TIM-3 is expressed on activated human CD4+ T cells and regulates Th1 and Th17 cytokines

Tim-3: an activation marker and activation limiter of innate immune cells

Tim-3 was initially identified on activated Th1, Th17, and Tc1 cells and induces T cell death or exhaustion after binding to its ligand, Gal-9. The observed relationship between dysregulated Tim-3 expression on T cells and the progression of many clinical diseases has identified this molecule as an important target for intervention in adaptive immunity. Recent data have shown that it also plays critical roles in regulating the activities of macrophages, monocytes, dendritic cells, mast cells, natural killer cells, and endothelial cells. Although the underlying mechanisms remain unclear, dysregulation of Tim-3 expression on these innate immune cells leads to an excessive or inhibited inflammatory response and subsequent autoimmune damage or viral or tumor evasion. In this review, we focus on the expression and function of Tim-3 on innate immune cells and discuss (1) how Tim-3 is expressed and regulated on different innate immune cells; (2) how it affects the activity of different innate immune cells; and (3) how dysregulated Tim-3 expression on innate immune cells affects adaptive immunity and disease progression. Tim-3 is involved in the optimal activation of innate immune cells through its varied expression. A better understanding of the physiopathological role of the Tim-3 pathway in innate immunity will shed new light on the pathogenesis of clinical diseases, such as autoimmune diseases, chronic viral infections, and cancer, and suggest new approaches to intervention.

Do inhibitory immune receptors play a role in the etiology of autoimmune disease?

Inhibitory receptors are thought to be important in balancing immune responses. The general assumption is that lack of inhibition predisposes for autoimmune diseases. As reviewed here, various experimental and clinical data support this assumption. However, in humans genetic evidence implicates only a limited number of inhibitory receptors. GWAS have established common variation in a few inhibitory receptor genes, such as FCγRIIB, PD-1 and CTLA-4 as risk factors. The question arises whether inhibitory receptor function is a major determinant of autoimmune disease. In this respect, the finding that genetic variation in CSK and PTPN22 is strongly associated with multiple autoimmune diseases is of interest. We propose a model in which the molecules encoded by these genes are downstream of inhibitory receptors. We conclude that common genetic variation of inhibitory receptors, with few exceptions, is not a determining factor for autoimmunity in humans. However, common downstream signaling pathways are.

A novel soluble form of Tim-3 associated with severe graft-versus-host disease

The T cell Ig and mucin domain 3 (Tim-3) receptor has been implicated as a negative regulator of adaptive immune responses. We have utilized a proteomic strategy to identify novel proteins associated with graft versus host disease (GVHD) after allogeneic hematopoietic cell transplantation (HCT). Mass spectrometry analysis of plasma from subjects with mid-gut and upper-gut GVHD compared with those without GVHD identified increased levels of a protein identified with high confidence as Tim-3. A follow-up validation study using an immunoassay to measure Tim-3 levels in individual plasma samples from 127 patients demonstrated significantly higher plasma Tim-3 concentrations in patients with the more severe mid-gut GVHD, compared with those with upper-gut GVHD (P = .005), patients without GVHD (P = .002), and normal controls (P < .0001). Surface expression of Tim-3 was increased on CD8(+) T cells from patients with grade 2 to 4 acute GVHD (P = .01). Mass spectrometry-based profiling of plasma from multiple subjects diagnosed with common diseases provided evidence for restricted release of soluble Tim-3 in the context of GVHD. These findings have mechanistic implications for the development of novel strategies for targeting the Tim-3 immune regulatory pathway as an approach to improving control of GVHD.

T-cell immunoglobulin and mucin domain 3 acts as a negative regulator of atherosclerosis

OBJECTIVE

Atherosclerosis is a chronic autoimmune-like disease in which lipids and fibrous elements accumulate in the arterial blood vessels. T cells are present within atherosclerotic plaques, and their activation is partially dependent on costimulatory signals, which can either provide positive or negative signals that promote T-cell activation or limit T-cell responses, respectively. T-cell immunoglobulin and mucin domain 3 (Tim-3) is a coinhibitory type 1 transmembrane protein that affects the function of several immune cells involved in atherosclerosis, such as monocytes, macrophages, effector T cells, and regulatory T cells. In the present study, we determined the role of Tim-3 in the development of atherosclerosis.

APPROACH AND RESULTS

Western-type diet-fed low-density lipoprotein receptor-deficient (LDLr(-/-)) mice were treated with an anti-Tim-3 antibody for 3 and 8 weeks. Anti-Tim-3 administration increased fatty streak formation with 66% and increased atherosclerotic plaque formation after 8 weeks with 35% in the aortic root and with 50% in the aortic arch. Furthermore, blockade of Tim-3 signaling increased percentages of circulating monocytes with 33% and lesional macrophages with 20%. In addition, anti-Tim-3 administration increased CD4(+) T cells with 17%, enhanced their activation status, and reduced percentages of regulatory T cells with 18% and regulatory B cells with 37%.

CONCLUSIONS

It is known that Tim-3 acts as a negative regulator of both innate and adaptive immune responses, and in the present study, we show that anti-Tim-3 treatment augments lesion development, accompanied by an increase in the number of monocytes/macrophages and CD4(+) T cells and by decreased regulatory T cells and regulatory B cells.

Cis association of galectin-9 with Tim-3 differentially regulates IL-12/IL-23 expressions in monocytes via TLR signaling

Human monocytes/macrophages (M/M_Ф) of the innate immunity sense and respond to microbial products via specific receptor coupling with stimulatory (such as TLR) and inhibitory (such as Tim-3) receptors. Current models imply that Tim-3 expression on M/M_Ø can deliver negative signaling to TLR-mediated IL-12 expression through trans association with its ligand Galectin-9 (Gal-9) presented by other cells. However, Gal-9 is also expressed within M/M_Ø, and the effect of intracellular Gal-9 on Tim-3 activities and inflammatory responses in the same M/M_Ø remains unknown. In this study, our data suggest that Tim-3 and IL-12/IL-23 gene transcriptions are regulated by enhanced or silenced Gal-9 expression within monocytes through synergizing with TLR signaling. Additionally, TLR activation facilitates Gal-9/Tim-3 cis association within the same M/M_Ø to differentially regulate IL-12/IL-23 expressions through STAT-3 phosphorylation. These results reveal a ligand (Gal-9) compartment-dependent regulatory effect on receptor (Tim-3) activities and inflammatory responses via TLR pathways—a novel mechanism underlying cellular responses to external or internal cues.

Dexamethasone reduces IL-17 and Tim-3 expression in BALF of asthmatic mice

This study investigated the expression of interleukin-17 (IL-17) and T cell immunoglobulin mucin and domain-containing molecule-3 (Tim-3) in bronchoalveolar lavage fluid (BALF) of asthmatic mice and the effect of dexamethasone (DEX) on these factors. Thirty-six mice were randomly divided into three groups: normal group, asthmatic group and DEX group. The mouse model of asthma was established by sensitization with ovalbumin in both the asthmatic and DEX groups. The levels of IL-6, IL-10, IL-17 and TGF-β were measured in BALF by enzyme-linked immunesorbent assay (ELISA). The mRNA expression level of Tim-3 was detected by reverse transcription polymerase chain reaction (RT-PCR). The ratio of Tim-3+CD4+ cells to total CD4+ cells in BALF was determined by flow cytometry. Differential inflammatory cells in BALF were detected. The correlations among IL-17, IL-6, IL-10, Tim-3 and inflammatory cells were analyzed. The results showed that the levels of IL-17, IL-6 and Tim-3 were substantially increased and the IL-10 level decreased in BALF in the asthmatic mice, which was significantly reversed by DEX treatment. IL-17 expression was positively correlated with IL-6 and Tim-3 expression and the number of inflammatory cells but negatively with IL-10 expression. These results indicate that the increased expression of IL-17 and Tim-3 in BALF may be implicated in the occurrence and development of asthmatic inflammation; the mechanism by which DEX suppresses asthmatic airway inflammation involves down-regulation of IL-17 and Tim-3 levels.

