FTY720: a novel transplantation drug that modulates lymphocyte traffic rather than activation

The influence of sphingosine-1-phosphate receptor signaling on lymphocyte trafficking: how a bioactive lipid mediator grew up from an "immature" vascular maturation factor to a "mature" mediator of lymphocyte behavior and function

Since the initial observations that highlighted the importance of lymphocyte trafficking for immune responses, the pathways utilized by B and T lymphocytes to recirculate and properly position themselves have been intensely studied. Most of the chemoattractants along with their cognate receptors that affect lymphocyte trafficking have been identified. Some of their functions are promotion of lymphocyte ingress into immune organs, localization of cells to specific regions within those organs, maintenance of lymphocyte basal motility in immune organs, facilitation of lymphocyte egress from these organs, and control of migration and homing of lymphocytes in the periphery. Since the seminal discovery that agonism of sphingosine-1-phosphate receptors evokes changes in lymphocyte homing and trafficking, considerable effort has been undertaken to characterize the mechanism utilized by these receptors to influence lymphocyte behavior. This review will focus on the influence of sphingosine-1-phosphate signaling system on lymphocyte localization, egress from lymph organs, and its effects on the lymphatic vasculature.

An investigation of the impact of the location and timing of antigen-specific T cell division on airways inflammation

It is widely accepted that allergic asthma is orchestrated by T helper type 2 lymphocytes specific for inhaled allergen. However, it remains unclear where and when T cell activation and division occurs after allergen challenge, and whether these factors have a significant impact on airways inflammation. We therefore employed a CD4-T cell receptor transgenic adoptive transfer model in conjunction with laser scanning cytometry to characterize the location and timing of T cell division in asthma in vivo. Thus, for the first time we have directly assessed the division of antigen-specific T cells in situ. We found that accumulation of divided antigen-specific T cells in the lungs appeared to occur in two waves. The first very early wave was apparent before dividing T cells could be detected in the lymph node (LN) and coincided with neutrophil influx. The second wave of divided T cells accumulating in lung followed the appearance of these cells in LN and coincided with peak eosinophilia. Furthermore, accumulation of antigen-specific T cells in the draining LN and lung tissue, together with accompanying pathology, was reduced by intervention with the sphingosine 1-phosphate receptor agonist FTY720 2 days after challenge. These findings provide greater insight into the timing and location of antigen-specific T cell division in airways inflammation, indicate that distinct phases and locations of antigen presentation may be associated with different aspects of pathology and that therapeutics targeted against leukocyte migration may be useful in these conditions.

FTY720 (fingolimod) for relapsing multiple sclerosis

FTY720 (fingolimod) is a structural analogue of sphingosine, an endogenous lysophospholipid, which targets sphingosine-1-phosphate receptors after biotransformation to FTY720-phosphate. The immunomodulatory properties of this agent are mainly related to its ability to entrap lymphocytes in secondary lymphoid organs, reducing their availability for cell-mediated immune responses. Emerging evidence suggests that FTY720 also exerts direct actions on glial and precursor cells of the CNS which may be relevant for the process of tissue repair after injury. The therapeutic effects of the drug observed in animal models of human multiple sclerosis have provided the experimental basis for its clinical application. A recent Phase II study has demonstrated that oral FTY720 is effective in reducing disease activity in relapsing multiple sclerosis with a favorable adverse-effect profile. These results are awaiting confirmation in the three ongoing Phase III clinical trials evaluating FTY720 for relapsing-remitting multiple sclerosis.

Allogeneic islet transplantation

Significant progress has been made in the field of beta-cell replacement therapies by islet transplantation in patients with unstable Type 1 diabetes mellitus (T1DM). Recent clinical trials have shown that islet transplantation can reproducibly lead to insulin independence when adequate islet numbers are implanted. Benefits include improvement of glycemic control, prevention of severe hypoglycemia and amelioration of quality of life. Numerous challenges still limit this therapeutic option from becoming the treatment of choice for T1DM. The limitations are primarily associated with the low islet yield of human pancreas isolations and the need for chronic immunosuppressive therapies. Herein the authors present an overview of the historical progress of islet transplantation and outline the recent advances of the field. Cellular therapies offer the potential for a cure for patients with T1DM. The progress in beta-cell replacement treatment by islet transplantation as well as those of emerging immune interventions for the restoration of self tolerance justify great optimism for years to come.

FTY720 Story. Its Discovery and the following Accelerated Development of Sphingosine 1-Phosphate Receptor Agonists as Immunomodulators Based on Reverse Pharmacology

Fingolimod (FTY720) is the first of a novel class: sphingosine 1-phosphate (S1P) receptor modulator and is currently in phase 3 clinical trials for multiple sclerosis (MS). FTY720 was first synthesized in 1992 by chemical modification of an immunosuppressive natural product, ISP-I (myriocin). ISP-I was isolated from the culture broth of Isaria sinclairii, a type of vegetative wasp that was an ‘eternal youth’ nostrum in traditional Chinese medicine. ISP-I is an amino acid having three successive asymmetric centers and some functionalities. We simplified the structure drastically to find a nonchiral symmetric 2-substitued-2-aminopropane-1,3-diol framework for an in vivo immunosuppressive activity (inhibition of rat skin allograft rejection test or prolonging effect on rat skin allograft survival) and finally discovered FTY720. During the course of the lead optimization process, we encountered an unexpected dramatic change of the mechanism of action with an in vivo output unchanged. Since it proved that FTY720 did not inhibit serine palmitoyltransferase that is the target enzyme of ISP-I, reverse pharmacological approaches have been preformed to elucidate that FTY720 is mainly phosphorylated by sphingosine kinease 2 in vivo and the phosphorylated drug acts as a potent agonist of four of the five G protein coupled receptors for S1P: S1P1, S1P3, S1P4 and S1P5. Evidence has accumulated that immunomodulation by FTY720-P is based on agonism at the S1P1 receptor. Medicinal chemistry targeting S1P1 receptor agonists is currently in progress. The FTY720 story provides a methodology where in vivo screens rather than in vitro screens play important roles in the lead optimization. Unlike recent drug discovery methodologies, such a strategy as adopted by the FTY720 program would more likely meet serendipity.

