Co-inhibitory roles for glucocorticoid-induced TNF receptor in CD1d-dependent natural killer T cells

GITR controls intestinal inflammation by suppressing IL-15-dependent NK cell activity

Glucocorticoid-induced TNFR family related gene (GITR) is a member of the TNFR superfamily that is expressed on cells of the immune system. Although the protective and pathogenic roles of GITR in T cell immunity are well characterized, the role of GITR in innate immunity in the intestinal tissues has not been well clarified. In this study, using a dextran sulfate sodium (DSS)-induced colitis model in mice, we found that GITR-deficiency rendered mice more susceptible to acute intestinal inflammation and that a significantly higher number of activated natural killer (NK) cells was accumulated in the colonic lamina propria of Gitr^-/- mice as compared to wild-type mice. Additionally, Rag2^-/- Gitr^-/- mice, which lack T cells but have NK cells, also displayed more severe colonic inflammation than Rag2^-/- mice. In contrast, an anti-GITR agonistic antibody significantly alleviated colitis in Rag2^-/- mice. Engagement of GITR inhibited IL-15-mediated activating signaling events in NK cells, which include cell activation and proliferation, and production of cytokines and cytotoxic granules. Taken together, our results provide the first evidence that GITR negatively controls intestinal inflammation through NK cell functions.

Invariant NKT Cell-Mediated Modulation of ILC1s as a Tool for Mucosal Immune Intervention

Non-NK group 1 innate lymphoid cells (ILC1s), mainly investigated in the mucosal areas of the intestine, are well-known to contribute to anti-parasitic and anti-bacterial immune responses. Recently, our group revealed that lung ILC1s become activated during murine influenza infection, thereby contributing to viral clearance. In this context, worldwide seasonal influenza infections often result in severe disease outbreaks leading to high morbidity and mortality. Therefore, new immune interventions are urgently needed. In contrast to NK cells, the potential of non-NK ILC1s to become functionally tailored by immune modulators to contribute to the combat against mucosal-transmitted viral pathogens has not yet been addressed. The present study aimed at assessing the potential of ILC1s to become modulated by iNKT cells activated through the CD1d agonist αGalCerMPEG. Our results demonstrate an improved functional responsiveness of murine lung and splenic ILC1s following iNKT cell stimulation by the mucosal route, as demonstrated by enhanced surface expression of TNF-related apoptosis-inducing ligand (TRAIL), CD49a and CD28, and increased secretion of IFNγ. Interestingly, iNKT cell stimulation also induced the expression of the immune checkpoint molecules GITR and CTLA-4, which represent crucial points of action for immune regulation. An in vivo influenza infection model revealed that intranasal activation of ILC1s by αGalCerMPEG contributed to increased viral clearance as shown by reduced viral loads in the lungs. The findings that ILC1s can become modulated by mucosally activated iNKT cells in a beneficial manner emphasize their up to now underestimated potential and renders them to be considered as targets for novel immune interventions.

A novel role for coinhibitory receptors/checkpoint proteins in the immunopathology of sepsis

Coinhibitory molecules, such as PD-1, CTLA-4, 2B4, and BTLA, are an important new family of mediators in the pathophysiology of severe bacterial and/or fungal infection, as well as the combined insults of shock and sepsis. Further, the expression of these molecules may serve as indicators of the immune status of the septic individual. Using PD-1:PD-L as an example, we discuss in this review how such checkpoint molecules may affect the host response to infection by mediating the balance between effective immune defense and immune-mediated tissue injury. Additionally, we explore how the up-regulation of PD-1 and/or PD-L1 expression on not only adaptive immune cells (e.g., T cells), but also on innate immune cells (e.g., macrophages, monocytes, and neutrophils), as well as nonimmune cells during sepsis and/or shock contributes to functional alterations often with detrimental sequelae.

Effect of Immunosuppression on Target Blood Immune Cells Within 1 Year After Lung Transplantation: Influence of Age on T Lymphocytes

Background

Lymphocytes are targeted by immunosuppressive therapy in solid organ transplantation and they influence allograft outcome.

Material/Methods

Peripheral blood lymphocyte subsets (PBLS) determined by flow cytometry during the first year post-transplant from patients who underwent a first lung transplantation in a French University Hospital between December 2011 and July 2013 were retrospectively analyzed according to recipient characteristics and allograft outcome.

