Natural killer,but not natural killer T,cells play a necessary role in the promotion of an innate antitumor response induced by IL-18

IL-18 administration promotes innate immunity resulting in significant antitumor effects in multiple murine tumor models. Here, we examined the effector population mediating the innate immunity. Most NK cells and some NKT cells express IL-18Rs without prior stimulation (65% positive in NK cells, 18% positive in NKT cells), though few naive T cells do. In vivo depletion of NK cells, but not NKT cells, using AsGM1 antibody significantly reduces IL-18-induced cytotoxicity. However, NK-like activity of hepatic MNCs for the NK target YAC-1 was present in Valpha 14 NKT cell-deficient animals. Furthermore, administration of rIL-18 greatly reduced B16 pulmonary metastases in vivo in NKT cell-deficient animals. When sorted NK and NKT cells were exposed to IL-18 in vitro, NK cells showed more IFN-gamma production and cytolysis against YAC-1 than NKT cells in response to IL-18. These results are consistent with the notion that NK cells, but not NKT cells, are the major effectors in IL-18-induced innate immunity.     

NK and CD8+ T cell-mediated eradication of poorly immunogenic B16-F10 melanoma by the combined action of IL-12 gene therapy and 4-1BB costimulation

In previous reports, systemic administration of a stimulatory monoclonal antibody directed against the 4-1BB receptor had no effect on survival or tumor burden in mice inoculated with the poorly immunogenic B16-F10 melanoma. We combined IL-12 gene transfer with 4-1BB costimulation to explore a previously noted cooperative anti-tumor effect against this model tumor. We hypothesize that the innate immune response mediated by IL-12-activated natural killer (NK) cells initiates the activation of the immune system, leading to the priming of T cells, whereas 4-1BB costimulation enhances the function of primed tumor-specific T cells. The effect of the combination therapy on the growth of subcutaneous (s.c.) tumors and pulmonary metastasis was examined. The combination therapy significantly retarded the growth of subcutaneously-inoculated tumors, and 50% of tumor-bearing mice survived with complete tumor regression. In contrast, neither IL-12 gene transfer nor anti-4-1BB antibody administration alone was as effective. Enhanced CTL activity against both B16-F10 tumor cells and TRP-2-pulsed EL4 syngeneic tumor cells was observed in tumor-bearing animals treated with the combination therapy 2 weeks after treatment and, in long-term survivors from this combination therapy, at >120 days. In a pulmonary metastatic model, only the combination therapy generated significant protection against metastasis. In vivo depletion of NK or CD8(+) but not CD4(+) subsets eliminated the protective immunity. Furthermore, NK cell depletion significantly reduced both tumor-specific CTL activity and the number of tumor-specific IFN-gamma-producing cells, suggesting that this synergistic effect requires the participation of both NK and CD8(+) T cells.     

Synergy of brief activation of CD8 T-cells in the presence of IL-12 and adoptive transfer into lymphopenic hosts promotes tumor clearance and anti-tumor memory

Adoptive T-cell therapy holds great promise for the treatment of metastatic melanoma. However, prohibitive costs associated with current technology required for culture and expansion of tumor-reactive T-cells, the need for intense preconditioning regimens to induce lymphopenia, and the unpredictable anti-tumor effect of adoptively transferred T-cells remain significant impediments for its clinical implementation. Here we report a simplified combinatorial approach that involves short activation of CD8(+) T cells in the presence of IL-12 followed by adoptive transfer into tumor bearing animals after a single injection of cyclophosphamide. This approach resulted in complete eradication of B16 melanoma, and the establishment of long term immunological memory capable of fully protecting mice after a second B16 melanoma challenge. The activated donor cells were unique because they simultaneously exhibited traits for cytotoxic effector function, central memory-like, homing, and senescence. After tumor eradication and within three months after transfer, CD8+ cells exhibited a conventional memory CTL phenotype. Moreover, these memory CTLs acquired functional attributes characteristic of memory stem cells, including the ability to resist chemotherapy-induced toxicity. Our results suggest that short-term T-cell receptor signaling in the presence of IL-12 promotes promiscuous qualities in na?ve CTL which - upon transfer into lymphopenic hosts- are sufficient to eradicate tumors and generate life-long tumor-specific memory.     

