iNKT Function Research Articles

CSF-1R+ Macrophages Control the Gut Microbiome-Enhanced Liver Invariant NKT Function through IL-18.

The gut microbiome is an important modulator of the host immune system. In this study, we found that altering the gut microbiome by oral vancomycin increases liver invariant NKT (iNKT) cell function. Enhanced iNKT cytokine production and activation marker expression were observed in vancomycin-treated mice following both Ag-specific and Ag-independent invivo iNKT stimulations, with a more prominent effect in the liver than in the spleen. Fecal transplantation studies demonstrated that the iNKT functional regulation is mediated by altering the gut microbiome but uncoupled from the modulation of iNKT cell population size. Interestingly, when stimulated invitro, iNKT cells from vancomycin-treated mice did not show increased activation, suggesting an indirect regulation. iNKT cells expressed high levels of IL-18 receptor, and vancomycin increased the expression of IL-18 in the liver. Blocking IL-18 by neutralizing Ab or using genetically deficient mice attenuated the enhanced iNKT activation. Liver macrophages were identified as a major source of IL-18. General macrophage depletion by clodronate abolished this iNKT activation. Using anti-CSF-1R depletion or LyzCrexCSF-1RLsL-DTR mice identified CSF-1R+ macrophages as a critical modulator of iNKT function. Vancomycin treatment had no effect on iNKT cell function invivo in IL-18 knockout macrophage reconstituted mice. Together, our results demonstrate that the gut microbiome controls liver iNKT function via regulating CSF-1R+ macrophages to produce IL-18.

Ets1 represses a T-bet dependent migration program and stabilizes the iNKT1 adhesome

Abstract iNKT cells are innate-like T cells that recognize glycolipids presented on MHCI-like CD1d using a semi-invariant TCR. Upon activation, iNKTs rapidly produce cytokines to direct the adaptive response towards a T H1, T H2 or T H17 response. The transcription factor ETS1 is important for iNKT cell development, but its roles in iNKT function and homeostasis are not well characterized. Utilizing a novel mouse model for targeted deletion of Ets1 in iNKT1s, we show that ETS1 limits expression of T-bet, the signature transcription factor of the iNKT1 lineage. Ets1 Δ/Δhepatic iNKT1 cells upregulated a gene program associated with migration and had reduced expression of LFA-1 and ICAM-1, receptors critical for retention in the liver. Remarkably, Ets1 Δ/Δliver iNKT1s remained tissue resident but no longer required LFA-1/ICAM-1 for retention. Heterozygous deletion of T-bet abrogated expression of multiple migration-associated genes, restored LFA-1 and ICAM-1, and re-established reliance on LFA-1/ICAM-1 for retention. Our data demonstrate that ETS1 controls the mechanisms of hepatic iNKT1 cell residency by limiting a T-bet-dependent migration and adhesion program. Supported by NIH/NIAID grant R01 AI106352

Inhibition of iNKT Cells by the HLA-G-ILT2 Checkpoint and Poor Stimulation by HLA-G-Expressing Tolerogenic DC.

Invariant Natural Killer T (iNKT) cells are a small and distinct population of T cells crucial in immunomodulation. After activation by alpha-GalactosylCeramide (αGC), an exogenic glycolipid antigen, iNKT cells can rapidly release cytokines to enhance specific anti-tumor activity. Several human clinical trials on iNKT cell-based anti-cancer are ongoing, however results are not as striking as in murine models. Given that iNKT-based immunotherapies are dependent mainly on antigen-presenting cells (APC), a human tolerogenic molecule with no murine homolog, such as Human Leucocyte Antigen G (HLA-G), could contribute to this discrepancy. HLA-G is a well-known immune checkpoint molecule involved in fetal-maternal tolerance and in tumor immune escape. HLA-G exerts its immunomodulatory functions through the interaction with immune inhibitory receptors such as ILT2, differentially expressed on immune cell subsets. We hypothesized that HLA-G might inhibit iNKT function directly or by inducing tolerogenic APC leading to iNKT cell anergy, which could impact the results of current clinical trials. Using an ILT2-transduced murine iNKT cell line and human iNKT cells, we demonstrate that iNKT cells are sensitive to HLA-G, which inhibits their cytokine secretion. Furthermore, human HLA-G+ dendritic cells, called DC-10, failed at inducing iNKT cell activation compared to their autologous HLA-G‒ DCs counterparts. Our data show for the first time that the HLA-G/ILT2 ICP is involved in iNKT cell function modulation.

