Successful human islet isolation utilizing recombinant collagenase

HLA-G1+ Expression in GGTA1KO Pigs Suppresses Human and Monkey Anti-Pig T, B and NK Cell Responses

The human leukocyte antigen G1 (HLA-G1), a non-classical class I major histocompatibility complex (MHC-I) protein, is a potent immunomodulatory molecule at the maternal/fetal interface and other environments to regulate the cellular immune response. We created GGTA1-/HLAG1+ pigs to explore their use as organ and cell donors that may extend xenograft survival and function in both preclinical nonhuman primate (NHP) models and future clinical trials. In the present study, HLA-G1 was expressed from the porcine ROSA26 locus by homology directed repair (HDR) mediated knock-in (KI) with simultaneous deletion of α-1-3-galactotransferase gene (GGTA1; GTKO) using the clustered regularly interspersed palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9) (CRISPR/Cas9) gene-editing system. GTKO/HLAG1+ pigs showing immune inhibitory functions were generated through somatic cell nuclear transfer (SCNT). The presence of HLA-G1 at the ROSA26 locus and the deletion of GGTA1 were confirmed by next generation sequencing (NGS) and Sanger's sequencing. Fibroblasts from piglets, biopsies from transplantable organs, and islets were positive for HLA-G1 expression by confocal microscopy, flow cytometry, or q-PCR. The expression of cell surface HLA-G1 molecule associated with endogenous β2-microglobulin (β2m) was confirmed by staining genetically engineered cells with fluorescently labeled recombinant ILT2 protein. Fibroblasts obtained from GTKO/HLAG1+ pigs were shown to modulate the immune response by lowering IFN-γ production by T cells and proliferation of CD4+ and CD8+ T cells, B cells and natural killer (NK) cells, as well as by augmenting phosphorylation of Src homology region 2 domain-containing phosphatase-2 (SHP-2), which plays a central role in immune suppression. Islets isolated from GTKO/HLA-G1+ genetically engineered pigs and transplanted into streptozotocin-diabetic nude mice restored normoglycemia, suggesting that the expression of HLA-G1 did not interfere with their ability to reverse diabetes. The findings presented here suggest that the HLA-G1+ transgene can be stably expressed from the ROSA26 locus of non-fetal maternal tissue at the cell surface. By providing an immunomodulatory signal, expression of HLA-G1+ may extend survival of porcine pancreatic islet and organ xenografts.

A Preliminary Characterization of a Novel Recombinant Clostridial Collagenase Blend

Clostridial collagenases are essential biotechnological tissue dissociation agents owing to their ability to cleave different types of collagen. Standardization of collagenase-based protocols has been hampered by impurities in products manufactured from Clostridium histolyticum. To enhance the purification process, we produced recombinant collagenase classes G and H, taking advantage of the Escherichia coli expression system. The respective gene sequences were derived from C. histolyticum and modified by addition of a C-terminal polyhistidine tag. Harvested bacteria were lysed and the collagenase protein was affinity purified using a His-tag column. The purity, identity, integrity of the eluted collagenases G and H were determined by SDS electrophoresis and Western blot. The proteolytic activity of the collagenase G and H blend (rColGH) was determined by the standard FALGPA assay. The tissue dissociation activity was verified using a standardized method for isolation of rat pancreatic islets. Biocompatibility of the blend was validated by a standardized viability assay on the isolated islets. Two batches of rColGH were produced and compared to a commercially available collagenase. Based on our results, we conclude that rColGH is a functional and non-toxic novel recombinant collagenase worth further characterization and blend optimization in order to make it a competitive commercial product.

Recombinant collagenase from Grimontia hollisae as a tissue dissociation enzyme for isolating primary cells

Collagenase products are crucial to isolate primary cells in basic research and clinical therapies, where their stability in collagenolytic activity is required. However, currently standard collagenase products from Clostridium histolyticum lack such stability. Previously, we produced a recombinant 74-kDa collagenase from Grimontia hollisae, which spontaneously became truncated to ~60 kDa and possessed no stability. In this study, to generate G. hollisae collagenase useful as a collagenase product, we designed recombinant 62-kDa collagenase consisting only of the catalytic domain, which exhibits high production efficiency. We demonstrated that this recombinant collagenase is stable and active under physiological conditions. Moreover, it possesses higher specific activity against collagen and cleaves a wider variety of collagens than a standard collagenase product from C. histolyticum. Furthermore, it dissociated murine pancreata by digesting the collagens within the pancreata in a dose-dependent manner, and this dissociation facilitated isolation of pancreatic islets with masses and numbers comparable to those isolated using the standard collagenase from C. histolyticum. Implantation of these isolated islets into five diabetic mice led to normalisation of the blood glucose concentrations of all the recipients. These findings suggest that recombinant 62-kDa collagenase from G. hollisae can be used as a collagenase product to isolate primary cells.

The challenge of correctly reporting hormones content and secretion in isolated human islets

Background

An increased access of research laboratories to isolated human islets has improved our understanding of the biology of the endocrine pancreas and hence the mechanisms causing diabetes. However, in vitro studies of human islets remain technically challenging, and optimal use of such precious material requires a minimum of rigor and coordination to optimize the reliability and share of the information. A detailed report of the demographics of pancreas donors and of the procedures of islet handling after isolation is important but insufficient. Correct characterization of islet basic functions (a token of quality) at the time of experimentation is also crucial.

Scope of review

I have analyzed the literature reporting measurements of insulin and glucagon in the human pancreas or isolated human islets. The published information is often fragmentary. Elementary features such as islet size, insulin content, or rate of hormone secretion are either unreported or incorrectly reported in many papers. Although internal comparisons between control and test groups may remain valid, comparisons with data from other laboratories are problematic. The drawbacks, pitfalls and errors of common ways of expressing hormone content or secretion rates are discussed and alternatives to harmonize data presentation are proposed.

Major Conclusions

Greater coherence and rigor in the report of in vitro studies using human islets are necessary to ensure optimal progress in our understanding of the pathogenesis of diabetes.

