Molecular mechanisms underlying IFN-gamma-mediated tumor growth inhibition induced during tumor immunotherapy with rIL-12

Preclinical and Clinical Immunotherapeutic Strategies in Epithelial Ovarian Cancer

In the past 20 years, the immune system has increasingly been recognized as a major player in tumor cell control, leading to considerable advances in cancer treatment. While promising with regards to melanoma, renal cancer and non-small cell lung cancer, immunotherapy provides, for the time being, limited success in other cancers, including ovarian cancer, potentially due to insufficient immunogenicity or to a particularly immunosuppressive microenvironment. In this review, we provide a global description of the immune context of ovarian cancer, in particular epithelial ovarian cancer (EOC). We describe the adaptive and innate components involved in the EOC immune response, including infiltrating tumor-specific T lymphocytes, B lymphocytes, and natural killer and myeloid cells. In addition, we highlight the rationale behind the use of EOC preclinical mouse models to assess resistance to immunotherapy, and we summarize the main preclinical studies that yielded anti-EOC immunotherapeutic strategies. Finally, we focus on major published or ongoing immunotherapy clinical trials concerning EOC.

The immunopathogenic and immunomodulatory effects of interleukin-12 in periodontal disease

Interleukin 12 (IL-12) is an inflammatory cytokine that promotes the response of the immune system. This cytokine has been implicated as a potent stimulator of several diseases characterized by inflammatory-induced bone destruction, such as rheumatoid arthritis and periodontitis. Yet, the exact role of IL-12 in the development and progress of periodontitis has not been clarified. Several studies have demonstrated a positive correlation between the level of IL-12 and the severity of periodontal destruction. Deletion of IL-12 in mice with periodontitis significantly suppressed the level of bone destruction. Interestingly, next to a role in modulating the pathogenesis, IL-12 also has immunological-regulatory properties. This cytokine induces expression of immunosuppressive molecules, such as indoleamine-pyrrole 2,3-dioxygenase (IDO). Thus, these findings suggest both negative and positive influences of IL-12 in periodontal disease. It is currently proposed that the diversity of action of cytokines is a molecular key which regulates biological development and homeostasis. Accordingly, the actions of IL-12 might be one of the mechanisms that regulate homeostasis of periodontal tissue during and following inflammation. Therefore, this article aims to review both destructive and protective functionalities of IL-12 with an emphasis on periodontal disease.

Understanding the role of the kynurenine pathway in human breast cancer immunobiology

Breast cancer (BrCa) is the leading cause of cancer related death in women. While current diagnostic modalities provide opportunities for early medical intervention, significant proportions of breast tumours escape treatment and metastasize. Gaining increasing recognition as a factor in tumour metastasis is the local immuno-surveillance environment. Following identification of the role played by the enzyme indoleamine dioxygenase 1 (IDO1) in mediating maternal foetal tolerance, the kynurenine pathway (KP) of tryptophan metabolism has emerged as a key metabolic pathway contributing to immune escape. In inflammatory conditions activation of the KP leads to the production of several immune-modulating metabolites including kynurenine, kynurenic acid, 3-hydroxykynurenine, anthranilic acid, 3-hydroxyanthranilic acid, picolinic acid and quinolinic acid. KP over-activation was first described in BrCa patients in the early 1960s. More evidence has since emerged to suggest that the IDO1 is elevated in advanced BrCa patients and is associated with poor prognosis. Further, IDO1 positive breast tumours have a positive correlation with the density of immune suppressive Foxp3+ T regulatory cells and lymph node metastasis. The analysis of clinical microarray data in invasive BrCa compared to normal tissue showed, using two microarray databank (cBioportal and TCGA), that 86.3% and 91.4% BrCa patients have altered KP enzyme expression respectively. Collectively, these data highlight the key roles played by KP activation in BrCa, particularly in basal BrCa subtypes where expression of most KP enzymes was altered. Accordingly, the use of KP enzyme inhibitors in addition to standard chemotherapy regimens may present a viable therapeutic approach.

Interleukin-12 modulates the immunomodulatory properties of human periodontal ligament cells

BACKGROUND AND OBJECTIVE

The cytokine interleukin 12 (IL-12) has been implicated as a potent stimulator of tissue degradation in the pathogenesis of several inflammatory diseases, including periodontitis. In patients with periodontitis, an increased level of IL-12 is found in serum and gingival crevicular fluid. As inflammatory cytokines have been demonstrated to induce activation of the immunomodulatory properties of mesenchymal stem cells (MSCs), this study aimed to investigate the influence of IL-12 on these properties in human periodontal ligament (hPDL) cells.

MATERIAL AND METHODS

Human PDL cells were isolated from periodontal tissue and incubated with 0-10 ng/mL of IL-12 for 24 h. The levels of expression of interferon gamma (IFN-γ), indoleamine 2,3-dioxygenase (IDO) and human leukocyte antigen G (HLA-G), as well as of the stem cell markers, CD73, CD90 and CD105, were assessed by quantitative PCR. The level of IFN-γ protein was measured by ELISA, and IDO activity was measured by activity assay. The participation of IFN-γ in the expression of IDO and HLA-G was analyzed using neutralizing antibody against IFN-γ.

RESULTS

IL-12 upregulated the expression of IFN-γ in a dose-dependent manner. Moreover, IL-12 induced the expression of the immunomodulatory proteins IDO and HLA-G via an IFN-γ-dependent pathway, as indicated by experiments using an IFN-γ neutralizing antibody. Addition of exogenous IFN-γ upregulated the expression of HLA-G and IDO. Expression of the stem cell markers CD73, CD90 and CD105, as well as the pluripotent markers Nanog homeobox, octamer-binding transcription factor 4 and SRY-box 2, were also upregulated in IL-12-treated hPDL cells. Finally, IL-12 inhibited osteogenic differentiation of the hPDL cells and preserved the self-clonal expansion property of these cells, as assessed by Alizarin Red S staining and the colony-forming unit assay.

CONCLUSION

Expression of IL-12 during periodontitis may play an important role in the control of the inflammatory response via the induction of immunosuppressive molecules by hPDL cells. We hypothesize that this immunomodulatory property of IL-12 will serve as a protective mechanism to preserve a population of stem cells under inflammatory conditions.

Spontaneous and mitogen-induced cytokine production in lymphoproliferative diseases

The levels of spontaneous and mitogen-induced production of pro- and anti-inflammatory cytokines were studied in patients with chronic lymphoid leukemia, non-Hodgkin's lymphocytic lymphomas, and multiple myeloma during the course of chemotherapy. Cytokine concentrations varied within a great range and did not conform to the normal distribution law. The levels of granulocyte and granulocyte-macrophage CSF were high during the debut, progress, and remission of the lymphoproliferative diseases. Imbalance of a wide spectrum of pro- and anti-inflammatory cytokines was observed during the debut and progress of the lymphoproliferative diseases, more often in chronic lymphoid leukemia and non-Hodgkin's lymphocytic lymphomas than in multiple myeloma.

