NKT cells enhance CD4+ and CD8+ T cell responses to soluble antigen in vivo through direct interaction with dendritic cells

Intranasal but not intravenous delivery of the adjuvant α-galactosylceramide permits repeated stimulation of natural killer T cells in the lung

Efficient induction of antigen-specific immunity is achieved by delivering multiple doses of vaccine formulated with appropriate adjuvants that can harness the benefits of innate immune mediators. The synthetic glycolipid α-galactosylceramide (α-GalCer) is a potent activator of NKT cells, a major innate immune mediator cell type effective in inducing maturation of DCs for efficient presentation of co-administered antigens. However, systemic administration of α-GalCer results in NKT cell anergy in which the cells are unresponsive to subsequent doses of α-GalCer. We show here that α-GalCer delivered as an adjuvant by the intranasal route, as opposed to the intravenous route, enables repeated activation of NKT cells and DCs, resulting in efficient induction of cellular immune responses to co-administered antigens. We show evidence that after intranasal delivery,α-GalCer is selectively presented by DCs for the activation of NKT cells, not B cells. Furthermore, higher levels of PD-1 expression, a potential marker for functional exhaustion of the NKT cells when α-GalCer is delivered by the intravenous route, are not observed after intranasal delivery. These results support a mucosal route of delivery for the utility of α-GalCer as an adjuvant for vaccines, which often requires repeated dosing to achieve durable protective immunity.

Baculovirus capsid display potentiates OVA cytotoxic and innate immune responses

Baculoviruses (BV) are DNA viruses that are pathogenic for insects. Although BV infect a range of mammalian cell types, they do not replicate in these cells. Indeed, the potential effects of these insect viruses on the immune responses of mammals are only just beginning to be studied. We show in this paper that a recombinant Autographa californica multiple nuclear polyhedrosis virus carrying a fragment of ovalbumin (OVA) on the VP39 capsid protein (BV-OVA) has the capacity to act as an adjuvant and vector of antigens in mice, thereby promoting specific CD4 and cytotoxic T cell responses against OVA. BV also induced in vivo maturation of dendritic cells and the production of inflammatory cytokines, thus promoting innate and adaptive immune responses. The OVA-specific response induced by BV-OVA was strong enough to reject a challenge with OVA-expressing melanoma cells (MO5 cells) and effectively prolonged survival of MO5 bearing mice. All these findings, together with the absence of pre-existing immunity to BV in humans and the lack of viral gene expression in mammalian cells, make BV a candidate for vaccination.

NKT cells inhibit antigen-specific effector CD8 T cell induction to skin viral proteins

We recently demonstrated that CD1d-restricted NKT cells resident in skin can inhibit CD8 T cell-mediated graft rejection of human papillomavirus E7-expressing skin through an IFN-γ-dependent mechanism. In this study, we examined the role of systemically derived NKT cells in regulating the rejection of skin grafts expressing viral proteins. In lymph nodes draining transplanted skin, Ag-specific CD8 T cell proliferation, cytokine production, and cytotoxic activity were impaired by NKT cells. NKT cell suppression was mediated via CD11c(+) dendritic cells. Inhibition of CD8 T cell function did not require Foxp3(+) regulatory T cells or NKT cell-secreted IFN-γ, IL-10, or IL-17. Thus, following skin grafting or immunization with human papillomavirus-E7 oncoprotein, NKT cells reduce the capacity of draining lymph node-resident APCs to cross-present Ag to CD8 T cell precursors, as evidenced by impaired expansion and differentiation to Ag-specific CD8 T effector cells. Therefore, in the context of viral Ag challenge in the skin, systemic NKT cells limit the capacity for effective priming of adaptive immunity.

Developing understanding of the roles of CD1d-restricted T cell subsets in cancer: reversing tumor-induced defects

Invariant natural killer T-cells ('iNKT') are the best-known CD1d-restricted T-cells, with recently-defined roles in controlling adaptive immunity. CD1d-restricted T-cells can rapidly produce large amounts of Th1 and/or Th2//Treg/Th17-type cytokines, thereby regulating immunity. iNKT can stimulate potent anti-tumor immune responses via production of Th1 cytokines, direct cytotoxicity, and activation of effectors. However, Th2//Treg-type iNKT can inhibit anti-tumor activity. Furthermore, iNKT are decreased and/or reversibly functionally impaired in many advanced cancers. In some cases, CD1d-restricted T-cell cancer defects can be traced to CD1d(+) tumor interactions, since hematopoietic, prostate, and some other tumors can express CD1d. Ligand and IL-12 can reverse iNKT defects and therapeutic opportunities exist in correcting such defects alone and in combination. Early stage clinical trials have shown potential for reconstitution of iNKT IFN-gamma responses and evidence of activity in a subset of patients, with rational new approaches to capitalize on this progress ongoing, as will be discussed here.

Comparison of clinical and immunological effects of intravenous and intradermal administration of α-galactosylceramide (KRN7000)-pulsed dendritic cells

PURPOSE

Human Vα24+Vβ11+ natural killer T-cells (NKT cells) have antitumor activity via direct cytotoxicity and by induction of antitumor actions of T and NK cells. Activation of NKT cells is crucial for their antitumor activity and is induced by α-galactosylceramide (α-GalCer, KRN7000) presented by CD1d on dendritic cells (DC). We conducted a phase I clinical trial of therapy with α-GalCer-pulsed DC to determine safety, tolerability, immune effects and an optimal dose, and administration route.

EXPERIMENTAL DESIGN

Twelve subjects (3 cohorts) with metastatic malignancy received 4 treatments of α-GalCer-pulsed DC, 2 treatments intravenously (IV), and 2 treatments intradermally (ID). Each successive cohort received a log higher cell dose. Clinical and immunological outcomes were evaluated, including secondary effects on NK and T cells.

RESULTS

Substantial effects on peripheral blood NKT cells were observed but were greater following IV treatment. Secondary immune effects including activation of T and NK cells, increases in T- and NK-cell cytoplasmic interferon-γ, and increases in serum interferon-γ levels were seen after IV but not after ID treatment. Therapy was well tolerated, but 9 of 12 subjects had tumor flares with clinical findings consistent with transient tumor inflammation. Disease response (minor) or stabilization of disease progressing up to enrollment was observed in 6 of the 12 subjects. Stabilization of previously progressive disease lasted for at least one year in three subjects.

CONCLUSION

We conclude that therapy with α-GalCer-pulsed DC induced clinically beneficial immune responses that are highly dependent on cell dose and administration route.

