Partial hepatectomy augments the liver's antitumor response

Despite adequate locoregional control, colorectal metastasis to the liver remains a significant cause of death. Resection of hepatic metastasis improves five-year survival 18% to 34%. A study of the impact of 40% partial hepatectomy on cytokine production in the liver was undertaken. Nonparenchymal liver cells (NPCs) were prepared by collagenase perfusion and metrizamide gradient from partially hepatectomized and laparotomized control C57BL/6Ros mice. Nonparenchymal cell from partially hepatectomized mice compared with laparotomized mice showed a twofold to threefold increase in interferon (IFN) activity. Both interferon alpha/beta and supernatants from cultured NPCs of partially hepatectomized mice suppressed the proliferation of liver-derived MCA-38 colon adenocarcinoma cells in vitro. This tumor has been shown to metastasize to the liver of C57BL/6Ros mice. The production of various cytokines by NPCs induced by partial hepatectomy may provide a possible antimetastatic mechanism.     

AsGM1+ NK cells prevent metastasis of invading LD-MCA-38 tumor cells in the nude mouse.

BACKGROUND: Although the liver is a potent tumor cell killing organ it is frequently the site of lethal metastases often signifying the endstage for patients with colorectal cancers. Enhancing hepatic-associated immunity remains elusive until the interactions among hepatic nonparenchymal cells (NPC) are deciphered. We sought to modulate the cellular components of the hepatic immune system of mice with anti-NK and anti-T-cell-neutralizing antibodies in order to determine the cell type most efficacious in preventing liver metastasis. MATERIALS AND METHODS: Liver-derived murine colon adenocarcinoma (LD-MCA-38) cells were injected into the ileocolic vein (ICV) of immunocompetent and immunodeficient C57BL/6 mice. Mice were pretreated 1 day prior to tumor cell injection with one of three antibodies: anti-AsGM1, Anti-NK1.1, or Anti-Thy1.2. On Day 21 laparotomy was performed to determine the extent of hepatic tumor foci. The number of hepatic tumor foci was recorded and compared by the Wilcoxon rank sum test. RESULTS: Mice pretreated with anti-AsGM1 or Anti-NK1.1 developed a massive increase in the number of hepatic tumor foci and decreased survival compared to the control treated mice. Pretreatment with anti-Thy1.2 antibody resulted in a significant decrease in the number of hepatic tumor foci. LD-MCA-38 tumor cells were unable to colonize the liver of C57BL/6 athymic nude mice; however, anti-AsGM1 antibody abolished this antimetastatic effect. There was no difference in the extent of hepatic metastasis and survival between immunodeficient C57BL/6 bg/bg and their conventional littermates bg/+. CONCLUSION: AsGM1+ NK cells exhibit a significant antitumor response in the absence of T-cells. The concept of stimulating NK cell activity and suppressing T-cell function may enhance liver-associated immunity and serve as a deterrent for blood-borne tumor cells metastasizing to the liver.     

全反式维甲酸对人结肠癌生长、肝转移的抑制作用

目的 观察全反式维甲酸(ATRA)对人结肠癌细胞生长及肝转移的抑制作用.方法 0、2、4、8μmol／LATRA分别作用于SW480/M5细胞48 h,免疫组织化学检测SW480/M5细胞血管内皮生长因子-A(VEGF-A)的表达水平.以SW480/M5细胞建立裸鼠原位肿瘤种植模型,随机分为5组,分别以生理盐水、溶剂对照液及5、15、45 mg/kg ATRA对裸鼠隔日灌胃,6周后观察裸鼠原位种植瘤及肝转移瘤的生长,实时荧光定量聚合酶链反应(RT-PCR)检测肿瘤组织VEGF-A mRNA表达水平,免疫组织化学检测裸鼠肿瘤组织微血管密度(MVD).结果 SW480/M5细胞VEGF-A阳性率随着ATRA作用浓度的增加逐渐下降,差异有统计学意义(x2=630.96,P＜0.01).各ATRA作用组原位肿瘤的抑瘤率为4.1％、31.6％及49.7％,肝转移发生率为63.6％、36.4％及20.0％,差异均有统计学意义(分别为P＜0.01及P＜0.05).与对照组比较,中剂量及高剂量组裸鼠原位肿瘤显著缩小(P＜0.05)、肿瘤肝转移程度明显降低(P＜0.05),肿瘤组织的VEGF-A mRNA水平及MVD值亦显著下降(P＜0.05).结论 ATRA能下调人结肠癌原位种植肿瘤和肝转移瘤组织VEGF-A的表达,减少肿瘤新生血管的形成,对结肠癌生长和肝转移具有抑制作用.     

