Clinical islet transplantation--registry report, accomplishments in the past and future research needs

A Prospective Comparison of Discontinuous Euroficoll and Eurodextran Gradients for Islet Purification

Density gradient separation of islets from exocrine tissue is usually performed with Ficoll. However, this reagent adds significantly to the cost of the isolation. The aim of this study was to evaluate the performance of Dextran as a potential low-cost substitute for Ficoll and to evaluate the effects of cold storage of the pancreatic digest prior to purification. Pancreases were procured from mongrel dogs, loaded with collagenase and mechanically dissociated. Washed pancreatic digest was collected and divided into two fractions that were purified using discontinuous gradients on the Cobe 2991 processor using identically prepared EuroFicoll (EF) or EuroDextran (ED) gradients. Alternate groups were suspended in EC and stored on ice, while the other fraction were resuspended in the 1.108-g/mL gradient layer (either EF or ED) and loaded into the COBE. This tissue layer was overlaid with layers of densities 1.096 and 1.037 g/mL and a HBSS cap, and centrifuged for 5 min at 800 × g. Purified islets were collected from the interface between the 1.037 and 1.096 layers and islet recovery, purity, and function were assessed. From a series of eight isolations, 72.9 ± 8.2% (mean ± SEM) of the islets were recovered from the EF purified gradients compared with 62.6 ± 8.3% from ED gradients ( p = NS, paired t-test). Gradients of ED that were run following hypothermic storage of the digest in cold EC solution (stored ED) had reduced islet recovery when compared with islet recovery from gradients prepared in EF(stored EF) (51.6 ± 9.6% for ED stored vs. 72.9 ± 11.9 for EF stored, p < 0.05). Islet recovery from EF gradients was equivalent between the stored and nonstored groups. The purity of preparations from the stored ED gradients was also reduced (71.3 ± 4.3%) when compared with islets that were immediately purified after dissociation (82.5 ± 4.8%, p < 0.05). Static glucose stimulation assay showed equivalence between the islets from ED and EF gradients. The stimulation index (SI) was 9.3 ± 0.9 for EF islets compared with 7.9 ± 1.4 for ED islets for digest purified immediately. However, if the digest was hypothermically stored in EC solution, a decrease in functional viability was observed in both the EF and the ED groups (7.7 ± 1.4 and 5.9 ± 0.8, respectively). Out of five alloxan-induced diabetic nude mice transplanted under the kidney capsule with 2000 islets isolated from the nonstored groups, three remained euglycemic >50 days posttrans-plant with either EF or ED islets. These experiments demonstrate effective recovery of equivalent numbers of canine islets using discontinuous gradients of ED or EF immediately following enzymatic digestion. However, following storage of the digest in cold EC solution results in a reduction in both islet recovery and function when gradients of ED are utilized. © 1998 Elsevier Science Inc.

Evaluation of a Purified Enzyme Blend for the Recovery and Function of Canine Pancreatic Islets

Recently developed technologies enabling the production of a reproducible, purified enzyme blend for optimal human pancreatic islet isolation has renewed interest in clinical islet transplantation. The canine model has been an ideal preclinical model for the development of islet transplantation protocols. As seen in other species, the application of crude collagenase for isolating canine islets resulted in highly variable islet yields, extensive islet fragmentation, and variable islet functionality. We compared the function of commercially available crude collagenases with that of Liberase™-CI purified enzyme blend for canine islet isolation. We also compared two manufacturing runs of Liberase-CI enzyme (lots 1 and 2) to demonstrate reproducibility of islet recovery and function. We report on the improved recovery and function of islets isolated using Liberase-CI enzyme. No difference in dog age, mean body weight, or pancreas weight were observed between the experimental groups. We observed a significantly higher postpurification recovery of islet equivalent number (IE) from pancreases processed using two lots of Liberase-CI enzyme (189 ± 20 × 103 IE, n = 4) and lot 2 (234 ± 39 × 103 IE, n = 7) than that obtained from pancreases processed with Sigma Type V (116.8 ± 27 × 103 IE, n = 5), Serva collagenase (49 ± 11.6 × 103 IE, n = 5, p < 0.05) or Boehringer–Mannheim (BM) Type P collagenase (85.4 ± 25 × 103 IE, n = 5, p < 0.05, ANOVA). No significant differences were observed in islet yield recovery from pancreases processed using the two production lots of Liberase-CI enzyme. Islet survival after 48 h in culture at 37°C was significantly higher from islets isolated using Liberase-CI enzyme (88 ± 3.7% survival) when compared to Sigma Type V (81.8 ± 3.3%), Serva (71.7 ± 2.8%), and BM Type P (77 ± 7.2%) (p < 0.05). Islet functional testing in vitro demonstrated islets isolated using crude collagenase had an increased insulin basal release and a reduced insulin stimulated response when compared with islets isolated using the two lots of Liberase-CI enzyme. The calculated stimulation index was 7.8 ± 1.7, 3.1 ± 0.6, and 4.8 ± 1.1 for Sigma Type V, Serva, and BM Type P isolated islets, respectively, compared to 15.7 ± 1.6 and 16.2 ± 1.9 for islets isolated with Liberase-CI enzyme production lots 1 and 2, respectively (p < 0.05). This evaluation demonstrates that a purified enzyme blend can significantly improve islet recovery and function. It also demonstrates the manufacturing reproducibility of Liberase-CI enzyme lots resulting in the isolation of canine islets with the same degree of efficacy. A blend of purified enzymes, specifically formulated for canine islet isolation, can consistently yield large numbers of islets that survive longer in culture and demonstrate an improved insulin response in vitro.

Development of an Automated Computer-Controlled Islet Isolation System

Before clinical islet transplantation can become an effective and reliable treatment for type 1 diabetic patients, there must be significant improvements in the methods employed for the isolation of islets of Langerhans. We have developed an automated cell extraction system (ACES), which allows computer control of the isolation process. As well, it incorporates a novel method of recombining dissociated pancreatic tissue. Following initial system design and testing to determine the optimal system configuration, a series of 12 consecutive canine islet isolations were performed. Pancreases were perfused with collagenase via the duct and dissociated and recombined using either the standard Ricordi-based protocol (group 1, n = 6) or dissociated and recombined using the ACES system (group 2, n = 6). A total of 90.8 ± 21 x 103 islet equivalents (IE) (mean ± SEM) were recovered in group 1 vs. 99 ± 14 x 103 IE in group 2 (p = NS, student unpaired t-test). Following Ficoll purification the recovery was 56.2 ± 14 x 103 IE for group 1 vs. 54.7 ± 11 x 103 IE for group 2 (p = NS). Viability was equivalent with an 8.6-fold increase in insulin secretion for group 1 and an 8.8-fold increase for group 2 when the islets were exposed to high glucose solution supplemented with IBMX (3-isobutyl-1-methylxanthine) during static incubation. In vivo function was equivalent following transplantation of 2000 IE under the kidney capsule of alloxan-induced diabetic nude mice with five of six and five of seven mice surviving long-term (>50 days posttransplant) (groups 1 and 2, respectively). This data shows that an entirely automated pancreatic islet extraction system can result in effective canine islet recovery without compromising islet yields and viability. The ACES system has several ad van tages over the standard isolation protocol. These include: 1) computer control and monitoring over all phases of the isolation, 2) a single-use sterile disposable tubing set, and 3) a novel method of tissue recombination. Copyright © 1997 Elsevier Science Inc.

