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A S Chong

Publications and source records attributed to A S Chong.

At least 19 recordsLinked to original sources
PubMed2006

Concurrent antiviral and immunosuppressive activities of leflunomide in vivo.

We previously reported that the immunosuppressive malononitrileamides leflunomide and FK778 exert antiviral activity against cytomegalovirus (CMV). In the current investigation, we tested the hypothesis that leflunomide exerts concurrent antiviral activity and immune suppression in CMV-infected cardiac allograft recipients. Lewis rats were transplanted with Brown Norway hearts and then inoculated with rat CMV. Plaque assay demonstrated that leflunomide (30 mg/kg/day) reduced viral loads by 4-6 logs, and that the reduction in viral load was unaffected by administration of uridine. Leflunomide was as effective as cyclosporine A (CsA) or tacrolimus in preservation of allograft integrity through day 28. These studies directly demonstrate the bifunctionality of leflunomide as concurrently immunosuppressive and antiviral, enhancing the promise of this agent as a clinical option for treatment of transplant recipients.

Animals↗
PubMed2006

Liver ischemia contributes to early islet failure following intraportal transplantation: benefits of liver ischemic-preconditioning.

Early graft failure following intraportal islet transplantation (IPIT) represents a major obstacle for successful islet transplantation. Here, we examined the role of islet emboli in the induction of early graft failure and utilized a strategy of ischemic-preconditioning (IP) to prevent early islet destruction in a model of syngeneic IPIT in STZ-induced diabetic mice. Numerous focal areas of liver necrosis associated with the islet emboli were observed within 24 h post-IPIT. Pro-inflammatory cytokines, IL-1beta and IL-6, were significantly increased 3 h after IPIT, while TNF-alpha was elevated for up to 5 days post-IPIT. Caspase-3 and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling positive cells were observed in the transplanted islets trapped in areas of necrotic liver at 3 h and 1 day post-IPIT. Hyperglycemia was corrected immediately following IPIT of 200 islets, but recurrence of hyperglycemia was observed within 14 days associated with a poor response to glucose challenge. IP, a procedure of pre-exposure of the liver to transient ischemia and reperfusion, protected the liver from embolism-induced ischemic injury and prevented early islet graft failure. These data suggest that islet embolism in the portal vein is a major cause of functional loss following IPIT that can be prevented by liver IP.

Animals↗
PubMed2001

The structure of anti-Gal immunoglobulin genes in naïve and stimulated Gal knockout mice.

BACKGROUND: Naturally occurring antibodies (Nabs) that bind to terminal galactose alpha1,3-galactose carbohydrate structures (Gal) are present in humans and Old World monkeys but are negatively regulated in other mammalian species because they express Gal epitopes on their cell surfaces. A Gal knockout mouse (Gal-/-) model, generated by homologous disruption of alpha1,3-galactosyltransferase gene, is capable of producing natural anti-Gal Abs. METHODS: To study the genetic control of the anti-Gal response, we have generated anti-Gal hybridomas from Gal-/- mice and analyzed VH genes of anti-Gal Abs from naïve animals and from mice stimulated by rat heterotopic heart transplantation. RESULTS: Six immunoglobulin (Ig)M anti-Gal hybridomas derived from naïve Gal-/- mice exhibited anti-Gal binding activity with some cross-reactivity to related carbohydrate structures. These naïve anti-Gal Abs used five different VH genes in a germline configuration. Anti-Gal IgM hybridomas isolated after a rat heterotopic heart xenograft (4 days) utilized germline VH gene segments from the VH7183 family and exhibited less cross-reactivity. In contrast to mice 4 days after xenograft, we have predominantly isolated IgG anti-Gal hybridomas from mice 21 days after rat heterotopic heart xenografts, indicating an isotype switch. Nine of the IgG anti-Gal hybridomas secreted IgG3 subclass and one produced IgG1. Sequence analysis of the VH gene usage from the induced anti-Gal IgG antibodies demonstrated a restricted gene utilization (VHJ606-V14A). CONCLUSION: Our results demonstrate that the anti-Gal response in naïve Gal-/- mice is encoded by multiple germline progenitors. In response to a xenograft, the induced anti-Gal Abs exhibited a restricted gene usage and somatic mutations, indicating a positive selection.

Animals↗
PubMed2001

Lewis rat pancreas, but not cardiac xenografts, are resistant to anti-gal antibody mediated hyperacute rejection.

