Site For Islet Transplantation Research Articles

Where’s Waldo? Extrahepatic Site Options for Islet Transplantation

The current predominant location for allo- and auto-transplantation of islet cells is into the liver via the portal venous system. Despite the relative success of this site over the last several decades, further study has revealed multiple disadvantages. Portal hypertension, portal vein thrombosis, bleeding, low oxygen tension, instant blood mediated inflammatory reaction, inadequate alpha cell function, and delays in neovascularization are factors that continue to drive researchers to explore alternative extrahepatic sites for islet transplantation. The spleen, kidney, intestinal wall, bone marrow, omentum, peritoneum and other sites have been evaluated for islet transplant. Factors to include in choosing an optimal site includes: capacity, transplant efficacy, portal venous drainage, high oxygen tension, easy retrivability and access. Some sites have been explored only in a experimental capacity with preclinical work, while other sites, such as the omentum, are currently undergoing clinical trials. The various benefits and limitations of these sites are reviewed in this article.

Vascularization of PLGA-based bio-artificial beds by hypoxia-preconditioned mesenchymal stem cells for subcutaneous xenogeneic islet transplantation.

Subcutaneous tissue is an attractive extra-hepatic heterotopic site for islet transplantation; however, poor oxygen tension and blood supply during early engraftment of implanted islets have limited the use of this site in clinical applications. This study investigated the vascularization potential of hypoxia-preconditioned mesenchymal stem cells (3% O2 ; hypo-MSCs) in PLGA-based bio-artificial beds for subsequent subcutaneous islet transplantation. Sheet-typed polymeric PLGA scaffolds coated with hypo-MSCs or normo-MSCs (MSCs cultured under normoxia conditions, 21% O2 ) were implanted subcutaneously in mice. Compared to normo-MSCs, hypo-MSCs significantly enhanced vasculogenesis, both on the interior and exterior surfaces of the implanted PLGA devices, which peaked 4weeks after implantation. Further, infusion of porcine islets inside the prevascularized PLGA bed restored normal glycemic control in 6 of 6 STZ-induced diabetic mice. The mass of the marginal islet was approximately 2000 IEQs, which is comparable to that required for the renal subcapsular space, a highly vascularized site. Therefore, PLGA-based bio-artificial devices prevascularized with hypo-MSCs could be a useful modality for successful subcutaneous islet transplantation, which is of high clinical relevance.

Acceptance of Murine Islet Allografts without Immunosuppression in the Inguinal Subcutaneous White Adipose Tissue Pretreated with bFGF

Prevention of immune rejection without immunosuppression is a goal for transplant immunology. Previous report demonstrated that rejection of rat islet allografts in sc space of the back between low responder strains was prevented by pretreatment of the site with bFGF (AJT2014). However, it was not in the high responder combination of mice (BALB/c to C57BL/6). Here, we determined whether islet allografts in the inguinal subcutaneous white adipose tissue (ISWAT), a novel site of islet transplantation (tx), pretreated with bFGF are accepted without immunosuppression in mice. An agarose rod containing bFGF was buried in the ISWAT of a C57BL/6 mouse, and 1-3 weeks later 400 BALB/c islets (2 donors) were grafted in the space after the removal of a rod. Recipients were made diabetic by STZ (180mg/kg, iv) at 3 days prior to tx. Eventually, we found that 10μg bFGF/50μl/rod with 2 week interval is the optimal, in which 11/14 recipient mice remained normoglycemic (<200mg/dl) for more than 60 days. Removal of the ISWAT with islets promptly made recipient mice hyperglycemic again. Histologically, intact islets were seen in the ISWAT. In contrast, islet allografts (n=7) in the ISWAT pretreated with vehicle were rejected by 10 days. FACS revealed an expansion of CD8 T cells in the ISWAT rejecting but not accepting islet allografts. In the latter, IL-10+cells including Gr-1+ cells were seen. Re-tx of BALB/c islets (n=3) to the contralateral ISWAT of normoglycemic mice induced rejection of the initial BALB/c grafts and made recipient mice hyperglycemic again, while that of C3H (n=3) did not. These findings indicate that acceptance of murine islet allografts without immunosuppression was achieved when the ISWAT pretreated with bFGF was the site and that the acceptance appeared mediated by local rather than systemic unresponsiveness. Disclosure Y. Nakafusa: None. N. Nitta: None. M. Nakamura: None. Y. Yasunami: None.

