FTY720 enhances the activation-induced apoptosis of donor T cells and modulates graft-versus-host disease

Separation of GVL from GVHD -location, location, location

Allogeneic hematopoietic cell transplantation (HCT) is a curative therapy for various hematologic malignancies. However, alloimmune response is a double-edged sword that mediates both beneficial graft-versus-leukemia (GVL) effects and harmful graft-versus-host disease (GVHD). Separation of GVL effects from GVHD has been a topic of intense research to improve transplant outcomes, but reliable clinical strategies have not yet been established. Target tissues of acute GVHD are the skin, liver, and intestine, while leukemic stem cells reside in the bone marrow. Tissue specific effector T-cell migration is determined by a combination of inflammatory and chemotactic signals that interact with specific receptors on T cells. Specific inhibition of donor T cell migration to GVHD target tissues while preserving migration to the bone marrow may represent a novel strategy to separate GVL from GVHD. Furthermore, tissue specific GVHD therapy, promoting tissue tolerance, and targeting of the tumor immune microenvironment may also help to separate GVHD and GVL.

Mocravimod, a S1P receptor modulator, increases T cell counts in bone marrow biopsies from patients undergoing allogeneic hematopoietic stem cell transplantation

Graft-versus-leukemia (GvL) effects are critical to prevent relapses after allogeneic hematopoietic cell transplantation (allo-HCT). However, the success of allo-HCT is limited by graft-versus-host disease (GvHD). Both, CD4⁺ and CD8⁺ T cells contribute to GvHD and GvL. The sphingosine-1-phosphate receptor (S1PR) signaling plays a crucial role in lymphocyte trafficking. Mocravimod is an S1PR modulator and its administration leads to blocking lymphocyte egress from lymphoid organs. We hypothesized that this applies to the bone marrow (BM) too, and analyzed BM biopsies from the clinical study with mocravimod (phase I trial in allo-HCT patients; NCT01830010) by immunohistochemical staining for CD3, CD4, CD8, TIA1, FoxP3, PD1, T-Bet, GATA3, and ROR-γt to identify and quantify T cell subsets in situ. Allo-HCT patients without receiving mocravimod were used as controls. BM from 9 patients in the mocravimod group and 10 patients in the control group were examined. CD3⁺ T cells were found to accumulate in the BM of mocravimod-treated patients compared to controls, both on day 30 and 90 post-transplant. The effect was stronger for CD4⁺ T cells, than CD8⁺ T cells, which is in line with data from murine studies showing that CD4⁺ T cells are more sensitive to mocravimod treatment than CD8⁺ T cells. Clinically-relevant acute GvHD events (grade II-IV) were slightly lower, but comparable to controls when mocravimod was administered. Taken together, data are supportive of mocravimod's mode of action and bring additional evidence of fewer relapses for allo-HCT patients treated with S1PR modulators.

Hematopoietic stem cell-derived Tregs are essential for maintaining favorable B cell lymphopoiesis following posttransplant cyclophosphamide

Posttransplant cyclophosphamide (PTCy) is associated with a low incidence of chronic graft-versus-host disease (cGVHD) following hematopoietic stem cell (HSC) transplantation. Previous studies have shown the important roles of B cell immunity in cGVHD development. Here, we investigated the long-term reconstitution of B lymphopoiesis after PTCy using murine models. We first demonstrated that the immune homeostatic abnormality leading to cGVHD is characterized by an initial increase in effector T cells in the bone marrow and subsequent B and Treg cytopenia. PTCy, but not cyclosporine A or rapamycin, inhibits the initial alloreactive T cell response, which restores intra-bone marrow B lymphogenesis with a concomitant vigorous increase in Tregs. This leads to profound changes in posttransplant B cell homeostasis, including decreased B cell activating factors, increased transitional and regulatory B cells, and decreased germinal center B cells. To identify the cells responsible for PTCy-induced B cell tolerance, we selectively depleted Treg populations that were graft or HSC derived using DEREG mice. Deletion of either Treg population without PTCy resulted in critical B cytopenia. PTCy rescued B lymphopoiesis from graft-derived Treg deletion. In contrast, the negative effect of HSC-derived Treg deletion could not be overcome by PTCy, indicating that HSC-derived Tregs are essential for maintaining favorable B lymphopoiesis following PTCy. These findings define the mechanisms by which PTCy restores homeostasis of the B cell lineage and reestablishes immune tolerance.