Prevention of rat colon cancer metastases by perioperative immunostimulation

Major intra-abdominal operations result in profound immunodepression. In addition, manipulation of malignant tumors may release tumor cells into the systemic and portal circulations. The additive effects of immunodepression and tumor cell release may enhance the metastatic potential of tumors. Perioperative correction of immune depression by levamisole can restore lymphocyte proliferation levels in rats. We have developed a model in which rat colon carcinoma cells transplanted into the portal venous system consistently induce hepatic metastases by 4 weeks and death within 9 weeks. Rats pretreated with levamisole (4 mg/kg administered intraperitoneally) the day before and the day of tumor implantation developed fewer metastases (41% of animals treated with levamisole compared with 6% of animals not treated with levamisole had less than or equal to two metastases per liver). Twenty percent of the rats treated with levamisole developed no hepatic metastases. Comparison of median liver weights between the group treated with levamisole and the nontreated, tumor-bearing group was highly significant (p less than 0.005). We conclude that the perioperative period is critical for the implantation and growth of metastases and that perioperative immunostimulation may be a factor in decreasing the incidence of metastases. This model may have relevance to the adjuvant treatment of human colon cancer.     

Adenovirus-mediated delivery of a soluble form of the VEGF receptor Flk1 delays the growth of murine and human pancreatic adenocarcinoma in mice

BACKGROUND: Because pancreatic adenocarcinoma is poorly responsive to chemotherapy and radiation therapy, novel treatments such as antiangiogenic gene therapy may have use in the adjuvant treatment of this malignancy. We evaluated the antitumor effects of the in vivo administration of an adenovirus vector encoding a soluble form of Flk1 (Flk1-Fc), a receptor for vascular endothelial growth factor, in 3 murine models of pancreatic adenocarcinoma. METHODS: In a first model, immunocompetent C57Bl/6 mice were injected subcutaneously with Panc02 murine pancreatic adenocarcinoma cells before treatment. In a second model, immunodeficient severe combined immunodeficiency mice were injected subcutaneously with BxPc-3 human pancreatic adenocarcinoma cells before treatment. In a third model, C57Bl/6 mice were injected with Panc02 cells through an intrasplenic route before treatment, in an effort to model metastatic disease. In each model, half the tumor-bearing mice were injected intravenously with 10(9) Flk1-Fc adenovirus particles and half with control adenovirus. RESULTS: In subcutaneous tumor models, Ad Flk1-Fc-treated animals were found to have 75% smaller murine and 78% smaller human pancreatic tumor volumes, relative to tumor volumes of Ad Fc-treated animals, 6 weeks after vector administration. In animals injected with tumor through the intrasplenic route, pathologic and histologic analyses made 10 days after injection of tumor revealed hepatic, pancreatic, and splenic tumors, together with a desmoplastic response consistent with pathologic findings in human pancreatic cancer. Cohorts of these tumor-bearing mice treated with Ad Flk1-Fc demonstrated significantly longer survival and decreased liver replacement with tumor at the time of death, relative to animals treated with Ad Fc. CONCLUSION: A recombinant adenovirus encoding soluble Flk-1 inhibited pancreatic tumor growth in mice. These studies suggest that the delivery of gene products such as Flk1-Fc through in vivo gene transfer may be useful in the future treatment of patients with pancreatic cancer.     

