Islet Transplant Recipients Research Articles

HLA Class I Sensitization in Islet Transplant Recipients: Report from the Collaborative Islet Transplant Registry

Pancreatic islet transplantation is a promising treatment option for patients severely affected with type 1 diabetes. This report from CITR presents pre- and posttransplant human leukocyte antigen (HLA) class I sensitization rates in islet-alone transplantation. Data came from 303 recipients transplanted with islet-alone between January 1999 and December 2008. HLA class I sensitization was determined by the presence of anti-HLA class I antibodies. Panel-reactive antibodies (PRA) from prior to islet infusion and at 6 months, and yearly posttransplant was correlated to measures of islet graft failure. The cumulative number of mismatched HLA alleles increased with each additional islet infusion from a median of 3 for one infusion to 9 for three infusions. Pretransplant PRA was not predictive of islet graft failure. However, development of PRA >20% posttransplant was associated with 3.6-fold (p < 0.001) increased hazard ratio for graft failure. Patients with complete graft loss who had discontinued immunosuppression had significantly higher rate of PRA ≥ 20% compared to those with functioning grafts who remained on immunosuppression. Exposure to repeat HLA class I mismatch at second or third islet infusions resulted in less frequent development of de novo HLA class I antibodies when compared to increased class I mismatch. The development of HLA class I antibodies while on immunosuppression is associated with subsequent islet graft failure. The risk of sensitization may be reduced by minimizing the number of islet donors used per recipient, and in the absence of donor-specific anti-HLA antibodies, repeating HLA class I mismatches with subsequent islet infusions.

Rescue of a Pancreatic Islet Graft After Steroid Therapy

Rescue of a Pancreatic Islet Graft After Steroid Therapy

Tolerance-Inducing Strategies in Islet Transplantation

Allogeneic islet transplantation is a promising approach for restoring normoglycemia in type 1 diabetic patients. Current use of immunosuppressive therapies for management of islet transplant recipients can be counterintuitive to islet function and can lead to complications in the long term. The induction of donor-specific tolerance eliminates the dependency on immunosuppression and allows recipients to retain responses to foreign antigens. The mechanisms by which tolerance is achieved involve the deletion of donor-reactive T cells, induction of T-cell anergy, immune deviation, and generation of regulatory T cells. This review will outline the various methods used for inducing donor-specific tolerance in islet transplantation and will highlight the previously unforeseen potential of tissue stromal cells in promoting islet engraftment.

Stem Cells as a Tool to Improve Outcomes of Islet Transplantation

The publication of the promising results of the Edmonton protocol in 2000 generated optimism for islet transplantation as a potential cure for Type 1 Diabetes Mellitus. Unfortunately, follow-up data revealed that less than 10% of patients achieved long-term insulin independence. More recent data from other large trials like the Collaborative Islet Transplant Registry show incremental improvement with 44% of islet transplant recipients maintaining insulin independence at three years of follow-up. Multiple underlying issues have been identified that contribute to islet graft failure, and newer research has attempted to address these problems. Stem cells have been utilized not only as a functional replacement for β cells, but also as companion or supportive cells to address a variety of different obstacles that prevent ideal graft viability and function. In this paper, we outline the manners in which stem cells have been applied to address barriers to the achievement of long-term insulin independence following islet transplantation.

Effect of Exenatide on Gastric Emptying and Graft Survival in Islet Allograft Recipients