The immune adaptor ADAP plays a pivotal role invariant natural killer T cell functions

Abstract Invariant natural killer T cells (iNKTs) comprise a sub-lineage of T lymphocytes that express an “invariant” T cell receptor (TCR) with specificity for glycolipid antigens (Ag) such as a-galactosyl ceramide (aGC), when presented in complex with the MHC class I molecule CD1d. Following TCR engagement, iNKTs rapidly secrete cytokines and trans-activate the anti-tumor functions of dendritic cells (DC), natural killer (NK), T and B cells as well as directly kill tumor cells. Based on their dual functions as potent cytokine producers and tumor killers, iNKTs serve as a powerful tool for use in cell-based immunotherapies for cancer. Although TCR-CD1d interactions are generally required for iNKT cell functions, the signaling mechanisms that co-operate with the TCR to promote maximal iNKT cell responses remain poorly understood. Our previous studies demonstrate that the adaptor protein SAP and its signaling partner, Fyn (a Src-tyrosine kinase) is critical for iNKT cell functions. We recently investigated the role of ADAP (adhesion and degranulation promoting adaptor protein), a Fyn-binding protein in iNKT functions. We observe that aGC-induced iNKT cell activation, cytokine production, and bystander immune cell activation as well as anti-tumor response are remarkably reduced in ADAP-deficient (Adap−/−) mice. These data suggest that ADAP is a critical regulator of Ag-induced iNKT cell functions. Studies are currently underway to elucidate the mechanism(s) by which ADAP regulates iNKT cell functions. These studies will have an impact by establishing new paradigms for iNKT cell signaling and offering insights into how iNKTs can be best activated to enhance host immunity and treat cancer.

In vivo NKTT320-induced activation of invariant Natural Killer T-cells (iNKTs) and potential applications for use in AIDS pathogenesis modulation

Abstract iNKTs are unique, innate T cells with an invariant TCRα chain that recognize glycolipids presented by nonpolymorphic MHC class-I-like CD1d molecules. Activated iNKTs rapidly secrete a range of cytokines and thus have diverse functions including potentiation of anti-tumor and pathogen-specific humoral and cellular immunity and resolution of inflammation. iNKT depletion and dysfunction are common in pathogenic HIV/SIV infection and may hasten AIDS progression. In this study, we tested a novel monoclonal antibody, NKTT320, that specifically binds to the iNKT cell TCRα as a tool for direct in vivo iNKT activation in Mauritian cynomolgus macaques (MCM). Dose-escalation NKTT320 pharmacokinetic studies were performed in 11 SIV-negative MCM. Plasma NKTT320 levels were measured by ELISA while kinetics of iNKT activation and effect on other immune cell subsets were evaluated by flow cytometry. NKTT320 plasma levels peaked between 6.6–47.2 μg/ml within 24 hours of a single IV doses of 100–1000 μg/kg and declined below detection by 4–6 weeks. NKTT320 administration resulted in rapid iNKT activation and proliferation of CD4+ more than CD8+ iNKTs, without non-specific T cell activation. Transient elevation of several plasma analytes (IL-2, IL-6, IL-17, MCP-1, MDC and IP-10) and increased proliferation of non-T immune cell subsets were observed suggesting downstream potentiation of innate and adaptive immunity. Repeated doses of NKTT320 increased iNKT responsiveness indicating that treatment did not lead to iNKT anergy. NKTT320-mediated iNKT activation may be a useful therapeutic tool to preserve and enhance iNKT function, thereby preventing immunodeficiency and aberrant immune activation in pathogenic SIV infection.

Monoclonal Invariant NKT (iNKT) Cell Mice Reveal a Role for Both Tissue of Origin and the TCR in Development of iNKT Functional Subsets.

Invariant NKT (iNKT) cell functional subsets are defined by key transcription factors and output of cytokines, such as IL-4, IFN-γ, IL-17, and IL-10. To examine how TCR specificity determines iNKT function, we used somatic cell nuclear transfer to generate three lines of mice cloned from iNKT nuclei. Each line uses the invariant Vα14Jα18 TCRα paired with unique Vβ7 or Vβ8.2 subunits. We examined tissue homing, expression of PLZF, T-bet, and RORγt, and cytokine profiles and found that, although monoclonal iNKT cells differentiated into all functional subsets, the NKT17 lineage was reduced or expanded depending on the TCR expressed. We examined iNKT thymic development in limited-dilution bone marrow chimeras and show that higher TCR avidity correlates with higher PLZF and reduced T-bet expression. iNKT functional subsets showed distinct tissue distribution patterns. Although each individual monoclonal TCR showed an inherent subset distribution preference that was evident across all tissues examined, the iNKT cytokine profile differed more by tissue of origin than by TCR specificity.

