TRAIL expression by activated human CD4(+)V alpha 24NKT cells induces in vitro and in vivo apoptosis of human acute myeloid leukemia cells

Human Valpha24NKT cells are activated by alpha-galactosylceramide (alpha-GalCer)-pulsed dendritic cells in a CD1d-dependent and a T-cell receptor-mediated manner. Here, we demonstrate that CD4(+)V alpha 24NKT cells derived from a patient with acute myeloid leukemia (AML) M4 are phenotypically similar to those of healthy donors and, in common with those derived from healthy donors, express tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) when the cells are activated by alpha-GalCer-pulsed dendritic cells but not prior to activation. We also show that myeloid leukemia cells from patients with AML M4, but not from patients with AML M0 or M1, undergo apoptosis following culture with TRAIL-expressing autologous or allogeneic healthy donor V alpha 24NKT cells. Apoptosis of AML M4 leukemia cells from patient peripheral blood was almost completely blocked by a neutralizing monoclonal antibody against TRAIL, indicating that TRAIL on V alpha 24NKT cells is essential for the induction of apoptosis in AML M4 leukemia cells. A nonobese diabetic-severe combined immunodeficient human leukemia (AML M4) model showed that human activated CD4(+)V alpha 24NKT cells induced apoptosis of human leukemia cells in vivo. This is the first evidence that activated V alpha 24NKT cells express TRAIL and that TRAIL causes apoptosis of monocytic leukemia cells from patients with AML M4 in vitro and in vivo. Adoptive immune therapy with activated V alpha 24NKT cells, or other strategies to increase activated V alpha 24NKT cells in vivo, may be of benefit to patients with AML M4. (Blood. 2001;97:2067-2074)

MHC-II-independent CD4+ T cells induce colitis in immunodeficient RAG-/- hosts

CD4(+) alpha beta T cells from either normal C57BL/6 (B6) or MHC-II-deficient (A alpha(-/-) or A beta(-/-)) B6 donor mice engrafted into congenic immunodeficient RAG1(-/-) B6 hosts induced an aggressive inflammatory bowel disease (IBD). Furthermore, CD4(+) T cells from CD1d(-/-) knockout (KO) B6 donor mice but not those from MHC-I(-/-) (homozygous transgenic mice deficient for beta(2)-microglobulin) KO B6 mice induced a colitis in RAG(-/-) hosts. Abundant numbers of in vivo activated (CD69(high)CD44(high)CD28(high)) NK1(+) and NK1(-) CD4(+) T cells were isolated from the inflamed colonic lamina propria (cLP) of transplanted mice with IBD that produced large amounts of TNF-alpha and IFN-gamma but low amounts of IL-4 and IL-10. IBD-associated cLP Th1 CD4(+) T cell populations were polyclonal and MHC-II-restricted when derived from normal B6 donor mice, but oligoclonal and apparently MHC-I-restricted when derived from MHC-II-deficient (A alpha(-/-) or A beta(-/-)) B6 donor mice. cLP CD4(+) T cell populations from homozygous transgenic mice deficient for beta(2)-microglobulin KO B6 donor mice engrafted into RAG(-/-) hosts were Th2 and MHC-II restricted. These data indicate that MHC-II-dependent as well as MHC-II-independent CD4(+) T cells can induce a severe and lethal IBD in congenic, immunodeficient hosts, but that the former need the latter to express its IBD-inducing potential.

Human CD1d-glycolipid tetramers generated by in vitro oxidative refolding chromatography

CD1 molecules are specialized in presenting lipids to T lymphocytes, but identification and isolation of CD1-restricted lipid specific T cells has been hampered by the lack of reliable and sensitive techniques. We here report the construction of CD1d-glycolipid tetramers from fully denatured human CD1d molecules by using the technique of oxidative refolding chromatography. We demonstrate that chaperone- and foldase-assisted refolding of denatured CD1d molecules and beta(2)-microglobulin in the presence of synthetic lipids is a rapid method for the generation of functional and specific CD1d tetramers, which unlike previously published protocols ensures isolation of CD1d tetramers loaded with a single lipid species. The use of human CD1d-alpha-galactosylceramide tetramers for ex vivo staining of peripheral blood lymphocytes and intrahepatic T cells from patients with viral liver cirrhosis allowed for the first time simultaneous analysis of frequency and specificity of natural killer T cells in human clinical samples. Application of this protocol to other members of the CD1 family will provide powerful tools to investigate lipid-specific T cell immune responses in health and in disease.

