Synthetic glycolipid activators of natural killer T cells as immunotherapeutic agents

Ganglioside GM3-based anticancer vaccines: Reviewing the mechanism and current strategies

Ganglioside GM3 is one of the most common membrane-bound glycosphingolipids. The over-expression of GM3 on tumor cells makes it defined as a tumor-associated carbohydrate antigen (TACA). The specific expression property in cancers, especially in melanoma, make it become an important target to develop anticancer vaccines or immunotherapies. However, in the manner akin to most TACAs, GM3 is an autoantigen facing with problems of low immunogenicity and easily inducing immunotolerance, which means itself only cannot elicit a powerful enough immune response to prevent or treat cancer. With a comparative understanding of the mechanisms that how immune system responses to the carbohydrate vaccines, this review summarizes the studies on the recent efforts to development GM3-based anticancer vaccines.

A structural perspective of how T cell receptors recognise the CD1 family of lipid antigen-presenting molecules

The CD1 family of antigen-presenting molecules adopt a Major Histocompatibility Complex class I (MHC-I) fold. Whereas MHC molecules present peptides, the CD1 family has evolved to bind self- and foreign-lipids. The CD1 family of antigen-presenting molecules comprises four members, CD1a, CD1b, CD1c, CD1d, that differ in their architecture around the lipid-binding cleft, thereby enabling diverse lipids to be accommodated. These CD1-lipid complexes are recognised by T cell receptors (TCRs) expressed on T cells, either through dual recognition of CD1 and lipid or in a new model whereby the TCR directly contacts CD1, thereby triggering an immune response. Chemical syntheses of lipid antigens, and analogues thereof, have been crucial in understanding the underlying specificity of T cell-mediated lipid immunity. This review will focus on our current understanding of how TCRs interact with CD1-lipid complexes, highlighting how it can be fundamentally different from TCR-MHC-peptide co-recognition.

A Humanized Mouse Model Coupled with Computational Analysis Identifies Potent Glycolipid Agonist of Invariant NKT Cells

Invariant natural killer T (iNKT) cells play an important role in many innate and adaptive immune responses, with potential applications in cancer immunotherapy. The glycolipid KRN7000, an α-galactosylceramide, potently activates iNKT cells but has shown limited anticancer effects in human clinical trials conducted so far. In spite of almost three decades of structure-activity relationship studies, no alternative glycolipid has yet emerged as a superior clinical candidate. One reason for the slow progress in this area is that standard mouse models do not accurately reflect the specific ligand recognition by human iNKT cells and their requirements for activation. Here we evaluated a series of KRN7000 analogues using a recently developed humanized mouse model that expresses a human αTCR chain sequence and human CD1d. In this process, a more stimulatory, previously reported but largely overlooked glycolipid was identified, and its activity was probed and rationalized via molecular simulations.

Conformationally Restricted Analogues of α-Galactosylceramide as Adjuvant in COVID-19 Subunit Vaccine

iNKT cells are a type of T lymphocyte that recognizes glycolipid antigens presented by CD1d protein. αGC is an agonistic glycolipid that activates iNKT cells and triggers immune modulatory cytokine responses, making it a promising vaccine adjuvant. To find more potent immunostimulating glycolipids, we prepared 4,6-O-galactosyl conformationally restricted analogues of αGC. Mice vaccinated with the SARS-CoV-2 RBD-Fc vaccine adjuvanted with these newly developed glycolipids produced robust anti-RBD antibody responses, comparable to those achieved with αGC. Importantly, we also found that omitting αGC, α-C-GalCer (Th1-type agonist), or C20:2 (Th2-type agonist) from the booster vaccine had negligible impact on antibody and cellular responses, potentially reducing the frequency of adjuvant use required to maintain potent immune responses.

Small Molecule Targeting Immune Cells: A Novel Approach for Cancer Treatment

Conventional and cancer immunotherapies encompass diverse strategies to address various cancer types and stages. However, combining these approaches often encounters limitations such as non-specific targeting, resistance development, and high toxicity, leading to suboptimal outcomes in many cancers. The tumor microenvironment (TME) is orchestrated by intricate interactions between immune and non-immune cells dictating tumor progression. An innovative avenue in cancer therapy involves leveraging small molecules to influence a spectrum of resistant cell populations within the TME. Recent discoveries have unveiled a phenotypically diverse cohort of innate-like T (ILT) cells and tumor hybrid cells (HCs) exhibiting novel characteristics, including augmented proliferation, migration, resistance to exhaustion, evasion of immunosurveillance, reduced apoptosis, drug resistance, and heightened metastasis frequency. Leveraging small-molecule immunomodulators to target these immune players presents an exciting frontier in developing novel tumor immunotherapies. Moreover, combining small molecule modulators with immunotherapy can synergistically enhance the inhibitory impact on tumor progression by empowering the immune system to meticulously fine-tune responses within the TME, bolstering its capacity to recognize and eliminate cancer cells. This review outlines strategies involving small molecules that modify immune cells within the TME, potentially revolutionizing therapeutic interventions and enhancing the anti-tumor response.

Towards a better understanding of human iNKT cell subpopulations for improved clinical outcomes

Invariant natural killer T (iNKT) cells are a unique T lymphocyte population expressing semi-invariant T cell receptors (TCRs) that recognise lipid antigens presented by CD1d. iNKT cells exhibit potent anti-tumour activity through direct killing mechanisms and indirectly through triggering the activation of other anti-tumour immune cells. Because of their ability to induce potent anti-tumour responses, particularly when activated by the strong iNKT agonist αGalCer, they have been the subject of intense research to harness iNKT cell-targeted immunotherapies for cancer treatment. However, despite potent anti-tumour efficacy in pre-clinical models, the translation of iNKT cell immunotherapy into human cancer patients has been less successful. This review provides an overview of iNKT cell biology and why they are of interest within the context of cancer immunology. We focus on the iNKT anti-tumour response, the seminal studies that first reported iNKT cytotoxicity, their anti-tumour mechanisms, and the various described subsets within the iNKT cell repertoire. Finally, we discuss several barriers to the successful utilisation of iNKT cells in human cancer immunotherapy, what is required for a better understanding of human iNKT cells, and the future perspectives facilitating their exploitation for improved clinical outcomes.

Role of NKT cells in cancer immunotherapy-from bench to bed

Natural killer T (NKT) cells are a specific T cell subset known to express the αβ-T cell receptor (TCR) for antigens identification and express typical NK cell specifications, such as surface expression of CD56 and CD16 markers as well as production of granzyme. Human NKT cells are divided into two subgroups based on their cytokine receptor and TCR repertoire. Both of them are CD1-restricted and recognize lipid antigens presented by CD1d molecules. Studies have demonstrated that these cells are essential in defense against malignancies. These cells secret proinflammatory and regulatory cytokines that stimulate or suppress immune system responses. In several murine tumor models, activation of type I NKT cells induces tumor rejection and inhibits metastasis's spread. However, type II NKT cells are associated with an inhibitory and regulatory function during tumor immune responses. Variant NKT cells may suppress tumor immunity via different mechanisms that require cross-talk with other immune-regulatory cells. NKT-like cells display high tumor-killing abilities against many tumor cells. In the recent decade, different studies have been performed based on the application of NKT-based immunotherapy for cancer therapy. Moreover, manipulation of NKT cells through administering autologous dendritic cell (DC) loaded with α-galactosylceramide (α-GalCer) and direct α-GalCer injection has also been tested. In this review, we described different subtypes of NKT cells, their function in the anti-tumor immune responses, and the application of NKT cells in cancer immunotherapy from bench to bed.