Binding strength and dynamics of invariant natural killer cell T cell receptor/CD1d-glycosphingolipid interaction on living cells by single molecule force spectroscopy

Invariant natural killer T (iNKT) cells are a population of T lymphocytes that play an important role in regulating immunity to infection and tumors by recognizing endogenous and exogenous CD1d-bound lipid molecules. Using soluble iNKT T cell receptor (TCR) molecules, we applied single molecule force spectroscopy for the investigation of the iNKT TCR affinity for human CD1d molecules loaded with glycolipids differing in the length of the phytosphingosine chain using either recombinant CD1d molecules or lipid-pulsed THP1 cells. In both settings, the dissociation of the iNKT TCR from human CD1d molecules loaded with the lipid containing the longer phytosphingosine chain required higher unbinding forces compared with the shorter phytosphingosine lipid. Our findings are discussed in the context of previous results obtained by surface plasmon resonance measurements. We present new insights into the energy landscape and the kinetic rate constants of the iNKT TCR/human CD1d-glycosphingolipid interaction and emphasize the unique potential of single molecule force spectroscopy on living cells.

Impairment of CD1d-restricted natural killer T cells in chronic HIV type 1 clade C infection

Recent studies suggest that natural killer T (NKT) cells play a role in early antiviral pathogenesis and are rapidly depleted in chronic human immunodeficiency virus type 1 (HIV-1) clade B infection. We aimed to characterize the phenotypic and functional characteristics of NKT cells in HIV-1 clade C-infected Africans at different stages of HIV-1 disease. NKT cell frequencies, subsets, and ex vivo effector functions were assessed using multiparametric flow cytometry in a cross-sectional analysis of cryopreserved peripheral blood mononuclear cells from a cohort of 53 HIV-1 clade C chronically infected South African adults with CD4 T cell counts ranging from 94 to 839 cells/μl. We observed a significant decline of NKT cell numbers in advanced HIV-1 disease as well as activation and functional impairment of NKT cells in individuals with low CD4 T cell counts. The loss of NKT cells was largely driven by a reduction in the CD4(+) and CD4(-)CD8(-) NKT cell subsets in advanced disease. These findings demonstrate significant impairment of the NKT cell compartment in progressive HIV-1 clade C disease that might play an important role in the modulation of immune function in HIV-1 infection.

Reduction of CD1d expression in vivo minimally affects NKT-enhanced antibody production but boosts B-cell memory

The CD1d-binding glycolipid α-galactosylceramide exerts potent adjuvant effects on T-dependent humoral immunity. The mechanism is driven by cognate interaction between CD1d-expressing B cells and TCR-expressing type I CD1d-restricted NKT cells. Thus, far positive effects of alpha-galactosylceramide have been observed on initial and sustained antibody titers as well as B-cell memory. Following vaccination, each of these features is desirable, but good B-cell memory is of paramount importance for long-lived immunity. We therefore tested the hypothesis that CD1d expression in vivo differentially affects initial antibody titers versus B-cell memory responses. CD1d(+/+) and CD1d(+/-) mice were generated and immunized with antigen plus CD1d ligand before analysis of cytokine expression, CD40L expression, initial and longer term antibody responses and B-cell memory. As compared with CD1d(+/+) controls, CD1d(+/-) mice had equivalent numbers of total NKT cells, lower cytokine production, fewer CD40L-expressing NKT cells, lower initial antibody responses, similar long-term antibody responses and higher B-cell memory. Our data indicate that weak CD1d antigen presentation may facilitate good B-cell memory without compromising antibody responses. This work may impact vaccine design since over-stimulation of NKT cells at the time of vaccination may not lead to optimal B-cell memory.

Exploiting the role of endogenous lymphoid-resident dendritic cells in the priming of NKT cells and CD8+ T cells to dendritic cell-based vaccines

Transfer of antigen between antigen-presenting cells (APCs) is potentially a physiologically relevant mechanism to spread antigen to cells with specialized stimulatory functions. Here we show that specific CD8⁺ T cell responses induced in response to intravenous administration of antigen-loaded bone marrow-derived dendritic cells (BM-DCs), were ablated in mice selectively depleted of endogenous lymphoid-resident langerin⁺ CD8α⁺ dendritic cells (DCs), suggesting that the antigen is transferred from the injected cells to resident APCs. In contrast, antigen-specific CD4⁺ T cells were primed predominantly by the injected BM-DCs, with only very weak contribution of resident APCs. Crucially, resident langerin⁺ CD8α⁺ DCs only contributed to the priming of CD8⁺ T cells in the presence of maturation stimuli such as intravenous injection of TLR ligands, or by loading the BM-DCs with the glycolipid α-galactosylceramide (α-GalCer) to recruit the adjuvant activity of activated invariant natural killer-like T (iNKT) cells. In fact, injection of α-GalCer-loaded CD1d^−/− BM-DCs resulted in potent iNKT cell activation, suggesting that this glycolipid antigen can also be transferred to resident CD1d⁺ APCs. While iNKT cell activation per se was independent of langerin⁺ CD8α⁺ DCs, some iNKT cell-mediated activities were reduced, notably release of IL-12p70 and transactivation of NK cells. We conclude that both protein and glycolipid antigens can be exchanged between distinct DC species. These data suggest that the efficacy of DC-based vaccination strategies may be improved by the incorporation of a systemic maturation signal aimed to engage resident APCs in CD8⁺ T cell priming, and α-GalCer may be particularly well suited to this purpose.

Activation of natural killer T cells by α-carba-GalCer (RCAI-56), a novel synthetic glycolipid ligand, suppresses murine collagen-induced arthritis

Alpha-carba-GalCer (RCAI-56), a novel synthetic analogue of α-galactosylceramide (α-GalCer), stimulates invariant natural killer T (NK T) cells to produce interferon (IFN)-γ. IFN-γ exhibits immunoregulatory properties in autoimmune diseases by suppressing T helper (Th)-17 cell differentiation and inducing regulatory T cells and apoptosis of autoreactive T cells. Here, we investigated the protective effects of α-carba-GalCer on collagen-induced arthritis (CIA) in mice. First, we confirmed that α-carba-GalCer selectively induced IFN-γ in CIA-susceptible DBA/1 mice in vivo. Then, DBA/1 mice were immunized with bovine type II collagen (CII) and α-carba-GalCer. The incidence and clinical score of CIA were significantly lower in α-carba-GalCer-treated mice. Anti-IFN-γ antibodies abolished the beneficial effects of α-carba-GalCer, suggesting that α-carba-GalCer ameliorated CIA in an IFN-γ-dependent manner. Treatment with α-carba-GalCer reduced anti-CII antibody production [immunoglobulin (Ig)G and IgG2a] and CII-reactive interleukin (IL)-17 production by draining lymph node (DLN) cells, did not induce apoptosis or regulatory T cells, and significantly increased the ratio of the percentage of IFN-γ-producing T cells to IL-17-producing T cells (Th1/Th17 ratio). Moreover, the gene expression levels of IL-6 and IL-23p19, Th17-related cytokines, were reduced significantly in mice treated with α-carba-GalCer. In addition, we observed higher IFN-γ production by NK T cells in α-carba-GalCer-treated mice in the initial phase of CIA. These findings indicate that α-carba-GalCer polarizes the T cell response toward Th1 and suppresses Th17 differentiation or activation, suggesting that α-carba-GalCer, a novel NK T cell ligand, can potentially provide protection against Th17-mediated autoimmune arthritis by enhancing the Th1 response.

