Melanoma cell expression of Fas(Apo-1/CD95) ligand: implications for tumor immune escape

CD54 expression is predictive for lymphatic spread in human gastric carcinoma

Even among gastric carcinoma cases with a similar extent of lymphatic invasion, the number of diseased lymph nodes may vary. Other factors might also contribute to the process of lymphangitic metastasis. Primary gastric tumors with the same extent of pathologic lymphatic invasion were studied in 78 patients. We investigated the correlation between CD54 expression on cancer cells and clinicopathologic features. Decreased CD54 expression on cancer cells was significantly correlated with the number of involved lymph nodes and the extent of lymph node spread. The number of diseased lymph nodes was associated with the prognosis of patients with gastric carcinoma. The CD54-negative group had a significantly worse prognosis than the CD54-positive group. These findings suggested that CD54 expression is predictive for lymphatic spread and prognosis in human gastric carcinoma.

Addressing the "Fas counterattack" controversy: blocking fas ligand expression suppresses tumor immune evasion of colon cancer in vivo

Fas ligand (FasL/CD95L) is a transmembrane protein belonging to the tumor necrosis factor superfamily that can trigger apoptotic cell death following ligation to its receptor, Fas (CD95/APO-1). Expression of FasL may help to maintain tumor cells in a state of immune privilege by inducing apoptosis of antitumor immune effector cells-the "Fas counterattack." However, the ability of FasL to mediate tumor immune privilege is controversial due to studies that indicate FasL has both pro- and anti-inflammatory activities. To resolve this controversy and functionally define the role of FasL in tumor immune evasion, we investigated if suppression of endogenously expressed FasL in colon tumor cells resulted in reduced tumor development and improved antitumor immune challenge in vivo. Specifically, FasL expression in CMT93 colon carcinoma cells was down-regulated following stable transfection with a plasmid encoding antisense FasL cDNA. Down-regulation of FasL expression had no effect on tumor growth in vitro but significantly reduced tumor development in syngeneic immunocompetent mice in vivo. Tumor size was also significantly decreased. Reduced FasL expression by tumor cells led to increased lymphocyte infiltration. The overall level of neutrophils present in all of the tumors examined was low, with no difference between the tumors, irrespective of FasL expression. Thus, down-regulation of FasL expression by colon tumor cells results in an improved antitumor immune challenge in vivo, providing functional evidence in favor of the "Fas counterattack" as a mechanism of tumor immune evasion.

Tumor counterattack: fact or fiction?

Cancer development relies on a variety of mechanisms that facilitate tumor growth despite the presence of a functioning immune system. Understanding these mechanisms may foster novel therapeutic approaches for oncology and organ transplantation. By expression of the apoptosis-inducing protein CD95L (FasL, APO-1L, CD178), tumors may eliminate tumor-infiltrating lymphocytes and suppress anti-tumor immune responses, a phenomenon called "tumor counterattack". On the one hand, preliminary evidence of tumor counterattack in human tumors exists, and CD95L expression can prevent T-cell responses in vitro. On the other hand, CD95L-expressing tumors are rapidly rejected and induce inflammation in mice. Here, we summarize and discuss the consequences of CD95L expression of tumor cells and its contribution to immune escape.

Mechanisms of tumor evasion

The results from in vitro immunological experiments, murine tumor models and patients with cancer clearly demonstrate that tumors have multiple mechanisms to evade the immune response. During the early stages of tumor development malignant cells can be poor stimulators, present poor targets or become resistant to the innate immune response, while at later stages, progressively growing tumors impair the adaptive immune response by blocking the maturation and function of antigen presenting cells and causing alterations in T cell signal transduction and function. Preliminary results also suggest a correlation between some of these changes and an increased metastatic potential of the tumor cells, a diminished response to immunotherapy, and poor prognosis. Carefully coordinated basic research studies and clinical immunotherapy trials will be required to fully determine the impact on the outcome of the disease and the response to treatment. However, understanding the mechanisms used by tumor cells to evade the immune system could result in new therapeutic approaches for preventing and/or reversing these immune alterations and have the potential of improving the current results of immunotherapy trials.

The characteristics of human NKT cells in lung cancer--CD1d independent cytotoxicity against lung cancer cells by NKT cells and decreased human NKT cell response in lung cancer patients

The activation of human Valpha24+Vbeta11+natural killer T cells (NKT) cells (Valpha24 NKT cells) induces effective antitumor responses with secondary immune effects through activation of conventional T cells and natural killer cells. In this study, we attempted to analyze the characteristics of human NKT cells in lung cancer patients. Valpha24 NKT cells stimulated with alpha-GalCer from healthy volunteers exhibited direct cytotoxic activity against two (RERF-LC-OK and PC-3) of seven human lung cancer cell lines studied. Cytotoxicity by Valpha24 NKT cells against human lung cancer cells was dependent on the perforin pathway and independent of Fas/FasL pathway. Intracellular adhesion molecule (ICAM)-1 expression on tumor cells was clearly associated with the cytotoxicity of Valpha24 NKT cells. On the other hand, the proportion of Valpha24 NKT cells in the patients with lung cancer was lower than that in the healthy volunteers. Furthermore, the proliferative response of Valpha24 NKT cells to alpha-GalCer was significantly lower in the peripheral blood mononuclear cells in the patients with lung cancer. Addition of granulocyte colony-stimulating factor moderately restored the low proliferative response of Valpha24 NKT cells in the patients with lung cancer, however the percentage by which the response was restored in these patients was still lower than the natural response in healthy volunteers. These results suggest that Valpha24 NKT cells may play a pivotal role or the antitumor response in lung cancer.

Increase in autoantibodies against Fas (CD95) during carcinogenesis in the human colon: a hope for the immunoprevention of cancer?

A thorough understanding of the naturally occurring events in the immune system in response to carcinogenesis will facilitate the development of strategies for the immunoprevention of cancer. The adenoma-carcinoma sequence in the human colon is a well-established clinical example of multi-step carcinogenesis and can be used for immunological studies. Based on previous observations that both apoptosis and the expression of Fas (Apo-1, CD95) are altered during carcinogenesis in the human colon, we asked the question whether serum titers of autoantibodies against Fas show any modification during the adenoma-carcinoma sequence. Healthy controls (38), patients with colorectal adenomas (38) and patients with colorectal adenocarcinomas (21) were investigated. Anti-Fas antibody titers were found to be significantly higher in patients with colorectal adenomas than in healthy controls and higher still in patients with colorectal adenocarcinomas. This increase in anti-Fas autoantibody titers during carcinogenesis might reflect the activation of natural defense mechanisms by the immune system.

Tissue microarray analysis of Fas and FasL expressions in human non-small cell lung carcinomas; with reference to the p53 and bcl-2 overexpressions

Lack of surface Fas expression is a main route for apoptotic resistance which is considered an important mechanism of tumorigenesis and tumor progression. Fas and FasL expressions in 110 non-small cell lung carcinomas (NSCLCs) were investigated to evaluate their roles in pulmonary carcinogenesis and to examine the clinicopathologic significance of Fas expression with its relationship with p53 and bcl-2 overexpressions. Immunohistochemical analysis using tissue microarray demonstrated that a large proportion of NSCLC patients (60%) showed lack of membranous Fas expression. The Fas-negative cases revealed the significantly lower survival rate than Fas-positive ones. Also, the loss of Fas receptor expression was found more frequently in advanced stage and higher nodal status. FasL protein was increased in most NSCLCs (89%) compared to normal lungs. p53 and bcl-2 overexpressions showed no association with Fas expression. Conclusively, reduced membranous Fas expression as a mechanism of apoptotic resistance is considered to play an important part of the pulmonary carcinogenesis, which may predict poor survival and have a bad prognostic influence. Increased FasL expression is thought to be a basis for the immune evasion in NSCLCs. The rare bcl-2 overexpression suggests that this anti-apoptotic protein is unlikely to play a role in the apoptotic resistance of NSCLCs.