A successful liver metastasis model in mice with neuraminidase treated colon 26

The aim of this study was to establish a reproducible and quantitative liver metastasis model in mice. The in vitro colon 26 (C-26) cultured cell line was initially taken from an in vivo transplantable C-26 adenocarcinoma tumor mass using the standard enzymatic treatments, collagenase and DNAse. In vitro cultured cells ×10⁴ were introduced into the portal vein of syngeneic BALB/c mice to induce liver metastases and, 3 weeks later metastatic foci were found in approximately 50% to 70% of the mice. In contrast, C-26 cells desialylated by neuraminidase (Nase) treatment greatly increased the incidence of hepatic metastases with countable hepatic colonies being found in all mice (100%). This result seems to be related to the liver-characteristic D-galactose receptors, since pre-injection with an excess amount of galactocerebroside completely prevented tumor colonization in the liver. Thus, although we cannot disregard the involvement of other adhesion molecules in this system as yet, our experimental model may become a useful tool for the analysis of hepatic metastases from colon cancer in the future.     

Tumor cell-surface galactose correlates with the degree of colorectal liver metastasis

The phenotypic heterogeneity of tumor cell-surface galactose expression within a cell population may dictate metastatic potential. The hepatic asialoglycoprotein receptor, whose known function is to bind to terminal galactose residues of desialylated glycoproteins and effete cells, may participate in the arrest and subsequent growth of subpopulations of tumor cells with high galactose expression. To test this hypothesis, murine colon carcinoma cells (CT-26) were sorted, using the galactose-specific lectin, soybean agglutinin (SBA), and fluorescence-activated cell-sorting (FACS) technology, into two subpopulations--one low in surface galactose and one high in surface galactose. After intrasplenic injection of tumor cell subpopulations, liver metastasis was found to be proportional to the degree of tumor cell-surface galactose expression. These data suggest that tumor galactose expression and hepatic recognition may be important components of a specific mechanism of colorectal liver metastasis.     

Early events of hepatic metastasis formation in mice: role of Kupffer and NK-cells in natural and interferon-gamma-stimulated defense

Surgical manipulation of a tumor may result in increased influx of tumor cells into the systemic and portal circulation and give rise to formation of metastases. In addition, major surgery has been reported to cause profound immunosuppression. In an attempt to increase the host-antitumor immune mechanisms following surgery we have studied the effect of preoperative administration of interferon-gamma, related to the antimetastatic effects of Kupffer cells (KC) and natural killer cells (NK-cells) in the early phase of liver metastasis formation. Colon carcinoma cells were injected into the superior mesenteric vein of syngeneic mice and after 17 days metastases were quantified by weight, number, and uptake of [125I]iododeoxyuridine. Unstimulated control mice developed 10.5 surface nodules per liver 17 days following injection of colon carcinoma cells into the superior mesenteric vein of syngeneic mice. This figure was only 2.6 in mice stimulated with a single dose of 1000 IU IFN-gamma 4 h prior to inoculation of tumor cells. Administration of GdCl3, which is reported to deplete and block the function of Kupffer cells, 24 h prior to tumor cell inoculation resulted in a 5-fold tumor mass increase relative to control. Injection of anti-asiolo-GM1 antiserum, which eliminates the hepatic NK-cells, induced a 10-fold increase in tumor mass. These results indicate an important early antimetastatic function of hepatic NK-cells and KC and that presurgical administration of IFN-gamma may be important for eliminating circulating tumor cells and inhibiting development of residual tumors.     

A novel dendritic cell-based cancer vaccine produces promising results in a syngenic CC-36 murine colon adenocarcinoma model