Mocravimod, a Selective Sphingosine-1-Phosphate Receptor Modulator, in Allogeneic Hematopoietic Stem Cell Transplantation for Malignancy

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains the sole curative option for patients with acute myelogenous leukemia. Outcomes are limited by leukemia relapse, graft-versus-host disease (GVHD), and abnormal immune reconstitution. Mocravimod (KRP203) is an oral sphingosine-1-phosphate receptor (S1PR) modulator that blocks the signal required by T cells to egress from lymph nodes and other lymphoid organs. Mocravimod retains T cell effector function, a main differentiator to immunosuppressants. In preclinical models, mocravimod improves survival by maintaining graft-versus-leukemia (GVL) activity while reducing GVHD. In patients undergoing allo-HSCT for hematological malignancies, mocravimod is postulated to prevent GVHD by redistributing allogeneic donor T cells to lymphoid tissues while allowing a sufficient GVL effect in the lymphoid, where malignant cells usually reside. The primary objective of this study was to assess the safety and tolerability of mocravimod in patients undergoing allo-HSCT for hematologic malignancies. Secondary objectives were to determine the pharmacokinetic profiles of mocravimod and its active metabolite mocravimod-phosphate in this patient group, as well as to assess GVHD-free, relapse free survival at 6 months after the last treatment. In this 2-part, single- and 2-arm randomized, open-label trial, we evaluated the safety, tolerability, and pharmacokinetics of mocravimod in allo-HSCT recipients (ClinicalTrials.gov identifier NCT01830010). Patients received either 1 mg or 3 mg mocravimod per day on top of standard of care GVHD prophylaxis with either cyclosporine A/methotrexate or tacrolimus/methotrexate. We found that mocravimod can be safely added to standard treatment regimens in patients with hematologic malignancies requiring allo-HSCT. Mocravimod resulted in a significant reduction of circulating lymphocyte numbers and had no negative impact on engraftment and transplantation outcomes. Our results indicate that mocravimod is safe and support a larger study to investigate its efficacy in a homogeneous acute myelogenous leukemia patient population undergoing allo-HSCT.

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.

Retention of Donor T Cells in Lymphohematopoietic Tissue and Augmentation of Tissue PD-L1 Protection for Prevention of GVHD While Preserving GVL Activity

Allogeneic hematopoietic cell transplantation (Allo-HCT) is a curative therapy for hematological malignancies (i.e., leukemia and lymphoma) due to the graft-versus-leukemia (GVL) activity mediated by alloreactive T cells that can eliminate residual malignant cells and prevent relapse. However, the same alloreactive T cells can cause a serious side effect, known as graft-versus-host disease (GVHD). GVHD and GVL occur in distinct organ and tissues, with GVHD occurring in target organs (e.g., the gut, liver, lung, skin, etc.) and GVL in lympho-hematopoietic tissues where hematological cancer cells primarily reside. Currently used immunosuppressive drugs for the treatment of GVHD inhibit donor T cell activation and expansion, resulting in a decrease in both GVHD and GVL activity that is associated with cancer relapse. To prevent GVHD, it is important to allow full activation and expansion of alloreactive T cells in the lympho-hematopoietic tissues, as well as prevent donor T cells from migrating into the GVHD target tissues, and tolerize infiltrating T cells via protective mechanisms, such as PD-L1 interacting with PD-1, in the target tissues. In this review, we will summarize major approaches that prevent donor T cell migration into GVHD target tissues and approaches that augment tolerization of the infiltrating T cells in the GVHD target tissues while preserving strong GVL activity in the lympho-hematopoietic tissues.

Fluvastatin-Pretreated Donor Cells Attenuated Murine aGVHD by Balancing Effector T Cell Distribution and Function under the Regulation of KLF2

Prevention of acute graft-versus-host disease (aGVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is still to be explored. Statins are potent immunomodulatory agents that hold promise as novel and safe agents for aGVHD prophylaxis, yet the controversial effect and regulatory mechanism are incompletely understood. Here, in an MHC mismatched murine model, we found that Fluvastatin-pretreated donor cells could attenuate aGVHD severity by remission tissue pathological injury. Fluvastatin served to restrain effector T cells entry into aGVHD target organs from secondary lymphoid organs (SLOs). The potential mechanism of correcting the effector T cell biased distribution was that Fluvastatin elevated CD62L and CCR7 expression while decreased CXCR3 and CD44 levels, which were correlated with Kruppel-like factor 2 (KLF2) sustention in donor-derived cells. In addition, Fluvastatin was contributed to reducing cytokines IFN-γ, TNF-α, and granzyme-B production in allogeneic effector CD4⁺ and CD8⁺ T cells. Furthermore, evidence confirmed that Fluvastatin had a long-lasting effect to sustain KLF2 expression both in vitro and in vivo even under the stimulated circumstance. In conclusion, administration of Fluvastatin to donor mice showed protective effects against recipient aGVHD when compared to untreated mice due to the retention of effector T cells in lymphoid organs accompanying with reduction of nonlymphatic infiltration and related inflammatory cytokines.

