Survival Of Rat Islet Xenografts Research Articles

Rat islets are not rejected by anti-islet antibodies in mice treated with costimulation blockade.

Costimulation blockade can prevent rejection of islet xenografts in naïve but not sensitized recipients. Donor-specific antibodies (DSA) may partly explain this observation. The effect of DSA on rat islet xenograft survival in mice receiving costimulation blockade was investigated. Naïve C57BL/6 mice with alloxan-induced diabetes were transplanted under the left kidney capsule with 100 Lewis rat islets. Recipients were divided into three groups receiving: (i) isotype control antibodies (Abs); (ii) anti-CD154 and CTLA4Ig; or (iii) anti-CD154, CTLA4Ig, and anti-LFA-1 every second day, day 0-8. At the time of transplantation (Tx), half of the animals in each group received naïve mouse serum and half xenoimmune serum derived from mice previously transplanted with rat islets. Non-fasting blood glucose levels and body weight were followed daily. Cured mice were examined by intraperitoneal glucose tolerance (IPGT) tests at 1 and 4 months after transplantation. Donor-specific antibodies were detected in immune serum-injected recipients up to at least 96 h post-Tx. Short term (≤96 h), there was no significant difference with regard to graft mass, infiltrating and apoptotic cells between groups of mice receiving naïve and immune sera. A moderate infiltration of polymorphonuclear and mononuclear cells was seen 96 h post-Tx in mice given control Abs, whether or not they received immune or naïve mouse serum. Mice given costimulation blockade had well-maintained endocrine tissue and very little cell infiltration. There was no significant difference in islet xenograft function and survival long term between groups receiving naïve and immune sera in combination with costimulation blockade. About half of the mice receiving costimulation blockade lost graft function within 110 days. The presence at Tx of DSA does not appear to negatively influence early and late islet xenograft survival in mice receiving costimulation blockade.

Transient B-Cell Depletion Combined With Apoptotic Donor Splenocytes Induces Xeno-Specific T- and B-Cell Tolerance to Islet Xenografts

Peritransplant infusion of apoptotic donor splenocytes cross-linked with ethylene carbodiimide (ECDI-SPs) has been demonstrated to effectively induce allogeneic donor-specific tolerance. The objective of the current study is to determine the effectiveness and additional requirements for tolerance induction for xenogeneic islet transplantation using donor ECDI-SPs. In a rat-to-mouse xenogeneic islet transplant model, we show that rat ECDI-SPs alone significantly prolonged islet xenograft survival but failed to induce tolerance. In contrast to allogeneic donor ECDI-SPs, xenogeneic donor ECDI-SPs induced production of xenodonor-specific antibodies partially responsible for the eventual islet xenograft rejection. Consequently, depletion of B cells prior to infusions of rat ECDI-SPs effectively prevented such antibody production and led to the indefinite survival of rat islet xenografts. In addition to controlling antibody responses, transient B-cell depletion combined with ECDI-SPs synergistically suppressed xenodonor-specific T-cell priming as well as memory T-cell generation. Reciprocally, after initial depletion, the recovered B cells in long-term tolerized mice exhibited xenodonor-specific hyporesponsiveness. We conclude that transient B-cell depletion combined with donor ECDI-SPs is a robust strategy for induction of xenodonor-specific T- and B-cell tolerance. This combinatorial therapy may be a promising strategy for tolerance induction for clinical xenogeneic islet transplantation.

The Effect of Co-Stimulation Blockade on Memory T Cell Responses in a Rat-To-Mouse Islet Xenotransplantation Model

