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BACKGROUND Hepatitis C virus (HCV) reinfection after liver transplantation may lead to recirrhosis and seems to be influenced by genetic factors. The aim of our study was to evaluate the role of STAT-4-polymorphisms in the development of HCV-related graft disease based on protocol biopsies. METHODS One hundred sixty transplant patients with HCV recurrence were genotyped for STAT-4 (rs7574865) by polymerase chain reaction. Fibrosis stages were determined based on Desmet and Scheuer classification. SPSS was used for the statistical analysis of genotype distribution and of time to the development of advanced fibrosis among the genotypes. RESULTS During a comparable observation period of 86.2 months (P=0.654), 65 patients (46.5%) developed advanced fibrosis. Advanced fibrosis was observed significantly more frequent in patients (n=34) with at least one T-allele (53.1 vs. 32.3%; P=0.013) compared with homozygotes for G-allele (n=31). Significant differences in the duration of advanced fibrosis development were detected between patients with at least one T-allele compared with G-allele (34.4 vs. 49.0 months; P=0.022). No impact was observed regarding the outcome of interferon-based antiviral treatment (P=0.297) and the occurrence of acute cellular rejection (P=0.365). CONCLUSION Present results indicate a possible impact of genetic confounders in the recipient on graft fibrogenesis, thus explaining significantly different graft behavior observed after transplantation for HCV-associated liver disease. STAT-4-T-allele is identified as fibrogenic factor and seems to have a negative impact on HCV-induced fibrosis development.

BACKGROUND The development of liver graft disease is partially determined by individual genetic background. Interleukin 28B (IL28B) is strongly suspected to be involved in susceptibility for hepatitis C virus (HCV) infection, inflammation, and antiviral treatment response before and after liver transplantation (LT). Currently, the role of IL28B polymorphism (rs12979860) in the development of hepatocellular carcinoma (HCC) is unclear, and only limited data are available on the course of HCV recurrence. METHODS One hundred sixty-seven HCV-positive patients after LT were genotyped for IL28B (C→T; rs12979860). Sixty-one patients with histologically confirmed HCC in the explanted liver were compared with 106 patients without HCC regarding IL28B genotypes. Among patients with HCC, IL28B genotypes were correlated with tumor histology and pretransplant α-fetoprotein (AFP) levels. Furthermore, the role of IL28B polymorphism was evaluated regarding interferon-based treatment success and fibrosis progression after LT. RESULTS The prevalence of HCC in explanted livers was significantly higher among patients with TT genotype, suggesting a protective role of the C allele in HCC development (P=0.041). Median AFP level was closely to significance higher in the presence of T allele (P=0.052). Significant differences in IL28B genotype distribution were detected between AFP-negative and AFP-positive HCCs ( 15 μg/L; P=0.008). Although no impact could be observed regarding acute cellular rejection (P=0.940), T allele was significantly associated with antiviral therapy failure (P=0.028) and faster development of advanced fibrosis (P=0.017) after LT. CONCLUSION IL28B polymorphism seems to be involved in the development of HCV-induced HCC and in the course of HCV recurrence after LT. T allele may be regarded as a genetic risk factor for HCV-related carcinogenesis, posttransplant fibrosis progression, and antiviral therapy failure.

BACKGROUND The development of kidney dysfunction is one of the most important after liver transplantation (LT). Genetic variants of pathogenetically relevant cytokines may influence the development and course of the disease. The aim of our study was to evaluate the role of transforming growth factor-β1 (TGF-β1) polymorphism in this context. METHODS Four hundred eighty-six liver graft recipients were genotyped for TGF-β1 codon 25 (guanine → cytosine, G → C) by polymerase chain reaction. Renal function before and after LT was characterized by estimation of glomerular filtration rate (GFR) using four-parameter-modification of diet in renal disease formula on defined dates. GFR was compared among TGF-β1-genotype groups of the entire cohort within the median observation period of 7 years. For the assessment of renal function recovery after LT, patients were divided into three groups by GFR difference (ΔGFR = ± 10 mL/min). RESULTS Mean pretransplant GFR differed significantly among TGF-β1-genotype groups (GG: 85.0 mL/min vs. GC/CC: 75.3 mL/min; P=0.016). The significance disappeared in the follow-up period. Although GG genotype demonstrated higher mean GFR levels, patients with GC/CC genotype tended to improve kidney function compared with GG genotype (P=0.013). Interestingly, lower mean GFR rates were observed among female compared with male recipients before (P=0.002), separately at all dates and cumulatively after LT (P

