The Fas Counterattack: A Molecular Mechanism of Tumor Immune Privilege

TRAIL-dependent apoptosis of peritoneal mesothelial cells by NK cells promotes ovarian cancer invasion

A crucial requirement for metastasis formation in ovarian high-grade serous carcinoma (HGSC) is the disruption of the protective peritoneal mesothelium. Using co-culture systems of primary human cells, we discovered that tumor-associated NK cells induce TRAIL-dependent apoptosis in mesothelial cells via death receptors DR4 and DR5 upon encounter with activated T cells. Upregulation of TRAIL expression in NK cells concomitant with enhanced cytotoxicity toward mesothelial cells was driven predominantly by T-cell-derived TNFα, as shown by affinity proteomics-based analysis of the T cell secretome in conjunction with functional studies. Consistent with these findings, we detected apoptotic mesothelial cells in the peritoneal fluid of HGSC patients. In contrast to mesothelial cells, HGSC cells express negligible levels of both DR4 and DR5 and are TRAIL resistant, indicating cell-type-selective killing by NK cells. Our data point to a cooperative action of T and NK in breaching the mesothelial barrier in HGSC patients.

MMP-7 marks severe pancreatic cancer and alters tumor cell signaling by proteolytic release of ectodomains

Pancreatic cancer incurs the worst survival rate of the major cancers. High levels of the protease matrix metalloproteinase-7 (MMP-7) in circulation correlate with poor prognosis and limited survival of patients. MMP-7 is required for a key path of pancreatic tumorigenesis in mice and is present throughout tumor progression. Enhancements to chemotherapies are needed for increasing the number of pancreatic tumors that can be removed and for preventing relapses after surgery. With these ends in mind, selective inhibition of MMP-7 may be worth investigation. An anti-MMP-7 monoclonal antibody was recently shown to increase the susceptibility of several pancreatic cancer cell lines to chemotherapeutics, increase their apoptosis, and decrease their migration. MMP-7 activities are most apparent at the surfaces of innate immune, epithelial, and tumor cells. Proteolytic shedding of multiple protein ectodomains by MMP-7 from such cell surfaces influence apoptosis, proliferation, migration, and invasion. These activities warrant targeting of MMP-7 selectively in pancreatic cancer and other tumors of mucosal epithelia. Competitive and non-competitive modes of MMP-7 inhibition are discussed.

Mathematical model of tumor-immune surveillance

We present a novel mathematical model involving various immune cell populations and tumor cell populations. The model describes how tumor cells evolve and survive the brief encounter with the immune system mediated by natural killer (NK) cells and the activated CD8(+) cytotoxic T lymphocytes (CTLs). The model is composed of ordinary differential equations describing the interactions between these important immune lymphocytes and various tumor cell populations. Based on up-to-date knowledge of immune evasion and rational considerations, the model is designed to illustrate how tumors evade both arms of host immunity (i.e. innate and adaptive immunity). The model predicts that (a) an influx of an external source of NK cells might play a crucial role in enhancing NK-cell immune surveillance; (b) the host immune system alone is not fully effective against progression of tumor cells; (c) the development of immunoresistance by tumor cells is inevitable in tumor immune surveillance. Our model also supports the importance of infiltrating NK cells in tumor immune surveillance, which can be enhanced by NK cell-based immunotherapeutic approaches.

The emerging role of viruses in the treatment of solid tumours

There is increasing optimism for the use of non-pathogenic viruses in the treatment of many cancers. Initial interest in oncolytic virotherapy was based on the observation of an occasional clinical resolution of a lymphoma after a systemic viral infection. In many cancers, by comparison with normal tissues, the competency of the cellular anti-viral mechanism is impaired, thus creating an exploitable difference between the tumour and normal cells, as an unimpeded viral proliferation in cancer cells is eventually cytocidal. In addition to their oncolytic capability, these particular viruses may be engineered to facilitate gene delivery to tumour cells to produce therapeutic effects such as cytokine secretion and anti -tumour immune responses prior to the eventual cytolysis. There is now promising clinical experience with these viral strategies, particularly as part of multimodal studies, and already several clinical trials are in progress. The limitations of standard cancer chemotherapies, including their lack of specificity with consequent collateral toxicity and the development of cross-resistance, do not appear to apply to viral-based therapies. Furthermore, virotherapy frequently restores chemoradiosensitivity to resistant tumours and has also demonstrated efficacy against cancers that historically have a dismal prognosis. While there is cause for optimism, through continued improvements in the efficiency and safety of systemic delivery, through the emergence of alternative viral agents and through favourable clinical experiences, clinical trials as part of multimodal protocols will be necessary to define clinical utility. Significant progress has been made and this is now a major research area with an increasing annual bibliography.