Natural and induced T regulatory cells in cancer

CD4+Foxp3+ T regulatory (Treg) cells control many facets of immune responses ranging from autoimmune diseases, to inflammatory conditions, and cancer in an attempt to maintain immune homeostasis. Natural Treg (nTreg) cells develop in the thymus and constitute a critical arm of active mechanisms of peripheral tolerance particularly to self antigens. A growing body of knowledge now supports the existence of induced Treg (iTreg) cells which may derive from a population of conventional CD4+ T cells. The fork-head transcription factor (Foxp3) typically is expressed by natural CD4+ Treg cells, and thus serves as a marker to definitively identify these cells. On the contrary, there is less consensus on what constitutes iTreg cells as their precise definition has been somewhat elusive. This is in part due to their distinct phenotypes which are shaped by exposure to certain inflammatory or "assault" signals stemming from the underlying immune disorder. The "policing" activity of Treg cells tends to be uni-directional in several pathological conditions. On one end of the spectrum, Treg cell suppressive activity is beneficial by curtailing T cell response against self-antigens and allergens thus preventing autoimmune diseases and allergies. On the other end however, their inhibitory roles in limiting immune response against pseudo-self antigens as in tumors often culminates into negative outcomes. In this review, we focus on this latter aspect of Treg cell immunobiology by highlighting the involvement of nTreg cells in various animal models and human tumors. We further discuss iTreg cells, relationship with their natural counterpart, and potential co-operation between the two in modulating immune response against tumors. Lastly, we discuss studies focusing on these cells as targets for improving anti-tumor immunity.

Natural and induced T regulatory cells in cancer

CD4+Foxp3+ T regulatory (Treg) cells control many facets of immune responses ranging from autoimmune diseases, to inflammatory conditions, and cancer in an attempt to maintain immune homeostasis. Natural Treg (nTreg) cells develop in the thymus and constitute a critical arm of active mechanisms of peripheral tolerance particularly to self antigens. A growing body of knowledge now supports the existence of induced Treg (iTreg) cells which may derive from a population of conventional CD4+ T cells. The fork-head transcription factor (Foxp3) typically is expressed by natural CD4+ Treg cells, and thus serves as a marker to definitively identify these cells. On the contrary, there is less consensus on what constitutes iTreg cells as their precise definition has been somewhat elusive. This is in part due to their distinct phenotypes which are shaped by exposure to certain inflammatory or “assault” signals stemming from the underlying immune disorder. The “policing” activity of Treg cells tends to be uni-directional in several pathological conditions. On one end of the spectrum, Treg cell suppressive activity is beneficial by curtailing T cell response against self-antigens and allergens thus preventing autoimmune diseases and allergies. On the other end however, their inhibitory roles in limiting immune response against pseudo-self antigens as in tumors often culminates into negative outcomes. In this review, we focus on this latter aspect of Treg cell immunobiology by highlighting the involvement of nTreg cells in various animal models and human tumors. We further discuss iTreg cells, relationship with their natural counterpart, and potential co-operation between the two in modulating immune response against tumors. Lastly, we discuss studies focusing on these cells as targets for improving anti-tumor immunity.

FcRγ controls the fas-dependent regulatory function of lymphoproliferative double negative T cells

Patients with autoimmune lymphoproliferative syndrome (ALPS) and lymphoproliferation (LPR) mice are deficient in Fas, and accumulate large numbers of αβ-TCR⁺, CD4⁻, CD8⁻ double negative (DN) T cells. The function of these DN T cells remains largely unknown. The common γ subunit of the activating Fc receptors, FcRγ, plays an important role in mediating innate immune responses. We have shown previously that a significant proportion of DN T cells express FcRγ, and that this molecule is required for TCR transgenic DN T cells to suppress allogeneic immune responses. Whether FcRγ plays a critical role in LPR DN T cell-mediated suppression of immune responses to auto and allo-antigens is not known. Here, we demonstrated that FcRγ⁺, but not FcRγ⁻ LPR DN T cells could suppress Fas⁺ CD4⁺ and CD8⁺ T cell proliferation in vitro and attenuated CD4⁺ T cell-mediated graft-versus host disease. Although FcRγ expression did not allow LPR DN T cells to inhibit the expansion of Fas-deficient cells within the LPR context, adoptive transfer of FcRγ⁺, but not FcRγ⁻, DN T cells inhibited lymphoproliferation in generalized lymphoproliferative disease (GLD) mice. Furthermore, FcRγ acted in a cell-intrinsic fashion to limit DN T cell accumulation by increasing the rate of apoptosis in proliferated cells. These results indicate that FcRγ can confer Fas-dependent regulatory properties on LPR DN T cells, and suggest that FcRγ may be a novel marker for functional DN Tregs.

Rejection and regulation: a tight balance

PURPOSE OF REVIEW

Achieving allograft tolerance is the holy grail of transplantation. However, tolerance and rejection are two extreme ends of a scale that can be tipped in either direction. We review the novel effector and regulatory mechanisms involved and factors that tip the balance in favor of rejection or regulation.

RECENT FINDINGS

It is increasingly recognized that established T-cell phenotypes could change their commitments. New data point to the plasticity of Th17 cells in vivo with a reciprocal balance of Th17 cells and regulatory T cells (Tregs) driven by the local cytokine environment. Treg-cell profiles have been linked to acute and chronic allograft outcomes, and emerging data also indicate a novel role of a regulatory B-cell population. Current research efforts are looking into factors that tip the balance toward allograft tolerance by targeting cytokines, novel costimulatory pathways such as T-cell immunoglobulin mucin molecules, and components of innate immunity, particularly dendritic cells.

SUMMARY

The balance of effector and regulatory mechanisms contributing to allograft outcome is very complex. It is likely that targeting multiple pathways will be required to achieve tolerance. Further studies are warranted to define this balance and identify optimal combination of therapeutic interventions.

The influence of T cell Ig mucin-3 signaling on central nervous system autoimmune disease is determined by the effector function of the pathogenic T cells

Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the CNS mediated by self-reactive, myelin-specific T cells. Both CD4(+) and CD8(+) T cells play important roles in the pathogenesis of MS. MS is studied using experimental autoimmune encephalomyelitis (EAE), an animal model mediated by myelin-specific T cells. T cell Ig mucin-3 (Tim-3) is a cell surface receptor expressed on CD4(+) IFN-γ-secreting Th1 cells, and triggering Tim-3 signaling ameliorated EAE by inducing death in pathogenic Th1 cells in vivo. This suggested that enhancing Tim-3 signaling might be beneficial in patients with MS. However, Tim-3 is also expressed on activated CD8(+) T cells, microglia, and dendritic cells, and the combined effect of manipulating Tim-3 signaling on these cell types during CNS autoimmunity is unknown. Furthermore, CD4(+) IL-17-secreting Th17 cells also play a role in MS, but do not express high levels of Tim-3. We investigated Tim-3 signaling in EAE models that include myelin-specific Th17, Th1, and CD8(+) T cells. We found that preventing Tim-3 signaling in CD4(+) T cells altered the inflammatory pattern in the CNS due to differential effects on Th1 versus Th17 cells. In contrast, preventing Tim-3 signaling during CD8(+) T cell-mediated EAE exacerbated disease. We also analyzed the importance of Tim-3 signaling in EAE in innate immune cells. Tim-3 signaling in dendritic cells and microglia did not affect the manifestation of EAE in these models. These results indicate that the therapeutic efficacy of targeting Tim-3 in EAE is dependent on the nature of the effector T cells contributing to the disease.

TIM-3 does not act as a receptor for galectin-9

T cell immunoglobulin and mucin protein 3 (TIM-3) is a type I cell surface protein that was originally identified as a marker for murine T helper type 1 cells. TIM-3 was found to negatively regulate murine T cell responses and galectin-9 was described as a binding partner that mediates T cell inhibitory effects of TIM-3. Moreover, it was reported that like PD-1 the classical exhaustion marker, TIM-3 is up-regulated in exhausted murine and human T cells and TIM-3 blockade was described to restore the function of these T cells. Here we show that the activation of human T cells is not affected by the presence of galectin-9 or antibodies to TIM-3. Furthermore, extensive studies on the interaction of galectin-9 with human and murine TIM-3 did not yield evidence for specific binding between these molecules. Moreover, profound differences were observed when analysing the expression of TIM-3 and PD-1 on T cells of HIV-1-infected individuals: TIM-3 was expressed on fewer cells and also at much lower levels. Furthermore, whereas PD-1 was preferentially expressed on CD45RA⁻CD8 T cells, the majority of TIM-3-expressing CD8 T cells were CD45RA⁺. Importantly, we found that TIM-3 antibodies were ineffective in increasing anti-HIV-1 T cell responses in vitro, whereas PD-L antibodies potently reverted the dysfunctional state of exhausted CD8 T cells. Taken together, our results are not in support of an interaction between TIM-3 and galectin-9 and yield no evidence for a functional role of TIM-3 in human T cell activation. Moreover, our data indicate that PD-1, but not TIM-3, is a promising target to ameliorate T cell exhaustion.

