Ability of donor splenocytes with costimulation blockade to induce mixed hematopoietic chimerism and transplantation tolerance

Transition from preclinical to clinical application of CTLA4-Ig co-stimulation blockage in beta-cell replacement therapy

Beta-cell replacement therapies, including islet and pancreas transplantation, offer promising results in term of glycemic control for patients with type 1 diabetes experiencing high glycemic variability and severe hypoglycemia. However, long-term insulin independence remains challenging due to progressive graft function decline. Immunosuppressive regimens, especially calcineurin inhibitors such as tacrolimus, are known to be diabetogenic, contributing to the paradox of impaired beta-cell function in a diabetes treatment setting. Recent studies have focused on CTLA4-Ig (e.g., belatacept) as a potential alternative to calcineurin inhibitors, showing promising results in preclinical and clinical models. This review summarizes key advancements and remaining challenges in CTLA4 applications for beta-cell replacement. First, genetic engineering approaches aiming for CTLA4 expression in islets demonstrated initial success in delaying rejection but remain hindered by immune escape and limited integration efficacy. Coating techniques and exogenous CTLA4-Ig administration offer simpler, albeit transient, immunosuppressive effects, which, combined with encapsulation technologies, can improve graft survival. In non-human primate models, islet transplantation with immunosuppressant regimen using CTLA4-Ig combined with agents such as sirolimus or anti-CD154 has shown extended insulin independence, though full immune tolerance remains elusive. A limited number of human studies using belatacept for beta-cell replacement indicate reduced HbA1c levels and avoidance of severe hypoglycemia, yet consistent absence of rejection remains unachieved. Future research on BCR with CTLA4-Ig should explore graft survival in human islets transplantation and refine immunosuppressive protocols to leverage CTLA4-Ig potential in improving long-term graft function, thus enhancing the sustainability of CTLA4-Ig in clinical beta-cell replacement approach.

Assessing Islet Transplantation Outcome in Mice

Islet transplantation is a potential treatment for Type 1 diabetes; however, improvements need to be made before it could become clinically widely available. In preclinical studies, the mouse is often used to model islet transplantation, with most studies aiming to improve transplantation outcome by manipulating the islets prior to transplantation or by treating the recipient mouse. Here, we describe the process of islet transplantation in the mouse, including how one can make the mouse diabetic, isolate donor islets, and transplant the islets into two different sites. Finally, we discuss how to assess the outcome of the transplantation in order to determine whether the experimental intervention has been beneficial.

Cell Loss during Pseudoislet Formation Hampers Profound Improvements in Islet Lentiviral Transduction Efficacy for Transplantation Purposes

Islet transplantation is a promising treatment in type 1 diabetes, but the need for chronic immunosuppression is a major hurdle to broad applicability. Ex vivo introduction of agents by lentiviral vectors—improving β-cell resistance against immune attack—is an attractive path to pursue. The aim of this study was to investigate whether dissociation of islets to single cells prior to viral infection and reaggregation before transplantation would improve viral transduction efficacy without cytotoxicity. This procedure improved transduction efficacy with a LV-pWPT-CMV-EGFP construct from 11.2 ± 4.1% at MOI 50 in whole islets to 80.0 ± 2.8% at MOI 5. Viability (as measured by Hoechst/PI) and functionality (as measured by glucose challenge) remained high. After transplantation, the transfected pseudoislet aggregates remained EGFP positive for more than 90 days and the expression of EGFP colocalized primarily with the insulin-positive β-cells. No increased vulnerability to immune attack was observed in vitro or in vivo. These data demonstrate that dispersion of islets prior to lentiviral transfection and reaggregation prior to transplantation is a highly efficient way to introduce genes of interest into islets for transplantation purposes in vitro and in vivo, but the amount of β-cells needed for normalization of glycemia was more than eightfold higher when using dispersed cell aggregates versus unmanipulated islets. The high price to pay to reach stable and strong transgene expression in islet cells is certainly an important cell loss.

Genetically engineered islets and alternative sources of insulin-producing cells for treating autoimmune diabetes: quo vadis?

