FTY720 impairs CD8 T-cell function independently of the sphingosine-1-phosphate pathway

Drug Resistance: The Role of Sphingolipid Metabolism

A significant challenge in cancer treatment is the rising problem of drug resistance that reduces the effectiveness of therapeutic strategies. Current knowledge shows that multiple mechanisms play a role in cancer drug resistance. Another mechanism that has gained attention is the alteration in sphingolipid trafficking and the dysregulation of its metabolism, which was reported to cause cancer-associated drug resistance. Sphingolipids are lipids containing sphingosine and have multiple roles, ranging from lipid raft formation, apoptosis, and cell signaling to immune cell trafficking. Recent studies show that in developing cancer cells, altered or dysregulated sphingolipids are associated with drug efflux and promote the survival of cancer cells by bypassing apoptosis. Upregulated levels of the glucosylceramide synthase (GCS), an enzyme that functions in sphingolipid metabolism, lead to the upregulated ABCB1 gene that induces drug efflux from the cancer cells. These bypass mechanisms make drugs that induce apoptosis in tumor cells ineffective. By highlighting the current findings, this review aims to provide a mechanism of drug resistance caused by the dysregulation of glucosylceramide synthase, sphingosine kinase, and acid ceramidase enzymes as possible therapeutic targets to enhance the effectiveness of the currently used chemotherapeutic agents.

Recent Insight into the Role of Sphingosine-1-Phosphate Lyase in Neurodegeneration

Sphingosine-1-phosphate lyase (SPL) is a pyridoxal 5'-phosphate-dependent enzyme involved in the irreversible degradation of sphingosine-1-phosphate (S1P)-a bioactive sphingolipid that modulates a broad range of biological processes (cell proliferation, migration, differentiation and survival; mitochondrial functioning; and gene expression). Although SPL activity leads to a decrease in the available pool of S1P in the cell, at the same time, hexadecenal and phosphoethanolamine, compounds with potential biological activity, are generated. The increased expression and/or activity of SPL, and hence the imbalance between S1P and the end products of its cleavage, were demonstrated in several pathological states. On the other hand, loss-of-function mutations in the SPL encoding gene are a cause of severe developmental impairments. Recently, special attention has been paid to neurodegenerative diseases as the most common pathologies of the nervous system. This review summarizes the current findings concerning the role of SPL in the nervous system with an emphasis on neurodegeneration. Moreover, it briefly discusses pharmacological compounds directed to inhibit its activity.

An update on the use of sphingosine 1-phosphate receptor modulators for the treatment of relapsing multiple sclerosis

INTRODUCTION

Multiple sclerosis (MS) is an immune-mediated disorder of the CNS manifested by recurrent attacks of neurological symptoms (related to focal inflammation) and gradual disability accrual (related to progressive neurodegeneration and neuroinflammation). Sphingosine-1-phosphate-receptor (S1PR) modulators are a class of oral disease-modifying therapies (DMTs) for relapsing MS. The first S1PR modulator developed and approved for MS was fingolimod, followed by siponimod, ozanimod, and ponesimod. All are S1P analogues with different S1PR-subtype selectivity. They restrain the S1P-dependent lymphocyte egress from lymph nodes by binding the lymphocytic S1P-subtype-1-receptor. Depending on their pharmacodynamics and pharmacokinetics, they can also interfere with other biological functions.

AREAS COVERED

Our narrative review covers the PubMed English literature on S1PR modulators in MS until August 2022. We discuss their pharmacology, efficacy, safety profile, and risk management recommendations based on the results of phase II and III clinical trials. We briefly address their impact on the risk of infections and vaccines efficacy.

EXPERT OPINION

S1PR modulators decrease relapse rate and may modestly delay disease progression in people with relapsing MS. Aside their established benefit, their place and timing within the long-term DMT strategy in MS, as well as their immunological effects in the new and evolving context of the post-COVID-19 pandemic and vaccination campaigns warrant further study.

S1P/S1PR1 signaling differentially regulates the allogeneic response of CD4 and CD8 T cells by modulating mitochondrial fission

Graft-versus-host disease (GVHD) significantly contributes to patient morbidity and mortality after allogeneic hematopoietic cell transplantation (allo-HSCT). Sphingosine-1-phosphate (S1P) signaling is involved in the biogenetic processes of different immune cells. In the current study, we demonstrated that recipient sphingosine kinase 1 (Sphk1), but not Sphk2, was required for optimal S1PR1-dependent donor T-cell allogeneic responses by secreting S1P. Using genetic and pharmacologic approaches, we demonstrated that inhibition of Sphk1 or S1PR1 substantially attenuated acute GVHD (aGVHD) while retaining the graft-versus-leukemia (GVL) effect. At the cellular level, the Sphk1/S1P/S1PR1 pathway differentially modulated the alloreactivity of CD4+ and CD8+ T cells; it facilitated T-cell differentiation into Th1/Th17 cells but not Tregs and promoted CD4+ T-cell infiltration into GVHD target organs but was dispensable for the CTL activity of allogeneic CD8+ T cells. At the molecular level, the Sphk1/S1P/S1PR1 pathway augmented mitochondrial fission and increased mitochondrial mass in allogeneic CD4+ but not CD8+ T cells by activating the AMPK/AKT/mTOR/Drp1 pathway, providing a mechanistic basis for GVL maintenance when S1P signaling was inhibited. For translational purposes, we detected the regulatory efficacy of pharmacologic inhibitors of Sphk1 and S1PR1 in GVHD induced by human T cells in a xenograft model. Our study provides novel mechanistic insight into how the Sphk1/S1P/S1PR1 pathway modulates T-cell alloreactivity and validates Sphk1 or S1PR1 as a therapeutic target for the prevention of GVHD and leukemia relapse. This novel strategy may be readily translated into the clinic to benefit patients with hematologic malignancies and disorders.

S1P/S1PR1 signaling differentially regulates the allogeneic response of CD4 and CD8 T cells by modulating mitochondrial fission

Graft-versus-host disease (GVHD) significantly contributes to patient morbidity and mortality after allogeneic hematopoietic cell transplantation (allo-HSCT). Sphingosine-1-phosphate (S1P) signaling is involved in the biogenetic processes of different immune cells. In the current study, we demonstrated that recipient sphingosine kinase 1 (Sphk1), but not Sphk2, was required for optimal S1PR1-dependent donor T-cell allogeneic responses by secreting S1P. Using genetic and pharmacologic approaches, we demonstrated that inhibition of Sphk1 or S1PR1 substantially attenuated acute GVHD (aGVHD) while retaining the graft-versus-leukemia (GVL) effect. At the cellular level, the Sphk1/S1P/S1PR1 pathway differentially modulated the alloreactivity of CD4⁺ and CD8⁺ T cells; it facilitated T-cell differentiation into Th1/Th17 cells but not Tregs and promoted CD4⁺ T-cell infiltration into GVHD target organs but was dispensable for the CTL activity of allogeneic CD8⁺ T cells. At the molecular level, the Sphk1/S1P/S1PR1 pathway augmented mitochondrial fission and increased mitochondrial mass in allogeneic CD4⁺ but not CD8⁺ T cells by activating the AMPK/AKT/mTOR/Drp1 pathway, providing a mechanistic basis for GVL maintenance when S1P signaling was inhibited. For translational purposes, we detected the regulatory efficacy of pharmacologic inhibitors of Sphk1 and S1PR1 in GVHD induced by human T cells in a xenograft model. Our study provides novel mechanistic insight into how the Sphk1/S1P/S1PR1 pathway modulates T-cell alloreactivity and validates Sphk1 or S1PR1 as a therapeutic target for the prevention of GVHD and leukemia relapse. This novel strategy may be readily translated into the clinic to benefit patients with hematologic malignancies and disorders.