BACKGROUND: The objective of this study was to evaluate the role of anti-Gal Abs and non-anti-Gal Abs in hyperacute rejection (HAR) of concordant pancreas xenografts compared with heart xenografts. In addition, we tested whether rejection of Lewis rat pancreas grafts was T-cell dependent and could be prevented by anti-T-cell treatment. METHODS: To determine the role of anti-Gal Abs in the induction of HAR, Lewis rat pancreas and heart xenografts were transplanted into alpha1,3Galactosyltransferase knockout (GT-Ko) mice treated with normal human serum (NHS) or hyperimmune serum, or into presensitized GT-Ko mice. To investigate whether rejection of pancreas xenograft was mediated by a T-cell dependent response, Lewis rat pancreas grafts were transplanted into streptozotocin (STZ)-induced diabetic GT-Ko mice treated with FK506, anti-CD4 mAbs (GK1.5), and thymectomy. Antidonor-specific IgM and IgG and anti-Gal Abs were analyzed by flow cytometry. Rejected and long-term surviving pancreas xenografts were assessed by functional (blood glucose) and histopathological examination. RESULTS: HAR of Lewis rat pancreas xenografts could not be induced by NHS (0.4 ml), whereas NHS (0.2 ml) resulted in HAR of Lewis heart xenografts. Infusion of Lewis rat-specific hyperimmune serum (0.2 ml) resulted in HAR of Lewis rat pancreas xenografts. In addition, second Lewis rat pancreas grafts were hyperacutely rejected by presensitized GT-Ko mice. Immunohistochemical staining showed a low expression of Galalpha1,3Gal antigen in the endocrine tissue compared with that in the cardiac grafts. The levels of anti-Gal Abs in pancreas xenograft transplantation did not increase in GT-Ko mice after pancreas xenograft transplantation that was significantly increased after heart transplantation. FK506 treatment induced long-term survival of Lewis pancreas xenografts (mean survival time (MST) >90 days). Anti-CD4 treatment delayed rejection of Lewis rat pancreas xenografts with MST of 34.3 days, whereas anti-CD4, in combination with thymectomy, synergistically prolonged survival of pancreas xenograft (MST=70.4 days). CONCLUSION: Pancreas xenograft is resistant to anti-Gal Abs-induced HAR but is susceptible to anti-donor specific Abs. Rejection of Lewis pancreas xenograft in STZ-induced, diabetic, GT-Ko mice is T-cell dependent.

Acute Disease↗
PubMed2001

Inhibition of herpes simplex virus type 1 by the experimental immunosuppressive agent leflunomide.

BACKGROUND: Despite advances in antiviral chemotherapy, herpes simplex virus type 1 (HSV-1), continues to complicate the clinical course of many allograft recipients. We have previously demonstrated that the experimental immunosuppressive agent leflunomide inhibits production of cytomegalovirus by interference with virion assembly. We test the hypothesis that this agent exerts similar antiviral activity against HSV-1. METHODS AND RESULTS: Plaque assay of virus yield from endothelial or Vero cells after inoculation with each of four clinical HSV-1 isolates demonstrated a dose-dependent reduction of virus production in the presence of pharmacologic concentrations of A77 1726, the active metabolite of leflunomide. DNA dot blot and biochemical assay of viral DNA polymerase activity indicated that A77 does not inhibit viral DNA synthesis. Rather, as visualized by transmission electron microscopic method, this agent seems to disrupt virion assembly by preventing nucleocapsid tegumentation. CONCLUSIONS: These findings, in demonstrating that leflunomide exerts antiviral activity against HSV-1 by mechanisms similar to those we have previously shown with cytomegalovirus, imply that this agent may possess broad spectrum activity against other herpesviruses.

Animals↗
PubMed2000

Tolerance of T-independent xeno-antibody responses in the hamster-to-rat xenotransplantation model is species-restricted but not tissue-specific.

