Composition of human islet cell preparations for transplantation

RGD peptide-modified adenovirus expressing hepatocyte growth factor and X-linked inhibitor of apoptosis improves islet transplantation

BACKGROUND

Islet transplantation has the potential for treating type I diabetes; however, its widespread clinical application is limited by the massive apoptotic cell death and poor revascularization of transplanted islet grafts.

METHODS

We constructed a surface-modified adenoviral vector with RGD (Arg-Gly-Asp) sequences encoding human X-linked inhibitor of apoptosis and hepatocyte growth factor (RGD-Adv-hHGF-hXIAP). In vitro transgene expression in human islets was determined by enzyme-liniked immunosorbent assay. RGD-Adv-hHGF-hXIAP-transduced human islets were transplanted under the kidney capsule of streptozotocin-induced diabetic NOD/SCID mice. The blood glucose levels of mice were measured weekly. The kidneys bearing islets were isolated at the end of the experiment and subjected to immunofluorescence staining.

RESULTS

The transduction efficiency on human islets was significantly improved using RGD-modified adenovirus. HGF and XIAP gene expressions were dose-dependent after viral transduction. When exposed to a cocktail of inflammatory cytokines, RGD-Adv-hHGF-hXIAP-transduced human islets showed decreased caspase 3 activity and reduced apoptotic cell death. Prolonged normoglycemic control could be achieved by transplanting RGD-Adv-hHGF-hXIAP-transduced human islets. Immunofluorescence staining of kidney sections bearing RGD-Adv-hHGF-hXIAP-transduced islets was positive for insulin and von Willebrand factor (vWF) at 200 days after transplantation.

CONCLUSIONS

These results indicated that ex vivo transduction of islets with RGD-Adv-hHGF-hXIAP decreased apoptotic islet cell death and improved islet revascularization, and eventually might improve the outcome of human islet transplantation.

Anti-diabetic functions of soy isoflavone genistein: mechanisms underlying its effects on pancreatic β-cell function

Type 2 diabetes is a result of chronic insulin resistance and loss of functional pancreatic β-cell mass. Strategies to preserve β-cell mass and a greater understanding of the mechanisms underlying β-cell turnover are needed to prevent and treat this devastating disease. Genistein, a naturally occurring soy isoflavone, is reported to have numerous health benefits attributed to multiple biological functions. Over the past 10 years, numerous studies have demonstrated that genistein has anti-diabetic effects, in particular, direct effects on β-cell proliferation, glucose-stimulated insulin secretion and protection against apoptosis, independent of its functions as an estrogen receptor agonist, antioxidant, or tyrosine kinase inhibitor. Effects are structure-specific and not common to all flavonoids. While there are limited data on the effects of genistein consumption in humans with diabetes, there are a plethora of animal and cell-culture studies that demonstrate a direct effect of genistein on β-cells at physiologically relevant concentrations (<10 μM). The effects appear to involve cAMP/PKA signaling and there are some studies that suggest an effect on epigenetic regulation of gene expression. This review focuses on the anti-diabetic effects of genistein in both in vitro and in vivo models and potential mechanisms underlying its direct effects on β-cells.

The potential benefit of non-purified islets preparations for islet transplantation

Since the advent of islet transplantation, there has been a significant emphasis on the importance of islet purity despite an inevitable associated loss of islet mass during the purification process. One of the key elements of the 'Edmonton Protocol' for islet transplantation published in 2000 was an emphasis on the need for sequential transplants of highly purified islets (averaging 24% beta cell purity) and the close correlation between the numbers of islets transplanted and the success of the procedure. However, the emphasis on islet purity may warrant further consideration as auto transplantation of non-purified islets currently provides the most successful insulin independence rates within the field of islet transplantation. While the role of auto and allo immunity could contribute to the differences in the success rates it is clear that within the clinical setting, significant acinar and ductal contamination is well tolerated. However, one could go further and hypothesize that extra-insular tissue including acinar tissue, ductal tissue, peri-pancreatic lymph nodes and vascular tissue actually confer an advantage to islet survival/function and may even contribute to the insulin secreting capacity of the graft post transplant. As such this review will assess the influence of extra-insular pancreatic tissue on the results of islet transplantation based on published evidence and will also explore the possibility that non-islet pancreatic cells are capable of differentiating into a beta cell phenotype in vivo contributing to an ongoing regeneration of endocrine mass during the period following transplantation.