Sphingolipid metabolism in T cell responses after allogeneic hematopoietic cell transplantation

Allogeneic hematopoietic cell transplantation (allo-HCT) is an effective immunotherapy against hematopoietic malignancies. The infused donor lymphocytes attack malignant cells and normal tissues, termed a graft-verse-leukemia (GVL) effect and graft-verse-host (GVH) response or disease (GVHD), respectively. Although engineering techniques toward donor graft selection have made HCT more specific and effective, primary tumor relapse and GVHD are still major concerns post allo-HCT. High-dose systemic steroids remain to be the first line of GVHD treatment, which may lead to steroid-refractory GVHD with a dismal outcome. Therefore, identifying novel therapeutic strategies that prevent GVHD while preserving GVL activity is highly warranted. Sphingolipid metabolism and metabolites play pivotal roles in regulating T-cell homeostasis and biological functions. In this review, we summarized the recent research progress in this evolving field of sphingolipids with a focus on alloreactive T-cell responses in the context of allo-HCT. We discussed how sphingolipid metabolism regulates T-cell mediated GVH and GVL responses in allo-HCT and presented the rationale and means to target sphingolipid metabolism for the control of GVHD and leukemia relapse.

Molecular Pharmacology and Novel Potential Therapeutic Applications of Fingolimod

Fingolimod is a well-tolerated, highly effective disease-modifying therapy successfully utilized in the management of multiple sclerosis. The active metabolite, fingolimod-phosphate, acts on sphingosine-1-phosphate receptors (S1PRs) to bring about an array of pharmacological effects. While being initially recognized as a novel agent that can profoundly reduce T-cell numbers in circulation and the CNS, thereby suppressing inflammation and MS, there is now rapidly increasing knowledge on its previously unrecognized molecular and potential therapeutic effects in diverse pathological conditions. In addition to exerting inhibitory effects on sphingolipid pathway enzymes, fingolimod also inhibits histone deacetylases, transient receptor potential cation channel subfamily M member 7 (TRMP7), cytosolic phospholipase A2α (cPLA2α), reduces lysophosphatidic acid (LPA) plasma levels, and activates protein phosphatase 2A (PP2A). Furthermore, fingolimod induces apoptosis, autophagy, cell cycle arrest, epigenetic regulations, macrophages M1/M2 shift and enhances BDNF expression. According to recent evidence, fingolimod modulates a range of other molecular pathways deeply rooted in disease initiation or progression. Experimental reports have firmly associated the drug with potentially beneficial therapeutic effects in immunomodulatory diseases, CNS injuries, and diseases including Alzheimer's disease (AD), Parkinson's disease (PD), epilepsy, and even cancer. Attractive pharmacological effects, relative safety, favorable pharmacokinetics, and positive experimental data have collectively led to its testing in clinical trials. Based on the recent reports, fingolimod may soon find its way as an adjunct therapy in various disparate pathological conditions. This review summarizes the up-to-date knowledge about molecular pharmacology and potential therapeutic uses of fingolimod.

Blocking T-cell egress with FTY720 extends DNA vaccine expression but reduces immunogenicity

Optimal immunogenicity from nucleic acid vaccines requires a balance of antigen expression that effectively engages the host immune system without generating a cellular response that rapidly destroys cells producing the antigen and thereby limiting vaccine antigen expression. We investigated the role of the cellular response on the expression and antigenicity of DNA vaccines using a plasmid DNA construct expressing luciferase. Repeated intramuscular administration led to diminished luciferase expression, suggesting a role for immune-mediated clearance of expression. To investigate the role of cell trafficking, we used the sphingosine 1-phosphate receptor (S1PR) modulator, FTY720 (Fingolimod), which traps lymphocytes within the lymphoid tissues. When lymphocyte trafficking was blocked with FTY720, DNA transgene expression was maintained at a constant level for a significantly extended time period. Both continuous and staggered administration of FTY720 prolonged transgene expression. However, blocking lymphocyte egress during primary transgene administration did not result in an increase of transgene expression during secondary administration. Interestingly, there was a disconnect between transgene expression and immunogenicity, as increasing expression by this approach did not enhance the overall immune response. Furthermore, when FTY720 was administered alongside a DNA vaccine expressing the HIV gp140 envelope antigen, there was a significant reduction in both antigen-specific antibody and T-cell responses. This indicates that the developing antigen-specific cellular response clears DNA vaccine expression but requires access to the site of expression in order to develop an effective immune response.

Longitudinal Imaging of T Cells and Inflammatory Demyelination in a Preclinical Model of Multiple Sclerosis Using 18F-FAraG PET and MRI

Lymphocytes and innate immune cells are key drivers of multiple sclerosis (MS) and are the main target of MS disease-modifying therapies (DMT). Ex vivo analyses of MS lesions have revealed cellular heterogeneity and variable T cell levels, which may have important implications for patient stratification and choice of DMT. Although MRI has proven valuable to monitor DMT efficacy, its lack of specificity for cellular subtypes highlights the need for complementary methods to improve lesion characterization. Here, we evaluated the potential of 2'-deoxy-2'-18F-fluoro-9-β-d-arabinofuranosylguanine (18F-FAraG) PET imaging to noninvasively assess infiltrating T cells and to provide, in combination with MRI, a novel tool to determine lesion types. Methods: We used a novel MS mouse model that combines cuprizone and experimental autoimmune encephalomyelitis to reproducibly induce 2 brain inflammatory lesion types, differentiated by their T cell content. 18F-FAraG PET imaging, T2-weighted MRI, and T1-weighted contrast-enhanced MRI were performed before disease induction, during demyelination with high levels of innate immune cells, and after T cell infiltration. Fingolimod immunotherapy was used to evaluate the ability of PET and MRI to detect therapy response. Ex vivo immunofluorescence analyses for T cells, microglia/macrophages, myelin, and blood-brain barrier (BBB) integrity were performed to validate the in vivo findings. Results:18F-FAraG signal was significantly increased in the brain and spinal cord at the time point of T cell infiltration. 18F-FAraG signal from white matter (corpus callosum) and gray matter (cortex, hippocampus) further correlated with T cell density. T2-weighted MRI detected white matter lesions independently of T cells. T1-weighted contrast-enhanced MRI indicated BBB disruption at the time point of T cell infiltration. Fingolimod treatment prevented motor deficits and decreased T cell and microglia/macrophage levels. In agreement, 18F-FAraG signal was decreased in the brain and spinal cord of fingolimod-treated mice; T1-weighted contrast-enhanced MRI revealed intact BBB, whereas T2-weighted MRI findings remained unchanged. Conclusion: The combination of MRI and 18F-FAraG PET enables detection of inflammatory demyelination and T cell infiltration in an MS mouse model, providing a new way to evaluate lesion heterogeneity during disease progression and after DMT. On clinical translation, these methods hold great potential for stratifying patients, monitoring MS progression, and determining therapy responses.