Long-Term Function of Islet Allografts Transplanted on the Omentum Using a Biological Scaffold

The liver is the preferred site for islet transplantation (ITx) but not ideal due to limitations affecting engraftment. We evaluated the safety and efficacy of ITx in the omentum using a resorbable biological scaffold in 3 subjects with type 1 diabetes and negative C-peptide. Islets were combined with autologous plasma and thrombin to generate a biologic scaffold and layered laparoscopically on the omentum. Induction was with anti-thymocyte globulin and etanercept. Maintenance was with mycophenolate sodium and tacrolimus. Demographics, islet dose and metabolic data are shown in the Table.Subject #Age (years)Duration T1DM (years)BMI (Kg/m2)IEQ†/KgMMTT‡ Stimulated Glucose (mg/dl)/C-peptide (ng/ml)Insulin dose U/Kg/day (Units/day)HbA1c%6 months12 months24 monthsPre-ITxLatestPre-ITxLatest1432621.511,386181/3.32277/1.79317/0.490.62 (33)0.14 (7)6.85.32321625.39,635372/0.88374/0.65332/0.52*0.45 (31)0.45 (30)5.75.6346422412,648277/2.47--0.45 (20)0.2 (11)6.36.3* 18 months Post-ITx † IEQ= islet equivalents ‡ MMTT = mixed meal tolerance test Subject 1 was insulin independent for 15 months and maintains stable glycemic control. Subject 2 had marginal graft function with persistence of severe hypoglycemia (SH) and then underwent intrahepatic ITx resulting in insulin independence. Subject 3 had a 55% reduction in insulin dose and maintains excellent glycemic control. Our initial experience demonstrates feasibility and safety of ITx on the omentum. Graft function persisted throughout follow-up (6-24 months) resulting in improved glycemic control and absence of SH (subjects 1 and 3). Results suggest a significant loss of islets early post-ITx followed by gradual functional decline similar to intrahepatic ITx. Strategies to improve oxygen delivery and neo-vascularization and minimize immunosuppression are needed to improve long-term outcomes at this site. Disclosure D. Baidal: None. C. Ricordi: None. D.M. Berman: Stock/Shareholder; Self; Pfizer Inc. A. Pileggi: Stock/Shareholder; Self; Converge Biotech, Inc.. Stock/Shareholder; Spouse/Partner; Converge Biotech, Inc. A.M. Alvarez Gil: None. N. Padilla: None. G. Ciancio: None. E. Linetsky: None. R. Alejandro: None.

A Novel Subcutaneous Site of Islet Transplantation Superior to the Liver

Islet transplantation is an attractive treatment for patients with insulin-dependent diabetes mellitus, and currently, the liver is the favored transplantation site. However, an alternative site is desirable because of the low efficiency of hepatic transplantation, requiring 2 to 3 donors for a single recipient, and because the transplanted islets cannot be accessed or retrieved. We developed a novel procedure of islet transplantation to the inguinal subcutaneous white adipose tissue (ISWAT) of mice and described functional and morphological characteristics of transplanted syngeneic islets. Also, it was determined whether islet allograft rejection in the ISWAT can be prevented by immunosuppressive agents. Furthermore, it was examined whether human islets function when grafted in this particular site of immune-deficient mice. In this site, transplanted islets are engrafted as clusters and function to reverse streptozotocin-induced diabetes in mice. Importantly, transplanted islets can be visualized by computed tomography and are easily retrievable, and allograft rejection is preventable by blockade of costimulatory signals. Of much importance, the efficiency of islet transplantation in this site is superior to the liver, in which hyperglycemia of diabetic recipient mice is ameliorated after transplantation of 200 syngeneic islets (the islet number yielded from 1 mouse pancreas) to the ISWAT but not to the liver. Furthermore, human islets transplanted in this particular site function to reverse diabetes in immune-deficient mice. Thus, the ISWAT is superior to the liver as the site of islet transplantation, which may lead to improved outcome of clinical islet transplantation.