BACKGROUND: This study was conducted to test the efficacy of a new cancer vaccine, composed of dendritic cells (DCs) pulsed with an interleukin-2 gene-encoded vaccinia virus tumor oncolysate (DC-IL-2VCO) in a CC-36 murine colon adenocarcinoma model. MATERIALS AND METHODS: CC-36 tumor cells were injected subcutaneously into the left flank of four- to six-week old male BALB/c mice. The mice were divided into three groups, each of which received one of the following treatments: (1) DCs pulsed with the IL-2 gene-encoded vaccinia oncolysate (DC-IL-2VCO), (2) DCs pulsed with the tumor oncolysate alone (DC-CO), or (3) no treatment (control). Tumor incidence was measured, and survival rates were compared using a paired Student's t-test. Cytolytic T cell activity was measured in peripheral blood lymphocytes (PBL) and splenic lymphocytes using a (51)Cr-release assay. Lastly, mice were depleted of either CD4+ or CD8+ lymphocytes prior to receiving the vaccine to test the mechanism of tumor immunity in these mice. RESULTS: Mice treated with DC-IL-2VCO demonstrated decreased tumor burden, increased survival, and greater cytolytic activity compared with control mice and mice receiving DC-CO. In addition, mice depleted of CD8+ T cells prior to immunization with IL-2VV + DC-IL-2VCO had a significant increase in the incidence of tumor, similar to the untreated control mice. CONCLUSIONS: DCs pulsed with an IL-2 gene-encoded vaccinia virus tumor oncolysate (DC-IL-2VCO) produced safe and effective immune responses in a murine CC-36 colon adenocarcinoma model. This vaccine (DC-MelVac; Patent no. 11221/5) has the potential to treat humans with cancer, and has received FDA approval for use in Phase I clinical trials.     

Survival of transplanted neural progenitor cells enhanced by brain irradiation

OBJECT: Authors of previous studies have reported that adult transplanted neural progenitor cells (NPCs) are suitable for brain cell replacement or gene delivery. In this study, the authors evaluated survival and integration of adult rat-derived NPCs after transplantation and explored the potential impact on transplant survival of various mechanical and biological factors of clinical importance. METHODS: Adult female Fischer 344 rats were used both as a source and recipient of transplanted NPCs. Both 9L and RG2 rat glioma cells were used to generate in vivo brain tumor models. On the 5th day after tumor implantation, NPCs expressing green fluorescent protein (GFP) were administered either intravenously (3.5 x 10(7) cells) or by stereotactic injection (1 x 10(4)-1 x 10(6) cells) into normal or tumor-bearing brain. The authors evaluated the effect of delivery method (sharp compared with blunt needles, normal compared with zero-volume needles, phosphate-buffered saline compared with medium as vehicle), delivery sites (intravenous compared with intratumoral compared with intraparenchymal), and pretreatment with an immunosuppressive agent (cyclosporin) or brain irradiation (20-40 Gy) on survival and integration of transplanted NPCs. RESULTS: Very few cells survived when less than 10(5) cells were transplanted. When 10(5) cells or more were transplanted, only previously administered brain irradiation significantly affected survival and integration of NPCs. Although GFP-containing NPCs could be readily detected 1 day after injection, few cells survived 4 days to 1 week unless preceded by whole-brain radiation (20 or 40 Gy in a single fraction), which increased the number of GFP-containing NPCs within the tissue more than fivefold. CONCLUSIONS: The authors' findings indicate that most NPCs, including those from a syngeneic autologous source, do not survive at the site of implantation, but that brain irradiation can facilitate subsequent survival in both normal and tumor-bearing brain. An understanding of the mechanisms of this effect could lead to improved survival and clinical utility of transplanted NPCs.     

瘤体内直接注射白细胞介素-7基因抗小鼠乳腺肿瘤免疫效应的研究

目的 观察瘤体内直接注射白细胞介素(IL)-7基因抗小鼠乳腺肿瘤免疫效应.方法 构建IL-7真核表达质粒(pcDNA3-IL-7);建立乳腺癌TM40D细胞BALB/C小鼠移植模型;瘤体内直接注射pcDNA3-IL-7,观察小鼠肿瘤体积变化;酶联免疫吸附试验(ELISA)法检测外周血干扰素(IFN)-γ含量;流式细胞仪检测胞内IFN-γ的分泌量;局部肿瘤经治疗后行常规病理分析.结果 成功构建pcDNA3-IL-7;与对照磷酸盐缓冲液(PBS)组(115.2±11.8) ng/L、pcDNA3组(133.6±9.4) ng/L比较,pcDNA3 -IL-7注射组(242.3±10.1)ng/L外周血IFN-γ明显增高;pcDNA3-IL-7明显抑制肿瘤生长(P＜0.05);流式细胞仪检测显示pcDNA3-IL-7显著促进CD4+T细胞、CD8+T细胞内IFN-γ的分泌量;常规病理显示pcDNA3 -IL-7注射组肿瘤组织大量坏死,炎性细胞和大量淋巴细胞浸润.结论 瘤体内直接注射pcDNA3-IL-7明显抑制小鼠乳腺肿瘤生长,显著促进IFN-γ分泌,增强了小鼠机体抗乳腺肿瘤的免疫效应.     