Inhibitory costimulatory receptors are a hallmark of exhausted T cells, which accumulate during chronic infection with viruses like HIV-1. Recently, TIM-3 was described as functional receptor on exhausted human T cells. Galectin-9 was reported as an inhibitory ligand for TIM-3 on murine T cells, but it was not known whether galectin-9 has a role in human T cell activation processes. We have found that the activation of human T cells is not affected by the presence of galectin-9 or antibodies to TIM-3. Furthermore, we demonstrate that galectin-9 does not serve as a ligand of human or murine TIM-3. Analysis of T cells of HIV-infected individuals regarding the expression of TIM-3 and PD-1 demonstrates that TIM-3 is expressed on fewer cells and also at much lower levels. In fact, TIM-3 expression characterizes a T cell population that is distinct from the PD-1 expressing exhausted T cells. Our results indicate that PD-1, but not TIM-3, is a promising target to ameliorate T cell exhaustion.

Coinhibitory molecules in cancer biology and therapy

The adaptive immune response is controlled by checkpoints represented by coinhibitory molecules, which are crucial for maintaining self-tolerance and minimizing collateral tissue damage under physiological conditions. A growing body of preclinical evidence supports the hypothesis that unleashing this immunological break might be therapeutically beneficial in the fight against cancer, as it would elicit an effective antitumor immune response. Remarkably, recent clinical trials have demonstrated that this novel strategy can be highly effective in the treatment of patients with cancer, as shown by the paradigmatic case of ipilimumab (a monoclonal antibody blocking the coinhibitory molecule cytotoxic T lymphocyte associated antigen-4 [CTLA4]) that is opening a new era in the therapeutic approach to a chemoresistant tumor such as cutaneous melanoma. In this review we summarize the biology of coinhibitory molecules, overview the experimental and clinical attempts to interfere with these immune checkpoints to treat cancer and critically discuss the challenges posed by such a promising antitumor modality.

T cell Ig mucin-3 promotes homeostasis of sepsis by negatively regulating the TLR response

Sepsis is an excessive inflammatory condition with a high mortality rate and limited prediction and therapeutic options. In this study, for the first time, to our knowledge, we found that downregulation and/or blockade of T cell Ig and mucin domain protein 3 (Tim-3), a negative immune regulator, correlated with severity of sepsis, suggesting that Tim-3 plays important roles in maintaining the homeostasis of sepsis in both humans and a mouse model. Blockade and/or downregulation of Tim-3 led to increased macrophage activation, which contributed to the systemic inflammatory response in sepsis, whereas Tim-3 overexpression in macrophages significantly suppressed TLR-mediated proinflammatory cytokine production, indicating that Tim-3 is a negative regulator of TLR-mediated immune responses. Cross-talk between the Tim-3 and TLR4 pathways makes TLR4 an important contributor to Tim-3-mediated negative regulation of the innate immune response. Tim-3 signaling inhibited LPS-TLR4-mediated NF-κB activation by increasing PI3K-AKT phosphorylation and A20 activity. This negative regulatory role of Tim-3 reflects a new adaptive compensatory and protective mechanism in sepsis victims, a finding of potential importance for modulating innate responses in these patients.

T-cell immunoglobulin- and mucin-domain-containing molecule 3 gene polymorphisms and prognosis of non-small-cell lung cancer

Lung cancer is the leading cause of death worldwide. Non-small-cell lung cancer (NSCLC) accounts for most of these cases. T-cell immunoglobulin- and mucin-domain-containing molecule 3 (TIM-3) has been established as a negative regulatory molecule and plays a critical role in immune tolerance. Studies have shown that polymorphisms in TIM-3 gene can be associated with various diseases. The aim of this study was to investigate whether polymorphisms in the TIM-3 gene were associated with susceptibility to NSCLC. Three polymorphisms in TIM-3 gene (-1516G/T, -574G/T, and +4259T/G) were identified by polymerase chain reaction-restriction fragment length polymorphism in 432 NSCLC patients and 466 healthy controls. Results showed that frequencies of TIM-3 +4259TG genotype for cases and controls were 10.9 and 4.1 %, respectively; subjects carrying the +4259TG genotype had a 2.81-fold increased risk of NSCLC compared to the wild-type genotype (P < 0.0001). The TIM-3 -1516G/T and -574G/T polymorphisms did not show any correlation with NSCLC. In addition, when analyzing the survival time of NSCLC patients with TIM-3 +4259T/G polymorphism, cases with +4259TG genotype had significantly shorter survival time compared to the wild-type patients (15.2 months vs. 26.7 months, P = 0.007). These results suggested polymorphism in TIM-3 gene is associated with increased susceptibility to NSCLC and could be used as prognostic factor for this malignancy.

Tim-3/galectin-9 regulate the homeostasis of hepatic NKT cells in a murine model of nonalcoholic fatty liver disease

T cell Ig and mucin domain (Tim)-3 is well known to interact with its natural ligand, Galectin-9 (Gal-9), to regulate T cell function. However, little is known about the function of Tim-3/Gal-9 signaling in the pathogenesis of nonalcoholic fatty liver disease (NAFLD) mediated by hepatic NKT cells that also express Tim-3. In the current study, we define the role and the mechanism of Tim-3/Gal-9 signaling in hepatic NKT cell regulation in a mouse model of diet-induced NAFLD. Adult male wild-type or CD1d knockout C57BL/6 mice were fed a high-fat diet to induce steatosis. Some of the mice also received one or a combination of Gal-9, anti-IL-15R/IL-15 mAb, rIL-15, α-galactosylceramide, and multilamellar liposomes containing Cl(2)MDP. The expression of Tim-3 and various markers reflecting cell proliferation, activation, cytokine production, and apoptosis was analyzed. Liver histology, steatosis grade, and hepatic triglyceride content were also evaluated. In the liver, Tim-3(+) NKT cells are in an activated state, and Gal-9 directly induces Tim-3(+) NKT cell apoptosis and contributes to the depletion of NKT cells in diet-induced steatosis. However, Gal-9 also interacts with Tim-3-expressing Kupffer cells to induce secretion of IL-15, thus promoting NKT cell proliferation. Exogenous administration of Gal-9 significantly ameliorates diet-induced steatosis by modulating hepatic NKT cell function. In summary, the Tim-3/Gal-9-signaling pathway plays a critical role in the homeostasis of hepatic NKT cells through activation-induced apoptosis and secondary proliferation and, thus, contributes to the pathogenesis of NAFLD.

The Tim3-galectin 9 pathway induces antibacterial activity in human macrophages infected with Mycobacterium tuberculosis

T cell Ig and mucin domain 3 (Tim3) is an inhibitory molecule involved in immune tolerance, autoimmune responses, and antiviral immune evasion. However, we recently demonstrated that Tim3 and Galectin-9 (Gal9) interaction induces a program of macrophage activation that results in killing of Mycobacterium tuberculosis in the mouse model of infection. In this study, we sought to determine whether the Tim3-Gal9 pathway plays a similar role in human pulmonary TB. We identified that pulmonary TB patients have reduced expression of Tim3 on CD14(+) monocytes in vivo. By blocking Tim3 and Gal9 interaction in vitro, we show that these molecules contribute to the control of intracellular bacterial replication in human macrophages. The antimicrobial effect was partially dependent on the production of IL-1β. Our results establish that Tim3-Gal9 interaction activates human M. tuberculosis -infected macrophages and leads to the control of bacterial growth through the production of the proinflammatory cytokine IL-1β. Data presented in this study suggest that one of the potential pathways activated by Tim3/Gal9 is the secretion of IL-1β, which plays a crucial role in antimicrobial immunity by modulating innate inflammatory networks.

