Magnetic Resonance Imaging of Mouse Islet Grafts Labeled with Novel Chitosan-Coated Superparamagnetic Iron Oxide Nanoparticles

Object

To better understand the fate of islet isografts and allografts, we utilized a magnetic resonance (MR) imaging technique to monitor mouse islets labeled with a novel MR contrast agent, chitosan-coated superparamagnetic iron oxide (CSPIO) nanoparticles.

Materials and Methods

After being incubated with and without CSPIO (10 µg/ml), C57BL/6 mouse islets were examined under transmission electron microscope (TEM) and their insulin secretion was measured. Cytotoxicity was examined in α (αTC1) and β (NIT-1 and βTC) cell lines as well as islets. C57BL/6 mice were used as donors and inbred C57BL/6 and Balb/c mice were used as recipients of islet transplantation. Three hundred islets were transplanted under the left kidney capsule of each mouse and then MR was performed in the recipients periodically. At the end of study, the islet graft was removed for histology and TEM studies.

Results

After incubation of mouse islets with CSPIO (10 µg/mL), TEM showed CSPIO in endocytotic vesicles of α- and β-cells at 8 h. Incubation with CSPIO did not affect insulin secretion from islets and death rates of αTC1, NIT-1 and βTC cell lines as well as islets. After syngeneic and allogeneic transplantation, grafts of CSPIO-labeled islets were visualized on MR scans as persistent hypointense areas. At 8 weeks after syngeneic transplantation and 31 days after allogeneic transplantation, histology of CSPIO-labeled islet grafts showed colocalized insulin and iron staining in the same areas but the size of allografts decreased with time. TEM with elementary iron mapping demonstrated CSPIO distributed in the cytoplasm of islet cells, which maintained intact ultrastructure.

Conclusion

Our results indicate that after syngeneic and allogeneic transplantation, islets labeled with CSPIO nanoparticles can be effectively and safely imaged by MR.     

PD-L1 Deficiency within Islets Reduces Allograft Survival in Mice

Background

Islet transplantation may potentially cure type 1 diabetes mellitus (T1DM). However, immune rejection, especially that induced by the alloreactive T-cell response, remains a restraining factor for the long-term survival of grafted islets. Programmed death ligand-1 (PD-L1) is a negative costimulatory molecule. PD-L1 deficiency within the donor heart accelerates allograft rejection. Here, we investigate whether PD-L1 deficiency in donor islets reduces allograft survival time.

Methods

Glucose Stimulation Assays were performed to evaluate whether PD-L1 deficiency has detrimental effects on islet function. Islets isolated from PDL1-deficient mice or wild- type (WT) mice (C57BL/6j) were implanted beneath the renal capsule of streptozotocin (STZ)-induced diabetic BALB/c mice. Blood glucose levels and graft survival time after transplantation were monitored. Moreover, we analyzed the residual islets, infiltrating immune cells and alloreactive cells from the recipients.

Results

PD-L1 deficiency within islets does not affect islet function. However, islet PD-L1 deficiency increased allograft rejection and was associated with enhanced inflammatory cell infiltration and recipient T-cell alloreactivity.

Conclusions

This is the first report to demonstrate that PD-L1 deficiency accelerated islet allograft rejection and regulated recipient alloimmune responses.     

Beneficial Effect of Insulin Treatment on Islet Transplantation Outcomes in Akita Mice

