Antitumor effects on mouse melanoma elicited by local secretion of interleukin-12 and their enhancement by treatment with interleukin-18

Bioengineering strategies to enhance the interleukin-18 bioactivity in the modern toolbox of cancer immunotherapy

Cytokines are the first modern immunotherapeutic agents used for activation immunotherapy. Interleukin-18 (IL-18) has emerged as a potent anticancer immunostimulatory cytokine over the past three decades. IL-18, structurally is a stable protein with very low toxicity at biological doses. IL-18 promotes the process of antigen presentation and also enhances innate and acquired immune responses. It can induce the production of proinflammatory cytokines and increase tumor infiltration of effector immune cells to revert the immunosuppressive milieu of tumors. Furthermore, IL-18 can reduce tumorigenesis, suppress tumor angiogenesis, and induce tumor cell apoptosis. These characteristics present IL-18 as a promising option for cancer immunotherapy. Although several preclinical studies have reported the immunotherapeutic potential of IL-18, clinical trials using it as a monotherapy agent have reported disappointing results. These results may be due to some biological characteristics of IL-18. Several bioengineering approaches have been successfully used to correct its defects as a bioadjuvant. Currently, the challenge with this anticancer immunotherapeutic agent is mainly how to use its capabilities in a rational combinatorial therapy for clinical applications. The present study discussed the strengths and weaknesses of IL-18 as an immunotherapeutic agent, followed by comprehensive review of various promising bioengineering approaches that have been used to overcome its disadvantages. Finally, this study highlights the promising application of IL-18 in modern combinatorial therapies, such as chemotherapy, immune checkpoint blockade therapy, cell-based immunotherapy and cancer vaccines to guide future studies, circumventing the barriers to administration of IL-18 for clinical applications, and bring it to fruition as a potent immunotherapy agent in cancer treatment.

Potential Role of Diabetes Mellitus-Associated T Cell Senescence in Epithelial Ovarian Cancer Omental Metastasis

Epithelial ovarian cancer (EOC) is one of the most common causes of cancer-related deaths among women and is associated with age and age-related diseases. With increasing evidence of risks associated with metabolic inflammatory conditions, such as obesity and type 2 diabetes mellitus (T2DM), it is important to understand the complex pathophysiological mechanisms underlying cancer progression and metastasis. Age-related conditions can lead to both genotypic and phenotypic immune function alterations, such as induction of senescence, which can contribute to disease progression. Immune senescence is a common phenomenon in the ageing population, which is now known to play a role in multiple diseases, often detrimentally. EOC progression and metastasis, with the highest rates in the 75-79 age group in women, have been shown to be influenced by immune cells within the "milky spots" or immune clusters of the omentum. As T2DM has been reported to cause T cell senescence in both prediabetic and diabetic patients, there is a possibility that poor prognosis in EOC patients with T2DM is partly due to the accumulation of senescent T cells in the omentum. In this review, we explore this hypothesis with recent findings, potential therapeutic approaches, and future directions.

Combination of NKT14m and Low Dose IL-12 Promotes Invariant Natural Killer T Cell IFN-γ Production and Tumor Control

Invariant natural killer T (iNKT) cells are innate-like T lymphocytes characterized by the expression of an invariant T cell receptor (iTCR) that recognizes glycolipid antigens presented by the MHC I-like CD1d molecule. Following antigenic stimulation, iNKT cells rapidly produce large amounts of cytokines that can trans-activate dendritic cells (DC) and promote the anti-tumor functions of cytotoxic lymphocytes, such as natural killer (NK) and CD8 T cells. Additionally, iNKT cells can mediate robust and direct cytotoxicity against CD1d⁺ tumor targets. However, many tumors down-regulate CD1d and evade iNKT cell attack. To circumvent this critical barrier to iNKT cell anti-tumor activity, a novel monoclonal antibody (mAb), NKT14 has been recently developed. This agonistic antibody binds directly and specifically to the iTCR of murine iNKT cells. In the current study, we demonstrate that NKT14m mediates robust activation, cytokine production and degranulation of murine iNKT cells, in vitro. Consistently, NKT14m also promoted iNKT cell activation and immunomodulatory functions, in vivo. Finally, administration of NKT14m with low dose interleukin (IL)-12 further augmented iNKT cell IFN-γ production in vivo, and this combination conferred superior suppression of tumor cell growth compared to NKT14m or IL-12 alone. Together, these data demonstrate that a combination treatment consisting of low dose IL-12 and iTCR-specific mAb may be an attractive alternative to activate iNKT cell anti-tumor functions.

Robust Antitumor Effects of Combined Anti-CD4-Depleting Antibody and Anti-PD-1/PD-L1 Immune Checkpoint Antibody Treatment in Mice

Depletion of CD4(+) cells in tumor-bearing mice has strong antitumor effects. However, the mechanisms underlying these effects and the therapeutic benefits of CD4(+) cell depletion relative to other immunotherapies have not been fully evaluated. Here, we investigated the antitumor effects of an anti-CD4-depleting mAb as a monotherapy or in combination with immune checkpoint mAbs. In B16F10, Colon 26, or Lewis lung carcinoma subcutaneous tumor models, administration of the anti-CD4 mAb alone had strong antitumor effects that were superior to those elicited by CD25(+) Treg depletion or other immune checkpoint mAbs, and which were completely reversed by CD8(+) cell depletion. CD4(+) cell depletion led to the proliferation of tumor-specific CD8(+) T cells in the draining lymph node and increased infiltration of PD-1(+)CD8(+) T cells into the tumor, with a shift toward type I immunity within the tumor. Combination treatment with the anti-CD4 mAb and immune checkpoint mAbs, particularly anti-PD-1 or anti-PD-L1 mAbs, synergistically suppressed tumor growth and greatly prolonged survival. To our knowledge, this work represents the first report of robust synergy between anti-CD4 and anti-PD-1 or anti-PD-L1 mAb therapies.

IL-18 expression results in a recombinant vaccinia virus that is highly attenuated and immunogenic

Interferon-γ (IFN-γ) is an attenuating factor for vaccinia virus (VACV), decreasing its virulence in vivo by more than a million fold. It is also a highly effective adjuvant when administered at the time of immunization with protein antigens. However, recombinant VACV (rVACV) vaccines expressing IFN-γ do not induce enhanced immune responses. It is possible that the IFN-γ expressed by rVACVs induces both an antiviral state and increased immunological clearance, thus resulting in decreased levels of antigen expression due to reduced viral replication and spread. We conjectured that delaying expression of IFN-γ would result in enhanced production of antigens by rVACVs thus resulting in increased immune responses to foreign antigens. Interleukin (IL)-18, also known as IFN-γ inducing factor, is a cytokine that induces T and NK cells to produce IFN-γ. In this study, we demonstrated that an rVACV expressing bioactive murine IL-18 replicated to low but detectable levels in vivo, unlike an rVACV expressing IFN-γ. Moreover, the rVACV expressing IL-18 was significantly attenuated in both immunocompromised and immunocompetent mice. This attenuation was dependent on IFN-γ, as IL-18 expression failed to attenuate VACV in IFN-γ knock-out mice. Cytotoxic T-cell (CTL) and anamnestic antibody responses were slightly increased in animals vaccinated with the rVACV expressing IL-18. Thus, induction of IFN-γ because of IL-18 expression resulted in an rVACV that replicated to low but detectable levels in vivo, yet elicited slightly better CTL and anamnestic humoral immune responses.