A humanized mouse model for in vivo evaluation of invariant Natural Killer T cell responses

Invariant natural killer T (iNKT) cells mediate immune responses when stimulated by glycolipid agonists presented by CD1d. In extensive studies of synthetic analogues of α-galactosyl ceramides, we identified numerous examples of significant differences in the recognition of specific glycolipids in wild type mice versus human iNKT cell clones or PBMC samples. To predict human iNKT cell responses more accurately in a mouse model, we derived a mouse line in which compound genetic modifications were used to express a human-like iNKT cell TCR along with human CD1d in place of the endogenous mouse proteins. Detailed transcriptional and phenotypic profiling demonstrated that these partially humanized mice developed an expanded population of T cells recognizing CD1d-presented glycolipid antigens, among which a subset characterized by expression of chemokine receptor CXCR6 had features characteristic of authentic iNKT cells. Responses to iNKT cell activating glycolipids in these mice generated cytokine production in vitro and in vivo that showed a pattern of fine specificity that closely resembled that of cultured human iNKT cell clones. Anti-tumor responses to variants of α-galactosyl ceramide in VαKI mice also correlated with their potency for stimulating human iNKT cells. This genetically modified mouse line provides a practical model for human presentation and recognition of iNKT cell activators in the context of a normally functioning immune system, and may furnish valuable opportunities for preclinical evaluation of iNKT cell-based therapies.

Antibiotics and Carbohydrate-Containing Drugs Targeting Bacterial Cell Envelopes: An Overview

Certain bacteria constitute a threat to humans due to their ability to escape host defenses as they easily develop drug resistance. Bacteria are classified into gram-positive and gram-negative according to the composition of the cell membrane structure. Gram-negative bacteria have an additional outer membrane (OM) that is not present in their gram-positive counterpart; the latter instead hold a thicker peptidoglycan (PG) layer. This review covers the main structural and functional properties of cell wall polysaccharides (CWPs) and PG. Drugs targeting CWPs are discussed, both noncarbohydrate-related (β-lactams, fosfomycin, and lipopeptides) and carbohydrate-related (glycopeptides and lipoglycopeptides). Bacterial resistance to these drugs continues to evolve, which calls for novel antibacterial approaches to be developed. The use of carbohydrate-based vaccines as a valid strategy to prevent bacterial infections is also addressed.

Harnessing invariant natural killer T cells to control pathological inflammation

Invariant natural killer T (iNKT) cells are innate T cells that are recognized for their potent immune modulatory functions. Over the last three decades, research in murine models and human observational studies have revealed that iNKT cells can act to limit inflammatory pathology in a variety of settings. Since iNKT cells are multi-functional and can promote inflammation in some contexts, understanding the mechanistic basis for their anti-inflammatory effects is critical for effectively harnessing them for clinical use. Two contrasting mechanisms have emerged to explain the anti-inflammatory activity of iNKT cells: that they drive suppressive pathways mediated by other regulatory cells, and that they may cytolytically eliminate antigen presenting cells that promote excessive inflammatory responses. How these activities are controlled and separated from their pro-inflammatory functions remains a central question. Murine iNKT cells can be divided into four functional lineages that have either pro-inflammatory (NKT1, NKT17) or anti-inflammatory (NKT2, NKT10) cytokine profiles. However, in humans these subsets are not clearly evident, and instead most iNKT cells that are CD4⁺ appear oriented towards polyfunctional (T_H0) cytokine production, while CD4^- iNKT cells appear more predisposed towards cytolytic activity. Additionally, structurally distinct antigens have been shown to induce T_H1- or T_H2-biased responses by iNKT cells in murine models, but human iNKT cells may respond to differing levels of TCR stimulation in a way that does not neatly separate T_H1 and T_H2 cytokine production. We discuss the implications of these differences for translational efforts focused on the anti-inflammatory activity of iNKT cells.

The role of lymphocytes in neonatal encephalopathy

Neonatal encephalopathy is a syndrome characterised by abnormal neurological function often caused by a hypoxic insult during childbirth. Triggers such as hypoxia-ischaemia result in the release of cytokines and chemokines inducing the infiltration of neutrophils, natural killer cells, B cells, T cells and innate T cells into the brain. However, the role of these cells in the development of the brain injury is poorly understood. We review the mechanisms by which lymphocytes contribute to brain damage in NE. NK, T and innate T cells release proinflammatory cytokines contributing to the neurodegeneration in the secondary and tertiary phase of injury, whereas B cells and regulatory T cells produce IL-10 protecting the brain in NE. Targeting lymphocytes may have therapeutic potential in the treatment of NE in terms of management of inflammation and brain damage, particularly in the tertiary or persistent phases.

Natural Killer T (NKT) Cells and Periodontitis: Potential Regulatory Role of NKT10 Cells

Natural killer T (NKT) cells constitute a unique subset of T lymphocytes characterized by specifically interacting with antigenic glycolipids conjugated to the CD1d receptor on antigen-presenting cells. Functionally, NKT cells are capable of performing either effector or suppressor immune responses, depending on their production of proinflammatory or anti-inflammatory cytokines, respectively. Effector NKT cells are subdivided into three subsets, termed NKT1, NKT2, and NKT17, based on the cytokines they produce and their similarity to the cytokine profile produced by Th1, Th2, and Th17 lymphocytes, respectively. Recently, a new subgroup of NKT cells termed NKT10 has been described, which cooperates and interacts with other immune cells to promote immunoregulatory responses. Although the tissue-specific functions of NKT cells have not been fully elucidated, their activity has been associated with the pathogenesis of different inflammatory diseases with immunopathogenic similarities to periodontitis, including osteolytic pathologies such as rheumatoid arthritis and osteoporosis. In the present review, we revise and discuss the pathogenic characteristics of NKT cells in these diseases and their role in the pathogenesis of periodontitis; particularly, we analyze the potential regulatory role of the IL-10-producing NKT10 cells.

The interaction between iNKT cells and B cells

Invariant natural killer T cells (iNKTs) bridge the innate immunity with the adaptive immunity and their interaction with B cells has been extensively studied. Here, we give a complete overview of these two cells, from their mechanism of interaction to clinical prospects and existing problems. In our introduction, we describe the relationship between iNKTs and B cells and explore the current research hotspots and future directions. We begin with how B cells interact and benefit from the innate and adaptive help of iNKTs. Next, we describe the multiple roles of these cells in infections, autoimmunity, and cancers. Lastly, we look into the potential immunotherapies that can be based on iNKTs and the possible treatments for infectious, autoimmune, and other diseases.

Harnessing NKT cells for vaccination

Natural killer T (NKT) cells are innate-like T cells capable of enhancing both innate and adaptive immune responses. When NKT cells are stimulated in close temporal association with co-administered antigens, strong antigen-specific immune responses can be induced, prompting the study of NKT cell agonists as novel immune adjuvants. This activity has been attributed to the capacity of activated NKT cells to act as universal helper cells, with the ability to provide molecular signals to dendritic cells and B cells that facilitate T cell and antibody responses, respectively. These signals can override the requirement for conventional CD4⁺ T cell help, so that vaccines can be designed without need to consider CD4⁺ T cell repertoire and major histocompatibility complex Class II diversity. Animal studies have highlighted some drawbacks of the approach, namely, concerns around induction of NKT cell hyporesponsiveness, which may limit vaccine boosting, and potential for toxicity. Here we highlight studies that suggest these obstacles can be overcome by targeted delivery in vivo. We also feature new studies that suggest activating NKT cells can help encourage differentiation of T cells into tissue-resident memory cells that play an important role in prophylaxis against infection, and may be required in cancer therapy.

