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Biomedical subjects

M H Sayegh

Publications and source records attributed to M H Sayegh.

At least 73 records · Page 4Linked to original sources
PubMed1998

Comparative studies of specific acquired systemic tolerance induced by intrathymic inoculation of a single synthetic Wistar-Furth (RT1U) allo-MHC class I (RT1.AU) peptide or WAG (RT1U)-derived class I peptide.

BACKGROUND: Because T cell receptor-MHC class I/self-peptide interactions regulate T-cell development, the presence of MHC allopeptides in the thymus may influence T-cell tolerance to alloantigens. This hypothesis is supported by our most recent finding that intrathymic (IT) inoculation of nonimmunogenic synthetic peptides derived from "WAG" RT1.A induces tolerance to cardiac allografts in the Wistar-Furth (WF)-to-ACI model. To evaluate whether in vivo immunogenicity of MHC peptides is relevant to tolerance induction and to examine the effect of peptide specificity, we compared the effects on graft survival of well-defined, strain-specific immunogenic WF MHC class I peptides (RT1.AU) with closely related but non-strain-specific class I peptides derived from WAG (RT1U). METHODS: In vivo immunization of seven MHC class I peptides synthesized from RT1.AU sequences showed that two (u-5 and u-7) were immunogenic, whereas five others were not immunogenic in ACI recipients. We then examined the effects on cardiac allograft survival in the WF-to-ACI model of the two immunogenic RT1.AU peptides (u-5 and u-7) and three immunogenic WAG-derived peptides (peptides 1, 2, and 5). RESULTS: A combination of equal amounts (150 microg or 300 microg) of u-5 or u-7 each with 0.5 ml of antilymphocyte serum (ALS) on day -7 led to 60% and 100% permanent graft survival (>150 days), respectively. IT injection of the individual peptides on day -7 showed that only 300 microg of u-5 significantly prolonged graft survival to a median survival time of 17.3 days from 10.5 days in naive recipients. IT injection of 150, 300, and 600 microg of u-5 combined with 0.5 ml of ALS on day -7 led to permanent graft survival (> 150 days) in four of six, nine of nine, and six of six ACI recipients, respectively, compared with a median survival time of 15.4 days in ALS alone-treated controls. In contrast, similar treatments with peptide u-7 with or without 0.5 ml of ALS did not prolong graft survival, thus demonstrating that peptide u-5 alone mediates the observed effects on graft prolongation. A total of 300 microg of u-5 injected IT combined with ALS led to acute rejection of third-party (Lewis) grafts. Intravenous injection of 300 microg of u-5 with ALS also did not prolong WF graft survival in ACI recipients. The long-term unresponsive ACI recipients accepted permanently donor-type (WF) but not third-party (Lewis) second-set cardiac and islet allografts. Similarly, we showed that although IT injection of 600 and 1200 microg of a mixture of immunogenic WAG-derived peptides 1, 2, and 5 combined with 0.5 ml of ALS on day -7 led to permanent WF graft survival in ACI, only IT injection of 300 microg of peptide 2 combined with ALS led to permanent graft survival (>150 days) in four of five animals. To define the underlying mechanisms of tolerance, we examined in vitro the mixed lymphocyte reaction (MLR), cell-mediated lymphocytotoxicity, and cytokine profile of unresponsive recipients. Although the results showed nonspecific T-cell suppression in the MLR at 25 days after transplantation, which correlated with the persistence of ALS immunosuppression, long-term unresponsive animals showed normal MLR to donor and third-party antigens. In contrast, the donor-specific reactive cytotoxic T lymphocytes remained suppressed in short-term and long-term unresponsive rats. CONCLUSION: Of interest is our finding that IT injection of a short segment of WAG-derived MHC class I peptide induces active acquired tolerance similar to results obtained with the use of pure WF-derived peptide u-5 in the WF-to-ACI rat combination. It is noteworthy that we could not confirm the T helper (Th)1/Th2 paradigm in this model by initial cytokine analysis. Whether induction of tolerance by IT injection of allo-MHC peptides will have clinical usefulness must await results of similar studies in large animals. However, of major interest is the finding that a short segment of RT1.AU represents the tolerogenic

Animals↗
PubMed1998

Effects of explosive brain death on cytokine activation of peripheral organs in the rat.