Enhanced suppression of pulmonary metastasis of malignant melanoma cells by combined administration of alpha-galactosylceramide and interleukin-18

α-Galactosylceramide (α-GalCer) shows antitumor effects by activating natural killer (NK) cells indirectly through stimulation of the secretion of cytokines by NKT cells, whereas interleukin (IL)-18 shows antitumor effects by activating NK cells directly. In the present study, we examined the antitumor effect of the combined administration of α-GalCer and IL-18. An injection of NK cell-sensitive mouse B16 melanoma cells into a mouse tail vein produced pulmonary metastasis. The daily administration of α-GalCer or IL-18 alone for 4 days starting 1 day after the injection of B16 melanoma cells markedly suppressed the number of pulmonary metastatic foci, and their combined administration enhanced the antitumor effect compared with single administration. The antitumor effect of their combined administration was completely abolished by treatment of mice with anti-asialo GM1 serum, which depletes NK cells but not NKT cells. Combined administration of α-GalCer and IL-18 enhanced the cytotoxicity of NK cells and increased the number of NK cells in the lung. Analysis of NKT cell-dependent and NK cell-independent secretion of cytokines, to which NK cells can respond, showed that the administration of α-GalCer increased the secretion of IL-2, IL-4, interferon-γ, IL-12, granulocyte-macrophage colony-stimulating factor, tumor necrosis factor-α, and IL-10, and the combined administration of α-GalCer and IL-18 enhanced the secretion of IL-2, IL-4, interferon-γ, and granulocyte-macrophage colony-stimulating factor further but only slightly. These results show that IL-18 in combination with α-GalCer exerts an antitumor effect on NK cell-sensitive tumors primarily by the direct stimulation of NK cells by IL-18 and the indirect stimulation of NK cells by α-GalCer through its activation of NKT cells. ( Cancer Sci 2008; 99: 113–120)     

Cytotoxicity and clinical application of activated NK cells

We have shown that the patients with myelogenous leukemia display several defects in the NK cell lytic mechanism. However, this cytotoxic defect could be corrected after culture of effector cells from these patients with IL-2. The cytotoxic potential of IL-2-activated killer cells could be further augmented by treatment with OKT3 monoclonal antibody. Interleukin-2-activated lymphocytes were effective in killing not only a variety of tumor cell lines, but also autologous leukemic cells. Moreover, these cells were not stationary, but proliferated actively in culture with IL-2. Characterization studies, using the monoclonal antibodies against NK cell (CD16 and NKH1/Leu-19) or T-cell (CD3 and CD5) surface molecules showed that the antileukemia-directed cytotoxic cells were NK cells and not T-cells. In contrast, the T-cells (and not NK cells) exhibited an ability to down-regulate clonogenic activity of hematopoietic progenitors and to inhibit proliferation of bone marrow cells. Our data suggest that adoptive therapy with highly-enriched IL-2-activated NK cells may result in more powerful anti-leukemia effect. Alternatively, activated NK cells may be effective in eradication of leukemic cells from bone marrow for autologous bone marrow transplantation purposes.     

Natural killer cell-mediated ablation of metastatic liver tumors by hydrodynamic injection of IFNalpha gene to mice

