Long-term graft acceptance in rat heart transplantation by CTLA4Ig gene transfection combined with FTY720 treatment

Bilirubin oxidation provoked by nitric oxide radicals predicts the progression of acute cardiac allograft rejection

Bilirubin, a strong intrinsic antioxidant, quenches free radicals produced under inflammatory conditions. The oxidized bilirubin metabolites, i.e. biopyrrins, are immediately excreted into urine and can indicate the intensity of oxidation in vivo. Our preliminary studies suggested the involvement of reactive nitrogen species (RNS) in generation of biopyrrins. However, little is known about biological significance of bilirubin oxidation by RNS. Here, we analyzed the correlation between bilirubin oxidation and nitric oxide (NO) radicals during rat acute cardiac allograft rejection. In allograft recipients, urinary biopyrrins steeply increased on day 3 prior to the increase in myocardial tissue damage marker, serum troponin-T. In contrast, no significant changes in urinary biopyrrins were evident in recipients of isografts or cyclosporine-A treated allografts. Urinary nitrotyrosine, a marker of oxidation by NO radicals also increased on day 3, while administration of a NO synthase inhibitor, N(G)-monomethyl-L-arginine apparently diminished the elevation of urinary biopyrrins as well as nitrotyrosine. Immunohistochemistry revealed enhanced local expression of heme oxygenase-1, biopyrrins and nitrotyrosine in allografts in accordance with the cellular infiltrates, suggesting that changes in urinary biopyrrins reflect the bilirubin oxidation in grafts undergoing rejection. These results indicate that locally evoked bilirubin oxidation by NO radicals can predict the progression of rejection.

Time course of gene expression after the injection of adenoviral vectors containing CTLA4IG gene

INTRODUCTION

In vivo gene transfection using a recombinant adenoviral vector leads to diminished gene expression in a time-dependent manner that disappears within 4 weeks. CTLA4Ig blocks CD28-mediated costimulatory signal, and inhibits immune responses. We investigated the duration of transgene expression after administration of adenoviral vector containing CTLA4Ig gene (AdCTLA4Ig).

METHODS

We injected 1 x 10(9) plaque forming units (pfu) of AdCTLA4Ig into rats (n = 7) via the tail vein. Thereafter, the blood samples were collected for assay of serum CTLA4Ig levels using enzyme-linked immunosorbent assay.

RESULTS

The CTLA4Ig level reached the maximum (range, 65-86 microg/mL; average, 75 microg/mL) on days 3 to 5 after injection. Detectable levels of CTLA4Ig were observed up to 49 days. When we injected AdCTLA4Ig in combination with FTY720 administration, the maximum levels were higher and the detectable levels persisted longer.

CONCLUSIONS

Because directly injected adenoviral transgene expression had been reported to disappear between 21 to 30 days, we conclude that AdCTLA4Ig inhibits the immune response and prolongs the transgene (CTLA4Ig gene) expression. Some additional immunosuppressants, like FTY720, may be useful to enhance AdCTLA4Ig effects.

FTY720: from bench to bedside

FTY720, a synthetic myriocin analogue derived from culture filtrates of Isaria sinclairii, is a novel immunosuppressant that in experimental animals and nonhuman primates produces lymphocytopenia and prolongs allograft survival in dose-dependent fashion. FTY720 exerts synergistic interactions not only with calcineurin antagonists, but also with proliferation signal inhibitors. These interactions offer the possibility of reducing exposure to and mitigating toxicity of existing drugs. The mechanism of drug action is not entirely clear. FTY720 appears to undergo phosphorylation by sphingosine phosphokinase 2, rendering it capable of interacting with the specific G protein-linked receptors for its structural homologue-sphingosine-1-phosphate. However, it is not clear how this interaction leads to emigration of lymphocytes from the peripheral blood and sequestration in secondary lymphoid structures. Present theories suggest that the drug prevents emigration rather than directing the onset of sequestration. Thus, the drug is the archetype of a new class of agents that alter lymphocyte homing patterns: the adhesion-migration paradigm. These modalities reduce interstitial infiltration of grafts and attenuate their release from lymph nodes. Since FTY720 seems to spare nonspecific elements of host resistance, it may not only represent a useful addition to the immunosuppressive armamentarium but also address the not infrequent complications of infections associated with existing therapies.

Protective effects of FTY720 on chronic allograft nephropathy by reducing late lymphocytic infiltration

BACKGROUND

Lymphocytic infiltration is obvious throughout early and late stages of chronic allograft nephropathy. Early infiltrating lymphocytes are involved in initial insults to kidney allografts, but the contribution of late infiltration to long-term allograft attrition is still controversial. Early application of FTY720 reduced the number of graft infiltrating lymphocytes, and inhibited acute rejection. The present study investigated the potential of FTY720 to reduce the number of infiltrating lymphocytes even at a late stage, and, thus, slow the pace of chronic allograft nephropathy.