BACKGROUND: The success rate of transplanted organs from brain-dead cadaver donors is consistently inferior to that of living sources. As cadaver and living unrelated donors are equally genetically disparate with a given recipient, the difference must lie within the donor himself and/or the effects of organ preservation and storage. We have hypothesized that irreversible central nervous system injury may up-regulate proinflammatory mediators and cell surface molecules in peripheral organs to be engrafted, making them more prone to host inflammatory and immunological responses. METHODS: Rats undergoing surgically induced acutely increased intracranial pressure (explosive brain death) were followed for 6 hr. Their peripheral tissues were examined by reverse transcriptase polymerase chain reaction and immunohistology, serum factors were assessed by enzyme-linked immunosorbent assay, and the influence of inflammatory molecules in the blood stream was determined by cross-circulation experiments with normal animals. RESULTS: mRNA expression of both lymphocyte- and macrophage-associated products increased dramatically in all tissues. Similar factors in serum were coincidentally increased; these were shown to be active in vivo by cross-circulation with normal animals. The organs of all control groups, including animals with important ischemic injury and with hemorrhagic shock, were negative. Up-regulation of MHC class I and II antigens and the co-stimulatory molecule B7 suggests increased immunogenicity of the peripheral organs. These changes could be inhibited by: (i) administration of a recombinant soluble P-selectin glycoprotein ligand-Ig, a P- and E-selectin antagonist; and (ii) a fusion protein, cytotoxic T lymphocyte antigen 4-Ig, which blocks B7-mediated T-cell co-stimulation. CONCLUSIONS: Activation of peripheral organs following explosive brain death may be caused by various interrelated events, including the effects of massive acute central injury, hypotension, and circulating factors. Almost complete suppression of these changes could be produced by biological agents. Such interventions, if reproducible in humans, could improve the quality of organs from "marginal" donors, broadening the criteria for donor acceptance.

Animals↗
PubMed1998

Extrathymic T cell deletion and allogeneic stem cell engraftment induced with costimulatory blockade is followed by central T cell tolerance.

A reliable, nontoxic method of inducing transplantation tolerance is needed to overcome the problems of chronic organ graft rejection and immunosuppression-related toxicity. Treatment of mice with single injections of an anti-CD40 ligand antibody and CTLA4Ig, a low dose (3 Gy) of whole body irradiation, plus fully major histocompatibility complex-mismatched allogeneic bone marrow transplantation (BMT) reliably induced high levels (>40%) of stable (>8 mo) multilineage donor hematopoiesis. Chimeric mice permanently accepted donor skin grafts (>100 d), and rapidly rejected third party grafts. Progressive deletion of donor-reactive host T cells occurred among peripheral CD4(+) lymphocytes, beginning as early as 1 wk after bone marrow transplantation. Early deletion of peripheral donor-reactive host CD4 cells also occurred in thymectomized, similarly treated marrow recipients, demonstrating a role for peripheral clonal deletion of donor-reactive T cells after allogeneic BMT in the presence of costimulatory blockade. Central intrathymic deletion of newly developing T cells ensued after donor stem cell engraftment had occurred. Thus, we have shown that high levels of chimerism and systemic T cell tolerance can be reliably achieved without myeloablation or T cell depletion of the host. Chronic immunosuppression and rejection are avoided with this powerful, nontoxic approach to inducing tolerance.

Abatacept↗
PubMed1998

Late blockade of T cell costimulation interrupts progression of experimental chronic allograft rejection.

Early blockade of T cell-costimulatory activation pathways prevents development of experimental chronic allograft rejection. Ongoing T cell recognition of alloantigen and activation may also play an important role in progression of chronic rejection, but definitive evidence is lacking. We used the fusion protein CTLA4Ig to block CD28-B7 T cell costimulation late after the onset of initial graft injury. Using the F334 into LEW rat model of chronic renal allograft rejection, transplant recipients were treated with a 10-d course of cyclosporine, and a subgroup received a single injection of CTLA4Ig at 8 wk after transplant. Functionally, CTLA4Ig administration prevented development of progressive proteinuria (14.3+/-4.1 mg/24 h versus 41.0+/-12.0 mg/24 h at 24 wk after transplant, P < 0.05). Histologically, graft mononuclear cell infiltration, glomerular hypertrophy, focal and segmental glomerulosclerosis, and intimal vascular hyperplasia were all attenuated in CTLA4Ig-treated animals. Lastly, reverse transcriptase-PCR and immunohistologic studies showed a significant reduction in the intragraft expression of key products of T cell and macrophage activation, and upregulation of what have recently been termed as "protective" genes, including the bcl family members, Bcl-2 and Bcl-xL, and hemoxygenase. Our data are the first to demonstrate that blocking T cell-costimulatory activation late after transplantation, after initial graft injury, prevents progression of chronic allograft rejection supporting the hypothesis that ongoing T cell recognition of alloantigen and activation are key mediators of ongoing chronic allograft rejection.