Dendritic cells rapidly undergo apoptosis in vitro following culture with activated CD4+ Valpha24 natural killer T cells expressing CD40L

Human Valpha24 natural killer T (Valpha24NKT) cells are activated by alpha-glycosylceramide-pulsed dendritic cells (DCs) in a CD1d-dependent and T-cell receptor-mediated manner. There are two major subpopulations of Valpha24NKT cells, CD4- CD8- Valpha24NKT and CD4+ Valpha24NKT cells. We have recently shown that activated CD4- CD8- Valpha24NKT cells have cytotoxic activity against DCs, but knowledge of the molecules responsible for cytotoxicity of Valpha24NKT cells is currently limited. We aimed to investigate whether CD4+ Valpha24NKT cells also have cytotoxic activity against DCs and to determine the mechanisms underlying any observed cytotoxic activity. We demonstrated that activated CD4+ Valpha24NKT cells [CD40 ligand (CD40L) -positive] have cytotoxic activity against DCs (strongly CD40-positive), but not against monocytes (weakly CD40-positive) or phytohaemagglutinin blast T cells (CD40-negative), and that apoptosis of DCs significantly contributes to the observed cytotoxicity. The apoptosis of DCs following culture with activated CD4+ Valpha24NKT cells, but not with resting CD4+ Valpha24NKT cells (CD40L-negative), was partially inhibited by anti-CD40L mAb. Direct ligation of CD40 on the DCs by the anti-CD40 antibody also induced apoptosis of DCs. Our results suggest that CD40-CD40L interaction plays an important role in the induction of apoptosis of DCs following culture with activated CD4+ Valpha24NKT cells. The apoptosis of DCs from normal donors, triggered by the CD40-CD40L interaction, may contribute to the homeostatic regulation of the normal human immune system, preventing the interminable activation of activated CD4+ Valpha24NKT cells by virtue of apoptosis of DCs.

Glycolipid antigen processing for presentation by CD1d molecules

The requirement for processing glycolipid antigens in T cell recognition was examined with mouse CD1d-mediated responses to glycosphingolipids (GSLs). Although some disaccharide GSL antigens can be recognized without processing, the responses to three other antigens, including the disaccharide GSL Gal(alpha1-->2)GalCer (Gal, galactose; GalCer, galactosylceramide), required removal of the terminal sugars to permit interaction with the T cell receptor. A lysosomal enzyme, alpha-galactosidase A, was responsible for the processing of Gal(alpha1-->2)GalCer to generate the antigenic monosaccharide epitope. These data demonstrate a carbohydrate antigen processing system analogous to that used for peptides and an ability of T cells to recognize processed fragments of complex glycolipids.

IL-18 enhances IL-4 production by ligand-activated NKT lymphocytes: a pro-Th2 effect of IL-18 exerted through NKT cells

NKT cells are a remarkably versatile population whose functional capacities are determined by cytokines present in their microenvironment. In this study, we provide evidence for a new immunoregulatory effect of the proinflammatory cytokine IL-18 on NKT cells. We found that IL-18, mainly known for its involvement in NK cell activation and in Th 1 immune responses, substantially enhanced IL-4 production as well as the percentage of IL-4(+) cells among NKT lymphocytes activated by their specific ligand alpha-galactosylceramide (alpha-GalCer). The effect of IL-18 on IL-4 production by activated NKT cells took place both in vivo and in vitro and was not affected by IL-12 which increased IFN-gamma secretion in the same conditions. We show that NKT cells are the main targets for IL-18-induced IL-4 production since it occurred neither in NKT-deficient mice nor after stimulation of Th2 lymphocytes. Finally, we provide evidence that the IL-4 promptly generated by NKT cells in response to IL-18 plus alpha-galactosylceramide in vivo can effectively contribute to the adaptive Th2 immune response by up-regulating the early activation marker CD69 on B cells. Our data support the notion that, in contrast to the exclusive IFN-gamma inducer IL-12, IL-18 acts in a more subtle manner as a costimulatory factor in both pro-Th1 and pro-Th2 responses depending on the nature of the stimulation and the target cells.