Metabolic Reprogramming-A New Era How to Prevent and Treat Graft Versus Host Disease After Allogeneic Hematopoietic Stem Cell Transplantation Has Begun

Allogeneic hematopoietic stem cell transplantation (HSCT) is the solitary therapeutic therapy for many types of hematological cancers. The benefits of this procedure are challenged by graft vs. host disease (GVHD), causing significant morbidity and mortality. Recent advances in the metabolomics field have revolutionized our understanding of complex human diseases, clinical diagnostics and allow to trace the de novo biosynthesis of metabolites. There is growing evidence for metabolomics playing a role in different aspects of GVHD, and therefore metabolomic reprogramming presents a novel tool for this disease. Pre-transplant cytokine profiles and metabolic status of allogeneic transplant recipients is shown to be linked with a threat of acute GVHD. Immune reactions underlying the pathophysiology of GVHD involve higher proliferation and migration of immune cells to the target site, requiring shifts in energy supply and demand. Metabolic changes and reduced availability of oxygen result in tissue and cellular hypoxia which is extensive enough to trigger transcriptional and translational changes. T cells, major players in acute GVHD pathophysiology, show increased glucose uptake and glycolytic activity. Effector T (Teff) cells activated during nutrient limiting conditions in vitro or multiplying during GVHD in vivo, depend more on oxidative phosphorylation (OXPHOS) and fatty acid oxidation (FAO). Dyslipidemia, such as the increase of medium and long chain fatty and polyunsaturated acids in plasma of GVHD patients, has been observed. Sphingolipids associate with inflammatory conditions and cancer. Chronic GVHD (cGVHD) patients show reduced branched-chain amino acids (BCAAs) and increased sulfur-containing metabolites post HSCT. Microbiota-derived metabolites such as aryl hydrocarbon receptor (AhR) ligands, bile acids, plasmalogens and short chain fatty acids vary significantly and affect allogeneic immune responses during acute GVHD. Considering the multitude of possibilities, how altered metabolomics are involved in GVHD biology, multi-timepoints related and multivariable biomarker panels for prognosticating and understanding GVHD are needed. In this review, we will discuss the recent work addressing metabolomics reprogramming to control GVHD in detail.

Chinese Medicine Treatment on Graft-Versus-Host Disease after Allogeneic Hematopoietic Stem Cell Transplantation

Graft-versus-host disease (GVHD) is the most common complication after allogeneic hematopoietic stem cell transplantation, and also an important factor affecting the survival and quality of life in patients after transplantation. Currently, immunosuppressive therapy is commonly used for GVHD, but the curative effect is not ideal. How to effectively prevent and treat GVHD is one of the difficulties to be solved urgently in the field of transplantation. In this paper, we summarize the latest progress in pathogenesis, prevention and treatment of GVHD with Chinese medicine (CM). We hope it will provide ideas and methods for exploring the mechanism and establishing a new comprehensive therapy for GVHD with CM.

Short-term KRP203 and posttransplant cyclophosphamide for graft-versus-host disease prophylaxis

Posttransplant high-dose cyclophosphamide (PTCY) has been increasingly used as graft-versus-host disease (GVHD) prophylaxis after HLA-haploidentical or matched hematopoietic stem cell transplantation (SCT). However, PTCY alone is insufficient and requires additional immunosuppressants such as calcineurin inhibitors. In the current study, we evaluated effects of a novel GVHD prophylaxis with PTCY in combination with short-term KRP203, a selective agonist of sphingosine-1-phosphate receptor 1 that regulates egress of lymphocytes from the secondary lymphoid organs (SLOs) in mice. Short-term oral administration of KRP203 alone induced apoptosis of donor T cells in the SLOs and ameliorated GVHD. Administration of KRP203 significantly preserved graft-versus-leukemia effects compared to cyclosporin. A combination of KRP203 on days 0 to +4 and PTCY on day +3 synergistically suppressed donor T-cell migration into the intestine and skin, and ameliorated GVHD more potently than PTCY alone. A combination of short-term KRP203 and PTCY is a promising novel calcineurin-free GVHD prophylaxis in HLA-haploidentical SCT.

Prolongation of skin graft survival in mice by an azaphenothiazine derivative

Azaphenothiazines are predominantly immunosuppressive compounds. We evaluated the efficacy of an azaphenothiazine derivative, 6-chloroethylureidoethyldiquino[3,2-b;2',3'-e][1,4]thiazine (DQT) in prolongation of survival of skin allografts between BALB/c and C57Bl/6 mice. The mice were treated intraperitoneally (i.p.) with 100 μg of DQT on alternate days, on days 1-13 of the experiment (7 doses). The effect of DQT on a two-way mixed lymphocyte reaction (MLR) in the human model, as well as its effect on production of TNF α and IL-10 in a whole blood cell culture, stimulated by lipopolysaccharide (LPS), were evaluated. In addition, DQT effects were investigated regarding the proportion of T cell subsets in human peripheral blood lymphocytes (PBMC) by flow cytometry. Lastly, the effect of DQT on expression of signaling molecules involved in pro apoptotic pathways was determined by RT PCR. The results showed that DQT significantly extended skin graft survival. The compound also strongly suppressed two-way MLR in the human model at a concentration range of 2.5-5.0 μM. In addition, DQT inhibited LPS-inducible TNF α, but not IL-10 production. The compound preferentially caused a loss of the CD3-CD8+CD11b + PBMC cell subset, and transformed CD3+CD8+^high into CD3+CD8+^low cells. Lastly, we demonstrated significant increases in expression of caspases (in particular caspase 8) and of p53 in a culture of Jurkat T cells. We conclude that the immunosuppressive actions of the compound in allograft rejection may be predominantly associated with induction of cell apoptosis and inhibition of TNF α production. The apoptosis could be predominantly selective for the CD3-CD8+CD11b + cell phenotype.