Targeting Sphingolipids for Cancer Therapy

Sphingolipids are an extensive class of lipids with different functions in the cell, ranging from proliferation to cell death. Sphingolipids are modified in multiple cancers and are responsible for tumor proliferation, progression, and metastasis. Several inhibitors or activators of sphingolipid signaling, such as fenretinide, safingol, ABC294640, ceramide nanoliposomes (CNLs), SKI-II, α-galactosylceramide, fingolimod, and sonepcizumab, have been described. The objective of this review was to analyze the results from preclinical and clinical trials of these drugs for the treatment of cancer. Sphingolipid-targeting drugs have been tested alone or in combination with chemotherapy, exhibiting antitumor activity alone and in synergism with chemotherapy in vitro and in vivo. As a consequence of treatments, the most frequent mechanism of cell death is apoptosis, followed by autophagy. Aslthough all these drugs have produced good results in preclinical studies of multiple cancers, the outcomes of clinical trials have not been similar. The most effective drugs are fenretinide and α-galactosylceramide (α-GalCer). In contrast, minor adverse effects restricted to a few subjects and hepatic toxicity have been observed in clinical trials of ABC294640 and safingol, respectively. In the case of CNLs, SKI-II, fingolimod and sonepcizumab there are some limitations and absence of enough clinical studies to demonstrate a benefit. The effectiveness or lack of a major therapeutic effect of sphingolipid modulation by some drugs as a cancer therapy and other aspects related to their mechanism of action are discussed in this review.

Polymeric Pathogen-Like Particles-Based Combination Adjuvants Elicit Potent Mucosal T Cell Immunity to Influenza A Virus

Eliciting durable and protective T cell-mediated immunity in the respiratory mucosa remains a significant challenge. Polylactic-co-glycolic acid (PLGA)-based cationic pathogen-like particles (PLPs) loaded with TLR agonists mimic biophysical properties of microbes and hence, simulate pathogen-pattern recognition receptor interactions to safely and effectively stimulate innate immune responses. We generated micro particle PLPs loaded with TLR4 (glucopyranosyl lipid adjuvant, GLA) or TLR9 (CpG) agonists, and formulated them with and without a mucosal delivery enhancing carbomer-based nanoemulsion adjuvant (ADJ). These adjuvants delivered intranasally to mice elicited high numbers of influenza nucleoprotein (NP)-specific CD8+ and CD4+ effector and tissue-resident memory T cells (T_RMs) in lungs and airways. PLPs delivering TLR4 versus TLR9 agonists drove phenotypically and functionally distinct populations of effector and memory T cells. While PLPs loaded with CpG or GLA provided immunity, combining the adjuvanticity of PLP-GLA and ADJ markedly enhanced the development of airway and lung T_RMs and CD4 and CD8 T cell-dependent immunity to influenza virus. Further, balanced CD8 (Tc1/Tc17) and CD4 (Th1/Th17) recall responses were linked to effective influenza virus control. These studies provide mechanistic insights into vaccine-induced pulmonary T cell immunity and pave the way for the development of a universal influenza and SARS-CoV-2 vaccines.

The ameliorative effects of capsidiol isolated from elicited Capsicum annuum on mouse splenocyte immune responses and neuroinflammation

Capsidiol, is an anti-fungal phytoalexin produced by plants of Solanaceae. Capsidiol was examined in cultures of primary splenocytes (SPLCs) isolated from healthy C57BL/6 mice and from those with induced experimental autoimmune encephalomyelitis (EAE) as a mouse model for autoimmune neurodegenerative multiple sclerosis (MS). We also examined the impact of capsidiol in IFN-γ-stimulated mouse BV2 microglial cells. Capsidiol resulted in a significant reduction in the anti-CD3/CD28 (αCD3/CD28)-induced IFN-γ⁺ CD4⁺ (Th1) and IFN-γ⁺ CD8⁺ (Tc1) populations as well as in the production of cytokines (IFN-γ, IL-17A, IL-6, IL-2, TNF-α, and IP-10). Specifically, the CD4⁺ and CD8⁺ populations (T-bet⁺ IFN-γ^- , T-bet⁺ IFN-γ⁺ , and T-bet^- IFN-γ⁺ ) and cytokine production mediated by Th1/Tc1 polarization were diminished by 25 μM capsidiol. MOG_35-55 restimulation of SPLCs from EAE mice resulted in an increase in antigen-specific T cells, including Th1, IL-17A⁺ CD4⁺ (Th17), and IL-17A⁺ CD8⁺ (Tc17) populations. By contrast, capsidiol resulted in a decrease in the proportions of Th17 and Tc17 cells; MOG_35-55 -specific cytokine production was also diminished by capsidiol. Capsidiol treatment resulted in diminished levels of IFN-γ-induced nitric oxide and IL-6; expression of iNOS and COX-2 were suppressed by 50 μM capsidiol in IFN-γ-stimulated BV2 cells. This is the first report of capsidiol-mediated immunomodulatory and antineuroinflammatory activities that may serve to prevent neurodegeneration.

Adjuvant-free nanofiber vaccine induces in situ lung dendritic cell activation and TH17 responses

The current paradigm that subunit vaccines require adjuvants to optimally activate innate immunity implies that increased vaccine reactogenicity will invariably be linked to improved immunogenicity. Countering this paradigm, nanoparticulate vaccines have been reported to act as delivery systems for vaccine antigens and induce immunity without the need for exogenous adjuvants or local inflammation; however, the mechanisms underlying the immunogenicity of nanoparticle vaccines are incompletely identified. Here, we show that antigens displayed on self-assembling nanofiber scaffolds and delivered intranasally are presented by CD103⁺ and CD11b⁺ lung dendritic cells that up-regulate CD80 and migrate into the draining lymph node (LN). This was accompanied by a nearly exclusive priming and accumulation of antigen-specific T_H17 cells occurring independently in both LN and lung. Thus, self-assembling peptide nanofiber vaccines may represent a novel, needle- and adjuvant-free means of eliciting protective immunity against fungal and bacterial infections at skin and mucosal barrier surfaces.