Targeting the Fas/Fas ligand pathway in cancer

Fas is a transmembrane receptor that can induce apoptosis after cross-linking with either agonistic antibodies or with Fas ligand (FasL). Although originally described as an important regulator of peripheral immune homeostasis, accumulating evidence suggests that the Fas/FasL system plays an important role in tumour development. In addition to its proapoptotic functions, accumulating evidence demonstrates that Fas can activate numerous nonapoptotic signalling pathways, and that activation of these pathways can result in increased tumourigenicity and metastasis. This review summarises the current understanding of the Fas/FasL system in tumorigenesis and discusses attempts to utilise the Fas/FasL system in the treatment of cancer.

Viruses with deletions in antiapoptotic genes as potential oncolytic agents

Replication-selective oncolytic viruses have emerged as a new treatment platform for cancers. However, selectivity and potency need to be improved before virotherapy can become a standard treatment modality. In addition, mechanisms that can be incorporated to enable targeting a broad range of cancer types are highly desirable. Cancer cells are well known to have multiple blocks in apoptosis pathways. On the other hand, viruses have evolved to express numerous antiapoptotic genes to antagonize apoptosis induced upon infection. Viruses with deletions in antiapoptotic genes can therefore be complemented by antiapoptotic genetic changes in cancer cells for efficient replication and oncolysis. In this review, we summarize the recent development of this concept, the potential obstacles, and future directions for optimization.

The role of Fas ligand as an effector molecule in corneal graft rejection

Previous studies have shown that the expression of Fas ligand (FasL; CD95L) by donor corneas is critical to their survival when placed on allogeneic recipients. Since there have been reports that the cornea expresses Fas, we tested the idea that FasL on lymphoid cells could be an effector molecule during rejection episodes. When FasL defective BALB/c-gld mice were engrafted with allogeneic corneas, significantly more of these corneas were accepted than by normal BALB/c mice. However, this was not due to impaired FasL-mediated effector function in these mice as the allogeneic corneas did not express detectable Fas by Western blot or RT-PCR analysis. Furthermore, donor corneas without Fas were given no survival advantage, but were rejected similar to wild-type donor allogeneic corneas. Examination of the T cell compartment in gld mice revealed that these cells express higher levels of Fas and are more susceptible to Fas-mediated death than wild-type cells. These results indicate that FasL is not an effector molecule in corneal graft rejection and that gld mice show reduced graft rejection due to greater susceptibility of their T cells to Fas-mediated apoptosis.

Attenuation of the Fas-L independent b16bL6 melanoma lymphocidic capacity by H-2K class I molecules

We have previously reported that the capacity of highly malignant B16BL6 murine melanoma cells to induce cell death in naive syngeneic lymphocytes stems from the absence of major histocompatibility complex (MHC) class I glycoproteins in these melanoma cells. Our present study provides evidence that the above-mentioned lymphocidic activities of B16BL6 cells are selectively attenuated when the expression of H-2K (but not H-2D or H-2L) MHC class I glycoproteins is reconstituted in these cells. The induction of apoptosis in naive lymphocytes by H-2K-deficient melanoma cells does not involve the Fas ligand (Fas-L)/FAS signaling module, as demonstrated by employing lymphocytes derived from Fas-L(gld)- or Fas(lpr)-deficient mice in co-culture experiments. Furthermore, these tumor cells fail to induce Fas-L-mediated fratricide in co-cultured lymphocytes and do not express Fas-L either when grown alone or co-cultured with lymphocytes. These findings explain the previously widely reported selective down-regulation of certain MHC class I-encoded glycoproteins (H-2K, bur not H-2D or H-2L) during tumor progression. Namely, the initiation of an effective immune response against H-2K-deficient cells could be abrogated at very early steps, as the result of the induction of Fas-L/Fas-independent cell death among naive lymphoid cells.

Transfer of efficient anti-melanocyte T cells from vitiligo donors to melanoma patients as a novel immunotherapeutical strategy

BACKGROUND

Vitiligo is a relatively common progressive depigmentary condition that is believed to be due to the autoimmune-mediated loss of epidermal melanocytes. High frequencies of self-reactive T lymphocytes directed toward melanocyte differentiation antigens are found in vitiligo patients and might be directly responsible for the pathogenesis of the disease. An interesting aspect of vitiligo is its relation to melanoma: cytotoxic T lymphocytes directed to self antigens shared by normal melanocytes and melanoma cells are found in both conditions, but the resulting immune reactions are completely different. From this standpoint, the selective destruction of pigment cells that occurs in cases of vitiligo is the therapeutic goal sought in melanoma research.

PRESENTATION OF THE HYPOTHESIS

Our working hypothesis is that vitiligo patients might represent a unique source of therapeutic cells to be used in allo-transfer for HLA-matched melanoma patients. The adoptive transfer of ex-vivo generated autologous tumor-specific T cells is a therapy that has met with only limited success, essentially because of inability to isolate therapeutically valuable T cells from the majority of tumor patients. Ideally, model systems where strong and efficient responses against the same (tumor) antigens are achieved would represent a better source of therapeutic cells. We believe it is possible to identify one such model in the melanoma-vitiligo dichotomy: T lymphocytes specific for different melanocyte differentiation antigens are found in vitiligo and represent the effective anti-melanocyte reactivity that is often ineffective in melanoma.

TESTING THE HYPOTHESIS

Melanocyte-specific T cell clones can be isolated from the peripheral blood of vitiligo patients and tested for their capacity to efficiently expand in vitro without loosing their cytotoxic activity and to migrate to the skin. Cytotoxicity against melanoma patients' non-tumor cells can also be tested. In addition, it would be interesting to attempt an in vivo animal model. If the results obtained from these validation steps will be satisfactory, it might be possible to plan the clinical grade preparation of relevant clones for transfer.

IMPLICATIONS OF THE HYPOTHESIS

When translated into a clinical trial, the possibility of in vitro selecting few effective tumor-specific T cell clones for infusion, inherent with this approach, could enhance the therapeutic graft-versus-tumor effect while possibly decreasing the risk of graft-versus-host disease.