Evaluation of collagenase gold plus BP protease in isolating islets from human pancreata

Selection of enzymes for optimal pancreas digestion is essential for successful human islet isolations. The aim of this study was to evaluate the efficacy and outcome of using Collagenase Gold plus BP protease (VitaCyte) (n = 8) by comparing it to two commercially available enzymes, Liberase MTF C/T (Roche) (n = 48) and Collagenase NB1/NP (Serva) (n = 15). The isolation outcomes were assessed by islet counting, viability, glucose-stimulated oxygen consumption rate (OCR), and successful graft-rate following transplantation in diabetic NOD scid mice. The pancreas donor characteristics were not significantly different between the tested enzyme groups regarding their BMI, pancreas weight, cold ischemia time (CIT) and HbA1c. The results show that digested tissue volume was not statistically significant between the VitaCyte enzyme (34.25 ± 5.4 mL) and the Roche enzyme (55.25 ± 3.42 mL, p = 0.073), however, this was significant with Serva enzyme (64.07 ± 7.95 mL, p = 0.020). Interestingly, the islet yields were not statistically different between all enzyme groups. Moreover, when islets were transplanted into NOD scid mice, the reversal rate of diabetes for the VitaCyte enzyme group was similar to all enzyme groups. In conclusion, the effectiveness of Collagenase Gold plus BP protease is comparable to the MTF C/T and the Collagenase NB1/NP enzymes; the low cost could facilitate the use of more pancreata for islet isolations.

Beneficial effect of recombinant rC1rC2 collagenases on human islet function: Efficacy of low-dose enzymes on pancreas digestion and yield

A high number of human islets can be isolated by using modern purified tissue dissociation enzymes; however, this requires the use of >20 Wunsch units (WU)/g of pancreas for digestion. Attempts to reduce this dose have resulted in pancreas underdigestion and poor islet recovery but improved islet function. In this study, we achieved a high number of functional islets using a low dose of recombinant collagenase enzyme mixture (RCEM-1200 WU rC2 and 10 million collagen-degrading activity [CDA] U of rC1 containing about 209 mg of collagenase to digest a 100-g pancreas). The collagenase dose used in these isolations is about 42% of the natural collagenase enzyme mixture (NCEM) dose commonly used to digest a 100-g pancreas. Low-dose RCEM was efficient in digesting entire pancreases to obtain higher yield (5535 ± 830 and 2582 ± 925 islet equivalent/g, P < .05) and less undigested tissue (16.7 ± 5% and 37.8 ± 3%, P < .05) compared with low-dose NCEM (12WU/g). Additionally, low-dose RCEM islets retained better morphology (confirmed with scanning electron microscopy) and higher in vitro basal insulin release (2391 ± 1342 and 1778 ± 978 μU/mL; P < .05) compared with standard-dose NCEM. Nude mouse bioassay demonstrated better islet function for low-dose RCEM (area under the curve [AUC] 24 968) compared with low-dose (AUC-38 225) or standard-dose NCEM (AUC-38 685), P < .05. This is the first report indicating that islet function can be improved by using low-dose rC1rC2 (RCEM).

Enzyme Development for Human Islet Isolation: Five Decades of Progress or Stagnation?

In comparison to procedures used for the separation of individual cell types from other organs, the process of human pancreatic islet isolation aims to digest the pancreatic exocrine matrix completely without dispersing the individual cells within the endocrine cell cluster. This objective is unique within the field of tissue separation, and outlines the challenge of islet isolation to balance two opposing priorities. Although significant progress has been made in the characterization and production of enzyme blends for islet isolation, there are still numerous areas which require improvement. The ultimate goal of enzyme production, namely the routine production of a consistent and standardized enzyme blend, has still not been realized. This seems to be mainly the result of a lack of detailed knowledge regarding the structure of the pancreatic extracellular matrix and the synergistic interplay between collagenase and different supplementary proteases during the degradation of the extracellular matrix. Furthermore, the activation of intrinsic proteolytic enzymes produced by the pancreatic acinar cells, also impacts on the chance of a successful outcome of human islet isolation. This overview discusses the challenges of pancreatic enzymatic digestion during human islet isolation, and outlines the developments in this field over the past 5 decades.

Synergistic Effect of Neutral Protease and Clostripain on Rat Pancreatic Islet Isolation

BACKGROUND

Islet isolation currently requires collagenase, neutral protease and other components. Thermolysin (TL) from Bacillus thermoproteolyticus is the gold standard neutral protease. However, we speculated that neutral protease derived from Clostridium histolyticum (Ch; ChNP) would be biologically superior for islet isolation. Tryptic-like activity has also been reported to be important. Therefore, we focused on clostripain (CP), since it is one of the main proteases in Clostridium histolyticum which possesses tryptic-like activity. We then examined the synergistic effects of highly purified ChNP and CP on rat islet isolation.

METHODS

The same amount of collagenase was used in all four groups (TL, ChNP, TL+CP and ChNP+CP; n = 12/group). The efficiency was evaluated by the islet yield and function. An immunohistochemical analysis, in vitro digestion assay for each enzyme component and evaluation of the activation of endogenous exocrine proteases during islet isolation were also performed.

RESULTS

The islet yield of the TL group was significantly higher than that of the ChNP group (P < 0.01). The islet yield was dose dependently increased in the ChNP+CP group, but was decreased in the TL + CP group. The islet yield in the ChNP + CP group was significantly higher than that in the TL group, but their islet function was similar. Different specificities for laminin, especially laminin-511, were observed in the TL, ChNP, and CP groups.

CONCLUSIONS

Clostripain had a strong synergistic effect with ChNP, but not with TL. Therefore, ChNP and CP, in combination with collagenase derived from the same bacteria, may effectively increase the isolation efficiency without affecting the quality of islets.