The systemic cytokine environment is permanently altered in multiple myeloma

Multiple myeloma (MM) is an incurable bone marrow malignancy of the B cell lineage. Utilizing multiplex Luminex technology we measured levels of 25 cytokines in the plasma of normal donors (n = 177), those with monoclonal gammopathy of undetermined significance (n = 8), and MM patients (n = 55) with either active disease, on treatment, or in remission. The cytokine levels were compared between normal donors and MM patients as well as between various phases of MM, and discriminant analysis was used to create a predictive classification model based on the differentially expressed cytokines. Evaluating age- and gender-dependence of cytokine expression, we determined that with age there is a shift toward a pro-inflammatory environment. Moreover, we observed a strong gender bias in cytokine expression. However, the profile of differentially expressed cytokines was heavily skewed toward an anti-inflammatory, pro-tumorigenic response in patients with MM. Significantly, our predictive model placed all patients in remission in the same category as those with active disease. Thus, our study demonstrates that the homeostasis of systemic cytokines is not restored when MM patients enter remission, suggesting that once an individual has cancer, the microenvironment is permanently altered and the system is primed for a relapse.

Psychosocial stress and inflammation in cancer

Stress-induced immune dysregulation results in significant health consequences for immune related disorders including viral infections, chronic autoimmune disease, and tumor growth and metastasis. In this mini-review we discuss the sympathetic, neuroendocrine and immunologic mechanisms by which psychosocial stress can impact cancer biology. Both human and animal studies have shown the sympathetic and neuroendocrine responses to psychosocial stress significantly impacts cancer, in part, through regulation of inflammatory mediators. Psychosocial stressors stimulate neuroendocrine, sympathetic, and immune responses that result in the activation of the hypothalamic-pituitary-adrenal (HPA)-axis, sympathetic nervous system (SNS), and the subsequent regulation of inflammatory responses by immune cells. Social disruption (SDR) stress, a murine model of psychosocial stress and repeated social defeat, provides a novel and powerful tool to probe the mechanisms leading to stress-induced alterations in inflammation, tumor growth, progression, and metastasis. In this review, we will focus on SDR as an important model of psychosocial stress in understanding neural-immune mechanisms in cancer.

The indoleamine-2,3-dioxygenase (IDO) inhibitor 1-methyl-D-tryptophan upregulates IDO1 in human cancer cells

1-methyl-D-tryptophan (1-D-MT) is currently being used in clinical trials in patients with relapsed or refractory solid tumors with the aim of inhibiting indoleamine-2,3-dioxygenase (IDO)-mediated tumor immune escape. IDO is expressed in tumors and tumor-draining lymph nodes and degrades tryptophan (trp) to create an immunsuppressive micromilieu both by depleting trp and by accumulating immunosuppressive metabolites of the kynurenine (kyn) pathway. Here we show that proliferation of alloreactive T-cells cocultured with IDO1-positive human cancer cells paradoxically was inhibited by 1-D-MT. Surprisingly incubation with 1-D-MT increased kyn production of human cancer cells. Cell-free assays revealed that 1-D-MT did not alter IDO1 enzymatic activity. Instead, 1-D-MT induced IDO1 mRNA and protein expression through pathways involving p38 MAPK and JNK signalling. Treatment of cancer patients with 1-D-MT has transcriptional effects that may promote rather than suppress anti-tumor immune escape by increasing IDO1 in the cancer cells. These off-target effects should be carefully analyzed in the ongoing clinical trials with 1-D-MT.

IDO-Mediated Tryptophan Degradation in the Pathogenesis of Malignant Tumor Disease

Immune escape is a fundamental trait of cancer in which the Th1-type cytokine interferon- γ (IFN-γ) seems to play a key role. Among other tumoricidal biochemical pathways, IFN-γ induces the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO) in a variety of cells including macrophages, dendritic cells (DCs) and tumor cells. IDO activity has been shown to reflect the extent and the course in a plethora of malignancies including prostate, colorectal, pancreatic, cervical, endometrial, gastric, lung, bladder, ovarian, esophageal and renal cell carcinomas, glioblastomas, mesotheliomas, and melanomas. Furthermore IDO activity during malignant tumor diseases seems to be part of the tumoricidal immune defense strategy, which in the long run is detrimental to the host, when tryptophan deprivation and production of pro-apoptotic tryptophan catabolites counteract T-cell responsiveness.

Phase-I clinical trial of IL-12 plasmid/lipopolymer complexes for the treatment of recurrent ovarian cancer

A phase-I trial to assess the safety and tolerability of human interleukin-12 (IL-12) plasmid (phIL-12) formulated with a synthetic lipopolymer, polyethyleneglycol-polyethyleneimine-cholesterol (PPC), was conducted on women with chemotherapy-resistant recurrent ovarian cancer. A total of 13 patients were enrolled in four dose-escalating cohorts and treated with 0.6, 3, 12 or 24 mg m(-2) of the formulated plasmid once every week for 4 weeks. Administration of phIL-12/PPC was generally safe and well-tolerated. Common side effects included low-grade fever and abdominal pain. Stable disease and reduction in serum CA-125 levels were clinically observed in some patients. Measurable levels of IL-12 plasmid were detectable in PF samples collected throughout the course of phIL-12/PPC treatment. In comparison, serum samples either did not contain detectable amounts of plasmid DNA or contained <1% of the amount found in the corresponding PF samples. Treatment-related increases in IFN-gamma levels were observed in PF but not in serum. These data demonstrate that IL-12 gene delivery with a synthetic delivery system is feasible for ovarian cancer patients.

Intracerebral interleukin 12 induces glioma rejection in the brain predominantly by CD8+ T cells and independently of interferon-gamma

The prognosis of gliomas is generally poor since these tumors elude established therapeutic approaches. Immunotherapy might present an effective therapy in particular because the glioma cells are diffusely dispersed in the infiltration zone of the tumor and show a strong propensity to invade the surrounding brain along white matter tracts. Although various immune therapies for brain tumors are successful in rodents, there is currently no effective therapy in humans. In the present study, we investigated the mechanisms by which intracerebral IL-12 mediates rejection of GL261 cells in a syngenic mouse glioma model. Wild type mice revealed smaller tumors as compared to mice lacking functional T and B cells indicating that considerable immune dependent tumor rejection occurs physiologically in this model. However, glioma rejection was significantly enhanced in mice expressing IL-12 in the CNS and was predominantly dependent on the presence of CD8+ T cells while CD4+ T cells had less impact. Interestingly, the rejection of tumors was independent of IFN-gamma. Our findings contrast results obtained after in vitro or systemic stimulation with IL-12 and demonstrate that successful IL-12 induced glioma rejection critically depends on the localization, duration and time of IL-12 expression.

Characterization of a recombinant adenovirus vector encoding heat-inducible feline interleukin-12 for use in hyperthermia-induced gene-therapy

Interleukin-12 (IL-12) is a pro-inflammatory cytokine that has shown great promise as a therapeutic agent in experimental models of infectious disease and cancer. However, it is also a highly toxic molecule and for that reason has not been accepted readily into the clinic. A replication-deficient adenoviral vector was designed to deliver the feline interleukin-12 gene into tumour cells. The interleukin-12 gene has been placed under control of a heat inducible promoter, human heat shock promoter 70b, with the intent of spatially and temporally controlling the expression of IL-12, thus limiting its toxicity. In vitro, the transfection efficiency of the adenoviral vector, the effect of multiplicity of infection and the production of biologically active feline IL-12 were studied in the infected cells in response to a range of temperatures. This adenoviral vector will be a useful tool to examine the effects of intra-tumoural IL-12 delivery in a spontaneously occurring feline soft tissue sarcoma model.

Inhibitors of indoleamine-2,3-dioxygenase for cancer therapy: can we see the wood for the trees?

