Systemic administration of rIL-12 induces complete tumor regression and protective immunity: response is correlated with a striking reversal of suppressed IFN-gamma production by anti-tumor T cells

Reduced immunologic cell performance as a prognostic parameter for advanced cervical cancer

The proliferative response of lymphocytes to mitogens is known to be decreased in cancer patients; this phenomenon is thought to play an important role in disease progression, but it has not been studied as a prognostic factor in cervical cancer patients receiving treatment. Fourteen patients with advanced cervical cancer submitted to chemotherapy with cis-platinum (100 mg/m2/cycle) and bleomycin (30 mg/cycle) over three cycles every 4 weeks were evaluated. Mean follow-up time was 30 months. The following laboratory tests carried out on peripheral blood lymphocytes collected before and at the end of chemotherapy were used as prognostic factors: proliferative response of lymphocytes to phytohemagglutinin (PHA) and stimulated with interleukin 12 (IL-12), capacity of gamma interferon production (IFN-gamma), and variations in memory T cell (CD45-RO) and naive T cell (CD45-RA) subsets. A clear correlation was obtained between response to treatment, survival rates, and PHA-induced proliferative response. A significant difference was observed in the number of CD45-RO lymphocyte at the pre-chemotherapy period and IFN-gamma production at the post-chemotherapy period in the group of good responders to treatment. The use of IL-12 produced a leveling in both groups for lymphocyte proliferation, i.e., a recovery from the deficiency presented by the lymphocyte of the poor responders group. The parameters of immunologic assays, especially proliferative response, appears to be correlated with prognosis and survival rates and therefore are good discriminating factors for the selection of groups of patients that will benefit from this type of treatment. IL-12 seems to play an important role in the regulation of the antitumor immune response and should be considered for therapeutic use.

Cytokines and soluble cytokine receptor induction after IL-12 administration in cancer patients

This study shows that subcutaneous administration of increasing doses of IL-12, once a week, in 21 cancer patients increased the expression of cytokine genes (interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), IP-10, MIG, IL-10, IL-4) in peripheral blood mononuclear cells even at very low doses (30 ng/kg). Surprisingly, no circulating TNF-alpha or IL-4 could be detected in the plasma of patients treated with IL-12. However, a marked increase of soluble IL-4 receptor was demonstrated in the plasma of five of the six patients studied, which may represent an additional mechanism by which IL-12 inhibits the development of the Th2 response in vivo. A marked decline of IFN-gamma and IP10 induction was recorded after repeated cycles of IL-12. In contrast, in most patients IL-12 increased IL-10 expression with no subsequent decrease during the course of therapy, and even an earlier peak of IL-10 induction at the 6th cycle. In addition, a constant up-regulation of serum soluble IFN-gamma receptor levels was observed after each cycle of IL-12 treatment with a delayed peak compared with the IFN-gamma peak. The constant rise of IL-10 and soluble IFN-gamma receptor during IL-12 therapy may therefore contribute to the inhibition of IFN-gamma activity detected after repeated cycles of IL-12. Lastly, a marked heterogeneity of cytokine induction was observed from one patient to another, which appeared to be independent of the dose of IL-12 administered. These data may lead to a better understanding of the biological activity of IL-12 and the in vivo mechanisms of its regulation.

Vaccines With Interleukin-12–Transduced Acute Myeloid Leukemia Cells Elicit Very Potent Therapeutic and Long-Lasting Protective Immunity

Interleukin-12 (IL-12) is a heterodimeric cytokine mediating a dynamic interplay between T cells and antigen-presenting cells (APCs). Preclinical studies have demonstrated that recombinant murine IL-12 (rmIL-12) promotes specific antitumor immunity mediated by T cells in several types of tumors. However, the in vivo antitumor properties of IL-12 in acute myeloid leukemia (AML) have not been previously reported. We show here in a murine AML model that systemic administration of rmIL-12 significantly delays tumor growth but is incapable of rescuing mice from lethal leukemia. In contrast, AML cells genetically modified to express IL-12 (IL12-AML) using murine stem cell virus (MSCV) p40 + p35 elicit very potent antileukemic activity. Vaccines with lethally irradiated IL12-AML cells protect naive mice against challenge with wild-type AML cells and, more importantly, can cure mice bearing a considerable leukemic burden. Immunized mice show no signs of systemic IL-12 toxicity and their spleen histology is comparable with naive mice spleen. In vivo depletion of IL-12, interferon-γ (IFN-γ), or CD8+ T cells after injections with live IL12-AML cells abrogates completely the antileukemia immune responses. Studies on the in vitro effects of IFN-γ on AML cells demonstrate enhanced expression of major histocompatibility complex (MHC) and accessory molecules and induction of the costimulatory molecules B7.1 and B7.2, but no significant direct antiproliferative effect. 51Cr release assays show that rejection of live IL12-AML cells supports the development of long-lasting leukemia-specific cytotoxic T lymphocyte (CTL) activity. In conclusion, our results demonstrate that IL12-AML vaccination is a safe and potent immunotherapeutic approach that has a great potential to eliminate minimal residual disease in patients with AML.

Vaccines With Interleukin-12–Transduced Acute Myeloid Leukemia Cells Elicit Very Potent Therapeutic and Long-Lasting Protective Immunity

Interleukin-12 (IL-12) is a heterodimeric cytokine mediating a dynamic interplay between T cells and antigen-presenting cells (APCs). Preclinical studies have demonstrated that recombinant murine IL-12 (rmIL-12) promotes specific antitumor immunity mediated by T cells in several types of tumors. However, the in vivo antitumor properties of IL-12 in acute myeloid leukemia (AML) have not been previously reported. We show here in a murine AML model that systemic administration of rmIL-12 significantly delays tumor growth but is incapable of rescuing mice from lethal leukemia. In contrast, AML cells genetically modified to express IL-12 (IL12-AML) using murine stem cell virus (MSCV) p40 + p35 elicit very potent antileukemic activity. Vaccines with lethally irradiated IL12-AML cells protect naive mice against challenge with wild-type AML cells and, more importantly, can cure mice bearing a considerable leukemic burden. Immunized mice show no signs of systemic IL-12 toxicity and their spleen histology is comparable with naive mice spleen. In vivo depletion of IL-12, interferon-γ (IFN-γ), or CD8+ T cells after injections with live IL12-AML cells abrogates completely the antileukemia immune responses. Studies on the in vitro effects of IFN-γ on AML cells demonstrate enhanced expression of major histocompatibility complex (MHC) and accessory molecules and induction of the costimulatory molecules B7.1 and B7.2, but no significant direct antiproliferative effect. 51Cr release assays show that rejection of live IL12-AML cells supports the development of long-lasting leukemia-specific cytotoxic T lymphocyte (CTL) activity. In conclusion, our results demonstrate that IL12-AML vaccination is a safe and potent immunotherapeutic approach that has a great potential to eliminate minimal residual disease in patients with AML.