Potent expansion of human natural killer T cells using alpha-galactosylceramide (KRN7000)-loaded monocyte-derived dendritic cells, cultured in the presence of IL-7 and IL-15

Natural killer T (NKT) cells have an extremely restricted T-cell receptor repertoire, in man consisting of a Valpha24 chain preferentially paired with a Vbeta11 chain, and play crucial roles in various immune responses. Characterization of circulating Valpha24(+)Vbeta11(+)-T cells is hampered by their low frequencies. The alpha-galactosylceramide KRN7000 was reported to be presented by CD1d to NKT cells. Since dendritic cells (DC) are potent antigen presenting cells, and have been shown to express CD1d, we analyzed whether these cells could efficiently mediate expansion of Valpha24(+)Vbeta11(+)-T cells. During a 7-day co-culture of peripheral blood mononuclear cells and KRN7000-loaded mature monocyte derived DC (moDC) in the presence of interleukin-7 (IL-7) and IL-15, we observed up to 76-fold expansion of Valpha24(+)Vbeta11(+)-T cells. The expanded Valpha24(+)Vbeta11(+)-T cells expressed the cytotoxic molecule granzyme B, showed negligible expression of Fas ligand and could be induced to express high levels of interferon-gamma, while retaining the capacity to produce IL-4. B cells, expressing CD1d, could also present KRN7000, but Valpha24(+)Vbeta11(+)-T cell expansion was only observed in the presence of IL-7 and/or IL-15. Considering the low frequency of circulating Valpha24(+)Vbeta11(+)-T cells, the present method for expansion of Valpha24(+)Vbeta11(+)-T cells using KRN7000-loaded mature moDC will be of value for the further characterization of this unique T cell subset.

Low expression level but potent antigen presenting function of CD1d on monocyte lineage cells

CD1d is a key antigen-presenting molecule involved in the selection and activation of a highly conserved T cell subset known as NK T cells. In this study, we analyzed the expression, regulation and function of human CD1d by various antigen-presenting cells (APC) of myeloid origin, including circulating monocytes, monocyte-derived dendritic cells and macrophages. CD1d was expressed as a mature glycoprotein by these cells, and unlike the other members of the human CD1 family its expression was constitutive and was not strongly up-regulated by GM-CSF and IL-4 or a range of other cytokines. Despite their remarkably low surface expression of CD1d, all myeloid lineage cells tested were extremely potent APC for responses of NK T cell clones to the synthetic glycolipid antigen, alpha-galactosyl ceramide. Prominent localization of CD1d to the endocytic system of monocyte lineage cells was observed, and functional studies suggested that this was important for achieving efficient antigen loading onto CD1d. Overall, these results support the view that monocyte lineage cells are important stimulators of CD1d-restricted immune responses, while also underscoring the unique regulation of CD1d expression by these cells.

NKT lymphocyte ontogeny and function are impaired in low antibody-producer Biozzi mice: gene mapping in the interval-specific congenic strains raised for immunomodulatory genes

NKT cells are CD4(+) or CD4(-)CD8(-) CD1d-restricted lymphocytes, characterized by the property to rapidly produce IL-4 and IFN-gamma in response to TCR ligation. This IL-4 burst is lacking in autoimmunity-prone SJL and NOD strains of mice, which suggests an immunoregulatory role for NKT cells. The NKT cell status was thus investigated in the genetically selected high (H) and low (L) antibody-producer mice. The results show that (i) the frequency of cells expressing the NKT cell markers is 3- to 4-fold lower in thymus and spleen from L than H mice, (ii) L mice spleen cells did not produce IL-4 following injection of anti-TCR alpha beta antibody, and (iii) L mice thymus and spleen cells failed to produce IL-4 after in vitro stimulation by anti-TCR alpha beta antibody or alpha-galactosylceramide, a newly described NKT cell ligand. These parameters were investigated in six interval-specific congenic strains raised for the quantitative trait loci which contain the immunomodulatory genes responsible for the high/low antibody production phenotypes. IL-4 production recovery occurred only in the congenic strain in which the H origin chromosome 4 segment was introgressed on the L background. This finding was not due to increased NKT cell frequency but appeared dependent of antigen-presenting cells in co-culture experiments. This result strongly suggests the presence of gene(s) modulating NKT function on chromosome 4, close to several genes predisposing to autoimmunity.

