Lymphocyte apoptosis induced by Fas ligand- expressing ovarian carcinoma cells. Implications for altered expression of T cell receptor in tumor-associated lymphocytes

Treatment of intracranial glioma with in situ interferon-gamma and tumor necrosis factor-alpha gene transfer

Interferon-gamma (IFNgamma) and tumor necrosis factor-alpha (TNFalpha) are potent immunostimulatory cytokines with demonstrated tumoricidal effects in a variety of cancers. With the aim of investigating their ability to generate antitumor immune responses in malignant brain tumors, we describe the use of in situ adenoviral-mediated IFNgamma and TNFalpha gene transfer in glioma-bearing rodents. Survival was prolonged in mice treated with AdmIFNgamma or AdTNFalpha compared to AdLacZ- and saline-inoculated controls, and AdmIFNgamma- or AdTNFalpha-treated animals revealed significantly smaller tumors. These effects were accompanied by significant up-regulation of tumor MHC-I expression in AdmIFNgamma-inoculated animals, and of MHC-II in AdTNFalpha-treated tumors. Significantly enhanced intratumoral infiltration with CD4(+) and CD8(+) T cells was visible in animals treated with AdmIFNgamma, AdTNFalpha, or a combination of AdmIFNgamma and AdTNFalpha. In addition, AdTNFalpha therapy down-regulated the expression of endothelial Fas ligand, a cell membrane protein implicated as a contributor to immune privilege in cancer. These findings demonstrate the effectiveness of local IFNgamma and TNFalpha gene transfer as a treatment strategy for glioma and illustrate possible physiological pathways responsible for the therapeutic benefit observed.

IFN-gamma protects short-term ovarian carcinoma cell lines from CTL lysis via a CD94/NKG2A-dependent mechanism

IFN-gamma regulates the immunogenicity of target cells by increasing their expression of HLA class I molecules. This facilitates the T cell receptor-mediated recognition by CD8(+) T cells but decreases target cell sensitivity to lysis by NK cells due to engagement of inhibitory NK receptors. In this study, short-term tumor cell lines from patients with advanced ovarian carcinomas were established. We demonstrate the paradoxical finding that IFN-gamma treatment of these short-term ovarian carcinoma cell lines (OVACs) resulted in resistance of tumor cells to lysis by peptide- and allospecific CD8(+) T cells. Blocking experiments revealed that this phenomenon was dependent on enhanced inhibitory signalling via CD94/NKG2A receptors expressed on the effector cells. This was associated with increased expression of HLA-E mRNA and HLA-G at the protein level in IFN-gamma-treated OVACs. Furthermore, pulsing of untreated OVACs with the leader sequence peptide of HLA-G protected these cells from lysis by CTLs, thus mimicking the inhibitory effect of IFN-gamma. This study provides evidence that CD94/NKG2A receptors play an important role in regulating T cell activity against tumors and shows that IFN-gamma modulation of target cells may shift the balance of triggering and inhibitory signals to T cells, turning off their cytolytic activity.

Expression of functional Fas ligand in choriocarcinoma

PROBLEM

In the course of pregnancy, fetal trophoblast cells and in that of choriocarcinoma-etiology, trophoblast derived tumor cells, invade the uterine mucosa without causing rejection by decidual leukocytes. Fas ligand (FasL, CD95L, APO-IL), a central regulator of the immune system, has been implicated in the maintenance of immune privileged sites, such as the eye, the testis and the pregnant uterus by inducing apoptosis in activated infiltrating leukocytes. In normal pregnancy FasL, which is expressed by trophoblast cells, appears to contribute to the immune privilege of the pregnant uterus. As choriocarcinoma derives from trophoblast we wanted to assess the expression of FasL in this tissue.

METHOD OF STUDY

Immunohistochemistry, immunofluorescence, TUNEL-assay, Western blotting, coculture experiments and flourescence-associated cell sorter-analysis were the techniques used.

RESULTS

Expression of FasL was found on cells of choriocarcinoma in paraffin sections in situ and on three choriocarcinoma cell lines such as JEG-3, JAR and BeWo. These results were confirmed by Western blotting. In coculture experiments choriocarcinoma cells induced apoptosis in a Jurkat cell line - sensitive to FasL mediated killing. However, when the Jurkat cells were pre-incubated with a Fas-blocking monoclonal antibody, apoptosis was abolished to a great extent.

CONCLUSION

Our findings show that choriocarcinoma cells express FasL and this aforementioned molecule is biologically active. We assume that FasL expression on choriocarcinoma cells may contribute to control of anti-tumor responses by inducing apoptosis in activated Fas bearing leukocytes.

The biological role of the Fas/FasL system during tumor formation and progression

The cells of an organism are constantly exposed to conflicting environmental cues that signal cell survival or cell death. Survival signals are delivered by autocrine or paracrine factors that actively suppress a default death pathway. This default death pathway appears to be activated by dedicated death receptors such as Fas, the TRAIL-receptors and other tumor necrosis factor receptor superfamily proteins (TNFR SFPs). Our understanding of how these counteracting receptor systems are modulated during tumorigenesis is only moderate. Nevertheless, there is now broad evidence that susceptibility of tumor cells towards Fas-mediated apoptosis is largely reduced. In addition, tumor cells frequently exhibit de novo expression of Fas-ligand (FasL) which plays a significant role in local tissue destruction, metastatic spread and immune escape of the tumor cells. Restoring the apoptotic potential of cancer cells upon modulating the expression and activity of certain key components of the cell death machinery is an attractive and obvious therapeutic anti-cancer strategy.

Shed membrane fragment modulation of CD3-zeta during pregnancy: link with induction of apoptosis

Our objective was to identify shed placental plasma membrane fragments in the maternal circulation and determine whether these fragments are capable of down-regulating CD3-zeta chain expression and inducing apoptosis in T lymphocytes. Sera, isolated from the blood of pregnant women at 26-29 weeks gestation that subsequently had uncomplicated term deliveries, were subjected to high exclusion-limit gel chromatography to isolate placental membrane fragments. The placental origin of the fragments was confirmed by the presence of placental-type alkaline phosphates. These shed membrane fragments were further analyzed for the presence of Fas ligand (FasL) and modulation of CD3-zeta expression on cultured T-lymphocytes (Jurkat cells). The ability of the shed membrane fragments to induce apoptosis was assayed using a cell death ELISA. Components associated with Fas-dependent apoptosis (caspase-3, bcl-2 and bax) were characterized using western immunoblot following exposure to serum-derived membrane fragments. Placental membrane fragments were identified in all pregnancy sera, but not in non-pregnant controls. The 41 kDa FasL was identified in membrane fragment isolates and all samples were capable of inducing apoptosis as determined by the ELISA assay. Exposure of T lymphocytes to isolated membrane fragments suppressed the expression of CD3-zeta. The induction of apoptosis correlated with the induction and activation of caspase 3 and the induction of bax. Placenta-derived membrane fragments are detectable in the maternal circulation. These membrane fragment isolates are capable of inducing FasL-mediated apoptosis and down-regulating CD3-zeta expression, which may contribute to the immune tolerance of the fetus.