Background: Co-stimulatory signals have been reported to play an important role in islet xenograft rejection. Co-stimulation blockade cannot inhibit graft rejection in sensitized recipients. We investigated whether pre-existing donor-specific antibodies influenced islet xenograft survival in recipients treated with co-stimulation blockade. Methods: MaleC57BL/6 mice with alloxan-induced diabetes were used as recipients and male Lewis rats as donors. Xenoimmune serum was collected from mice transplanted with 200 Lewis rat islets and used as source of immune antibodies. Diabetic naïve C57BL/6 mice were transplanted under the left kidney capsule with 100 Lewis rat islets and the recipients were divided into three groups receiving: i) isotype control antibodies; ii) anti-CD154 and CTLA4Ig; and iii) anti-CD 154, CTLA4Ig, and anti-LFA-1 every second day from day 0 to day 8. Half of the animals in each group received naïve mouse serum (as source of control antibody) and half xenoimmune serum at the time of transplantation. Graft survival was followed by daily recordings of non-fasting blood glucose levels and body weight. Cured mice were examined by the IPGT test at 4 and 6-8 weeks after transplantation. Results: Anti-donor antibody was detected in the immune antibody injected recipient serum at 48 hours after transplantation but disappeared after 96 hour. There was no significant difference in graft survival between immune antibody and naive antibody injected groups. Mice receiving isotype control antibodies rejected their grafts within 13 days, and histology showed severe infiltration of both PMN and lymphocytes with few or no remaining grafts. The graft function in mice receiving double and triple treatment survived longer (>70 days), however, approximately half of them lost graft function after 100 days. In cured mice, islet grafts were verified by histological examination. Most of them showed mononuclear cell infiltration around the grafts. In mice rejecting the grafts, no or very little graft mass was seen with severe infiltration of mononuclear cells and some PMNs. In the IPGTT at 6-8 weeks after transplantation, return of normoglycemia was significantly delayed compared to the response in the IPGTT done at 4 weeks, indicating a gradual graft loss during the observation period. Mixed lymphocyte cultures in vitro showed no significant difference in T-cell proliferation between islet rejecting and accepting hosts. Anti-donor antibodies developed even in mice maintaining graft function. Conclusion: Xenoimmune antibody alone did not affect rat islet xenograft survival in naïve mice when their T cell immunity was impaired through co-stimulation blockade. Co-stimulation blockade could not induce permanent graft survival in the rat-to-mouse islet xenotransplantation model.

Monotherapy with Anti-LFA-1 Monoclonal Antibody Promotes Long-Term Survival of Rat Islet Xenografts

Previously we demonstrated that anti-LFA-1 monoclonal (mAb) could promote long-term survival of discordant porcine islet xenografts in mice. The aim of this study, therefore, was to determine whether a shortterm administration of anti-LFA-1 mAb would promote long-term survival of concordant rat islet xenografts in mice, and whether combining short-term administration of anti-LFA-1 mAb therapy with an immunosuppressive drug, rapamycin, would facilitate islet xenograft survival. Streptozotocin-induced diabetic BALB/c mice were transplanted with 500 Wistar-Furth rat islets under the kidney capsule and were either left untreated or treated with short-term administration of rapamycin (0.2 mg/kg) alone, anti-LFA-1 mAb (0.2 mg/ dose) alone, or a combination of rapamycin and anti-LFA-1 mAb using the same doses. All untreated mice rejected their grafts by 24 days posttransplantation with a mean graft survival time of 18.8 +/- 2.5 days posttransplantation (n = 5). All mice treated with rapamycin alone had prolonged islet graft survival but eventually rejected their islet grafts by 81 days posttransplantation. In contrast, the majority of the mice (27/ 28) treated with anti-LFA-1 mAb alone maintained long-term normoglycemia (>100 days). Rapamycin in combination with anti-LFA-1 mAb proved equally effective with 29 of 30 mice maintaining normoglycemia for more than 100 days posttransplantation. Low levels of mouse anti-rat antibodies, as well as a decrease in the degree of mononuclear cell infiltration of the islet graft, closely correlated with long-term islet xenograft survival. These results demonstrate that monotherapy with anti-LFA-1 mAb is highly effective in promoting long-term survival of rat islet xenografts and that combination of anti-LFA-1 mAb with rapamycin does not facilitate nor abrogate the induction of long-term xenograft survival by anti-LFA-1 mAb therapy in BALB/c mice. Our study indicates that immunomodulation through mAb therapy could form a significant component of future antirejection therapies in clinical islet xenotransplantation.