S1P1 receptor expression regulates emergence of NKT cells in peripheral tissues

The S1P1 receptor, on the surface of lymphocytes and endothelial cells, regulates the unique trafficking behavior of certain lymphocyte populations. We have examined whether the S1P1 receptor also dictates the distinctive tissue distribution of V alpha14-J alpha18 natural killer T (NKT) cells, whose trafficking pattern is not well understood. Mice (TCS1P1 KO) were established with a conditional deletion of the S1P1 receptor in thymocytes that included precursors of NKT cells. Within the thymus, NKT cells were found at normal or increased levels, indicating that S1P1 receptor expression was dispensable for NKT cell development. However, substantially reduced numbers of NKT cells were detected in the peripheral tissues of the TCS1P1 KO mice. Short-term S1P1 deletion after NKT cells had established residence in the periphery did not substantially alter their distribution in tissues, except for a partial decrease in the spleen. FTY720, a S1P1 receptor ligand that has potent effects on the trafficking of conventional T cells, did not alter the preexisting distribution of NKT cells within peripheral tissues of wild-type mice. Our results indicate that the S1P1 receptor expression on NKT cells is dispensable for development within thymus but is essential for the establishment of their tissue residency in the periphery.

Reduction of CD4 positive T cells and improvement of pathological changes of collagen-induced arthritis by FTY720

FTY720 belongs to a new class of immunosuppressants. Little is known about its influence on T cell subtypes and pathological changes in arthritis. Here we illustrated the effect of FTY720 on peripheral T cell subsets and joint damage of collagen-induced arthritis rats. Rats were administered FTY720 or prednisone daily from day 0 to day 28. Body weight, hind paw swelling and arthritis index were measured. Bone destruction was determined by micro-computed tomography and histopathology, and T cell subsets were analyzed by flow cytometry and immunohistochemistry. The results showed that FTY720 inhibited the development of arthritis. Radiological analysis revealed that FTY720 treated collagen-induced arthritic rats had much less joint damage in comparison to untreated collagen-induced arthritic rats. Histological study showed that collagen-induced arthritic rats suffered from inflammatory cell infiltration and synovial hyperplasia in their joints, and FTY720 treatment clearly reduced these pathological changes. Immunohistochemical analysis showed that FTY720 treatment significantly decreased the number of CD4(+) T cells in the synovium of collagen-induced arthritic rats. Collagen-induced arthritic rats appeared to have more CD4(+), but not CD8(+) T cells in their peripheral blood than normal control rats. Following FTY720 treatment, peripheral blood CD3(+) and CD4(+) T cells in collagen-induced arthritic rats were significantly decreased. In conclusion, FTY720 is an effective compound in the treatment of collagen-induced arthritic rats and in reducing CD4(+) T cells in collagen-induced arthritic rats.

Sphingosine 1-phosphate receptors in health and disease: mechanistic insights from gene deletion studies and reverse pharmacology

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid that is critically involved in the embryonic development of the cardiovascular and central nervous systems. In the adult, S1P can produce cytoskeletal re-arrangements in many cell types to regulate immune cell trafficking, vascular homeostasis and cell communication in the central nervous system. S1P is contained in body fluids and tissues at different concentrations, and excessive production of the pleiotropic mediator at inflammatory sites may participate in various pathological conditions. Gene deletion studies and reverse pharmacology (techniques aiming to identify both ligands and function of receptors) provided evidence that many effects of S1P are mediated via five G-protein-coupled S1P receptor subtypes, and novel therapeutic strategies based on interaction with these receptors are being initiated. The prototype S1P receptor modulator, FTY720 (fingolimod), targets four of the five S1P receptor subtypes and may act at several levels to modulate lymphocyte trafficking via lymphocytic and endothelial S1P1 and, perhaps, other inflammatory processes through additional S1P receptor subtypes. A recently completed Phase II clinical trial suggested that the drug may provide an effective treatment of relapsing-remitting multiple sclerosis. FTY720 is currently being evaluated in larger-scale, longer-term, Phase III studies. This review provides an overview on S1P activities and S1P receptor function in health and disease, and summarizes the clinical experience with FTY720 in transplantation and multiple sclerosis.

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.

Current perspectives on FTY720

The search for effective immunosuppressants with fewer side effects continues not only for transplantation, but also for autoimmune diseases. With a novel mechanism of action (sphingosine-1 receptor modulation), oral FTY720 (fingolimod) has the potential to address this need. FTY720 has been preclinically tested with promising results in transplantation and autoimmune disease models. Phase I studies explored the pharmacokinetics and pharmacodynamics of this novel therapeutic concept. Recently, the surprising results of two sister Phase III studies in de novo renal transplant patients, as well as a Phase II study in patients with relapsing multiple sclerosis, were published. This review discusses these findings as well as their implications for the future of sphingosine-1 receptor modulation.

FTY720, an immunomodulatory sphingolipid mimetic: translation of a novel mechanism into clinical benefit in multiple sclerosis

FTY720 (fingolimod; 2-amino-2[2-(4-octylphenyl)ethyl]-1,3-propanediol, Novartis) is the prototype of a new generation of immunomodulators. The drug is the result of extensive chemical derivatisation based on the natural product myriocin, isolated from the ascomycete Isaria sinclairii. FTY720 bears structural similarity to sphingosine, a naturally occurring sphingolipid. As with sphingosine, FTY720 is effectively phosphorylated by sphingosine kinases in vivo and the phosphorylated drug targets G-protein-coupled receptors for sphingosine-1-phosphate (S1P). Gene deletion and reverse pharmacology studies have shown that FTY720 acts at S1P1 receptors on lymphocytes and the endothelium, thereby inhibiting the egress of T- and B cells from secondary lymphoid organs into the blood and their recirculation to inflamed tissues. Animal studies suggest that this novel mechanism translates into effective treatments for several autoimmune diseases and a recently completed Phase II clinical trial highlighted FTY720 as a potential therapy for relapsing-remitting multiple sclerosis.