The role of costimulatory molecules in directing the functional differentiation of alloreactive T helper cells

Costimulatory molecules are a heterogenous group of cell surface molecules that act to amplify or counteract the initial activating signals provided to T cells from the T cell receptor following its interaction with an antigen/major histocompatibility complex, thereby influencing T cell differentiation and fate. Although costimulation was previously thought to be indispensable for T cell activation at all stages of development, it is now known that the requirements for costimulation, and the costimulatory molecules involved, vary according to the stage of T cell differentiation. The ability to influence T cell fate is of paramount interest in the field of transplantation as we seek therapeutic options that inhibit detrimental alloimmune responses whilst simultaneously promoting allograft tolerance. As with many immune mechanisms, there is a degree of functional overlap between certain costimulatory molecules, whereas some have diametrically opposite effects on different T cell subsets despite sharing common ligands. This is a critical point when considering these molecules as therapeutic targets in transplantation, as blockade of a costimulatory pathway, although desirable in itself, may prevent the ligation of an essential regulatory coinhibitory molecule. This review discusses the T helper cell lineages pertinent to transplantation and the costimulatory molecules involved in their differentiation.

T cell immunoglobulin-3 as a new therapeutic target for rheumatoid arthritis

T cell immunoglobulin-3 (Tim-3) is a surface molecule expressed on various cell types of the immune system which plays a central role in immune regulation. Recently, identification of galectin-9 (Gal-9) as a ligand for Tim-3 has established the Tim-3-Gal-9 pathway as an important regulator of Th1 immunity and induction of tolerance. The interaction of Tim-3 with Gal-9 induces cell death; the in vivo blockade of this interaction results in exacerbated autoimmunity and abrogation of tolerance in experimental models, thus establishing Tim-3 as a negative regulatory molecule. A number of previous studies have demonstrated that Tim-3 influences chronic autoimmune diseases, such as multiple sclerosis and systemic lupus erythematosus. In addition, an association between Tim-3 polymorphisms and susceptibility to several autoimmune diseases has been identified in various autoimmune diseases, including rheumatoid arthritis (RA). Recent work has focused on the role of Tim-3 in RA, and the results indicate that Tim-3 may represent a novel target for the treatment of RA. In this article we will discuss the Tim-3 pathway and the therapeutic potential of modulating the Tim-3 pathway in RA.

T-cell inhibitors: a bench-to-bedside review

Allergic contact dermatitis is the quintessential example of a delayed-in-time and T-cell-mediated immune response. In the last decade, many of the molecular events required to initiate (or block) such a response have been uncovered. Textbook and journal reviews have emphasized the costimulatory requirements, with less focus on the coinhibitory signals that are of equal importance in understanding this central event of adaptive immunity. To fill this gap, we offer a compendium of discoveries characterizing the ligand-receptor pairs inhibiting T-cell activation and of selected illnesses and therapeutic applications that illuminate their role in health and disease.

Underexpression of TIM-3 and blunted galectin-9-induced apoptosis of CD4+ T cells in rheumatoid arthritis

The aim of this study is to compare the expression of TIM-3 from CD4+ T cells from rheumatoid arthritis (RA) patients and healthy controls and to evaluate the effect of galectin-9 (Gal-9) on apoptosis of CD4+ T cells in these patients. CD4+ T cells from RA patients and healthy controls were isolated from peripheral blood mononuclear cells and were activated. The expression of TIM-3 mRNA in CD4+ T cells was measured using real-time polymerase chain reaction. CD4+ T cells were activated in the presence of graded doses of Gal-9 or control, and Gal-9-induced cytotoxicity and apoptotic activity of CD4+ T cells were analyzed using MTT assays and annexin-V staining, respectively. TIM-3 mRNA expression was significantly lower in CD4+ T cells from RA patients compared with those in healthy controls (p = 0.028). CD4+ T cell survival as measured by MTT assay when incubated with Gal-9 (15 nM) was significantly higher in RA patients than in healthy controls (p = 0.002). Apoptotic activity of CD4+ T cells from healthy controls as measured by annexin staining increased with graded doses of Gal-9 (0 nM vs. 30 nM, 0 nM vs. 90 nM, p = 0.016 each). However, apoptotic activity of CD4+ T cells from RA patients did not change despite the stimulation with Gal-9. Gal-9-mediated apoptosis of CD4+ T cells is dysfunctional in RA patients. Blunted Gal-9-mediated apoptosis may be exerted through underexpression of TIM-3 that negatively regulates Th1 response. Our data suggest that TIM-3 and its interaction with Gal-9 may play an important role in the pathogenesis of RA and may represent a potential therapeutic target.

The role of TIM-containing molecules in airway disease and their potential as therapeutic targets

T cell immunoglobulin and mucin-domain (TIM)-containing molecules have emerged as promising therapeutic targets to correct abnormal immune function in several autoimmune and chronic inflammatory conditions. Despite the initial discovery linking TIM-containing molecules and the airway hyperreactivity regulatory locus in mice, there is a paucity of studies on the function of TIM-containing molecules in lung inflammatory disease. Initially, studies were limited to mice models of asthma. More recently however, TIM-containing molecules have been implicated in an ever-expanding list of airway conditions that includes pneumonia, tuberculosis, influenza, sarcoidosis, lung cancer, and cystic fibrosis. This present review discusses the role of TIM-containing molecules and their ligands in the lung, as well as their potential as therapeutic targets in airway disease.

Enhanced Tim3 activity improves survival after influenza infection

Influenza is a major cause of morbidity and mortality in the United States. Studies have shown that excessive T cell activity can mediate pneumonitis in the setting of influenza infection, and data from the 2009 H1N1 pandemic indicate that critical illness and respiratory failure postinfection were associated with greater infiltration of the lungs with CD8+ T cells. T cell Ig and mucin domain 3 (Tim3) is a negative regulator of Th1/Tc1-type immune responses. Activation of Tim3 on effector T cells has been shown to downregulate proliferation, cell-mediated cytotoxicity, and IFN-γ production, as well as induce apoptosis. In this article, we demonstrate that deletion of the terminal cytoplasmic domain of the Tim3 gene potentiates its ability to downregulate Tc1 inflammation, and that this enhanced Tim3 activity is associated with decreased phosphorylation of the TCR-CD3ζ-chain. We then show that mice with this Tim3 mutation infected with influenza are protected from morbidity and mortality without impairment in viral clearance or functional heterotypic immunity. This protection is associated with decreased CD8+ T cell proliferation and decreased production of inflammatory cytokines, including IFN-γ. Furthermore, the Tim3 mutation was protective against mortality in a CD8+ T cell-specific model of pneumonitis. These data suggest that Tim3 could be targeted to prevent immunopathology during influenza infection and demonstrate a potentially novel signaling mechanism used by Tim3 to downregulate the Tc1 response.

The impaired immune regulation of autoimmune hepatitis is linked to a defective galectin-9/tim-3 pathway

In autoimmune hepatitis (AIH), liver-damaging CD4 T cell responses are associated with defective CD4(pos) CD25(pos) regulatory T cells (T-regs). Galectin-9 (Gal9), a β-galactosidase-binding protein expressed by T-regs, is key to their function, inhibiting T helper 1 immune responses by binding T cell immunoglobulin and mucin domain 3 (Tim-3) on CD4 effector cells. We investigated whether impaired immunoregulation in AIH results from reduced expression of Gal9 in T-regs and/or Tim-3 on CD4 effector cells. Circulating Gal9(pos) CD4(pos) CD25(pos) and Tim-3(pos) CD4(pos) CD25(neg) T cell phenotype was assessed by flow cytometry in 75 AIH patients. To evaluate whether Tim-3 expression renders CD4(pos) CD25(neg) T cells amenable to T-reg control, purified CD4(pos) CD25(neg) Tim-3(pos) (Tim-3(pos)) and CD4(pos) CD25(neg) Tim-3(neg) (Tim-3(neg)) cells were cocultured with T-regs. To determine whether Gal9 expression is essential to function, T-regs were treated with small interfering RNA (siRNA) to repress Gal-9 translation; T-reg suppressor function was assessed by proliferation. In AIH, Tim-3(pos) cells within CD4(pos) CD25(neg) cells and their T-bet(pos) and RORC(pos) subsets were fewer and contained higher numbers of interferon-γ (IFNγ)(pos) and interleukin (IL)-17(pos) cells than healthy subjects (HS). In AIH and HS, Tim-3(pos) cells proliferated less vigorously and were more susceptible to T-reg control than Tim-3(neg) cells. In AIH, Gal9(pos) T-regs were fewer and contained less FOXP3(pos), IL-10(pos), and transforming growth factor β(pos) and more IFNγ(pos) and IL-17(pos) cells than HS. siRNA treatment of Gal-9(pos) T-regs drastically reduced T-reg ability to suppress CD4(pos) CD25(neg) and Tim-3(pos) cell proliferation in AIH and HS. Tim-3(pos) cell percentage correlated inversely with aminotransferase and CD25(neg) T-bet(pos) cell values.