Intratumoral CD4+ T lymphodepletion sensitizes poorly immunogenic melanomas to immunotherapy with an OX40 agonist

Previous studies have shown that the antitumor effects of OX40 agonists depend on the immunogenicity of the tumor and that poorly immunogenic tumors such as B16F10 melanomas do not respond to OX40 agonist treatment. In this study, we have shown that intratumoral CD4+ T lymphodepletion sensitized poorly immunogenic B16F10 melanomas to immunotherapy with an OX40 agonist. CD4+ T lymphodepletion dramatically altered the tumor immune microenvironment, making it more susceptible to the antitumor effects of an OX40 agonist by enhancing the accumulation of CD8+ T cells and natural killer (NK) cells in tumor tissue. However, unexpectedly, the number of CD11b+ Gr-1(+) myeloid-derived suppressor cells (MDSCs) within tumor tissues also significantly increased as a result of CD4+ T lymphodepletion. As a countermeasure against CD8+ T-cell accumulation, CCR2-positive CD11b+ Gr-1(int) (monocytic) MDSCs predominantly increased. Treatment with an OX40 agonist under CD4+ T lymphodepletion neither reduced MDSCs nor increased CD8+ T cells and NK cells, but further enhanced the expression of cytotoxic molecules from tumor-infiltrating effector cells. Our results suggest that combined immunotherapy using both an OX40 agonist and CD4+ T lymphodepletion could be a promising therapeutic strategy for poorly immunogenic tumors and might be more effective if further combined with a therapeutic strategy targeting MDSCs.

Introduction of 65 kDa Antigen ofMycobacterium tuberculosisto Cancer Cells Enhances Anti-Tumor Effect of BCG Therapy

Bacillus Calmette Guerin (BCG) immunotherapy has anti-tumorigenic effects against bladder cancer. To improve the efficacy of BCG therapy, we introduced the gene encoding the 65 kDa heat shock protein (hsp) of Mycobacterium tuberculosis into a mouse malignant melanoma cell line (B16). An expression vector harboring the 65 kDa antigen gene was transfected into B16 using Lipofectamine, then expression of the antigen was confirmed by RT-PCR and Western blotting. Several cell lines expressing 65 kDa antigen were established (B16/65 kDa). We also established a control cell line transfected with the vector alone (B16/con). All cell lines (B16, B16/con, B16/65 kDa) were injected intraperitoneally into syngeneic mice with or without BCG prior immunization and the development of tumor ascites was examined. To analyze the mechanism of the anti-tumor effect, CD4 T cells or CD8 T cells were depleted in vivo by administering the corresponding monoclonal antibody. B16/65k Da expressed the 65 kDa hsp of M. tuberculosis. The tumor growth of B16/65 kDa was slightly retarded in naive mice, but significantly inhibited by BCG. The anti-tumor effect was totally abrogated in mice deficient in CD4 T cells, suggesting that CD4 T cells are involved in this process. The 65 kDa hsp of M. tuberculosis was expressed after gene transduction in a malignant melanoma cell line and significantly enhanced the anti-tumor effect of BCG immunotherapy. CD4 T cells play an important role in this anti-tumor effect.

Post-Chemotherapeutic Administration of Interleukin-12 Retards Tumor Growth and Enhances Immune Cell Function: Combination Therapy Using Paclitaxel and IL-12

The antineoplastic agent paclitaxel (TAXOL) is a potent inhibitor of tumor cell division that also suppresses lymphocyte proliferative responses. Because chemotherapy-induced immunosuppression may limit the patient's antitumor responses, we investigated the possibility that the T cell stimulatory cytokine interleukin-12 (IL-12) could be used to reverse paclitaxel-mediated lymphocyte suppression. Recognizing that IL-12 treatment following paclitaxel exposure promotes T cell responses in vitro, we evaluated the antitumor efficacy of IL-12 administration concurrent and subsequent to paclitaxel treatment. Simultaneous administration of IL-12 and paclitaxel failed to limit tumor outgrowth or extend survival beyond chemotherapy alone, although IL-12 did not manifest negative effects. In contrast, post-chemotherapeutic IL-12 significantly delayed tumor outgrowth and extended survival in tumor-burdened BALB/c mice. Correlative enhancements in ex vivo immune cell effector function were also observed following paclitaxel and temporally delayed IL-12 therapy. Collectively, these data demonstrate an immunotherapeutic efficacy of IL-12 that augments the chemotherapeutic activities of paclitaxel when delivered in the appropriate temporal sequence.

A phase 2, randomized study of SB-485232, rhIL-18, in patients with previously untreated metastatic melanoma

BACKGROUND

Phase 1 studies demonstrated evidence of recombinant human IL-18 (rhIL-18)-mediated immunomodulatory and clinical activity, and defined a biologically active dose range.

METHODS

A phase 2 study of rhIL-18 was conducted in untreated AJCC stage IV melanoma. Patients were randomized to 1 of 3 dose groups (0.01, 0.1, and 1.0 mg/kg/d) of rhIL-18 administered as 5 daily intravenous infusions repeated every 28 days. A 2-stage design with a stopping rule was used.

RESULTS

A total of 64 patients (median age, 57.5 years) with metastatic melanoma (M1a/b (30), M1c (34)) were accrued to stage I, and randomized to 3 groups (21 [0.01 mg/kg/d], 21 [0.1 mg/kg/d], 22 [1.0 mg/kg/d]). Five patients experienced 10 grade 3 drug-related adverse events (AEs): polyarthritis (1 subject: 0.01 mg/kg); deep vein thrombosis, pulmonary embolism (1:0.01 mg/kg); cognitive disorder (1:0.1 mg/kg); fatigue, dyspnea, pleural effusion, lymphopenia (1:1.0 mg/kg); fatigue, lymphopenia (1:1.0 mg/kg). One patient experienced a grade 4 AE of increased lipase (0.1 mg/kg) that led to permanent discontinuation from the study. Among 63 subjects evaluable for response, 1 (M1c; 0.01 mg/kg) achieved a partial response after 4 cycles. Four subjects (3 at 0.01 mg/kg and 1 at 1.0 mg/kg) had stable disease maintained for 6 months or longer. Due to the low apparent level of clinical efficacy using RECIST criteria, the study was terminated at the end of stage 1. The median progression free survival for the 3 groups was 7.5 (0.01), 7.4 (0.1), and 7.3 (1.0) weeks.

CONCLUSIONS

rIL-18 as tested in this trial was well tolerated, but had limited activity as a single agent in patients with metastatic melanoma.

Role of Interleukins and Nitric Oxide Secretion by Peritoneal Macrophages in Differential Tumoricidal Effect to Transplantable Melanomas as Regarding their Biological Properties

The secretion of interleukins (IL-18, IL-12) and Nitric Oxide (NO) by peritoneal macrophages from hamsters bearing two lines of transplantable melanoma was estimated. Macrophages of animals with melanoma lines secreted less IL-18 but more IL-12 and NO in comparison with the control macrophages. The distinctly higher cytotoxic activity of macrophages from animals with amelanotic line in comparison with the melanotic line was not accompanied by significant differences in the IL-18 and IL-12 secretion between studied groups of macrophages. Thus, it seems that IL-18 play the role in innate immunity but not in adaptive cellular immunity, whereas IL-12 and NO take part in macrophages tumoricidal activity.