Objective To evaluate the effect of exenatide on gastric emptying and long-term metabolic control. Methods Ten islet allograft recipients treated with exenatide up to 4 years. Data from a mixed meal test with (MMT+) versus without (MMT−) administration of exenatide before boost ingestion were analyzed at 6, 12, 24, 36, or 48 months after initiation of exenatide treatment. None of the subjects were symptomatic for gastroparesis before or during the study. The c-peptide, acetaminophen absorption and glucose responses to MMT were analyzed by Student t test and analysis of variance. Results Average exenatide dose was 12.75 ± 9.46 μg/dL. The MMT subjects included two groups those with acetaminophen peak ≤120 minutes (“good gastric emptying; n = 4”) versus those with an acetaminophen peak ≥180 minutes (“delayed gastric emptying”). Among the MMT+, acetaminophen absorption was the same in both groups ( P = .27). Up to 48 months exenatide delayed time to peak of glucose, c-peptide, and acetaminophen as well as suppressed the glucagon response to MMT mean peak: 70.89 ± 12.45 versus 43.24 ± 4.67. The mean values of c-peptide and glucose responses to MMT were not significantly different. Conclusions Long-term exenatide administration up to 4 years was safe in islet transplant recipients, even in the presence of delayed gastric emptying. The effects of exenatide were acute and reversible when the agent was withdrawn. The main difficulty with the use of exenatide in islet transplant subjects is their poor tolerability, although the physiological effects are clearly evident even at low doses. Approximately 63% of total subjects under exenatide treatment discontinued the drug due to nausea and vomiting. The use of new GLP1 analogs with longer half lives and fewer side effects may help to attain higher GLP1 levels, therefore improving islet function and survival.

Hypersensitivity to Rabbit Antithymocyte Globulin in an Islet Transplant Recipient: A Case Report

Objective The aim was to describe a case of hypersensitivity to rabbit antithymocyte globulin (rATG) occurring in the context of islet transplantation. Methods A 36-year-old woman with type 1 diabetes was admitted for islet transplantation. rATG was administered the first day (1.5 mg/kg) with methylprednisolone (2 mg/kg), and on the second day (1.5 mg/kg) without glucocorticoid to avoid potential toxicity to the anticipated islet transplant. Results At the end of the rATG infusion on the second day she developed hives over her face, chest, and back and tender erythema at her intravenous site (Arthus reaction). Islet transplantation was not performed. She reported exposure to a pet rabbit for 2 years in childhood. Overnight, fever developed and the rash evolved into an erythematous morbilliform eruption affecting the torso. Serum high-sensitivity C-reactive protein (hsCRP) and the erythrocyte sedimentation rate (ESR) were elevated; serum complements C3 and C4 were normal. She received prednisone (50 mg) with subsequent resolution of the rash. Nine days after her initial reaction, she developed a recurrence of the rash and fever with arthralgias; levels of C3 and C4 had fallen. Methylprednisolone (125 mg, twice) was required for symptom improvement, and was gradually tapered as prednisone over the next 4 weeks with resolution of the complement, ESR, and hsCRP abnormalities. Five months after the initial attempt at islet transplantation, she returned to receive 7,879 IE/kg via portal vein infusion under basiliximab, etanercept, tacrolimus, and sirolimus immunosuppression and has required no to low-dose (0.1 U/kg/d) insulin to maintain near-normal glycemic control for > 12 months after transplantation. Conclusions Our patient's initial hypersensitivity reaction to rATG was followed by immune-complex type 3 hypersensitivity (serum sickness) requiring high-dose glucocorticoids. Canceling the initial islet infusion proved to be wise, and the patient subsequently did well with islet transplantation under an alternative induction agent.

Soluble Donor DNA and Islet Injury After Transplantation

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. 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. 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. 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.

Integrin Antagonists for Transplant Immunosuppression: Panacea or Peril?

Integrin Antagonists for Transplant Immunosuppression: Panacea or Peril?

CC Chemokine Receptor 5 Deficiency Does Not Prevent Local Immune Responses to Adenovirus Vector in Islet Transplant Recipients

CC chemokine receptor 5 (CCR5) plays an important role in mediating inflammation. We examined the effect of CCR5 on the immune response to adenovirus vectors and graft function in islet transplant model. Syngeneic wild-type (WT) or CCR5-deficient (KO) mouse islets transduced with adenovirus encoding β-gal were transplanted under the renal capsule. After transplant, blood glucose, glucose tolerance, graft cellular infiltration, transgene and chemokine/receptor expression, and systemic anti-adenoviral/-β-gal immune response were evaluated. Diabetes was reversed in 1 d in both WT and KO untransduced recipients, while islets transduced with adenovirus failed to reverse diabetes until 10d post-transplant in WT recipients or even longer (>15d) in KO recipients (P < 0.05). A profound infiltration of CD4(+), CD8(+) cells and macrophages was observed in both WT and KO transduced grafts at 25 d. Though transgene expression was significantly reduced, insulin and β-gal expression persisted over 3mo. Glucose tolerance was impaired in all grafts in KO recipients compared with untransduced grafts in WT recipients at 25 d post-transplant, but was equivalent at 3 mo. Early expression of CCR2 mRNA was increased in transduced grafts in both WT and KO recipients. No systemic antivector immunity was demonstrated in any recipient group. Transduction of islets with adenovirus causes significant local inflammation in islet grafts and impairs early graft function in CCR5-deficient recipients, but long-term graft function is preserved. Thus, CCR5 absence does not prevent the local immune response to adenovirus transduction, and vector-associated graft dysfunction is not mediated by CCR5.

