FTY720, a novel transplantation drug, modulates lymphocyte migratory responses to chemokines

FTY720 markedly increases alloengraftment but does not eliminate host anti-donor T cells that cause graft rejection on its withdrawal

The immunomodulator FTY720 (FTY) is beneficial in models of graft-versus-host disease, solid organ transplantation, and autoimmunity and has been approved for use in patients with multiple sclerosis. FTY modifies the homing and migration of many cell types. We report that FTY has profound positive and negative effects on allogeneic bone marrow (BM) engraftment in sublethally irradiated recipients. FTY increased donor hematopoietic progenitors in the BM, resulting in high donor engraftment in the B cell, myeloid cell, and natural killer cell, but not T cell, lineages. Donor T cell progenitors within the thymus of FTY-treated recipients were dramatically reduced, resulting in a lack of donor T cell reconstitution. In addition to preventing the ingress of donor (and host) T cell progenitors, FTY prevented the egress of fully functional host CD4+CD8- and CD4-CD8+ thymocytes that on cessation of FTY administration were able to exit from the thymus and contribute to a rapid and complete rejection of a well-established donor BM graft. When used in combination with anti-CD40L mAbs to block the CD40L:CD40 costimulatory pathway, FTY markedly enhanced anti-CD40L mAb-mediated alloengraftment promotion. In contrast to FTY alone, the combination of anti-CD40L mAb and FTY resulted in a surprisingly stable, multilineage, long-term donor chimerism. These data illustrate FTY's profound migration modulating effects and suggest a use in combinatorial therapy in achieving stable alloengraftment under nonmyeloablative conditions.

Role of early growth response 1 in liver injury

Liver injury is a sophisticated pathophysiological process caused by many factors. Currently, the role of early growth response 1 (EGR1) in liver injury is still controversial. Some studies show that EGR1 can amplify the systemic inflammatory response and promote apoptosis in galactosamine/lipopolysaccharide-induced acute liver injury and alpha-naphthylisothiocyanate (ANIT)-induced intrahepatic cholestasis as well as other non-liver injuries, while some other studies indicate that EGR1 protects the liver from CCl₄ exposure by regulating the expression of inducible nitric oxide synthase, cyclooxygenase-2, and tumor necrosis factor-α-regulated genes that have hepatoprotective function.

Local inactivation of sphingosine 1-phosphate in lymph nodes induces lymphopenia

Sphingosine 1-phosphate (S1P) initiates T and B cell exit from lymphoid tissues by activating the S1P(1) receptor on lymphocytes. To define the mechanistic details of this ligand-receptor interaction, the biological activity of the S1P-blocking Ab Sphingomab was investigated. Treatment of mice with Sphingomab resulted in blood B and T cell lymphopenia. Although Sphingomab blocked S1P(1)-mediated calcium flux and receptor downregulation by S1P in vitro, plasma from Sphingomab-treated mice demonstrated a 4-fold increase in S1P concentration and largely retained its stimulating activity on S1P receptors. Plasma-borne S1P was obviously not sufficiently inactivated by Sphingomab to account for the observed lymphopenia. Therefore, we addressed the local S1P-blocking activity of Sphingomab in spleen and peripheral lymph nodes (pLNs) as a potential cause of PBL depletion. Transwell chemotaxis assays revealed the migration of freshly isolated splenocytes, but not pLN cells to S1P. However, chemotaxis of pLN cells was regained after culture in S1P-low medium, and pLN cells isolated from Sphingomab-treated mice also revealed enhanced chemotaxis to S1P, indicating substantial local inactivation of S1P in pLN after Sphingomab treatment. We conclude that treatment with the S1P-blocking Ab Sphingomab induces lymphopenia by inactivating S1P locally in pLN and not systemically in plasma. Consequently, the presence of local S1P amounts in secondary lymphoid organs contributes to B and T cell egress.

United airways: circulating Th2 effector cells in an allergic rhinitis model are responsible for promoting lower airways inflammation

BACKGROUND

Allergic rhinitis (AR) and asthma often coexist and are referred to as 'united airways' disease. However, the molecular and cellular pathways that are crucially involved in the interaction between upper and lower airways remain to be identified.

OBJECTIVE

We sought to assess whether and how AR exacerbates lower airway inflammation upon allergen challenge in mice.

METHODS

We previously developed an intranasal ovalbumin (OVA)-driven AR model, characterized by nasal eosinophilic inflammation, enhanced serum levels of OVA-specific IgE and Th2 cytokine production in cervical lymph nodes. In OVA-sensitized mice with or without AR, a lower airway challenge was given, and after 24 h, lower airway inflammation was analysed.

RESULTS

We found that AR mice were more susceptible to eosinophilic inflammation following a lower airway OVA challenge than OVA-sensitized controls. AR mice manifested increased numbers of eosinophils in bronchoalveolar lavage fluid and increased inter-cellular adhesion molecule-1 (ICAM-1) expression on lung endothelium, when compared with OVA-sensitized controls. Depletion of T cells in OVA-challenged AR mice completely abrogated all hallmarks of lower airway inflammation, including enhanced IL-5 and tissue eosinophilia. Conversely, adoptive transfer of Th2 effector cells in naïve animals induced lower airway eosinophilic inflammation after challenge with OVA. Blocking T cell recirculation during AR development by the spingosine-1 analogue FTY720 also prevented lower airway inflammation including ICAM-1 expression in AR mice upon a single lower airway challenge.

CONCLUSION

Our mouse model of 'united airways' disease supports epidemiological and clinical data that AR has a significant impact on lower airway inflammation. Circulating Th2 effector cells are responsible for lung priming in AR mice, most likely through up-regulation of ICAM-1.