Abatacept↗
PubMed1998

Mechanisms of indirect allorecognition: characterization of MHC class II allopeptide-specific T helper cell clones from animals undergoing acute allograft rejection.

BACKGROUND: Recent evidence indicates that T cells primed via the indirect pathway of allorecognition play an important role in allograft rejection, although the effector mechanisms remain unknown. The purpose of this study was to characterize and study the in vivo function of self-restricted MHC allopeptide-specific T-cell clones generated from animals undergoing allograft rejection. METHODS AND RESULTS: We generated self-restricted class II MHC allopeptide-specific T-cell clones from the spleen and kidney of Lewis (LEW; RT1l) rats undergoing acute rejection of MHC-incompatible Wistar Furth (WF; RT1u) renal allografts. RT1.Du/beta20-44 peptide-specific CD4+ T helper 1 clones from the spleen and kidney of rejecting animals expressed a restricted T cell receptor (TCR) Vbeta repertoire: Vbeta4, 8.2, or 9. In comparison, clones generated from RT1.Dubeta20-44 immunized LEW rats all expressed TCR Vbeta9. The amino acid sequence of RT1.Dl (LEW) and RT1.Du (WF) residues 20-44 differ only at positions 30 and 38. T-cell clones expressing TCR Vbeta9 preferentially proliferated to the peptide fragment RT1.Dubeta20-33. T-cell clones expressing TCR Vbeta4 proliferated weakly to peptide fragments RT1.Dubeta20-33 and 31-44, whereas those expressing TCR Vbeta8.2 proliferated preferentially to the peptide fragment 31-44. Adoptive transfer of T-cell clones expressing TCR Vbeta9 or Vbeta8.2, but not Vbeta4, to naive LEW animals elicited significant delayed-type hypersensitivity responses after challenge with the RT1.Dubeta20-44 peptide or allogeneic WF (RT1u) splenocytes. CONCLUSION: This is the first report on the cellular, molecular, and functional characterization of self-restricted MHC allopeptide-specific T-cell clones from animals undergoing acute rejection. Our data provide support for a biologically significant role of indirect allorecognition in allograft rejection.

Acute Disease↗
PubMed1998

Mechanisms of acquired thymic tolerance in vivo: intrathymic injection of antigen induces apoptosis of thymocytes and peripheral T cell anergy.

Intrathymic injection of Ag induces Ag-specific tolerance in several clinically relevant experimental autoimmune and transplantation models. However, the exact mechanisms of acquired thymic tolerance in vivo remain unclear. We investigated the mechanisms of acquired thymic tolerance in mice that are transgenic for the TCR specific for peptide 323-339 of OVA. Intrathymic injection of OVA leads to apoptosis of thymocytes starting as early as 3 h after injection and persisting up to 7 days. Double positive thymocytes undergo apoptosis earlier than single positive thymocytes, and significantly higher percentages of double positive thymocytes ultimately die as compared with single positive cells. Apoptotic cells show decreased surface expression of CD4. In the periphery, T cells from intrathymically injected animals had suppressed proliferation and IL-2 production to OVA compared with T cells from control Ag-injected mice. We conclude that intrathymic injection of Ag induces apoptosis of immature thymocytes and a subpopulation of mature thymocytes and induces prolonged anergy in peripheral T cells in vivo. Understanding the mechanisms of acquired thymic tolerance may lead to development of novel clinical strategies to prevent autoimmune disease and transplant rejection.

Animals↗
PubMed1998

Antibody-induced transplant arteriosclerosis is prevented by graft expression of anti-oxidant and anti-apoptotic genes.

We investigated the pathogenesis of chronic allograft rejection in mouse cardiac allografts. Long-term survival occurred after administration of monoclonal antibody to CD4 or CD40-ligand (CD40L) plus donor cells. Both treatments induced permanent graft survival, but, in contrast to transplants in mice treated with CD4 monoclonal antibody, grafts in mice treated with CD40L monoclonal antibody lacked evidence of chronic rejection, including transplant arteriosclerosis. Freedom from chronic rejection in the group treated with CD40L monoclonal antibody correlated with vascular expression of the 'protective' genes heme oxygenase-1 (HO-1), Bcl-xL and A20. Moreover, arteriosclerosis was induced in allografts in immunoglobulin-deficient mice by antibody transfer only when the transfer was done before expression of protective genes. A direct role for protective gene expression in endothelial cells was demonstrated by in vitro experiments in which induction of HO-1 or Bcl-xL suppressed alloantibody-stimulated endothelial activation. Finally, induction of HO-1 in vivo protected allografts against chronic injury. These data show a role for protective genes in the prevention of chronic rejection, and indicate new approaches to protect grafts against development of transplant arteriosclerosis.