Progress in islet transplantation in patients with type 1 diabetes mellitus

More than 500 patients with type 1 diabetes mellitus have now received islet transplants at over 50 institutions worldwide in the past 5 years. Rates of insulin independence at 1 year with current protocols are impressive. However, inexorable decay of islet function over time indicates that there are many opportunities for improvement. Improved control of glycosylated hemoglobin and reduced risk of recurrent hypoglycemia are seen as important benefits of islet transplantation, irrespective of the status regarding insulin independence. For the use of islet transplantation to expand it is essential that the donor-to-recipient ratio be reliably reduced to 1 : 1. Enormous opportunities lie ahead for the development of successful living donor islet transplantation, single donor protocols, improved engraftment, islet proliferation in vitro and in the recipient, alternative islet sources, and novel tolerizing drugs. With these emerging opportunities, islet transplantation may expand to include more patients with type 1 diabetes, including children, and will not be restricted to the most unstable forms of the disease, as it is today.

Identifying Effective Enzyme Activity Targets for Recombinant Class I and Class II Collagenase for Successful Human Islet Isolation

Isolation following a good manufacturing practice-compliant, human islet product requires development of a robust islet isolation procedure where effective limits of key reagents are known. The enzymes used for islet isolation are critical but little is known about the doses of class I and class II collagenase required for successful islet isolation.

METHODS

We used a factorial approach to evaluate the effect of high and low target activities of recombinant class I (rC1) and class II (rC2) collagenase on human islet yield. Consequently, 4 different enzyme formulations with divergent C1:C2 collagenase mass ratios were assessed, each supplemented with the same dose of neutral protease. Both split pancreas and whole pancreas models were used to test enzyme targets (n = 20). Islet yield/g pancreas was compared with historical enzymes (n = 42).

RESULTS

Varying the Wunsch (rC2) and collagen degradation activity (CDA, rC1) target dose, and consequently the C1:C2 mass ratio, had no significant effect on tissue digestion. Digestions using higher doses of Wunsch and CDA resulted in comparable islet yields to those obtained with 60% and 50% of those activities, respectively. Factorial analysis revealed no significant main effect of Wunsch activity or CDA for any parameter measured. Aggregate results from 4 different collagenase formulations gave 44% higher islet yield (>5000 islet equivalents/g) in the body/tail of the pancreas (n = 12) when compared with those from the same segment using a standard natural collagenase/protease mixture (n = 6). Additionally, islet yields greater than 5000 islet equivalents/g pancreas were also obtained in whole human pancreas.

CONCLUSIONS

A broader C1:C2 ratio can be used for human islet isolation than has been used in the past. Recombinant collagenase is an effective replacement for the natural enzyme and we have determined that high islet yield can be obtained even with low doses of rC1:rC2, which is beneficial for the survival of islets.

High Seeding Density Induces Local Hypoxia and Triggers a Proinflammatory Response in Isolated Human Islets

Hypoxia is the main threat to morphological and functional integrity of isolated pancreatic islets. Lack of oxygen seems to be of particular importance for functionality of encapsulated islets. The present study was initiated as an experimental model for the environment experienced by human islets in a confined space present during culture, shipment, and in an implanted macrodevice. Quadruplicate aliquots of isolated human islets (n = 12) were cultured for 24 h at 37°C under normoxic conditions using 24-well plates equipped with 8-µm pore size filter inserts and filled with islet aliquots adjusted to obtain a seeding density of 75, 150, 300, or 600 IEQ/cm(2). After culture viability, glucose-stimulated insulin release, DNA content as well as Bax and Bcl-2 gene expression were measured. Culture supernatants were collected to determine production of VEGF and MCP-1. Viability correlated inversely with IEQ seeding density (r = -0.71, p < 0.001), while the correlation of VEGF and MCP-1 secretion with seeding density was positive (r = 0.78, p < 0.001; r = 0.54, p < 0.001). Decreased viability corresponded with a significant increase in the Bax/Bcl-2 mRNA ratio at 300 and 600 IEQ/cm(2) and with a sigificantly reduced glucose-stimulated insulin secretion and insulin content compared to 75 or 150 IEQ/cm(2) (p < 0.01). The present study demonstrates that the seeding density is inversely correlated with islet viability and in vitro function. This is associated with a significant increase in VEGF and MCP-1 release suggesting a hypoxic and proinflammatory islet microenvironment.

The Choice of Enzyme for Human Pancreas Digestion is a Critical Factor for Increasing the Success of Islet Isolation

BACKGROUND

We evaluated three commercially available enzymes for pancreatic digestion by comparing key parameters during the islet isolation process, as well as islet quality post-isolation.

METHODS

Retrospectively compared and analyzed islet isolations from pancreata using three different enzyme groups: Liberase HI (n=63), Collagenase NB1/Neutral Protease (NP) (n=43), and Liberase Mammalian Tissue Free Collagenase/Thermolysin (MTF C/T) (n=115). A standardized islet isolation and purification method was used. Islet quality assessment was carried out using islet count, viability, in vitro glucose-stimulated insulin secretion (GSIS), glucose-stimulated oxygen consumption rate (ΔOCR), and in vivo transplantation model in mice.

RESULTS

Donor characteristics were not significantly different among the three enzyme groups used in terms of age, sex, hospital stay duration, cause of death, body mass index (BMI), hemoglobin A1c (HbA1c), cold ischemia time (CIT), and pancreas weight. Digestion efficacy (percentage of digested tissue by weight) was significantly higher in the Liberase MTF C/T group (73.5 ± 1.5 %) when compared to the Liberase HI group (63.6 ± 2.3 %) (p<0.001) and the Collagenase NB1/NP group (61.7 ± 2.9%) (p<0.001). The stimulation index for GSIS was significantly higher in the Liberase MTF C/T group (5.3 ± 0.5) as compared to the Liberase HI (2.9 ± 0.2) (p<0.0001) and the Collagenase NB1/NP (3.6 ± 2.9) (p=0.012) groups. Furthermore, the Liberase MTF C/T enzymes showed the highest success rate of transplantation in diabetic NOD Scid mice (65%), which was significantly higher than the Liberase HI (42%, p=0.001) and the Collagenase NB1/NP enzymes (41%, p<0.001).