FTY720 (fingolimod) in Multiple Sclerosis: therapeutic effects in the immune and the central nervous system

FTY720 (fingolimod) is a first-in-class sphingosine 1-phosphate (S1P) receptor modulator that was highly effective in Phase II clinical trials for Multiple Sclerosis (MS). FTY720 is phosphorylated in vivo by sphingosine kinase-2 to form the active moiety FTY720-phosphate that binds to four of the five G protein-coupled S1P receptor subtypes. Studies using conditional S1P1 receptor-deficient and sphingosine kinase-deficient mice showed that the egress of lymphocytes from lymph nodes requires signalling of lymphocytic S1P1 receptors by the endogenous ligand S1P. The S1P mimetic FTY720-phosphate causes internalization and degradation of cell membrane-expressed S1P1, thereby antagonizing S1P action at the receptor. In models of human MS and demyelinating polyneuropathies, functional antagonism of lymphocytic S1P1 slows S1P-driven egress of lymphocytes from lymph nodes, thereby reducing the numbers of autoaggressive TH17 cells that recirculate via lymph and blood to the central nervous system and the sciatic/ischiatic nerves. Based on its lipophilic nature, FTY720 crosses the blood-brain barrier, and ongoing experiments suggest that the drug also down-modulates S1P1 in neural cells/astrocytes to reduce astrogliosis, a phenomenon associated with neurodegeneration in MS. This may help restore gap-junctional communication of astrocytes with neurons and cells of the blood-brain barrier. Additional effects may result from (down-) modulation of S1P3 in astrocytes and of S1P1 and S1P5 in oligodendrocytes. In conclusion, FTY720 may act through immune-based and central mechanisms to reduce inflammation and support structural restoration of the central nervous system parenchyma. Beyond the autoimmune indications, very recent studies suggest that short-term, low-dose administration of FTY720 could help treat chronic (viral) infections. Differential effects of the drug on the trafficking of naïve, central memory and effector memory T cell subsets are discussed.

FTY720 (fingolimod) in renal transplantation

FTY720 (Fingolimod) is a novel immunomodulator with a mode of action that is completely different from classical immunosuppressants. FTY is a structural and functional analogue of the natural serum lipid, sphingosine, and is the first in a new class of drugs called sphingosine 1-phosphate receptor (S1P-R) modulators. This review discusses the recent findings on the mechanism of action, preclinical models and outlines the results of the ongoing clinical development program. FTY is highly effective in prolonging allograft survival in preclinical models of transplantation and in experimental models of autoimmune diseases. In clinical trials, this novel compound was investigated in de novo renal transplantation and in multiple sclerosis. Pharmacokinetics are characterized by a prolonged absorption phase, a large volume of distribution, and a long elimination half-life. FTY induces a rapid and transient decrease in lymphocyte counts, which supports the modulatory effects of the drug on lymphocyte sequestration. The most common adverse event was asymptomatic transient bradycardia, a pharmacodynamic effect modulated by atrial S1 P-R. FTY failed to show an improvement in efficacy for the prevention of renal allograft rejection in two large phase III studies. FTY treatment regimens were associated with impaired renal function and the development of macula edema. Consequently, the further development in renal transplantation was stopped. Because initial clinical studies strongly suggest that FTY is highly effective in multiple sclerosis FTY is now being explored in phase III studies for the treatment of demyelinating diseases, Ongoing studies in multiple sclerosis are eagerly awaited because they may provide novel therapeutic options for patients with autoimmune diseases.

Sphingosine kinase: biochemical and cellular regulation and role in disease

Sphingolipids have emerged as molecules whose metabolism is regulated leading to generation of bioactive products including ceramide, sphingosine, and sphingosine-1-phosphate. The balance between cellular levels of these bioactive products is increasingly recognized to be critical to cell regulation; whereby, ceramide and sphingosine cause apoptosis and growth arrest phenotypes, and sphingosine-1-phosphate mediates proliferative and angiogenic responses. Sphingosine kinase is a key enzyme in modulating the levels of these lipids and is emerging as an important and regulated enzyme. This review is geared at mechanisms of regulation of sphingosine kinase and the coming to light of its role in disease.

FTY720 treatment of kidney transplant patients: A differential effect on B cells, naïve T cells, memory T cells and NK cells

FTY720 alters lymphocyte recirculation and homing by interfering with S1P receptors on lymphocytes, possibly in combination with chemokine receptors, and induces a decrease in PBL counts. In fresh, whole blood samples of 14 kidney transplant patients, we analyzed by flow cytometry the effect of FTY on the number of NK cells, monocytes, naïve (CCR7+) T cells, memory (CCR5+) T cells and B cells. Patients treated with 0.5, 2.5 or 5mg FTY/day showed a strong decrease in T and B cell numbers. NK cells and monocytes were not affected. FTY reduced primarily naïve T cells. From the memory T cells (CCR5+), predominantly CD8 cells, 40-60% remained in the circulation. The majority of the CCR7+ cells disappeared from the circulation within 3-6h, while a further reduction was achieved later. The more slowly decrease in naïve CCR7+ T cell numbers was also observed in the group treated with 0.25mg FTY/day. Elispot assays revealed no IL-4 producing cells and a low frequency of IFN-gamma producing cells. We suggest that both CCR7 dependent and independent mechanisms are involved in the depletion of T cells from peripheral blood.