Mitomycin-C Treatment Followed by Culture Produces Long-Term Survival of Islet Xenografts in a Rat-to Mouse Model

One of the goals of islet transplantation is to transplant viable islets without host immunosuppression. The present study was designed to determine whether pretreatment of islets with mitomycin-C (MMC) followed by culture enhances islet survival in a rat-to-mouse xenogeneic combination. WS(RT1k) rat islets pretreated with various concentrations of MMC (0, 3.2, 10, 32, 100, 320, and 1000 microg/ml) were tested for viability by in vitro insulin secretory capacity and vital staining of islets. The MMC-treated islets (10 microg/ml) cultured for various periods (4, 20, or 40 h, 3 or 7 days) were transplanted into the renal subcapsular space of STZ-induced diabetic C57BL/6 (B6: H-2b) mice. MMC-treated or nontreated islets were subjected to microarray gene analysis and immunohistological study. Evaluation of in vitro insulin secretory capacity and vital staining of islets indicated that MMC at a dose < or =32 microg/ml is nontoxic and preserves islet function. Marked prolongation of graft survival was noted with half of islet grafts surviving indefinitely (>100 days) when 10 microg/ml of MMC-treated islets was transplanted after 40 h or 3 days in culture, but not when they were transplanted within 4 h following treatment or at 7 days following treatment, indicating that there is a critical culture period necessary for successful islet graft survival. Microarray analysis suggested possible genes for this prolongation with TGF-beta highly expressed in MMC-treated islets subjected to culture for 3 days. Our results indicate that MMC treatment followed by a critical culture period induces marked prolongation of rat islet xenograft survival in nonimmunosuppressed recipient mice, offering a strategy for islet transplantation without immunosuppression.

Autoimmune Diabetes and Resistance to Xenograft Transplantation Tolerance in NOD Mice

Costimulation blockade induces prolonged rat islet and skin xenograft survival in C57BL/6 mice. Nonobese diabetic (NOD) mice, which are used to model human autoimmune diabetes, are resistant to costimulation blockade-induced allograft tolerance. We tested the hypothesis that NOD mice would also be resistant to costimulation blockade-induced rat xenograft tolerance. We report that rat islet xenograft survival is short in spontaneously diabetic NOD mice treated with a tolerizing regimen of donor-specific transfusion and anti-CD154 antibody. Rat islet xenograft survival is only marginally longer in chemically diabetic NOD mice treated with costimulation blockade but is prolonged further in NOD Idd congenic mice bearing C57-derived chromosome 3 loci. Reciprocally, the presence of NOD-derived chromosome 3 loci shortens islet xenograft survival in tolerized C57BL/6 mice. Islet xenograft survival is longer in tolerized NOD.CD4a(-/-) and (NOD x C57BL/6)F1 mice than in NOD mice but still much shorter than in C57BL/6 mice. Skin xenograft survival in (NOD x C57BL/6)F1 mice treated with costimulation blockade is short, suggesting a strong genetic resistance to skin xenograft tolerance induction. We conclude that the resistance of NOD mice to xenograft tolerance induction involves some mechanisms that also participate in the expression of autoimmunity and other mechanisms that are distinct.

Prolonged survival of rat islet xenografts in mice after CD45RB monotherapy.

Pancreatic islet transplantation can correct the disordered glucose metabolism of type 1 diabetes, but the number of successful transplants has been low because of the need for long-term immunosuppression and the limited availability of human islets. New approaches, such as the use of tolerance-inducing treatment modalities and the use of islets of nonhuman sources, can possibly improve the success of islet transplantation. In the present study, the authors investigated the effect of anti-CD45RB treatment on the survival of islet xenografts. Chemically induced diabetic mice underwent xenografting with rat islets and were treated with CD45RB antibodies on days -1, 0, and 5. Immunohistology and real-time polymerase chain reaction were used to study the effect of the treatment in the xenografts. The effect of anti-CD45RB treatment in peripheral blood of normal mice was measured with flow cytometry. In the treated mice, survival of the grafts was prolonged substantially. In the treated mice with functioning grafts, no lymphocytes were found infiltrating the transplanted islets on day 6; whereas in the untreated animals with functioning grafts, signs of rejection were evident. In the grafts of the treated animals, significantly less mRNA for interleukin (IL)-2, interferon-gamma, and IL-4 was found compared with the untreated mice. After CD45RB treatment, there was depletion or decrease of CD45RBbright cells from the peripheral blood. Our results show that a short course of anti-CD45RB monotherapy prolongs the survival of rat islet xenografts in C57BL/6 mice.

