Differential role of Fas/Fas ligand interactions in cytolysis of primary and metastatic colon carcinoma cell lines by human antigen-specific CD8+ CTL

Physical immune escape: Weakened mechanical communication leads to escape of metastatic colorectal carcinoma cells from macrophages

The significance of biochemical cues in the tumor immune microenvironment in affecting cancer metastasis is well established, but the role of physical factors in the microenvironment remains largely unexplored. In this article, we investigated how the mechanical interaction between cancer cells and immune cells, mediated by extracellular matrix (ECM), influences immune escape of cancer cells. We focus on the mechanical regulation of macrophages' targeting ability on two distinct types of colorectal carcinoma (CRC) cells with different metastatic potentials. Our results show that macrophages can effectively target CRC cells with low metastatic potential, due to the strong contraction exhibited by the cancer cells on the ECM, and that cancer cells with high metastatic potential demonstrated weakened contractions on the ECM and can thus evade macrophage attack to achieve immune escape. Our findings regarding the intricate mechanical interactions between immune cells and cancer cells can serve as a crucial reference for further exploration of cancer immunotherapy strategies.

In vitro Characterization of Enhanced Human Immune Responses by GM-CSF Encoding HSV-1-Induced Melanoma Cells

PURPOSE

We studied the innate and adaptive immune response against melanoma cells after JS-1 (wild-type herpes simplex virus 1, wt HSV-1) or Talimogene laherparepvec (T-VEC) infection and evaluated the antitumoral efficacy in human melanoma cells. We analyzed the putative synergistic biological and immunological effects of JS-1 or T-VEC combined with cytostatic drugs in human tumor and immune cells. T-VEC is a genetically modified strain of HSV-1. Genetic modifications (insertion of the granulocyte-macrophage colony-stimulating factor (GM-CSF) gene) were made to attenuate the virus and increase selectivity for cancer cells. In addition to the direct oncolytic effect, we investigated the immune stimulatory effects of T-VEC by comparing it with JS-1. JS-1 is identical T-VEC except for the inserted GM-CSF gene.

MATERIALS AND METHODS

We analyzed the effects of T-VEC and JS-1 with cytostatic drugs in human tumor-immune cell coculture experiments. After coculture, the surface markers CD80, CD83 and CD86 were measured by fluorescence-activated cell sorting and the cytokines, interleukin (IL)-2, IL-6, tumor necrosis factor (TNF)-α and GM-CSF, by enzyme-linked immunosorbent assays. Furthermore, we analyzed the potential of the viruses to induce T cell activation, measured on the basis of CD4, CD8 and CD69. Analysis of these markers and cytokines allows for conclusions to be drawn concerning the maturation of dendritic cells (DCs) and the immunostimulatory effects of the treatment.

RESULTS

We documented increased activation of human cytotoxic T lymphocytes after infection by both HSV-1 strains and treatment with cytostatic drugs without significant differences between T-VEC and JS-1.

CONCLUSION

We demonstrated an immune response as a result of infection with both viruses, but T-VEC was in vitro not stronger than JS-1. The immunostimulatory effects of the viruses could be partially increased by chemotherapy, providing a rationale for future preclinical studies designed to explore T-VEC in combined regimens.

Protein phosphatase 2A inactivation induces microsatellite instability, neoantigen production and immune response

Microsatellite-instable (MSI), a predictive biomarker for immune checkpoint blockade (ICB) response, is caused by mismatch repair deficiency (MMRd) that occurs through genetic or epigenetic silencing of MMR genes. Here, we report a mechanism of MMRd and demonstrate that protein phosphatase 2A (PP2A) deletion or inactivation converts cold microsatellite-stable (MSS) into MSI tumours through two orthogonal pathways: (i) by increasing retinoblastoma protein phosphorylation that leads to E2F and DNMT3A/3B expression with subsequent DNA methylation, and (ii) by increasing histone deacetylase (HDAC)2 phosphorylation that subsequently decreases H3K9ac levels and histone acetylation, which induces epigenetic silencing of MLH1. In mouse models of MSS and MSI colorectal cancers, triple-negative breast cancer and pancreatic cancer, PP2A inhibition triggers neoantigen production, cytotoxic T cell infiltration and ICB sensitization. Human cancer cell lines and tissue array effectively confirm these signaling pathways. These data indicate the dual involvement of PP2A inactivation in silencing MLH1 and inducing MSI.

The immunoregulatory function of polyphenols: implications in cancer immunity

Polyphenols have demonstrated several potential biological activities, notably antitumoral activity dependent on immune function. In the present review, we describe studies that investigated antitumor immune responses influenced by polyphenols and the mechanisms by which polyphenols improve the immune response. We also discuss the limitations in related areas, especially unexplored areas of research, and next steps required to develop a therapeutic approach utilizing polyphenols in oncology.

Loss of Fas Expression and Function Is Coupled with Colon Cancer Resistance to Immune Checkpoint Inhibitor Immunotherapy

