host using an Affymetrix GeneChip® Array assay. A set of islet associated transcripts (IAT) was developed, and subsequently shown to have high level of expression in islet allografts and isografts harvested either five- or ten-days after transplant. Furthermore, specific analysis of transcriptome differences between islet isografts and pre-rejection allografts (ten-day), reveal a series of islet rejection associated transcripts (IRAT). Nearly half of IRAT show overlap with previously described pathogenesis based transcript sets identified in the setting of mouse kidney allograft rejection. The novel transcripts identified to be associated with islet rejection include those involved in chemotaxis or lymphocyte function. Although use of biopsy based monitoring of humans islet transplants remains difficult at the present time, this study provides proof of principle for a transcriptome based technique for islet graft rejection monitoring and describes the transcripts associated with islet graft dysfunction.

Detection of β cell death in diabetes using differentially methylated circulating DNA

In diabetes mellitus, β cell destruction is largely silent and can be detected only after significant loss of insulin secretion capacity. We have developed a method for detecting β cell death in vivo by amplifying and measuring the proportion of insulin 1 DNA from β cells in the serum. By using primers that are specific for DNA methylation patterns in β cells, we have detected circulating copies of β cell-derived demethylated DNA in serum of mice by quantitative PCR. Accordingly, we have identified a relative increase of β cell-derived DNA after induction of diabetes with streptozotocin and during development of diabetes in nonobese diabetic mice. We have extended the use of this assay to measure β cell-derived insulin DNA in human tissues and serum. We found increased levels of demethylated insulin DNA in subjects with new-onset type 1 diabetes compared with age-matched control subjects. Our method provides a noninvasive approach for detecting β cell death in vivo that may be used to track the progression of diabetes and guide its treatment.

Soluble donor DNA and islet injury after transplantation

INTRODUCTION

A large proportion of clinical islet transplant recipients fail to initially achieve or sustain meaningful independence from exogenous insulin use. We hypothesized that immediate allograft injury is a key constraint on independence from exogenous insulin use.

METHODS

Standard human leukocyte antigen genotyping was reviewed to identify nonshared polymorphisms between 21 prospectively recruited islet transplant recipients from a single institution and their respective donors. Human leukocyte antigen polymorphism-specific quantitative polymerase chain reaction was used to quantify donor DNA shed into blood by injured islets from serial sera acquired over the first 10 days postprocedure and examined for correlation with achievement of insulin independence.

RESULTS

Nearly fourfold higher serum concentrations of donor DNA were detected in subjects whose grafts failed to generate insulin independence. The median for the average area under the curve in recipients who did and did not achieve insulin independence was 12 (range, 1-61) and 45 (range, 14-255) donor genome equivalents (gEq)-day/mL (p=0.03), respectively.

CONCLUSIONS

These findings represent the first direct testing of allograft injury in humans undergoing islet cell transplantation. Injury to donor islets very soon after transplantation may represent an important barrier to achieving insulin independence other than adaptive immune responses targeting allografts at later times. In addition, soluble donor DNA merits further development as a quantifiable biomarker to evaluate new interventions aimed at mitigating immediate islet injury.

The caspase inhibitor IDN-6556 (PF3491390) improves marginal mass engraftment after islet transplantation in mice

BACKGROUND

Islet transplantation has become a viable option for selected type 1 diabetic patients; however, a significant portion need to return to exogenous insulin. The predominant factors include impaired islet engraftment and early islet loss. Caspase inhibition is a potent way to improve islet engraftment, but all tested compounds so far have not been clinically relevant. IDN-6556 (PF3491390) has already been used clinically and can be delivered orally with high portal vein concentrations.

METHODS

Mice were given a marginal mass islet graft of either mouse or human islets and treated with either IDN-6556 (10 or 20 mg/kg ip bid) or vehicle and followed for diabetes reversal. At 1 month post-transplant, mice were subjected to a glucose tolerance test and an assessment of graft mass. In separate experiments, human islets were cultured with IDN-6556 or vehicle to assess for islet survival and viability.

RESULTS

In both syngeneic mouse islets and human islets transplanted into immunodeficient mice, IDN-6556 (20 mg/kg) given for 7 days post-transplant led to a significantly enhanced rate of diabetes reversal as compared to vehicle. In addition, mice receiving caspase inhibitor displayed improved glucose tolerance and graft survival at the 1-month point. We also found protective effects in vitro for islet viability and marked reduction in apoptosis in vivo.

CONCLUSION

Taken together, these results demonstrate the effectiveness of caspase inhibition with IDN-6556 on islet transplantation and in particular islet engraftment and survival.

Immune monitoring of pancreatic islet graft: towards a better understanding, detection and treatment of harmful events

IMPORTANCE OF THE FIELD

Long-term clinical outcomes of islet transplantation are hampered by rejection and recurrence of autoimmunity, which lead to a gradual decrease in islet function usually taking place over the first five years after transplantation. An accurate monitoring strategy could allow for the detection and treatment of harmful immune events, potentially resulting in higher rates of insulin-independence.

