Janus-like role of regulatory iNKT cells in autoimmune disease and tumour immunity

Prevention of type 1 diabetes by invariant NKT cells is independent of peripheral CD1d expression

Invariant NKT (iNKT) cells can prevent diabetes by inhibiting the differentiation of anti-islet T cells. We recently showed that neither iNKT cell protection against diabetes nor iNKT cell inhibition of T cell differentiation in vitro requires cytokines such as IL-4, IL-10, IL-13, and TGF-beta. In contrast, cell-cell contacts were required for iNKT cell inhibition of T cell differentiation in vitro. The present study was designed to determine whether the CD1d molecule is involved in the inhibitory function of iNKT cells. Experiments were performed in vitro and in vivo, using cells lacking CD1d expression. The in vivo experiments used CD1d-deficient mice that were either reconstituted with iNKT cells or expressed a CD1d transgene exclusively in the thymus. Both mouse models had functional iNKT cells in the periphery, even though CD1d was not expressed in peripheral tissues. Surprisingly, both in vitro inhibition of T cell differentiation by iNKT cells and mouse protection against diabetes by iNKT cells were CD1d-independent. These results reveal that iNKT cells can exert critical immunoregulatory effects in the absence of CD1d recognition and that different molecular interactions are involved in iNKT cell functions.

The evaluation of psoriasis therapy with biologics leads to a revision of the current view of the pathogenesis of this disorder

Psoriasis is a common chronic, recurring skin disease that is characterised by typical macroscopic and microscopic skin alterations. It is widely accepted that the immune system plays an important role in the pathogenesis of this disorder. Since the early 1990s, the dominant role of a subpopulation of T cells, so-called T1 cells, and their prominent cytokine IFN-gamma has been assumed in the pathogenesis of psoriasis. Surprisingly, the comparison of the therapeutic success of treatments with recombinant proteins directed against defined immunological structures shows that those that directly affect T cells (alefacept, efalizumab, Hu-max-CD4, OKTcdr4a) were clearly less effective than those targeting TNF-alpha (etanercept, adalimumab, infliximab). For this reason, the authors critically re-evaluated the view of psoriasis pathogenesis and postulate that in the majority of patients the T1 cells do not play a dominant role in the clinical, visible stage of this disease.

Invariant natural killer T (iNKT) cells in asthma: a novel insight into the pathogenesis of asthma and the therapeutic implication of glycolipid ligands for allergic diseases

Allergic bronchial asthma is a complex inflammatory diseases originated from dysregulated immune responses in the respiratory mucosa. The inflammatory state in asthmatic lung is characterized by massive infiltration with eosinophils, lymphocytes, and mast cells in the airway mucosa leading to airway hyperseisitivity, goblet cell hyperplasia and mucus overproduction. The inflammatory process is thought to be the result of intensive T helper (Th) 2-biased immune response. Over the past several years, there has been enormous progress in understanding the mechanisms for development of Th2-biased responses after inhaled exposure to allergens and the characteristics of CD4+ T cells prominently involved in this process. Recently, a new population of T cells, invariant natural killer T (iNKT) cells has been shown to play an important role in the pathogenesis of mouse model of allergic airway inflammation. iNKT cells are one of the most potent immune modulators through a massive production of a various cytokines including IL-4 and IFN-gamma upon activation, and are involved in a variety of immunoregulations including infection, autoimmunity, and tumor surveillance. The potent pathogenic role of iNKT cells in the development of bronchial asthma is due to their ability to produce predominant Th2 cytokines in a given condition. The involvement of iNKT cells in the pathogenesis of asthma might have been underestimated in the past studies demonstrating the involvement of CD4+ T cells in asthma because of the difficulty in the detection of iNKT cells. Meanwhile, growing evidences have demonstrated that iNKT cells could be a promising target for immune-based therapies for autoimmune diseases, tumor, and infection due to the invariance of their TCR usage, the restriction to the evolutionally-conserved non-polymorphic antigen-presenting molecule CD1d, and their outstanding ability to produce both Th1- and Th2-cytokines. In this review, we will overview current understanding of the pathophysiological roles of iNKT cells in asthma. We would also discuss on possible therapeutic approaches to bronchial asthma employing glycolipid ligands for iNKT cells.

Innate immune defenses in HIV-1 infection: prospects for a novel immune therapy

HIV-1 infection leads to a severe decrease of CD4(+) T lymphocytes, dysregulation of several leukocyte subpopulations and generalized immune activation, with the subsequent development of opportunistic infections and malignancies. Administration of highly active antiretroviral therapy (HAART) has been successful in reducing HIV-1 plasma viremia; however, the ability of HAART to restore immunocompetence appears incomplete, particularly in patients with chronic and advanced disease. Several components of the innate immune system have direct anti-HIV-1 effects, and studies to analyze the benefits of enhancing the function of the innate response during HIV-1 infection are increasing. Development of any complementary therapeutic approaches to HIV-1 infection, particularly those able to compensate for the limitations of HAART, and enhance the anti-HIV-1 innate immune activity would be of interest. The stimulation of innate immune responses using Toll-like receptor agonists, such as monophosphoryl lipid A and oligodeoxynucleotides with CpG motifs, are currently being investigated and their benefit in HIV-1-infected patients are under evaluation.

Frontiers of immunological tolerance

Herein, we succinctly review mechanisms underlying self-tolerance and the roles of dendritic leukocytes (DCs) in T-cell tolerance to self and foreign antigens. We also consider the properties of naturally arising and other populations of regulatory T cells (Treg), together with growing evidence that interplay between DCs and Treg cells can sustain antigen-specific tolerance. B-cell tolerance and the role of hematopoietic cell chimerism in the induction and maintenance of tolerance are also discussed, as is the impact of cosignaling pathway manipulation on tolerance induction. This overview also surveys prospects for technological advances in the monitoring and prediction of tolerance and the application of genomic and proteomic analysis. In addition, we consider potential novel therapeutic targets for promotion of tolerance induction.

Improving antitumor immune responses by circumventing immunoregulatory cells and mechanisms

Although numerous immunotherapeutic strategies have been studied in patients with cancer, consistent induction of clinical responses remains a formidable challenge. Cancer vaccines are often successful at generating elevated numbers of tumor-specific T lymphocytes in peripheral blood, however, despite this, tumors usually continue to grow unabated. Recent evidence suggests that endogenous regulatory cells, known to play a major role in the induction of immune tolerance to self and prevention of autoimmunity, as well as suppressive myeloid cells invoked in the tumor-bearing state, may be largely responsible for preventing effective antitumor immune responses. This review will focus on the major regulatory cell subtypes, including CD4(+)CD25(+) T-regulatory cells, type 1 regulatory T cells, natural killer T cells, and immature myeloid cells. Studies in humans and in animal models have shown a role for all of these cells in tumor progression, although the mechanisms by which they act to suppress immunity remain largely undefined. Elucidation of the dominant molecular mechanisms mediating immune suppression in vivo will allow more precise targeting of the relevant regulatory cell populations, as well as the development of novel strategies and clinical reagents that will directly block molecules that induce the suppression of antitumor immunity.