Enumeration of islets by nuclei counting and light microscopic analysis

Islet enumeration in impure preparations by conventional dithizone staining and visual counting is inaccurate and operator dependent. We examined nuclei counting for measuring the total number of cells in islet preparations, and we combined it with morphological analysis by light microscopy (LM) for estimating the volume fraction of islets in impure preparations. Cells and islets were disrupted with lysis solution and shear, and accuracy of counting successively diluted nuclei suspensions was verified with (1) visual counting in a hemocytometer after staining with crystal violet, and automatic counting by (2) aperture electrical resistance measurement and (3) flow cytometer measurement after staining with 7-aminoactinomycin-D. DNA content averaged 6.5 and 6.9 pg of DNA per cell for rat and human islets, respectively, in agreement with literature estimates. With pure rat islet preparations, precision improved with increasing counts, and samples with about ≥160 islets provided a coefficient of variation of about 6%. Aliquots of human islet preparations were processed for LM analysis by stereological point counting. Total nuclei counts and islet volume fraction from LM analysis were combined to obtain the number of islet equivalents (IEs). Total number of IE by the standard method of dithizone staining/manual counting was overestimated by about 90% compared with LM/nuclei counting for 12 freshly isolated human islet research preparations. Nuclei counting combined with islet volume fraction measurements from LM is a novel method for achieving accurate islet enumeration.

Quantitative analysis of cell composition and purity of human pancreatic islet preparations

Despite improvements in outcomes for human islet transplantation, characterization of islet preparations remains poorly defined. This study used both light microscopy (LM) and electron microscopy (EM) to characterize 33 islet preparations used for clinical transplants. EM allowed an accurate identification and quantification of cell types with measured cell number fractions (mean±s.e.m.) of 35.6±2.1% β-cells, 12.6±1.0% non-β-islet cells (48.3±2.6% total islet cells), 22.7±1.5% duct cells, and 25.3±1.8% acinar cells. Of the islet cells, 73.6±1.7% were β-cells. For comparison with the literature, estimates of cell number fraction, cell volume, and extracellular volume were combined to convert number fraction data to volume fractions applicable to cells, islets, and the entire preparation. The mathematical framework for this conversion was developed. By volume, β-cells were 86.5±1.1% of the total islet cell volume and 61.2±0.8% of intact islets (including the extracellular volume), which is similar to that of islets in the pancreas. Our estimates produced 1560±20 cells in an islet equivalent (volume of 150-μm diameter sphere), of which 1140±15 were β-cells. To test whether LM analysis of the same tissue samples could provide reasonable estimates of purity of the islet preparations, volume fraction of the islet tissue was measured on thin sections available from 27 of the clinical preparations by point counting morphometrics. Islet purity (islet volume fraction) of individual preparations determined by LM and EM analyses correlated linearly with excellent agreement (R²=0.95). However, islet purity by conventional dithizone staining was substantially higher with a 20-30% overestimation. Thus, both EM and LM provide accurate methods to determine the cell composition of human islet preparations and can help us understand many of the discrepancies of islet composition in the literature.

Histologic graft assessment after clinical islet transplantation

BACKGROUND

An accurate monitoring would help understanding the fate of islet grafts after transplantation.

METHODS

This work assessed the feasibility of needle biopsy monitoring after intraportal islet transplantation (n=16), and islet graft morphology was studied with the addition of autopsy samples (n=2). Pancreas autopsy samples from two nondiabetic individuals were used as control.