A subset of NKT cells that lacks the NK1.1 marker, expresses CD1d molecules, and autopresents the alpha-galactosylceramide antigen

In the present report, we characterize a novel T cell subset that shares with the NKT cell lineage both CD1d-restriction and high reactivity in vivo and in vitro to the alpha-galactosylceramide (alpha-GalCer) glycolipid. These cells preferentially use the canonical Valpha14-Jalpha281 TCR-alpha-chain and Vbeta8 TCR-beta segments, and are stimulated by alpha-GalCer in a CD1d-dependent fashion. However, in contrast to classical NKT cells, they lack the NK1.1 marker and express high surface levels of CD1d molecules. In addition, this NK1.1(-) CD1d(high) T subset, further referred to as CD1d(high) NKT cells, can be distinguished by its unique functional features. Although NK1.1(+) NKT cells require exogenous CD1d-presenting cells to make them responsive to alpha-GalCer, CD1d(high) NKT cells can engage their own surface CD1d in an autocrine and/or paracrine manner. Furthermore, in response to alpha-GalCer, CD1d(high) NKT cells produce high amounts of IL-4 and moderate amounts of IFN-gamma, a cytokine profile more consistent with a Th2-like phenotype rather than the Th0-like phenotype typical of NK1.1(+) NKT cells. Our work reveals a far greater level of complexity within the NKT cell population than previously recognized and provides the first evidence for T cells that can be activated upon TCR ligation by CD1d-restricted recognition of their ligand in the absence of conventional APCs.

Fas/Fas ligand interactions promote activation-induced cell death of NK T lymphocytes

NKT cells are a versatile population whose immunoregulatory functions are modulated by their microenvironment. We demonstrate herein that in addition to their IFN-gamma production, NKT lymphocytes stimulated with IL-12 plus IL-18 in vitro underwent activation in terms of CD69 expression, blast transformation, and proliferation. Yet they were unable to survive in culture because, once activated, they were rapidly eliminated by apoptosis, even in the presence of their survival factor IL-7. This process was preceded by up-regulation of Fas (CD95) and Fas ligand expression in response to IL-12 plus IL-18 and was blocked by zVAD, a large spectrum caspase inhibitor, as well as by anti-Fas ligand mAb, suggesting the involvement of the Fas pathway. In accordance with this idea, NKT cells from Fas-deficient C57BL/6-lpr/lpr mice did not die in these conditions, although they shared the same features of cell activation as their wild-type counterpart. Activation-induced cell death occurred also after TCR engagement in vivo, since NKT cells became apoptotic after injection of their cognate ligand, alpha-galactosylceramide, in wild-type, but not in Fas-deficient, mice. Taken together, our data provide the first evidence for a new Fas-dependent mechanism allowing the elimination of TCR-dependent or -independent activated NKT cells, which are potentially dangerous to the organism.

Natural killer T cell activation inhibits hepatitis B virus replication in vivo

We have previously reported that hepatitis B virus (HBV)-specific CD8(+) cytotoxic T lymphocytes and CD4(+) helper T lymphocytes can inhibit HBV replication in the liver of HBV transgenic mice by secreting interferon (IFN)-gamma when they recognize viral antigen. To determine whether an activated innate immune system can also inhibit HBV replication, in this study we activated natural killer T (NKT) cells in the liver of HBV transgenic mice by a single injection of alpha-galactosylceramide (alpha-GalCer), a glycolipid antigen presented to Valpha14(+)NK1.1(+) T cells by the nonclassical major histocompatibility complex class I-like molecule CD1d. Within 24 h of alpha-GalCer injection, IFN-gamma and IFN-alpha/beta were detected in the liver of HBV transgenic mice and HBV replication was abolished. Both of these events were temporally associated with the rapid disappearance of NKT cells from the liver, presumably reflecting activation-induced cell death, and by the recruitment of activated NK cells into the organ. In addition, prior antibody-mediated depletion of CD4(+) and CD8(+) T cells from the mice did not diminish the ability of alpha-GalCer to trigger the disappearance of HBV from the liver, indicating that conventional T cells were not downstream mediators of this effect. Finally, the antiviral effect of alpha-GalCer was inhibited in mice that are genetically deficient for either IFN-gamma or the IFN-alpha/beta receptor, indicating that most of the antiviral activity of alpha-GalCer is mediated by these cytokines. Based on these results, we conclude that alpha-GalCer inhibits HBV replication by directly activating NKT cells and by secondarily activating NK cells to secrete antiviral cytokines in the liver. In view of these findings, we suggest that, if activated, the innate immune response, like the adaptive immune response, has the potential to control viral replication during natural HBV infection. In addition, the data suggest that therapeutic activation of NKT cells may represent a new strategy for the treatment of chronic HBV infection.