Turning On/Off Tumor-Specific CTL Response during Progressive Tumor Growth

Therapeutic vaccinations used to induce CTLs and treat firmly established tumors are generally ineffective. To understand the mechanisms underlying the failure of therapeutic vaccinations, we investigated the fate of tumor-specific CD8+ T cells in tumor-bearing mice with or without vaccinations. Our data demonstrate that tumor-specific CD8+ T cells are activated at the early stage of tumor growth, tumor-specific CTL response reaches a maximal level during progressive tumor growth, and tumor-specific CD8+ T cells lose cytolytic function at the late stage of tumor growth. The early stage therapeutic vaccination induces efficient antitumor activity by amplifying the CTL response, whereas the late-stage therapeutic vaccination is invalid due to tumor-induced dysfunction of CD8+ T cells. However, at the late stage, tumor-specific CD8+ T cells are still present in the periphery. These tumor-specific CD8+ T cells lose cytolytic activity, but retain IFN-gamma secretion function. In contrast to in vitro cultured tumor cells, in vivo growing tumor cells are more resistant to tumor-specific CTL killing, despite an increase of tumor Ag gene expression. Both tumor-induced CD8+ T cell dysfunction at the late stage and immune evasion developed by in vivo growing tumor cells contribute to an eventual inefficacy of therapeutic vaccinations. Our study suggests that it is important to design a vaccination regimen according to the stages of tumor growth and the functional states of tumor-specific CD8+ T cells.

Current concepts of tumor-infiltrating lymphocytes in human malignancies

Tumor-infiltrating lymphocytes (TILs) develop as manifestations of the recognition and defense against malignant cells by the host immune system. TILs were literally defined as "tumor-infiltrating lymphocytes", which a posteriori locate within the tumor tissues. Although such cells can be found, they fail to control the growth of tumor. Many have proposed diverse mechanisms for dysfunction of TILs with regard to the roles of immunosurveillance against cancer. However, only a few cancer types, e.g. melanoma, have seen the benefits brought by activating these cells for immunotherapy. Functional defects of TILs have been linked to abnormalities of signaling molecules; however, there is conflicting data. The death of TILs was attributed to expression of cancer-derived FasL, PD-1 and RCAS1, and cancer-induced activation-induced cell death (AICD). Confirmed by studies using TILs and animal models, the compromise of tumor-specific immune responses was thought to result from not only mechanisms of clonal anergy but also exhaustion and/or deletion. Furthermore, functional cytotoxic CD8(+) TILs might be rendered incompetent by cancer-induced up-regulation of inhibitory NK receptors or proximal signaling abnormalities. Additionally, immune privilege was partly attributed to recruitment of regulatory T cells to the tumor sites. The failure of IL-2 signaling, which stands at the center of T cell functionalities, had been linked to the enzymatic activity of cancer-derived matrix metalloproteinases (MMPs). Finally, the exploitation of IDO expression, an important enzyme in pregnancy-related immunosuppression, by cancer cells might play a role in tumor immunity. The disparity of cancer types, origin, developmental stages and individual genetic backgrounds likely account for differences, or even contradictions, which might be the reason why immunotherapy works only on a few cancer types. Delineating the mechanisms behind functional defects of TILs can help not only boost chances of the development of a successful cure but understand the not fully identified roles played by immune system in the face of malignancies.

Secreted protein acidic and rich in cysteine produced by human melanoma cells modulates polymorphonuclear leukocyte recruitment and antitumor cytotoxic capacity

The expression of secreted protein acidic and rich in cysteine (SPARC) has been associated with the malignant progression of different types of human cancer. SPARC was associated with tumor cell capacity to migrate and invade, although its precise role in tumor progression is still elusive. In the present study, we show that SPARC produced by melanoma cells modulates the antitumor activity of polymorphonuclear leukocytes (PMN). Administration to nude mice of human melanoma cells in which SPARC expression was transiently or stably knocked down by antisense RNA (SPARC-sup cells) promoted PMN recruitment and obliterated tumor growth even when SPARC-sup cells accounted for only 10% of injected malignant cells. In addition, SPARC-sup cells stimulated the in vitro migration and triggered the antimelanoma cytotoxic capacity of human PMN, an effect that was reverted in the presence of SPARC purified from melanoma cells or by reexpressing SPARC in SPARC-sup cells. Leukotrienes, interleukin 8, and growth-related oncogene, in combination with Fas ligand and interleukin 1, mediated SPARC effects. These data indicate that SPARC plays an essential role in tumor evasion from immune surveillance through the inhibition of the antitumor PMN activity.

Glioblastomas induce T-lymphocyte death by two distinct pathways involving gangliosides and CD70

Here we report that glioblastoma multiforme (GBM) mediates immunosuppression by promoting T-cell death via tumor-associated CD70 and gangliosides that act through receptor-dependent and receptor-independent pathways, respectively. GBM lines cocultured with T cells induced lymphocyte death. The GBM lines were characterized for their expression of CD70, Fas ligand (FasL), and tumor necrosis factor-alpha (TNF-alpha), and the possible participation of those molecules in T-cell killing was assessed by doing GBM/T cell cocultures in the presence of anti-CD70 antibodies, Fas fusion proteins, or anti-TNF-alpha antibodies. CD70 but not TNF-alpha or FasL is responsible for initiating T-cell death via the receptor-dependent pathway. Of the four GBM cell lines that induced T-cell death, three highly expressed CD70. Two nonapoptogenic GBM lines (CCF3 and U138), on the other hand, had only minimally detectable CD70 expression. Blocking experiments with the anti-CD70 antibody confirmed that elevated CD70 levels were involved in the apoptogenicity of the three GBM lines expressing that molecule. Gangliosides were found to participate in the induction of T-cell apoptosis, because the glucosylceramide synthase inhibitor (PPPP) significantly reduced the abilities of all four apoptogenic lines to kill the lymphocytes. High-performance liquid chromatography (HPLC) and mass spectroscopy revealed that GM2, GM2-like gangliosides, and GD1a were synthesized in abundance by all four apoptogenic GBM lines but not by the two GBMs lacking activity. Furthermore, gangliosides isolated from GBM lines as well as HPLC fractions containing GM2 and GD1a were directly apoptogenic for T cells. Our results indicate that CD70 and gangliosides are both products synthesized by GBMs that may be key mediators of T-cell apoptosis and likely contribute to the T-cell dysfunction observed within the tumor microenvironment.

Plasmacytoid dendritic cells induce CD8+ regulatory T cells in human ovarian carcinoma

To directly dissect the role of each immune component in human tumor immunopathogenesis, we have studied the interaction between dendritic cells and T cells in the tumor environment of patients with ovarian carcinoma. We previously reported that functional plasmacytoid dendritic cells, but not functionally mature myeloid dendritic cells, accumulated in tumor microenvironments. We now show that tumor ascites macrophage-derived dendritic cells induced tumor-associated antigen-specific CD8+ T cells with effector functions. Strikingly, tumor ascites plasmacytoid dendritic cells induced interleukin-10+ CCR7+ CD45RO+ CD8+ regulatory T cells. Four characteristics have been identified in tumor plasmacytoid dendritic cell-induced CD8+ regulatory T cells: (a) induction of CD8+ regulatory T cells is independent of CD4+ CD25+ T cells; (b) CD8+ regulatory T cells significantly suppress myeloid dendritic cell-mediated tumor-associated antigen-specific T cell effector functions through interleukin-10; (c) repetitive myeloid dendritic cell stimulation can recover CD8+ regulatory T cell-mediated poor T cell proliferation, but not T cell effector function; (d) CD8+ regulatory T cells express functional CCR7, and efficiently migrate with lymphoid homing chemokine MIP-3beta. Primary suppressive CCR7+ CD45RO+ CD8+ T cells are found in the tumor environment of patients with ovarian cancers. Thus, tumor-associated plasmacytoid dendritic cells contribute to the tumor environmental immunosuppressive network. Collectively, tumors manipulate tumor microenvironmental dendritic cell subset distribution and function to subvert tumor immunity. The data are relevant to understanding tumor immunopathology as well as reevaluating tumor immunotherapeutic strategies.