CONCLUSION

Reduced levels of Tim-3 on CD4(pos) CD25(neg) effector cells and of Gal9 in T-regs contribute to impaired immunoregulation in AIH by rendering effector cells less prone to T-reg control and T-regs less capable of suppressing.

Immune checkpoints in central nervous system autoimmunity

A number of autoimmune diseases, including multiple sclerosis, are mediated by self-reactive T cells that have escaped the deletional mechanisms of central tolerance. Usually, these T cells are kept at bay through peripheral tolerance mechanisms, including regulation through coinhibitory receptors and suppression by regulatory T cells. However, if these mechanisms fail, self-reactive T cells are activated and autoimmune responses ensue. This review outlines how the coinhibitory receptors CTLA-4 (cytotoxic T-lymphocyte antigen-4), PD-1 (programed death-1), Tim-3 (T-cell immunoglobulin- and mucin domain-containing molecule 3), and TIGIT (T-cell immunoreceptor with immunoglobulin and ITIM domains) act at different checkpoints to inhibit autoreactive T cells and suppress the development of central nervous system autoimmunity. Loss of each of these receptors predisposes to autoimmunity, indicating a non-redundant role in maintaining peripheral tolerance. At the same time, their functional patterns seem to overlap to a large degree. Therefore, we propose that only the concerted action of a combination of inhibitory receptors is able to maintain peripheral tolerance and prevent autoimmunity.

Th17 helper cell and T-cell immunoglobulin and mucin domain 3 involvement in Guillain-Barré syndrome

OBJECTIVE AND DESIGN

We investigated the involvement of Th17 cells and T-cell immunoglobulin and mucin domain 3 (TIM-3) in Guillain-Barré syndrome (GBS) in comparison to healthy subjects.

MATERIALS AND SUBJECTS

Peripheral blood samples were obtained from 29 healthy subjects and 29 GBS patients.

TREATMENT

Peripheral blood mononuclear cells (PBMCs) and CD4(+) T cells were stimulated with anti-CD3 and anti-CD28 mAbs, in the absence or presence of anti-TIM-3 mAb.

METHODS

mRNA levels of TIM-3 and the transcription factor retinoic acid-related orphan receptor γt (RORγt) were determined by RT-PCR and were expressed relative to β-actin mRNA (housekeeping gene). Serum IFN-γ and IL-17 levels were determined by ELISA.

RESULTS

Compared to controls, relative TIM-3 mRNA levels were lower in both stimulated and unstimulated PBMCs from GBS patients. Unstimulated GBS CD4(+) T cells and GBS CD4+ T cells stimulated with anti-CD3 and CD28 mAbs had higher relative RORγt mRNA expression compared to controls. GBS CD4(+) T cells secreted significantly more IFN-γ and IL-17 in the presence of anti-TIM-3 mAb. GBS patients had (1) higher numbers of Th17, but not Th1 or Th2 cells in peripheral blood and (2) higher serum concentrations of IFN-γ and IL-17 compared to controls.

CONCLUSION

TIM-3 may inhibit Th17 cell activation, thereby modulating their cytokine secretion patterns. Th17 cell differentiation, IL-17 levels, and TIM-3 regulation may be involved in the pathogenesis of GBS.

Allograft rejection is restrained by short-lived TIM-3+PD-1+Foxp3+ Tregs

Tregs play a pivotal role in inducing and maintaining donor-specific transplant tolerance. The T cell immunoglobulin and mucin domain-3 protein (TIM-3) is expressed on many fully activated effector T cells. Along with program death 1 (PD-1), TIM-3 is used as a marker for exhausted effector T cells, and interaction with its ligand, galectin-9, leads to selective death of TIM-3+ cells. We report herein the presence of a galectin-9-sensitive CD4+FoxP3+TIM-3+ population of T cells, which arose from CD4+FoxP3+TIM-3- proliferating T cells in vitro and in vivo and were often PD-1+. These cells became very prominent among graft-infiltrating Tregs during allograft response. The frequency and number of TIM-3+ Tregs peaked at the time of graft rejection and declined thereafter. Moreover, these cells also arise in a tolerance-promoting donor-specific transfusion model, representing a pool of proliferating, donor-specific Tregs. Compared with TIM-3- Tregs, TIM-3+ Tregs, which are often PD-1+ as well, exhibited higher in vitro effector function and more robust expression of CD25, CD39, CD73, CTLA-4, IL-10, and TGF-β but not galectin-9. However, these TIM-3+ Tregs did not flourish when passively transferred to newly transplanted hosts. These data suggest that a heretofore unrecognized graft-infiltrating, short-lived subset of Tregs can restrain rejection.

Contrasting acute graft-versus-host disease effects of Tim-3/galectin-9 pathway blockade dependent upon the presence of donor regulatory T cells

T-cell immunoglobulin mucin-3 (Tim-3) is expressed on pathogenic T cells, and its ligand galectin-9 (gal-9) is up-regulated in inflamed tissues. When Tim-3(+) T cells encounter high gal-9 levels, they are deleted. Tim-3 is up-regulated on activated T cells during GVHD. Inhibition of Tim-3/gal-9 binding by infusion of a Tim-3-Ig fusion protein or Tim-3(-/-) donor T cells increased T-cell proliferation and GVHD lethality. When the Tim-3/gal-9 pathway engagement was augmented using gal-9 transgenic recipients, GVHD lethality was slowed. Together, these data indicate a potential for modulating this pathway to reduce disease by increasing Tim-3 or gal-9 engagement. Paradoxically, when Tim-3/gal-9 was inhibited in the absence of donor T-regulatory cells (Tregs), GVHD was inhibited. GVHD reduction was associated with decreased colonic inflammatory cytokines as well as epithelial barrier destruction. CD25-depleted Tim-3(-/-) donor T cells underwent increased activation-induced cell death because of increased IFN-γ production. To our knowledge, these studies are the first to show that although the absence of Tim-3/gal-9 pathway interactions augments systemic GVHD, concurrent donor Treg depletion paradoxically and surprisingly inhibits GVHD. Thus, although donor Tregs typically inhibit GVHD, under some conditions, such Tregs actually may contribute to GVHD by reducing activation-induced T-cell death.

Ectopic expression of TIM-3 in lung cancers: a potential independent prognostic factor for patients with NSCLC

T-cell immunoglobulin- and mucin domain-3-containing molecule 3 (TIM-3) is a membrane protein expressed in various kinds of immune cells and plays a pivotal role in immune regulation. Recently, TIM-3 was reported to be expressed aberrantly in melanoma cells, contributing to the low adhesion ability of tumor cells and promoting the survival of melanoma cells. We investigated TIM-3 expression in non-small cell lung cancers (NSCLCs), and further analyzed whether the aberrant expression of TIM-3 is related to the prognosis for patients with lung cancer. Tumor tissue samples from 30 patients with NSCLC were involved. Results of immunohistochemical analysis showed that TIM-3 stained positive on tumor cells in 86.7% (26/30) patients with primary NSCLC. The TIM-3 expression in NSCLC tumor cells was correlated with histologic type and pathologic T classification of the disease (P < .05). More importantly, patients with TIM-3-positive tumor cells had a significantly shorter survival time than those with TIM-3-negative tumors. Multivariate analysis demonstrated the significant role of TIM-3 expression in tumor cells as an independent prognostic factor for patients with NSCLC (relative risk, 4.481; 95% confidence interval, 1.790-11.22; P = .0005). Our results suggest that the ectopic expression of TIM-3 in tumor cells may be a potential, independent prognostic factor for patients with NSCLC.