Tracking the response of natural killer T cells to a glycolipid antigen using CD1d tetramers

A major group of natural killer (NK) T cells express an invariant Valpha14(+) T cell receptor (TCR) specific for the lipoglycan alpha-galactosylceramide (alpha-GalCer), which is presented by CD1d. These cells may have an important immune regulatory function, but an understanding of their biology has been hampered by the lack of suitable reagents for tracking them in vivo. Here we show that tetramers of mouse CD1d loaded with alpha-GalCer are a sensitive and highly specific reagent for identifying Valpha14(+) NK T cells. Using these tetramers, we find that alpha-GalCer-specific T lymphocytes are more widely distributed than was previously appreciated, with populations of largely NK1.1(-) but tetramer-binding T cells present in the lymph nodes and the intestine. Injection of alpha-GalCer leads to the production of both interferon gamma and interleukin 4 by nearly all NK T cells in the liver and the majority of the spleen within 2 h. These cells mostly disappear by 5 h, and they do not reappear after 1 wk. Curiously, tetramer-positive thymocytes do not rapidly synthesize cytokines, nor do they undergo decreases in cell number after lipid antigen stimulation, although they express equivalent TCR levels. In summary, the data presented here demonstrate that alpha-GalCer-specific NK T cells undergo a unique and highly compartmentalized response to antigenic stimulation.

Alpha-glycosylceramides enhance the antitumor cytotoxicity of hepatic lymphocytes obtained from cancer patients by activating CD3-CD56+ NK cells in vitro

Alpha-glycosylceramides, such as alpha-galactosylceramide and alpha-glucosylceramide, induce antitumor immunity in various murine cancer models. In the murine hepatic metastasis model, V alpha 14 TCR+NK1.1+ T cells, which accumulate preferentially in the liver, are considered to play a key role in the induction of antitumor immunity by alpha-glycosylceramides. We recently reported that V alpha 24 TCR+ NKT cells, the human homologues of murine V alpha 14 TCR+NK1.1+ cells, are rarely seen among freshly isolated human hepatic lymphocytes. Therefore, it is important to examine whether alpha-glycosylceramides also enhance the antitumor cytotoxicity of human hepatic lymphocytes, as they have been shown to do in murine systems, to determine the usefulness of alpha-glycosylceramides in cancer immunotherapy in humans. Here, we show that alpha-glycosylceramides greatly enhance the cytotoxicity of human hepatic lymphocytes obtained from cancer patients against the tumor cell lines, K562 and Colo201, in vitro. The direct effector cells of the elicited cytotoxicity were CD3-CD56+ NK cells. Even though V alpha 24 TCR+NKT cells proliferated remarkably in response to alpha-glycosylceramides, they did not contribute directly to the cytotoxicity. Our observations strongly suggest the potential usefulness of alpha-glycosylceramides for immunotherapy of liver cancer in humans based on their ability to activate CD3-CD56+ NK cells in the liver.

alpha -galactosylceramide-activated Valpha 14 natural killer T cells mediate protection against murine malaria

Natural killer T (NKT) cells are a unique population of lymphocytes that coexpress a semiinvariant T cell and natural killer cell receptors, which are particularly abundant in the liver. To investigate the possible effect of these cells on the development of the liver stages of malaria parasites, a glycolipid, alpha-galactosylceramide (alpha-GalCer), known to selectively activate Valpha14 NKT cells in the context of CD1d molecules, was administered to sporozoite-inoculated mice. The administration of alpha-GalCer resulted in rapid, strong antimalaria activity, inhibiting the development of the intrahepatocytic stages of the rodent malaria parasites Plasmodium yoelii and Plasmodium berghei. The antimalaria activity mediated by alpha-GalCer is stage-specific, since the course of blood-stage-induced infection was not inhibited by administration of this glycolipid. Furthermore, it was determined that IFN-gamma is essential for the antimalaria activity mediated by the glycolipid. Taken together, our results provide the clear evidence that NKT cells can mediate protection against an intracellular microbial infection.