Bulk Cryopreservation of Isolated Islets of Langerhans

Current methods to isolate human islets of Langerhans are limited and multiple donors are required for successful reversal of longstanding Type 1 diabetes mellitus. Cryopreservation of isolated islets is an effective method of storing and pooling islets. Current cryopreservation protocols are cumbersome due to current practices of placing small aliquots of islets per individual freezer tube. In the present study, we examined the application of a blood freezer bag for the cryopreservation of isolated islets by slow cooling and rapid thawing. Freezing and thawing profiles generated using thermocouples placed inside a 500 mL Cryocyte (Baxter) blood freezer bag showed that a longer equilibration period at −7.4°C was necessary to consistently achieve nucleation and cooling profiles similar to those observed in glass tubes. When known numbers of rat islets were placed in the freezer bag and the cryoprotectant dimethyl sulfoxide (DMSO) was added in a stepwise fashion and removed using a sucrose dilution, the islet recovery compared with glass tubes was 92 ± 4.8 vs. 90 ± 2.3% (n = 4, p = ns, Mann-Whitney U-test). When purified canine islets were cryopreserved in a single freezer bag or in multiple glass tubes, the recovery was similar (78.8 ± 12.5% recovery for freezer bag vs. 82.3 ± 5.3% for glass tubes; n = 6, p = ns). In vitro function was equivalent for both groups. The stimulation index of insulin release during glucose perifusion (stimulated over basal insulin secretion) for canine islets cryopreserved in a freezer bag vs. glass tubes was 3.2 ± 1.0 and 2.3 ± 1.3, respectively (n = 6, p = ns). These values were significantly lower than the nonfrozen control islets (6.9 ± 2.4, p < 0.05). When 2000 canine islets cryopreserved in either a freezer bag, or glass tubes were transplanted into diabetic nude mice, the animals became and remained normoglycemic posttransplant. We conclude that the survival of freshly isolated canine islets cryopreserved in a single freezer bag is equivalent to the glass tube method. Bulk cryopreservation of islets in a single freezer bag will facilitate effective low temperature tissue banking to support ongoing clinical trials of islet transplantation.

Osmotic Separation of Pancreatic Exocrine Cells from Crude Islet Cell Preparations

A novel approach is introduced here to selectively lyse exocrine cells in an islet preparation by hypoosmotic treatment. Time to hypotonic cell lysis required for the islet cells was much longer than that for the exocrine cells, which permits a possibility of selectively killing the exocrine cells by hypotonic treatment. The first set of experiments was designed to select an appropriate osmolality for the hypotonic treatment. Kinetic changes in cell volume in response to extracellular anisosmolalities (30 to 90 mOsm/kg) were recorded using an electronic particle counter. The results indicated that, when exposed to a 30 mOsm/kg solution, islet cells swelled slowly to reach volumetric equilibrium in approximately 3 min. There was no significant hypotonic cell lysis observed even at the end of 4 min (n = 4). In contrast, pancreatic exocrine cells, when exposed to the same solution, expanded rapidly to the lytic volume and burst within 30 s. Significant exocrine cell lysis was invariably achieved within 30 s when cells were exposed to the osmolalities below 60 mOsm/kg. For osmolalities between 70 to 80 mOsm/kg, exocrine cell lysis was highly variable. When cells were exposed to 80 to 90 mOsm/kg, no significant cell lysis was observed. Thus, an osmolality of 50 mOsm/kg is recommended for hypotonic treatment, as it maximizes the lysis of exocrine cells without unnecessarily stressing (osmotically) the islet cells. The second set of experiments (time-course experiments, 20 to 120 s) was designed to determine the length of exposure time for which the exocrine cells were irreversibly damaged but the islet cells had only swollen to such a degree that cell function is restored upon returning to an isotonic condition. Viability of the hypotonic treated cells was evaluated at two different levels: membrane integrity, measured by combined fluorescent dye staining with propidium iodide (PI) and carboxyfluorescein diacetate (CFDA), and mitochondrial function, measured by colorimetric MTT assay. The results showed that hypotonic treatment in a 50 mOsm/kg solution for 30 s resulted in over 85% loss of the membrane integrity for the exocrine cells. About 90% of these membrane lysed cells lost mitochondrial function (n = 3). By contrast, under the same treatment, less than 15% of the islet cells lost membrane integrity and mitochondrial function (n = 3). In conclusion, hypotonic treatment with a 50 mOsm/kg solution for 20 to 30 s at room temperature is sufficient to lyse the majority of the contaminating exocrine cells in an islet cell preparation, while maintaining function in the islet cells.

Comparison of Methods Used for the Removal of Dmso following Cryopreservation and the Development of an Automated Protocol

Current methods of islet isolation are limited, thus requiring islets to be pooled from multiple donors to provide sufficient islet mass to permit insulin independence following islet transplantation. Low temperature banking is one approach used to pool islet preparations. Recently, we developed a method for bulk cryopreservation of islets in a single freezer bag system that is less labor-intensive and more readily kept sterile. As a further improvement to this bulk cryopreservation protocol we examined islet survival following slow-step dilution or our standard sucrose dilution protocol. Known numbers of canine islets were cryopreserved in DMSO by slow cooling to -40°C, storing at -196°C, and rapid thawing. When islets were frozen and thawed in glass tubes the recovery of islets after 48 h of tissue culture was significantly higher when the DMSO was removed using either a slow step (71.7 + 2.7%) or a modified slow step (75.7 + 3.9%) protocol as compared with the standard sucrose dilution protocol (65.7 + 3.0%) (p < 0.05, unpaired t-test). Insulin secretion in vitro and in vivo graft function was similar between the experimental groups. Similarly, when islets were frozen then thawed in freezer bags, islet recovery following 48 h postcryopreser-vation tissue culture at 37° C was 74.8 + 2.4% for slow-step dilution compared with 66.2 + 2.7% for the standard sucrose dilution group (p < 0.05, unpaired t-test). Islets thawed in the freezer bag using the modified slow-step dilution protocol showed equivalent functional viability during static incubation to nonfrozen controls. Bulk cryopreservation of isolated islets in single blood freezer bags is a practical alternative to cryopreservation in glass tubes. Development of an automated protocol for the slow stepwise removal of the cryoprotectant from islets in freezer bags will facilitate low temperature tissue banking of islets.

Glucoregulation after Canine Islet Transplantation: Contribution of Insulin Secretory Capacity, Insulin Action, and the Entero-Insular Axis

The physiological glucoregulatory mechanisms after islet transplantation have been incompletely investigated. We studied the insulin secretory capacity (ISC) by intravenous arginine stimulation during 35-mM glucose clamps, insulin action during hyperinsulinemic euglycemic clamps, and mixed-meal stimulation at 6-9 mo after intrasplenic islet autotransplantation in 8 dogs, as compared with 30 controls. The enteroinsular axis in the recipients was examined by infusion of porcine glucose-dependent insulinotropic polypeptide (GIP) and human glucagon-like peptide-1 (GLP-1) (7-36 amide) under 8.5-mM glycemic clamp conditions in order to mimic the postprandial glycemia after transplantation. The grafts comprised 25% of the native islet mass, and the ISC likewise averaged 25% of the control value. The postprandial insulin response, in contrast, had increased to 140% after transplantation—albeit with a concomitant glucose excursion to approximately 8.5 mM. Insulin action declined on average by 45% posttransplant. The ISC correlated both with the postprandial glucose excursion and insulin action in the grafted dogs. Insulin action did not correlate with the postprandial glucose excursion. Infusion of GIP had no effect, but GLP-1 nearly doubled glucose-stimulated insulin. Thus, a hyperglycemia-enhanced insulinotropic effect of GLP-1, and perhaps other gut hormones, may account for the difference in the insulin response to the intravenous and oral challenges. Because the ISC reflects the engrafted islet mass and appears to be the primary determinant of glucose tolerance, transplantation of higher islet doses should allow prolonged near-normal glucoregulation—at least, in the autotransplant setting.

