Islet Allograft Rejection Research Articles

In Vivo Introduction of an Extrachromosomal Plasmid Expressing Long-term Human Alpha-1-antitrypsin protects Islet Allografts (141.48)

Abstract Alpha-1-antitrypsin (AAT) exerts anti-inflammatory and tolerogenic activities during islet allograft transplantation in diabetes mouse models. Although a serine protease inhibitor, evidence suggests that AAT possesses activities that are independent of protease inhibition. The previously reported plasmid, pEF-hAAT, contains the genomic sequence of human AAT (hAAT) and sustains circulating levels after single hydrodynamic tail-vein injection (HDI) in mice. To asses whether expression of hAAT by pEF-hAAT protects islets from acute rejection, pEF-hAAT (100 μg, n = 6) or PBS (n = 4, control) were hydrodynamically introduced to mice. Liver expression and circulating hAAT levels were determined. Supernatant of transfected Hepa1c cells exhibited anti-elastase activity. Sixteen days post HDI mice were injected streptozotocin (225 mg/kg) and grafted with 450 allogenic islets. Circulating hAAT levels (1-350 μg/ml) persisted for over 30 days. Normoglycemia was achieved and islets were accepted in 6 out of 6 recipients that expressed hAAT. All 4 control animals exhibited acute islet allograft rejection by day 12. We conclude that plasmid-derived long-term expression of as low as 1 μg/ml hAAT exhibits islet-allograft protection. Using site-directed mutagenesis of pEF-hAAT we will examine whether activities that are independent of protease inhibition partake in the protection of islet allografts.

CD103 is dispensable for anti-viral immunity and autoimmunity in a mouse model of virally-induced autoimmune diabetes

Recent studies suggest a beneficial role for blocking CD103 signaling in preventing islet allograft rejection and thus Type 1 diabetes (T1D) in non-obese diabetic (NOD) mice. However, antibody blockade approaches generally raise anti-microbial safety issues, necessitating additional studies to address the possible adverse effects of antibody therapy. Here we report that CD103 had no significant impact on the development of primary and memory CD8 + or CD4 + responses after acute lymphocytic choriomeningitis virus (LCMV) infection. In addition, CD103 was found to be dispensable for T1D progression in a rapid, CD8-mediated virally-induced T1D model (the rat insulin promoter [RIP]–LCMV), suggesting that its previous efficacy in the NOD mouse model may not be related to its effect on the generation, memory conversion and/or effector function of CD8 + or CD4 + T cells. While the data does not preclude a role for CD103 in T1D in its entirety, the current study does provide much evidence to suggest that CD103 blockade may prove to be a safe intervention for autoimmunity and allo-transplantation. While in cases of rapid microbial (CD8)-driven T1D CD103 antibody blockade may not limit disease progression or severity, in mucosally-driven cases of T1D anti-CD103 antibody treatment may provide a new and safe therapeutic avenue.

EFFECT OF CYCLOSPORIN-A AS AN IMMUNOSUPPRESSIVE DRUG ON ISLET CELLS TRANSPLANTATION IN MICE

Transplantation of normal isolated islets of langerhans for the treatment of diabetes remains an elusive goal in clinical practice. Perhaps the major problem preventing clinical islet transplantation has been limited by the inability to prevent islet allograft or xenograft rejection. Cyclosporin A is an immunosuppressive agent that improves survival of transplant. This exciting immunosuppressive agent was first used clinically in renal transplantation in 1978 (Ferguson and Fidlus 1982).The aim of this study was the isolation , purification and transplantation of hamster pancreatic islet as xenograft transplantation for the treatment of diabetic mice. It is also aimed to study the effect of cyclosporin A as an immunosuppressive agent on some biochemical parameters e.g blood glucose and blood insulin levels to induce maximum suppression of mice immune system and consequently realizing maximum survival of transplanted islets. A total of 30 streptozotocin induced mice were randomized to receive islets xenografts from golden syrian hamsters by three different approaches ,the first group of ten mice received islets only in the renal subcapsular space, the 2nd of ten mice received islets in the renal subcapsular space and was given cyclosporin A in a dose of 15 mg/kg/day for three days.The 3rd group of ten mice were received islets in the renal subcapsular space and were given cyclosporin A orally every day at a dose of 15 mg/kg/day for three days which was gradually decreased to 5 mg/kg/day. Non of the mice of group 1 became normoglycemic. All mice of group 2 became normoglycemic for 11±4 ( range 6-18 days) . only mice of group 3 enjoyed normoglycemic as long as cyclosporin-A was administrated. Consequantly, prolonged survival of islets xenografts may be achieved with administration of cyclosporin-A.