Expression of FasL in squamous cell carcinomas of the cervix and cervical intraepithelial neoplasia and its role in tumor escape mechanism

BACKGROUND

To date, several mechanisms have been described by which malignant cells escape from the immune system. One of these is through the expression of FasL. The authors hypothesized that the Fas/FasL interaction enables cervical carcinoma cells to induce apoptosis of the cells of the immune system and thereby escape from them.

METHODS

The authors tested the expression of FASL on the surface of cervical carcinoma tissues. Next, they stained the same cervical tissues with anti-human leukocyte common antigen and TUNEL to identify apoptotic cells. An in vitro functional assay was then done to test if the FASL expressed on the surface of cervical carcinoma cell lines was or was not responsible for inducing apoptosis in T-cells. Finally, they compared the expression of FASL on normal and dysplastic cervical tissues.

RESULTS

Ninety-four percent of the cervical carcinoma tissues the authors tested expressed FasL and the majority of the apoptotic cells in the specimens were leukocytes with very few tumor cells. In the in vitro functional assay, only the Fasl expressing cell line and not the Fasl negative cell line was able to induce apoptosis of the Fas-expressing Jurkat cells. On examining the normal cervical tissues, the authors found that the expression of Fasl was confined to the basal cell layer with loss of expression observed in the suprabasal layers, which made it an immune privileged site. Conversely, there was persistent expression of FasL in the dysplastic layers in cervical dysplasia and squamous cell carcinoma specimens.

CONCLUSIONS

The findings of the current study support the authors' hypothesis that persistent expression of FasL plays a role in the ability of cervical carcinoma cells to escape from the immune system.

Prognostic significance of Bax and Fas Ligand in erionite and asbestos induced Turkish malignant pleural mesothelioma

Environmentally exposed erionite is a potent and unique inducer of malignant pleural mesothelioma (MPM) in Central Anatolia in Turkey. Previous studies have shown that erionite induced MPM has different biological behavior than asbestos induced MPM. Although impaired apoptosis has been implicated in tumor biology, the relationship between the type of environmental exposure and apoptosis has not yet been evaluated in MPM. The purpose of this study was to determine the expression of apoptosis regulating proteins and their prognostic significance in erionite and asbestos induced MPM. Thirty-five patients with MPM (16 erionite and 19 asbestos induced), and 17 patients with adenocarcinoma were comparatively evaluated. Expression of Bcl-2, Bax, Fas and Fas Ligand, were assessed by immunohistochemistry. Bcl-2 and Fas did not stain in almost all specimens. The staining extension of Bax was 13.75 +/- 19.27%, 5.89 +/- 14.51% and 7.38 +/- 14.53% for erionite and asbestos induced MPM and adenocarcinoma, respectively (p = 0.566). The staining extension of Fas Ligand was 26.87 +/- 31.87%, 46.10 +/- 37.30% and 26.47 +/- 23.23% for erionite and asbestos induced MPM, and adenocarcinoma, respectively (p = 0.123). Bax negative patients in erionite group had longer survival than Bax positive patients (18 months versus 14 months) (p = 0.06). Fas Ligand positive patients showed statistically better survival than Fas Ligand negative patients in all MPM group (15 months versus 12 months) (p = 0.05). Although all proteins expressed in similar extension in all samples, Bax staining displayed an inverse relation with survival in erionite group. This may implicate a difference in Bax functioning in erionite induced MPM. However, Fas Ligand may be functionally intact to reduce tumor survival.

Fas ligand expression in colon cancer: A possible mechanism of tumor immune privilege

AIM: To detect the expression of Fas ligand (FasL) in colon cancer tissues and cell lines and analyze the function of FasL-expressing colon cancer cells in inducing Fas-sensitive T lymphocyte apoptosis.

METHODS: Ninety surgically resected colon cancer tissues and 15 hepatic metastasis specimens were investigated by immunohistochemical method with normal colon mucosa and colon adenoma as control. The relationship between FasL expression and pathologic features was also analyzed. FasL expression of 4 colon cancer cell lines, SW620, Lovo, LS-174T and SW1116, were detected by Western blotting assay. The function of FasL expressed on colon cancer cells was determined by coculture assay with Jurkat T lymphocytes, the apoptotic rate of which was detected by flow cytometry assay.

RESULTS: Fifty-six (62.22%) cases of all the 90 colon cancer tissues and all (100%) the liver metastasis specimens expressed FasL, significantly higher than normal colon mucosa and colonic adenoma. Higher expression of FasL was found in more advanced stage of colon cancer and in cancer tissues with lymphatic or hepatic metastasis. All the colon cancer cell lines were found to express FasL. After coculture with the SW1116 cells for 24 h with an effector: target ratio 10:1, the rate of apoptosis of Jurkat cells rose from 1.9% to 21.0%.