Melanocyte-specific, cytotoxic T cell responses in vitiligo: the effective variant of melanoma immunity?

Vitiligo is a relatively common progressive depigmentary condition that is believed to be due to the autoimmune-mediated loss of epidermal melanocytes. An interesting aspect of vitiligo is its relation to melanoma: cytotoxic T lymphocytes directed to self-antigens shared by normal melanocytes and melanoma cells are found in both conditions and might prove important in melanocyte destruction, yet the resulting immune reactions are completely different. From this standpoint, the selective destruction of pigment cells that occurs in cases of vitiligo is the therapeutic goal sought in melanoma research. In the present article, we will address these issues by reviewing current literature on the subject as well as by posing some speculations.

Squamous cell carcinoma of the lower lip: FAS/FASL expression, lymphocyte subtypes and outcome

Squamous cell carcinoma (SCC) of the lip is a relatively common malignancy of the head and neck region. Tumour thickness, grading and perineural invasion are significant prognostic indicators. However, there is still the need of new reliable biological markers able to predict the prognosis of the single cases with an unfavourable biological behaviour unpredictable by the classic clinical-pathological parameters. 32 cases of (SCC) of the lower lip were analysed for their clincopathologic features, and immunohistochemical expression of Fas/FasL in neoplastic cells and in inflammatory infiltrate. Moreover the density and phenotype of tumour-infiltrating lymphocytes (TIL) were analysed. The results were related with the follow-up of the patients ranging from 2 to 6 years. The cases with over-expression of Fas/FasL in neoplastic cells and Fas+ in T cells preferentially showed a more aggressive clinical behaviour (P<0.01). Moreover we found an alteration of the normal expression of CD4 and CD8 lymphocyte types in ten cases. This data suggest that the Fas/FasL pathway is involved in the close relation between neoplastic cells and T cells and so in the biological behaviour of these tumours.

Fas-ligand gene silencing in basal cell carcinoma tissue with small interfering RNA

Basal cell carcinoma (BCC) is the most frequent cancer in the Caucasian population. Cells of BCC strongly express Fas-ligand (FasL), a member of the tumor necrosis family, which induces apoptosis in Fas receptor-expressing cells. It has been suggested that by expression of FasL, BCC cells may evade the attack of Fas-positive immune effector cells allowing the tumor to expand. Thus, downregulation of FasL should prime BCC to the assault of immune effector cells. Recently, it has been shown that RNA interference is a highly successful approach to specifically silence a gene of interest in single cells and some animal models. However, RNAi in human tissues has not been shown so far. Here, we provide evidence that small interfering RNAs (siRNAs) efficiently transfect tumor tissue ex vivo and silence the gene of interest. We demonstrate that a specific siRNA efficiently downregulates FasL not only in FasL-positive indicator cells but also in surgically excised BCC tissue at both the protein and the mRNA level. The successful transfection of tumor tissues with siRNAs now allows to test the function of the molecule under study and opens up the investigation of other target genes in the tumor.

Chronic lymphocytic leukemia cells induce changes in gene expression of CD4 and CD8 T cells

To examine the impact of tumors on the immune system, we compared global gene expression profiles of peripheral blood T cells from previously untreated patients with B cell chronic lymphocytic leukemia (CLL) with those from age-matched healthy donors. Although the cells analyzed were not part of the malignant clone, analysis revealed differentially expressed genes, mainly involved in cell differentiation in CD4 cells and defects in cytoskeleton formation, vesicle trafficking, and cytotoxicity in CD8 cells of the CLL patients. In coculture experiments using CLL cells and T cells from healthy allogeneic donors, similar defects developed in both CD4 and CD8 cells. These changes were induced only with direct contact and were not cytokine mediated. Identification of the specific pathways perturbed in the T cells of cancer-bearing patients will allow us to assess steps to repair these defects, which will likely be required to enhance antitumor immunity.

Fas signal links innate and adaptive immunity by promoting dendritic-cell secretion of CC and CXC chemokines

Dendritic cells (DCs) and chemokines are important in linking innate and adaptive immunity. We previously reported that Fas ligation induced interleukin 1beta (IL-1beta)-dependent maturation and IL-1beta-independent survival of DCs, with extracellular signal-regulated kinase (ERK) and nuclear factor-kappaB (NF-kappaB) signaling pathways involved, respectively. We describe here that Fas ligation induced DCs to rapidly produce both CXC and CC chemokines, including macrophage inflammatory protein 2 (MIP-2), MIP-1alpha, MIP-1beta, monocyte chemoattractant protein 1 (MCP-1), RANTES (regulated on activation normal T cell expressed and secreted), and TARC (thymus and activation-regulated chemokine), resulting in enhanced chemoattraction of neutrophils and T cells by Fas-ligated DCs in vivo or by its supernatant in vitro. These chemokines work synergistically in chemoattraction of neutrophils and T cells with MIP-2 more important for neutrophils, MIP-1alpha and TARC more important for T cells. Moreover, Fas-ligated DCs increased endocytosis by neutrophils and activation and proliferation of antigen-specific naive T cells. Fas ligation-induced DC secretion of chemokines involves Ras/Raf/mitogen-activated protein kinase kinase (MEK)/ERK activation and is ERK, but not NF-kappaB, dependent. Activation of caspases, including caspase 1, but not IL-1 autocrine action, is involved in this process. These data indicate that Fas signaling provides a key link between innate response and adaptive immunity by promoting DC chemokine production.

Genomic instability in radial growth phase melanoma cell lines after ultraviolet irradiation

BACKGROUND/AIMS

Although ultraviolet (UV) irradiation, apoptosis, and genomic instability are all potentially involved in the pathogenesis of melanoma, in vitro studies investigating these changes in the radial growth phase of this neoplasm are still lacking; therefore, this study was designed to investigate these changes.

METHOD

An in vitro system consisting of three radial growth phase Wistar melanoma cell lines (WM35, WM3211, and WM1650) was established. Cells were UV irradiated (10 mJ/cm2 for UVB and 6 J/cm2 for UVA), harvested after UV exposure, and evaluated for viability and apoptosis using Trypan blue and terminal deoxynucleotidyl transferase mediated dUTP digoxigenin nick end labelling assays, respectively. Polymerase chain reaction based microsatellite assays were used to examine the cell lines for the presence of microsatellite instability (MSI) using 21 markers at the 1p, 2p, 3p, 4q, 9p, and 17p regions.

RESULTS

Exposure to UV initiated progressive cell death associated with pronounced apoptosis, with UVA having a greater effect than UVB. MSI was found in UVB (WM35 and WM3211) and UVA (WM35) irradiated cell lines at 1p, 9p, and 17p, but not in non-irradiated cells. The prevalence of MSI was higher after UVB irradiation (14%) than UVA irradiation (4.7%), and was most frequently found at D1S233.

CONCLUSIONS

The ability of erythemogenic UV irradiation to induce both apoptosis and MSI in radial growth phase melanoma cells is suggestive of its role in melanoma pathogenesis. This instability may reflect a hypermutability state, oxidative stress induced DNA damage, replication infidelity, or a combination of these factors.