Indoleamine-2,3-dioxygenase (IDO) is an immunosuppressive enzyme capable of inhibiting a destructive maternal T cell response against allogeneic fetuses. Expression of IDO is evident in tumours and is thought to enable escape from immunologically mediated rejection. Consequently, clinical trials using an inhibitor of IDO, 1-methyltryptophan (1MT), have been initiated. However, a review of the current literature indicates that we are far from understanding the biological relevance of IDO expression during tumorigenesis. A better understanding of IDO biology is needed to comprehend the effect of IDO inhibitors and to provide a rationale for their therapeutic application in cancer.

Myeloid suppressor cell-associated immune dysfunction in CSA1M fibrosarcoma tumor-bearing mice

CSA1M tumor-bearing mice exhibited a severe immune dysfunction but the underlying mechanism remained unclear. In this study, we demonstrated that the myeloid suppressor cell (Mac-1(+)Gr-1(+) cells)-(MSC) related T cell immunosuppression in this tumor-bearing model. In mice at the late stage of CSA1M tumor-bearing (Late TB [8-10 weeks after cell inoculation in male BALB/c mice]), the percentages for CD4(+) and CD8(+) T cells decreased but Mac-1(+) cells increased in spleens with severe splenomegaly. There was no deficit for concanavalin A-induced CD4(+) and CD8(+) T cell proliferation, interferon-gamma (IFN-gamma) and interleukin (IL)-4 production, but delayed-type hypersensitivity reaction were attenuated. Analysis of cytokine production in unfractionated spleen cells showed a significant reduction of IFN-gamma and a marked increase of IL-10 and IL-4. In Late-TB mice, splenic MSC number intensively accumulated; the mRNA expressions of the signal transducer and activator of transcription 1, interferon regulatory factor 1 (IRF-1), and inducible nitric-oxide synthase (iNOS) were enhanced in MSC; the nitric oxide production and arginase enzyme activity increased in MSC as well. Furthermore, the concanavalin A-induced T cell proliferation was inhibited in the presence of lipopolysaccharide- or IFN-gamma-activated MSC from Late-TB mice, which could be reversed by the iNOS specific inhibitor L-NMMA. iNOS seemed to be required more than arginase for the suppressive activity of MSC. Taken together, our results suggest that the immune dysfunction in tumor-bearing mice might be causally associated with the accumulation of MSC and its tumor-favoring property.

The anti-tumor effect of interleukin-12 is enhanced by mild (fever-range) thermal therapy

The cytokine interleukin 12 (IL-12) has resulted in notable anti-tumor activity in animal models and in patients and as a result there is considerable interest in learning how to maximize its therapeutic potential while at the same time reducing its known toxic side effects. Strategies which could maintain its effectiveness while permitting reduced dosage could be especially valuable. In this study we used BALB/c mice bearing CT26 tumors as a model for testing whether combining murine IL-12 with a mild (fever range) whole body hyperthermia protocol could result in such a strategy. Our data revealed that 100 ng of IL-12/mouse/day used in combination with FR-WBH was as effective as one in which 300 ng of IL-12/mouse/day was used alone. Importantly, the mice receiving the combination treatment exhibited fewer treatment related toxicities compared to those that received high dose IL-12 alone. Initiation of the IL-12 treatment immediately after FR-WBH induced the greatest anti-tumor effect. This effect does not appear to depend on differences in IL-12-induced IFN-gamma, but may involve production of nitric oxide (NO), since treatment of mice with a NOS inhibitor, NG-monomethyl-L-arginine (L-NMA), abolishes the additive anti-tumor effect of the combination treatment. Collectively, these data suggest that modification of physiological parameters in the host by mild fever-like thermal stimuli may be an effective and feasible adjuvant for cytokine-based immunotherapeutic strategies.

Differential regulation of indoleamine 2,3-dioxygenase by lipopolysaccharide and interferon gamma in murine bone marrow derived dendritic cells

Indoleamine 2,3-dioxygenase (IDO) is a rate-limiting enzyme in the L-tryptophan-kynurenine pathway, which converts an essential amino acid, L-tryptophan, to N-formylkynurenine. The expression of IDO increases when inflammation is induced by wounding, infection or tumor growth. Although recent studies have suggested that IDO expression is up-regulated by IFN-gamma in various cell types and that the induction of IDO can also be mediated through an IFN-gamma-independent mechanism, these mechanisms still remain unknown. In this study, we investigated whether lipopolysaccharide (LPS) induces the expression of IDO through an IFN-gamma-mediated signaling pathway or not. IFN-gamma-induced expression of IDO expression was inhibited only by JAK inhibitor I. However, LPS-induced expression of IDO was inhibited by LY294002 and SP600125 but not by JAK inhibitor I, SB203580, or U0126. These findings clearly indicate that LPS can induce the IDO expression via an IFN-gamma-independent mechanism and PI3 kinase and JNK in the LPS-induced pathway leading to IDO expression.

Interleukin-12- and interferon-gamma-mediated natural killer cell activation by Agaricus blazei Murill

Dried fruiting bodies of Agaricus blazei Murill (A. blazei) and its extracts have generally used as complementary and alternative medicines (CAMs). Here, we report that the oral administration of A. blazei augmented cytotoxicity of natural killer (NK) cells in wild-type (WT) C57BL/6, C3H/HeJ, and BALB/c mice. Augmented cytotoxicity was demonstrated by purified NK cells from treated wild-type (WT) and RAG-2-deficient mice, but not from interferon-gamma (IFN-gamma) deficient mice. NK cell activation and IFN-gamma production was also observed in vitro when dendritic cell (DC)-rich splenocytes of WT mice were coincubation with an extract of A. blazei. Both parameters were largely inhibited by neutralizing anti-interleukin-12 (IL-12) monoclonal antibody (mAb) and completely inhibited when anti-IL-12 mAb and anti-IL-18 mAb were used in combination. An aqueous extract of the hemicellulase-digested compound of A. blazei particle; (ABPC) induced IFN-gamma production more effectively, and this was completely inhibited by anti-IL-12 mAb alone. NK cell cytotoxicty was augmented with the same extracts, again in an IL-12 and IFN-gamma-dependent manner. These results clearly demonstrated that A. blazei and ABPC augmented NK cell activation through IL-12-mediated IFN-gamma production.

The biology and therapeutic potential of interleukin 27

Interleukin (IL-) 27 is a helical cytokine of the greater IL-6/IL-12 family with a broad range of pro- and anti-inflammatory properties. It can skew T helper cell development, suppress T cell proliferation, stimulate cytotoxic T cell activity, induce isotype switching in B cells, and has diverse effects on innate immune cells. In vivo, its most important role appears to be that of immune regulation, as mice with defects in IL-27 or its receptor display enhanced immune responses in a range of infectious and noninfectious situations. In this review, we discuss the body of knowledge on IL-27 and its potential therapeutic utility.

Interferon-gamma produced by interleukin-12-activated tumor infiltrating CD8+T cells directly induces apoptosis of mouse hepatocellular carcinoma

BACKGROUND/AIMS

Interleukin-12 (IL-12), a cytokine with antitumor activity, was examined for the suppressive effect on hepatocellular carcinoma (HCC) in mouse model, and its mechanism of antitumor activity was analyzed.

METHODS

Mice implanted with MIH-2 HCC cells were treated with recombinant mouse IL-12 (500 ng/mouse). Involvement of CD4(+), CD8(+), NK cells and interferon (IFN)-gamma on tumor suppression by IL-12 was examined by treatment of mice with each antibody. Interferon-gamma (IFN-gamma) production by tumor infiltrating cells was analyzed by immunofluorescence microscopy and flow cytometric analysis. Signal transduction for apoptosis induction was examined by immunoblot analysis.