RESULTS

Islet tissue was found in five needle samples (31%). Sampling success was related to size (100% sampling for the four biopsies of 1.8 cm in length or higher, P<or=0.01). Mild liver abnormalities included localized steatosis (n=8), mild nodular regenerative hyperplasia and mild portal venopathy (n=3), and hepatocyte swelling (n=2). Endocrine cell composition and distribution were similar between islet grafts and normal islets within the native pancreas. There was no or minimal immune cell infiltrate in patients on and off exogenous insulin, including two patients with ongoing negative metabolic events (increasing HbA1c or insulin requirement). The infiltrate was mainly composed of CD4- and CD8-positive cells.

CONCLUSION

This study demonstrates that needle biopsy is feasible after clinical islet transplantation but with a limited practical value because of its low islet sampling rate using current sampling and analysis methods. Both biopsy and autopsy samples demonstrated the well-preserved islet endocrine composition after transplantation and the presence of focal areas of steatosis. Islet grafts showed no or minimal immune cell infiltration, even in the case of ongoing islet loss. On the basis of the findings, possible reasons for allograft islet loss are discussed.

Morphological changes of isolated rat pancreatic islets: a structural, ultrastructural and morphometric study

Improved techniques for pancreatic islet extraction can yield a reasonable number of transplantable cells. However, the isolation and purification process may damage the islets and impair their physiological functions. The aim of this study was to determine the effect of the isolation procedure on the structure of isolated islets and to correlate this with their functionality. Islets were isolated from rat pancreata and purified by Eurocollins-Ficoll discontinuous density gradient processing, and then processed for light microscopy, and scanning and transmission electron microscopy. Morphometric analysis was also performed. Islet functionality was determined by reversal of streptozotocin-induced diabetes and the intraperitoneal glucose tolerance test in a syngeneic rat model of pancreatic islet transplantation. Fragments of variable size and shape comprised a relatively large proportion (26%) of the isolated endocrine tissue. Isolated islets showed slight alterations of cell ultrastructure. Major damage (including breakage of the plasma membrane) and loss of cells were observed in the peripheral cells of the isolated islets. An equal mass of islet equivalent (IEq, islets with an average diameter of 150 microm), but with a different islet equivalent/islet number ratio, was transplanted in diabetic animals. When larger and more complete islets were transplanted (higher ratio), better function of the graft was observed by reversal of hyperglycaemia and response to the glucose tolerance test as compared with the functionality and response of smaller (fragmented) islets transplanted (lower ratio). Digestion, trauma and hypoxia during isolation are responsible for qualitative and quantitative changes of isolated islets. Alterations in normal secretory function after the transplant were related to lower islet equivalent/islet number ratio. The incomplete integrity of the islets may explain the failure of the fine glycaemic metabolic regulation.

Decreased alloreactivity to human islets secreting recombinant viral interleukin 10

The objective of this study was to analyze allogeneic lymphocyte proliferative responses to cultured human pancreatic islets after gene transfer of viral interleukin (IL)-10 to the islets using replication-defective adenoviral vector. Human islets, either whole or dispersed into single cells, were cocultured with adenovector containing an expression cassette encoding the viral IL-10 gene under control of an SV40 promoter, this sequence replacing viral E1A and part of E1B early viral protein sequences. Subsequent production of recombinant protein by islets was determined by ELISA, and was found dependent on the multiplicity of infection (or ratio of vector to target cells). Protein was secreted by transfected islets at high levels 3-7 days after gene transfer. At high multiplicity of infection (100:1), islet viability was normal, but insulin secretion in response to glucose stimulation was blunted by 50%. Low-level recombinant viral IL-10 secretion by the islets was associated with increased allogeneic lymphocyte proliferation in mixed islet lymphocyte reactions. At protein levels in islet supernatant above 5 ng/ml, lymphocyte proliferation was significantly reduced. This pattern of viral IL-10 effect on lymphocyte proliferation correlated well with mixed lymphocyte reaction assays using purified protein. We conclude that transferred cytokine sequences are secreted by transfected islets as a function of the initial vector inoculum. The functional effect of the secreted cytokine viral IL-10 on allogeneic lymphocyte proliferation is dose dependent. Low-level recombinant protein secretion tended to augment lymphocyte proliferation, whereas high-level secretion significantly down-regulates this response.