Results

Fifty-seven recipients were enrolled and 890 PBLS were collected. T lymphocytes and NK cells were rapidly decreased, below normal range, from the first postoperative days. B cells decreased more gradually, remaining within normal range, with the lowest level reached after day 100. In multivariate analysis, greater T lymphopenia was found in older recipients (−414 [−709 to −119] cells/μL, p=0.007). According to the outcome, multivariate analysis evidenced lower levels of lymphocytes when bacterial and viral infection occurred (−177 [−310 to −44] cells/μL, p=0.009 and (−601 [−984 to −218] cells/μL, p=0.002, respectively), higher CD8+ T lymphocytes with BOS (+324 [+94 to +553] cells/μL, p=0.006), and higher leukocytes with restrictive allograft syndrome (+3770 [+418 to +7122] cells/μL, p=0.028).

Conclusions

Aging is associated in our cohort with more severe T lymphopenia after induction therapy for lung transplantation. The analysis of leukocytes and PBLS is associated with specific profile according to the allograft outcome.

Mixed Signals: Co-Stimulation in Invariant Natural Killer T Cell-Mediated Cancer Immunotherapy

Invariant natural killer T (iNKT) cells are an integral component of the immune system and play an important role in antitumor immunity. Upon activation, iNKT cells can directly kill malignant cells as well as rapidly produce cytokines that stimulate other immune cells, making them a front line defense against tumorigenesis. Unfortunately, iNKT cell number and activity are reduced in multiple cancer types. This anergy is often associated with upregulation of co-inhibitory markers such as programmed death-1. Similar to conventional T cells, iNKT cells are influenced by the conditions of their activation. Conventional T cells receive signals through the following three types of receptors: (1) T cell receptor (TCR), (2) co-stimulation molecules, and (3) cytokine receptors. Unlike conventional T cells, which recognize peptide antigen presented by MHC class I or II, the TCRs of iNKT cells recognize lipid antigen in the context of the antigen presentation molecule CD1d (Signal 1). Co-stimulatory molecules can positively and negatively influence iNKT cell activation and function and skew the immune response (Signal 2). This study will review the background of iNKT cells and their co-stimulatory requirements for general function and in antitumor immunity. We will explore the impact of monoclonal antibody administration for both blocking inhibitory pathways and engaging stimulatory pathways on iNKT cell-mediated antitumor immunity. This review will highlight the incorporation of co-stimulatory molecules in antitumor dendritic cell vaccine strategies. The use of co-stimulatory intracellular signaling domains in chimeric antigen receptor-iNKT therapy will be assessed. Finally, we will explore the influence of innate-like receptors and modification of immunosuppressive cytokines (Signal 3) on cancer immunotherapy.

Improved proliferation of antigen-specific cytolytic T lymphocytes using a multimodal nanovaccine

The present study investigated the immunoenhancing property of our newly designed nanovaccine, that is, its ability to induce antigen-specific immunity. This study also evaluated the synergistic effect of a novel compound PBS-44, an α-galactosylceramide analog, in boosting the immune response induced by our nanovaccine. The nanovaccine was prepared by encapsulating ovalbumin (ova) and an adjuvant within the poly(lactic-co-glycolic acid) nanoparticles. Quantitative analysis of our study data showed that the encapsulated vaccine was physically and biologically stable; the core content of our nanovaccine was found to be released steadily and slowly, and nearly 90% of the core content was slowly released over the course of 25 days. The in vivo immunization studies exhibited that the nanovaccine induced stronger and longer immune responses compared to its soluble counterpart. Similarly, intranasal inhalation of the nanovaccine induced more robust antigen-specific CD8⁺ T cell response than intraperitoneal injection of nanovaccine.

Natural killer T cell anergy, co-stimulatory molecules and immunotherapeutic interventions

Natural killer T (NKT) cells are a unique subset of glycolipid-reactive T lymphocytes that share properties with natural killer (NK) cells. These lymphocytes can produce array of cytokines and chemokines that modulate the immune response, and play a pivotal role in cancer, autoimmunity, infection and inflammation. Owing to these properties, NKT cells have gained attentions for its potential use in antitumor immunotherapies. To date several NKT cell-based clinical trials have been performed in patients with cancer using its potent ligand α-galactosylceramide (α-GalCer). However, inconsistent therapeutic benefit, and inevitable health risks associated with drug dose and NKT cell activation have been observed. α-GalCer-activated NKT cells become anergic and produce both Th1 and Th2 cytokines that may function antagonistically, limiting the desired effector functions. Besides, various co-stimulatory and signaling molecules such as programmed death-1 (PD-1; CD279), casitas B-cell lymphoma-b (Cbl-b) and CARMA1 have been shown to be implicated in the induction of NKT cell anergy. In this review, we discuss the role of such key regulators and their functional mechanisms that may facilitate the development of improved approaches to overcome NKT cell anergy. In addition, we describe the evidences indicating that tailored-ligands can optimally activate NKT cells to obtain desired immune responses.