Differentiation of promyelocytic leukaemia: alterations in Fas (CD95/Apo-1) and Fas ligand (CD178) expression

The survival of leukaemic blasts contributes to the pathological mechanism of acute promyelocytic leukaemia (APL). While treatment of APL using retinoic acid (RA) is a model of differentiation therapy, little is known about possible effects of this treatment on the Fas/FasL system. Investigation of APL cells from patients undergoing differentiation therapy with RA and of promyelocytic HL-60 and monoblastic U-937 cells cultured with RA revealed a reduction of surface expression of both Fas and its ligand. Accordingly, the sensitivity of the cells to anti-Fas-induced apoptosis decreased proportionally and the reduced expression of FasL resulted in a decreased ability of the leukaemic cells to induce apoptosis in T cells. Our findings demonstrate that there are significant changes in Fas and FasL expression during RA treatment of APL, which probably have consequences for the interaction between host immune and leukaemia cells, and thus may be involved in the beneficial effects of differentiation therapy.

Expression of the signal transduction molecule zeta in peripheral and tumour-associated lymphocytes in Hodgkin's disease in relation to the Epstein-Barr virus status of the tumour cells

We investigated whether the described immune evasion of Epstein-Barr virus (EBV)-infected malignant Hodgkin and Reed-Sternberg (HRS) cells in Hodgkin's disease (HD) is paralleled by a disturbed expression of the signal transduction molecule zeta associated with CD3 and CD16 in tumour-associated T lymphocytes (TAL). Flow cytometric analysis revealed a significantly lower zeta expression in CD3+/4+, CD3+/8+ and CD16+ patient peripheral blood lymphocytes (PBL; n = 10) compared with normal donor PBLs (n = 11). When patient PBLs were compared with the corresponding TAL, the latter showed a significantly higher (CD3+/4+) or equal (CD3+/8+) zeta expression. The EBV status of the tumours did not correlate with zeta expression in the TAL. Immunohistochemical staining revealed zeta-positive lymphocytes among the adjacent bystander cells of the HRS cells in all analysed tumours (n = 8), irrespective of tumour EBV status. In conclusion, these results do not support downregulation of zeta in TAL as a critical mechanism contributing specifically to the immune escape of EBV+ HRS cells.

Modulation of T-cell CD3-zeta chain expression during normal pregnancy

The objectives of this study were to assess the modulation of T-cell CD3-zeta expression by factor(s) present in sera of pregnant women, to correlate this activity with markers of T-cell function associated with pregnancy, and to identify the presence of a circulating pregnancy-associated factor responsible for the suppression of CD3-zeta chain. The suppression of TcR/CD3-zeta expression on cultured T-lymphocytes (Jurkat cells) by sera and amniotic fluids from pregnant women was examined by Western immunoblots and quantitated by densitometry. This suppression was correlated with the induction of T-cell apoptosis and reduced production of IL-2. The serum component suppressing zeta expression was characterized by ultrafiltration and protease sensitivity. Incubation of Jurkat cells with sera obtained from women in the first trimester produced a slight, but not statistically significant, suppression of zeta expression; however, sera from pregnant women in the second and third trimesters and amniotic fluids significantly suppressed zeta levels in a dose-dependent manner. The loss of zeta chain correlated with both reduced secretion of IL-2 and induction of lymphocyte apoptosis. Fractionation of sera by ultrafiltration demonstrated that the zeta chain suppressive factor was <5 kDa, and its trypsin-sensitivity suggests a proteinaceous moiety. Pregnancy is associated with a progressive suppression of cell-mediated immunity. These suppressed T-cell functions have been linked to Fas/Fas ligand-induced apoptosis and suppression of Th1 cytokines, including IL-2. We demonstrate that these pregnancy-associated events are mimicked by a factor(s) present in patient-derived fluids. Suppression of zeta expression appears to be due to a circulating low-molecular-weight protein that suppresses CD3-zeta in a concentration-dependent manner.

CD3-zetachain expression of intratumoral lymphocytes is closely related to survival in gastric carcinoma patients

BACKGROUND

Impaired or reduced CD3 zeta chain (CD3-zeta) expression in T cells has been identified in various cancers and may be associated with an ineffective immune response. The clinical significance of CD3-zeta chain expression in tumor-infiltrating lymphocytes (TILs) in gastric carcinoma remains unclear.

METHODS

The authors immunohistochemically investigated CD3-zeta expression in TILs in 185 patients who had undergone curative gastrectomy. CD3-zeta/CD3 epsilon (CD3-epsilon) ratios were calculated. Patients were divided into two groups: a normal CD3-zeta group (n = 121) and a reduced CD3-zeta group (n = 64). Patients with a zeta per epsilon ratio of greater than 66% were placed in the normal CD3-zeta group.

RESULTS

Patients in the normal CD3-zeta group had fewer lymph node metastasis (P < 0.01) and a shallower depth of invasion (P < 0.05) than those in the reduced CD3-zeta group. The 5-year survival rate was 72% in the normal CD3-zeta group, which was significantly better than that in the reduced CD3-zeta group (55%; P < 0.01). When stratified according to clinical stage, the prognostic value was significantly different only in Stage IV patients. Multivariate analysis showed that CD3-zeta expression was an independent prognostic factor (P = 0.03) next to depth of invasion and lymph node involvement.

CONCLUSIONS

Reduced CD3-zeta expression in TILs was strongly correlated with progressive disease in gastric carcinomas. CD3-zeta expression in TILs is considered an immunologic, independent prognostic marker in gastric carcinoma patients. CD3-zeta normalization with cytokine treatment may lead to prolonged survival in advanced gastric carcinoma patients.

Fas receptor-mediated apoptosis: a clinical application?

Fas is a membrane protein belonging to the death receptor family. Cross-linking of Fas by its ligand, FasL, or agonistic anti-Fas antibodies, induces apoptosis of cells expressing Fas on the membrane by triggering a cascade of caspases. Since many different tumours express Fas on their membrane, targeting Fas-mediated apoptosis by anti-Fas antibodies may be a promising anticancer therapy. Unfortunately, not all Fas-expressing cells are sensitive to Fas-mediated apoptosis. This has resulted in the discovery of many different inhibition mechanisms of Fas-mediated apoptosis. In addition, mutations in the Fas or p53 gene can also influence the sensitivity for Fas-mediated apoptosis. However, the role of wild-type p53 in Fas expression is still controversial. Because several different cytotoxic drugs are able to induce Fas membrane expression, combination therapy of anticancer drugs with anti-Fas antibodies or FasL is conceivable as an anticancer strategy. The efficiency of the induction of Fas-mediated apoptosis by anti-Fas antibodies, FasL-expressing cells or recombinant FasL (rFasL) in tumours has been demonstrated in vivo in solid tumours implanted in mice. Unfortunately, systemic treatment with anti-Fas antibodies or rFasL causes severe damage to the liver, so most preclinical studies are now focusing on circumvention of this problem by local administration of FasL, or on the use of inducible FasL-expressing vectors as gene therapy.

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.