CONCLUSION: The expression of FasL is upregulated in colon cancer and the functionally expressed FasL can induce apoptosis of Fas-expressing T lymphocytes.

The Roles of Thymidylate Synthase and p53 in Regulating Fas-Mediated Apoptosis in Response to Antimetabolites

Fas (CD95/Apo-1) is a member of the tumor necrosis factor receptor family. Receptor binding results in activation of caspase 8, leading to activation of proapoptotic downstream molecules. We found that expression of Fas was up-regulated >10-fold in MCF-7 breast and HCT116 and RKO colon cancer cell lines after treatment with IC(60) doses of 5-fluorouracil (5-FU) and raltitrexed (RTX). Combined treatment with the agonistic Fas antibody CH-11 and either 5-FU or RTX resulted in a highly synergistic induction of apoptosis in these cell lines. Similar results were obtained for another antifolate, Alimta. Induction of thymidylate synthase expression inhibited Fas induction in response to RTX and Alimta, but not in response to 5-FU. Furthermore, thymidylate synthase induction abrogated the synergy between CH-11 and both antifolates but had no effect on the synergistic interaction between 5-FU and CH-11. Inactivation of p53 in MCF-7 and HCT116 cell lines blocked 5-FU- and antifolate-mediated up-regulation of Fas. Furthermore, Fas was not up-regulated in response to 5-FU or antifolates in the p53-mutant H630 colon cancer cell line. Lack of Fas up-regulation in the p53-null and -mutant lines abolished the synergistic interaction between 5-FU and CH-11. Interestingly, synergy was still observed between the antifolates and CH-11 in the p53-null HCT116 and p53-mutant H630 cell lines, although this was significantly reduced compared with the p53 wild-type cell lines. Our results indicate that Fas is an important mediator of apoptosis in response to both 5-FU and antifolates.

The human melanoma cell line MelJuSo secretes bioactive FasL and APO2L/TRAIL on the surface of microvesicles. Possible contribution to tumor counterattack

Tumor cells have developed multiple mechanisms to evade control by the immune system. Tumoral cells expressing Fas ligand (FasL) have been proposed to "counterattack" against activated antitumoral effector immune cells, although some authors have indicated that FasL is not expressed on the surface of the same tumors, such in the case of melanoma cells. However, other factors could be implicated, such as the balance of soluble versus membrane-bound forms or the secretion of death ligands on the surface of microvesicles, as described previously by our group in human T cells. In the present study, we analyzed the expression and secretion of FasL and APO2 ligand (APO2L)/TRAIL in the human melanoma cell line MelJuSo. We have observed the expression of preformed FasL and APO2L/TRAIL in these cells, their secretion associated with microvesicles upon melanoma activation with PHA or with alpha-melanocyte stimulating hormone (alpha-MSH), and the toxicity of these microvesicles against normal human T cell blasts. We have also observed that the mechanism of secretion of FasL and APO2L/TRAIL from melanoma cells is depending both on microtubules and actin filaments. From these data, it can be concluded that the MelJuSo melanoma cell line has the possibility to "counterattack" against activated immune effector cells. However, the in vivo outcome seems more complex since it has been also described that FasL expressed in tumors has a proinflammatory effect.

Tumor-induced death of immune cells: its mechanisms and consequences

FasL is a death-inducing as well as pro-inflammatory molecule. The seemingly opposing consequences of Fas/FasL interactions appear to be dependent on the context of the tumor or tissue microenvironment. The term 'contextual' has been coined to describe cellular and molecular events that may be opposing, yet are mediated by the engagement of the same receptor-ligand pair. Because Fas is one of the death-inducing receptors, its ligand is dangerous. Hence, the availability of FasL for cross-linking of the receptor has to be extremely carefully regulated. Different levels of control appear to exist, some involving cell membrane-associated MMPs and others depending on cytokines released from neighboring cells. In tumors, which shape their microenvironment to make it unwelcome to immune effector cells, FasL is used to kill infiltrating cells without damage to the tumor, which develops multiple means of hiding/inhibiting the death pathway. On the other hand, in situations provoking inflammatory responses such as allograft rejection, infection, and tissue necrosis, FasL assumes the role of attractant for inflammatory cells. In these situations, FasL acts in conjunction with other cytokines, and its effects might be modified in the context of unfolding events. When put in the context of biologic interactions that take place at the tumor site, the Fas/FasL pathway emerges as a molecular mechanism, which contributes to immune privilege and tumor escape, but which can also enhance anti-tumor inflammatory responses. FasL, like many cytokines, is pleiotropic. It is also worth bearing in mind that other molecular players, including the other known members of the TNF family, almost certainly participate in establishing immune privilege status of tumors. While a broad body of new information has contributed to clarifying the dual role of FasL in the tumor biology, much remains to be learned about molecular mechanisms that control its effects in the tumor and in normal tissues.