Control of early acute xenograft rejection xenoreactions in the hamster-to-Lewis rat xenotransplantation model with cyclosporine (CsA) and leflunomide subdues early T-independent xenoreactivity and uncovers a late immune response that can be controlled by CsA alone. We had attributed this acquired responsiveness to CsA to the induction of tolerance of T-independent xeno-antibody responses in the recipient and recently reported that this tolerance is species-specific. Here we have further characterized the specificity and nature of this tolerant state. Lewis rats transplanted with either hearts, skin, kidney or spleen/pancreas from Golden Syrian hamsters were treated with leflunomide (5 mg/kg/day by gavage) for 14-21 days and CsA (20 mg/kg/day by gavage) continuously from the day of transplant. Some Lewis rats received a second graft of hearts or skin from Golden Syrian hamsters (day 21-30 after first transplant), and a third heart graft from Balb/c mice (day 60 after the first transplant). Serum was harvested and the titers of xenoreactive antibodies were quantified by flow cytometry. All grafts were harvested at the end of each experiment and examined by histological and immunohistochemical methods. The combination of CsA and leflunomide was able to completely inhibit the rejection of kidney, spleen and pancreas xenografts in this hamster-to-rat xenotransplantation model. In addition, only a transient treatment with leflunomide was necessary, and long-term graft survival could subsequently be maintained by CsA alone. Histological examination of these grafts at > 80 days post-transplantation indicated minimal signs of rejection. These immediately vascularized organs induced T-independent B-cell tolerance, so that second grafts of hamster hearts and skin could be maintained with CsA alone. Under the same immunosuppressive regimen, only four out of nine Lewis rats exhibited long-term hamster skin survival, probably reflecting the increased immunogenicity of the skin compared with other vascularized grafts. Nonetheless, all rats that did not reject the hamster skin graft also did not reject the hamster heart while on CsA alone. Finally, we demonstrate that the tolerant state could be maintained for up to 30 days in the absence of xenograft. The vigorous T-independent antibody response that mediates acute xenograft rejection in the hamster-to-rat model can be tolerized by the immunosuppressive regimen of CsA and leflunomide. The lack of organ specificity for the induction of this tolerance suggests that the xenoantigens inducing tolerance may be common endothelial cell antigens. Finally, the presence of the xenograft has been previously shown to be critical for the induction of T-independent B-cell tolerance, however, the tolerant state is relatively stable and persists after the removal of the xenograft.

Animals↗
PubMed2000

Non-depleting anti-CD4, but not anti-CD8, antibody induces long-term survival of xenogeneic and allogeneic hearts in alpha1,3-galactosyltransferase knockout (GT-Ko) mice.

The anti-galactose-alpha1,3-galactose (Gal) antibody (Ab) response following pig-to-human transplantation is vigorous and largely resistant to currently available immunosuppression. The recent generation of GT-Ko mice provides a unique opportunity to study the immunological basis of xenograft-elicited anti-Gal Ab response in vivo, and to test the efficacy of various strategies at controlling this Ab response [1]. In this study, we compared the ability of non-depleting anti-CD4 and anti-CD8 to control rejection and antibody production in GT-Ko mice following xenograft and allograft transplantation. Hearts from baby Lewis rat or C3H mice were transplanted heterotopically into GT-Ko. Non-depleting anti-CD4 (YTS177) and anti-CD8 (YTS105) Abs were used at 1 mg/mouse, and given as four doses daily from day -2 to 1 then q.o.d. till day 21. Xenograft rejection occurred at 3 to 5 days post-transplantation in untreated GT-Ko recipients, and was histologically characterized as vascular rejection. Anti-CD4, but not anti-CD8, Ab treatment prolonged xenograft survival to 68 to 74 days and inhibited anti-Gal Ab as well as xeno-Ab production. In four of the five hearts from anti-CD4 mAbs-treated GT-Ko mice, we observed classic signs of chronic rejection, namely, thickened intima in the lumen of vessels, significant IgM deposition, fibrosis and modest mononuclear cell infiltrate of Mac-1+ macrophages and scattered T cells (CD8>CD4). Xenograft rejection in untreated, as well as anti-CD4- and anti-CD8-treated, recipients was associated with increased intragraft IL-6, IFN-gamma and IL-10 mRNA. C3H allografts were rejected in 7 to 9 days by untreated GT-Ko mice and were histologically characterized as cellular rejection. Treatment with anti-CD4 and anti-CD8 mAb resulted in graft survivals of >94.8 and 11.8 days, respectively. Anti-CD4 mAb treatment resulted in a transient inhibition of alloreactive and anti-Gal Ab production. The presence of circulating alloreactive and anti-Gal Abs at >50 days post-transplant was associated with significant IgM and IgG deposition in the graft. Yet, in the anti-CD4 mAb-treated group, the allografts showed no signs of rejection at the time of sacrifice (>100 days post-transplantation). All rejected allografts had elevated levels of intragraft IL-6, IFN-gamma and IL-10 mRNA, while the long-surviving anti-CD4-treated allografts had reduced mRNA levels of these cytokines. Collectively, our studies suggest that the elicited xeno-antibody production and anti-Gal Ab production in GT-Ko mice are CD4+ T-cell dependent. The majority of xenografts succumbed to chronic rejection, while allografts survived with minimal histological change, despite elevated levels of circulating alloAbs. Thus, immunosuppression with anti-CD4 mAb therapy induces long-term survival of allografts more effectively than to xenografts.