The Spleen as an Optimal Site for Islet Transplantation and a Source of Mesenchymal Stem Cells.

This review demonstrates the unique potential of the spleen as an optimal site for islet transplantation and as a source of mesenchymal stem cells. Islet transplantation is a cellular replacement therapy used to treat severe diabetes mellitus; however, its clinical outcome is currently unsatisfactory. Selection of the most appropriate transplantation site is a major factor affecting the clinical success of this therapy. The spleen has long been studied as a candidate site for islet transplantation. Its advantages include physiological insulin drainage and regulation of immunity, and it has recently also been shown to contribute to the regeneration of transplanted islets. However, the efficacy of transplantation in the spleen is lower than that of intraportal transplantation, which is the current representative method of clinical islet transplantation. Safer and more effective methods of islet transplantation need to be established to allow the spleen to be used for clinical transplantation. The spleen is also of interest as a mesenchymal stem cell reservoir. Splenic mesenchymal stem cells contribute to the repair of damaged tissue, and their infusion may thus be a promising therapy for autoimmune diseases, including type 1 diabetes mellitus and Sjogren’s syndrome.

Design of a vascularized synthetic poly(ethylene glycol) macroencapsulation device for islet transplantation

The use of immunoisolating macrodevices in islet transplantation confers the benefit of safety and translatability by containing transplanted cells within a single retrievable device. To date, there has been limited development and characterization of synthetic poly(ethylene glycol) (PEG)-based hydrogel macrodevices for islet encapsulation and transplantation. Herein, we describe a two-component synthetic PEG hydrogel macrodevice system, designed for islet delivery to an extrahepatic islet transplant site, consisting of a hydrogel core cross-linked with a non-degradable PEG dithiol and a vasculogenic outer layer cross-linked with a proteolytically sensitive peptide to promote degradation and enhance localized vascularization. Synthetic PEG macrodevices exhibited equivalent passive molecular transport to traditional microencapsulation materials (e.g., alginate) and long-term stability in the presence of proteases in vitro and in vivo, out to 14 weeks in rats. Encapsulated islets demonstrated high viability within the device in vitro and the incorporation of RGD adhesive peptides within the islet encapsulating PEG hydrogel improved insulin responsiveness to a glucose challenge. In vivo, the implementation of a vasculogenic, degradable hydrogel layer at the outer interface of the macrodevice enhanced vascular density within the rat omentum transplant site, resulting in improved encapsulated islet viability in a syngeneic diabetic rat model. These results highlight the benefits of the facile PEG platform to provide controlled presentation of islet-supportive ligands, as well as degradable interfaces for the promotion of engraftment and overall graft efficacy.

Posttransplant oxygen inhalation improves the outcome of subcutaneous islet transplantation: A promising clinical alternative to the conventional intrahepatic site.

Subcutaneous tissue is a promising site for islet transplantation, due to its large area and accessibility, which allows minimally invasive procedures for transplantation, graft monitoring, and removal of malignancies as needed. However, relative to the conventional intrahepatic transplantation site, the subcutaneous site requires a large number of islets to achieve engraftment success and diabetes reversal, due to hypoxia and low vascularity. We report that the efficiency of subcutaneous islet transplantation in a Lewis rat model is significantly improved by treating recipients with inhaled 50% oxygen, in conjunction with prevascularization of the graft bed by agarose-basic fibroblast growth factor. Administration of 50% oxygen increased oxygen tension in the subcutaneous site to 140mmHg, compared to 45mmHg under ambient air. In vitro, islets cultured under 140mmHg oxygen showed reduced central necrosis and increased insulin release, compared to those maintained in 45mmHg oxygen. Six hundred syngeneic islets subcutaneously transplanted into the prevascularized graft bed reversed diabetes when combined with postoperative 50% oxygen inhalation for 3days, a number comparable to that required for intrahepatic transplantation; in the absence of oxygen treatment, diabetes was not reversed. Thus, we show oxygen inhalation to be a simple and promising approach to successfully establishing subcutaneous islet transplantation.