RESULTS

The growth of implanted MIH-2 tumors was significantly suppressed by IL-12 and the suppression was inhibited by depletion of CD8(+)T cells. IL-12 treatment caused numerous IFN-gamma-producing CD8(+)T cells to infiltrate into MIH-2 tumors. Antitumor activity of IL-12 was blocked by treating mice with anti-IFN-gamma mAb. CD8(+)T cells from IL-12-treated mice attached to MIH-2 cells and produced IFN-gamma in vitro. Cell attachment might be associated with intercellular adhesion molecule-1 induced by IFN-gamma. In vitro treatment with IFN-gamma induced apoptosis of MIH-2 cells via a mitochondria-dependent pathway.

CONCLUSIONS

IL-12 suppressed HCC growth in mouse model. IFN-gamma produced by IL-12-activated tumor-infiltrating CD8(+)T cells directly induced apoptosis of HCC cells.

Inducible nitric oxide synthase (iNOS) in tumor biology: the two sides of the same coin

Inducible nitric oxide synthase (iNOS) is one of three key enzymes generating nitric oxide (NO) from the amino acid l-arginine. iNOS-derived NO plays an important role in numerous physiological (e.g. blood pressure regulation, wound repair and host defence mechanisms) and pathophysiological (inflammation, infection, neoplastic diseases, liver cirrhosis, diabetes) conditions. iNOS is the synthase isoform most commonly associated with malignant disease. Nevertheless, the role of iNOS during tumor development is highly complex, and incompletely understood. Both promoting and deterring actions have been described, presumably depending upon the local concentration of iNOS within the tumor microenvironment. In particular, pivotal effects such as malingnant transformation, angiogenesis, and metastasis are modulated by iNOS. On the other hand, NO derived from macrophages has a potentially cytotoxic/cytostatic effect upon tumor cells. Hence, therapeutical interference with iNOS activity is of considerable interest, especially in tumors where metastatic activity, host defence mechanisms and the level of differentiation seem to be correlated to iNOS expression. This review will aim to summarize the dual actions of iNOS as simultaneous tumor promoter and suppressor.

B7.2-Ig fusion proteins enhance IL-4-dependent differentiation of tumor-sensitized CD8+ cytotoxic T lymphocyte precursors

The B7/CD28 co-stimulatory pathway plays a critical role in T cell activation and differentiation. Our previous study demonstrated that administration of B7.2-Ig fusion proteins to tumor-bearing mice elicits IL-4-dependent, CD8+ T cell-mediated tumor regression. Here, we investigated whether B7.2-Ig stimulation of tumor-sensitized CD8+ CTL precursors during in vitro antigen re-sensitization actually results in their differentiation into mature CTLs and if so, whether such a process depends on IL-4 signals. Splenocytes from tumor-sensitized (tumor-bearing or tumor-immunized) mice exhibited low levels of anti-tumor CTL responses upon culturing alone, but induced strikingly enhanced CTL responses when stimulated in vitro with B7.2-Ig fusion proteins. Because CTLs were not generated from normal splenocytes even by B7.2-Ig stimulation, the expression of the B7.2-Ig effect required the in vivo tumor sensitization of CD8+ CTL precursors. Administration of anti-CD4 or anti-CD40 ligand (CD40L) to mice before tumor sensitization resulted in almost complete inhibition of CTL responses generated in the subsequent culture containing B7.2-Ig. In contrast, anti-IL-4 did not influence in vivo tumor sensitization required for CTL induction. However, B7.2-Ig stimulation of tumor-sensitized splenocytes enhanced IL-4 production and neutralization of this IL-4 with anti-IL-4 potently down-regulated CTL responses. These results indicate that B7.2-Ig enhances IL-4-dependent differentiation of anti-tumor CD8+ CTL precursors that can be sensitized in vivo depending on collaboration with CD4+ T cells involving CD40L function.

Impaired interferon-gamma production as a consequence of STAT4 deficiency after autologous hematopoietic stem cell transplantation for lymphoma

Production of interferon gamma (IFN-gamma) is critical for optimal antitumor immunotherapy in several preclinical animal models. Interleukin-12 (IL-12)-induced IFN-gamma production is markedly defective after autologous stem cell transplantation. Quantitative deficiency in CD4 T cells, relative increase in CD25+CD4+ T cells, and bias toward T helper 2 (Th2) differentiation are not the primary mechanisms of defective IFN-gamma production. IL-12 receptor beta1 (IL-12Rbeta1) and IL-12Rbeta2 are expressed at equivalent or higher levels on posttransplantation patient peripheral blood mononuclear cells (PBMCs) as compared with control PBMCs. IL-12-induced tyrosine phosphorylation of signal transducer and activator of transcription 4 (STAT4) was undetectable or barely detectable in posttransplantation patient PBMCs, whereas IL-4-induced tyrosine phosphorylation of STAT6 did not differ in posttransplantation patient and control PBMCs. Levels of STAT4 protein were decreased by 97% in posttransplantation patient PBMCs. Levels of STAT4 mRNA were also significantly decreased in posttransplantation patient PBMCs. Incubation with IL-12 and IL-18 in combination partially reversed the defective IFN-gamma production by posttransplantation patient PBMCs. IFN-gamma production in response to IL-12 plus IL-18 did not require increased expression of STAT4 but was dependent on the activity of p38 mitogen-activated protein kinase (MAPK). These results indicate that defective IFN-gamma production is due to an intrinsic deficiency in STAT4 expression by posttransplantation patient lymphocytes and suggest strategies for circumventing this deficiency in cancer immunotherapy.

Induction of Tumor Regression by Administration of B7-Ig Fusion Proteins: Mediation by Type 2 CD8+T Cells and Dependence on IL-4 Production

CD28 signals contribute to either type 1 or type 2 T cell differentiation. Here, we show that administration of B7.2-Ig fusion proteins to tumor-bearing mice induces tumor regression by promoting the differentiation of antitumor type 2 CD8(+) effector T cells along with IL-4 production. B7.2-Ig-mediated regression was not induced in IL-4(-/-) and STAT6(-/-) mice. However, it was elicited in IFN-gamma(-/-) and STAT4(-/-) mice. By contrast, IL-12-induced tumor regression occurred in IL-4(-/-) and STAT6(-/-) mice, but not in IFN-gamma(-/-) and STAT4(-/-) mice. Moreover, B7.2-Ig treatment was effective in a tumor model not responsive to IL-12. B7.2-Ig administration elicited elevated levels of IL-4 production. Tumor regression was predominantly mediated by CD8(+) T cells, although the induction of these effector cells required CD4(+) T cells. Tumor regression induced by CD8(+) T cells alone was inhibited by neutralizing the IL-4 produced during B7.2-Ig treatment. Thus, these results indicate that stimulation in vivo of CD28 with B7.2-Ig in tumor-bearing mice results in enhanced induction of antitumor type 2 CD8(+) T cells (Tc2) leading to Tc2-mediated tumor regression.