Recovery of zeta-chain expression and changes in spontaneous IL-10 production after PSA-based vaccines in patients with prostate cancer

Circulating T lymphocytes of patients with prostate cancer have been reported to have functional deficits, including low or absent zeta-chain expression. To determine whether these functional impairments could be reversed by prostate specific antigen-based vaccination therapy, 10 patients treated with recombinant human prostate specific antigen plus GM-CSF and eight others receiving prostate specific antigen plus oil emulsion in two pilot clinical trials were evaluated prior to and after vaccination for several immunologic end points, including zeta-chain expression and cytokine production by circulating T cells as well as the frequency of T cells able to respond to prostate specific antigen in ELISPOT assays. The flow cytometry assay for zeta-chain expression was standardized to allow for a reliable comparison of pre- vs post-vaccination samples. Prior to therapy, the patients were found to have significantly lower zeta-chain expression in circulating CD3(+) cells and a higher percentage of zeta-chain negative CD3(+) and CD4(+) cells than normal donors. The patients' peripheral blood mononuclear cells spontaneously produced more IL-10 ex vivo than those of normal controls. After vaccination, recovery of zeta-chain expression was observed in 50% of patients in both clinical trials. Also, spontaneous IL-10 secretion by peripheral blood mononuclear cells decreased following immunotherapy in patients treated with prostate specific antigen and GM-CSF. The frequency of prostate specific antigen-reactive T cells was detectable in 7 out of 18 patients vs 4 out of 18 patients prior to vaccination. Only one of 18 patients was a clinical responder. The vaccine had stimulatory effects on the patients' immune system, but post-vaccine immune recovery could not be correlated to progression-free survival in this small cohort of patients with prostate cancer.

Cancer vaccines and immunotherapy

It is now clear that many human tumour antigens can be recognised by the immune system. These tumour antigens can be classified into several groups including cancer-testis, differentiation, tissue specific, over-expressed, and viral-associated antigens. In many cases, there is a known molecular basis of carcinogenesis which provides the explanation for the differentiated expression of these antigens in tumours compared with normal cells. Improved understanding of the biology of the immune response, particularly of immune recognition and activation of T-cells, allow better design of vaccines. Pre-clinical comparative studies allow evaluation of optimal vaccine strategies which can then be delivered to the clinic. Currently, a range of cancer vaccines are being tested including those using tumour cells, proteins, peptides, viral vectors, DNA or dendritic cells. Ultimately, this research should give rise to an entirely new modality of cancer treatments.

Induction of systemic CTL responses in melanoma patients by dendritic cell vaccination: cessation of CTL responses is associated with disease progression

Two HLA-A2-positive patients with advanced stage IV melanoma were treated with monocyte-derived dendritic cells (DC) pulsed with either tumor peptide antigens from gp100, MART-1 and MAGE-3 alone or in combination with autologous oncolysates. Clinically, the rapid progression of disease was substantially stalled and both patients were alive for more than 15 months after initiation of therapy. Specific CTL reactivity against several tumor antigens was detectable in peripheral blood, which declined just before reactivation of disease progression. Furthermore, CD3 zeta-chain expression detected by Western lotting was decreased in PBL at this time. In summary, our data confirm that DC-based vaccinations induce peptide-specific T cells in the peripheral blood of advanced-stage melanoma patients. Although successful induction of systemic tumor antigen-specific CTL may not lead to objective clinical tumor regression, their presence are indicative of a prolonged survival.

Retinoic acid and vitamin E modulate expression and release of CD178 in carcinoma cells: consequences for induction of apoptosis in CD95-sensitive cells

CD178 (CD95-ligand) is expressed on several tumor cells and likely influences the interaction of the tumor with the host immune system. However, little is known about the mechanisms that regulate its expression on the cell surface. We have evaluated the ability of various compounds and cytokines to regulate cell surface expression and release of soluble CD178 in various carcinoma cell lines. Vitamin E succinate (VES) and retinoic acid (RA) were found to reduce CD178 surface expression, whereas interferon-gamma stimulated a slight upregulation. At 48 h, the regulation of surface CD178 by VES and RA arose from a small decrease in CD178 mRNA and to a greater extent due to an increase in the release of soluble CD178; the latter was blocked by addition of a metalloproteinase inhibitor. Accordingly, VES and RA treatment diminished the ability of tumor cells to kill CD95-sensitive cells and this effect was markedly reduced by the presence of a metalloproteinase inhibitor. Our results indicate that, in vitro, CD178 expression on the cell surface of tumor cells can be regulated by agents that alter both expression and release of the ligand. In vivo, such treatments may play an important role in the outcome of tumor sensitivity or resistance to host immune mechanisms.

Increased levels of interleukin-10 and transforming growth factor-beta in the plasma and ascitic fluid of patients with advanced ovarian cancer

OBJECTIVES

To assess expression of the immunosuppressive cytokines IL-10 and TGF-beta in the ascitic fluid and plasma of advanced ovarian cancer patients.

DESIGN

A prospective study.

SETTING

The Department of Obstetrics and Gynaecology at the University of Arkansas for Medical Sciences.

POPULATION

Twenty-eight women diagnosed with advanced ovarian cancer and ten normal female controls.

METHODS

Plasma and ascitic samples were collected at the time of surgery and analysed for the presence of IL-10 and TGF-beta using a sensitive enzyme-linked immunosorbent assay.

RESULTS

Elevated levels of IL-10 were detected in the plasma [mean (SD) = 12 (5) pg/mL; range 8 to 23 pg/mL] and in the peritoneal fluid [mean (SD) = 165 (137) pg/mL; range 50 to 556 pg/mL] of ovarian cancer patients, while no detectable IL-10 was found in any of the normal control plasma samples tested. Similarly, plasma levels of TGF-beta in ovarian cancer patients were significantly higher [mean (SD) = 1,506 (246) pg/mL; range 1,020 to 2,070 pg/mL] compared with controls [mean (SD) = 937 (187) pg/mL; range 770 to 1,140 pg/mL](P < 0.001). Surprisingly, however, although elevated TGF-beta levels were also detected in the peritoneal fluid of all ovarian cancer patients [mean (SD) = 407 (158) pg/mL; range 140 to 770 pg/mL], these levels were significantly lower than those seen in matched plasma samples (P < 0.001).

CONCLUSIONS

Local and systemic secretion of immunosuppressive cytokines may play an important role in the impaired anti-tumour immune function commonly observed in advanced ovarian cancer. However, the observation that plasma levels of TGF-beta are significantly higher than those detected in the ascitic fluid raises the possibility that cells other than tumour cells are responsible for TGF-beta release in the bloodstream of these patients.