Humanized Mice for the Study of Type 1 Diabetes and Beta Cell Function

Our understanding of the basic biology of diabetes has been guided by observations made using animal models, particularly rodents. However, humans are not mice, and outcomes predicted by murine studies are not always representative of actual outcomes in the clinic. In particular, investigators studying diabetes have relied heavily on mouse and rat models of autoimmune type 1-like diabetes, and experimental results using these models have not been representative of many of the clinical trials in type 1 diabetes. In this article, we describe the availability of new models of humanized mice for the study of three areas of diabetes. These include the use of humanized mice for the study of (1) human islet stem and progenitor cells, (2) human islet allograft rejection, and (3) human immunity and autoimmunity. These humanized mouse models provide an important preclinical bridge between in vitro studies and rodent models and the translation of discoveries in these model systems to the clinic.

The Role of Macrophage Migration Inhibitory Factor in Mouse Islet Transplantation

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine produced by many tissues including pancreatic beta-cells. This study investigates the impact of MIF on islet transplantation using MIF knock-out (MIFko) mice. Early islet function, assessed with a syngeneic marginal islet mass transplant model, was enhanced when using MIFko islets (P<0.05 compared with wild-type [WT] controls). This result was supported by increased in vitro resistance of MIFko islets to apoptosis (terminal deoxynucleotide tranferase-mediated dUTP nick-end labeling assay), and by improved glucose metabolism (lower blood glucose levels, reduced glucose areas under curve and higher insulin release during intraperitoneal glucose challenges, and in vitro in the absence of MIF, P<0.01). The beneficial impact of MIFko islets was insufficient to delay allogeneic islet rejection. However, the rejection of WT islet allografts was marginally delayed in MIFko recipients by 6 days when compared with WT recipient (P<0.05). This effect is supported by the lower activity of MIF-deficient macrophages, assessed in vitro and in vivo by cotransplantation of islet/macrophages. Leukocyte infiltration of the graft and donor-specific lymphocyte activity (mixed lymphocyte reaction, interferon gamma ELISPOT) were similar in both groups. These data indicate that targeting MIF has the potential to improve early function after syngeneic islet transplantation, but has only a marginal impact on allogeneic rejection.

RAGE Ligation Affects T Cell Activation and Controls T Cell Differentiation

The pattern recognition receptor, RAGE, has been shown to be involved in adaptive immune responses but its role on the components of these responses is not well understood. We have studied the effects of a small molecule inhibitor of RAGE and the deletion of the receptor (RAGE-/- mice) on T cell responses involved in autoimmunity and allograft rejection. Syngeneic islet graft and islet allograft rejection was reduced in NOD and B6 mice treated with TTP488, a small molecule RAGE inhibitor (p < 0.001). RAGE-/- mice with streptozotocin-induced diabetes showed delayed rejection of islet allografts compared with wild type (WT) mice (p < 0.02). This response in vivo correlated with reduced proliferative responses of RAGE-/- T cells in MLRs and in WT T cells cultured with TTP488. Overall T cell proliferation following activation with anti-CD3 and anti-CD28 mAbs were similar in RAGE-/- and WT cells, but RAGE-/- T cells did not respond to costimulation with anti-CD28 mAb. Furthermore, culture supernatants from cultures with anti-CD3 and anti-CD28 mAbs showed higher levels of IL-10, IL-5, and TNF-alpha with RAGE-/- compared with WT T cells, and WT T cells showed reduced production of IFN-gamma in the presence of TTP488, suggesting that RAGE may be important in the differentiation of T cell subjects. Indeed, by real-time PCR, we found higher levels of RAGE mRNA expression on clonal T cells activated under Th1 differentiating conditions. We conclude that activation of RAGE on T cells is involved in early events that lead to differentiation of Th1(+) T cells.

