Auto- and alloimmune reactivity to human islet allografts transplanted into type 1 diabetic patients. (1/1197)

Allogeneic islet transplantation can restore an insulin-independent state in C-peptide-negative type 1 diabetic patients. We recently reported three cases of surviving islet allografts that were implanted in type 1 diabetic patients under maintenance immune suppression for a previous kidney graft. The present study compares islet graft-specific cellular auto- and alloreactivity in peripheral blood from those three recipients and from four patients with failing islet allografts measured over a period of 6 months after portal islet implantation. The three cases that remained C-peptide-positive for >1 year exhibited no signs of alloreactivity, and their autoreactivity to islet autoantigens was only marginally increased. In contrast, rapid failure (<3 weeks) in three other cases was accompanied by increases in precursor frequencies of graft-specific alloreactive T-cells; in one of them, the alloreactivity was preceded by a sharply increased autoreactivity to several islet autoantigens. One recipient had a delayed loss of islet graft function (33 weeks); he did not exhibit signs of graft-specific alloimmunity, but developed a delayed increase in autoreactivity. The parallel between metabolic outcome of human beta-cell allografts and cellular auto- and alloreactivity in peripheral blood suggests a causal relationship. The present study therefore demonstrates that T-cell reactivities in peripheral blood can be used to monitor immune mechanisms, which influence survival of beta-cell allografts in diabetic patients.  (+info)

Antifactor VIII antibody inhibiting allogeneic but not autologous factor VIII in patients with mild hemophilia A. (2/1197)

Two unrelated patients with the same Arg2150His mutation in the factor VIII (FVIII) C1 domain, a residual FVIII activity of 0.09 IU/mL, and inhibitor titres of 300 and 6 Bethesda Units, respectively, were studied. Further analysis of patient LE, with the highest inhibitor titer, showed that (1) plasma or polyclonal IgG antibodies prepared from LE plasma inhibited the activity of allogeneic (wild-type) but not of self FVIII; (2) the presence of von Willebrand factor (vWF) increased by over 10-fold the inhibitory activity on wild-type FVIII; (3) the kinetics of FVIII inhibition followed a type II pattern, but in contrast to previously described type II inhibitors, LE IgG was potentiated by the presence of vWF instead of being in competition with it; (4) polyclonal LE IgG recognized the FVIII light chain in enzyme-linked immunosorbent assay and the recombinant A3-C1 domains in an immunoprecipitation assay, indicating that at least part of LE antibodies reacted with the FVIII domain encompassing the mutation site; and (5) LE IgG inhibited FVIII activity by decreasing the rate of FVIIIa release from vWF, but LE IgG recognized an epitope distinct from ESH8, a murine monoclonal antibody exhibiting the same property. We conclude that the present inhibitors are unique in that they clearly distinguish wild-type from self, mutated FVIII. The inhibition of wild-type FVIII by LE antibody is enhanced by vWF and is associated with an antibody-dependent reduced rate of FVIIIa release from vWF.  (+info)

Prevention of graft-versus-host disease (GVHD) by elimination of recipient-reactive donor T cells with recombinant toxins that target the interleukin 2 (IL-2) receptor. (3/1197)

Graft-versus-host disease (GVHD), due to the presence of recipient-reactive T cells, limits the usefulness of bone marrow transplantation (BMT) and is a major contributor to patient mortality. To prevent GVHD, murine and human T cells were activated by antigen or mitogens and treated with a genetically engineered form of Pseudomonas exotoxin A (PE) directed against the IL-2 receptor. Treatment with the chimeric toxin eliminated alloreactive cytotoxic T lymphocytes (CTL) as determined by cytotoxicity and mixed lymphocyte culture assays. Precursor frequencies of alloreactive cytotoxic T cells and proliferative T cells were reduced up to 100-fold as shown by limiting dilution assays. Flow cytometric analyses revealed that treatment with the chimeric toxin completely eliminated CD25+ cells from the cultures. Toxin treatment had no significant effect on hematopoietic stem and progenitor cells as determined in vitro by colony-forming assays and in vivo by long-term hematopoietic recovery after 950 rad irradiation. Toxin treatment decreased GVHD in transplanted mice to less than 10% (as compared to 88% in untreated controls). Thus, it is possible to prevent life-threatening GVHD after BMT by using a CD25 receptor-directed toxin to eliminate host-reactive T cells from bone marrow grafts.  (+info)

The role of the human Fc receptor Fc gamma RIIA in the immune clearance of platelets: a transgenic mouse model. (4/1197)

