Research Highlights: Immunotherapy

Natural killer T cells are important in the pathogenesis of asthma: The many pathways to asthma

β-Glycoglycosphingolipid-Induced Alterations of the STAT Signaling Pathways Are Dependent on CD1d and the Lipid Raft Protein Flotillin-2

Natural killer (NK) and natural killer T (NKT) cells are two important cell subsets of the innate immune system. NK and NKT cells share many phenotypes and functions for anti-tumor immunity; however, the dynamic changes in phenotypes and functional interactions within the tumor microenvironment during tumor development and progression are unknown. Here we report that NK and NKT cells have distinct properties, metabolic profiles, and functions during tumor development. Using the mouse E0771 breast cancer and B16 melanoma models, we found that both NK and NKT cells are dynamically involved in the immune responses to cancer but have distinct distributions and phenotypic profiles in tumor sites and other peripheral organs during the course of tumor development and progression. In the early stages of tumor development, both NK and NKT cells exhibit effector properties. In the later cancer stages, NK and NKT cells have impaired cytotoxic capacities and dysfunctional states. NK cells become senescent cells, while NKT cells, other than invariant NKT (iNKT) cells, are exhausted in the advanced cancers. In contrast, iNKT cells develop increases in activation and effector function within the breast tumor microenvironment. In addition, senescent NK cells have heightened glucose and lipid metabolism, but exhausted NKT cells display unbalanced metabolism in tumor microenvironments of both breast cancer and melanoma tumor models. These studies provide a better understanding of the dynamic and distinct functional roles of NK and NKT cells in anti-tumor immunity, which may facilitate the development of novel immunotherapies targeting NK and NKT cells for cancer treatment.

Hepatitis B is a noncytopathic virus, which exclusively replicates within the liver and affects 350 million people worldwide [1]. Chronic infection can lead to variable disease manifestations such as cirrhosis, decompensated liver disease and hepatocellular carcinoma causing 1 million deaths per year [2]. These important clinical outcomes are a consequence of the host immune response to HBV, which constitutes a double-edged sword responsible for both viral clearance and hepatocellular damage. <br> <br> The precipitants for natural history milestones such as HBV-related hepatic flares (HF) and hepatitis B e Antigen (HBeAg) seroconversion remain unknown. Virus-specific and non-specific cytotoxic T lymphocytes (CTLs), T regulatory (Treg) cells, Natural Killer (NK), Natural Killer T (NKT) cells and dendritic cells (DCs) have been postulated to play a role [3]. The contribution of these immune cells and the nature of their interaction in the immune pathogenesis of HBV-related liver disease require further characterization. The logistical restraints of longitudinal, peripheral and intrahepatic sampling of the human host as well as inadequate small animal and cell culture models have hampered investigation of these immune mechanisms. As a caveat to human based studies in HBV, the circulating immunological cells may not reflect the phenotype and function of equivalent cells sequestered within the human liver. Current knowledge about the immune response to HBV is extrapolated from transgenic mouse models, many of which are models of viral replication rather than liver injury. <br> <br> Natural Killer (NK) and Natural Killer T (NKT) cells are cytotoxic lymphocytes that constitute a key effector arm of the innate immune system. Efforts to characterise the immunological determinants of Hepatitis B virus (HBV) infection have focused on the adaptive immune system whilst overlooking the potential interaction between virus, hepatocyte and NK or NKT cells, which play an important role in host defense against viral pathogens through direct cytotoxicity and the production of proinflammatory and immune regulatory cytokines. There is debate as to whether NK or NKT cells are effectors of antiviral activity or mediators of hepatic injury and fibrogenesis in chronic hepatitis B infection. NK and NKT cells have been implicated in the pathogenesis of liver disease due to other hepatotropic viruses such as hepatitis C and E as well as autoimmune liver disease, as shown in animal models of liver injury [4]. Human intrahepatic lymphocytes consist of 30%-50% NK and 5-10% NKT cells. Peripheral blood lymphocytes contain 13% NK cells and 2% NKT cells [5]. The hepatic enrichment of NK and NKT cells reflects their role as regulators at the interface between the innate and adaptive immune response to liver disease. NK and NKT cells in the peripheral and intrahepatic compartments share effector functions such as direct killing of viral-infected cells and cytokine production. The latter is considered the more important effector function in CHB [4]. NK and NKT cells demonstrate reciprocal interactions (“crosstalk”) with hepatic macrophages, Kupffer cells (KC), DCs and T cells as part of an amalgamated immune response to HBV [4]. <br> <br> The role of NK and NKT cells in the initiation and orchestration of a dynamic host immune response against HBV-related liver disease is investigated in this thesis. This hepatotrophic virus has evolved direct and indirect strategies to evade or inhibit the large hepatic reservoir of NK and NKT cells. In this thesis, I will focus on the dynamic phenotype and function of NK and NKT cells throughout the different phases of HBV infection, which so far have been poorly characterized. I will also examine the effect of activated NK and NKT cells on liver injury, fibrosis, and their attenuation following <br> HBV treatment, which remains controversial. Understanding the role of NK and NKT cells in the pathogenesis of CHB may help to develop new biomarkers for disease and treatment activity and design novel immunotherapies.