CONCLUSIONS

Liberase MTF C/T is superior to Liberase HI and Collagenase NB1/NP in terms of digestion efficacy and glucose-stimulated insulin secretion in vitro. Moreover, Liberase MTF C/T had a significantly higher success rate of transplantation in diabetic NOD Scid mice compared to Liberase HI and Collagenase NB1/NP enzymes.

Effects of Donor-, Pancreas-, and Isolation-Related Variables on Human Islet Isolation Outcome: A Systematic Review

Different factors have been reported to influence islet isolation outcome, but their importance varies between studies and are hampered by the small sample sizes in most studies. The purpose of this study was to perform a systematic review to assess the impact of donor-, pancreas-, and isolation-related variables on successful human islet isolation outcome. PubMed, Embase, and Web of Science were searched electronically in April 2009. All studies reporting on donor-, pancreas-, and isolation-related factors relating to prepurification and postpurification islet isolation yield and proportion of successful islet isolations were selected. Seventy-four retrospective studies had sufficient data and were included in the analyses. Higher pre- and postpurification islet yields and a higher proportion of successful islet isolations were obtained when pancreata were preserved with the two-layer method rather than University of Wisconsin solution in donors with shorter cold ischemia times (CITs) [1 h longer CIT resulted in an average decline of prepurification and postpurification yields and proportion of successful isolations of 59 islet equivalents (IEQs)/g, 54 IEQs/g, and 21%, respectively]. Higher prepurification yields and higher percentage of successful islet isolations were found in younger donors with higher body mass index. Lower yields were found in donation after brain death donors compared to donation after cardiac death donors. Higher postpurification yields were found for isolation with Serva collagenase. This review identified donor-, pancreas-, and isolation-related factors that influence islet isolation yield. Standardized reports of these factors in all future studies may improve the power and identify additional factors and thereby contribute to improving islet isolation yield.

Different digestion enzymes used for human pancreatic islet isolation: a mixed treatment comparison (MTC) meta-analysis

Collagenases are critical reagents determining yield and quality of isolated human pancreatic islets and may affect islet transplantation outcome. Some islet transplantation centers have compared 2 or more collagenase blends; however, the results regarding differences in quantity and quality of islets are conflicting. Thus, for the first time, a mixed treatment comparison (MTC) meta-analysis was carried out to compile data about the effect of different collagenases used for human pancreas digestion on islet yield, purity, viability and stimulation index (SI). Pubmed, Embase and Cochrane libraries were searched. Of 755 articles retrieved, a total of 15 articles fulfilled the eligibility criteria and were included in the MTC meta-analysis. Our results revealed that Vitacyte and Liberase MTF were associated with a small increase in islet yield (islet equivalent number/g pancreas) when compared with Sevac enzyme [standardized mean difference (95% credible interval - CrI) = -2.19 (-4.25 to -0.21) and -2.28 (-4.49 to -0.23), respectively]. However, all other enzyme comparisons did not show any significant difference regarding islet yield. Purity and viability percentages were not significantly different among any of the analyzed digestion enzymes. Interestingly, Vitacyte and Serva NB1 were associated with increased SI when compared with Liberase MTF enzyme [unstandardized weighted mean difference (95% CrI) = -1.69 (-2.87 to -0.51) and -1.07 (-1.79 to -0.39), respectively]. In conclusion, our MTC meta-analysis suggests that the digestion enzymes currently being used for islet isolation works with similar efficiency regarding islet yield, purity and viability; however, Vitacyte and Serva NB1 enzymes seem to be associated with an improved SI as compared with Liberase MTF.

Proteomic protease specificity profiling of clostridial collagenases reveals their intrinsic nature as dedicated degraders of collagen

Clostridial collagenases are among the most efficient degraders of collagen. Most clostridia are saprophytes and secrete proteases to utilize proteins in their environment as carbon sources; during anaerobic infections, collagenases play a crucial role in host colonization. Several medical and biotechnological applications have emerged utilizing their high collagenolytic efficiency. However, the contribution of the functionally most important peptidase domain to substrate specificity remains unresolved. We investigated the active site sequence specificity of the peptidase domains of collagenase G and H from Clostridium histolyticum and collagenase T from Clostridium tetani. Both prime and non-prime cleavage site specificity were simultaneously profiled using Proteomic Identification of protease Cleavage Sites (PICS), a mass spectrometry-based method utilizing database searchable proteome-derived peptide libraries. For each enzyme we identified > 100 unique-cleaved peptides, resulting in robust cleavage logos revealing collagen-like specificity patterns: a strong preference for glycine in P3 and P1′, proline at P2 and P2′, and a slightly looser specificity at P1, which in collagen is typically occupied by hydroxyproline. This specificity for the classic collagen motifs Gly-Pro-X and Gly-X-Hyp represents a remarkable adaptation considering the complex requirements for substrate unfolding and presentation that need to be fulfilled before a single collagen strand becomes accessible for cleavage.

Biological significance

We demonstrate the striking sequence specificity of a family of clostridial collagenases using proteome derived peptide libraries and PICS, Proteomic Identification of protease Cleavage Sites. In combination with the previously published crystal structures of these proteases, our results represent an important piece of the puzzle in understanding the complex mechanism underlying collagen hydrolysis, and pave the way for the rational design of specific test substrates and selective inhibitors.

This article is part of a Special Issue entitled: Can Proteomics Fill the Gap Between Genomics and Phenotypes?

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Active site specificity profiling of 3 clostridial collagenases—ColG and H from C. histolyticum, and ColT from C. tetani.

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Their high sequence specificity to collagen-like sequence points towards a co-evolution with the mammalian substrate.

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Significant differences to MMPs and a more promiscuous cleavage mechanism facilitating rapid collagenolysis were revealed.

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Human proteome-derived peptide libraries & PICS are suitable for active site specificity profiling of pathogenic proteases.

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Results pave the way for rational design of test substrates and selective inhibitors.