Magnetic Resonance Imaging Study of Mouse Islet Allotransplantation

Although only 10% of islet transplant recipients maintain insulin independence, 80% of them are C-peptide positive at 5 years. To better understand the fate of transplanted islets, a magnetic resonance imaging (MRI) technique has been used to detect superparamagnetic iron oxide (SPIO)–labeled transplanted islets. Recently, we successfully used a novel MRI contrast agent, chitosan-coated SPIO (CSPIO) nanoparticles, to monitor mouse islet isografts for 18 weeks after transplantation. In the present study, we tested whether CSPIO could be applied to monitor islet allografts, which are supposedly rejected without immune interventions. Male C57BL/6 and Balb/c mice were used as donors and recipients of islet transplantation, respectively. After overnight incubation with or without CSPIO (10 μg/mL), 300 C57BL/6 islets were transplanted under the left kidney capsule of each Balb/c mouse. Starting from day 10 after transplantation, 3.0-Tesla MRI of the recipients was performed weekly. Four mice were followed for ≥38 days. At 38 and 45 days, 1 islet graft was removed for insulin and Prussian blue staining, respectively. From days 10 to 45 after transplantation, CSPIO-labeled islet grafts were visualized on MRI scans as sustained distinct hypointense spots homogeneously located at the upper pole of left kidney, the site of transplantation. At days 38 and 45, the histology of CSPIO-labeled islet grafts revealed insulin and iron staining colocalized in the same areas. Our results in a mouse allotransplantation model indicated that CSPIO-labeled islets survived as long as 45 days with positive MRI.

Actions of the Japanese Pancreas and Islet Transplantation Association Regarding Transplanted Human Islets Isolated Using Liberase HI

Purpose The potential for introducing transmissible spongiform encephalopathy (TSE) into islet cells was indicated by recognizing that Liberase HI is isolated from Clostridium histolyticum grown in media containing brain–heart infusion broth. A national team within the Japanese Pancreas and Islet Transplantation Association implemented an islet transplantation program in Japan using Liberase HI. The program comprised 65 islet isolations from non–heart-beating donors and 34 transplants into 18 patients. Herein, we have summarized how the Association followed these recipients over the long term. Procedures We established an ad hoc committee to follow recipients transplanted with islets isolated using Liberase HI after becoming informed of the associated dangers of using this enzyme. We also stopped islet transplantations using Liberase. The committee addressed the major concerns of the risk of the collagenase being contaminated with TSE and of the recipient follow-up. All recipients were examined by diffusion MRI and EEG and then scheduled for evaluation and follow-up by specialists in Creutzfeldt-Jakob disease (CJD). Bioassays of bovine spongiform encephalopathy prions in the enzyme proceeded using knock-in mice expressing bovine prion protein. These assays could detect contaminating prions at a dilution of 1 × 10 4. After inactivating its collagenase activity, Liberase HI was injected into the abdominal cavities of knock-in mice. Four months later, prion infectivity in Liberase HI was evaluated by immunohistochemical staining and Western blotting of spleen homogenates using anti-prion protein antibodies. Main findings Western blotting and immunohistochemical staining did not detect prions in Liberase HI. Diffusion MRI and EEG evaluations performed by CJD specialists confirmed that none of the transplanted recipients had CJD. Conclusions Three years of follow-up revealed that none of the Japanese recipients of islet transplants developed CJD. Prion bioassays showed that the Liberase HI used to isolate islets for transplantation was free of infectious TSE prions.