Reduced expression of IL-18 is a marker of ultraviolet radiation-induced melanomas

We previously showed that mice carrying an activated Cdk4 mutation together with melanocyte-specific mutant Hras (Cdk4(R24C/R24C)/TPras) develop melanoma spontaneously, but penetrance is increased and age of onset reduced after neonatal ultraviolet radiation (UVR) exposure. UVR-treated mice were more likely to develop multiple primary lesions, and these melanomas more often expressed Trp53, and less often expressed c-Myc, than melanomas from nonirradiated mice (Hacker et al., Cancer Res 2006;66:2946-52). These data suggest differences in mechanisms of tumorigenesis between melanomas developing spontaneously, or as a result of UVR exposure. To further delineate these differences, we compared global gene expression between spontaneous and UVR-induced melanomas from these mice using microarrays. We found 264 genes differentially expressed between these groups (ANOVA, p < 0.05). Selected candidate genes were validated using qRT-PCR, which confirmed upregulation of Gpr155 and Bmp7, and downregulation of Plagl1, Akap12 and Il18 in UVR-induced mouse melanomas. In humans, epidemiological studies suggest that there may be 2 predominant pathways to melanoma development. One characterized by chronic UVR exposure and which leads mainly to melanomas on sun-exposed sites; the other associated with low UVR exposure and leading predominantly to melanomas on less-exposed body sites. We found by immunohistochemical analysis that, comparing a series of human melanomas from the head (a chronically sun-exposed site; N = 82) with a set from the trunk (an intermittently exposed site; N = 65), the prevalence of IL-18 expression was significantly lower in melanomas on the head (16%) than on truncal melanomas (34%, p = 0.011). We conclude that loss of IL-18 is a marker of UVR-induced melanoma, both in animal models and humans.

Synergistic effects of IL-2, IL-12 and IL-18 on cytolytic activity, perforin expression and IFN-γ production of porcine natural killer cells

Natural killer (NK) cells are one of the main cellular components of the innate immune system. They play an important role in the immune response against infections as well as tumour cells and therefore have two major properties: production of immune regulatory cytokines and chemokines as well as cytolytic destruction of particular target cells. The existence of NK cells in swine is well known as well as the phenotype of resting NK cells, but their response following activation by cytokines is still poorly understood. Therefore, we tested the influence of the immune regulatory cytokines IL-2, IL-12 and IL-18 on cytolytic activity, phenotype, IFN-gamma production and the accumulation of perforin in cytoplasm of peripheral blood mononuclear cells (PBMC) as well as purified NK cells. NK cells were enriched from PBMC using a magnetic cell separation (MACS) strategy with monoclonal antibodies against CD3, CD21 and SWC3, thereby removing T-, B- and myeloid cells. Respective fractions were used in flow cytometry (FCM) based cytolytic assays with the human tumour cell line K562 as target. After stimulation with the cytokines described above, the NK cell enriched CD3(-)CD21(-)SWC3(-) fraction showed an evident increase in the cytolytic activity compared to PBMC. This enhanced cytolytic activity was accompanied by a strong enrichment of IFN-gamma producing cells when a combination of all three cytokines (IL-2/IL-12/IL-18) was used; as determined in ELISPOT assays and intracellular staining of IFN-gamma in FCM. Also, the combination of these three cytokines led to an accumulation of perforin in the cytoplasm and an up-regulation of CD25 compared to control cultures incubated in medium without cytokines. The experiments performed clearly indicate a stimulatory role and strong synergistic effects of the investigated cytokines in the activation of porcine NK cells in vitro, inducing IFN-gamma, perforin production and cytotoxicity against target cells.

Particle-mediated cytokine gene therapy leads to antitumor and antimetastatic effects in mouse carcinoma models

BACKGROUND

We investigated the effects of continuous cancer gene therapy including (antigen-presenting cell) (APC) engineering and local stimulation of the immune system.

MATERIALS AND METHODS

Lewis lung carcinomas and B16 melanomas, intradermally established on C57/Bl6 mice, were shot using a gene gun every 4th day with a combination of plasmids. The first therapy group received plasmids coding the genes for interleukin (IL)-12 and IL-2. The second therapy group was treated with plasmids coding for B7.1 interferon-gamma (IFN-gamma)/IL-12 alternated by a plasmid coding IL-2. Control were mice without any therapy or treatment with the empty plasmid.

RESULTS

Gene therapy led to reduced tumor sizes in the therapy groups of both models (significant for the Lewis lung carcinoma). We found an enhanced survival and reduced tumor growth rate in the therapy groups; however, the effects were not significant. IL- 12/IL-2 therapy was more effective, compared to B7.1/IFN-gamma/IL-12 and IL-2. Cytokine gene transfer let to a significantly lower metastasis rate in Lewis lung carcinoma.

CONCLUSIONS

Continuous particle-mediated gene transfer is easy to handle and shows good results. Gene therapy combining the genes coding for IL-12 and IL-2 was superior to additional IFN-gamma/B7.1. APC engineering does not appear to be sufficient in these poorly antigenic tumors.

Reactive arthritis following BCG immunotherapy for urinary bladder carcinoma: a systematic review

Intravesical instillation of Bacillus Calmette-Guerin (BCG) is used with efficacy and safety in the treatment of patients with intermediate and high-risk superficial bladder carcinoma. Arthralgia and/or arthritis is one of the rare severe complications following intravesical BCG immunotherapy. We searched MEDLINE in order to analyze the frequency of this clinical complication, its pathogenesis and outcome. The electronic search was conducted using the following key words: "BCG immunotherapy" and "Arthritis, arthralgias and BCG immunotherapy". At the end of a process of abstract analysis, 48 papers were included in the systematic review. All the selected papers, except one that was a clinical review, described at least one case of arthritis after BCG therapy. The BCG immunotherapy resulted to be safe and efficacious in the treatment of bladder cancer; the development of reactive arthritis is rare and can evolve in a chronic process. The review of the literature highlighted that reactive arthritis following BCG intravesical instillation is a complication usually well controlled with the discontinuation of the immunotherapy and nonsteroidal anti-inflammatory drugs (NSAIDs) treatment. Only a small portion of patients with a particular genetic background will develop a chronic process.

IL-18 enhances SCF production of melanoma cells by regulating ROI and p38 MAPK activity

It has been reported that interleukin-18 (IL-18) is secreted by B16 murine melanoma cells and that this endogenous IL-18 is involved in the immune escape of murine melanoma cells. The present study investigated whether interleukin (IL)-18 can regulate stem cell factor (SCF) expression, known to be associated with melanocyte proliferation, in B16F10 murine melanoma cells. SCF expression was examined by RT-PCR, intracellular FACS analysis, and ELISA in IL-18 antisense transfectants. Transfection with IL-18 antisense cDNA reduced SCF expression and the expression was enhanced by addition of exogenous IL-18. In addition, the effect of IL-18 was blocked by the antioxidant, N-acetyl-L-cysteine (NAC), indicating that IL-18 regulates ROI production, which is involved in SCF production. Furthermore, inhibitors of p38 mitogen-activated protein kinase (MAPK), such as SB203580, blocked enhanced SCF expression, indicating that p38 MAPK activity is required for IL-18-enhanced SCF production. Taken together, these results suggest that IL-18 plays a critical role as a regulatory factor of SCF expression via ROI and p38 MAPK activity in B16F10 murine melanoma cells.