Alpha-fetoprotein triggers hepatoma cells escaping from immune surveillance through altering the expression of Fas/FasL and tumor necrosis factor related apoptosis-inducing ligand and its receptor of lymphocytes and liver cancer cells

AIM

To investigate the mechanism of alpha-fetoprotein (AFP) in escaping from the host immune surveillance of hepatocellular carcinoma.

METHODS

AFP purified from human umbilical blood was administrated into the cultured human lymphoma Jurkat T cell line or hepatoma cell line, Bel7402 in vitro. The expression of tumor necrosis factor related apoptosis-inducing ligand (TRAIL) and its receptor (TRAILR) mRNA were analyzed by Northern blot and Western blot was used to detect the expression of Fas and Fas ligand (FasL) protein.

RESULTS

AFP (20 mg/L) could promote the expression of FasL and TRAIL, and inhibit the expression of Fas and TRAILR of Bel7402 cells. For Jurkat cell line, AFP could suppress the expression of FasL and TRAIL, and stimulate the expression of Fas and TRAILR. AFP also could synergize with Bel7402 cells to inhibit the expression of FasL protein and TRAIL mRNA in Jurkat cells. The monoclonal antibody against AFP (anti-AFP) could abolish these functions of AFP.

CONCLUSION

AFP is able to promote the expression of FasL and TRAIL in hepatoma cells and enhance the expression of Fas and TRAILR in lymphocytes. These could elicit the escape of hepatocellular carcinoma cells from the host's lymphocytes immune surveillance.

Cryptococcus neoformans capsular glucuronoxylomannan induces expression of fas ligand in macrophages

The major component of capsular material of Cryptococcus neoformans is glucuronoxylomannnan (GXM), a polysaccharide that exhibits potent immunosuppressive properties in vitro and in vivo. The results reported here show that 1) soluble purified GXM induces a prompt, long-lasting, and potent up-regulation of Fas ligand (FasL) on macrophages, 2) the up-regulation of FasL is related to induced synthesis and increased mobilization to the cellular surface, 3) this effect is largely mediated by interaction between GXM and TLR4, 4) FasL up-regulation occurs exclusively in GXM-loaded macrophages, 5) macrophages that show up-regulation of FasL induce apoptosis of activated T cells expressing Fas and Jurkat cells that constitutively express Fas, and 6) anti-Fas Abs rescue T cells from apoptosis induced by GXM. Collectively our results reveal novel aspects of the immunoregulatory properties of GXM and suggest that this nontoxic soluble compound could be used to dampen the immune response, to promote or accelerate the death receptor, and to fix FasL expression in a TLR/ligand-dependent manner. In the present study, we delineate potential new therapeutic applications for GXM that exploit death receptors as key molecular targets in regulating cell-mediated cytotoxicity, immune homeostasis, and the immunopathology of diseases.

Fas ligand expression in metastatic renal cell carcinoma during interleukin-2 based immunotherapy: no in vivo effect of Fas ligand tumor counterattack

PURPOSE

It has been hypothesized that tumor cells expressing Fas ligand (FasL) might be able to counterattack and neutralize tumor-infiltrating lymphocytes. We assessed the effect of FasL tumor counterattack on the clinical outcome of interleukin-2 (IL-2)-based immunotherapy in metastatic renal cell carcinoma.

EXPERIMENTAL DESIGN

Tumor core needle biopsies were obtained before IL-2-based immunotherapy in 86 patients and repeated within the first cycle in 57 patients. Tumor cells expressing FasL and intratumoral lymphocyte subsets expressing CD4, CD8, CD56, and CD57 were analyzed by immunohistochemistry.

RESULTS

At baseline, negative FasL staining in tumor cells was seen in 10 of 86 (12%) biopsies, whereas intense FasL staining was seen (a) in fewer than 10% of tumor cells in 26 (30%) biopsies; (b) in 11 to 50% of tumor cells in 25 (29%) biopsies; (c) in 51 to 90% of tumor cells in 18 (21%) biopsies; and (d) in >90% of tumor cells in 7 (8%) biopsies. On treatment, tumor FasL expression did not change from baseline levels. Moreover, tumor FasL expression was not correlated with objective response or survival whereas the absolute number of CD4(+), CD8(+), CD56(+), and CD57(+) cells per mm(2) tumor tissue at baseline was significantly higher in responding patients compared with nonresponding patients (P = 0.01, P = 0.008, P = 0.015, and P < 0.001, respectively). During the first course of immunotherapy, the absolute number of CD4(+), CD8(+), and CD57(+) cells per mm(2) tumor tissue was significantly higher in responding patients compared with nonresponding patients (P = 0.034, P < 0.001, and P < 0.001, respectively). However, no correlation was observed between the number of intratumoral lymphocytes and tumor FasL expression level.

CONCLUSION

These observations do not support the hypothesis that FasL tumor "counterattack" has an effect on the clinical outcome in metastatic renal cell carcinoma during IL-2-based immunotherapy.

Synthesis of Selected LeY and KH-1 Analogues: A Medicinal Chemistry Approach to Vaccine Optimization

[structure: see text] As part of our ongoing anticancer vaccine program, we recently found that antibodies generated in response to the KH-1-KLH construct recognized not only KH-1 antigen but also the Lewis Y (Le(y)) antigen as well, with antibody titer levels much higher than those observed after immunization with individual Le(y)-KLH vaccine constructs. In an attempt to explore the structure-antigenic relationship of these carbohydrate epitopes, several analogues of both KH-1 and Le(y) were synthesized. A convergent synthetic approach to the analogues was designed on the basis of well-established glycal methodology, employing a minimum number of building blocks to generate competent antigens with high stereoselectivity and reasonable yield.

Nonmyeloablative stem cell transplantation using lymphoablative rather than myeloablative conditioning in the prefludarabine era by ATG and limiting doses of cyclophosphamide

The feasibility of using lymphoablative rather than myeloablative conditioning for durable engraftment of allogeneic stem cells and subsequent cell therapy with donor lymphocytes was pioneered in the prefludarabine era in patients with resistant lymphoma and metastatic solid tumors. Between July 1995 and August 1996, 15 patients, five males and 10 females, median age 50 (range 20-57) years, were enrolled in a protocol that consisted of different doses of cyclophosphamide (Cy), 50 mg/kg/day for 1, 2, 3 or 4 consecutive days in parallel with a fixed dose of rabbit antithymocyte globulin (ATG) (Fresenius) 10 mg/kg/day for 4 consecutive days. All patients, except one treated with a single dose of Cy, achieved full tri-lineage engraftment and no late graft failure was observed. Only three patients suffered from grade III-IV graft-versus-host disease (GVHD). Three patients out of the 15 survived long term (follow-up >93 to >96 months). We concluded that lymphoablative conditioning with ATG and intermediate-to-high-dose Cy is well tolerated and can result in durable engraftment with acceptable GVHD in heavily pretreated patients with advanced malignancies. Hence, induction of tolerance to donor alloantigens by lymphoablative conditioning while avoiding myeloablative chemotherapy or radiation therapy may serve as a platform for subsequent cell therapy with donor lymphocytes.