Functional natural killer T cells in experimental mouse strains, including NK1.1- strains

Natural killer T (NKT) cells are a newly discovered subset of lymphocytes. It appears that this subset has potential as important regulators of immune responses. But because there are relatively few NKT cells in lymphoid organs and because of technical difficulties in detecting NKT cells in most mouse strains, the roles of NKT cells have not been fully identified and little attention has been paid to the roles of NKT cells in immunological experiments in which NK1.1- strains were used. To examine the existence of functional NKT cells in various strains of experimental mice, including NK1.1- strains, we utilized alpha-galactosylceramide (KRN7000) which is thought to react specifically with NKT cells. Indeed, we could confirm that early cytokine (IL-4 and IFN-gamma) secretion at 2 h after the injection of KRN7000 was dependent on NKT cells. With this in vivo system, we have successfully detected the presence of functional NKT cells in various mouse strains, including AKR/N, BALB/c, C3H/HeJ, C3H/HeN, C57BL/6, C.B-17, CBA/N, NC, NOD, SJL, W/Wv, aly/aly and aly/+. Notable increases of serum IL-4 were detected in W/Wv and aly/+ strains, and defective response of IFN-gamma in SJL mice and that of IL-4 in NOD mice were observed. This is the first report to show the functional significance of NKT cells in cytokine secretion in various mouse strains in response to a ligand for the T cell receptor of NKT cells.

Activation of natural killer T cells by alpha-galactosylceramide in the presence of CD1d provides protection against colitis in mice

BACKGROUND & AIMS

CD1d is a major histocompatibility complex class I-like molecule that presents glycolipid antigens to a subset of natural killer (NK)1.1(+) T cells. These NK T cells exhibit important immunoregulatory functions in several autoimmune disease models.

METHODS

To investigate whether CD1d and NK T cells have a similar role in intestinal inflammation, the effects of the glycolipid, alpha-galactosylceramide (alpha-GalCer), on dextran sodium sulfate (DSS)-induced colitis were examined. Wild-type (WT), CD1d(-/-), and RAG(-/-) mice were examined for their response to either alpha-GalCer or the control analogue, alpha-mannosylceramide (alpha-ManCer).

RESULTS

WT mice, but not CD1d(-/-) and RAG(-/-) mice, receiving alpha-GalCer had a significant improvement in DSS-induced colitis based on body weight, bleeding, diarrhea, and survival when compared with those receiving alpha-ManCer. Elimination of NK T cells through antibody-mediated depletion resulted in a reduction of the effect of alpha-GalCer. Furthermore, adoptive transfer of NK T cells preactivated by alpha-GalCer, but not alpha-ManCer, resulted in diminished colitis. Using a fluorescent-labeled analogue of alpha-GalCer, confocal microscopy localized alpha-GalCer to the colonic surface epithelium of WT but not CD1d(-/-) mice, indicating alpha-GalCer binds CD1d in the intestinal epithelium and may be functionally active at this site.

CONCLUSIONS

These results show an important functional role for NK T cells, activated by alpha-GalCer in a CD1d-restricted manner, in regulating intestinal inflammation.

Neonatal invariant Valpha24+ NKT lymphocytes are activated memory cells

NKT cells are a small subset of T lymphocytes which express an invariant V(alpha24JalphaQ TCR and recognize glycolipids presented by CD1d. In adults, NKT cells have a memory phenotype, frequently associated with oligoclonal expansion, express NK cell markers, and produce TO cytokines upon primary stimulation. Because of these features, NKT cells are regarded as lymphocytes of innate immunity. We investigated NKT cells from cord blood to see how these cells appear in the absence of exogenous stimuli. We found that NKT cells are present at comparable frequencies in cord blood and adult peripheral blood mononuclear cells and in both cases display a memory (CD45RO+CD62L-) phenotype. However, neonatal NKT cells differ from their adult counterparts by the following characteristics: (1) they express markers of activation, such as CD25; (2) they are polyclonal; (3) they do not produce cytokines in response to primary stimulation. Together, our data show that human NKT cells arise in the newborn with an activated memory phenotype, probably due to recognition of an endogenous ligand(s). The absence of oligoclonal expansion and primary effector functions also suggest that neonatal NKT cells, despite their activated memory phenotype, require a further priming/differentiation event to behave as fully functional cells of innate immunity.