FTY720 ameliorates Th1-mediated colitis in mice by directly affecting the functional activity of CD4+CD25+ regulatory T cells

Following the present concepts, the synthetic sphingosine analog of myriocin FTY720 alters migration and homing of lymphocytes via sphingosine 1-phosphate receptors. However, several studies indicate that the immunosuppressive properties of FTY720 may alternatively be due to tolerogenic activities via modulation of dendritic cell differentiation or based on direct effects on CD4(+)CD25(+) regulatory T cells (Treg). As Treg play an important role for the cure of inflammatory colitis, we used the Th1-mediated 2,4,6-trinitrobenzene sulfonic acid (TNBS) colitis model to address the therapeutic potential of FTY720 in vivo. A rectal enema of TNBS was given to BALB/c mice. FTY720 was administered i.p. from days 0 to 3 or 3 to 5. FTY720 substantially reduced all clinical, histopathologic, macroscopic, and microscopic parameters of colitis analyzed. The therapeutic effects of FTY720 were associated with a down-regulation of IL-12p70 and subsequent Th1 cytokines. Importantly, FTY720 treatment resulted in a prominent up-regulation of FoxP3, IL-10, TGFbeta, and CTLA4. Supporting the hypothesis that FTY720 directly affects functional activity of CD4(+)CD25(+) Treg, we measured a significant increase of CD25 and FoxP3 expression in isolated lamina propria CD4(+) T cells of FTY720-treated mice. The impact of FTY720 on Treg induction was further confirmed by concomitant in vivo blockade of CTLA4 or IL-10R which significantly abrogated its therapeutic activity. In conclusion, our data provide clear evidence that in addition to its well-established effects on migration FTY720 leads to a specific down-regulation of proinflammatory signals while simultaneously inducing functional activity of CD4(+)CD25(+) Treg. Thus, FTY720 may offer a promising new therapeutic strategy for the treatment of IBD.

FTY720 suppresses interleukin-1beta-induced secretory phospholipase A2 expression in renal mesangial cells by a transcriptional mechanism

BACKGROUND AND PURPOSE

FTY720 is a potent immunomodulatory prodrug that is converted to its active phosphorylated form by a sphingosine kinase. Here we have studied whether FTY720 mimicked the action of sphingosine-1-phosphate (S1P) and exerted an anti-inflammatory potential in renal mesangial cells.

EXPERIMENTAL APPROACH

Prostaglandin E(2) (PGE(2)) was quantified by an enzyme-linked immunosorbent-assay. Secretory phospholipase A(2) (sPLA(2)) protein was detected by Western blot analyses. mRNA expression was determined by Northern blot analysis and sPLA(2)-promoter activity was measured by a luciferase-reporter-gene assay.

KEY RESULTS

Stimulation of cells for 24 h with interleukin-1beta (IL-1beta) is known to trigger increased PGE(2) formation which coincides with an induction of the mRNA for group-IIA-sPLA(2) and protein expression. FTY720 dose-dependently suppressed IL-1beta-induced IIA-sPLA(2) protein secretion and activity in the supernatant. This effect is due to a suppression of cytokine-induced sPLA(2) mRNA expression which results from a reduced promoter activity. As a consequence of suppressed sPLA(2) activity, PGE(2) formation is also reduced by FTY720. Mechanistically, the FTY720-suppressed sPLA(2) expression results from an activation of the TGFbeta/Smad signalling cascade since inhibition of the TGFbeta receptor type I by a specific kinase inhibitor reverses the FTY720-mediated decrease of sPLA(2) protein expression and sPLA(2) promoter activity.

CONCLUSIONS AND IMPLICATIONS

In summary, our data show that FTY720 was able to mimic the anti-inflammatory activity of TGFbeta and blocked cytokine-triggered sPLA(2) expression and subsequent PGE(2) formation. Thus, FTY720 may exert additional in vivo effects besides the well reported immunomodulation and its anti-inflammatory potential should be considered.

The immunomodulator FTY720 and its phosphorylated derivative activate the Smad signalling cascade and upregulate connective tissue growth factor and collagen type IV expression in renal mesangial cells

1.--The immunomodulating agent FTY720 is a substrate for the sphingosine kinase and the phosphorylated form is able to bind to sphingosine 1-phosphate (S1P) receptors. In this study, we show that exposure of renal mesangial cells to phospho-FTY720 leads to a rapid and transient activation of several protein kinase cascades, including the mitogen- and stress-activated protein kinases. The nonphosphorylated FTY720 also increased MAPK phosphorylation, but with a reduced potency and a more delayed time course. In addition, phospho-FTY720 and FTY720 are able to increase phosphorylation of Smad proteins which are classical members of the transforming growth factor-beta (TGF-beta) signalling device, thus suggesting a crosstalk between FTY720 and TGF-beta signalling. 2.--Pretreatment with the S1P(3) receptor antagonist suramin inhibits FTY720 and phospho-FTY720-induced Smad phosphorylation, whereas pertussis toxin pretreatment, which blocks G(i/0) proteins, has no effect on Smad phosphorylation. 3.--Since TGF-beta is a potent profibrotic cytokine in mesangial cells and upregulates the connective tissue growth factor (CTGF) and collagen as important hallmarks in the fibrotic sequelae, we investigated whether FTY720 and phospho-FTY720 are able to mimic these effects of TGF-beta. Indeed, FTY720 and phospho-FTY720 markedly upregulate CTGF and collagen type IV protein expressions. In addition, the tissue inhibitor of metalloproteinase-1 is transcriptionally activated by FTY720, whereas cytokine-induced matrix metalloproteinase-9 is down-regulated by FTY720. 4.--Depletion of the TGF-beta receptor type II by the siRNA transfection technique blocks not only Smad phosphorylation but also CTGF upregulation. Similarly, Smad-4 depletion by siRNA transfection also abrogates CTGF upregulation induced by FTY720 and phospho-FTY720. 5.--In summary, our data show that FTY720 and phospho-FTY720 not only activate the Smad signalling cascade in mesangial cells, but also upregulate the expression of CTGF and collagen. These findings suggest that FTY720 may have additional effects besides the established immunomodulatory action and, importantly, a profibrotic activity has to be considered in future experimental approaches.