FTY720 ameliorates GvHD by blocking T lymphocyte migration to target organs and by skin fibrosis inhibition

BACKGROUND

Fibrosis is the formation of excess connective tissue in an organ or tissue during a reparative or reactive process. Graft-versus-host disease (GvHD) is a medical complication of allogeneic tissue transplantation with transplanted donor T cell-mediated inflammatory response; it is characterized by a severe immune response with fibrosis in the final stage of the inflammatory process. T helper 17 cells play a critical role in the pathogenesis of GvHD. Fingolimod (FTY720), an analogue of sphingosine-1-phosphate (S1P), is an effective immunosuppressive agent in experimental transplantation models.

METHODS

In this study, we evaluated the effects of FTY720 as a treatment for an animal GvHD model with inflammation and fibrosis. The splenocytes, lymph nodes, blood, tissues from Syngeneic mice and GvHD-induced mice treated vehicle or FTY720 were compared using flow cytometry, hematological analyses, histologic analyses.

RESULTS

FTY720 reduced clinical scores based on the following five clinical parameters: weight loss, posture, activity, fur texture, and skin integrity. FACS data showed that T lymphocyte numbers increased in mesenteric lymph nodes and decreased in splenocytes of FTY720-treated mice. Tissue analysis showed that FTY720 reduced skin, intestinal inflammation, and fibrotic markers. FTY720 dramatically decreased α-smooth muscle actin, connective tissue growth factor, and fibronectin protein levels in keloid skin fibroblasts.

CONCLUSIONS

Thus, FTY720 suppressed migration of pathogenic T cells to target organs, reducing inflammation. FTY720 also inhibited fibrogenesis marker expression in vitro and in vivo. Together, these results suggest that FTY720 prevents GvHD progression via immunosuppression of TH17 and simultaneously acts an anti-fibrotic agent.

Molecular Interventions towards Multiple Sclerosis Treatment

Multiple sclerosis (MS) is an autoimmune life-threatening disease, afflicting millions of people worldwide. Although the disease is non-curable, considerable therapeutic advances have been achieved through molecular immunotherapeutic approaches, such as peptides vaccination, administration of monoclonal antibodies, and immunogenic copolymers. The main aims of these therapeutic strategies are to shift the MS-related autoimmune response towards a non-inflammatory T helper 2 (Th2) cells response, inactivate or ameliorate cytotoxic autoreactive T cells, induce secretion of anti-inflammatory cytokines, and inhibit recruitment of autoreactive lymphocytes to the central nervous system (CNS). These approaches can efficiently treat autoimmune encephalomyelitis (EAE), an essential system to study MS in animals, but they can only partially inhibit disease progress in humans. Nevertheless, modern immunotherapeutic techniques remain the most promising tools for the development of safe MS treatments, specifically targeting the cellular factors that trigger the initiation of the disease.

The Immunosuppressant Fingolimod (FTY720) for the Treatment of Mechanical Force-Induced Abnormal Scars

Aim

Abnormal scars such as hypertrophic scars (HSs) and keloids are excessively growing scars that exhibit chronic inflammation and capillary vasculogenesis. The lipid mediator sphingosine-1-phosphate (S1P) is important in inflammatory cell recruitment and angiogenesis. Fingolimod (FTY720) is an analog of S1P and thus functionally antagonizes S1P receptors and inhibits the enzyme that produces S1P. We examined the effects of topical FTY720 injections on mechanical force-induced HS progression.

Methods

Mechanical force-induced HSs were generated in C57BL6/J mice by suturing a dorsal incision and applying a stretching device on Days 6, 8, 10, and 12. On Days 8, 10, and 12, intracutaneous FTY720 (10 μM) or control vehicle injections were performed. On Day 14, scar tissues and blood were procured and subjected to histology and flow cytometry.

Results

Flow cytometry showed that FTY720 decreased the frequencies of macrophages with M2 predominance in the scars but had no effect on total, CD4⁺, or CD8a⁺ T cell frequencies. FTY720 also decreased the vascular endothelial cell frequencies in the scar along with the microvessels, as determined by immunohistochemistry. Compared to the vehicles, FTY720 treatment significantly reduced the gross scar area and the cross-sectional scar area on histology. On the other hand, FTY720 tended to reduce white blood cells and significantly reduced the lymphocyte frequencies in the blood.

Conclusion

Topical FTY720 induces M2 predominance and impairs angiogenesis. Therefore, its local immunosuppressive mechanisms differ from those of conventional immunosuppressive agents. Topical FTY720 can be a novel therapeutic option for abnormal scars that are difficult to control with corticosteroids. Its lymphocytopenic effects may be limited by careful optimization of the treatment regimen.

Fingolimod retains cytolytic T cells and limits T follicular helper cell infection in lymphoid sites of SIV persistence

Lymph nodes (LN) and their resident T follicular helper CD4+ T cells (Tfh) are a critical site for HIV replication and persistence. Therefore, optimizing antiviral activity in lymphoid tissues will be needed to reduce or eliminate the HIV reservoir. In this study, we retained effector immune cells in LN of cART-suppressed, SIV-infected rhesus macaques by treatment with the lysophospholipid sphingosine-1 phosphate receptor modulator FTY720 (fingolimod). FTY720 was remarkably effective in reducing circulating CD4+ and CD8+ T cells, including those with cytolytic potential, and in increasing the number of these T cells retained in LN, as determined directly in situ by histocytometry and immunohistochemistry. The FTY720-induced inhibition of T cell egress from LN resulted in a measurable decrease of SIV-DNA content in blood as well as in LN Tfh cells in most treated animals. In conclusion, FTY720 administration has the potential to limit viral persistence, including in the critical Tfh cellular reservoir. These findings provide rationale for strategies designed to retain antiviral T cells in lymphoid tissues to target HIV remission.

FTY720 (fingolimod), a drug approved by the FDA for treatment of multiple sclerosis, blocks the egress of lymphocytes from the lymph node (LN). To determine whether FTY720 retention activity could improve cytolytic responses in the LN and affect SIV persistence, we studied for the first time tolerability and biological activity of two doses of FTY720 in cART-suppressed, SIV-infected rhesus macaques. FTY720 was remarkably effective in reducing circulating CD4+ and CD8+ T cells, including those with cytolytic potential, and in increasing the number of cytolytic T cells in LN. FTY720 administration reduced SIV-DNA content in blood as well as in LN Tfh cells in most of the animals. These results suggest that FTY720 limits viral persistence, including Tfh cellular reservoir, by increasing the number of cytolytic cells in the LN, critical site for HIV/SIV replication and persistence.