Immune defects observed in patients with primary malignant brain tumors

Malignant glioblastomas (gliomas) account for approximately one third of all diagnosed brain tumors. Yet, a decade of research has made little progress in advancing the treatment of these tumors. In part this lack of progress is linked to the challenge of discovering how glial tumors are capable of both modulating host immune function and neutralizing immune-based therapies. Patients with gliomas exhibit a broad suppression of cell-mediated immunity. The impaired cell-mediated immunity observed in patients with gliomas appears to result from immunosuppressive factor(s) secreted by the tumor. This article reviews what has been elucidated about the immune defects of patients harboring glioma and the glioma-derived factors which mediate this immunosuppression. A model involving systemic cytokine dysregulation is presented to suggest how the immune defects arise in these individuals.

Immunostimulatory effects of human recombinant interleukin-12 on peripheral blood mononuclear cells from normal dogs

Interleukin-12 (IL-12) plays a pivotal role in regulating cellular immune responses involving autoimmunity, infectious disease, and cancer. Human recombinant (hr) IL-12 is being evaluated for therapy of human cancer. We investigated the potential of hrIL-12 to activate canine peripheral blood mononuclear cells (PBMC) using proliferation and cytotoxicity as readouts. Human rIL-12 caused increased proliferation of PBMC, and enhanced lysis of allogeneic canine tumor targets mediated by PBMC from normal dogs in vitro. In addition, antibody-dependent cellular cytotoxicity (ADCC) mediated by canine PBMC was enhanced by hrIL-12. These results indicate that hrIL-12 is recognized by canine immune cells, triggering a number of immune responses in canine PBMC, that may be important for immunotherapy of canine cancer. Information from this investigation provides impetus for evaluation of the effects of hrIL-12 on PBMC from tumor-bearing dogs and should be helpful in the development of hrIL-12 as an immune cell activator in vivo in the dog.

Cytokine gene therapy of mesothelioma. Immune and antitumor effects of transfected interleukin-12

Malignant mesothelioma (MM) is a solid tumor of the mesothelium for which there is no curative treatment. MM appears to be sensitive to immunotherapeutic approaches, and one of the most powerful immunomodulatory cytokines with antitumor effects is interleukin (IL)-12. We have previously shown in a murine model of MM that systemic administration of recombinant IL-12 induces a potent anti-MM immune response. The nature and accessibility of MM tumors means that they are suitable candidates for direct cytokine and gene-transfer therapeutic approaches. Therefore, we undertook a study to assess the antitumor effects induced by the local production of IL-12 within MM tumors by transfecting a murine MM line with the genes for IL-12. The IL-12 transfectant (AB1-IL-12) did not produce tumors in normal mice, but did so in athymic nude mice, implicating T cells in the prevention of MM tumor growth. In mixing experiments, paracrine IL-12 production inhibited growth of untransfected MM cells provided that cells producing IL-12 represented more than 50-80% of the inoculum. Furthermore, BALB/c mice previously challenged with AB1-IL-12 were protected against rechallenge with parental AB1 tumor, indicating that the transfectant induced long-term immunity. AB1-IL-12 induced systemic immunity that was effective at reducing the incidence of parental AB1 tumor at a distal site, but its effects were dose-dependent. Though both CD4(+) and CD8(+) cells infiltrated the rejecting tumor, CD8(+) effector cells were essential for protection against development of parental AB1 tumor. This study shows that paracrine secretion of IL-12, generated by gene transfer, can induce immunity against MM that can act locally and also at a distant site. In addition, there was no evidence of toxicity, which has been associated with the systemic administration of IL-12, indicating that this cytokine is a good candidate for experimental gene therapy in MM.

Intradermal Delivery of IL-12 Naked DNA Induces Systemic NK Cell Activation and Th1 Response In Vivo That Is Independent of Endogenous IL-12 Production

In this study four murine IL-12 naked DNA expression plasmids (pIL-12), containing both the p35 and p40 subunits, were shown to induce systemic biological effects in vivo after intradermal injection. Three of the four IL-12 expression vectors augmented NK activity and induced expression of the IFN-γ and IFN-γ-inducible Mig genes. Both IL-12 p70 heterodimer and IFN-γ proteins were documented in the serum within 24 h after intradermal injection of the pIL-12o− plasmid, which also induced the highest level of NK activity in the spleen and liver among the IL-12 constructs. Interestingly, both p40 mRNA expression at the injection site and serum protein levels followed a biphasic pattern of expression, with peaks on days 1 and 5. Subsequent studies revealed that the ability of intradermally injected pIL-12o− to augment NK lytic activity was prevented by administration of a neutralizing anti-IL-12 mAb. Finally, injection of the pIL-12o− into BALB/c IL-12 p40−/− mice also resulted in a biphasic pattern of IL-12 p70 appearance in the serum, and induced IFN-γ protein and activated NK lytic activity in liver and spleen. These results demonstrate that injection of delivered naked DNA encoding the IL-12 gene mediates the biphasic systemic production of IL-12-inducible genes and augments the cytotoxic function of NK cells in lymphoid and parenchymal organs as a direct result of transgene expression. The results also suggest that these naked DNA plasmids may be useful adjuvants for vaccines against infectious and neoplastic diseases.

B7-1 (CD80)-gene transfer combined with interleukin-12 administration elicits protective and therapeutic immunity against mouse hepatocellular carcinoma

Human hepatocellular carcinoma (HCC) frequently recurs after primary therapy, resulting in poor prognosis. To try to find a way to prevent this, we examined the combined effectiveness of B7-1 (CD80)-gene transfer and interleukin-12 (IL-12) on the induction of protective antitumor immunity against poorly immunogenic BNL1ME A.7R. 1 (BNL) mouse HCC cells. We introduced mouse B7-1 gene into BNL1ME A. 7R.1 cells. Overexpression of B7-1 on BNL1ME A.7R.1 cells resulted in significant inhibititon of subcutaneous tumor development in syngeneic BALB/c mice, but not in complete rejection, suggesting that strong expression of B7-1 molecules may enhance the immunogenicity of BNL1ME A.7R.1 cells in immunocompetent mice. Lymphocyte study revealed that the cytolytic activity generated by immunization with B7-1 transfectants against BNL1ME A.7R.1 cells was mediated mainly by CD8(+) cytotoxic T lymphocytes (CTL). We examined the synergistic effect of IL-12 and immunization with B7-1 transfectants. The combination led to rejection of BNL1ME A.7R.1 cells in 6 of 10 tested mice and delayed tumor development in the remaining mice. Furthermore, the combined treatment against pre-established BNL1ME A.7R.1 tumors resulted in rejection in 3 of 8 tested mice or in significant inhibition of tumor growth in the remaining mice. In vivo lymphocyte subset depletion study indicated that the combined antitumor effect was dependent on the presence of both CD8(+) and CD4(+) T cells. In conclusion, the combination of immunization of B7-1-transfected HCC cells and IL-12 could induce protective and therapeutic immunity against parental HCC cells, and this combination may be therapeutically useful for suppressing recurrence of HCC.