Islet transplantation is a promising therapy for patients with type 1 diabetes that can provide moment-to-moment metabolic control of glucose and allow them to achieve insulin independence. However, two major problems need to be overcome: (1) detrimental immune responses, including inflammation induced by the islet isolation/transplantation procedure, recurrence autoimmunity, and allorejection, can cause graft loss and (2) inadequate numbers of organ donors. Several gene therapy approaches and pharmaceutical treatments have been demonstrated to prolong the survival of pancreatic islet grafts in animal models; however, the clinical applications need to be investigated further. In addition, for an alternative source of pancreatic β-cell replacement therapy, the ex vivo generation of insulin-secreting cells from diverse origins of stem/progenitor cells has become an attractive option in regenerative medicine. This paper focuses on the genetic manipulation of islets during transplantation therapy and summarizes current strategies to obtain functional insulin-secreting cells from stem/progenitor cells.

Genetic vaccination for re-establishing T-cell tolerance in type 1 diabetes

Type 1 diabetes (T1D) is a T-cell mediated autoimmune disease resulting in the destruction of the insulin-secreting β cells. Currently, there is no established clinical approach to effectively suppress long-term the diabetogenic response. Genetic-based vaccination offers a general strategy to reestablish β-cell specific tolerance within the T-cell compartment. The transfer of genes encoding β-cell autoantigens, anti-inflammatory cytokines and/or immunomodulatory proteins has proven to be effective at preventing and suppressing the diabetogenic response in animal models of T1D. The current review will discuss genetic approaches to prevent and treat T1D with an emphasis on plasmid DNA- and adeno-associated virus-based vaccines.

RNA interference for improving the outcome of islet transplantation

Islet transplantation has the potential to cure type 1 diabetes. Despite recent therapeutic success, it is still not common because a large number of transplanted islets get damaged by multiple challenges including instant blood mediated inflammatory reaction, hypoxia/reperfusion injury, inflammatory cytokines, and immune rejection. RNA interference (RNAi) is a novel strategy to selectively degrade target mRNA. The use of RNAi technologies to downregulate the expression of harmful genes has the potential to improve the outcome of islet transplantation. The aim of this review is to gain a thorough understanding of biological obstacles to islet transplantation and discuss how to overcome these barriers using different RNAi technologies. This eventually will help improve islet survival and function post transplantation. Chemically synthesized small interferring RNA (siRNA), vector based short hairpin RNA (shRNA), and their critical design elements (such as sequences, promoters, and backbone) are discussed. The application of combinatorial RNAi in islet transplantation is also discussed. Last but not the least, several delivery strategies for enhanced gene silencing are discussed, including chemical modification of siRNA, complex formation, bioconjugation, and viral vectors.

Improving adenovirus based gene transfer: strategies to accomplish immune evasion

Adenovirus (Ad) based gene transfer vectors continue to be the platform of choice for an increasing number of clinical trials worldwide. In fact, within the last five years, the number of clinical trials that utilize Ad based vectors has doubled, indicating growing enthusiasm for the numerous positive characteristics of this gene transfer platform. For example, Ad vectors can be easily and relatively inexpensively produced to high titers in a cGMP compliant manner, can be stably stored and transported, and have a broad applicability for a wide range of clinical conditions, including both gene therapy and vaccine applications. Ad vector based gene transfer will become more useful as strategies to counteract innate and/or pre-existing adaptive immune responses to Ads are developed and confirmed to be efficacious. The approaches attempting to overcome these limitations can be divided into two broad categories: pre-emptive immune modulation of the host, and selective modification of the Ad vector itself. The first category of methods includes the use of immunosuppressive drugs or specific compounds to block important immune pathways, which are known to be induced by Ads. The second category comprises several innovative strategies inclusive of: (1) Ad-capsid-display of specific inhibitors or ligands; (2) covalent modifications of the entire Ad vector capsid moiety; (3) the use of tissue specific promoters and local administration routes; (4) the use of genome modified Ads; and (5) the development of chimeric or alternative serotype Ads. This review article will focus on both the promise and the limitations of each of these immune evasion strategies, and in the process delineate future directions in developing safer and more efficacious Ad-based gene transfer strategies.