Nrf2 regulates CD4+ T cell-induced acute graft-versus-host disease in mice

Nuclear factor erythroid-derived 2-like 2 (Nrf2) is a ubiquitously expressed transcription factor that is well known for its role in regulating the cellular redox pathway. Although there is mounting evidence suggesting a critical role for Nrf2 in hematopoietic stem cells and innate leukocytes, little is known about its involvement in T-cell biology. In this study, we identified a novel role for Nrf2 in regulating alloreactive T-cell function during allogeneic hematopoietic cell transplantation (allo-HCT). We observed increased expression and nuclear translocation of Nrf2 upon T-cell activation in vitro, especially in CD4+ donor T cells after allo-HCT. Allo-HCT recipients of Nrf2 -/- donor T cells had significantly less acute graft-versus-host disease (GVHD)-induced mortality, morbidity, and pathology. This reduction in GVHD was associated with the persistence of Helios+ donor regulatory T cells in the allograft, as well as defective upregulation of the gut-homing receptor LPAM-1 on alloreactive CD8+ T cells. Additionally, Nrf2 -/- donor CD8+ T cells demonstrated intact cytotoxicity against allogeneic target cells. Tumor-bearing allo-HCT recipients of Nrf2 -/- donor T cells had overall improved survival as a result of preserved graft-versus-tumor activity and reduced GVHD activity. Our findings characterized a previously unrecognized role for Nrf2 in T-cell function, as well as revealed a novel therapeutic target to improve the outcomes of allo-HCT.

Fingolimod can act as a facilitator to establish the primary T-cell response with reduced need of adjuvants

The CD8⁺ T-cell response is an essential part of the adaptive immunity. Adjuvants are routinely required for priming of T cells against antigens encountered in lymph nodes (LNs) to generate antigen-specific immunity but may concomitantly trigger unexpected inflammatory responses. Sphingosine-1-phosphate (S1P) induces transient desensitization of S1P receptors on LN T cells and temporarily blocks their egress, leading to prolonged intranodal retention that allows effective immunosurveillance and increases the chance of priming. In light of the regulatory role of S1P in T-cell migration, we here develop a strategic approach to the T-cell priming with protein vaccine containing low-dose TLR-based adjuvants (LDAV) to induce antigen-specific CD8⁺ T cell responses as efficiently as using regular dose adjuvants in vaccine (RDAV). We found that when combined with one low dose of the S1P analog fingolimod administered into the same vaccination site posteriorly at a specific time, LDAV can elicit a primary response that reaches the level of that induced by RDAV with respect to the response magnitude and functionality. Time-course studies indicate that LDAV and fingolimod in combination act to mimic the expansion kinetics of RDAV-primed antigen-specific CD8⁺ T cells. Further, intranodal accumulation of cDC1 is markedly enhanced in mice receiving the combination vaccination despite the decrease in adjuvant use. Of particular note is the marginal cutaneous inflammation at the injection site, indicating an added benefit of using fingolimod. Therefore, fingolimod as a nonadjuvant agent essentially facilitates antigen-specific T-cell priming with reduced need of adjuvants and minimized adverse reactions.

Sphingosine 1-Phosphate Signaling and Its Pharmacological Modulation in Allogeneic Hematopoietic Stem Cell Transplantation

Allogeneic haemopoietic stem cell transplantation (HSCT) is increasingly used to treat haematological malignant diseases via the graft-versus-leukaemia (GvL) or graft-versus-tumour effects. Although improvements in infectious disease prophylaxis, immunosuppressive treatments, supportive care, and molecular based tissue typing have contributed to enhanced outcomes, acute graft-versus-host disease and other transplant related complications still contribute to high mortality and significantly limit the more widespread use of HSCT. Sphingosine 1-phosphate (S1P) is a zwitterionic lysophospholipid that has been implicated as a crucial signaling regulator in many physiological and pathophysiological processes including multiple cell types such as macrophages, dendritic cells, T cells, T regulatory cells and endothelial cells. Recent data suggested important roles for S1P signaling in engraftment, graft-versus-host disease (GvHD), GvL and other processes that occur during and after HSCT. Based on such data, pharmacological intervention via S1P modulation may have the potential to improve patient outcome by regulating GvHD and enhancing engraftment while permitting effective GvL.

Advances in targeting co-inhibitory and co-stimulatory pathways in transplantation settings: the Yin to the Yang of cancer immunotherapy

In the past decade, the power of harnessing T-cell co-signaling pathways has become increasingly understood to have significant clinical importance. In cancer immunotherapy, the field has concentrated on two related modalities: First, targeting cancer antigens through highly activated chimeric antigen T cells (CAR-Ts) and second, re-animating endogenous quiescent T cells through checkpoint blockade. In each of these strategies, the therapeutic goal is to re-ignite T-cell immunity, in order to eradicate tumors. In transplantation, there is also great interest in targeting T-cell co-signaling, but with the opposite goal: in this field, we seek the Yin to cancer immunotherapy's Yang, and focus on manipulating T-cell co-signaling to induce tolerance rather than activation. In this review, we discuss the major T-cell signaling pathways that are being investigated for tolerance induction, detailing preclinical studies and the path to the clinic for many of these molecules. These include blockade of co-stimulation pathways and agonism of coinhibitory pathways, in order to achieve the delicate state of balance that is transplant tolerance: a state which guarantees lifelong transplant acceptance without ongoing immunosuppression, and with preservation of protective immune responses. In the context of the clinical translation of immune tolerance strategies, we discuss the significant challenge that is embodied by the fact that targeted pathway modulators may have opposing effects on tolerance based on their impact on effector vs regulatory T-cell biology. Achieving this delicate balance holds the key to the major challenge of transplantation: lifelong control of alloreactivity while maintaining an otherwise intact immune system.