Systematic optimization of active protein expression using GFP as a folding reporter

Many recombinant proteins have been used as drugs; however, human proteins expressed using heterologous hosts are often insoluble. To obtain correctly folded active proteins, many optimizations of expression have been attempted but usually are found to be applicable only for specific targets. Interleukin-18 (IL-18) has a key role in many severe disorders including autoimmune diseases, and therapeutic approaches using IL-18 have been reported. However, production of IL-18 in Escherichia coli resulted in extensive inclusion body formation and previous conventional screenings of expression conditions could obtain only a condition with a low yield. To address the problem, we applied a folding reporter system using green fluorescent protein (GFP) for screening of the expression conditions for hIL-18. The established system efficiently screened many conditions, and optimized conditions for the expression of hIL-18 significantly enhanced the final yield of the active protein. Systematic screening using a GFP reporter system could be applied for the production of other proteins and in other organisms.

CpG immunostimulatory oligodeoxynucleotide 1826 enhances antitumor effect of interleukin 12 gene-modified tumor vaccine in a melanoma model in mice

PURPOSE

The effectiveness of interleukin (IL)-12-secreting tumor vaccines in the treatment of mouse tumors could be enhanced by concurrent application of cytokines and costimulatory molecules. We investigated the therapeutic potential of IL-12 gene-transduced melanoma vaccine in combination with CpG immunostimulatory oligodeoxynucleotide (ODN) 1826, an adjuvant known to favor development of Th1-biased immune response, in a B78-H1 (B78) melanoma model in mice.

EXPERIMENTAL DESIGN

Mice injected with B78 melanoma cells were treated with irradiated IL-12 gene-transduced B78 cells [B78/IL-12(X)] and/or ODN 1826. Mechanisms responsible for the antitumor effects of the treatment were investigated using fluorescence-activated cell sorter analysis, a standard (51)Cr releasing assay, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and ELISA.

RESULTS

Single injection of B78/IL-12(X) cells had no effect on tumor growth, whereas seven consecutive daily injections of ODN 1826 markedly inhibited tumor progression with occasional curative effects. When used in combination, B78/IL-12(X) cells and ODN 1826 caused additional tumor growth reduction and eradication of tumors in 62% of treated mice. The combined treatment activated local inflammatory response against tumor but also induced systemic antitumor immunity. In vitro studies have shown that when used together, B78/IL-12(X) cells and ODN 1826 induced a potent Th1 response and suggested the role of IFN-gamma in activation of the host immune response. The antitumor effects in double-treated mice were accompanied by the development of cytotoxic effectors in the spleen and activation of macrophages.

CONCLUSIONS

The results provided the evidence that the combination of IL-12 gene-modified melanoma vaccine and ODN 1826 induces synergistically systemic and local antitumor immunity.

In vivo elimination of CD25+ regulatory T cells leads to tumor rejection of B16F10 melanoma, when combined with interleukin-12 gene transfer

CD4(+)CD25(+) T cells are an important population that plays a crucial role in the maintenance of peripheral self-tolerance. Recently, it was shown that the elimination of these cells by in vivo administration of anti-CD25 monoclonal antibody (mAb) caused the regression of highly immunogenic tumors in syngeneic mice. In this study, we examined whether B16F10 melanoma cells regressed with the elimination of CD25(+) regulatory T cells. We found the melanoma cells were not affected at all by in vivo anti-CD25 mAb administration alone but tumor rejection resulted in all mice when the administration was combined with IL-12 gene transfer to tumor cells. In vivo, depletion of natural killer (NK) cells or CD8(+) T cells cancelled the tumor rejection. NK-cell depletion allowed IL-12-transfected B16F10 melanoma (B16/IL-12) to grow from an early stage and resulted in a more rapid tumor growth of B16/IL-12 than that in mice without administration of anti-CD25 mAb. On the other hand, CD8(+) T-cell depletion did not affect the tumor growth in the early phase but allowed B16/IL-12 to grow in rather a late phase and resulted in almost the same degree of tumor growth as in mice without administration of anti-CD25 mAb. In a previous study, we showed that the elimination of CD4(+) T cells enhanced the antitumor effect of B16/IL-12 and induced vitiligo-like coat color alteration. Therefore, we also examined the frequency of the change to a vitiligo-like coat color in mice showing tumor rejection caused by CD25(+) T-cell elimination to compare with the mechanism enhancing the antitumor effects by cell elimination. The elimination of CD25(+) T cells did not induce vitiligo-like coat color changes, though that of CD4(+) T cells induced the change in 60% of mice. Furthermore, we confirmed that elimination of CD25(+) T cells did not affect the T-helper (Th) 1/Th2 cytokine profile, while that of CD4(+)T cells abrogated the Th2 cytokines (IL-4 and IL-10) and resulted in a Th1-dominant cytokine profile in the tumor-draining lymph nodes (TDLNs) of B16/IL-12-bearing mice. These results indicate that in vivo depletion of CD25(+) regulatory T cells is a potent useful adjuvant in immunotherapy of B16F10 melanoma, when combined with IL-12 gene transfer and that the enhancement of the antitumor effect by CD25(+) T-cell depletion is mediated through CD8(+) T cells and may differ from the enhancing mechanism caused by CD4(+) T-cell depletion.

Heterogeneous expression of interleukin-18 and its receptor in B-cell lymphoproliferative disorders deriving from naive, germinal center, and memory B lymphocytes

PURPOSE

Dysregulated cytokine/cytokine receptor expression may occur in B-cell lymphoproliferative disorders. Little information is available on interleukin-18 receptor (IL-18R) and IL-18 expression in normal and malignant B cells. Our purpose was to investigate this issue in human naive, germinal center (GC) and memory B cells, and in their neoplastic counterparts.

EXPERIMENTAL DESIGN

We have evaluated IL-18 expression and production in tonsil naive, GC, and memory B cells and in their presumed neoplastic counterparts by reverse transcription-PCR and ELISA. Moreover, IL-18Ralpha and beta expression was investigated in the same cells by reverse transcription-PCR, flow cytometry, and immunohistochemistry.

RESULTS

We found that: (a) IL-18 mRNA was expressed in tonsil naive, GC, and memory B cells. Bioactive IL-18 was secreted by naive and GC, but not by memory B cells; (b) IL-18Ralpha and beta transcripts were expressed in the three B-cell subsets. IL-18Ralpha was detected on the surface of naive, GC, and memory B lymphocytes, and IL-18Rbeta was detected on GC and memory, but not naive, B cells; (c) mantle zone, follicular, marginal zone, Burkitt lymphoma (BL), and B-cell chronic lymphocytic leukemia (B-CLL) cells expressed IL-18 mRNA. B-CLL and BL cells did not produce bioactive IL-18; and (d) lymphoma B cells displayed heterogeneous expression of either or both IL-18R chain mRNA. In contrast, B-CLL cells expressed both IL-18R chains at the mRNA and protein levels.

CONCLUSIONS

Dysregulated expression of IL-18 and/or IL-18R in chronic B-cell lymphoproliferative disorders may sometimes contribute to tumor escape from the host immune system.

