Rejection following donor or recipient preoperative treatment with FTY720 in rat small bowel transplantation

BACKGROUND: Severe rejection of small bowel transplantation (SBTx) has been ascribed to abundant lymphoid tissues in the small intestine without well-established evidence. However, the role of donor lymphocytes in rejection is still unclear. The novel immunosuppressant, FTY720, is reported to transfer peripheral blood lymphocytes (PBLs) to lymphoid tissues such as mesenteric lymph nodes (MLNs) and Peyer patches (PP). In the present study, the number of donor lymphocytes in the graft was increased by FTY720, and the influence on rejection was studied in a rat model. Furthermore, the number of the PBL of recipient was decreased by FTY720 before SBTx and the effect on rejection was examined. MATERIALS AND METHODS: Orthotopic total SBTx was performed in Brown-Norway and Lewis rats. In the donor pretreatment study, FTY720 was administrated to donor rats 24 h prior to harvesting to increase the number of graft lymphocytes (FTY donor-pretreated group). In contrast, MLNs were surgically removed from the grafts to decrease the number of graft lymphocytes (MLN-resected group). In the recipient pretreatment study, FTY720 was administrated to recipient rats 24 h before SBTx to decrease recipient PBL (FTY group). In contrast, a subclinical dose of cyclosporine A (CsA) was administrated after SBTx (CsA group). Rats were administrated preoperative FTY720 combined with post-SBTx CsA (FTY+CsA group). Graft survival, pathology, lymphocyte count, and subtype were examined. RESULTS: In the donor pretreatment study, pretreatment with FTY720 did not enhance graft rejection. MLN resection did not prolong graft survival. In the recipient pretreatment study, FTY720 caused a significant reduction in the number of infiltrating lymphocytes in the graft, as well as the percentage of recipient CD4+ and CD25+ cells within the graft. FTY720 and CsA synergistically prolonged graft survival. CONCLUSION: SBTx rejection correlated with the number of recipient PBL, and not with the number of donor lymphocytes transplanted together with the graft. The pretreatment of the recipient with FTY720 was effective in the case of combined use of the low-dose postoperative CsA.     

Prevention of GVHD and graft rejection by a new S1P receptor agonist, W-061, in rat small bowel transplantation

BackgroundIn small bowel transplantation (SBTx), inhibition of both graft-versus-host disease (GVHD) and allograft rejection is necessary.MethodsWe investigated the potency of a new sphingosine-1-phosphate receptor agonist, W-061, for these two immune responses in SBTx. W-061 has a completely different molecular structure from FTY720. Heterotopic SBTx was performed from Wistar-Furth (WF) into (WF × ACI) F1 rats as a GVHD model or F1 to WF rats as a rejection model. Recipients were orally given 3 mg/kg/day W-061 for 14 days after SBTx. Recipient survival, body weight, histopathology, lymphocyte subpopulations, and the cytokine profile were evaluated.ResultsW-061 treatment significantly prolonged graft survival over 100 days in four out of six recipients in the GVHD group and over 60 days in three out of six recipients in the rejection group. W-061 strongly inhibited GVHD and rejection as seen histopathologically in comparison with untreated control rats. W-061 caused a significant reduction in donor-derived T cells in target organs and infiltrating T cells in allografts by promoting these cells to home into the secondary lymphoid tissues and sequestrating those cells there. W-061 significantly decreased production of interferon-γ in target organs and allografts.ConclusionTherefore, these data suggest that W-061 has considerable potential as a new therapeutic immunosuppressant in patients with SBTx.     