Pivotal advance: alpha-galactosylceramide induces protection against lipopolysaccharide-induced shock

alpha-galactosylceramide, a natural killer T cell ligand, and its synthetic homolog, KRN7000, consistently influence IFN-gamma and TNF-alpha release, both mediators of LPS-induced shock. To modify the course of endotoxin shock, we injected KRN7000 at different time points of experimental systemic Shwartzman reaction. Mice treated with KRN7000 survived when it was injected within 2 h before and after LPS challenge. Mice survival was associated with low levels of T helper 1 (Th1) cytokines, such as IFN-gamma and TNF-alpha. By contrast, protection from endotoxin shock was associated with an increase of T helper 2 (Th2) cytokines, like IL-4 and IL-10. A role of Th2 cytokines in counteracting LPS-induced shock was supported by experiments in which the protection against Shwartzman reaction by KRN7000 was abrogated by in vivo coadministration of anti-Th2 cytokines antibodies. In addition, cytofluorimetric analysis showed that surviving animals have higher percentages of NKT-IL-10-positive cells and lower percentages of NKT-IFN-gamma and macrophages/TNF-alpha-stained cells than nonprotected mice. Taken together, our data demonstrate that KRN7000 treatment given at times near LPS challenge is protective for endotoxin shock inhibiting IFN-gamma and TNF-alpha release. Moreover, KRN7000-mediated protection occurs through an increased production of IL-4 and IL-10, which are mainly secreted by NKT cells. Since IFN-gamma release by NKT requires a longer TCR stimulation than that required for Th2 cytokines production, we demonstrate that timing of KRN7000 in vivo exposure affect the pattern of cytokines expression protecting animals by endotoxin shock.

A phase I study of in vitro expanded natural killer T cells in patients with advanced and recurrent non-small cell lung cancer

PURPOSE

Human Valpha24 natural killer T (Valpha24 NKT) cells bearing an invariant Valpha24JalphaQ antigen receptor are activated by a glicolipid ligand alpha-galactosylceramide (alphaGalCer; KRN7000) in a CD1d-dependent manner. The human Valpha24 NKT cells activated with alphaGalCer and interleukin-2 have been shown to produce large amounts of cytokines, such as IFN-gamma, and also exerting a potent killing activity against various tumor cell lines. We did a phase I study with autologous activated Valpha24 NKT cell therapy.

EXPERIMENTAL DESIGN

Patients with advanced or recurrent non-small cell lung cancer received i.v. injections of activated Valpha24 NKT cells (level 1: 1 x 10(7)/m2 and level 2: 5 x 10(7)/m2) to test the safety, feasibility, and clinical response of this therapeutic strategy. Immunomonitoring was also done in all cases.

RESULTS

Six patients were enrolled in this study. No severe adverse events were observed during this study in any patients. After the first and second injection of activated Valpha24 NKT cells, an increased number of peripheral blood Valpha24 NKT cells was observed in two of three cases receiving a level 2 dose of activated Valpha24 NKT cells. The number of IFN-gamma-producing cells in peripheral blood mononuclear cells increased after the administration of activated Valpha24 NKT cells in all three cases receiving the level 2 dose. No patient was found to meet the criteria for either a partial or a complete response.

CONCLUSIONS

The clinical trial with activated Valpha24 NKT cell administration was well tolerated and carried out safely with minor adverse events even in patients with advanced diseases.

Invariant natural killer T cells in the response to bacteria: the advent of specific antigens

Invariant natural killer T (iNKT) cells are a unique subset of T lymphocytes that have been implicated in diverse immune reactions, ranging from self-tolerance and development of autoimmunity to responses to pathogens and tumors. Although some degree of autoreactivity of iNKT cells has been shown, it remained controversial whether the T-cell antigen receptor expressed by these cells could recognize microbial antigens, hampering the investigation of their physiological role during tolerance and immunity. Several recent publications have now defined natural antigens for the majority of iNKT cells in some Proteobacteria and in Borrelia burgdorferi, demonstrating specificity of these cells for microbes in addition to self-reactivity. The characterization of natural antigens from bacteria, and the iNKT cell response to bacteria containing them, are decisive steps toward the clarification of the natural role of iNKT cells in host defense against pathogens, and will likely spur numerous findings in the near future.

Protection from Type 1 Diabetes by Invariant NK T Cells Requires the Activity of CD4+CD25+ Regulatory T Cells

Invariant NK T (iNKT) cells regulate immune responses, express NK cell markers and an invariant TCR, and recognize lipid Ags in a CD1d-restricted manner. Previously, we reported that activation of iNKT cells by alpha-galactosylceramide (alpha-GalCer) protects against type 1 diabetes (T1D) in NOD mice via an IL-4-dependent mechanism. To further investigate how iNKT cells protect from T1D, we analyzed whether iNKT cells require the presence of another subset(s) of regulatory T cells (Treg), such as CD4+ CD25+ Treg, for this protection. We found that CD4+ CD25+ T cells from NOD.CD1d(-/-) mice deficient in iNKT cell function similarly in vitro to CD4+ CD25+ T cells from wild-type NOD mice and suppress the proliferation of NOD T responder cells upon alpha-GalCer stimulation. Cotransfer of NOD diabetogenic T cells with CD4+ CD25+ Tregs from NOD mice pretreated with alpha-GalCer demonstrated that activated iNKT cells do not influence the ability of T(regs) to inhibit the transfer of T1D. In contrast, protection from T1D mediated by transfer of activated iNKT cells requires the activity of CD4+ CD25+ T cells, because splenocytes pretreated with alpha-GalCer and then inactivated by anti-CD25 of CD25+ cells did not protect from T1D. Similarly, mice inactivated of CD4+ CD25+ T cells before alpha-GalCer treatment were also not protected from T1D. Our data suggest that CD4+ CD25+ T cells retain their function during iNKT cell activation, and that the activity of CD4+ CD25+ Tregs is required for iNKT cells to transfer protection from T1D.

Participatory role of natural killer and natural killer T cells in atherosclerosis: lessons learned from in vivo mouse studies

Atherosclerosis is a multifactor, highly complex disease with numerous aetiologies that work synergistically to promote lesion development. One of the emerging components that drive the development of both early- and late-stage atherosclerotic lesions is the participation of both the innate and acquired immune systems. In both humans and animal models of atherosclerosis, the most prominent cells that infiltrate evolving lesions are macrophages and T lymphocytes. The functional loss of either of these cell types reduces the extent of atherosclerosis in mice that were rendered susceptible to the disease by deficiency of either apolipoprotein E or the LDL (low density lipoprotein) receptor. In addition to these major immune cell participants, a number of less prominent leukocyte populations that can modulate the atherogenic process are also involved. This review will focus on the participatory role of two "less prominent" immune components, namely natural killer (NK) cells and natural killer T (NKT) cells. Although this review will highlight the fact that both NK and NKT cells are not sufficient for causing the disease, the roles played by both these cells types are becoming increasingly important in understanding the complexity of this disease process.

Activation of plasmacytoid dendritic cells with TLR9 agonists initiates invariant NKT cell-mediated cross-talk with myeloid dendritic cells

CD1d-restricted invariant NK T (iNKT) cells and dendritic cells (DCs) have been shown to play crucial roles in various types of immune responses, including TLR9-dependent antiviral responses initiated by plasmacytoid DCs (pDCs). However, the mechanism by which this occurs is enigmatic because TLRs are absent in iNKT cells and human pDCs do not express CD1d. To explore this process, pDCs were activated with CpG oligodeoxyribonucleotides, which stimulated the secretion of several cytokines such as type I and TNF-alpha. These cytokines and other soluble factors potently induced the expression of activation markers on iNKT cells, selectively enhanced double-negative iNKT cell survival, but did not induce their expansion or production of cytokines. Notably, pDC-derived factors licensed iNKT cells to respond to myeloid DCs: an important downstream cellular target of iNKT cell effector function and a critical contributor to the initiation of adaptive immune responses. This interaction supports the notion that iNKT cells can mediate cross-talk between DC subsets known to express mutually exclusive TLR and cytokine profiles.