Islet transplantation is a promising potential therapy for patients with type 1 diabetes. The outcome of islet transplantation depends on the transplantation of a sufficient amount of β-cell mass. However, the initial loss of islets after transplantation is problematic. We hypothesized the hyperglycemic status of the recipient may negatively affect graft survival. Therefore, in the present study, we evaluated the effect of insulin treatment on islet transplantation involving a suboptimal amount of islets in Akita mice, which is a diabetes model mouse with an Insulin 2 gene missense mutation. Fifty islets were transplanted under the left kidney capsule of the recipient mouse with or without insulin treatment. For insulin treatment, sustained-release insulin implants were implanted subcutaneously into recipient mice 2 weeks before transplantation and maintained for 4 weeks. Islet transplantation without insulin treatment did not reverse hyperglycemia. In contrast, the group that received transplants in combination with insulin treatment exhibited improved fasting blood glucose levels until 18 weeks after transplantation, even after insulin treatment was discontinued. The group that underwent islet transplantation in combination with insulin treatment had better glucose tolerance than the group that did not undergo insulin treatment. Insulin treatment improved graft survival from the acute phase (i.e., 1 day after transplantation) to the chronic phase (i.e., 18 weeks after transplantation). Islet apoptosis increased with increasing glucose concentration in the medium or blood in both the in vitro culture and in vivo transplantation experiments. Expression profile analysis of grafts indicated that genes related to immune response, chemotaxis, and inflammatory response were specifically upregulated when islets were transplanted into mice with hyperglycemia compared to those with normoglycemia. Thus, the results demonstrate that insulin treatment protects islets from the initial rapid loss that is usually observed after transplantation and positively affects the outcome of islet transplantation in Akita mice.     

Maintenance of Islet Morphology Is Beneficial for Transplantation Outcome in Diabetic Mice

We have previously shown that co-transplantation of islets and Mesenchymal Stem Cells (MSCs) improves islet graft function and revascularisation, which was associated with the maintenance of normal islet morphology. The aim of the current study was to determine whether maintaining islet morphology in the absence of additional islet-helper cells would improve transplantation outcome in diabetic mice. Islets were isolated from C57BL/6 mice. Recipient streptozotocin-diabetic C57BL/6 mice were transplanted with a minimal mass of 150 islets as a single pellet or islets that were either manually dispersed or dispersed within a matrigel plug beneath the kidney capsule. Blood glucose concentrations were monitored for one month. Islet graft morphology and vascularisation were analysed by histology. Islets dispersed either alone or within matrigel plugs maintained near normal morphology, in contrast to pelleted islets, where individual islets fused to form large endocrine aggregates. The vascularisation of manually dispersed islets and islets dispersed within matrigel plugs was increased relative to respective control pelleted islet grafts. After one month 1/6 mice transplanted with pelleted islets cured compared to 5/6 mice transplanted with manually dispersed islets. The curative capacity of islets dispersed in matrigel was also better than that of pelleted islets (5/8 islet-matrigel implanted mice vs. 1/7 mice transplanted with pelleted islets cured by one month). Therefore, this study demonstrates that the maintenance of islet morphology is associated with improved graft function and revascularisation in diabetic mice.     

The Effects of Exendin-4 Treatment on Graft Failure: An Animal Study Using a Novel Re-Vascularized Minimal Human Islet Transplant Model

Islet transplantation has become a viable clinical treatment, but is still compromised by long-term graft failure. Exendin-4, a glucagon-like peptide 1 receptor agonist, has in clinical studies been shown to improve insulin secretion in islet transplanted patients. However, little is known about the effect of exendin-4 on other metabolic parameters. We therefore aimed to determine what influence exendin-4 would have on revascularized minimal human islet grafts in a state of graft failure in terms of glucose metabolism, body weight, lipid levels and graft survival. Introducing the bilateral, subcapsular islet transplantation model, we first transplanted diabetic mice with a murine graft under the left kidney capsule sufficient to restore normoglycemia. After a convalescent period, we performed a second transplantation under the right kidney capsule with a minimal human islet graft and allowed for a second recovery. We then performed a left-sided nephrectomy, and immediately started treatment with exendin-4 with a low (20μg/kg/day) or high (200μg/kg/day) dose, or saline subcutaneously twice daily for 15 days. Blood was sampled, blood glucose and body weight monitored. The transplanted human islet grafts were collected at study end point and analyzed. We found that exendin-4 exerts its effect on failing human islet grafts in a bell-shaped dose-response curve. Both doses of exendin-4 equally and significantly reduced blood glucose. Glucagon-like peptide 1 (GLP-1), C-peptide and pro-insulin were conversely increased. In the course of the treatment, body weight and cholesterol levels were not affected. However, immunohistochemistry revealed an increase in beta cell nuclei count and reduced TUNEL staining only in the group treated with a low dose of exendin-4 compared to the high dose and control. Collectively, these results suggest that exendin-4 has a potential rescue effect on failing, revascularized human islets in terms of lowering blood glucose, maintaining beta cell numbers, and improving metabolic parameters during hyperglycemic stress.     