In vivo non-viral gene delivery of human vascular endothelial growth factor improves revascularisation and restoration of euglycaemia after human islet transplantation into mouse liver

AIMS/HYPOTHESIS

Delivery of the gene for human vascular endothelial growth factor (VEGF, also known as VEGFA) to both the transplanted islets and the surrounding tissue may promote islet revascularisation and survival. We previously showed the effective delivery of VEGF gene to rat myocardium by an ultrasound-mediated gene-transfer method named ultrasound-targeted microbubble destruction (UTMD). Here we examined the effect of non-viral VEGF delivery using UTMD on transplanted islets in vivo.

METHODS

A marginal number of human islets were transplanted into livers of mice which were a model for diabetes. Then, non-viral plasmid vectors encoding VEGF (VEGF group, n = 11) or the gene for green fluorescent protein (GFP) (GFP group, n = 7) were introduced into the host liver by UTMD. Transplantation without gene delivery was performed as a control (no-UTMD group, n = 8). Blood glucose, serum human insulin, C-peptide levels and the revascularisation in graft islets were evaluated.

RESULTS

Restoration of euglycaemia occurred in 13% in the no-UTMD group and 14% in the GFP group, whereas 73% mice in the VEGF group became euglycaemic at day 30 (p < 0.05 in no-UTMD vs VEGF). Serum human insulin and C-peptide were significantly higher in the VEGF group at day 32 (insulin: no-UTMD, 17 +/- 8; GFP, 37 +/- 17; VEGF, 109 +/- 26 pmol/l, respectively, p < 0.05; C-peptide: no-UTMD, 68 +/- 38; GFP, 115 +/- 58; VEGF, 791 +/- 230 pmol/l, respectively, p < 0.05). Vessel density in graft islets was significantly higher in the VEGF group (no-UTMD, 169 +/- 36; GFP, 227 +/- 39; VEGF, 649 +/- 51 counts/mm(2), respectively, p < 0.05).

CONCLUSIONS/INTERPRETATION

Delivery of VEGF gene to host liver using UTMD promoted islet revascularisation after islet transplantation and improved the restoration of euglycaemia.

Gene therapy in diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease, whereby auto-reactive cytotoxic T cells target and destroy insulin-secreting β-cells in pancreatic islets leading to insulin deficiency and subsequent hyperglycemia. These individuals require multiple daily insulin injections every day of their life without which they will develop life-threatening diabetic ketoacidosis (DKA) and die. Gene therapy by viral vector and non-viral transduction may be useful techniques to treat T1D as it can be applied from many different angles; such as the suppression of autoreactive T cells to prevent islet destruction (prophylactic) or the replacement of the insulin gene (post-disease). The need for a better method for providing euglycemia arose from insufficient numbers of cadaver islets for transplantation and the immunosuppression required post-transplant. Ectopic expression of insulin or islet modification have been examined, but not perfected. This review examines the various gene transfer methods, gene therapy techniques used to date and promising novel techniques for the maintenance of euglycemia in the treatment of T1D.

Dendritic cells expressing soluble CTLA4Ig prolong antigen-specific skin graft survival

Dendritic cells (DCs) and CTLA4Ig are important in regulating T-cell responses and therefore represent potential therapeutic tools in transplantation. In this study, CTLA4Ig was expressed in a C57BL/6 murine DC line (JAWS II) by lentiviral transduction and these cells were used to examine T-cell immunomodulatory effects in vitro and in vivo. A lower stimulation index to C57BL/6 was observed with splenocytes from BALB/c mice primed with JAWS II-CTLA4Ig compared with control JAWS II-green fluorescent protein (JAWS II-GFP). Mice primed with JAWS II-CTLA4Ig cells had significantly prolonged antigen-specific C57BL/6 skin graft survival compared with either JAWS II-GFP-primed or naïve mice (median 13, 11 and 11 days, respectively, P=0.0001). Furthermore, JAWS II-CTLA4Ig-primed mice that had been previously transplanted with skin grafts were re-transplanted with skin grafts 6 months later without immune manipulation. These mice demonstrated specific prolongation of second-set rejection responses, indicating systemic immune modulation induced by genetically modified DC. The mechanism was not due to expression of indoleamine 2,3-dioxygenase or induction of circulating regulatory T cells as assessed by flow cytometry of the peripheral blood lymphocytes. This potent effect demonstrated with skin grafts and second-set responses highlights the potential use of this strategy for transplantation more generally.