Ethanol extract of Glycyrrhizae Radix modulates the responses of antigen-specific splenocytes in experimental autoimmune encephalomyelitis

BACKGROUND

Multiple sclerosis (MS) is an autoimmune disorder resulting in paralysis, and the responses of reactive T cells against self-antigens are hallmarks. Glycyrrhizae Radix (GR) has been used for detoxification and reducing inflammation. However, very few reports have described the effects of GR on MS.

PURPOSE

The immunomodulatory effects of GR extract on autoimmune responses were evaluated through in vitro, ex vivo, and in vivo assays using primary mouse splenocytes (SPLC), mouse microglia BV2 cell line, and a mouse model of experimental autoimmune encephalomyelitis (EAE).

STUDY DESIGN

Ethanol extract of GR was used in vitro with primary SPLC in the condition of anti-CD3/CD28 stimulation and interferon (IFN)-γ-producing CD4+ (TH1)/CD8+ (TC1) polarization as well as IFN-γ-stimulated BV2 cells. For EAE induction, female C57BL/6 mice were immunized with 200 μg of myelin oligodendrocyte glycoprotein (MOG)35-55 without pertussis toxin. EAE SPLC (ex vivo) and EAE mice (in vivo) were treated with GR extract to evaluate the changes in antigen-specific responses. SPLC media containing antigen-specific responses were used to stimulate BV2 cells.

RESULTS

GR extract effectively modulated the responses of reactive splenic T cells through the reduction in IFN-γ+ T cell populations, the expressions of cell adhesion molecules (CAMs), and secretions of cytokines containing IFN-γ and a chemokine IFN-γ-induced protein 10 (IP-10) in vitro. In addition, GR extract significantly decreased nitric oxide production and secretion of tumor necrosis factor (TNF)-α and IP-10 in IFN-γ-stimulated BV2 cells. The antigen-specific TH1 and TC1 populations were decreased following administration of 100 mg/kg of GR extract, whereas CD8+IL-17A+ (TC17) population was increased on day 36 after EAE induction. Moreover, IFN-γ, which showed the highest secretion among examined cytokines, and IP-10 decreased on day 36. SPLC media derived from 100 mg/kg GR extract-administered EAE mice revealed the ameliorative effects on BV2 cell stimulation.

CONCLUSION

This is the first report on the immunomodulatory effects of GR extract on antigen-specific SPLC responses in EAE. These results could be helpful for the discovery of drug candidates for MS by focusing on IFN-γ-related autoimmune responses.

Fingolimod modulates T cell phenotype and regulatory T cell plasticity in vivo

Fingolimod is an approved therapeutic option for patients with relapsing-remitting multiple sclerosis that primarily functions by sequestering T cells in lymph nodes inhibiting their egress to the central nervous system. However, recent data suggests that Fingolimod may also directly affect the immune cell function. Here we examined the in vivo effects of Fingolimod in modulating the phenotype and function of T cell and Foxp3 regulatory T cell populations in patients with multiple sclerosis under Fingolimod treatment. Besides decreasing the cell numbers in peripheral blood and sera levels of pro-inflammatory cytokines, Fingolimod inhibited the expression of Th1 and Th17 cytokines on CD4⁺ T cells and increased the expression of exhaustion markers. Furthermore, treatment increased the frequency of regulatory T cells in blood and inhibited the Th1-like phenotype that is characteristic of patients with multiple sclerosis, augmenting the expression of markers associated with increased suppressive function. Overall, our data suggest that Fingolimod performs other important immunomodulatory functions besides altering T cell migratory capacities, with consequences for other autoimmune pathologies characterized by excessive Th1/Th17 responses and Th1-like regulatory T cell effector phenotypes.

Lymphocyte Autophagy in Homeostasis, Activation, and Inflammatory Diseases

Autophagy is a catabolic mechanism, allowing the degradation of cytoplasmic content via lysosomal activity. Several forms of autophagy are described in mammals. Macroautophagy leads to integration of cytoplasmic portions into vesicles named autophagosomes that ultimately fuse with lysosomes. Chaperone-mediated autophagy is in contrast the direct translocation of protein in lysosomes. Macroautophagy is central to lymphocyte homeostasis. Although its role is controversial in lymphocyte development and in naive cell survival, it seems particularly involved in the maintenance of certain lymphocyte subtypes. Its importance in memory B and T cells biology has recently emerged. Moreover, some effector cells like plasma cells rely on autophagy for survival. Autophagy is central to glucose and lipid metabolism, and to the maintenance of organelles like mitochondria and endoplasmic reticulum. In addition macroautophagy, or individual components of its machinery, are also actors in antigen presentation by B cells, a crucial step to receive help from T cells, this crosstalk favoring their final differentiation into memory or plasma cells. Autophagy is deregulated in several autoimmune or autoinflammatory diseases like systemic lupus erythematosus, rheumatoid arthritis, multiple sclerosis, and Crohn’s disease. Some treatments used in these pathologies impact autophagic activity, even if the causal link between autophagy regulation and the efficiency of the treatments has not yet been clearly established. In this review, we will first discuss the mechanisms linking autophagy to lymphocyte subtype survival and the signaling pathways involved. Finally, potential impacts of autophagy modulation in lymphocytes on the course of these diseases will be approached.

Characterization of the effects of immunomodulatory drug fingolimod (FTY720) on human T cell receptor signaling pathways

Immune responses against gene therapy products limit its therapeutic efficacy and present a safety risk. Identification of agents that blunt immune reactions may aid in developing novel immunomodulatory therapies. Fingolimod (FTY720) is an FDA approved immunomodulatory drug for treating multiple sclerosis that inhibits lymphocyte egress from lymphoid tissues by down regulating sphingosine-1 phosphate receptor (S1PR). Recent studies found that FTY720 inhibits T cell activation (TCA) in a S1PR-independent manner; however, the mechanism is incompletely understood. Here we characterized the effects of FTY720 on human T cell receptor (TCR) signaling pathways. FTY720 inhibited both the TCR-dependent and independent activation of primary human T cells. FTY720 did not affect proximal TCR signaling events as measured by phosphorylation of Lck, ZAP-70 and LAT; however, inhibited PMA/Ionomycin induced distal TCR signaling as measured by IL-2, IFN-γ release and CD25 expression. FTY720 induced aberrant NFAT1, AP1 and NFκB activation which were associated with increased acetylation of histone (H3K9). Phosphorylated FTY720 did not inhibit TCA, and arachidonic acid did not rescue FTY720 mediated inhibition of TCA. These data suggest that FTY720 mediated inhibition of TCA is due to inhibition of distal TCR signaling. Understanding FTY720-mediated inhibition of TCA may aid in developing novel FTY720-based immunomodulatory agents.