Cytokine gene single nucleotide polymorphisms and susceptibility to and prognosis in cutaneous malignant melanoma

Cutaneous malignant melanoma (CMM) is a potentially fatal malignancy in which exposure to UV light is the most important risk factor. Several lines of evidence suggest that CMM patients develop an immune response to their tumours, although, in most cases, anti-tumour immune responses are insufficient to abrogate tumour development. Polymorphism in genes regulating the immune response and cell growth may result in increased susceptibility to and/or poorer prognosis in certain individuals. In this study, we addressed whether single nucleotide polymorphisms (SNPs) associated with differential expression of selected pro- and anti-inflammatory cytokines and growth factors [interleukin (IL)-1beta-35 and -511, IL-2 -330, IL-4 -590, IL-6 -174, IL-8 -251, interferon (IFN)-gamma+874 and transforming growth factor (TGF)beta1 +915] or as markers of candidate cytokine genes (IL-12 +1188) are associated with susceptibility to or known prognostic indicators (e.g. initial tumour growth phase, Breslow thickness, mitotic count in vertical growth phase tumours, tumour regression) in CMM. One hundred and sixty-nine British caucasian CMM patients and 261 controls were included in the study and all SNPs were genotyped by ARMS-PCR. No SNP genotypes or alleles showed significant associations with CMM susceptibility and only the IL-1beta-511 TT genotype was associated with thinner invasive tumours at presentation, as assessed by Breslow thickness at the clinically significant cut-off point of 1.5 mm [occurring in 2/51 (3.9%) thicker vs. 14/78 (17.9%) thinner tumours (P = 0.03; relative risk = 0.29 (95% confidence interval 0.05-0.95)]. These findings suggest that - with the possible exception of IL-1beta- genetic variation associated with differential expression of the selected pro- and anti-inflammatory cytokines is unlikely to play a major role in susceptibility to and prognosis in CMM.

Paracrine release of IL-12 stimulates IFN-gamma production and dramatically enhances the antigen-specific T cell response after vaccination with a novel peptide-based cancer vaccine

Interleukin-12 can act as a potent adjuvant for T cell vaccines, but its clinical use is limited by toxicity. Paracrine administration of IL-12 could significantly enhance the response to such vaccines without the toxicity associated with systemic administration. We have developed a novel vaccine delivery system (designated F2 gel matrix) composed of poly-N-acetyl glucosamine that has the dual properties of a sustained-release delivery system and a potent adjuvant. To test the efficacy of paracrine IL-12, we incorporated this cytokine into F2 gel matrix and monitored the response of OT-1 T cells in an adoptive transfer model. Recipient mice were vaccinated with F2 gel/SIINFEKL, F2 gel/SIINFEKL/IL-12 (paracrine IL-12), or F2 gel/SIINFEKL plus systemic IL-12 (systemic IL-12). Systemic levels of IL-12 were lower in paracrine IL-12-treated mice, suggesting that paracrine administration of IL-12 may be associated with less toxicity. However, paracrine administration of IL-12 was associated with an enhanced Ag-specific T cell proliferative and functional response. Furthermore, paracrine IL-12 promoted the generation of a stable, functional memory T cell population and was associated with protection from tumor challenge. To study the mechanisms underlying this enhanced response, wild-type and gene-deficient mice were used. The enhanced immune response was significantly reduced in IFN-gamma(-/-) and IL-12R beta 2(-/-) recipient mice suggesting that the role of IL-12 is mediated, at least in part, by host cells. Collectively, the results support the potential of F2 gel matrix as a vaccine delivery system and suggest that sustained paracrine release of IL-12 has potential clinical application.

Serum interleukin-12 and interleukin-18 levels as a tumor marker in patients with esophageal carcinoma

Interleukin (IL)-12 and IL-18 participate in tumor immunology. Serum IL-12 and IL-18 levels were determined in patients with esophageal carcinoma, and the relationship between clinicopathologic factors and prognosis was investigated. Peripheral blood samples were obtained from 15 healthy volunteers and from 70 patients with esophageal carcinoma before curative surgery. IL-12 and IL-18 levels were determined in each serum sample by enzyme-linked immunosorbent assay. Mean serum IL-12 and IL-18 levels were significantly higher in patients with esophageal carcinoma compared with healthy volunteers (P < 0.05) and mean serum IL-12 and IL-18 levels increased in patients as the pathologic stage progressed. A positive correlation was observed between serum IL-12 and IL-18 levels (P < 0.01). In patients with esophageal carcinoma, increasing serum IL-12 and IL-18 levels correlated with tumor growth and progression. The function of these two interleukin in the host immune response remains unclear. However, this part of the host immune response did not appear to contribute to the postoperative prognosis. Serum IL-12 and IL-18 levels might correlate with a certain depth of invasion and might be useful tumor markers in patients with esophageal carcinoma.

Generation of highly stable IL-18 based on a ligand–receptor complex structure

Human interleukin-18 (hIL-18), initially cloned as an IFN-gamma-inducing factor, has a key role in many inflammatory diseases. We have previously developed a high production system for correctly folded active hIL-18 protein, leading to the revelation of the 3D-structure and the receptor binding mode. These findings can strongly indicate the experimental and medical applications of IL-18; however, the recombinant protein is prone to be inactivated forming multimers. Recently, therapeutic approaches using recombinant IL-18 have shown the effectiveness for treatment of cancer; indicating the necessity of a more stable protein for therapy with intertrial reliability. Here we have generated a highly stable hIL-18 with replacement of cysteine by serine based on the tertiary structure and the binding mechanism, retaining the biological activity. Similar rational designs can be applied to develop new therapeutic molecules of other cytokines.

Bovine lactoferrin inhibits tumor-induced angiogenesis

Recent studies have demonstrated that bovine lactoferrin (bLF) suppresses tumor growth and metastasis in the mouse and rat and moreover may inhibit angiogenesis. To determine whether angiogenesis inhibition might contribute to antitumor activity, we examined the influence of bLF on tumor-induced angiogenesis and endothelial cell functions as well as angiogenesis-related cytokine production. Bovine LF exhibited dose-dependent inhibition of angiogenesis on 4-6-day-old chick embryo chorioallantoic membranes (CAMs) that lack a mature immune response. This inhibition was reversed when bLF was simultaneously treated with basic fibroblast growth factor (bFGF). It also inhibited in vitro formation of tube-like structures of mouse endothelial KOP2.16 cells. Moreover, it potently suppressed bFGF- or VEGF-induced proliferation of mouse endothelial KOP2.16 cells, but not of mouse fibroblast A31 cells and Lewis lung carcinoma (3LL) cells. In mice, both orally and intraperitoneally administered bLF significantly and dose-dependently suppressed 3LL cell-induced angiogenesis in a dorsal air sac assay. As orally administered bLF was reported to exhibit antitumor activity through production of interferon (IFN)-gamma and interleukin (IL)-18 in intestinal mucosa (Kuhara T et al., Nutr Cancer 2000;38:192-9), production of these cytokines in mouse serum and peritoneal macrophages by bLF was examined. IFN-gamma was not detected in serum by bLF administration. However, bLF markedly elevated IL-18 concentration in serum by oral administration, but not by intraperitoneal administration. It also induced IL-18 in peritoneal macrophages in vitro. These results suggest that bLF participates as a regulator of angiogenesis, possibly explained by blocking endothelial function and inducing IL-18 production. Antitumor activity of bLF may thus be partly mediated by angiogenesis inhibition.