In humans, the Fc receptor for IgG, FcgammaRIIA, is expressed on macrophages and platelets and may play an important role in the pathophysiology of immune-mediated thrombocytopenia. Mice lack the genetic equivalent of human FcgammaRIIA. To better understand the role of FcgammaRIIA in vivo, FcgammaRIIA transgenic mice were generated and characterized. One transgenic mouse line expressed FcgammaRIIA on platelets and macrophages at levels equivalent to human cells, and cross-linking FcgammaRIIA on these platelets induced platelet aggregation. Immune-mediated thrombocytopenia in this transgenic line was studied using i.v. and i.p. administration of anti-mouse platelet Ab. In comparison with matched wild-type littermates that are negative for the FcgammaRIIA transgene, Ab-mediated thrombocytopenia was significantly more severe in the FcgammaRIIA transgenic mice. In contrast, FcR gamma-chain knockout mice that lack functional expression of the Fc receptors FcgammaRI and FcgammaRIII on splenic macrophages did not demonstrate Ab-mediated thrombocytopenia. We generated FcgammaRIIA transgenic x FcR gamma-chain knockout mice to examine the role of FcgammaRIIA in immune clearance in the absence of functional FcgammaRI and FcgammaRIII. In FcgammaRIIA transgenic x FcR gamma-chain knockout mice, severe immune thrombocytopenia mediated by FcgammaRIIA was observed. These results demonstrate that FcgammaRIIA does not require the FcR gamma-chain for expression or function in vivo. Furthermore, taken together, the data suggest that the human Fc receptor FcgammaRIIA plays a significant role in the immune clearance of platelets in vivo.  (+info)

Marked mitigation of transplant vascular sclerosis in FasLgld (CD95L) mutant recipients. The role of alloantibodies in the development of chronic rejection. (5/1197)

BACKGROUND: In the acute rejection of allografts, the interaction between Fas (CD95) and its ligand (FasL; CD95L) has been shown to be involved in mediating apoptotic cell death. The role, however, of these molecules in the pathogenesis of transplant vascular sclerosis is as yet undetermined. The present study was therefore designed to address this issue. MATERIAL: C3H/HEJ FasLgld (FasL-; H2k) spontaneously mutant mice were used either as donors or recipients of aortic allografts; wild-type C57B1/6 (B6; H2b) were used as corresponding recipients or donors (n=6/group), respectively. Controls included aortas transplanted across appropriate allogeneic and syngeneic strain combinations. For histopathological evaluations, the grafts were harvested at day 40 after transplantation, at which time, splenocytes and sera were also obtained for mixed leukocyte reaction and complement-mediated microcytotoxicity assays, respectively. RESULTS: Similar to aortas obtained from allogeneic controls, allografts harvested from FasL- -->B6 recipients had morphological evidence of chronic rejection characterized by circumferential intimal thickening with partial disruption of the elastic membranes. Correspondingly, heightened antidonor cellular reactivity was also witnessed in these recipients. On the contrary, B6 allografts harvested from the majority of C3H-->FasL- recipients exhibited marked preservation of aortic morphology. Although these recipients had diminished antidonor cellular proliferation, the titers of alloantibodies were markedly elevated. CONCLUSION: The presence of FasL-expressing functional cytotoxic T cells is required for the pathogenesis of transplant vascular sclerosis. The significant reduction and/or absence of chronic rejection with the concomitant retention of antidonor humoral response in C3H FasL- recipients of B6 aortas prompt us to suggest that perhaps posttransplantation vasculopathy is initiated by cell-mediated cytotoxicity with its perpetuation facilitated by alloantibodies.  (+info)

Rapamycin reverses chronic graft vascular disease in a novel cardiac allograft model. (6/1197)