Immunocytochemical detection and characterization of intrahepatic human pancreatic islets after combined liver-islet allotransplantation

The unique availability of an explanted liver-islet allograft, removed for primary nonfunction of the liver, led us to evaluate distribution and phenotype of exocrine and endocrine components of the pancreatic graft. Immunocytochemistry was used to map patterns of gene products for islet hormones, proprotein processing enzymes, panneuroendocrine markers, and pancreatic exocrine markers. When compared with age-matched control pancreases, insulin-, glucagon-, somatostatin-, and pancreatic polypeptide-producing cells were similarly represented and distributed within the grafted islet. We also demonstrate that the intrahepatic transplanted islets retained the enzyme machinery able to process the hormone precursors into bioactive fragments. In the clinical setting, this resulted in an immediate functioning of the graft and insulin-independence of the patient one month after transplantation. The purity in islets, as assessed by immunocytochemistry with antibodies to tissue constituents of endocrine and exocrine lineages, was around 40%. Despite the massive intraportal presence of pancreatic acinar tissue, no signs or symptoms attributable to ectopic hypersecretion of exocrine enzymes occurred. In fact, when tested with antibodies to such enzymes, low levels of immunoreactivity were observed in the grafted acinar cells.

Improved functional survival of human islets of Langerhans in three-dimensional matrix culture

The current study evaluates functional survival of human islets maintained in tissue culture for up to 4 wk in suspension media (CMRL-1066 with supplements) and contrasts these results with immobilizing three-dimensional matrices (agarose or alginate). The absolute number and volume of islets retrieved from agarose is significantly higher after two and four wk of culture compared to conventional free-floating media. In vitro function of islets, assessed by insulin/DNA content, insulin secretion into the culture media over 24 h and glucose-theophylline stimulated insulin release in a dynamic perifusion system, was not significantly different between free-floating and matrix preserved islets. In vivo islet function was evaluated by the effectiveness for reversal of insulin-dependent diabetes mellitus by transplantation of the islets under the kidney capsule of nude mice. Although adequate insulin responses to glucose were seen after culture in conventional or matrix media, only agarose embedded islets were consistently able to induce normoglycemia in diabetic recipients after 14 days of culture. Additional transplantation experiments defined the threshold level required to reverse diabetes to be between 1,000 and 1,500 agarose preserved islets. Our data suggest improved engraftment of human islets after agarose culture. This culture method may be of benefit for the accumulation of functionally competent human islets, thus facilitating the implementation of clinical protocols that utilize freshly isolated islets from multiple donors without the need for cryopreservation.

Frequency of kidney rejection in diabetic patients undergoing simultaneous kidney and pancreatic islet cell transplantation

An increased frequency of kidney rejection has been reported in diabetic patients who have simultaneous pancreas and kidney transplantation compared with patients who have a kidney transplant alone. Kidney graft outcome is similar in the two groups. The mechanism for increased kidney graft rejection with a simultaneous pancreas graft is not clear. It is ascribed to the immunogenicity of the exocrine pancreas that initiates migration of activated cells from the peripheral blood that are entrapped in the kidney. Since the volume of the transplanted tissue is less in islet transplantation (usually < 2 ml) than in pancreas transplantation, one might not expect an increased frequency of kidney rejection in islet cell recipients. We looked at biopsy-proven kidney rejection episodes in patients who had combined kidney and islet transplants and compared this with the frequency of rejection in diabetic and nondiabetic patients who underwent a kidney transplant alone under the same immunosuppression. Diabetic patients who had kidney islet transplants (n = 9) had a higher frequency of rejection (100%) compared with diabetic patients (n = 107, 55.1%) and nondiabetic patients (n = 327, 65%) who had a kidney transplant alone. The 1-year graft and patient survival rates were not different among the groups. Although the number of patients is small, it would appear that transplantation of a low volume of islet cells with high purity can lead to an increased frequency of kidney rejection. This is unlikely to be explained solely on the basis of fewer antigen matches in these recipients but may reflect the inherent immunogenicity of the purified islet preparations. Alternatively, there may be an effect of their direct infusion into the portal vein.