Magnetic Resonance Imaging of Transplanted Mouse Islets Labeled With Chitosan-Coated Superparamagnetic Iron Oxide Nanoparticles

Although only 10% of islet recipients maintain insulin independence, 80% of them are C-peptide positive at 5 years after transplantation. To better understand the fate of transplanted islets, a magnetic resonance imaging (MRI) technique has been used to detect Feridex-labeled islet grafts in rodents. In this study, we used a novel MRI contrast agent, chitosan-coated superparamagnetic iron oxide (CSPIO) nanoparticles, to monitor mouse islet grafts. Male inbred C57BL/6 mice were used as donors and recipients of islet transplantation. The islet cytotoxicity was evaluated by fluorescein diacetate and propidium iodide staining for RAW cells incubated with CSPIO. After being incubated overnight with and without CSPIO (10 mg/mL), 300 islets were transplanted under the left kidney capsule of each mouse. After transplantation, 3.0-Tesla MRI of the recipients was performed biweekly until 19 weeks. At the end of study, the islet graft was removed for insulin and Prussian blue staining. The cell death rates in RAW cells did not increase with increasing CSPIO concentrations or incubation time. The grafts of CSPIO-labeled islets were visualized on MRI scans as distinct hypointense spots homogeneously located at the upper pole of left kidney. Their MRI signal was 30%–50% that of control islets and was maintained throughout the follow-up period. At 18 weeks, the histology of CSPIO-labeled islet graft revealed the insulin- and iron-stained areas to be almost identical. Our results indicate that isolated mouse islets labeled with CSPIO nanoparticles can be effectively and safely imaged by using MRI as long as 18 weeks after transplantation.

Pharmacokinetics of Mycophenolic Acid and its Glucuronidated Metabolites in Stable Islet Transplant Recipients

Given the paucity of data on pharmacokinetics of mycophenolic acid (MPA) in islet transplant, the aim of this study was to characterize pharmacokinetic parameters of MPA and its 2 glucuronidated metabolites in stable islet transplant recipients. Sixteen subjects were entered into this open-label study after written informed consent. Upon administration of a steady-state morning mycophenolate mofetil dose, 12-hour serial concentrations of MPA and its phenolic glucuronide (MPAG) and acyl-glucuronide (AcMPAG) were measured by a validated high-performance liquid chromatography method and pharmacokinetic parameters analyzed by noncompartmental modeling. Subjects included 11 women and 5 men who had received 2.7 +/- 0.8 islet transplants. Age was 50 +/- 8 years, weight 64 +/- 11 kg, serum albumin 4.2 +/- 0.3 g/dL, and serum creatinine 1.1 +/- 0.4 mg/dL. All patients were also on tacrolimus-based steroid-free immunosuppressant regimens. Mycophenolate mofetil dosage ranged from 1 to 2 g daily (25.4 +/- 6.1 mg/kg/d). Pharmacokinetic parameters for MPA were area under the curve 42.9 +/- 21.6 microg h/mL; dose-normalized AUC 52.9 +/- 25.4 microg h/mL/g; maximal concentration (Cmax) 13.0 +/- 6.2 microg/mL; time to Cmax (tmax) 1.2 +/- 0.4 hours; minimum concentration (Cmin) 1.4 +/- 1.0 microg/mL; and MPA-free fraction 1.2% +/- 1.0%. Area under the curve ratios of MPAG/MPA and AcMPAG/MPA were 17.8 +/- 12.4 and 0.1 +/- 0.1, respectively. The wide interpatient variability in all pharmacokinetic parameters of MPA and metabolites are consistent with results from the only other published pharmacokinetic study in islet transplant recipients. A population model and a search for significant covariates may help reduce this variability. Pharmacokinetic parameters calculated in the present study, coupled with findings from the only other published MPA study in islet transplant, form a preliminary base on which to build a population model for future multicenter studies of this little-studied transplant subpopulation.