Type I Natural Killer T Cells as Key Regulators of the Immune Response to Infectious Diseases

The immune system must work in an orchestrated way to achieve an optimal response upon detection of antigens. The cells comprising the immune response are traditionally divided into two major subsets, innate and adaptive, with particular characteristics for each type. Type I natural killer T (iNKT) cells are defined as innate-like T cells sharing features with both traditional adaptive and innate cells, such as the expression of an invariant T cell receptor (TCR) and several NK receptors. The invariant TCR in iNKT cells interacts with CD1d, a major histocompatibility complex class I (MHC-I)-like molecule. CD1d can bind and present antigens of lipid nature and induce the activation of iNKT cells, leading to the secretion of various cytokines, such as gamma interferon (IFN-γ) and interleukin 4 (IL-4). These cytokines will aid in the activation of other immune cells following stimulation of iNKT cells. Several molecules with the capacity to bind to CD1d have been discovered, including α-galactosylceramide. Likewise, several molecules have been synthesized that are capable of polarizing iNKT cells into different profiles, either pro- or anti-inflammatory. This versatility allows NKT cells to either aid or impair the clearance of pathogens or to even control or increase the symptoms associated with pathogenic infections. Such diverse contributions of NKT cells to infectious diseases are supported by several publications showing either a beneficial or detrimental role of these cells during diseases. In this article, we discuss current data relative to iNKT cells and their features, with an emphasis on their driving role in diseases produced by pathogenic agents in an organ-oriented fashion.

Allogeneic CAR T Cells: An Alternative to Overcome Challenges of CAR T Cell Therapy in Glioblastoma

Chimeric antigen receptor (CAR) T cell therapy has emerged as one of the major breakthroughs in cancer immunotherapy in the last decade. Outstanding results in hematological malignancies and encouraging pre-clinical anti-tumor activity against a wide range of solid tumors have made CAR T cells one of the most promising fields for cancer therapies. CAR T cell therapy is currently being investigated in solid tumors including glioblastoma (GBM), a tumor for which survival has only modestly improved over the past decades. CAR T cells targeting EGFRvIII, Her2, or IL-13Rα2 have been tested in GBM, but the first clinical trials have shown modest results, potentially due to GBM heterogeneity and to the presence of an immunosuppressive microenvironment. Until now, the use of autologous T cells to manufacture CAR products has been the norm, but this approach has several disadvantages regarding production time, cost, manufacturing delay and dependence on functional fitness of patient T cells, often reduced by the disease or previous therapies. Universal “off-the-shelf,” or allogeneic, CAR T cells is an alternative that can potentially overcome these issues, and allow for multiple modifications and CAR combinations to target multiple tumor antigens and avoid tumor escape. Advances in genome editing tools, especially via CRISPR/Cas9, might allow overcoming the two main limitations of allogeneic CAR T cells product, i.e., graft-vs.-host disease and host allorejection. Here, we will discuss how allogeneic CAR T cells could allow for multivalent approaches and alteration of the tumor microenvironment, potentially allowing the development of next generation therapies for the treatment of patients with GBM.

Serial Stimulation of Invariant Natural Killer T Cells with Covalently Stabilized Bispecific T-cell Engagers Generates Antitumor Immunity While Avoiding Anergy

CD1d-restricted invariant natural killer T cells (iNKT cells) mediate strong antitumor immunity when stimulated by glycolipid agonists. However, attempts to develop effective iNKT cell agonists for clinical applications have been thwarted by potential problems with dose-limiting toxicity and by activation-induced iNKT cell anergy, which limits the efficacy of repeated administration. To overcome these issues, we developed a unique bispecific T-cell engager (BiTE) based on covalent conjugates of soluble CD1d with photoreactive analogues of the glycolipid α-galactosylceramide. Here we characterize the in vivo activities of iNKT cell-specific BiTEs and assess their efficacy for cancer immunotherapy in mouse models using transplantable colorectal cancer or melanoma tumor lines engineered to express human Her2 as a tumor-associated antigen. Systemic administration of conjugated BiTEs stimulated multiple iNKT cell effector functions including cytokine release, secondary activation of NK cells, and induction of dendritic cell maturation and also initiated epitope spreading for tumor-specific CD8⁺ cytolytic T-cell responses. The antitumor effects of iNKT-cell activation with conjugated BiTEs were further enhanced by simultaneous checkpoint blockade with antibodies to CTLA-4, providing a potential approach for combination immunotherapy. Multiple injections of covalently stabilized iNKT cell-specific BiTEs activated iNKT cells without causing iNKT cell anergy or exhaustion, thus enabling repeated administration for effective and nontoxic cancer immunotherapy regimens. SIGNIFICANCE: Covalently stabilized conjugates that engage the antigen receptors of iNKT cells and target a tumor antigen activate potent antitumor immunity without induction of anergy or depletion of the responding iNKT cells.

Natural and synthetic carbohydrate-based vaccine adjuvants and their mechanisms of action

Modern subunit vaccines based on homogeneous antigens offer more precise targeting and improved safety compared with traditional whole-pathogen vaccines. However, they are also less immunogenic and require an adjuvant to increase the immunogenicity of the antigen and potentiate the immune response. Unfortunately, few adjuvants have sufficient potency and low enough toxicity for clinical use, highlighting the urgent need for new, potent and safe adjuvants. Notably, a number of natural and synthetic carbohydrate structures have been used as adjuvants in clinical trials, and two have recently been approved in human vaccines. However, naturally derived carbohydrate adjuvants are heterogeneous, difficult to obtain and, in some cases, unstable. In addition, their molecular mechanisms of action are generally not fully understood, partly owing to the lack of tools to elucidate their immune-potentiating effects, thus hampering the rational development of optimized adjuvants. To address these challenges, modification of the natural product structure using synthetic chemistry emerges as an attractive approach to develop well-defined, improved carbohydrate-containing adjuvants and chemical probes for mechanistic investigation. This Review describes selected examples of natural and synthetic carbohydrate-based adjuvants and their application in synthetic self-adjuvanting vaccines, while also discussing current understanding of their molecular mechanisms of action.

Amide-Linked C4″-Saccharide Modification of KRN7000 Provides Potent Stimulation of Human Invariant NKT Cells and Anti-Tumor Immunity in a Humanized Mouse Model

Activation of invariant natural killer T (iNKT) cells by α-galactosylceramides (α-GalCers) stimulates strong immune responses and potent anti-tumor immunity. Numerous modifications of the glycolipid structure have been assessed to derive activating ligands for these T cells with altered and potentially advantageous properties in the induction of immune responses. Here, we synthesized variants of the prototypical α-GalCer, KRN7000, with amide-linked phenyl alkane substitutions on the C4″-position of the galactose ring. We show that these variants have weak iNKT cell stimulating activity in mouse models but substantially greater activity for human iNKT cells. The most active of the C4″-amides in our study showed strong anti-tumor effects in a partially humanized mouse model for iNKT cell responses. In silico analysis suggested that the tether length and degree of flexibility of the amide substituent affected the recognition by iNKT cell antigen receptors of the C4″-amide substituted glycolipids in complex with their antigen presenting molecule CD1d. Our findings establish the use of stable C4″-amide linked additions to the sugar moiety for further exploration of the immunological effects of structural modifications of iNKT cell activating glycolipids and highlight the critical need for more accurate animal models to assess these compounds for immunotherapeutic potential in humans.