Asp274 and his346 are essential for heme binding and catalytic function of human indoleamine 2,3-dioxygenase

L-Tryptophan is the least abundant essential amino acid in humans. Indoleamine 2,3-dioxgyenase (IDO) is a cytosolic heme protein which, together with the hepatic enzyme tryptophan 2,3-dioxygenase, catalyzes the first and rate-limiting step in the major pathway of tryptophan metabolism, the kynurenine pathway. The physiological role of IDO is not fully understood but is of great interest, because IDO is widely distributed in human tissues, can be up-regulated via cytokines such as interferon-gamma, and can thereby modulate the levels of tryptophan, which is vital for cell growth. To identify which amino acid residues are important in substrate or heme binding in IDO, site-directed mutagenesis of conserved residues in the IDO gene was undertaken. Because it had been proposed that a histidine residue might be the proximal heme ligand in IDO, mutation to alanine of the three highly conserved histidines His16, His303, and His346 was conducted. Of these, only His346 was shown to be essential for heme binding, indicating that this histidine residue may be the proximal ligand and suggesting that neither His303 nor His16 act as the proximal ligand. Site-directed mutagenesis of Asp274 also compromised the ability of IDO to bind heme. This observation indicates that Asp274 may coordinate to heme directly as the distal ligand or is essential in maintaining the conformation of the heme pocket.

Indoleamine 2,3-dioxygenase contributes to tumor cell evasion of T cell-mediated rejection

The priming of an appropriate anti-tumor T cell response rarely results in the rejection of established tumors. The characteristics of tumors that allow them to evade a T cell-mediated rejection are unknown for many tumors. We report on evidence that the expression of the immunosuppressive enzyme, indoleamine 2,3-dioxygenase (IDO) by mononuclear cells that invade tumors and tumor-draining lymph nodes, is 1 mechanism that may account for this observation. Lewis lung carcinoma (LLC) cells stimulated a more robust allogeneic T cell response in vitro in the presence of a competitive inhibitor of IDO, 1-methyl tryptophan. When administered in vivo this inhibitor also resulted in delayed LLC tumor growth in syngeneic mice. Our study provides evidence for a novel mechanism whereby tumors evade rejection by the immune system, and suggests the possibility that inhibiting IDO may be developed as an anti-cancer immunotherapeutic strategy.

Production of interferon-gamma by tumor-sensitized T cells is essential for interleukin-12-induced complete tumor eradication

BACKGROUND

Interferon-gamma (IFN-gamma) is essential for eradication of established large tumors by interleukin-12 (IL-12), but the critical source of IFN-gamma has not been defined. Adoptive transfer of T cells into T cell-deficient mice allows for evaluation of the role of T cells and T cell production of IFN-gamma in the antitumor immune response.

METHODS

Wild-type C57BL/6, IL-12 receptor-beta1 knockout (IL-12Rbeta1 KO), IFN-gamma knockout (IFN-gamma KO), and IFN-gamma receptor-alpha knockout (IFN-gammaRalpha KO) mice were immunized and used as donors for adoptive transfer. Transfer of either splenocytes or CD90(+) T cells was performed into recipient T cell receptor-beta knockout (TCRbeta KO) and IFN-gamma/TCRbeta double knockout mice bearing 14-day subcutaneous MCA207 tumors. Half of the mice were treated with IL-12, and cure rates were compared.

RESULTS

Transfer of either 1/4 immunized spleen equivalent or 10(7) immunized T cells into both TCRbeta KO and IFN-gamma/TCRbeta KO mice resulted in 80% to 100% cure when given with IL-12. However, transfer of 10(7) immunized T cells from IFN-gamma KO mice into TCRbeta KO mice was ineffective with or without IL-12. T cell response to IL-12, but not IFN-gamma, was required for tumor regression.

CONCLUSIONS

Production of IFN-gamma by IL-12-responsive tumor-sensitized T cells is both necessary and sufficient for complete tumor eradication induced by IL-12. T cells are the source, but not the target, of IFN-gamma during tumor regression.

Pre-existing tumor-sensitized T cells are essential for eradication of established tumors by IL-12 and cyclophosphamide plus IL-12

The antitumor immune response activated by IL-12, especially by a combination of cyclophosphamide and IL-12 (Cy+IL-12), is clinically significant in certain experimental tumor models, in that a number of well-established (10-20 mm in diameter) s.c. tumors are completely eradicated. Furthermore, Cy+IL-12 treatment is also able to eradicate well-established grossly detectable experimental lung metastases and advanced ascites tumors. Despite the dramatic antitumor effects seen in some tumor models, Cy+IL-12 fails to induce regression of other established tumors. Characterization of tumor immunogenicity shows that all tumors responding to IL-12 and Cy+IL-12 treatments are immunogenic tumors, in that an antitumor immune response is detectable in tumor-bearing hosts upon tumor establishment. In contrast, none of the nonimmunogenic tumor responds to IL-12 and Cy+IL-12 treatments. Analysis of cellular requirements for successful tumor rejection through an adoptive cell transfer approach reveals that the presence of tumor-sensitized, but not naive, T cells is essential for tumor rejection by IL-12 and Cy+IL-12. Transfer of these tumor-sensitized T cells must be conducted before, but not after, IL-12 treatment in order for tumor rejection to occur. The requirement of sensitized T cells is also tumor specific. In mice bearing immunogenic tumors, the presence of pre-existing tumor-sensitized T cells is demonstrated by adoptive cell transfer experiments using purified spleen T cells from these mice. Results from our study show that Cy+IL-12-based immunotherapy of cancer may be highly effective and that pre-existing tumor-sensitized T cells are essential for the success of the therapy.

Independent contributions of GR-1+ leukocytes and Fas/FasL interactions to induce apoptosis following interleukin-12 gene therapy in a metastatic model of prostate cancer

In a mouse model of prostate cancer, adenovirus-mediated interleukin-12 (Ad.mIL-12) gene therapy resulted in significant growth inhibition of both the injected primary tumor and synchronous metastases. Within 2 days of vector injection, two distinct patterns of apoptosis were detected within the primary tumor, the inhibition of which with a caspase inhibitor substantially negated growth suppression. The dominant pattern displayed localized sheets of apoptotic cells in close association with necrosis containing polymorphic neutrophils (PMNs). Depletion of PMNs resulted in the loss of this pattern of apoptosis and reduced growth suppression. A second major wave of growth suppression within the primary tumor was mediated by an immune response. Natural killer (NK) cell activity was detected within tumor-infiltrating lymphocytes (TIL) by the eighth day post-vector injection, the depletion of which resulted in a significant loss of survival enhancement. A more modest role for T cells was identified, which in the absence of documented cytotoxic T lymphocyte (CTL) activity may be related to a significant reduction in interferon-gamma (IFN-gamma) levels found in mice depleted of T cells, thereby reducing the secondary influences of IFN-gamma. However, depletion of NK cells or T cells had no discernible negative effect on IL-12-mediated anti-metastatic activity. Attention focused on the role of IFN-gamma, observed following Ad.mIL-12 therapy, to mediate the diffuse pattern of apoptosis seen in the primary and metastatic lesions. In vitro studies noted the ability of IFN-gamma to up-regulate tumor cell expression of Fas and FasL to mediate apoptosis, whereas in vivo blockage of Fas/FasL interactions with soluble Fas resulted in a modest reduction in primary tumor growth suppression but complete abrogation within metastatic lesions.

Lipopolysaccharide induction of indoleamine 2,3-dioxygenase is mediated dominantly by an IFN-gamma-independent mechanism

Indoleamine 2,3-dioxygenase (IDO) is a rate-limiting enzyme in the L-tryptophan-kynurenine pathway, which converts an essential amino acid, L-tryptophan, to N-formylkynurenine. It has been speculated that IFN-gamma is a dominant IDO inducer in vivo. The present study used IFN-gamma or TNF-alpha gene-disrupted mice and IFN-gamma antibody-treated mice to demonstrate that lipopolysaccharide (LPS)-induced systemic IDO is largely dependent on TNF-alpha rather than IFN-gamma. IFN-gamma-independent IDO induction was also demonstrated in vitro with LPS-stimulated monocytic THP-1 cells. These findings clearly indicate that there is an IFN-gamma-independent mechanism of IDO induction in addition to the IFN-gamma-dependent mechanism.