Activated Effector and Memory T Cells Contribute to Circulating sCD30: Potential Marker for Islet Allograft Rejection

T-cell activation up-regulates CD30 resulting in an increase in serum soluble CD30 (sCD30). CD4+ T cells, a major source for sCD30, play a significant role in the pathogenesis of rejection. In this study, sCD30 was measured pre- and posttransplant in mouse islet allograft models and human islet allograft recipients. sCD30 was measured by ELISA in diabetic C57BL/6, CD4Knockout (KO) and CD8KO islet allograft recipients. sCD30 increased significantly prior to rejection (1.8 +/- 1 days) in 80% of allograft recipients. Sensitization with donor splenocytes, or a second graft, further increased sCD30 (282.5 +/- 53.5 for the rejecting first graft vs. 374.6 +/- 129 for the rejecting second graft) prior to rejection suggesting memory CD4+ T cells contribute to sCD30. CD4KO failed to reject islet allograft and did not demonstrate sCD30 increase. CD8KO showed elevated (227 +/- 107) sCD30 (1 day) prior to rejection. High pretransplant sCD30 (>20 U/ml) correlated with poor outcome in human islet allograft recipients. Further, increase in sCD30 posttransplant preceded (3-4 months) loss of islet function. We conclude that sCD30 is released from activated CD4 T cells prior to islet allograft rejection and monitoring sCD30 can be a valuable adjunct in the follow-up of islet transplant recipients.

HUMAN REGULATORY T CELLS PREVENT ISLET ALLOGRAFT REJECTION

Background: Type 1 diabetes mellitus represents a significant burden on global healthcare. Pancreatic islet transplantation offers an effective means of controlling the disease, but shortage of donor tissue, graft thrombosis, and immunological rejection after transplantation remain obstacles that need to be overcome. Our aim was to assess the ability of ex vivo expanded human regulatory T cells (Treg) in modulating the rejection response against a human islet allograft in a clinically relevant model of human pancreatic islet transplantation. Methods: We studied the rejection response against allogeneic human islets in acohort of 32 immunodeficient mice which had been reconstituted with a functional human immune system. Thirteen subjects were transplanted with human islets without further immunological modification; graft survival was compared with that of thirteen subjects treated additionally with human regulatory T cells. Six controls were given a human islet transplant, but not reconstituted with human immune cells to demonstrate the functionality of the islet graft in the absence of immunological rejection. Graft function was assessed with serial blood glucose measurements, immunohistochemistry,immunoflourescence, and flow cytometry. Findings: Human islet allografts were rapidly rejected in subjects that did notreceive Treg. With Treg treatment, however, human islet allograft rejection was prevented (median survival time (MST) of &gt; 45 days with Treg, as opposed to an MST of 23 days without Treg). Ex vivo expanded Treg homed to the lymphoid tissue draining the graft site where they suppressed the priming, activation, proliferation, and effector cytokine production of alloreactive T cells. Interpretation: These findings in a clinically relevant model of human pancreatic islet transplantation demonstrate the ability of ex vivo expanded human Treg to attenuate acute islet allograft rejection, and provide further support for their use in cellular immunotherapy.

A new immunodeficient hyperglycaemic mouse model based on the Ins2Akita mutation for analyses of human islet and beta stem and progenitor cell function.