Local delivery of fingolimod from three-dimensional scaffolds impacts islet graft efficacy and microenvironment in a murine diabetic model.

The local delivery of immunosuppressive agents could significantly promote the success of islet transplantation for the treatment of Type 1 diabetes. Fingolimod, a clinically-approved sphingosine-1-phosphate receptor agonist, has been found to dampen allograft islet rejection in rodent models when delivered systemically. Herein, we engineered a platform for the local delivery of fingolimod by incorporating it within a macroporous polydimethylsiloxane (PDMS) scaffold specifically designed for islet transplantation. In vitro drug release studies quantifying kinetics confirmed sustained release within targeted dose levels for >7 days. Fingolimod-PDMS scaffolds containing syngeneic islets were subsequently transplanted into diabetic mice for examination of the effect of local fingolimod release on engraftment. Surprisingly, either delayed or abrogated efficacy was observed when scaffolds contained a dosage of fingolimod >0.5% w/w; despite drug release rates estimated at ~80-fold less than published systemic delivery reports where no detrimental effects were noted. Histological analysis of explants indicated a dose-dependent modulation of cellular migration and phenotype at the graft site, with high doses impairing host infiltration and engraftment while lower doses promoted leucocyte migration. Mechanistic in vivo and in vitro studies observed unique host and islet responses to local fingolimod delivery, with impairment of murine islet viability and function. Overall, this study confirmed the ability to modulate local delivery of fingolimod in a sustained-release manner using a three-dimensional PDMS scaffold; however, the observed detrimental impacts at the site of islet transplantation do not support further investigation of local delivery at the graft site in murine models.

A Retrievable, Efficacious Polymeric Scaffold for Subcutaneous Transplantation of Rat Pancreatic Islets.

We aim on developing a polymeric ectopic scaffold in a readily accessible site under the skin. The liver as transplantation site for pancreatic islets is associated with significant loss of islets. Several extrahepatic sites were tested in experimental animals, but many have practical limitations in the clinical setting and do not have the benefit of easy accessibility. Functional survival of rat islets was tested during 7 days of culture in the presence of poly(D,L-lactide-co-ε-caprolactone) (PDLLCL), poly(ethylene oxide terephthalate)/polybutylene terephthalate (PEOT/PBT) block copolymer, and polysulfone. Tissue responses were studied in vivo after subcutaneous implantation in rats. Culture on PEOT/PBT and polysulfone profoundly disturbed function of islets, and induced severe tissue responses in vivo. Modification of their hydrophilicity did not change the suitability of the polymers. PDLLCL was the only polymer that promoted functional survival of rat islets in vitro and was associated with minor tissue reactions after 28 days. Rat islets were transplanted in the PDLLCL scaffold in a diabetic rat model. Before islet seeding, the scaffold was allowed to engraft for 28 days to allow the tissue response to dampen and to allow blood vessel growth into the device. Islet transplantation into the scaffold resulted in normoglycemia within 3 days and for the duration of the study period of 16 weeks. In conclusion, we found that some polymers such as PEOT/PBT and polysulfone interfere with islet function. PDLLCL is a suitable polymer to create an artificial islet transplantation site under the skin and supports islet survival.

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.

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

The anterior chamber of the eye as a site for pancreatic islet transplantation

Abstract The most viable therapy for curing type 1 diabetes mellitus is pancreatic islet transplantation. However, they are unavoidable in terms of immunogenicity, which is differently affected by transplantation site. Therefore, it is necessary to determine alternate sites to permit successful islet transplantation outcomes. This paper reviews evidence that the anterior chamber of the eye (ACE) could be a good site for islet transplantation when compared to other alternate sites. In addition, this site may be a promising technical platform for noninvasive in vivo imaging of transplanted pancreatic islets.

Intraportal islet transplantation: the impact of the liver microenvironment.