Animals↗
PubMed2000

Differential immune responses to alpha-gal epitopes on xenografts and allografts: implications for accommodation in xenotransplantation.

Xenograft recipients produce large amounts of high-affinity anti-Gal IgG in response to Galalpha1-3Galbeta1- 4GlcNAc-R (alpha-gal) epitopes on the graft. In contrast, ABO-mismatched allograft recipients undergo "accommodation," a state of very weak immune response to ABO antigens. These differences in anti-carbohydrate immune response were studied in alpha1,3galactosyltransferase knock-out mice. Pig kidney membranes administered to these mice elicited extensive production of anti-Gal IgG, whereas allogeneic kidney membranes expressing alpha-gal epitopes elicited only a weak anti-Gal IgM response. Anti-Gal IgG response to xenograft membranes depended on helper T cell activation and was inhibited by anti-CD40L antibody. These T cells were activated by xenopeptides and not by alpha-gal epitopes. Moreover, allogeneic cell membranes manipulated to express xenoproteins also induced anti-Gal IgG response. Xenoglycoproteins with alpha-gal epitopes are processed by anti-Gal B cells. Xenopeptides presented by these cells activate a large repertoire of helper T cells required for the differentiation of anti-Gal B cells into cells secreting anti-Gal IgG. Alloglycoproteins with alpha- gal epitopes have very few immunogenic peptides and fail to activate helper T cells. Similarly, ineffective helper T-cell activation prevents a strong immune response to blood group antigens in ABO-mismatched allograft recipients, thus enabling the development of accommodation.

Animals↗
PubMed1999

Transcriptional regulation of Fas gene expression by GA-binding protein and AP-1 in T cell antigen receptor.CD3 complex-stimulated T cells.

Fas (CD95 or APO-1), a transmembrane cell surface receptor of the tumor necrosis factor receptor family, is up-regulated in activated T lymphocytes. Our present study identified an upstream enhancer element (between nucleotide positions -862 and -682) containing a GA-binding protein (GABP) site and a low affinity activating protein-1 (AP-1)-binding site. T cell activation increased the DNA binding of GABP and AP-1 to this enhancer site. The specificity of GABP and AP-1 binding was demonstrated by competition electrophoretic mobility shift assay and supershift electrophoretic mobility shift assay with antibodies against GABP and AP-1, respectively. Mutational analysis of Fas promoter revealed that both GABP- and AP-1-binding sites were required for initiating Fas gene transcription. We further show that anti-CD3 mAb, phorbol 12-myristate 13-acetate, and phorbol 12-myristate 13-acetate/ionomycin strongly activated promoters carrying multiple copies of the Fas enhancer, and mutation of either the GABP or AP-1 binding site severely reduced transcriptional activity. Taken together, these results suggest that the transcription factors GABP and AP-1 play a critical role in the induction of Fas gene expression in T cell antigen receptor.CD3-stimulated Jurkat cells.

Base Sequence↗
PubMed1999

In vitro and in vivo antitumor activity of a novel immunomodulatory drug, leflunomide: mechanisms of action.