CD38 Is Required for the Peripheral Survival of Immunotolerogenic CD4+Invariant NK T Cells in Nonobese Diabetic Mice

T cell-mediated autoimmune type-1 diabetes (T1D) in NOD mice partly results from this strain's numerical and functional defects in invariant NK T (iNKT) cells. T1D is inhibited in NOD mice treated with the iNKT cell superagonist alpha-galactosylceramide through a process involving enhanced accumulation of immunotolerogenic dendritic cells in pancreatic lymph nodes. Conversely, T1D is accelerated in NOD mice lacking CD38 molecules that play a role in dendritic cell migration to inflamed tissues. Unlike in standard NOD mice, alpha-galactosylceramide pretreatment did not protect the CD38-deficient stock from T1D induced by an adoptively transferred pancreatic beta cell-autoreactive CD8 T cell clone (AI4). We found that in the absence of CD38, ADP-ribosyltransferase 2 preferentially activates apoptotic deletion of peripheral iNKT cells, especially the CD4+ subset. Therefore, this study documents a previously unrecognized role for CD38 in maintaining survival of an iNKT cell subset that preferentially contributes to the maintenance of immunological tolerance.

Natural killer T cells and haemopoiesis

Invariant natural killer T (iNKT) cells are a small but powerful subset of regulatory T cells involved in the modulation of a variety of normal and pathological immune responses. In contrast to conventional or other types of regulatory T cells, they are activated by glycolipid and phospholipid ligands that are presented to them by the non-polymorphic, major histocompatibility complex class I-like molecule CD1d. The in-depth understanding of their function has resulted in successful, iNKT cell-centred experimental therapeutic interventions including prevention of graft-versus-host disease and anti-leukaemia effects. Extending these successes into the clinical arena will require better understanding of their contribution to the pathogenesis of human, including haematological, diseases.

CD4+CD25+ Tregs and NKT cells: regulators regulating regulators

CD4+CD25+ regulatory T cells (Tregs) and natural killer T (NKT) cells are two populations of T lymphocytes that can independently regulate adaptive and innate immune responses. Although most studies have investigated the regulatory properties of these T-cell subsets independently of each other, recent reports have provided evidence for cross-talk between Tregs and NKT cells, and, consequently, the immunoregulatory networks are seen in a new perspective. Activated NKT cells seem to modulate quantitatively and qualitatively Treg function through IL-2-dependent mechanisms, whereas Tregs can suppress the proliferation, cytokine release and cytotoxic activity of NKT cells by cell-contact-dependent mechanisms. Importantly, Tregs and NKT cells share crucial signaling pathways that could be responsible for their concerted responses. The advances in our understanding of the interactions between distinct subsets of regulatory T cells in autoimmunity might unveil new methods for harnessing these cells with immunotherapeutic properties.

Animal models of allergen-induced tolerance in asthma: are T-regulatory-1 cells (Tr-1) the solution for T-helper-2 cells (Th-2) in asthma?

Non-specific anti-inflammatory medication is actually the treatment of choice for controlling the T-helper type 2 (Th-2) cell-driven airway inflammation in asthma. The induction of counterbalancing Th-1 cell clones, long considered a promising approach for immunotherapy, has failed to fulfil its promise because of potentially detrimental side-effects. This is therefore probably not a valid option for the treatment of asthma. With the increasing awareness that active immune mechanisms exist to control inflammatory responses, interest rises to investigate whether these can be exploited to control allergen-induced airway disease. The induction of antigen-specific T cells with suppressive characteristics (regulatory T cells) is therefore a potentially interesting approach. These regulatory T cells mediate tolerance in healthy, non-atopic individuals and have the potential of becoming an effective means of preventing allergen-induced airway inflammation and possibly of suppressing ongoing allergic immune responses. Here we review the available knowledge about allergen-induced suppressive immunity obtained from animal models taking into account the different developmental stages of allergic airway disease.

CD1d-Restricted Natural Killer T Cells Can Down-regulate Tumor Immunosurveillance Independent of Interleukin-4 Receptor-Signal Transducer and Activator of Transcription 6 or Transforming Growth Factor-β

It has been shown previously that the suppression of tumor immunosurveillance may be a mechanism by which tumors resist immune detection and elimination. In this study, we evaluated the role of the immunoregulatory natural killer T (NKT) cells in the biology of immunosurveillance of osteosarcoma. The K7M2 mouse osteosarcoma cell line was implanted orthotopically into wild-type and NKT cell-deficient CD1d knockout (KO) BALB/c mice, and mice were monitored for growth of primary tumors. Further, we examined the role of CD4(+) and/or CD8(+) cells by depleting the cells in vivo and measuring CTL activity in vitro. We also asked the role of interleukin (IL)-4 receptor alpha (IL-4Ralpha)-signal transducer and activator of transcription 6 (STAT6) signaling, including IL-13, and transforming growth factor beta (TGF-beta) by using gene-disrupted mice or treating mice with cytokine antagonists. We were surprised to find a high rate of rejection of osteosarcoma primary tumors in 88% (14 of 16) of CD1d KO mice compared with syngeneic wild-type BALB/c mice that showed rejection of tumor in <24% of mice. Further studies suggested that the rejection of tumor in CD1d KO mice was dependent on CD8(+) lymphocytes. Distinct from other murine tumor models, the negative regulation induced by CD1d-restricted NKT cells was not dependent on IL-4Ralpha-STAT6 signaling, including IL-13, or on TGF-beta. These data suggest that a novel CD1d-restricted NKT cell-mediated mechanism for tumor immunosuppression is active in the K7M2 osteosarcoma model and that NKT cells can regulate immunosurveillance through more than one pathway.

NKT cells and IFN-gamma establish the regulatory environment for the control of diabetogenic T cells in the nonobese diabetic mouse

In type 1 diabetes mellitus (T1DM), T cell-mediated destruction of insulin-producing pancreatic beta cells leads to the acute onset of hyperglycemia. The nonobese diabetic mouse model of human T1DM reveals that T cells capable of inducing diabetes can escape normal central tolerance, and can cause T1DM if left unchecked. However, several regulatory T cell subsets can temper autoaggressive T cells, although it remains undetermined when and how, and by which subset, homeostatic control of diabetogenic T cells is normally achieved in vivo. Using a cotransfer model, we find that NKT cells efficiently dampen the action of diabetogenic CD4+ T cells, and do so in an indirect manner by modifying the host environment. Moreover, the NKT cell-containing population modifies the host via production of IFN-gamma that is necessary for driving the inhibition of diabetogenic T cells in vivo.

Differential antitumor immunity mediated by NKT cell subsets in vivo

We showed previously that NKT cell–deficient TCR Jα18^−/− mice are more susceptible to methylcholanthrene (MCA)-induced sarcomas, and that normal tumor surveillance can be restored by adoptive transfer of WT liver-derived NKT cells. Liver-derived NKT cells were used in these studies because of their relative abundance in this organ, and it was assumed that they were representative of NKT cells from other sites. We compared NKT cells from liver, thymus, and spleen for their ability to mediate rejection of the sarcoma cell line (MCA-1) in vivo, and found that this was a specialized function of liver-derived NKT cells. Furthermore, when CD4⁺ and CD4⁻ liver-derived NKT cells were administered separately, MCA-1 rejection was mediated primarily by the CD4⁻ fraction. Very similar results were achieved using the B16F10 melanoma metastasis model, which requires NKT cell stimulation with α-galactosylceramide. The impaired ability of thymus-derived NKT cells was due, in part, to their production of IL-4, because tumor immunity was clearly enhanced after transfer of IL-4–deficient thymus-derived NKT cells. This is the first study to demonstrate the existence of functionally distinct NKT cell subsets in vivo and may shed light on the long-appreciated paradox that NKT cells function as immunosuppressive cells in some disease models, whereas they promote cell-mediated immunity in others.

Stem cell mobilization with G-CSF analogs: a rational approach to separate GVHD and GVL?

