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

International Survey of Clinical Monitoring Practices in Pancreas and Islet Transplantation

BACKGROUND

The long-term outcomes of both pancreas and islet allotransplantation have been compromised by difficulties in the detection of early graft dysfunction at a time when a clinical intervention can prevent further deterioration and preserve allograft function. The lack of standardized strategies for monitoring pancreas and islet allograft function prompted an international survey established by an International Pancreas and Islet Transplant Association/European Pancreas and Islet Transplant Association working group.

METHODS

A global survey was administered to 24 pancreas and 18 islet programs using Redcap. The survey addressed protocolized and for-cause immunologic and metabolic monitoring strategies following pancreas and islet allotransplantation. All invited programs completed the survey.

RESULTS

The survey identified that in both pancreas and islet allograft programs, protocolized clinical monitoring practices included assessing body weight, fasting glucose/C-peptide, hemoglobin A1c, and donor-specific antibody. Protocolized monitoring in islet transplant programs relied on the addition of mixed meal tolerance test, continuous glucose monitoring, and autoantibody titers. In the setting of either suspicion for rejection or serially increasing hemoglobin A1c/fasting glucose levels postpancreas transplant, Doppler ultrasound, computed tomography, autoantibody titers, and pancreas graft biopsy were identified as adjunctive strategies to protocolized monitoring studies. No additional assays were identified in the setting of serially increasing hemoglobin A1c levels postislet transplantation.

CONCLUSIONS

This international survey identifies common immunologic and metabolic monitoring strategies utilized for protocol and for cause following pancreas and islet transplantation. In the absence of any formal studies to assess the efficacy of immunologic and metabolic testing to detect early allograft dysfunction, it can serve as a guidance document for developing monitoring algorithms following beta-cell replacement.

Human pluripotent stem-cell-derived islets ameliorate diabetes in non-human primates

Human pluripotent stem-cell-derived islets (hPSC-islets) are a promising cell resource for diabetes treatment^1,2. However, this therapeutic strategy has not been systematically assessed in large animal models physiologically similar to humans, such as non-human primates³. In this study, we generated islets from human chemically induced pluripotent stem cells (hCiPSC-islets) and show that a one-dose intraportal infusion of hCiPSC-islets into diabetic non-human primates effectively restored endogenous insulin secretion and improved glycemic control. Fasting and average pre-prandial blood glucose levels significantly decreased in all recipients, accompanied by meal or glucose-responsive C-peptide release and overall increase in body weight. Notably, in the four long-term follow-up macaques, average hemoglobin A1c dropped by over 2% compared with peak values, whereas the average exogenous insulin requirement reduced by 49% 15 weeks after transplantation. Collectively, our findings show the feasibility of hPSC-islets for diabetic treatment in a preclinical context, marking a substantial step forward in clinical translation of hPSC-islets.

Immunological aspects of allogeneic pancreatic islet transplantation: a comparison between mouse and human

Pancreatic islet allotransplantation is a treatment for patients with severe forms of type 1 diabetes. As long-term graft function and survival are not yet optimal, additional studies are warranted in order to continue improving transplant outcomes. The mechanisms of islet graft loss and tolerance induction are often studied in murine diabetes models. Despite numerous islet transplantation studies successfully performed over recent years, translation from experimental mouse models to human clinical application remains elusive. This review aims at critically discussing the strengths and limitations of current mouse models of diabetes and experimental islet transplantation. In particular, we will analyze the causes leading to diabetes and compare the immunological mechanisms responsible for rejection between mouse and human. A better understanding of the experimental mouse models should facilitate translation to human clinical application.

Functional Role of Circular RNA in Regenerative Medicine

Every year, millions of people around the world suffer from different forms of tissue trauma. Regenerative medicine refers to therapy that replaces the injured organ or cells. Stem cells are the frontiers and hotspots of current regenerative medicine research. Circular RNAs (circRNAs) are essential for the early development of many species. It was found that they could guide stem cell differentiation through interacting with certain microRNAs (miRNAs). Based on this concept, it is meaningful to look into how circRNAs influence stem cells and its role in regenerative medicine. In this chapter we will discuss the functional roles of circRNAs in the prevention, repair, or progression of chronic diseases, through the communication between stem cells.