The S1P-analog FTY720 differentially modulates T-cell homing via HEV: T-cell-expressed S1P1 amplifies integrin activation in peripheral lymph nodes but not in Peyer patches

Sphingosine-1-phosphate (S1P) and its receptor S1P1 control T-cell egress from thymus and secondary lymphoid organs (SLOs). To further define the role of S1P1 in lymphocyte trafficking, we performed adoptive transfer experiments and intravital microscopy (IVM) using both S1P1-/- lymphocytes and recipient wild-type (WT) mice treated with FTY720, an immunosuppressant that downmodulates S1P receptors. S1P1 deficiency and FTY720 caused rapid disappearance of T cells from blood, prolonged retention in SLOs, and accumulation in bone marrow, but did not alter interstitial T-cell motility in peripheral lymph nodes (PLNs) as assessed by multiphoton IVM. However, S1P1-/- lymphocytes displayed reduced short-term homing to PLNs due to attenuated integrin-mediated firm arrest in high endothelial venules (HEVs). By contrast, S1P1-/- T cells homed normally to Peyer patches (PPs), whereas S1P1-/- B cells had a marked defect in homing to PPs and arrested poorly in PP HEVs. Therefore, S1P1 not only controls lymphocyte egress from SLOs, but also facilitates in a tissue- and subset-specific fashion integrin activation during homing. Interestingly, FTY720 treatment enhanced accumulation of both S1P1 sufficient and S1P1-/- T cells in PPs by enhancing integrin-mediated arrest in HEVs. Thus, FTY720 exerts unique effects on T-cell traffic in PPs that are independent of T-cell-expressed S1P1.

Pharmacokinetic/pharmacodynamic relationships of FTY720 in kidney transplant recipients

FTY720 is a new and effective immunosuppressive agent, which produces peripheral blood lymphopenia through a lymphocyte homing effect. We investigated the relationship between the dose of FTY720 or blood concentration (pharmacokinetics, PK) and peripheral lymphopenia (pharmacodynamics, PD) in 23 kidney transplant recipients randomized to receive FTY720 (0.25-2.5 mg/day) or mofetil mycophenolate (2 mg/day) in combination with cyclosporine and steroids. FTY720 dose, blood concentrations and lymphocyte counts were determined weekly before and 4 to 12 weeks after transplantation. The effect of PD was calculated as the absolute lymphocyte count or its reductions. PK/PD modeling was used to find the best-fit model. Mean FTY720 concentrations were 0.36 +/- 0.05 (0.25 mg), 0.73 +/- 0.12 (0.5 mg), 3.26 +/- 0.51 (1 mg), and 7.15 +/- 1.41 ng/ml (2.5 mg) between 4 and 12 weeks after transplantation. FTY720 PK was linear with dose (r(2) = 0.98) and showed low inter- and intra-individual variability. FTY720 produced a dose-dependent increase in mean percent reduction of peripheral lymphocyte counts (38 vs 42 vs 56 vs 77, P < 0.01, respectively). The simple Emax model [E = (Emax * C)/(C + EC50)] was the best-fit PK/PD modeling for FTY720 dose (Emax = 87.8 +/- 5.3% and ED50 = 0.48 +/- 0.08 mg, r(2) = 0.94) or concentration (Emax = 78.3 +/- 2.9% and EC50 = 0.59 +/- 0.09 ng/ml, r(2) = 0.89) vs effect (% reduction in peripheral lymphocytes). FTY720 PK/PD is dose dependent and follows an Emax model (EC50 = 0.5 mg or 0.6 ng/ml). Using lymphopenia as an FTY720 PD surrogate marker, high % reductions (~80%) in peripheral lymphocytes are required to achieve best efficacy to prevent acute allograft rejection.

Novel mediators of FTY720 in human lymphocytes

FTY720 (FTY), a novel immunosuppressive drug, can be distinguished from other immunosuppressive drugs by a completely different mechanism of action. FTY induces altered lymphocyte trafficking, leading to peripheral blood lymphopenia and to increased lymphocyte counts in lymph nodes. FTY mediates its immune-modulating effects by binding to sphingosine 1-phosphate receptors expressed on lymphocytes. In an attempt to identify mediators of the FTY-induced signal transduction, we used a proteomic approach. FTY-treated peripheral blood lymphocytes (PBLs) were investigated for the expression of 622 proteins. We identified 15 differentially expressed proteins in PBLs possibly related to FTY action. As indicated by protein function, several identified proteins could be linked to the cytoskeleton/cell motility, to cell adhesion, and vesicle trafficking. No changes were found concerning the expression of various apoptosis regulators as well as the immunophilins FKBP12 and calcineurin. Our data suggest that FTY affects cytoskeleton rearrangements, cell adhesion, and vesicle trafficking/sorting in human PBLs.

Structural and functional characteristics of S1P receptors

The sphingosine-1-phosphate (S1P) family of G protein-coupled receptors (GPCR) regulates essential cellular processes such as proliferation, migration, cytoskeletal organization, adherens junction assembly, and morphogenesis. S1P, a product from the breakdown of sphingomyelin, binds to the five members of this receptor family, S1P(1), S1P(2), S1P(3), S1P(4), and S1P(5), previously referred to as endothelial differentiation gene (EDG)-1, -5, -3, -6, and -8. S1P receptors are widely expressed in different tissues, so it is not surprising that the S1P receptor family regulates many physiological processes, such as vascular maturation, cardiac development, lymphocyte trafficking, and vascular permeability. FTY720, a new S1P receptor agonist, is undergoing clinical trials as an immunosuppressor. Understanding the physiological role of these receptors and the basics of the ligand-receptor interaction will potentially provide new therapies to control a variety of diseases.

Modulation of adaptive immune responses by sphingosine-1-phosphate

Sphingosine-1-phosphate (S1P) has long been recognized as a mediator of a variety of cell functions. A growing body of evidence has accumulated demonstrating its role in cell migration and as a mediator of growth factor-induced events. In recent years, it has become apparent that S1P also mediates many cytokine and chemokine functions. Cells of the immune system function and migrate in response to a complex network of cytokines and chemokines, and the outcome is determined by the interplay of the effects of these molecules on the target cell. S1P may be a bona fide component of these networks and influence the responses of cells to these immune modulators.