Interferon (IFN) alpha is a pleiotropic cytokine acting as an antiviral substance, cell growth inhibitor and immunomodulator. To evaluate the therapeutic efficacy and mechanisms of IFNalpha on hepatic metastasis of tumor cells, we hydrodynamically injected naked plasmid DNA encoding IFNalpha1 (pCMV-IFNa1) into Balb/cA mice having 2 days hepatic metastasis of CT-26 cells. Single injection of pCMV-IFNa1 efficiently enhanced the natural killer (NK) activity of hepatic mononuclear cells, induced production of IFNgamma in serum and led to complete rejection of tumors in the liver. Mice protected from hepatic metastasis by IFNalpha therapy displayed a tumor-specific cytotoxic T cell response and were resistant to subcutaneous challenge of CT-26 cells. NK cells were critically required for IFNalpha-mediated rejection of hepatic metastasis, because their depletion by injecting anti-asialo GM1 antibody completely abolished the antimetastatic effect. To find whether NK cells are directly activated by IFNalpha and are sufficient for the antimetastatic effect, the responses to IFNalpha were examined in SCID mice lacking T cells, B cells and NKT cells. IFNalpha completely rejected hepatic metastasis in SCID mice and efficiently activated SCID mononuclear cells, as evidenced by activation of STAT1 and a variety of genes, such as MHC class I, granzyme B, tumor necrosis factor-related apoptosis-inducing ligand and IFNgamma, and also enhanced Yac1 lytic ability. Study of IFNgamma knockout mice revealed that IFNgamma was not necessary for IFNalpha-mediated NK cell activation and metastasis protection. In conclusion, IFNalpha efficiently activates both innate and adaptive immune responses, but NK cells are critically required and sufficient for IFNalpha-mediated initial rejection of hepatic metastasis of microdisseminated tumors.     

Transgenic expression of IL-33 activates CD8 T cells and NK cells and inhibits tumor growth and metastasis in mice

IL-33 is a multifunctional cytokine in immune regulation that activates Th1 cells, Th2 cells, CD8⁺ T cells and NK cells. Our study showed that transgenic expression of IL-33 attenuated tumor metastasis in the B16 melanoma and Lewis lung carcinoma (LLC) metastatic models. The percentages and cytotoxicity of CD8⁺ T cells and NK cells and their infiltration into the tumor tissues were significantly increased by the transgenic expression of IL-33 in tumor-bearing mice. Treatment with recombinant IL-33 could also increase the cytotoxicity of CD8⁺ T cells and NK cells in vitro. In addition, depletion of CD8⁺ T cells and NK cells using anti-CD8 or anti-asialo GM1 antibody abolished the pulmonary metastasis inhibition mediated by IL-33. Furthermore, IL-33 stimulated the activation of NF-κB and increased CD69 expression, which is a marker of the activated form of the two cell subsets, in CD8⁺ T cells and NK cells. Our results suggest that IL-33 stimulated NF-κB signaling and promoted the proliferation, activation and infiltration of CD8⁺ T cells and NK cells, which resulted in the inhibition of pulmonary metastasis in B16 melanoma and LLC mice models.     

Natural killer T cell-mediated antitumor immune responses and their clinical applications

A unique lymphocyte population, CD1d-restricted NKT cells, has been revealed to be a key player in both the innate and acquired immune responses, including antitumor effects. Recent studies revealed that at least two subsets of CD1d-restricted NKT cells exist: type I, having invariant Valpha14 receptor; and type II, having heterogeneous non-Valpha14 receptor. The specific glycolipid ligand, alpha-GalCer, effectively stimulates mouse and human type I NKT cells. The activation of type I NKT cells substantially influences function of other various cell types, particularly DC, NK cells, CD4 Th1 cells, and CD8 cytotoxic T cells, all contributing to the antitumor immune responses. Recent studies also indicated that, unlike type I NKT cells, type II NKT cells have a potential to repress antitumor immune responses. In this review, we summarize the characteristics of the antitumor immune responses mediated by both mouse and human CD1d-restricted NKT cells and discuss their potential in clinical applications against cancer.     

Role of NK and T cells in IL-12-induced anti-tumor response against hepatic colon carcinoma.