Nude mouse resists hepatic metastasis of the allogeneic tumor,colon-26

The ability of the host-immune defense mechanism of nude mice and their immunocompetent littermates to prevent liver metastases from the murine colon carcinoma, colon-26, was assessed. Give thousand tumor cells suspended in 0.05 ml of Hank's balanced salt solution were inoculated into the spleens of BALB/c nu/+and BALB/c nu/nu mice. On the 21st day after inoculation, all the mice were sacrificed, and the liver metastases counted and the livers weighed. All the BALB/c nu/+mice were found to have developed hepatic metastases with a mean of 10 nodules, whereas no hepatic metastases were observed in any of the 10 BALB/c nude mice. On the other hand, 4 of 6 nude mice developed hepatic metastases after treatment with anti-asialo GM1 antibody. These results indicate that the BALB/c nude mouse has an excellent host-immune defense mechanism for preventing liver metastasis, with NK cells in the liver and/or blood circulation perhaps playing an important role.     

Nude mouse resists hepatic metastasis of the allogeneic tumor, colon-26

The ability of the host-immune defense mechanism of nude mice and their immunocompetent littermates to prevent liver metastases from the murine colon carcinoma, colon-26, was assessed. Give thousand tumor cells suspended in 0.05 ml of Hank's balanced salt solution were inoculated into the spleens of BALB/c nu/+ and BALB/c nu/nu mice. On the 21st day after inoculation, all the mice were sacrificed, and the liver metastases counted and the livers weighed. All the BALB/c nu/+ mice were found to have developed hepatic metastases with a mean of 10 nodules, whereas no hepatic metastases were observed in any of the 10 BALB/c nude mice. On the other hand, 4 of 6 nude mice developed hepatic metastases after treatment with anti-asialo GM1 antibody. These results indicate that the BALB/c nude mouse has an excellent host-immune defense mechanism for preventing liver metastasis, with NK cells in the liver and/or blood circulation perhaps playing an important role.     

Lymphocyte migration to tumors after hyperthermia and immunotherapy.

We have previously shown that the combination of immunotherapy with interleukin 2 (IL-2) and local hyperthermia (LHT) abrogates the growth of murine subcutaneous tumors significantly more than either modality alone. This study was undertaken to investigate whether the beneficial effect of combined modality therapy could be attributed to increased trafficking of effector cells to the tumor. After inducing MCA-105 sarcomas in the hindlimbs of C57BL/6 mice, animals were given no therapy, LHT, IL-2, or IL-2 + LHT followed by an iv injection of 51Cr-labeled syngeneic splenocytes or LAK cells. Select organs and the tumor-bearing extremity were counted in a gamma counter. IL-2 or LHT alone did not affect lymphocyte migration, while IL-2 + LHT significantly decreased trafficking (P less than 0.001) to the tumor. LAK cells showed increased migration to the tumor site compared to splenocytes in all treatment groups (P less than 0.02). IL-2 caused increased migration of LAK cells but not splenocytes to the lung; this was not affected by LHT. LAK cell trafficking to the spleen was decreased by IL-2 and IL-2 + LHT, while splenocyte migration was decreased in the LHT and combined treatment groups. LHT and IL-2 had no effect on trafficking of either effector cell type to liver or kidney. These results show that the beneficial effect of combined modality therapy may not be due to increased trafficking of lymphocytes to the tumor area. In addition, LAK cells traffic more to subcutaneous tumors than splenocytes, and this cannot be explained by the differential trafficking to other organs. The results of this study will be important in the planning of future experiments with combined adoptive immunotherapy and hyperthermia.     