A Single-Chain IL-12 IgG3 Antibody Fusion Protein Retains Antibody Specificity and IL-12 Bioactivity and Demonstrates Antitumor Activity

IL-12 is a heterodimeric cytokine with many actions on innate and cellular immunity that may have antitumor and antimetastatic effects. However, systemic administration of IL-12 can be toxic. Tumor-specific Abs provide a means to selectively target a metastatic/residual nodule and deliver therapeutic quantities of an immunostimulatory molecule like IL-12 with lower systemic levels and ideally, toxicity. We report the construction and characterization of an Ab fusion protein in which single-chain murine IL-12 is fused to an anti-Her2/neu Ab at the amino terminus (mscIL-12.her2.IgG3). The use of single-chain IL-12 in the fusion protein simplifies vector construction, ensures equimolar concentrations of the two IL-12 subunits, and may confer greater stability to the fusion protein. SDS-PAGE analysis shows this 320-kDa protein is secreted and correctly assembled. FACS analysis demonstrates that this fusion protein binds to cells transfected with the Her2/neu Ag, thus retaining Ab specificity; this fusion protein also binds to a cell line and to PHA-activated PBMC that express the IL-12R, thus demonstrating cytokine receptor specificity. T cell proliferation assays and NK cytotoxicity assays demonstrate that this fusion protein exhibits IL-12 bioactivity comparable to recombinant murine IL-12. In vivo studies demonstrate that this fusion protein has antitumor activity. These results are significant and suggest that this IL-12 Ab fusion protein can effectively combine the therapeutic potential of IL-12 with the tumor-targeting ability of the Ab and may provide a viable alternative to systemic administration of IL-12.

Interleukin-12-secreting human papillomavirus type 16-transformed cells provide a potent cancer vaccine that generates E7-directed immunity

The development of a vaccine that would be capable of preventing or curing the (pre)cancerous lesions induced by genital oncogenic human papillomaviruses (HPVs) is the focus of much research. Many studies are presently evaluating vaccines based on the viral E6 and E7 oncoproteins, both of which are continually expressed by tumor cells. The success of a cancer vaccine relies, in large part, on the induction of a tumor-specific Th1-type immunity. In this study, we have evaluated the ability of B7-related and/or interleukin-12 (IL-12)-expressing, non-immunogenic murine HPV16-transformed BMK-16/myc cells, to achieve this goal. BMK-16/myc cells engineered to express surface B7-1 or B7-2 molecules remain tumorigenic in syngeneic BALB/c mice, suggesting that expression of these molecules alone is not sufficient to induce tumor regression. In contrast, mice injected with tumor cells engineered to secrete IL-12 remained tumor-free, demonstrating that IL-12 expression is sufficient to induce tumor rejection. IL-12-secreting BMK-16/myc cells were further shown to induce potent and specific long-term tumor resistance, even after irradiation. B7-1 was found to slightly but systematically improve anti-tumor immunity elicited by IL-12-secreting BMK-16/myc cells. Injection of irradiated B7-1/IL-12+ BMK-16/myc cells generates long-lasting, Th1-type, BMK-16/myc-directed immunity in tumor-resistant mice. These mice display a memory-type, E7-specific, cell-mediated immune response, which is potentially significant for clinical applications.

Different Doses of Adenoviral Vector Expressing IL-12 Enhance or Depress the Immune Response to a Coadministered Antigen: the Role of Nitric Oxide

Joint immunization with two recombinant adenoviruses, one expressing hepatitis C virus (HCV) core and E1 proteins and another expressing IL-12 (RAdIL-12), strongly potentiates cellular immune response against HCV Ags in BALB/c mice when RAdIL-12 was used at doses of 1 × 105–1 × 107 plaque-forming units. However, cellular immunity against HCV Ags was abolished when higher doses (1 × 108 plaque-forming units) of RAdIL-12 were used. This immunosuppressive effect was associated with marked elevation of IFN-γ and nitric oxide in the serum and increased cell apoptosis in the spleen. Administration of N-nitro-l-arginine methyl ester (l-NAME), an inhibitor of nitric oxide synthase, to mice that received high doses of RAdIL-12 was lethal, whereas no apparent systemic toxicity by l-NAME was observed in those immunized with lower doses of the adenovirus. Interestingly, in mice immunized with recombinant adenovirus expressing core and E1 proteins of HCV in combination with RAdIL-12 at low doses (1 × 107 plaque-forming units), l-NAME inhibited T cell proliferation and CTL activity in response to HCV Ags and also production of Abs against adenoviral proteins. In conclusion, gene transfer of IL-12 can increase or abolish cell immunity against an Ag depending of the dose of the vector expressing the cytokine. IL-12 stimulates the synthesis of NO which is needed for the immunostimulating effects of IL-12, but apoptosis of T cells and immunosuppression ensues when IFN-γ and NO are generated at very high concentrations.

Human Glioma-Induced Immunosuppression Involves Soluble Factor(s) That Alters Monocyte Cytokine Profile and Surface Markers

Patients with gliomas exhibit deficient in vitro and in vivo T cell immune activity, and human glioblastoma culture supernatants (GCS) inhibit in vitro T lymphocyte responses. Because APC are essential for initiating and regulating T cell responses, we investigated whether GCS would affect cytokines produced by monocytes and T cells from healthy donors of PBMC. Incubation of PBMC with GCS decreased production of IL-12, IFN-γ, and TNF-α, and increased production of IL-6 and IL-10. The GCS-induced changes in IL-12 and IL-10 occurred in monocytes, and involved changes in IL-12 p40 and IL-10 mRNA expression. Incubation with GCS also resulted in reduced expression of MHC class II and of CD80/86 costimulatory molecules on monocytes. The immunosuppressive effects were not the result of IL-6 or TGF-β1 that was detected in GCS. However, it was due to a factor(s) that is resistant to pH extremes, differentially susceptible to temperature, susceptible to trypsin, and has a minimum molecular mass of 40 kDa. Our findings show that glioblastoma-generated factors that are known to suppress T cell responses alter the cytokine profiles of monocytic APC that, in turn, inhibit T cell function. This model indicates that monocytes can serve as an intermediate between tumor-generated immune-suppressive factors and the T cell responses that are suppressed in gliomas.