Activated invariant NKT cells regulate osteoclast development and function

Invariant NKT (iNKT) cells modulate innate and adaptive immune responses through activation of myeloid dendritic cells and macrophages and via enhanced clonogenicity, differentiation, and egress of their shared myeloid progenitors. Because these same progenitors give rise to osteoclasts (OCs), which also mediate the egress of hematopoietic progenitors and orchestrate bone remodeling, we hypothesized that iNKT cells would extend their myeloid cell regulatory role to the development and function of OCs. In this study, we report that selective activation of iNKT cells by α-galactosylceramide causes myeloid cell egress, enhances OC progenitor and precursor development, modifies the intramedullary kinetics of mature OCs, and enhances their resorptive activity. OC progenitor activity is positively regulated by TNF-α and negatively regulated by IFN-γ, but is IL-4 and IL-17 independent. These data demonstrate a novel role of iNKT cells that couples osteoclastogenesis with myeloid cell egress in conditions of immune activation.

Hepatitis C virus soluble E2 in combination with QuilA and CpG ODN induces neutralizing antibodies in mice

Several studies have emphasized the importance of an early, highly neutralizing antibody response in the clearance of Hepatitis C virus (HCV) infection. The envelope glycoprotein E2 is a major target for HCV neutralizing antibodies. Here, we compared antibody responses in mice immunized with native soluble E2 (sE2) from the H77 1a isolate coupled with different adjuvants or combinations of adjuvants. Adjuvanting sE2 with Freund's, monophosphoryl lipid A (MPL), cytosine phosphorothioate guanine oligodeoxynucleotide (CpG ODN), or alpha-galactosylceramide (αGalCer) derivatives elicited only moderate antibody responses. In contrast, immunizations with sE2 and QuilA elicited exceptionally high anti-E2 antibody titers. Sera from these mice effectively neutralized HCV pseudoparticles (HCVpp) 1a entry. Moreover, the combination of QuilA and CpG ODN further enhanced neutralizing antibody titers wherein cross-neutralization of HCVpp 4 was observed. We conclude that the combination of QuilA and CpG ODN is a promising adjuvant combination that should be further explored for the development of an HCV subunit vaccine. Our work also emphasizes that the ideal combination of adjuvant and immunogen has to be determined empirically.

Invariant natural killer T cell-based immunotherapy for cancer

Human Valpha24 invariant natural killer T (iNKT) cells are a distinct lymphocyte population, characterized by an invariant T-cell receptor Valpha24 chain paired mainly with Valpha11. Valpha24 iNKT cells are activated by a glycolipid ligand - alpha-galactosylceramide - and produce a large amount of Th1 and Th2 cytokines, thereby modulating the function of other cells. iNKT cells have the capability to control a wide variety of immune responses, including antitumor immunity. Abnormalities in the number and function of Valpha24 iNKT cells have been observed in patients with malignant diseases accompanied with a poor clinical outcome. Therefore, therapeutic strategies that focused on the restoration of Valpha24 iNKT cell population and function would be a reasonable rationale for the treatment of cancer. In this article, the progress to date in the clinical studies of iNKT cell-based immunotherapy is briefly reviewed and the role of Valpha24 iNKT cells in cancer immunotherapy is highlighted.

α-Galactosylceramide activates antitumor immunity against liver tumor

AIM

  α-Galactosylceramide (α-GalCer) has been attracting attention as a novel approach to treat metastatic liver cancer. We investigated the detailed process of activating liver dendritic cells (DC) and immune cells after α-GalCer treatment in the mouse liver tumor model.

METHODS

  BALB/c mice bearing CMS4 liver tumor (p53 peptide-expressing tumor) were treated by α-GalCer. We evaluated the activation of liver DC and immune cells after α-GalCer treatment. Interferon (IFN)-γ enzyme-linked immunosorbent spot (ELISPOT) assay was performed to detect p53 peptide-specific cytotoxic T lymphocytes (CTL). To assess the impact of systemic acquired immunity by α-GalCer treatment, 28 days after liver tumor treatment, CMS4 cells or Colon26 cells were re-challenged s.c.

RESULTS

  The liver weights of α-GalCer-treated mice were significantly lighter than those of vehicle-treated mice. Depletion experiments revealed that natural killer (NK) cells were essential for the antitumor effect of α-GalCer. α-GalCer treatment significantly increased the population of DC and NK cells in the liver. The expressions of co-stimulatory molecules on liver DC significantly increased with the peak at 1 day after α-GalCer administration. IFN-γ ELISPOT assay demonstrated that p53 peptide-specific CTL was generated efficiently in α-GalCer-treated mice. (51) Cr-release assay revealed that CD8(+) , not CD4(+) , CTL against CMS4 cells were generated in α-GalCer-treated mice. The mice that had been protected from CMS4 liver tumor by α-GalCer injection became resistant against s.c. CMS4 re-challenge, but not against Colon26 re-challenge.

CONCLUSION

  These results demonstrated the therapeutic potential of α-GalCer against liver cancer through activating liver DC and immune cells in the liver.

Expression of the SLAM family of receptors adapter EAT-2 as a novel strategy for enhancing beneficial immune responses to vaccine antigens

Recent studies have shown that activation of the signaling lymphocytic activation molecule (SLAM) family of receptors plays an important role in several aspects of immune regulation. However, translation of this knowledge into a useful clinical application has not been undertaken. One important area where SLAM-mediated immune regulation may have keen importance is in the field of vaccinology. Because SLAM signaling plays such a critical role in the innate and adaptive immunity, we endeavored to develop a strategy to improve the efficacy of vaccines by incorporation of proteins known to be important in SLAM-mediated signaling. In this study, we hypothesized that coexpression of the SLAM adapter EWS-FLI1-activated transcript 2 (EAT-2) along with a pathogen-derived Ag would facilitate induction of beneficial innate immune responses, resulting in improved induction of Ag-specific adaptive immune responses. To test this hypothesis, we used rAd5 vector-based vaccines expressing murine EAT-2, or the HIV-1-derived Ag Gag. Compared with appropriate controls, rAd5 vectors expressing EAT-2 facilitated bystander activation of NK, NKT, B, and T cells early after their administration into animals. EAT-2 overexpression also augments the expression of APC (macrophages and dendritic cells) surface markers. Indeed, this multitiered activation of the innate immune system by vaccine-mediated EAT-2 expression enhanced the induction of Ag-specific cellular immune responses. Because both mice and humans express highly conserved EAT-2 adapters, our results suggest that human vaccination strategies that specifically facilitate SLAM signaling may improve vaccine potency when targeting HIV Ags specifically, as well as numerous other vaccine targets in general.