IL-12 is an immuno-regulatory cytokine that has been shown to generate a potent NK and Th1 response in a variety of laboratory models. However, the detailed immune development in the hepatic tumor model by IL-12-mediated gene therapy has not been clarified. In our previous study, intra-tumoral transfer of Adv.mIL-12 (5 x 10(8) pfu) to the MCA26 colon carcinoma liver tumor induced an effective anti-tumor response, extending the median survival time from 29 to over 54 days, while 25% of the animals became tumor-free after a single treatment. In this work, we show that NK cells are responsible for the early, and both NK and T cells for the long-term, Adv.mIL-12-induced immune response. Immunohistopathological analysis of the tumor and in vitro cytotoxicity study of the mononuclear cells of the liver show that NK cells are the first to infiltrate and mediate tumor cell killing, as early as 48 hr after Adv.mIL-12 treatment. In vivo and in vitro depletion of these cells completely abolishes this early anti-tumor response. This activity can be observed in both populations of conventional NK and NKT cells in vitro and in athymic nude mice in vivo. However, the early NK response alone is not sufficient. In vivo T-cell depletion in both the primary tumor treatment and the long-term survival rechallenge study reveals that T cells in addition to NK cells are required in the development of the long-term survival and immunity attributed to Adv.mIL-12 gene therapy in this orthotopic tumor model of colon carcinoma.     

Antitumor activity of alpha-galactosylceramide, KRN7000, in mice with the melanoma B16 hepatic metastasis and immunohistological study of tumor infiltrating cells

Liver metastasis of primary tumors is clinically a major problem. We examined the antitumor activity of KRN7000, an alpha-galactosylceramide, in mice with liver metastasis of the B16 melanoma. KRN7000 significantly inhibited tumor growth in the liver, and its potency was similar to that of interleukin-12. The KRN7000 administration resulted in a high percentage of cured mice, which acquired tumor-specific immunity. To study what kinds of antitumor effector cells participated in killing tumor cells, we then performed immunohistological analysis of tumor-infiltrating cells, and found that KRN7000 induced marked invasion of NK1.1+ cells, CD8+ cells, and F4/80+ cells (macrophages) into B16 tumor nodules. In addition, it appeared that KRN7000-treated, liver-associated macrophages possessed strong lytic activity against tumor cells. These results suggest that NK cells, NK1.1+ T (NKT) cells, cytotoxic T lymphocytes, and macrophages play an important role in killing tumor cells in the liver, and that KRN7000 may be useful for the treatment of cancer liver metastasis.     

A3 adenosine receptor agonist potentiates natural killer cell activity

Activation of the Gi-protein-coupled A3 adenosine receptor (A3AR) has been reported to be involved in the inhibition of tumor cell growth. A3AR is highly expressed in tumor cells whereas lower expression was noted in a variety of normal cells. Recently we showed that A3AR activation in melanoma cells resulted in growth inhibition via a direct anti-proliferative effect which entailed cell cycle arrest in the G0/G1 and down-regulation of cyclin D1 and c-Myc. In the present study we present an additional mechanism demonstrating that A3AR agonists activate natural killer (NK) cells which further enhance the anti-tumor effect of this group of molecules. NK cells mediate the natural cytotoxicity and their number and function is reduced in cancer patients. We show Cl-IB-MECA to inhibit tumor development via the activation of NK cells is an additional mechanism which accounts for the anti-tumor effect of A3AR agonists. This effect was noted at a low dose of 10 micro g/kg, demonstrating that the response is exclusively A3AR mediated. Treatment of na?ve mice for four days yielded the highest effect on NK cell potentiation. In mice inoculated with B16-F10 melanoma cells and treated each orally with Cl-IB-MECA, melanoma growth inhibition correlated with higher serum level of IL-12 and potentiation of NK cells. Moreover, in adoptive transfer experiments in melanoma bearing mice, marked inhibition of lung metastatic foci was noted upon engraftment with splenocytes derived from Cl-IB-MECA treated mice. Taken together, the ability of Cl-IB-MECA to inhibit tumor development via the activation of NK cells is an additional mechanism which accounts for the anti-tumor effect of A3AR agonists.     