Vaccination-induced skin-resident memory CD8+ T cells mediate strong protection against cutaneous melanoma

Memory CD8⁺ T cell responses have the potential to mediate long-lasting protection against cancers. Resident memory CD8⁺ T (Trm) cells stably reside in non-lymphoid tissues and mediate superior innate and adaptive immunity against pathogens. Emerging evidence indicates that Trm cells develop in human solid cancers and play a key role in controlling tumor growth. However, the specific contribution of Trm cells to anti-tumor immunity is incompletely understood. Moreover, clinically applicable vaccination strategies that efficiently establish Trm cell responses remain largely unexplored and are expected to strongly protect against tumors. Here we demonstrated that a single intradermal administration of gene- or protein-based vaccines efficiently induces specific Trm cell responses against models of tumor-specific and self-antigens, which accumulated in vaccinated and distant non-vaccinated skin. Vaccination-induced Trm cells were largely resistant to in vivo intravascular staining and antibody-dependent depletion. Intradermal, but not intraperitoneal vaccination, generated memory precursors expressing skin-homing molecules in circulation and Trm cells in skin. Interestingly, vaccination-induced Trm cell responses strongly suppressed the growth of B16F10 melanoma, independently of circulating memory CD8⁺ T cells, and were able to infiltrate tumors. This work highlights the therapeutic potential of vaccination-induced Trm cell responses to achieve potent protection against skin malignancies.

Fingolimod-improved axonal and myelin integrity of white matter tracts associated with multiple sclerosis-related functional impairments

AIMS

Fingolimod hydrochloride is an effective immunomodulatory drug in improving relapsing-remitting multiple sclerosis (RRMS). However, data on the neuroradiologic effects on white matter (WM) have not been demonstrated. In this study, we aimed elucidating the impact of 1-year fingolimod treatment on WM integrity in patients with RRMS.

METHODS

Diffusion tensor imaging (DTI) was applied to assess axonal and myelin integrity in specific WM tracts of patients with RRMS prior to and 1 year postfingolimod treatment (n = 30). The fractional anisotropy (FA), radial diffusivity (RD), axial diffusivity, and mean diffusivity were analyzed using tract-based spatial statistics on specific regions of interest associated with impaired Expanded Disability Status Scale functional scores before treatment.

RESULTS

In patients with impaired pyramidal function at baseline (average score 2.3 ± 0.2, n = 25), fingolimod induced a significant increase in FA (P = 0.002) and decrease in RD (P = 0.03) in the corticospinal tract. In patients with impaired cerebellar function at baseline (average score 2.0 ± 0.1, n = 19), significant increases in FA and decreases in RD were observed in the superior (P = 0.02, P = 0.01, respectively) and inferior (P = 0.03, P = 0.05, respectively) cerebellar peduncles.

CONCLUSION

The observed results suggest increased microstructural integrity and decreased demyelination of damaged WM tracts and support the possible direct mechanism of fingolimod action.

Successful treatment with fingolimod of graft-versus-host disease of the central nervous system

Fingolimod could be efficient to treat GVHD of the central nervous system.Further research should explore the use of fingolimod and other sphingosine-1-phosphate receptor agonists to prevent or treat GVHD.

The Role of Inflammatory Response in Stroke Associated Programmed Cell Death

Stroke represents devastating pathology which is associated with a high morbidity and mortality. Initial damage caused directly by the onset of stroke, primary injury, may be eclipsed by secondary injury which may have a much more devastating effect on the brain. Primary injury is predominantly associated with necrotic cell death due to fatal insufficiency of oxygen and glucose. Secondary injury may on the contrary, lead apoptotic cell death due to structural damage which is not compatible with cellular functions or which may even represent the danger of malign transformation. The immune system is responsible for surveillance, defense and healing processes and the immune system plays a major role in triggering programmed cell death. Severe pathologies, such as stroke, are often associated with deregulation of the immune system, resulting in aggravation of secondary brain injury. The goal of this article is to overview the current knowledge about the role of immune system in the pathophysiology of stroke with respect to programmed neuronal cell death as well as to discuss current therapeutic strategies targeting inflammation after stroke.

Narcolepsy Type 1 as an Autoimmune Disorder: Evidence, and Implications for Pharmacological Treatment

Narcolepsy type 1 (NT1) is a rare sleep disorder caused by the very specific loss of hypothalamic hypocretin (Hcrt)/orexin neurons. The exact underlying process leading to this destruction is yet unknown, but indirect evidence strongly supports an autoimmune origin. The association with immune-related genetic factors, in particular the strongest association ever reported in a disease with an allele of a human leukocyte antigen (HLA) gene, and with environmental factors (i.e., the H1N1 influenza infection and vaccination during the pandemic in 2009) are in favor of such a hypothesis. The loss of Hcrt neurons is irreversible, and NT1 is currently an incurable and disabling condition. Patients are managed with symptomatic medication, targeting the main symptoms (excessive daytime sleepiness, cataplexy, disturbed nocturnal sleep), and they require a lifelong treatment. Improved diagnostic tools, together with an increased understanding of the pathogenesis of NT1, may lead to new therapeutic and even preventive interventions. One future treatment could include Hcrt replacement, but this neuropeptide does not cross the blood-brain barrier. However, Hcrt receptor agonists may be promising candidates to treat NT1. Another option is immune-based therapies, administered at disease onset, with already some initiatives to slow down or stop the dysimmune process. Whether immune-based therapy could be beneficial in NT1 remains, however, to be proven.

Cerebral toxoplasmosis in an MS patient receiving Fingolimod

Multiple Sclerosis (MS) is an autoimmune disease in which lymphocytes target putative myelin antigens in the CNS, causing inflammation and neurodegeneration. Fingolimod (FTY720) is an immunosuppressive drug used as a second line therapy for relapsing forms of MS due to its safety profile and good response to treatment. Despite its safety, there are still concerns about the possibility of Fingolimod being linked to the development of opportunistic infections like disseminated varicella zoster infections and herpes simplex encephalitis. In this case report, we describe one patient with past medical history of MS in current treatment with Fingolimod for the last year which presents herself with hemiparesis, fever and fatigue. The initial MRI showed multiple demyelinating-like lesions that could have corresponded to the tumefactive form of MS relapse. The blood work up revealed leukopenia with lymphopenia and a CD4+ count of 200 cell/mm³. Treatment for acute relapse was initiated with little to no response. Further examination was carried by the clinicians, a lumbar puncture was performed and it showed pleocytosis with increased protein levels. Later, several serologic studies were performed and both IgM and IgG antibodies for Toxoplasma were positive. Diagnosis of cerebral toxoplasmosis was made and there was no evidence of HIV infection or other causes of secondary immunodeficiency in this patient, except the use of fingolimod. Evidence of decreased levels of CD4+ due to Fingolimod use is concerning. The risk of opportunistic infections in these patients must be considered in order to start or continue therapy with these agents. Further studies are needed to determine the percentage of the population at risk of immunosuppression and its long-term consequences as well as new actions to prevent infections.