Animals↗
PubMed1998

Interactions between cyclosporine and newer antidepressant medications.

The favorable safety profile of the newer antidepressant drugs recently introduced has lead to their increased use in transplant recipients. These new agents are a chemically diverse group of compounds that have selective serotonin reuptake inhibitory properties. Most of these medications inhibit one or more hepatic microsomal cytochrome p450 isoenzymes. Because cyclosporine is metabolized predominantly by CYP3A3/4 isoenzymes, inhibition of this system can lead to the buildup of toxic levels. Two case reports of cyclosporine toxicity attributable to interactions with the novel antidepressants nefazodone and fluvoxamine are presented. The serum creatinine and whole blood cyclosporine levels were found to be elevated at a routine clinic visit. Although it was subsequently possible to reduce the dose of cyclosporine by between 33% and 50%, the frequency of blood draws and consultations was greatly increased in both patients over several weeks, resulting in considerable patient anxiety. Interestingly, both nefazodone and fluvoxamine are known to potently inhibit the CYP3A3/4 isoenzymes. It is concluded that the introduction of a novel antidepressant to a cyclosporine-treated allograft recipient may be complicated by cyclosporine toxicity. Intensive monitoring of the serum creatinine and cyclosporine level is indicated under such circumstances, with dose reductions performed as indicated.

Antidepressive Agents, Second-Generation↗
PubMed1998

Both CD80 and CD86 co-stimulatory molecules regulate allergic pulmonary inflammation.

We examined the roles of CD80 (B7-1) and CD86 (B7-2) in a model of allergic pulmonary inflammation and airway hyper-responsiveness (AHR) by selectively inhibiting either CD80 or CD86. Inhibition of co-stimulation by either CD80 or CD86 affected multiple parameters of the allergic response. Specifically, blockade of either CD80 or CD86 in ovalbumin-sensitized and challenged mice resulted in reduced expression of IL-2Ralpha (CD25) on CD4+ T lymphocytes, decreased airway eosinophilia, lower serum IgE production and diminished AHR. Importantly, blockade of CD80 and CD86 inhibited production of IL-4 and IL-2, and enhanced IFN-gamma production. Our observations support a role for both CD80- and CD86-mediated co-stimulation in development of allergic pulmonary inflammation.

Animals↗
PubMed1998

Cytokine analysis of human renal allograft aspiration biopsy cultures supernatants predicts acute rejection.

BACKGROUND: A Th1 response is said to be associated with transplant rejection and Th2 with tolerance, although this is not agreed by all. Cytokines evaluation in peripheral blood and urine in kidney transplants produces variable results. We hypothesized that measurement of major cytokines involved in Th1/Th2 paradigm on transplant renal-infiltrating cells could bring valuable scientific and clinical information. METHODS: Fifty-six adult cadaver kidney transplants were subdivided into 21 stable patients (group A), 22 suffering acute rejection (group B), 10 with chronic rejection (group C) and three with CMV disease (group D). Fine-needle aspiration biopsies were cultured and their supernatants analysed for IL-2, IL-4, IL-10 and IFN-gamma. RESULTS: Group A produced small amounts of both IL-2 and IL-10 while group B synthetized significantly higher IL-2 and significantly lower IL-10 amounts than group A. Group B produced significantly more IL-2 than A on day 7 post-transplantation, several days before rejection supervened. Group C produced IL-10 and very low amount of IL-2. Group D produced both IL-2 and IL-10. We did not find any IL-4, and IFN-gamma was present in a few samples. For IL-2, sensitivity, specificity, negative and positive predictive values for acute rejection were 100, 87.2, 94.7 and 83.3%, respectively. CONCLUSIONS: Cytokine analysis in fine-needle aspiration biopsy cultures supernatants is a very useful immunological screening method for kidney transplants. IL-2 synthesis on day 7 post-transplantation reliably predicted the risk of impending acute rejection during the first weeks. The cytokine pattern suggests that acute rejection is associated with Th1, stable patients with Th0/Th2, and chronic rejection with Th2 patterns.

Acute Disease↗
PubMed1998

Predictors of mortality and the provision of dialysis in patients with acute tubular necrosis. The Auriculin Anaritide Acute Renal Failure Study Group.