FTY720介导淋巴细胞凋亡抑制小肠移植的移植物抗宿主免疫反应

目的 探讨免疫调节药物FTY720对小肠移植后急性移植物抗宿主病（GVHD）的治疗效果及其作用机制.方法 应用Wistar-Furth（WF）大鼠作为供体,WF和ACI大鼠的子代（F1）作为受体,同种异基因异位全小肠移植的技术方法建立GVHD的动物模型.移植受体分为实验组和对照组,每组6只.实验组从移植手术当日开始予以FTY720治疗,持续14 d;对照组在相同的时间段口服蒸馏水.术后第15天,提取受体靶器官肝脏、小肠及移植物小肠的淋巴细胞,应用免疫组织化学（免疫组化）TUNEL法和流式细胞仪检测两组淋巴细胞凋亡的变化.结果 对照组大鼠术后均死亡于GVHD,平均生存时间（16.0±1.7）d,实验组大鼠均长期成活超过100 d,两组差异具有统计学意义（P＜0.01）.免疫组化TUNEL法检测结果显示,实验组肝脏和移植物小肠黏膜的淋巴细胞凋亡比率均明显高于对照组,差异具有统计学意义（P＜0.05）.流式细胞技术分析结果显示,实验组大鼠移植物小肠黏膜内凋亡的淋巴细胞百分比为19.4%,明显高于对照组的11.8%（P＜0.05）;而肝脏凋亡的淋巴细胞百分比两组差异无统计学意义（P＞0.05）.结论 FTY720可能通过诱导淋巴细胞的凋亡,减少和抑制GVHD对靶器官的损害,改善移植大鼠的预后.     

FTY720 reduces T-cell recruitment into murine intestinal allograft and prevents activation of graft-infiltrating cells

BACKGROUND: Effective immunosuppression is a critical determinant of graft survival in small-bowel transplantation (SBTx). The present study was designed to determine the potency of FTY720, a newly synthesized immunosuppressant, in rat SBTx and examine the phenotype of graft-infiltrating cells to evaluate its effect on intestinal allografts. MATERIALS AND METHODS: A segment of intestine of Dark Agouti rats was transplanted heterotopically into Lewis rats. The recipients were treated with or without oral FTY720 at a dose of 1 mg/kg per day. Six days after surgery, peripheral blood lymphocytes and lymphocytes from the mesenteric lymph nodes, Peyer's patches, intraepithelial site, and lamina propria of the intestinal allograft were isolated. After the number of lymphocytes in each site was counted, the lymphocyte subpopulations in the intestinal allograft were evaluated by means of a FACScan flow cytometer using several monoclonal antibodies. RESULTS: FTY720 treatment significantly prolonged recipient survival and strongly inhibited rejection histologically in comparison with control rats. FTY720 immunosuppression resulted in a marked reduction of lymphocyte number in the graft epithelium and lamina propria and the proportion of CD8+ and CD25+ cells. FTY720 also significantly decreased T-cell receptors and increased B cells in the graft Peyer's patches. CONCLUSION: FTY720 promoted long-term SBTx recipient survival and maintained the architecture of intestinal allografts. FTY720 immunosuppression may be associated with a reduction of T-cell recruitment subsequent to the redistribution of lymphocyte subpopulations to control the proliferation and activation of graft-infiltrating cells in intestinal allografts.     

Preoperative administration of FTY720 prolonged renal allograft survival

BACKGROUND: FTY729 is an immunomodulator obtained by chemical modification of Myriocin(ISI-1) which exists in the culture filtrate of an ascomycete, Isaria sinclairii. It has been reported that postoperative administration of FTY720 prolonged survival of various kinds of transplanted organs. In the present study, we evaluated the effect of 2-day preoperative administration of FTY 720 on graft survival. MATERIALS AND METHODS: We used a rat renal transplantation model in which Wistar King Aptekman Hokkaido (WKAH, RT1K) served as the organ donor and Lewis (LEW, RTl) as the recipient. FTY720 was given to the recipients consecutively 2 days (day-2, day-1) before transplantation at the doses of 1, 3 or 5 mg/kg/day. Renal allograft survivals, hematological parameters of recipient blood and phenotypic analysis of recipient splenic cells and graft infiltrate were evaluated. RESULTS: Consecutive 2-day preoperative oral administration of FTY 720 at the doses of 1, 3 or 5 mg/kg/day significantly prolonged WKAH allograft survivals compared with those of the untreated recipients. The number of peripheral blood lymphocytes was markedly decreased in the recipients treated with FTY720 at the doses of 3 mg/kg/day or 5 mg/kg/day on the 5th postoperative day. Preoperative FTY 720 administration significantly decreased the number of CD4 positive cells and the percentage of interleukin 2 receptor (IL-2 R) positive cells infiltrating both spleen and allograft at the dose of 3 mg/kg/day or 5 mg/kg/day. CONCLUSION: FTY 720 could act as a safe and potent immunomodulator by decreasing the number of peripheral lymphocytes, especially CD4 positive cells and IL-2R positive cells when it is given to the recipient preoperatively.     