Severe murine limb-girdle muscular dystrophy type 2C pathology is diminished by FTY720 treatment

INTRODUCTION

Limb-girdle muscular dystrophy type 2C (LGMD-2C) is caused by mutations in γ-sarcoglycan and is a devastating, progressive, and fully lethal human muscle-wasting disease that has no effective treatment. This study examined the efficacy of the sphingosine-1-phosphate receptor modulator FTY720 in treating Sgcg^-/- DBA2/J, a severe mouse model of LGMD-2C. FTY720 treatment was expected to target LGMD-2C disease progression at 2 key positions by reducing chronic inflammation and fibrosis.

METHODS

The treatment protocol was initiated at age 3 weeks and was continued with alternate-day injections for 3 weeks.

RESULTS

The treatment produced significant functional benefit by plethysmography and significant reductions of membrane permeability and fibrosis. Furthermore, the protocol elevated protein levels of δ-sarcoglycan, a dystrophin-glycoprotein family member.

CONCLUSION

This study showed that FTY720 is an effective muscular dystrophy treatment when therapy is initiated early in the disease progression. Muscle Nerve 56: 486-494, 2017.

High-Resolution Expression Profiling of Peripheral Blood CD8+ Cells in Patients with Multiple Sclerosis Displays Fingolimod-Induced Immune Cell Redistribution

Fingolimod, a sphingosine-1-phosphate (S1P) receptor modulator, is an oral drug approved for the treatment of active relapsing-remitting multiple sclerosis (RRMS). It selectively inhibits the egress of lymphocytes from lymph nodes. We studied the changes in the transcriptome of peripheral blood CD8⁺ cells to unravel the effects at the molecular level during fingolimod therapy. We separated CD8⁺ cells from the blood of RRMS patients before the first dose of fingolimod as well as 24 h and 3 months after the start of therapy. Changes in the expression of coding and non-coding genes were measured with high-density Affymetrix Human Transcriptome Array (HTA) 2.0 microarrays. Differentially expressed genes in response to therapy were identified by t test and fold change and analyzed for their functions and molecular interactions. No gene was expressed at significantly higher or lower levels 24 h after the first administration of fingolimod compared to baseline. However, after 3 months of therapy, 861 transcripts were found to be differentially expressed, including interleukin and chemokine receptors. Some of the genes are associated to the S1P pathway, such as the receptor S1P5 and the kinase MAPK1, which were significantly increased in expression. The fingolimod-induced transcriptome changes reflect a shift in the proportions of CD8⁺ T cell subsets, with CCR7^- effector memory T cells being relatively increased in frequency in the blood of fingolimod-treated patients. In consequence, CCR7 mRNA levels were reduced by >80 % and genes involved in T cell activation and lymphocyte cytotoxicity were increased in expression. Gene regulatory programs caused by downstream S1P signaling had only minor effects.

Fingolimod therapy modulates circulating B cell composition, increases B regulatory subsets and production of IL-10 and TGFβ in patients with Multiple Sclerosis

Fingolimod, an oral therapeutic agent approved for patients with relapsing-remitting Multiple Sclerosis (MS), has been shown to prevent lymphocyte egress from secondary lymphoid tissues; however the specific drug effect on B cells in fingolimod-treated patients remains to be fully elucidated. We present here a comprehensive analysis on the proportions of B cell subsets in the periphery, and the levels of activation, functional surface markers and cytokine profile of B cells in MS patients, following initiation of fingolimod therapy, using flow cytometry and cytokine bead array. Fingolimod therapy increased the ratio of naïve to memory cells, elevated the percentage of plasma cells and highly increased the proportion of transitional B cells as well as additional regulatory subsets, including: IL10(+), CD25(+) and CD5(+) B cells. The percentage of activated CD69(+) cells was highly elevated in the remaining circulating B cells, which produced increased levels of IL10, TGFβ, IL6, IL4, LTα, TNFα and IFNγ cytokines, with an overall increased ratio of TGFβ to pro-inflammatory cytokines. Furthermore, fingolimod therapy reduced ICAM-1(+) cells, suggesting a possible reduction in antigen-presenting capacity. Phosphorylated-fingolimod was shown in vitro to reduce S1PR1 RNA and protein, to slightly increase viability and to activate anti-apoptotic Bcl2 in transformed B cells of patients with MS. In conclusion, fingolimod therapy modulates significantly the composition of circulating B cells, promoting regulatory subsets and an anti-inflammatory cytokine repertoire.

Sphingosine-1-Phosphate Signaling in Immune Cells and Inflammation: Roles and Therapeutic Potential

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite involved in many critical cell processes. It is produced by the phosphorylation of sphingosine by sphingosine kinases (SphKs) and exported out of cells via transporters such as spinster homolog 2 (Spns2). S1P regulates diverse physiological processes by binding to specific G protein-binding receptors, S1P receptors (S1PRs) 1-5, through a process coined as "inside-out signaling." The S1P concentration gradient between various tissues promotes S1PR1-dependent migration of T cells from secondary lymphoid organs into the lymphatic and blood circulation. S1P suppresses T cell egress from and promotes retention in inflamed peripheral tissues. S1PR1 in T and B cells as well as Spns2 in endothelial cells contributes to lymphocyte trafficking. FTY720 (Fingolimod) is a functional antagonist of S1PRs that induces systemic lymphopenia by suppression of lymphocyte egress from lymphoid organs. In this review, we summarize previous findings and new discoveries about the importance of S1P and S1PR signaling in the recruitment of immune cells and lymphocyte retention in inflamed tissues. We also discuss the role of S1P-S1PR1 axis in inflammatory diseases and wound healing.

Fingolimod targeting protein phosphatase 2A differently affects IL-33 induced IL-2 and IFN-γ production in CD8(+) lymphocytes

Multiple sclerosis patients are treated with fingolimod (FTY720), a prodrug that acts as an immune modulator. FTY720 is first phosphorylated to FTY720-P and then internalizes sphingosine-1-phosphate receptors, preventing lymphocyte sequestration. IL-33 is released from necrotic endothelial cells and contributes to MS severity by coactivating T cells. Herein we analyzed the influence of FTY720, FTY720-P, and S1P on IL-33 induced formation of IL-2 and IFN-γ, by using IL-33 receptor overexpressing EL4 cells, primary CD8(+) T cells, and splenocytes. EL4-ST2 cells released IL-2 after IL-33 stimulation that was inhibited dose-dependently by FTY720-P but not FTY720. In this system, S1P increased IL-2, and accordingly, inhibition of S1P producing sphingosine kinases diminished IL-2 release. In primary CD8(+) T cells and splenocytes IL-33/IL-12 stimulation induced IFN-γ, which was prevented by FTY720 but not FTY720-P, independently from intracellular phosphorylation. The inhibition of IFN-γ by nonphosphorylated FTY720 was mediated via the SET/protein phosphatase 2A (PP2A) pathway, since a SET peptide antagonist also prevented IFN-γ formation and the inhibition of IFN-γ by FTY720 was reversible by a PP2A inhibitor. While our findings directly improve the understanding of FTY720 therapy in MS, they could also contribute to side effects of FTY720 treatment, like progressive multifocal leukoencephalopathy, caused by an insufficient immune response to a viral infection.