BACKGROUND: The scarcity of appropriate donor organs remains to be a major problem in transplantation surgery today. This has led to increased acceptance of so-called marginal grafts, incorporating the increased risk of poor posttransplant function. Erythropoietin has been shown to reduce ischemia-reperfusion injury in transplanted rat livers. We investigated whether these capacities may contribute to improve marginal organ function. METHODS: One hundred and forty Lewis rats were used. Fatty liver (>or=50% steatosis) was induced by a special diet in 70 donor animals. Seventy recipients received liver transplantation after donor organ treatment with 1000 IU rhuEpo or saline injection (controls) into portal veins (cold ischemia 6 hr, University of Wisconsin solution). Recipients were allocated to two groups which received 1000 IU rHuEpo at reperfusion or an equal amount of saline (control). Analysis of liver enzymes, histology (hematoxylin-eosin and periodic acid Schiff stain), immunostaining (terminal deoxynucleotide transferase- mediated dUTP nick-end labeling, hypoxyprobe, and tumor necrosis factor-alpha), and reverse transcriptase-polymerase chain reaction of cytokine messenger RNA (interleukin-1, interleukin-6, hypoxia induced factor-1 alpha, vascular endothelial growth factor, and hepatocyte growth factor) were performed at defined time points (2, 4.5, 24, 48 hr, and 7 days postoperatively). RESULTS: Alanine aminotransferase values were significantly reduced for epo-treated rats 48 hr after reperfusion; however, at all other time points enzyme levels were without significant differences. Terminal deoxynucleotide transferase-mediated dUTP nick-end labeling and hypoxyprobe analysis and necrotic index evaluation displayed significant reduction of apoptosis and hypoxic cells in rHuEpo-treated graft livers. Overall survival was significantly improved among epo-treated rats. CONCLUSION: Erythropoietin improves marginal graft function and recipient survival after transplantation of fatty livers in rats.

Background There are no data on the effects of mycophenolate mofetil (MMF) on the incidence of bronchiolitis obliterans syndrome (BOS) in lung-transplant patients. This study attempted to determine whether MMF reduces the incidence of BOS in de novo lung transplant recipients compared with azathioprine (AZA). Methods This prospective, randomized, open-label, multicenter study compared the effects of MMF with AZA in combination with induction therapy, cyclosporine (Neoral) and corticosteroids in patients receiving their first lung transplant. Primary endpoint was incidence of BOS at 3 years. Secondary endpoints were incidence of acute rejection, time to first rejection event, and survival. Results The incidence of acute rejection and the time to first rejection event at 1 and 3 years did not differ between groups (54.1% vs. 53.8% and 56.6% vs. 60.3% for MMF and AZA respectively). Survival at 1 year tended to be better in patients receiving MMF (88 vs. 80%, P = 0.07). At year 3, there was no difference in survival or in the incidence, severity or time to acquisition of BOS between the two groups. Treatment was generally well tolerated, however more patients withdrew from AZA treatment than from MMF (59.6% vs. 46.5%, P = 0.02). As a result, there was an imbalance in the observation times of the two groups (876 +/- 395 vs. 947 +/- 326 days). Conclusions No differences were seen in the incidence of acute rejection or BOS in lung transplant recipients treated with MMF or AZA. This null result may have been influenced by the shorter observation time for AZA patients.