Inhibition of inducible nitric oxide synthase and cyclooxygenase-2 expression by flavonoids isolated from Tanacetum microphyllum

Plant flavonoids show anti-inflammatory activity both in vitro and in vivo. Some flavonoids have been reported previously to inhibit nitric oxide (NO) and prostaglandin E2 (PGE2) production by suppressing inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression. The present study focuses on the effect of various naturally occurring flavonoids (santin, ermanin, centaureidin and 5,3'-dihydroxy-4'-methoxy-7-methoxycarbonylflavonol) on modulation of lipopolysaccharide (LPS)-induced iNOS and COX-2 expression in RAW 264.7 cells. Western blotting showed that all flavonoids suppressed the induction of both iNOS and COX-2. Ermanin and 5,3'-dihydroxy-4'-methoxy-7-methoxycarbonylflavonol were the most potent inhibitors. This study suggests that inhibition of iNOS and COX-2 expression by flavonoids may be one of the mechanisms responsible for their anti-inflammatory effects, and that they may be potential agents for use in the treatment of inflammatory diseases.

Bioactive sphingolipids in the modulation of the inflammatory response

Inflammation is viewed as a protective response against insults to the organism. It involves the recruitment of many cell types and the production of various inflammatory mediators in attempts to contain and reverse the insult. However, inflammation can lead to irreversible tissue destruction by itself and, therefore, can represent a disease state that causes significant morbidity and mortality. Understanding the molecular mechanisms controlling the inflammatory response is essential to formulate therapeutic strategies for the treatment of inflammatory conditions. In fact, substantial research has unveiled important aspects of the inflammatory machinery, both at the cellular and molecular levels. Recently, sphingolipids (SLs) have emerged as signaling molecules that regulate many cell functions, and ample evidence emphasizes their role in the regulation of inflammatory responses. Here, we review the role of bioactive SL as regulators and mediators of inflammatory responses.

Physiologically based pharmacokinetic modeling of FTY720 (2-amino-2[2-(-4-octylphenyl)ethyl]propane-1,3-diol hydrochloride) in rats after oral and intravenous doses

FTY720 (2-amino-2[2-(-4-octylphenyl)ethyl]propane-1,3-diol hydrochloride) is a new sphingosine-1-phosphate receptor agonist being developed for multiple sclerosis and prevention of solid organ transplant rejection. A physiologically based pharmacokinetic model was developed to predict the concentration of FTY720 in various organs of the body. Single oral and intravenous doses of FTY720 were administered to male Wistar rats, with blood and tissue sampling over 360 h analyzed by liquid chromatography/tandem mass spectrometry. A well stirred model (perfusion rate-limited) described FTY720 kinetics in heart, lungs, spleen, muscle, kidneys, bone, and liver, with a permeability rate-limited model being required for brain, thymus, and lymph nodes. Tissue-to-blood partition coefficients (RT) ranged from 4.69 (muscle) to 41.4 (lungs). In lymph nodes and spleen, major sites for FTY720-induced changes in sequestration of lymphocytes, RT values were 22.9 and 34.7, respectively. Permeability-surface area products for brain, thymus, and lymph nodes were 39.3, 122, and 176 ml/min. Intrinsic hepatic clearance was 23,145 l/h/kg for the free drug in blood (f(ub) 0.000333); systemic clearance was 0.748 l/h/kg and terminal half-life was 23.4 h. The fraction orally absorbed was 71%. The model characterized well FTY720 disposition for this extensive dosing and tissue collection study in the rat. On scaling the model to dogs and humans, good agreement was found between the actual and predicted blood concentration-time profiles. More importantly, brain concentrations in dogs were well predicted from those of the rat. In absolute terms, the predictions were slightly lower than observed values, just under a 1.5-fold deviation, but the model accurately predicted the terminal elimination of FTY720 from the brain.

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.

Pancreatic islet transplantation for treating diabetes

Pancreatic islet transplantation is one of the options for treating diabetes and has been shown to improve the quality of life of severe diabetic patients. Since the Edmonton protocol was announced, islet transplantation have advanced considerably, including islet after kidney transplantation, utilisation of non-heart-beating donors, single-donor islet transplantation and living-donor islet transplantation. These advances were based on revised immunosuppression protocols, improved pancreas procurement and islet isolation methods, and enhanced islet engraftment. Further improvements are necessary to make islet transplantation a routine clinical treatment. To synergise efforts towards a cure for type 1 diabetes, a Diabetes Research Institute (DRI) Federation is currently being established to include leading diabetes research centres worldwide, including DRIs in Miami, Edmonton and Kyoto among others.

The sphingosine 1-phosphate receptor agonist FTY720 differentially affects the sequestration of CD4+/CD25+ T-regulatory cells and enhances their functional activity

The sphingosine 1-phosphate (S1P) receptor agonist FTY720 is well known for its immunomodulatory activity, sequestering lymphocytes from blood and spleen into secondary lymphoid organs and thereby preventing their migration to sites of inflammation. Because inflammation is critically dependent on a balance between Ag-specific Th/effector cells and T-regulatory cells, we investigated the effect of FTY720 on T-regulatory cell trafficking and functional activity. An increased number of CD4+/CD25+ T cells was found in blood and spleens of FTY720-treated mice, and transfer of these cells resulted in a significantly more pronounced accumulation in spleens but not lymph nodes after treatment, suggesting that this compound differentially affects the homing properties of T-regulatory cells compared with other T cell subsets. Indeed, CD4+/CD25+ T cells express lower levels of S1P1 and S1P4 receptors and demonstrate a reduced chemotactic response to S1P. Moreover, analysis of the functional response of FTY720-treated CD4+/CD25+ T cells revealed an increased suppressive activity in an in vitro Ag-specific proliferation assay. This correlated with enhanced function in vivo, with T-regulatory cells obtained from FTY720-treated mice being able to suppress OVA-induced airway inflammation. Thus, FTY720 differentially affects the sequestration of T-regulatory cells and importantly, increases the functional activity of T-regulatory cells, suggesting that it may have disease-modifying potential in inflammatory disorders.

Biological effects of lysophospholipids

Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) are potent biologically active lipid mediators that exert a wide range of cellular effects through specific G protein-coupled receptors. To date, four LPA receptors and five S1P receptors have been identified. These receptors are expressed in a large number of tissues and cell types, allowing for a wide variety of cellular responses to lysophospholipid signaling, including cell adhesion, cell motility, cytoskeletal changes, proliferation, angiogenesis, process retraction, and cell survival. In addition, recent studies in mice show that specific lysophospholipid receptors are required for proper cardiovascular, immune, respiratory, and reproductive system development and function. Lysophospholipid receptors may also have specific roles in cancer and other diseases. This review will cover identification and expression of the lysophospholipid receptors, as well as receptor signaling properties and function. Additionally, phenotypes of mice deficient for specific lysophospholipid receptors will be discussed to demonstrate how these animals have furthered our understanding of the role lysophospholipids play in normal biology and disease.