Natural killer T (NKT) cells are a unique subset of T cells that display markers characteristic of both natural killer (NK) cells and T cells1. Unlike classical T cells, NKT cells recognize lipid antigen in the context of CD1 molecules2. NKT cells express an invariant TCRα chain rearrangement: Vα14Jα18 in mice and Vα24Jα18 in humans, which is associated with Vβ chains of limited diversity3-6, and are referred to as canonical or invariant NKT (iNKT) cells. Similar to conventional T cells, NKT cells develop from CD4-CD8- thymic precursor T cells following the appropriate signaling by CD1d 7. The potential to utilize NKT cells for therapeutic purposes has significantly increased with the ability to stimulate and expand human NKT cells with α-Galactosylceramide (α-GalCer) and a variety of cytokines8. Importantly, these cells retained their original phenotype, secreted cytokines, and displayed cytotoxic function against tumor cell lines. Thus, ex vivo expanded NKT cells remain functional and can be used for adoptive immunotherapy. However, NKT cell based-immunotherapy has been limited by the use of autologous antigen presenting cells and the quantity and quality of these stimulator cells can vary substantially. Monocyte-derived DC from cancer patients have been reported to express reduced levels of costimulatory molecules and produce less inflammatory cytokines9,10. In fact, murine DC rather than autologous APC have been used to test the function of NKT cells from CML patients11. However, this system can only be used for in vitro testing since NKT cells cannot be expanded by murine DC and then used for adoptive immunotherapy. Thus, a standardized system that relies on artificial Antigen Presenting Cells (aAPC) could produce the stimulating effects of DC without the pitfalls of allo- or xenogeneic cells12, 13. Herein, we describe a method for generating CD1d-based aAPC. Since the engagement of the T cell receptor (TCR) by CD1d-antigen complexes is a fundamental requirement of NKT cell activation, antigen: CD1d-Ig complexes provide a reliable method to isolate, activate, and expand effector NKT cell populations.

Natural killer T (NKT) cells are a unique subset of T cells that display markers characteristic of both natural killer (NK) cells and T cells1. Unlike classical T cells, NKT cells recognize lipid antigen in the context of CD1 molecules2. NKT cells express an invariant TCRα chain rearrangement: Vα14Jα18 in mice and Vα24Jα18 in humans, which is associated with Vβ chains of limited diversity3-6, and are referred to as canonical or invariant NKT (iNKT) cells. Similar to conventional T cells, NKT cells develop from CD4-CD8- thymic precursor T cells following the appropriate signaling by CD1d 7. The potential to utilize NKT cells for therapeutic purposes has significantly increased with the ability to stimulate and expand human NKT cells with α-Galactosylceramide (α-GalCer) and a variety of cytokines8. Importantly, these cells retained their original phenotype, secreted cytokines, and displayed cytotoxic function against tumor cell lines. Thus, ex vivo expanded NKT cells remain functional and can be used for adoptive immunotherapy. However, NKT cell based-immunotherapy has been limited by the use of autologous antigen presenting cells and the quantity and quality of these stimulator cells can vary substantially. Monocyte-derived DC from cancer patients have been reported to express reduced levels of costimulatory molecules and produce less inflammatory cytokines9,10. In fact, murine DC rather than autologous APC have been used to test the function of NKT cells from CML patients11. However, this system can only be used for in vitro testing since NKT cells cannot be expanded by murine DC and then used for adoptive immunotherapy. Thus, a standardized system that relies on artificial Antigen Presenting Cells (aAPC) could produce the stimulating effects of DC without the pitfalls of allo- or xenogeneic cells12, 13. Herein, we describe a method for generating CD1d-based aAPC. Since the engagement of the T cell receptor (TCR) by CD1d-antigen complexes is a fundamental requirement of NKT cell activation, antigen: CD1d-Ig complexes provide a reliable method to isolate, activate, and expand effector NKT cell populations.

