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Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tumors escape immunological rejection by a diversity of mechanisms. In this report, we demonstrate that the colon cancer cell SW620 expresses functional Fas ligand (FasL), the triggering agent of Fas receptor (FasR)-mediated apoptosis within the immune system. FasL mRNA and cell surface FasL were detected in SW620 cells using reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemical staining, respectively. We show that SW620 kills Jurkat T cells in a Fas-mediated manner. FasR-specific antisense oligonucleotide treatment, which transiently inhibited FasR expression, completely protected Jurkat cells from killing by SW620. FasL-specific antisense oligonucleotide treatment of SW620 inhibited its Jurkat-killing activity. FasL has recently been established as a mediator of immune privilege in mouse retina and testis. Our finding that colon cancer cells express functional FasL suggests it may play an analogous role in bestowing immune privilege on human tumors. HT29 and SW620 colon cancer cells were found to express FasR mRNA and cell surface FasR using RT-PCR and immunofluorescence flow cytometry, respectively. However, neither of these cells underwent apoptosis after treatment by the anti-FasR agonistic monoclonal antibody CH11. Our results therefore suggest a Fas counterattack model for immune escape in colon cancer, whereby the cancer cells resist Fas-mediated T cell cytotoxicity but express functional FasL, an apoptotic death signal to which activated T cells are inherently sensitive.
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PMID:The Fas counterattack: Fas-mediated T cell killing by colon cancer cells expressing Fas ligand. 906 24

Fas (CD95) and its ligand are central regulatory molecules in hematopoietic cells. Previous studies have suggested a role for Fas in the regulation of tumor progression, but Fas has not yet been conclusively identified as a tumor suppressor. Fas-deficient individuals lack malignant tumors, perhaps because of regulation by T cells. To investigate such a possibility, mice deficient in both T cells and Fas were generated, and they were found to develop severe B cell dysregulation characterized by malignant, lethal B cell lymphoma. Lymphoma arose from a monoclonal B220+CD19-CD5-CD23- B cell secreting immunoglobulin M, kappa rheumatoid factor. In contrast, animals containing alpha beta T cells, gamma delta T cells, and/or functional Fas suppressed the development of lymphoma. These data indicate that Fas functions as a tumor suppressor, and identifies roles for both alpha beta T cells and gamma delta T cells in Fas-independent tumor regulation.
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PMID:A tumor-suppressor function for Fas (CD95) revealed in T cell-deficient mice. 906 31

Some anticancer drugs kill tumor cells through the mechanism of apoptosis. Fas antigen has been generally noticed as an apoptosis-signalling receptor molecule on the surface of different cells. Recently, it has become clear that some tumor cells express Fas antigen on their surface, and apoptosis is induced in those cells by IgM-anti-Fas monoclonal antibody (IgM-anti-Fas MoAb). If it is possible to induce apoptosis in tumor cells effectively by anticancer drugs in combination with IgM-anti-Fas MoAb, then we may be able to develop a new strategy for cancer chemotherapy. HL60 human leukemic cell line was incubated with anticancer drugs adriamycin (ADM) or cytosine arabinoside (Ara-C) at different doses alone and in combination with IgM-anti-Fas MoAb. We then observed the morphologic changes of tumor cells, the DNA fragmentation by agarose gel electrophoresis, and the changes in the amount of Fas antigen expression in their cell surface by using flow cytometry. In ADM- or Ara-C-treated tumor cells, apoptotic cells increased in number time- and dose-dependently. By the combination of ADM or Ara-C with IgM-anti-Fas MoAb, the induction of apoptosis in HL60 cells was enhanced significantly. The DNA electrophoresis supported those results. The amount of Fas antigen expression was slightly increased only in cells treated with a low dose of Ara-C, not in others. Our results suggest that apoptosis is a major process of leukemic cell death induced by anticancer drugs. Furthermore, it has become clear that the combination of anticancer drugs with IgM-anti-Fas MoAb enhances leukemic cell death through apoptosis in vitro, though the mechanism remains to be resolved.
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PMID:Induction of apoptosis in HL60 leukemic cells by anticancer drugs in combination with anti-Fas monoclonal antibody. 906 48