FTY720 attenuates hepatic ischemia-reperfusion injury in normal and cirrhotic livers

Hepatic ischemia-reperfusion injury is an inevitable consequence during liver surgery. The outcome is particularly poor in cirrhotic livers, which are more prone to hepatic ischemia-reperfusion injury. We aim to study whether FTY720 could attenuate hepatic ischemia-reperfusion injury both in normal and in cirrhotic livers. We applied a 70% liver-ischemia (60 min) model in rats with normal or cirrhotic livers. FTY720 was given 20 min before ischemia and 10 min before reperfusion (1 mg/kg, i.v.). Liver tissues and blood were sampled at 20 min, 60 min, 90 min, 6 h and 24 h after reperfusion for detection of MAPK-Egr-1, Akt pathways and caspase cascade. Hepatic ultrastructure and apoptosis were also compared. FTY720 significantly improved liver function in the rats with normal and cirrhotic livers. Akt pathway was activated at 6 and 24 h after reperfusion. FTY720 significantly down-regulated Egr-1, ET-1, iNOS and MIP-2 accompanied with up-regulation of A20, IL-10, HO-1 and Hsp70. MAPK (Raf-MEK-Erk) pathway was down-regulated. Hepatic ultrastructure was well maintained and fewer apoptotic liver cells were found in the FTY720 groups. In conclusion, FTY720 attenuates ischemia-reperfusion injury in both normal and cirrhotic livers by activation of cell survival Akt signaling and down-regulation of Egr-1 via Raf-MEK-Erk pathway.

FTY720: from bench to bedside

FTY720, a synthetic myriocin analogue derived from culture filtrates of Isaria sinclairii, is a novel immunosuppressant that in experimental animals and nonhuman primates produces lymphocytopenia and prolongs allograft survival in dose-dependent fashion. FTY720 exerts synergistic interactions not only with calcineurin antagonists, but also with proliferation signal inhibitors. These interactions offer the possibility of reducing exposure to and mitigating toxicity of existing drugs. The mechanism of drug action is not entirely clear. FTY720 appears to undergo phosphorylation by sphingosine phosphokinase 2, rendering it capable of interacting with the specific G protein-linked receptors for its structural homologue-sphingosine-1-phosphate. However, it is not clear how this interaction leads to emigration of lymphocytes from the peripheral blood and sequestration in secondary lymphoid structures. Present theories suggest that the drug prevents emigration rather than directing the onset of sequestration. Thus, the drug is the archetype of a new class of agents that alter lymphocyte homing patterns: the adhesion-migration paradigm. These modalities reduce interstitial infiltration of grafts and attenuate their release from lymph nodes. Since FTY720 seems to spare nonspecific elements of host resistance, it may not only represent a useful addition to the immunosuppressive armamentarium but also address the not infrequent complications of infections associated with existing therapies.

Lysophospholipid receptors: signaling and biology

Lysophospholipids (LPs), such as lysophosphatidic acid and sphingosine 1-phosphate, are membrane-derived bioactive lipid mediators. LPs can affect fundamental cellular functions, which include proliferation, differentiation, survival, migration, adhesion, invasion, and morphogenesis. These functions influence many biological processes that include neurogenesis, angiogenesis, wound healing, immunity, and carcinogenesis. In recent years, identification of multiple cognate G protein-coupled receptors has provided a mechanistic framework for understanding how LPs play such diverse roles. Generation of LP receptor-null animals has allowed rigorous examination of receptor-mediated physiological functions in vivo and has identified new functions for LP receptor signaling. Efforts to develop LP receptor subtype-specific agonists/antagonists are in progress and raise expectations for a growing collection of chemical tools and potential therapeutic compounds. The rapidly expanding literature on the LP receptors is herein reviewed.

Attenuation of small-for-size liver graft injury by FTY720: significance of cell-survival Akt signaling pathway

To investigate the protective mechanism of FTY720 in small-for-size liver grafts, we applied a rat orthotopic liver transplantation model using 40% of liver grafts. FTY720 was administered (1 mg/kg, i.v.) at 20 min before graft harvesting in the donor, immediately before total hepatectomy and immediately after graft reperfusion in the recipient. The 7-day graft survival rates in the FTY720 group were significantly improved compared with the control group [100% (6/6) vs. 40% (4/10), p = 0.034]. FTY720 significantly reduced serum ALT and AST levels at 24 h after liver transplantation. The cell-survival Akt signaling pathway was activated in FTY720 groups by phosphorylation of Glycogen Synthase Kinase-3beta, Bad and Forkhead Transcription Factor at 6 and 24 h after liver transplantation. The cleaved-caspases 3, 7 and 9 were down-regulated, accompanied with less apoptotic nuclei after FTY720 treatment. Acute-phase inflammatory MAPK pathway was down-regulated by dephosphorylation of c-Raf, Mek and Erk in the treatment groups. A20 and endothelial nitric oxide synthase were up-regulated together with down-regulation of iNOS. Hepatic sinusoids were well preserved in the FTY720 group but disrupted in the control group. In conclusion, FTY720 attenuates small-for-size liver graft injury by activation of cell-survival Akt signaling and down-regulation of the MAPK pathway.

FTY720-enhanced T cell homing is dependent on CCR2, CCR5, CCR7, and CXCR4: evidence for distinct chemokine compartments

FTY720 stimulates CCR7-driven T cell homing to peripheral lymph nodes (LN) by direct activation of sphingosine 1-phosphate receptors, along with the participation of multidrug transporters, 5-lipoxygenase, and G protein-coupled receptors for chemokines. In this study, we demonstrate that FTY720 also directly stimulates in vitro T cell chemotaxis to CCR2-CCL2, but not to a variety of other chemokines, including CCR5-CCL3/4/5 and CXCR4-CXCL12. FTY720 influences CCR2-CCL2-driven migration through activation of the multidrug transporters, Abcb1 and Abcc1, and through 5-lipoxygenase activity. In vivo administration of FTY720 induces chemokine-dependent migration of T cells in the thymus, peripheral blood, LN, and spleen. The CCR7 and CCR2 chemokine ligands are required for both T cell sequestration in LN and thymic T cell egress following FTY720 administration. Furthermore, FTY720 administration uncovers a requirement for CXCR4 ligands for LN homing, but not for thymic egress, and CCR5 for thymic egress, but not LN homing. FTY720-driven splenic and peripheral blood T cell egress are both independent of CCR2, CCR5, CCR7, or CXCR4. These results indicate that FTY720- and sphingosine 1-phosphate receptor-stimulated T cell migration are dependent on the restricted usage of chemokine receptor-ligand pairs within discrete anatomic compartments.