TCR Vaccines Against T Cell Lymphoma: QS-21 and IL-12 Adjuvants Induce a Protective CD8+ T Cell Response

Tumor-specific TCR can serve as an effective target for active immunotherapy of T cell malignancies. Using the murine T cell tumor model C6VL, vaccination with C6VL TCR protected mice from a subsequent lethal dose of tumor cells. This study characterizes the immune mechanisms involved in the tumor protection, and the influence of immunologic adjuvants in inducing a protective immune response. Immune responses induced by TCR vaccines formulated with various adjuvants: QS-21, IL-12, SAF-1, CD40L, and GM-CSF were compared. QS-21, IL-12, and SAF-1 biased the humoral immune response toward Th1-type, reflected by the induction of IgG2a and IgG2b anti-C6VL TCR Abs. CD40L and GM-CSF exclusively produced IgG1 Abs, reflecting a Th2-type immune response. In our tumor model system, only vaccines containing adjuvants that induced a Th1-type immune response favored tumor protection. Furthermore, we demonstrated that CD8+ T cells were necessary and sufficient for tumor protection using anti-CD8 mAb depletion and adoptive cell transfer experiments. Transfer of hyperimmune serum containing anti-C6VL TCR Abs into naïve mice had modest anti-tumor effects and was not sufficient to prevent tumor growth. TCR-vaccinated B cell-deficient mice were not protected against C6VL tumor, and tumor protection was not completely restored after hyperimmune serum transfer. Thus, B cells may serve as important APCs in inducing a protective immune response. Based on these results future TCR vaccines should be designed to maintain native TCR conformation, as well as induce a strong Th1-type immune response.

Mycobacterium phlei cell wall complex directly induces apoptosis in human bladder cancer cells

Intact mycobacteria and mycobacterial cell wall extracts have been shown to inhibit the growth of human and murine bladder cancer. Their mechanism of action is, however, poorly understood. Mycobacterium phlei mycobacterial cell complex (MCC) is a cell wall preparation that has mycobacterial DNA in the form of short oligonucleotides complexed on the cell wall surface. In this study, we have investigated the possibility that MCC has anti-cancer activity that is mediated by two different mechanisms--a direct effect on cancer cell proliferation and viability and an indirect effect mediated by the production of interleukin 12 (IL-12), a cytokine known to possess anti-cancer activity. We have found that, although MCC is a potent inducer of IL-12 and IL-6 synthesis in monocytes and macrophages either in vitro or in vivo, it is unable to induce the synthesis of either IL-12, IL-6 or granulocyte-macrophage colony-stimulating factor (GM-CSF) by the human transitional bladder cancer cell lines HT-1197 and HT-1376. MCC is not directly cytotoxic towards these cancer cells, but induces apoptosis as determined by nuclear DNA fragmentation and by the release of nuclear mitotic apparatus protein. Mycobacterium phlei DNA associated with MCC is responsible for the induction of apoptosis. Our results indicate that MCC directly effects bladder cancer cells by inhibiting cellular proliferation through the induction of apoptosis, and has the potential for an indirect anti-cancer activity by stimulating cancer-infiltrating monocytes/macrophages to synthesize IL-12.

Interleukin-12 induces an effective antitumor response in malignant mesothelioma

Malignant mesothelioma (MM) is a fatal solid tumor of the mesothelium for which there is currently no ameliorating treatment. Using our murine model of this malignancy, which closely resembles the human disease, we have shown that immunotherapy may be of value in the treatment of MM. Because recombinant interleukin-12 (rIL-12) has strong immunomodulatory effects in vivo, we studied the effects of rIL-12 on murine antitumor immune responses, using a nonimmunogenic murine MM tumor cell line (AB1) in vivo. Systemic administration of rIL-12 at the time of tumor inoculation prevented AB1 tumor growth in up to 70% of treated mice, 50% of which were still resistant to AB1 upon rechallenge, indicating that long-term immunologic antitumor effects had been established. This rIL-12-induced effect was dependent on the involvement of both CD4(+) and CD8(+) but not natural killer (NK) cells. Importantly, treatment of established tumors with intralesional injections of rIL-12 resulted in temporary tumor regression or growth inhibition. This effect was dependent on the continuous presence of rIL-12 and correlated with increased numbers of CD4(+) and CD8(+) cells infiltrating the remaining tumor mass. Effective inhibition of tumor growth also occurred when IL-12 was released within MM tumors by coadministration of MM cells that had been stably transfected with the gene for IL-12. These data indicate that IL-12 has potential in the immunotherapy of MM, through gene transfer or local cytokine administration, provided that significant intratumor levels of IL-12 can be achieved for prolonged periods.

Gene-Modified Tumor Vaccine with Therapeutic Potential Shifts Tumor-Specific T Cell Response from a Type 2 to a Type 1 Cytokine Profile

Vaccination with a poorly immunogenic/nonimmunogenic tumor fails to protect the host from a subsequent challenge with the same tumor. The mechanisms underlying the failure of these tumors to sensitize therapeutic T cells are not clearly understood, but the inability of host T cells to recognize tumor has been implicated. In this study, vaccination with the poorly immunogenic B16BL6-D5 (D5 H-2b) tumor fails to generate therapeutic T cells from the tumor vaccine-draining lymph nodes (TVDLN) in our adoptive immunotherapy model. However, if vaccination is performed with an allogeneic MHC class I gene (H-2 Kd)-modified tumor, the T cells obtained from the TVDLN are therapeutic after activation with anti-CD3 and IL-2. Lymph nodes (LN) draining both D5 and D5-Kd tumor vaccines contained increased numbers of cells with reduced expression of L-selectin (L-selectinlow/−) compared with naive LN. This implies that vaccination led to sensitization of T cells even in LN draining the unmodified D5 tumor. L-selectinlow/− cells from D5-Kd, but not D5, TVDLN were therapeutic in our animal model. No antitumor activity was seen in the high level L-selectin T cells. L-selectinlow/− T cells exhibited tumor-specific cytokine release that was type 2 (IL-4, IL-10) following vaccination with native D5 and type 1 (IFN-γ) following vaccination with gene-modified D5-Kd. Our data suggest that the failure of unmodified D5 to generate therapeutic T cells is not due to an inability to recognize tumor Ags, but, rather, to the induction of an immune response that is ineffective in mediating tumor regression, i.e., immune deviation.