Immunosuppressive activity of FTY720, sphingosine 1-phosphate receptor agonist: I. Prevention of allograft rejection in rats and dogs by FTY720 and FTY720-phosphate

FTY720, a new class of immunomodulator, induces lymphopenia by sequestration of circulating lymphocytes into secondary lymphoid tissues. FTY720 at 0.1 to 1 mg/kg significantly prolonged the allograft survival in a dose-dependent manner and showed a marked synergistic effect in combination with cyclosporine (CsA) in rat skin and cardiac allograft models. In addition, the canine renal allograft survival was significantly prolonged by combination therapy with FTY720 at 0.03 to 1 mg/kg and CsA at 10 mg/kg as compared with monotherapy of FTY720 or CsA. By contrast, the combination therapy with CsA and azathioprine or CsA and mycophenolate mofetil resulted in only an additive effect in rat skin allograft. When FTY720 was administered to rats, FTY720 was metabolized by omega-oxidation of the octyl side chain, and beta-oxidation subsequently, or phosphorylated by sphingosine kinase. Omega- and beta-oxidized 4 metabolities of FTY720 at 10 mg/kg i.v. showed neither lymphopenia nor immunosuppressive activity in rat skin allograft. On the other hand, (S)-enantiomer of FTY720-phosphate at 0.1 and 1 mg/kg intravenously induced a marked lymphopenia and significantly prolonged the allograft survival in the rat allotransplantation. From these results, it is suggested the lymphopenia and the immunosuppression induced by FTY720 administration is due to the agonistic activity against SIP receptors of the active metabolite, (S)-FTY720-phosphate.

The Effect of a Novel Immunosuppressant, FTY720, in Mice Without Secondary Lymphoid Organs

PURPOSE

FTY720 is a novel immunosuppressive agent that is thought to reduce the number of peripheral blood lymphocytes (PBL) by directing them toward secondary lymphoid organs such as the lymph nodes and Peyer's patches. We studied the effects of FTY720 on aly/aly mice that do not have either lymph nodes or Peyer's patches, as well as on splenectomized aly/aly mice.

METHODS

FTY720 was orally administered by gavage (1 mg/kg) to aly/aly mice as well as to aly/+ mice with and without a splenectomy on 14 consecutive days. The number of lymphocytes was then counted using True Cell beads and flow cytometry. The number of B220-, CD3-, and CD4-positive cells was also determined. In addition, skin grafts from C3H donor mice were performed on these mice.

RESULTS

FTY720 was effective in significantly reducing the total lymphocyte count as well as the B220-, CD3-, and CD4-positive subtypes in the peripheral blood of aly/+ mice as well as in aly/aly mice with and without a splenectomy. While we did observe allograft skin graft rejection in both the aly/+ mice as well as the aly/aly mice recipients and splenectomized aly/aly mice, the graft survival was prolonged in all groups. The skin allografts treated by FTY720 thus demonstrated fewer lymphocytic cells and less infiltration of CD4-positive cells.

CONCLUSIONS

The administration of FTY720 to mice without lymph nodes, Peyer's patches, or spleens still results in peripheral lymphopenia. In all groups, FTY720 was found to prevent the infiltration of CD4-positive cells in skin allografts while also prolonging skin allograft survival. The fate of these lymphocytes, however, is unclear.

FTY720, a new class of immunomodulator, inhibits lymphocyte egress from secondary lymphoid tissues and thymus by agonistic activity at sphingosine 1-phosphate receptors

FTY720 is the first of a new immunomodulator class: sphingosine 1-phosphate (S1P) receptor agonist. In 1994, an immunosuppressive natural product, ISP-I (myriocin), was isolated from the culture broth of Isaria sinclairii, a type of vegetative wasp. The chemical modification of ISP-I yielded a new compound, FTY720, which has more potent immunosuppressive activity and less toxicity than ISP-I does. FTY720 has been shown to be highly effective in experimental allotransplantation models and autoimmune disease models. A striking feature of FTY720 is the induction of a marked decrease in peripheral blood T- and B-cells at doses that show immunosuppressive activity in these models. Reportedly, FTY720 is rapidly converted to FTY720-phosphate (FTY720-P) by sphingosine kinase 2 in vivo, and FTY720-P acts as a potent agonist at S1P receptors. Recently, it has been suggested that FTY720-P internalizes S1P1 on lymphocytes and thereby inhibits the migration of lymphocytes toward S1P. Thus, it is likely that the reduction of circulating lymphocytes by FTY720 is due to the inhibition of S1P/S1P1-dependent lymphocyte egress from secondary lymphoid tissues and thymus. Because FTY720 displays a novel mechanism of action that has not been observed with other immunosuppressive agents and shows a synergism with cyclosporin A (CsA) and tacrolimus, it is presumed that FTY720 provides a useful tool for the prevention of transplant rejection and a new therapeutic approach for autoimmune diseases including multiple sclerosis and rheumatoid arthritis.

A novel immunomodulator, FTY720, prevents spontaneous dermatitis in NC/Nga mice

Oral administration of a novel immunomodulator, FTY720 (0.1 mg/kg, once a week), completely prevented the spontaneous development of dermatitis in NC/Nga mice. It also strongly suppressed hyper IgE production in serum, as well as hypertrophy of the epidermis and the degranulation of granulocytes in the skin, all of which were observed in mice in which the dermatitis had become established. These results strongly suggest that FTY720 is a promising candidate for treatment of human atopic dermatitis.

A Novel Immunomodulator, FTY720, Prevents Development of Experimental Autoimmune Myasthenia Gravis in C57BL/6 Mice

Prophylactic oral administration of a novel immunomodulator (immunosuppressant), FTY720 (1 mg/kg, three times a week), completely prevented the development of experimental autoimmune myasthenia gravis (EAMG) in C57BL/6 mice. EAMG has been used as an animal model for human myasthenia gravis, and was established by immunizing the mice with acetylcholine receptor (AChR) from Torpedo californica. FTY720 also suppressed the production of both anti-Torpedo californica AChR antibody and anti-mouse AChR autoantibody by the mice, which were observed in mice in which EAMG had become established. These results strongly suggest that FTY720 is a promising candidate for treatment of human myasthenia gravis.