Leflunomide, a novel immunomodulatory drug, has two biochemical activities: inhibition of tyrosine phosphorylation and inhibition of pyrimidine nucleotide synthesis. In the present study, we first showed that A77 1726 [N-(4-trifluoromethylphenyl-2-cyano-3-hydroxycrotoamide)], the active metabolite of leflunomide, was more effective at inhibiting the tyrosine kinase activity of platelet-derived growth factor (PDGF) receptor than that of epidermal growth factor (EGF) receptor, and had no effect on the tyrosine kinase activity of the fibroblast growth factor receptor. In the presence of exogenous uridine, A77 1726 was more effective at inhibiting the PDGF-stimulated proliferation of PDGF receptor-overexpressing C6 glioma than the EGF-stimulated proliferation of EGF receptor-overexpressing A431 cells. In vivo studies demonstrated that leflunomide treatment strongly inhibited the growth of the C6 glioma but had only a modest effect on the growth of the A431 tumor. Uridine co-administered with leflunomide did not reverse the antitumor activity of leflunomide on C6 and A431 tumors significantly. Quantitation of nucleotide levels in the tumor tissue revealed that leflunomide treatment significantly reduced pyrimidine nucleotide levels in the fast-growing C6 glioma but had no effect on the relatively slow-growing A431 tumor. Whereas uridine co-administration normalized pyrimidine nucleotide levels, it had minimal effects on the antitumor activity of leflunomide in both tumor models. Immunohistochemical analysis revealed that leflunomide treatment significantly reduced the number of proliferating cell nuclear antigen-positive cells in C6 glioma, and that uridine only partially reversed this inhibition. These results collectively suggest that the in vivo antitumor effect of leflunomide is largely independent of its inhibitory effect on pyrimidine nucleotide synthesis. The possibility that leflunomide exerts its antitumor activity by inhibition of tyrosine phosphorylation or by a yet unidentified mode of action is discussed.

3T3 Cells↗
PubMed1999

The portosystemic shunt protects liver against ischemic reperfusion injury.

BACKGROUND: The goal of this study was to characterize the importance of splanchnic viscera in liver ischemic reperfusion injury and to enhance the tolerance of liver to warm ischemia injury with portosystemic shunt. METHODS: The hepatic blood flow of male Sprague Dawley rats was subjected to 45, 60, 120, and 150 min liver warm ischemia with or without portosystemic shunt (splenic-caval shunt). The production of tumor necrosis factor a (TNFa), nuclear factor-kappaB activation, inducible NO synthase (iNOS) expression, and apoptosis were examined. RESULTS: A total of 67% of rats with 45 min liver warm ischemia (n=6) and 100% of rats with 60 min liver warm ischemia (n=6) died within 1 day. However, all rats with 120 min (n=8) liver warm ischemia in splenic-caval shunt group survived for over 1 day, 6/8 for over 3 days, and 5/8 for over 5 days without significant histological changes of the liver. Serum tumor necrosis factor levels in liver warm ischemic rats were increased, This increase was significantly reversed after portosystemic shunt. After challenge with lipopolysaccharide (1 mg/kg, p.v.), naive rats survived for over 5 days (n=4) with the peak value of rat tumor necrosis factor (240 pg/ml) at 90 min. In contrast, all rats died within one day (n=5) with the peak value of rat tumor necrosis factor a (465 pg/ml) at 45 min after administration of lipopolysaccharide in the rats with liver warm ischemia plus splenic-caval shunt. iNOS expression and nuclear factor-kappaB activation were very strongly increased in the hepatocytes after liver warm ischemia with portosystemic shunt, compared with liver ischemia without portosytemic shunt. CONCLUSIONS: We conclude that the splanchnic viscera can contribute to liver ischemic reperfusion injury. Portosystemic shunt enhances the tolerance of liver to warm ischemia through the protective role of iNOS and nuclear factor-kappaB (NF-kappaB).

Animals↗
PubMed1999

Novel mechanism of inhibition of cytomegalovirus by the experimental immunosuppressive agent leflunomide.

BACKGROUND: Despite progress in antiviral chemotherapy, cytomegalovirus (CMV) remains a major cause of morbidity and mortality among pharmacologically immunosuppressed organ transplant recipients, frequently engaging the clinician in a struggle to balance graft preservation with control of CMV disease. Leflunomide, an inhibitor of protein kinase activity and pyrimidine synthesis, is an experimental immunosuppressive agent effective against acute and chronic allograft rejection in animal models. Because a number of CMV proteins are known to be phosphorylated, we tested the hypothesis that this agent might exert inhibitory activity against CMV. METHODS AND RESULTS: Plaque assays demonstrated dramatic dose-dependent attenuation of production of multiple clinical CMV isolates in leflunomide-treated human fibroblasts and endothelial cells, common targets for CMV infection in vivo. As shown by Northern blot analysis and immunohistochemical staining, leflunomide neither interferes with transcription of immediate early or late viral genes, nor with expression of corresponding proteins. CMV-specific DNA dot blots and biochemical enzyme assays indicated that, in contrast to currently approved anti-CMV drugs, leflunomide exerts no inhibitory effect on the accumulation of viral DNA in infected cells, or on viral DNA polymerase activity. Rather, as visualized by transmission electron microscopy, this agent appears to act at a late stage in virion assembly by preventing tegument acquisition by viral nucleocapsids. Finally we have demonstrated equivalent inhibitory activity of leflunomide against multi-drug-resistant CMV isolates. CONCLUSIONS: These findings imply that leflunomide, an effective immunosuppressive agent, shows potential to concurrently attenuate a major complication of immunosuppression, CMV disease, by a novel mechanism of antiviral activity.