Rapid recruitment of macrophages in interleukin-12-mediated tumour regression

In order to study the mechanism of interleukin-12 (IL-12) antitumour activity, RH7777 rat hepatoma cells were engineered to express mouse IL-12 (mIL-12) (RH7777/mIL-12) under the tight control of doxycycline (dox). The production of the mIL-12 protein was regulated by the concentration of dox that was present in the culture medium. RH7777/mIL-12 cells appeared to have the same tumorigenic activity as did parental RH7777 cells, when subcutaneously injected into syngeneic rat (BUF/N) in the absence of dox. However, the tumorigenicity of RH7777/mIL-12, but not RH7777, cells were significantly decreased when dox was administrated to the animals. In addition, established tumours of RH7777/mIL-12 cells gradually disappeared upon the induction of mIL-12 by dox. To elucidate the kinetic profile of immune cells involved in the mIL-12-induced tumour regression, both histological and immunohistochemical analyses were performed 1, 3 and 14 days after the dox treatment on rats bearing tumours that were approximately 0. 5 cm in diameter. Tumour-infiltrating macrophages began to appear at the tumour site one day after dox treatment. As time elapsed, the number of tumour infiltrates including CD4+, CD8+, natural killer (NK) cells and macrophages gradually increased. In particular, CD8+ and NK cells constituted the major population of the tumour-infiltrated cells. Furthermore, it was found that resting peritoneal macrophages (PM) from rats were chemoattracted in response to mIL-12. The effects of mIL-12 on PM chemotaxis were reproducibly observed in concentrations as low as 0.1 ng/ml. These findings suggest that IL-12 can directly recruit macrophages into tumour sites which, in turn, leads to a broad and intense immunological response against tumour.

In Vivo Retargeting of T Cell Effector Function by Recombinant Bispecific Single Chain Fv (Anti-CD3 × Anti-Idiotype) Induces Long-Term Survival in the Murine BCL1 Lymphoma Model

As demonstrated in several preclinical models, bispecific Abs are attractive immunotherapeutic agents for tumor treatment. We have previously reported that a bacterially produced anti-CD3 × antitumor bispecific single chain variable fragment of Ab fragment (BsscFv), which is capable of retargeting CTLs toward BCL1 tumor cells, exhibits antitumor activity in vitro. To further facilitate BsscFv production, the coding sequence was subcloned in a eukaryotic expression vector and introduced into Chinese hamster ovary cells for large-scale production. In this report, we have determined the serum stability and the clearance rate from the circulation of BsscFv. Most important, we prove here the therapeutic value of BsscFv in the treatment of BCL1 lymphoma, a murine model for human non-Hodgkin’s lymphoma. Tumor-bearing mice that were treated with rscFv in combination with staphylococcal enterotoxin B superantigen, human rIL-2, or murine rIL-12 showed long-term survival, whereas untreated mice all died. This is the first report of the successful in vivo use of BsscFv as an immunotherapeutic agent. Furthermore, long-term survival was the result of complete tumor removal and was not due to the induction of dormancy.

Reconstitution of immune systems in RAG2-/- mice by transfer with interleukin-12-induced splenic hematopoietic progenitor cells

The administration of a high dose of IL-12 into the mice resulted in the induction of splenomegaly. From the flow cytometry analysis of cellularity in an enlarged spleen, it was demonstrated that Thyl.2-CD45RB-c-Kit + Sca-1 + Lin- hematopoietic progenitor cells markedly increased in IL-12-administered mouse spleen compared with untreated mouse spleen. The IL-12-induced hematopoietic progenitor cells showed a greatly enhanced colony-forming activity in CFU-granulocyte/macrophage (CFU-GM), blast-forming units-erythroid (BFU-E) and CFU-spleen (CFU-S) assay. Moreover, it was initially demonstrated that the transfer of IL-12-induced splenic hematopoietic progenitor cells into immunodeficient RAG2-/- mice caused a complete reconstitution of their immune functions including T- and B-cell-mediated immunity. Thus, the evidence that IL-12 has a capability of inducing hematopoietic progenitor cells possessing stem cell-like activity in vivo, indicated another important immunomodulating activity of IL-12 in immunotherapy.

Interferon gamma-independent rejection of interleukin 12-transduced carcinoma cells requires CD4+ T cells and Granulocyte/Macrophage colony-stimulating factor

We analyzed the ability of interferon (IFN)-gamma knockout mice (GKO) to reject a colon carcinoma transduced with interleukin (IL)-12 genes (C26/IL-12). Although the absence of IFN-gamma impaired the early response and reduced the time to tumor onset in GKO mice, the overall tumor take rate was similar to that of BALB/c mice. In GKO mice, C26/IL-12 tumors had a reduced number of infiltrating leukocytes, especially CD8 and natural killer cells. Analysis of the tumor site, draining nodes, and spleens of GKO mice revealed reduced expression of IFN- inducible protein 10 and monokine induced by gamma-IFN. Despite these defects, GKO mice that rejected C26/IL-12 tumor, and mice that were primed in vivo with irradiated C26/IL-12 cells, showed the same cytotoxic T lymphocyte activity but higher production of granulocyte/macrophage colony-stimulating factor (GM-CSF) as compared with control BALB/c mice. Treatment with monoclonal antibodies against GM-CSF abrogated tumor regression in GKO but not in BALB/c mice. CD4 T lymphocytes, which proved unnecessary or suppressive during rejection of C26/IL-12 cells in BALB/c mice, were required for tumor rejection in GKO mice. CD4 T cell depletion was coupled with a decline in GM-CSF expression by lymphocytes infiltrating the tumors or in the draining nodes, and with the reduction and disappearance of granulocytes and CD8 T cells, respectively, in tumor nodules. These results suggest that GM-CSF can substitute for IFN-gamma in maintaining the CD8-polymorphonuclear leukocyte cross-talk that is a hallmark of tumor rejection.

T Cell- and NK Cell-Independent Inhibition of Hepatic Metastases by Systemic Administration of an IL-12-Expressing Recombinant Adenovirus

IL-12 is a potent immunoregulatory cytokine that has been shown to mediate tumor regression in a variety of tumor models. We describe the construction of AdCMV-IL-12, a recombinant adenovirus that encodes both subunits of IL-12 under transcriptional control of the CMV promoter. This recombinant virus efficiently infects a wide variety of cell types leading to the production of high levels of biologically active IL-12. Because the liver is a primary site of infection after i.v.-administered adenovirus, we tested the therapeutic efficacy of this virus in a murine hepatic metastasis tumor model. Systemic administration of AdCMV-IL-12 dramatically inhibited the formation of 3-day Renca hepatic metastases (mean of 16 metastases per liver) compared with the control virus AdCMV-βgal (mean of 209) or vehicle alone (mean of 272). Histologic analysis indicated that metastatic growth inhibition was accompanied by a dramatic perivascular infiltrate consisting of T cells, macrophages, and neutrophils. Therapeutic efficacy was not diminished in animals depleted of CD4+ or CD8+ T cells, or in SCID mice, even after NK cell ablation. In the latter case, a hepatic perivascular infiltrate composed of macrophages and neutrophils was observed after AdCMV-IL-12-treatment, while numerous activated Kupffer cells were noted in the hepatic parenchyma. Analysis of therapy-induced changes in hepatic gene expression demonstrated increased levels of IP-10 and Mig RNAs, but no increase in iNOS, Fas, or FasL RNA levels was observed. Our data suggest a model of metastatic growth inhibition mediated by nonlymphocyte effector cells including macrophages and neutrophils and that may involve anti-angiogenic chemokines.