Cytokines in cancer immunity and immunotherapy

The concept that the immune system recognizes and controls cancer was first postulated over a century ago, and cancer immunity has continued to be vigorously debated and experimentally tested. Mounting evidence in humans and mice supports the involvement of cytokines in tumor initiation, growth, and metastasis. The idea that the immune system detects stressed, transformed, and frankly malignant cells underpins much of the excitement currently surrounding new cytokine therapies in cancer treatment. In this review, we define the contrasting roles that cytokines play in promoting tumor immunity, inflammation, and carcinogenesis. We also discuss the more promising aspects of clinical cytokine use in cancer patients.

Clinical importance of circulating and cellular expression levels of Fas and Fas ligand in pediatric patients with lymphoproliferative malignancies

Objectives of this study were to determine the extend of soluble Fas (sFas) and soluble FasL (sFasL) at the time of diagnosis and to evaluate its prognostic relevance under chemotherapy in childhood lymphoproliferative malignancies. The authors measured the circulating sFas and sFasL by ELISA in 25 children with newly diagnosed either ALL or NHL, as well as their expression of Fas and FasL at the time of diagnosis and remission. They did not observe any statistically significant difference between the patient group and age-matched healthy controls for sFas levels, whereas sFasL concentration in study population at the time of diagnosis was significantly higher than that in control subjects (1.05 +/- 1.46 vs. 0.36 +/- 0.18 ng/mL, p = .024). At remission the authors observed a significant decrease in the sFasL levels of all patients whose sFasL concentrations were above the minimal detectable level at the time of diagnosis (p = .008). sFasL and Fas/FasL immunohistochemical staining did not have an effect on survival. sFasL may be a marker in monitoring complete remission in children with LPM.

Opposing effects of bovine papillomavirus type 1 E6 and E7 genes on Fas-mediated apoptosis

Programmed cell death (PCD), best exemplified by apoptosis, is a genetically programmed process of cellular destruction that is indispensable for normal development and homeostasis of multicellular organisms. Tumor necrosis factor alpha (TNF) and related cytokines are employed by host defenses to eliminate virally infected cells through induction of apoptosis. Many viruses have evolved specific gene products to modulate this process. We have recently shown that the bovine papillomavirus type 1 (BPV-1) E6 and E7 genes independently sensitize mouse cells to TNF-induced apoptosis. In this report, we investigated the effect of E6 and E7 expression on Fas-mediated apoptosis. In contrast to TNF-mediated apoptosis, E6 and E7 demonstrated opposite effects: while E7 potentiated apoptosis triggered by an agonistic Fas antibody, E6 attenuated the effect. The mitochondrial pathway leading to the activation of caspases appears to be involved in Fas-mediated apoptosis in C127 cells. To further explore the mechanisms by which E6 and E7 modulate Fas-mediated apoptosis, we examined the surface expression of Fas in cells expressing E6 and E7. Significantly, levels of surface Fas expression correlated with the opposing effects of E6 and E7 on Fas-mediated apoptosis. Specifically, while E7 increased the surface expression of Fas, E6 reduced surface Fas expression. Mutational analysis demonstrated a correlation of E6's ability to downregulate surface Fas expression and apoptosis. Since the tumor suppressor p53 can be targeted for degradation by human papillomavirus and has been shown to induce apoptosis by upregulating surface Fas expression, we investigated the role of p53 in BPV-1 E6 and E7 modulation of Fas-mediated apoptosis. Our results demonstrated that the modulatory effects by E6 and E7 could occur in the absence of p53. Interestingly, the reduced Fas protein level on the cell surface is not accompanied by a decrease in total Fas levels in E6-expressing cells. Instead, considerably more Fas protein is found in the cytoplasm of cells expressing E6. These results highlight a novel activity of E6 and E7 that may be involved in viral pathogenesis.

B7-H1 expression on non-small cell lung cancer cells and its relationship with tumor-infiltrating lymphocytes and their PD-1 expression

PURPOSE

B7-H1/PD-L1 (B7-H1) and B7-DC/PD-L2 (B7-DC) are ligands for the receptor PD-1, which is known to negatively regulate T-cell activation. In the present study, we investigated the expression of B7-H1 and B7-DC in tumor specimens of non-small cell lung cancer and their relationships with clinicopathological variables and postoperative survival. Furthermore, we examined the correlation between B7-H1 expression on tumor cells and the number of tumor-infiltrating lymphocytes (TILs) or PD-1 expression on TILs.

EXPERIMENTAL DESIGN

The expression of B7-H1 and B7-DC in 52 surgically resected specimens of non-small cell lung cancer was evaluated immunohistochemically.

RESULTS

Expression of B7-H1 and B7-DC was focally observed in all non-small cell lung cancer tumor specimens. No relationship was found between the expression of B7-H1 or B7-DC and clinicopathological variables or postoperative survival. However, in the same sections evaluated, significantly fewer TILs were identified in B7-H1-positive tumor regions than in B7-H1-negative tumor regions in a subset of five patients (P = 0.01). Moreover, the percentage of TILs expressing PD-1 was significantly lower in B7-H1-positive tumor regions than in B7-H1-negative tumor regions (P = 0.02).

CONCLUSIONS

The expression of B7-H1 on tumor cells in local areas reciprocally correlated with the number of TILs, and this may contribute to negative regulation in antitumor immune responses in non-small cell lung cancer.

FADD adaptor in cancer

FADD (Fas Associated protein with Death Domain) is a key adaptor molecule transmitting the death signal mediated by death receptors. In addition, this multiple functional protein is implicated in survival/proliferation and cell cycle progression. FADD functions are regulated via cellular sublocalization, protein phosphorylation, and inhibitory molecules. In the present review, we focus on the role of the FADD adaptor in cancer. Increasing evidence shows that defects in FADD protein expression are associated with tumor progression both in mice and humans. Better knowledge of the mechanisms leading to regulation of FADD functions will improve understanding of tumor growth and the immune escape mechanisms, and could open a new field for therapeutic interventions.

N/A

N/A

Human cytotoxic T lymphocytes with reduced sensitivity to Fas-induced apoptosis

Effector-memory T cells expressing Fas (Apo-1/CD95) are switched to an apoptotic program by cross-linking with Fas-ligand (FasL). Consequently, tumors that express FasL can induce apoptosis of infiltrating Fas-positive T lymphocytes and subdue any antitumor host immune response. Since Epstein-Barr virus (EBV)-associated tumors such as Hodgkin lymphoma (HL) and nasopharyngeal carcinoma (NPC) express FasL, we determined whether EBV-specific cytotoxic T lymphocytes (EBV-CTLs) could be modified to resist this evasion strategy. We show that long-term down-modulation of Fas can be achieved in EBV-CTLs by transduction with small interfering RNA (siRNA) encoded in a retrovirus. Modified T cells resisted Fas/FasL-mediated apoptosis compared with control cells and showed minimal cleavage of the caspase3 substrate poly(ADP-ribose) polymerase (PARP) protein after Fas engagement. Prolonged Fas stimulation selected a uniformly Fas(low) and FasL resistant population. Removal of responsiveness to this single death signal had no other discernible effects on EBV-CTLs. In particular, it did not lead to their autonomous growth since the modified EBV-CTLs remained polyclonal, and their survival and proliferation retained dependence on antigen-specific stimulation and on the presence of other physiologic growth signals. EBV-CTLs with knocked down Fas should have a selective functional and survival advantage over unmodified EBV-CTLs in the presence of tumors expressing FasL and may be of value for adoptive cellular therapy.