Y chromosome-linked B and NK cell deficiency in mice

There are no primary immunodeficiency diseases linked to the Y chromosome, because the Y chromosome does not contain any vital genes. We have established a novel mouse strain in which all males lack B and NK cells and have Peyer's patch defects. By 10 wk of age, 100% of the males had evident immunodeficiencies. Mating these immunodeficient males with wild-type females on two different genetic backgrounds for several generations demonstrated that the immunodeficiency is linked to the Y chromosome and is inherited in a Mendelian fashion. Although multicolor fluorescence in situ hybridization analysis showed that the Y chromosome in the mutant male mice was one third shorter than that in wild-type males, exome sequencing did not identify any significant gene mutations. The precise molecular mechanisms are still unknown. Bone marrow chimeric analyses demonstrated that an intrinsic abnormality in bone marrow hematopoietic cells causes the B and NK cell defects. Interestingly, fetal liver cells transplanted from the mutant male mice reconstituted B and NK cells in lymphocyte-deficient Il2rg(-/-) recipient mice, whereas adult bone marrow transplants did not. Transducing the EBF gene, a master transcription factor for B cell development, into mutant hematopoietic progenitor cells rescued B cell but not NK cell development both in vitro and in vivo. These Y chromosome-linked immunodeficient mice, which have preferential B and NK cell defects, may be a useful model of lymphocyte development.

Correlation of circulating glucocorticoid-induced TNFR-related protein ligand levels with disease activity in patients with systemic lupus erythematosus

The aim of this paper is to investigate the correlation of glucocorticoid-induced tumor necrosis factor receptor- (TNFR-) related protein ligand (GITRL) with disease activity and organ involvement in patients with systemic lupus erythematosus (SLE). Serum GITRL levels were measured in 58 patients with SLE and 30 healthy controls matched for age and sex. Patients were assessed for clinical and laboratory variables. Correlations of serum GITRL levels with SLEDAI, laboratory values, and clinical manifestations were assessed. Serum GITRL levels were determined by ELISA. Serum GITRL levels were markedly increased in patients with SLE compared with healthy controls (mean 401.3 ng/mL and 36.59 ng/mL, resp.; P < 0.0001). SLE patients with active disease showed higher serum GITRL levels compared to those with inactive disease (mean 403.3 ng/mL and 136.3 ng/mL, resp; P = 0.0043) as well as normal controls (36.59 ng/mL; P < 0.0001). Serum GITRL levels were positively correlated with SLEDAI, titers of anti-dsDNA antibody, erythrocyte sedimentation rate (ESR), and IgM and negatively correlated with complement3 (C3). Serum GITRL levels were higher in SLE patients with renal involvement and vasculitis compared with patients without the above-mentioned manifestations.

Pharmacological modulation of GITRL/GITR system: therapeutic perspectives

Glucocorticoid-induced TNFR-related (gitr) is a gene coding for a member of the TNF receptor superfamily. GITR activation by its ligand (GITRL) influences the activity of effector and regulatory T cells, thus participating in the development of immune response against tumours and infectious agents, as well as in autoimmune and inflammatory diseases. Notably, treating animals with GITR-Fc fusion protein ameliorates autoimmune/inflammatory diseases while GITR triggering, by treatment with anti-GITR mAb, is effective in treating viral, bacterial and parasitic infections, as well in boosting immune response against tumours. GITR modulation has been indicated as one of the top 25 most promising research areas by the American National Cancer Institute, and a clinical trial testing the efficacy of an anti-GITR mAb in melanoma patients has been started. In this review, we summarize results regarding: (i) the mechanisms by which GITRL/GITR system modulates immune response; (ii) the structural and functional studies clearly demonstrating differences between GITRL/GITR systems of mice and humans; (iii) the molecules with pharmacological activities including anti-GITR mAbs, GITR-Fc and GITRL-Fc fusion proteins, GITRL in monomer or multimer conformation; and (iv) the possible risks deriving from GITRL/GITR system pharmacological modulation. In conclusion, GITR triggering and inhibition could be useful in treating tumours, infectious diseases, as well as autoimmune and inflammatory diseases. However, differences between mouse and human GITRL/GITR systems suggest that further preclinical studies are needed to better understand how safe therapeutic results can be obtained and to design appropriate clinical trials.