CD1d expression level in tumor cells is an important determinant for anti-tumor immunity by natural killer T cells

Invariant natural killer T (iNKT) cells are thought to regulate anti-tumor immunity. Human iNKT (i.e. Valpha24+ NKT) cells have been reported to recognize CD1d on target cells and show cytotoxicity directly on the target cells in vitro. However, the anti-tumor effect of mouse iNKT (i.e. Valpha14+ NKT) cells has been repeatedly reported to be dependent on the activity of natural killer (NK) cells via interferon-gamma, with no evidence of direct cytotoxicity. In the present study, we report that in vitro cytolysis of EL-4 mouse lymphoblastic lymphoma cells by Valpha24+ NKT cells and in vivo eradication of these cells are both dependent on the level of CD1d expression on the tumor cell surface. These observations possibly suggest that direct cytotoxicity of tumor cells by iNKT cells is common to both humans and mice, and that the high expression level of CD1d may be a predictor whether the tumor is a good target of iNKT cells.     

CD1d-mediated stimulation of natural killer T cells selectively activates hepatic natural killer cells to eliminate experimentally disseminated hepatoma cells in murine liver

Since hepatocellular carcinomas (HCCs) develop from transformed hepatocytes, sometimes in a multicentrical manner, immunological deletion of such small intrahepatic regions should be an important strategy to prevent HCC development. The liver contains abundant innate cell lineages including natural killer (NK) cells and natural killer T (NKT) cells, the latter of which become activated in a CD1d-restricted manner by alpha-galactosylceramide (alpha-GalCer). In our study, we investigated the anti-tumor effect elicited by alpha-GalCer administration against transplanted hepatoma cells in the liver, in comparison with that in extrahepatic sites. alpha-GalCer administration completely suppressed the growth of BNL 1MEA.7R.1 (BNL) hepatoma cells disseminated in the liver of syngeneic BALB/c mouse but had no anti-tumor effect on subcutaneously implanted BNL cells. Hepatic NKT cells became rapidly activated after alpha-GalCer administration compared to splenic NKT cells and then disappeared. Hepatic NK cells substantially increased their population as well as up-regulated their cytotoxic activity against BNL cells, but NK cells in other tissues, including the spleen, blood and lymph node, did not. Anti-asialo GM1 antibody treatment, which depleted NK cells in vivo, resulted in hepatic tumor formation in alpha-GalCer-treated mice, indicating the critical involvement of NK cells in the alpha-GalCer-induced anti-tumor effect in the liver. In conclusion, our study demonstrates clear differences in NK cell activation and anti-tumor effect through stimulation of NKT cells by alpha-GalCer between the liver and extrahepatic tissues. Sequential activation of these innate cell lineages may be an attractive strategy for controlling micro-disseminated hepatoma cells in the liver.     

Antitumor activity of alpha-galactosylceramide, KRN7000, in mice with EL-4 hepatic metastasis and its cytokine production.

Liver metastasis of primary tumor is a clinically major problem. KRN7000, an alpha-galactosylceramide, significantly augments natural killer (NK) activity of spleen cells and shows strong antitumor activity in mice with lung metastasis of melanoma B16 cells. To test whether KRN7000 has an antitumor activity in mice with hepatic metastasis of tumors, we examined the effect of KRN7000 on NK activity of hepatic mononuclear cells (MNC) and the antitumor activity in mice with liver metastasis of EL-4 cells. The in vivo administration of KRN7000 significantly augmented NK activity of hepatic MNC and inhibited tumor growth of EL-4 cells in the liver more markedly than chemotherapeutic agents, leading to a relatively high rate of cured mice. In addition, it appeared that the KRN7000 treatment is effective in mice with established EL-4 tumors. Moreover, we found that KRN7000 can produce significant amounts of interleukin 2 (IL-2), IL-4, IL-12, and interferon-gamma in a dose-dependent manner. These results suggest that KRN7000 will be useful for the treatment of cancer liver metastasis.     