AREAS COVERED IN THIS REVIEW

This article provides a critical review of the various assays currently available for the assessment of allo- and autoimmunity both prior to and after islet transplantation. The accuracy in predicting clinical outcome is specifically addressed.

WHAT THE READER WILL GAIN

Most current tests based on the assessment of allo- and auto-immune antibody are of minimal help in clinical practice. Cell-based tests (including the assessment of cytotoxic T lymphocyte precursors, proliferation tests, enzyme-linked immunospot) have the potential to allow earlier and more accurate detection of harmful events.

TAKE HOME MESSAGE

A specific and accurate immune monitoring has the potential to significantly improve islet transplant outcomes. The development and use of such tests (favouring cell-based tests) should be promoted.

Detecting rejection after mouse Islet transplantation utilizing islet protein-stimulated ELISPOT

Improved posttransplant monitoring and on-time detection of rejection could improve islet transplantation outcome. The present study explored the possibility of detecting harmful events after mouse islet transplantation measuring the immune responsiveness against islet extracts. Mouse islet transplantations were performed using various donor/recipient combinations, exploring autoimmune (NOD/SCID to NOD, n = 6) and alloimmune events (C57BL/6 to BALB/c, n = 20), a combination of both (C57BL/6 to NOD, n = 8), the absence of both (BALB/c to BALB/c, n = 21), or naive, nontransplanted control mice (n = 14). The immune reactivity was measured by ELISPOT, looking at the ex vivo release of IFN-γ from splenocytes stimulated by islet donor extracts (sonicated islets). The immune reactivity was not altered in the syngeneic and autoimmune models, demonstrating similar levels as nontransplanted controls (p = 0.46 and p = 0.6). Conversely, the occurrence of an allogeneic rejection alone or in combination to autoimmunity was associated to an increase in the level of immune reactivity (p = 0.023 and p = 0.003 vs. respective controls). The observed increase was transient and lost in the postrejection period or after treatment with CTLA4-Ig. Overall, allogeneic rejection was associated to a transient increase in the reactivity of splenocytes against islet proteins. Such a strategy has the potential to improve islet graft monitoring in human and should be further explored.

Assessment of human islet labeling with clinical grade iron nanoparticles prior to transplantation for graft monitoring by MRI

Ex vivo labeling of islets with superparamagnetic iron oxide (SPIO) nanoparticles allows posttransplant MRI imaging of the graft. In the present study, we compare two clinical grade SPIOs (ferucarbotran and ferumoxide) in terms of toxicity, islet cellular uptake, and MRI imaging. Human islets (80-90% purity) were incubated for 24 h with various concentrations of SPIOs (14-280 μg/ml of iron). Static incubations were performed, comparing insulin response to basal (2.8 mM) or high glucose stimulation (16.7 mM), with or without cAMP stimulation. Insulin and Perl's (assessment of iron content) staining were performed. Electronic microscopy analysis was performed. Labeled islets were used for in vitro or in vivo imaging in MRI 1.5T. Liver section after organ removal was performed in the same plane as MRI imaging to get a correlation between histology and radiology. Postlabeling islet viability (80 ± 10%) and function (in vitro static incubation and in vivo engraftment of human islets in nude mice) were similar in both groups. Iron uptake assessed by electron microscopy showed iron inclusions within the islets with ferucarbotran, but not with ferumoxide. MRI imaging (1.5T) of phantoms and of human islets transplanted in rats, demonstrated a strong signal with ferucarbotran, but only a weak signal with ferumoxide. Signal persisted for >8 weeks in the absence of rejection. An excellent correlation was observed between radiologic images and histology. The hepatic clearance of intraportally injected ferucarbotran was faster than that of ferumoxide, generating less background. A rapid signal decrease was observed in rejecting xenogeneic islets. According to the present data, ferucarbotran is the most appropriate of available clinical grade SPIOs for human islet imaging.

Histologic graft assessment after clinical islet transplantation

BACKGROUND

An accurate monitoring would help understanding the fate of islet grafts after transplantation.

METHODS

This work assessed the feasibility of needle biopsy monitoring after intraportal islet transplantation (n=16), and islet graft morphology was studied with the addition of autopsy samples (n=2). Pancreas autopsy samples from two nondiabetic individuals were used as control.

RESULTS

Islet tissue was found in five needle samples (31%). Sampling success was related to size (100% sampling for the four biopsies of 1.8 cm in length or higher, P<or=0.01). Mild liver abnormalities included localized steatosis (n=8), mild nodular regenerative hyperplasia and mild portal venopathy (n=3), and hepatocyte swelling (n=2). Endocrine cell composition and distribution were similar between islet grafts and normal islets within the native pancreas. There was no or minimal immune cell infiltrate in patients on and off exogenous insulin, including two patients with ongoing negative metabolic events (increasing HbA1c or insulin requirement). The infiltrate was mainly composed of CD4- and CD8-positive cells.