Control of intestinal allograft rejection by FTY720 and costimulation blockade

INTRODUCTION: The clinical application of small bowel transplantation (SBTx) is hampered by its pronounced immunogenicity. In this study we examined the effects of the novel immunosuppressant FTY720 and costimulation blockade by an anti-CD40L mAb (MR-1) in a stringent mouse model of SBTx. METHODS: SBTx was performed in mice with a full MHC mismatch (donors: C3H=H-2(k); recipients: C57BL/6=H-2(b)). Recipients were divided into four groups: 1, untreated group; 2, MR1 monotherapy (500 microg IV on days 0, 2, 4, and 7); 3, FTY720 monotherapy (1 mg/kg body weight PO for 14 consecutive days after transplantation); 4, FTY720 plus MR1-treated group. Graft rejection grades were assessed by H&E staining. Graft mesenteric lymph nodes (MLNs), Peyer's patches (PPs), as well as intraepithelial lymphocytes (IELs) and lamina propria lymphocytes (LPLs) were analyzed by flow cytometry and three-color immunofluorescence staining. RESULTS: Neither FTY720 nor MR1 monotherapy was efficient in preventing the rejection of mouse intestinal allografts, whereas FTY720 plus MR1 profoundly inhibited the rejection response at the 14th posttransplant day. The infiltration of host lymphocytes was reduced in graft MLNs, PPs, IELs, and LPLs by FTY720 therapy. FTY720 plus MR1 inhibited host CD8(+) T-cell infiltration in graft LPLs when compared with grafts treated with FTY720 only. Additionally, two subpopulations, CD11b(+high) Gr1(-) and CD11b(+intermediate) Gr1(+) cells, were decreased in FTY720-treated grafts. CONCLUSIONS: FTY720 plus MR1 efficiently delayed intestinal allograft rejection in a mouse model by preventing the infiltration of host lymphocytes, particularly of CD8(+) cells.     

Long-term Graft Acceptance in Rat Heart Transplantation by CTLA4Ig Gene Transfection Combined with FTY720 Treatment

CTLA4Ig strongly adheres to B7 molecules on antigen-presenting cells to block intracellular signal transduction via CD28 on helper T cells, which eventually inhibits immune responses. We have demonstrated that the administration to recipient animals of adenoviral vectors containing CTLA4Ig gene (adCTLA4Ig) prolonged graft survival, although the gene expression diminished in a time-dependent manner and the grafts were finally rejected. In addition, recipient animals treated with FTY720, a new immunosuppressant, exhibited a decrease in the number of peripheral lymphocytes due to apoptosis. In this study, we performed adCTLA4Ig transfection combined with FTY720 treatment in heart-grafted rats to determine if the combination could induce a mutual effect on graft survival. The recipient animals were given injections of 1 x 10(9) plaque-forming units of adCTLA4Ig via the tail vein immediately after grafting. On the day before transplantation we administered FTY720 orally to some of these animals at a dosage of 5 mg/kg and again on the day of transplantation. The median graft survival period in the adCTLA4Ig-only group was 27 days, whereas that in the combination group was markedly prolonged to 56 days. Of 15 grafts, 5 survived indefinitely. In these groups we observed detectable levels of CTLA4Ig in the sera 49 days after grafting; the levels were always higher in the combination group than in the adCTLA4Ig-only group. As a result, this study revealed that FTY720 and adCTLA4Ig have a potent mutual effect on graft survival during rat heart transplantation. Furthermore, it is highly possible that FTY720 enhances gene expression of adCTLA4Ig, which may be related to the long-term acceptance of grafts.     