Hypoosmotic Exposure of Canine Pancreatic Digest as a Means to Purify Islet Tissue

The development of more effective means to separate pancreatic islets from the unwanted exocrine tissue would greatly advance the field of clinical islet allotransplantation in the treatment of insulin-dependent diabetes mellitus. Recent experiments with hamster islets have demonstrated a selective destruction of dissociated single exocrine cells when exposed to hypotonic conditions. It was the aim of this study to extend these observations to the canine model with collagenase dissociated pancreatic tissue and to evaluate the treatment's effect on islet function. Pancreases from five mongrel dogs were digested using an automated protocol of intraductal delivery of collagenase, and gentle dissociation. Duplicate samples of pancreatic digest were removed for insulin and amylase determination prior to and immediately following exposure to 50 mOsm/kg salt solution for a period of 30, 60, or 300 s before returning the digest to isoosmotic conditions. The remaining digest was cultured for a period of 48 h at 37°C before the tissue was recombined, washed, and a third sample removed for insulin and amylase. In vitro viability was then assessed using a static incubation assay with insulin content measured using a double-antibody radioimmunoassay, and amylase was determined using a colorimetric assay system. No difference in the insulin or amylase levels between the experimental groups was observed immediately following the hypotonic exposure; however, a significant decrease in the amylase content was observed following the 48-h culture period in digest that had been hypoosmotically exposed for 60 or 300 s compared with the pretreatment group (2.83 ± 0.41 IU amylase/mg pancreas vs. 1.29 ± 0.21 and 0.83 ± 0.12, mean ± SEM, p < 0.05). Insulin content was also significantly reduced in the 300-s exposure group compared with nontreated controls (3.2 ± 0.6 mU insulin/mg pancreas vs. 2.0 ± 0.2). The insulin/amylase ratio (I/A), a measure of islet and exocrine content, was 1.1 ± 0.13 following pancreas dissociation and 1.34 ± 0.21 for control tissue cultured for 48 h. The I/A ratio increased following hypoosmotic exposure to 1.50 ± 0.31 for tissue exposed for 30 s, 1.77 ± 0.19 for 60-s exposure, and 2.54 ± 0.13 for tissue exposed for 300 s (p < 0.05, vs. pretreatment group). In vitro insulin secretion was equivalent with the exception of the tissue exposed for 300 s, which had an increased basal level of insulin resulting in a significantly decreased stimulation index (3.8 ± 0.5 vs. 8.1 ± 1.2 for the purified islet control group, p < 0.05). These results suggest that a brief hypotonic exposure to pancreatic digest can alter the insulin/amylase ratio; however, there is a functional impairment on subsequent islet function after a period of in vitro tissue culture.

Site for Unpurified Islet Transplantation is an Important Parameter for Determination of the Outcome of Graft Survival and Function

Transplantation of unpurified islets into the liver, unlike that of purified islets, causes portal hypertension and coagulopathy. The aim of this project was to determine the most suitable alternative site for transplantation of unpurified pancreatic islets in autotransplanted dogs. Twenty-five female mongrel dogs were divided into 5 groups depending on the site of islet transplantation: liver (3), spleen (7), skeletal muscle (5), omental pouch (6), and renal subcapsule (4). Pancreatic digestion of the total pancreatectomized specimen was carried out by distension of the pancreas with 1.5 mg/mL collagenase suspended in 250 mL Hanks' balanced salt solution using a semiautomatic method. The total number of islets equivalent isolated from 25 dogs was 90948 ± 6053. Only islets > 60 μm in diameter were counted, and the mean islet equivalent transplanted per kg body wt was 6762 ± 429. Islet function was achieved with transplantation into spleen in 71%, omental pouch in 50%, and muscle in 20%, but none in the renal subcapsule or liver groups. Glucose tolerance test at 30 d showed a mean K Value (decline in glucose, %/min) of 1.94 ± 0.73,0.79 ± 0.15 and 1.02 in the splenic, omental pouch and muscle groups, respectively. All animals in the liver group, 2 from the splenic group, and 2 from the renal subcapsule group died of diffuse bleeding. Four out of 5 dogs in the muscle group developed necrosis at the site of transplantation and the islets never functioned. This study demonstrates that in dogs, spleen and omental pouch appear to be suitable sites for transplantation of unpurified islets.

Intravenous vs intraperitoneal transplantation of umbilical cord mesenchymal stem cells from Wharton's jelly in the treatment of streptozotocin-induced diabetic rats

AIM

To evaluate the efficiency of mesenchymal stem cells isolated from Wharton's jelly (WJ-MSCs) through either the intravenous or intraperitoneal transplantations into streptozotocin (STZ)-induced diabetic rats as a therapy for type 1 diabetes mellitus (T1DM).

METHODOLOGY

A rat model with STZ induction was established and the rats were divided into 3 groups: a tail vein injection group, an intraperitoneal injection group and a STZ control group. Following transplantation, blood glucose levels were monitored weekly then the pancreatic tissues were collected to examine the pancreatic islets by histopathology and morphometric studies.

RESULTS

Intravenous transplantation of WJ-MSCs ameliorated hyperglycemia at day 7 after transplantation, with sustained decreased fasting blood glucose (FBG) levels until day 56. Further, these cells ameliorated at least partially the damage induced by STZ in the pancreas and produced a similar morphology to normal islets. On the contrary, intraperitoneal transplantation of WJ-MSCs failed to maintain normoglycemia or ameliorate the damaged pancreas in STZ-injected rats.

CONCLUSION

These findings conclude that the intravenous administration method was effective in transplanting WJ-MSCs for the treatment of T1DM, whereas the intraperitoneal transplantation showed no therapeutic effect in our animal experiments.

Novel immunological strategies for islet transplantation

Islet transplantation has been demonstrated to improve glycometabolic control, to reduce hypoglycemic episodes and to halt the progression of diabetic complications. However, the exhaustion of islet function and the side effects related to chronic immunosuppression limit the spread of this technique. Consequently, new immunoregulatory protocols have been developed, with the aim to avoid the use of a life-time immunosuppression. Several approaches have been tested in preclinical models, and some are now under clinical evaluation. The development of new small molecules and new monoclonal or polyclonal antibodies is continuous and raises the possibility of targeting new costimulatory pathways or depleting particular cell types. The use of stem cells and regulatory T cells is underway to take advantage of their immunological properties and to induce tolerance. Xenograft islet transplantation, although having severe problems in terms of immunological compatibility, could theoretically provide an unlimited source of donors; using pigs carrying human immune antigens has showed indeed promising results. A completely different approach, the use of encapsulated islets, has been developed; synthetic structures are used to hide islet alloantigen from the immune system, thus preserving islet endocrine function. Once one of these strategies is demonstrated safe and effective, it will be possible to establish clinical islet transplantation as a treatment for patients with type 1 diabetes long before the onset of diabetic-related complications.

Evaluation of a high-yield technique for pancreatic islet isolation from deceased canine donors

Type 1 diabetes mellitus is one of the most frequently diagnosed endocrinopathies in dogs, and prevalence continues to increase. Pancreatic islet transplantation is a noninvasive and potentially curative treatment for type 1 diabetes mellitus. Institution of this treatment in dogs will require a readily available source of canine islets. We hypothesized that clinically acceptable islet yield and purity could be achieved by using deceased canine donors and standard centrifugation equipment. Pancreata were procured from dogs euthanized for reasons unrelated to this study. Initial anatomic studies were performed to evaluate efficacy of pancreatic perfusion. Infusion into the accessory pancreatic duct resulted in perfusion of approximately 75% of the pancreas. Additional cannulation of the distal right limb of the pancreas allowed complete perfusion. Collagenase digestion was performed with a Ricordi chamber and temperature-controlled perfusion circuit. Islets were separated from the exocrine tissue with the use of a discontinuous density gradient and a standard laboratory centrifuge. After isolation, islet yield was calculated and viability was assessed with dual fluorescent staining techniques. Islet isolation was completed in 6 dogs. Median (interquartile range) islet yield was 36,756 (28,527) islet equivalents per pancreas. A high degree of islet purity (percentage of endocrine tissue; 87.5% [10%]) and viability (87.4% [12.4%]) were achieved. The islet yield achieved with this technique would require approximately 1 pancreas per 5 kg body weight of the recipient dog. Purity and viability of the isolated islets were comparable with those achieved in human islet transplantation program. According to initial results, clinically relevant islet yield and quality can be obtained from deceased canine donors with the use of standard laboratory equipment.