Combined nifuroxazide and SAT05f therapy reduces graft-versus-host disease after experimental allogeneic bone marrow transplantation

Acute graft-versus-host disease (aGvHD) is the major barrier to the broader use of allogenetic hematopoietic stem cells. However, currently these are no highly specific and efficient drugs. Monotherapy is not sufficient and more efficient and safe therapeutic regimen are urgent need. Studies demonstrated TLR9 and Stat3 signal pathways are critical for antigen-presenting cell maturation and T-cell activation, which are important mediators in aGvHD. Specific block these two critical signal pathways using their inhibitors SAT05f and nifuroxazide may be the novel strategies for aGvHD therapy. The results showed combined therapy significantly decreased the severity of aGvHD and prolonged the survival rate. Furthermore, after treatment, the activation of CD4⁺ effect T cells was reduced, whereas Treg cells was increased, and the cytokine release was inhibited. In conclusion, combined therapy of nifuroxazide with SAT05f may be potential for the prevention or treatment of aGvHD, providing theoretic and experimental basis.

Translational Implications for Off-the-shelf Immune Cells Expressing Chimeric Antigen Receptors

Chimeric antigen receptor (CAR) endows specificity to T-cells independent of human leukocyte antigen (HLA). This enables one immunoreceptor to directly target the same surface antigen on different subsets of tumor cells from multiple HLA-disparate recipients. Most approaches manufacture individualized CAR(+)T-cells from the recipient or HLA-compatible donor, which are revealing promising clinical results. This is the impetus to broaden the number of patients eligible to benefit from adoptive immunotherapy such as to infuse third-party donor derived CAR(+)T-cells. This will overcome issues associated with (i) time to manufacture T-cells, (ii) cost to generate one product for one patient, (iii) inability to generate a product from lymphopenic patients or patient's immune cells fail to complete the manufacturing process, and (iv) heterogeneity of T-cell products produced for or from individual recipients. Establishing a biobank of allogeneic genetically modified immune cells from healthy third-party donors, which are cryopreserved and validated in advance of administration, will facilitate the centralizing manufacturing and widespread distribution of CAR(+)T-cells to multiple points-of-care in a timely manner. To achieve this, it is necessary to engineer an effective strategy to avoid deleterious allogeneic immune responses leading to toxicity and rejection. We review the strategies to establish "off-the-shelf" donor-derived biobanks for human application of CAR(+)T-cells as a drug.

Preclinical models of acute and chronic graft-versus-host disease: how predictive are they for a successful clinical translation?

Despite major advances in recent years, graft-versus-host disease (GVHD) remains a major life-threatening complication of allogeneic hematopoietic cell transplantation (allo-HCT). To improve our therapeutic armory against GVHD, preclinical evidence is most frequently generated in mouse and large animal models of GVHD. However, because every model has shortcomings, it is important to understand how predictive the different models are and why certain findings in these models could not be translated into the clinic. Weaknesses of the animal GVHD models include the irradiation only-based conditioning regimen, the homogenous donor/recipient genetics in mice, canine or non-human primates (NHP), anatomic site of T cells used for transfer in mice, the homogenous microbial environment in mice housed under specific pathogen-free conditions, and the lack of pharmacologic GVHD prevention in control groups. Despite these major differences toward clinical allo-HCT, findings generated in animal models of GVHD have led to the current gold standards for GVHD prophylaxis and therapy. The homogenous nature of the preclinical models allows for reproducibility, which is key for the characterization of the role of a new cytokine, chemokine, transcription factor, microRNA, kinase, or immune cell population in the context of GVHD. Therefore, when carefully balancing reasons to apply small and large animal models, it becomes evident that they are valuable tools to generate preclinical hypotheses, which then have to be rigorously evaluated in the clinical setting. In this study, we discuss several clinical approaches that were motivated by preclinical evidence, novel NHP models and their advantages, and highlight the recent advances in understanding the pathophysiology of GVHD.

Treatment with a sphingosine analog after the inception of house dust mite-induced airway inflammation alleviates key features of experimental asthma

Background

In vivo phosphorylation of sphingosine analogs with their ensuing binding and activation of their cell-surface sphingosine-1-phosphate receptors is regarded as the main immunomodulatory mechanism of this new class of drugs. Prophylactic treatment with sphingosine analogs interferes with experimental asthma by impeding the migration of dendritic cells to draining lymph nodes. However, whether these drugs can also alleviate allergic airway inflammation after its onset remains to be determined. Herein, we investigated to which extent and by which mechanisms the sphingosine analog AAL-R interferes with key features of asthma in a murine model during ongoing allergic inflammation induced by Dermatophagoides pteronyssinus.