CONCLUSION

This study demonstrates that needle biopsy is feasible after clinical islet transplantation but with a limited practical value because of its low islet sampling rate using current sampling and analysis methods. Both biopsy and autopsy samples demonstrated the well-preserved islet endocrine composition after transplantation and the presence of focal areas of steatosis. Islet grafts showed no or minimal immune cell infiltration, even in the case of ongoing islet loss. On the basis of the findings, possible reasons for allograft islet loss are discussed.

The caspase selective inhibitor EP1013 augments human islet graft function and longevity in marginal mass islet transplantation in mice

OBJECTIVE

Clinical islet transplantation can provide insulin independence in patients with type 1 diabetes, but chronic graft failure has been observed. This has been attributed in part to loss of >or=60% of the transplanted islets in the peritransplant period, resulting in a marginal implant mass. Strategies designed to maximize survival of the initial islet mass are likely to have major impact in enhancing long-term clinical outcomes. EP1013 (N-benzyloxycabonyl-Val Asp-fluoromethyl ketone [zVD-FMK]), is a broad-spectrum caspase selective inhibitor with no observed toxicity in rodents.

RESEARCH DESIGN AND METHODS

The therapeutic benefit of EP1013 was examined in a syngeneic rodent islet transplant model using deceased donor human islets to determine whether the amount of tissue required to restore euglycemia in diabetic animals could be reduced.

RESULTS

EP1013 (combined pretransplant islet culture for 2 h and in vivo treatment for days 0-5 posttransplant) significantly improved marginal islet mass function following syngeneic islet transplantation in mice, even at lower doses, compared with previous studies using the pan-caspase inhibitor N-benzyloxycabonyl-Val Ala-Asp-fluoromethyl ketone (zVAD-FMK). EP1013 supplementation in vitro improved human islet yields following prolonged culture and reversed diabetes following implantation of a marginal human islet mass (80-90% reduction) into mice.

CONCLUSIONS

Our data suggest that EP1013 therapy will markedly reduce the islet mass required in clinical islet transplantation, improving insulin independence rates following single-donor infusion.

Positron emission tomography: a real-time tool to quantify early islet engraftment in a preclinical large animal model

BACKGROUND

Clinical islet transplantation is currently being explored as a therapeutic option for persons with type I diabetes and hypoglycemic unawareness. Techniques to monitor graft survival are urgently needed to optimize the procedure. Therefore, the objective of the present study was to develop a technique for imaging survival of transplanted islets in the peritransplant and early posttransplant phase.

METHODS

Isolated porcine islets were labeled in vitro with 2-deoxy-2[F]fluoro-D-glucose ([F]FDG) and infused intraportally into anesthetized pigs (n=10). Dynamic examination was performed on a positron emission tomography/computed tomography hybrid system.

RESULTS

More than 95% of the radioactivity was confined to the islets at the time of transplantation. The peak percentage of infused radioactivity within the liver, quantified at the end of the islet infusion, was only 54+/-5.1%. The distribution of the radioactivity in the liver was found to be heterogeneous. A whole-body examination showed no accumulation in the lungs or brain; extrahepatic radioactivity was, except urinary excretion, evenly distributed in the pig body.

CONCLUSIONS

Our results imply that almost 50% of the islets were damaged to the extent that the FDG contained was release within minutes after intraportal transplantation. The distribution of radioactivity without accumulation in the brain indicates that the activity is released from lysed islet cells in the form of [F]FDG-6P rather than native [F]FDG. The presented technique shows promise to become a powerful and quantitative tool, readily available in the clinic, to evaluate initial islet engraftment and survival.

Monitoring of the islet graft

The Edmonton trials have brought about a marked improvement in the short-term rate of success of islet transplantation with rates of insulin-independence of 80% at 1-year being reported by several institutions worldwide. Unfortunately, this rate consistently decreases to 10-15% by 5 years post-transplantation. Several mechanisms have been proposed to explain this apparent 'islet exhaustion', but are difficult to pinpoint in a given patient. Understanding the reasons for islet graft exhaustion and its kinetics is a prerequisite for the improvement of islet transplantation outcome. In this regard, efficient monitoring tools for the islet graft have been conspicuously lacking and are required to detect islet damage and diagnose its mechanisms in a timely fashion, so as to initiate salvage therapy such as antirejection treatment. Tools for the monitoring of the islet graft include follow-up of metabolic function but mostly indicate dysfunction when it is too late to take action. Progress is likely to arise in the fields of immune monitoring, molecular monitoring and islet imaging, notably thanks to magnetic resonance (MR) or positron emission tomography (PET) technologies.