PD-1 and its ligand PD-L1 are progressively up-regulated on CD4 and CD8 T-cells in HIV-2 infection irrespective of the presence of viremia

OBJECTIVE

Hyper-immune activation is a main determinant of HIV disease progression, potentially counter-acted by T-cell inhibitory pathways. Here we investigated, for the first time, inhibitory molecules in HIV-2 infection, a naturally occurring attenuated form of HIV disease, associated with reduced viremia and very slow rates of CD4 T-cell decline.

DESIGN

Programmed death (PD)-1/PD-L1, an important pathway in limiting immunopathology, and its possible relationship with T-cell immunoglobulin and mucin-domain containing molecule-3 (TIM-3), a recently identified inhibitory molecule, were studied in untreated HIV-2 and HIV-1 cohorts, matched for degree of CD4 T-cell depletion, and noninfected individuals.

METHODS

Flow cytometric analysis of T-cell expression of PD-1, PD-L1 and TIM-3, combined with markers of cell differentiation, activation, cycling and survival. Statistical analysis was performed using ANOVA, Mann-Whitney/Wilcoxon tests, Spearman's correlations, multiple linear regressions and canonical correlation analysis.

RESULTS

T-cell expression of PD-1 and PD-L1 was tightly associated and directly correlated with CD4 T-cell depletion and immune activation in HIV-2 infection. No such correlation was found for PD-L1 expression in HIV-1-positive patients. Central memory and intermediate memory cells, rather than terminally differentiated T-cells, expressed the highest levels of both PD-1 and PD-L1 molecules. Conversely, TIM-3 expression was independent of T-cell differentiation and dissociated from cell cycling, suggesting distinct induction mechanisms. Importantly, in contrast with HIV-1, no significant increases in TIM-3 expression were found in the HIV-2 cohort.

CONCLUSIONS

Our data suggest that PD-1/PD-L1 molecules, rather than markers of T-cell exhaustion, may act as modulators of T-cell immune activation, contributing to the slower course of HIV-2 infection. These data have implications for the design of antiretroviral therapy-complementary immune-based strategies.

Increased bovine Tim-3 and its ligand expressions during bovine leukemia virus infection

The immunoinhibitory receptor T cell immunoglobulin domain and mucin domain-3 (Tim-3) and its ligand, galectin-9 (Gal-9), are involved in the immune evasion mechanisms for several pathogens causing chronic infections. However, there is no report concerning the role of Tim-3 in diseases of domestic animals. In this study, cDNA encoding for bovine Tim-3 and Gal-9 were cloned and sequenced, and their expression and role in immune reactivation were analyzed in bovine leukemia virus (BLV)-infected cattle. Predicted amino acid sequences of Tim-3 and Gal-9 shared high homologies with human and mouse homologues. Functional domains, including tyrosine kinase phosphorylation motif in the intracellular domain of Tim-3 were highly conserved among cattle and other species. Quantitative real-time PCR analysis showed that bovine Tim-3 mRNA is mainly expressed in T cells such as CD4⁺ and CD8⁺ cells, while Gal-9 mRNA is mainly expressed in monocyte and T cells. Tim-3 mRNA expression in CD4⁺ and CD8⁺ cells was upregulated during disease progression of BLV infection. Interestingly, expression levels for Tim-3 and Gal-9 correlated positively with viral load in infected cattle. Furthermore, Tim-3 expression level closely correlated with up-regulation of IL-10 in infected cattle. The expression of IFN-γ and IL-2 mRNA was upregulated when PBMC from BLV-infected cattle were cultured with Cos-7 cells expressing Tim-3 to inhibit the Tim-3/Gal-9 pathway. Moreover, combined blockade of the Tim-3/Gal-9 and PD-1/PD-L1 pathways significantly promoted IFN-γ mRNA expression compared with blockade of the PD-1/PD-L1 pathway alone. These results suggest that Tim-3 is involved in the suppression of T cell function during BLV infection.

Contact-dependent interference with invariant NKT cell activation by herpes simplex virus-infected cells

Invariant CD1d-restricted NKT (iNKT) cells play important roles in generating protective immune responses against infections. In this study, we have investigated the role of human iNKT cells in HSV-1 infection and their interaction with epidermal keratinocytes. These cells express CD1d and are the primary target of the virus. Keratinocytes loaded with α-galactosyl ceramide (α-GalCer) could stimulate IFN-γ production and CD25 upregulation by iNKT cells. However, both α-GalCer-dependent and cytokine-dependent activation of iNKT cells was impaired after coculture with HSV-1-infected cells. Notably, CD1d downregulation was not observed on infected keratinocytes, which were also found to inhibit TCR-independent iNKT cell activation. Further examination of the cytokine profile of iNKT-keratinocyte cocultures showed inhibition of IFN-γ, IL-5, IL-10, IL-13, and IL-17 secretion but upregulation of IL-4 and TNF-α after the infection. Moreover, cell-to-cell contact between infected keratinocytes and iNKT cells was required for the inhibition of activation, as the cell-free supernatants containing virus did not affect activation. Productive infection of iNKT cells was however not required for the inhibitory effect. After coculture with infected cells, iNKT cells were no longer responsive to further stimulation with α-GalCer-loaded CD1d-expressing cells. We found that exposure to HSV-1-infected cells resulted in impaired TCR signaling downstream of ZAP70. Additionally, infected cells upregulated the expression of the negative T cell regulator, galectin-9; however, blocking experiments indicated that the impairment of iNKT cell responses was independent of galectin-9. Thus, interference with activation of human iNKT cells by HSV-1 may represent a novel immunoevasive strategy used by the virus to avoid immune clearance.

The role of coinhibitory signaling pathways in transplantation and tolerance

Negative costimulatory molecules, acting through so-called inhibitory pathways, play a crucial role in the control of T cell responses. This negative “second signal” opposes T cell receptor activation and leads to downregulation of T cell proliferation and promotes antigen specific tolerance. Much interest has focused upon these pathways in recent years as a method to control detrimental alloresponses and promote allograft tolerance. However, recent experimental data highlights the complexity of negative costimulatory pathways in alloimmunity. Varying effects are observed from molecules expressed on donor and recipient tissues and also depending upon the activation status of immune cells involved. There appears to be significant overlap and redundancy within these systems, rendering this a challenging area to understand and exploit therapeutically. In this article, we will review the literature at the current time regarding the major negative costimulation pathways including CTLA-4:B7, PD-1:PD-L1/PD-L2 and PD-L1:B7-1, B7-H3, B7-H4, HVEM:BTLA/CD160, and TIM-3:Galectin-9. We aim to outline the role of these pathways in alloimmunity and discuss their potential applications for tolerance induction in transplantation.

Antigen-independent induction of Tim-3 expression on human T cells by the common γ-chain cytokines IL-2, IL-7, IL-15, and IL-21 is associated with proliferation and is dependent on the phosphoinositide 3-kinase pathway

T cell Ig mucin domain-containing molecule 3 (Tim-3) is a glycoprotein found on the surface of a subset of CD8(+) and Th1 CD4(+) T cells. Elevated expression of Tim-3 on virus-specific T cells during chronic viral infections, such as HIV-1, hepatitis B virus, and hepatitis C virus, positively correlates with viral load. Tim-3(+) cytotoxic T cells are dysfunctional and are unable to secrete effector cytokines, such as IFN-γ and TNF-α. In this study, we examined potential inducers of Tim-3 on primary human T cells. Direct HIV-1 infection of CD4(+) T cells, or LPS, found to be elevated in HIV-1 infection, did not induce Tim-3 on T cells. Tim-3 was induced by the common γ-chain (γc) cytokines IL-2, IL-7, IL-15, and IL-21 but not IL-4, in an Ag-independent manner and was upregulated on primary T cells in response to TCR/CD28 costimulation, as well as γc cytokine stimulation with successive divisions. γc cytokine-induced Tim-3 was found on naive, effector, and memory subsets of T cells. Tim-3(+) primary T cells were more prone to apoptosis, particularly upon treatment with galectin-9, a Tim-3 ligand, after cytokine withdrawal. The upregulation of Tim-3 could be blocked by the addition of a PI3K inhibitor, LY 294002. Thus, Tim-3 can be induced via TCR/CD28 costimulation and/or γc cytokines, likely through the PI3K pathway.