To develop and validate a new immunodeficient mouse strain that spontaneously develops a non-autoimmune hyperglycaemia to serve as a diabetic host for human islets and human beta stem and progenitor cells without the need for induction of hyperglycaemia by toxic chemicals with their associated side effects. We generated and characterised a new strain of immunodeficient spontaneously hyperglycaemic mice, the NOD-Rag1null Prf1null Ins2Akita strain and compared this strain with the NOD-scid Il2rgammanull (also known as Il2rg) immunodeficient strain rendered hyperglycaemic by administration of a single dose of streptozotocin. Hyperglycaemic mice were transplanted with human islets ranging from 1,000 to 4,000 islet equivalents (IEQ) and were monitored for normalisation of blood glucose levels. NOD-Rag1null Prf1null Ins2Akita mice developed spontaneous hyperglycaemia, similar to Ins2Akita-harbouring strains of immunocompetent mice. Histological examination of islets in the host pancreas validated the spontaneous loss of beta cell mass in the absence of mononuclear cell infiltration. Human islets transplanted into spontaneously diabetic NOD-Rag1null Prf1null Ins2Akita and chemically diabetic NOD-scid Il2rgammanull mice resulted in a return to euglycaemia that occurred with transplantation of similar beta cell masses. The NOD-Rag1null Prf1null Ins2Akita mouse is the first immunodeficient, spontaneously hyperglycaemic mouse strain described that is based on the Ins2Akita mutation. This strain is suitable as hosts for human islet and human beta stem and progenitor cell transplantation in the absence of the need for pharmacological induction of diabetes. This strain of mice also has low levels of innate immunity and can be engrafted with a human immune system for the study of human islet allograft rejection.

OX40 Controls Islet Allograft Tolerance in CD154 Deficient Mice by Regulating FOXP3+ Tregs

The role of OX40 in the islet allograft tolerance, especially in the absence of CD154 costimulation, remains poorly defined. In the present study, we used CD154 deficient mice to critically examine the role of OX40 in the activation of T effector cells and Foxp3+ Tregs and the effect of blocking OX40 on the induction of islet allograft tolerance. We found that blocking OX40 costimulation in CD154 deficient mice induced donor specific tolerance but stimulating OX40 resulted in prompt islet allograft rejection. We also found that OX40 differentially regulates T effector cells and Foxp3+ Tregs, OX40 signaling mediates proliferation of CD154 deficient T effector cells but blocks the induction and suppressor functions of Foxp3+ Tregs. Our data suggest that the role of OX40 in the induction of islet allograft tolerance involves modifying not only the T effector cells but also the Foxp3+ Tregs in CD154 deficient mice.

Prolonging Islet Allograft Survival Using In Vivo Bioluminescence Imaging to Guide Timing of Antilymphocyte Serum Treatment of Rejection

Bioluminescence imaging (BLI) is a sensitive and noninvasive method for tracking the fate of transplanted islets. The aim of this study was to investigate whether early detection of rejection by BLI can aid in the timing of antilymphocyte serum (ALS) treatment for prolonging islet graft survival. Transgenic islets (200 per recipient) expressing the firefly luciferase from FVB/NJ strain (H-2q) mice were transplanted under the kidney capsule of streptozotocin-induced diabetic allogeneic Balb/c strain (H-2q) mice. BLI signals and serum glucose levels were measured daily after transplant. Four groups of mice were transplanted: group 1 recipients were untreated controls (n=12), group 2 (n=8) received ALS before transplant, group 3 (n=10) received ALS at a time after transplant when normoglycemic but prompted by a reduction (approximately 30%) in BLI signal intensity for 2 consecutive days, and group 4 (n=5) received ALS after transplant when prompted by blood glucose levels increasing approximately 20% from the normoglycemic baseline (BLI reduction approximately 70%). The incidence of graft loss from rejection in groups 1, 2, 3, and 4 was 92.3%, 88%, 40%, and 100%, respectively. The mean (+/-SE) time to graft loss in groups 1, 2, 3 and 4 was 22.5+/-4.8, 29.2+/-9.9, 53.5+/-17.9, and 22.1+/-2.4 days, respectively. Noninvasive imaging modalities of functional islet mass, such as BLI (but not blood glucose levels), can prompt the appropriate timing of ALS treatment of islet allograft rejection and significantly prolong graft survival or protect the grafts from permanent loss.