To explore the natural history of critically ill patients with acute renal failure due to acute tubular necrosis, we evaluated 256 patients enrolled in the placebo arm of a randomized clinical trial. Death and the composite outcome, death or the provision of dialysis, were determined with follow-up to 60 d. The relative risks (RR) and 95% confidence intervals (95% CI) associated with routinely available demographic, clinical, and laboratory variables were estimated using proportional hazards regression. Ninety-three (36%) deaths were documented; an additional 52 (20%) patients who survived received dialysis. Predictors of mortality included male gender (RR, 2.01; 95% CI, 1.21 to 3.36), oliguria (RR, 2.25; 95% CI, 1.43 to 3.55), mechanical ventilation (RR, 1.86; 95% CI, 1.18 to 2.93), acute myocardial infarction (RR, 3.14; 95% CI, 1.85 to 5.31), acute stroke or seizure (RR, 3.08; 95% CI, 1.56 to 6.06), chronic immunosuppression (RR, 2.37; 95% CI, 1.16 to 4.88), hyperbilirubinemia (RR, 1.06; 95% CI, 1.03 to 1.08 per 1 mg/dl increase in total bilirubin) and metabolic acidosis (RR, 0.95; 95% CI, 0.90 to 0.99 per 1 mEq/L increase in serum bicarbonate concentration). Predictors of death or the provision of dialysis were oliguria (RR, 5.95; 95% CI, 3.96 to 8.95), mechanical ventilation (RR, 1.53; 95% CI, 1.07 to 2.21), acute myocardial infarction (RR, 1.95; 95% CI, 1.24 to 3.07), arrhythmia (RR, 1.51; 95% CI, 1.04 to 2.19), and hypoalbuminemia (RR, 0.56; 95% CI, 0.42 to 0.74 per 1 g/dl increase in serum albumin concentration). Neither mortality nor the provision of dialysis was related to patient age. These observations can be used to estimate risk early in the course of acute tubular necrosis. Furthermore, these and related models may be used to adjust for case-mix variation in quality improvement efforts, and to objectively stratify patients in future intervention trials aimed at favorably altering the course of hospital-acquired acute renal failure.

Adult↗
PubMed1998

Comparative strategies to induce long-term graft acceptance in fully allogeneic renal versus cardiac allograft models by CD28-B7 T cell costimulatory blockade: role of thymus and spleen.

Blocking CD28-B7 T cell costimulatory activation by the fusion protein CTLA4Ig prevents rejection and induces long-term graft acceptance in various experimental transplant models. There are reported differences in the efficacy of CTLA4Ig in renal and cardiac rodent allograft models, but it is not clear whether these are due to the strain or species differences investigated in the different studies reported. This study investigates the effect of blocking CD28-B7 T cell costimulation with murine CTLA4Ig in rat models of acute renal and cardiac allograft rejection models, using the same complete major histocompatibility complex-incompatible strain combination. A single injection of murine CTLA4Ig 2 d after engraftment was able to induce long-term graft acceptance (> 100 d) in 54% of Lewis rat recipients of Wistar-Furth kidneys. Transferring this protocol into the acute Wistar-Furth to Lewis heart allograft model resulted in a mean graft survival time of 24.7+/-16.9 d, and all grafts were ultimately rejected. Only concomitant injection of donor cells (4 x 10(7) splenocytes) plus a single injection of CTLA4Ig on the day of transplant could induce long-term graft acceptance in 50% of animals. In both the cardiac and renal transplant models, the thymus and spleen were required for induction of tolerance. The maintenance phase of tolerance, however, did not require an intact thymus but did require the presence of a spleen. These data have important clinical applicability because human studies with T cell costimulatory blockade are being planned.

Abatacept↗
PubMed1998

Immune parameters affecting adenoviral vector gene therapy in the brain.

Gene therapy utilizing replication deficient adenoviral vectors represents a potentially promising approach to the treatment of brain tumors. Limited duration of systemic transgene expression and inefficient transduction following repeat systemic vector administration secondary to an effective anti-vector immune response limits the potential application of first generation adenoviral vectors. Whether host immune responses will significantly limit the use of these vectors within the immunopriviledged environment of the central nervous system remains to be elucidated. Following a single intravenous injection of a beta-galactosidase expressing adenoviral vector (Ad.CMV-betagal), we found maximal betagal transgene expression in systemic sites (i.e. liver) at day 4, with almost complete disappearance by day 7. In contrast, significant beta-galactosidase activity was seen for greater than 28 days following a single intracerebral inoculum of virus. Rechallenge experiments demonstrated complete protection against repeat systemic vector administration, whereas intracerebral transgene expression was not affected by prior systemic or intracerebral exposure to adenoviruses. These data suggest that systemic anti-adenoviral vector immune responses are attenuated within the central nervous system and may not pose as significant a problem for the treatment of brain tumors as for other systemic indications.

Adenoviruses, Human↗