Despite the remarkable efficacy of immune checkpoint inhibitor (ICI) immunotherapy in various types of human cancers, colon cancer, except for the approximately 4% microsatellite-instable (MSI) colon cancer, does not respond to ICI immunotherapy. ICI acts through activating CTLs that use the Fas-FasL pathway as one of the two effector mechanisms to suppress tumor. Cancer stem cells are often associated with resistance to therapy including immunotherapy, but the functions of Fas in colon cancer apoptosis and colon cancer stem cells are currently conflicting and highly debated. We report here that decreased Fas expression is coupled with a subset of CD133⁺CD24^lo colon cancer cells in vitro and in vivo. Consistent of the lower Fas expression level, this subset of CD133⁺CD24^loFas^lo colon cancer cells exhibits decreased sensitivity to FasL-induced apoptosis. Furthermore, FasL selectively enriches CD133⁺CD24^loFas^lo colon cancer cells. CD133⁺CD24^loFas^lo colon cancer cells exhibit increased lung colonization potential in experimental metastatic mouse models and decreased sensitivity to tumor-specific CTL adoptive transfer and ICI immunotherapies. Interestingly, FasL challenge selectively enriched this subset of colon cancer cells in microsatellite-stable (MSS) but not in the MSI human colon cancer cell lines. Consistent with the downregulation of Fas expression in CD133⁺CD24^lo cells, lower Fas expression level is significantly correlated with decreased survival in patients with human colon cancer. IMPLICATIONS: Our data determine that CD133⁺CD24^loFas^lo colon cancer cells are capable to evade Fas-FasL cytotoxicity of tumor-reactive CTLs and targeting this subset of colon cancer cells is potentially an effective approach to suppress colon cancer immune evasion.

The Circular RNA Profiles of Colorectal Tumor Metastatic Cells

Circular RNAs (circRNAs) have been reported that can be used as biomarkers for colorectal cancers (CRC) and other types of tumors. However, a limited number of studies have been performed investigating the potential role of circRNAs in tumor metastasis. Here, we examined the circRNAs in two CRC cell lines (a primary tumor cell SW480 and its metastasis cell SW620), and found a large set of circRNA (2,919 ncDECs) with significantly differential expression patterns relative to normal cells (NCM460). In addition, we uncovered a set of 623 pmDECs that differ between the primary CRC cells and its metastasis cells. Both differentially expressed circRNA (DEC) sets contain many previously unknown putative CRC-related circRNAs, thereby providing many new circRNAs as candidate biomarkers for CRC development and metastasis. These studies are the first large-scale identification of metastasis-related circRNAs for CRC and provide valuable candidate biomarkers for diagnostic and a starting point for additional investigations of CRC metastasis.

miR-153 supports colorectal cancer progression via pleiotropic effects that enhance invasion and chemotherapeutic resistance

Although microRNAs (miRNA) have been broadly studied in cancer, comparatively less is understood about their role in progression. Here we report that miR-153 has a dual role during progression of colorectal cancer by enhancing cellular invasiveness and platinum-based chemotherapy resistance. miRNA profiling revealed that miR-153 was highly expressed in a cellular model of advanced stage colorectal cancer. Its upregulation was also noted in primary human colorectal cancer compared with normal colonic epithelium and in more advanced colorectal cancer stages compared with early stage disease. In colorectal cancer patients followed for 50 months, 21 of 30 patients with high levels of miR-153 had disease progression compared with others in this group with low levels of miR-153. Functional studies revealed that miR-153 upregulation increased colorectal cancer invasiveness and resistance to oxaliplatin and cisplatin both in vitro and in vivo. Mechanistic investigations indicated that miR-153 promoted invasiveness indirectly by inducing matrix metalloprotease enzyme 9 production, whereas drug resistance was mediated directly by inhibiting the Forkhead transcription factor Forkhead box O3a (FOXO3a). In support of the latter finding, we found that levels of miR-153 and FOXO3a were inversely correlated in matched human colorectal cancer specimens. Our findings establish key roles for miR-153 overexpression in colorectal cancer progression, rationalizing therapeutic strategies to target expression of this miRNA for colorectal cancer treatment.

A novel function for Cyclin A2: control of cell invasion via RhoA signaling

Cyclin A2 plays a key role in cell cycle regulation. It is essential in embryonic cells and in the hematopoietic lineage yet dispensable in fibroblasts. In this paper, we demonstrate that Cyclin A2-depleted cells display a cortical distribution of actin filaments and increased migration. These defects are rescued by restoration of wild-type Cyclin A2, which directly interacts with RhoA, or by a Cyclin A2 mutant unable to associate with Cdk. In vitro, Cyclin A2 potentiates the exchange activity of a RhoA-specific guanine nucleotide exchange factor. Consistent with this, Cyclin A2 depletion enhances migration of fibroblasts and invasiveness of transformed cells via down-regulation of RhoA activity. Moreover, Cyclin A2 expression is lower in metastases relative to primary colon adenocarcinoma in matched human tumors. All together, these data show that Cyclin A2 negatively controls cell motility by promoting RhoA activation, thus demonstrating a novel Cyclin A2 function in cytoskeletal rearrangements and cell migration.

Glypican-3 could be an effective target for immunotherapy combined with chemotherapy against ovarian clear cell carcinoma

Glypican-3 (GPC3) is useful not only as a novel tumor marker, but also as an oncofetal antigen for immunotherapy. We recently established HLA-A2-restricted GPC3(144-152) peptide-specific CTL clones from hepatocellular carcinoma patients after GPC3(144-152) peptide vaccination. The present study was designed to evaluate the tumor reactivity of a HLA-A2-restricted GPC3(144-152) peptide-specific CTL clone against ovarian clear cell carcinoma (CCC) cell lines. The GPC3(144-152) peptide-specific CTL clone could recognize HLA-A2-positive and GPC3-positive ovarian CCC cell lines on interferon (IFN)-γ enzyme-linked immunospot assay and showed cytotoxicity against KOC-7c cells. The CTL clone recognized naturally processed GPC3-derived peptide on ovarian CCC cells in a HLA class I-restricted manner. Moreover, we confirmed that the level of GPC3 expression was responsible for CTL recognition and that subtoxic-dose chemotherapy made tumor cells more susceptible to the cytotoxic effect of CTL. Thus, it might be possible to treat ovarian CCC patients by combining chemotherapy with immunotherapy. Our data suggest that GPC3 could be an effective target for immunotherapy against ovarian CCC.