On/off TLR signaling decides proinflammatory or tolerogenic dendritic cell maturation upon CD1d-mediated interaction with invariant NKT cells

Invariant NKT (iNKT) cells play an effector/adjuvant function during antimicrobial and antitumoral immunity and a regulatory role to induce immune tolerance and prevent autoimmunity. iNKT cells that differentially modulate adaptive immunity do not bear a unique phenotype and/or specific cytokine secretion profile, thus opening questions on how a single T cell subset can exert opposite immunological tasks. In this study, we show that iNKT cells perform their dual roles through a single mechanism of action relying on the cognate interaction with myeloid dendritic cells (DCs) and leading to opposite effects depending on the presence of other maturation stimuli simultaneously acting on DCs. The contact of murine purified iNKT cells with immature autologous DCs directly triggers the tolerogenic maturation of DCs, rendering them able to induce regulatory T cell differentiation and prevent autoimmune diabetes in vivo. Conversely, the interaction of the same purified iNKT cells with DCs, in the presence of simultaneous TLR4 stimulation, significantly enhances proinflammatory DC maturation and IL-12 secretion. The different iNKT cell effects are mediated through distinct mechanisms and activation of different molecular pathways within the DC: CD1d signaling and activation of the ERK1/2 pathway for the tolerogenic action, and CD40-CD40L interaction and NF-κB activation for the adjuvant effect. Our data suggest that the DC decision to undergo proinflammatory or tolerogenic maturation results from the integration of different signals received at the time of iNKT cell contact and could have important therapeutic implications for exploiting iNKT cell adjuvant/regulatory properties in autoimmune diseases, infections, and cancer.

NKT cell costimulation: experimental progress and therapeutic promise

Invariant natural killer T (iNKT) cells are innate lymphocytes with unique specificity for glycolipid antigens and remarkable immunomodulatory properties. The role of costimulatory interactions in iNKT cell responses has recently come under scrutiny. Although iNKT cells and their prototype glycolipid agonist α-galactosylceramide (α-GalCer) have shown promise in several clinical trials conducted in patients with cancer or viral diseases, current iNKT cell-based therapies are far from effective. The concomitant targeting of T cell receptors (TCRs) and costimulatory molecules on iNKT cells represents an exciting new opportunity to optimize such therapeutic approaches. Here, we review recent advances in our understanding of iNKT cell costimulation and discuss potential treatment modalities based on the responsiveness of iNKT cells to disease-tailored glycolipids and select costimulatory ligands.

Designing vaccines based on biology of human dendritic cell subsets

The effective vaccines developed against a variety of infectious agents, including polio, measles, and hepatitis B, represent major achievements in medicine. These vaccines, usually composed of microbial antigens, are often associated with an adjuvant that activates dendritic cells (DCs). Many infectious diseases are still in need of an effective vaccine including HIV, malaria, hepatitis C, and tuberculosis. In some cases, the induction of cellular rather than humoral responses may be more important because the goal is to control and eliminate the existing infection rather than to prevent it. Our increased understanding of the mechanisms of antigen presentation, particularly with the description of DC subsets with distinct functions, as well as their plasticity in responding to extrinsic signals, represent opportunities to develop novel vaccines. In addition, we foresee that this increased knowledge will permit us to design vaccines that will reprogram the immune system to intervene therapeutically in cancer, allergy, and autoimmunity.

Invariant NKT cells modulate the suppressive activity of IL-10-secreting neutrophils differentiated with serum amyloid A

Neutrophils are the main effector cells during inflammation, but they can also control excessive inflammatory responses by secreting anti-inflammatory cytokines. However, the mechanisms that modulate their plasticity remain unclear. We now show that systemic serum amyloid A 1 (SAA-1) controls the plasticity of neutrophil differentiation. SAA-1 not only induced anti-inflammatory interleukin 10 (IL-10)-secreting neutrophils but also promoted the interaction of invariant natural killer T cells (iNKT cells) with those neutrophils, a process that limited their suppressive activity by diminishing the production of IL-10 and enhancing the production of IL-12. Because SAA-1-producing melanomas promoted differentiation of IL-10-secreting neutrophils, harnessing iNKT cells could be useful therapeutically by decreasing the frequency of immunosuppressive neutrophils and restoring tumor-specific immune responses.

NKT cells in sepsis

Sepsis is currently a leading cause of death in hospital intensive care units. Previous studies suggest that the pathophysiology of sepsis involves the hyperactivation of complex proinflammatory cascades that include the activation of various immune cells and the exuberant secretion of proinflammatory cytokines by these cells. Natural killer T-cells (NKTs) are a sublineage of T cells that share characteristics of conventional T cells and NK cells and bridge innate and adaptive immunity. More recently, NKT cells have been implicated in microbial immunity, including the onset of sepsis. Moreover, apolipoprotein E (apoE), a component of triglyceride-rich lipoproteins, has been shown to be protective in endotoxemia and gram-negative infections in addition to its well-known role in lipid metabolism. Here, we will review the role of NKT cells in sepsis and septic shock, the immunoregulatory role of apoE in the host immune response to infection, and propose a mechanism for this immunoregulation.

Invariant NKT cells are required for antitumor responses induced by host-versus-graft responses

Based on clinical observations, we have previously shown in a murine model that recipient leukocyte infusion (RLI) induces a host-versus-graft reaction in mixed bone marrow chimeras and that rejection of donor cells leads to a specific antitumor response against recipient malignancies. This response is dependent on T cells and IFN-gamma. We investigated the role of NKT cells (NKTs) in this phenomenon. Depletion of recipient NK1.1(+) cells led to loss of an anti-tumor effect induced by RLI in mixed bone marrow chimeras. In recipients specifically lacking host invariant NKT cells (iNKTs), RLI did not induce an antitumor effect, indicating a critical role for recipient iNKTs. Conversely, specific activation of iNKTs enhanced the anti-tumor effect induced by RLI. Following RLI, recipient iNKTs, NK cells, dendritic cells (DCs), and CD8 T cells were activated. CD8 T cells were the major producers of IFN-gamma. Lack of recipient iNKTs resulted in failure of activation of NK cells and DCs by RLI. Our studies demonstrate a central role for iNKTs in promoting RLI-induced anti-tumor effects and suggest that this pathway involved promotion of the activation of recipient NK cells and DCs.