Identification of natural antibodies to interleukin-18 in the sera of normal humans and three nonhuman primate species

Natural antibodies to cytokines can be found in the sera of normal healthy individuals in the absence of specific immunostimulation. However, the function, impact, and purpose of natural antibody development have yet to be fully elucidated. Interleukin (IL)-18 is a cytokine that exerts proinflammatory activities and induces natural killer (NK) cell activity. Recombinant human IL-18 (rHuIL-18) is currently in development as a cancer immunotherapy. In this study, the presence of natural antibodies to IL-18 in the sera of normal humans and three nonhuman primate species was evaluated by electrochemiluminescence immunoassay (ECLIA). Of the human sera tested, 6 of 47 samples were positive for natural antibodies to IL-18. Of the nonhuman primate sera tested, 22 of 80 cynomolgus monkey samples, 4 of 31 rhesus monkey samples, and 2 of 20 chimpanzee samples were positive for natural antibodies to IL-18. Natural anti-IL-18 antibodies were neutralizing in 5 of 22 cynomolgus and 2 of 4 rhesus sera. None of the chimpanzee or human sera were able to neutralize IL-18 induction of interferon (IFN)-gamma in vitro. In vivo activity of rHuIL-18 was compared in IL-18 natural antibody-positive and -negative cynomolgus monkeys. The presence of natural antibodies to IL-18 did not alter rHuIL-18 systemic exposure levels, induction of neopterin, or induction of treatment-induced antibodies following intravenous administration of rHuIL-18. In conclusion, our data indicate that, as has been found with other cytokines, natural anti-IL-18 antibodies are relatively common. Moreover, natural anti-IL-18 antibodies do not appear to influence rHuIL-18 activity in vivo and are not predictive of a heightened immune response, suggesting that natural anti-IL-18 antibodies do not impact IL-18 therapy. Finally, our data suggest that the ability to detect natural anti-cytokine antibodies may be a useful measure of the adequacy of an assay for deployment in clinical trials.

Antitumoral and antimetastatic effects of continuous particle-mediated cytokine gene therapy

We established a mice tumor model to investigate the effects of continuous cancer gene therapy, including antigen-presenting cell (APC) engineering and local stimulation of the immune system. B16 melanoma or Lewis lung carcinoma cells were injected intradermally on the back of C57/BL6 mice. The overlaying dermis or the tumor was shot with a gene gun (particle-mediated gene transfer) starting 8 days after tumor implantation in the case of the melanoma (Lewis lung carcinoma start day 7), continuing every fourth day thereafter until death. Control groups were mice without any therapy (A) or gene therapy with the empty plasmid (B). Therapy groups (Melanoma) received the genes as follows: group C--day 8, IL-12; day 12, IL-2...; group D--day 8, IFN-gamma/B7.1; day 12, IFN-gamma/B7.1...; group E--day 8, IFN-gamma/B7.1; day 12, IL-12, day 16, IL-2.... Melanoma: Mean survival time was enhanced in all therapy groups significantly, whereby the greatest survival time was found in group C. Tumor growth was reduced in all therapy groups similarly (C and D significant). Lewis Lung: Only mice of group C had an enhanced survival and reduced tumor growth (both significant). An antimetastatic effect was seen in all therapy groups.

In vivo antitumor activity of NKT cells activated by the combination of IL-12 and IL-18

Interleukin-12 and IL-18 have been demonstrated to potentiate innate immunity in a variety of experimental tumor models, but the functional roles of NK and/or NKT cells and their mechanism of action in these models have not been fully addressed. Through adoptive transfer of NKT cells activated in vitro with a combination of IL-12 plus IL-18 (IL-12/IL-18 NKT) into syngeneic animals, we demonstrate in this study that IL-12/IL-18 NKT cells are essential and collaborate with the host's own NK cells in natural host immunity against the growth of ALC and MC57X syngeneic tumors. The relative roles of the adoptively transferred IL-12/IL-18 NKT cells and endogenous NK cells in host protection were first shown in normal C57BL/6 (B6) mice treated with anti-asialo GM1 Ab that selectively depletes NK cells; second, in B6.TCRJalpha281(-/-) mice specifically deficient for NKT cells; and third, in B6.scid mice that also lack NKT cells. Furthermore, by injecting normal B6 mice with anti-IL-2 and/or anti-IFN-gamma mAb, we could demonstrate that effective innate immunity against both types of syngeneic tumors was dependent on the production of IL-2 and IFN-gamma by the adoptively transferred NKT cells. In vitro studies confirmed both the secretion of IL-2 and IFN-gamma by the IL-12/IL-18-activated NKT cells and their collaborative role with NK cells for lysis of ALC and MC57X syngeneic tumor targets. This is the first description of an antitumor function of IL-12/IL-18 NKT cells adoptively transferred into syngeneic hosts that provides the basis for a new modality in the cellular immunotherapy of cancer.

Generating potent Th1/Tc1 T cell adoptive immunotherapy doses using human IL-12: Harnessing the immunomodulatory potential of IL-12 without the in vivo-associated toxicity

Interleukin (IL)-12 is a cytokine originally identified from medium conditioned by an Epstein-Barr virus transformed cell line. IL-12 has been shown to increase IFN-gamma secretion from NK and T cells, significantly enhance cytolytic activity in both of these cell types, and promote the development of Th1/Tc1 immune responses. These properties make IL-12 an attractive candidate for the development of various clinical protocols ranging from the treatment of viral diseases to tumor immunotherapy. The initial attempts to use IL-12 in the treatment of tumors demonstrated toxicity at potentially therapeutic doses. To circumvent the toxicity associated with IL-12 administration, the authors have developed an adoptive immunotherapy protocol that uses IL-12 for a brief period during ex vivo T cell activation. They show that IL-12 conditioning may be achieved without altering the growth characteristics of the in vitro expanding T cells. T cells generated in the presence of IL-12 show a shift to a Th1/Tc1 dominant phenotype. The resultant cells are more potent killers in vitro and in vivo as assessed by CTL assays and tumor regression. The ability to harness the potent Th1/Tc1 generating potential of IL-12 while avoiding its associated in vivo toxicity has the potential to benefit a large number of clinical trial protocols using adoptive transfer of T cells specific for tumors, viruses, or intracellular pathogens.

Expression of IL-18 by SIV does not modify the outcome of the antiviral immune response

Interleukin 18 (IL-18) is a proinflammatory cytokine expressed by several cell types, including activated dendritic cells and macrophages, that acts in synergy with IL-12 as an important amplifying factor for IFN-gamma production and Th1 development. To study the immunological and virological effects of IL-18 expression in the context of a lentiviral infection, we inoculated rhesus macaques with a high dose of replication-competent simian immunodeficiency virus (SIV) vectors carrying the rhesus IL-18 gene in the sense (SIV(IL-18)) or antisense (SIV(FIGI)) orientation. Both vectors behaved as attenuated viruses, resulting in low viral loads, induction of low and transient levels of inflammatory cytokines, no CD4(+) T cell depletion, and mild activation of T lymphocytes. Although IL-18-expressing virus could be isolated from some SIV(IL18)-infected macaques for 12 weeks postinfection, the anti-SIV humoral and cellular immune responses of macaques inoculated with SIV(IL18) and SIV(FIGI) were similar to each other, with the exception of an early IFN-gamma response in animals infected with SIV(IL18). In summary, expression of IL-18 during the acute phase of SIV infection does not increase viral replication or influence the outcome of the antiviral immune response.