The separation of graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) remains the "holy grail" of allogeneic stem cell transplantation, and improvements are urgently needed to allow more effective therapy of malignant disease. The use of G-CSF-mobilized peripheral blood as a clinical stem cell source is associated with enhanced GVL effects without amplification of significant acute GVHD. Preclinical studies have demonstrated that G-CSF modulates donor T cell function before transplantation, promoting T(H)2 differentiation and regulatory T cell function. In addition, the expansion of immature antigen-presenting cells (APCs) and plasmacytoid dendritic cells (DCs) favors the maintenance of this pattern of T cell differentiation after transplantation. Although these patterns of T cell differentiation attenuate acute GVHD, they do not have an impact on the cytolytic pathways of the CD8(+) T cells that are critical for effective GVL. Recently, it has been demonstrated that modification of G-CSF, either by pegylation of the native cytokine or conjugation to Flt-3L, results in the expansion and activation of donor iNKT cells, which significantly augment CD8(+) T cell-mediated cytotoxicity and GVL effects after transplantation. Given that these cytokines also enhance the expansion of regulatory T cells and APCs, they further separate GVHD and GVL, offering potential clinical advantages for the transplant recipient.

Localization of Idd11 is not associated with thymus and nkt cell abnormalities in NOD mice

Congenic mouse strains provide a unique resource for genetic dissection and biological characterization of chromosomal regions associated with diabetes progression in the nonobese diabetic (NOD) mouse. Idd11, a mouse diabetes susceptibility locus, was previously localized to a region on chromosome 4. Comparison of a panel of subcongenic NOD mouse strains with different intervals derived from the nondiabetic C57BL/6 (B6) strain now maps Idd11 to an approximately 8-Mb interval. B6-derived intervals protected congenic NOD mice from diabetes onset, even though lymphocytic infiltration of pancreatic islets was similar to that found in NOD mice. In addition, neither thymic structural irregularities nor NKT cell deficiencies were ameliorated in diabetes-resistant congenic NOD mice, indicating that Idd11 does not contribute to these abnormalities, which do not need to be corrected to prevent disease.

The influence of CD1d in postselection NKT cell maturation and homeostasis

After being positively selected on CD1d-expressing thymocytes, NKT cells undergo a series of developmental changes that can take place inside or outside the thymus. We asked whether CD1d continues to play a role in late-stage NKT cell development and, in particular, during the functionally significant acquisition of NK1.1 that is indicative of NKT cell maturity. We report that CD1d is indeed crucial for this step, because immature NK1.1(-) NKT cells fail to fully mature when transferred to a CD1d-deficient environment. Surprisingly, however, the lack of CD1d did not greatly affect the long-term survival of NKT cells, and they continued to express CD69 and slowly proliferate. This directly contradicts the currently held view that these phenomena are caused by autoreactivity directed against CD1d/TCR-restricted self-Ags. Our findings demonstrate an ongoing role for TCR-mediated signaling throughout NKT cell development, but the characteristic semiactivated basal state of NKT cells is controlled by CD1d-independent factors or is intrinsic to the cells themselves.

Loss of IL-4 secretion from human type 1a diabetic pancreatic draining lymph node NKT cells

Altered frequency and function of peripheral invariant NKT (iNKT) cells have been implicated in the regulation of murine and human type 1a diabetes. To examine regulatory cells from the site of drainage of autoinflammatory tissue and autoantigenic T cell priming in diabetes, we directly cloned iNKT cells from human pancreatic draining lymph nodes (PLN). From 451 T cell clones from control and diabetic PLN, we derived 55 iNKT cells by two methods and analyzed function by cytokine secretion. iNKT cell clones isolated from control PLN secreted IL-4 and IFN-gamma upon TCR stimulation. For type 1a diabetic subjects, PLN iNKT cell clones from three samples secreted IFN-gamma and no IL-4. In a rare recent onset diabetic sample with islet-infiltrating CD4+ T cells, the phenotype of PLN iNKT cell clones was mixed. From normal and diabetic PLN, one-third of CD1d tetramer+-sorted T cell clones were reactive with CD1d transfectants or proliferated/secreted cytokine in response to alpha-galactosylceramide-pulsed PBMCs; tetramer-staining T cell clones from diabetic PLN did not secrete IL-4. This is the first report directly examining iNKT cells from lymph nodes draining the site of autoimmunological attack in humans; iNKT cells were altered in cytokine secretion as previously reported for circulating iNKT cells in human type 1a diabetes.

Structural basis for CD1d presentation of a sulfatide derived from myelin and its implications for autoimmunity

Sulfatide derived from the myelin stimulates a distinct population of CD1d-restricted natural killer T (NKT) cells. Cis-tetracosenoyl sulfatide is one of the immunodominant species in myelin as identified by proliferation, cytokine secretion, and CD1d tetramer staining. The crystal structure of mouse CD1d in complex with cis-tetracosenoyl sulfatide at 1.9 Å resolution reveals that the longer cis-tetracosenoyl fatty acid chain fully occupies the A′ pocket of the CD1d binding groove, whereas the sphingosine chain fills up the F′ pocket. A precise hydrogen bond network in the center of the binding groove orients and positions the ceramide backbone for insertion of the lipid tails in their respective pockets. The 3′-sulfated galactose headgroup is highly exposed for presentation to the T cell receptor and projects up and away from the binding pocket due to its β linkage, compared with the more intimate binding of the α-glactosyl ceramide headgroup to CD1d. These structure and binding data on sulfatide presentation by CD1d have important implications for the design of therapeutics that target T cells reactive for myelin glycolipids in autoimmune diseases of the central nervous system.

NKT cell-dependent leukemia eradication following stem cell mobilization with potent G-CSF analogs

NKT cells have pivotal roles in immune regulation and tumor immunosurveillance. We report that the G-CSF and FMS-like tyrosine kinase 3 ligand (Flt-3L) chimeric cytokine, progenipoietin-1, markedly expands the splenic and hepatic NKT cell population and enhances functional responses to alpha-galactosylceramide. In a murine model of allogeneic stem cell transplantation, donor NKT cells promoted host DC activation and enhanced perforin-restricted CD8+ T cell cytotoxicity against host-type antigens. Following leukemic challenge, donor treatment with progenipoietin-1 significantly improved overall survival when compared with G-CSF or control, attributable to reduced graft-versus-host disease mortality and paradoxical augmentation of graft-versus-leukemia (GVL) effects. Enhanced cellular cytotoxicity was dependent on donor NKT cells, and leukemia clearance was profoundly impaired in recipients of NKT cell-deficient grafts. Enhanced cytotoxicity and GVL effects were not associated with Flt-3L signaling or effects on DCs but were reproduced by prolonged G-CSF receptor engagement with pegylated G-CSF. Thus, modified G-CSF signaling during stem cell mobilization augments NKT cell-dependent CD8+ cytotoxicity, effectively separating graft-versus-host disease and GVL and greatly expanding the potential applicability of allogeneic stem cell transplantation for the therapy of malignant disease.

Mechanisms of the self/non-self-survey in the defense against cancer: Potential for chemoprevention?

When compared to a reference population, several large epidemiological studies with long-term follow-up have reported a three- to five-fold increased risk of neoplasia amongst patients who have received organ transplants, with an incidence curve that rises in a linear fashion with time. The relationship between the immune system and cancer is complex. The ability to discriminate "self" from "non-self" is one of the central roles of the immune system. Since tumors arise from transformation of host cells, it is not surprising that some aspects of tumor immunity resemble autoimmunity. The immune response to tumors shares aspects of both self- and non-self-immune recognition. What accounts for the apparent failure of immunity? In this review article, we address the role of the self/non-self-survey in the immune response to tumors, we describe mechanisms of immune surveillance against tumor cells, and we discuss models of ignorance, tolerance and tumor evasion of the immune response. The overall aim of the article is to demonstrate the scope for prevention of cancer in individuals at increased risk of developing malignancy due to immune compromise. Interventional strategies may involve the use of pro-differentiation agents such as retinoids, modifiers of polyamine biosynthesis or inhibitors of cyclooxygenase isozymes.