An IgM-kappa rat monoclonal antibody specific for the type 1 sphingosine 1-phosphate G protein-coupled receptor with antagonist and agonist activities

Sphingosine 1-phosphate (S1P) type 1G protein-coupled receptors (S1P1 GPCRs) are specific high-affinity transducers for this lipid growth factor and cellular mediator. S1P1 GPCRs are widely-expressed and physiologically critical in the cardiovascular and immune systems. Functional rat monoclonal antibodies (MoAbs) have been generated against human S1P1 GPCRs expressed in rat null-cell transductants to provide bioavailable agents capable of stimulating or suppressing the S1P-S1P1 GPCR axis. The rat IgM-kappa anti-S1P1 GPCR MoAb designated 4B5.2 binds specifically to native human or mouse S1P1 GPCRs in cell membranes, but not to solubilized and denatured S1P1 GPCRs. Specific binding of 32P-S1P to cellular S1P1 GPCRs is not blocked by 4B5.2. T cell chemotactic responses to S1P and S1P suppression of T cell chemotaxis to chemokines both are inhibited selectively by 4B5.2. In contrast, generation of gamma-interferon by stimulated T cells is diminished by 4B5.2 as by S1P. T cell S1P1 GPCR-selective antagonist and agonist effects of 4B5.2 in vivo may alter immune responses as distinctively as the available poly-S1P GPCR-directed pharmacological agents, without the undesirable side-effects attributable to actions of these agents on other S1P GPCRs.

Future immunosuppressive agents in solid-organ transplantation

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and safety of mycophenolate sodium, everolimus, and FTY720.

STUDY SELECTION AND DATA EXTRACTION

Clinical trials and abstracts evaluating mycophenolate sodium, everolimus, and FTY720 in solid-organ transplantation were considered for evaluation. English-language studies and published abstracts were selected for inclusion.

DATA SYNTHESIS

Mycophenolate sodium has recently been approved by the Food and Drug Adminstration for marketing in the United States; everolimus and FTY720 are immunosuppressive agents that may soon be available in the United States. These agents have proven efficacy in reducing the incidence of acute rejection in solid-organ transplantation. Clinical trials have shown that these newer agents are relatively well tolerated. The most common adverse events associated with these agents were gastrointestinal and hematologic effects (mycophenolate sodium); hyperlipidemia, increased serum creatinine, and hematologic effects (everolimus): and gastrointestinal effects, headache, and bradycardia (FTY720).

CONCLUSION

Mycophenolate sodium has been approved in some European countries and the United States. Everolimus has been approved in some European countries and a new drug application has been submitted to the Food and Drug Administration. FTY720 is currently in phase III clinical trials and submission to the Food and Drug Administration for approval is a few years away. The approval of these agents will furnish the transplant practitioner with even more options for immunosuppression.

FTY720 suppresses humoral immunity by inhibiting germinal center reaction

FTY720 is a novel immunosuppressant that is highly effective in inhibiting rejection of allografts and autoimmunity in various animal models. It has been shown that the sphingosine 1 phosphate (S1P) receptors are the direct molecular targets of FTY720. However, the mechanisms responsible for inhibiting specific immune responses by FTY720 are not well resolved. In particular, there is no available information on whether or how this compound affects humoral immunity. We have investigated the effect of FTY720 treatment on B-cell response during the immune response to a well-defined T-dependent antigen. Our data demonstrated that germinal center reaction was significantly reduced in peripheral lymphoid tissues of mice treated with FTY720. In addition, FTY720 treatment inhibited the production of high-affinity, class-switched antibodies, but not the production of low-affinity, immunoglobulin M (IgM) antibody. Consistently, FTY720 did not have a significant effect on antibody response to a T-independent antigen. Our results may have important implications in application of FTY720 in immune regulation.

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.

Sphingosine 1-phosphate receptor agonists attenuate relapsing–remitting experimental autoimmune encephalitis in SJL mice

FTY720 is a prodrug for FTY-phosphate, an agonist at four of the five known receptors for sphingosine-1-phosphate (S1P). We show that administration of either FTY720 or FTY-P to SJL mice with established relapsing-remitting experimental autoimmune encephalitis (EAE) results in a rapid and sustained improvement in their clinical status, and a reversal of changes in expression of mRNAs encoding some myelin proteins and inflammatory mediators. EAE produced by adoptively transferring lymph node cells from immunized mice to naïve hosts is similarly ameliorated by FTY-P. Treatment with FTY-P is accompanied by a dose-responsive peripheral lymphopoenia.

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.

FTY720: sphingosine 1-phosphate receptor-1 in the control of lymphocyte egress and endothelial barrier function

The novel immunomodulator FTY720 is effective in experimental models of transplantation and autoimmunity, and is currently undergoing Phase III clinical trials for prevention of kidney graft rejection. In contrast to conventional immunosuppressants, FTY720 does not impair T- and B-cell activation, proliferation and effector function, but interferes with cell traffic between lymphoid organs and blood. The molecular basis for the mode of action of the drug has only recently been established. FTY720, after phosphorylation, acts as a high-affinity agonist at the G protein-coupled sphingosine 1-phosphate receptor-1 (S1P(1)) on thymocytes and lymphocytes, thereby inducing aberrant internalization of the receptor. This renders the cells unresponsive to the serum lipid sphingosine 1-phosphate (S1P), depriving them from an obligatory signal to egress from lymphoid organs. As a consequence, lymphocytes are unable to recirculate to peripheral inflammatory tissues and graft sites but remain functional in the lymphoid compartment. In addition to the effects on lymphocyte recirculation, the drug acts on endothelial cells and preserves vascular integrity by enhancing adherens junction assembly and endothelial barrier function. The available data establish S1P(1) as a key target for FTY720, and further point to therapeutically relevant effects of the drug on lymphocytes and vascular endothelium.