Heterogeneity in phenotype and function of CD8+ and CD4/CD8 double-negative Natural Killer T cell subsets in sooty mangabeys

BACKGROUND

We have recently reported the presence of CD8(+) and CD4/8 double-negative (DN) natural killer T (NKT) lymphocytes in sooty mangabeys. To investigate differences in the two NKT cell subsets, we compared the phenotype and function of sooty mangabey CD8(+) and DN NKT cells.

METHODS

Flow-sorted NKT lymphocytes from one SIV-negative sooty mangabey were subjected to limiting dilution cloning. Invariant NKT clones were characterized by flow cytometry and cytokine ELISA.

RESULTS

The majority of NKT clones displayed an effector memory phenotype and expressed CXCR3 and NKG2D. While CD8(+) NKT subsets expressed significantly higher levels of granzyme B and perforin and produced more IFN-gamma, the DN NKT subsets secreted significantly more IL-4, IL-13, and IL-10.

CONCLUSIONS

The Th1 and Th2 cytokine bias of CD8(+) and DN NKT cells, respectively, indicates the presence of functionally heterogeneous populations of NKT cells in sooty mangabeys.

The dangerous liaison between iNKT cells and dendritic cells: does it prevent or promote autoimmune diseases?

Invariant natural killer T (iNKT) cells represent an important regulatory T-cell subset that perceives signals of danger and/or cellular distress and modulate the adaptive immune response accordingly. In the presence of pathogens, iNKT cells acquire an adjuvant function that is fundamental to boost anti-microbial and anti-tumor immunity. At the same time, iNKT cells can play a negative regulatory function to maintain peripheral T-cell tolerance toward self-antigens and to prevent autoimmune disease. Both these effects of iNKT cells involve the modulation of the activity of dendritic cells (DCs) through cell-cell interaction. Indeed, iNKT cells can either boost Th1 immunity by enhancing maturation of pro-inflammatory DCs or promote immune tolerance through the maturation of tolerogenic DCs. This dual action of iNKT cells opens questions on the modalities by which a single-cell subset can exert opposite effects on DCs and may even put in question the overall immunosuppressive properties of iNKT cells. This review presents the large body of evidence that shows the ability of iNKT cells to negatively regulate autoimmunity and to prevent autoimmune diseases including multiple sclerosis, type 1 diabetes, rheumatoid arthritis, and systemic lupus erythematosus. In addition, an update is provided on the mechanisms of iNKT-DCs interactions and how this can result in inflammatory or tolerogenic responses.

Murine induced pluripotent stem cells can be derived from and differentiate into natural killer T cells

NKT cells demonstrate antitumor activity when activated to produce Th1 cytokines by DCs loaded with alpha-galactosylceramide, the prototypic NKT cell-activating glycolipid antigen. However, most patients do not have sufficient numbers of NKT cells to induce an effective immune response in this context, indicating a need for a source of NKT cells that could be used to supplement the endogenous cell population. Induced pluripotent stem cells (iPSCs) hold tremendous potential for cell-replacement therapy, but whether it is possible to generate functionally competent NKT cells from iPSCs has not been rigorously assessed. In this study, we successfully derived iPSCs both from embryonic fibroblasts from mice harboring functional NKT cell-specific rearranged T cell receptor loci in the germline and from splenic NKT cells from WT adult mice. These iPSCs could be differentiated into NKT cells in vitro and secreted large amounts of the Th1 cytokine IFN-gamma. Importantly, iPSC-derived NKT cells recapitulated the known adjuvant effects of natural NKT cells and suppressed tumor growth in vivo. These studies demonstrate the feasibility of expanding functionally competent NKT cells via an iPSC phase, an approach that may be adapted for NKT cell-targeted therapy in humans.

Plasticity of invariant NKT cell regulation of allergic airway disease is dependent on IFN-gamma production

Invariant NKT cells (iNKT cells) play a pivotal role in the development of allergen-induced airway hyperresponsiveness (AHR) and inflammation. However, it is unclear what role they play in the initiation (sensitization) phase as opposed to the effector (challenge) phase. The role of iNKT cells during sensitization was examined by determining the response of mice to intratracheal transfer of OVA-pulsed or OVA-alpha-galactosylceramide (OVA/alphaGalCer)-pulsed bone marrow-derived dendritic cells (BMDCs) prior to allergen challenge. Wild-type (WT) recipients of OVA-BMDCs developed AHR, increased airway eosinophilia, and increased levels of Th2 cytokines in bronchoalveolar lavage fluid, whereas recipients of OVA/alphaGalCer BMDCs failed to do so. In contrast, transfer of these same OVA/alphaGalCer BMDCs into IFN-gamma-deficient (IFN-gamma(-/-)) mice enhanced the development of these lung allergic responses, which was reversed by exogenous IFN-gamma treatment following OVA-BMDC transfer. Further, Jalpha18-deficient recipients, which lack iNKT cells, developed the full spectrum of lung allergic responses following reconstitution with highly purified WT liver or spleen iNKT cells and transfer of OVA-BMDCs, whereas reconstituted recipients of OVA/alphaGalCer BMDCs failed to do so. Transfer of iNKT cells from IFN-gamma(-/-) mice restored the development of these responses in Jalpha18-deficient recipients following OVA-BMDC transfer; the responses were enhanced following OVA/alphaGalCer BMDC transfer. iNKT cells from these IFN-gamma(-/-) mice produced higher levels of IL-13 in vitro compared with WT iNKT cells. These data identify IFN-gamma as playing a critical role in dictating the consequences of iNKT cell activation in the initiation phase of the development of AHR and airway inflammation.

Identification of an important immunological difference between virulent varicella-zoster virus and its avirulent vaccine: viral disruption of dendritic cell instruction

Virulent varicella-zoster virus (VZV) can spread in immunocompetent humans, resulting in symptoms mostly of the skin. In contrast, vaccine Oka (V-Oka), the attenuated VZV vaccine strain, only rarely causes clinical reactions. The mechanisms underlying these pathogenetic differences are unclear. In this study, we comparatively analyzed the ability of virulent VZV and V-Oka to modulate instruction of dendritic cells (DCs) by innate signals. DCs isolated from normal human skin were susceptible to infection with VZV and V-Oka. Moreover, inflammatory DCs, which play a crucial role in the stimulation of Th1 immune responses, accumulated in herpes zoster lesions. Infection of inflammatory DCs generated in vitro with virulent VZV or V-Oka resulted in upregulation of CD1c. Upon coculture with CD1c-restricted innate cells, DCs developed a mature phenotype whether infected with virulent VZV or V-Oka. Intriguingly, a striking difference was detected on the functional level. The release of IFN-gamma and IL-12, the signature cytokines of Th1 responses, was enhanced by V-Oka but blocked by virulent VZV. V-Oka and virulent VZV efficiently synergized with CD40L, eliminating the possibility that CD40 signaling was a target of VZV-associated immune evasion. Instead, virulent VZV selectively interfered with signaling through TLR2, which is known to sense VZV. Thus, virulent VZV subverts Th1-promoting instruction of human DCs by blocking TLR2-mediated innate signals that prime IL-12 production by DCs. Taken together, our results demonstrate a novel immune-evasion mechanism of virulent VZV that has been lost during the attenuation process leading to the VZV vaccine strain.