Augmentation of the immune response of the murine liver by levamisole.

Murine hepatic nonparenchymal cells (NPC) were studied following in vivo treatment with levamisole. This agent was found to increase the cytolytic action of these cells against YAC-1 and P815 target cells. An increase in the cytostatic activity against liver-derived murine colon adenocarcinoma 38 tumor cells was also observed. Treatment with levamisole also augmented the proliferation of the hepatic NPC. Supernatants generated by these cells contained an agent capable of stimulating the proliferation of bone marrow cells from the same mice. The effect of levamisole on different subsets of NPC derived from the liver in this model is discussed.     

Changes of T Cells and Cytokines TGF-β1 and IL-10 in Mice During Liver Metastasis of Colon Carcinoma: Implications for Liver Anti-tumor Immunity

Background

The local and systemic regulation of the immune system may play important roles in the process of liver metastasis of colorectal carcinoma. The aim of this study was to establish a reproducible experimental liver metastasis model, to identify changes in T cells and cytokines TGF-β1 and IL-10, and to explore a possible mechanism of liver metastasis of colon carcinoma.

Methods

We used a colon carcinoma liver metastasis model, in which different numbers of CT-26 murine colon carcinoma cells (1?×?10³, 5?×?10³, 1?×?10⁴, 5?×?10⁴, and 1?×?10⁵) were injected into the spleen. The liver and spleen tissues were examined for T cell markers using flow cytometry. Liver tissues were analyzed for IL-10 and transforming growth factor beta 1 (TGF-β1) expression using immunohistochemistry.

Results

Spleen injection of colon carcinoma cells is a reproducible animal model for liver metastases, which resulted in quantity-dependent metastatic growth. We provided a snapshot of the hepatic immune microenvironment in the mouse liver metastasis model. Injection of A large number of tumor cells (5?×?10⁴ and 1?×?10 ⁵ ) decreased anti-tumor cell counts, such as CD4⁺ and CD8⁺ T cells, and increased immune-suppressive cell counts (CD4⁺CD25⁺ T_reg cells). In addition, the expression levels of immunosuppressive cytokines IL-10 and TGF-β1 were also increased with the number of tumor cells.

Conclusions

Changes in the systemic and local immunological environment contribute to immunological escape mechanisms during liver metastasis of colon carcinoma, and therapies aiming at immune microenvironment may prove a useful strategy in the treatment of metastatic disease in the future.     

氩氦刀冷冻联合CpG寡脱氧核苷酸治疗小鼠皮下移植性结肠癌

目的 探讨氩氦刀冷冻消融联合CpG寡脱氧核苷酸（ODN）对小鼠移植性结肠癌的治疗作用.方法 BALB/c小鼠皮下接种结肠癌CT26细胞建立荷瘤鼠模型,小鼠被分成PBS组（6只,瘤周注射PBS组）、氩氦刀组（6只,氩氦刀冷冻组）、CpG ODN组（6只,瘤周注射CpG ODN）和联合治疗组（6只,氩氦刀冷冻加瘤周注射CpG ODN）.观察各组小鼠存活及肿瘤生长情况;采用酶联免疫吸附试验检测小鼠外周血中IL-12和IFN-γ的含量;利用流式细胞仪检测小鼠外周血中CD3＋CD4＋T细胞与CD3＋CD8＋T细胞比例;对氩氦刀组和氩氦刀联合CpG ODN组治愈小鼠进行再攻击实验,观察小鼠再次成瘤率.结果 氩氦刀组和联合治疗组小鼠的平均生存时间为（80.3±5.4）d和（83.8±5.5）d,明显长于PBS组[（53.7±3.7）d]和CpG ODN组[（51.5±6.8）d],差异均有统计学意义（P＜0.05）.氩氦刀组和联合治疗组抑瘤率分别为83.8%和86.2%.治疗后20 d,氩氦刀组和联合治疗组的CD3＋CD4＋T细胞/CD3＋CD8＋T细胞比值、IL-12和IFN-γ水平均高于PBS组和CpGODN组,差异有统计学意义（P＜0.05）;与氩氦刀组比较,联合治疗组CD3＋CD4＋T细胞/CD3＋CD8＋T细胞比值差异无统计学意义,但IL-12和IFN-γ水平则显著升高（P＜0.05）.肿瘤再攻击后,氩氦刀组和联合治疗组分别有5只（5/6）和1只（1/6）再次成瘤,差异有统计学意义（P＜0.05）.结论 氩氦刀冷冻联合CpG ODN可以增强荷瘤鼠的抗肿瘤免疫应答,增强了氩氦刀治疗小鼠的免疫功能,减少了肿瘤再次攻击的成瘤率.     