Fas ligand expression and depletion of T-cell infiltration in astrocytic tumors

Fas (APO-1/CD95) ligand (FasL) and its receptor, Fas, play a key role in the regulation of apoptosis in the immune system. FasL acts as a cytotoxic effector molecule to Fas-expressing malignant tumor cells; however, it has recently been suggested that FasL also acts as a possible mediator of tumor immune privilege. We studied FasL expression in glioblastoma cell lines and a series of human glioma specimens by Western blotting and immunohistochemistry. In addition, quantitative analysis of T-cell infiltration in these tumors was performed. FasL expression was seen in all cell lines and in 9 of 14 specimens by Western blotting and immunohistochemistry. The distribution of FasL was recognized in the cytoplasm of tumor cells (5 of 9) and in the vascular endothelium (4 of 9). Both types of FasL expression were associated with a significant reduction (p < 0.05) in T-cell infiltration when compared with FasL-negative areas within the same tumor or FasL-negative specimens. Since T-cell apoptosis could be induced by FasL-expressing tumor cells, the present findings suggest that apoptosis induction by FasL expressed on tumor cells and/or vascular endothelium might be one mechanism for T-cell depletion in astrocytic tumor tissues.

Alterations of Fas (APO-1/CD 95) gene and its relationship with p53 in non small cell lung cancer

The Fas (APO-1/CD95) system regulates a number of physiological and pathological processes of cell death. The ligand for Fas induces apoptosis by interacting with a transmembrane cell surface Fas receptor. The key role of the Fas system has been studied mostly in the immune system, but Fas mutations, one of the possible mechanisms for resistance to apoptosis signaling, may be involved in the pathogenesis of non-lymphoid malignancies as well. To better understand the potential involvement of Fas system in non-small cell lung cancer (NSCLC) we evaluated Fas and Fas-ligand mRNA expression by polymerase chain reaction in 102 tumor samples and in 44 normal surrounding tissues. Although over 60% of the human NSCLC analysed expressed both genes, they seem to be unable to induce apoptosis in vivo by autocrine suicide. In this regard, we investigated in 79 cases, the promoter and the entire coding region of the Fas gene by polymerase chain reaction, single strand conformation polymorphism and DNA sequencing for detecting putative alterations. Sixteen tumors (20.25 %) were found to have Fas alterations, in promoter and/or exon region. In all cases samples carried heterozygous alterations and mostly showed simultaneous mutations of p53 gene. Moreover, the quantitative analysis of Fas mRNA expression showed high levels of Fas messenger associated with p53 wild-type status alone. Taken together, these findings point to an involvement of Fas/Fas-ligand system in the development of NSCLC, suggesting that the loss of its apoptotic function might be linked to p53 alterations which contribute to the self-maintenance of cancer cells.

Expression of Fas and Fas ligand in uveal melanoma: biological implication and prognostic value

The interaction between Fas and Fas ligand is one possible immune escape mechanism used by tumour cells. In the present study, melanoma tissue from 103 patients who underwent enucleation for malignant uveal melanoma (iris melanomas excluded) was stained by immunohistochemistry with monoclonal antibodies specific for Fas, Fas ligand, CD3, CD8, and CD68. Histological and clinical data for these tumours were assessed. Both Fas and Fas ligand were detected in uveal melanomas. Cells of the monocyte/macrophage lineage rather than T-cells were the predominant group of tumour-infiltrating cells. The metastasis-free 5-year survival rates in the univariate analyses were considerably lower in patients with tumours that lacked Fas ligand expression (< 35% of the tumour cells), in the presence of more than 50 CD8-positive cells in 20 high-power fields and in the presence of more than 100 CD3-positive cells in 20 high-power fields. Fas and Fas ligand expression was associated with scleral infiltration. After adjustment for scleral infiltration, the predictive value of both Fas and Fas ligand expression was markedly decreased. In addition, the CD3- and CD8-positive cell count was positively associated with the histological cell type. Cox proportional hazards models showed that the presence of CD3- and CD8-positive cells was not an independent prognostic factor after adjusting for histological cell type. This preliminary observation deserves further investigation, which may shed more light on the immune escape mechanisms of this tumour and thus enable novel therapeutic strategies. The clinical relevance of this observation is limited, as more predictive parameters have been described for uveal melanoma.