Antiviral Agents↗
PubMed1999

In vivo activity of leflunomide: pharmacokinetic analyses and mechanism of immunosuppression.

BACKGROUND: Leflunomide is an experimental drug with demonstrated ability to prevent and reverse acute allograft and xenograft rejection. The two biochemical activities reported for the active metabolite of leflunomide, A77 1726, are inhibition of tyrosine phosphorylation and inhibition of dihydroorotate dehydrogenase, an enzyme necessary for de novo pyrimidine synthesis. These activities can be distinctly separated in vitro by the use of uridine, which reverses the anti-proliferative effects of A77 1726 caused by inhibition of de novo pyrimidine synthesis. We report the effect of uridine on the in vivo immunosuppressive activities of leflunomide. METHODS: We first quantified the serum levels of A77 1726, the active metabolite of leflunomide, after a single treatment of leflunomide (5, 15, and 35 mg/kg). Additionally, we quantified the levels of serum uridine and of nucleotide triphosphates in the liver, spleen, and lymph nodes of Lewis rats after the administration of a single dose of uridine (500 mg/kg; i.p.). Lewis rats heterotopically transplanted with brown Norway or Golden Syrian hamster hearts were treated for 50 or 75 days with leflunomide (5, 15, and 35 mg/kg/day; gavage) alone or in combination with uridine (500 mg/ kg/day; i.p.). Hematocrits were determined and the levels of alloreactive or xenoreactive immunoglobulin (Ig)M and IgG were determined by flow cytometric analysis. The allograft and xenografts, small bowel, liver, kidney, and spleen were subjected to pathological examination. RESULTS: A linear relationship was observed between the serum A77 1726 concentrations in Lewis rats and the dose of leflunomide administered. Peak A77 1726 concentrations were 20.9, 71.8 and 129.3 mg/l (77.5, 266.1 and 478.8 microM) for the 5, 15, and 35 mg/kg doses of leflunomide, respectively. The concentration of uridine in the serum of normal Lewis rats is 6.5 microM; after i.p. administration of 500 mg/kg uridine, the serum uridine concentrations peaked at 384.1 microM in 15-30 min. The rapid elimination of uridine was not reflected in the lymphoid compartments, and the pharmacokinetics of pyrimidine nucleotides in the spleen resembled that of A77 1726. This dose of uridine, when administered daily (500 mg/kg/day, i.p.), weakly antagonized the immunosuppressive activities of leflunomide (5, 15, and 35 mg/kg/day) in the allotransplantation model. In contrast, in the xenotransplantation model, the same concentration of uridine completely antagonized the immunosuppressive activities of low-dose leflunomide (15 mg/kg/day) and partially antagonized the immunosuppressive activities of high-dose leflunomide (35 mg/kg/day). Toxicities associated with high-dose leflunomide (35 mg/kg/day) were anemia, diarrhea, and pathological changes in the small bowel and liver. These toxicities were significantly reduced by uridine co-administration. CONCLUSION: These studies reveal that the blood levels of A77 1726 in Lewis rats satisfy in vitro requirements for both inhibition of de novo pyrimidine synthesis and protein tyrosine kinase activity. Our data also illustrate that the in vivo mechanism of immunosuppression by leflunomide is complex and is affected by at least the following four factors: type and vigor of the immune response, availability of uridine for salvage by proliferating lymphocytes, species being investigated, and concentration of serum A77 1726.

Aniline Compounds↗
PubMed1999

Inhibition of cytomegalovirus in vitro and in vivo by the experimental immunosuppressive agent leflunomide.