Supplemental Islet Infusions Restore Insulin Independence After Graft Dysfunction in Islet Transplant Recipients

The ability of supplemental islet infusions (SII) to restore insulin independence in islet transplant recipients with graft dysfunction has been attributed to the coadministration of exenatide. However, improving islet transplant outcomes could explain the success of SII. We aimed to determine the effect on islet graft function and insulin independence of SII using these new protocols, without the use of exenatide. Seventeen islet transplant recipients underwent SIIs after developing graft dysfunction requiring insulin use. For induction therapy, four subjects received daclizumab induction therapy, whereas 13 subjects received thymoglobulin and etanercept. Maintenance immunosuppression consisted of sirolimus+tacrolimus or tacrolimus+cellcept. SII was performed 49.3+/-4.8 months (mean+/-SEM) after the preceding islet transplant. Subjects received significantly lower islet mass with their SII compared with initial transplant(s) (6076+/-492 vs. 9071+/-796 IEQ/kg; P=0.003). Fifteen of the 17 subjects (88.2%) became insulin independent 2.4+/-0.5 months after SII. Insulin-independent duration after SII exceeded that of the initial transplant(s) (24.8+/-2.2 vs. 14.2+/-2.6 months by Kaplan-Meier analysis, P=0.009). Subjects show improved glycemic control after SII (HbA1c 7.0%+/-0.2% pre-SII vs. 6.1%+/-0.2% post-SII, P=0.005) and did not become immunosensitized. Using current protocols, SII in the absence of exenatide results in impressive insulin-independence rates and the durability of insulin independence seems to be promising. However, a beneficial effect of exenatide should not be discounted until tested in randomized controlled studies.

β-Cell Secretory Capacity and Demand in Recipients of Islet, Pancreas, and Kidney Transplants

beta-Cell secretory capacity, a measure of functional beta-cell mass, is often impaired in islet transplant recipients, likely because of a low engrafted beta-cell mass, although calcineurin inhibitor toxicity is often cited as the explanation. We sought to determine whether use of the calcineurin inhibitor tacrolimus was associated with reduced beta-cell secretory capacity or with increased beta-cell secretory demand independent of engrafted islet mass. We compared metabolic measures in five intraportal islet recipients vs. 10 normal controls and in seven portally-drained pancreas-kidney and eight nondiabetic kidney recipients vs. nine kidney donor controls. All transplant groups received comparable exposure to tacrolimus, and each transplant group was matched for kidney function to its respective control group. All participants underwent glucose-potentiated arginine testing where acute insulin responses to arginine (5 g) were determined under fasting (AIR(arg)), 230 mg/dl (AIR(pot)), and 340 mg/dl (AIR(max)) clamp conditions, and AIR(max) gives the beta-cell secretory capacity. Insulin sensitivity (M/I) and proinsulin secretory ratios (PISRs) were assessed to determine whether tacrolimus increased beta-cell secretory demand. Insulin responses were significantly lower than normal in the islet group for AIR(arg) (P < 0.05), AIR(pot) (P < 0.01), and AIR(max) (P < 0.01), whereas responses in the pancreas-kidney and kidney transplant groups were not different than in the kidney donor group. M/I and PISRs were not different in any of the transplant vs. control groups. Impaired beta-cell secretory capacity in islet transplantation is best explained by a low engrafted beta-cell mass and not by a deleterious effect of tacrolimus.

Limited Sampling Strategies for Predicting Area Under the Concentration-Time Curve of Mycophenolic Acid in Islet Transplant Recipients