Induction of tolerance using Fas ligand: a double-edged immunomodulator

Apoptosis mediated by Fas ligand (FasL) interaction with Fas receptor plays a pivotal regulatory role in immune homeostasis, immune privilege, and self-tolerance. FasL, therefore, has been extensively exploited as an immunomodulatory agent to induce tolerance to both autoimmune and foreign antigens with conflicting results. Difficulties associated with the use of FasL as a tolerogenic factor may arise from (1) its complex posttranslational regulation, (2) the opposing functions of different forms of FasL, (3) different modes of expression, systemic versus localized and transient versus continuous, (4) the level and duration of expression, (5) the sensitivity of target tissues to Fas/FasL-mediated apoptosis and the efficiency of antigen presentation in these tissues, and (6) the types and levels of cytokines, chemokines, and metalloproteinases in the extracellular milieu of the target tissues. Thus, the effective use of FasL as an immunomodulator to achieve durable antigen-specific immune tolerance requires careful consideration of all of these parameters and the design of treatment regimens that maximize tolerogenic efficacy, while minimizing the non-tolerogenic and toxic functions of this molecule. This review summarizes the current status of FasL as a tolerogenic agent, problems associated with its use as an immunomodulator, and new strategies to improve its therapeutic potential.

FAS and FAS-L expression by tumor cells and lymphocytes in breast carcinomas and their lymph node metastases

FAS receptor (FAS, CD95) and FAS ligand (FAS-L, CD95-L) are complementary members of a particular apoptotic pathway that plays a major role in immune regulation. The activation of FAS-L may trigger cytotoxic mechanisms leading to the death of FAS-expressing cells. Tumor cells and tumor-infiltrating lymphocytes (TIL) may express FAS and FAS-L in various proportions, and their interplay may affect tumor behavior. In the present study, we explored the expression of FAS and FAS-L in 28 mammary carcinomas (19 ductal and 9 lobular) and in their lymph node metastases. The expression of these mediators in immunostained sections was graded and evaluated comparatively between normal and neoplastic mammary epithelium, between tumor cells and TILs, and between mammary carcinoma cells and their lymph node metastases. We demonstrated the coexpression of FAS and FAS-L by breast carcinoma cells and TIL, with FAS expressed more strongly by normal epithelial cells and TIL than tumor cells. FAS-L was better stained on tumor cells than on TIL. There was equal or greater expression of FAS and FAS-L in the primary tumors and their TIL than in the metastatic counterparts. Comparing the expression of FAS with that of FAS-L, we recorded FAS equal or stronger than FAS-L in the primary mammary tumors and the reversal of their expression, FAS-L greater than FAS in the lymph node metastases. These results are consistent with reports of studies with other tumors, suggesting that the upregulated FAS-L indicates an increased ability of tumor cells to induce apoptosis in TIL and in the normal tissues invaded. However, it is understood that the FAS/FAS-L system, although essential for apoptosis, is only a contributing factor to the complex process of tumor invasion and antitumor defense.

Apoptosis-related factors in the epithelial components of dental follicles and dentigerous cysts associated with impacted third molars of the mandible

OBJECTIVE

Radiolucencies adjacent to the crowns of impacted third molars can represent follicular remnants or cysts. To clarify the possible role of apoptosis-related factors in pericoronal odontogenic tissues, expression of Fas, bcl-2, and single-stranded DNA (ssDNA) was examined in epithelial components of dental follicles (DFs) and dentigerous cysts (DCs) associated with impacted third molars of the mandible. The results were compared with immunoreactivity for Ki-67, a marker of cell proliferation.

STUDY DESIGN

Specimens of 80 DFs and 27 DCs were examined immunohistochemically using antibodies against Fas, bcl-2, ssDNA, and Ki-67.

RESULTS

Expression of Fas and ssDNA was detected in superficial epithelial cells of DFs and DCs. Expression of bcl-2 and Ki-67 was found in epithelial cells neighboring the basement membrane. The positive ratio of bcl-2 in DFs was significantly lower than that in DCs. ssDNA-positive cells were slightly more numerous in DFs, while Ki-67-positive cells were slightly more numerous in DCs. In DFs, epithelial tissues with proliferative rete processes showed significantly higher Ki-67 labeling than did those without proliferative rete processes. DFs with marked inflammatory changes showed slightly higher rates of ssDNA and Ki-67 positivity than did DFs without marked inflammation.

CONCLUSIONS

Apoptosis-related factors and proliferative marker differ between DFs and DCs. Apoptosis and cell proliferation may play a role in the pathogenesis of DCs. In DFs, expression of apoptosis-related factors and proliferative marker is most likely modulated by the morphologic characteristics of epithelial components as well as by inflammatory changes.

Colon cancer: genomics and apoptotic events

Colon cancer is the third most common cancer globally. The risk of developing colon cancer is influenced by a number of factors that include age and diet, but is primarily a genetic disease, resulting from oncogene over-expression and tumour suppressor gene inactivation. The induction and progression of the disease is briefly outlined, as are the cellular changes that occur in its progression. While colon cancer is uniformly amenable to surgery if detected at the early stages, advanced carcinomas are usually lethal, with metastases to the liver being the most common cause of death. Oncogenes and genetic mutations that occur in colon cancer are featured. The molecules and signals that act to eradicate or initiate the apoptosis cascade in cancer cells, are elucidated, and these include caspases, Fas, Bax, Bid, APC, antisense hTERT, PUMA, 15-LOX-1, ceramide, butyrate, tributyrin and PPARgamma, whereas the molecules which promote colon cancer cell survival are p53 mutants, Bcl-2, Neu3 and COX-2. Cancer therapies aimed at controlling colon cancer are reviewed briefly.

Roles of CXC chemokines and macrophages in the recruitment of inflammatory cells and tumor rejection induced by Fas/Apo-1 (CD95) ligand-expressing tumor

The role of CD95 ligand (FasL/Apo-1L)-expressing tumors in immunosuppression or immunopotentiation is controversial. CD95L-transfected tumors induce immunopotentiation after vigorous neutrophil infiltration. Thus, the induction of neutrophil infiltration by CD95L seems to play an important role in tumor rejection. The mechanism by which CD95L-expressing tumors cause neutrophil infiltration and antitumor immunity has not been well understood. CXC chemokine receptor 2 (CXCR2) knockout (KO) mice are a powerful tool for studying CXC chemokine-mediated neutrophil infiltration. We investigated the roles of CD95L and chemokines in CD95L-induced antitumor activity by using CXCR2 KO mice and CD95LcDNA-transfected MethA (MethA + CD95L) fibrosarcoma. MethA + CD95L cells were completely rejected in wild-type (WT) and even in KO mice. MethA + CD95L cells injected intraperitoneally (i.p.) induced the recruitment of both neutrophils and macrophages in WT but only macrophages in KO mice, although CXC and CC chemokines were released in both mice. Macrophages incubated with MethA + CD95L cells released CXC and CC chemokines. Macrophages derived from WT and KO but not neutrophils from WT mice induced the recruitment of neutrophils when adoptively i.p. transferred with MethA + CD95L cells into CD95L/CD95-deficient mice. The different recruitment of inflammatory cells between WT and KO mice was attributed to bone marrow (BM) cells by BM transfer experiment. Our results demonstrated that CXC chemokines are essential for neutrophil recruitment and that macrophages but not neutrophils play a critical role in the CD95L-induced infiltration of inflammatory cells and the eradication of CD95L-expressing tumor cells.