Apoptosis, proliferation, and Fas (APO-1, CD95)/Fas ligand expression in medullary carcinoma of the breast

Medullary carcinoma (MC) of the breast is a unique subtype of infiltrating ductal carcinoma that is characterized by a prominent lymphoid infiltrate and improved prognosis. Activated granzyme B(+)/CD8(+) cytotoxic T-lymphocytes (CTLs) infiltrating tumour cell nests constitute a major subset within the lymphoid infiltrate. As CTLs destroy target tumour cells by triggering apoptosis, it would be of interest to determine whether the apoptotic rate in MC is increased. This study evaluates the extent of apoptosis in relation to Fas (APO-1, CD95)/Fas ligand (FasL) expression in MC. Fourteen cases of typical MC (TMC) and 15 cases of atypical MC (AMC) classified according to the Ridolfi criteria, as well as 19 cases of poorly differentiated infiltrating ductal carcinoma (PDC) were evaluated. The apoptotic index (AI) was assessed by the TUNEL method on paraffin-embedded tissue. Cell proliferation was evaluated immunohistochemically by PCNA staining. The level of Fas/FasL expression was determined semiquantitatively by immunohistochemistry using a four-grade scoring system. The AI was significantly increased in TMC and AMC as opposed to the PDC subgroup (2.2+/-0.8, 2.1+/-0.8, and 1.3+/-0.6, respectively; p<0.05). A significant proportion (31.8+/-7.9% in TMC and 25.8+/-9.7% in AMC) of the apoptotic tumour cells within tumour nests were in close contact with CD3(+) lymphocytes. Increased apoptosis was not accompanied by increased proliferation of tumour cells. The extent of Fas expression did not differ between the three subgroups. FasL was expressed both by tumour infiltrating lymphocytes in MC and by tumour epithelium in all three subgroups. The observation that the majority of MCs express Fas and are infiltrated by lymphocytes expressing FasL suggests that increased apoptosis in MC is mediated by Fas/FasL. However, our observation that the majority of MCs also express FasL and the fact that tumours co-expressing Fas and FasL did not show increased apoptosis suggest that there may be additional cytotoxic pathways that lead to tumour apoptosis in MC.

Release from apoptosis correlates with tumor progression in the AKR lymphoma

Disturbance of apoptosis is an established factor in tumorigenesis. The role of apoptosis in tumor progression is not yet clear. In the present study we compared the tendency to spontaneous apoptosis (and the proliferative capacity) of tumor cells derived from primary (PT) and metastatic tumor (MT) cells of several AKR lymphoma variants. Apoptosis-related gene expression was also compared. Our results indicate that release from apoptosis has a role in the tumor progression of this T cell lymphoma. At the cellular level, a markedly lower apoptotic tendency was observed in MT than in PT cells. The existence of macrophages only in PT also supports the presence of apoptotic cells in local but not in MTs. By contrast, proliferative capacity does not determine tumor aggressiveness in this system. At the molecular level, we found a higher staining intensity for bcl-2 in MT than in PT cells, suggesting that bcl-2 might be responsible for the reduced apoptosis in MT compared to PT cells. Evidence for p53 overexpression was found in the MT cells of one of the variants but in none of the PT. Comparison of Fas receptor, unexpectedly showed an increased expression in MT versus PT cells, possibly indicating resistance to Fas-induced apoptosis in the MT cells.

Altered mechanisms of apoptosis in colon cancer: Fas resistance and counterattack in the tumor-immune conflict

Fas (CD95/APO-1) is a cell surface "death receptor" that mediates apoptosis upon engagement by its ligand, FasL. Fas-mediated apoptosis of lymphocytes normally serves immunoregulatory roles, including tolerance acquisition, immune response termination, and maintenance of immune privilege in certain organs. Colon tumors can exploit this lymphocyte death program by expressing FasL. This may enable colon tumors to mount a "Fas counterattack" against antitumor lymphocytes, impairing antitumor immune responses. FasL-expressing colon tumor-derived cell lines can trigger Fas-mediated apoptosis of cocultured T cells in vitro. FasL expressed in esophageal cancer has been significantly associated with apoptosis and depletion of tumor-infiltrating lymphocytes (TIL) in vivo. FasL may also facilitate metastatic colonization of Fas-sensitive organs such as the liver, by inducing apoptosis of target organ cells. Normal colonic epithelial cells express Fas and are relatively sensitive to Fas-mediated apoptosis. By contrast, colon tumor-derived cell lines are usually resistant to induction of Fas-mediated apoptosis, and colon cancer cells frequently coexpress Fas and FasL. The mechanisms allowing resistance to Fas-mediated apoptosis are complex, and defects have been identified at several levels of Fas signal transduction. The "Bcl-2 rheostat" may be pitched against apoptosis in colon cancer, inasmuch as overexpression of Bcl-2, downregulation of Bak, and mutation of Bax are common defects in colon tumors. Caspase-1 is also downregulated in colon cancer. The high frequency of p53 mutations in late-stage cancers may also inhibit Fas signaling. Fundamental defects in apoptosis signaling may contribute to both immuno- and chemoresistance in colon cancer and allow expression of FasL to counterattack antitumor lymphocytes.