Overexpression of thioredoxin in islets transduced by a lentiviral vector prolongs graft survival in autoimmune diabetic NOD mice

   

Pancreatic islet transplantation is considered an appropriate treatment to achieve insulin independence in type I diabetic patients. However, islet isolation and transplantation-induced oxidative stress and autoimmune-mediated destruction are still the major obstacles to the long-term survival of graft islets in this potential therapy. To protect islet grafts from inflammatory damage and prolong their survival, we transduced islets with an antioxidative gene thioredoxin (TRX) using a lentiviral vector before transplantation. We hypothesized that the overexpression of TRX in islets would prolong islet graft survival when transplanted into diabetic non-obese diabetic (NOD) mice.     

Combined Strategy of Endothelial Cells Coating,Sertoli Cells Coculture and Infusion Improves Vascularization and Rejection Protection of Islet Graft

Improving islet graft revascularization and inhibiting rejection become crucial tasks for prolonging islet graft survival. Endothelial cells (ECs) are the basis of islet vascularization and Sertoli cells (SCs) have the talent to provide nutritional support and exert immunosuppressive effects. We construct a combined strategy of ECs coating in the presence of nutritious and immune factors supplied by SCs in a co-culture system to investigate the effect of vascularization and rejection inhibition for islet graft. In vivo, the combined strategy improved the survival and vascularization as well as inhibited lymphocytes and inflammatory cytokines. In vitro, we found the combinatorial strategy improved the function of islets and the effect of ECs-coating on islets. Combined strategy treated islets revealed higher levels of anti-apoptotic signal molecules (Bcl-2 and HSP-32), survival and function related molecules (PDX-1, Ki-67, ERK1/2 and Akt ) and demonstrated increased vascular endothelial growth factor receptor 2 (KDR) and angiogenesis signal molecules (FAk and PLC-γ). SCs effectively inhibited the activation of lymphocyte stimulated by islets and ECs. Predominantly immunosuppressive cytokines could be detected in culture supernatants of the SCs coculture group. These results suggest that ECs-coating and Sertoli cells co-culture or infusion synergistically enhance islet survival and function after transplantation.     

Dipeptidyl Peptidase IV Inhibition Activates CREB and Improves Islet Vascularization through VEGF-A/VEGFR-2 Signaling Pathway

Substitution of pancreatic islets is a potential therapy to treat diabetes and it depends on reconstitution of islet’s capillary network. In this study, we addressed the question whether stabilization of Glucagon-Like-Peptide-1 (GLP-1) by inhibiting Dipeptidyl Peptidase-IV (DPP-IV) increases β-cell mass by modulating vascularization. Mouse or porcine donor islets were implanted under kidney capsule of diabetic mice treated with DPP-IV inhibitor sitagliptin. Grafts were analyzed for insulin production, β-cell proliferation and vascularization. In addition, the effect of sitagliptin on sprouting and Vascular Endothelial Growth Factor (VEGF)-A expression was examined ex vivo. The cAMP response element-binding (CREB) and VEGF-A/ Vascular Endothelial Growth Factor Receptor (VEGFR)-2 signaling pathway leading to islet vascularization was explored. Sitagliptin increased mean insulin content of islet grafts and area of insulin-positive tissue as well as β-cell proliferation. Interestingly, sitagliptin treatment also markedly increased endothelial cell proliferation, microvessel density and blood flow. Finally, GLP-1 (7-36) stimulated sprouting and VEGF expression, which was significantly enhanced by sitagliptin- mediated inhibition of DPP-IV. Our in vivo data demonstrate that sitagliptin treatment phosphorylated CREB and induced islet vascularization through VEGF-A/VEGFR-2 signaling pathway. This study paves a new pathway for improvement of islet transplantation in treating diabetes mellitus.     