Human islet mass, morphology, and survival after cryopreservation using the Edmonton protocol

The aim of this study was to assess recovery, cell death, and cell composition of post-thaw cultured human islets. Cryopreserved islets were provided by the Clinical Islet Transplant Program, Edmonton, Canada. Islets were processed using media prepared in accordance with Pre-Edmonton and Edmonton protocols. Cryopreserved islets were rapidly thawed and cultured for 24 h, 3 d, 5 d, and 7 d, following which they were processed for histology. Islet quantification, integrity, morphology and tissue turnover were studied via hematoxylin and eosin stained sections. Ultrastructure was studied by electron microscopy and endocrine cell composition by immunohistochemistry. Using the Pre-Edmonton protocol, islet recovery was 50.1% and islet survival was 50% at 24 h while for the Edmonton protocol, the islet recovery was 69.4% (p<0.001) and islet survival, 50% at ≈2.5 d. With an increasing culture duration although the physical integrity was retained there was an increasing loss of cohesivity both at light microscopic and at ultrastructure level regardless of the protocols used. Percentage islet survival and tissue turnover correlated negatively with culture duration in both protocols. The Edmonton protocol appears to preserve the islets better. However, culture duration adversely affects islet survival and quality, indicating the need for more optimal cryopreservation and culture techniques.

Case report: gastrointestinal hemorrhage caused by a pancreas transplant arteriovenous fistula with large psuedoanuerysm 9 years after transplantation

Reported cases of arteriovenous fistulae in transplant recipients are uncommon. We present a case of an arteriovenous fistula associated with a large pseudoaneurysm in the root of the small bowel mesentery of a pancreas transplant. Uniquely, in our case, the arteriovenous fistula presented with an episode of gastrointestinal (GI) hemorrhage 9 years postoperatively. Radiographic imaging including coronal computed tomography angiogram and conventional angiogram demonstrated an arteriovenous fistula in the patient's pancreas transplant between the distal superior mesenteric artery (SMA) and superior mesenteric vein (SMV) with 6 cm aneurysmal dilatation. The tremendous flow in the fistula in the root of the graft small intestine mesentery led to graft duodenal mucosal congestion and lower GI hemorrhage. After successful embolization of the SMA-SMV fistula and pseudoaneurysm using interventional radiographic techniques, the arteriovenous fistula remained thrombosed. The patient had no further episodes of GI bleeding and her endoscopic evaluation was otherwise negative. The presence of arteriovenous fistulae and pseudoaneurysms in pancreas transplant recipients is uncommon, but has been previously documented. This case is further distinguished from previous reports by the notable 9-year interval between transplantation and the onset of hemorrhage. Historically, symptomatic vascular malformations have been associated with significant patient morbidity and mortality. Successful patient management involves timely and accurate diagnosis and intervention.

Impact of islet transplantation on diabetes complications and quality of life

Insulin represents a life-saving therapy for patients with type 1 diabetes but, despite appropriate treatment, it prevents only partially long-term diabetic complications, while generating fatal hypoglycemic episodes. Islet transplantation gained attention because of its safety, effectiveness, and minimal invasiveness; however it remains a procedure reserved for a selected group of patients. The introduction of the Edmonton Protocol in 2000, based on a newly designed steroid-free immunosuppressive protocol, revamped the course of islet transplantation. The main goal of islet transplantation remains insulin independence, although the effect of islet transplantation can be more comprehensively evaluated in terms of frequency of hypoglycemic episodes and impact on diabetic complications and quality of life. Islet transplantation was shown to have positive consequences on cardiovascular, renal, neurologic, and ocular diabetic complications. The proof of concept for cellular replacement therapy in diabetes has been established with islet transplantation, it only needs to be improved and rendered widely available.

Pancreatic islet cell transplantation: update and new developments

Pancreatic islet cell transplantation is a treatment alternative for patients with type 1 diabetes who experience hypoglycemic unawareness despite maximal care. The good results obtained by the group from Edmonton and other centers, with 80% insulin independence at 1 year posttransplant, are not sustainable over time, with 5-year insulin independence achieved in only 10% of patients. However, persistent graft function, even without insulin independence, results in improved glucose control and avoidance of hypoglycemic events. Changes in organ preservation, islet processing technique, and immunosuppression regimens can result in improvement of results in the future. Islet autotransplantation is an option for patients who undergo total pancreatectomy for chronic pancreatitis with debilitating pain, in which reinfusion of the islets from the resected pancreas can result in avoidance of postsurgical diabetes or enhanced glucose control.

Pancreatic islet cell transplant for treatment of diabetes

Islet cell transplantation recently has emerged as one the most promising therapeutic approaches to improving glycometabolic control in type 1 diabetic patients, and, in many cases, to obtaining insulin independence. Islet cell transplantation requires a relatively short hospital stay and has the advantage of being a relatively noninvasive procedure. The rate of insulin independence 1 year after islet cell transplantation has improved significantly in recent years (60% at 1 year after transplantation compared to the 15% in the past years). Data from a recent international trial confirmed that islet cell transplantation potentially can be a cure for type 1 diabetes. Recent data indicate that insulin independence after islet cell transplantation is associated with an improvement in glucose metabolism and quality of life and with a reduction in hypoglycemic episodes. Islet cell transplantation is still in its initial stages, and many obstacles still need to be overcome. Once clinical islet transplantation has been established, this treatment could be offered to diabetic patients long before the onset of diabetic complications or to patients with life-threatening hypoglycemic unawareness and brittle diabetes.

New therapies aimed at the preservation or restoration of beta cell function in type 1 diabetes

Type 1 diabetes is caused by an immune-mediated destruction of the insulin-secreting beta cells in the pancreas. The disease can become clinically apparent at any age. At diagnosis, there is invariably some residual beta cell function and more so in adults than in children. Recent studies--including one conducted mainly in Belgium--have provided proof of principle that short-term anti-T-cell antibody treatment is able to preserve residual beta cell function for at least 18 months. The resultant stabilizing effect on metabolic control is expected to delay or limit chronic complications in these patients. With a similar goal in mind, nonuremic C-peptide negative patients are offered beta cell transplantation. The outcome of these implants looks promising but their final applicability hinges on finding ways to induce immune tolerance to the donor beta cells. A widespread application, however, will only occur if the shortage of viable human donor cells can be overcome. Both xenotransplantation and stem cell therapy provide possible strategies to solve this problem and represent areas of intense investigation. The ultimate goal is prevention of clinical disease. Studies by the Belgian Diabetes Registry and others in first degree family members of type 1 diabetic patients have refined the identification of individuals at very high risk of hyperglycaemia so that new immunological treatments can be tested in the prediabetic phase.

Alloreactivity Against Repeated HLA Mismatches of Sequential Islet Grafts Transplanted in Non-Uremic Type 1 Diabetes Patients

BACKGROUND

Islet transplantation can restore insulin production in type 1 diabetes patients. However, survival of the islet allografts will face rejection or recurrence of autoimmunity or a combination of both. In a study on islet-after-kidney transplants, we previously reported that islet cell recipients presented low T-cell alloresponses for HLA mismatches that were shared by the islet cell graft and the prior kidney graft, that is, repeated mismatch, while vigorous responses were measured against novel HLA mismatches.

METHODS

We now investigated T-cell alloreactivity to repeated HLA-mismatches in three non-uremic type 1 diabetic patients each receiving three sequential islet cell implants.