Stimulation of vascularization of a subcutaneous scaffold applicable for pancreatic islet-transplantation enhances immediate post-transplant islet graft function but not long-term normoglycemia

The liver as transplantation site for pancreatic islets is associated with significant loss of islets, which can be prevented by grafting in a prevascularized, subcutaneous scaffold. Supporting vascularization of a scaffold to limit the period of ischemia is challenging and was developed here by applying liposomes for controlled release of angiogenic factors. The angiogenic capacity of platelet-derived growth factor, vascular endothelial growth factor, acidic fibroblast growth factor (aFGF), and basic FGF were compared in a tube formation assay. Furthermore, the release kinetics of different liposome compositions were tested. aFGF and L-α-phosphatidylcholine/cholesterol liposomes were selected to support vascularization. Two dosages of aFGF-liposomes (0.5 and 1.0 μg aFGF per injection) were administered weekly for a month after which islets were transplanted. We observed enhanced efficacy in the immediate post-transplant period compared to the untreated scaffolds. However, on the long-term, glucose levels of the aFGF treated animals started to increase to diabetic levels. These results suggest that injections with aFGF liposomes do improve vascularization and the immediate restoration of blood glucose levels but does not facilitate the long-term survival of islets. Our data emphasize the need for long-term studies to evaluate potential beneficial and adverse effects of vascularization protocols of scaffolds. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2533-2542, 2017.

The Efficacy of a Prevascularized, Retrievable Poly(D,L,-lactide-co-ε-caprolactone) Subcutaneous Scaffold as Transplantation Site for Pancreatic Islets

BACKGROUND

The liver as transplantation site for human pancreatic islets is a harsh microenvironment for islets and it lacks the ability to retrieve the graft. A retrievable, extrahepatic transplantation site that mimics the pancreatic environment is desired. Ideally, this transplantation site should be located subdermal for easy surgical-access but this never resulted in normoglycemia. Here, we describe the design and efficacy of a novel prevascularized, subcutaneously implanted, retrievable poly (D,L-lactide-co-ε-caprolactone) scaffold.

METHOD

Three dosages of rat islets, that is, 400, 800, and 1200, were implanted in immune compromised mice to test the efficacy (n = 5). Islet transplantation under the kidney capsule served as control (n = 5). The efficacy was determined by nonfasting blood glucose measurements and glucose tolerance tests.

RESULTS

Transplantation of 800 (n = 5) and 1200 islets (n = 5) into the scaffold reversed diabetes in respectively 80 and 100% of the mice within 6.8 to 18.5 days posttransplant. The marginal dose of 400 islets (n = 5) induced normoglycemia in 20%. The glucose tolerance test showed major improvement of the glucose clearance in the scaffold groups compared to diabetic controls. However, the kidney capsule was slightly more efficacious because all 800 (n = 5) and 1200 islets (n = 5) recipients and 40% of the 400 islets (n = 5) recipients became normoglycemic within 8 days. Removal of the scaffolds or kidney grafts resulted in immediate return to hyperglycemia. Normoglycemia was not achieved with 1200 islets in the unmodified skin group.

CONCLUSIONS

Our findings demonstrate that the prevascularized poly (D,L-lactide-co-ε-caprolactone) scaffold maintains viability and function of islets in the subcutaneous site.

Clinical pancreatic islet transplantation

Clinical pancreatic islet transplantation can be considered one of the safest and least invasive transplant procedures. Remarkable progress has occurred in both the technical aspects of islet cell processing and the outcomes of clinical islet transplantation. With >1,500 patients treated since 2000, this therapeutic strategy has moved from a curiosity to a realistic treatment option for selected patients with type 1 diabetes mellitus (that is, those with hypoglycaemia unawareness, severe hypoglycaemic episodes and glycaemic lability). This Review outlines the techniques required for human islet isolation, in vitro culture before the transplant and clinical islet transplantation, and discusses indications, optimization of recipient immunosuppression and management of adjunctive immunomodulatory and anti-inflammatory strategies. The potential risks, long-term outcomes and advances in treatment after the transplant are also discussed to further move this treatment towards becoming a more widely available option for patients with type 1 diabetes mellitus and eventually a potential cure.