Analysis of human V alpha 24+ CD4+ NKT cells activated by alpha-glycosylceramide-pulsed monocyte-derived dendritic cells

Human V alpha 24+ NKT cells with an invariant TCR (V alpha 24-J alpha Q) have been shown to be specifically activated by synthetic glycolipids such as alpha-galactosylceramide and alpha-glucosylceramide in a CD1d-restricted and V alpha 24 TCR-mediated manner. We recently characterized V alpha 24+ CD4- CD8- double negative (DN) NKT cells using alpha-galactosylceramide-pulsed monocyte-derived dendritic cells. Here, we compare V alpha 24+ CD4+ NKT cells with human V alpha 24+ DN NKT cells from the same donor using alpha-galactosylceramide-pulsed monocyte-derived dendritic cells. Human V alpha 24+ CD4+ NKT cells were phenotypically and functionally similar to the human V alpha 24+ DN NKT cells characterized previously. Both of them use V alpha 24-J alpha Q-V beta 11 TCR and express CD161 (NKR-P1A), but not the other NK receptors tested so far. They also produce cytokines such as IL-4 and IFN-gamma, and, in regard to IL-4 production, V alpha 24+ CD4+ NKT cells produce more IL-4 than V alpha 24+ DN NKT cells. The cells exhibit marked cytotoxic activity against the U937 tumor cell line, but not against the NK target cell line, K562. Although at least some of the factors responsible for the stimulation of V alpha 24+ NKT cells have been clarified, little is known regarding the killing phase of these cells. Here we show that the cytotoxic activity of V alpha 24+ NKT cells against U937 cells is mediated mainly through the perforin pathway and that ICAM-1/LFA-1 as well as CD44/hyaluronic acid interactions are important for the effector phase of V alpha 24+ NKT cell-mediated cytotoxicity against U937 cells.

CD1-mediated antigen presentation of glycosphingolipids

CD1 proteins are distinguished by their ability to present lipid antigens to T cells. Group II CD1 or CD1d molecules are recognized by the specialized NK T-cell subset, and this reactivity can be greatly augmented by alpha-galactosylceramide, a glycosphingolipid derived from a marine sponge. Human CD1b, which is only distantly related to the CD1d molecules, can present mammalian glycosphingolipids (gangliosides) to autoreactive T-cell clones derived from multiple sclerosis patients. Thus, CD1 responsive and glycosphingolipid-reactive cells may play an important immune regulatory role, in addition to their well-characterized role in the response to microbial lipids.

Synergistic effect of KRN7000 with interleukin-15, -7, and -2 on the expansion of human V alpha 24+V beta 11+ T cells in vitro

KRN7000, (2S, 3S, 4R)-1-O-(alpha-D-galactopyranosyl)-2-(N-hexacosanoylamino)-1, 3, 4-octadecanetriol, has been shown to prevent tumor metastasis to the liver through the activation of natural killer (NK) T cells in mice. In this study, the proliferation of human NK T cells, which express an invariant T cell antigen receptor (TCR) consisting of a Valpha24 chain and a Vbeta11 chain, was investigated using KRN7000, interleukin (IL)-15, IL-7, and IL-2 in vitro. KRN7000 stimulated the expansion of Valpha24(+)Vbeta11(+) T cells derived from peripheral blood mononuclear cells in a dose-dependent fashion, with some fluctuation between donors. IL-15, IL-7, and IL-2 synergistically stimulated the expansion of Valpha24(+)Vbeta11(+) T cells when combined with KRN7000. Intracellular expression of interferon (IFN)-gamma and IL-4 in Valpha24(+)Vbeta11(+) T cells expanded in the presence of KRN7000 was identified using flow cytometry. Valpha24(+)Vbeta11(+) T cells, expanded in the presence of KRN7000, contained granzyme (Gr) B-positive granules and perforin-positive granules. The addition of IL-15 to the culture containing KRN7000 increased GrB expression in Valpha24(+)Vbeta11(+) T cells while IL-7 and IL-2 failed to do it. In conclusion, the antitumor effect of KRN7000 may depend, in part, on granule-mediated cell killing through the activation of NK T cells and IL-15 may potentiate this effect.