Chemokine regulation of naïve T cell traffic in health and disease

A central feature of the immune response is the precise spatio-temporal convergence of T cells and antigen presenting cells (APC) in particular microenvironments within secondary lymphoid organs (SLO). CCR7 and its ligands CCL19 and CCL21 have been identified as the gatekeepers for both naïve T lymphocytes and dendritic cells (DC) to these defined anatomical compartments. A new perception on the regulation of lymphocyte traffic in lymph nodes (LN) has come from observations that sphingosine-1-phosphate (S1P) receptor agonists affect T cell entry and exit from these organs. Recent developments in intravital microscopy (IVM) techniques reveal unexpected autonomous random motion of lymphocytes within secondary lymphoid tissues, and provoke questions about the mechanisms that guide their compartmental navigation.

Sphingosine-1-phosphate receptors: receptor specificity versus functional redundancy

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that has recently been shown to bind cell surface S1P receptors (previously called endothelial differentiation gene (Edg) receptors), which are members of the G-protein-coupled family of receptors. Signaling via S1P is a complex process, as cells usually express a number of these receptors on their surfaces. Many of the S1P receptors share common G-proteins, invoking the question of how these receptors are specific in their actions. This review describes the coupling pathways of S1P receptors, and highlights the in vitro and in vivo evidence for the "uniqueness" of each receptor in activating downstream signaling pathways, taking the effect of S1P on migration as an example.

FTY720 prolongs clear corneal allograft survival with a differential effect on different lymphocyte populations

BACKGROUND

FTY720 is a potent immunomodulator with unique effects on lymphocyte homing and has recently proved to be safe and effective in renal transplantation in man. The authors investigated the potency of FTY720 in inhibiting allograft rejection in the rat model of orthotopic allogeneic penetrating keratoplasty.

METHODS

Penetrating keratoplasties were performed using Fisher rats as donors and Lewis rats as recipients or donors: group 1 (n = 10), allogeneic control; group 2 (n = 10), Lewis/Lewis syngeneic control; group 3 (n = 9), mycophenolate mofetile (MMF) 40 mg/kg; group 4 (n = 10), FTY720 1.2 mg/kg; group 5 (n = 8), FTY720 0.3 mg/kg. Four animals from each group were sacrificed for immunohistological evaluation on day 14. Medication in the therapy groups was given for 18 days.

RESULTS

The mean (SD) rejection free graft survival time was 11.3 (0.8) days for the allogeneic control (group 1), 24.6 (2.5) days for group 3 (MMF), 44.5 (5.7) days for group 4 (FTY720 1.2 mg/kg), and 35.3 (5.7) days for group 5 (FTY720 0.3 mg/kg) (p<0.05). The allogeneic control showed a dense infiltration with CD4+, CD8+, CD161+ (NK-cells), CD25+ (IL2 receptor), and macrophages. In the therapy groups the density of infiltrating CD4+, CD8+, CD161+ (NK-cells), and CD25+ (IL2 receptor) cells was notably reduced compared with the allogeneic control (p<0.05). In group 5 however, the reduction of infiltration by CD4+ cells was higher than the reduction of infiltration by CD8+ (p<0.05) and CD161+ (NK) cells.

DISCUSSION

Oral immunosuppression with FTY720 significantly prolongs corneal allograft survival in this transplant model. The results suggest that FTY720 has a different effect on certain lymphocyte populations. CD4+ cells seem to be more affected than CD8+ cells and NK-cells.

Immune Responses in Kidney Preservation and Reperfusion Injury

Organ preservation and reperfusion injury have significant detrimental effects on both short- and long-term organ function. Ischemia reperfusion injury (IRI) underlies organ transplant dysfunction, myocardial infarction, stroke, and shock. Multiple molecular pathways are engaged in reactive oxygen production, apoptosis, signaling, and tissue regeneration. There has been an increased understanding of the important role of immune and inflammatory pathways in IRI, both in humans and in experimental models. Both cellular and soluble components of the immune system are directly activated during IRI, and there is evidence that immune mediators directly contribute to organ dysfunction. Immune activation during IRI likely underlies the enhanced immunogenicity of ischemic organs, with resultant increased rejection and fibrosis. Novel human therapies targeting T and B cells for classic immune diseases can now be considered to prevent and treat IRI. Organ preservation injury and cold ischemia could well have distinct pathophysiology from warm IRI and represent an opportunity to develop improved preservation methods.

Therapeutic effects of a new lymphocyte homing reagent FTY720 in interleukin-10 gene-deficient mice with colitis

BACKGROUND

FTY720 is a novel reagent that possesses potent immunosuppressive activity. The immunosuppression induced by FTY720 is mediated by completely different mechanisms from those of conventional immunosuppressants, that is, by altering the tissue distribution of lymphocytes rather than inhibiting activation. In this study, we examined the efficacy of FTY720 in the treatment of chronic colitis in an interleukin-10 gene-deficient (IL-0-/-) mouse model.

METHODS

FTY720 was administered orally for 4 weeks to IL-10-/- mice with clinical signs of colitis. The gross and histologic appearance of the colon and the numbers, phenotype, cytokine production, and apoptosis of lymphocytes were compared with those characteristics in a control group.

RESULTS

Single-dose administration of FTY720 resulted in the sequestration of circulating lymphocytes within the secondary lymphoid tissues. Four-week administration resulted in a significant reduction of the CD4+ T lymphocytes subpopulation in the colonic lamina propria and IFN-gamma production of the colonic lymphocytes, accompanied by a significant decrease in the severity of colitis.