Mycophenolate mofetil is widely used in islet transplant recipients and its active metabolite, mycophenolic acid (MPA), exhibits wide pharmacokinetic variability. However, to our knowledge, no limited sampling strategy (LSS) exists for monitoring MPA in this subpopulation. To define optimal LSSs for MPA monitoring and to test their predictive performance in islet transplant recipients. After written informed consent was obtained and upon administration of a steady-state morning mycophenolate mofetil dose, blood samples were collected at 0, 0.3, 0.6, 1, 1.5, 2, 3, 4, 6, 8, 10, and 12 hours from 16 stable islet transplant recipients. MPA concentrations were measured by a validated high-performance liquid chromatography method with ultraviolet detection and pharmacokinetic parameters analyzed by noncompartmental modeling. All 16 patients' profiles were used to develop the LSSs via multiple regression analysis. Potential LSSs were restricted to ones having R(2) 0.90 or greater and 3 or fewer time points within the first 4 hours postdose. Resulting equations were validated for their predictive performance using the jackknife method, with acceptable criteria for bias and precision preset to within +/-15%. In addition, 14 published LSSs (in the renal transplant population) were tested in our islet transplant patients. Five LSSs met preset criteria and had conventional sampling times: AUC = 1.783 + 1.248C1 + 0.888C2 + 8.027C4 (R2 = 0.98, bias = -3.09%, precision = 9.53%) AUC = 2.778 + 1.413C1 + 0.963C3 + 7.511C4 (R2 = 0.97, bias = -3.22%, precision = 11.02%) AUC = 1.448 + 1.239C1 + 0.271C1.5 + 9.108 C4 (R2 = 0.96, bias = -1.90%, precision = 11.46) AUC = 1.410 - 0.259C0 + 1.443C1 + 9.622C4 (R2 = 0.96, bias = -2.68%, precision = 11.53%) AUC = 1.547 + 1.417C1 + 9.448C4 (R2 = 0.96, bias = -2.46%, precision = 11.14%) where AUC = area under the concentration-time curve. None of the other published LSSs in the renal transplant population met the preset criteria for bias and precision. To our knowledge, these are the first precise and accurate LSSs for predicting MPA AUC developed specifically for islet transplant recipients. The LSS that we recommend is the one utilizing 2 concentrations: AUC = 1.547 + 1.417C1 + 9.448C4. This equation is convenient and clinically feasible. Other islet transplant centers may wish to validate our equation in their population or use our template as a guide to develop accurate and precise LSSs specific to their patient population.

Lipotoxicity and Decreased Islet Graft Survival

OBJECTIVETo evaluate if baseline serum lipids are associated with islet graft survival in type 1 diabetes islet transplant (ITx) recipients.RESEARCH DESIGN AND METHODSBaseline fasting lipid profile was collected from 44 ITx recipients. Comparisons were performed between subjects below and above the median values of each lipid fraction. Differences in outcomes were compared by Kaplan-Meier curves and Cox regression analysis.RESULTSSubjects with baseline fasting plasma triglycerides and VLDL cholesterol above the median had shorter islet graft survival (triglycerides: 39.7 ± 6.1 vs. 61.3 ± 6.6 months, P = 0.029, and VLDL: 41.5 ± 5.7 vs. 62.8 ± 7.3 months, P = 0.032). Total, LDL, and HDL cholesterol did not influence islet function. Triglycerides (odds ratio 2.97 [95% CI 1.03–8.52], P = 0.044) maintained its association with graft failure after adjustments for confounders.CONCLUSIONSHigher baseline triglycerides are associated with earlier decline in islet graft function. Prospective clinical trials should address whether it is directly caused by lipotoxicity and if strategies focusing on lowering serum lipids may prolong islet graft survival.

Long-Term Metabolic and Hormonal Effects of Exenatide on Islet Transplant Recipients with Allograft Dysfunction

The initial success of islet transplantation (ITx) is followed by graft dysfunction (GDF) and insulin reintroduction. Exenatide, a GLP-1 agonist, increases insulin and decreases glucagon secretion and has potential for beta-cell regeneration. To improve functional islet mass, exenatide treatment was given to ITx recipients with GDF. The objective of this study was to assess metabolic and hormonal effects of exenatide in GDF. In this prospective, single-arm, nonrandomized study, 11 type 1 diabetes recipients of ITx with GDF had HbA1c, weight, insulin requirements, and 5-h mixed meal tolerance test (MMTT; with/without exenatide given before test) at baseline, 3, 6, and 12 months after initiating exenatide treatment. Baseline MMTT showed postprandial hyperglycemia and hyperglucagonemia. Daily exenatide treatment resulted in improved glucose, increased amylin/insulin ratio, and decreased proinsulin/insulin ratio as assessed by MMTT. Glucagon responses remained unchanged. Exenatide administration 1 h before MMTT showed decreased glucagon and glucose at 0 min and attenuation in their postprandial rise. Time-to-peak glucose was delayed, followed by insulin, proinsulin, amylin, and C-peptide, indicating glucose-driven insulin secretion. Five subjects completed 12-month follow-up. Glucose and glucagon suppression responses after MMTT with exenatide were no longer observed. Retrospective 3-month analysis of these subjects revealed higher and sustained glucagon levels that did not suppress as profoundly with exenatide administration, associated with higher glucose levels and increased C-peptide responses. In conclusion, Exenatide suppresses the abnormal postprandial hyperglucagonemia and hyperglycemia observed in GDF. Changes in amylin and proinsulin secretion may reflect more efficient insulin processing. Different degrees of responsiveness to exenatide were identified. These may help guide the clinical management of ITx recipients.