Synergistic effect of PEGylation and pentoxifylline addition on immunoprotection of pancreatic islets

In this study, a method is proposed to reduce immunological response of immune system against Langerhans islets by PEGylation of islets combined with adjuvant therapy. For this purpose, the best composition for a mixture of succinimidyl valeric acid activated mPEG (mPEG-SVA) with different molecular weights (MWs) and for a mixture of succinimidyl carbonate activated mPEG (mPEG-SC) with different MWs was determined separately. Then, the effect of pentoxifylline (PTX) as an adjuvant drug on immunological response against PEGylated islets at best mPEG composition was studied. The extent of mPEGs reaction, the amount of interlukin-2 (IL-2) and perforin secretion, and the viability of lymphocytes and islets in homo and co-cultures in the presence of PTX at different concentrations were considered for the in vitro evaluation of the proposed method. It was found, that a mixture of mPEG-SVA with MWs of 10 and 5 kDa at a composition of 75 and 25%, respectively, was the best formulation. Also, the addition of PTX drug to co-culture medium increased the protection of PEGylated islets against immune system and a concentration of 75 μg mL^-1 of PTX was suitable for islet protection with no adverse effect on immune cells.

Alloimmune Monitoring After Islet Transplantation: A Prospective Multicenter Assessment of 25 Recipients

Islet transplantation is an effective treatment for selected patients with type 1 diabetes. However, an accurate test still lacks for the early detection of graft rejection. Blood samples were prospectively collected in four university centers (Geneva, Grenoble, Montpellier, and Strasbourg). Peripheral blood mononuclear cells were stimulated with donor splenocytes in the presence of interleukin-2. After 24 h of incubation, interferon- (IFN-) ELISpot analysis was performed. After a total of 5 days of incubation, cell proliferation was assessed by fluorescence-activated cell sorting (FACS) analysis for Ki-67. Immunological events were correlated with adverse metabolic events determined by loss of 1 point of -score and/or an increased insulin intake 10%. Twenty-five patients were analyzed; 14 were recipients of islets alone, and 11 combined with kidney. Overall, 76% (19/25) reached insulin independence at one point during a mean follow-up of 30.7 months. IFN- ELISpot showed no detectable correlation with adverse metabolic events [area under the curve (AUC)=0.57]. Similarly, cell proliferation analysis showed no detectable correlation with adverse metabolic events (CD3+/CD4+ AUC=0.54; CD3+/CD8+ AUC=0.55; CD3/CD56+ AUC=0.50). CD3/CD56+ cell proliferation was significantly higher in patients with combined kidney transplantation versus islet alone (6 months, p=0.010; 12 months, p=0.016; and 24 months, p=0.018). Donor antigen-stimulated IFN- production and cell proliferation do not predict adverse metabolic events after islet transplantation. This suggests that the volume of transplanted islets is too small to produce a detectable systemic immune response and/or that alloimmune rejection is not the sole reason for the loss of islet graft function.

Stem cell therapy. Use of differentiated pluripotent stem cells as replacement therapy for treating disease

Pluripotent stem cells (PSCs) directed to various cell fates holds promise as source material for treating numerous disorders. The availability of precisely differentiated PSC-derived cells will dramatically affect blood component and hematopoietic stem cell therapies and should facilitate treatment of diabetes, some forms of liver disease and neurologic disorders, retinal diseases, and possibly heart disease. Although an unlimited supply of specific cell types is needed, other barriers must be overcome. This review of the state of cell therapies highlights important challenges. Successful cell transplantation will require optimizing the best cell type and site for engraftment, overcoming limitations to cell migration and tissue integration, and occasionally needing to control immunologic reactivity, as well as a number of other challenges. Collaboration among scientists, clinicians, and industry is critical for generating new stem cell-based therapies.