Using agonists for iNKT cells in cancer therapy

The capacity of α-galactosylceramide (α-GalCer) to act as an anti-cancer agent in mice through the specific stimulation of type I NKT (iNKT) cells has prompted extensive investigation to translate this finding to the clinic. However, low frequencies of iNKT cells in cancer patients and their hypo-responsiveness to repeated stimulation have been seen as barriers to its efficacy. Currently the most promising clinical application of α-GalCer, or its derivatives, is as stimuli for ex vivo expansion of iNKT cells for adoptive therapy, although some encouraging clinical results have recently been reported using α-GalCer pulsed onto large numbers of antigen presenting cells (APCs). In on-going preclinical studies, attempts to improve efficacy of injected iNKT cell agonists have focussed on optimising presentation in vivo, through encapsulation in particulate vectors, making structural changes that help binding to the presenting molecule CD1d, or injecting agonists covalently attached to recombinant CD1d. Variations on these same approaches are being used to enhance the APC-licencing function of iNKT cells in vivo to induce adaptive immune responses to associated tumour antigens. Looking ahead, a unique capacity of in vivo-activated iNKT cells to facilitate formation of resident memory CD8⁺ T cells is a new observation that could find a role in cancer therapy.

Natural Killer T-Cell Agonist α-Galactosylceramide and PD-1 Blockade Synergize to Reduce Tumor Development in a Preclinical Model of Colon Cancer

Murine and human invariant natural killer T (iNKT) lymphocytes are activated by α-galactosylceramide (α-GalCer) presented on CD1d. α-GalCer was first described as a lipid that had strong anti-metastatic effects in a mouse melanoma model, and it has subsequently been shown to induce efficient iNKT cell dependent tumor immunity in several tumor models. We have shown that α-GalCer treatment leads to a weak reduction of polyp burden in the autochthonous Apc^Min/+ mouse model for human colon cancer, however this treatment resulted in upregulation of the inhibitory receptor PD-1 on iNKT cells. While anti-PD-1 treatment can prevent immune-suppression in other cancer types, human colon cancer is generally resistant to this treatment. Here we have used the Apc^Min/+ model to investigate whether a combined treatment with α-GalCer and PD-1 blockade results in improved effects on polyp development. We find that PD-1 expression was high on T cells in polyps and lamina propria (LP) of Apc^Min/+ mice compared to polyp free ^Apc+/+ littermates. Anti-PD-1 treatment alone promoted Tbet expression in iNKT cells and CD4 T cells, but did not significantly reduce polyp numbers. However, the combined treatment with anti-PD-1 and α-GalCer had synergistic effects, resulting in highly significant reduction of polyp numbers in the small and large intestine. Addition of PD-1 blockade to α-GalCer treatment prevented loss of iNKT cells that were skewed towards a TH1-like iNKT1 phenotype specifically in polyps. It also resulted in TH1 skewing and increased granzyme B expression of CD4 T cells. Taken together this demonstrates that a combination of immune stimulation targeting iNKT cells and checkpoint blockade may be a promising approach to develop for improved tumor immunotherapy.

Recent advances in the mass spectrometric analysis of glycosphingolipidome - A review

Aberrant expression of glycosphingolipids has been implicated in a myriad of diseases, but our understanding of the strucural diversity, spatial distribution, and biological function of this class of biomolecules remains limited. These challenges partly stem from a lack of sensitive tools that can detect, identify, and quantify glycosphingolipids at the molecular level. Mass spectrometry has emerged as a powerful tool poised to address most of these challenges. Here, we review the recent developments in analytical glycosphingolipidomics with an emphasis on sample preparation, mass spectrometry and tandem mass spectrometry-based structural characterization, label-free and labeling-based quantification. We also discuss the nomenclature of glycosphingolipids, and emerging technologies like ion mobility spectrometry in differentiation of glycosphingolipid isomers. The intrinsic advantages and shortcomings of each method are carefully critiqued in line with an individual's research goals. Finally, future perspectives on analytical sphingolipidomics are stated, including a need for novel and more sensive methods in isomer separation, low abundance species detection, and profiling the spatial distribution of glycosphingolipid molecular species in cells and tissues using imaging mass spectrometry.

Host defense mechanisms against Mycobacterium tuberculosis

Tuberculosis (TB), which is caused by Mycobacterium tuberculosis (Mtb), remains the leading cause of death worldwide from a single infectious pathogen. Mtb is a paradigmatic intracellular pathogen that primarily invades the lungs after host inhalation of bacteria-containing droplets via the airway. However, the majority of Mtb-exposed individuals can spontaneously control the infection by virtue of a robust immune defense system. The mucosal barriers of the respiratory tract shape the first-line defense against Mtb through various mucosal immune responses. After arriving at the alveoli, the surviving mycobacteria further encounter a set of host innate immune cells that exert multiple cellular bactericidal functions. Adaptive immunity, predominantly mediated by a range of different T cell and B cell subsets, is subsequently activated and participates in host anti-mycobacterial defense. During Mtb infection, host bactericidal immune responses are exquisitely adjusted and balanced by multifaceted mechanisms, including genetic and epigenetic regulation, metabolic regulation and neuroendocrine regulation, which are indispensable for maintaining host immune efficiency and avoiding excessive tissue injury. A better understanding of the integrated and equilibrated host immune defense system against Mtb will contribute to the development of rational TB treatment regimens especially novel host-directed therapeutics.

Immunology of carbohydrate-based vaccines

Carbohydrates are considered as promising targets for vaccine development against infectious diseases where cell surface glycan's on many infectious agents are attributed to playing an important role in pathogenesis. Understanding the relationship between carbohydrates and immune components at a molecular level is crucial for the development of well-defined vaccines. Recently, carbohydrate immunology research has been accelerated by the development of new technologies that contribute to the design of optimum antigens, synthesis of antigens and the studies of antigen-antibody interactions, and as a result, several promising carbohydrate-based vaccine candidates have been prepared in recent years. This article briefly presents the mechanistic pathways of polysaccharide, glycoconjugate, glycolipid and zwitterionic vaccines and the interplay between carbohydrate antigen and immune response.

A glycolipid adjuvant, 7DW8-5, provides a protective effect against colonic inflammation in mice by the recruitment of CD1d-restricted natural killer T cells

Background/Aims

The modulation of CD1d-restricted natural killer T (NKT) cells by glycolipids has been considered as a potential therapy against immunologic diseases, including inflammatory bowel disease. A recently identified a glycolipid analog, 7DW8-5, which is derived from α-galactosylceramide (α-GalCer), is as much as 100-fold more active at stimulating both human and mice NKT cells when compared to α-GalCer. We explored the effects of 7DW8-5 in mouse models of acute and chronic colitis.

Methods

We investigated the effects of 7DW8-5 on intestinal inflammation by assessing the effects of 7dW8-5 on a murine dextran sulfate sodium (DSS)-induced acute colitis model and a chronic colitis-associated tumor model.

Results

The acute DSS-induced colitis model showed a dose-dependent response to 7DW8-5, as mice administered 7DW8-5 showed a significant improvement in DSS-induced colitis based on their disease activity index, histologic analysis, and serum C-reactive protein levels, when compared to mice administered vehicle alone. However, DSS-induced colitis in CD1d-KO mice showed no response to 7DW8-5. A fluorescence-activating cell sorting analysis revealed an increase in NKT cells in colonic tissues of 7DW8-5-treated mice. RNA-seq and real-time quantitative polymerase chain reaction showed a significant increase in the expression of interleukin (IL)-4, IL-13, and interferon-gamma in 7DW8-5-treated mice. In addition, 7DW8-5 treatment reduced colitis-associated tumor development in an azoxymethane/DSS mouse model.