Attenuation of invariant natural killer T-cell anergy induction through intradermal delivery of alpha-galactosylceramide

CD1d restricted, alpha-galactosylceramide (alphaGC) responsive invariant (i)NKT cells positively regulate immune responses. Both intravenous and intradermal administered alphaGC are known to activate iNKT cells. iNKT cells become unresponsive to a second intravenous alphaGC injection, whereas no data are available regarding potential anergy upon intradermal administration. Here, comparative analysis of two intradermal versus two intravenous injections in mice demonstrated that iNKT cell anergy was prevented by intradermal injection and when combined with a vaccine, superior tumor protection afforded by intradermally administered alphaGC. Moreover, human skin dendritic cells (DC) took up intradermally injected alphaGC and activated iNKT cells upon migration, while iNKT cells in human skin-draining lymph nodes expanded in response to alphaGC presented either by exogenously added DC or by CD1d positive antigen presenting cells in the lymph nodes. In conclusion, glycolipids such as alphaGC may greatly improve the efficacy of skin immunization strategies, targeting cutaneous and lymph node DC.

Synthetic iNKT cell-agonists as vaccine adjuvants--finding the balance

The unique position of invariant natural killer T (iNKT) cells at the interface of the innate and adaptive arms of the immune response, combined with their ability to modulate the activity of antigen-presenting cells, has led to their intensive investigation as a means of augmenting the immune response both in vaccination strategies for microbial infections and in tumor immunotherapy. Several synthetic iNKT-cell agonists that have potential as vaccine adjuvants have been identified, but these are not without their limitations-strong agonists can lead to the undesirable effects associated with overstimulation of the immune system, whereas too weak agonists may provide insufficient iNKT cell help to stimulate maturation of dendritic cells and differentiation of B cells. In this article we explore strategies being investigated as means of increasing the specificity of and controlling the magnitude of the immune response generated by activation of iNKT cells with synthetic agonists.

Fatty acid amide hydrolase shapes NKT cell responses by influencing the serum transport of lipid antigen in mice

The potent regulatory properties of NKT cells render this subset of lipid-specific T cells a promising target for immunotherapeutic interventions. The marine sponge glycolipid alpha-galactosylceramide (alphaGalCer) is the proto-typic NKT cell agonist, which elicits this function when bound to CD1d. However, our understanding of the in vivo properties of NKT cell agonists and the host factors that control their bioactivity remains very limited. In this report, we isolated the enzyme fatty acid amide hydrolase (FAAH) from mouse serum as an alphaGalCer-binding protein that modulates the induction of key effector functions of NKT cells in vivo. FAAH bound alphaGalCer in vivo and in vitro and was required for the efficient targeting of lipid antigens for CD1d presentation. Immunization of Faah-deficient mice with alphaGalCer resulted in a reduced systemic cytokine production, but enhanced expansion of splenic NKT cells. This distinct NKT response conferred a drastically increased adjuvant effect and strongly promoted protective CTL responses. Thus, our findings identify not only the presence of FAAH in normal mouse serum, but also its critical role in the tuning of immune responses to lipid antigens by orchestrating their transport and targeting for NKT cell activation. Our results suggest that the serum transport of lipid antigens directly shapes the quality of NKT cell responses, which could potentially be modulated in support of novel vaccination strategies.

Regulation of the induction and function of cytotoxic T lymphocytes by natural killer T cell

Cytotoxic T lymphocytes (CTLs) play a crucial role in the infections and the antitumor immunity. Induction and activation of antigen-specific CTLs is an important strategy in immunotherapy for various diseases, and several researchers have focused on the modulation of CTL induction and function. Natural killer T (NKT) cells are an important focus area of researchers studying immunomodulatory responses to tumors and infectious diseases. CD1d-restricted NKT cells consist of type I NKT cells and type II NKT cells. α-galactosylceramide (α-GalCer)-activated type I NKT cells secrete both Th1 (e.g., IFN-γ) and Th2 cytokines, affect the expression of costimulatory molecules in immune cells, and regulate the host immune system. Type II NKT cells, however, are stimulated by sulfatide, a self-glycolipid derived from myelin, and play an immunosuppressive role in animal model of autoimmune diseases. CTL generation, activation, and suppression are strongly affected by activated type I and type II NKT cells. Thus, the regulation of these NKT cells leads to the modification of CTL function. CTLs contribute to antimicrobial responses, antitumor immune and autoimmune responses. Understanding the role of NKT cells in the regulation of CTL generation, activation, and suppression enable the development of novel treatment strategies for these diseases.

Nasal vaccination with P6 outer membrane protein and alpha-galactosylceramide induces nontypeable Haemophilus influenzae-specific protective immunity associated with NKT cell activation and dendritic cell expansion in nasopharynx

The efficacy of alpha-galactosylceramide (alpha-GalCer) as a mucosal adjuvant was examined. Mice were immunized intranasally with nontypeable Haemophilus influenzae (NTHi) P6 protein and alpha-GalCer. P6-specific antibody responses in the form of P6-specific IgA in nasal washes and serum IgG titers were significantly elevated. Splenic CD4(+) T cells expressed P6-specific Th1 and Th2 cytokine mRNA. In addition, NTHi was quantified in nasal washes following NTHi challenges, and the clearance of NTHi from the nasopharynx was also enhanced. These results indicate that alpha-GalCer might be an effective mucosal adjuvant.

Autoreactive natural killer T cells: promoting immune protection and immune tolerance through varied interactions with myeloid antigen-presenting cells

Natural killer T (NKT) cells are innate T lymphocytes that are restricted by CD1d antigen-presenting molecules and recognize lipids and glycolipids as antigens. NKT cells have attracted attention for their potent immunoregulatory effects. Like other types of regulatory lymphocytes, a high proportion of NKT cells appear to be autoreactive to self antigens. Thus, as myeloid antigen-presenting cells (APCs) such as monocytes, dendritic cells (DCs) and myeloid-derived suppressor cells (MDSCs) constitutively express CD1d, NKT cells are able to interact with these APCs not only during times of immune activation but also in immunologically quiescent periods. The interactions of NKT cells with myeloid APCs can have either pro-inflammatory or tolerizing outcomes, and a central question is how the ensuing response is determined. Here we bring together published results from a variety of model systems to highlight three critical factors that influence the outcome of the NKT-APC interaction: (i) the strength of the antigenic signal delivered to the NKT cell, as determined by antigen abundance and/or T-cell receptor (TCR) affinity; (ii) the presence or absence of cytokines that costimulate NKT cells [e.g. interleukin (IL)-12, IL-18 and interferon (IFN)-alpha]; (iii) APC intrinsic factors such as differentiation state (e.g. monocyte versus DC) and Toll-like receptor (TLR) stimulation. Together with recent findings that demonstrate new links between NKT cell activation and endogenous lipid metabolism, these results outline a picture in which the functions of NKT cells are closely attuned to the existing biological context. Thus, NKT cells may actively promote tolerance until a critical level of danger signals arises, at which point they switch to activating pro-inflammatory immune responses.