Factors affecting transplant outcomes in diabetic nude mice receiving human, porcine, and nonhuman primate islets: analysis of 335 transplantations

BACKGROUND

In the absence of a reliable islet potency assay, nude mice (NM) transplantation is the criterion standard to assess islet quality for clinical transplantation. There are factors other than islet quality that affect the transplant outcome.

METHODS

Here, we analyzed the transplant outcomes in 335 NM receiving islets from human (n=103), porcine (n=205), and nonhuman primate (NHP; n=27) donors. The islets (750, 1000, and 2000 islet equivalents [IEQ]) were transplanted under the kidney capsule of streptozotocin-induced diabetic NM.

RESULTS

The proportion of mice that achieved normoglycemia was significantly higher in the group implanted with 2000 IEQ of human, porcine, or NHP islets (75% normoglycemic) versus groups that were implanted with 750 IEQ (7% normoglycemic) and 1000 IEQ (30% normoglycemic). In this study, we observed that the purity of porcine islet preparations (P≤0.001), islet pellet size in porcine preparations (P≤ 0.01), and mice recipient body weight for human islet preparations (P=0.013) were independently associated with successful transplant outcome. NHP islets of 1000 IEQ were sufficient to achieve normoglycemic condition (83%). An islet mass of 2000 IEQ, high islet purity, increased recipient body weight, and high islet pellet volume increased the likelihood of successful reversal of diabetes in transplanted mice. Also, higher insulin secretory status of islets at basal stimulus was associated with a reduced mouse cure rate. The cumulative incidence of graft failure was significantly greater in human islets (56.12%) compared with porcine islets (35.57%; P≤0.001).

CONCLUSION

Factors affecting NM bioassay were identified (islet mass, islet purity, pellet size, in vitro insulin secretory capability, and mouse recipient body weight) and should be considered when evaluating islet function.

Neuronal restrictive silencing factor silencing induces human amniotic fluid-derived stem cells differentiation into insulin-producing cells

Islet cell replacement represents the most promising approach for the treatment of type I diabetes. However, it is limited by a shortage of pancreas donors. Here, we report that human amniotic fluid-derived stem cells (hAFSCs) can be induced to differentiate into functional insulin-producing cells by knocking down neuronal restrictive silencing factor (NRSF). In this study, lentiviral vectors were used to deliver small interference NRSF (siNRSF) RNA into hAFSCs. After infection with lentivirus containing siNRSF, hAFSCs were successfully induced to differentiate into insulin-producing cells. The differentiated siNRSF-hAFSCs expressed genes specific for islet cells, such as Pdx1, Hnf4α, Isl-1, Nkx6.1, Insulin, and Glut2. These cells also produced and released C-peptide in a glucose-responsive manner. These findings indicated that hAFSCs could be induced to differentiate into insulin-producing β-like cells by NRSF silencing.

Islet transplantation: lessons learned since the Edmonton breakthrough

This work sought to summarize the main issues of the last decade in the field of clinical islet transplantation. Ten years ago in Edmonton, a new protocol initiated for islet transplantation brought a breakthrough to the field. The earlier, rather poor results were in a sharp contrast to the first published results of 100% insulin freedom at 1 year. However, later it became clear that the promising initial results decline with time; at around 5 years, only about 10% of the patients maintain freedom from external insulin. Despite that fact, a milestone was set and intensive research started worldwide. New hopes were raised for patients. Modifications of the original protocol have been implemented to improve clinical results; however, islet transplantation remains an experimental procedure to date.

Liraglutide, a long-acting human glucagon-like peptide 1 analogue, improves human islet survival in culture

The culture of human islets is associated with approximately 10-20% islet loss, occasionally preventing transplantation. Preconditioning of the islets to improve postculture yields would be of immediate benefit, with the potential to increase both the number of transplanted patients and their metabolic reserve. In this study, the effect of liraglutide, a long-acting human glucagon-like peptide 1 analogue, on cultured human islets was examined. Culture with liraglutide (1 micromol/l) was associated with a preservation of islet mass (significantly more islets at 24 and 48 h, compared to control; P < or = 0.05 at 24 and 48 h) and with the presence of larger islets (P < or = 0.05 at 48 h). These observations were supported by reduced apoptosis rates after 24 h of treatment. We also demonstrated that human islet engraftment is improved in C57Bl/6-RAG(-/-) mice treated with liraglutide 200 microg/kg sc twice daily (P < or = 0.05), suggesting that liraglutide should be continued after transplantation. Overall, these data demonstrate the beneficial effect of liraglutide on cultured human islets, preserving islet mass. They support the design of clinical studies looking at the effect of liraglutide in clinical islet transplantation.

Multicenter analysis of novel and established variables associated with successful human islet isolation outcomes

Islet transplantation is a promising therapy used to achieve glycometabolic control in a select subgroup of individuals with type I diabetes. However, features that characterize human islet isolation success prior to transplantation are not standardized and lack validation. We conducted a retrospective analysis of 806 isolation records from 14 pancreas-processing laboratories, considering variables from relevant studies in the last 15 years. The outcome was defined as post-purification islet equivalent count, dichotomized into yields > or =315 000 or < or =220 000. Univariate analysis showed that donor cause of death and use of hormonal medications negatively influenced outcome. Conversely, pancreata from heavier donors and those containing elevated levels of surface fat positively influence outcome, as did heavier pancreata and donors with normal amylase levels. Multivariable logistic regression analysis identified the positive impact on outcome of surgically intact pancreata and donors with normal liver function, and confirmed that younger donors, increased body mass index, shorter cold ischemia times, no administration of fluid/electrolyte medications, absence of organ edema, use of University of Wisconsin preservation solution and a fatty pancreas improves outcome. In conclusion, this multicenter analysis highlights the importance of carefully reviewing all donor, pancreas and processing parameters prior to isolation and transplantation.