The portal vein remains the preferred site for pancreatic islet transplantation due to its easy access and low morbidity. However, despite great progress in isolation and transplantation protocols over the past few years, it is still associated with the early loss of some 50-70% of transplanted islets. The complex liver microenvironment itself presumably plays an important role in this loss. The present review focuses on the specifics of the liver microenvironment, notably the localized hepatic ischemia/reperfusion injury following transplantation, the low oxygenation of the portal vein, the instant blood-mediated inflammatory reaction, the endogenous liver immune system, and the gut-liver axis, and how they can each have an impact on the transplanted islets. It identifies the potential, or already applied, clinical interventions for improving intraportal islet survival, and pinpoints those promising areas still lacking preclinical research. Future interventions on clinical intraportal islet transplantation need to take into account the global context of the liver microenvironment, with multi-point interventions being most likely to improve early islet survival and engraftment.

An engineered macroencapsulation membrane releasing FTY720 to precondition pancreatic islet transplantation.

Macroencapsulation is a powerful approach to increase the efficiency of extrahepatic pancreatic islet transplant. FTY720, a small molecule that activates signaling through sphingosine-1-phosphate receptors, is immunomodulatory and pro-angiogenic upon sustained delivery from biomaterials. While FTY720 (fingolimod, Gilenya) has been explored for organ transplantation, in the present work the effect of locally released FTY720 from novel nanofiber-based macroencapsulation membranes is explored for islet transplantation. We screened islet viability during culture with FTY720 and various biodegradable polymers. Islet viability is significantly reduced by the addition of high doses (≥500 ng/mL) of soluble FTY720. Among the polymers screened, islets have the highest viability when cultured with poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Therefore, PHBV was blended with polycaprolactone (PCL) for mechanical stability and electrospun into nanofibers. Islets had no detectable function ex vivo following 5 days or 12 h of subcutaneous implantation within our engineered device. Subsequently, we explored a preconditioning scheme in which islets are transplanted 2 weeks after FTY720-loaded nanofibers are implanted. This allows FTY720 to orchestrate a local regenerative milieu while preventing premature transplantation into avascular sites that contain high concentrations of FTY720. These results provide a foundation and motivation for further investigation into the use of FTY720 in preconditioning sites for efficacious islet transplantation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 555-568, 2018.

The Spleen Is an Ideal Site for Inducing Transplanted Islet Graft Expansion in Mice.

Alternative islet transplantation sites have the potential to reduce the marginal number of islets required to ameliorate hyperglycemia in recipients with diabetes. Previously, we reported that T cell leukemia homeobox 1 (Tlx1)+ stem cells in the spleen effectively regenerated into insulin-producing cells in the pancreas of non-obese diabetic mice with end-stage disease. Thus, we investigated the spleen as a potential alternative islet transplantation site. Streptozotocin-induced diabetic C57BL/6 mice received syngeneic islets into the portal vein (PV), beneath the kidney capsule (KC), or into the spleen (SP). The marginal number of islets by PV, KC, or SP was 200, 100, and 50, respectively. Some plasma inflammatory cytokine levels in the SP group were significantly lower than those of the PV group after receiving a marginal number of islets, indicating reduced inflammation in the SP group. Insulin contents were increased 280 days after islet transplantation compared with those immediately following transplantation (p<0.05). Additionally, Tlx1-related genes, including Rrm2b and Pla2g2d, were up-regulated, which indicates that islet grafts expanded in the spleen. The spleen is an ideal candidate for an alternative islet transplantation site because of the resulting reduced inflammation and expansion of the islet graft.

The Optimal Timing for Pancreatic Islet Transplantation into Subcutaneous Scaffolds Assessed by Multimodal Imaging.

Subcutaneously implanted polymeric scaffolds represent an alternative transplantation site for pancreatic islets (PIs) with the option of vascularisation enhancement by mesenchymal stem cells (MSC). Nevertheless, a proper timing of the transplantation steps is crucial. In this study, scaffolds supplemented with plastic rods were implanted into diabetic rats and two timing schemes for subsequent transplantation of bioluminescent PIs (4 or 7 days after rod removal) were examined by multimodal imaging. The cavities were left to heal spontaneously or with 10 million injected MSCs. Morphological and vascularisation changes were examined by MRI, while the localisation and viability of transplanted islets were monitored by bioluminescence imaging. The results show that PIs transplanted 4 days after rod removal showed the higher optical signal and vascularisation compared to transplantation after 7 days. MSCs slightly improved vascularisation of the graft but hindered therapeutic efficiency of PIs. Long-term glycaemia normalisation (4 months) was attained in 80% of animals. In summary, multimodal imaging confirmed the long-term survival and function of transplanted PIs in the devices. The best outcome was reached with PIs transplanted on day 4 after rod removal and therefore the suggested protocol holds a potential for further applications.