Inosine protects against the development of diabetes in multiple-low-dose streptozotocin and nonobese diabetic mouse models of type 1 diabetes

Inosine, a naturally occurring purine, was long considered to be an inactive metabolite of adenosine. However, recently inosine has been shown to be an immunomodulator and anti-inflammatory agent. The aim of this study was to determine whether inosine influences anti-inflammatory effects and affects the development of type 1 diabetes in murine models. Type 1 diabetes was induced either chemically by streptozotocin or genetically using the nonobese diabetic mouse (NOD) model. Mice were treated with inosine (100 or 200 mg kg(-1)d(-1)d) and diabetes incidence was monitored. The effect of inosine on pancreas immune cell infiltration, oxidative stress, and cytokine profile also was determined. For the transplantation model islets were placed under the renal capsule of NOD mice and inosine (200 mg kg(-1)d d(-1)d) treatment started the day of islet transplantation. Graft rejection was diagnosed by return of hyperglycemia accompanied by glucosuria and ketonuria. Inosine reduced the incidence of diabetes in both streptozotocin-induced diabetes and spontaneous diabetes in NOD mice. Inosine decreased pancreatic leukocyte infiltration and oxidative stress in addition to switching the cytokine profile from a Th1 to a Th2 profile. Inosine prolonged pancreatic islet graft survival, increased the number of surviving beta cells, and reduced the number of infiltrating leukocytes. Inosine protects against both the development of diabetes and against the rejection of transplanted islets. The purine exerts anti-inflammatory effects in the pancreas, which is its likely mode of action. The use of inosine should be considered as a potential preventative therapy in humans susceptible to developing Type 1 diabetes and as a possible antirejection therapy for islet transplant recipients.     

Improving islet transplantation by gene delivery of hepatocyte growth factor (HGF) and its downstream target, protein kinase B (PKB)/Akt

Clinical studies have demonstrated that islet transplantation may be a useful procedure to replace beta cell function in patients with Type 1 diabetes. Islet transplantation faces many challenges, including complications associated with the procedure itself, the toxicity of immunosuppression regimens, and to the loss of islet function and insulin-independence with time. Despite the current successes, and residual challenges, these studies have pointed out an enormous scarcity of islet tissue that precludes the use of islet transplantation in a clinical setting on a wider scale. To address this problem, many research groups are trying to identify different islet growth factors and intracellular molecules capable of improving islet graft survival and function, therefore reducing the number of islets needed for successful transplantation. Among these growth factors, hepatocyte growth factor (HGF), a factor known to improve transplantation of a variety of organs/cells, has shown promising results in increasing islet graft survival and reducing the number of islets needed for successful transplantation in four different rodent models of islet transplantation. Protein kinase B (PKB)/Akt, a pro-survival intracellular signaling molecule is known to be activated in the beta cell by several different growth factors, including HGF. PKB/Akt has also shown promising results for improving human islet graft survival and function in a minimal islet mass model of islet transplantation in diabetic SCID mice. Increasing our knowledge on how HGF, PKB/Akt and other emerging molecules work for improving islet transplantation may provide substrate for future therapeutic approaches aimed at increasing the number of patients in which beta cell function can be successfully replaced.     