Protection of mouse small bowel allografts by FTY720 and costimulation blockade

BACKGROUND: The clinical application of small bowel transplantation (SBTx) is hampered by its pronounced immunogenicity. We aimed to test the hypothesis that prolonged sequestration of lymphocytes in secondary lymphoid organs may enhance the alloprotective effect of costimulation blockade. METHODS: For this purpose, recipients of intestinal allografts were treated with MR1, FTY720, combined FTY720 plus MR1, or were left untreated. Grafts were examined 6 and 14 days after transplantation by applying a histologic rejection score, multiparameter-immunofluorescent staining, and flow cytometry. RESULTS: FTY720 or MR1 monotherapy did not prevent the rejection of mouse intestinal allografts, whereas combined therapy with FTY720 plus MR1 profoundly inhibited rejection at day 6 and day 14 after transplantation. In FTY720-treated mice infiltration of host lymphocytes in graft mesenteric lymph nodes, Peyer's patches, intraepithelial lymphocytes, and lamina propria lymphocytes (LPLs) was reduced on day 6. Anti-CD40L antibody improved the rejection score at day 14 but had no effect at day 6. Importantly, host CD8 T-cell infiltration in graft LPLs was significantly reduced compared with all other groups. CONCLUSION: FTY720 plus MR1 effectively inhibited intestinal allograft rejection in mice, possibly by enhancing the alloprotective effects of costimulation blockade by prolonged sequestration of lymphocytes in secondary lymphoid organs.     

Sphingosine 1-phosphate receptor agonism impairs skin dendritic cell migration and homing to secondary lymphoid tissue: association with prolonged allograft survival

The novel immunomodulator FTY720 is a prototypic sphingosine-1-phosphate (S1P) receptor agonist that regulates lymphocyte migration and prolongs allograft survival. Skin dendritic cells (DC) play important roles in cutaneous immunity. We investigated the migration and function of skin DC exposed to FTY720 in vivo, or to its metabolite FTY720 phosphate (P) in vitro. C57BL/10 (H2(b)) recipient (but not donor) FTY720 treatment prolonged median skin C3H (H2(k)) allograft survival significantly, from 12 to 34.5 days. Non-transplanted, FTY720-treated mice revealed a marked increase in skin DC, although total DC in skin-draining lymph nodes (DLN) were unchanged compared with controls. Fewer allogeneic donor DC migrated to DLN of FTY720-treated graft recipients. DC that migrated from the skin of FTY720-treated mice showed reduced MHC class II, CD86 and CCR7 expression, suggesting impaired migratory potential to secondary lymphoid tissue, that correlated with DC retention in skin, and reduced T cell stimulatory activity. Fewer DC migrated from normal skin explants exposed to the FTY720 metabolite, FTY720P than to control medium. DC that did migrate expressed lower levels of MHC class II, CD86 and CCR7, and inferior T cell stimulatory ability. These data demonstrate S1P signaling regulates skin DC trafficking and modulates MHC class II, costimulatory, and homing receptor molecule expression that impairs their ability to elicit allogeneic T cell responses.     

Adoptive transfer of FTY720‐treated immature BMDCs significantly prolonged cardiac allograft survival

A sphingosine 1 phosphate receptor modulator, FTY720, has been used to alleviate symptoms in allotransplantation and autoimmune disease models with impressive efficacy, while it only achieved moderate success in clinical trials. Infusion of immature bone marrow‐derived dendritic cell (BMDC) progenitors before transplantation could induce donor specific tolerance. In this study, we investigated the possibility of using FTY720‐DCs (FTY720‐treated immature BMDCs) to prevent severe alloimmune response. Our results indicate that FTY720‐DCs could markedly prolong graft survival compared with Ctrl‐DCs (nonconditioned immature BMDCs) as manifested by reduced inflammatory infiltration into the graft. IFN‐γ production by CD4⁺ and CD8⁺ T cells were significantly reduced, while FoxP3⁺ regulatory T cells among CD4⁺ T cells were upregulated. Although FTY720 seldom altered the phenotype or the phagocytosis of BMDCs in vitro, it severely hampered their capability to trigger antigen‐specific and allogeneic T‐cell response. When splenic T cells were co‐cultured with FTY720‐DCs, the proportion of regulatory T cells increased, accompanied by elevated IL‐10 production. Consistently, infusion of FTY720‐DCs could preferentially promote Treg proliferation and upregulate PD‐1 expression on conventional T cells in allogeneic mature BMDC priming experiment. These results suggest that infusion of FTY720‐DCs before cardiac transplantation could significantly prolong functional graft survival by acting as a balancer of alloimmune response.     