METHODS

Fisher (F344) rat kidneys were orthotopically transplanted into Lewis recipients with an initial 10-day course of cyclosporine A (1.5 mg/kg/day). FTY720, at a dose of 0.5 mg/kg/day, or vehicle was administered to recipients either from weeks 12 to 24 or from 20 to 24 after transplantation. Animals were harvested 24 weeks after transplantation for histologic, immunohistologic, and molecular analysis.

RESULTS

FTY720, either initiated at 12 or 20 weeks after transplantation, reduced urinary protein excretion, and significantly ameliorated glomerulosclerosis, interstitial fibrosis, tubular atrophy, and intimal proliferation of graft arteries at 24 weeks after transplantation. Furthermore FTY720 markedly suppressed lymphocyte infiltration and decreased mRNA levels of interleukin-10 (IL-10), transforming growth factor-beta (TGF-beta), and platelet-derived growth factor-B (PDGF-B) but enhanced the number of apoptotic cells in grafts.

CONCLUSIONS

FTY720 ameliorated chronic allograft nephropathy even at advanced stages. Furthermore, our data suggest that this effect was achieved by a reduction of graft infiltrating lymphocytes.

FTY720: A new kid on the block for transplant immunosuppression

FTY720, a synthetic analogue of myriocin (ISP-1), is derived from culture filtrates of the fungus Isaria sinclairii. As a sphingosine analogue, FTY720 appears to undergo phosphorylation and thereby interact with specific G-protein-linked receptors. In vivo, FTY720 causes emigration of lymphocytes from peripheral blood to secondary lymphoid structures. Thus, the drug is the archetype of a new class of agents that alter cellular homing patterns: the adhesion-migration paradigm. Since FTY720 seems to spare nonspecific elements of host resistance, it may address the not infrequent complications of infections associated with existing therapies. In experimental rodent, canine and non-human primate models, FTY720 produces lymphopenia and immunosuppression, prolonging the survival of allografts. Because of synergistic interactions, it promotes the immunosuppressive effects not only of calcineurin antagonists, but also of proliferation signal inhibitors. These interactions proffer the possibility of large reductions in exposure to and mitigated toxicity of existing drugs. In humans, FTY720 causes dose-dependent peripheral blood lymphopenia, a reduced incidence of acute rejection episodes and only one apparent adverse reaction - a negative chronotropic effect - particularly after the loading dose. While the clinical utility of FTY720 is difficult to predict before completion of Phase III studies that elucidate its benefits versus unanticipated side effects, the initial data suggest several potential advantages: it does not produce hyperlipidaemia, diabetes mellitus, nephrotoxicity, neurotoxicity or myelosuppression, which are characteristic of other immunosuppressants. Furthermore, it displays high oral bioavailability and a low interindividual coefficient of variation. Clearly, structural analogues, as well as other agents that alter the balance of chemokines or affect cellular adhesion to activated endothelium, will represent important components of future regimens.

The influence of immunosuppressive drugs on tolerance induction through bone marrow transplantation with costimulation blockade

We recently developed a murine protocol for the induction of allogeneic mixed chimerism and tolerance employing nonmyeloablative total body irradiation (TBI), standard-dose bone marrow transplantation (BMT), and costimulation blockade (cobl) with an anti-CD154 monoclonal antibody (mAb) plus CTLA4Ig. We now evaluated whether a short course (1 month) of immunosuppressive drugs, which would be ethically required in the clinical setting of organ transplantation to prevent graft loss in case tolerance is not achieved, interferes with tolerance induced with this regimen. Our results show that calcineurin inhibitors (cyclosporin A [CyA] or tacrolimus [FK]) inhibit development of long-term chimerism and abrogate tolerance induction in this model. Rapamycin (rapa), methylprednisolone (MP), FTY720, and mycophenolate mofetil (MMF), in contrast, have no negative effect on chimerism or tolerance development. Peripheral deletion of donor-reactive T cells, which usually occurs in the weeks following BMT in this model, is blocked by CyA and FK, but not by the other drugs tested. Furthermore, we found that the additional use of compatible immunosuppressive drugs (rapa plus MMF plus MP) allows the dose of TBI to be reduced, so that mixed chimerism and donor skin-graft acceptance can be achieved with 1 Gy using clinically feasible cell numbers. Thus, this protocol of BMT with costimulation blockade can be safely combined with a clinically tested immunosuppressive regimen to permit success with a lower dose of irradiation. These results should facilitate clinical application of this tolerance strategy.