BACKGROUND In cystic fibrosis (CF), absorption of cyclosporine A (CsA) through the gastrointestinal tract is often impaired because of fat malabsorption. The aim of this study was to compare the steady-state pharmacokinetics of CsA and the inter- and intrasubject variability of CsA exposure in stable lung transplant recipients with and without CF and to determine the best single-time predictors of the area under the curve (AUC). METHODS Ten lung transplant recipients without CF and 10 lung transplant recipients with CF were studied. All patients received Neoral twice daily. Blood samples were obtained predose and at 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 8, and 12 h postdose on three separate days within a 5-day period. RESULTS CsA exposure and pharmacokinetic variables were similar in the two groups, although exposure-per-milligram-per-dose was approximately 25% lower in CF patients. Coefficients of intersubject variability were numerically higher in CF patients, but the difference between groups did not reach significance. On the other hand, the maximum concentration (Cmax), the concentration 2 hours after administration (C2), AUC0-12, and AUC0-4 showed a twofold greater intrasubject variability in CF patients. CsA trough concentration did not predict accurately the AUC, but C2 was a good predictor of the AUC0-4 in both CF (r2=0.90) and non-CF (r2=0.78) patients. CONCLUSION Compared to patients without CF, patients with CF show a lower bioavailability of CsA and a greater intrasubject variability of Cmax, C2, and AUC. C2 is the best single-point predictor of the AUC0-4 in lung transplant recipients with and without CF.

Background Peripheral blood mononuclear cells (PBMC) of stable renal or cardiac transplant recipients were previously shown to respond to allogeneic cells but not to soluble protein antigens. The aim of the present study was to assess the T-cell and antigen-presenting cell (APC) functions of stable lung transplant (LT) recipients. Methods We obtained PBMC from 38 stable LT recipients. PBMC from healthy volunteers served as controls. PBMC were stimulated with either anti-CD3 monoclonal antibody, allogeneic PBMC, or tetanus toxoid (TT). T-cell activation was assessed by determination of interleukin (IL)-2 levels in culture supernatants; in some experiments, interferon-y levels were also determined. Patients' APC function was tested in a mixed leukocyte reaction using patients' PBMC as stimulators. The expression of class II MHC, B7.2, and CD40 molecules on patients' APC was determined by flow cytometry, and their production of IL-10 and IL-12 at the basal state and upon CD40 ligation was also measured. Results Patients' T cells produced normal amounts of IL-2 in response to anti-CD3 monoclonal antibody and allogeneic PBMC. In contrast, the response of memory T cells to TT was severely blunted both in terms of IL-2 and interferon-y production. Patients' PBMC were poor stimulators in mixed leukocyte reaction, and class II MHC expression on patients' monocytes was significantly reduced. Patients' APC presented a modest but significant increase in basal IL-10 production and produced significantly less IL-12 upon CD40 ligation than control APC. Conclusions T cells from stable LT recipients respond normally to stimuli that do not depend on autologous APC. The major impairment in the T-cell response to TT is caused by APC dysfunction, which involves decreased class II MHC expression and deficient IL-12 synthesis.

BACKGROUND Despite blockade of the interleukin-2/interleukin 2 receptor (IL-2/IL-2R) pathway by the murine anti-CD25 (i.e., IL-2R alpha chain) monoclonal antibody BT563, cardiac rejection can still occur. In these cases, growth factors other than IL-2 may contribute to allograft rejection. We studied the expression of IL-15, a macrophage-derived cytokine associated with T-cell activation, which interacts with the beta and gamma chains of the IL-2R during rejection episodes under anti-CD25 therapy. METHODS We measured intragraft IL-15 mRNA expression and the number of IL-15- and CD68-positive cells in posttransplantation endomyocardial biopsies (EMBs; n=45) and in nontransplanted, donor-heart specimens (n=11) by competitive template reverse transcription-polymerase chain reaction and immunohistochemistry, respectively. RESULTS IL-15 mRNA expression was present in the majority of posttransplantation EMB specimens (91%, 41/45) and in nontransplanted donor-heart specimens (91%, 10/11). Relative IL-15 mRNA levels were neither associated with transplantation nor with rejection status. After transplantation, the number of IL-15- and CD68-positive cells significantly increased (P