CONCLUSIONS

Treatment of established colitis in IL-10-/- mice with FTY720 ameliorated the colitis, probably as a result of decreasing the number of lymphocytes in the colonic mucosa and an associated reduction in IFN-gamma production.

FTY720 MEDIATES APOPTOSIS-INDEPENDENT LYMPHOPENIA IN HUMAN RENAL ALLOGRAFT RECIPIENTS: DIFFERENT EFFECTS ON CD62L+ AND CCR5+ T LYMPHOCYTES

BACKGROUND

The sphingolipid FTY720 (FTY), a novel immune modulator, induces lymphopenia and prevents allograft rejection. This study was designed to study the effect of FTY on lymphocyte subpopulations and apoptosis in stable renal allograft recipients.

METHODS

Stable renal allograft recipients received a single oral dose of 0.25 to 3.5 mg of FTY (n= 13) or placebo (n= 3). Whole blood was drawn immediately before and at 4, 8, 12, 24, 72, and 96 hr after administration. The number of lymphocyte subpopulations, with an emphasis on surface markers involved in lymphocyte migration, was analyzed by flow cytometry. Apoptotic lymphocytes were detected following Annexin V-FITC/PI staining. Lymphocyte mobility was investigated in a modified Boyden chamber.

RESULTS

FTY induced a transient lymphopenia by an apoptosis-independent mechanism. In vitro experiments with peripheral blood mononuclear cells (PBMC) confirmed that clinically relevant concentrations of FTY (0.1 microM) increased lymphocyte mobility, whereas only suprapharmacologic concentrations of FTY (10 microM) could induce apoptosis. FTY-treated patients had reversible changes in the composition of peripheral lymphocyte subpopulations. CD62L+ T cells decreased to the greatest extent (-57%). In contrast, CCR5+ T-cell counts declined only marginally (-10%). In vitro, treatment of PBMC with FTY (1 mM-10 microM) did not induce changes in the expression of these surface markers.

CONCLUSIONS

The data indicate that FTY mediates apoptosis-independent lymphopenia in human renal allograft recipients. FTY-induced lymphopenia preferentially affects CD62L+ and CCR5- T-lymphocyte subpopulations.

Protective effects of sphingosine 1-phosphate in murine endotoxin-induced inflammatory lung injury

Our prior in vitro studies indicate that sphingosine 1-phosphate (S1P), a phospholipid angiogenic factor, produces endothelial cell barrier enhancement through ligation of endothelial differentiation gene family receptors. We hypothesized that S1P may reduce the vascular leak associated with acute lung injury and found that S1P infusion produced a rapid and significant reduction in lung weight gain (more than 50%) in the isolated perfused murine lung. The effect of S1P was next assessed in a murine model of LPS-mediated microvascular permeability and inflammation with marked increases in parameters of lung injury at both 6 and 24 hours after intratracheal LPS. Each parameter assessed was significantly reduced by intravenous S1P (1 microM final) and in selected experiments by the S1P analogue FTY720 (0.1 mg/kg, intraperitoneally) delivered 1 hour after LPS. S1P produced an approximately 40-50% reduction in LPS-mediated extravasation of Evans blue dye albumin, bronchoalveolar lavage protein content, and lung tissue myeloperoxidase activity (reflecting phagocyte infiltration). Consistent with systemic barrier enhancement, S1P significantly decreased Evans blue dye albumin extravasation and myeloperoxidase content in renal tissues of LPS-treated mice. These studies indicate that S1P significantly decreases pulmonary/renal vascular leakage and inflammation in a murine model of LPS-mediated acute lung injury and may represent a novel therapeutic strategy for vascular barrier dysfunction.

The effect of immunomodulators on prevention of autoimmune diabetes is stage dependent: FTY720 prevents diabetes at three different stages in the diabetes-resistant biobreeding rat

BACKGROUND

Autoimmune diabetes of the diabetes-resistant biobreeding (DRBB) rat shares similarities with diabetes in humans and has stages of diabetes that can be controlled and compared. FTY720 is an immunomodulator that has been efficacious in transplant and autoimmune models without inducing an immunosuppressed state. We determined the stages of diabetes that are affected by FTY720 in the DRBB rat.

METHODS

Autoimmune diabetes was induced with RT6.1 T-cell-depleting antibody and polyIC starting at 4 weeks of age. FTY720 (1 mg/kg/d) was started at day 0, 5, 7, and 14 following the start of depletion. The rats that did not develop diabetes were maintained for 60 d following the last dose of FTY720 before undergoing a second course of depletion.

RESULTS

FTY720 starting at day 0, 5, 7, and 14 of depletion prevented diabetes in 100, 100, 50, and 20% of the DRBB rats compared to 0% of the control rats. The surviving rats in the 5-, 7-, and 14-d groups developed diabetes after FTY720 treatment was stopped. Histological examination indicated insulitis in the control rats between day 7 and 11 of depletion and end-stage insulitis by day 18 of depletion compared to negligible insulitis in rats without diabetes. Redepletion in the surviving day 0 rats resulted in development of diabetes in 25% of these rats compared to none of the age-matched controls.

SUMMARY

FTY720 can prevent autoimmune diabetes, if administered before and/or during stimulation and expansion of the autoreactive T cells or in the early stages of insulitis. The effectiveness diminishes with each successive stage of diabetes.