The role of Fas and FasL as mediators of anticancer chemotherapy

Fas Ligand (FasL) is a member of the TNF superfamily that induces apoptosis in susceptible cells upon cross-linking of its own receptor, Fas (Apo-1/CD95). FasL-induced apoptosis contributes to immune homeostasis and cell-mediated cytotoxicity. Several groups have suggested that it also participates in the mechanism of action of DNA-damaging anticancer drugs. However, others have disputed this hypothesis, based largely on the inability of exogenously added anti-Fas/FasL reagents to attenuate drug-induced apoptosis in their studies. In this minireview, we discuss the most recent evidence for and against the involvement of FasL/Fas in the sensitivity and resistance to chemotherapy in a variety of models. In our own model of Ewing's sarcoma (ES), we have extensively investigated the involvement of the FasL/Fas pathway in doxorubicin (Dox)-induced apoptosis. We have generated clones of the Fas-sensitive, Dox-sensitive ES cell line SK-N-MC that were either Fas-resistant or FasL-deficient, and found that they were significantly resistant to Dox. Cleavage of FasL by MMP-7 (matrilysin) protected the parental SK-N-MC cells from Dox, whereas inhibition of MMP-7 activity increased their sensitivity. Transfection of a construct encoding soluble (decoy) Fas protected SK-N-MC cells from Dox. However, incubation with anti-Fas or anti-FasL neutralizing antibodies or exogenous addition of pre-synthesized recombinant soluble Fas decoy protein had no protective effect. This raises the possibility that the proposed Fas/FasL suicidal interaction may take place in an intracellular compartment and thus is not accessible to exogenously added reagents. Therefore, commercially available Fas/FasL neutralizing reagents may not be a reliable indicator of the involvement of the Fas pathway in anticancer-drug-induced apoptosis and experiments using these agents should be carefully re-evaluated. The combined use of MMP inhibitors with conventional, cytotoxic chemotherapy may hold therapeutic benefit.

Loss of T-cell receptor-CD3zeta and T-cell function in tumor-infiltrating lymphocytes but not in tumor-associated lymphocytes in ovarian carcinoma

BACKGROUND

Impaired T-cell function has been noted in tumor-infiltrating lymphocytes (TIL). Recently, loss of function was found to be associated with modifications in T-cell receptor complex (TCR)-mediated signaling. A common feature is loss or reduced expression levels of the signaling chain, TCRzeta. We evaluated whether loss of function in TIL and tumor-associated lymphocytes (TAL) from patients with ovarian cancer is associated with changes in TCRzeta expression, and which factors can cause these defects.

METHODS

TIL and TAL were isolated from multiple patients and evaluated for their proliferative capacity by stimulation with a polyclonal stimulus. In addition, expression of TCRzeta and CD3epsilon was evaluated in fresh TIL and TAL by the Western blot technique. Finally, various conditions within a tumor environment were tested for their effect on TCRzeta and CD3epsilon.

RESULTS

TIL, but not TAL, were significantly impaired in their proliferative response, even when both populations were derived from the same patient (P <.05). Reduced proliferation levels were associated with loss of expression of TCRzeta but not of CD3epsilon. Exposure of normal T cells to relative ischemia or heat shock, or culture in medium without IL-2, did not significantly reduce expression of TCRzeta compared with CD3epsilon. However, coculture of T cells with tumor-derived macrophages or tumor-derived factors led to a selective loss of TCRzeta compared with CD3epsilon (P <.05). Further analysis suggested that oxides such as hydrogen peroxide secreted by macrophages may be responsible for loss of TCRzeta and high molecular weight factors secreted by certain tumors.

CONCLUSIONS

TIL but not TAL show impaired T-cell function, which is associated with loss of TCRzeta. In addition to macrophages secreting oxides, loss of TCRzeta may be caused by tumor-derived soluble factors.

Modulation of TcR/CD3-zeta chain expression by a circulating factor derived from ovarian cancer patients

In women with ovarian cancer, suppression of components of the immune system may promote tumour development. Previous studies in ovarian cancer have demonstrated that decreased expression and function of the T-cell receptor (TcR)-associated signal transducing zeta-chain correlates with deficient immune responsiveness of T cells. In this study, sera and ascitic fluids obtained from woman with advanced ovarian cancer were found to suppress the expression of TcR-associated zeta chain. This suppression of zeta chain expression was dose-dependent and was not observed with biologic fluids obtained from healthy women. The factor responsible for the loss of zeta chain was purified from ascites and characterized as a protein with an appropriate molecular weight of 14 kD. Suppression of T-cell TcR-zeta was specific, since neither lck nor ZAP-70 expression was affected, while zeta chain was almost completely suppressed. This selective suppression of TcR-zeta expression by the 14 kD ascites-derived factor was shown to operate at the mRNA level. By defining the mechanism through which this protein modulates TcR-zeta chain levels, it might be possible to ultimately prevent the suppressive influences of the tumour microenvironment and restor immune competence in patients with ovarian carcinoma.

CD8+ tumor-infiltrating lymphocytes are primed for Fas-mediated activation-induced cell death but are not apoptotic in situ

Induction of Fas-mediated activation-induced cell death in antitumor T cells has been hypothesized to permit tumor escape from immune destruction. Several laboratories have proposed that expression of Fas ligand (L) by tumor is the basis for this form of T cell tolerance. In this study, we characterized murine tumor-infiltrating lymphocytes (TIL) for activation status, cell cycle status, level of apoptosis, cytokine secretion, and proliferative capacity. TILs express multiple activation markers (circa CD69, CD95L, CD122, and LFA-1) and contain IL-2 and IFN-gamma mRNAs, but are neither cycling nor apoptotic in situ. In addition, TIL are dramatically suppressed in proliferative response and do not secrete IL-2 and IFN-gamma. However, upon purification and activation in vitro, TIL secrete high levels of IL-2 and IFN-gamma, enter S phase, and then die by Fas-mediated apoptosis. Activation by injection of anti-TCR Ab or IL-2 into tumor-bearing mice induced TIL entrance into S phase preceding apoptosis, showing that TIL have functional TCR-mediated signal transduction in situ. Our data demonstrate that TIL, not tumor, express both Fas and FasL, are arrested in G(1), do not secrete cytokine in situ, and, upon activation in vitro and in vivo, rapidly die by activation-induced cell death.

Apoptosis and its clinical impact

BACKGROUND

Apoptosis or programmed cell death is an orderly cascade that can be regulated and ultimately results in the demise of the cell. Induction of apoptosis can occur by various chemical and biologic agents. Initiation of apoptosis leads to activation of effector molecules particularly caspases. These proteases cleave distinct protein substrates, resulting in the morphologic changes seen in apoptosis. This form of cell death is involved in almost every physiologic and pathogenic process in the body. For this reason the ability to control apoptosis has important therapeutic ramifications.

RESULTS

This article reviews the history of the investigation of apoptosis and summarizes the most important pathways and regulatory molecules involved in this process. The major regulators of apoptosis, including the Bcl-2, caspase, and inhibitor of apoptosis families, are examined. The two major apoptotic pathways, including the extrinsic/cell surface death receptor and the intrinsic/mitochondrial pathways, are discussed. A major emphasis is given to examining the relationship between apoptosis and certain disease processes. This review specifically focuses on the importance of apoptosis research in the development of new methods of management of cancer with an emphasis in head and neck oncology.

CONCLUSIONS

Apoptosis is a rapidly growing field. The understanding of the mechanisms and effector molecules controlling this form of cell death is evolving. On the basis of increasing knowledge of how programmed cell death is regulated and the improvements in designing and developing gene therapies and chemicals that are more accurate in targeting specific molecules, the control of apoptosis will become more important in the clinical setting. This possibility will open the door for new therapeutic endeavors in many areas of medicine and specifically in the area of oncology.