Methods

BALB/c mice were exposed to either D. pteronyssinus or saline, intranasally, once-daily for 10 consecutive days. Mice were treated intratracheally with either AAL-R, its pre-phosphorylated form AFD-R, or the vehicle before every allergen challenge over the last four days, i.e. after the onset of allergic airway inflammation. On day 11, airway responsiveness to methacholine was measured; inflammatory cells and cytokines were quantified in the airways; and the numbers and/or viability of T cells, B cells and dendritic cells were assessed in the lungs and draining lymph nodes.

Results

AAL-R decreased airway hyperresponsiveness induced by D. pteronyssinus by nearly 70%. This was associated with a strong reduction of IL-5 and IL-13 levels in the airways and with a decreased eosinophilic response. Notably, the lung CD4⁺ T cells were almost entirely eliminated by AAL-R, which concurred with enhanced apoptosis/necrosis in that cell population. This inhibition occurred in the absence of dendritic cell number modulation in draining lymph nodes. On the other hand, the pre-phosphorylated form AFD-R, which preferentially acts on cell-surface sphingosine-1-phosphate receptors, was relatively impotent at enhancing cell death, which led to a less efficient control of T cell and eosinophil responses in the lungs.

Conclusion

Airway delivery of the non-phosphorylated sphingosine analog, but not its pre-phosphorylated counterpart, is highly efficient at controlling the local T cell response after the onset of allergic airway inflammation. The mechanism appears to involve local induction of lymphocyte apoptosis/necrosis, while mildly affecting dendritic cell and T cell accumulation in draining lymph nodes.

Graft versus host disease: New insights into A2A receptor agonist therapy

Allogeneic transplantation can cure many disorders, including sickle cell disease, chronic granulomatous disease (CGD), severe combined immunodeficiency (SCID) and many types of cancers. However, there are several associated risks that can result in severe immunological reactions and, in some cases, death. Much of this morbidity is related to graft versus host disease (GVHD) [1]. GVHD is an immune mediated reaction in which donor T cells recognize the host as antigenically foreign, causing donor T cells to expand and attack host tissues. The current method of treating recent transplant patients with immunosuppressants to prevent this reaction has met with only partial success, emphasizing a need for new methods of GVHD treatment and prevention. Recently, a novel strategy has emerged targeting adenosine A_2A receptors (A_2AR) through the use of adenosine agonists. These agonists have been shown in vitro to increase the TGFβ-induced generation of FoxP3⁺ regulatory T cells (T_regs) and in vivo to improve weight gain and mortality as well as inhibit the release of pro-inflammatory cytokines in GVHD murine models [2,3]. Positive results involving A_2AR agonists in vitro and in vivo are promising, suggesting that A_2AR agonists should be a part of the management of clinical GvHD.

The S1P1 receptor-selective agonist CYM-5442 reduces the severity of acute GVHD by inhibiting macrophage recruitment

FTY720, an agonist for four of the five known sphingosine-1-phosphate (S1P) receptors, has been reported to inhibit acute graft-versus-host disease (aGVHD). Because FTY720 functions through multiple S1P receptors, the mechanism of action through one or more of these receptors may account for its side effects. Thus, more selective S1P receptor modulators are needed to evaluate the roles of different S1P receptors and their therapeutic efficacies. In this study, we investigated the effect of an S1P1-selective agonist, CYM-5442, on the progression of aGVHD. We showed that CYM-5442 significantly inhibited but did not prevent aGVHD. CYM-5442 did not affect the infiltration of the donor T cells into the target organs, while the number of macrophages in GVHD organs was significantly reduced by CYM-5442 treatment. In vivo proliferation assays showed that the proliferation of macrophages was not suppressed by CYM-5442. Further studies using human endothelial cells demonstrated that CYM-5442 treatment downregulated CCL2 and CCL7 expression in endothelial cells, therefore reducing the migration of monocytes, from which tissue macrophages originate. Our data demonstrate the therapeutic efficacy of an S1P1-selective agonist in aGVHD and its possible mechanism of action. The results suggest that further investigations are needed regarding CYM-5442 as a potential therapeutic regimen for aGVHD.

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

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

Advances in graft-versus-host disease biology and therapy

Allogeneic haematopoietic stem cell transplantation is used to treat a variety of disorders, but its efficacy is limited by the occurrence of graft-versus-host disease (GVHD). The past decade has brought impressive advances in our understanding of the role of stimulatory and suppressive elements of the adaptive and innate immune systems from both the donor and the host in GVHD pathogenesis. New insights from basic immunology, preclinical models and clinical studies have led to novel approaches for prevention and treatment. This Review highlights the recent advances in understanding the pathophysiology of GVHD and its treatment, with a focus on manipulations of the immune system that are amenable to clinical application.