Background. Quadruple immunosuppressive induction therapy has been shown to markedly reduce the incidence of acute rejection episodes without increasing the incidence of infectious complications after liver transplantation. However, the use of polyclonal antibody preparations (e.g. antithymocyte globulin [ATG]) is associated with side effects such as fever and tachycardia. To evaluate the efficacy and the safety of a monoclonal antibody directed against the interleukin-2 receptor (BT563) in comparison with ATG as part of a quadruple induction regimen, a prospective, randomized study was conducted. Methods. Eighty consecutive adult recipients of primary orthotopic liver transplants were randomized to receive either BT563 (10 mg/day; days 0-12; n=39) or ATG (5 mg/kg/day; days 0-6; n=41) in addition to the standard immunosuppressive protocol consisting of cyclosporine, and prednisolone, and azathioprine. Results. Patients treated with BT563 had a significantly lower incidence of steroid-sensitive rejection episodes (3 vs. 11; P

Background. It has been postulated that chimerism after transplantation might promote graft acceptance. In the present study, we prospectively assessed blood chimerism in 10 lung transplant recipients during the first posttransplant year and investigated whether chimerism was associated with an immunologically stable situation of the graft. Methods. The recipients' peripheral blood mononuclear cells were obtained before transplantation and at various time points during the first postoperative year. Donor cells were detected using nested polymerase chain reaction amplification of a donor-specific HLA-DRB1 allele. Clinical graft acceptance was determined by the number of rejection episodes. Results. The incidence of blood chimerism was high during the first 3 postoperative months and then decreased over time. All patients experienced at least one acute rejection episode, and three patients developed chronic rejection. Conclusion. We, thus, conclude that rejection of the lung allograft may occur in the presence of blood chimerism.

Background. Although human herpesvirus (HHV)-6 is now recognized as a frequent pathogen after transplantation, the real impact of this infection in patients undergoing transplantation remains unclear. Methods. During 27 months, 30 consecutive heart-lung- and lung-transplant recipients were included on the day of transplantation and prospectively followed during 100 days for HHV-6 infection. Results. HHV-6 infection occurred in 20 (66%) patients after a median delay of 18 days after transplantation. The virus was detected by polymerase chain reaction or culture, or both, in 15.7 % of blood specimens, in 14.5% of bronchoalveolar lavage fluids, and in many organs at postmortem examination; it was found by culture in eight patients. No clinical manifestations could clearly be associated with HHV-6 alone. However, patients with HHV-6 infection had a higher mortality rate than patients without HHV-6 infection (7 of 20 vs. 0 of 10; P=0.04), and all the deceased patients died during periods of HHV-6 infection. We did not observe higher incidence of infectious or graft-rejection episodes in HHV-6-positive patients. However, eight of nine viral or fungal infections occurred during HHV-6 infection and three were directly responsible for death. Conclusion. Although frequently detected after transplantation, HHV-6 was not associated with any specific clinical manifestation. The higher mortality rate observed in patients with HHV-6 infection was not related to a higher incidence of bacterial infections or graft rejection but might be associated with more viral and fungal infections.