Apoptosis-resistant mitochondria in T cells selected for resistance to Fas signaling

Jurkat leukemic T cells are highly sensitive to the extrinsic pathways of apoptosis induced via the death receptor Fas or tumor necrosis factor-related apoptosis-inducing ligand as well as to the intrinsic/mitochondrial pathways of death induced by VP-16 or staurosporin. We report here that clonal Jurkat cell lines selected for resistance to Fas-induced apoptosis were cross-resistant to VP-16 or staurosporin. Each of the apoptotic pathways was blocked at an apical phase, where common regulators of apoptosis have not yet been defined. The Fas pathway was blocked at the level of caspase-8, whereas the intrinsic pathway was blocked at the mitochondria. No processing or activity of caspases was detected in resistant cells in response to either Fas-cross-linking or VP-16 treatment. Also, no apoptosis-associated alterations in the mitochondrial inner membrane, outer membrane, or matrix were detected in resistant Jurkat cells treated with VP-16. Thus, no changes in permeability transition, loss in inner membrane cardiolipin, generation of reactive oxygen species, or release of cytochrome c were observed in resistant cells treated with VP-16. Further, unlike purified mitochondria from wild type cells, those obtained from resistant cells did not release cytochrome c or apoptosis-inducing factor in response to recombinant Bax or truncated Bid. These results identify a defect in mitochondria ability to release intermembrane proteins in response to Bid or Bax as a mechanism of resistance to chemotherapeuetic drugs. Further, the selection of VP-16-resistant mitochondria via elimination of Fas-susceptible cells may suggest the existence of a shared regulatory component between the extrinsic and intrinsic pathways of apoptosis.

Circulating soluble Fas ligand in patients with gastric carcinoma

BACKGROUND

The Fas/Fas ligand (FasL) system is involved in cancer cell death induced by the immune system. Most of the tumors may escape the host immune attack by imitating themselves as immune-privileged sites by overexpressing FasL. FasL is synthesized as a membrane-bound protein that can be cleaved to the soluble isoform (sFasL). The objectives of this work were to determine whether the serum concentrations of sFasL in patients with gastric carcinoma were correlated with clinicopathologic features and survival rates.

METHODS

The authors examined the circulating sFasL concentration in 43 healthy people and 166 primary gastric carcinoma patients at the time of diagnosis by enzyme linked immunoadsorbent assay. The results were categorized by clinical and histopathologic variables.

RESULTS

The serum sFasL levels of healthy subjects were all less than 0.1 ng/mL. Among the 166 gastric carcinoma patients, the median concentration of sFasL was 0.04 ng/mL. There were no significant differences between the healthy controls and the gastric carcinoma patients group (P = 0.738). The sFasL levels were significantly increased in patients with gastric carcinoma in a manner reflective of the disease stages such as the depth of tumor invasion, lymph node metastasis, and distant metastasis. The authors determined the cutoff value (0.08 ng/mL) as a 90th percentile of healthy controls. The survival analysis demonstrated that patients with high sFasL levels had a worse prognosis than those with low levels (P < 0.001). Multivariable analysis confirmed that the sFasL concentration was an independent prognostic indicator of overall survival (P = 0.041).

CONCLUSIONS

Our results indicated that sFasL concentrations could not be a new marker for early detection of gastric carcinoma but a prognostic tumor marker for the assessment of the progression of advanced gastric carcinoma.

Alleviating oxidative stress in cancer immunotherapy: a role for histamine?

Interleukin-2 is a remarkable activator of lymphocytes with anti-neoplastic properties such as T-cells or natural killer cells, but tumor regression only rarely occurs in interleukin-2-treated cancer patients. In this review, we focus on interactions between monocytes/macrophages and T-cells/natural killer-cells, and in particular the role of such interactions for the outcome of cancer immunotherapy with interleukin-2. We propose that interleukin-2 therapy should be supplemented with compounds that alleviate toxicity inflicted by monocyte/macrophage-derived reactive oxygen metabolites within and around tumors. The hypothesis is founded on data demonstrating that (i) functions of intratumoral lymphocytes in many human malignant tumors are inhibited by reactive oxygen metabolites, generated by neighboring monocytes/macrophages, (ii) interleukin-2 only weakly activates T-cells or natural killer cells in an environment of oxidative stress, and (iii) inhibitors of the formation of reactive oxygen metabolites or scavengers of reactive oxygen metabolites synergize with interleukin-2 to activate these lymphocyte subsets. We also review the preclinical background to the use of histamine dihydrochloride, an inhibitor of reactive oxygen metabolite formation in monocytes/macrophages, as a supplement to cancer immunotherapy with interleukin-2.

Promotion of activated human B cell apoptosis and inhibition of Ig production by soluble CD95 ligand: CD95-based downregulation of Ig production need not culminate in activated B cell death

CD95/CD95L interactions are vital to normal lymphoid homeostasis and in the protection against autoimmunity. To directly assess the effects of CD95L on activated B cell survival and Ig responses, purified human peripheral blood B cells, activated in vitro with SAC + rIL2, were incubated with a soluble CD95L fusion protein (fp) and assayed for apoptosis and IgG/IgM production. CD95L fp reproducibly increased apoptosis of these activated B cells and inhibited their Ig production. However, CD95L fp-mediated effects on activated B cell survival could be uncoupled from those on Ig production in that a soluble CD40L fp was incapable of reversing CD95L fp-mediated downregulation of Ig responses despite inhibiting CD95L fp-mediated apoptosis. Moreover, despite the specific caspase-8 inhibitor z-IETD-fmk substantially protecting transformed CL-01 B cells from CD95L fp-mediated apoptosis and permitting their ongoing proliferation, caspase-8 inhibition had no protective effects on CD95L fp-mediated inhibition of constitutive IgM production by CL-01 B cells. Collectively, these results point to a CD95-based downregulatory pathway in activated B cells that need not necessarily culminate in their death.

Regulation of fas ligand expression in breast cancer cells by estrogen: functional differences between estradiol and tamoxifen

During neoplastic growth and metastasis, the immune system responds to the tumor by developing both cellular and humoral immune responses. In spite of this active response, tumor cells escape immune surveillance. We previously showed that FasL expression by breast tumor plays a central role in the induction of apoptosis of infiltrating Fas-immune cells providing the mechanism for tumor immune privilege. In the present study, we showed that FasL in breast tissue is functionally active, and estrogen and tamoxifen regulate its expression. We identified an estrogen recognizing element like-motif in the promoter region of the FasL gene, suggesting direct estrogen effects on FasL expression. This was confirmed by an increase in FasL expression in both RNA and protein levels in hormone sensitive breast cancer cells treated with estradiol. This effect is receptor mediated since tamoxifen blocked the estrogenic effect. Interestingly, tamoxifen also inhibited FasL expression in estrogen-depleted conditions. Moreover, an increase in FasL in breast cancer cells induces apoptosis in Fas bearing T cells and, tamoxifen blocks the induction of apoptosis. These studies provide evidence that tamoxifen inhibits FasL expression, allowing the killing of cancer cells by activated lymphocytes. This partially explains the protective effect of tamoxifen against breast cancer.