Proinflammatory consequences of transgenic fas ligand expression in the heart

Expression of Fas ligand (FasL) renders certain tissues immune privileged, but its expression in other tissues can result in severe neutrophil infiltration and tissue destruction. The consequences of enforced FasL expression in striated muscle is particularly controversial. To create a stable reproducible pattern of cardiomyocyte-specific FasL expression, transgenic (Tg) mice were generated that express murine FasL specifically in the heart, where it is not normally expressed. Tg animals are healthy and indistinguishable from nontransgenic littermates. FasL expression in the heart does result in mild leukocyte infiltration, but despite coexpression of Fas and FasL in Tg hearts, neither myocardial tissue apoptosis nor necrosis accompanies the leukocyte infiltration. Instead of tissue destruction, FasL Tg hearts develop mild interstitial fibrosis, functional changes, and cardiac hypertrophy, with corresponding molecular changes in gene expression. Induced expression of the cytokines TNF-alpha, IL-1beta, IL-6, and TGF-beta accompanies these proinflammatory changes. The histologic, functional, and molecular proinflammatory consequences of cardiac FasL expression are transgene-dose dependent. Thus, coexpression of Fas and FasL in the heart results in leukocyte infiltration and hypertrophy, but without the severe tissue destruction observed in other examples of FasL-directed proinflammation. The data suggest that the FasL expression level and other tissue-specific microenvironmental factors can modulate the proinflammatory consequences of FasL.

Selection of metastatic tumour phenotypes by host immune systems

Metastasis and the processes underlying this phenomenon make epithelial cancers so malignant. Local control of cancers by surgery is sometimes possible but locoregional and distant recurrence commonly lead to the failure of treatment with ensuing morbidity and mortality. Tumour cells express a range of new antigens during growth and there are opportunities for the host immune system to interact with these antigens. This immune interaction eliminates the tumour or allows selection of phenotypic variants. Cell phenotypes selected by an incomplete immune response resemble the cell type commonly associated with metastases. Thus we propose that the host immune system may be responsible for selection of this phenotype and progression of the disease.

Resistance to Fas (APO-1/CD95)-mediated apoptosis and expression of Fas ligand in esophageal cancer: the Fas counterattack

The mechanisms by which esophageal tumors escape immunologic recognition and clearance are only partly understood at the molecular level. Esophageal cancers have been shown to evade host recognition by down-regulation of antigen presentation and production of immunosuppressive factors. Recently, two independent reports have shown that esophageal tumor cells abundantly express Fas ligand (FasL) in vivo. As the triggering agonist for Fas receptor (Fas or APO-1/CD95)-mediated apoptosis of lymphocytes, FasL normally plays immune down-regulatory roles, including activation-induced cell death of T and B cells, as well as maintaining immune privilege in certain organs. Fas ligand expressed by esophageal cell lines has been shown to induce apoptosis of cocultured Fas-sensitive lymphoid cells in vitro. FasL expression by esophageal carcinomas in vivo has been associated with significantly reduced tumor-infiltrating lymphocytes (TILs) in FasL-positive tumor nests, concomitant with significantly increased TIL apoptosis in these nests. These studies support a 'Fas counterattack' mechanism of immune escape in esophageal cancer. By expressing functional Fas ligand, esophageal cancer cells can deplete antitumor lymphocytes by inducing apoptosis. To express functional FasL, esophageal carcinomas also acquire molecular mechanisms to resist autocrine Fas-mediated apoptosis of tumor cells.

Fas ligand and Fas receptor are coexpressed in normal human esophageal epithelium: a potential mechanism of apoptotic epithelial turnover

Fas (CD95/Apo-1) receptor (FasR) is a cell-surface receptor that mediates apoptotic cell death upon triggering by Fas ligand (FasL). We sought to determine whether normal human esophageal epithelial cells express FasL and/or FasR and whether their localization is consistent with a role in the turnover of normal esophageal epithelium. Normal esophageal epithelium was immunohistochemically positive for FasL in upper prickle cell layers and in mature squamous cells, but the proliferative basal layer was negative. FasL mRNA was detected in the same epithelial cell layers by in situ hybridization. Co-localization of FasL mRNA and protein therefore confirmed that FasL expression is induced in esophageal epithelial cells as they reach terminal differentiation. FasR was immunohistochemically detected throughout the esophageal epithelium. Positive TUNEL (terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling) staining confirmed cell death of the FasL and FasR coexpressing mature epithelial cells. CD45-positive immunocytes were notably absent from FasL-expressing upper epithelial layers. The findings are consistent with a contributory role for Fas-mediated autocrine suicide or paracrine fratricide in the apoptotic turnover of normal esophageal epithelium.