RESULTS

These islet-after-islet recipients patients exhibited low or absent responses to repeated mismatches to the first graft which was accompanied by sustained graft function, and reduced responsiveness towards subsequent grafts. In one patient, T-cell responses towards these mismatches were noticed following new mismatches in subsequent grafts, with loss of graft function.

CONCLUSION

These case reports further support the view that subsequent islet implantations can reduce alloreactivity for repeated HLA mismatches. They demonstrate the usefulness of monitoring T-cell reactivity against islet allografts to correlate immune function with graft survival and to identify conditions for preservation of beta-cell function.

Tolerance induction and endogenous regeneration of pancreatic beta-cells in established autoimmune diabetes

Studies aimed at the understanding of the multifactorial development of autoimmune diabetes have made substantial contributions toward elucidating the molecular mechanisms that open the road to an effective prevention of defective immune responses. Immunomodulatory regimens capable of inducing tolerance are shown to be effective even in the reversal of established autoimmune diabetes in animal models. Experimental trials including the reeducation of autoreactive T cells, depletion of macrophages, dendritic cells, and T cells, as well as the use of monoclonal antibodies, have yielded encouraging results, but have not yet been translated into beneficial clinical outcomes. In addition, we are now seeing an emergence of promising new directions aimed at the induction of islet regeneration by endogenous factors, suggesting that the repair of pancreatic tissue is possible without the need for an engraftment of donor tissue. These recent waves of technological progress have injected new hope for a combined therapy to offer diabetic patients long-term benefits of insulin independence. This article reviews the latest findings on diabetic pathogenesis and discusses promising avenues to tolerance induction and islet regeneration.

Diabetic heart dysfunction: is cell transplantation a potential therapy?

The presence of long-standing diabetes mellitus leads to the development of a number of typical end organ complications. These complications include coronary heart disease, stroke, peripheral arterial disease, diabetic retinopathy, diabetic nephropathy, diabetic neuropathy and diabetic cardiomyopathy. From an epidemiological and clinical standpoint, cardiovascular disease remains the most important complication of diabetes. Cardiovascular complications are the most common causes of morbidity and mortality in diabetics, accounting for up to 85% of the mortality in diabetic patients. The increasing prevalence of obesity and sedentary lifestyle in Western society are leading to an increase in the prevalence in diabetes. As such diabetes is an increasing cause of cardiovascular disease.

Solving the organ shortage: potential strategies and the likelihood of success

The discrepancy between the demand and supply of organs for clinical transplantation remains a major problem. The current incidence of end-stage renal disease results in a patient population that doubles every decade. However, there have been no advancements in developing a comparable increase in the number of available allografts. There are three potential approaches to solving the shortage. In the near-term, the development of technology to access the pool of warm ischemically damaged organs may represent a solution. To achieve this goal, it will be necessary to develop technology that mimics the physiologic processes of wound repair. Alternatively, it has been proposed that an increased supply of organs can be developed with xenografts. To make xenotransplantation a clinical reality, it will be necessary to overcome the barriers that exist in nature between the species. Recent work in the area of stem cell research has provided evidence supporting the potential of generating biohybrid organs. A major undertaking of this emerging field will be to develop the ability to define and control the differentiation processes involved in organ specificity. The following is a review of the current status and relative issues involved with these three potential approaches to solving the organ shortage.

A view on beta cell transplantation in diabetes

Organ donors also offer a source of insulin-producing tissue that might be used for the treatment of diabetes. Clinical protocols for transplantation of this tissue aim for the prevention of chronic diabetes complications without introducing new serious side effects. Pancreas and islet cell transplantation are discussed in this perspective. The future of islet cell implants looks favorable but depends on finding ways to induce immune tolerance to the donor beta cells. Clinical trials can take advantage of relevant progress in animal models. In a limited study, recipient treatment with antilymphocyte antibodies and culture of donor cell preparations appeared useful to induce a state of operational immune tolerance in type 1 diabetic patients, as indirectly judged by graft survival and by analysis of auto- and alloreactivities in recipients. Use of cultured beta cell preparations also allows donor cell recruitment from suboptimal donor organs and increases the degree of standardization and quality control of islet cell grafts. The future of these grafts will depend on the development of techniques for the neogenesis of beta cells.

Transduction of human and mouse pancreatic islet cells using a bicistronic recombinant adeno-associated viral vector

Recent reports indicate successful transduction of pancreatic islets using recombinant adeno-associated viral (rAAV) vectors. This advance offers new possibilities in rendering islets resistant to rejection and recurrence of autoimmune destruction in the setting of islet transplantation as treatment of type 1 diabetes. Most gene delivery approaches using islets have thus far involved transduction with a single gene. However, the concomitant delivery of more than one gene encoding cytoprotective and/or immunoregulatory molecules may offer superior clinical utility. Here, we have generated a bicistronic rAAV (serotype 2) vector incorporating a viral internal ribosome entry site (IRES), derived from polio virus type 1, to allow for translation of two coupled cDNAs from a single mRNA transcript. Our study demonstrates the ability of this vector to produce significant expression of two reporter proteins in human and mouse islets in vitro. This expression did not interfere with beta-cell function. Transduction was maintained in vivo following transplantation of mouse islets. These data are the first report of efficient islet cell transduction with two genes using a single bicistronic rAAV vector and have direct implications for strategies aimed at enhancing islet transplant survival.

Improved quality and yield of islets isolated from human pancreata using a two-step digestion method

A new approach, involving a two-step digestion process and Los Angeles preservation solution #1 (LAP-1), a cold storage solution, was developed for isolation of high-quality islets from human pancreata for transplantation. This approach markedly improves the islet yield, purity and viability, and the isolation success rate. In this method, the pancreas was digested first in warm collagenase solution for up to 20 minutes. After decanting the enzyme solution, partially digested tissue was dissociated by gentle agitation in cold LAP-1 solution without additional collagenase. The digested tissues were stored in cold LAP-1 solution until islet purification on Euro-Ficoll. Forty-six islet isolations were performed consecutively by the new method (group 1). These results were compared to those obtained earlier with 46 consecutive isolations, using our previous method that had been used before development of the new method (group 2). Our old method was a modification of Ricordi's method involving only warm collagenase digestion and the storage of digested tissues in cold Hanks balanced salt solution. All pancreata were partial, containing the body and tail. There were no significant differences in both groups with regard to the donor age, cold ischemic time, harvesting conditions, and pancreatic weight. Pancreas digestion was completed in approximately 1 hour in both groups. The isolation success rate as determined by viable islets after 2 days in culture was 93.5% (43 of 46 cases) in group 1, and 56.5% (26 of the 46) in group 2. Immediately after isolation, the new method yielded a total of 335,739 +/- 36,244 islets equivalent to 150 microm (IEQ) and 6,233 +/- 681 IEQ/g of pancreas with 83 +/- 2.5% purity, whereas the old method yielded a total of 195,587 +/- 25,242 IEQ and 3,763 +/- 5,509 IEQ/g with 69.2 +/- 4.7% purity. Isolated islets in group 1 maintained a good three-dimensional structure, displayed normal insulin release to high glucose stimulation in vitro, and restored euglycemia after transplantation into streptozotocin-diabetic athymic mice. The two-step digestion method provides a sufficient number of islets for transplantation from a single pancreas.

Antibodies for transplantation

The use of antibodies in transplantation has become a clinical reality. Antibodies have been used to both dampen the recipient's immune response and to obscure the immunogenicity of the donor graft. Traditionally, antibodies have been administered to the transplant recipient to transiently inactivate the host's T cells, the lymphocytes responsible for recognizing and attacking foreign proteins, cells, and tissues. Antibodies can also be used to eliminate any highly immunogenic passenger cells from a donor graft prior to transplantation, and antibodies can mask or conceal antigens present on donor cells that might trigger rejection.