Conclusions

7DW8-5 activates NKT cells through CD1d and provides a protective effect against intestinal inflammation in mice. Therefore, 7DW8-5 may be a promising therapeutic agent for treatment of inflammatory bowel disease.

Decreased invariant natural killer T-cell-mediated antitumor immune response in patients with gastric cancer

Gastric cancer (GC) is the third most common cause of cancer-related death worldwide. Invariant natural killer T (iNKT) cells are innate-like cytotoxic T lymphocytes involved in tumor immune surveillance. They can be activated either through CD1d-presented glycolipid antigens recognized by their invariant T-cell receptor, cytokines or by sensing tumor-associated stress-induced ligands through the natural killer group 2, member D (NKG2D) receptor. Although the number and functionality of iNKT cells may be decreased in several types of cancer, here we show that GC patients presented a mild increase in iNKT cell frequencies and numbers in the blood compared with healthy donors. In GC patients, iNKT cells, expanded in vitro with α-galactosyl ceramide and stimulated with phorbol 12-myristate 13-acetate and ionomycin, produced higher levels of interleukin-2 and transforming growth factor-beta, while their capacity to degranulate remained preserved. Because tumor-derived epithelial cell adhesion molecule-positive epithelial cells did not display surface CD1d, and NKG2D ligands (NKG2DLs) were detected in the gastric tumor milieu, we envisioned a role for NKG2D in iNKT cell functions. Peripheral iNKT cells from GC patients and controls presented similar levels of NKG2D; nevertheless, the percentages of interferon-γ-producing and CD107a-positive iNKT cells from patients were reduced upon challenge with CD1d-negative, NKG2DL-positive K562 cells, suggesting a compromised response by iNKT cells in GC patients, which may not result from impaired NKG2D/NKG2DL signaling. The decreased response of iNKT cells may explain the fact that higher frequencies of circulating iNKT cells did not confer a survival benefit for GC patients. Therefore, functional impairment of iNKT cells in GC may contribute to tumor immune escape and favor disease progression.

Gut dysbiosis and multiple sclerosis

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) and T cell-mediated autoimmune processes are assumed to be involved in its pathogenesis. Recently, accumulating evidence has indicated that commensal bacteria interact with the host immune system and that the alteration of commensal bacteria composition, termed dysbiosis, is associated with various autoimmune diseases including CNS autoimmune diseases. In this review, we introduce recent findings regarding the association between gut microbiota and MS and related diseases and microbiota function in an animal model of MS.

Synthesis and biological activities of amino acids functionalized α-GalCer analogues

Invariant natural killer T-cells (iNKT-cells) are promising targets for manipulating the immune system, which can rapidly release a large amount of Th1 and Th2 cytokines upon the engagement of their T cell receptor with glycolipid antigens presented by CD1d. In this paper, we wish to report a novel series of α-GalCer analogues which were synthesized by incorporation of l-amino acid methyl esters in the C-6' position of glycolipid. The evaluation of these synthetic analogues for their capacities to stimulate iNKT-cells into producing Th1 and Th2 cytokines both in vitro and in vivo indicated that they were potent CD1d ligands and could stimulate murine spleen cells into a higher release of the Th1 cytokine IFN-γ in vitro. In vivo, Gly-α-GalCer (1) and Lys-α-GalCer (3) showed more Th1-biased responses than α-GalCer, especially analogue 3 showed the highest selectivity for IFN-γ production (IFN-γ/IL-4 = 5.32) compared with α-GalCer (IFN-γ/IL-4 = 2.5) in vivo. These novel α-GalCer analogues might be used as efficient X-ray crystallographic probes to reveal the relationship between glycolipids and CD1d proteins in α-GalCer/CD1d complexes and pave the way for developing new potent immunostimulating agents.

α-Lactosylceramide Protects Against iNKT-Mediated Murine Airway Hyperreactivity and Liver Injury Through Competitive Inhibition of Cd1d Binding

Invariant natural killer T (iNKT) cells, which are activated by T cell receptor (TCR)-dependent recognition of lipid-based antigens presented by the CD1d molecule, have been shown to participate in the pathogenesis of many diseases, including asthma and liver injury. Previous studies have shown the inhibition of iNKT cell activation using lipid antagonists can attenuate iNKT cell-induced disease pathogenesis. Hence, the development of iNKT cell-targeted glycolipids can facilitate the discovery of new therapeutics. In this study, we synthesized and evaluated α-lactosylceramide (α-LacCer), an α-galactosylceramide (α-GalCer) analog with lactose substitution for the galactose head and a shortened acyl chain in the ceramide tail, toward iNKT cell activation. We demonstrated that α-LacCer was a weak inducer for both mouse and human iNKT cell activation and cytokine production, and the iNKT induction by α-LacCer was CD1d-dependent. However, when co-administered with α-GalCer, α-LacCer inhibited α-GalCer-induced IL-4 and IFN-γ production from iNKT cells. Consequently, α-LacCer also ameliorated both α-GalCer and GSL-1-induced airway hyperreactivity and α-GalCer-induced neutrophilia when co-administered in vivo. Furthermore, we were able to inhibit the increases of ConA-induced AST, ALT and IFN-γ serum levels through α-LacCer pre-treatment, suggesting α-LacCer could protect against ConA-induced liver injury. Mechanistically, we discerned that α-LacCer suppressed α-GalCer-stimulated cytokine production through competing for CD1d binding. Since iNKT cells play a critical role in the development of AHR and liver injury, the inhibition of iNKT cell activation by α-LacCer present a possible new approach in treating iNKT cell-mediated diseases.

A molecular switch in mouse CD1d modulates natural killer T cell activation by α-galactosylsphingamides

Type I natural killer T (NKT) cells are a population of innate like T lymphocytes that rapidly respond to α-GalCer presented by CD1d via the production of both pro- and anti-inflammatory cytokines. While developing novel α-GalCer analogs that were meant to be utilized as potential adjuvants because of their production of pro-inflammatory cytokines (Th1 skewers), we generated α-galactosylsphingamides (αGSA). Surprisingly, αGSAs are not potent antigens in vivo despite their strong T-cell receptor (TCR)-binding affinities. Here, using surface plasmon resonance (SPR), antigen presentation assays, and X-ray crystallography (yielding crystal structures of 19 different binary (CD1d-glycolipid) or ternary (CD1d-glycolipid-TCR) complexes at resolutions between 1.67 and 2.85 Å), we characterized the biochemical and structural details of αGSA recognition by murine NKT cells. We identified a molecular switch within murine (m)CD1d that modulates NKT cell activation by αGSAs. We found that the molecular switch involves a hydrogen bond interaction between Tyr-73 of mCD1d and the amide group oxygen of αGSAs. We further established that the length of the acyl chain controls the positioning of the amide group with respect to the molecular switch and works synergistically with Tyr-73 to control NKT cell activity. In conclusion, our findings reveal important mechanistic insights into the presentation and recognition of glycolipids with polar moieties in an otherwise apolar milieu. These observations may inform the development αGSAs as specific NKT cell antagonists to modulate immune responses.