The interleukin-12/interleukin-12-receptor system: role in normal and pathologic immune responses

Interleukin-12 (IL-12) is a heterodimeric cytokine that plays a central role in promoting type 1 T helper cell (Th1) responses and, hence, cell-mediated immunity. Its activities are mediated through a high-affinity receptor composed of two subunits, designated beta 1 and beta 2. Of these two subunits, beta 2 is more restricted in its distribution, and regulation of its expression is likely a central mechanism by which IL-12 responsiveness is controlled. Studies with neutralizing anti-IL-12 antibodies and IL-12-deficient mice have suggested that endogenous IL-12 plays an important role in the normal host defense against infection by a variety of intracellular pathogens. However, IL-12 appears also to play a central role in the genesis of some forms of immunopathology. Inhibition of IL-12 synthesis or activity may be beneficial in diseases associated with pathologic Th1 responses, such as multiple sclerosis or Crohn's disease. On the other hand, administration of recombinant IL-12 may have utility in the treatment of diseases associated with pathologic Th2 responses such as allergic disorders and asthma.

Accumulation of IL-12-activated antitumor effector cells into lymph nodes of tumor-bearing mice

Simultaneous administration of high dose of IL-12 into tumor-inoculated mice resulted in a marked reduction of tumor growth in parallel with the augmented generation of cytotoxic T-cells, natural killer (NK) cells and IFN-gamma-producing Th cells. We found that these IL-12-activated antitumor effector cells preferentially accumulated in peripheral lymph nodes concomitantly with lymphadenopathy. However, IL-12 rather induced disappearance of antitumor effector cells including CD4+ T, CD8+ T and NK cells from spleen in spite of inducing splenomegaly. Lymph node cells obtained from IL-12-treated B16F0-bearing mice showed a marked IFN-gamma production in response to not only IL-2, IL-12, anti CD3 mAb but also B16F0 melanoma cells. Moreover, they could lyse B16F0 melanoma cells in a long-term cytotoxicity assay. It was also confirmed that IL-12-activated IFN-gamma producing Th1 cells were accumulated in tumor local site. Thus, IL-12 appeared to have a capability of stimulating selective migration of antitumor cells into lymph nodes and tumor local sites.

Clinicopathological study on hepatocellular carcinoma with lymphocytic infiltration

We examined the clinicopathologic features of 11 surgically resected hepatocellular carcinomas (HCCs) less than 3 cm in diameter with marked inflammatory cell infiltration (LHCCs). In comparison with the other 152 HCCs without such an infiltration (controls), there were no significant differences in male/female ratio, age, serum alpha-fetoprotein levels, and laboratory and imaging findings. All the 11 LHCC cases were hepatitis B surface antigen (HBsAg) negative and hepatitis C virus antibody positive. Among the 152 controls, 116 cases were also HBsAg negative and HCVAb positive and were referred to as HCV-only controls. The clinical features were not significantly different between the LHCC and the HCV-only controls. The LHCC group tended to have higher numbers of lymphocytes and monocytes in pre- and post-operative peripheral blood, but there were no significant group differences. Recurrence rate was 9.1% in the LHCC group, 47.7% in the controls and 47.5% in the HCV-only controls (P < .01). Five-year survival rate was 100% in the LHCC group, 65.1% in the controls and 68.1% in the HCV-only controls (P < .01). Histologically, remarkable inflammatory cell infiltration, mostly lymphocytic, was observed in the cancerous tissue of the LHCC group. Varying degrees of piecemeal necrosis of cancer nests produced by infiltrating lymphocytes were observed in all the 11 cases. Lymph follicle formation was also found in 10 of 11 cases (90.9%). Liver cirrhosis was associated in 6 LHCC cases (54.5%), in 117 control cases (77.0%), and in 91 HCV-only controls (78.4%). Tumor invasion into the portal vein in the vicinity of the tumor was found in 1 LHCC case (9.1%), in 54 controls (35.5%), and in 34 HCV-only controls (29.3%). Immunohistochemically, most of the infiltrating lymphocytes, other than those in the lymph follicle, were identified as T lymphocyte, and CD8+ T lymphocyte was more predominant than CD4+ T lymphocyte. Better prognosis of the LHCC group could attribute to the anti-tumor effect induced by cellular immunity of CD8+ and CD4+ T lymphocytes, and partly by humoral immunity of B cells which formed lymph follicles.

Systemic administration of interleukin-12 can restore the anti-tumor potential of B16 melanoma-draining lymph node cells impaired at a late tumor-bearing state

We investigated the effect of the systemic administration of interleukin (IL)-12 on the anti-tumor potential of tumor-draining lymph nodes (LNs). Tumor-draining LN cells on day 10 after s.c. inoculation of B16 melanoma showed a significant anti-tumor effect against established pulmonary metastases after in vitro expansion, whereas those on either day 20 or 30 exhibited an impaired anti-tumor potential. However, i.p. injections of IL-12 (0.5 microg) on days 18, 20 and 22 significantly increased the total number of tumor-draining LN cells on day 24 and, furthermore, restored their anti-tumor potential after in vitro expansion. In addition, i.p. injection of IL-12 (0.1 microg) on days 20, 22, 24, 26 and 28 significantly suppressed the growth of s.c.-inoculated B16 melanoma and finally cured the tumors in 6 of 12 mice (50%), whereas dissection of the tumor-draining LNs on day 18, prior to the IL-12 treatment, decreased both the IL-12-induced anti-tumor effect and the percentage of cured mice (8.3%). Cured mice acquired a specific protective immunity. Collectively, our results indicate that the systemic administration of IL-12 can restore the immunotherapeutic potential of tumor-draining LNs, which was impaired at the late tumor-bearing state, and that the IL-12-induced systemic anti-tumor activity is preceded by the restoration of an anti-tumor response in tumor-draining LNs.

Immunoregulation by interleukin-12 in MB49.1 tumor-bearing mice: cellular and cytokine-mediated effector mechanisms

Administration of recombinant murine interleukin (rmIL)-12 to MB49.1 tumor-bearing mice results in dose-dependent regression of the primary tumor and the generation of protective antitumor immunity in the majority of animals. rmIL-12 administration is associated with a marked increase in lymph node cellularity that is predominantly due to the expansion of B220+ B cells as well as CD8+ T cells. Stimulation of lymph node cells from rmIL-12-treated, but not control tumor-bearing mice, with MB49.1 tumor cells in vitro was shown to enhance the secretion of interferon (IFN)-gamma. The magnitude of this in vitro response was dependent on the dose of rmIL-12 administered in vivo and mirrored the change in circulating serum IFN-gamma. Furthermore, at the height of the in vitro response to tumor stimulation, the addition of a neutralizing antibody to murine IL-12 suppressed IFN-gamma production, indicating a role for endogenous IL-12 in this antigen-specific cytokine response. Although studies in SCID mice confirmed that an appropriate T cell response was required for rmIL-12-mediated antitumor activity, in immunocompetent animals early tumor regression was not accompanied by cellular infiltration of the tumor. In contrast, a profound increase in tumor-associated inducible nitric oxide synthase (iNOS) was observed in mice receiving rmIL-12 which preceded T cell infiltration of the tumor which could be detected during the second week of IL-12 treatment. Direct tumor killing through the cytotoxic actions of NO via the iNOS pathway may serve as a way of generating tumor antigen which enables the host to mount a subsequent T cell response against the tumor.