Bcl-2 Reduced and Fas Activated by the Inhibition of Stem Cell Factor/KIT Signaling in Murine Melanocyte Precursors

Stem cell factor (SCF) and its receptor, KIT, are essential to the migration and differentiation of melanocytes during embryogenesis. We previously demonstrated that apoptosis is induced by blocking survival function of the SCF/KIT interaction in a mouse neural crest cell (NCC) primary culture. Using the NCCmelb4 cell line, we investigated the occurrence of apoptosis in the cultured cells when KIT receptors were blocked by the monoclonal anti-KIT antibody (ACK2). Apoptosis following treatment with ACK2 was detected by DNA fragmentation assay, in situ apoptosis detection, and electron microscopy. We noted a decrease in extracellular signal-related kinase (ERK) and ribosomal S6 kinase (RSK) protein expression following ACK2 incubation. Western blot analysis and real-time quantitative RT-PCR revealed an apparent time-dependent reduction in Bcl-2 protein levels with respect to ACK2 within the NCCmelb4 cells. In terms of Bax expression, a difference was not found. Fas and caspase8 proteins increased time-dependently in proportion to ACK2 incubation. We noted apoptotic cell death upon addition of ACK2, with evidence of possible involvement of Bcl-2 and Fas in the induction of apoptosis. In contrast, no significant correlation between Fas ligand (Fas-L) expression and ACK2 was found. Fas activation appears to occur independent of Fas-L during ACK2-induced cell death. Therefore, we propose that Fas-L expression in NCCmelb4 cells does not play a major role in facilitating apoptosis. Furthermore, we hypothesize that these molecules combined with SCF/KIT play an important role in regulating the induction of vertebrate NCC apoptosis during embryogenesis.

CD95L mediates tumor counterattack in vitro but induces neutrophil-independent tumor rejection in vivo

Many tumors express CD95L (CD178, FasL, APO-1L) and may thus kill tumor-infiltrating lymphocytes, a phenomenon called tumor counterattack. However, presently it is not clear whether tumor counterattack is a relevant immune escape mechanism. To characterize the effect of CD95L expression of tumor cells on tumor-specific T cells, we established an in vitro system with TCR tg T cells and a model tumor antigen. Preactivated antitumor T cells were able to kill CD95L(-) and CD95L(+) tumor cells. CD95L(+) tumor cells killed activated T cells in vitro and inhibited the expansion of cytotoxic antitumor T cells in mixed lymphocyte tumor reactions. In vivo CD95L expression led to delayed tumor growth or complete tumor rejection. Neutrophils were not responsible for the delayed growth of the CD95L(+) tumors tested. In mice with neutrophils deficient for important cytotoxicity mechanisms (p47phox(-/-) or iNOS(-/-) mice), CD95L(+) tumors grew similarly as in wild-type mice. Incidence and growth rate of CD95L(+) tumors in mice injected with a neutrophil-depleting or an isotype control antibody was the same. In CD95-deficient lpr mice, tumor growth was not altered as compared to wild-type mice. Taken together, CD95L mediated tumor counterattack in vitro, but led to neutrophil-independent tumor rejection in vivo.

Histological expression of tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) in human primary melanoma

AIMS

Tumour necrosis factor-related apoptosis ligand (TRAIL) appears to selectively induce apoptosis in a wide range of cultured malignant cells, including melanoma. This study was designed to attempt to clarify the role of TRAIL in the biology of human melanoma.

METHODS

Tissue sections cut from formalin-fixed, paraffin-embedded tissue blocks of 45 primary cutaneous melanomas were tested for expression of TRAIL using immunohistochemistry. The intensity, pattern of staining and percentage of positively stained tumour cells were evaluated in each melanoma. Breslow thickness, ulcerative state, dermal mitotic rate and the presence of tumour infiltrating lymphocytes were measured/determined in each case. Median follow up for the cohort of patients was 10 months (range 1-18). Survival analysis was conducted using the Kaplan-Meier method. The level of expression of TRAIL was compared with the various histological determinants using the two-tailed Fisher's exact test and the chi2-test.

RESULTS

Overall and disease-free survival were 72 and 48%, respectively, and did not correlate with TRAIL expression. Among the pathological prognostic determinants, only mitotic rate showed a statistically significant correlation with TRAIL expression using the chi2-test (P=0.04).

CONCLUSION

We conclude that TRAIL expression in melanoma defines a more aggressive/proliferative phenotype, either through selection of apoptotic resistant cells or by secondary induction of other factors enhancing proliferation of more malignant cells. Analysis of a larger group of patients with longer follow-up is required to determine whether TRAIL expression correlates with survival of patients.

FLIP overexpression inhibits death receptor-induced apoptosis in malignant mesothelial cells

Tumors have developed several forms of resistance to receptor-induced cell death. Here, we show that malignant mesothelial (MM) cell lines as well as primary MM cells and normal mesothelial (NM) cells express Fas and TNF-related apoptosis-inducing ligand (TRAIL) receptors DR4 and DR5. We found that, although Fas expression levels are comparable, only MM cells are resistant to cell death. Furthermore, MM cells show resistance to TRAIL-induced apoptosis. Caspase-8 (FLICE) is not activated by death receptors triggering in malignant cells whereas it is well activated by nonreceptor stimuli, such as UV radiation. We found that FLIP (FLICE-Inhibitory Protein) is constitutively expressed in all MM cell lines and is more expressed in primary MM cells than in NM cells. Knockdown of FLIP expression in MM cell lines, by a FLIPsiRNA, re-established the normal response to apoptosis induced by Fas or DR4/DR5, which was blocked by pretreatment with the caspase-8 inhibitor z-IETD-fmk. These results indicate that MM cells develop an intrinsic resistance to apoptosis induced by death receptors upregulating the expression of the antiapoptotic protein c-FLIP.

Vitamin C downregulates interleukin-18 production by increasing reactive oxygen intermediate and mitogen-activated protein kinase signalling in B16F10 murine melanoma cells

We recently reported that interleukin-18 (IL-18) is highly expressed in malignant skin tumours such as melanomas, and may play a key role in the malignancy of such tumours. This study was designed to investigate the mechanisms of IL-18 regulation by vitamin C in B16F10 murine melanoma cells. Cells were treated with vitamin C, and the expression of IL-18 was measured by reverse transcription-polymerase chain reaction and intracellular flow cytometry analysis. Decreased IL-18 production and a significant reduction in IL-18 mRNA transcript were detected in cells treated with vitamin C. The effect of vitamin C treatment was blocked by the antioxidant N-acetyl-L-cysteine, suggesting that vitamin C affects IL-18 expression by up-regulating intracellular reactive oxygen intermediate (ROI) levels. To investigate whether the mitogen-activated protein kinase (MAPK) signalling pathway is involved in the downregulation of IL-18 production, cells were pretreated with SB203580, an inhibitor of p38 MAPK, prior to the addition of vitamin C. This pretreatment blocked the decrease in IL-18 production. However, vitamin C treatment enhanced the expression of phosphorylated p38 MAPK. Taken together, we conclude that vitamin C increases intracellular ROI levels, and regulates IL-18 production through the MAPK signalling pathway.