The sphingosine 1-phosphate receptor agonist FTY720 supports CXCR4-dependent migration and bone marrow homing of human CD34+ progenitor cells

The novel immunosuppressant FTY720 activates sphingosine 1-phosphate receptors (S1PRs) that affect responsiveness of lymphocytes to chemokines such as stromal cell-derived factor 1 (SDF-1), resulting in increased lymphocyte homing to secondary lymphoid organs. Since SDF-1 and its receptor CXCR4 are also involved in bone marrow (BM) homing of hematopoietic stem and progenitor cells (HPCs), we analyzed expression of S1PRs and the influence of FTY720 on SDF-1/CXCR4-mediated effects in human HPCs. By reverse transcriptase-polymerase chain reaction (RT-PCR), S1PRs were expressed in mobilized CD34+ HPCs, particularly in primitive CD34+/CD38- cells. Incubation of HPCs with FTY720 resulted in prolonged SDF-1-induced calcium mobilization and actin polymerization, and substantially increased SDF-1-dependent in vitro transendothelial migration, without affecting VLA-4, VLA-5, and CXCR4 expression. In nonobese diabetic-severe combined immunodeficient (NOD/SCID) mice, the number of CD34+/CD38- cells that homed to the BM after 18 hours was significantly raised by pretreatment of animals and cells with FTY720, tending to result in improved engraftment. In addition, in vitro growth of HPCs (week-5 cobblestone area-forming cells [CAFCs]) was 2.4-fold increased. We conclude that activation of S1PRs by FTY720 increases CXCR4 function in HPCs both in vitro and in vivo, supporting homing and proliferation of HPCs. In the hematopoietic microenvironment, S1PRs are involved in migration and maintenance of HPCs by modulating the effects of SDF-1.

FTY720 exerts differential effects on CD4+ and CD8+ T-lymphocyte subpopulations expressing chemokine and adhesion receptors

BACKGROUND

FTY720 (FTY), a novel immunomodulator with the potential to improve immunosuppressive therapy after organ transplantation, is currently under clinical investigation. Previous experimental animal studies have shown that FTY has a unique mechanism of action associated with altered lymphocyte recirculation.

METHODS

Participating in a phase I clinical trial, we studied the pharmacodynamic effects of FTY in stable renal allograft recipients. We analysed the effect of FTY on surface marker expression on T-cell subpopulations by flow cytometry.

RESULTS

A single oral dose of FTY (0.25-3.5 mg) significantly reduced peripheral lymphocyte counts by 30-70%. FTY reduced all T-lymphocyte subsets, CD4(+) cells more than CD8(+) cells. However, we observed that lower doses of FTY (0.25-2 mg, n = 11) did not affect peripheral CD4(+)CCR5(+) T-lymphocyte counts, while the highest FTY dose of 3.5 mg (n = 2) exerted a rapid reduction of CD4(+)CCR5(+) cells. Peripheral CD8(+)CCR5(+) T-lymphocyte counts were reduced by either low (0.25-2 mg) or high (3.5 mg) doses of FTY. In contrast to CCR5(+) cells, cells expressing CD62L were preferentially reduced after administration of FTY. In particular, CD4(+)CD62L(+) T cells declined after treatment. CD4(+) and CD8(+) T-lymphocyte subpopulations expressing the other chemokine and adhesion receptors (CXCR4, CD11a and CD49d) were reduced to a similar extent as compared with overall CD4(+) or CD8(+) T-lymphocyte counts.

CONCLUSIONS

Despite the limited number of patients, especially in the placebo (n = 3) and the high-dose groups (n = 2), our observations suggest that FTY exerts differential effects on T-cell subpopulations. FTY predominantly reduces CD4(+)CD62L(+) cells in the peripheral blood suggesting increased migration into lymph nodes. It seems that only FTY doses above 2 mg are able to reduce peripheral CD4(+)CCR5(+) T lymphocytes, which are potentially capable of infiltrating into the allograft during rejection.

The immunosuppressant FTY720 down-regulates sphingosine 1-phosphate G-protein-coupled receptors

FTY720 is an immunosuppressant that reduces circulating levels of naïve lymphocytes by increasing their localization and sequestration in secondary lymphoid organs. It is considered to be an agonist for sphingosine 1-phosphate (S1P) G protein-coupled receptors (GPCRs) after phosphorylation at micromolar concentrations. We now describe its nonagonist and noncompetitive inhibitory activity at low nanomolar concentrations for types 1 and 5 S1P-GPCRs and of moderate potency for type 2 S1P-GPCRs. FTY720 blocks S1P signaling through S1P1,2,5 by inducing their internalization and intracellular partial degradation without affecting S1P3 or S1P4. S1P-R internalization is maximal several hours after only seconds of incubation with FTY720 at 37 degrees C and washing, and continues for days before recovery of surface expression and functions. The timing and extent of S1P-R internalization are highly dependent on FTY720 concentration. FTY720 is therefore an S1P-GPCR-selective and noncompetitive inhibitor with a unique mechanism of action.

Pharmacodynamics, pharmacokinetics, and safety of multiple doses of FTY720 in stable renal transplant patients: a multicenter, randomized, placebo-controlled, phase I study

BACKGROUND

FTY720, a novel immunomodulator, displays potent immunosuppressive activity in a variety of preclinical transplant models. This study examined the safety, pharmacodynamics, and pharmacokinetics of multiple doses of FTY720 in stable renal transplant patients.

METHODS

This randomized, multicenter, double-blind, placebo-controlled, phase I study included adults who had been maintained on a regimen of cyclosporine A (CsA) microemulsion and prednisone (or its equivalent) for at least 1 year after renal transplantation. Patients received once-daily doses of 0.125, 0.25, 0.5, 1.0, 2.5, or 5.0 mg FTY720, or placebo for 28 days. After completion of study drug administration, the patients were monitored until day 56 by serial laboratory tests, clinical examinations, and recording of adverse events. The study includes 76 treatment courses (61 FTY720 and 15 placebo), with 65 patients enrolled once and 11 reenrolled.

RESULTS

FTY720 doses greater than or equal to 1.0 mg/day produced a significant reduction in peripheral blood lymphocyte count by up to 85%, which reversed within 3 days after discontinuation of study medication. Compared with placebo-treated patients, FTY720 subjects did not show a major increase in adverse events or a change in renal function. Pharmacokinetic measurements revealed that FTY720 displayed linear relations of doses and concentrations over a wide range, but had no effect on CsA exposure.