Inhibition of Nuclear Factor-κB Activation in Pancreatic β-Cells Has a Protective Effect on Allogeneic Pancreatic Islet Graft Survival

Pancreatic islet transplantation, a treatment for type 1 diabetes, has met significant challenges, as a substantial fraction of the islet mass fails to engraft, partly due to death by apoptosis in the peri- and post-transplantation periods. Previous evidence has suggested that NF-κB activation is involved in cytokine-mediated β-cell apoptosis and regulates the expression of pro-inflammatory and chemokine genes. We therefore sought to explore the effects of β-cell-specific inhibition of NF-κB activation as a means of cytoprotection in an allogeneic model of islet transplantation. To this end, we used islets isolated from the ToI-β transgenic mouse, where NF-κB signalling can specifically and conditionally be inhibited in β-cells by expressing an inducible and non-degradable form of IκBα regulated by the tet-on system. Our results show that β-cell-specific blockade of NF-κB led to a prolonged islet graft survival, with a relative higher preservation of the engrafted endocrine tissue and reduced inflammation. Importantly, a longer delay in allograft rejection was achieved when mice were systemically treated with the proteasome inhibitor, Bortezomib. Our findings emphasize the contribution of NF-κB activation in the allograft rejection process, and suggest an involvement of the CXCL10/IP-10 chemokine. Furthermore, we suggest a potential, readily available therapeutic agent that may temper this process.     

Thioredoxin-1 Attenuates Early Graft Loss after Intraportal Islet Transplantation in Mice

Aims

Recent studies suggest that decreasing oxidative stress is crucial to achieve successful islet transplantation. Thioredoxin-1 (TRX), which is a multifunctional redox-active protein, has been reported to suppress oxidative stress. Furthermore, it also has anti-inflammatory and anti-apoptotic effects. In this study, we investigated the effects of TRX on early graft loss after islet transplantation.

Methods

Intraportal islet transplantation was performed for two groups of streptozotocin-induced diabetic mice: a control and a TRX group. In addition, TRX-transgenic (Tg) mice were alternately used as islet donors or recipients.

Results

The changes in blood glucose levels were significantly lower in the TRX group compared with the TRX-Tg donor and control groups (p<0.01). Glucose tolerance and the residual graft mass were considerably better in the TRX group. TRX significantly suppressed the serum levels of interleukin-1β (p<0.05), although neither anti-apoptotic nor anti-chemotactic effects were observed. Notably, no increase in the 8-hydroxy-2′-deoxyguanosine level was observed after islet infusion, irrespective of TRX administration.

Conclusions

The present study demonstrates that overexpression of TRX on the islet grafts is not sufficient to improve engraftment. In contrast, TRX administration to the recipients exerts protective effects on transplanted islet grafts by suppressing the serum levels of interleukin-1β. However, TRX alone appears to be insufficient to completely prevent early graft loss after islet transplantation. We therefore propose that a combination of TRX and other anti-inflammatory treatments represents a promising regimen for improving the efficacy of islet transplantation.     

Overexpression of suppressor of cytokine signaling 1 in islet grafts results in anti-apoptotic effects and prolongs graft survival

AimsA significant portion of islet grafts are destroyed by apoptosis and fail to become functional after transplantation. Strategies that enhance islet resistance to apoptosis may prevent graft loss. The aim of this study was to investigate whether overexpression of suppressor of cytokine signaling 1 (SOCS1) in islet grafts could achieve an anti-apoptotic effect and prolong graft survival.Main methodsWe used a chimeric adenovirus vector (Ad5F35) to enhance SOCS1 expression in isolated rat islets, and assessed its protective action against TNF-α-induced apoptosis. After transplanting SOCS1-overexpressing islets into allogeneic recipients with streptozotocin-induced diabetes, graft survival and in situ apoptosis were analyzed using immunohistochemistry.Key findingsThe isolated rat islets infected with Ad5F35–SOCS1 showed significantly higher SOCS1 expression than Ad5F35–EGFP and mock infected islets. The Ad5F35 transfection and SOCS1 overexpression on islets did not affect their insulin secretory function. After treatment with rat TNF-α and cycloheximide in vitro, Ad5F35–-SOCS1 infected islets exhibited a lower apoptotic ratio than controls (Ad5F35–EGFP and mock infected islets). The diabetic recipients transplanted with Ad5F35–SOCS1 infected islets displayed longer time of normoglycemia than recipients transplanted with mock infected islets. Furthermore, histological analysis indicated that the infected grafts with local overexpression of SOCS1 showed decreased apoptosis in the early post-transplant period.SignificanceThese results demonstrate that overexpression of SOCS1 in islet grafts prior to transplantation can significantly protect them from apoptotic loss and prolong their survival. This approach might find a clinical counterpart.     