Effect of a novel immunosuppressant, FTY720, on allograft survival after renal transplant in rats

FTY720 was developed by chemical modification of ISP-1 which was purified from culture filtrates of an ascomycete, Isaria sinclairii. We evaluated the effect of FTY720 on allograft survival using a rat renal transplantation model in which Wistar King Aptekman Hokkaido rats (WKAH, RT1(K)) served as the organ donor and Lewis rats (LEW, RT1(l)) as the recipient. WKAH renal allografts were acutely rejected by the untreated LEW recipients at a mean graft survival +/- SD of 7.2 +/- 0.4 days (n = 5). Consecutive oral administration of FTY720 following transplantation significantly prolonged allograft survival in a dose-dependent manner over the range of 0. 05-3 mg/kg/day. The mean allograft survival of the recipients treated with FTY720 at a doses of 0.05, 0.1, 0.5, 1, and 3 mg/kg/day was 12.2 +/- 3.3 (n = 5, p < 0.05, vs. untreated host), 11.2 +/- 2.4 (n = 5, p < 0.05, vs. untreated host), 13.6 +/- 0.9 (n = 5, p < 0.01, vs. untreated host), 14.6 +/- 1.7 (n = 5, p < 0.01, vs. untreated host) and 20.2 +/- 0.8 days (n = 5, p < 0.01, vs. untreated host). In the recipients treated with FTY720 (3 mg/kg/day), the number of peripheral blood lymphocytes significantly decreased. From the results of the flow cytometric study, FTY720 significantly diminished the percentage of interleukin-2 receptor (IL-2R)-positive cells in the allografts (6.34 +/- 0.81% in the untreated recipients vs. 3.10 +/- 0.86% in the recipients treated with FTY720, p < 0.05). As to the CD4/CD8 ratio of splenic cells and graft infiltrate, there was no significant difference between the untreated hosts and the recipients treated with FTY720. In conclusion, FTY720 significantly extended rat renal allograft survival and the immunosuppressive effects of FTY720 may be due to a reduction in not only the number of peripheral lymphocytes but also the percentage of IL-2R-positive cells in the allografts.     

FTY720 inhibits TH1-mediated allogeneic humoral immune response

Phosphorylated FTY720 is an analog of Sphingosine 1 Phosphate (S1P) with immunosuppressive activity that negatively regulates the expression of S1P-Receptor 1. It also inhibits the migration of CD4 and CD8 single-positive T cells from the thymus to the periphery, sequesters peripheral blood lymphocytes in lymph nodes and Peyer's patches, and delays the exit of effector T cells toward the graft. The aim of our work was to study the effect of FTY720 on the kinetics of skin allograft rejection in a fully mismatched model; euthymic (Euthy) versus thymectomized (ATX) C57BL/6 mice (haplotype H-2(b)) recipients of BALB/c mice (haplotype H-2(d)) donor cells. The animals were injected daily with FTY720 (1 mg/kg) intraperitoneally for 2 weeks. To monitor the humoral immune response, serum samples collected at day 0 (pre-immune) and at day 23 after skin graft rejection were examined using BALB/c thymocytes as antigens in flow cytometry. To confirm the effect of FTY720 on peripheral lymphocytes, peripheral blood was analyzed by flow cytometry. Euthy and ATX FTY720-treated mice showed prolongation of skin allograft survival when compared with nontreated Euthy and ATX controls (P < .005). Unexpectedly, FTY720-treated Euthy mice showed significantly delayed graft rejection when compared to similarly treated ATX mice (P < .005). The delayed graft rejection in FTY720-treated Euthy mice correlated with a reduced content of Th1-mediated IgG(2a) and IgG(2b) antibodies when compared with FTY720-treated ATX mice (P < .05). In conclusion, FTY720 delays the kinetics of allograft rejection in a fully mismatched model by inhibiting Th1-mediated humoral immune responses. The presence of the host thymus appears to be required for this phenomenon.     