Role of apoptosis resistance in immune evasion and metastasis of colorectal cancer

The host immune system functions as a guardian against tumor development. It has been demonstrated that cytotoxic T lymphocyte (CTL)-mediated cytotoxic pathways function to inhibit or delay human colorectal cancer development. However, the host anti-tumor immune responses also 'edit' the tumor and select for more aggressive variants, resulting in immune evasion and tumor escape. Fas is a death receptor that mediates one of the major cytotoxic effector mechanisms of the CTLs. Fas is highly expressed in normal human colon epithelial cells but is frequently silenced in colorectal carcinoma, especially in metastatic colorectal carcinoma, suggesting that loss of Fas expression and function may be an immune evasion and tumor escape mechanism. In addition, recent studies indicated that Fas also mediates cellular proliferation signaling pathways to promote tumor development. Therefore, the death receptor Fas may not only transduce death signals to suppress tumor development but also activate cellular proliferation and the migration process to promote tumor growth and progression. Thus, understanding the mechanisms by which the Fas receptor and its associated protein complex transduces the death and survival signals may identify molecular targets for the development of therapeutic strategy to enhance the Fas-mediated death signals to increase the efficacy of cancer immunotherapy.

ICAM-1 has a critical role in the regulation of metastatic melanoma tumor susceptibility to CTL lysis by interfering with PI3K/AKT pathway

Human primary melanoma cells (T1) were found to be more susceptible to lysis by a Melan-A/MART-1-specific CTL clone (LT12) than their metastatic derivative (G1). We show that this differential susceptibility does not involve antigen presentation by target cells, synapse formation between the metastatic target and CTL clone, or subsequent granzyme B (GrB) polarization. Although PI-9, an inhibitor of GrB, was found to be overexpressed in metastatic G1 cells, knockdown of the PI-9 gene did not result in the attenuation of G1 resistance to CTL-induced killing. Interestingly, we show that whereas T1 cells express high levels of intercellular adhesion molecule-1 (ICAM-1), a dramatically reduced expression was noted on G1 cells. We also showed that sorted ICAM-1+ G1 cells were highly sensitive to CTL-induced lysis compared with ICAM-1- G1 cells. Furthermore, incubation of metastatic G1 cells with IFN-gamma resulted in the induction of ICAM-1 and the potentiation of their susceptibility to lysis by LT12. More importantly, we found that the level of ICAM-1 expression by melanoma cells correlated with decreased PTEN activity. ICAM-1 knockdown in T1 cells resulted in increased phosphorylation of PTEN and the subsequent activation of AKT. We have additionally shown that inhibition of the phosphatidylinositol (3,4,5)-triphosphate kinase (PI3K)/AKT pathway by the specific inhibitor wortmannin induced a significant potentiation of susceptibility of G1 and ICAM-1 small interfering RNA-treated T1 cells to CTL-induced lysis. The present study shows that a shift in ICAM-1 expression, which was associated with an activation of the PI3K/AKT pathway, can be used by metastatic melanoma cells to escape CTL-mediated killing.

Dissection of spontaneous cytotoxicity by human intestinal intraepithelial lymphocytes: MIC on colon cancer triggers NKG2D-mediated lysis through Fas ligand

Human intestinal intraepithelial lymphocytes (IELs), which are T-cell receptor alphabeta+ CD8+ T cells located between epithelial cells (ECs), are likely to participate in the innate immune response against colon cancer. IELs demonstrate spontaneous cytotoxic (SC) activity specifically directed against EC tumours but not against other solid tumour types. The aim of this study was to dissect out the mechanism of SC activity, focusing on the interaction of NKG2D on IELs with its ligands [major histocompatibility complex (MHC) class I chain-related protein (MIC) and UL16 binding protein (ULBP)] found mainly on EC tumours. A novel series of events occurred. The NKG2D-MIC/ULBP interaction induced Fas ligand (FasL) production and FasL-mediated SC activity against HT-29 cells and MIC-transfectants. Tumour necrosis factor-alpha and interferon-gamma, produced independently of this interaction, promoted SC activity. The immune synapse was strengthened by the interaction of CD103 on IELs with E-cadherin on HT-29 cells. Neither T-cell receptor nor MHC class I was involved. While the HT-29 cells were destroyed by soluble FasL, tumour necrosis factor-alpha and interferon-gamma, the IELs were resistant to the effects of these mediators and to FasL expressed by the HT-29 cells. This unidirectional FasL-mediated cytotoxicity of IELs against HT-29 cells, triggered through NKG2D, is unique and is likely to be a property of those CD8+ tumour-infiltrating lymphocytes that phenotypically resemble IELs.

Progress in studies on the Fas/FasL expression system and colon carcinoma

Cell apoptosis or programmed cell death is the term used to describe active cell death to maintain stability under physiological and pathological conditions. Interaction of the death receptor and death ligand is one of the main ways to induce apoptosis, of which, the Fas/FasL system is considered as the major signal transduction pathway to mediate apoptosis. Colon carcinoma is one of the common malignant tumors that are a threat to human health. The occurrence and development of colon carcinoma is related to the regulation imbalance of cell apoptosis. This article reviews the relationship between the Fas/FasL expression system and the occurrence and development of colon carcinoma.

Adoptive T cell therapy for cancer in the clinic

The transfusion of lymphocytes, referred to as adoptive T cell therapy, is being tested for the treatment of cancer and chronic infections. Adoptive T cell therapy has the potential to enhance antitumor immunity, augment vaccine efficacy, and limit graft-versus-host disease. This form of personalized medicine is now in various early- and late-stage clinical trials. These trials are currently testing strategies to infuse tumor-infiltrating lymphocytes, CTLs, Th cells, and Tregs. Improved molecular biology techniques have also increased enthusiasm and feasibility for testing genetically engineered T cells. The current status of the field and prospects for clinical translation are reviewed herein.