Cutting edge: the tumor counterattack hypothesis revisited: colon cancer cells do not induce T cell apoptosis via the Fas (CD95, APO-1) pathway

The counterattack hypothesis, suggesting that cancer cells express Fas ligand (FasL) and are able to kill Fas-expressing tumor-infiltrating activated T cells, was supported by reports of the killing of Jurkat cells by FasL-expressing human colon cancer cell lines. Through the use of an improved cytotoxic assay in which soluble FasL and FasL-transfected KFL9 cells were used as positive controls, we show that none of seven human colon cancer cell lines induce apoptosis of two Fas-expressing target cell lines, Jurkat and L1210-Fas cells. Moreover, in coculture experiments, cancer cell monolayers do not inhibit the growth of Fas-expressing lymphoid cells. Although FasL mRNA and protein were detected in the extracts of the colon cancer cell lines, flow cytometry and confocal microscopy failed to detect the protein on the surface of tumor cells. These results suggest that the counterattack of tumor-infiltrating T lymphocytes by cancer cells may not account for immune tolerance toward tumor cells.

B7.1 on human carcinomas: costimulation of T cells and enhanced tumor-induced T-cell death

Human squamous cell carcinomas of the head and neck (SCCHN) do not express the costimulatory molecules B7.1 or B7.2 in situ or in culture. Transduction of B7.1(-) SCCHN cells with the retroviral B7. 1 and neo(r) genes resulted in the expression of high levels of the transgene in these tumor cells. When B7.1(+) SCCHN cells were used as stimulators of autologous or allogeneic PBL in mixed lymphocyte-tumor cultures (MLTC), T-cell proliferation and generation of antitumor effector T cells as well as levels of their lytic activity were significantly increased. At the same time, a proportion of activated T cells seen to undergo apoptosis was found to be significantly higher upon coincubation with B7.1(+) SCCHN than with B7.1(-) SCCHN. Both B7.1(+) and B7.1(-) SCCHN cells were found to express FasL on the cell surface and in the cytoplasm, as well as mRNA for FasL and mRNA for TRAIL. However, expression of the B7.1 transgene did not lead to increased expression of FasL protein on tumor cells. Yet, up to 50% of activated CD28(+) allogeneic T cells, which were CD95(+), showed evidence of DNA fragmentation in JAM and TUNEL assays upon incubation with an excess of B7.1(+) SCCHN for 24 h. Tumor-induced T-cell death was equally and only in part blocked by anti-Fas antibodies in both B7.1(+) and B7.1(-) MLTC. While surface expression of B7.1 molecules on SCCHN cells enhanced T-cell costimulation via B7.1-CD28 interactions, it did not rescue activated T cells from tumor-induced apoptosis. The outcome of MLTC under these conditions was dependent on the ratio of tumor to T cells. Thus, in the presence of an excess of B7.1(+) tumor cells, activated T cells showed increased sensitivity to apoptosis which did not appear to be Fas/FasL mediated. These data are important for the development of B7.1 gene therapy and efforts directed at the generation of effector cells in MLTC.

Nonlymphoid cultured cells possess a system controlling cellular compatibility

We show that various nonlymphoid cultured cells can activate the production of cytotoxic factors in response to direct contact with cells of a different kind. Accumulation of cytotoxic factors in the medium was detected 1 h after contact of K562 and L929 cells or after contact of L929 cells with purified membranes of K562 cells. TNF-alpha or immunologically related proteins, or both, but not Fas-ligand or lymphotoxin, were also accumulated in membranes of K562 and L929 cells shortly after these cells had been allowed to contact each other. The cytotoxic factors expressed by nonlymphoid cells trigger apoptosis of target cells. These observations strongly suggest that nonlymphoid cells possess molecular mechanisms controlling cellular compatibility.

Antigen-specific induction of peripheral T cell tolerance in vivo by codelivery of DNA vectors encoding antigen and Fas ligand

Fas ligand (FasL, CD95L) induces apoptosis in activated T cells with upregulated Fas (CD95) expression through the process termed activation-induced cell death (AICD). We postulated that coexpression of antigen and FasL within individual antigen-presenting cells would lead to antigen-specific activation of T cells and to their consequent deletion by FasL-mediated AICD. A DNA-gelatin coacervate containing transferrin cell ligand, calcium, and the lysosomatropic agent chloroquine, a formulation previously shown to achieve high-level transfection of immune and muscle cells in vivo, was used to codeliver plasmids encoding FasL and antigen. Mice developed a strong cytolytic T cell response to beta-Gal when injected with DNA encoding beta-galactosidase (LacZ) model antigen, either as naked DNA or DNA nanoparticles, but failed to respond when there was concomitant injection of nanoparticles containing both the LacZ and murine FasL DNA vectors. This loss of T cell response was systemic, specific for beta-Gal, complete when nanoparticles were administered before antigen challenge, and decreased the T cell response from prior immunization with LacZ DNA. In effect, this "tolerization" injection induced antigen-specific peripheral tolerance in study mice, and represents a possible approach to the treatment of autoimmune diseases and transplantation rejection.

Immunology and immunotherapy of human cancer: present concepts and clinical developments

Immunotherapy of cancer is entering into a new phase of active investigation both at the pre-clinical and clinical level. This is due to the exciting developments in basic immunology and tumour biology that have allowed a tremendous increase in our understanding of mechanisms of interactions between the immune system and tumour cells. This review briefly summarizes the state of the art in basic tumour immunology before discussing the clinical applications of the new concepts in the clinical setting. Clinical approaches are diverse but can now be based on strong scientific rationales. The analysis of the available clinical results suggests that, despite some disappointments, there is room for optimism that both active immunotherapy (vaccination) and adoptive immunotherapy may soon become part of the therapeutic arsenal to combat cancer in a more efficient way.

Tumor-induced apoptosis of T lymphocytes: elucidation of intracellular apoptotic events

Our recent studies suggest that human squamous cell carcinoma of the head and neck (SCCHN) is capable of activating an intrinsic mechanism of programmed-cell death in interacting lymphocytes in situ and in vitro. The current study used Jurkat T-cell line as a model to investigate intracellular apoptotic events in T cells interacting with SCCHN. Apoptosis induced in T lymphocytes by tumor cells was in part Fas-mediated, since it was partially, but significantly, inhibited in the presence of anti-Fas ligand Ab or in Fas-resistant Jurkat cells. The synthetic caspase inhibitors, N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (Z-VAD-FMK) and N-benzyloxycarbonyl-Asp-glu-Val-Asp-fluoromethyl ketone (Z-DEVD-FMK), effectively blocked apoptosis of Jurkat cells co-incubated with SCCHN cell lines, suggesting the involvement of caspases in tumor-induced apoptosis of lymphocytes. Overexpression of CrmA, an inhibitor of caspase-1 and caspase-8, partially inhibited tumor-induced T-cell death. Caspase-8 and caspase-3 were identified as effector molecules in the execution of tumor-induced T-cell death, since the proform enzymes were processed into active subunits during co-incubation of T cells with tumor cells. Furthermore, co-incubation with tumor cells resulted in cleavage of poly(ADP-ribose) polymerase (PARP), a common caspase-3 substrate, and in cleavage of TcR-ζ chain, shown by us to be a T-cell specific caspase-3 substrate. Overexpression of Bcl-2 did not provide protection of T cells from SCCHN-induced DNA degradation. Instead, the Bcl-2 protein was cleaved in the target T cells during their co-incubation with tumor cells. These findings demonstrate that tumor cells can trigger in T lymphocytes caspase-dependent apoptotic cascades, which are not effectively protected by Bcl-2.