Evidence that FTY720 induces rat thymocyte apoptosis

FTY720, a novel immunomodulator with the potential to improve immunosuppressive therapy after organ transplantation, is currently under clinical investigation. FTY720 drastically decreases blood lymphocytes, especially T cells, accelerating lymphocyte homing to secondary lymphoid organs. However, its immunosuppressive effects remain unknown. We investigated these effects in rat thymocytes. Rats were intramuscularly injected with 10mg/kg/day FTY720 or saline for 7days. Thymuses were removed on days 0, 1, 3, 5, 7 and 14 after treatment. Three-color analysis was performed with a flow cytofluorometer. Apoptotic nuclei in the tissue sections were identified by TUNEL. Genomic DNA was then extracted and samples were electrophoresed on 2.0% agarose gel. FTY720 reduced the total number of thymocytes and, with time, significantly reduced the percentage of CD4+8+ TCRalphabeta(negative/low) thymocytes. Light microscopy of thymuses of FTY720-treated rats revealed obvious reductions in the size of the cortical region. TUNEL analysis showed that FTY720 induced thymocyte apoptosis in the cortical region. Furthermore, DNA fragmentation was observed in thymocytes treated with FTY720, indicating thymocyte apoptosis. FTY720 reduced the number of CD4+8+ thymocytes before TCRalphabeta expression resulting in impaired thymocyte differentiation and maturation. This might be an immunosuppressive effect of FTY720.     

FTY720 in corneal concordant xenotransplantation

BACKGROUND.: Currently, there are no effective treatments for the control of corneal xenograft rejection. We evaluated the efficacy and mode of action of a novel immunosuppressant, FTY720, in a model of corneal xenograft transplantation. METHODS.: Rat-to-mouse corneal xenografts were performed and the effects of treatment with daily intraperitoneal injections of FTY720 (0.5 or 3.0 mg/kg/day) or saline from 2 days pretransplantation were assessed clinically. Immunohistochemical studies of the grafts and flow cytometry of the draining lymph node subpopulations were performed at the time of clinical rejection. RESULTS.: Treatment with FTY720 delayed the onset of corneal rejection, from 8 days postgraft in saline-treated mice to 12.0 +/- 0.89 days for low-dose FTY720 treatment and 15.6 +/- 3.1 days for high-dose FTY720 treatment (both P<0.001). Histologically, FTY-treated animals had a markedly reduced inflammatory response in the anterior chamber and cornea after replacement of the xenograft epithelium with normal healthy host epithelium. In contrast, saline-treated xenografts had persisting corneal epithelial defects and ulceration. In the draining lymph nodes, FTY720 not only inhibited the increase in the cell number observed in saline-treated recipients of xenografts, but also reduced the expression of activation markers on B cells (MHC class II and CD86). CONCLUSIONS.: FTY720 treatment significantly delayed rejection and decreased its severity in a dose-dependent manner in a rat-to-mouse model of corneal xenotransplantation. Since corneal xenograft rejection is mediated not by natural antibodies or CD8+ T cells directly, but by CD4+ T cells, the data from these experiments imply that FTY720 mediated its effect via CD4+ T cells.     

The presence of donor-reactive CD4 T cells in early-phase liver-induced tolerance in rats: analysis using donor passenger leukocytes from the recipient