Cytokine polarized natural killer T cells modulate effector T cell function in leprosy.

Histamine (HA) is one of the most versatile biogenic amines with multiple physiological functions in the central nervous system (CNS), the respiratory and the intestinal tract due to its ability to induce severe inflammatory reactions. More recently, a number of studies have established that besides its most obvious contribution in allergic reactions, HA also exerts more subtle regulatory functions influencing the orientation of the immune response, thus rekindling interest in this field of investigation. It can influence numerous functions of the cells involved in the regulation of immune responses and hematopoiesis of macrophages, dendritic cells, T lymphocytes, B lymphocytes and endothelial cells. All these cells express histamine receptors and also secrete histamine, which can selectively recruit major effector cells into tissue sites and affect their maturation, activation, polarization, and effector functions leading to chronic inflammation. Histamine regulates antigen-specific T-helper 1 (Th1) and T-helper 2 (Th2) cells, as well as related isotype specific antibody responses. Histamine acts through its receptor called as histamine receptor (H1-H4) subtypes, which positively interferes with the peripheral antigen tolerance induced by T-regulatory cells (Tregs) through several pathways. Natural killer T (NKT) cells are the heterogeneous population of innate immune T cells that have been attracted the attention of many researchers due to their potential to regulate immune responses to a variety of pathogens, tumors, autoimmune diseases etc. A majority of NKT cells in mice are invariant NKT (iNKT) cells and are considered to be immunoregulatory in nature, due to their ability to promptly produce both Th1 and Th2 cytokines rapidly upon activation. In this chapter, we have tried to focus on HA participation in NKT cell activation by functional tuning to ensure optimal cytokine production, which leads to the recruitment and activation of other immune cells involved in inflammatory responses mediated through eosinophils, mast cells, neutrophils, conventional T lymphocytes, dendritic cells etc.

The pathogenesis of HIV-1 infection is a complex process in which Natural Killer (NK) and Natural Killer T (NKT) cells play an important role. NKT cells express markers for NK cells and a TCR of the conventional T cells and recognize lipid antigens presented by the non-polymorphic CD1 molecule. CD1d-restricted type I NKT cells express an invariant TCR and can recognize αGalCer, whereas a major subset of type II NKT expressing diverse TCR can recognize a self-glycolipid, sulfatide. It has been shown that CD4+ type I NKT cells are infected by HIV-1 and decreased in HIV-1-infected individuals. However, their exact role in HIV-1 infection as well as the biology and function of the type II NKT cell subset in HIV-1 infection and disease progression are not known. Our earlier studies have shown that activation of CD1d-restricted type II NKT cells by sulfatide and their interactions with plasmacytoid dendritic (pDC) and myeloid dendritic (mDC) cells result in anergy induction in type I NKT cells in several models. Here we used SCID-Hu (Thy/Liv) animals, co-implanted with human fetal liver and thymus, and found that these implants contain both type I and type II NKT cells, CD161+CD3+ NKT cells, NK cells and dendritic cells during HIV-infection. We found that the administration of sulfatide (bi-weekly, 20 μg/animal, i.p.) in SCID-Hu animals inhibits HIV-1 replication more efficiently than treatment with the nucleoside analog reverse transcriptase inhibitor, AZT. Virus replication was lowered significantly up to 4-8 weeks post infection. Furthermore sulfatide administration also resulted in significant retention of hematopoeisis that is lost during HIV-1 infection. Advantageously, sulfatide administration itself was not associated with anemia or bone marrow suppression, that are severe side effects of HAART. Since the CD1d-mediated immune pathway is highly conserved between rodents and humans, sulfatide treatment may represent a novel HLA-independent approach for intervention of HIV-1 pathogenesis.