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

Abstract

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

Methods

Islets were isolated from NOD mice and transduced with lentivirus carrying TRX (Lt-TRX) or enhanced green fluorescence protein (Lt-eGFP), respectively. Transduced islets were transplanted under the left kidney capsule of female diabetic NOD mice, and blood glucose concentration was monitored daily after transplantation. The histology of the islet graft was assessed at the end of the study. The protective effect of TRX on islets was investigated.

Results

The lentiviral vector effectively transduced islets without altering the glucose-stimulating insulin-secretory function of islets. Overexpression of TRX in islets reduced hydrogen peroxide-induced cytotoxicity in vitro. After transplantation into diabetic NOD mice, euglycemia was maintained for significantly longer in Lt-TRX-transduced islets than in Lt-eGFP-transduced islets; the mean graft survival was 18 vs. 6.5 days (n = 9 and 10, respectively, p < 0.05).

Conclusion

We successfully transduced the TRX gene into islets and demonstrated that these genetically modified grafts are resistant to inflammatory insult and survived longer in diabetic recipients. Our results further support the concept that the reactive oxygen species (ROS) scavenger and antiapoptotic functions of TRX are critical to islet survival after transplantation.

Expression of a CD200 transgene is necessary for induction but not maintenance of tolerance to cardiac and skin allografts

CD200, a type 2 transmembrane molecule of the Ig supergene family, can induce immunosuppression in a number of biological systems, as well as promote increased graft acceptance, following binding to its receptors (CD200Rs). Skin and cardiac allograft acceptance are readily induced in transgenic mice overexpressing CD200 under control of a doxycycline-inducible promoter, both of which are associated with increased intragraft expression of mRNAs for a number of genes associated with altered T cell subset differentiation, including GATA-3, type 2 cytokines (IL-4, IL-13), GITR, and Foxp3. Interestingly, some 12-15 days after grafting, induction of transgenic CD200 expression can be stopped (by doxycycline withdrawal), without obvious significant effect on graft survival. However, neutralization of all CD200 expression (including endogenous CD200 expression) by anti-CD200 mAb caused graft loss, as did introduction of an acute inflammatory stimulus (LPS, 10 microg/mouse, delivered by i.p. injection). We conclude that even with apparently stably accepted tissue allografts, disruption of the immunoregulatory balance by an intense inflammatory stimulus can cause graft loss.

Transduction of rat pancreatic islets with pseudotyped adeno-associated virus vectors

Background

Pancreatic islet transplantation is a promising treatment for type I diabetes mellitus, but current immunosuppressive strategies do not consistently provide long-term survival of transplanted islets. We are therefore investigating the use of adeno-associated viruses (AAVs) as gene therapy vectors to transduce rat islets with immunosuppressive genes prior to transplantation into diabetic mice.

Results

We compared the transduction efficiency of AAV2 vectors with an AAV2 capsid (AAV2/2) to AAV2 vectors pseudotyped with AAV5 (AAV2/5), AAV8 (AAV2/8) or bovine adeno-associated virus (BAAV) capsids, or an AAV2 capsid with an insertion of the low density lipoprotein receptor ligand from apolipoprotein E (AAV2apoE), on cultured islets, in the presence of helper adenovirus infection to speed expression of a GFP transgene. Confocal microscopy and flow cytometry were used. The AAV2/5 vector was superior to AAV2/2 and AAV2/8 in rat islets. Flow cytometry indicated AAV2/5-mediated gene expression in approximately 9% of rat islet cells and almost 12% of insulin-positive cells. The AAV2/8 vector had a higher dependence on the helper virus multiplicity of infection than the AAV 2/5 vector. In addition, the BAAV and AAV2apoE vectors were superior to AAV2/2 for transducing rat islets. Rat islets (300 per mouse) transduced with an AAV2/5 vector harboring the immunosuppressive transgene, tgfβ1, retain the ability to correct hyperglycemia when transplanted into immune-deficient diabetic mice.