Renal transplantation: basic concepts and evolution of therapy

Within the last 5 years, dramatic changes in the area of renal transplantation have occurred. There have been shifts in the dominant types of rejection, and in the types and utilization of immunosuppressants. Hyperacute rejection is now rarely seen, and acute cellular rejection within the first 6 to 12 months has been reduced to about 10%. However, humoral/antibody-mediated rejection has become a more prevalent problem. In the area of immunosuppressants, the ability to reduce acute cellular rejection to about 10% has been achieved through more judicious use of calcineurin inhibitors (cyclosporine and tacrolimus), increased use of mycophenolate mofetil, and the recent introduction of sirolimus (rapamycin). The polyclonal antibody (antithymocyte globulin), as well as monoclonal antibodies directed against the alpha chain of CD25 (daclizumab and basilixamab), have added substantially to the improved success of renal allografts. Because of numerous serious toxicities from glucocorticoids and calcineurin inhibitors, particularly cyclosporine, new studies are utilizing calcineurin-free and/or glucocorticoid avoidance or rapid elimination protocols often in combination with a monoclonal antibody and sirolimus. New immunosuppressants such as FTY720 and Campath-1 are also under study. In addition to its use in treating patients with low-level donor-specific antibody before transplantation in order to avoid hyperacute rejection, apheresis is utilized in various combination protocols after transplantation in the management of humoral/antibody-mediated rejection, in the treatment of hemolytic uremia syndrome that sometimes occurs with calcineurin inhibitors and sirolimus, as well as in the treatment of focal segmental glomerulosclerosis that has a major risk of recurrence in renal transplants.

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.

Inhibition of Th1- and Th2-mediated airway inflammation by the sphingosine 1-phosphate receptor agonist FTY720

The sphingosine 1-phosphate receptor agonist FTY720 is a novel immunomodulator that sequesters lymphocytes in secondary lymphoid organs and thereby prevents their migration to sites of inflammation. However, there is currently no information available on whether this drug affects Th1 or Th2 cell-mediated lung-inflammatory responses. The effect of FTY720 was therefore investigated in a murine airway inflammation model using OVA-specific, in vitro differentiated, and adoptively transferred Th1 and Th2 cells. Both Th1 and Th2 cells express a similar pattern of FTY720-targeted sphingosine 1-phosphate receptors. The OVA-induced Th1-mediated airway inflammation characterized by increased numbers of lymphocytes and neutrophils in bronchoalveolar lavage fluid was significantly inhibited by oral FTY720 treatment. Similarly, FTY720 suppressed the Th2 cell-induced bronchoalveolar lavage fluid eosinophilia and the infiltration of T lymphocytes and eosinophils into the bronchial tissue. Moreover, the Ag-induced bronchial hyperresponsiveness to inhaled metacholine was almost completely blocked. The inhibitory effect of FTY720 on airway inflammation, induction of bronchial hyperresponsiveness, and goblet cell hyperplasia could be confirmed in an actively Ag-sensitized murine asthma model, clearly indicating that Th2 cell-driven allergic diseases such as asthma could benefit from such treatment.

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.

Sphingosine 1-phosphate (S1P) receptor subtypes S1P1 and S1P3, respectively, regulate lymphocyte recirculation and heart rate

Sphingosine 1-phosphate (S1P) influences heart rate, coronary artery caliber, endothelial integrity, and lymphocyte recirculation through five related high affinity G-protein-coupled receptors. Inhibition of lymphocyte recirculation by non-selective S1P receptor agonists produces clinical immunosuppression preventing transplant rejection but is associated with transient bradycardia. Understanding the contribution of individual receptors has been limited by the embryonic lethality of the S1P(1) knock-out and the unavailability of selective agonists or antagonists. A potent, S1P(1)-receptor selective agonist structurally unrelated to S1P was found to activate multiple signals triggered by S1P, including guanosine 5'-3-O-(thio)triphosphate binding, calcium flux, Akt and ERK1/2 phosphorylation, and stimulation of migration of S1P(1)- but not S1P(3)-expressing cells in vitro. The agonist also alters lymphocyte trafficking in vivo. Use of selective agonism together with deletant mice lacking S1P(3) receptor reveals that agonism of S1P(1) receptor alone is sufficient to control lymphocyte recirculation. Moreover, S1P(1) receptor agonist plasma levels are causally associated with induction and maintenance of lymphopenia. S1P(3), and not S1P(1), is directly implicated in sinus bradycardia. The sustained bradycardia induced by S1P receptor non-selective immunosuppressive agonists in wild-type mice is abolished in S1P(3)-/- mice, whereas S1P(1)-selective agonist does not produce bradycardia. Separation of receptor subtype usage for control of lymphocyte recirculation and heart rate may allow the identification of selective immunosuppressive S1P(1) receptor agonists with an enhanced therapeutic window. S1P(1)-selective agonists will be of broad utility in understanding cell functions in vitro, and vascular physiology in vivo, and the success of the chemical approach for S1P(1) suggests that selective tools for the resolution of function across this broad lipid receptor family are now possible.

Expression of the sphingosine 1-phosphate receptor, S1P1, on T-cells controls thymic emigration

S1P(1) is a widely distributed G protein-coupled receptor whose ligand, sphingosine 1-phosphate, is present in high concentrations in the blood. The sphingosine 1-phosphate receptor-signaling pathway is believed to have potent effects on cell trafficking in the immune system. To determine the precise role of the S1P(1) receptor on T-cells, we established a T-cell-specific S1P(1) knock-out mouse. The mutant mice showed a block in the egress of mature T-cells into the periphery. The expression of the S1P(1) receptor was up-regulated in mature thymocytes, and its deletion altered the chemotactic responses of thymocytes to sphingosine 1-phosphate. The results indicated that the expression of the S1P(1) receptor on T-cells controls their exit from the thymus and entry into the blood and, thus, has a central role in regulating the numbers of peripheral T-cells.

Predictability of FTY720 efficacy in experimental autoimmune encephalomyelitis by in vivo macrophage tracking: Clinical implications for ultrasmall superparamagnetic iron oxide-enhanced magnetic resonance imaging

PURPOSE

To examine the efficacy of FTY720 as a new agent to reduce inflammatory activity in an animal model of multiple sclerosis (MS) by in vivo macrophage tracking.