Islet isolation for clinical transplantation

Islet transplantation is emerging as a viable treatment option for selected patients with type 1 diabetes. Following the initial report in 2000 from Edmonton of insulin independence in seven out of seven consecutive recipients, there has been a huge expansion in clinical islet transplantation. The challenge we now face is the apparent decline in graft function over time. Isolating high-quality human islets which survive and function for a longer period will no doubt contribute to further improvement in long-term clinical outcome. This chapter reviews the selection of appropriate donors for islet isolation and transplantation, describes each step during islet isolation, and discusses the scope for further improvements.

The effect of different concentrations of Liberase HI used in a non automated method for human adult pancreatic islet isolation

Liberase HI has many advantages over traditional collagenases. Liberase performs the rapid dissociation of human pancreata and allows for the preservation of the morphological and functional integrity of isolated islets. The aim of this study was to investigate the effect of different concentrations of Liberase HI (1.5, 2.5 and 3.5 mg/ml) on the yield, viability and function of islets isolated by a non-automated method. Based on our results, the Liberase HI concentration 1.5 mg/ml is recommended for this method of isolation. .

Human islet isolation for autologous transplantation: comparison of yield and function using SERVA/Nordmark versus Roche enzymes

Islet autotransplantation (IAT) is used to preserve as much insulin-secretory capacity as possible in patients undergoing total pancreatectomy for painful chronic pancreatitis. The enzyme used to dissociate the pancreas is a critical determinant of islet yield, which is correlated with posttransplant function. Here, we present our experience with IAT procedures to compare islet product data using the new enzyme SERVA/Nordmark (SN group; n = 46) with the standard enzyme Liberase-HI (LH group; n = 40). Total islet yields (mean +/- standard deviation; 216,417 +/- 79,278 islet equivalent [IEQ] in the LH group; 227,958 +/- 58,544 IEQ in the SN group; p = 0.67) were similar. However, the percentage of embedded islets is higher in the SN group compared to the LH group. Significant differences were found in pancreas digestion time, dilution time, and digested pancreas weight between the two groups. Multivariate linear regression analysis showed the two groups differed in portal venous pressure changes. The incidence of graft function and insulin independence was not different between the two groups. The SN and LH enzymes are associated with similar outcomes for IAT. Further optimization of the collagenase/neutral protease ratio is necessary to reduce the number of embedded islets obtained when using the SN enzyme.

Collagenase isoforms for pancreas digestion

The available information concerning the characteristics and composition of collagenase batches, which are effective in the digestion of human pancreas for islet transplants, is scarce and incomplete. A large inter- and intrabatched variability in activity and efficiency of blend enzymes available for isolation has been observed. The aim of this study was to characterize enzyme blend components. Liberase batches were characterized by SDS-PAGE analyses, microelectrophoresis, and then by MALDI-TOF MS analysis. Three main bands were detected by SDS-PAGE analysis and submitted to MALDI-TOF MS analysis. Two bands were found to correspond to class I (isoform beta and another of 106 kDa) and one to class II (isoform delta) collagenase. These results represent an important step towards a complete characterization of enzymes, with the final aim of identifying key components for a standardized product.

Current status of islet cell transplantation

Despite substantial advances in islet isolation methods and immunosuppressive protocol, pancreatic islet cell transplantation remains an experimental procedure currently limited to the most severe cases of type 1 diabetes mellitus. The objectives of this treatment are to prevent severe hypoglycemic episodes in patients with hypoglycemia unawareness and to achieve a more physiological metabolic control. Insulin independence and long term-graft function with improvement of quality of life have been obtained in several international islet transplant centers. However, experimental trials of islet transplantation clearly highlighted several obstacles that remain to be overcome before the procedure could be proposed to a much larger patient population. This review provides a brief historical perspective of islet transplantation, islet isolation techniques, the transplant procedure, immunosuppressive therapy, and outlines current challenges and future directions in clinical islet transplantation.

High-level expression of his-tagged clostridial collagenase in Clostridium perfringens

Clostridium histolyticum collagenase is used to isolate cells from various organs and tissues for tissue engineering, and also to treat destructive fibrosis; thus, the demand for high-grade enzyme preparations is increasing. In this study, we constructed a plasmid encoding C. histolyticum type II collagenase (ColH) with a C-terminal hexahistidine tag (ColH-his) to facilitate the purification of the enzyme through immobilized metal affinity chromatography (IMAC). When ColH-his was expressed in a protease-deficient mutant of Clostridium perfringens, it was produced in the culture supernatant more efficiently than the untagged ColH. ColH-his exhibited the same hydrolytic activity as ColH against 4-phenylazobenzyloxy-carbonyl-Pro-Leu-Gly-Pro-D-Arg (Pz peptide), a synthetic collagenase substrate. From 100 ml of the culture supernatant, approximately 1 mg of ColH-his was purified by ammonium sulfate precipitation, IMAC, and high-performance liquid chromatography on a MonoQ column. When IMAC was performed on chelating Sepharose charged with Zn(2+) instead of Ni(2+), a potential carcinogenic metal, the specific activities against Pz peptide and type I collagen decreased slightly. However, they were comparable to those reported for other recombinant ColHs and a commercial C. histolyticum collagenase preparation, suggesting that this expression system is useful for large-scale preparation of high-grade clostridial collagenases.

Characterization of collagenase blend enzymes for human islet transplantation

BACKGROUND

Efficient islet isolation represents a necessary requirement for successful islet transplantation as a treatment for type 1 diabetes. The choice of collagenase for pancreas digestion is critical for the isolation outcome, and Liberase is the most widely used enzyme, although large intra-batched variability in activity and efficiency has been observed.

METHODS

The aim of this study was to characterize Liberase components and their relative role in pancreas digestion. Liberase batches were characterized by microelectrophoresis.

RESULTS

By means of microelectrophoresis, we identified three main proteins each with different prevalences between batches. Two proteins were found to correspond to class I (CI) and one to class II (CII) collagenase. In a series of 163 islet isolations, we observed that the CII correlated with islet yield (P<0.001) and digestion time (P<0.001); additionally, CI directly correlated with purity (P=0.028). Finally, when CII and one of the CI isoforms were >50 percentile, 15 of 36 preparations were transplanted, with 27 of 127 transplanted in the other cases (P=0.013).