Apoptosis and tumorigenesis in human cholangiocarcinoma cells. Involvement of Fas/APO-1 (CD95) and calmodulin

We have previously demonstrated that tamoxifen inhibits the growth of human cholangiocarcinoma cells in culture and inhibits tumor growth when cells are injected into nude mice. However, the mechanism of action of tamoxifen remains unknown. Here we demonstrate that tamoxifen and trifluoperazine, both potent calmodulin antagonists, induce apoptosis in vitro, probably acting via the Fas system, in human cholangiocarcinoma cells. Human cholangiocarcinoma cell lines heterogeneously express Fas antigen on their surface. Fas-negative and Fas-positive surface-expressing cells were isolated, cloned, and cultured. Fas antibody, tamoxifen, and trifluoperazine induced dose-dependent apoptosis only in Fas-positive cells; Fas-negative cells were unaffected. Furthermore, apoptosis induced by tamoxifen in Fas-positive cells was blocked by an inhibitory Fas antibody. Tamoxifen was not acting through an anti-estrogenic mechanism, because neither Fas-negative nor Fas-positive cells expressed estrogen receptors and the pure anti-estrogen compound, ICI 182780, did not induce apoptosis in either cell line. Fas-negative cells, but not Fas-positive cells, were able to produce tumors when subcutaneously injected into nude mice. These findings suggest Fas may be a candidate oncogene involved in the pathogenesis of cholangiocarcinoma. Furthermore, the similarity between the pro-apoptotic effects of tamoxifen and trifluoperazine support an underlying molecular mechanism for Fas-mediated apoptosis that involves calmodulin.

Expression of Fas (CD95/APO-1) ligand by human breast cancers: significance for tumor immune privilege

Breast cancers have been shown to elicit tumor-specific immune responses. As in other types of cancer, the antitumor immune response fails to contain breast tumor growth, and a reduction in both the quantity and cytotoxic effectiveness of tumor-infiltrating lymphocytes (TILs) is associated with a poorer prognosis. Fas ligand (FasL) induces apoptotic death of activated lymphocytes that express its cell surface receptor, FasR (CD95/APO-1). FasL-mediated apoptosis of activated lymphocytes contributes to normal immune downregulation through its roles in tolerance acquisition, immune response termination, and maintenance of immune privilege in the eye, testis, and fetus. In this report, we demonstrate that breast carcinomas express FasL. Using in situ hybridization and immunohistochemistry, we show that breast tumors constitutively express FasL at both the mRNA and protein levels, respectively. FasL expression is prevalent in breast cancer: 100% of breast tumors (17 of 17) were found to express FasL, and expression occurred over more than 50% of the tumor area in all cases. By immunohistochemistry, FasR was found to be coexpressed with FasL throughout large areas of all the breast tumors. This suggests that the tumor cells had acquired intracellular defects in FasL-mediated apoptotic signaling. FasL and FasR expression were independent of tumor type or infiltrative capacity. FasL expressed by tumor cells has previously been shown to kill Fas-sensitive lymphoid cells in vitro and has been associated with apoptosis of TILs in vivo. We conclude that mammary carcinomas express FasL in vivo as a potential inhibitor of the antitumor immune response.

Prolonged neoadjuvant treatment in locally advanced tumours: a novel concept based on biological considerations

BACKGROUND

Neoadjuvant chemotherapy is increasingly applied in patients with locally advanced cancers of many tumour types. Usually three cycles of chemotherapy are administered to reduce the tumour size prior to local therapy, and another three cycles thereafter. The chemotherapy certainly contributes to the improved outcome of this approach. However, biological factors within the primary tumour have been neglected, while they might also contribute to the eradication of micrometastases. We believe that the neoadjuvant strategy can be improved by optimally exploiting certain biological factors inherent to the primary tumour. In a group of patients with locally advanced breast cancer (LABC) we studied this concept. Recently we described the clinical results of this phase II study in patients with LABC treated with neoadjuvant chemotherapy plus granulocyte-macrophage colony-stimulating factor (GM-CSF). A remarkable good response and survival was seen. In contrast to other studies we applied six cycles of neoadjuvant treatment in stead of a sandwich approach consisting of three cycles before and three cycles after local therapy, leaving the primary tumour and draining lymph nodes in situ for a prolonged period. In addition, GM-CSF was administered as a haematopoietic growth factor in stead of granulocyte colony-stimulating factor (G-CSF) as GM-CSF has also immuno-stimulating properties. Our findings definitely warrant further exploration of prolonged neoadjuvant systemic treatment in combination with GM-CSF in other high risk primary tumours.