Conclusion

AAV2/5 vectors may therefore be useful for pre-treating donor islets prior to transplantation.

Molecular mechanisms of death ligand-mediated immune modulation: a gene therapy model to prolong islet survival in type 1 diabetes

Type 1 diabetes results from the T cell-mediated destruction of pancreatic beta cells. Islet transplantation has recently become a potential therapeutic approach for patients with type 1 diabetes. However, islet-graft failure appears to be a challenging issue to overcome. Thus, complementary gene therapy strategies are needed to improve the islet-graft survival following transplantation. Immune modulation through gene therapy represents a novel way of attacking cytotoxic T cells targeting pancreatic islets. Various death ligands of the TNF family such as FasL, TNF, and TNF-Related Apoptosis-Inducing Ligand (TRAIL) have been studied for this purpose. The over-expression of TNF or FasL in pancreatic islets exacerbates the onset of type 1 diabetes generating lymphocyte infiltrates responsible for the inflammation. Conversely, the lack of TRAIL expression results in higher degree of islet inflammation in the pancreas. In addition, blocking of TRAIL function using soluble TRAIL receptors facilitates the onset of diabetes. These results suggested that contrary to what was observed with TNF or FasL, adenovirus mediated TRAIL gene delivery into pancreatic islets is expected to be therapeutically beneficial in the setting of experimental models of type 1 diabetes. In conclusion; this study mainly reveals the fundamental principles of death ligand-mediated immune evasion in diabetes mellitus.

Exendin-4 does not promote Beta-cell proliferation or survival during the early post-islet transplant period in mice

Current pancreatic islet transplantation protocols achieve remarkable short-term success, but long-term insulin independence remains elusive. Hypoxic and inflammatory insults cause substantial early posttransplant graft loss while allo/autoimmunity and immunosuppressive drug toxicity threaten long-term graft mass and function. Exendin-4 (Ex4) is a GLP-1 receptor agonist that promotes beta-cell proliferation, survival, and differentiation. To determine whether Ex-4 displays potential as a graft-supportive agent, we transplanted 500 murine islets under the kidney capsule of syngeneic or allogeneic streptozocin-treated recipient mice and immediately initiated daily treatment with vehicle or Ex4. Graft beta-cell proliferation, death, and vascularity were assessed at 1, 3, and 10 days after syngeneic islet transplantation. For allogeneic recipients, blood glucose and body weight were assessed until glycemic deterioration. Ex-4 did not promote graft beta-cell proliferation, reduce beta-cell death, or enhance graft vascularity over the first 10 days after syngeneic islet transplantation. A trend toward prolongation of posttransplant euglycemia was observed with Ex4 treatment in nonimmune-suppressed allograft recipients, but its use in this setting was associated with frequent, severe hypoglycemia over the first 2 posttransplant days. Our findings do not support a beneficial effect of Ex-4 on islet grafts during the critical early posttransplant period, further, they demonstrate a significant hypoglycemic potential of Ex-4 in the first days after islet transplantation in mice. Optimal application of GLP-1 receptor agonists for long-term proliferative and survival benefits in transplantation may require earlier intervention prior to and/or during islet isolation for peri-transplant cytoprotection and administration beyond the period of engraftment.

Prevention of recurrent but not spontaneous autoimmune diabetes by transplanted NOD islets adenovirally transduced with immunomodulating molecules