MATERIAL AND METHODS

FTY720 was used for treatment of rats in a model of chronic relapsing experimental autoimmune encephalomyelitis (EAE) at an oral dose of 0.3 mg/kg/day. Magnetic resonance imaging (MRI) based on in vivo tracking of macrophages labeled with ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles, immunohistological staining (IHC), and neurological readouts was used to study the burden of disease in treated and untreated animals.

RESULTS

While untreated animals showed severe paralysis of the hind paws, intense accumulation of macrophages in brain tissue, and areas of blood-brain barrier (BBB) disruption, FTY720-treated animals displayed no signs of inflammatory activity or neurological impairment. These observations were made for both acute phase and first relapse.

CONCLUSION

Tracking of macrophages by MRI provides direct evidence of the immunomodulatory efficacy of FTY720 in the EAE model and correlates well with neurological symptoms and histology.

Islet transplantation in patients with diabetes mellitus: choice of immunosuppression

Islet transplantation offers patients with type 1 diabetes mellitus freedom from long-term insulin therapy and a degree of metabolic control that is far superior to injected insulin. The hope is that near-perfect glucose control sustained over time will prevent progression of secondary diabetic complications. The selection of optimal immunosuppressive agents for islet transplantation has been a formidable challenge, given the need to overcome both autoimmune and alloimmune barriers, as well as the potential toxicity of immunosuppressive agents on transplanted islets. Early strategies relied on protocols that had proven success in solid organ transplantation and consisted of azathioprine, cyclosporine and corticosteroids. Under these protocols, fewer than 10% of patients were able to achieve insulin independence. The development of the 'Edmonton Protocol' dramatically transformed clinical outcomes in islet transplantation in recent years through the introduction of a more potent, less diabetogenic, and corticosteroid-free immunosuppressive regimen consisting of sirolimus, low-dose tacrolimus, and induction anti-interleukin-2 receptor antibody. While insulin independence rates under this protocol have been highly successful, patients must be maintained on lifelong immunosuppression. While the risk of malignancy, post-transplant lymphoma and sepsis have been low and diminishing in transplanted patients to date, fears of these complications and a host of drug-related adverse effects have precluded broader application. Patients undergoing islet transplantation today must exchange insulin for chronic immunosuppressive therapy, and therefore the procedure can only be justified in patients with very unstable forms of diabetes, or in those with another solid organ allograft who already endure the risks of immunosuppression. Advances in more specific and less toxic immunosuppressive agents together with progress in better understanding the biology of diabetes will lead to more suitable strategies to control both alloimmune and recurrent autoimmune reactions. These protocols, ultimately aimed at establishing tolerance, are an essential pre-requisite to move towards providing islet transplantation earlier in the course of the disease, including transplantation in children. This review addresses the evolution of immunosuppressive strategies in islet transplantation, and highlights some novel agents in pre-clinical development or in early clinical trials that may offer considerable promise in facilitating the induction of tolerance.

Egress: a receptor-regulated step in lymphocyte trafficking

Blood lymphocyte numbers, which are maintained by recirculation through secondary lymphoid organs, are essential for the efficient development of immune responses. Recirculating populations of B and T lymphocytes are regulated by the sphingosine-1-phosphate (S1P) receptor-dependent control of lymphocyte egress. T-cell egress from thymus into blood, egress from lymph node and Peyer's patch into lymph, and B-cell egress into lymph are rapidly and completely inhibited by agonism of S1P receptors. Mesenteric lymph nodes show log-jamming of lymphocytes subjacent to sinus-lining endothelium. Agonism of S1P receptors produces rapid peripheral blood lymphopenia, which is maintained in the presence of receptor agonist. Effector CD4+ and CD8+ T cells, produced by clonal expansion in draining lymph node in response to antigen, are sequestered in lymph node and fail to reach the peripheral blood. The S1P receptor system may represent an early physiological link between the non-specific inflammatory response and the alteration of lymphocyte traffic through draining lymph nodes. Pharmacological subversion of the S1P receptor system, through systemic S1P agonist-induced inhibition of lymphocyte egress, suppresses antigenic responses to peripheral, but not to systemically, delivered antigen. This inhibition induces significant immunosuppression in models of transplantation and autoimmune tissue damage that may prove to be of clinical benefit.

Transduction of multiple effects of sphingosine 1-phosphate (S1P) on T cell functions by the S1P1 G protein-coupled receptor

Sphingosine 1-phosphate (S1P) in blood, lymph, and immune tissues stimulates and regulates T cell migration through their S1P(1) (endothelial differentiation gene encoded receptor-1) G protein-coupled receptors. We show now that S1P(1)Rs also mediate suppression of T cell proliferation and cytokine production. Uptake of [(3)H]thymidine by mouse CD4 T cells stimulated with anti-CD3 mAbs plus either anti-CD28 or IL-7 was inhibited up to 50% by 10(-9)-10(-6) M S1P. Suppression by S1P required Ca(2+) signaling and was reduced by intracellular cAMP. S1P decreased CD4 T cell generation of IFN-gamma and IL-4, without affecting IL-2. A Th1 line from D011.10 TCR transgenic mice without detectable S1P(1) was refractory to S1P until introduction of S1P(1) by retroviral transduction. S1P then evoked chemotaxis, inhibited chemotaxis to CCL-5 and CCL-21, and suppressed Ag-stimulated proliferation and IFN-gamma production. Thus, S1P(1) signals multiple immune functions of T cells as well as migration and tissue distribution.

Sphingosine 1-phosphate pathway therapeutics: a lipid ligand-receptor paradigm

New insights have been gained into the therapeutic relevance of the sphingosine 1-phosphate (S1P) pathway, on the basis of reverse pharmacological approaches to defining the mechanism of action of the immunosuppressive agent FTY720. Natural and synthetic sphingosine 1-phosphate receptor agonists can make picomolar interactions with their cognate G-protein-coupled receptors, and provide chemical approaches to defining the contribution of distinct receptor subtypes to pathology, physiology and treatment. The chemistry of S1P receptors and their synthetic ligands present a paradigm for the understanding of lipid-receptor interactions and their contribution to physiology and pathology. These approaches can potentially be extended to a broad, related family of G-protein-coupled receptors that share ligands and ligand similarities.