Pretransplant Immune Parameters Associate With Islet Allograft Outcome

Extensive and informative immunological assessments of islet transplant recipients have been limited due, in part, to the smaller numbers of patients transplanted compared with solid organ trials. Limitations related to blood volume and the logistical challenges of collecting multiple posttransplant samples for drug levels as well as clinical and metabolic parameters also pose challenges. Several variables affect islet allograft outcome, including allo- and autoimmune responses to transplanted islets, β-cell mass and islet quality, efficacy of the immunosuppressive regimen and its effect on islet function, as well as glycemic control. In fact, much debate has centered on whether or not islet attrition is due to immune-mediated loss, death of overworked cells caused by insufficient mass, and/or diabetogenic effect of various immune intervention agents. In addition, many of these parameters may have differing effects based on the transplanted mass, with marginal mass transplants being more susceptible to immune-mediated or stress-induced loss. Recently, several studies have demonstrated immunological alterations in islet allograft patients. Posttransplant changes in lymphocytes and lymphocyte subsets were reported to be variable depending on the immune suppression used but have not yet been associated with graft status or specific clinical outcomes (1–4). Higher posttransplant cytotoxic T-cell precursor frequency against donor antigens was associated with poorer outcome at 6 months in recipients treated with sirolimus-based maintenance therapy but not tacrolimus–mycophenolate mofetil (5). In one study, cytokine production in allogeneic mixed lymphocyte reactions (MLRs) was skewed toward …

Impaired Proinsulin Processing is a Characteristic of Transplanted Islets

We sought to determine whether recipients of islet transplants have defective proinsulin processing. Individuals who had islet allo- or autotransplantation were compared to healthy nondiabetic subjects. Insulin (I), total proinsulin (TP), intact proinsulin and C-peptide (CP) were measured in samples of fasting serum by immunoassay, and the ratios of TP/TP+I and TP/CP were calculated. Islet allotransplant recipients had elevated TP levels relative to nondiabetic controls (16.8 [5.5-28.8] vs. 8.4 [4.0-21.8] pmol/L; p < 0.05) and autologous transplant recipients (7.3 [0.3-82.3] pmol/L; p < 0.05). Islet autotransplant recipients had significantly higher TP/TP+I ratios relative to nondiabetic controls (35.9 +/- 6.4 vs. 13.9 +/- 1.4%; p < 0.001). Islet allotransplant recipients, some of whom were on insulin, tended to have higher TP/TP+I ratios. The TP/CP ratio was significantly higher in both islet autotransplant (8.9 [0.6-105.2]; p < 0.05) and allotransplant recipients (2.4 [0.8-8.8]; p < 0.001) relative to nondiabetic controls (1.4 [0.5-2.6]%). Consistent with these findings, TP/TP+I and TP/CP values in islet autotransplant recipients increased significantly by 1-year posttransplant compared to preoperative levels (TP/CP: 3.8 +/- 0.6 vs. 23.3 +/- 7.9%; p < 0.05). Both allo- and autotransplant subjects who received <10,000 IE/kg had higher TP/CP ratios than those who received >10,000 IE/kg. Islet transplant recipients exhibit defects in the processing of proinsulin similar to that observed in subjects with type 2 diabetes manifest as higher levels of total proinsulin and increased TP/TP+I and TP/CP ratios.