Synthesis of polyfluoroalkyl sp2-iminosugar glycolipids and evaluation of their immunomodulatory properties towards anti-tumor, anti-leishmanial and anti-inflammatory therapies

Immunomodulatory glycolipids, among which α-galactosylceramide (KRN7000) is an iconic example, have shown strong therapeutic potential in a variety of conditions ranging from cancer and infection to autoimmune or neurodegenerative diseases. A main difficulty for those channels is that they often provoke a cytokine storm comprising both pro- and anti-inflammatory mediators that antagonize each other and negatively affect the immune response. The synthesis of analogues with narrower cytokine secretion-inducing capabilities is hampered by the intrinsic difficulty at controlling the stereochemical outcome in glycosidation reactions, particularly if targeting the α-anomer, which seriously hampers drug optimization strategies. Here we show that replacing the monosaccharide glycone by a sp²-iminosugar glycomimetic moiety allows accessing N-linked sp²-iminosugar glycolipids (sp²-IGLs) with total α-stereocontrol in a single step with no need of protecting groups or glycosidation promotors. The lipid tail has been then readily tailored by incorporating polyfluoroalkyl segments of varied lengths in view of favouring binding to the lipid binding site of the master p38 mitogen activated protein kinase (p38 MAPK), thereby polarizing the immune response in a cell-context dependent manner. The compounds have been evaluated for their antiproliferative, anti-leishmanial and anti-inflammatory activities in different cell assays. The size of the fluorous segment was found to be critical for the biological activity, probably by regulating the aggregation and membrane-crossing properties, whereas the hydroxylation profile (gluco or galacto-like) was less relevant. Biochemical and computational data further support a mechanism of action implying binding to the allosteric lipid binding site of p38 MAPK and subsequent activation of the noncanonical autophosphorylation route. The ensemble of results provide a proof of concept of the potential of sp²-IGLs as immunoregulators.

Defining a novel subset of CD1d-dependent type II natural killer T cells using natural killer cell-associated markers

Natural killer T (NKT) cells are αβ T cell receptor (TCR) expressing innate‐like T cells that display natural killer (NK) cell markers. Based on TCR characteristics, they are divided into two groups restricted to the MHC class I‐like molecule CD1d. Type I NKT cells, most extensively studied, are identified by a semi‐invariant Vα14‐Jα18 (mouse, Vα24‐Jα18 in humans) TCR reactive to the prototypic ligand α‐galactosylceramide presented on CD1d. In contrast, type II NKT cells display diverse TCR reacting to different CD1d‐presented ligands. There are no reagents that identify all type II NKT cells, limiting their exploration. Here, we searched for novel type II NKT cells by comparing Jα18^−/−MHCII^−/− mice that harbour type II but not type I NKT cells, and CD1d^−/−MHCII^−/− mice, lacking all NKT cells. We identified significantly larger populations of CD4⁺ and CD4⁻CD8⁻ (double negative, DN) TCRβ⁺ cells expressing NKG2D or NKG2A/C/E in Jα18^−/−MHCII^−/− mice compared with CD1d^−/−MHCII^−/− mice, suggesting that 30%‐50% of these cells were type II NKT cells. They expressed CD122, NK1.1, CXCR3 and intermediate/low levels of CD45RB. Further, the CD4⁺ subset was CD69⁺, while the DN cells were CD49b⁺ and CD62L⁺. Both subsets expressed the NKT cell‐associated promyelocytic leukaemia zinc finger (PLZF) transcription factor and Tbet, while fewer cells expressed RORγt. NKG2D⁺ CD4⁺ and DN populations were producers of IFN‐γ, but rarely IL‐4 and IL‐17. Taken together, we identify a novel subset of primary CD4⁺ and DN type II NKT cells that expresses NKG2 receptors have typical NKT cell phenotypes and a TH1‐like cytokine production.

Promotion or Suppression of Murine Intestinal Polyp Development by iNKT Cell Directed Immunotherapy

The glycosphingolipid α-galactosylceramide (α-GalCer) is a well-described immune activator with strong anti-tumor properties in animal models. It is presented on CD1d and acts by stimulating the invariant, type I, natural killer T (iNKT) lymphocytes to rapidly secrete TH1 and TH2 associated cytokines. This in turn promotes activation of a diversity of immune cells including natural killer (NK) cells with anti-tumor functions. Prior to tumor development, iNKT cells can also perform tumor surveillance and naturally protect from emergence of cancer. In contrast, we have recently demonstrated that iNKT cells naturally promote polyps in the spontaneous murine adenomatous polyposis coli (Apc) Apc^Min/+ model for colon cancer, associated with suppressed TH1 immunity and enhanced immunoregulation. Here we investigated whether iNKT cell directed immunotherapy could subvert the polyp promoting function of iNKT cells and reduce polyp growth in this model. We treated Apc^Min/+ mice with α-GalCer, or synthetic derivatives of this ligand (C-glycoside and C20:2) that have enhanced immunoregulatory properties. Treatment with iNKT cell ligands led to increased iNKT cell division, but reduced iNKT cell frequencies, lower NK1.1 expression and elevation of PD-1. Apc^Min/+ mice that had been treated either long-term (5–15 weeks of age), or short-term (12–15 weeks of age) with α-GalCer demonstrated a significant decrease in polyp burden. Surprisingly, long-term treatment with the TH1 biasing ligand C-glycoside did not have significant effects on polyps, while long-term treatment with the TH2 biasing ligand C20:2 enhanced polyp growth. In stark contrast, short-term treatment with C20:2 led to reduction in polyp numbers and size. Reduced polyp burden after long-term treatment was associated with increased expression of genes indicating a pro-inflammatory polyp microenvironment. Polyp-reducing short-term treatment led to CD8 T cell activation specifically in polyps, and decreased tumor infiltrating and splenic macrophages, and a switch toward a pro-inflammatory phenotype. Thus, iNKT cell directed therapy could subvert the natural polyp enhancing function of iNKT cells, overcome immunosuppression, and reduce polyps. However, different iNKT cell activating ligands had opposite effects, and the timing of treatment had a major influence on outcomes.

Photoactivable Glycolipid Antigens Generate Stable Conjugates with CD1d for Invariant Natural Killer T Cell Activation

Activation of invariant natural killer T lymphocytes (iNKT cells) by α-galactosylceramide (α-GC) elicits a range of pro-inflammatory or anti-inflammatory immune responses. We report the synthesis and characterization of a series of α-GC analogues with acyl chains of varying length and a terminal benzophenone. These bound efficiently to the glycolipid antigen presenting protein CD1d, and upon photoactivation formed stable CD1d-glycolipid covalent conjugates. Conjugates of benzophenone α-GCs with soluble or cell-bound CD1d proteins retained potent iNKT cell activating properties, with biologic effects that were modulated by acyl chain length and the resulting affinities of conjugates for iNKT cell antigen receptors. Analysis by mass spectrometry identified a unique covalent attachment site for the glycolipid ligands in the hydrophobic ligand binding pocket of CD1d. The creation of covalent conjugates of CD1d with α-GC provides a new tool for probing the biology of glycolipid antigen presentation, as well as opportunities for developing effective immunotherapeutics.

CD1d-Invariant Natural Killer T Cell-Based Cancer Immunotherapy: α-Galactosylceramide and Beyond

CD1d-restricted invariant natural killer T (iNKT) cells are considered an attractive target for cancer immunotherapy. Upon their activation by glycolipid antigen and/or cytokines, iNKT cells can induce direct lysis of tumor cells but can also induce an antitumor immune response via their rapid production of proinflammatory cytokines that trigger the cytotoxic machinery of other components of the innate and adaptive immune system. Here, we provide an overview of various therapeutic approaches that have been evaluated or that are currently being developed and/or explored. These include administration of α-GalCer or alternative (glyco) lipid antigens, glycolipid-loaded antigen-presenting cells and liposomes, strategies that enhance CD1d expression levels or are based on ligation of CD1d, adoptive transfer of iNKT cells or chimeric antigen receptor iNKT cells, and tumor targeting of iNKT cells.