Immunoglobulin-Like Transcript 3-Fc Suppresses T-Cell Responses to Allogeneic Human Islet Transplants in hu-NOD/SCID Mice

OBJECTIVE—The aim of our study was to explore the immunomodulatory activity of soluble immunoglobulin (Ig)-like transcript (ILT) 3-Fc in pancreatic islet transplantation and to determine its mechanism of action.RESEARCH DESIGN AND METHODS—NOD/SCID mice in which diabetes was induced by streptozotocin injection were transplanted with human pancreatic islet cells. Mice in which the transplant restored euglycemia were humanized with allogeneic peripheral blood mononuclear cells and treated with ILT3-Fc or control human IgG or left untreated. The blood glucose level was monitored twice a week, and rejection was diagnosed after two consecutive readings >350 mg/dl. Tolerated and rejected grafts were studied histologically and by immunostaining for human T-cells and insulin production. CD4 and CD8 T-cells from the spleen were studied for suppressor activity, expression of cytokines, and CD40L.RESULTS—Although human T-cell engraftment was similar in all groups, ILT3-Fc–treated mice tolerated the islets for the entire period of observation (91 days), whereas control mice rejected the graft within 7 weeks (P < 0.0001). ILT3-Fc treatment suppressed the expression of cytokines and CD40L and induced the differentiation of human CD8+ T suppressor cells that inhibited Th alloreactivity against graft HLA antigens. T-cells allostimulated in vitro in the presence of ILT3-Fc inhibited CD40L-induced upregulation of CD40 in human pancreatic islet cells. Histochemical studies showed dramatic differences between human pancreatic islets from tolerant, ILT3-Fc–treated mice and control recipients rejecting the grafts.CONCLUSIONS—The data indicated that ILT3-Fc is a potent immunoregulatory agent that suppressed islet allograft rejection in humanized NOD/SCID mice.

“Indirect” Acute Islet Allograft Destruction in Nonobese Diabetic Mice Is Independent of Donor Major Histocompatibility Complex and Requires Host B Lymphocytes

Islet allografts are destroyed rapidly in spontaneously diabetic nonobese diabetic (NOD) mice. However, whether this process is more similar to conventional allograft immunity, islet-specific autoimmune pathogenesis, or both remains controversial. In particular, we sought to determine whether C57BI/6 donor islet major histocompatibility complex (MHC) class I or class II expression was required for islet allograft destruction in autoimmune prone NOD mice versus non-autoimmune–prone BALB/c mice. Results show that islet allografts deficient in both MHC I and II are uniformly accepted in BALB/c mice. In sharp contrast, such MHC-deficient allografts were destroyed acutely in spontaneously diabetic NOD mice. Such donor MHC-independent rejection implicates “indirect” (host MHC-restricted) immunity as a pathway responsible for islet injury. To determine whether host NOD B lymphocytes could contribute to indirect graft recognition, wild-type and MHC I/II–deficient allografts were grafted into B-lymphocyte–deficient (μMT) NOD mice. Whereas wild-type NOD mice could reject MHC-I/II–deficient islet allografts, such grafts were all accepted in B-lymphocyte–deficient NOD mice. Taken together, these results indicate that NOD mice are capable of vigorous donor MHC-independent islet allograft rejection not found in non-autoimmune–prone recipients. Importantly, B lymphocytes may play a key role as antigen-presenting cells in this exuberant host ’indirect’ response found in NOD mice.

A new Hu-PBL model for the study of human islet alloreactivity based on NOD- scid mice bearing a targeted mutation in the IL-2 receptor gamma chain gene