CONCLUSION

These results represent an important step toward the characterization of enzymes, with the final aim of identifying key components for a standardized product.

Factors influencing the collagenase digestion phase of human islet isolation

Substantial advances in human islet isolation technology have occurred during the past decade. However, it is still difficult to recover the entire quantity of islets contained in a pancreas. A major obstacle to successful human islet isolation has been the variability of the collagenase digestion phase of islet isolation. Future advances in enzyme technology will make it possible to optimally liberate islets with enzyme blends "tailor-made" for each individual donor pancreas. Such innovative strategies will be advantageous in improving islet isolation efficiency, recovery, viability, and ultimately posttransplant function.

Pancreatic islet transplantation for treating diabetes

Pancreatic islet transplantation is one of the options for treating diabetes and has been shown to improve the quality of life of severe diabetic patients. Since the Edmonton protocol was announced, islet transplantation have advanced considerably, including islet after kidney transplantation, utilisation of non-heart-beating donors, single-donor islet transplantation and living-donor islet transplantation. These advances were based on revised immunosuppression protocols, improved pancreas procurement and islet isolation methods, and enhanced islet engraftment. Further improvements are necessary to make islet transplantation a routine clinical treatment. To synergise efforts towards a cure for type 1 diabetes, a Diabetes Research Institute (DRI) Federation is currently being established to include leading diabetes research centres worldwide, including DRIs in Miami, Edmonton and Kyoto among others.

Internal assessment of a novel islet isolation facility in Spain

Islet transplantation is a promising therapy in the treatment of diabetes mellitus. Herein we present the result from the first series of islet isolations carried out in our new islet isolation facility. The aims of study were to analyze the influence of various donor characteristics on the success of islet isolation and compare these outcomes with other European and American groups. Data from 22 completed islet isolation were used to compare donor and isolation variables among successful (>300,000 IEQs) versus unsuccessful isolations. The successful isolation rate from our laboratory was 31.8%. We did not see any significant differences between successful and unsuccessful groups according to donor characteristics, although age was close to significance (38.57 +/- 10.29 versus 48.33 +/- 12.39; P = .08). Donor age (1.12 [1.23; 0.99]) and body mass index (0.065 [1.32; 3.08]) were associated with isolation success in a logistic regression model. We did not find differences among intraprocedure variables with the exception of IEQ prepurification (409,073 +/- 115,041 versus 263,776 +/- 128,988; P < .05). IEQpre and IEQpost were positively correlated (P < .05). In comparison with other groups, we observed differences in some cases related to islet yield prepurification (P < .05) but not postpurification. Purity from our islet preparations was the highest from all considered groups (P < .05). Recovery was similar in all groups.

CONCLUSIONS

In our experience, donor characteristics have no influence on the success rate. The digestion step is a critical factor for success. Our results with respect to IE yield were close to that of experienced groups.

Methods of human islet culture for transplantation

The ability to maintain isolated human islet preparations in tissue culture has recently been adopted by most islet transplant centers, and improves the safety as well as the practicality of islet transplantation. Maintaining islet viability and recovery, however, remains challenging in a clinical setting, due to stringent conditions required for culture. Islet culture is further complicated by the fact that islets do not form a monolayer. This review aims to clarify media, supplementation, and conditions that have been shown to be relevant to human islets, as well as to offer avenues of future research. Factors examined that may influence islet survival include base medium, glucose concentration, vitamin, inorganic ion, lipid, hormone, growth factor, amino acid, and binding protein composition and concentration, as well as culture temperature and seeding density. In addition, this article reviews novel techniques, such as coculture and matrices, that have been employed in an attempt to improve islet survival and functional viability.

Current status of clinical islet transplantation

Islet transplantation is currently being explored as a treatment for patients with type 1 diabetes. At present, the number of patients becoming insulin-independent is rapidly increasing world-wide applying the transplantation protocol originally described by the group in Edmonton. A hallmark in this procedure is repeated infusions of islets obtained from 2 to 4 donors until normoglycemia is achieved. In order to establish islet transplantation as a widely accepted treatment modality, and make tolerance induction regimes applicable, it is essential that the donor:recipient ratio is brought down to 1:1. A conceivable strategy to achieve this goal in clinical islet transplantation is discussed.

Differentiation of insulin-producing cells from human neural progenitor cells

BACKGROUND

Success in islet-transplantation-based therapies for type 1 diabetes, coupled with a worldwide shortage of transplant-ready islets, has motivated efforts to develop renewable sources of islet-replacement tissue. Islets and neurons share features, including common developmental programs, and in some species brain neurons are the principal source of systemic insulin.

METHODS AND FINDINGS

Here we show that brain-derived human neural progenitor cells, exposed to a series of signals that regulate in vivo pancreatic islet development, form clusters of glucose-responsive insulin-producing cells (IPCs). During in vitro differentiation of neural progenitor cells with this novel method, genes encoding essential known in vivo regulators of pancreatic islet development were expressed. Following transplantation into immunocompromised mice, IPCs released insulin C-peptide upon glucose challenge, remained differentiated, and did not form detectable tumors.

CONCLUSION

Production of IPCs solely through extracellular factor modulation in the absence of genetic manipulations may promote strategies to derive transplantable islet-replacement tissues from human neural progenitor cells and other types of multipotent human stem cells.

A simple method using a polymethylpenten chamber for isolation of human pancreatic islets

OBJECTIVES

Isolation of large numbers of intact and functional human islets remains difficult and expensive. We describe a novel method using a polymethylpenten chamber (PMPC) and compare its efficacy to the classic method using a stainless steel chamber (SSC).

METHODS

Five pancreases obtained from cadaveric donors were processed with the SSC method, and the islets were purified with a Cobe cell separator. The next 15 pancreases (similar donor characteristics) were distended with Liberase HI, minced, and digested in a PMPC whose thermic properties did not require continuous heating to maintain temperature of the prewarmed medium at 37 degrees C. The digestion was done in 2 phases to avoid damaging the first freed islets. Digested tissue was filtered on a column of 6-mm glass beads and 500-microm mesh screen, so that tissue volume was small enough to permit purification on discontinuous Ficoll gradients in tubes.