A CD200FC immunoadhesin prolongs rat islet xenograft survival in mice.

A solubilized form of the CD200 molecule, CD200Fc, has been shown to suppress allograft rejection and development of collagen-induced arthritis in mice. We investigated whether the same molecule could prolong survival of rat islet xenografts. Streptozocin-treated mice, receiving injections with anti-asialo-GM1 antibody, received rat islets ( approximately 400/mouse) under the kidney capsule or injected into the portal vein, along with rapamycin treatment. Thereafter mice received injections of CD200Fc (10 microg/mouse/injection) or control mouse IgG2. Blood glucose was monitored daily. Some mice received additional injections of anti-CD200/-CD200R monoclonal antibodies. Portal vein delivery of islets led to more extended resolution of diabetes than did transplantation under the kidney capsule. CD200Fc further prolonged survival in either case, an effect abolished by anti-CD200 or F(ab')2 anti-CD200R mAbs, but not by whole anti-CD200R (anti-CD200R Ig). Spleen cells taken from CD200Fc-treated mice showed polarization to type-2 cytokine production (interleukin-4, interleukin-10) on restimulation with rat splenocytes in culture, in comparison to cells from control mice (type-1 cytokines, interlulin-2, interferon-gamma). CD200:CD200R interactions are important in regulating rat islet xenograft survival.

Prolongation of rat islet xenograft survival in the liver of IFN-gamma-deficient mice.

The cellular mechanisms involved in islet xenograft rejection remain undetermined. In the present study, the role of interferon-gamma (IFN-gamma) in rat islet xenograft rejection was examined with the use of IFN-gamma-deficient mice as recipients and the results were compared with allografts. There was no significant difference in the survival of intrahepatic islet allografts in IFN-gamma-deficient mice compared with that in wild-type mice. In contrast, a marked prolongation of rat islet xenograft survival was obtained in IFN-gamma-deficient mice without immunosuppression when compared with the survival in wild-type mice. In order to dissect the difference, infiltrating cells in the liver in association with rejection were examined with flow cytometry. An expansion of CD8 T cells was seen in the liver of wild-type mice rejecting xenografts compared with isografts. There was no significant change in other cell populations. In IFN-gamma-deficient mice, the expansion of CD8 T cells was seen in the liver rejecting xenografts; however, the time of development was markedly delayed by the time of rejection. These findings suggest that the acute rejection of rat islet xenografts in mice is IFN-gamma-dependent although the exact mechanisms remain unknown.

Pancreatic islet xenograft tolerance after short-term costimulation blockade is associated with increased CD4+ T cell apoptosis but not immune deviation.

Our purpose was to determine if short-term inhibition of the CD40/CD40L and CD28/B7 costimulatory pathways was capable of inducing specific unresponsiveness to pancreatic islet xenografts and to ascertain the mechanism of tolerance induction. Diabetic B6AF1 mice were transplanted with Wistar or DA rat islets and were treated short term with CTLA4-Fc and anti-CD40L mAb (MR1). Coadministration of CTLA4-Fc with MR1, resulted in indefinite rat islet xenograft survival in mice. Tolerance was species but not strain specific as long-term surviving recipients rejected third party BALB/c islet allografts but accepted a second rat islet xenograft from the same or different donor strain. Tolerance induction was associated with a large leukocyte infiltrate that did not exhibit features of immune deviation as intragraft T cell-specific cytokine gene expression was globally reduced. In particular, interleukin-4 gene expression was markedly suppressed. There was a complete inhibition of anti-donor IgG, IgG1, and IgM antibody in the serum of CTLA4-Fc/MR1- treated animals. Tolerance induction was associated with increased CD4+ T cell apoptosis as there was an increased proportion of annexin-V staining and Fas expressing CD4+ T cells and a decrease in CD4+ T cell Bcl-2 expression in the grafts and draining lymph nodes of CTLA4-Fc/MR1-treated recipients. Combined costimulatory blockade was capable of producing tolerance to pancreatic islet xenografts. The induction of this tolerant state was associated with increased T cell apoptosis, whereas the maintenance phase of tolerance was associated with the accumulation of a large number of inactive lymphocytes within the graft.