Secretion from islets and single islet cells following cryopreservation

The ability to cryopreserve pancreatic islets has allowed the development of low-temperature banks that permit pooling of islets from multiple donors and allows time for sterility and viability testing. However, previous studies have shown that during cryopreservation and thawing there is a loss of islet mass and a reduction in islet function. The aim of this study was to measure and compare insulin secretion from cultured nonfrozen and frozen-thawed canine islets and beta-cells. Canine islets were isolated from mongrel dogs using intraductal collagenase distention, mechanical dissociation, and EuroFicoll purification. One group of purified islets was cultured overnight before dissociation into single cells and subsequent analysis. Remaining islets were cultured overnight (22 degrees C) and then cryopreserved in 2 M dimethyl sulfoxide (DMSO) solution using a slow stepwise addition protocol with slow cooling to -40 degrees C before storage in liquid nitrogen (-196 degrees C). Frozen islets were rapidly thawed (200 degrees C/min) and the DMSO removed using a sucrose dilution. From a series of seven consecutive canine islet isolations, islet recovery following postcryopreservation tissue culture was 81.5 +/- 4.8% compared to precryopreservation counts. In vitro islet function was equivalent between cultured nonfrozen and frozen-thawed islets with a calculated stimulation index of 10.4 +/- 1.5 (mean +/- SEM) for the frozen-thawed islets, compared with 12.4 +/- 1.2 for the cultured nonfrozen controls (p = ns, n = 7 paired experiments). Amperometric detection of secretion from single beta-cells in vitro has the sensitivity and temporal resolution to detect single exocytotic events and allows secretion to be monitored from single beta-cells in real time. Secretion from single beta-cells elicited by chemical stimulation was detected using a carbon fiber microelectrode. The frequency of exocytosis events was equivalent between the cultured nonfrozen and frozen-thawed beta-cells with an average of 7.0 +/- 1.32 events per stimulation for the cultured nonfrozen group compared with 6.0 +/- 1.45 events from the frozen then thawed preparations (minimum of 10 cells per run per paired experiment, p = ns) following stimulation with tolbutamide. The average amount of insulin released per individual exocytosis event was equivalent for the cultured nonfrozen and frozen-thawed islets. In addition, beta-cells responded to both tolbutamide and muscarinic stimulation following cryopreservation. It was determined that beta-cells recovered following cryopreservation are capable of secreting insulin at levels and frequencies comparable to those of cultured nonfrozen islet preparations.

The effects of microencapsulation on pancreatic islet osmotically induced volumetric response

Microencapsulation of pancreatic islets has been proposed as a means to prevent allograft rejection and to protect islets during cryopreservation. The aim of this study was to investigate: 1) the effects of the cryoprotectants (CPAs) dimethyl sulfoxide (DMSO) and ethylene glycol (EG) on the volume of Ca2+ alginate microcapsules, and 2) the effects of microencapsulation on the volumetric response of human and canine pancreatic islets during CPA equilibration. Stock sodium alginate with a high mannuronic acid content (HM) or a high guluronic acid content (HG) was used to generate empty capsules (mean diameter 200 microm) with an electrostatic generator. The capsules were held in place by a holding pipette system and videotaped during the addition of 2 or 3 M CPA at 22 degrees C. Islets (isolated from human cadaveric donors and mongrel dogs and then cultured overnight at 37 degrees C) were encapsulated in alginate (HM), loaded into a microperfusion chamber, and the change in islet volume was videotaped after exposure to the same CPAs and concentrations. These were compared to the volume responses of nonencapsulated islets. Images were analyzed using a computerized image analysis system and the data were analyzed using ANOVA. HG microcapsules showed a significant (p < 0.05) increase in volume following exposure to EG but not to DMSO. HM microcapsule volume did not change significantly following exposure to either EG or DMSO and was therefore chosen as the substrate for islet encapsulation. Free, nonencapsulated canine and human islets responded to the osmotic challenge of the 2 M DMSO by shrinking to 70.00 +/- 1.04% (mean +/- SEM) and 70.11 +/- 1.05%, and in 2 M EG to 72.89 +/- 1.93% and 69.33 +/- 1.38%, respectively, of the isotonic volume before returning to the original cell volume. Exposure to 3 M DMSO or EG resulted in a further dehydration to 65.89 +/- 0.91% and 67.67 +/- 1.91% for canine and 62.22 +/- 0.66.% or 65.89 +/- 1.30% for human islets. Minimum volumes were reached within 30-40 s after exposure to the cryoprotectant. Encapsulated human islets reached 86.88 +/- 1.47% of their original volume in 2 M and 80.33 +/- 0.89% in 3 M DMSO, and 87.33 +/- 1.86% in 2 M and 82.80 +/- 1.57% in 3 M EG. This volume change was significantly less (p < 0.01) than that observed in corresponding free islets. Encapsulated canine islets reached 83.67 +/- 2.13% of their original volume in 2 M and 78.22 +/- 0.95% in 3 M DMSO, and 85.44 +/- 1.92% in 2 M and 78.11 +/- 2.01% in 3 M EG. As with human islets, this was significantly different than free islets (p < 0.01). These minimal volumes were reached within 30-50 s. These results demonstrate that there are cryoprotectant and alginate-specific interactions and that microencapsulation modulates the degree of osmotically induced shrinkage of islets. The development or modification of existing cryopreservation protocols to improve postcryopreservation recovery or function must account for these factors.

Islet cryopreservation protocols

Low temperature banking of islets has facilitated ongoing clinical trials, allowing for the collection and long-term storage of islets during which viability and sterility assessment can be carried out. Islets from most species of animals have been cryopreserved using various freeze-thaw protocols; however, the best to date is slow cooling to -40 degrees C and rapid thawing from -196 degrees C. If one carefully follows the three distinct steps of freezing and thawing human islets can be successfully cryopreserved, allowing for the establishment of a low temperature bank with diverse HLA (Human Leukocyte Antigen) and ABO phenotypes. Using a combination of fresh and cryopreserved islets to transplant type I diabetic patients, long-term insulin independence has been obtained.

Pretreatment of crude pancreatic islets with mitomycin C prolongs graft survival time in xenogeneic rat-to-mouse model

BACKGROUND

Rejection of pancreatic islet grafts is still a serious problem. We evaluated the effect of mitomycin C (MMC) on the survival of crude islets grafts after xenogeneic islet transplantation.

METHODS

WS (RT1k) rat islets pretreated with various concentrations of MMC (0, 1, 3.2, 10, 32, 50, 100, 320, and 1,000 microg/ml) were transplanted into C57BL/6 mice with streptozotocin-induced diabetes. In vivo graft function was assessed by a daily measurement of nonfasting blood glucose concentration in each animal. We also examined the separate effect of MMC on purified islets and contaminants present in the crude islet preparation.

RESULTS

MMC at doses of 10, 32, 50, and 100 microg/ml resulted in a significant prolongation of the mean graft survival time from a control of 12.4+/-2.5 days to 23+/-7.4, 17.5+/-5.4, 25.5+/-14.7, and 26.7+/-8.9 days, respectively. Deterioration of glucose metabolism was noted when the dose exceeded 32 microg/ml, whereas at 320 microg/ ml, MMC failed to restore normoglycemia. Prolongation of survival time of crude islets was the result of its effect on islets and contaminant components of the crude islet preparation. In vitro study showed that MMC treatment at a higher concentration than 10 microg/ml reduces the stimulatory as well as proliferative capacity of lymph node cells.

CONCLUSIONS

Pretreatment of pancreatic islets with MMC at 10 microg/ml prolongs xenograft survival without deterioration of in vivo graft function. This novel treatment modality represents a new strategy for the modulation of immunity of islets and contaminants in crude islet preparations.