Peripheral blood mononuclear cells (PBMC) of stable renal or cardiac transplant recipients were previously shown to respond to allogeneic cells but not to soluble protein antigens. The aim of the present study was to assess the T-cell and antigen-presenting cell (APC) functions of stable lung transplant (LT) recipients.We obtained PBMC from 38 stable LT recipients. PBMC from healthy volunteers served as controls. PBMC were stimulated with either anti-CD3 monoclonal antibody, allogeneic PBMC, or tetanus toxoid (TT). T-cell activation was assessed by determination of interleukin (IL)-2 levels in culture supernatants; in some experiments, interferon-y levels were also determined. Patients' APC function was tested in a mixed leukocyte reaction using patients' PBMC as stimulators. The expression of class II MHC, B7.2, and CD40 molecules on patients' APC was determined by flow cytometry, and their production of IL-10 and IL-12 at the basal state and upon CD40 ligation was also measured.Patients' T cells produced normal amounts of IL-2 in response to anti-CD3 monoclonal antibody and allogeneic PBMC. In contrast, the response of memory T cells to TT was severely blunted both in terms of IL-2 and interferon-y production. Patients' PBMC were poor stimulators in mixed leukocyte reaction, and class II MHC expression on patients' monocytes was significantly reduced. Patients' APC presented a modest but significant increase in basal IL-10 production and produced significantly less IL-12 upon CD40 ligation than control APC.T cells from stable LT recipients respond normally to stimuli that do not depend on autologous APC. The major impairment in the T-cell response to TT is caused by APC dysfunction, which involves decreased class II MHC expression and deficient IL-12 synthesis.

BACKGROUND Despite anti-CD25 (interleukin [IL]-2 receptor alpha chain) monoclonal antibody (mAb) therapy, rejection can still occur. T-cell activation through the IL-2 receptor beta and gamma chains by IL-2 or other growth factors may contribute to this rejection. Recently, we have demonstrated that the T-cell growth factor IL-15 was abundantly present in rejecting cardiac grafts during anti-CD25 mAb treatment. METHODS To test whether IL-2- and IL-15-responsive T cells play an active role in rejection during anti-CD25 mAb therapy, we measured the frequency of IL-2- and IL-15-proliferative T cells in peripheral blood from treated patients during rejection (n=12). Measurements were made by limiting dilution analysis in the absence and presence of extra in vitro-added mouse anti-human CD25 mAb. RESULTS In the absence of anti-CD25 mAb, the frequencies of peripheral T cells responding to recombinant human (rh)IL-2 and rhIL-15 from patients were lower than those measured in samples of healthy controls (n=7): median of IL-2-responding T cells 78 per 10(6) (range 31-210 per 10(6)) vs. 154 per 10(6) (122-484 per 10(6), P=0.008) and median of IL-15-responding T cells 62 per 10(6) (range 19-207 per 10(6)) vs. 129 per 10(6) (range 79-192 per 10(6), P=0.02), respectively. In the presence of extra in vitro-added anti-CD25 mAb, frequencies of IL-2-responding T cells from patients significantly decreased, although a considerable number of T cells still proliferated on rhIL-2 (median 85%, range 46-100%). In contrast, the frequencies of IL-15 T cells still responding remained stable (median 2%, range 0-50%, P

Despite blockade of the interleukin-2/interleukin 2 receptor (IL-2/IL-2R) pathway by the murine anti-CD25 (i.e., IL-2R alpha chain) monoclonal antibody BT563, cardiac rejection can still occur. In these cases, growth factors other than IL-2 may contribute to allograft rejection. We studied the expression of IL-15, a macrophage-derived cytokine associated with T-cell activation, which interacts with the beta and gamma chains of the IL-2R during rejection episodes under anti-CD25 therapy.We measured intragraft IL-15 mRNA expression and the number of IL-15- and CD68-positive cells in posttransplantation endomyocardial biopsies (EMBs; n=45) and in nontransplanted, donor-heart specimens (n=11) by competitive template reverse transcription-polymerase chain reaction and immunohistochemistry, respectively.IL-15 mRNA expression was present in the majority of posttransplantation EMB specimens (91%, 41/45) and in nontransplanted donor-heart specimens (91%, 10/11). Relative IL-15 mRNA levels were neither associated with transplantation nor with rejection status. After transplantation, the number of IL-15- and CD68-positive cells significantly increased (P0.001), but IL-15-positive cell counts did not reflect the histological rejection grade. Anti-CD25 treatment, in contrast to its effects on the IL-2/IL-2R complex, had no influence on intragraft IL-15 mRNA and protein production. In rejection EMB specimens, during (n=5) and after (n=8) anti-CD25 therapy, no differences in relative IL-15 mRNA levels, or in IL-15- and CD68-positive cell counts, were measured.After heart transplantation, high numbers of IL-15- and CD68-positive cells infiltrate the graft. This phenomenon is independent of the rejection status. IL-15 remains present during blockade of the IL-2/IL-2R pathway by anti-CD25 monoclonal antibodies, and it may participate in T cell-dependent donor-directed immune responses, thereby explaining the occurrence of rejection in the absence of IL-2.