Tim-3 marks human natural killer cell maturation and suppresses cell-mediated cytotoxicity

Natural killer (NK) cells are innate lymphocytes that play an important role against viral infections and cancer. This effect is achieved through a complex mosaic of inhibitory and activating receptors expressed by NK cells that ultimately determine the magnitude of the NK-cell response. The T-cell immunoglobulin- and mucin domain-containing (Tim)-3 receptor was initially identified as a T-helper 1-specific type I membrane protein involved in regulating T-cell responses. Human NK cells transcribe the highest amounts of Tim-3 among lymphocytes. Tim-3 protein is expressed on essentially all mature CD56(dim)CD16(+) NK cells and is expressed heterogeneously in the immature CD56(bright)CD16(-) NK-cell subset in blood from healthy adults and in cord blood. Tim-3 expression was induced on CD56(bright)CD16(-) NK cells after stimulation with IL-15 or IL-12 and IL-18 in vitro, suggesting that Tim-3 is a maturation marker on NK cells. Whereas Tim-3 has been used to identify dysfunctional T cells, NK cells expressing high amounts of Tim-3 are fully responsive with respect to cytokine production and cytotoxicity. However, when Tim-3 was cross-linked with antibodies it suppressed NK cell-mediated cytotoxicity. These findings suggest that NK-cell responses may be negatively regulated when NK cells encounter target cells expressing cognate ligands of Tim-3.

TIM-3 expression characterizes regulatory T cells in tumor tissues and is associated with lung cancer progression

Background

T cell immunoglobulin-3 (TIM-3) has been established as a negative regulatory molecule and plays a critical role in immune tolerance. TIM-3 is upregulated in exhausted CD8⁺ T cells in both chronic infection and tumor. However, the nature of TIM-3⁺CD4⁺ T cells in the tumor microenvironment is unclear. This study is to characterize TIM-3 expressing lymphocytes within human lung cancer tissues and establish clinical significance of TIM-3 expression in lung cancer progression.

Methodology

A total of 51 human lung cancer tissue specimens were obtained from pathologically confirmed and newly diagnosed non-small cell lung cancer (NSCLC) patients. Leukocytes from tumor tissues, distal normal lung tissues, and peripheral blood mononuclear cells (PBMC) were analyzed for TIM-3 surface expression by flow cytometry. TIM-3 expression on tumor-infiltrating lymphocytes (TILs) was correlated with clinicopathological parameters.

Conclusions

TIM-3 is highly upregulated on both CD4⁺ and CD8⁺ TILs from human lung cancer tissues but negligibly expressed on T cells from patients' peripheral blood. Frequencies of IFN-γ⁺ cells were reduced in TIM-3⁺CD8⁺ TILs compared to TIM-3⁻CD8⁺ TILs. However, the level of TIM-3 expression on CD8⁺ TILs failed to associate with any clinical pathological parameter. Interestingly, we found that approximately 70% of TIM-3⁺CD4⁺ TILs expressed FOXP3 and about 60% of FOXP3⁺ TILs were TIM-3⁺. Importantly, TIM-3 expression on CD4⁺ T cells correlated with poor clinicopathological parameters of NSCLC such as nodal metastasis and advanced cancer stages. Our study reveals a new role of TIM-3 as an important immune regulator in the tumor microenvironment via its predominant expression in regulatory T cells.

Down-regulation of interleukin-2 production by CD4(+) T cells expressing TIM-3 through suppression of NFAT dephosphorylation and AP-1 transcription

TIM-3 is expressed by TH1 cells and negatively regulates cytokine production by these cells. The aim of the present study was to explore the mechanisms by which IL-2 production is suppressed in TIM-3-expressing T cells. First, the activity of two transcription factors that bind to the IL-2 promoter was examined in Jurkat T cells expressing TIM-3. Both AP-1 and NFAT activity were reduced in TIM-3-expressing cells stimulated with a phorbol ester and a calcium ionophore. At the same time, expression of the AP-1 components, c-Fos and c-Jun, was induced to a lesser extent in stimulated human primary CD4(+) T cells expressing high levels of TIM-3 than in those expressing low levels of TIM-3. Furthermore, TIM-3-expression inhibited the stimulation-induced dephosphorylation and nuclear translocation of NFAT in Jurkat T cells and primary CD4(+) T cells. Finally, the cytoplasmic tail of TIM-3 was required for the suppression of IL-2 production and for AP-1 and NFAT activation. Taken together, these results suggest that IL-2 production by T cells may be downregulated by TIM-3-mediated signals, leading to suppression of NFAT dephosphorylation and AP-1 transcription.

Galectin-9 ameliorates herpes simplex virus-induced inflammation through apoptosis

Galectin-9 (Gal-9) has been identified as a Tim-3 ligand (L). The Tim-3-Tim-3L interaction serves as a specific down-regulator of the Th1 immune response. It has been reported that Tim-3 expression is higher in patients with inflammatory disorders such as rheumatoid arthritis compared to controls. In a herpes simplex virus-induced Behcet's disease (BD) mouse model, Tim-3 was expressed in a similarly high level. The expression of Gal-9 in macrophages from BD-like mice was lower than in asymptomatic BD normal mice; therefore, we injected 100 μg of Gal-9 into BD-like mice five times at 3 day intervals and subsequently observed changes in symptoms over 15 days. Gal-9 improved the symptoms of inflammation, decreased the severity score, and increased regulatory T cell expression in treated mice. Moreover, pro-inflammatory cytokine levels were lower in the Gal-9-treated group compared to the control group. Therefore, in the present study, Tim-3-Tim-3L interaction was found to influence inflammatory symptoms in BD-like mice.

The emerging role of the TIM molecules in transplantation

Since their discovery in 2001, the T-cell immunoglobulin mucin (TIM) family members have been shown to play important roles in the regulation of immune responses. The TIM family comprises of eight genes in the mouse, three of which are conserved in humans (TIM-1, TIM-3 and TIM-4). Initially, TIM-1 and TIM-3 were thought to be expressed solely on T cells. However, emerging data suggest a much broader expression pattern where their presence on APCs confers differing functions, including the ability to mediate phagocytosis. In contrast, TIM-4 is exclusively expressed on APCs. Together, the TIM molecules provide a functional repertoire for determining the fate of T-cell activation and differentiation. To date, much of the knowledge about the TIM family members has been garnered from the models of asthma, allergy and autoimmunity. More recently, data from experimental models of transplantation demonstrate that TIM family members also have a key role in alloimmunity. This review will serve to highlight the emerging data regarding this unique family of molecules and to identify their potential in transplantation tolerance.

Identification of CCL1 as a Gene Differentially Expressed in CD4 T Cells Expressing TIM-3

BACKGROUND

T cell immunoglobulin mucin containing molecule (TIM)-3 is expressed in differentiated Th1 cells and is involved in the suppression of the cytokine production by these cells. However, the regulation of the expression of other T cell genes by TIM-3 is unclear. Herein, we attempted to identify differentially expressed genes in cells abundantly expressing TIM-3 compared to cells with low expression of TIM-3.

METHODS

TIM-3 overexpressing cell clones were established by transfection of Jurkat T cells with TIM-3 expression vector. For screening of differentially expressed genes, gene fishing technology based on reverse transcription-polymerase chain reaction (RT-PCR) using an annealing control primer system was used. The selected candidate genes were validated by semi quantitative and real-time RT-PCR.

RESULTS

The transcription of TIMP-1, IFITM1, PAR3 and CCL1 was different between TIM-3 overexpressing cells and control cells. However, only CCL1 transcription was significantly different in cells transiently transfected with TIM3 expression vector compared with control cells. CCL1 transcription was increased in primary human CD4(+) T cells abundantly expressing TIM-3 but not in cells with low expression of TIM-3.

CONCLUSION

CCL1 was identified as a differentially transcribed gene in TIM-3-expressing CD4(+) T cells.

Immune suppression in tumors as a surmountable obstacle to clinical efficacy of cancer vaccines

Human tumors are usually not spontaneously eliminated by the immune system and therapeutic vaccination of cancer patients with defined antigens is followed by tumor regressions only in a small minority of the patients. The poor vaccination effectiveness could be explained by an immunosuppressive tumor microenvironment. Because T cells that infiltrate tumor metastases have an impaired ability to lyse target cells or to secrete cytokine, many researchers are trying to decipher the underlying immunosuppressive mechanisms. We will review these here, in particular those considered as potential therapeutic targets. A special attention will be given to galectins, a family of carbohydrate binding proteins. These lectins have often been implicated in inflammation and cancer and may be useful targets for the development of new anti-cancer therapies.