A critical role for IL-12 in CCR5 induction on T cell receptor-triggered mouse CD4(+) and CD8(+) T cells

Despite increasing evidence for the role of the chemokine system in leukocyte trafficking, the mechanism underlying the induction of chemokine receptors is poorly understood. Here, we investigated how CCR5, a chemokine receptor implicated in T cell migration to inflammatory sites, is induced in the T cell. CCR5 mRNA was hardly detected in resting T cells and marginally induced following T cell receptor (TCR) stimulation. However, TCR-triggered T cells expressed IL-12 receptor, and stimulation with recombinant IL-12 resulted in high levels of CCR5 expression on both CD4(+) and CD8(+) T cells. In contrast, IL-2 failed to up-regulate CCR5 expression. The effect of IL-12 was selective to CCR5 because IL-12 did not up-regulate CXCR3 expression. Surface expression of CCR5 was shown by staining with anti-CCR5 monoclonal antibody. Stimulation of these CCR5-positive T cells with the relevant chemokine MIP-1 alpha elicited Ca(2+) influx, showing that IL-12-induced CCR5 is functional. These results indicate a critical role for IL-12 in the induction of CCR5 on TCR-triggered T cells.

Intratumoral delivery of interleukin 12 expression plasmids with in vivo electroporation is effective for colon and renal cancer

We report on an antitumor treatment involving electrogene therapy (EGT), a newly developed in vivo gene transfer method using electroporation. We carried out in vivo EGT in a subcutaneous model of CT26 colon carcinoma cells, using plasmid DNAs encoding interleukin 12 (IL-12) subunits. For this purpose, we developed two IL-12 expression systems: a cotransfer system using a plasmid encoding the IL-12 p40 subunit and a plasmid encoding the IL-12 p35 subunit, and a single-vector system using a plasmid expressing a p40-p35 fusion protein. Both transfer systems significantly inhibited the growth of CT26 tumor. Immunohistochemical analysis of IL-12 EGT-treated tumors revealed enhanced infiltration of CD8(+) cells into the tumor tissue, while reverse transcriptase-polymerase chain reaction confirmed the increased expression of interferon gamma within treated tumors. The same IL-12 EGT applied to the nude mouse model was not effective, suggesting the critical role of T cell infiltration in this treatment. The inhibitory effects revealed in experiments in which previously treated mice were rechallenged with a second inoculation of CT26 tumor cells suggested that IL-12 EGT may also establish partial systemic antitumor immunity. The growth of IL-12 EGT-treated Renca tumors, a renal cell carcinoma, was also significantly inhibited. These findings suggest that EGT of the IL-12 gene has the potential to be an effective anticancer gene therapy.

Nitric oxide-dependent apoptosis in ovarian carcinoma cell lines

OBJECTIVE

In a recent study, we found different profiles of inducible nitric oxide synthase (iNOS) gene expression in the ovarian carcinoma cell lines OVCAR-3, HOC-7, and 2774 following stimulation by proinflammatory cytokines. The present study was performed to determine whether nitric oxide (NO) synthesis correlates with programmed cell death in these cells.

METHODS

NO-Dependent apoptosis was detected by DNA fragmentation analysis and fluorescence-activated cell sorter analysis.

RESULTS

NO formation in response to interferon gamma (IFN-gamma), interleukin-1beta (IL-1beta), and tumor necrosis factor alpha (TNF-alpha) was correlated with programmed cell death in the investigated cells. DNA fragmentation was most prominent in OVCAR-3 (34.17 +/- 1.81%), less pronounced in HOC-7 (12.86 +/- 0.45%), and undetectable in 2774 (4.54 +/- 0.40%) cells. The rate of apoptosis correlated with the amount of NO formation in cytokine-treated cells. Moreover, coincubation of OVCAR-3 and HOC-7 with the specific iNOS inhibitor aminoguanidine suppressed apoptosis induced by IFN-gamma, IL-1beta, and TNF-alpha.

CONCLUSION

Our data indicate that in OVCAR-3 and HOC-7 cells, NO synthesis induced by IFN-gamma, IL-1beta, and TNF-alpha is correlated with the degree of apoptotic cell death. In clinical situations, this might in part explain the benefit of cytokine application in ovarian carcinoma patients (e.g., documented for IFN-gamma).

Interleukin 12 gene therapy of cancer by peritumoral injection of transduced autologous fibroblasts: outcome of a phase I study

A phase I dose-escalation clinical trial of peritumoral injections of interleukin 12 (IL-12)-transduced autologous fibroblasts was performed in patients with disseminated cancer for whom effective treatment does not exist. The goals of this study were to assess the safety and toxicities as well as the efficacy, and ancillarily the immunomodulatory effects, of peritumoral IL-12 gene transfer. Primary dermal fibroblasts cultured from the patients were transduced with retroviral vector carrying human IL-12 genes (p35 and p40) as well as the neomycin phosphotransferase gene (TFG-hIL-12-Neo). Patients received four injections at intervals of 7 days. Nine patients were enrolled in this dose-escalation study, with secreted IL-12 doses ranging from 300 ng/24 hr for the first three patients to 1000, 3000, and 5000 ng/24 hr for two patients in each subsequent dosage level. Although a definite statement cannot be made, there appears to be perturbation of systemic immunity. Also, the locoregional effects mediated by tumor necrosis factor alpha (TNF-alpha) and CD8+ T cells were observed with tumor regression. Treatment-related adverse events were limited to mild to moderate pain at the injection site; clinically significant toxicities were not encountered. Transient but clear reductions of tumor sizes were observed at the injected sites in four of nine cases, and at noninjected distant sites in one melanoma patient. Hemorrhagic necrosis of tumors was observed in two melanoma patients. These data indicate that gene therapy by peritumoral injection of IL-12-producing autologous fibroblasts is feasible, and promising in patients with advanced cancer.

Coordination of chemokine and adhesion systems in intratumoral T cell migration responsible for the induction of tumor regression

T cell migration into tumor masses is critical to the process of immunologically induced tumor regression. Like other lymphoid populations, T cells are recruited to inflammatory sites depending on the interaction of T cell integrin receptors with their ligands expressed on vasculature. It is increasingly becoming evident that the adhesive capacity of integrins is upregulated by signals from chemokine receptors. A model of intratumoral T cell migration has been established using IL-12 to induce tumor regression. Focusing on this particular model, we review how IL-12 works to upregulate the expression and/or function of chemokines/chemokine receptors as well as adhesion molecules and to induce collaboration between chemokine and adhesion systems. This article will also describe why such an IL-12-induced activation of chemokine and adhesion systems leads to T cell-mediated tumor regression in some tumor models, but not in others.