Roles of CD122+ cells in resistance against Neospora caninum infection in a murine model

Innate cells, such as natural killer (NK) cells and NKT cells, play essential roles as primary effector cells at the interface between the host and parasite until establishment of adaptive immunity. However, the roles of NK and NKT cells in defense against Neospora caninum have not been well clarified. NK and NKT cells were depleted by the treatment with an anti-CD122 (interleukin-2 receptor beta chain) monoclonal antibody (mAb, TM-β1) in vivo. The parasite burden in the brain of mice was promoted by the treatment with anti-CD122 mAb. However, there was no significant difference in the infection rates between controls and the mice treated with anti-asialoGM1 antibody to deplete NK cells. Activation of CD4+ T cells was suppressed in the mice treated with anti-CD122 mAb compared with controls and the mice treated with anti-asialoGM1 antibody. On the other hand, depletion of CD122+ cells or NK cells did not affect the number of activated CD8+ T cells, dendritic cells and B cells following N. caninum infection. These results indicate that CD122+ cells (probably NKT cells) play a crucial role in host defense by activating CD4+ T cells against N. caninum infection.

NKT cell-dependent regulation of secondary antigen-specific, conventional CD4+ T cell immune responses

NKT cells are considered to be innate-like regulatory cells. However, their regulatory functions in adaptive immune responses have not been studied in detail. In this study, we investigated the immunoregulatory functions of NKT cells during the secondary phase of an Ag-specific CD4(+) T cell response. When compared with OVA-specific effector CD4(+) T cells adoptively transferred into NKT cell-deficient naive CD1d(-/-) mice, the same T cells transferred into naive CD1d(+/-) mice exhibited substantially stronger immune responses on OVA challenge. The enhanced immune response of the transferred CD4(+) T cells in the presence of NKT cells correlated with an increase in their proliferation in vivo. In addition, T cells transferred into CD1d(+/-) recipients showed enhanced cytokine productions relative to T cells in CD1d(-/-) recipients. To elucidate the physiological relevance of the regulatory role of NKT cells in a disease setting, OVA-specific asthma was induced in recipient mice after adoptive transfer of OVA-specific CD4(+) T cells. CD1d(+/-) recipients showed stronger asthmatic phenotypes in all indications when compared with CD1d(-/-) recipients. Taken together, these results suggest that NKT cells are critical for the regulation of Ag-specific, conventional CD4(+) T cells during the secondary phase of an adaptive immune response.

CD169(+) macrophages present lipid antigens to mediate early activation of iNKT cells in lymph nodes

Invariant natural killer T cells (iNKT cells) are involved in the host defense against microbial infection. Although it is known that iNKT cells recognize glycolipids presented by CD1d, how and where they encounter antigen in vivo remains unclear. Here we used multiphoton microscopy to visualize the dynamics and activation of iNKT cells in lymph nodes. After antigen administration, iNKT cells became confined in a CD1d-dependent manner in close proximity to subcapsular sinus CD169(+) macrophages. These macrophages retained, internalized and presented lipid antigen and were required for iNKT cell activation, cytokine production and population expansion. Thus, CD169(+) macrophages can act as true antigen-presenting cells controlling early iNKT cell activation and favoring the fast initiation of immune responses.

Paucity of CD4+ natural killer T (NKT) lymphocytes in sooty mangabeys is associated with lack of NKT cell depletion after SIV infection

Lack of chronic immune activation in the presence of persistent viremia is a key feature that distinguishes nonpathogenic simian immunodeficiency virus (SIV) infection in natural hosts from pathogenic SIV and HIV infection. To elucidate novel mechanisms downmodulating immune activation in natural hosts of SIV infection, we investigated natural killer T (NKT) lymphocytes in sooty mangabeys. NKT lymphocytes are a potent immunoregulatory arm of the innate immune system that recognize glycolipid antigens presented on the nonpolymorphic MHC-class I-like CD1d molecules. In a cross-sectional analysis of 50 SIV-negative and 50 naturally SIV-infected sooty mangabeys, ligand alpha-galactosylceramide loaded CD1d tetramers co-staining with Valpha24-positive invariant NKT lymphocytes were detected at frequencies >or=0.002% of circulating T lymphocytes in approximately half of the animals. In contrast to published reports in Asian macaques, sooty mangabey NKT lymphocytes consisted of CD8(+) and CD4/CD8 double-negative T lymphocytes that were CXCR3-positive and CCR5-negative suggesting that they trafficked to sites of inflammation without being susceptible to SIV infection. Consistent with these findings, there was no difference in the frequency or phenotype of NKT lymphocytes between SIV-negative and SIV-infected sooty mangabeys. On stimulation with alpha-galactosylceramide loaded on human CD1d molecules, sooty mangabey NKT lymphocytes underwent degranulation and secreted IFN-gamma, TNF-alpha, IL-2, IL-13, and IL-10, indicating the presence of both effector and immunoregulatory functional capabilities. The unique absence of CD4(+) NKT lymphocytes in sooty mangabeys, combined with their IL-10 cytokine-secreting ability and preservation following SIV infection, raises the possibility that NKT lymphocytes might play a role in downmodulating immune activation in SIV-infected sooty mangabeys.

Alternative cross-priming through CCL17-CCR4-mediated attraction of CTLs toward NKT cell-licensed DCs

Cross-priming allows dendritic cells (DCs) to induce cytotoxic T cell (CTL) responses to extracellular antigens. DCs require cognate 'licensing' for cross-priming, classically by helper T cells. Here we demonstrate an alternative mechanism for cognate licensing by natural killer T (NKT) cells recognizing microbial or synthetic glycolipid antigens. Such licensing caused cross-priming CD8alpha(+) DCs to produce the chemokine CCL17, which attracted naive CTLs expressing the chemokine receptor CCR4. In contrast, DCs licensed by helper T cells recruited CTLs using CCR5 ligands. Thus, depending on the type of antigen they encounter, DCs can be licensed for cross-priming by NKT cells or helper T cells and use at least two independent chemokine pathways to attract naive CTLs. Because these chemokines acted synergistically, this can potentially be exploited to improve vaccinations.