Requirement for Valpha14 NKT cells in IL-12-mediated rejection of tumors

A lymphocyte subpopulation, the Valpha14 natural killer T (NKT) cells, expresses both NK1.1 and a single invariant T cell receptor encoded by the Valpha14 and Jalpha281 gene segments. Mice with a deletion of the Jalpha281 gene segment were found to exclusively lack this subpopulation. The Valpha14 NKT cell-deficient mice could no longer mediate the interleukin-12 (IL-12)-induced rejection of tumors. Although the antitumor effect of IL-12 was thought to be mediated through natural killer cells and T cells, Valpha14 NKT cells were found to be an essential target of IL-12, and they mediated their cytotoxicity by an NK-like effector mechanism after activation with IL-12.

Augmented human-tumor-cytolytic activity of peripheral blood lymphocytes and cells from a mixed lymphocyte/tumor culture activated by interleukin-12 plus interleukin-2, and the phenotypic characterization of the cells in patients with advanced carcinoma

In this study, we evaluated the ability of combination regimens of interleukin-12 (IL-12) and interleukin-2 (IL-2) to induce effective killer cells against human tumors in vitro, in peripheral blood lymphocytes (PBL) from 15 cancer patients and mixed lymphocyte/tumor culture (MLTC) cells from 16 cancer patients, and carried out a phenotypic analysis of the cells responsible for the lysis of the human tumors. The freshly prepared PBL were cultivated with IL-2 alone or IL-12/IL-2 for 10 days [lymphokine-activated killer (LAK) cell generation system]. The MLTC cells (PBL cultured with mitomycin-C-treated allogeneic G-415 tumor cells for 3 days) were further cultivated with IL-2 or IL-12/IL-2 for 7 days [cytotoxic T lymphocytes (CTL) generation system]. The cytolytic activities of the lymphoid cells cultivated with IL-12/IL-2 were significantly augmented in both the LAK and CTL generation systems, as compared with those of cells treated with IL-2 alone. In the LAK generation system, the cytolytic activities of the cells cultivated with IL-12/IL-2 were significantly decreased by the method of negative selection of CD11b- or CD56+ cells using immunomagnetic beads. The CD8(+)-depleted cells showed a slight decrease of activity. The killer cell activities of the CD4(+)-depleted cells remained unchanged. In the CTL generation system, the activity was markedly reduced by the elimination of the CD8+ or CD11b+ or CD56+ cells. The combined data suggested that IL-12/IL-2-induced killer effector cells in the LAK generation system were mainly of the natural killer (NK) type, comprising CD8-CD11b+, CD8- CD16b+, CD3-CD56+, and partly possible CD8+ CD11b- T cells. CD8+ CD11b- T cells mixed with cells of the NK type, comprising CD8-CD11b+, CD8- CD16b+ and CD3-CD56+ cells, were the population of killer effector cells induced by IL-12/IL-2 in the CTL generation system.

Suppression of allograft responses induced by interleukin-6, which selectively modulates interferon-gamma but not interleukin-2 production

BACKGROUND

Interferon (IFN)-gamma produced by activated T cells represents an important effector cytokine in mediating an inflammatory response.

METHODS

The present study investigated the modulation of allograft responses by inhibiting IFN-gamma production. C57BL/6 (B6) lymph node cells were stimulated with class II H2-disparate B6-C-H-2bm12 (bm12) spleen cells.

RESULTS

Addition of interleukin (IL)-6 to the primary B6 anti-bm12 mixed lymphocyte reaction (MLR) inhibited neither proliferative responses nor IL-2 production. However, IL-6 induced a dose-dependent suppression of IFN-gamma production in the same MLR cultures. B6 mice were engrafted with bm12 skin grafts, and IL-6 was given to bm12 skin graft recipients every other day. T cells from these recipient mice produced significantly less IFN-gamma in secondary B6 anti-bm12 MLR than those from bm12 skin graft recipients that had not received IL-6 injections. IFN-gamma production by these T cells was suppressed more strongly when the secondary MLR was conducted in the presence of IL-6. In addition to suppression of IFN-gamma expression, IL-6 injections resulted in prolongation of bm12 skin graft survival. The critical involvement of IFN-gamma in anti-bm12 rejection responses was substantiated by evidence that administration of anti-IFN-gamma monoclonal antibody strikingly prolonged bm12 skin graft survival. The prolongation of graft survival by in vivo treatment with either IL-6 or anti-IFN-gamma monoclonal antibody was found to be induced without blocking cellular infiltration of the grafts.

CONCLUSIONS

These results indicate that IFN-gamma acts as a key cytokine in a B6 anti-bm12 allograft response and that IL-6 may down-regulate this response by inhibiting IFN-gamma production of alloreactive T cells.

Cytokine gene therapy of cancer using gene gun technology: superior antitumor activity of interleukin-12

We compared the antitumor effect of several transgene expression plasmids encoding specific cytokines, including interleukin-2 (IL-2), IL-4, IL-6, IL-12, interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and granulocyte-macrophage colony-stimulating factor (GM-CSF), following gene gun-mediated DNA delivery into the epidermis overlying an established intradermal murine tumor. IL-12 gene therapy was much more effective than treatment with any other tested cytokine gene for induction of tumor regression. Strong activation of antitumor immunity in response to IL-12 gene therapy was evidenced by an augmented CD8+ T cell-mediated cytolytic activity in the draining lymph nodes of tumor-bearing mice. Furthermore, following the IL-12 gene therapy protocol, test mice were able to eradicate not only the treated but also the untreated solid tumors at distant sites. This systemic antitumor effect of IL-12 gene therapy was not associated with visible signs of toxicity or significantly elevated systemic levels of IFN-gamma. These results show that gene gun-mediated in vivo delivery of IL-12 cDNA clearly distinguishes itself from the other cytokine gene therapy approaches tested in parallel, suggesting that this delivery system may be employed as an efficient model for comparative studies of in vivo cytokine gene therapy. The results also suggest that the current IL-12 gene therapy strategy may provide a safer alternative to IL-12 protein therapy for clinical treatment of cancers.