Pancreatic islet transplantation has the potential to maintain normoglycemia in patients with established type 1 diabetes, thereby obviating the need for frequent insulin injections. Our previous study showed that recombinant IL-12p40-producing islets prevented the recurrence of NOD diabetes. First, to see which immunomodulating molecule-secreting islet grafts can most powerfully prevent diabetes development in NOD mice without immunosuppressant, NOD islets were transfected with one of the following adenoviral vectors: Ad.IL-12p40, Ad.TGF-beta, Ad.CTLA4-Ig, or Ad.TNF-alpha after which they were transplanted under the renal capsule of acutely diabetic NOD mice. The immunomodulating molecules produced by these adenovirus-transfected islets in vitro were 74+/-19ng, 50+/-4ng, 821+/-31ng, and 77+/-18ng/100 islets, respectively. Transplantation of IL-12p40, TNF-alpha, and CTLA4-Ig but not TGF-beta-secreting islets displayed enhanced survival and delayed diabetes recurrence in recent-onset diabetic recipients. IL-12p40-producing islet grafts most powerfully prevented recurrent diabetes in NOD mice. In addition, local production of TNF-alpha and CTLA4-Ig significantly prolonged islet graft survival. In second series of experiment, these manipulated islets were transplanted under the renal capsule of 10-week-old NOD recipients and were also transplanted subcutaneously into 2-week-old NOD recipients. Transplantation of these islets into 2- or 10-week-old pre-diabetic mice failed to protect them from developing diabetes; in fact, transplantation of Ad.TNF-alpha-transfected islets into 2-week-old mice actually accelerated diabetes onset. Taken together, this approach was ineffectual as a prophylactic protocol. In conclusion, this study showed comparisons of the immunomodulating effects of 4 different adenoviral vectors in the same transplantation model and local production of IL-12p40, TNF-alpha and CTLA4-Ig significantly prevented recurrent diabetes in NOD mice.

How not to be seen: immune-evasion strategies in gene therapy

The development of efficient and safe vectors for gene delivery paved the way for evolution of gene therapy as a new modality for treatment of various inherited disorders and for cancer. The current vectors, viral and non-viral, have their limitations. Innate and adaptive immune responses to vector particles and components may restrict the efficiency of gene transfer and the persistence of expression of the transgene. Results from preclinical studies in animals and more recently data from clinical studies have demonstrated the potential impact of the cellular and the humoral immune response on the therapeutic efficacy. Not only the vector components, but also the transgene products may induce an immune response that negatively affects the therapeutic efficacy. The induction of a cytotoxic T-cell response to transgene-encoded peptides, as well as the production of antibodies directed against secreted proteins have been reported in preclinical and clinical studies, and these may thwart those applications that require long-term expression. Here we will review some of the options to blunt the acquired immune responses to transgene-encoded polypeptides.

Preventive effect of pcDNA3-CTLA4Ig plasmid transfection on islet allograft rejection in mice

AIM: To study the effect of pcDNA3-CTLA4Ig plasmid on islet allograft rejection in mice.

METHODS: C57BL/6 mice were randomly divided into control group, blank group and experiment group (transfected with pcDNA3-CTLA4Ig plasmid). The level of serum CTLA4Ig was detected by Western blot on day 5 after transfection. Blood glucose was examined after operation every other day. Immunohistochemical staining was used to determine the expression of insulin. ³H-thymidine incorporation was performed to detect the ability of T lymphocyte increment and the levels of CD4⁺ and CD8⁺ T lymphocytes were detected by flow cytometry on day 7 after transplantation.

RESULTS: Five days after transfection, Western blot demonstrated serum expression of CTLA4Ig, and the transfection efficacy was 27.50%. Blood glucose maintained at the normal level for a longer period of time in the experiment group, and on day 7, the proliferation of lymphocytes was markedly decreased (P < 0.05). The levels of CD4⁺ and CD8⁺ T lymphocytes were significantly lower in the experiment group than those in the control and blank group (CD4⁺: 14.38% ± 0.84% vs 20.56% ± 0.68%, 21.04% ± 1.14%, P < 0.05; CD8⁺: 14.77% ± 0.92% vs 24.63% ± 1.30%, 23.84% ± 1.21%, P < 0.05), and the intensity of immunohistochemical staining was also stronger.

CONCLUSION: CTLA4 gene can be transferred into mouse muscular cells by cation liposome and express its products in the serum, which leads to the inhibition of islet allograft rejection by the blockage of B7/CD28 signal pathway.

Influence of heme oxygenase-1 gene transfer on the viability and function of rat islets in in vitro culture

AIM: To investigate the influence of heme oxygenase-1 (HO-1) gene transfer on the viability and function of cultured rat islets in vitro.