Langerin+ CD8alpha+ dendritic cells are critical for cross-priming and IL-12 production in response to systemic antigens

Distinct dendritic cell (DC) subsets differ with respect to pathways of Ag uptake and intracellular routing to MHC class I or MHC class II molecules. Murine studies suggest a specialized role for CD8alpha(+) DC in cross-presentation, where exogenous Ags are presented on MHC class I molecules to CD8(+) T cells, while CD8alpha(-) DC are more likely to present extracellular Ags on MHC class II molecules to CD4(+) T cells. As a proportion of CD8alpha(+) DC have been shown to express langerin (CD207), we investigated the role of langerin(+)CD8alpha(+) DC in presenting Ag and priming T cell responses to soluble Ags. When splenic DC populations were sorted from animals administered protein i.v., the ability to cross-present Ag was restricted to the langerin(+) compartment of the CD8alpha(+) DC population. The langerin(+)CD8alpha(+) DC population was also susceptible to depletion following administration of cytochrome c, which is known to trigger apoptosis if diverted to the cytosol. Cross-priming of CTL in the presence of the adjuvant activity of the TLR2 ligand N-palmitoyl-S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-[R]-Cys-[S]-Serl-[S]-Lys4-trihydrochloride or the invariant NKT cell ligand alpha-galactosylceramide was severely impaired in animals selectively depleted of langerin(+) cells in vivo. The production of IL-12p40 in response to these systemic activation stimuli was restricted to langerin(+)CD8alpha(+) DC, and the release of IL-12p70 into the serum following invariant NKT cell activation was ablated in the absence of langerin(+) cells. These data suggest a critical role for the langerin(+) compartment of the CD8alpha(+) DC population in cross-priming and IL-12 production.

Potent anti-tumor responses to immunization with dendritic cells loaded with tumor tissue and an NKT cell ligand

Cancer immunotherapy is well tolerated and specific, but its efficacy remains variable. To enhance anti-tumor CD8(+) T-cell responses induced by immunization with antigen-loaded dendritic cells (DCs), we explored the impact of eliciting a potent source of T-cell help from activated invariant natural killer (NK)-like T cells (iNKT cells) using the specific glycolipid ligand alpha-galactosylceramide (alpha-GalCer). As cytokines released by iNKT cells may drive proliferation of CD4(+)CD25(+) regulatory T cells (Tregs), we assessed this immunization strategy in animals treated with anti-CD25 antibody to inactivate Treg function. Combining DC immunization with iNKT cell activation was found to significantly enhance anti-tumor activity, which was improved further by the prior inactivation of Tregs. The improved anti-tumor activity with Treg inactivation was associated with a prolonged proliferative burst of responding CD8(+) T cells. We could find no evidence that inclusion of alpha-GalCer in the vaccine enhanced Treg numbers, or that the 'helper' function of iNKT cells was improved in the absence of Treg activity. Rather, the two activities appeared to act independently to improve the tumor-specific T-cell response. Inactivating regulatory T cells and eliciting iNKT cell activation are therefore two useful strategies that can be used in combination to improve anti-tumor immunization with antigen-loaded DCs.

A double-edged sword: the role of NKT cells in malaria and HIV infection and immunity

NKT cells are known to play a role against certain microbial infections, including malaria and HIV, two major global infectious diseases. NKT cells exhibit either protective or pathogenic role against malaria. They are depleted by HIV infection and have a direct pathogenic role against many opportunistic infections common in end-stage AIDS. This review discusses the various features of the interaction between NKT cells and malaria parasites and HIV, and the potential to harness this interaction for therapeutic and vaccine strategies.

Endogenous IL-21 restricts CD8+ T cell expansion and is not required for tumor immunity

IL-21 has antitumor activity through actions on NK cells and CD8(+) T cells, and is currently in clinical development for the treatment of cancer. However, no studies have addressed the role of endogenous IL-21 in tumor immunity. In this study, we have studied both primary and secondary immune responses in IL-21(-/-) and IL-21R(-/-) mice against several experimental tumors. We found intact immune surveillance toward methylcholanthrene-induced sarcomas in IL-21(-/-) and IL-21R(-/-) mice compared with wild-type mice and B16 melanomas showed equal growth kinetics and development of lung metastases. IL-21R(-/-) mice showed competent NK cell-mediated rejection of NKG2D ligand (Rae1beta) expressing H-2b(-) RMAS lymphomas and sustained transition to CD8(+) T cell-dependent memory against H-2b(+) RMA lymphomas. alpha-Galactosylceramide stimulation showed equal expansion and activation of NKT and NK cells and mounted a powerful antitumor response in the absence of IL-21 signaling, despite reduced expression of granzyme B in NKT, NK, and CD8(+) T cells. Surprisingly, host IL-21 significantly restricted the expansion of Ag-specific CD8(+) T cells and inhibited primary CD8(+) T cell immunity against OVA-expressing EG7 lymphomas, as well as the secondary expansion of memory CD8(+) T cells. However, host IL-21 did not alter the growth of less immunogenic MC38 colon carcinomas with dim OVA expression. Overall, our results show that endogenous IL-21/IL-21R is not required for NK, NKT, and CD8(+) T cell-mediated tumor immunity, but restricts Ag-specific CD8(+) T cell expansion and rejection of immunogenic tumors, indicating novel immunosuppressive actions of this cytokine.

A new model for the presentation of tumor-associated antigens and the quest for an anticancer vaccine: a solution to the synthesis challenge via ring-closing metathesis

Fully synthetic, carbohydrate-based antitumor vaccine candidates have been synthesized in highly clustered modes. Multiple copies of tumor-associated carbohydrate antigens, Tn and STn, were assembled on a single cyclic peptide scaffold in a highly convergent manner. Ring-closing metathesis-mediated incorporation of an internal cross-linker was also demonstrated. In particular, this rigidified cross-linked construct would enhance a cluster-recognizing antibody response by retaining an appropriate distance between glycans attached to the peptide platform. Details of the design and synthesis of highly clustered antigens are described herein.

The specialized iNKT cell system recognizes glycolipid antigens and bridges the innate and acquired immune systems with potential applications for cancer therapy

Invariant NKT (iNKT) cells bridge innate and acquired immunity and play an important role in both protective and regulatory responses. The nature of the response is dictated by the initial cytokine environment: interaction with IL-10-producing cells induces negative regulatory T(h)2/regulatory T cell-type iNKT cells, while that with IL-12-producing cells results in pro-inflammatory T(h)1-type responses. Particularly, in the anti-tumor response, iNKT cells mediate adjuvant activity by their production of IFN-gamma, which in turn activates both innate and acquired immune systems. Thus, upon activation of iNKT cells, both MHC(-) and MHC(+) tumor cells can be efficiently eliminated. On the basis of these mechanisms, iNKT cell-targeted adjuvant cell therapies have been developed and have shown great promise in initial clinical trials on cancer patients.