Regulation of acute graft-versus-host disease by microRNA-155

Acute graft-versus-host disease (aGVHD) remains a major complication of allogeneic hematopoietic stem cell transplant (alloHSCT), underscoring the need to further elucidate its mechanisms and develop novel treatments. Based on recent observations that microRNA-155 (miR-155) is up-regulated during T-cell activation, we hypothesized that miR-155 is involved in the modulation of aGVHD. Here we show that miR-155 expression was up-regulated in T cells from mice developing aGVHD after alloHSCT. Mice receiving miR-155-deficient donor lymphocytes had markedly reduced lethal aGVHD, whereas lethal aGVHD developed rapidly in mice recipients of miR-155 overexpressing T cells. Blocking miR-155 expression using a synthetic anti-miR-155 after alloHSCT decreased aGVHD severity and prolonged survival in mice. Finally, miR-155 up-regulation was shown in specimens from patients with pathologic evidence of intestinal aGVHD. Altogether, our data indicate a role for miR-155 in the regulation of GVHD and point to miR-155 as a novel target for therapeutic intervention in this disease.

Regulatory T cells and IL-17-producing cells in graft-versus-host disease

Graft-versus-host disease (GvHD), a major complication following allogeneic hematopoietic stem cell transplantation, is mediated by donor-derived T cells. On activation with alloantigens expressed on host antigen-presenting cells, naive CD4+ T cells differentiate into T-helper cell subsets of effector T cells expressing distinct sets of transcriptional factors and cytokines. Classically, acute GvHD was suggested to be predominantly related to Th1 responses. However, we now face a completely different and complex scenario involving possible roles of newly identified Th17 cells as well as Tregs in GvHD. Accumulating data from experimental and clinical studies suggest that the fine balance between Th1, Th2, Th17 and Tregs after transplantation may be an important determinant of the severity, manifestation and tissue distribution of GvHD. Understanding the dynamic process of reciprocal differentiation of regulatory and T-helper cell subsets as well as their interactions will be important in establishing novel strategies for preventing and treating GvHD.

Redirected tumor-specific allogeneic T cells for universal treatment of cancer

Adoptive cell transfer of allogeneic tumor-specific T cells could potentially be used as a universal treatment for cancer. We present a novel approach for adoptive immunotherapy using fully MHC-mismatched allogeneic T cells redirected with tumor-specific, non-MHC-restricted antibody-based chimeric antigen receptor (T-bodies) in the absence of GVHD. Mice bearing systemic metastatic disease were lymphodepleted by irradiation and treated with Her2/neu re-directed T cells. Lymphodepletion created a 'therapeutic window', which allowed the allo-T-bodies to attack the tumor before their rejection. A single split dose administration of allogeneic T-bodies extended the survival of tumor-bearing mice similarly to syngeneic T-bodies, and to a significantly greater extent than nonspecific allogeneic T cells. Blocking egress of lymphocytes from lymphoid organs using the sphingosine-1-phosphate agonist, FTY720, extended the persistence of allogeneic T cells such that allogeneic T-bodies provided superior therapeutic benefit relative to syngeneic ones, and dramatically extended the median survival time of the treated mice for more than a year. Therefore, we suggest that ex-vivo generated MHC-mismatched T-bodies can be used universally for off-the-shelf cancer immunotherapy and that their graft-versus-host reactivity can be safely harnessed to potentiate adoptive cell therapy.

Adenosine A2A receptor activation limits graft-versus-host disease after allogenic hematopoietic stem cell transplantation

GVHD is a major barrier to broader use of allogenic HSCT for nonmalignancy clinical applications such as the treatment of primary immunodeficiencies and hemoglobinopathies. We show in a murine model of C57BL/6J (H2-k(b)) --> B6D2F1/J (H2-k(b/d)) acute GVHD that when initiated 2 days before transplant, the activation of the adenosine A(2A)R with the selective agonist ATL146e inhibits the weight loss and mortality associated with disease progression. Furthermore, circulating levels of proinflammatory cytokines and chemokines, including IFN-gamma, IL-6, CCL2, KC, and G-CSF, are reduced significantly by 14-day ATL146e treatment. The up-regulation of CD25, CD69, and CD40L expression by donor CD4(+) and CD8(+) T cells is inhibited by A(2A)R activation; fewer CD3(+) T cells are found in the liver, skin, and colon of ATL146e-treated mice as compared with vehicle-treated controls; and associated tissue injury is lessened. The delayed administration of ATL146e, beginning 9 days after HSCT, reverses GVHD-associated body weight loss successfully, and improvement is sustained for the duration of treatment. We conclude that the selective activation of the A(2A)R has therapeutic potential in the prevention and treatment of acute GVHD.