DX5/CD49b-positive T cells are not synonymous with CD1d-dependent NKT cells

NKT cells are typically defined as CD1d-dependent T cells that carry an invariant TCR alpha-chain and produce high levels of cytokines. Traditionally, these cells were defined as NK1.1+ T cells, although only a few mouse strains express the NK1.1 molecule. A popular alternative marker for NKT cells has been DX5, an Ab that detects the CD49b integrin, expressed by most NK cells and a subset of T cells that resemble NKT cells. Interpretation of studies using DX5 as an NKT cell marker depends on how well DX5 defines NKT cells. Using a range of DX5 and other anti-CD49b Abs, we reveal major differences in reactivity depending on which Ab and which fluorochrome are used. The brightest, PE-conjugated reagents revealed that while most CD1d-dependent NKT cells expressed CD49b, they represented only a minority of CD49b+ T cells. Furthermore, CD49b+ T cell numbers were near normal in CD1d-/- mice that are completely deficient for NKT cells. CD1d tetramer- CD49b+ T cells differ from NKT cells by their activation and memory marker expression, tissue distribution, and CD4/CD8 coreceptor profile. Interestingly, both NKT cells and CD1d tetramer- CD49b+ T cells produce cytokines, but the latter are clearly biased toward Th1-type cytokines, in contrast to NKT cells that produce both Th1 and Th2 cytokines. Finally, we demonstrate that expression of CD49b by NKT cells does not dramatically alter with age, contrasting with earlier reports proposing DX5 as a maturation marker for NKT cells. In summary, our data demonstrate that DX5/CD49b is a poor marker for identifying CD1d-dependent NKT cells.

Dietary factors alter hepatic innate immune system in mice with nonalcoholic fatty liver disease

Dietary factors promote obesity and obesity-related disorders, such as fatty liver disease. Natural killer T (NKT) cells are components of the innate immune system that regulate proinflammatory (Th-1) and anti-inflammatory (Th-2) immune responses. Previously, we noted that NKT cells are selectively reduced in the fatty livers of obese, leptin-deficient ob/ob mice and demonstrated that this promotes proinflammatory polarization of hepatic cytokine production, exacerbating lipopolysaccharide (LPS) liver injury in these animals. In the current study, we show that hepatic NKT cells are also depleted by diets that induce obesity and fatty livers in wild-type mice, promoting Th-1 polarization of hepatic cytokine production and sensitization to LPS liver injury despite persistent leptin. Adult male C57BL6 mice fed diets containing high amounts of either fat or sucrose, or combined high-fat, high-sucrose, develop increased hepatic NKT cell apoptosis and reduced liver NKT cells. The hepatic lymphocytes are more Th-1 polarized with increased intracellular interferon gamma and tumor necrosis factor alpha. Mice fed high-fat diets also exhibit more liver injury, reflected by 2-fold greater serum alanine aminotransferase (ALT) than control animals after receiving LPS. In conclusion, when otherwise normal mice are fed with high-fat or sucrose diet, they become obese, develop fatty livers, and acquire hepatic innate immune system abnormalities, including increased NKT cell apoptosis. The latter reduces liver NKT cell populations and promotes excessive hepatic production of Th-1 cytokines that promote hepatic inflammation. These diet-induced alterations in the hepatic innate immune system may contribute to obesity-related liver disease.

Involvement of sulfatide in beta cells and type 1 and type 2 diabetes

Mammalian tissues express beta-isoforms of glycosphingolipids and, among these, sulfatide (sulphated galactosylceramide) is present in the beta cells, and it is here that the short fatty acid chain (C16) isoform is predominately found. In vitro studies have shown that sulfatide preserves insulin crystals and facilitates insulin monomerisation under certain biochemical conditions. It also activates beta cell potassium channels and moderates insulin secretion. Anti-sulfatide antibodies are seen in type 1 diabetes, and immunological presentation of glycosphingolipids by the non-classical CD1 molecules has recently been reported. It is via this mechanism that alpha-galactosylceramide and sulfatide are able to influence the innate immune system and inhibit autoimmunity, possibly through regulatory natural killer T cells. Administration of sulfatide substantially reduces the incidence of diabetes in non-obese diabetic mice and prevents antigen-induced experimental autoimmune encephalomyelitis in wild-type mice. Sulfatide has specific anti-inflammatory properties, increasing the number of CD3+CD25+ regulatory T cells and reducing production of several cytokines, including TNF-alpha. Patients with type 2 diabetes have low serum concentrations of sulfatide, and some animal models of type 2 diabetes have low pancreatic expression of C16:0 sulfatide; administration of this increases insulin secretion and improves first-phase insulin response in Zucker fatty rats. Glycosphingolipids in general, and sulfatide in particular, appear relevant to both type 1 and type 2 diabetes.

Valpha14 NK T cell-triggered IFN-gamma production by Gr-1+CD11b+ cells mediates early graft loss of syngeneic transplanted islets

Pancreatic islet transplantation is a highly promising approach for the treatment of insulin-dependent diabetes mellitus. However, the procedure remains experimental for several reasons, including its low efficiency caused by the early graft loss of transplanted islets. We demonstrate that Gr-1⁺CD11b⁺ cells generated by transplantation and their IFN-γ production triggered by Vα14 NKT cells are an essential component and a major cause of early graft loss of pancreatic islet transplants. Gr-1⁺CD11b⁺ cells from Vα14 NKT cell–deficient (Jα281^−/−) mice failed to produce IFN-γ, resulting in efficient islet graft acceptance. Early graft loss was successfully prevented through the repeated administration of α-galactosylceramide, a specific ligand for Vα14 NKT cells, resulting in dramatically reduced IFN-γ production by Gr-1⁺CD11b⁺ cells, as well as Vα14 NKT cells. Our study elucidates, for the first time, the crucial role of Gr-1⁺CD11b⁺ cells and the IFN-γ they produce in islet graft rejection and suggests a novel approach to improving transplantation efficiency through the modulation of Vα14 NKT cell function.

The involvement of V(alpha)14 natural killer T cells in the pathogenesis of arthritis in murine models

OBJECTIVE

To examine the physiologic role of natural killer T (NKT) cells bearing V(alpha)14 T cell receptor (TCR) in the pathogenesis of collagen-induced arthritis (CIA) and antibody-induced arthritis in mice.

METHODS

NKT cells were stained with alpha-galactosylceramide-loaded CD1 dimer, and then assessed using flow cytometry. CIA was induced in mice by immunization on days 0 and 21 with type II collagen (CII) emulsified with an equal volume of Freund's complete adjuvant. Anti-CII antibodies were measured by enzyme-linked immunosorbent assay. For antibody-induced arthritis, mice were injected with anti-CII monoclonal antibodies (mAb) followed by lipopolysaccharide, or with serum from KRN TCR-transgenic mice crossed with nonobese diabetic mice (K/BxN). The severity of arthritis was monitored with a macroscopic scoring system.

RESULTS

The number of NKT cells increased in the liver at the peak of the clinical course of CIA. Administration of anti-CD1 mAb inhibited development of CIA. The severity of CIA in NKT cell-deficient mice was reduced compared with that in wild-type mice. The IgG1:IgG2a ratio of anti-CII was elevated and production of interleukin-10 from draining lymph node cells was increased in NKT cell-deficient mice. NKT cell-deficient mice were significantly less susceptible to antibody-induced arthritis.

CONCLUSION

NKT cells contribute to the pathogenesis of arthritis by enhancing autoantibody-mediated inflammation. NKT cells also contribute to the disease process in a deleterious way, due, at least in part, to the alteration of the Th1/Th2 balance in T cell response to CII.

Of mice and men: use of animal models to identify possible interventions for the prevention of autoimmune type 1 diabetes in humans

Animal model and clinical studies indicate that type 1 diabetes (T1D) results from T cell-mediated autoimmune destruction of insulin-producing pancreatic beta-cells. This review discusses the knowledge gained from animal models about the nature of the autoreactive T cells that cause T1D and the possible basis for their development. Based on this information, the possible positive and negative aspects of various antigen-specific and non-specific immunotherapies, which could potentially prevent the onset of T1D in at risk individuals, are discussed.