Treating diabetes with islet transplantation: lessons from the past decade in Lille

Type 1 diabetes (T1D) is due to the loss of both beta-cell insulin secretion and glucose sensing, leading to glucose variability and a lack of predictability, a daily issue for patients. Guidelines for the treatment of T1D have become stricter as results from the Diabetes Control and Complications Trial (DCCT) demonstrated the close relationship between microangiopathy and HbA1c levels. In this regard, glucometers, ambulatory continuous glucose monitoring, and subcutaneous and intraperitoneal pumps have been major developments in the management of glucose imbalance. Besides this technological approach, islet transplantation (IT) has emerged as an acceptable safe procedure with results that continue to improve. Research in the last decade of the 20th century focused on the feasibility of islet isolation and transplantation and, since 2000, the success and reproducibility of the Edmonton protocol have been proven, and the mid-term (5-year) benefit-risk ratio evaluated. Currently, a 5-year 50% rate of insulin independence can be expected, with stabilization of microangiopathy and macroangiopathy, but the possible side-effects of immunosuppressants, limited availability of islets and still limited duration of insulin independence restrict the procedure to cases of brittle diabetes in patients who are not overweight or have no associated insulin resistance. However, various prognostic factors have been identified that may extend islet graft survival and reduce the number of islet injections required; these include graft quality, autoimmunity, immunosuppressant regimen and non-specific inflammatory reactions. Finally, alternative injection sites and unlimited sources of islets are likely to make IT a routine procedure in the future.

Endocrine secretory reserve and proinsulin processing in recipients of islet of langerhans versus whole pancreas transplants

OBJECTIVE

β-Cells have demonstrated altered proinsulin processing after islet transplantation. We compare β-cell metabolic responses and proinsulin processing in pancreas and islet transplant recipients with respect to healthy control subjects.

RESEARCH DESIGN AND METHODS

We studied 15 islet and 32 pancreas transplant recipients. Islet subjects were subdivided into insulin-requiring (IR-ISL, n = 6) and insulin-independent (II-ISL, n = 9) groups. Ten healthy subjects served as control subjects. Subjects were administered an intravenous arginine stimulation test, and insulin, C-peptide, total proinsulin, intact proinsulin, and proinsulin fragment levels were determined from serum samples. Acute insulin response (AIR) and proinsulin processing rates were calculated.

RESULTS

We found that basal insulin and C-peptide levels were higher in the pancreas group than in all other groups. II-ISL patients had basal insulin and C-peptide levels similar to healthy control subjects. The IR-ISL group had significantly lower AIRs than all other groups. Basal processing rates were higher in the pancreas and II-ISL groups than in healthy control subjects and the IR-ISL group. After arginine stimulation, all groups had elevated processing rates, with the exception of the IR-ISL group.

CONCLUSIONS

Our data suggest that II-ISL transplant recipients can maintain basal metabolic parameters similar to healthy control subjects at the cost of a higher rate of proinsulin processing. IR-ISL transplant recipients, on the other hand, demonstrate both lower insulin response and lower basal rates of proinsulin processing even after arginine stimulation.

Alloantibody and autoantibody monitoring predicts islet transplantation outcome in human type 1 diabetes

Long-term clinical outcome of islet transplantation is hampered by the rejection and recurrence of autoimmunity. Accurate monitoring may allow for early detection and treatment of these potentially compromising immune events. Islet transplant outcome was analyzed in 59 consecutive pancreatic islet recipients in whom baseline and de novo posttransplant autoantibodies (GAD antibody, insulinoma-associated protein 2 antigen, zinc transporter type 8 antigen) and donor-specific alloantibodies (DSA) were quantified. Thirty-nine recipients (66%) showed DSA or autoantibody increases (de novo expression or titer increase) after islet transplantation. Recipients who had a posttransplant antibody increase showed similar initial performance but significantly lower graft survival than patients without an increase (islet autoantibodies P < 0.001, DSA P < 0.001). Posttransplant DSA or autoantibody increases were associated with HLA-DR mismatches (P = 0.008), induction with antithymocyte globulin (P = 0.0001), and pretransplant panel reactive alloantibody >15% in either class I or class II (P = 0.024) as independent risk factors and with rapamycin as protective (P = 0.006) against antibody increases. DSA or autoantibody increases after islet transplantation are important prognostic markers, and their identification could potentially lead to improved islet cell transplant outcomes.