Prolonged survival of rat islet and skin xenografts in mice treated with donor splenocytes and anti-CD154 monoclonal antibody.

Treatment of C57BL/6 mice with one transfusion of BALB/c spleen cells and a brief course of anti-CD154 (anti-CD40 ligand) antibody permits BALB/c islet grafts to survive indefinitely and BALB/c skin grafts to survive for approximately 50 days without further intervention. We now report adaptation of this protocol to the transplantation of islet and skin xenografts. We observed prolonged survival of rat islet xenografts in mice treated with donor-specific spleen cell transfusion and anti-CD154 monoclonal antibody (mAb). Challenge islet xenografts placed on these animals indicated that graft acceptance was species-specific but not strain specific. Spleen cells from recipients bearing intact grafts led to rejection of rat islet xenografts in scid mice, suggesting that graft acceptance was not due to complete clonal deletion of xenoreactive cells. We also observed prolonged survival of rat skin xenografts in mice treated with donor-specific transfusion and anti-CD154 mAb. Prolonged survival of skin xenografts was also species specific. We conclude that treatment with appropriately timed donor-specific transfusion and anti-CD154 mAb induces durable survival of both islet and skin xenografts in mice. Because this procedure is targeted directly at CD154, a co-activation molecule expressed predominantly by activated CD4+ T-cells, the results suggest that CD4+ cells have a major role in the cellular immune response to xenografts.

Prolonged survival of rat islet and skin xenografts in mice treated with donor splenocytes and anti-CD154 monoclonal antibody

Treatment of C57BL/6 mice with one transfusion of BALB/c spleen cells and a brief course of anti-CD154 (anti-CD40 ligand) antibody permits BALB/c islet grafts to survive indefinitely and BALB/c skin grafts to survive for ∼50 days without further intervention. We now report adaptation of this protocol to the transplantation of islet and skin xenografts. We observed prolonged survival of rat islet xenografts in mice treated with donor-specific spleen cell transfusion and anti-CD154 monoclonal antibody (mAb). Challenge islet xenografts placed on these animals indicated that graft acceptance was species-specific but not strain specific. Spleen cells from recipients bearing intact grafts led to rejection of rat islet xenografts in scid mice, suggesting that graft acceptance was not due to complete clonal deletion of xenoreactive cells. We also observed prolonged survival of rat skin xenografts in mice treated with donor-specific transfusion and anti-CD154 mAb. Prolonged survival of skin xenografts was also species specific. We conclude that treatment with appropriately timed donor-specific transfusion and anti-CD154 mAb induces durable survival of both islet and skin xenografts in mice. Because this procedure is targeted directly at CD154, a co-activation molecule expressed predominantly by activated CD4+ T-cells, the results suggest that CD4+ cells have a major role in the cellular immune response to xenografts.

Tumor necrosis factor-alpha prevents rejection of islet xenografts (rat to mouse).