Intrasplenic vaccination against experimental melanoma

The immunodominant component of a formalinized extracellular antigen (fECA) vaccine prepared from B16 F10 melanoma cells is the melanoma-associated antigen B700. We now demonstrate that a single prophylactic intrasplenic inoculation of B700 antigen (1-10 mu g) stimulates the production of antibodies which have antiproliferative effects on B16 F10 melanoma cells in vitro. In addition, potential cytotoxic effects of splenocytes from B700 antigen inoculated mice were evaluated for two cellular immune effector functions, natural killer (NK) cell activity and lymphokine activated killer (LAK) cell activity; both activities were increased following B700 antigen inoculation. Intrasplenic injection of B700 antigen elicited an increase in the expression of the CD25 surface antigen (IL-2 R alpha) by T lymphocytes and up-regulated the expression of IL-2 R alpha mRNA. Thus both humoral and cellular cytotoxic immune responses might play roles in the decreased growth of primary tumors in B700 antigen inoculated mice and in the higher survival rate in this group of animals.     

Human CD4+ CD25+ regulatory T cells suppress NKT cell functions

CD4+CD25+ regulatory T cells play an important role in peripheral tolerance. These cells have been reported to be capable of suppressing the response of CD4+CD25- T cells in vitro. The depletion of these cells evokes effective immune responses to tumor cells in vivo. In this study, we demonstrate that CD4+CD25+ T cells also suppress all subsets of Valpha24+NKT cells (Valpha24+CD4-CD8- double negative, Valpha24+CD4+, and Valpha24+CD8+) in both proliferation and cytokine production [IFN-gamma, interleukin-4 (IL-4), IL-13, and IL-10]. This suppression is mediated by cell-to-cell contact but not by a humoral factor or the inhibition of antigen-presenting cells. Moreover, the cytotoxic activity of Valpha24+NKT cells against some tumor cell lines is suppressed by CD4+CD25+ T cells. This finding is important in developing an effective immunotherapy for cancer.     

CD3+CD56+NKT细胞及CD3-CD56+NK细胞在恶性肿瘤患者的临床意义研究

背景与目的细胞毒性淋巴细胞在抗肿瘤免疫效应中发挥着重要作用,CD3 CD56 NKT细胞作为一类新的具有细胞毒性的效应细胞,目前关于其抗肿瘤意义的探讨主要集中于血液系统恶性疾病,而在实体肿瘤中的应用和临床价值研究尚少。本研究旨在初步探讨抗肿瘤细胞CD3 CD56 NKT细胞及CD3-CD56 NK细胞在恶性肿瘤患者外周血的表达状态及其临床意义。方法采用流式细胞术分析118例恶性肿瘤患者(55例肺癌患者和63例乳腺癌患者)及46例健康对照组外周血中的T细胞亚群及CD3 CD56 NKT细胞、CD3-CD56 NK细胞表达。结果恶性肿瘤患者组CD3 CD8 T细胞、CD3 CD56 NKT细胞以及CD3-CD56 NK细胞表达率均明显高于健康对照组(P<0.01)。肺癌患者中以CD3 CD8 T细胞和CD3 CD56 NKT细胞明显增加为主;乳腺癌患者中以CD3 CD56 NKT细胞和CD3-CD56 NK细胞明显增加为主。结论CD3 CD56 NKT细胞在肺癌和乳腺癌患者的抗肿瘤效应中占据重要地位,而CD3 CD8 CTL和CD3-CD56 NK细胞在不同类型肿瘤患者中具有不同的重要性。     

Effective treatment of preexisting melanoma with whole cell vaccines expressing alpha(1,3)-galactosyl epitopes