Transplanted human pancreatic islets after long-term insulin independence

Long-term insulin independence after islets of Langerhans transplantation is rarely achieved. The aims of this study were to identify the histological and immunological features of islets transplanted in a type 1 diabetic patient who died of a cerebral hemorrhage after >13 years insulin independence. Islets were pooled from two donors with respectively one and five HLA mismatches. Insulin-positive islets were found throughout the right and left liver, and absent in the pancreas. Two- and three-dimensional analysis showed that islets lost their initial rounded and compact morphology, had a mean diameter of 136 μm and were constituted of an unfolded epithelial band of 39.1 μm. Leukocyte phenotyping showed no evidence of a tolerogenic environment in the islet-containing portal spaces. Finally, HLA typing of microdissected islets showed HLA from the best matched donor in all 23 microdissection samples, compared to 1/23 for the least matched donor. This case report demonstrates that allogeneic islets can survive over 13 years while maintaining insulin independence. Allogeneic islets had unique morphologic features and implanted in the liver regardless of their size. Finally, our results suggest that, in this case, rejection had been prevalent over autoimmunity, although this hypothesis warrants further investigation.

Immune rejection after pancreatic islet cell transplantation: in vivo dual contrast-enhanced MR imaging in a mouse model

PURPOSE

To detect adoptively transferred immune attack in a mouse model of islet cell transplantation by using a long-circulating paramagnetic T1 contrast agent, a protected graft copolymer (PGC) that is covalently linked to gadolinium-diethylenetriaminepentaacetic acid with fluorescein isothiocyanate (Gd-DTPA-F), which accumulates in the sites of inflammation that are characterized by vascular disruption.

MATERIALS AND METHODS

All animal experiments were performed in compliance with institutional guidelines and approved by the subcommittee on research animal care. Six nonobese diabetic severe combined immunodeficiency mice received transplanted human islet cells under the kidney capsule and adoptively transferred 5 × 10(6) splenocytes from 6-week-old nonobese diabetic mice. These mice also served as control subjects for comparison of pre- and postadoptive transfer MR imaging results. Mice that received phosphate-buffered saline solution only were included as nonadoptive-transfer control subjects (n = 2). In vivo magnetic resonance (MR) imaging was performed before and 17 hours after intravenous injections of PGC-Gd-DTPA-F, followed by histologic examination. Statistical differences were analyzed by means of a paired Student t test and repeated two-way analysis of variance.

RESULTS

MR imaging results showed significantly greater accumulation of PGC-Gd-DTPA-F in the graft area after immune attack initiated by adoptive transfer of splenocytes compared with that of the same area before the transfer (T1, 137.2 msec ± 39.3 and 239.5 msec ± 17.6, respectively; P < .001). These results were confirmed at histologic examination, which showed considerable leakage of the contrast agent into the islet cell interstitium.

CONCLUSION

PGC-Gd-DTPA-F-enhanced MR imaging allows for the in vivo assessment of vascular damage of the graft T cell challenge.

Posttransplant Cellular Immune Reactivity against Donor Antigen Correlates with Clinical Islet Transplantation Outcome: Towards a Better Posttransplant Monitoring

The aim of the present study was to assess the efficiency of cell-based immune assays in the detection of alloreactivity after islet transplantation and to correlate these results with clinical outcome. Mixed lymphocyte cultures were performed with peripheral blood mononuclear cells from recipients ( n = 14), donors, or third party. The immune reactivity was assessed by the release of IFN-γ (ELISpot), cell proliferation (FACS analysis for Ki67), and cytokine quantification (Bioplex). Islet function correlated with the number of IFN-γ-secreting cells following incubation with donor cells ( p = 0.007, r = –0.50), but not with third party cells ( p = 0.61). Similarly, a high number of donor-specific proliferating cells was associated with a low islet function ( p = 0.006, r = −0.51). Proliferating cells were mainly CD3+CD4+ lymphocytes and CD3-CD56+ natural killer cells (with low levels of CD3+CD8+ lymphocytes). Patients with low islet function had increased levels of CD4+Ki67+cells ( p ≤ 0.0001), while no difference was observed in CD8+Ki67+ and CD56+Ki67+ cells. IFN-γ, IL-5, and IL-17 levels were increased in patients with low islet function, but IL-10 levels tended to be lower. IFN-γ-ELISpot, proliferation, and cytokines were similarly accurate in predicting clinical outcome (AUC = 0.77 ± 0.088, 0.85 ± 0.084, and 0.88 ± 0.074, respectively). Cellular immune reactivity against donor cells correlates with posttransplant islet function. The tested assays have the potential to be of substantial help in the management of islet graft recipients and deserve prospective validation.