The enhanced IL-18 production by UVB irradiation requires ROI and AP-1 signaling in human keratinocyte cell line (HaCaT)

Based on our recent observation that enhanced IL-18 expression positively correlates with malignant skin tumors, such as SCC and melanoma, we examined the possible role of UVB, known to be associated with skin cancer development, in the enhancement of IL-18 production using primary human epidermal keratinocytes and human keratinocyte cell line HaCaT. After cells were exposed to UVB irradiation in vitro, IL-18 production was examined by Northern blot analysis and ELISA, and it was found that IL-18 production is enhanced by UVB irradiation in a dose- and time-dependent manner. In addition, we confirmed that it is functionally active form of IL-18 using the inhibitor of caspase-1. The effect of UVB irradiation was blocked by antioxidant, N-acetyl-L-cysteine (NAC), which suggested the involvement of reactive oxygen intermediates (ROI) in the signal transduction of UVB irradiation-enhanced IL-18 synthesis. We also found that UVB irradiation increased AP-1 binding activity by using EMSA with AP-1-specific oligonucleotide. Furthermore, inhibitors of UVB-induced AP-1 activity, such as PD98059, blocked enhanced IL-18 production, indicating that AP-1 activation is required for UVB-induced IL-18 production. Taken together, our results suggest that UVB irradiation-enhanced IL-18 production is selectively mediated through the generation of ROI and the activation of AP-1.

Gene transfer of secreted-type modified interleukin-18 gene to B16F10 melanoma cells suppresses in vivo tumor growth through inhibition of tumor vessel formation

Interleukin-18 is a novel cytokine identified as a strong inducer of interferon-gamma. Interleukin-18 has been shown to have similar bioactivities to interleukin-12 and to have antitumor efficacy in experimental models. In this study, we investigated whether the introduction of the interleukin-18 gene to B16F10 melanoma cells can induce antitumor response or not. Before the transfection, we modified the interleukin-18 gene to enable transfected tumor cells to secrete bioactive interleukin-18, because interleukin-18 does not have a signal sequence and requires processing by the interleukin-1 converting enzyme to attain the mature form. We found that B16 melanoma cells transduced with hybrid cDNA consisting of the interferon-beta signal sequence and mature interleukin-18 sequence, but not native interleukin-18, secreted a large amount of interleukin-18 and exhibited retarded tumor growth when injected in syngeneic mice. The antitumor effect was mostly abrogated by administration of anti-interferon-gamma antibody, but was not affected by in vivo depletion of CD8+ T cells or natural killer cells. Histologic analysis revealed that vascularization was markedly reduced and that necrosis was extensively induced in interleukin-18-secreting B16F10 melanoma (B16/IL18) tissues, whereas abundant tumor vessel formation was observed in B16/IL18 tissues of interferon-gamma-neutralized mice. We also found that chemokines, interferon-inducible protein-10 and monokine induced by interferon-gamma, were produced in B16/IL18 tissues and that the expression of both chemokines was dependent on that of interferon-gamma in the tumor tissues. Further, we showed that B16 melanoma cells secreted both chemokines in response to interferon-gamma. In addition, the expression of angiogenin, an angiogenic factor of melanoma, in B16 melanoma cells was reduced by interferon-gamma treatment. These results indicate that gene transfer of secreted-type interleukin-18 to B16F10 melanoma cells is a useful method of triggering an antitumor response without any systemic adverse effects and that the antitumor efficacy is mainly mediated by antiangiogenic activity, which is possibly involved in at least two dynamic changes induced by interferon-gamma inside B16 melanoma cells: the upregulation of antiangiogenic chemokines, interferon-inducible protein-10 and monokine induced by interferon-gamma, and the downregulation of angiogenic factor, angiogenin.

Roles of interleukin-18 in tissue destruction and compensatory reactions

Interleukin (IL)-18 is a member of the IL-1 cytokine family. Pro-IL-18 is cleaved by caspase-1 (IL-1beta-converting enzyme) to yield biologically active 18-kDa IL-18. Interleukin-18 is recognized by a heterodimeric receptor, consisting of a ligand-binding alpha-chain (IL-18Ralpha/IL-1Rrp) and an associating beta-chain (IL-18Rbeta/AcPL), which transmits signals through MyD88/IRAK/TRAF-6 molecules. Interleukin-18 is expressed in various types of cells, including macrophages, keratinocytes, intestinal epitherial cells, osteoblastic cells, chondrocytes, and adrenal cortex cells. Interleukin-18 promotes IFN-gamma production and Th1 helper T-cell development, synergistically with IL-12. However, IL-18 itself shows capabilities to induce IL-4, IL-5, IL-10, and IL-13 from T and natural killer cells. It also induces PGE2 production from activated macrophages. Moreover, many diseases are characterized by the production of IL-18 in the lesion. Taking these data together, our working hypothesis on how IL-18 is involved in "destructive" and "compensatory" pathways is proposed in this issue.

IL-12 induces monocyte IL-18 binding protein expression via IFN-gamma

IL-18 is a Th1 cytokine that synergizes with IL-12 and IL-2 in the stimulation of lymphocyte IFN-gamma production. IL-18 binding protein (IL-18BP) is a recently discovered inhibitor of IL-18 that is distinct from the IL-1 and IL-18 receptor families. In this report we show that IL-18BPa, the IL-18BP isoform with the highest affinity for IL-18, was strongly induced by IL-12 in human PBMC. Other Th1 cytokines, including IFN-gamma, IL-2, IL-15, and IL-18, were also capable of augmenting IL-18BPa expression. In contrast, IL-1alpha, IL-1beta, TNF-alpha, IFN-gamma-inducible protein-10, and Th2 cytokines such as IL-4 and IL-10 did not induce IL-18BPa. Although monocytes were found to be the primary source of IL-18BPa, the induction of IL-18BPa by IL-12 was mediated through IFN-gamma derived predominantly from NK cells. IL-18BPa production was observed in cancer patients receiving recombinant human IL-12 and correlated with the magnitude of IFN-gamma production. The IFN-gamma/IL-18BPa negative feedback loop identified in this study may be capable of broadly controlling immune activation by cytokines that synergize with IL-18 to induce IFN-gamma and probably plays a key role in the modulation of both innate and adaptive immunity.

Preoperative serum interleukin-18 level as a postoperative prognostic marker in patients with gastric carcinoma

BACKGROUND

Interleukin-18 (IL-18), a recently described cytokine produced mainly by macrophages, stimulates interferon-gamma (IFN-gamma) production by natural killer cells and T cells. Although it has been reported that serum IL-18 levels are higher in patients with advanced tuberculosis and acute graft-versus-host disease compared with normal controls, the authors found no reports regarding serum IL-18 levels in patients with malignant solid tumors. The purpose of this study was to determine serum IL-18 levels and their clinical significance in patients with gastric carcinoma.

METHODS

Peripheral blood samples were obtained from 94 patients with gastric carcinoma who underwent curative surgery and from 50 healthy volunteers. The serum IL-18 level, the IFN-gamma, level, and the Helicobacter pylori (HP) serology status were determined in each sample with an enzyme-linked immunosorbent assay.

RESULTS

The mean serum IL-18 level for all patients was significantly higher compared with the mean level in healthy volunteers (P < 0.01). IFN-gamma titers were below the level of detection in all samples tested. When the patients were subdivided into groups, it was found that the serum IL-18 level in patients with Stage II and III disease was significantly higher compared with the level found in healthy volunteers (P < 0.01). The serum IL-18 level decreased after patients underwent surgical resection. However, there was no significant difference in the serum IL-18 level between healthy controls and patients with Stage I or IV disease. Patients with IL-18 levels >or= 310 pg/mL (i.e., equal to or greater than the mean levels +/- 1 standard deviation in the healthy volunteers) experienced a significantly lower survival rate compared with patients who had IL-18 levels < 310 pg/mL after undergoing surgery (P < 0.05) despite a lack of any discernible difference in clinicopathologic factors between the two groups. The serum IL-18 level was identified as an independent postoperative prognostic factor in multivariate survival analysis using a Cox proportional hazards model (hazard ratio, 4.89; P = 0.01). There was no significant correlation between HP serology status and serum IL-18 levels.