In previous studies, we showed that the recipient spleen 12 h after liver transplantation included highly immunogenic donor passenger leukocytes (PLs) in the non-rejector rat strain combination (Lewis: LEW-->Wistar Furth: WF). Furthermore, we noted that giving anti-CD4 mAb to WF recipients at the time of liver grafting prolonged the liver damage due to primary rejection reaction, suggesting that CD4 T-cell regulation but not the deletional mechanism played a dominant role during the induction phase of tolerance in this combination. We proposed that in vitro CD4 T-cell response to the donor PLs from the recipient lymphoid organ may be observed in the early phase of tolerance induction. We initially observed donor-specific acceptance by 10 days after liver transplantation from the result of secondary heart transplantation, and showed that donor (LEW) PLs in recipient WF spleen 12 h after grafting were able to prime cytotoxic CD8 T cells in vivo. We then isolated functional donor PLs from the recipient WF spleen and established in vitro proliferation assay. When the enriched donor PLs were used as stimulator cells in the proliferation assay, a powerful alloimmunostimulatory ability was observed. Moreover, a potent response of recipient splenocytes to the PLs was observed on postoperative day 14. From these observations, we confirmed that clonal deletion of donor-reactive CD4 T cells did not participate in early phase of tolerance induction in this setting.     

Effect of peritransplant FTY720 alone or in combination with post-transplant tacrolimus in a rat model of cardiac allotransplantation

FTY720 is a recently discovered compound that is derived from the fungus Isaria sinclairii. Using a DA donor-to-LEW recipient rat combination, we assessed the efficacy of peritransplant FTY720 alone or in combination with post-transplant tacrolimus on the survival of cardiac allografts. Peritransplant FTY720 given orally at a dose of 5 mg/kg on days –1 and 0 prolonged graft survival from 5 to 13 days (P < 0.05). Combining peritransplant FTY720 with post-transplant tacrolimus resulted in a further prolongation of allograft survival. The lymphocyte count in transplanted rats decreased within 24 h to 46.6 %. Analysis of lymphocyte subsets by FACS revealed that FTY720 affected the total population of CD3-bearing T cells while the ratio of CD4 to CD8 cells remained unchanged. Kidney and liver biochemistry remained elevated for 2 weeks. In conclusion, FTY720 is a powerful immunosuppressive agent when used as induction therapy and may have an additive effect – perhaps a synergistic one – with post-transplant tacrolimus. Received: 27 October 1997 Received after revision: 23 March 1998 Accepted: 15 April 1998     

Leishmania (Leishmania) amazonensis Infection in Mice Treated With FTY720

In transplantation, parasite diseases are transmitted from the donor, or appear as de novo infections, or activate from a dormant insource as a consequence of immunosuppression. Clinical findings have shown that an intact immune system is crucial to prevent recurrence of Leishmania infection. We used BALB/c and C57BL/6 mice to evaluate the role of FTY720 in leishmaniasis. Mice inoculated with Leishmania (Leishmania) amazonensis were followed over 7 weeks for foot thickness measurements after initiation of FTY720 treatment. After 10 days of treatment, spleen, blood, and the foot were harvested for evaluation. BALB/c showed greater evident foot thickness than C57BL/6 mice. Oral treatment with FTY720 (1 mg/kg/d) over 10 days produced the same outcome. Increases in CD4⁺ and CD8⁺ T cells were observed after infection; FTY720 treatment was associated with a decrease in CD4⁺ T cells only in BALB/c mice, whereas CD8⁺ T cells were decreased in both mice strains. CD11b⁺ expression decreased after infection with a discrete increase after FTY720 treatment. Lymphopenia was observed among all FTY720-treated mice. In conclusion, we observed that FTY720 produced no worse an outcome as monotherapy in established infections with L (L) amazonensis.     

A novel immunosuppressant, FTY720, induces peripheral lymphodepletion of both T- and B cells and immunosuppression in baboons