NKT Cell Hyporesponsiveness Leads to Unrestrained Accumulation of Marginal Zone B Cells in Hypercholesterolemic Apolipoprotein E-Deficient Mice.

Recently, the role of B cells in atherosclerosis has gained more attention but studies have mainly focused on B1 and follicular B cell subsets. Therefore, the contribution of marginal zone (MZ) B cells in experimental atherosclerosis remains elusive. In the current study, we examined the MZ B cell compartment in atherosclerotic apoE-deficient (apoE-/-) mice and found that hypercholesterolemia in these mice was associated with an increased number and percentage of MZ B cells. This aberrant accumulation of MZ B cells was not associated with alterations in their development or increased proliferation but was due to decreased apoptotic cell death. This decrease in MZ B cell death in apoE-/- mice was associated with the reduced capacity of invariant NKT (iNKT) cells to produce IFN-γ and IL-4 after activation. Lowering cholesterol plasma levels with ezetimibe in apoE-/- mice reversed iNKT function and MZ B cell accumulation. To elucidate the mechanism whereby iNKT cells control MZ B cell accumulation in apoE-/- mice, we performed an adoptive transfer of iNKT cells and found that only wild-type iNKT cells but not IFN-γ-/- iNKT cells reversed MZ B cell accumulation in apoE-/- recipient mice. Our findings reveal that lipid changes associated with atherosclerotic disease induce decreased production of IFN-γ by iNKT, which in turn leads to aberrant accumulation of MZ B cells. This study further extends the importance of iNKT cells in regulating MZ B cell compartment.

The role of vitamin D towards immune tolerance in white adipose tissue (WAT).

Vitamin D and its active form 1α,25(OH)2D3 has been recently indicated to have a fundamental role in immune regulation. An interplay between gut and white adipose tissue (WAT), mainly mediated by enterogastric hormones and adipokines, such as leptin, adiponectin and ghrelin, actively participate in the immune homeostasis and modulation both of the innate/acquired immune response and between T-cell effector/T-cell regulatory skewing. Particularly for leptin, this action promotes and enhances immune tolerance at the gut level and pro-inflammatory effect at WAT level, while calcitriol participates in promoting and increasing an M2 macrophage-like skewing, a T-reg activity at WAT level and a iNKT function at gut level. The role of active vitamin D3 therefore is fundamental in the immune homeostasis of the WAT immune microenvironment and to support the role of WAT as an endocrine, tolerogenic organ.

Interleukin-15 enhances the expansion and function of natural killer T cells from adult peripheral and umbilical cord blood

Invariant natural killer T cells (iNKT cells) are innate-like non-conventional T cells restricted by the CD1d molecule that are unique in their ability to play a pivotal role in immune regulation. Deficient iNKT function has been reported in patients receiving umbilical cord blood (UCB) transplantation. We sought to determine the effect of interleukin (IL)-15 on α-galactosylceramide (α-GalCer)-expanded iNKT cell function from UCB and adult peripheral blood (APB) mononuclear cells (MNCs). Fresh APB and UCB MNCs were cultured with IL-15 (50ng/ml) in the presence or absence of α-GalCer (100ng/ml) for 10days. Cells were harvested for examination of cell yield, apoptosis, cytokine production and cytotoxic function of Vα24+/Vβ11+ iNKT cells. We observed that α-GalCer-expanded APB and UCB iNKT cells and such expansion was further enhanced with IL-15. The percentage of CD3+CD56+ NKT-like cells in both APB and UCB MNCs was increased with IL-15 but not with α-GalCer. Apoptosis of UCB iNKT cells was ameliorated by IL-15. Although APB and UCB iNKT cells secreted lower IFN-γ, it could be enhanced with IL-15. The expression of perforin in APB iNKT cells can also be enhanced with IL-15. UCB Vα24+Vβ11+ iNKT cells further augmented K562 cytotoxicity mediated by IL-15. Taken together, these results demonstrated the relative functional deficiencies of α-GalCer induced UCB iNKT cells, which can be ameliorated by IL-15. Our findings suggest a therapeutic benefit of IL-15 immunotherapy during the post-UCB transplant period when iNKT function remains poor.