To reach a clinically detectable size, neoplasms must be able to suppress or evade a host immune response. Activated T cells may enter apoptosis in the presence of Fas ligand (FasL) (1), and tissue expression of FasL has been shown to contribute to immune privilege in the eye and testis (2, 3). We have demonstrated that all human lung carcinoma cell lines tested (16 of 16) express a Mr 38,000 protein consistent with FasL by immunoblotting, whereas the majority of resected tumors (23 of 28) show positive staining for FasL by immunohistochemistry. DNA sequencing of reverse transcription-PCR products from lung cancer cells and resected lung tumors confirms the presence of human FasL mRNA in these neoplastic tissues. Furthermore, lung carcinoma cells are capable of killing a Fas-sensitive human T cell line (Jurkat) in coculture experiments; this killing was inhibited by a recombinant form of the soluble portion of the Fas receptor (FasFc). FasL expression by neoplastic cells represents a potential mechanism for peripheral deletion of tumor-reactive T-cell clones.
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PMID:Human lung carcinomas express Fas ligand. 906 60

A good prognosis is often achieved in patients who have undergone treatment for human papillary carcinoma of the thyroid. On the assumption that this may be partly attributable to an apoptotic tendency of this special type of tumor, we measured DNA fragmentation, cell death by enzyme-linked immunosorbent assay (ELISA), and the expression of apoptosis-related genes. DNA fragmentation occurred more extensively in malignant tumor cells than in benign thyroid tumors or normal thyroid tissue, as examined by agarose gel electrophoresis and confirmed by the quantitative method using an ELISA kit. Although only expression of the tumor suppressor gene, p53, was increased in the tumor tissue, no expression of other genes, such as Fas, TNF, c-myc, c-fos or bcl-2, was observed in the normal, benign, or malignant tumor tissues, indicating that the roles of these gene functions, if any, were minimal in these tissues. Since p53 is closely related to cellular apoptosis and no point mutation was observed in the transcripts expressed by malignant cells, apoptosis and/or the production of an angiogenesis inhibitor induced by wild-type p53 molecules may be related to the favorable prognosis of patients treated for papillary carcinoma of the thyroid.
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PMID:Expression of wild-type p53 tumor suppressor gene and its possible involvement in the apoptosis of thyroid tumors. 906 3

Astrocytomas are among the most common brain tumors that are usually fatal in their malignant form. They appear to progress without significant impedance from the immune system, despite the presence of intratumoral T cell infiltration. To date, this has been thought to be the result of T cell immunosuppression induced by astrocytoma-derived cytokines. Here, we propose that cell contact-mediated events also play a role, since we demonstrate the in vivo expression of Fas ligand (FasL/CD95L) by human astrocytoma and the efficient killing of Fas-bearing cells by astrocytoma lines in vitro and by tumor cells ex vivo. Functional FasL is expressed by human, mouse, and rat astrocytoma and hence may be a general feature of this nonlymphoid tumor. In the brain, astrocytoma cells can potentially deliver a death signal to Fas+ cells which include infiltrating leukocytes and, paradoxically, astrocytoma cells themselves. The expression of FasL by astrocytoma cells may extend the processes that are postulated to occur in normal brain to maintain immune privilege, since we also show FasL expression by neurons. Overall, our findings suggest that FasL-induced apoptosis by astrocytoma cells may play a significant role in both immunosuppression and the regulation of tumor growth within the central nervous system.
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PMID:Fas ligand expression by astrocytoma in vivo: maintaining immune privilege in the brain? 907 24

Apoptosis is the mechanism by which cells are programmed to die under a wide range of physiological and developmental stimuli. Several mediators of programmed cell death have been identified and signals of apoptosis have been found to utilize common pathways, some of which have been elucidated. This review focuses on a number of apoptotic systems that have been widely studied and discuss recent progress and opinion in these areas. These include studies on Fas signaling, tumor suppressor genes, cell cycle interfaces, stress responses, genetic systems, and the Bcl-2 family. Understanding apoptosis from these perspectives sheds substantial light on processes of biological homeostasis. Furthermore, the ability to manipulate the apoptotic response may lead to novel therapeutic interventions in cancer and other diseases.
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PMID:Mechanisms of apoptotic cell death. 909 84