Type 1 and type 2 CD8+ effector T cell subpopulations promote long-term tumor immunity and protection to progressively growing tumor

Cytolytic CD8+ effector cells fall into two subpopulations based on cytokine secretion. Type 1 CD8+ T cells (Tc1) secrete IFN-gamma, whereas type 2 CD8+ T cells (Tc2) secrete IL-4, IL-5, and IL-10. Using an OVA-transfected B16 lung metastases model, we assessed the therapeutic effects of adoptively transferred OVA-specific Tc1 and Tc2 subpopulations in mice bearing established pulmonary malignancy. Effector cell-treated mice exhibiting high (5 x 105) tumor burdens experienced significant (p < 0.05) delays in mortality compared with those of untreated control mice, whereas high proportions (70-90%) of mice receiving therapy with low (1 x 105) tumor burdens survived indefinitely. Long-term tumor immunity was evident by resistance to lethal tumor rechallenge, heightened levels of systemic OVA Ag-specific CTL responses ex vivo, and detection of long-lived TCR transgene-positive donor cells accompanied by an elevation in the total numbers of CD8+ CD44high activated and/or memory T cells at sites of tumor growth. Long-lasting protection by Tc2 and Tc1 effector cells were dependent, in part, on both the level of tumor burden and effector cell-derived IL-4, IL-5, and IFN-gamma, respectively. We conclude that Tc1 and Tc2 effector cells provide immunity by different mechanisms that subsequently potentiate host-derived antitumor responses.

CD95 ligand expression as a mechanism of immune escape in breast cancer

Interaction of CD95 (Apo-1/Fas) and its ligand (CD95L) plays an important role in the regulation of the immune response, since CD95+ lymphocytes may be killed after engagement of the CD95 receptor. Studying the CD95/CD95L system in 40 cases of breast cancer, the malignant cells expressed CD95L, but lost CD95 expression, when compared with non-malignant mammary tissue. Jurkat T cells incubated on breast cancer sections underwent CD95L-specific apoptosis. The rate of apoptosis correlated with the CD95L mRNA levels of the tissue samples. In four breast cancer cell lines, CD95L expression was increased by interferon-gamma (IFN-gamma), which resulted in higher levels of CD95L-specific apoptosis in co-cultured Jurkat T cells. Since IFN-gamma is mainly secreted by activated T cells, up-regulation of CD95L in breast cancer cells in response to IFN-gamma may thus counterselect activated tumour-infiltrating T cells and favour the immune escape of breast cancer. As demonstrated by inhibition of matrix metalloproteinases, CD95L expressed on breast cancer cells can also be shed from the cell membrane into the culture supernatant. Supernatants derived from cultured breast cancer cells induced apoptosis in Jurkat T cells via CD95L. In breast cancer patients, depletion of CD4+ and CD8+ peripheral blood lymphocytes was significantly correlated with CD95L expression in the tumours. This might be suggestive for a relationship between CD95L expression by breast cancer and systemic immunosuppression.

Tumor necrosis factor-alpha and interferon-gamma induce expression of functional Fas ligand on HT29 and MCF7 adenocarcinoma cells

Tumor cells develop diverse mechanisms to escape from immune surveillance, including expression of Fas ligand (FasL), a 40-kDa type II transmembrane protein that mediates apoptosis by binding to its cognate receptor Fas (APO-1/CD95). Upon activation, T lymphocytes and natural killer (NK) cells express Fas and thus become sensitive to FasL-mediated apoptosis. Here we show that tumor necrosis factor-alpha (TNF-alpha) in addition to interferon-gamma (IFN-gamma) induces cell surface expression of functional FasL in human HT29 colon and MCF7 breast adenocarcinoma cells that constitutively lack cell surface expression of FasL. These cells, expressing FasL, are capable of inducing apoptosis in Fas-positive Jurkat T cells mediated by plasma membrane-bound FasL and soluble forms of FasL. By contrast, mutational deletion of Fas cell surface expression as well as inhibition of caspase family proteases involved in Fas signaling and monoclonal antibodies neutralizing FasL protect Jurkat T cells from apoptosis caused by the FasL-expressing HT29 or MCF7 cells. These results demonstrate that TNF-alpha and IFN-gamma induce expression of functional FasL in adenocarcinoma cells which thereby can kill T lymphocytes by the FasL/Fas pathway.

Fas-mediated apoptosis in Ewing's sarcoma cell lines by metalloproteinase inhibitors

BACKGROUND

Fas ligand (FasL) is a transmembrane protein that induces apoptosis (programmed cell death) in susceptible cells by interacting with its receptor, Fas. Transmembrane FasL is cleaved by a metalloproteinase enzyme into a soluble form that is released into the extracellular medium. Tumors of the Ewing's sarcoma family express functional transmembrane FasL and release soluble FasL. This cleavage is inhibited by a matrix metalloproteinase inhibitor (MMPI). We therefore hypothesized that MMPIs can lead to apoptosis of tumor cells by inducing accumulation of transmembrane FasL.

METHODS

Ewing's sarcoma and neuroblastoma cell lines were treated with two synthetic MMPIs (BB-3103 and A-151011) and examined for apoptosis and expression of FasL and Fas.

RESULTS

Although MMPIs increase levels of FasL and Fas proteins on the surface of all tumor cells studied, they induced apoptosis in Fas-sensitive but not in Fas-resistant cell lines; the induction of apoptosis was inhibited by a Fas-neutralizing antibody. The increase in protein expression was not associated with enhanced transcription. Treatment with an MMPI sensitized the Ewing's sarcoma cells to Fas-activating antibody and to doxorubicin-induced apoptosis.

CONCLUSIONS

MMPIs cause accumulation of transmembrane FasL by inhibiting its cleavage, accumulation of Fas (probably secondarily to FasL cleavage inhibition), and decreased levels of soluble FasL. These effects lead to apoptosis in Fas-sensitive cell lines. The observed cooperative action of MMPIs and doxorubicin suggests a possible role of MMPIs in combination treatments with standard apoptosis-inducing chemotherapeutic agents.