Plasmacytoid dendritic cells prime alloreactive T cells to mediate graft-versus-host disease as antigen-presenting cells

Dendritic cells (DCs) can be classified into 2 distinct subsets: conventional DCs (cDCs) and plasmacytoid DCs (pDCs). cDCs can prime antigen-specific T-cell immunity, whereas in vivo function of pDCs as antigen-presenting cells remains controversial. We evaluated the contribution of pDCs to allogeneic T-cell responses in vivo in mouse models of graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation by an add-back study of MHC-expressing pDCs into major histocompatibility complex-deficient mice that were resistant to GVHD. Alloantigen expression on pDCs alone was sufficient to prime alloreactive T cells and cause GVHD. An inflammatory environment created by host irradiation has the decisive role in maturing pDCs for T-cell priming but this process does not require Toll-like receptor signaling. Thus, functional outcomes of pDC-T-cell interactions depend on the immunologic context of encounter. To our knowledge, these results are the first to directly demonstrate an in vivo pathogenic role of pDCs as antigen-presenting cells in an antigen-specific T cell-mediated disease in the absence of other DC subsets and to provide important insight into developing strategies for tolerance induction in transplantation.

Immunomodulation and pharmacological strategies in the treatment of graft-versus-host disease

BACKGROUND

Allogeneic hematopoietic stem cell transplantation offers great promise for the treatment of a variety of diseases including malignancies and other diseases of hematopoietic origin. However, morbidity and mortality due to graft-versus-host disease (GVHD) remain a major barrier to its application.

OBJECTIVE

This review will provide an overview of the pathophysiology of GVHD and discuss the recent advances in GVHD management in both preclinical and clinical studies.

METHODS

An extensive literature search on PubMed from 1995 to 2008 was performed.

RESULTS/CONCLUSION

There has been much progress in our understanding of GVHD and finding new means to control acute GVHD. While these approaches hold promise, as yet none has been able to replace the standard methods we may use routinely to decrease the incidence of the condition.

[FTY720 (Fingolimod) as a new therapeutic option for multiple sclerosis]

All currently available therapeutic options for multiple sclerosis have to be administered parenterally. Several oral substances are currently in the late clinical development stage. One of them, FTY720 (also known as fingolimod) is highlighted in this review. The biological effects of FTY720 are presented as well as animal data and first clinical data from a phase II trial in multiple sclerosis patients. The effects of FTY720 are based on an innovative approach and apparently target several key elements in the pathogenesis of multiple sclerosis. The first clinical data with FTY720 show very promising results, with a relapse reduction of over 50% compared to placebo and an acceptable safety profile. These results currently await confirmation in two international phase III studies which are recruiting patients worldwide.

Sphingosine-1-Phosphate Analogue FTY720 Causes Lymphocyte Redistribution and Hypercholesterolemia in ApoE-Deficient Mice

Objective— Resident immune cells are a hallmark of atherosclerotic lesions. The sphingolipid analogue drug FTY720 mediates retrafficking of immune cells and inhibits their homing to inflammatory sites. We have evaluated the effect of FTY720 on atherogenesis and lipid metabolism.

Methods and Results— ApoE −/− mice on a normal laboratory diet received oral FTY720 for 12 weeks, which led to a 2.4-fold increase in serum cholesterol (largely VLDL fraction) and a 1.8-fold increase in hepatic HMGCoA reductase mRNA. FTY720 increased plasma sphingosine-1-phosphate and induced marked peripheral blood lymphopenia. A discoordinate modulation of B, T and monocyte cell numbers was found in peripheral lymphoid organs. Overall depletion of T cells was accompanied by a relative (2-fold) increase in regulatory T cell content paralleled by a similar increase in effector memory T cells (CD4+CD44hiCD62lo) as absolute numbers of both subpopulations remained essentially unchanged. Lymphocyte function was unaltered as indicated by anti-OxLDL antibodies and T cell proliferation. There were no changes in atherosclerotic lesions in early and established atherosclerosis.

Conclusions— FTY720 mediated peripheral lymphocyte depletion and retrafficking without altering function and overall balance of pro- and antiatherogenic lymphocyte populations. A net decrease in lymphocyte numbers occurred concomitantly with a more proatherogenic hypercholesterolemia resulting in unaltered atherogenesis.

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.

Insights into the mechanism of FTY720 and compatibility with regulatory T cells for the inhibition of graft-versus-host disease (GVHD)

The immunomodulator FTY720 (FTY) has been shown to be beneficial in experimental models of organ transplantation and autoimmunity. We show that FTY significantly inhibited but did not prevent graft-versus-host disease (GVHD) in lethally irradiated or nonirradiated allogeneic recipients. Although most studies implicate prevention of lymphocyte egress from lymphoid organs as the primary mechanism of action, our data indicate that FTY effects on the host are more likely to be responsible for GVHD inhibition. FTY reduced splenic CD11c+ cells by 50%, and similarly reduced CD4+ and CD8+ T-cell responder frequencies in the spleen early after transplantation. Imaging of GFP+ effectors indicated that FTY modified donor effector T-cell migration to secondary lymphoid organs, but did not uniformly trap T cells in lymph nodes or prevent early effector migration to GVHD parenchymal target organs. Administration of FTY only prior to transplantation inhibited GVHD, indicating that the primary function of FTY may be targeted to host cells. FTY was additive with regulatory T cells for GVHD inhibition. FTY slightly impaired but did not abrogate a graft-versus-leukemia (GVL) effect against C1498, a myeloid leukemia. Our data further define the mechanisms of action and provide insight as to the potential clinical uses of FTY in allogeneic bone marrow transplant recipients.