Cancer vaccines: preclinical studies and novel strategies

The development of cancer vaccines, aimed to enhance the immune response against a tumor, is a promising area of research. A better understanding of both the molecular mechanisms that govern the generation of an effective immune response and the biology of a tumor has contributed to substantial progress in the field. Areas of intense investigation in cancer immunotherapy will be discussed here, including: (1) the discovery and characterization of novel tumor antigens to be used as targets for vaccination; (2) the investigation of different vaccine-delivery modalities such as cellular-based vaccines, protein- and peptide-based vaccines, and vector-based vaccines; (3) the characterization of biological adjuvants to further improve the immunogenicity of a vaccine; and (4) the investigation of multimodal therapies where vaccines are being combined with other oncological treatments such as radiation and chemotherapy. A compilation of data from preclinical studies conducted in vitro as well as in animal models is presented here. The results from these studies would certainly support the development of new vaccination strategies toward cancer vaccines with enhanced clinical efficacy.

Anti-idiotype antibody induced cellular immunity in mice transgenic for human carcinoembryonic antigen

In the present study, we have analysed the detailed cellular immune mechanisms involved in tumour rejection in carcinoembryonic antigen (CEA) transgenic mice after immunization with dendritic cells (DC) pulsed with an anti-idiotype (Id) antibody, 3H1, which mimics CEA. 3H1-pulsed DC vaccinations resulted in induction of CEA specific cytotoxic T lymphocyte (CTL) responses in vitro and the rejection of CEA-transfected MC-38 murine colon carcinoma cells, C15, in vivo (Saha et al.,Cancer Res 2004; 64: 4995-5003). These CTL mediated major histocompatibility complex (MHC) class I-restricted tumour cell lysis, production of interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha), and expression of Fas ligand (FasL) and TNF-related apoptosis-inducing ligand (TRAIL) in response to C15 cells. CTL used perforin-, FasL-, and TRAIL-mediated death pathways to lyse C15 cells, although perforin-mediated killing was the predominant lytic mechanism in vitro. The cytokines IFN-gamma and TNF-alpha synergistically enhanced surface expression of Fas, TRAIL receptor, MHC class I and class II on C15 cells that increased the sensitivity of tumour cells to CTL lysis. CTL activity generated in 3H1-pulsed DC immunized mice was directed against an epitope defined by the idio-peptide LCD-2, derived from 3H1. In vivo lymphocyte depletion experiments demonstrated that induction of CTL response and antitumour immunity was dependent on both CD4+ and CD8+ T cells. The analysis of splenocytes of immunized mice that had rejected C15 tumour growth revealed up-regulated surface expression of memory phenotype Ly-6C and CD44 on both CD4+ and CD8+ T cells. The adoptive transfer experiments also suggested the role of both CD4+ and CD8+ T cells in this model system. Furthermore, mice that had rejected C15 tumour growth, developed tumour-specific immunological memory.

Nitric oxide promotes resistance to tumor suppression by CTLs

Many human tumors express inducible NO synthetase (NOS2), but the roles of NO in tumor development are not fully elucidated. An important step during tumor development is the acquisition of apoptosis resistance. We investigated the dose-dependent effects of endogenously produced NO on apoptosis using ecdysone-inducible NOS2 cell lines. Our results show that short-term NOS2 expression enhances CD95-mediated apoptosis and T cell cytotoxicity dose dependently. Furthermore, we could show that during chronic exposure to NO, besides the primary cytotoxic NO effect, there is selection of cell clones resistant to NO that show cross-resistance to CD95-induced apoptosis and the killing by CTLs. We propose that NO production could initially act as an autocrine suicide or paracrine killing mechanism in cells undergoing malignant transformation. However, once failed, the outcome is fatal. NO promotes tumor formation by enhancing the selection of cells that can evade immune attack by acquiring apoptosis resistance.

Global alterations in mRNA polysomal recruitment in a cell model of colorectal cancer progression to metastasis

Tumour onset and progression are due to the accumulation of genomic lesions, which alter gene expression and ultimately proteome activities. These lesions are thought to affect primarily the transcriptional control of gene expression. In the present study, we aimed at evaluating the genome-wide occurrence of alterations in the translational control exploiting an isogenic, phenotypically validated cellular model of colorectal cancer (CRC) transition from invasive carcinoma to metastasis. In this model, microarray profiling shows that changes in the level of messenger ribonucleic acid (mRNA) association with polysomes occur more than 2-fold than changes in the level of total cellular mRNA. When common to both the total and polysomal compartments, these changes are also homodirectional, being amplified in magnitude at the polysomal level. Comparison between the transcriptional and the translational fluctuations revealed distinct signatures of statistically over-represented gene functions, involving the program of cell proliferation for both levels of analysis, while the apoptosis and the translation programs were affected mainly at translation. Looking for an upstream determinant of translational deregulation, we found an increase in the hyperphosphorylated form of the 4E-BP1 protein in the metastatic cell line, possibly resulting in an increased activation of cap-dependent translation due to increased activity of the eIF4E protein. Analysis of the distribution profiles for the 5' untranslated region (5'-UTR) length of the changed genes showed an association between longer 5'-UTRs and the probability for the relevant gene to be altered translationally, consistent with enhanced eIF4E function. This genome-wide analysis is in favour of a model of profound alteration of translational control in late CRC progression. It also suggests polysomal mRNA profiles as a new, informative dimension for the study of transcriptome imbalance in cancer.