Background. Gastrointestinal complications are a well-documented source of morbidity and mortality after heart and lung transplantation. Methods. We report on two patients who presented with gastric perforation caused by mucormycosis during the first 2 months after heart-lung and heart transplantation. Results. In the first patient, the clinical presentation was insidious and the diagnosis was made at an advanced stage of the disease. Despite surgery and aggressive antifungal treatment, the patient died. In the second patient, the diagnosis was made promptly, but despite antifungal treatment, he presented with gastric perforation within a week. Conclusions. These cases illustrate that fungal invasive disease may be a cause of early gastrointestinal perforation after solid organ transplantation.

BACKGROUND: Patients who have been exposed to the hepatitis B virus (HBV) and who were able to clear the hepatitis B surface antigen from the serum and to develop anti-hepatitis B surface antigen (anti-HBs) antibodies are not considered at risk for HBV reactivation after solid organ transplantation. METHODS AND RESULTS: We, however, observed three solid organ transplant recipients who demonstrated clinically significant HBV reactivation after transplantation. All patients presented normal liver enzymes and serological stigmates of healed HBV infection at the time of transplantation, as indicated by the absence of hepatitis B surface antigen and the presence of anti-HBs and anti-hepatitis B core antibodies in the serum. Patient 1, a renal transplant recipient, presented HBV reactivation 3 years after transplantation and developed chronic HBV hepatitis. Patient 2 developed HBV reactivation 7 months after a second cadaveric renal graft and died of cirrhosis four and a half years after transplantation. Patient 3, a heart-lung transplant recipient, developed HBV reactivation within months after transplantation, but died of unrelated causes. HBV reactivation in the presence of anti-HBs antibodies has been previously reported in other settings of immunosuppression, mainly in patients with acquired immunodeficiency syndrome and after bone marrow transplantation, and may lead to fatal liver disease. Data from our renal transplant recipients suggest that the incidence of HBV reactivation among patients with anti-HBs and anti-hepatitis B core antibodies is about 5%. CONCLUSIONS: Transplant physicians should be aware of the risk of HBV reactivation in patients presenting with healed HBV infection before transplantation.

Anti-interleukin (IL)-2 receptor (IL-2R) antibodies have been used as rejection prophylaxis after organ transplantation. Despite this induction treatment, acute rejections may occur. We wondered whether these rejections developed via the IL-2/IL-2R pathway.In a prospective trial using BT563, a murine IgG1 anti-IL-2R antibody, for rejection prophylaxis after heart transplantation, 20 patients were treated in combination with cyclosporine from the day of transplantation (group A). As a control group, 31 patients were also treated with BT563, but in these patients, cyclosporine treatment was initiated on day 3 (group B).Three patients from group A and two patients from group B died in the first postoperative month (of causes not related to acute rejection) and were left out of the analysis of rejection incidence. Freedom from acute rejection at 1 week after transplantation in group A (14/17; 82%) was lower than in group B (16/29; 55%), although the difference did not reach statistical significance. There was no difference in either the number of acute rejection episodes at 12 weeks or the required rejection treatments between groups A and B. Infectious complications were evenly distributed in both groups. Immunohistochemistry showed that during acute rejection, in the presence of circulating BT563, IL-2R-bearing cells were present in only one of five rejection biopsies (20%), whereas these cells were often present (6/8, or 75%) in rejections occurring in the absence of BT563. The presence of BT563 was associated with a similar difference in the mRNA expression of IL-2 (2/5 vs. 6/8).Apparently, despite adequate blockade of the IL-2/IL-2R pathway, patients may develop acute rejection, reflecting the redundancy of the cytokine network. The ever-present IL-15 may well be a candidate for overtaking the role of IL-2.