Induced pluripotent stem (iPS) cells inhibit apoptosis and fibrosis in streptozotocin-induced diabetic rats

Recent data suggests that transplanted bone marrow stem cells improve cardiac function in streptozotocin induced diabetic cardiomyopathy (SIDC). However, whether modified embryonic stem (ES) cells, induced pluripotent stem (iPS) cells, or factors released from these cells can inhibit apoptosis and fibrosis remains completely unknown. Therefore, we hypothesized that transplanted ES cells overexpressing pancreatic transcription factor 1 a (Ptf1a), a propancreatic endodermal transcription factor, iPS cells, or their respective conditioned media (CM) will attenuate cardiac remodeling and improve cardiac function in SIDC. Experimental diabetes was induced in male Sprague-Dawley rats (8-10 weeks old) by intraperitoneal injections of streptozotocin (STZ) (65 mg/kg body weight). Animals were divided into different groups including control, STZ, stem cells, and CM. Histology, TUNEL, caspase-3 activity, sarcomeric α-actin, and DHE stainings were performed to assess cardiac apoptosis, fibrosis, and oxidative stress. Animals transplanted with ES cells, iPS cells, or both CM showed a significant (p < 0.05) reduction in apoptosis compared with STZ treated animals. Furthermore, our data also shows that active apoptosis was present in cardiac myocytes as confirmed with combined stainings with TUNEL, sarcomeric α-actin, and active caspase-3 antibodies. Increased oxidative stress as evidenced by DHE staining was significantly (p < 0.05) reduced following stem cell or CM transplantation. Moreover, stem cells or CM also attenuated increased interstitial and vascular fibrosis in SIDC hearts. Echocardiography analysis showed a significant (p < 0.05) improvement in fractional shortening in stem cell and CM transplanted groups compared with respective controls. In conclusion, our data suggest that transplanted stem cells or their CM inhibit apoptosis, reduce fibrosis, and improve cardiac function in STZ-treated diabetic rats.

Molecular imaging: a promising tool to monitor islet transplantation

Replacement of insulin production by pancreatic islet transplantation has great potential as a therapy for type 1 diabetes mellitus. At present, the lack of an effective approach to islet grafts assessment limits the success of this treatment. The development of molecular imaging techniques has the potential to fulfill the goal of real-time noninvasive monitoring of the functional status and viability of the islet grafts. We review the application of a variety of imaging modalities for detecting endogenous and transplanted beta-cell mass. The review also explores the various molecular imaging strategies for assessing islet delivery, the metabolic effects on the islet grafts as well as detection of immunorejection. Here, we highlight the use of combined imaging and therapeutic interventions in islet transplantation and the in vivo monitoring of stem cells differentiation into insulin-producing cells.

Noninvasive imaging techniques in islet transplantation

Since the Edmonton trials, insulin independence can reproducibly be achieved after islet transplantation. However, a majority of patients resume insulin treatment in the first 5 years after transplantation. Several mechanisms have been proposed but are difficult to pinpoint in one particular patient. Current tools for the metabolic monitoring of islet grafts indicate islet dysfunction when it is too late to take action. Noninvasive imaging of transplanted islets could be used to study β-cell mass and β-cell function just after infusion, during vascularization or autoimmune and alloimmune attacks. This review will focus on the most recent advances in various imaging techniques (bioluminescence imaging, fluorescence optical imaging, MRI, and positron emission tomography). Emphasis will be placed on pertinent approaches for translation to human practice.