Overexpression of thymosin β-4 renders SW480 colon carcinoma cells more resistant to apoptosis triggered by FasL and two topoisomerase II inhibitors via downregulating Fas and upregulating Survivin expression, respectively

The present work was conducted to further examine the effects of thymosin beta-4 (Tbeta4) upregulation on the apoptosis of SW480 colon cancer cells induced by T cells and various chemotherapeutic agents because reduced susceptibility to the cytotoxicity of an anti-Fas IgM (CH-11) in Tbeta4-overexpressing cells has previously been reported by us. As expected, Tbeta4 overexpressers were also more resistant to the killing effect of FasL-bearing Jurkat T cells. On the other hand, pretreating these cells with an MMP inhibitor restored not only their Fas levels but also their sensitivity to CH-11, suggesting a pivotal role of MMP in downregulating Fas in Tbeta4 overexpressers. Interestingly, while the susceptibilities of Tbeta4 overexpressers to 5-FU and irinotecan remained unchanged, they were more resistant to doxorubicin and etoposide which triggered apoptosis via a mitochondrial pathway. Concordantly, activation of both caspases 9 and 3 in Tbeta4 overexpressers by the two aforementioned topoisomerase II inhibitors was dramatically abrogated which could be accounted mainly by an increased expression of Survivin, a critical anti-apoptotic factor. Finally, poor survival was found in stage III colon cancer patients whose tumors were stained positively by the anti-Survivin antibody. Thus, advantages such as immune evasion and resistance to anticancer drug-induced apoptosis acquired by colon cancer cells through Tbeta4 overexpression might facilitate their survival during metastasis and chemotherapy.

Chemosensitization of Pancreatic Carcinoma Cells to Enhance T Cell-Mediated Cytotoxicity Induced by Tumor Lysate-Pulsed Dendritic Cells

Dendritic cells (DCs) can induce cytotoxic T-cell (CTL) responses against tumor antigens in vitro and in vivo, yet few cancer patients experience tumor regression after DC-based vaccination. Combination with other treatment modalities, such as radiation or pharmacologic anticancer agents, may reduce tumor cell resistance against immune responses. The authors tested whether treatment with gemcitabine or cyclooxygenase-2 (COX-2) inhibitors increases the sensitivity of pancreatic carcinoma cells to CTL-mediated killing. Monocyte-derived DCs of HLA-A2+ donors were loaded with lysate from the HLA-A2+ pancreatic carcinoma cell line Panc-1 and co-cultured with autologous CD3+ T cells. ELISPOT and cytotoxicity assays performed after two rounds of in vitro stimulation confirmed induction of a tumor-specific CTL response. Changes in the magnitude and the effector mechanism of the CTL response were analyzed after treatment of Panc-1 cells with gemcitabine and COX-2 inhibitors. Compared with gemcitabine, COX-2 inhibitors more effectively sensitized Panc-1 cells to CTL-mediated killing and showed less inhibition of T-cell activation by DCs in vitro. Using anti-CD95 blocking antibody, the authors showed that the increase in CTL-mediated tumor cell killing observed after treatment with COX-2 inhibitors is dependent on CD95/CD95 ligand interaction. Increased apoptosis of Panc-1 cells treated with COX-2 inhibitor was also observed after incubation with agonistic anti-CD95 antibody. Sensitization of cancer cells to CD95-dependent killing by CTLs represents a novel mechanism of action for COX-2 inhibitors and provides a rationale for their concomitant use with immunotherapeutic strategies such as DC-based vaccination.

Antigen-specific CD8+ T lymphocytes generated from a DNA vaccine control tumors through the Fas-FasL pathway

Human papillomavirus, particularly type 16, and its oncogenic proteins, E6 and E7, are consistently expressed in most cervical cancers. One of the major issues facing cancer immunotherapy is that many human cancers evade the immune system by downregulating the expression of Fas molecules. An E7-expressing murine tumor model with a downregulated Fas expression--TC-1 P3(A15) tumors--was created. A DNA vaccine encoding calreticulin linked to E7 (CRT/E7) was able to generate protective and therapeutic antitumor effects against TC-1 P3(A15) tumors. In vitro Ab depletion and in vivo adoptive experiments showed that the antitumor effect of E7-specific CD8+ T lymphocytes against the TC-1 P3(A15) tumor cells was through the Fas-FasL-dependent CTL effector mechanism, and the TC-1 P3(A15) tumor cells needed higher numbers of antigen-specific CD8+ T lymphocytes for in vivo elimination. Our results demonstrated that chimeric CRT/E7 DNA vaccine resulted in control of tumors with downregulated Fas expression, highlighting the importance of the Fas-FasL pathway in the potent antitumor effect of antigen-specific CD8+ cytotoxic T lymphocytes and the role of Fas as part of in vivo tumor evasion.