Although CD8+ killer T cells reacting against human autologous tumor cells have recently been studied in detail, little is known about the cytotoxic mechanism of CD4+ T cells against such tumor cells. In order to investigate this, we have established CD4+ cytotoxic T lymphocyte TcOSC-20 lines. TcOSC-20 showed selective cytotoxic activity against autologous OSC-20 cells, derived from a cancer of the tongue, in an HLA-DR-restricted fashion. HLA-DR8 (DRB1*08032) is the only DR molecule expressed on OSC-20 cells, and anti-DR8 monoclonal antibody could inhibit the cytotoxicity, suggesting that HLA-DRB1*08032 is the tumor rejection antigen-presenting molecule to TcOSC-20. The Fas ligand was expressed on TcOSC-20 lines, and its expression was induced upon mixed lymphocyte-tumor cell culture of autologous peripheral blood lymphocytes. Furthermore, the cytotoxicity of TcOSC-20 was inhibited by anti-Fas ligand antibody. These data imply that TcOSC-20 lines recognize the tumor antigenic peptide presented by HLA-DR8, and exert cytotoxicity against autologous tumor cells via a Fas-mediated cytotoxic pathway.
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PMID:Cytotoxicity of histocompatibility leukocyte antigen-DR8-restricted CD4 killer T cells against human autologous squamous cell carcinoma. 911 48

As little is known about the molecular mechanisms responsible for lymphocyte-mediated rejection of xenografts, we have studied the relative contribution of perforin and Fas pathways in cytotoxic lymphocytes generated in mice transplanted with human cell lines. Responder lymphocytes generated in immunocompetent mice displayed significant lysis of human target cells, which suggests that mice can generate a strong lymphocytotoxic response to human cells. Effector cells generated in immunocompetent and gld (Fas ligand mutant) mice predominantly use a perforin-mediated cytotoxic mechanism. By contrast, a Fas-mediated pathway could be stimulated in perforin-deficient or beta2-microglobulin-deficient mice, providing the human target cells were sensitive to Fas-mediated lysis. In vitro depletion of effector CD3+ CD8+ T cells, but not CD4+ T or NK1.1+ cells, completely inhibited lysis of human target cells. This suggests that CD3+ CD8+ T cells were responsible for perforin-mediated xenospecific cytotoxicity. In vivo depletion of NK1.1+ cells and CD4+ T cells before the final immunization abrogated the capacity of lymph node cells to generate xenospecific CD8+ cytotoxic T lymphocytes. By contrast, in vitro depletion of CD4+ T cells was most effective in abrogating the xenospecific Fas-mediated cytotoxicity of perforin-deficient effector cells. Xenospecific cytotoxic T cells were also capable of mediating tumor rejection when adoptively transferred into scid/scid mice bearing established human COLO 205 xenografts. Overall, these data suggested that xenospecific cytotoxic T lymphocytes can lyse target cells via either perforin- or Fas-mediated pathways and that these cells can provide protective and specific immunity against tumor xenografts in the absence of an intact humoral immune system.
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PMID:Xenospecific cytotoxic T lymphocytes: potent lysis in vitro and in vivo. 913 81

In addition to the full length mRNA activated human peripheral blood mononuclear cells (PBMC) and T cell tumor lines express several alternatively spliced Fas variants. At least five of these code for soluble Fas (CD95) molecules. In vitro studies suggest that these soluble Fas isoforms inhibit apoptosis induced by agonistic antibodies and, more importantly, by the natural Fas ligand in Fas-bearing sensitive cells. Interestingly, this functional property can be assigned to the first 49 aminoacids of the mature protein, the only region shared by the soluble Fas molecules.
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PMID:Soluble Fas/Apo-1 splicing variants and apoptosis. 915 4


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