Psoriasis: dysregulation of innate immunity

The current understanding of the function of natural killer (NK) T cells in innate immunity and their potential to control acquired specific immunity, as well as the remarkable efficacy of antitumour necrosis factor-alpha biological treatments in psoriasis, forces us to refine the current T-cell hypothesis of psoriasis pathogenesis, and to give credit to the role of innate immunity. Psoriasis might be envisioned to be a genetically determined triggered state of otherwise dormant innate immunity. This aggravated state of innate immunity is represented by the activity of NK T cells, dendritic cells, neutrophils and keratinocytes, leading to the recruitment and activation of preferentially type 1 T cells, possibly in an antigen-independent way. Keratinocytes in psoriasis then are sensitive to the effects of T-cell activation and cytokine production, interferon (IFN)-gamma, by responding with psoriasiform hyperplasia. The chronic inflammation of psoriatic lesions suggests that this might be due to a deficiency in downregulation processes (e.g. a defect in the regulatory T-cell repertoire) and/or the persistence of an unknown trigger resulting in an exaggerated innate immune response.

Semi-mature IL-12 secreting dendritic cells present exogenous antigen to trigger cytolytic immune responses

Dendritic cells (DC) are candidates for antigen-presenting cells that present exogenous antigen on MHC class I molecules to cytotoxic T lymphocytes (CTL), a process referred to as cross-priming. We triggered interleukin (IL)-12 release from DC, which was limited to the first day after maturation induction, by a combination of lipopolysaccharide (LPS) and interferon (IFN)-gamma. To stimulate T lymphocytes, we used soluble protein derived from lysis of Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines (LCL) or ovalbumin loaded onto DC. Co-culture was initiated 2-6 or 48 h after maturation corresponding to "semi-mature" actively IL-12-secreting type 1 DC (sm-DC1) or a "fully mature" DC1 that had lost the ability to release IL-12 (fm-DC1), respectively. IL-12-secreting sm-DC1 but not fm-DC1 efficiently triggered cytolytic activity in autologous T lymphocytes. The combination of IL-1beta, IL-6, TNF-alpha, and prostaglandin E2 generated type 2 DC that did not secrete IL-12 (DC2) and could not prime T-cell cytolytic activity. However, supplementation of cultures using DC2 with IL-12 resulted in CTL activity while the presence of anti-IL-12 monoclonal antibodies in cultures using IL-12 secreting sm-DC1 suppressed CTL activity. Thus, actively IL-12-secreting sm-DC1 are necessary and sufficient for the antigen-specific expansion of CTL in response to exogenously provided soluble antigen.

Human CD1-restricted T cell recognition of lipids from pollens

Plant pollens are an important source of environmental antigens that stimulate allergic responses. In addition to acting as vehicles for foreign protein antigens, they contain lipids that incorporate saturated and unsaturated fatty acids, which are necessary in the reproduction of higher plants. The CD1 family of nonpolymorphic major histocompatibility complex–related molecules is highly conserved in mammals, and has been shown to present microbial and self lipids to T cells. Here, we provide evidence that pollen lipids may be recognized as antigens by human T cells through a CD1-dependent pathway. Among phospholipids extracted from cypress grains, phosphatidyl-choline and phosphatidyl-ethanolamine were able to stimulate the proliferation of T cells from cypress-sensitive subjects. Recognition of phospholipids involved multiple cell types, mostly CD4⁺ T cell receptor for antigen (TCR)αβ⁺, some CD4⁻CD8⁻ TCRγδ⁺, but rarely Vα24i⁺ natural killer–T cells, and required CD1a⁺ and CD1d⁺ antigen presenting cell. The responding T cells secreted both interleukin (IL)-4 and interferon-γ, in some cases IL-10 and transforming growth factor-β, and could provide help for immunoglobulin E (IgE) production. Responses to pollen phospholipids were maximally evident in blood samples obtained from allergic subjects during pollinating season, uniformly absent in Mycobacterium tuberculosis–exposed health care workers, but occasionally seen in nonallergic subjects. Finally, allergic, but not normal subjects, displayed circulating specific IgE and cutaneous weal and flare reactions to phospholipids.

A Defect in Lineage Fate Decision during Fetal Thymic Invariant NKT Cell Development May Regulate Susceptibility to Type 1 Diabetes

A numerical and functional deficiency in invariant NKT (iNKT) cells detectable by 3 wk of age in the thymus and spleen mediates the pathogenesis of type 1 diabetes in NOD mice, but the stage of T cell development at which this deficiency first occurs is unknown. We report in this study that this deficiency develops after the CD4(+)CD8(+) double-positive stage of thymic T cell development and is due to a lineage-specific depletion of CD4(-)CD8(-) double-negative alphabeta T cells and iNKT cells from the thymus between embryonic day 18 and day 1 after birth. Thus, an inheritable defect in a lineage fate decision that elicits a deficiency in fetal thymic iNKT cell development may predispose to susceptibility to type 1 diabetes.

Immunotherapeutic potential for ceramide-based activators of iNKT cells

Invariant natural killer T (iNKT) cells are a subpopulation of T cells that are reactive with glycolipids that are bound by CD1d antigen-presenting molecules. alpha-Galactosylceramide (alpha-GalCer) is a synthetic glycolipid that is a potential treatment for several autoimmune diseases, infectious diseases and cancer. Its therapeutic effect can be traced back to its ability to bind CD1d and activate iNKT cells, which results in the production of T helper 1 (Th1) and Th2 cytokines. However, the effectiveness of alpha-GalCer therapy is limited by the opposing actions of Th1 and Th2 cytokines. The alpha-GalCer analogs OCH and the recently designed and synthesized C-glycosidic alpha-GalCer selectively activate one of two types of cytokine profiles, possibly because either reduced or enhanced overall stability of the CD1d-glycolipid-T-cell-receptor complex leads to a higher potency in vivo, compared with the parent compound. These discoveries boost the potential of glycolipid-based therapies.

Commitment toward the natural T (iNKT) cell lineage occurs at the CD4+8+ stage of thymic ontogeny

T lineage commitment occurs in a discrete, stage-specific manner during thymic ontogeny. Intrathymic precursor transfer experiments and the identification of CD4(+)8+ double-positive (DP), V alpha 14J alpha 18 natural T (iNKT) cells suggest that commitment to this lineage might occur at the DP stage. Nevertheless, this matter remains contentious because others failed to detect V alpha 14J alpha 18-positive iNKT cells that are CD4(+)8+. In resolution to this issue, we demonstrate that retinoic acid receptor-related orphan receptor gamma (ROR gamma)0/0 thymi, which accumulate immature single-positive (ISP) thymocytes that precede the DP stage, do not rearrange V alpha 14-to-J alpha 18 gene segments, suggesting that this event occurs at a post-ISP stage. Mixed radiation bone marrow chimeras revealed that RORgamma functions in an iNKT cell lineage-specific manner. Further, introgression of a Bcl-x(L) transgene into ROR gamma(0/0) mice, which promotes survival and permits secondary rearrangements of distal V alpha and J alpha gene segments at the DP stage, rescues V alpha 14-to-J alpha 18 recombination. Similarly, introgression of a rearranged V alpha 14J alpha 18 transgene into ROR gamma(0/0) mice results in functional iNKT cells. Thus, our data support the "T cell receptor-instructive (mainstream precursor) model" of iNKT cell lineage specification where V alpha 14-to-J alpha 18 rearrangement, positive selection, and iNKT cell lineage commitment occur at or after the DP stage of ontogeny.

Activated CD1d-restricted natural killer T cells secrete IL-2: innate help for CD4+CD25+ regulatory T cells?