Dysregulated upregulation of T-cell immunoglobulin and mucin domain-3 on mucosal T helper 1 cells in patients with Crohn's disease

OBJECTIVE

T-cell immunoglobulin and mucin domain-3 (TIM-3) is a unique cell surface molecule expressed on T helper 1 (Th1) cells. Engagement of TIM-3 by ligand galectin-9 leads to dampened Th1 immunity. We investigated TIM-3 and galectin-9 expression in inflammatory bowel disease (IBD) patients and in healthy controls, and evaluated the immune role of the TIM-3 pathway in Crohn's disease (CD) pathogenesis.

MATERIAL AND METHODS

We used flow cytometry to investigate TIM-3 expression on mononuclear cells isolated from the intestinal mucosa and peripheral blood cells of patients with IBD and healthy controls. We also evaluated galectin-9 mRNA expression on endoscopically obtained intestinal mucosal cells.

RESULTS

TIM-3 was constitutively expressed on Th cells isolated from the intestinal mucosa of IBD patients and healthy controls. While we observed low TIM-3 expression on Th cells isolated from peripheral blood mononuclear cells (PBMCs), high TIM-3 expression was induced by Th1 stimulation. The level of TIM-3 expression on Th cells isolated from intestinal mucosa and stimulated PBMCs was significantly lower in CD patients than in healthy controls.

CONCLUSIONS

Our data show that TIM-3 upregulation on Th1 cells is dysregulated in patients with CD. Low TIM-3 expression on Th1 cells may provide a clue toward resolution of the inflammation associated with chronic inflammatory disease. These findings should contribute to develop understanding of CD pathogenesis.

Activation of mitogen activated protein kinase-Erk kinase (MEK) increases T cell immunoglobulin mucin domain-3 (TIM-3) transcription in human T lymphocytes and a human mast cell line

The immune regulatory molecule T cell immunoglobulin mucin domain (TIM-3) is expressed in activated T cells and in mast cells treated with transforming growth factor (TGF)-β, but underlying mechanisms for induction of TIM-3 transcription have not been well-explored. We studied the role of mitogen-activated protein kinase (MAPK) in TIM-3 transcription on the basis of the involvement of MAPK in T cell activation and TGF-β signaling. Inhibitors of MAPK-Erk kinase (MEK) as well as p38 suppressed TIM-3 transcription in phorbol myristic acid (PMA)-stimulated T cells, but inhibitors of c-Jun NH2-terminal kinase (JNK) did not. MEK over-expression enhanced TIM-3 transcription in PMA-stimulated T cells. Furthermore, -1.5kb TIM-3 promoter was activated by PMA stimulation and repressed by MEK inhibitors in Jurkat T cells. Similarly, MEK activation enhanced TIM-3 transcription in TGF-β-stimulated HMC-1 human mast cells, although MEK seemed not directly activated by TGF-β. Concordantly, -1.5kb TIM-3 promoter activity was reduced by MEK inhibitors, but was not responsive to TGF-β stimulation in HMC-1 cells. These results suggest the regulatory role of MEK in TIM-3 transcription by human CD4+ T cells and mast cells.

Revisiting immune exhaustion during HIV infection

Chronic immune activation is a hallmark of HIV infection, yet the underlying triggers of immune activation remain unclear. Persistent antigenic stimulation during HIV infection may also lead to immune exhaustion, a phenomenon in which effector T cells become dysfunctional and lose effector functions and proliferative capacity. Several markers of immune exhaustion, such as PD-1, LAG-3, Tim-3, and CTLA-4, which are also negative regulators of immune activation, are preferentially upregulated on T cells during HIV infection. It is not yet clear whether accumulation of T cells expressing activation inhibitory molecules is a consequence of general immune or chronic HIV-specific immune activation. Importantly, however, in vitro blockade of PD-1 and Tim-3 restores HIV-specific T-cell responses, indicating potential for immunotherapies. In this review we discuss the evolution of our understanding of immune exhaustion during HIV infection, highlighting novel markers and potential therapeutic targets.

Tim-3 negatively regulates IL-12 expression by monocytes in HCV infection

T cell immunoglobulin and mucin domain-containing protein 3 (Tim-3) is a newly identified negative immunomodulator that is up-regulated on dysfunctional T cells during viral infections. The expression and function of Tim-3 on human innate immune responses during HCV infection, however, remains poorly characterized. In this study, we report that Tim-3 is constitutively expressed on human resting CD14⁺ monocyte/macrophages (M/M_Ø) and functions as a cap to block IL-12, a key pro-inflammatory cytokine linking innate and adaptive immune responses. Tim-3 expression is significantly reduced and IL-12 expression increased upon stimulation with Toll-like receptor 4 (TLR4) ligand - lipopolysaccharide (LPS) and TLR7/8 ligand - R848. Notably, Tim-3 is over-expressed on un-stimulated as well as TLR-stimulated M/M_Ø, which is inversely associated with the diminished IL-12 expression in chronically HCV-infected individuals when compared to healthy subjects. Up-regulation of Tim-3 and inhibition of IL-12 are also observed in M/M_Ø incubated with HCV-expressing hepatocytes, as well as in primary M/M_Ø or monocytic THP-1 cells incubated with HCV core protein, an effect that mimics the function of complement C1q and is reversible by blocking the HCV core/gC1qR interaction. Importantly, blockade of Tim-3 signaling significantly rescues HCV-mediated inhibition of IL-12, which is primarily expressed by Tim-3 negative M/M_Ø. Tim-3 blockade reduces HCV core-mediated expression of the negative immunoregulators PD-1 and SOCS-1 and increases STAT-1 phosphorylation. Conversely, blocking PD-1 or silencing SOCS-1 gene expression also decreases Tim-3 expression and enhances IL-12 secretion and STAT-1 phosphorylation. These findings suggest that Tim-3 plays a crucial role in negative regulation of innate immune responses, through crosstalk with PD-1 and SOCS-1 and limiting STAT-1 phosphorylation, and may be a novel target for immunotherapy to HCV infection.

T lymphocyte surface expression of exhaustion markers as biomarkers of the efficacy of chemotherapy for tuberculosis

Predictive biomarkers illustrating the effectiveness of chemotherapeutic regimens for tuberculosis still remain elusive. To date, most are predicated on assays using sputum or serum; as a result, if not predictive, treatment failure in patients may not be evident for some time. We report here the results of a simple screening study in which T cell surface markers were examined in mice infected with Mycobacterium tuberculosis and then treated with drugs. These studies identified certain markers, the exhaustion markers PD-1 and TIM-3, as well as the marker KLRG-1, particularly on CD8 T cells, that changed in concert with reduction of the bacterial load in the lungs. While there is no guarantee these changes would also be seen on T cells in the blood, this approach should be further investigated.

Tim-4 inhibition of T-cell activation and T helper type 17 differentiation requires both the immunoglobulin V and mucin domains and occurs via the mitogen-activated protein kinase pathway

Emerging experimental data suggest an important role for the T-cell immunoglobulin mucin 1 (Tim-1):Tim-4 pathway in autoimmune and alloimmune responses in vivo. Using a Tim-4 ectodomain human IgG Fc fusion protein we studied the role of Tim-4 in T-cell activation, signalling and differentiation responses in vitro. We demonstrate that Tim-4Fc can inhibit naive and pre-activated T-cell activation, proliferation and cytokine secretion via a Tim-1-independent pathway. Tim-4 contains immunoglobulin variable (IgV) and mucin domains; to identify which domain accounts for the inhibitory effect novel Tim-4 fusion proteins containing either the IgV or mucin domain were generated. We demonstrate that both IgV and mucin domains are required for the inhibitory effects and that they are mediated at least in part by inhibition of extracellular signal-regulated kinase pathway activity. Given the emerging interest in the role of the Tim family in T helper type 17 (Th17) cells, which play an important role in autoimmune disease and transplantation tolerance, our data show that Tim-4Fc can prevent polarization of CD4(+) T cells to the Th17 phenotype. Collectively, our results highlight an inhibitory role for Tim-4Fc in vitro, which we propose is mediated by a receptor other than Tim-1. In addition, this study provides new insights into the role of Tim-4Fc in regulating Th17 immune responses and may open a new avenue for autoimmune therapy.