The effect of in vivo administration of exogenous tumor necrosis factor-alpha on the survival of rat islet xenografts in STZ-induced diabetic mice was examined. Daily subcutaneous injections of purified recombinant murine TNF-alpha (3 micrograms/day) for 7 days after transplantation of islets prolonged the survival of the xenografts (26.7 +/- 4.9 days) compared with controls (11.2 +/- 1.1 days). Extension of the treatment from 0 to 59 days after transplantation produced an even greater prolongation of graft survival (53.7 +/- 8.5 days). After cessation of treatment, an accelerated rejection of the grafts occurred. A most interesting finding was that delaying initiation of treatment until 3 days after transplantation and continuing until 60 days produced a remarkable prolongation of xenograft survival (mean survival time > 89.8 +/- 17.5 days) with 2 recipients still normoglycemic at 124 days. Removal of the grafts at this time returned the 2 mice to a diabetic state. A second islet transplant from the same donor rat strain (Wistar-Furth) had an accelerated rejection, indicating that the long-term survival of the xenografts was not because of induction of tolerance. Delaying initiation of TNF treatment until 6 days after transplantation produced only a slight prolongation of survival (17.5 +/- 1.2 days). Prolongation of islet xenograft survival also was obtained by continuous, subcutaneous delivery of TNF-alpha by a 7-day mini-osmotic pump (3 micrograms/day). Lower daily doses of TNF-alpha (0.003, 0.3, and 1.0 micrograms) had no effect on graft survival.(ABSTRACT TRUNCATED AT 250 WORDS)

Production of Marked Prolongation of Islet Xenograft Survival (Rat to Mouse) by Local Release of Mouse and Rat Antilymphocyte Sera at Transplant Site

Polymer rods impregnated with lyophilized particles of mouse (M) or rat (R) antilymphocyte serum (ALS) were placed adjacent to rat islet xenografts transplanted beneath the kidney capsule of diabetic mice. Insertion of rods containing only MALS or RALS had no effect on the survival time of the rat islet xenografts. In contrast, the insertion of both MALS and RALS rods with the graft produced a marked prolongation of islet xenograft survival (mean survival time greater than 55.5 +/- 10.9 days) compared with controls (14.7 +/- 2.5 days). One recipient was still normoglycemic at 100 days, and removal of the graft returned the animal to a diabetic state. The islet graft had a normal degree of beta-granulation, and a slight fibrotic reaction was present around the rods. The effect of the rods in prolonging survival of the xenografts resulted from a local slow release of MALS and RALS, because implantation of the MALS and RALS rods in the right kidney and the islets in the left kidney had no effect on prolonging islet xenograft survival. These findings indicate that local immunosuppression produced marked prolongation of rat islet xenograft survival in mice. This raises the possibility of using polymer rods for the local slow release of monoclonal antibodies to lymphokines and other agents for prevention of rejection of islet allografts and xenografts and to determine the effect of lymphokines in vivo on islet function.

Low-temperature culture of human islets or in vivo treatment with L3T4 antibody produces a marked prolongation of islet human-to-mouse xenograft survival.

In previous studies we have shown that rejection of islet xenografts transplanted between closely related species (rat to mouse) can be prevented by destruction or alteration of antigen-presenting cells in the donor islets and temporary immunosuppression of the recipients. Relatively few studies have been reported on the survival of islet xenografts transplanted between widely discordant species. In the present study, isolated human islets were transplanted beneath the renal capsule of B6 mice made diabetic by the injection of streptozotocin. The effect of culturing the human islets at 24 degrees C for 7 days with or without the administration of anti-L3T4 for 7 days after transplantation was determined. A marked prolongation of the mean survival time was obtained with low-temperature culture alone (greater than 40.2 +/- 9.9 days), with anti-L3T4 alone (greater than 45.2 +/- 6.3 days), and with the combination of these regimens (greater than 51.9 +/- 5.1 days) as compared to controls (7.5 +/- 1.1 days). The surprising finding was the marked effect of low-temperature culture alone on prolonging human islet xenograft survival because this treatment of the donor islets had no effect on the survival of rat islet xenografts. Intact human islets were present in approximately equal to 80% of the recipients after returning to a diabetic state, whereas xenografts of rat islets were completely destroyed. The findings indicate that complete rejection of islets across this widely discordant species barrier is slower than across a closely related barrier and may be occurring by a different rejection process.