CD4(+)CD25(+) and CD1d-restricted natural killer T (NKT) cells are thymus-derived self-reactive regulatory T cells that play a key role in the control of pathological immune responses. Little is known about functional cooperation between innate regulatory NKT cells and adaptive CD4(+)CD25(+) regulatory cells. Here we show that human CD4(+)Valpha24(+)Vbeta11(+) (CD4(+) NKT) cells isolated from peripheral blood by flow cytometric cell sorting secrete substantial amounts of IL-2 after stimulation with dendritic cells (DC) and alpha-Galactosylceramide. When cocultured with CD4(+)CD25(+) cells, CD4(+) NKT cells promoted moderate proliferation of CD4(+)CD25(+) cells. The proliferation of CD4(+)CD25(+) T cells was due to soluble IL-2 produced by activated CD4(+) NKT cells. The expanded CD4(+)CD25(+) cells remained anergic and retained their potent suppressive properties. These findings indicate that unlike conventional CD4(+) and CD8(+) T cells, which are susceptible to CD4(+)CD25(+) regulatory cell suppression, NKT cells promote CD4(+)CD25(+) regulatory cell proliferation. These data raise the possibility that NKT cells can function as helper cells to CD4(+)CD25(+) regulatory T cells, thereby providing a link between the two naturally occurring populations of regulatory T cells.

A Phase I Study of α-Galactosylceramide (KRN7000)–Pulsed Dendritic Cells in Patients with Advanced and Recurrent Non–Small Cell Lung Cancer

PURPOSE

Human Valpha24 natural killer T (NKT) cells bearing an invariant Valpha24JalphaQ antigen receptor, the counterpart of murine Valpha14 NKT cells, are activated by a specific ligand, alpha-galactosylceramide (alphaGalCer, KRN7000), in a CD1d-dependent manner. I.v. administration of alphaGalCer-pulsed dendritic cells (DC) induces significant activation and expansion of Valpha14 NKT cells in the lung and resulting potent antitumor activities in mouse tumor metastatic models. We did a phase I dose escalation study with alphaGalCer-pulsed DCs in lung cancer patients.

EXPERIMENTAL DESIGN

Patients with advanced non-small cell lung cancer or recurrent lung cancer received i.v. injections of alphaGalCer-pulsed DCs (level 1: 5 x 10(7)/m(2); level 2: 2.5 x 10(8)/m(2); and level 3: 1 x 10(9)/m(2)) to test the safety, feasibility, and clinical response. Immunomonitoring was also done in all completed cases.

RESULTS

Eleven patients were enrolled in this study. No severe adverse events were observed during this study in any patient. After the first and second injection of alphaGalCer-pulsed DCs, dramatic increase in peripheral blood Valpha24 NKT cells was observed in one case and significant responses were seen in two cases receiving the level 3 dose. No patient was found to meet the criteria for partial or complete responses, whereas two cases in the level 3 group remained unchanged for more than a year with good quality of life.

CONCLUSIONS

In this clinical trial, alphaGalCer-pulsed DC administration was well tolerated and could be safely done even in patients with advanced disease.

alpha-Galactosylceramide therapy for autoimmune diseases: prospects and obstacles

Autoimmune responses are normally kept in check by immune-tolerance mechanisms, which include regulatory T cells. In recent years, research has focused on the role of a subset of natural killer T (NKT) cells - invariant NKT (iNKT) cells, which are a population of glycolipid-reactive regulatory T cells - in controlling autoimmune responses. Because iNKT cells strongly react with a marine-sponge-derived glycolipid, alpha-galactosylceramide (alpha-GalCer), it has been possible to specifically target and track these cells. As I discuss here, although preclinical studies have shown considerable promise for the development of treatment with alpha-GalCer as a therapeutic modality for autoimmune diseases, several obstacles need to be overcome before moving alpha-GalCer therapy from the bench to the bedside.

Modulation of CD1d-restricted NKT cell responses by using N-acyl variants of alpha-galactosylceramides

A form of alpha-galactosylceramide, KRN7000, activates CD1d-restricted Valpha14-invariant (Valpha14i) natural killer (NK) T cells and initiates multiple downstream immune reactions. We report that substituting the C26:0 N-acyl chain of KRN7000 with shorter, unsaturated fatty acids modifies the outcome of Valpha14i NKT cell activation. One analogue containing a diunsaturated C20 fatty acid (C20:2) potently induced a T helper type 2-biased cytokine response, with diminished IFN-gamma production and reduced Valpha14i NKT cell expansion. C20:2 also exhibited less stringent requirements for loading onto CD1d than KRN7000, suggesting a mechanism for the immunomodulatory properties of this lipid. The differential cellular response elicited by this class of Valpha14i NKT cell agonists may prove to be useful in immunotherapeutic applications.

Activated NKT Cells Inhibit Autoimmune Diabetes through Tolerogenic Recruitment of Dendritic Cells to Pancreatic Lymph Nodes

NKT cell activation by alpha-galactosylceramide (alpha-GalCer) inhibits autoimmune diabetes in NOD mice, in part by inducing recruitment to pancreatic lymph nodes (PLNs) of mature dendritic cells (DCs) with disease-protective effects. However, how activated NKT cells promote DC maturation, and what downstream effect this has on diabetogenic T cells was unknown. Activated NKT cells were found to produce a soluble factor(s) inducing DC maturation. Initially, there was a preferential accumulation of mature DCs in the PLNs of alpha-GalCer-treated NOD mice, followed by a substantial increase in T cells. Adoptive transfer of a diabetogenic CD8 T cell population (AI4) induced a high rate of disease (75%) in PBS-treated NOD recipients, but not in those pretreated with alpha-GalCer (8%). Significantly, more AI4 T cells accumulated in PLNs of alpha-GalCer than PBS-treated recipients, while no differences were found in mesenteric lymph nodes from each group. Compared with those in mesenteric lymph nodes, AI4 T cells entering PLNs underwent greater levels of apoptosis, and the survivors became functionally anergic. NKT cell activation enhanced this process. Hence, activated NKT cells elicit diabetes protection in NOD mice by producing a soluble factor(s) that induces DC maturation and accumulation in PLNs, where they subsequently recruit and tolerize pathogenic T cells.

Single dose of OCH improves mucosal T helper type 1/T helper type 2 cytokine balance and prevents experimental colitis in the presence of valpha14 natural killer T cells in mice

BACKGROUND AND AIMS

Valpha14 natural killer T (NKT) cells seem to play important roles in the development of various autoimmune diseases. However, the pathophysiologic role of NKT cells in inflammatory bowel disease remains unclear. To clarify the mechanism by which the activation of NKT cells mediates protection against intestinal inflammation, we investigated the antiinflammatory role of specifically activated Valpha14 NKT cells by glycolipids in a mouse experimental model of colitis induced by dextran sulfate sodium (DSS).

METHODS

Colitis was induced in C57BL/6 mice by the oral administration of 1.5% DSS for 9 days. A single dose of OCH or alpha-galactosylceramide, a ligand for NKT cells, was administered on day 3 after the induction of colitis. Body weights and colonic mucosal injury were assessed in each glycolipid-treated group. Interferon-gamma and interleukin-4 levels in the supernatants from colonic lamina propria lymphocytes (LPLs) were measured by enzyme-linked immunosorbent assay.

RESULTS

The administration of a single dose of OCH attenuated colonic inflammation, as defined by body weights and histologic injury. The protective effects of OCH could not be observed in Valpha14 NKT cell-deficient mice. In vivo treatment with OCH had improved the interferon-gamma/interleukin-4 ratio from colonic LPLs on day 9 after DSS treatment.

CONCLUSION

The present data indicated that the activation of Valpha14 NKT cells by OCH plays a pivotal role in mediating intestinal inflammation via altered mucosal T-helper type 1/type 2 responses. Therapeutic strategies that are designed to activate specifically Valpha14 NKT cells may prove to be beneficial in treating intestinal inflammation.