BACKGROUND: Chronic graft vascular disease (CGVD) in cardiac allografts has been defined as a slowly evolving vasculopathy unresponsive to conventional immunosuppression. We compared 4 rodent models of CGVD to evaluate the reproducibility of CGVD in heart allografts. Rapamycin (Rapa) and cyclosporine (CSA) were then used to treat CGVD. METHODS AND RESULTS: Hearts were harvested and placed heterotopically into allogenic recipients. CGVD scores of PVG allografts from ACI recipients treated with CSA on days 1 through 10 were significantly elevated on day 90 (n=16) compared with other models (immunosuppression used): (1) Lewis to F344 recipients (CSA), (2) Brown Norway to Lewis (FK506), and (3) DA to Wistar-Firth (methylprednisolone, azathioprine, CSA). Although delayed (day 60 to 90) CSA treatment had no effect (n=6), delayed Rapa (3 mg. kg-1. d-1 IP) reversed CGVD in PVG grafts (0.22+/-0.19 on day 90, n=6). ACI isografts showed no evidence of CGVD (n=6) at day 90. Immunohistochemistry of PVG grafts revealed perivascular infiltrates consisting of CD4(+) T cells and limited numbers of macrophages persisting up to day 90. Flow cytometry demonstrated increased levels of anti-donor antibody at day 90, which was significantly inhibited by Rapa treatment. CONCLUSIONS: PVG grafts developed a significant increase in CGVD without evidence of ongoing myocardial rejection. This CGVD appeared to be mediated by both cellular and humoral mechanisms, given CD4(+) perivascular infiltrates and increased levels of anti-donor antibody. The anti-CGVD effectiveness of Rapa during a period in which there was little myocardial cellular infiltrate supports a novel mechanism of effect such as smooth muscle or B-cell inhibition.  (+info)

Alloantibody-mediated class I signal transduction in endothelial cells and smooth muscle cells: enhancement by IFN-gamma and TNF-alpha. (7/1197)

Chronic rejection is the major limiting factor to long term survival of solid organ allografts. The hallmark of chronic rejection is transplant atherosclerosis, which is characterized by the intimal proliferation of smooth muscle cells, endothelial cells, and fibroblasts, leading to vessel obstruction, fibrosis, and eventual graft loss. The mechanism of chronic rejection is poorly understood, but it is suspected that the associated vascular changes are a result of anti-HLA Ab-mediated injury to the endothelium and smooth muscle of the graft. In this study we have investigated whether anti-HLA Abs, developed by transplant recipients following transplantation, are capable of transducing signals via HLA class I molecules, which stimulate cell proliferation. In this report we show that ligation of class I molecules with Abs to distinct HLA-A locus and HLA-B locus molecules results in increased tyrosine phosphorylation of intracellular proteins and induction of fibroblast growth factor receptor expression on endothelial and smooth muscle cells. Treatment of cells with IFN-gamma and TNF-alpha up-regulated MHC class I expression and potentiated anti-HLA Ab-induced fibroblast growth factor receptor expression. Engagement of class I molecules also stimulated enhanced proliferative responses to basic fibroblast growth factor, which augmented endothelial cell proliferation. These findings support a role for anti-HLA Abs and cytokines in the transduction of proliferative signals, which stimulate the development of myointimal hyperplasia associated with chronic rejection of human allografts.  (+info)

Mixed chimerism induced without lethal conditioning prevents T cell- and anti-Gal alpha 1,3Gal-mediated graft rejection. (8/1197)

Gal alpha 1,3Gal-reactive (Gal-reactive) antibodies are a major impediment to pig-to-human xenotransplantation. We investigated the potential to induce tolerance of anti-Gal-producing cells and prevent rejection of vascularized grafts in the combination of alpha 1,3-galactosyltransferase wild-type (GalT(+/+)) and deficient (GalT(-/-)) mice. Allogeneic (H-2 mismatched) GalT(+/+) bone marrow transplantation (BMT) to GalT(-/-) mice conditioned with a nonmyeloablative regimen, consisting of depleting CD4 and CD8 mAb's and 3 Gy whole-body irradiation and 7 Gy thymic irradiation, led to lasting multilineage H-2(bxd) GalT(+/+) + H-2(d) GalT(-/-) mixed chimerism. Induction of mixed chimerism was associated with a rapid reduction of serum anti-Gal naturally occurring antibody levels. Anti-Gal-producing cells were undetectable by 2 weeks after BMT, suggesting that anti-Gal-producing cells preexisting at the time of BMT are rapidly tolerized. Even after immunization with Gal-bearing xenogeneic cells, mixed chimeras were devoid of anti-Gal-producing cells and permanently accepted donor-type GalT(+/+) heart grafts (>150 days), whereas non-BMT control animals rejected these hearts within 1-7 days. B cells bearing receptors for Gal were completely absent from the spleens of mixed chimeras, suggesting that clonal deletion and/or receptor editing may maintain B-cell tolerance to Gal. These findings demonstrate the principle that induction of mixed hematopoietic chimerism with a potentially relevant nonmyeloablative regimen can simultaneously lead to tolerance among both T cells and Gal-reactive B cells, thus preventing vascularized xenograft rejection.  (+info)

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