Despite progress in antiviral chemotherapy, cytomegalovirus (CMV) remains a major cause of morbidity and mortality among pharmacologically immunosuppressed transplant recipients, frequently engaging the clinician in a struggle to balance graft preservation with control of CMV disease. Leflunomide, an inhibitor of protein kinase activity and pyrimidine synthesis, is an experimental immunosuppressive agent effective against acute and chronic rejection in animal models. Herein we summarize our recent studies demonstrating that leflunomide inhibits the production of multiple clinical CMV isolates (including multi-drug-resistant virus) in both human fibroblasts and endothelial cells. In contrast to all other anti-CMV drugs currently in use, leflunomide does not inhibit viral DNA synthesis, but rather appears to interfere with virion assembly. Finally, preliminary studies in a rat model suggest that this agent reduces viral load in vivo. These findings imply that leflunomide, an effective immunosuppressive agent, shows potential to concurrently attenuate a major complication of immunosuppression, CMV disease, by a novel mechanism of antiviral activity.

Animals↗
PubMed1998

FK506 treatment in combination with leflunomide in hamster-to-rat heart and liver xenograft transplantation.

BACKGROUND: In the experiment described here, we investigated the effects of the immunosuppressants FK506 and leflunomide (Lef) on the survival of hamster hearts and liver xenografts in Lewis rats. METHODS: Lewis rats were used as recipients of hamster heart or liver grafts using different regimens of FK506 and Lef. Donor-matched heart grafts were transplanted into long-term surviving Lewis rat recipients of hamster xenografts to test donor-specific prolongation of xenograft survival. Hyperimmune, late xenograft rejection, and naive sera were transferred into long-term surviving Lewis rat recipients of hamster heart xenografts to determine whether these sera could inhibit the efficacy of donor-specific long-term survival. Anti-donor-specific antibodies were analyzed by flow cytometry. RESULTS: After a short induction with FK506 plus Lef, maintenance treatment with FK506 alone was sufficient to prolong survival of hamster xenografts. All hamster heart and four of six hamster liver xenografts survived for more than 3 months. Second hamster hearts were permanently accepted by Lewis rats bearing long-term surviving hamster heart xenografts when rats were treated with FK506 monotherapy (mean survival time >60 days, n=4). Long-term surviving hamster heart grafts were rejected after transfer of hyperimmune serum but not late xenograft rejection serum or naive serum. Lef and FK506 significantly reduced the production of anti-donor-specific antibodies in Lewis rats transplanted with hamster liver and heart xenografts. CONCLUSION: Long-term survival of hamster liver and heart xenografts in Lewis rats could be induced by a regimen of short-term FK506 in combination with Lef followed by FK506 monotherapy. The acquired sensitivity of late xenoreactivity to FK506 reflects primarily a modification in the host immune response to the hamster graft.

Animals↗
PubMed1998

Histological characterization and pharmacological control of chronic rejection in xenogeneic and allogeneic heart transplantation.

BACKGROUND: Chronic allograft rejection remains a major barrier to successful long-term allograft transplantation in humans. Chronic allograft rejection is characterized by the appearance of arterial lesions with concentric intimal thickening. This study investigates the development and control of chronic rejection in hamster cardiac xenografts transplanted into Lewis rats. METHODS: Chronic rejection in the xenograft model involves transplantation of hamster hearts into Lewis rats treated with leflunomide (Lef) continuously at 15 mg/kg/day. The allograft model involves transplantation of Lewis hearts into Fisher-334 rats treated with cyclosporine (CsA) at 2.5 mg/kg for 5 days. RESULTS: The average scores of arterial intimal thickening on day 45 after transplantation were 1.89+/-0.43 in the xenograft and 2.50+/-0.72 in the allograft. The basic pathology of both xenografts and allografts undergoing chronic rejection was arterial intimal thickening comprising smooth muscle cell proliferation, mononuclear cell infiltration, and fibrosis. The majority of cells infiltrating the arterial intima and myocardium were T cells and macrophages. Compared with the allograft, intimal edema, matrix deposition and fibrinoid necrosis were specifically presented in the xenografts and generally involved the larger arteries. The predominant isotype of antibody deposited was IgM in xenografts and IgG in allografts. When combined Lef and CsA therapy was initiated on day 45 after transplantation, the changes of chronic rejection were reversed in both xenografts and allografts by day 90. The scores of intimal thickening were significantly reduced to 0.97+/-0.45 and 1.48+/-0.56, respectively. CONCLUSIONS: We conclude that chronic rejection can be induced in xenografts under conditions of inadequate immunosuppression. Chronic rejection in xenografts involves arterial lesions that bear some histological similarities to, as well as differences from, those observed in chronically rejected allografts. Finally, combination therapy with CsA and Lef reduced the incidence and severity of the intimal lesions in both chronically rejecting xenografts and allografts.

Animals↗