Dendritic cell maturation by CD11c− T cells and Vα24+ natural killer T-cell activation by α-Galactosylceramide

Human invariant Valpha24+ natural killer T (NKT) cells display potent antitumor activity upon stimulation. Activation of endogenous Valpha24+ NKT cells would be one strategy for the treatment of cancer patients. For example, dendritic cells (DCs) loaded with a glycolipid NKT cell ligand, alpha-galactosylceramide (alphaGalCer, KRN7000), are a possible tool for the activation and expansion of functional Valpha24+ NKT cells in vivo. In this report, we demonstrate that the levels of expansion and the ability to produce IFN-gamma of Valpha24+ NKT cells induced by alphaGalCer-loaded whole PBMCs cultured with IL-2 and GM-CSF (IL-2/GM-CSF-cultured PBMCs) were superior to those of cells induced by monocyte-derived CD11c+ DCs (moDCs) developed with IL-4 and GM-CSF. Interestingly, CD11c+ cells in the IL-2/GM-CSF-cultured PBMCs showed a mature phenotype without further stimulation and exerted potent stimulatory activity on Valpha24+ NKT cells to enable them to produce IFN-gamma preferentially at an extent equivalent to mature moDCs induced by stimulation with LPS or a cytokine cocktail. Cocultivation with CD11c- cells in the IL-2/GM-CSF-cultured PBMCs induced maturation of moDCs. In particular, CD11c-CD3+ T cells appeared to play important roles in DC maturation. In addition, TNF-alpha was preferentially produced by CD11c-CD3+ T cells in IL-2/GM-CSF-cultured PBMCs and was involved in the maturation of moDCs. Thus, the maturation of DCs induced by CD11c- T cells through TNF-alpha production appears to result in the efficient expansion and activation of Valpha24+ NKT cells to produce IFN-gamma preferentially.

Unmasking immunosurveillance against a syngeneic colon cancer by elimination of CD4+ NKT regulatory cells and IL-13

We have previously observed a novel role of natural killer T (NKT) cells in negative regulation of antitumor immune responses against an immunogenic regressor tumor expressing a transfected viral antigen. Here, we investigated whether hidden spontaneous antitumor immunosurveillance, in the absence of a vaccine, could be revealed by disruption of this negative regulatory pathway involving CD4+ NKT cells and interleukin-13 (IL-13), in a murine pulmonary metastasis model of a nontransfected, nonregressor, syngeneic tumor, the CT26 colon carcinoma. Lung metastases of CT26 were decreased in CD4+ T cell-depleted BALB/c mice, suggesting that CD4+ T cells were involved in negative regulation of antitumor responses. CD1-knock out (CD1-KO) mice, which have conventional CD4+ T cells and CD4+CD25+ regulatory T cells but lack CD1-restricted CD4+ NKT cells, were significantly resistant to lung metastasis of CT26. The metastases were not further decreased in CD4+ T cell-depleted CD1-KO mice, implying that CD4+ NKT cells might be the primary negative regulator of antitumor immune responses in BALB/c mice. CD8+ T cells were found to act as effectors in antitumor immune responses, since the inhibition of lung metastases observed in naive CD1-KO or CD4+ T cell-depleted mice was abrogated by depletion of CD8+ T cells. Lung metastases were significantly decreased by treatment of mice with an IL-13 inhibitor, but not by deficiency or inhibition of IL-4. Thus, even for a nonregressor tumor, immunosurveillance exists but is negatively regulated via CD4+ NKT cells possibly mediated by IL-13, and can be unmasked by removal of these negative regulatory components.

Frequency of Vα24+Vβ11+ NKT cells in peripheral blood of human kidney transplantation recipients

There are still lacking data supporting a role for natural killer T (NKT) cells in the maintenance of human tissue-specific tolerance. We are interested to study NKT cell frequency in kidney transplant recipients and its correlation with graft function. Peripheral blood T cell receptors (TCR) Valpha24(+)Vbeta11(+) NKT cells were phenotyped according to CD4 and CD8 expression in normal controls (NC), in 10 years rejection-free cadaver kidney allografts maintained with minimal immunosuppression (long-term rejection free [LTRF]), in patients with acute rejection (AR) and in patients with acute tubular necrosis (ATN). Results were expressed as percentages of CD4(+)CD8(-) (CD4(+) NKT) or CD4(-)CD8(-) (double negative--DN NKT) Valpha24(+)Vbeta11(+) cells. The percentages of Valpha24(+)Vbeta11(+) cells were 0.09%, 0.14%, 0.02% and 0.09% on gated lymphocytes respectively in AR, ATN, LTRF and NC groups (p=0.263). DN NKT cells were more frequent in NC patients (52.11%) and less present in ATN patients (11.04%). In contrast, CD4(+) NKT (IL-4-producing NKT cells subset) was more frequent in AR (42.86%), and corresponded to almost 3 to 7 folds more what we obtained in the other groups. Although total Valpha24(+)Vbeta11(+) cells did not significantly differ among the groups, the lowest frequency was observed in the LTRF group. In conclusion, we observed that total number of NKT cells did not differ significantly among transplant patients when compared to normal controls, although specific-subsets seem to be more frequent in determined events.

Natural killer T cells as targets for immunotherapy of autoimmune diseases

CD1d-restricted natural killer T (NKT) cells are innate lymphocytes that play a regulatory role during an immune response. The identification of alpha-galactosylceramide (alpha-GalCer), a marine sponge-derived glycosphingolipid, as a potent stimulator of NKT cells led many laboratories to investigate the effects of NKT cell activation on the regulation of immune responses. These studies revealed that alpha-GalCer induces rapid and robust cytokine production by NKT cells, secondary activation of a variety of innate and adaptive immune cells, and modulation of Th cell responses. Further, alpha-GalCer influences disease progression in a variety of experimental models of autoimmunity and inflammation in mice, including models for type 1 diabetes, multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, inflammatory bowel disease, and atherosclerosis. While these studies have raised significant enthusiasm for manipulation of NKT cells as a means of preventing autoimmunity in the clinical setting, there are significant concerns regarding the safety of repeated alpha-GalCer injections in human subjects.

A subset of liver NK T cells is activated during Leishmania donovani infection by CD1d-bound lipophosphoglycan

Natural killer (NK) T cells are activated by synthetic or self-glycolipids and implicated in innate host resistance to a range of viral, bacterial, and protozoan pathogens. Despite the immunogenicity of microbial lipoglycans and their promiscuous binding to CD1d, no pathogen-derived glycolipid antigen presented by this pathway has been identified to date. In the current work, we show increased susceptibility of NK T cell–deficient CD1d^−/− mice to Leishmania donovani infection and Leishmania-induced CD1d-dependent activation of NK T cells in wild-type animals. The elicited response was Th1 polarized, occurred as early as 2 h after infection, and was independent from IL-12. The Leishmania surface glycoconjugate lipophosphoglycan, as well as related glycoinositol phospholipids, bound with high affinity to CD1d and induced a CD1d-dependent IFNγ response in naive intrahepatic lymphocytes. Together, these data identify Leishmania surface glycoconjugates as potential glycolipid antigens and suggest an important role for the CD1d–NK T cell immune axis in the early response to visceral Leishmania infection.

Going both ways: immune regulation via CD1d-dependent NKT cells

NKT cells are a unique T lymphocyte sublineage that has been implicated in the regulation of immune responses associated with a broad range of diseases, including autoimmunity, infectious diseases, and cancer. In stark contrast to both conventional T lymphocytes and other types of Tregs, NKT cells are reactive to the nonclassical class I antigen-presenting molecule CD1d, and they recognize glycolipid antigens rather than peptides. Moreover, they can either up- or downregulate immune responses by promoting the secretion of Th1, Th2, or immune regulatory cytokines. This review will explore the diverse influences of these cells in various disease models, their ability to suppress or enhance immunity, and the potential for manipulating these cells as a novel form of immunotherapy.