It has been postulated that chimerism after transplantation might promote graft acceptance. In the present study, we prospectively assessed blood chimerism in 10 lung transplant recipients during the first posttransplant year and investigated whether chimerism was associated with an immunologically stable situation of the graft.The recipients' peripheral blood mononuclear cells were obtained before transplantation and at various time points during the first postoperative year. Donor cells were detected using nested polymerase chain reaction amplification of a donor-specific HLA-DRB1 allele. Clinical graft acceptance was determined by the number of rejection episodes.The incidence of blood chimerism was high during the first 3 postoperative months and then decreased over time. All patients experienced at least one acute rejection episode, and three patients developed chronic rejection.We, thus, conclude that rejection of the lung allograft may occur in the presence of blood chimerism.

We studied the reactivity of cardiac graft-infiltrating cells, cultured from endomyocardial biopsy specimens, toward heart endothelial cells (Hec). In two cases, Hec derived from the specific donor heart or Hec compatible with the donor were lysed, but not the syngeneic B cell line. A vessel-derived endothelial cell line was not lysed. Panel studies suggest that the epitopes recognized are, in one case, a Hec-specific peptide presented in the context of HLA-Bw41 and, in the other case, a Hec-specific peptide presented by a subtype of HLA-B44. In conclusion, we showed that cardiac graft-infiltrating cells cultured from endomyocardial biopsy specimens can exhibit cytotoxic reactivity specifically directed against HLA-peptide complexes on Hec.

Brequinar sodium (BQR) prevents cell proliferation by virtue of its inhibition of de novo pyrimidine biosynthesis. BQR is capable of inhibiting immune responses in vitro and is effective in suppressing the development of contact sensitivity and adjuvant arthritis in rodent models. Based on the antiproliferative and immunosuppressive capacity of BQR, we have evaluated the efficacy of BQR in preventing allograft rejection utilizing experimental models of heterotopic heart and kidney and orthotopic liver transplantation in an MHC and non-MHC mismatched ACI----LEW rat strain combination. The immunosuppressive activity of BQR is illustrated by its ability to inhibit the development of delayed-type hypersensitivity to DNFB in mice. When BQR was administered orally throughout the sensitization and elicitation phases of the DNFB contact sensitivity response, it was found to be a potent immunosuppressant with an ED50 value of 0.5 mg/kg. This immunosuppressive activity is also seen in vitro, where BQR is capable of inhibiting the mixed lymphocyte response between allogeneic ACI and LEW rat strains with an IC50 of 150 ng/ml. The immunosuppressive activity of BQR is highly effective in prolonging heart, liver, and kidney allograft survival in the rat. Cardiac allografts are not rejected during the period of drug treatment at dosage levels of 12 to 24 mg/kg orally three times weekly. The grafts survive until the drug is discontinued (30 days posttransplantation), and the grafts are then rejected approximately 14 days later. Liver and kidney allografts are permanently accepted by approximately 50 to 90% of the recipient rats following 30 days of treatment with BQR at 12 mg/kg. The tolerance that is induced to the liver grafts extends in the majority of animals to greater than 250 days and is specific for the donor ACI strain. Challenge of long-term liver graft survivors with donor cardiac grafts is associated with permanent survival of donor, but not third-party, heart grafts. Combination therapy consisting of suboptimal doses of BQR and CsA demonstrates that the combination of these two immunosuppressive drugs results in an increased efficacy in prolonging graft survival. The results of these allograft experiments demonstrate that this new immunosuppressive agent is highly effective in preventing allograft rejection in the rat. The antiproliferative activity of BQR is effective for inhibiting T-lymphocyte-mediated immune responses, and Brequinar sodium should be an important addition to a polytherapeutic approach in the treatment of organ graft rejection.