CONCLUSIONS

The preoperative serum IL-18 level may represent a significant postoperative prognostic determinant in patients with gastric carcinoma. Its function in the host immune system remains to be elucidated.

Immune rejection of a large sarcoma following cyclophosphamide and IL-12 treatment requires both NK and NK T cells and is associated with the induction of a novel NK T cell population

Combined immunotherapy with cyclophosphamide (Cy) and IL-12, but not IL-12 alone, stimulates eradication of a large established solid tumor (20 mm), MCA207, a methylcholanthrene-induced murine sarcoma. In these studies we demonstrate that NK1.1(+) cells and CD1d-dependent NK T cells each play important yet distinct roles in regression of a large tumor in response to Cy and IL-12, and we define a novel NK T cell subset, selectively increased by this treatment. Mice depleted of NK1.1(+) cells demonstrated more rapid initial tumor growth and prolonged tumor regression following treatment, but tumors were eventually eradicated. In contrast, initial tumor regression following therapy was unimpaired in CD1d(-/-) mice, which are deficient in most NK T cells, but tumors recurred. No tumor regression occurred following Cy and IL-12 therapy in CD1d(-/-) mice that were depleted of NK1.1(+) cells. We found that Cy and IL-12 induced the selective increase in liver and spleen lymphocytes of a unique NK T subpopulation (DX5(+)NK1.1(-)CD3(+)). These cells were not induced by treatment in CD1d(-/-) mice. Our studies demonstrate a contribution of both NK and NK T cells to the Cy- and IL-12-stimulated anti-tumor response. We describe the selective induction of a distinct NK T cell subset by Cy and IL-12 therapy, not seen following IL-12 therapy alone, which we suggest may contribute to the successful anti-tumor response induced by this immunotherapeutic regimen.

Interleukin-18 regulates both Th1 and Th2 responses

Although interleukin-18 is structurally homologous to IL-1 and its receptor belongs to the IL-1R/Toll-like receptor (TLR) superfamily, its function is quite different from that of IL-1. IL-18 is produced not only by types of immune cells but also by non-immune cells. In collaboration with IL-12, IL-18 stimulates Th1-mediated immune responses, which play a critical role in the host defense against infection with intracellular microbes through the induction of IFN-gamma. However, the overproduction of IL-12 and IL-18 induces severe inflammatory disorders, suggesting that IL-18 is a potent proinflammatory cytokine that has pathophysiological roles in several inflammatory conditions. IL-18 mRNA is expressed in a wide range of cells including Kupffer cells, macrophages, T cells, B cells, dendritic cells, osteoblasts, keratinocytes, astrocytes, and microglia. Thus, the pathophysiological role of IL-18 has been extensively tested in the organs that contain these cells. Somewhat surprisingly, IL-18 alone can stimulate Th2 cytokine production as well as allergic inflammation. Therefore, the functions of IL-18 in vivo are very heterogeneous and complicated. In principle, IL-18 enhances the IL-12-driven Th1 immune responses, but it can also stimulate Th2 immune responses in the absence of IL-12.

Intratumoral IL-18 gene transfer improves therapeutic efficacy of antibody-targeted superantigen in established murine melanoma

Antibody-targeted superantigen C215Fab-SEA is a fusion protein of staphylococcal enterotoxin A (SEA) and the Fab region of the tumor-reactive C215 mAb. It can trigger CTL against C215 antigen-positive tumor cells and induce tumor-suppressive cytokines. However, the antitumor effect of C215Fab-SEA is not satisfactory because of suboptimal production of Th1 cytokines after repeated administration. Interleukin 18 (IL-18) is a novel cytokine with profound effects on Th1 cellular response. In this study, we showed that adenovirus-mediated intratumoral IL-18 gene transfer strongly improved the therapeutic efficacy of C215Fab-SEA in the pre-established C215 antigen-expressing B16 melanoma murine model. More significant tumor inhibition and prolonged survival time were observed in tumor-bearing mice received combined therapy of C215Fab-SEA and Ad IL-18 than those of mice treated with C215Fab-SEA or AdIL-18 alone. Combination therapy augmented NK and CTL activities of tumor-bearing mice more markedly. The production of IL-2 and IFN-gamma also increased more significantly. More potent antitumor effect of combined therapy was observed in IL-10 KO mice with enhanced Th1 response. Our data demonstrated that the antitumor effect of C215Fab-SEA immunotherapy could be potentiated significantly by combination with intratumoral IL-18 gene transfer through more efficient activation of Th1 immune responses.

Expression of the interleukin-18 gene from rhesus macaque by the simian immunodeficiency virus does not result in increased viral replication

Interleukin-18 (IL-18), previously known as interferon-gamma (IFN-gamma)-inducing factor (IGIF), is a proinflammatory cytokine expressed by activated macrophages that acts in synergy with IL-12 as an important amplifying factor for IFN-gamma production and Th1 development. To study the effect of IL-18 on a lentiviral infection, we cloned the IL-18 gene from a rhesus macaque and constructed replication-competent simian immunodeficiency virus (SIV) that expressed either the precursor pro-IL-18 (SIV(IL-18)) or the mature form (SIV(mIL-18)) of IL-18. The predicted amino acid sequence for rhesus IL-18 had 96% homology with the human one, differing in only 8 of 193 residues. SIV(IL-18) and SIV(mIL-18) replicated more slowly than control viruses in the CEM x 174 cell line and resulted in the development of chronically infected cell lines that expressed high levels of infectious SIV. The cell line generated by SIV(IL-18) released large quantities of IL-18 into the supernatant, whereas the one obtained from SIV(mIL-18) showed the accumulation of IL-18 in the cytoplasm. Similarly, SIV(IL-18) and SIV(mIL-18) replicated more slowly than the unmodified viral vector in rhesus peripheral blood mononuclear cells (PMBC), but only SIV(IL-18) expressed biologically active IL-18. These experiments show that the precursor form of IL-18 is necessary for the efficient release of the cytokine and that IL-18 does not promote increased replication of SIV in rhesus PBMC.

Interleukin-18 (IL-18) enhances innate IL-12-mediated resistance to Toxoplasma gondii

Innate resistance to Toxoplasma gondii is dependent on the ability of interleukin-12 (IL-12) to stimulate natural killer (NK) cell production of gamma interferon (IFN-gamma). Since IL-18 is a potent enhancer of IL-12-induced production of IFN-gamma by NK cells, SCID mice (which lack an adaptive immune response) were used to assess the role of IL-18 in innate resistance to T. gondii. Administration of anti-IL-18 to SCID mice infected with T. gondii resulted in an early reduction in serum levels of IFN-gamma but did not significantly decrease resistance to this infection. In contrast, administration of exogenous IL-18 to infected SCID mice resulted in increased production of IFN-gamma, reduced parasite burden, and a delay in time to death. The protective effects of IL-18 treatment correlated with increased NK cell numbers and cytotoxic activity at the local site of administration and with elevated levels of inducible nitrous oxide synthose in the spleens of treated mice. In addition, in vivo depletion studies demonstrated that the ability of exogenous IL-18 to enhance resistance to T. gondii was dependent on IL-12, IFN-gamma, and NK cells. Together, these studies demonstrate that although endogenous IL-18 appears to have a limited role in innate resistance to T. gondii, treatment with IL-18 can augment NK cell-mediated immunity to this pathogen.