Mesenchymal stromal cell secretory factors induce sustained improvements in islet function pre- and post-transplantation

Background aims

Mesenchymal stromal cells (MSCs) enhance islet function both in vitro and in vivo, at least in part by secreting ligands that activate islet G-protein coupled receptors (GPCRs). We assessed whether pre-treatment with a defined “cocktail” of MSC-secreted GPCR ligands enhances islet functional survival in vitro and improves the outcomes of islet transplantation in an experimental model of diabetes.

Co-transplantation of islets with mesenchymal stem cells in microcapsules demonstrates graft outcome can be improved in an isolated-graft model of islet transplantation in mice

Background aimsCo-transplantation of islets with mesenchymal stem cells (MSCs) has been shown to improve graft outcome in mice, which has been partially attributed to the effects of MSCs on revascularization and preservation of islet morphology. Microencapsulation of islets provides an isolated-graft model of islet transplantation that is non-vascularized and prevents islet aggregation to preserve islet morphology. The aim of this study was to investigate whether MSCs could improve graft outcome in a microencapsulated/isolated-graft model of islet transplantation.MethodsMouse islets and kidney MSCs were co-encapsulated in alginate, and their function was assessed in vitro. A minimal mass of 350 syngeneic islets encapsulated alone or co-encapsulated with MSCs (islet+MSC) were transplanted intraperitoneally into diabetic mice, and blood glucose concentrations were monitored. Capsules were recovered 6 weeks after transplantation, and islet function was assessed.ResultsIslets co-encapsulated with MSCs in vitro had increased glucose-stimulated insulin secretion and content. The average blood glucose concentration of transplanted mice was significantly lower by 3 weeks in the islet+MSC group. By week 6, 71% of the co-encapsulated group were cured compared with 16% of the islet-alone group. Capsules recovered at 6 weeks had greater glucose-stimulated insulin secretion and insulin content in the islet+MSC group.ConclusionsMSCs improved the efficacy of microencapsulated islet transplantation. Using an isolated-graft model, we were able to eliminate the impact of MSC-mediated enhancement of revascularization and preservation of islet morphology and demonstrate that the improvement in insulin secretion and content is sustained in vivo and can significantly improve graft outcome.     

Protection of rat pancreatic islet function and viability by coculture with rat bone marrow-derived mesenchymal stem cells

The maintenance of viable and functional islets is critical in successful pancreatic islet transplantation from cadaveric sources. During the isolation procedure, islets are exposed to a number of insults including ischemia, oxidative stress and cytokine injury that cause a reduction in the recovered viable islet mass. A novel approach was designed in which streptozotocin (STZ)-damaged rat pancreatic islets (rPIs) were indirectly cocultured with rat bone marrow-derived mesenchymal stem cells (rBM-MSCs) to maintain survival of the cultured rPIs. The results indicated that islets cocultured with rBM-MSCs secreted an increased level of insulin after 14 days, whereas non-cocultured islets gradually deteriorated and cell death occurred. The cocultivation of rBM-MSCs with islets and STZ-damaged islets showed the expression of IL6 and transforming growth factor-β1 in the culture medium, besides the expression of the antiapoptotic genes (Mapkapk2, Tnip1 and Bcl3), implying the cytoprotective, anti-inflammatory and antiapoptotic effects of rBM-SCs through paracrine actions.     