Interferon-gamma-inducing factor gene transfection into Lewis lung carcinoma cells reduces tumorigenicity in vivo

To investigate the immunoregulatory effect of murine interferon-gamma-inducing factor (mIGIF), we transfected Lewis lung carcinoma (LLC) cells with a mammalian expression vector containing the mIGIF complementary DNA. The culture medium of the transfectant cells stimulated interferon-gamma (IFN-gamma) production by spleen cells in vitro in the presence of anti-CD3 antibody and markedly potentiated the effect of interleukin-12 (IL-12) on IFN-gamma production by spleen cells. mIGIF transfectant cells showed reduction of tumorigenicity and induction of an in vivo immuno-protective effect against the parental LLC cells. To examine the combined effect of systemic administration of recombinant IL-12 (rIL-12) and local mIGIF on the tumorigenicity, mice were challenged with LLC or transfectant cells on day 0, and the tumor-bearing mice were injected with 50 ng of rIL-12 intraperitoneally from day 7 to 11. Systemic rIL-12 showed an anti-tumor effect. However, mIGIF gene expression did not potentiate this effect of systemic rIL-12 in vivo.

Direct intratumoral injection of an adenovirus expressing interleukin-12 induces regression and long-lasting immunity that is associated with highly localized expression of interleukin-12

Mice bearing breast tumors were treated with a single dose of an adenovirus expressing interleukin-12 (AdmIL-12.1) injected intratumorally, which produced regressions in greater than 75% of the treated tumors; approximately one-third of the animals remained tumor free. Complete regression was associated with immunity to secondary challenge with fresh tumor cells. Analysis of local cytokine expression demonstrated maximum expression of IL-12 within the tumor between 24 and 72 hr post-injection, reaching 600-800 ng per tumor, with elevated local levels of IL-12 detectable for at least 9 days. This expression was highly localized as serum IL-12 peaked at 40-60 ng/ml at 24 hr and was less than 10 ng/ml from day 3 onward. Interferon-gamma (IFN-gamma) concentrations were markedly increased within the tumor following AdmIL-12.1 administration, demonstrating that IL-12 was acting locally. Tumor-draining lymph node cells spontaneously produced IFN-gamma following AdmIL-12.1 treatment, suggesting these cells were activated by IL-12. These data demonstrate that AdmIL-12.1 can be used to deliver very high levels of localized cytokine production. Moreover, we have confirmed that the IL-12 produced from our vector actually affects the local cytokine environment of the tumor and activates responder cells present within the tumor.

Interferon-gamma-inducing factor enhances T helper 1 cytokine production by stimulated human T cells: synergism with interleukin-12 for interferon-gamma production

The novel cytokine interferon-gamma-inducing factor (IGIF) augments natural killer (NK) cell activity in cultures of human peripheral blood mononuclear cells (PBMC), similarly to the structurally unrelated cytokine interleukin (IL)-12. IGIF has been found to enhance the production of interferon-gamma (IFN-gamma) and granulocyte/macrophage colony-stimulating factor (GM-CSF) while inhibiting the production of IL-10 in concanavalin A (Con A)-stimulated PBMC. In this study, when anti-CD3 monoclonal antibody (mAb)-stimulated human enriched T cells were exposed to IGIF, the cytokine dose-dependently enhanced the proliferation of the cells and this could be completely inhibited by a neutralizing antibody against IL-2 at lower concentrations of IGIF. Neutralizing antibody against IFN-gamma had only insignificant inhibitory effects on T cell proliferation at higher concentrations of IGIF. Enzyme-linked immunosorbent assays (ELISA) revealed that, like PBMC, T cells exposed to IGIF produced large amounts of IFN-gamma; however, changes in the production of IL-4 and IL-10 were minimal. IGIF, but not IL-12, significantly enhanced IL-2 and GM-CSF production in T cell cultures, as determined by CTLL-2 bioassay and ELISA, respectively; however, both IGIF and IL-12 enhanced IFN-gamma production by the T cells. When T cells were exposed to a combination of IGIF and IL-12, a synergistic effect was observed on the production of IFN-gamma, but not on production of IL-2 and GM-CSF. In conclusion, IGIF enhances T cell proliferation apparently through an IL-2-dependent pathway and enhances Th1 cytokine production in vitro and exhibits synergism when combined with IL-12 in terms of enhanced IFN-gamma production but not IL-2 and GM-CSF production. Based on structural and functional differences from any known cytokines, it was recently proposed that this cytokine be designated interleukin-18.

Murine asialo GM1+CD8+ T cells as novel interleukin-12-responsive killer T cell precursors

Freshly isolated CD8+ T cells, but not CD4+ T cells, contained 20-30% of asialo GM1+ (ASGM1+) T cells which were distinct from ASGM1+NK1.1+ natural killer cells. This novel ASGM1+CD8+ T cell subpopulation showed a strong proliferative response to interleukin-12 (IL-12) in the presence of IL-2. Culture of ASGM1+CD8+ T cells with IL-12 plus IL-2 allowed the generation of anomalous killer T cells concomitantly with the accumulation of cytolytic molecules. Moreover, ASGM1+CD8+ T cells produced high levels of interferon-gamma (IFN-gamma), but not IL-4, upon stimulation with IL-12 plus IL-2. Such immune responses were not observed in ASGM1-CD8+ T cell subpopulations constituting the majority of CD8+ T cells. These results demonstrated that ASGM1+CD8+ T cells are a novel subpopulation of IL-12-responsive and IFN-gamma-producing killer T cell precursors.

Regulatory mechanisms of antitumor T cell responses in the tumor-bearing state

Tumor-bearing hosts develop antitumor immune responses. However, a number of immunosuppressive mechanisms come into operation with the progression of tumor growth. This article will review the observations regarding the modulation of antitumor immune responses in the tumor-bearing state, and consider the mechanisms underlying tumor-induced immune defects, especially in the light of the induction of an abnormal cytokine network. We will also describe the restoration of suppressed antitumor immune responses by administration of a particular cytokine, interleukin-12.

Induction of anti-tumor immunity by mouse tumor cells transfected with mouse interleukin-12 gene

Interleukin-12 (IL-12) is a heterodimeric cytokine. In order to transduce both cDNAs for p35 and p40 of IL-12 in the tumor cells, a polycistronic retroviral vector was constructed by inserting the internal ribosome entry site gene of encephalomyocarditis virus between two cDNAs. On the other hand, two cDNAs were sequentially transfected in the tumor cells. Both polycistronic gene transfectants and double transfectants produced biologically active mouse IL-12. IL-12-expressing tumor cells were all rejected in syngeneic mice, and induced cytotoxic T lymphocyte activity. The capacity to induce anti-tumor memory may depend on the amount of IL-12 produced by the transfectants, because the relatively higher IL-12 producer tumor cell line induced the anti-tumor memory in the rejected mice, but the lower producer did not.