Activation of CD40 in Cervical Carcinoma Cells Facilitates CTL Responses and Augments Chemotherapy-Induced Apoptosis

In this study, we describe the expression and function of CD40, a TNF receptor family member, in cervical carcinomas. CD40 was present at very low levels in normal cervical epithelium but was overexpressed in human papillomavirus-infected lesions and advanced squamous carcinomas of the cervix. The stimulation of CD40-positive cervical carcinoma cell lines with soluble CD40L (CD154) resulted in activation of the NF-kappaB and MAPK signaling pathways and up-regulation of cell surface markers and intracellular molecules associated with Ag processing and presentation. Concomitantly, the CD154-induced activation of CD40 in carcinoma cells was found to directly influence susceptibility to CTL-mediated killing. Thus, CD40 stimulation in cervical carcinoma cell lines expressing a TAP-dependent human papillomavirus 16 E6 Ag epitope resulted in their enhanced killing by specific CTLs. However, CD154 treatment of carcinoma cells expressing proteasome-dependent but TAP-independent Ags from the EBV-encoded BRLF1 and BMLF1 failed to increase tumor cell lysis by specific CTLs. Moreover, we demonstrate that chemotherapeutic agents that suppress protein synthesis and reverse the CD40-mediated dissociation of the translational repressor eukaryotic initiation factor 4E-binding protein from the initiation factor eukaryotic initiation factor 4E, such as 5-fluorouracil, etoposide, and quercetin, dramatically increase the susceptibility of cervical carcinoma cells to CD40L-induced apoptosis. Taken together, these observations demonstrate the functional expression of CD40 in epithelial tumors of the cervix and support the clinical exploitation of the CD40 pathway for the treatment of cervical cancer through its multiple effects on tumor cell growth, apoptosis, and immune recognition.

In vivo rejection of tumor cells dependent on CD8 cells that kill independently of perforin and FasL

Perforin/granzyme B- and Fas/FasL-mediated killing pathways are the main effector mechanisms of CTL and NK cells in antitumor immune responses. In this study, we investigated the relative role of these two lytic mechanisms in protection of the host from tumor progression, as well as spontaneous metastasis, using the D122 Lewis lung carcinoma and its gene-modified cells. Utilizing perforin knockout mice (B6-PKO) and Fas and FasL mutant (B6-MRL and B6-Smn) mice, we found that perforin expression in the host plays a crucial function in the prevention of metastasis. However, local tumor rejection of an H-2K(b) and B7-1 transfectant, 39.5-B7 cells, was not dependent either on perforin or Fas/FasL expression in vivo. In addition, CTL lysis of 39.5-B7 cells was independent of perforin and Fas/FasL interactions in 18-hour in vitro assays. We also confirmed that CD8 T-cells were responsible for rejecting 39.5-B7 local tumors, yet cytokines, TNF-alpha and gammaIFN were not involved in tumor rejection in vivo. Furthermore, blocking assays using caspase inhibitors (zVAD-fmk, zLETD-fmk and zLEHD-fmk) showed that, whereas caspase activation was partially required to induce 39.5-B7 lysis mediated by the perforin-dependent pathway, 39.5-B7 lysis by CTLs through the perforin-independent mechanism required caspase activation. Thus, these results suggested that perforin, Fas/FasL, gammaIFN and TNF-alpha independent lytic mechanisms, mediated by CD8 T cells, have a crucial role in rejection of 39.5-B7 cells in vivo. Caspase activation is a pre requisite for apoptosis of targets by CTLs.

Treatment of melanoma with 5-fluorouracil or dacarbazine in vitro sensitizes cells to antigen-specific CTL lysis through perforin/granzyme- and Fas-mediated pathways

Several factors may influence sensitivity of melanoma cells to CTL lysis. One is the avidity of the CTL TCR. A second is that certain cytotoxic drugs have been reported to sensitize cancer cells to CTL lysis through Fas-mediated apoptosis. In this study, we examined whether antineoplastic agents 5-fluorouracil (5-FU) and dacarbazine (DTIC) sensitize melanoma cells to lysis of G209 peptide-specific CTL. Our results show that CTL generated from PBMC are HLA-A2 restricted and gp100 specific. Treatment with 5-FU or DTIC sensitized melanoma cells to lysis of G209-specific CTL. Most importantly, 5-FU- or DTIC-treated melanoma cells also became sensitive to low-avidity CTL, which per se are less cytolytic to melanomas. We sought to identify apoptotic pathways mediating this effect. The enhanced cytolysis was mediated through the perforin/granzyme pathway. Although 5-FU up-regulated FasR expression on melanoma cells, sensitization was not blocked by anti-Fas Ab, and the G209-specific CTL was Fas ligand (FasL) negative. However, when G209-specific CTL were stimulated to express FasL, FasL signaling also contributed to enhanced cytolysis. DTIC treatment, which did not increase FasR expression, also sensitized FasL-mediated killing induced by neutralizing anti-Fas Ab. For CD95L-positive G209-specific CTL, the sensitization was primarily mediated through the perforin/granzyme pathway regardless of up-regulation of FasR. The findings demonstrate that cytotoxic drug-mediated sensitization primes both perforin/granzyme and Fas-mediated killing by melanoma-specific CTL. Considering that most of autoreactive antitumor CTL are low avidity, the findings provide experimental basis for understanding cytotoxic and immunologic therapeutic synergy in melanoma.

Exposure of human primary colon carcinoma cells to anti-Fas interactions influences the emergence of pre-existing Fas-resistant metastatic subpopulations

Fas, an important death receptor-mediated signaling pathway, has been shown to be down-regulated during human colon tumorigenesis; however, how alterations in Fas expression influence the metastatic process remains unresolved. In mouse models, loss of Fas function was found to be both necessary and sufficient for tumor progression. In this study, we investigated the link between functional Fas status and malignant phenotype using a matched pair of naturally occurring primary (Fas-sensitive) and metastatic (Fas-resistant) human colon carcinoma cell lines in both in vitro and in vivo (xenograft) settings. Metastatic sublines were produced in vitro from the primary tumor cell line by functional elimination of Fas-responsive cells. Conversely, sublines derived from the primary tumor in vivo at distal metastatic sites were Fas-resistant. In contrast, simply disrupting the Fas pathway by molecular-based strategies in the Fas-sensitive primary tumor failed to achieve the same metastatic outcome. Interestingly, both in vitro- and in vivo-produced sublines resembled the naturally occurring metastatic population, based on functional and morphologic studies and genome-scale gene expression profiling. Overall, using this human colon carcinoma model, we: 1) showed that loss of Fas function was linked to, but alone was insufficient for, acquisition of a detectable metastatic phenotype; 2) demonstrated that metastatic subpopulations pre-existed within the heterogeneous primary tumor, and that anti-Fas interactions served as a selective pressure for their outgrowth; and 3) identified a large set of differentially expressed genes distinguishing the primary from metastatic malignant phenotypes. Thus, Fas-based interactions may represent a novel mechanism for the biologic or immunologic selection of certain types of Fas-resistant neoplastic clones with enhanced metastatic ability.