CONCLUSIONS

At doses up to 5.0 mg/day for 28 days, stable renal transplant patients treated with FTY720 in combination with CsA and prednisone displayed a dose-dependent, reversible decline in peripheral blood lymphocytes without an enhanced incidence of collateral toxicities, except possibly bradycardia.

The emerging matrix of immunosuppressive agents

In recent years, significant milestones have been reached in the field of transplantation through the development of immunosuppressive drugs that inhibit lymphocyte activation, cytokine signal transduction, and cellular proliferation. However, the widespread tissue distribution of the molecular targets exploited to date-calcineurin, mammalian target of rapamycin (mTOR), and inosine monophosphate dehydrogenase-produces an array of collateral toxicities. Avoiding these side effects requires new strategies that selectively block destructive immune responses: a fifth generation of immunosuppressants. These agents must target molecules that are critical for and specific to the adaptive immune response.

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.

Role of homeostatic chemokine and sphingosine-1-phosphate receptors in the organization of lymphoid tissue

Chemokines regulate both homeostatic leukocyte recirculation and trafficking to sites of infection and inflammation. Apart from the well-established physiological functions, chemokines receive growing interest for their role in pathophysiological processes such as autoimmune diseases, cancer, and allograft rejection. The chemokine receptor CCR7, which is responsible for directing T cells, B cells, and dendritic cells (DCs) into secondary lymphoid organs and their precise positioning therein, has already been implicated in lymphoid organ infiltration by neoplastic cells and the localization of metastasis formation. We have shown that the differential expression of CCR7 by neoplastic cells in two entities of Hodgkin's disease (HD), classic HD (cHD) and the nodular lymphocyte predominant HD (NLPHD), may account for the differences observed in tumor cell dissemination within the affected lymph nodes. Because of the prominent role of the chemokine receptors CCR7 and CXCR5 in lymphocyte homing to secondary lymphoid organs, we hypothesized that they may also be involved in the action of FTY720, a synthetic immunosuppressant inducing lymphopenia. By using CXCR5 and CCR7 knockout mice, we have tested for a possible function of these receptors in the FTY720-induced migration of lymphocytes into Peyer's patches (PPs) and peripheral lymph nodes (PLNs). Lymphopenia is noticeably delayed in mice lacking CCR7, whereas CXCR5 knockout mice show a significant reduction of lymphocyte accumulation in secondary lymphoid organs that are infrequently present in these mice. However, FTY720-induced lymphocyte sequestration appears to be essentially independent of CCR7 and CXCR5.

Graft-versus-host disease can be separated from graft-versus-lymphoma effects by control of lymphocyte trafficking with FTY720

Graft-versus-host disease (GvHD) mediated by donor T cells recognizing host alloantigens is associated with beneficial graft-versus-tumor effects in recipients of allogeneic hematopoietic cell transplants. Since leukemias and lymphomas reside largely within the lymphohematopoietic system, we have proposed that the desired graft-versus-leukemia or graft-versus-lymphoma effect can be separated from the complication of GvHD by confinement of the graft-versus-host alloresponse to the lymphohematopoietic tissues. Since the new sphingosine-1-phosphate receptor agonist immunosuppressive drug FTY720 leads to trapping of T cells in secondary lymphoid tissues, we evaluated the possibility that this drug could diminish GvHD, a disease involving epithelial target tissues, while permitting a beneficial alloresponse to take place within the lymphohematopoietic system, leading to graft-versus-lymphoma effects. We demonstrate here that FTY720 markedly reduces GvHD in a clinically relevant, haploidentical strain combination, while permitting antitumor effects against a T cell lymphoma of unshared host MHC haplotype to proceed unhindered. These results establish a potential new immunotherapeutic approach to separating graft-versus-leukemia effects from GvHD.

Efficacy of mycophenolate sodium as monotherapy and in combination with FTY720 in a DA-to-Lewis-rat heart-transplantation model

BACKGROUND

Mycophenolate sodium (MPS), which is in clinical development as an enteric-coated tablet (Myfortic), has not yet been characterized as a combination partner of FTY720. We therefore report here the effects of MPS and FTY720 mono and combination therapy in a rat heart allograft model.

METHODS

Heterotopic heart allotransplantation was performed in the DA-to-Lewis-strain combinations. Groups of six rats were treated with placebo, MPS monotherapy, FTY720 monotherapy, and their combination. To circumvent pharmacokinetic problems, MPS was administered by Alza minipumps, while FTY720 was administered by gavage, both for 4 weeks. Graft survival was monitored daily, followed up by histology. Body weight and hematological parameters were determined at 1 and 4 weeks.

RESULTS

The median survival time (MST) was 6 days for placebo, 6, 14.5, and more than 56 days for doses 3, 10, and 30 mg/kg per day MPS, with severe side effects (diarrhea, weight loss, lymphopenia) at the highest dose, and 7 and 8 days for the 0.03 and 0.1 mg/kg per day FTY720. The combination of 3 mg/kg per day MPS with these two FTY720 doses still resulted in rejection under treatment. However, 10 mg/kg per day MPS in combination with 0.03 or 0.1 mg/kg per day FTY720 yielded MSTs of 41 and 43.5 days, respectively, well beyond the 4-week treatment period. Both combination regimens were well tolerated. Both FTY720 doses combined with the highest MPS dose again caused severe side effects.

CONCLUSIONS

MPS in monotherapy and combined with FTY720 resulted in steep dose-response curves. However, well tolerated combination regimens could be defined that prevented rejection.

FTY720: targeting G-protein-coupled receptors for sphingosine 1-phosphate in transplantation and autoimmunity

The novel immunomodulator FTY720 is remarkably effective in models of transplantation and autoimmunity. Recent data show that phosphorylated FTY720 is an agonist at four sphingosine 1-phosphate receptors. Stimulation of sphingosine 1-phosphate receptors leads to sequestration of lymphocytes in secondary lymphatic tissues and thus away from inflammatory lesions and graft sites.