The hyperacute immune response in humans is a potent mechanism of xenograft rejection mediated by complement-fixing natural antibodies recognizing alpha(1,3)-galactosyl epitopes (alphaGal) not present on human cells. We exploited this immune mechanism to create a whole cell cancer vaccine to treat melanoma tumors. B16 melanoma vaccines genetically engineered to express alphaGal epitopes (B16alphaGal) effectively treated preexisting s.c. and pulmonary alphaGal-negative melanoma (B16Null) tumors in the alpha(1,3)-galactosyltransferase knockout mouse model. T cells from mice vaccinated with B16alphaGal recognized B16Null melanoma cells measured by detection of intracellular tumor necrosis factor-alpha. We showed successful adoptive transfer of immunity to recipient mice bearing lung melanoma metastasis. Mice receiving lymphocytes from donors previously immunized with B16alphaGal had reduced pulmonary metastases. The transfer of lymphocytes from mice vaccinated with control vaccine had no effect in the pulmonary metastasis burden. This study unequivocally establishes for the first time efficacy in the treatment of preexisting melanoma tumors using whole cell vaccines expressing alphaGal epitopes. Vaccination with B16alphagal induced strong long-lasting cell-mediated antitumor immunity extended to B16Null. These data formed the basis for the testing of this therapeutic strategy in human clinical trials currently under way.     

Characteristics of tumor infiltration by adoptively transferred and endogenous natural-killer cells in a syngeneic rat model: Implications for the mechanism behind anti-tumor responses

Interleukin-2-activated, cultured NK cells (A-NK) cells were adoptively transferred into a syngeneic rat liver-tumor model. The kinetics of tumor infiltration by NK cells, originating either from adoptively transferred or from endogenous sources, the localization of these cells in the tumor, and their interactions with extracellular-matrix proteins were studied by immunohistochemistry and transmission-electron microscopy. The adoptive transfer of A-NK cells via the hepatic artery and s.c. injections of IL-2 into rats bearing sub-capsularly induced CC531 liver tumors, but also IL-2 monotherapy, resulted in a significant increase of the number of NK cells both at the tumor border and in the tumor center. The majority of tumor-infiltrating NK cells was present in the tumor stroma and only occasionally was an NK cell observed in a tumor nodule in direct contact with tumor cells. Observations by electron microscopy suggested that matrix proteins, abundantly present in the tumor stroma but absent in the tumor nodules, provide a substrate for migration of infiltrating cells, whereas tight structures of matrix proteins surrounding tumor nodules provide a barrier for establishment of direct NK-cell-to-tumor-cellcontact. Our results suggest that direct NK-cell-to-target-cell-contact-mediated lysis is of minor importance for attaining an anti-tumor effect in this model. We hypothesize that treatment of tumor-bearing rats with A-NK cells and/or IL-2 initiates a cascade of events (e.g., secretion of tumor-killing cytokines and/or infiltration of other immune cells) ultimately leading to tumor regression. Int. J. Cancer 78:783–789, 1998. © 1998 Wiley-Liss, Inc.     

Peripheral blood IFN-gamma-secreting Valpha24+Vbeta11+ NKT cell numbers are decreased in cancer patients independent of tumor type or tumor load

Natural killer T (NKT) cells are CD1d-restricted lymphoid cells and are characterized by an invariant T-cell receptor, which in humans consists of a Valpha24 chain paired with a Vbeta11 chain. These cells are known for their rapid production of large amounts of cytokines (e.g., IFN-gamma and IL-4), thereby modulating other cells of the immune system such as T cells, NK cells and dendritic cells. NKT cells have been reported to play important regulatory roles in many immune responses, including antitumor immune responses. Here, we demonstrate an age-dependent decrease in circulating Valpha24(+)Vbeta11(+) NKT cell numbers in both healthy controls and cancer patients and demonstrate that in both groups females have higher NKT cell levels compared to males. In a large group of 120 cancer patients, we show that circulating Valpha24(+)Vbeta11(+) NKT cell numbers are about 50% lower than in age- and gender-matched healthy controls and that this decrease is independent of tumor type or tumor load. This decrease was not restored upon tumor removal by means of surgery or radiotherapy. Even though the percentage of NKT cells that secrete IFN-gamma, as detected by ELISPOT, is normal in cancer patients, the absolute number of circulating IFN-gamma-secreting NKT cells is reduced. Together, our results suggest that the reduced circulating Valpha24(+)Vbeta11(+) NKT cell numbers in cancer patients are not affected by tumor load, but might actually reflect a risk factor for tumor development, e.g., by hampering efficient tumor immunosurveillance.