CD8+ T cells: GITR matters

As many members of the tumor necrosis factor receptor superfamily, glucocorticoid-induced TNFR-related gene (GITR) plays multiple roles mostly in the cells of immune system. CD8⁺ T cells are key players in the immunity against viruses and tumors, and GITR has been demonstrated to be an essential molecule for these cells to mount an immune response. The aim of this paper is to focus on GITR function in CD8⁺ cells, paying particular attention to numerous and recent studies that suggest its crucial role in mouse disease models.

ICOS-dependent stimulation of NKT cells by marginal zone B cells

Marginal zone (MZ) B cells express high levels of CD1d molecules. In accordance, MZ B cells, like splenic conventional DCs (cDCs), efficiently trigger NKT-cell proliferation. Importantly, MZ B cells exclusively induced production of IL-4 and IL-13 by such cells whereas cDCs induced robust production of mainly IFN-γ. NKT-cell proliferation, IL-4 and IL-13 production induced by MZ B cells were dependent on ICOS/ICOS ligand interaction while IFN-γ and IL-17 induction by cDCs required glucocorticoid-induced TNF receptor/glucocorticoid-induced TNF receptor ligand interplay. Our data illustrate that both MZ B cells and cDCs act as efficient APCs for NKT cells and might differentially influence the quality of the subsequent immune response.

Stimulation of the glucocorticoid-induced TNF receptor family-related receptor on CD8 T cells induces protective and high-avidity T cell responses to tumor-specific antigens

Treatment of tumor-bearing mice with a stimulatory Ab to glucocorticoid-induced TNFR family-related receptor (GITR) has previously been shown to elicit protective T cell responses against poorly immunogenic tumors. However, the role of GITR stimulation on CD8 T cells and the nature of tumor rejection Ags have yet to be determined. In this study, we show that a stimulatory mAb to GITR (clone DTA-1) acts directly on CD8 T cells, but not on CD4(+)CD25(+) regulatory T (T(reg)) cells, in B16 tumor-bearing mice to induce concomitant immunity against secondary B16 tumors, as well as protective memory following surgical excision of the primary tumor. Melanoma growth itself induced GITR expression on tumor-specific CD8 T cells, providing a mechanism whereby these cells may respond to stimulatory anti-GITR. Unexpectedly, in contrast to T(reg) cell depletion therapy with anti-CD4, GITR stimulation induced very weak CD8 T cell responses to melanocyte differentiation Ags expressed by the tumor, and did not induce autoimmune vitiligo. Accordingly, GITR-stimulated hosts that were primed with B16 melanoma rejected B16, but not the unrelated JBRH melanoma, indicating that tumor rejection Ags are tumor-specific rather than shared. In support of this, we show that GITR stimulation induces CD8 T cell responses to a tumor-specific Ag, and that these responses are of higher functional avidity compared with those induced by T(reg) cell depletion. We conclude that stimulation of GITR on effector CD8 T cells results in high-avidity T cell responses to tumor-specific Ags, thereby inducing potent antitumor immunity in the absence of autoimmunity.

NKT cell costimulation: experimental progress and therapeutic promise

Invariant natural killer T (iNKT) cells are innate lymphocytes with unique specificity for glycolipid antigens and remarkable immunomodulatory properties. The role of costimulatory interactions in iNKT cell responses has recently come under scrutiny. Although iNKT cells and their prototype glycolipid agonist α-galactosylceramide (α-GalCer) have shown promise in several clinical trials conducted in patients with cancer or viral diseases, current iNKT cell-based therapies are far from effective. The concomitant targeting of T cell receptors (TCRs) and costimulatory molecules on iNKT cells represents an exciting new opportunity to optimize such therapeutic approaches. Here, we review recent advances in our understanding of iNKT cell costimulation and discuss potential treatment modalities based on the responsiveness of iNKT cells to disease-tailored glycolipids and select costimulatory ligands.

Glucocorticoid-induced TNFR-related (GITR) protein and its ligand in antitumor immunity: functional role and therapeutic modulation

The ability of the tumor necrosis factor receptor (TNFR) family member GITR to modulate immune responses has been the subject of multiple studies. Initially thought to be critically involved in governing functions of regulatory T cells, GITR and its ligand GITRL have meanwhile been found to modulate the reactivity of various different cell types and to influence a broad variety of immunological conditions including the immune response against tumors. Not only GITR, but also GITRL is capable of transducing signals, and the consequences of GITR-GITRL interaction may vary among different effector cell types, differ upon signal transduction via the receptor, the ligand, or both, depend on the level of an ongoing immune response, and even differ among mice and men. In this paper, we address available data on GITR and its ligand in immune responses and discuss the role and potential therapeutic modulation of this molecule system in antitumor immunity.