An immunosuppressive regimen using FTY720 combined with cyclosporin in canine kidney transplantation

A Requirement of Protein Geranylgeranylation for Chemokine Receptor Signaling and Th17 Cell Function in an Animal Model of Multiple Sclerosis

Precisely controlled lymphocyte migration is critically required for immune surveillance and successful immune responses. Lymphocyte migration is strictly regulated by chemokines and chemokine receptors. Here we show that protein geranylgeranylation, a form of post-translational protein lipid modification, is required for chemokine receptor-proximal signaling. Mature thymocytes deficient for protein geranylgeranylation are impaired for thymus egress. Circulating mature T cells lacking protein geranylgeranylation fail to home to secondary lymphoid organs or to transmigrate in response to chemokines in vitro. Mechanistically, protein geranylgeranylation modifies the γ-subunits of the heterotrimeric small GTPases that are essential for chemokine receptor signaling. In addition, protein geranylgeranylation also promotes the differentiation of IL-17-producing T helper cells while inhibiting the differentiation of Foxp3+ regulatory T cells. Finally, mice with T cell lineage-specific deficiency of protein geranylgeranylation are resistant to experimental autoimmune encephalomyelitis induction. This study elucidated a critical role of protein geranylgeranylation in regulating T lymphocyte migration and function.

Sphingosine-1-Phosphate Metabolism and Signaling in Kidney Diseases

In the past few decades, sphingolipids and sphingolipid metabolites have gained attention because of their essential role in the pathogenesis and progression of kidney diseases. Studies in models of experimental and clinical nephropathies have described accumulation of sphingolipids and sphingolipid metabolites, and it has become clear that the intracellular sphingolipid composition of renal cells is an important determinant of renal function. Proper function of the glomerular filtration barrier depends heavily on the integrity of lipid rafts, which include sphingolipids as key components. In addition to contributing to the structural integrity of membranes, sphingolipid metabolites, such as sphingosine-1-phosphate (S1P), play important roles as second messengers regulating biologic processes, such as cell growth, differentiation, migration, and apoptosis. This review will focus on the role of S1P in renal cells and how aberrant extracellular and intracellular S1P signaling contributes to the pathogenesis and progression of kidney diseases.

Fingolimod: Lessons Learned and New Opportunities for Treating Multiple Sclerosis and Other Disorders

Fingolimod (FTY720, Gilenya) was the first US Food and Drug Administration-approved oral therapy for relapsing forms of multiple sclerosis (MS). Research on modified fungal metabolites converged with basic science studies that had identified lysophospholipid (LP) sphingosine 1-phosphate (S1P) receptors, providing mechanistic insights on fingolimod while validating LP receptors as drug targets. Mechanism of action (MOA) studies identified receptor-mediated processes involving the immune system and the central nervous system (CNS). These dual actions represent a more general theme for S1P and likely other LP receptor modulators. Fingolimod's direct CNS activities likely contribute to its efficacy in MS, with particular relevance to treating progressive disease stages and forms that involve neurodegeneration. The evolving understanding of fingolimod's MOA has provided strategies for developing next-generation compounds with superior attributes, suggesting new ways to target S1P as well as other LP receptor modulators for novel therapeutics in the CNS and other organ systems.

Sphingosine 1-phosphate receptor 1 as a useful target for treatment of multiple sclerosis

Sphingosine 1-phosphate (S1P), a lysophospholipid mediator, is generated from sphingosine by sphingosine kinases and binds five known cell surface receptors. S1P receptor 1 (S1P₁) plays an essential role in lymphocyte egress from secondary lymphoid organs (SLO), as evinced by the inability of lymphocytes to exit from the SLO in mice lacking lymphocytic S1P₁. Fingolimod hydrochloride (FTY720) is a first-in-class, orally active, S1P receptor modulator with a structure closely related to sphingosine. FTY720 was first synthesized by chemical modification of a natural product, myriocin. FTY720 is effectively converted to an active metabolite, FTY720 phosphate (FTY720-P) by sphingosine kinases. FTY720-P shows high affinity to 4 of the S1P receptors (S1P₁, S1P₃, S1P₄, and S1P₅). In particular, FTY720-P strongly induces internalization and degradation of S1P₁, inhibits S1P responsiveness of lymphocytes in the SLO, and acts as a functional antagonist at lymphocytic S1P₁. Consequently, FTY720 inhibits S1P₁-dependent lymphocyte egress from the SLO to decrease circulation of lymphocytes including autoreactive Th17 cells and is highly effective in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Because FTY720 shows a superior efficacy in relapsing remitting MS patients compared to intramuscular interferon-β-1a (Avonex^®), S1P₁ is presumed to be a useful target for the therapy of MS.

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.

Regulation of immunity by lysosphingolipids and their G protein-coupled receptors

T and B lymphocytes, as well as endothelial cells, express distinctive profiles of G protein-coupled receptors for sphingosine 1-phosphate, which is a major regulator of T cell development, B and T cell recirculation, tissue homing patterns, and chemotactic responses to chemokines. The capacity of drugs that act on type 1 sphingosine 1-phosphate receptors to suppress organ graft rejection in humans and autoimmunity in animal models without apparent impairment of host defenses against infections suggests that this system is a promising target for new forms of immunotherapy.

Crossing the bridge: large animal models in translational transplantation research

Many methods for reducing the immunosuppressive requirements of allotransplantation have been proposed based on a growing understanding of physiological and allospecific immunity. As these regimens are developed for clinical application, they require validation in models that are reasonably predictive of their performance in humans. This article provides an overview of the large animal models commonly used to test immunomodulatory organ transplant protocols. The rationale for the use of large animals and the effects of common immunosuppressants in the dog, pig, and non-human primate are reviewed. Promising methods for the induction of allospecific tolerance are surveyed with references to early human trials where appropriate.