OBJECTIVE: FTY720, a new immunosuppressant active in transplantation models, modulates lymphocyte re-circulation, leading to peripheral lymphopenia and increased lymphocytes in lymph nodes and Peyer's patches. Here, we investigated the susceptibility of baboons to FTY720 as an introductory study to transplantation protocols. METHODS: FTY720 was administered orally to Chacma baboons at 0.3 or 0.1 mg/kg/day for 3 days or at 0.03 mg/kg/day for 10 days. Haematological parameters, lymphocyte phenotype (CD3, CD4, CD8, CD20), cell apoptosis, ex vivo blood cell proliferation in response to mitogens and drug blood levels were monitored during treatment and up to 4 weeks thereafter. MAIN FINDINGS: FTY720 administered p.o. in baboons at 0.3 mg/kg/day caused a marked decrease in circulating lymphocytes within 4 h of treatment, reaching 60-80% decrease within 24-48 h. The effect of FTY720 was seen both on T- and B cells, although it was slightly more rapid/pronounced on T cells. CD4+ cells were slightly more affected than CD8+ cells. The response onset was faster and the duration longer at higher dose, but the maximal peripheral lymphodepletion achieved was similar within the dose range 0.03-0.3 mg/kg tested. Ex vivo mitogen-induced lymphoproliferation was drastically decreased after FTY720 treatment, corresponding to the reduced blood lymphocyte counts. The blood drug levels measured after FTY720 administration correlated well with the dose applied but there was a poor correlation between FTY720 blood levels and the extent of peripheral lymphodepletion, suggestive of a high tissue distribution of the drug. When compared with cynomolgus monkeys treated in the same way, baboons had a lower initial exposure and a slightly lower response 24 h after one or two doses of FTY720 0.03-0.3 mg/kg. However, the stabilized drug blood levels and peripheral lymphodepletion achieved after 7 days of FTY720 0.03 mg/kg/day were similar in both nonhuman primate species. CONCLUSIONS: FTY720 was well tolerated and was effective in terms of peripheral T- and B lymphodepletion in baboons, indicating that it could be used in protocols of allo- and xenotransplantation. The pharmacokinetic and pharmacodynamic profiles of FTY720 in baboons suggest the use of high induction doses to optimize immediate response followed by a reduced dose regimen for drug maintenance.     

FTY720 does not abrogate acute graft-versus-host disease in the dog leukocyte antigen-nonidentical unrelated canine model

BACKGROUND: Acute graft-versus-host disease (GVHD) remains a significant impediment to successful hematopoietic stem-cell transplantation (HSCT). Here, we examined the effectiveness of 2-amino-2-(2-[4-octylphenyl]ethyl)-1,3-propanediol hydrochloride (FTY720), an immunosuppressant that retraffics activated lymphocytes to secondary lymphoid organs, for the treatment of acute GVHD in an established dog leukocyte antigen-nonidentical unrelated canine HSCT model. METHODS: Dogs were given HSCT after conditioning with 920 cGy total body irradiation. The dogs received methotrexate 0.4 mg/kg/day on days 1, 3, 6, and 11 and FTY720 (5 mg/kg/day orally) after developing GVHD. RESULTS: Five of six dogs achieved engraftment, developed acute GVHD, and were treated with FTY720. FTY720 resulted in a profound decrease in lymphocytes and a temporary mitigation of clinical GVHD; however, GVHD recurred in all dogs. Four of five dogs were euthanized because of severe GVHD and the fifth because of severe inanition associated with moderate GVHD. CONCLUSIONS: Compared with controls, treatment of GVHD with FTY720 did not control this complication or significantly increase survival.     

CD8 T Cells Can Reject Major Histocompatibility Complex Class I-Deficient Skin Allografts

Following transplantation, recipient T cells can recognize and respond to donor antigens expressed directly on donor cells, and can respond to donor-derived peptides that have been processed and presented in the context of recipient MHC through the indirect pathway. Indirectly primed CD4⁺ T cells have been well studied in transplantation, but little information is available regarding whether indirectly primed CD8⁺ T cells participate in rejection. To address this, we placed MHC class I-deficient D^bK^b knockout skin grafts onto allogeneic H-2 ^k SCID recipients followed by adoptive transfer of purified H-2 ^k CD8⁺ T cells. The MHC class I-deficient grafts were rejected and only CD8⁺ T cells were detectable in the recipient lymphoid organs and in the skin grafts. Immunohistochemical analysis showed that CD8⁺ T cells were found in close proximity to vascular endothelial cells and to recipient infiltrating macrophages, suggesting specific interactions. The data demonstrate that cross-primed polyclonal CD8⁺ T cells can function as active participants in the effector phase of rejection. The findings confirm and extend previous studies using a monoclonal TCR transgenic T cell and shed light on mechanisms of acute and chronic graft injury that are potentially relevant to human transplant recipients.