Macrophage effector mechanisms in melanoma in an experimental study.

BACKGROUND: The tumor-bearing state is known to induce immune dysfunction that contributes to increased infectious complications and tumor progression. However, the mechanisms underlying this immunosuppression remain unclear. HYPOTHESIS: Macrophage (MO) dysfunction may play a role in tumor-induced immunosuppression. DESIGN AND MAIN OUTCOME MEASURES: Using a murine model, this study investigated the effects of melanoma growth on peritoneal macrophage effector molecule and prostaglandin production, MO-mediated cytotoxicity, and candidacidal mechanisms. Female C57BL/6 mice were inoculated with 106 B16 melanoma cells or a salt solution subcutaneously. Mice were euthanized 3 weeks later and peritoneal MOs were harvested and assayed for nitric oxide, superoxide anion, tumor necrosis factor alpha, and prostaglandin E(2)production. Macrophage-mediated cytotoxicity against B16 melanoma targets and MO candidacidal mechanisms were also measured. RESULTS: Macrophage production of nitric oxide, superoxide anion, and tumor necrosis factor alpha were significantly decreased, while prostaglandin E(2)production was increased in MOs from melanoma-bearing mice. Concomitantly, MO-mediated cytotoxicity and candidacidal mechanisms were significantly impaired. CONCLUSIONS: Melanoma growth leads to decreased MO effector molecule production, increased prostaglandin E(2)production, and impaired MO cytotoxic and candidacidal mechanisms. These results may help explain the observed increased infectious complications in the tumor-bearing host. Strategies aimed at restoring MO function may have therapeutic potential.     

Inhibition of Host Signal Transducer and Activator of Transcription Factor 6 Results in Cure With Cyclophosphamide and Interleukin 12 Immunotherapy

BACKGROUND: Interleukin (IL)-12 immunotherapy is highly effective against established immunogenic tumors. However, nonimmunogenic tumors fail to respond to IL-12 therapy. Analysis of tumor rejection of the immunogenic tumors shows that a preexisting antitumor immune response is required for an effective IL-12 response. It is not known whether this lack of a preexisting host antitumor immune response is a limiting factor for the lack of response to IL-12 therapy by nonimmunogenic tumors. METHODS: Experiments were done using the spontaneously arising nonimmunogenic metastatic murine breast 4T1 carcinoma in normal and STAT6 knockout BALB/c mice. RESULTS: 4T1 is nonimmunogenic in normal mice, and established subcutaneous tumors are resistant to immunotherapy with cyclophosphamide (Cy) plus IL-12. However, in STAT6 knockout mice, 4T1 becomes immunogenic, and established 4T1 tumors are eradicated by Cy plus IL-12. Adoptive transfer of spleen cells from normal mice into STAT6 knockout mice before tumor inoculation reduces both the immunogenicity and response to Cy plus IL-12 immunotherapy of 4T1 in the recipient mice. CONCLUSIONS: Cy plus IL-12 immunotherapy can eradicate nonimmunogenic tumors as long as a preexisting immunity is established in the tumor-bearing host. Furthermore, the STAT6 pathway is likely involved in the suppression of the development of host antitumor immunity.