A different pattern of cytotoxic T lymphocyte recognition against primary and metastatic tumor cells in a patient with nonsmall cell lung carcinoma

BACKGROUND

Lung carcinoma represents the most frequent cause of cancer death worldwide because of tumor metastases. The objective of the current study was to analyze the immunologic response during the progress of lung carcinoma metastasis.

METHODS

The authors established two tumor cell lines that were derived from primary and metastatic lesions in a patient with lung carcinoma (Patient G603). One cell line (G603L) was established from the primary lesion, and the other cell line (G603AD) was established from a metastatic lesion in the right adrenal gland 7 months after the patient underwent surgery for the primary lesion. Autologous regional lymph node lymphocytes were stimulated with CD80-transfected G603L cells, then cytotoxic T lymphocytes (CTLs) were induced against both lung carcinoma cell lines.

RESULTS

Both G603L cells and G603AD cells expressed Class I human leukocyte antigen, intracellular cell adhesion molecule 1, and lymphocyte-associated antigen type 3 (LFA-3), but not Fas or Fas ligand on their surfaces. By stimulation with CD80-transfected G603L cells, 2 CTL clones (H2/17 and H2/36) were established from the bulk CTLs. CTL clone H2/17 lysed G603L cells but not G603AD cells, suggesting that the antigen recognized by CTL clone H2/17 was abrogated during the process of metastasis. In contrast, CTL clone H2/36 lysed both G603L cells and G603AD cells, indicating that the antigen recognized by CTL clone H2/36 was maintained in the tumor cells throughout tumor progression.

CONCLUSIONS

The results demonstrated the possibility that some tumor-associated antigens may be abrogated during the process of metastasis, although others are maintained. The identification of these antigens will lead to a better understanding of their immunologic role during disease progression in patients with lung carcinoma.

Enhanced susceptibility of oral squamous cell carcinoma cell lines to FAS-mediated apoptosis by cisplatin and 5-fluorouracil

Our study was conducted to investigate whether anticancer drugs, cisplatin (CDDP) and/or 5-fluorouracil (5-FU), can modulate Fas-mediated apoptosis in oral squamous cell carcinoma (OSCC) cell lines. When OSCC cell lines, NA and HSC-4, were treated with CDDP and/or 5-FU, Fas and its mRNA expression on the plasma membrane were enhanced. An increase in caspase-3 and -8 activities was then observed by the addition of agonistic anti-Fas antibody, CH-11. Apoptosis of OSCC cells treated with anticancer drugs were significantly enhanced by CH-11, whereas untreated cells were nearly resistant to apoptosis. Moreover, the combination of CDDP and 5-FU resulted in an increasing susceptibility to apoptosis. Caspase-3 and -8 inhibitors, but not caspase-9 inhibitor, reduced Fas-mediated apoptosis enhanced by the anticancer drugs. Furthermore, OSCC cells treated with anticancer drugs exhibited decreased cellular FADD-like interleukin 1-converting enzyme-inhibitory protein (c-FLIP) levels, whereas neither the Fas-associated death domain-containing protein (FADD) nor procaspase-8 changed the expression. Moreover, antisense oligonucleotide to c-FLIP confirmed that down-regulation of c-FLIP induced sensitization to Fas-mediated apoptosis. These results suggest that CDDP and 5-FU may enhance the susceptibility to Fas-mediated apoptosis through down-regulation of c-FLIP. From these findings, a new potential strategy may be developed to improve the efficacy of anticancer drugs.

The Fas/Fas ligand pathway is important for optimal tumor regression in a mouse model of CTL adoptive immunotherapy of experimental CMS4 lung metastases

The mechanisms of CTL-mediated tumor regression in vivo remain to be fully understood. If CTL do mediate tumor regression in vivo by direct cytotoxicity, this may occur via two major effector mechanisms involving the secretion of perforin/granzymes and/or engagement of Fas by Fas ligand (FasL) expressed by the activated CTL. Although the perforin pathway has been considered the dominant player, it is unclear whether Fas-mediated cytotoxicity is additionally required for optimal tumor rejection. Previously, we produced H-2L(d)-restricted CTL reactive against the CMS4 sarcoma, which expresses a naturally occurring rejection Ag recognized by these CTL and harbors a cytokine (IFN-gamma plus TNF)-inducible, Fas-responsive phenotype. The adoptive transfer of these CTL to syngeneic BALB/c mice with minimal (day 3 established) or extensive (day 10 established) experimental pulmonary metastases resulted in strong antitumor responses. Here we investigated whether a FasL-dependent CTL effector mechanism was important for optimal tumor regression in this adoptive immunotherapy model. The approach taken was to compare the therapeutic efficacy of wild-type to FasL-deficient (gld) CTL clones by adoptive transfer. In comparison with wild-type CTL, gld-CTL efficiently mediated tumor cytolysis and produced comparable amounts of IFN-gamma, after tumor-specific stimulation, as in vitro assessments of Ag recognition. Moreover, gld-CTL mediated comparably potent antitumor effects in a minimal disease setting, but were significantly less effective under conditions of an extensive tumor burden. Overall, under conditions of extensive lung metastases, these data revealed for the first time an important role for a FasL-dependent CTL effector mechanism in optimal tumor regression.