Immunodeficient NOD-scid mice bearing a targeted mutation in the IL2 receptor common gamma chain (Il2rgamma(null)) readily engraft with human stem cells. Here we analyzed human peripheral blood mononuclear cells (PBMC) for their ability to engraft NOD-scid Il2rgamma(null) mice and established engraftment kinetics, optimal cell dose, and the influence of injection route. Even at low PBMC input, NOD-scid Il2rgamma(null) mice reproducibly support high human PBMC engraftment that plateaus within 3-4 weeks. In contrast to previous stocks of immunodeficient mice, we observed low intra- and inter-donor variability of engraftment. NOD-scid Il2rgamma(null) mice rendered hyperglycemic by streptozotocin treatment return to normoglycemia following transplantation with human islets. Interestingly, these human islet grafts are rejected following injection of HLA-mismatched human PBMC as evidenced by return to hyperglycemia and loss of human C-peptide. These data suggest that humanized NOD-scid Il2rgamma(null) mice may represent an important surrogate for investigating in vivo mechanisms of human islet allograft rejection.

Role of Intra-Islet Endothelial Cells in Islet Allo-Immunity

Intra-islet endothelial cells (IECs) express high levels of major histocompatibility complex (MHC) and are pivotal for posttransplant islet revascularization. We postulated that donor-specific sensitization would result in hyperacute rejection of IECs and prevent islet engraftment. Furthermore, ligation of endothelial cells with subsaturating concentrations of anti-MHC class I antibody (Ab) results in "accommodation" conferring protection against Ab/complement-mediated lysis. Therefore, we investigated whether accommodation of IECs would prevent hyperacute rejection of islets in sensitized recipients. Islets were transplanted beneath the kidney capsule and allograft survival monitored using daily blood glucose (diabetes >300 mg/dL, normoglycemia <150 mg/dL). Recipients were presensitized with donor islets, splenocytes, or skin. Accommodation was induced by incubating human or murine islets with varying concentrations of anti-MHC class I Ab ex vivo. Isografts remained functional for >100 days, whereas allografts were rejected by day 14. Islet allo-transplantation induced donor-specific but not third-party anti-MHC Abs. Donor-specific, but not third-party, sensitization induced hyperacute rejection of subsequent islet allografts (median survival 1 day) associated with complement deposition. Preincubation of islets with subsaturating concentrations of anti-MHC-I Abs (1-100 ng/mL) up-regulated Bcl-2, Bcl-xl, and HO-1 within CD31+ IEC. These accommodated islets were resistant against hyperacute rejection when transplanted into donor-(splenocyte) sensitized recipients without any immunosuppression (median survival 6 days). Pretransplant sensitization against donor antigens results in hyperacute rejection of murine islets. IECs may play a crucial role in development of donor-specific immunity after islet transplantation. Significantly, accommodation of IEC may confer resistance to hyperacute rejection in sensitized recipients.

Accommodation of intraislet endothelial cells (IEC) confers resistance to hyperacute islet allograft rejection

Accommodation of intraislet endothelial cells (IEC) confers resistance to hyperacute islet allograft rejection

Islet Allograft Rejection by Contact‐Dependent CD8+ T cells: Perforin and FasL Play Alternate but Obligatory Roles

Though CD8(+) T lymphocytes are important cellular mediators of islet allograft rejection, their molecular mechanism of rejection remains unidentified. Surprisingly, while it is generally assumed that CD8(+) T cells require classic cytotoxic mechanisms to kill grafts in vivo, neither perforin nor FasL (CD95L) are required for acute islet allograft rejection. Thus, it is unclear whether such contact-dependent cytotoxic pathways play an essential role in islet rejection. Moreover, both perforin and CD95L have been implicated in playing roles in peripheral tolerance, further obscuring the role of these effector pathways in rejection. Therefore, we determined whether perforin and/or FasL (CD95L) were required by donor MHC-restricted ('direct') CD8(+) T cells to reject islet allografts in vivo. Islet allograft rejection by primed, alloreactive CD8(+) T cells was examined independently of other lymphocyte subpopulations via adoptive transfer studies. Individual disruption of T-cell-derived perforin or allograft Fas expression had limited impact on graft rejection. However, simultaneous disruption of both pathways prevented allograft rejection in most recipients despite the chronic persistence of transferred T cells at the graft site. Thus, while there are clearly multiple cellular pathways of allograft rejection, perforin and FasL comprise alternate and necessary routes of acute CD8(+) T-cell-mediated islet allograft rejection.