Insights Into Mucosal-Associated Invariant T Cell Biology From Studies of Invariant Natural Killer T Cells

Mucosal-associated invariant T (MAIT) cells and invariant natural killer T (iNKT) cells are innate-like T cells that function at the interface between innate and adaptive immunity. They express semi-invariant T cell receptors (TCRs) and recognize unconventional non-peptide ligands bound to the MHC Class I-like molecules MR1 and CD1d, respectively. MAIT cells and iNKT cells exhibit an effector-memory phenotype and are enriched within the liver and at mucosal sites. In humans, MAIT cell frequencies dwarf those of iNKT cells, while in laboratory mouse strains the opposite is true. Upon activation via TCR- or cytokine-dependent pathways, MAIT cells and iNKT cells rapidly produce cytokines and show direct cytotoxic activity. Consequently, they are essential for effective immunity, and alterations in their frequency and function are associated with numerous infectious, inflammatory, and malignant diseases. Due to their abundance in mice and the earlier development of reagents, iNKT cells have been more extensively studied than MAIT cells. This has led to the routine use of iNKT cells as a reference population for the study of MAIT cells, and such an approach has proven very fruitful. However, MAIT cells and iNKT cells show important phenotypic, functional, and developmental differences that are often overlooked. With the recent availability of new tools, most importantly MR1 tetramers, it is now possible to directly study MAIT cells to understand their biology. Therefore, it is timely to compare the phenotype, development, and function of MAIT cells and iNKT cells. In this review, we highlight key areas where MAIT cells show similarity or difference to iNKT cells. In addition, we discuss important avenues for future research within the MAIT cell field, especially where comparison to iNKT cells has proven less informative.

Therapeutic Potential of Invariant Natural Killer T Cells in Autoimmunity

Tolerance against self-antigens is regulated by a variety of cell types with immunoregulatory properties, such as CD1d-restricted invariant natural killer T (iNKT) cells. In many experimental models of autoimmunity, iNKT cells promote self-tolerance and protect against autoimmunity. These findings are supported by studies with patients suffering from autoimmune diseases. Based on these studies, the therapeutic potential of iNKT cells in autoimmunity has been explored. Many of these studies have been performed with the potent iNKT cell agonist KRN7000 or its structural variants. These findings have generated promising results in several autoimmune diseases, although mechanisms by which iNKT cells modulate autoimmunity remain incompletely understood. Here, we will review these preclinical studies and discuss the prospects for translating their findings to patients suffering from autoimmune diseases.

The Role of Natural Killer T Cells in Cancer-A Phenotypical and Functional Approach

Natural killer T (NKT) cells are a subset of CD1d-restricted T cells at the interface between the innate and adaptive immune system. NKT cells can be subdivided into functional subsets that respond rapidly to a wide variety of glycolipids and stress-related proteins using T- or natural killer (NK) cell-like effector mechanisms. Because of their major modulating effects on immune responses via secretion of cytokines, NKT cells are also considered important players in tumor immunosurveillance. During early tumor development, T helper (T_H)1-like NKT cell subsets have the potential to rapidly stimulate tumor-specific T cells and effector NK cells that can eliminate tumor cells. In case of tumor progression, NKT cells may become overstimulated and anergic leading to deletion of a part of the NKT cell population in patients via activation-induced cell death. In addition, the remaining NKT cells become hyporesponsive, or switch to immunosuppressive T_H2-/T regulatory-like NKT cell subsets, thereby facilitating tumor progression and immune escape. In this review, we discuss this important role of NKT cells in tumor development and we conclude that there should be three important focuses of future research in cancer patients in relation with NKT cells: (1) expansion of the NKT cell population, (2) prevention and breaking of NKT cell anergy, and (3) skewing of NKT cells toward T_H1-like subsets with antitumor activity.

Liposomal formulation of glycosphingolipids from Sphingomonas paucimobilis induces antitumour immunity in mice

Natural Killer T (NKT) cells play an important role in host's anti-tumour immune response. Glycosphingolipids (GSLs) isolated from Sphingomonas paucimobilis have the ability to stimulate NKT cells. In this study, the activity of free GSLs or GSLs-incorporated liposomes (glycosphingosomes) was investigated against dimethyl-α-benzanthracene (DMBA)-induced tumours in mice. The anti-tumour immunity of GSLs- or glycosphingosomes-loaded bone marrow-derived dendritic cells (BMDCs) was investigated in tumour-bearing mice. The Immunotherapeutic potential of co-administration of liposomal doxorubicin (Lip-Dox) and GSLs or glycosphingosomes was assessed by measuring cytokine levels and VEGF in the tumour tissues. Pretreatment with glycosphingosomes significantly delayed the frequency of tumour formation. Immunotherapy with glycosphingosomes-loaded BMDCs increased serum IFN-γ level and survival rate in mice. The effect of immunotherapy was dependent on effector functions of NK cells because the depletion of NK cells abolished the effects of immunotherapy. There was reduced tumour growth with low expression of VEGF in the group of mice treated with glycosphingosomes and Lip-Dox combination. Moreover, the splenocytes secreted higher levels of IFN-γ, IL-12 and lower TGF-β level. The results of this study indicate that glycosphingosomes can induce better antitumour immunity and may be considered a novel formulation in antitumour therapy.

The Yin and Yang of Invariant Natural Killer T Cells in Tumor Immunity-Suppression of Tumor Immunity in the Intestine

CD1d-restricted invariant natural killer T (iNKT) cells are known as early responding, potent regulatory cells of immune responses. Besides their established role in the regulation of inflammation and autoimmune disease, numerous studies have shown that iNKT cells have important functions in tumor immunosurveillance and control of tumor metastasis. Tumor-infiltrating T helper 1 (TH1)/cytotoxic T lymphocytes have been associated with a positive prognosis. However, inflammation has a dual role in cancer and chronic inflammation is believed to be a driving force in many cancers as exemplified in patients with inflammatory bowel disease that have an increased risk of colorectal cancer. Indeed, NKT cells promote intestinal inflammation in human ulcerative colitis, and the associated animal model, indicating that NKT cells may favor tumor development in intestinal tissue. In contrast to other cancers, recent data from animal models suggest that iNKT cells promote tumor formation in the intestine by supporting an immunoregulatory tumor microenvironment and suppressing TH1 antitumor immunity. Here, we review the role of iNKT cells in suppression of tumor immunity in light of iNKT-cell regulation of intestinal inflammation. We also discuss suppression of immunity in other situations as well as factors that may influence whether iNKT cells have a protective or an immunosuppressive and tumor-promoting role in tumor immunity.