Coordinate regulation of IFN consensus sequence-binding protein and caspase-1 in the sensitization of human colon carcinoma cells to Fas-mediated apoptosis by IFN-gamma

Interferon-gamma is thought to be essential for the regulation of antitumor reactions. However, the degree of responsiveness of malignant cells to IFN-gamma may have a profound influence on the overall efficacy of an antitumor response. In this study, we examined the molecular basis by which IFN-gamma differentially sensitized human primary and metastatic colon carcinoma cells to Fas-mediated apoptosis. To that end, we analyzed IFN-gamma-induced gene expression at the genome scale, followed by an analysis of the expression and function of specific genes associated with IFN-gamma- and Fas-mediated signaling. We found that although both cell populations exhibited a similar gene expression profile at the genome scale in response to IFN-gamma, the expression intensities of the IFN-gamma-regulated genes were much greater in the primary tumor. Noteworthily, two genes, one involved in IFN-gamma-mediated signaling, IFN consensus sequence-binding protein (ICSBP), and one involved in Fas-mediated signaling, caspase-1, were clearly shown to be differentially induced between the two cell lines. In the primary tumor cells, the expression of ICSBP and caspase-1 was strongly induced in response to IFN-gamma, whereas they were weakly to nondetectable in the metastatic tumor cells. Functional studies demonstrated that both caspase-1 and ICSBP were involved in Fas-mediated apoptosis following IFN-gamma sensitization, but proceeded via two distinct pathways. This study also reports for the first time the expression of ICSBP in a nonhemopoietic tumor exhibiting proapoptotic properties. Overall, in a human colon carcinoma cell model, we identified important functional contributions of two IFN-gamma-regulated genes, ICSBP and caspase-1, in the mechanism of Fas-mediated death.

Tumor-specific CTL kill murine renal cancer cells using both perforin and Fas ligand-mediated lysis in vitro, but cause tumor regression in vivo in the absence of perforin

Kidney cancer is a devastating disease; however, biological therapies have achieved some limited success. The murine renal cancer Renca has been used as a model for developing new preclinical approaches to the treatment of renal cell carcinoma. Successful cytokine-based approaches require CD8(+) T cells, but the exact mechanisms by which T cells mediate therapeutic benefit have not been completely identified. After successful biological therapy of Renca in BALB/c mice, we generated CTLs in vitro using mixed lymphocyte tumor cultures. These CTL mediated tumor-specific H-2K(d)-restricted lysis and production of IFN-gamma, TNF-alpha, and Fas ligand (FasL) in response to Renca. CTL used both granule- and FasL-mediated mechanisms to lyse Renca, although granule-mediated killing was the predominant lytic mechanism in vitro. The cytokines IFN-gamma and TNF-alpha increased the sensitivity of Renca cells to CTL lysis by both granule- and FasL-mediated death pathways. Adoptive transfer of these anti-Renca CTL into tumor-bearing mice cured most mice of established experimental pulmonary metastases, and successfully treated mice were immune to tumor rechallenge. Interestingly, we were able to establish Renca-specific CTL from mice gene targeted for perforin (pfp(-/-)) mice. Although these pfp(-/-) CTL showed reduced cytotoxic activity against Renca, their IFN-gamma production in the presence of Renca targets was equivalent to that of wild-type CTL, and adoptive transfer of pfp(-/-) CTL was as efficient as wild-type CTL in causing regression of established Renca pulmonary metastases. Therefore, although granule-mediated killing is of paramount importance for CTL-mediated lysis in vitro, some major in vivo effector mechanisms clearly are independent of perforin.

Positive and negative consequences of soluble Fas ligand produced by an antigen-specific CD4(+) T cell response in human carcinoma immune interactions

The influence of a human CD4(+) T cell response in anti-carcinoma immune reactions remains largely uncharacterized. Here, we made use of a major histocompatibility complex (MHC) class-II-restricted, anti-ras oncogene-specific CD4(+) T cell line produced previously in vivo from a patient with metastatic carcinoma in a peptide-based phase I trial. Using this patient-derived T cell line as a potentially relevant cell type, we examined the consequences of the anti-carcinoma CD4(+) T cell response, with emphasis on specific lymphokines potentially important for the regulation of Fas/Fas ligand (FasL) interactions. Antigen (Ag)-specific CD4(+) T cells produced substantial amounts of IFN-gamma following recognition of MHC class-II-matched Ag-presenting cells expressing the cognate peptide. The IFN-gamma promoted significant upregulation of Fas on the surface of colon carcinoma cells and sensitized these targets to Fas-mediated apoptosis and Ag-specific CD8(+) cytotoxic T lymphocyte (CTL)-mediated lysis involving a Fas-based effector mechanism. Moreover, Ag-stimulated CD4(+) T cells secreted soluble FasL (sFasL), which induced the death of TNF-resistant/refractory colon, breast, and ovarian carcinoma cells. Interestingly, although CD4(+)-derived sFasL expressed cytotoxic activity, the recovery of carcinoma cells which resisted Fas-mediated lysis displayed enhanced metastatic ability in vivo, compared with the unselected parental population, in an athymic mouse model. Thus, a tumor-specific CD4(+) T cell response may have both positive and negative consequences in human carcinoma via the production of proinflammatory cytokines such as IFN-gamma and/or sFasL that may (1) improve or facilitate CTL-target engagement, contact-independent effector mechanisms, and the overall lytic outcome and (2) potentially select for Fas-resistant tumor cells that escape immune destruction, which may thus impact the metastatic process.