Dendritic cells are targets for human invariant Valpha24+ natural killer T-cell cytotoxic activity: an important immune regulatory function

OBJECTIVE

Human invariant Valpha24+ natural killer T (NKT) cells, a subpopulation of NK cell-receptor (NKR-P1A)-expressing T cells with an invariant Valpha24JalphaQ T-cell receptor (TCR), are stimulated by the glycolipid a-galactosylceramide (KRN7000), in a CD1d-dependent, TCR-mediated fashion. Little is known about invariant Valpha24+ NKT cell function or mechanisms of effector activity. Evidence suggests this cell population protects against autoimmunity and has antitumor effects against leukemia and solid tumors.

MATERIALS AND METHODS

We compared the phenotype and function of invariant Valpha24+ NKT cells, from patients with chronic myeloid leukemia (CML) and normal donors, generated by stimulation of peripheral blood mononuclear cells with alpha-galactosylceramide pulsed monocyte-derived dendritic cells. The CD4(-)CD8(-) (double negative) population was studied further.

RESULTS

Activated human invariant Valpha24+ NKT cells were cytotoxic against autologous and allogeneic peripheral blood dendritic cells and monocyte-derived dendritic cells but not against autologous or allogeneic T-cell PHA blasts, B-cell lymphoblastoid cell lines, monocytes, or leukemic cells from patients with CML. The findings are consistent with previous observations showing the importance of CD1d in target cell recognition. None of the Valpha24+ NKT cell lines expressed the NK markers CD16, CD56, CD94, or killer inhibitory receptors, but all expressed NKR-P1A. There was no difference in phenotype, function, or ease of generation of invariant Valpha24+ NKT cells between normal donors and patients with CML.

CONCLUSION

Based on our results and the previous evidence linking reduced Valpha24+ NKT cells to autoimmunity, we propose that double-negative Valpha24+ NKT cells have important immune regulatory functions, including contribution to the prevention of excessive antigen stimulation by virtue of cytotoxic activity against antigen presenting cells, particularly in dendritic cells.

Murine CD1d-restricted T cell recognition of cellular lipids

NKT cells are associated with immunological control of autoimmune disease and cancer and can recognize cell surface mCD1d without addition of exogenous antigens. Cellular antigens presented by mCD1d have not been identified, although NKT cells can recognize a synthetic glycolipid, alpha-GalCer. Here we show that after addition of a lipid extract from a tumor cell line, plate-bound mCD1d molecules stimulated an NKT cell hybridoma. This hybridoma also responded strongly to three purified phospholipids, but failed to recognize alpha-GalCer. Seven of sixteen other mCD1d restricted hybridomas also showed a response to certain purified phospholipids. These findings suggest NKT cells can recognize cellular antigens distinct from alpha-GalCer and identify phospholipids as potential self-antigens presented by mCD1d.

Human invariant valpha24+ natural killer T cells activated by alpha-galactosylceramide (KRN7000) have cytotoxic anti-tumour activity through mechanisms distinct from T cells and natural killer cells

Human Valpha24 + NKT cells, a subpopulation of natural killer cell receptor (NKR-P1A) expressing T cells with an invariant T-cell receptor (TCR; Valpha24JalphaQ) are stimulated by the glycolipid, alpha-galactosylceramide (KRN7000), in a CD1d-dependent, TCR-mediated fashion. Little is known about Valpha24 + NKT-cell function. The murine counterpart, Valpha14 + NKT cells, appear to have an important role in controlling malignancy. There are no human data examining the role of Valpha24 + NKT cells in controlling human malignancy. We report that Valpha24 + NKT cells have perforin-mediated cytotoxicity against haemopoietic malignancies. Valpha24 TCR, CD1d and alpha-galactosylceramide may all play a role in cytotoxicity but are not absolute requirements. The greatest cytotoxicity was observed against the U937 tumour cell line (95 +/- 5% lysis). THP-1, Molt4, C1R cells and allogeneic mismatched dendritic cells were also sensitive to Valpha24 + NKT cytotoxicity but neither the NK target, K562, nor lymphokine-activated killer-sensitive Daudi cells, were sensitive. These results indicate a killing pattern distinct from conventional major histocompatibility complex-restricted T cells, NK cells and other cytotoxic lymphoid cells previously described. We conclude that human Valpha24 + NKT cells have cytotoxic anti-tumour activity against haemopoietic malignancies through effector mechanisms distinct from conventional T cells and NK cells and that their specific stimulator KRN7000 may have therapeutic potential.