Identification of a novel mechanism of action of fingolimod (FTY720) on human effector T cell function through TCF-1 upregulation

Background

Fingolimod (FTY720), the first oral treatment for multiple sclerosis (MS), blocks immune cell trafficking and prevents disease relapses by downregulation of sphingosine-1-phosphate receptor. We determined the effect of FTY720 on human T cell activation and effector function.

Methods

T cells from MS patients and healthy controls were isolated to measure gene expression profiles in the presence or absence of FTY720 using nanostring and quantitative real-time polymerase chain reaction (qPCR). Cytokine protein expression was measured using luminex assay and flow cytometry analysis. Lentivirus vector carrying short hairpin RNA (shRNA) was used to knock down the expression of specific genes in CD4+ T cells. Chromatin immunoprecipitation was performed to assess T cell factor 1 (TCF-1) binding to promoter regions. Luciferase assays were performed to test the direct regulation of interferon gamma (IFN-γ) and granzyme B (GZMB) by TCF-1. Western blot analysis was used to assess the phosphorylation status of Akt and GSK3β.

Results

We showed that FTY720 treatment not only affects T cell trafficking but also T cell activation. Patients treated with FTY720 showed a significant reduction in circulating CD4 T cells. Activation of T cells in presence of FTY720 showed a less inflammatory phenotype with reduced production of IFN-γ and GZMB. This decreased effector phenotype of FTY720-treated T cells was dependent on the upregulation of TCF-1. FTY720-induced TCF-1 downregulated the pathogenic cytokines IFN-γ and GZMB by binding to their promoter/enhancer regions and mediating epigenetic modifications. Furthermore, we observed that TCF-1 expression was lower in T cells from multiple sclerosis patients than in those from healthy individuals, and FTY720 treatment increased TCF-1 expression in multiple sclerosis patients.

Conclusions

These results reveal a previously unknown mechanism of the effect of FTY720 on human CD4+ T cell modulation in multiple sclerosis and demonstrate the role of TCF-1 in human T cell activation and effector function.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0460-z) contains supplementary material, which is available to authorized users.

Adaptive Immune Responses in a Multiple Sclerosis Patient with Acute Varicella-Zoster Virus Reactivation during Treatment with Fingolimod

Fingolimod, an oral sphingosine 1-phosphate (S1P) receptor modulator, is approved for the treatment of relapsing forms of multiple sclerosis (MS). The interference with S1P signaling leads to retention particularly of chemokine receptor-7 (CCR7) expressing T cells in lymph nodes. The immunological basis of varicella zoster virus (VZV) infections during fingolimod treatment is unclear. Here, we studied the dynamics of systemic and intrathecal immune responses associated with symptomatic VZV reactivation including cessation of fingolimod and initiation of antiviral therapy. Key features in peripheral blood were an about two-fold increase of VZV-specific IgG at diagnosis of VZV reactivation as compared to the previous months, a relative enrichment of effector CD4+ T cells (36% versus mean 12% in controls), and an accelerated reconstitution of absolute lymphocytes counts including a normalized CD4+/CD8+ ratio and reappearance of CCR7+ T cells. In cerebrospinal fluid (CSF) the lymphocytic pleocytosis and CD4+/CD8+ ratios at diagnosis of reactivation and after nine days of fingolimod discontinuation remained unchanged. During this time CCR7+ T cells were not observed in CSF. Further research into fingolimod-associated VZV reactivation and immune reconstitution is mandatory to prevent morbidity and mortality associated with this potentially life-threatening condition.

Sphingosine 1-phosphate in acute dengue infection

Background

Vascular leak is the hallmark of severe dengue infections and leads to complications such as shock and multi-organ failure. Although many mediators have been implicated in the vascular leak in dengue, the role of sphingosine 1-phosphate (S1P) has not been investigated.

Metholodology/Principal findings

As S1P has been shown to be important in barrier integrity, we assessed the S1P levels in 28 patients with acute dengue and 12 healthy individuals. The S1P levels were significantly lower in patients with acute dengue (p = 0.002) and the levels in patients with grade IV dengue haemorrhagic fever (DHF) were significantly lower than those with dengue fever (p = 0.005). We then investigated the kinetics of S1P levels throughout the course of the illness in another 32 patients in serum samples obtained twice a day. We found that S1P levels were low throughout the course of illness and S1P levels were <0.5 µM in 12/23 patients with DHF when compared to 1/9 with DF.

Conclusions/Significance

As S1P has shown to be important in the endothelial barrier integrity and increases transendothelial resistance, low levels of S1P in acute dengue infection are likely to contribute to increased vascular permeability.

Fingolimod for the treatment of neurological diseases-state of play and future perspectives

Sphingolipids are a fascinating class of signaling molecules derived from the membrane lipid sphingomyelin. They show abundant expression in the brain. Complex sphingolipids such as glycosphingolipids (gangliosides and cerebrosides) regulate vesicular transport and lysosomal degradation and their dysregulation can lead to storage diseases with a neurological phenotype. More recently, simple sphingolipids such ceramide, sphingosine and sphingosine 1-phosphate (S1P) were discovered to signal in response to many extracellular stimuli. Forming an intricate signaling network, the balance of these readily interchangeable mediators is decisive for cell fate under stressful conditions. The immunomodulator fingolimod is the prodrug of an S1P receptor agonist. Following receptor activation, the drug leads to downregulation of the S1P₁ receptor inducing functional antagonism. As the first drug to modulate the sphingolipid signaling pathway, it was marketed in 2010 for the treatment of multiple sclerosis (MS). At that time, immunomodulation was widely accepted as the key mechanism of fingolimod’s efficacy in MS. But given the excellent passage of this lipophilic compound into the brain and its massive brain accumulation as well as the abundant expression of S1P receptors on brain cells, it is conceivable that fingolimod also affects brain cells directly. Indeed, a seminal study showed that the protective effect of fingolimod in experimental autoimmune encephalitis (EAE), a murine MS model, is lost in mice lacking the S1P₁ receptor on astrocytes, arguing for a specific role of astrocytic S1P signaling in MS. In this review, we discuss the role of sphingolipid mediators and their metabolizing enzymes in neurologic diseases and putative therapeutic strategies arising thereof.