Co-Graft of Allogeneic Immune Regulatory Neural Stem Cells (NPC) and Pancreatic Islets Mediates Tolerance,while Inducing NPC-Derived Tumors in Mice

Background

Data available on the immunomodulatory properties of neural stem/precursor cells (NPC) support their possible use as modulators for immune-mediated process. The aim of this study was to define whether NPC administered in combination with pancreatic islets prevents rejection in a fully mismatched allograft model.

Methodology/Principal Finding

Diabetic Balb/c mice were co-transplanted under the kidney capsule with pancreatic islets and GFP⁺ NPC from fully mismatched C57BL/6 mice. The following 4 groups of recipients were used: mice receiving islets alone; mice receiving islets alone and treated with standard immunosuppression (IL-2Rα chain mAbs + FK506 + Rapamycin); mice receiving a mixed islet/NPC graft under the same kidney capsule (Co-NPC-Tx); mice receiving the islet graft under the left kidney capsule and the NPC graft under the right kidney capsule (NPC-Tx). Our results demonstrate that only the co-transplantation and co-localization of NPC and islets (Co-NPC-Tx) induce stable long-term graft function in the absence of immunosuppression. This condition is associated with an expansion of CD4⁺CD25⁺FoxP3⁺ T regulatory cells in the spleen. Unfortunately, stable graft function was accompanied by constant and reproducible development of NPC-derived cancer mainly sustained by insulin secretion.

Conclusion

These data demonstrate that the use of NPC in combination with islets prevents graft rejection in a fully mismatched model. However, the development of NPC-derived cancer raises serious doubts about the safety of using adult stem cells in combination with insulin-producing cells outside the original microenvironment.     

Quantitative micro positron emission tomography (PET) imaging for the in vivo determination of pancreatic islet graft survival

Islet transplantation is an attractive approach for treating type-1 diabetes, but there is a massive loss of transplanted islets. It is currently only possible to estimate islet mass indirectly, through measurement of circulating C-peptide and insulin levels. This type of estimation, however, is not sufficiently sensitive or reproducible for follow-up of individuals who have undergone islet transplantation. Here we show that islet graft survival could be assessed for 1 month in diabetic NOD mice using 9-(4-[(18)F]-fluoro-3-hydroxymethylbutyl)guanine ([(18)F]FHBG)-positron emission tomography (PET) technology, the PET signal reflecting insulin secretory capacity of transplanted islets. Expression of the gene encoding viral interleukin-10 (vIL-10), was measurable in real time with PET scanning. Additionally, we addressed the clinical potential of this approach by visualizing transplanted islets in the liver, the preferred clinical transplantation site. We conclude that quantitative in vivo PET imaging is a valid method for facilitating the development of protocols for prolonging islet survival, with the potential for tracking human transplants.     

Cryopreservation of islets of Langerhans

Development of techniques for cryopreservation of pancreatic islets of Langerhans could potentially allow for increased freedom from the time restrictions presently affecting viability in islet cell transplantation. While several investigators have attempted islet cell freezing and have obtained favorable in vitro results after thawing, there have been few reported in vivo successes with islets transplanted after freezing. We have developed a simple system for freezing islet cell pancreatic fragments to ?196 °C and have either stored them in liquid nitrogen for 24 hr or immediately thawed the islets prior to transplantation. In addition, antilymphoblast globulin has been used as graft pretreatment modality in order to modify islet cell immunogenicity. We found that ALG was effective in prolongation of graft survival after freezing as well as on fresh nonfrozen transplants. The use of freezing and ALG appears, therefore, to have a favorable effect on the immunogenicity of the pancreatic islet cell allograft.