HYPOTHESES

The promising results of our study may be attributable to two potential biological phenomena. Firstly, the conservation of the tumour and its draining lymph nodes may prove to be an essential part of this approach, with particular emphasis on the activation of tumour specific cytotoxic T cells. Secondly, circulating angiogenesis inhibitors originating from the primary tumour may enhance the effect of chemotherapy on micrometastases.

CD95 ligand (CD95L) in normal human lymphoid tissues: a subset of plasma cells are prominent producers of CD95L

CD95(Fas/APO-1)-ligand (CD95L) mediates apoptosis by trimerization of the CD95 receptor on the surface of sensitive cells. In vitro studies have shown CD95L expression mainly by activated T cells and suggested a role for CD95L in the regulation of immune responses. Little is known, however, about the cellular distribution of CD95L in situ in the normal human immune system. We investigated CD95L expression in tissue sections of the thymus, lymph node, spleen, tonsil, and gastrointestinal tract using in situ hybridization and two monoclonal antibodies. In all these organs, cells expressing CD95L message and protein were scarce and comprised scattered lymphocytes, rare nonlymphoid cells, and a subset of epithelioid endothelial cells. Surprisingly, a subset of plasma cells turned out to be the most prominent producers of CD95L, matching the reports on CD95L in myeloma cells. CD95L+ plasma cells were most numerous in the mucosa-associated lymphoid tissue. This also applied to acquired mucosa-associated lymphoid tissue in chronic gastritis in which CD95L+ plasma cells were found scattered in the lamina propria. Our data suggest that plasma cells as yet may be neglected modulators of immune responses.

Fas ligand expression in primary colon adenocarcinomas: evidence that the Fas counterattack is a prevalent mechanism of immune evasion in human colon cancer

Fas ligand (FasL) kills sensitive Fas receptor (FasR)-bearing cells by inducing apoptosis. FasL expressed by non-lymphoid cells within the eye and the testis mediates immune privilege by inducing apoptosis of Fas-sensitive infiltrating pro-inflammatory immune effector cells. It has previously been demonstrated by the present authors that the colon cancer cell SW620 expresses FasL and can kill lymphoid cells by Fas-mediated apoptosis in vitro. This 'Fas counterattack' was subsequently confirmed by others as a potential mechanism of immune privilege in various malignancies. The aim of the present study was to ascertain the prevalence of FasL expression in human colon cancer and to confirm that neoplastic colonic epithelial cells express FasL in vivo. The study of FasL expression by colon cancer cell lines was extended: it was shown that seven of eight colon adenocarcinoma cell lines expressed FasL mRNA, using reverse transcription-polymerase chain reaction (RT-PCR). Prevalent expression of FasL was confirmed in vivo: all the resected colonic tumours examined (31/31) were found to express FasL. In the tumours, FasL were co-localized to neoplastic colonic epithelial cells, using immunohistochemistry and in situ hybridization, respectively. FasL expression was independent of Dukes' stage, suggesting that it may occur throughout colon cancer progression. These results suggest that FasL is a common mediation of immune privilege in colon cancer.

The Fas Counterattack In Vivo: Apoptotic Depletion of Tumor-Infiltrating Lymphocytes Associated with Fas Ligand Expression by Human Esophageal Carcinoma

Various cancer cell lines express Fas ligand (FasL) and can kill lymphoid cells by Fas-mediated apoptosis in vitro. FasL expression has been demonstrated in several human malignancies in vivo. We sought to determine whether human esophageal carcinomas express FasL, and whether FasL expression is associated with increased apoptosis of tumor-infiltrating lymphocytes (TIL) in vivo, thereby contributing to the immune privilege of the tumor. Using in situ hybridization and immunohistochemistry, respectively, FasL mRNA and protein were colocalized to neoplastic esophageal epithelial cells in all esophageal carcinomas (squamous, n = 6; adenocarcinoma, n = 2). The Extent of FasL expression was variable, with both FasL-positive and FasL-negative neoplastic regions occurring within tumors. TIL were detected by immunohistochemical staining for the leukocyte common Ag, CD45. FasL expression was associated with a mean fourfold depletion of TIL when compared with FasL-negative areas within the same tumors (range 1.6- to 12-fold, n = 6, p &lt; 0.05). Cell death of TIL was detected by dual staining of CD45 (immunohistochemistry) and DNA strand breaks (TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling). There was a mean twofold increase in detectable cell death among TIL in FasL-positive areas compared with FasL-negative areas (range 1.6- to 2.4-fold, n = 6, p &lt; 0.05). In conclusion, we demonstrate a statistically significant, quantitative reduction of TIL concomitant with significantly increased TIL apoptosis within FasL-expressing areas of esophageal tumors. Our findings suggest Fas-mediated apoptotic depletion of TIL in response to FasL expression by esophageal cancers, and provide the first direct, quantitative evidence to support the Fas counterattack as a mechanism of immune privilege in vivo in human cancer.