Intraductal collagenase delivery into the human pancreas using syringe loading or controlled perfusion

Effective intraductal delivery of the enzyme collagenase into the pancreas is crucial to the subsequent ability to isolate viable islets. Most clinical islet transplant centers load the enzyme into the pancreas by retrograde injection using a syringe following cannulation of the pancreatic duct. An alternative approach is to perfuse the pancreas via the pancreatic duct with collagenase solution using a recirculating perfusion device system. This provides control over perfusion pressures and collagenase temperature. This study reports on our evaluation of the delivery of Liberase-HI into the pancreas of 14 consecutive adult multiorgan cadaveric donors. Alternate glands were procured and processed using an identical protocol with the exception of collagenase delivery. The first group of pancreases was loaded using the perfusion technique where cold (4 degrees C) Liberase-HI was perfused at 80 mmHg for 5 min after which the pressure was increased to 180 mmHg. The collagenase solution was then slowly warmed to 35 degrees C, transferred to the dissociation chamber and mechanically dissociated, and then purified using discontinuous gradients of Ficoll. Pancreases in the second group were loaded with collagenase (28-32 degrees C) using the syringe technique before mechanical dissociation and purification. There were no significant differences in pancreas cold ischemia, donor age, body mass index, maximum blood glucose, or serum amylase of the donors between the two groups. Mean collagenase digestion time in the digestion chamber was not different between the two groups; however, the amount of undigested tissue remaining after dissociation was significantly higher in the syringe-loaded group (15.3 +/- 2.6 g vs. 4.6 +/- 2.1 g, mean +/- SEM, p < 0.05). Postdigestion recovery of islets was 471 +/- 83 x 10(3) IE in the perfusion group compared with 391 +/- 57 x 10(3) IE for the syringe-loaded group. Postpurification recovery was higher in the perfused group (379 +/- 45 vs. 251 +/- 28 x 10(3) IE, p < 0.05, two-tailed paired t-test). No difference in in vitro islet viability was observed between the two groups following glucose perifusion with the calculated stimulation index of 4.6 +/- 0.6 for the perfusion group and 4.2 +/- 0.7 for the syringe-loaded group. Controlled perfusion via the pancreatic duct allows the effective delivery of the enzyme achieving maximal distension to all regions of the pancreas leading to an increased recovery of the islets with no detrimental effect on subsequent in vitro islet function.

Studies on smaller (approximately 315 microM) microcapsules: IV. Feasibility and safety of intrahepatic implantations of small alginate poly-L-lysine microcapsules

The most successful transplantation site of nonencapsulated islets of Langerhans is the liver. Because usual alginate poly-L-lysine microcapsules were too large (700-1200 microm diameter) for intravascular implantations and were almost exclusively implanted intraperitoneally, the question of the preferred implantation site of microencapsulated islets has received little attention. The feasibility of implanting smaller (approximately 315 microm) alginate poly-L-lysine microcapsules into the liver and the effect of such implantations on portal pressure and liver histology was evaluated in Wistar rats. A bolus of 10,000 microcapsules of 315 microm diameter was injected intraportally (group 1; n = 22). The portal pressure increased from 6.4 +/- 1.8 mmHg to a maximum of 19 mmHg, returned to basal levels within 2 h, and remained normal after 2 months. In group 2 (n = 3), following the injection of 10,000 larger microcapsules (420 microm), the portal pressure increased to > 60 mmHg and two out of the three rats died within 3 h. When 5,000 microcapsules of 420-microm diameter were injected (group 3; n = 5), the portal pressure peaked to 30 +/- 8 mmHg and remained elevated after 4 h (12 +/- 3 mmHg), but returned to normal (8 +/- 1 mmHg) after 2 weeks. Histological studies showed normal hepatic architecture without collagen deposition into portal tracts occupied by microcapsules.

CONCLUSION

intrahepatic implantations of approximately 315-microm alginate poly-L-lysine microcapsules are feasible and safe. These results justify further investigation of this potential implantation site for microencapsulated islets.

Osmotic tolerance limits of canine pancreatic islets

Future improvements in the recovery and function of pancreatic islets following cryopreservation will require a more precise quantification of the stresses that occur at each stage of the cryopreservation protocol. Changes in solution osmolality during the addition and dilution of cryoprotectants and during freezing and thawing induce changes in islet volume that may exceed tolerable limits. The aim of this study was to determine the range of solution osmolalities that results in significant changes in islet function. Islets were isolated from canine pancreases by collagenase digestion and Euro-Ficoll purification. Following 12-h culture at 37 degrees C, islets were counted and dispensed into multiwell plate inserts. Islet function was assessed in each well immediately before and 24 h following a 10-min osmotic challenge with hypo- or hyperosmotic solutions of PBS (0, 75, 150, 300, 600, 1200, or 2300 mOsm/kg) at 22 degrees C. Canine islets reached their osmotic equilibrium within 10 min. Duplicate wells were used for each osmolality treatment for each of six donors (n = 12). No significant differences in basal or glucose-stimulated insulin secretion were found between wells prior to the osmotic challenge (3.35 +/- 0.45 and 20.98 +/- 3.36 microIU/IE/h, respectively). Following the osmotic challenge and 24-h in vitro tissue culture, a significant increase in basal secretion was observed for islets exposed to 0 and 75 mOsm/kg solutions and a significant decrease for islets exposed to 2300 mOsm/kg solution. Islets exposed to 0 and 2300 mOsm/kg solutions showed significant decreases in the stimulated insulin secretion when compared to controls. Solution osmolalities of 150-1200 mOsm/kg appear to be tolerated by canine islets with no significant deviations in insulin secretion. The corresponding tolerable volume range was 152.6 +/- 6.8% to 60 +/- 5.1% of the isotonic islet volume. The minimum critical volume was used in a theoretical analysis of the islet volumes that would result from equilibrium freezing in dimethyl sulfoxide (DMSO). The calculations show that 1.5 mol/l DMSO is sufficient to prevent damage to islets due to excessive shrinkage. Further refinement of cryoprotectant addition and dilution protocols, and cooling and warming protocols for canine islets, are now possible.

Effect of cryopreservation on the survival and function of murine islet isografts and allografts

We compared the efficacy of fresh and frozen/thawed islets by determining the minimum number required to consistently reverse diabetes in mice. Defined numbers of islets, isolated from Balb/c (H-2d) and CBA/J (H-2k) mice, were transplanted into streptozotocin-induced diabetic Balb/c mice. Frozen/thawed grafts were cooled slowly to -40 degrees C, stored at -196 degrees C, and thawed rapidly. At 100 days after transplantation, isografts were recovered for measurement of insulin content. Mean (+/-SD) recovery of cryopreserved islets after thawing was 80 +/- 3% (range 67-89%). For both fresh and frozen/thawed isografts and allografts, 200 islets were required to establish normoglycemia. The degree of metabolic function provided by equivalent quantities of fresh and frozen/thawed grafts was similar; and all normoglycemic isograft recipients remained so until graft nephrectomy. The insulin content of fresh and frozen/thawed isografts containing 200 and 300 islets were 151 +/- 25 and 126 +/- 8 mU and 259 +/- 36 and 278 +/- 20 mU, respectively. Among allograft recipients, median survival ranged from 15 to 20 days, and was not influenced by cryopreservation or graft size. The results of this study demonstrate a high rate of recovery of viable islets following cryopreservation. The function of equivalent quantities of fresh and cryopreserved islet isografts and allografts in nonimmunosuppressed recipients is similar.

End-stage cystic fibrosis: improved diabetes control 2 years after successful isolated pancreatic cell and double-lung transplantation

Over a period of years, insulin-dependent diabetes and respiratory insufficiency developed in a 35-year-old patient with end-stage cystic fibrosis. After waiting more than 4 years while receiving maintenance treatment with continuous liquid O2 and nasal ventilation, the patient underwent double-lung and pancreatic islet cell transplantation. Subsequently, the patient has enjoyed a normal life with full employment and much better control of his diabetes. Pancreatic islet cell transplantation is a simple and innocuous technique easily added to the end of lung transplantation. These new pancreatic cells, although locally injected, are still secreting more than 2 years later as assessed by repeated C-peptide measurements.