Ex vivo and systemic transfer of adenovirus-mediated CTLA4Ig gene combined with a short course of FK506 therapy prolongs islet graft survival

Adenovirus-mediated CTLA4Ig gene transfer has been reported to enhance graft survival in several rodent transplantation models. In this study, we investigated the efficacy of ex vivo and systemic transfer of the CTLA4Ig gene by adenoviral vectors in pancreatic islet allo-transplantation. Islet grafts from BN rats were transplanted to chemically induced diabetic LEW rats. First, ex vivo CTLA4Ig gene transfer into isolated islets was performed prior to transplantation. Survival of transduced grafts under the kidney capsule was slightly prolonged (8.6+/-1.3 days) compared with survival of untransduced grafts (6.7+/-1.2 days); when combined with a short course of FK506, graft survival was further extended (32.6+/-10.7 days vs. 13.7+/-1.0 days with FK506 alone). Secondly, systemic gene transfer was accomplished by intravenous administration immediately after the transplantation procedure. In these animals, islet grafts under the kidney capsule survived longer (15.2+/-3.3 days) than in controls (6.7+/-1.2 days), and when FK506 was administered perioperatively, all the islet grafts survived for more than 100 days. In systemically transduced recipients, the survival of islet grafts transplanted into the liver was not significantly different from that of the grafts placed under the kidney capsule. In order to examine organ-specific immunogenicity, heterotopic BN cardiac grafts were transplanted to LEW rats intra-abdominally, with the virus transferred systemically as in the islet model. In contrast to the islet grafts, all the cardiac grafts were accepted for longer than 100 days, even without FK506 therapy. Finally, the LEW recipients with long-surviving islet or cardiac grafts were re-transplanted with islet grafts from the same donor strain (BN) on day 100. The second islet grafts survived longer than 100 days in half of the cardiac recipients, but consistently failed in the islet recipients. We conclude that in this transplant model, CTLA4Ig gene transfer and FK506 treatment synergistically improved islet graft survival, systemic transfer of the gene was more effective than ex vivo transfer to the islets, and donor-specific tolerance could not be achieved for islet transplantation but was achieved for cardiac transplantation.

Systemic delivery of a high-capacity adenoviral vector expressing mouse CTLA4Ig improves skeletal muscle gene therapy

Adenoviral vectors (AdV) are promising vectors for gene transfer of skeletal muscle. To alleviate humoral and cellular immune responses that limit successful gene transfer, the present study determined the route of administration of AdmCTLA4Ig (an adenovirus that encodes a fusion protein of mouse cytotoxic T lymphocyte-associated protein 4 (CTLA4) and the Fc protion of immunoglobulin G (IgG), CTLA4Ig) that provided optimal AdV-mediated immunosuppression. AdmCTLA4Ig was administered either intramuscularly (i.m.), intravenously (i.v.), or in the footpad (f.p.) of mice that simultaneously received an i.m. injection of an AdV encoding enhanced green fluorescent protein (AdEGFP). EGFP expression in muscle and serum levels of CTLA4Ig were higher in the i.v. and f.p. groups than the i.m. group 30 days after treatment. The i.v. and f.p. groups showed lower levels of CD4(+) and CD8(+) T-cell infiltration and decreased interferon-gamma (IFN-gamma) and interleukin 2 (IL-2) production by splenocytes. The T helper cell (Th) 2 cytokine, interleukin 4 (IL-4), was increased 30 days after treatment in the i.v. group. Neutralizing antibodies to AdV were lower in the i.v. and f.p. groups, whereas total antibodies to AdV and EGFP were lower only in the f.p. group. Our results suggest that the optimal route of administration of AdmCTLA4Ig is i.v., providing at least 2 months of stable transgene expression in muscle. The inhibition of the cellular immune response, especially the Th1 response, appeared to play a critical role in prolonging transgene expression. These results suggest that AdV-mediated delivery of targeted immune suppression will be a useful adjunct to muscle gene delivery.

Prolonged survival in rat liver transplantation with mouse monoclonal antibody against an inducible costimulator (ICOS)

BACKGROUND

An inducible costimulator (ICOS), a recently identified costimulatory receptor with a close structural homology to CD28 and CTLA4, is expressed on activated T cells. Interaction with its ligand on antigen-presenting cells stimulates T-cell proliferation to produce a different spectrum of cytokine. The inhibition of ICOS-mediated signal transduction by an anti-ICOS antibody is considered to be capable of protecting against graft rejection in organ transplantation.

METHODS

An anti-rat ICOS antibody was intravenously administered into recipients of dark Agouti-to-Lewis liver transplantations. The recipient lymphocytes from mesenteric lymph nodes were harvested on day 7 after transplantation for fluorescence-activated cell sorting analysis, and tissue specimens from the grafts were removed for histologic evaluation. Antigen-specific T-cell proliferation responses were assessed in vitro with anti-ICOS antibody.

RESULTS

Monotherapy with the antibody significantly prolonged the graft survival time by inhibiting T-cell activation and its proliferation response. The graft-infiltrating cells, both CD4 and CD8 T cells, were not completely reduced even when rats were administered the antibody, whereas the expression of ICOS almost completely disappeared in these cells.

CONCLUSIONS

T-cell activation through the ICOS costimulatory pathway plays an important role in graft rejection, and manipulating its pathway is an effective method for modulating transplantation immunity.