The organotypic culture of HPV-transformed keratinocytes: an effective in vitro model for the development of new immunotherapeutic approaches for mucosal (pre)neoplastic lesions

The purpose of this study is to develop a reliable in vitro human model to test new immunotherapeutic approaches for squamous cell carcinoma that develop on mucosal surfaces. The organotypic (raft) culture permits cells to proliferate and differentiate at an air-liquid interface on a dermal equivalent support. Normal keratinocytes stratify and fully differentiate in a manner similar to the normal squamous epithelial tissues, while human papillomavirus-immortalized and established squamous carcinoma cell lines exhibit dysplastic morphologies similar to (pre)neoplastic lesions seen in vivo. We have demonstrated the ability of these organotypic cultures to be manipulated by altering the epithelial stratification with cytokines (interferon-gamma and tumor necrosis factor-alpha) and by integrating activated lymphocytes or dendritic cells into the in vitro formed epithelial sheet. This model may provide a useful tool to investigate the factors contributing to the presence and function of immunocompetent cells within a neoplastic epithelium that develops on a mucosal surface.

Inhibition of tumor metastasis by adoptive transfer of IL-12-activated Valpha14 NKT cells

A unique lymphocyte lineage, the Valpha14 NKT cells, expresses both NK1.1 and an invariant antigen receptor encoded by Valpha14 and Jalpha281 gene segments. Valpha14 NKT cells play crucial roles in various immune responses, including autoimmune diseases, allergic reactions and anti-tumor immunity. Valpha14 NKT cells were demonstrated to be essential for anti-tumor effect of IL-12 in vivo. Here, we report that adoptive transfer of IL-12-activated Valpha14 NKT cells prevents hepatic metastasis of B16 melanoma. The injection of large amounts of IL-2, IL-4, and IFN-gamma, which are cytokines produced by activated Valpha14 NKT cells, exhibited no significant inhibition of the metastasis of this melanoma. The cells prepared from the liver of IL-12-injected mice expressed a potent cytotoxic activity on B16 melanoma cells in vitro. Although the adoptive transfer of IL-12-activated Valpha14 NKT cells prevents hepatic metastasis of B16 melanoma, activated NK cells from IL-12-injected RAG-1-/- mice failed to inhibit the metastasis of this melanoma. Thus, the anti-tumor effect of IL-12 can be replaced by adoptive transfer of IL-12-activated Valpha14 NKT cells but not by IL-12-activated NK cells, suggesting a minor role of NK cells for the IL-12-mediated anti-tumor effect in this experimental system. Moreover, our studies have suggested the involvement of direct cytotoxic mechanisms rather than cytokine-mediated immune responses at the effector phase of the Valpha14 NKT cell-mediated anti-tumor activity.

Tumor vaccination that enhances antitumor T-cell responses does not inhibit the growth of established tumors even in combination with interleukin-12 treatment: the importance of inducing intratumoral T-cell migration

Interleukin-12 (IL-12) treatment is effective in the CSA1M but not in the Meth A and CSA1M-variant tumor models. The authors investigated the cause by which IL-12 treatment fails to induce tumor regression in these two tumor models. T cells from CSA1M-bearing mice have high levels of IL-12 responsiveness, whereas cells from Meth A-bearing mice display marginal levels of responsiveness. Because IL-12 responsiveness in T cells is induced after T-cell receptor stimulation, the lack of IL-12 responsiveness suggests that T cells in Meth A-bearing mice are not sensitized to Meth A tumor antigen. Immunization of normal mice with attenuated Meth A tumor cells resulted in a protective immunity, as shown by the rejection of challenged viable Meth A cells. Such an immunization, when performed in Meth A-bearing mice, induced potent IL-12 responsiveness in T cells. Nevertheless, IL-12 treatment in these mice did not inhibit tumor growth. In another IL-12-incurable (CSA1M-variant) model, IL-12 responsiveness was observed before tumor cell immunization. However, IL-12 treatment was ineffective regardless of whether tumor cell immunization was performed. In these two models, the failure of IL-12 treatment to induce tumor regression was associated with the lack of T-cell migration to tumor sites. These results indicate that the sensitization of T cells to tumor antigens and generation of IL-12 responsiveness are insufficient to induce tumor regression when these sensitized T cells are not allowed to migrate to tumor sites.

The anti-tumor activity of IL-12: mechanisms of innate immunity that are model and dose dependent

IL-12 has been demonstrated to have potent anti-tumor activities in a variety of mouse tumor models, but the relative roles of NK, NKT, and T cells and their effector mechanisms in these responses have not been fully addressed. Using a spectrum of gene-targeted or Ab-treated mice we have shown that for any particular tumor model the effector mechanisms downstream of IL-12 often mimic the natural immune response to that tumor. For example, metastasis of the MHC class I-deficient lymphoma, EL4-S3, was strictly controlled by NK cells using perforin either naturally or following therapy with high-dose IL-12. Intriguingly, in B16F10 and RM-1 tumor models both NK and NKT cells contribute to natural protection from tumor metastasis. In these models, a lower dose of IL-12 or delayed administration of IL-12 dictated a greater relative role of NKT cells in immune protection from tumor metastasis. Overall, both NK and NKT cells can contribute to natural and IL-12-induced immunity against tumors, and the relative role of each population is tumor and therapy dependent.

Expression and purification of recombinant human indoleamine 2, 3-dioxygenase

Indoleamine 2,3-dioxygenase, the first and rate-limiting enzyme in human tryptophan metabolism, has been implicated in the pathogenesis of many diseases. The human enzyme was expressed in Escherichia coli EC538 (pREP4) as a fusion protein to a hexahistidyl tag and purified to homogeneity in terms of electrophoretic and mass spectroscopic analysis, by a combination of phosphocellulose and nickel-agarose affinity chromatography. The yield of the fusion protein was 1.4 mg per liter of bacterial culture with an overall recovery of 56% from the crude extract. When the culture medium was supplemented with 7 microM hemin, the purified protein contained 0.8 mol of heme per mole of enzyme and exhibited an absorption spectrum consistent with the ferric form of hemoprotein. The pI value of the recombinant enzyme was 7.09 compared with 6.9 for the native enzyme. This was as expected from the addition of the hexahistidyl tag. Similar to the native enzyme, the recombinant enzyme required methylene blue and ascorbic acid for enzyme activity and oxidized not only l-tryptophan but also d-tryptophan and 5-hydroxy-l-tryptophan. The molecular activities for these substrates and their K(m) values were similar to those of the native enzyme, indicating that the addition of the hexahistidyl tag did not significantly affect catalytic activity. The recombinant protein can therefore be used to investigate properties of the native enzyme. This will aid the development of specific inhibitors of indoleamine 2,3-dioxygenase, which may be effective in halting disease progression.

Differential IL-12 responsiveness of T cells but not of NK cells from tumor-bearing mice in IL-12-responsive versus -unresponsive tumor models

While IL-12 administration induces tumor regression through stimulating T cells in tumor-bearing mice, this IL-12 effect is observed in some but not all tumor models. The present study aimed to compare IL-12 responsiveness of T cells from tumor-bearing mice in IL-12-responsive (CSA1M and OV-HM) and -unresponsive (Meth A) tumor models. Tumor regression in IL-12-responsive tumor models required the participation of T cells, but not of NK1.1(+) cells. Because a NK1.1(+) cell population was the major producer of IFN-gamma, comparable levels of IFN-gamma production were induced in IL-12-responsive and -unresponsive tumor-bearing mice. This indicates that the amount of IFN-gamma produced in tumor-bearing individuals does not correlate with the anti-tumor efficacy of IL-12. In contrast, IL-12 responsiveness of T cells differed between the responsive and unresponsive models: purified T cells from CSA1M/OV-HM-bearing or Meth A-bearing mice exhibited high or low IL-12 responsiveness respectively, when evaluated by the amounts of IFN-gamma produced in response to IL-12. T cells from CSA1M- or OV-HM-bearing but not from Meth A-bearing mice exhibited enhanced levels of mRNA for the IL-12 receptor (IL-12R). These results indicate that a fundamental difference exists in IL-12 responsiveness of T cells between IL-12-responsive and -unresponsive tumor models, and that such a difference is associated with the expression of IL-12R on T cells.