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(CD95) ligand expression by tumor cell variants can be unrelated to their capacity to induce tolerance or immune rejection

According to the results of in vitro experiments, Fas(CD95) ligand expression by cancer cells might induce apoptosis of activated T cells and contribute to immune tolerance. However, Fas ligand expression had never been explored in vivo in tumor cell models yielding either immune response or tolerance. In the present study, we analyzed the expression and function of Fas ligand in 2 clones of tumor cells originating from the same rat colon carcinoma. REGb cells were immunogenic and yielded tumors that regressed in immunecompetent syngeneic hosts, whereas PROb cells induced active tolerance and yielded progressive tumors. Fas ligand was expressed on the plasma membrane of both REGb and PROb cells, and its cDNA sequencing showed no mutation. However, neither REGb nor PROb cells induced apoptosis of co-cultured Fas-sensitive target cells. Our results show that surface expression of Fas ligand by tumor cells does not always induce killing of adjoining Fas-sensitive cells and that tumor cells may induce a protective immune response or an active tolerance independently of Fas ligand expression.

Induction of Antitumor Immunity with Fas/APO-1 Ligand (CD95L)-Transfected Neuroblastoma Neuro-2a Cells

Fas/Apo-1 (CD95)-Fas ligand (FasL) system has been implicated in the suppression and stimulation of immune responses. We examined the induction of antitumor immunity with neuroblastoma Neuro-2a cells transfected with FasL cDNA (Neuro-2a+FasL). Neuro-2a+FasL cells expressed FasL on the cell surface and secreted soluble FasL. Histologic and flow cytometric analyses revealed that Neuro-2a+FasL cells caused neutrophils to infiltrate into the injected site, resulting in strong inflammation. Neutrophil infiltration was inhibited by treatment with anti-FasL mAb and did not occur in Fas-deficient lpr mice. Normal syngeneic mice rejected Neuro-2a+FasL cells after the inflammation and acquired tumor-specific protective immunity. CD8+ T cells were responsible for the antitumor immunity. Neuro-2a+FasL cells formed tumors after far longer latency compared with mock-transfected Neuro-2a+Neo cells in nude mice, and immune competent mice rejected Neuro-2a cells but not sarcoma S713a cells when they were injected with Neuro-2a+FasL cells in a mixture. These results suggest that neutrophils attracted through the Fas-FasL system may impair tumor cells by inflammation at the initial step, followed by development of CD8+ T cell-dependent tumor-specific antitumor immunity, leading to complete eradication of tumor cells. Importantly, the treatment with Neuro-2a+FasL cells exhibited therapeutic efficacy against growing tumors.

Therapeutic Effects of Tumor-Reactive Type 1 and Type 2 CD8+ T Cell Subpopulations in Established Pulmonary Metastases

Cytolytic CD8+ T cells fall into two subpopulations based on cytokine-secretion. Type 1 CD8+ cells (Tc1) characteristically secrete IFN-γ, whereas type 2 CD8+ cells (Tc2) secrete IL-4 and IL-5. We assessed the relative therapeutic effects of adoptively transferred OVA-specific Tc1 and Tc2 CD8+ cells in mice bearing established OVA-transfected B16 melanoma lung metastases. Both Tc1 and Tc2 subpopulations mediated a reduction in lung tumor growth that subsequently prolonged survival times in mice with both early (day 7) and more advanced (day 14) levels of tumor development. CD8+ T cell populations recovered from spleens of tumor-bearing mice receiving Tc1 or Tc2 cells showed markedly enhanced tumor Ag-specific cytolytic and cytokine-releasing activities that correlated with delays in tumor cell growth and progression. Initially, both tumor-reactive Tc1 and Tc2 effector cells accumulated at the tumor site with nearly equal frequency. Tc1 cells persisted, whereas Tc2 cell numbers progressively diminished over time. Titration of Tc1 and Tc2 effector cells showed that protection was dose dependent with the former being 5-fold more effective. Tc2 cells achieved a comparable reduction in lung tumor cell growth at higher concentrations of cell transfer. Tc1 effectors from IFN-γ-deficient mice were less therapeutically effective than wild-type mice, but there was no significant reduction in activity between corresponding Tc2 populations. We speculate that the effectiveness of Tc1 and Tc2 cells may depend on different mechanisms. These studies suggest a potential role for Tc1 and Tc2 CD8+ subpopulations in tumor regression and immunotherapy.

Predominant expression of Fas (CD95) ligand in metastatic melanoma revealed by longitudinal analysis

The expression of Fas ligand has recently been proposed as a novel tumor escape mechanism for melanoma. To establish the characteristics of Fas ligand expression during the course of melanoma progression we performed a longitudinal study analyzing primary tumors as well as subsequently evolving metastases. In primary melanoma Fas ligand was expressed in two of 20 lesions; this expression was weak and restricted to few parts of the tumors. The Fas ligand positive primary melanomas were rather thick, i.e., 8.5 and 3.8 mm, versus a median of 2.4 mm of the remaining tumors. In contrast, for metastatic melanoma Fas ligand expression was present in six of 11 cases investigated. The metastases of primary tumors displaying Fas ligand maintained its expression. As Fas ligand positive melanoma cells are capable of inducing apoptosis in susceptible cells, e.g., Fas positive tumor infiltrating lymphocytes, we tested for the presence of apoptotic cells in situ by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling. This analysis revealed that apoptotic cells were present within the Fas ligand positive tumors. The number of apoptotic cells, however, never exceeded 5% of the total cells. Thus, Fas ligand mediated apoptosis does not seem to be a major immune escape mechanism for melanoma but its expression correlates with the stage of melanoma.

Fas-mediated induction of hepatocyte apoptosis in a neuroblastoma and hepatocyte coculture model

BACKGROUND

We have previously demonstrated an increase in hepatocyte apoptosis when they are cocultured with neuroblastoma cells. Death receptors in the tumor necrosis factor (TNF) family such as TNFR1 and Fas have been identified as regulators of apoptosis and may be responsible for the altered regulation of apoptosis seen in our coculture model. To evaluate the effects of released factors and remove the potential alterations induced by direct contact, a noncontact coculture system was used to study the interaction between hepatocytes and neuroblastoma cells.

METHODS

Human Chang hepatocytes (HC) were plated onto Falcon cell culture inserts with 0.45-micrometer pores in the permeable membrane. Human neuroblastoma cells (NB-IMR-32) were seeded into wells of the Falcon companion plate. After 24 h, inserts containing HC were placed into wells containing NB cells and incubated for 4 days. This provided a coculture environment without actual cellular contact. Immunohistochemical staining for TNFalpha, Fas, and Fas ligand (Fas-L) was performed. Apoptosis was detected via the TUNEL method. Images were analyzed with ImagePro-Plus. Statistical analyses were done with significance determined at P < 0.05.

RESULTS

Chang hepatocytes demonstrated a significant increase in the levels of TNF, Fas, and Fas-L when cocultured with neuroblastoma cells (P < 0.005). In addition, the cocultured hepatocytes had a 20-fold increase in the apoptotic rate (P < 0.001). Neuroblastoma cells had no demonstrable level of Fas or TNF when grown alone and in cocultures. Neuroblastoma cells that were grown alone had an elevated level of Fas-L, but this level diminished by 44% when cocultured with hepatocytes (P < 0.001).

CONCLUSION

An upregulated TNF/Fas receptor-ligand system may be responsible for increased apoptosis in hepatocytes when cocultured with neuroblastoma. This upregulation may be due to release of neuroblastoma-derived Fas ligand into the media. Tumors may alter the regulation of apoptosis in surrounding tissues via the death receptors.