Natural killer T (NKT) cell is a special type of T lymphocytes that has both receptor of natural killer (NK) cell (NK1.1, CD161c) and T cell (TCR) and express a conserved or invariant T cell receptor called in mice or Va24 in humans. Invariant NKT (iNKT) cell recognizes lipid antigen presented by CD1d molecules. Marine-sponge-derived glycolipid, -galactosylceremide (-GalCer), binds CD1d at the cell surface of antigen-presenting cells and is presented to iNKT cells. Within hours, iNKT cells become activated and start to secrete Interleukin-4 and interferon-. NKT cell prevents autoimmune diseases, such as type 1 diabetes, experimental allergic encephalomyelitis, systemic lupus erythematous, inflammatory colitis, and Graves' thyroiditis, by activation with -GalCer. In addition, NKT cell is associated with infectious diseases by mycobacteria, leshmania, and virus. Moreover NKT cell is associated with asthma, especially CD4+ iNKT cells. In this review, I will discuss the characteristics of NKT cell and the association with inflammatory diseases, especially asthma.

Function and Therapeutic Potential of In Vitro-Expanded Natural Killer T (NKT) Cells from Patients with Hematopoietic Malignancies.

Natural Killer T (NKT) cells play an important role in the immune system as demonstrated by their involvement in tumour surveillance, infection and inflammation. Unlike conventional T cells that recognises peptide antigens when presented by the Major Histocompatibility Complex (pMHC), NKT cells recognise glycolipids, presented by a MHC class I-like molecule (CD1d-α-GalCer) to invoke an immune response. Human semi-invariant NKT cells are unique as the majority of them express a T cell receptor (TCR) bearing an invariant α-chain and restricted β-chain repertoire (Vα24-Jα18;Vβ 11). The mouse orthologue also expresses an invariant α-chain (Vα14-Jα18) but a slightly more diverse β-chain repertoire (Vβ2, Vβ7 and Vβ8.2), where Vβ8.2 is most commonly expressed. The crystal structures of the human NKT TCR-CD1d-α-GalCer and mouse orthologue complexes have provided structural insights into how the NKT TCR can recognise a lipid antigen. While it is clear that the NKT TCR docks CD1d-α-GalCer in a different conformation compared to the TCR-pMHC complexes, there was no clear information on the energetic footprint of the NKT TCR's recognition of CD1d-α-GalCer and also how the NKT TCR can differentiate between closely related α-GalCer analogues to induce a biased cytokine response. In this study, an alanine scanning mutagenesis experiment carried out on the human NKT TCR (Vα24-Jα18;Vβ11) and CD1d, as well as the use of α-GalCer analogues, demonstrated that the Jα18-encoded CDR3α loop and Vβ11-encoded CDR2β loop of the NKT TCR play a crucial role in maintaining its interactions with CD1d-α-GalCer. The minimal usage of only six residues, which are also evolutionary conserved in the mouse NKT TCR (Vα14-Jα18;Vβ8.2), explains the semi-invariant nature of the NKT TCR as well as the basis of NKT cell cross-species reactivity. Furthermore, the interactions these residues made are localised directly above the F′ pocket of CD1d, distal from the galactosyl head group of α-GalCer. The use of α-GalCer analogues that contains glycosyl head group modifications, further demonstrated the lesser energetic contribution the NKT TCR CDR1α loop plays in its interactions with the sugar head group of α-GalCer. In contrast, the NKT TCR CDR3α loop, which makes interactions with α-GalCer as well as CD1d, was determined to be the key CDR loop that is energetically important in glycolipid recognition. NKT cells can differentiate between α-GalCer analogues with small modifications on their glycosyl head group to stimulate a biased T helper (Th) cytokine response. Therefore, the ability of how the mouse Vβ8.2 NKT TCR is able to distinguish between different α-GalCer analogues was further investigated through a combination of biophysical, structural and functional experiments. These data had provided further insight into how NKT cells can recognise and differentiate between structurally similar variants of α-GalCer, also referred to as Altered Glycolipid Ligands (AGLs). The crystal structures of all five NKT TCR-CD1d-AGL complexes revealed minimal structural differences. Variations in terms of affinity and kinetics of the NKT TCR engagement onto CD1d-AGLs as well as differences in cellular responses between AGLs were observed. Modifications on the glycosyl head group of the AGLs, directly impacted NKT cell activation as well as the affinity and t1/2 of the NKT TCR recognition. Furthermore, for these glycosyl head group modified AGLs, ligand potency, as determined by the amount of cytokines produced by the NKT cells, was directly affected by the t1/2 of the NKT TCR-CD1d-AGL interaction. In addition, modifications on the acyl chain of the AGLs do not affect the NKT TCR interaction but reduced NKT cell proliferation. This indicated an alternative antigen processing and presentation pathway for these AGLs by CD1d. On the other hand, truncation of the sphingosine chain resulted in a reduction of NKT TCR affinity resulting in an induced-fit mechanism by the NKT TCR. Collectively, the minimal binding requirements of CD1d restriction as well as the molecular basis of NKT fine specificity in CD1d-AGLs recognition were elucidated.