Osmotic characteristics of isolated human and canine pancreatic islets

Cryopreservation protocols for pancreatic islets may be optimized by modeling the changes in volume that occur during cryoprotectant addition/dilution and cooling/warming. Modeling may be facilitated if it can be demonstrated that isolated islets behave as ideal osmometers where the equilibrium volume is a linear function of the reciprocal of the osmolality of the extracellular medium (the Boyle van't Hoff relationship). The present study was performed to test the hypotheses that: (i) human and canine islets exhibit a linear osmotic response during exposure to hypo-, iso-, and hyperosmotic solutions and to determine the human and canine islets osmotically inactive fraction (Vbp); (ii) to determine if the ionic properties of a concentrated electrolyte solution have an effect on the osmotic response; and (iii) to determine if the osmotic response of pancreatic islets varies between species (human and canine). Islets were isolated from four human and four canine pancreases using standard collagenase digestion and EuroFicoll purification. After 12 h incubation at 37 degrees C, islets (n = 4 from each isolation) were exposed to varying salt or sucrose concentrations (75-1200 mOsm/kg). Islets were held by a micropipette system attached to an inverted microscope, and solutions were exchanged while videotaping. An imaging system was used to determine the cross-sectional area of the islet which was then used to estimate the spherical volume. The results of linear regression analysis indicated that both human and canine islets respond ideally to osmotic conditions within a range of 150-1200 mOsm/kg in both the electrolyte (salt) and the nonelectrolyte (sucrose) solutions. The Vbp value (mean +/- SD) of the four donors was 0.513 +/- 0.068 for canine islets in sucrose solutions, 0.474 +/- 0.068 for canine islets in salt solutions, 0. 425 +/- 0.073 for human islets in sucrose solutions, and 0.39 +/- 0. 073 for human islets in salt solutions. There was a significant difference between human and canine islets (P < 0.05) but not between experimental solutes (NaCl or sucrose) (P < 0.05). These data may be used in conjunction with osmotic tolerance data to develop improved methods for the cryopreservation of isolated islets.

Excellence of the two-layer method (University of Wisconsin solution/perfluorochemical) in pancreas preservation before islet isolation

BACKGROUND

In islet transplantation pancreatic preservation before islet isolation is an obstacle compromising islet yield and viability. We tested the feasibility of a two-layer method (University of Wisconsin solution [UW]/perfluorochemical) for pancreatic preservation before islet isolation.

METHODS

Dog pancreases were processed into pure islets by the method of Ricordi preceded by five different preservations (groups 1-a and 1-b, the two-layer method for 3 and 24 hours; groups 2-a and 2-b, simple cold storage in UW for 3 and 24 hours; group 3, without preservation). Islet yields and functional success after autotransplantation into the liver were compared among the groups.

RESULTS

Postpurification islet equivalents (IE)/gm pancreas and functional success rate were 5600 (mean), 83% in group 1-a; 4000, 56% in group 1-b; 4700, 33% in group 2-a; 1300, 0% in group 2-b; and 5000, 89% in group 3 (p < 0.05; 2b versus 1-a, 1-b, and 3), respectively. There was no statistical difference among groups 1-a, 1-b, and 3 in terms of islet yield and function (p > 0.2).

CONCLUSIONS

The two-layer method is more effective than conventional simple cold storage in UW for pancreatic preservation before islet isolation. Clinical trials with the two-layer method are warranted.

The determination of membrane permeability coefficients of canine pancreatic islet cells and their application to islet cryopreservation

Sufficient numbers of pancreatic islets for successful allotransplantation can be achieved by storing and then pooling islets from several donors. Optimal MHC matching and infectious disease screening also require long-term storage of islets, and cryopreservation is currently the only practical approach. Cryopreservation protocols may be optimized by modeling the changes in cell volume and the associated damage incurred during cryoprotectant addition and dilution and during cooling and warming. The objective of the present work was to determine the following biophysical parameters of canine islet cells; the osmotically inactive cell volume (Vb), hydraulic conductivity (Lp), cryoprotectant permeability coefficient (Ps), and the reflection coefficient sigma. A determination of these parameters allows the simulation of cell responses using computer models. Islets were isolated by collagenase digestion and Euro-Ficoll purification. After 24 h culture, islets were dissociated into single cells using trypsin and 2 mM EGTA. The kinetic change in cell volume as a function of time after exposure to 2 M dimethyl sulfoxide (Me2SO) was measured using an electronic particle counter at 22, 5, and -3 degrees C. At -11 degrees C, cells were preloaded with 1 M Me2SO and exposed to 4 M Me2SO to prevent the formation of ice in the working solution. Kedem-Katchalsky theory was used to describe the cell volume change kinetics, and a three-parameter curve fitting was performed using the Marquardt-Levenberg method to determine Lp, Ps, and sigma values. The Lp was determined to be 0.19 +/- 0.05, 0.037 +/- 0.005, 0.020 +/- 0.003, and 0.013 +/- 0.005 micron.min-1.atm-1 (mean +/- SD) at 22, 5, -3, and -11 degrees C, respectively. The Ps values were 1.05 +/- 0.50, 0.15 +/- 0.04, 0.096 +/- 0.028, and 0.067 +/- 0.029 x 10(-3) cm.min-1 at 22, 5, -3, and -11 degrees C, respectively. The sigma values were 0.81 +/- 0.16, 0.91 +/- 0.09, 0.80 +/- 0.21, and 0.98 +/- 0.04 at 22, 5, -3, and -11 degrees C, respectively. The temperature dependence or activation energy of Lp and Ps was calculated, using the Arrhenius equation, to be 12.7 and 13.5 kcal.mol-1, respectively. These permeability parameters were used to calculate cell water loss and the likelihood of lethal intracellular freezing during cooling, as well as both water flux and solute concentration gradients across the cell membrane during warming.

Standardization of procedure for efficient ex vivo gene transfer into porcine pancreatic islets with cationic liposomes

BACKGROUND

New strategies to improve the outcome of encapsulated porcine islet transplantation may involve the transfer of gene sequences affecting islet viability. While adenoviral vectors appear as the most efficient gene transfer system so far established for islets, non-viral-based vectors are most likely to fulfill microbiological safety criteria and be retained in the clinical setting. Our aim was to standardize the procedures of gene transfer into adult porcine islets using cationic liposome DOTAP.

METHODS

Porcine islets obtained by collagenase digestion and density gradient purification were lipofected with plasmids coding for luciferase or beta-galactosidase under the control of simian virus 40 or cytomegalovirus promoter. The following parameters were explored: exposure time to vector (1-48 hr), DNA amount (1-15 microg/500 islets), and DOTAP to DNA ratio (2-16). Reporter gene expression was determined 48-72 hr after lipofection.

RESULTS

Efficiency and reproducibility of transfection were maximal with the following procedure: 3-hr exposure time followed by islet washing, 12 microg of DNA per 500 islets (150 microm equivalent), and DOTAP to DNA ratio of 12 microl/microg. Freshly isolated islets in large aliquots (n=4000 in 50-ml tubes) were efficiently transduced with this procedure, and distribution of gene expression was homogenous when islets were subsequently plated in 500-islet aliquots. Luciferase gene expression was detected for a minimum of 7 days after lipofection. Gene expression was also evident up to 4 weeks after islet transplantation beneath the kidney capsule of athymic mice. Transfection of islets using the beta-galactosidase vector yielded 25% positive islets. Islet viability was not adversely affected.

CONCLUSIONS

This islet lipofection procedure may help achieve the local release of a bioactive peptide in the graft environment and have therapeutic applications in islet transplantation.