Invariant natural killer T cells recognize and restrict the transformation of B cells by Epstein-Barr virus (P4363)

Abstract Individuals with X-linked lymphoproliferative disease (XLP) lack invariant natural killer T (iNKT) cells and are uniquely susceptible to Epstein-Barr virus (EBV). To determine whether iNKT cells recognize or regulate EBV replication, human B cells were infected with GFP+ EBV 95.8 in the presence or absence of iNKT cells. We observed that iNKT cells significantly reduced early EBV titres and GFP+ B cell expansion but that within 72 hours of infection, B cells transformed into lymphoblastoid cell lines (LCL) by EBV had downregulated the iNKT antigen receptor CD1d, completely abrogating iNKT recognition of the lipid agonist α-galactosylceramide (αGalCer). To determine whether ectopic CD1d expression could restore iNKT recognition, LCL were treated with a synthetic retinoic acid receptor-α agonist AM580 known to modulate CD1d expression by regulating the nuclear protein lymphoid enhancer-binding factor-1 (LEF-1). AM580 treatment significantly reduced LEF-1 at the CD1d promoter, induced surface CD1d expression and enabled iNKT recognition of LCL loaded with αGalCer. Unexpectedly, AM580-treated LCL also activated iNKT function even in the absence of αGalCer suggesting that EBV infection and transformation triggers endogenous iNKT antigen expression. These observations indicate that iNKT cells may be important for the early recognition and control of EBV-infected B cells prior to CD1d downregulation and the loss of CD1d may allow EBV to circumvent iNKT-mediated immunosurveillance.

Invariant NKT Cells: Regulation and Function during Viral Infection

Natural killer T cells (NKT cells) represent a subset of T lymphocytes that express natural killer (NK) cell surface markers. A subset of NKT cells, termed invariant NKT cells (iNKT), express a highly restricted T cell receptor (TCR) and respond to CD1d-restricted lipid ligands. iNKT cells are now appreciated to play an important role in linking innate and adaptive immune responses and have been implicated in infectious disease, allergy, asthma, autoimmunity, and tumor surveillance. Advances in iNKT identification and purification have allowed for the detailed study of iNKT activity in both humans and mice during a variety of chronic and acute infections. Comparison of iNKT function between non-pathogenic simian immunodeficiency virus (SIV) infection models and chronic HIV-infected patients implies a role for iNKT activity in controlling immune activation. In vitro studies of influenza infection have revealed novel effector functions of iNKT cells including IL-22 production and modulation of myeloid-derived suppressor cells, but ex vivo characterization of human iNKT cells during influenza infection are lacking. Similarly, as recent evidence suggests iNKT involvement in dengue virus pathogenesis, iNKT cells may modulate responses to a number of emerging pathogens. This Review will summarize current knowledge of iNKT involvement in responses to viral infections in both human and mouse models and will identify critical gaps in knowledge and opportunities for future study. We will also highlight recent efforts to harness iNKT ligands as vaccine adjuvants capable of improving vaccination-induced cellular immune responses.

Activation of Invariant NKT Cells Ameliorates Experimental Ocular Autoimmunity by A Mechanism Involving Innate IFN-γ Production and Dampening of the Adaptive Th1 and Th17 Responses

Invariant NKT cells (iNKT cells) have been reported to play a role not only in innate immunity but also to regulate several models of autoimmunity. Furthermore, iNKT cells are necessary for the generation of the prototypic eye-related immune regulatory phenomenon, anterior chamber associated immune deviation (ACAID). In this study, we explore the role of iNKT cells in regulation of autoimmunity to retina, using a model of experimental autoimmune uveitis (EAU) in mice immunized with a uveitogenic regimen of the retinal Ag, interphotoreceptor retinoid-binding protein. Natural strain-specific variation in iNKT number or induced genetic deficiencies in iNKT did not alter baseline susceptibility to EAU. However, iNKT function seemed to correlate with susceptibility and its pharmacological enhancement in vivo by treatment with iNKT TCR ligands at the time of uveitogenic immunization reproducibly ameliorated disease scores. Use of different iNKT TCR ligands revealed dependence on the elicited cytokine profile. Surprisingly, superior protection against EAU was achieved with alpha-C-GalCer, which induces a strong IFN-gamma but only a weak IL-4 production by iNKT cells, in contrast to the ligands alpha-GalCer (both IFN-gamma and IL-4) and OCH (primarily IL-4). The protective effect of alpha-C-GalCer was associated with a reduction of adaptive Ag-specific IFN-gamma and IL-17 production and was negated by systemic neutralization of IFN-gamma. These data suggest that pharmacological activation of iNKT cells protects from EAU at least in part by a mechanism involving innate production of IFN-gamma and a consequent dampening of the Th1 as well as the Th17 effector responses.