METHODS: Islets were isolated from the pancreata of Sprague-Dawley rats by intraductal collagenase digestion, and purified by discontinuous Ficoll density gradient centrifugation. Purified rat islets were transfected with adenoviral vectors containing human HO-1 gene (Ad-HO-1) or enhanced green fluorescent protein gene (Ad-EGFP), and then cultured for seven days. Transfection was confirmed by fluorescence microscopy and Western blot. Islet viability was evaluated by acridine orange/ propidium iodide fluorescent staining. Glucose-stimulated insulin release was detected using insulin radioimmunoassay kits and was used to assess the function of islets. Stimulation index (SI) was calculated by dividing the insulin release upon high glucose stimulation by the insulin release upon low glucose stimulation.

RESULTS: After seven days culture, the viability of cultured rat islets decreased significantly (92% ± 6% vs 52% ± 13%, P < 0.05), and glucose-stimulated insulin release also decreased significantly (6.47 ± 0.55 mIU/L/30IEQ vs 4.57 ± 0.40 mIU/L/30IEQ, 14.93 ± 1.17 mIU/L/30IEQ vs 9.63 ± 0.71 mIU/L/30IEQ, P < 0.05). Transfection of rat islets with adenoviral vectors at an MOI of 20 was efficient, and did not impair islet function. At 7 d post-transfection, the viability of Ad-HO-1 transfected islets was higher than that of control islets (71% ± 15% vs 52% ± 13%, P < 0.05). There was no significant difference in insulin release upon low glucose stimulation (2.8 mmol/L) among Ad-HO-1 transfected group, Ad-EGFP transfected group, and control group (P > 0.05), while when stimulated by high glucose (16.7 mmol/L) solution, insulin release in Ad-HO-1 transfected group was significantly higher than that in Ad-EGFP transfected group and control group, respectively (12.50 ± 2.17 mIU/L/30IEQ vs 8.87 ± 0.65 mIU/L/30IEQ; 12.50 ± 2.17 mIU/L/30IEQ vs 9.63 ± 0.71 mIU/L/30IEQ, P < 0.05). The SI of Ad-HO-1 transfected group was also significantly higher than that of Ad-EGFP transfected group and control group, respectively (2.21 ± 0.02 vs 2.08 ± 0.05; 2.21 ± 0.02 vs 2.11 ± 0.03, P < 0.05).

CONCLUSION: The viability and function of rat islets decrease over time in in vitro culture, and heme oxygenase-1 gene transfer could improve the viability and function of cultured rat islets.

Long-term gene expression and metabolic control exerted by lentivirus-transduced pancreatic islets

BACKGROUND

Genetic modification of non-human islets before transplantation may provide means by which they can escape immunity and, thus, be used in a human host. To accomplish this, efficient gene transfer methods are needed. Lentiviral vectors are transgene vehicles capable of stably transducing a variety of primary, post-mitotic cells including islets.

METHODS

We investigated whether lentiviral transduction impaired rat pancreatic islet function long term. Following transduction, the gross morphology, viability and in vitro functionality of islets were evaluated by microscopy, adenylate nucleotide and insulin secretion assays, respectively. Further, in vivo functionality of transduced islets was assessed by transplanting the islets under the kidney capsule of diabetic nude mice.

RESULTS

All transduced islets contained green fluorescent protein (GFP)-positive cells. In single cell suspensions prepared from transduced islets, 33+/-8% (n = 3) of dispersed islet cells were GFP-positive. The ADP/ATP ratio was 0.07+/-0.01 for transduced islets and 0.06+/-0.01 for controls (normal range <0.11). No morphological changes were observed in transduced islets. Further, basal insulin secretion was comparable between the two islet groups. When transduced and non-transduced islets were challenged with insulin secretagogues, they showed similar increases in insulin release. Transduced and non-transduced islets were equally effective in normalizing blood glucose when transplanted into diabetic nude mice. Euglycemia was maintained for 8 weeks until the graft-bearing kidney was removed. Intense green fluorescence was seen in removed islet grafts. Histology revealed preserved islet morphology, with abundant insulin-producing cells, few apoptotic cells and infiltrating leukocytes in both transduced and non-transduced grafts.

CONCLUSIONS

Lentivirus transduction does not affect islet morphology or function. Lentiviral vectors will allow genetic modifications to be performed in islets before transplantation--modifications that can improve engraftment and/or prevent xenograft rejection.