Unique invariant natural killer T cells promote intestinal polyps by suppressing TH1 immunity and promoting regulatory T cells

CD1d-restricted invariant natural killer T (iNKT) cells are known as potent early regulatory cells of immune responses. Besides the established roles in the regulation of inflammation and autoimmune disease, studies have shown that iNKT cells have important roles in tumor surveillance and the control of tumor metastasis. Here we found that the absence of iNKT cells markedly decreased the total number of intestinal polyps in APC^Min/+ mice, a model for colorectal cancer. Polyp iNKT cells were enriched for interleukin-10 (IL-10)- and IL-17-producing cells, showed a distinct phenotype being CD4⁺, NK1.1^- CD44^int, and PD-1^lo, and they were negative for the NKT cell transcription factor promyelocytic leukemia zinc-finger. The absence of iNKT cells was associated with a reduced frequency of regulatory T (Tregs) cells and lower expression levels of FoxP3 protein and transcript uniquely in the polyps, and a switch to an inflammatory macrophage phenotype. Moreover, in iNKT cell-deficient APC^Min/+ mice, expression of T-helper (TH) 1-associated genes, such as IFN-γ and Nos2, was increased in polyps, concomitantly with elevated frequencies of conventional CD4⁺ and CD8⁺ T cells in this tissue. The results suggest that a population of regulatory iNKT cells locally promote intestinal polyp formation by enhancing Treg cells and immunosuppression of antitumor TH1 immunity.

Harnessing the Power of Invariant Natural Killer T Cells in Cancer Immunotherapy

Invariant natural killer T (iNKT) cells are a distinct subset of innate-like lymphocytes bearing an invariant T-cell receptor, through which they recognize lipid antigens presented by monomorphic CD1d molecules. Upon activation, iNKT cells are capable of not only having a direct effector function but also transactivating NK cells, maturing dendritic cells, and activating B cells, through secretion of several cytokines and cognate TCR-CD1d interaction. Endowed with the ability to orchestrate an all-encompassing immune response, iNKT cells are critical in shaping immune responses against pathogens and cancer cells. In this review, we examine the critical role of iNKT cells in antitumor responses from two perspectives: (i) how iNKT cells potentiate antitumor immunity and (ii) how CD1d+ tumor cells may modulate their own expression of CD1d molecules. We further explore hypotheses to explain iNKT cell activation in the context of cancer and how the antitumor effects of iNKT cells can be exploited in different forms of cancer immunotherapy, including their role in the development of cancer vaccines.

Alpha-Galactosylceramide/CD1d-Antibody Fusion Proteins Redirect Invariant Natural Killer T Cell Immunity to Solid Tumors and Promote Prolonged Therapeutic Responses

Major progress in cancer immunotherapies have been obtained by the use of tumor targeting strategies, in particular with the development of bi-functional fusion proteins such as ImmTacs or BiTes, which engage effector T cells for targeted elimination of tumor cells. Given the significance of invariant natural killer T (iNKT) cells in bridging innate and adaptive immunity, we have developed a bi-functional protein composed of the extracellular part of CD1d molecule that was genetically fused to an scFv fragment from high affinity antibodies against HER2 or CEA. Systemic treatments with the CD1d-antitumor fusion proteins loaded with the agonist alpha-galactosylceramide (αGalCer) led to specific iNKT cell activation, resulting in a sustained growth inhibition of established tumors expressing HER2 or CEA, while treatment with the free αGalCer was ineffective. Importantly, we discovered that αGalCer/CD1d-antitumor fusion proteins were able to maintain iNKT cells reactive to multiple re-stimulations in contrast to their anergic state induced after a single injection of free αGalCer. We further demonstrated that the antitumor effects by αGalCer/CD1d-antitumor fusion proteins were largely dependent on the iNKT cell-mediated transactivation of NK cells. Moreover, prolonged antitumor effects could be obtained when combining the CD1d-antitumor fusion protein treatment with a therapeutic peptide/CpG cancer vaccine, which favored the capacity of iNKT cells to transactivate cross-presenting DCs for efficient priming of tumor-specific CD8 T cells. We will also summarize these pre-clinical results with a special focus on the cellular mechanisms underlying iNKT cell unresponsiveness to antigen re-challenge. Finally, we will discuss the perspectives regarding iNKT cell-mediated tumor targeting strategy in cancer immunotherapy.

Glycolipid-peptide conjugate vaccines enhance CD8+ T cell responses against human viral proteins

An important goal of vaccination against viruses and virus-driven cancers is to elicit cytotoxic CD8⁺ T cells specific for virus-derived peptides. CD8⁺ T cell responses can be enhanced by engaging help from natural killer T (NKT) cells. We have produced synthetic vaccines that induce strong peptide-specific CD8⁺ T cell responses in vivo by incorporating an NKT cell-activating glycolipid. Here we examine the effect of a glycolipid-peptide conjugate vaccine incorporating an NKT cell-activating glycolipid linked to an MHC class I-restricted peptide from a viral antigen in human peripheral blood mononuclear cells. The vaccine induces CD1d-dependent activation of human NKT cells following enzymatic cleavage, activates human dendritic cells in an NKT-cell dependent manner, and generates a pool of activated antigen-specific CD8⁺ T cells with cytotoxic potential. Compared to unconjugated peptide, the vaccine upregulates expression of genes encoding interferon-γ, CD137 and granzyme B. A similar vaccine incorporating a peptide from the clinically-relevant human papilloma virus (HPV) 16 E7 oncoprotein induces cytotoxicity against peptide-expressing targets in vivo, and elicits a better antitumor response in a model of E7-expressing lung cancer than its unconjugated components. Glycolipid-peptide conjugate vaccines may prove useful for the prevention or treatment of viral infections and tumors that express viral antigens.

Natural Killer T Cells in Cancer Immunotherapy

Natural killer T (NKT) cells are specialized CD1d-restricted T cells that recognize lipid antigens. Following stimulation, NKT cells lead to downstream activation of both innate and adaptive immune cells in the tumor microenvironment. This has impelled the development of NKT cell-targeted immunotherapies for treating cancer. In this review, we provide a brief overview of the stimulatory and regulatory functions of NKT cells in tumor immunity as well as highlight preclinical and clinical studies based on NKT cells. Finally, we discuss future perspectives to better harness the potential of NKT cells for cancer therapy.

Innate immune cells for immunotherapy of autoimmune and cancer disorders

Modulation of the immune system has been widely targeted for the treatment of several immune-related diseases, such as autoimmune disorders and cancer, due to its crucial role in these pathologies. Current available therapies focus mainly on symptomatic treatment and are often associated with undesirable secondary effects. For several years, remission of disease and subsequently recovery of immune homeostasis has been a major goal for immunotherapy. Most current immunotherapeutic strategies are aimed to inhibit or potentiate directly the adaptive immune response by modulating antibody production and B cell memory, as well as the effector potential and memory of T cells. Although these immunomodulatory approaches have shown some success in the clinic with promising therapeutic potential, they have some limitations related to their effectiveness in disease models and clinical trials, as well as elevated costs. In the recent years, a renewed interest has emerged on targeting innate immune cells for immunotherapy, due to their high plasticity and ability to exert a potent and extremely rapid response, which can influence the outcome of the adaptive immune response. In this review, we discuss the immunomodulatory potential of several innate immune cells, as well as they use for immunotherapy, especially in autoimmunity and cancer.

Enhancement of Adjuvant Functions of Natural Killer T Cells Using Nanovector Delivery Systems: Application in Anticancer Immune Therapy

Type I natural killer T (NKT) cells have gained considerable interest in anticancer immune therapy over the last decade. This “innate-like” T lymphocyte subset has the unique ability to recognize foreign and self-derived glycolipid antigens in association with the CD1d molecule expressed by antigen-presenting cells. An important property of these cells is to bridge innate and acquired immune responses. The adjuvant function of NKT cells might be exploited in the clinics. In this review, we discuss the approaches currently being used to target NKT cells for cancer therapy. In particular, we highlight ongoing strategies utilizing NKT cell-based nanovaccines to optimize immune therapy.