Subcapsular Implantation of Pancreatic Islets in Syngeneic, Allogeneic, and Xenogeneic Mice

Reliable and reproducible transplantation is essential to the success of a number of particular investigations. Renal subcapsule is the most selected site for islet transplantation mainly owing to its easy access, readiness for retrieval, and possibility of reimplantation. Syngeneic, allogeneic, and xenogeneic islets were transplanted into kidney capsules of Balb/C and C57BL/6J mice, and the blood glucose levels of the experimental animals were periodically monitored. Detailed procedures on mouse diabetic model and islet implantation are described. The values of blood glucose measured under varied transplant circumstances are presented, covering syngeneic, allogeneic, and xenogeneic islet transplantations. The methodology is straightforward and has been proven to be practicable and reproducible. The parallel observations in different transplant situations provide a valuable contribution to and useful information for diabetes-related studies.

Gastric submucosa is inferior to the liver as transplant site for autologous islet transplantation in pancreatectomized diabetic Beagles.

Intraportal transplantation of islets is no longer considered to be an ideal procedure and finding the extrahepatic alternative site is becoming a subject of high priority. Herein, in this study, we would introduce our initial outcomes of using gastric submucosa (GS) and liver as sites of islet autotransplantation in pancreatectomized diabetic Beagles. Total pancreatectomy was performed in Beagles and then their own islets extracted from the excised pancreas were transplanted into GS (GS group, n=8) or intrahepatic via portal vein (PV group, n=5). Forty-eight hours post transplantation, graft containing tissue harvested from the recipients revealed the presence of insulin-positive cells. All recipients in GS group achieved euglycemia within 1 day, but returned to a diabetic state at 6 to 8 days post-transplantation (mean survival time, 7.16±0.69 days). However, all of the animals kept normoglycemic until 85 to 155 days post-transplantation in PV group (mean survival time, 120±28.58 days; P<0.01 vs. GS group). The results of intravenous glucose tolerance test (IVGTT) confirmed that the marked improvement in glycometabolism was obtained in intrahepatic islet autotransplantation. Thus, our findings indicate that the liver is still superior to the GS as the site of islet transplantation, at least in our islet autotransplant model in pancreatectomized diabetic Beagles.

Multimodal Imaging Reveals Improvement of Blood Supply to an Artificial Cell Transplant Site Induced by Bioluminescent Mesenchymal Stem Cells

PurposeAn artificial site for cell or pancreatic islet transplantation can be created using a polymeric scaffold, even though it suffers subcutaneously from improper vascularisation. A sufficient blood supply is crucial for graft survival and function and can be enhanced by transplantation of mesenchymal stem cells (MSCs). The purpose of this study was to assess the effect of syngeneic MSCs on neoangiogenesis and cell engraftment in an artificial site by multimodal imaging.ProceduresMSCs expressing a gene for luciferase were injected into the artificial subcutaneous site 7 days after scaffold implantation. MRI experiments (anatomical and dynamic contrast-enhanced images) were performed on a 4.7-T scanner using gradient echo sequences. Bioluminescent images were acquired on an IVIS Lumina optical imager. Longitudinal examination was performed for 2 months, and one animal was monitored for 16 months.ResultsWe confirmed the long-term presence (lasting more than 16 months) of viable donor cells inside the scaffolds using bioluminescence imaging with an optical signal peak appearing on day 3 after MSC implantation. When compared to controls, the tissue perfusion and vessel permeability in the scaffolds were significantly improved at the site with MSCs with a maximal peak on day 9 after MSC transplantation.ConclusionsOur data suggest that the maximal signal obtained by bioluminescence and magnetic resonance imaging from an artificially created site between 3 and 9 days after MSC transplantation can predict the optimal time range for subsequent cellular or tissue transplantation, including pancreatic islets.