Participation of endogenously produced interferon gamma in interleukin 4-mediated tumor rejection

To elucidate the molecular mechanism underlying IL-4-induced tumor rejection, we challenged mice with a mouse adenocarcinoma cell line, colon 26, genetically engineered to express constitutively IL-4 gene (colon 26/IL-4). Immunocompetent BALB/c mice rejected colon 26/IL-4 cells but not parental cells or cells transduced with a control gene (colon 26/control). Moreover, on rechallenge, parental cells and colon 26/control cells were rejected by normal BALB/c mice that had previously rejected colon 26/IL-4. However, both nude and severe combined immunodeficiency (SCID) mice failed to reject colon 26/IL-4 as well as parental or colon 26/control cells. In contrast, nude mice did reject colon 26/IL-4 after transfer of lymphocytes obtained from the draining lymph nodes of BALB/c mice injected with colon 26/IL-4. These results indicate that challenging mice with colon 26/IL-4 tumor cells resulted in the generation of memory cytotoxic T lymphocytes in the draining lymph nodes. At 3 days after the challenge, IFN-gamma, IL-12 p35, and p40 mRNA expression was selectively enhanced in the draining lymph nodes of mice bearing colon 26/IL-4 cells. Finally, mice deficient in the IFN-gamma gene did not reject colon 26/IL-4 cells. These results suggest that IL-4-induced memory cytotoxic T lymphocyte generation requires IFN-gamma production in the draining lymph nodes, in order to generate a protective immune response.

Enhancing effect of tumor necrosis factor (TNF)-alpha, but not IFN-gamma, on the tumor-specific cytotoxicity of gammadeltaT cells from glioblastoma patients

Adoptive immunotherapy using tumor-specific killer cells can be beneficial in inducing regression of advanced cancer. The roles of cytokines on effector cells in inducing maximal killing activity and the accompanying side-effects should be investigated in vitro and fully understood prior to their clinical use. The present study indicates that the gammadeltaT cells involved in autologous tumor-specific killing consist of several populations in terms of their T cell receptor (TCR) repertoire, but predominantly express the products of the Vgamma9/Vdelta2 gene locus of the TCR. We then examined the effect of TNF-alpha and IFN-gamma on these tumor-specific gammadeltaT cells for possible clinical use in cancer patients. TNF-alpha alone, at concentrations of 0.01-1.0 microg/ml, caused increased gammadeltaT cell cytotoxicity against autologous glioblastoma cells, whereas IFN-gamma alone had no effect. The combination of TNF-alpha (1 microg/ml) with IL-2 (50 units/ml) resulted in further enhancement of cytotoxicity. TNF-alpha, but not IFN-gamma, marginally inhibited the proliferative response of gammadeltaT cells; a similar result was seen when the cytokines were combined. TNF-alpha may, therefore, be one cytokine capable of inducing increased autologous tumor-specific activity in gammadeltaT cells, bearing mainly Vgamma9/Vdelta2 chains, which can be enhanced when combined with other cytokines.

Detection of nitrosylated epitopes in Trypanosoma brucei gambiense by polyclonal and monoclonal anti-conjugated-NO-cysteine antibodies

Activated macrophages with the Calmette/Guérin bacillus (BCG) have a cytotoxic/cytostatic effect on the extracellular parasite, Trypanosoma brucei gambiense. This effect was inhibited when the NO-synthase inhibitor NG-monomethyl-L-arginine (NMMA; 0.5 mM) was added to the culture media. Using an immunocytochemical method with rabbit polyclonal or mouse monoclonal antibodies directed against conjugated nitroso-epitopes (anti-conjugated-NO-cysteine), nitrosylated antigens were visualized in fixed trypanosomes. These results suggest that NO was synthesized by the activated macrophages and that it reacted with some parasitic proteins containing cysteine. The release of NO bound to parasitic proteins may cause the killing of trypanosomes. The immunoreactivity was positive when the trypanosomes were obtained from the supernatant of the BCG-activated macrophages that contains BSA (4 mg/mL). In contrast, the parasites cocultured with non-activated macrophages remained completely viable, and, the immunoreactivity was completely negative.

Perforin-dependent NK cell cytotoxicity is sufficient for anti-metastatic effect of IL-12

IL-12 exerts a potent anti-tumor effect, which is possibly mediated by multiple mechanisms including activation of NK and NKT cells, induction of cytotoxic T lymphocytes, and inhibition of angiogenesis. In the present study, we characterized the cytotoxic effector cells and mechanisms responsible for the anti-metastatic effect of IL-12. Administration of IL-12 had a comparable inhibitory effect on experimental lung metastasis of B16 melanoma cells in wild-type C57BL/6 mice and RAG-2-/- mice that lack T and NKT cells, which was abolished by depletion of NK cells. Cytotoxic activity of liver and splenic mononuclear cells against B16 was induced by IL-12 administration in RAG-2-/- mice at a level comparable to that in wild-type mice, which was also abolished by depletion of NK cells. Moreover, the anti-metastatic effect of IL-12 was abrogated by perforin deficiency, but not by Fas ligand deficiency, in association with a lack of IL-12-induced cytotoxic activity of liver and splenic mononuclear cells against B16. These results suggest that perforin-dependent cytotoxicity of IL-12-activated NK cells is sufficient for the anti-metastatic effect of IL-12.

Tumor-specific cytokine release by donor T cells induces an effective host anti-tumor response through recruitment of host naive antigen presenting cells

We recently reported that tumor eradication induced by immunotherapy (IT) in a congenic mouse model using tumor infiltrating lymphocytes (TIL) + recombinant interleukin-2 (rIL-2) is dependent on recruitment of naive host immune cells at the tumor sites. The recruitment of host immune cells was induced mainly through a local secretion of interferon-gamma (IFN-gamma) produced by donor T cells. We now further investigated how a non-specific inflammatory response progresses to a host T-cell-mediated tumor-specific response. In cross-over experiments using MCA-105 and MCA-205 sarcoma tumors, pulmonary metastatic disease was eradicated only in mice treated with tumor-matched TIL + rIL-2. In vitro, TIL stimulated with the tumor of origin secreted relatively high levels of IFN-gamma and granulocyte-macrophage colony stimulating factor (GM-CSF) compared to TIL stimulated with mismatched tumor cells. In lungs of tumor-bearing mice treated with matched TIL + rIL-2, significant increases in the percentages of IFN-gamma, GM-CSF and tumor necrosis factor-alpha (TNF-alpha) positive cells were detected, as well as of macrophages, natural killer (NK) cells and dendritic cells. Depletion of macrophages or NK cells did not inhibit the efficacy. In contrast, depletion of dendritic cells partially inhibited the efficacy of the treatment. Combined depletion of dendritic cells and macrophages abrogated more than 80% of the efficacy. Our data suggest that successful IT may require 3 steps: (1) release of inflammatory cytokines by donor TIL after restimulation by tumor cells; (2) infiltration of host immune cells in response to local cytokine production; and (3) activation of tumor-specific host immune cells by dendritic cells and to a lesser extent by macrophages.