Hyperexpression of Foxp3 and IDO During Acute Rejection of Islet Allografts

We investigated the hypothesis that Foxp3+ cells are an integral component of antiallograft immunity but are dominated by pathogenic effectors. Wild-type H-2b C57BL/6 (B6) mice or B6 mice with a targeted disruption of c-Rel gene (c-Rel-/-) were used as recipients of islet grafts from allogeneic DBA/2 (H-2d) mice or syngeneic B6 mice. We developed kinetic quantitative polymerase chain reaction assays and measured intragraft expression of mRNA for Foxp3, IDO, cytolytic molecules, proinflammatory cytokines, and chemokines/receptors. Intraislet levels of mRNA for Foxp3, IDO, CD3, CD25, tumor necrosis factor-alpha, RANTES, IP-10, and CXCR3 were highest in DBA/2 islet allografts from WT B6 recipients compared to DBA/2 islet allografts from c-Rel-/- B6 recipients or syngeneic B6 islet grafts from WT B6 mice. The ratio of granzyme B or IFN-gamma to Foxp3 was higher with the DBA/2 islet allografts from the WT B6 recipients compared to DBA/2 islet allografts from c-Rel-/- B6 recipients or B6 islet grafts from WT B6 recipients. Foxp3+ cells are an integral component of acute rejection of allografts but may be dominated by pathogenic effectors.

Toll‐like receptor 4 suppression leads to islet allograft survival

Carbon monoxide (CO) exposure of an islet donor frequently leads to islet allograft long-term survival and tolerance in recipients. We show here that CO confers its protective effects at least in part by suppressing Toll-like receptor 4 (TLR4) up-regulation in pancreatic beta cells. TLR4 is normally up-regulated in islets during the isolation procedure; donor treatment with CO suppresses TLR4 expression in isolated islets as well as in transplanted grafts. TLR4 up-regulation allows initiation of inflammation, which leads to islet allograft rejection; islet grafts from TLR4-deficient mice survive indefinitely in BALB/c recipients and show significantly less inflammation at various days after transplantation compared with grafts from a control donor. Isolated islets preinfected with a TLR4 dominant negative virus before transplantation demonstrated prolonged survival in recipients. Despite the salutary effects of TLR4 suppression, HO-1 expression is still needed in the recipient for islet survival: TLR4-deficient islets were rejected promptly after being transplanted into recipients in which HO-1 activity was blocked. In addition, incubation of an insulinoma cell line, betaTC3, with an anti-TLR4 antibody protects those cells from cytokine-induced apoptosis. Our data suggest that TLR4 induction in beta cells is involved in beta cell death and graft rejection after transplantation. CO exposure protects islets from rejection by blocking TLR4 up-regulation.

Characterization of Donor Dendritic Cells and Enhancement of Dendritic Cell Efflux With cc-Chemokine Ligand 21

Dendritic cells (DCs) are the most potent antigen-presenting cells, yet little data are available on the differential characteristics of donor and recipient DCs (dDCs and rDCs, respectively) during the process of islet allograft rejection. DTR-GFP-DC mice provide a novel tool to monitor DC trafficking and characteristics during allograft rejection. We show rapid migration of dDCs to recipient lymphoid tissues as early as 3 h post-islet allotransplantation. Compared with rDCs, dDCs express different patterns of chemokine receptors, display differential proliferative capacity, and exhibit a higher level of maturity; these findings could be attributed to the effects of injury that dDCs undergo during islet cell preparation and engraftment. Intriguingly, we detected dDCs in the spleen of recipients long after rejection of islet allografts. Given that dDCs express high levels of CCR7, islets were cultured before transplant with the ligand for CCR7 (CCL21). This novel method, which enabled us to enhance the efflux of dDCs from islet preparations, resulted in a prolongation of islet allograft survival in immunocompetent recipients. This study introduces dDCs and rDCs as two distinct types of DCs and provides novel data with clinical implications to use chemokine-based DC-depleting strategies to prolong islet allograft survival.