Starting Over: The Search for Endogenous NKT Cell Ligands

Both natural killer T (NKT) and natural killer (NK) cells are innate cytotoxic lymphoid cells that produce inflammatory cytokines and chemokines, and their role in the innate immune response to tumors and microorganisms has been investigated. Especially, emerging evidence has revealed their status and function in the tumor microenvironment (TME) of tumor cells. Some bacteria producing NKT cell ligands have been identified to exert antitumor effects, even in the TME. By contrast, tumor-derived lipids or metabolites may reportedly suppress NKT and NK cells in situ. Since NKT and NK cells recognize stress-inducible molecules or inhibitory molecules on cancer cells, their status or function depends on the balance between inhibitory and activating receptor signals. As a recent strategy in cancer immunotherapy, the mobilization or restoration of endogenous NKT or NK cells by novel vaccines or therapies has become a focus of research. As a new biological evidence, after activation, effector memory-type NKT cells lasted in tumor-bearing models, and NK cell-based immune checkpoint inhibition potentiated the enhancement of NK cell cytotoxicity against cancer cells in preclinical and clinical trials. Furthermore, several new modalities based on the characteristics of NKT and NK cells, including artificial adjuvant vector cells, chimeric antigen receptor-expressing NK or NKT cell therapy, or their combination with immune checkpoint blockade have been developed. This review examines challenges and future directions for improving these therapies.

CD1d-restricted natural killer T (NKT) cells, expressing the invariant T cell antigen receptor (TCR) chain encoded by Valpha14-Jalpha18 gene segments in mice and Valpha24-Jalpha18 in humans [invariant NKT (iNKT) cells], contribute to immunoregulatory processes, such as tolerance, host defense, and tumor surveillance. iNKT cells are positively selected in the thymus by CD1d molecules expressed by CD4(+)/CD8(+) cortical thymocytes. However, the identity of the endogenous lipid(s) responsible for positive selection of iNKT cells remains unclear. One candidate lipid proposed to play a role in positive selection is isoglobotrihexosylceramide (iGb3). However, no direct evidence for its physiological role has been provided. Therefore, to directly investigate the role of iGb3 in iNKT cell selection, we have generated mice deficient in iGb3 synthase [iGb3S, also known as alpha1-3galactosyltransferase 2 (A3galt2)]. These mice developed, grew, and reproduced normally and exhibited no overt behavioral abnormalities. Consistent with the notion that iGb3 is synthesized only by iGb3S, lack of iGb3 in the dorsal root ganglia of iGb3S-deficient mice (iGb3S(-/-)), as compared with iGb3S(+/-) mice, was confirmed. iGb3S(-/-) mice showed normal numbers of iNKT cells in the thymus, spleen, and liver with selected TCR Vbeta chains identical to controls. Upon administration of alpha-galactosylceramide, activation of iNKT and dendritic cells was similar in iGb3S(-/-) and iGb3S(+/-) mice, as measured by up-regulation of CD69 as well as intracellular IL-4 and IFN-gamma in iNKT cells, up-regulation of CD86 on dendritic cells, and rise in serum concentrations of IL-4, IL-6, IL-10, IL-12p70, IFN-gamma, TNF-alpha, and Ccl2/MCP-1. Our results strongly suggest that iGb3 is unlikely to be an endogenous CD1d lipid ligand determining thymic iNKT selection.