RESULTS

With the PMPC method, the extent of digestion (+/-70%), yield (approximately 5000 IEQ/g), and final purity (73%) and viability (84%) of the islets was similar to those with the SSC, but the proportion of large islets (>150 microm in diameter) was higher. Cell composition (beta vs. non-beta cells) of isolated islets was not different from that of islets in situ in the same pancreas. Islet function, assessed by perifusion, showed an excellent average stimulation index of approximately 13-fold (15 vs. 1 mmol/L glucose, without cAMP-raising agent).

CONCLUSIONS

This new method for isolation of human islets uses simple, low-cost, and potentially disposable material and requires a team of only 2 persons. The technique is as efficient as the classic SSC method and provides islets with excellent integrity and insulin-secreting capacity.

Assessment of a novel two-component enzyme preparation for human islet isolation and transplantation

BACKGROUND

Biologic characteristics of enzyme products used for islet isolation are critical for the success of islet transplantation. In particular, lot-to-lot variability significantly affects the yields of the isolation procedure. In this study, we have evaluated a new enzyme preparation in which highly purified collagenase can be blended with separately supplied neutral protease in a predetermined ratio.

METHODS

We compared the results of human-islet isolations performed either with Collagenase NB1 supplemented with Neutral Protease NB (group I, n=9) or with Liberase (group II, n=9).

RESULTS

Endotoxin contents of the enzyme preparations were lower in group I. Total islet yields were similar in both groups, but islet equivalents per gram of pancreas was higher in group I (4,020+/-1,240 vs. 2,360+/-1,350; P<0.05). Islet morphology was improved in group I with significantly higher proportion of free and intact islets (71+/-9% vs. 52+/-14%; P<0.01). In vitro function was improved and apoptosis rate was lower in group I.

CONCLUSIONS

This new enzyme blend was as efficient as Liberase in terms of islet yields and showed improvements in islet morphology, viability, and in vitro function. The possibility to control lot-to-lot variability and the low endotoxin contents make Collagenase NB1 a promising product for human-islet isolation.

Refinement of the automated method for human islet isolation and presentation of a closed system for in vitro islet culture

BACKGROUND

The procedure of human islet isolation needs further optimization and standardization. Here, we describe techniques to enhance enzymatic digestion and minimize mechanical forces during the digestion process. The isolation protocol has also been modified to meet current GMP (cGMP) standards. Moreover, the impact of donor- and process-related factors was correlated to the use of islets for clinical transplantation.

METHODS

One hundred twelve standardized consecutive islet isolations were evaluated. Metyltioninklorid and indermil (topical tissue adhesive) were applied to detect leakage of collagenase injected and to repair the damaged pancreatic glands. The effects of dye and glue were evaluated in terms of islet yield, islet function using the perifusion assay, and success rate of the isolation. To analyze key factors for successful isolations, both univariate and multivariate regression analysis were performed.

RESULTS

Both Metyltioninklorid and Indermil were effective to prevent leakage of enzyme solutions from the pancreatic glands. Both islet yield and success rate were higher when these tools were applied (4,516.1+/-543.0 vs. 3,447.7+/-323.5, P=0.02; 50.0% vs. 21.3%, P=0.02, respectively). No adverse effects on islet function or collagenase activity were observed. Multivariate regression analysis identified the maximal recorded amylase >100 U/L (P=0.026), BMI (P=0.03), and the use of catecholamine (P=0.04) as crucial donor-related factors. In addition, cold ischemia time (P=0.005), the dissection procedure using whole glands with duodenum (P=0.02), and the local procurement team (P=0.03) were identified as crucial isolation-related variables.

CONCLUSIONS

A standardized technique of islet isolation is presented applying novel means to improve enzymatic digestion and to meet cGMP standards.

Islet transplantation in type 1 diabetic patients

Islet transplantation has been shown to improve overall glucose homeostasis and retard the progression of complications in type I diabetic patients. Also the percentage of recipients achieving complete insulin independence has progressively increased over recent years. An unsolved problem is whether the short-term graft function is secondary to progressive islet exhaustion or to recurrent autoimmunity despite the immunosuppressive therapy. The indications for this procedure remain limited to selected type I diabetic patients. The risks of the immunosuppressive therapy are only proposed to type I diabetic recipients with uncontrolled disease, despite all efforts of the diabetologist and the patient (brittle diabetes), or with a poor quality of life due to unawareness hypoglycemia or severe chronic and progressive complications.

Clinical islet transplant: current and future directions towards tolerance

The ultimate goal of islet transplantation is to completely correct the diabetic state from an unlimited donor source, without the need for chronic immunosuppressive drug therapy. Although islet transplantation provides an opportunity to develop innovative strategies for tolerance in the clinic, both alloimmune and autoimmune barriers must be controlled, if stable graft function is to be maintained long-term. After islet extraction from the pancreas, the cellular graft may be stored in tissue culture or cryopreserved for banking, providing an opportunity not only to optimally condition the recipient but also to allow in vitro immunologic manipulation of the graft before transplantation, unlike solid organ grafts. As such, islets may be considered a "special case." Remarkable progress has occurred in the last three years, with dramatic improvements in outcomes after clinical islet transplantation. The introduction of a steroid-free, sirolimus-based, anti-rejection protocol and islets prepared from two (or rarely three) donors led to high rates of insulin independence. The "Edmonton Protocol" has been successfully replicated by other centers in an international multicenter trial. A number of key refinements in pancreas transportation, processing, purification on non-ficoll-based media, storage of islets in culture for two days and newer immunological conditioning and induction therapies have led to continued advancement through extensive collaboration between key centers. This review outlines the historical development of islet transplantation over the past 30 years, provides an update on current clinical outcomes, and summarizes a series of unique opportunities for development and early testing of tolerance protocols in patients.