Fas/Apo-1 (CD95)-mediated apoptosis of neutrophils with Fas ligand (CD95L)-expressing tumors is crucial for induction of inflammation by neutrophilic polymorphonuclear leukocytes associated with antitumor immunity

Polymorphonuclear Neutrophils and Tumors: Friend or Foe?

Tumor microenvironment (TME) is a dynamic network that apart from tumor cells includes also cells of the immune system, e.g., neutrophils, which are recruited from blood circulation. In TME, neutrophils are strongly implicated in the direct and indirect interactions with tumor cells or other immune cells, and they play roles in both preventing and/or facilitating tumor progression and metastasis. The dual role of neutrophils is determined by their high plasticity and heterogeneity. Analogous to the macrophages, neutrophils can express antitumoral (N1) and protumoral (N2) phenotypes which differ substantially in morphology and function. N1 phenotype characterizes with a high cytotoxic and proinflammatory activities, while N2 phenotype with immunosuppressive and prometastatic properties. The antitumoral effect of neutrophils includes for example the production of reactive oxygen species or proapoptotic molecules. The protumoral action of neutrophils relies on releasing of proangiogenic and prometastatic mediators, immunosuppressive factors, as well as on direct helping tumor cells in extravasation process. This chapter summarizes the heterogeneity of neutrophils in TME, as well as their dual role on tumor cells.

Neutrophil Suppresses Tumor Cell Proliferation via Fas /Fas Ligand Pathway Mediated Cell Cycle Arrested

While neutrophils have dutifully performed their function in injury and infection, the recent works have found that cytotoxicity and/or cytostatic of neutrophils has also been observed in tumor. Till now the molecular players that participate in this neutrophils antitumoral effect remain unclear. In the current study, we find that neutrophils from healthy donors have potent suppression to tumor cell lines by physical contact. Importantly, these suppression activities seem to be cancer cell-specific which is not observed in the normal cells. Further observations show that neutrophils mediated tumor cell lines growth inhibitory effect through early cell cycle arrested. Treatment with an antagonist Fas receptor in A549 cell line or knocking out of the Fas gene in A549 cell line recovers tumor cells cycle and lessen neutrophils anti-tumor effect. The interaction between neutrophils and A549 cell line through Fas ligand /Fas regulates the expression of cell cycle checkpoint proteins, leading to early cell cycle arrest. This phenomenon is also seen in other 3 tumor cell lines. Taken together, our results identified a new role of Fas ligand /Fas interaction in neutrophils antitumoral effect in tumors via arresting cell cycle.

Cell death-independent activities of the death receptors CD95, TRAILR1, and TRAILR2

Since their identification more than 20 years ago, the death receptors CD95, TRAILR1, and TRAILR2 have been intensively studied with respect to their cell death-inducing activities. These receptors, however, can also trigger a variety of cell death-independent cellular responses reaching from the activation of proinflammatory gene transcription programs over the stimulation of proliferation and differentiation to induction of cell migration. The cell death-inducing signaling mechanisms of CD95 and the TRAIL death receptors are well understood. In contrast, despite the increasing recognition of the biological and pathophysiological relevance of the cell death-independent activities of CD95, TRAILR1, and TRAILR2, the corresponding signaling mechanisms are less understood and give no fully coherent picture. This review is focused on the cell death-independent activities of CD95 and the TRAIL death receptors and addresses mainly three questions: (a) how are these receptors linked to noncell death pathways at the molecular level, (b) which factors determine the balance of cell death and cell death-independent activities of CD95 and the TRAIL death receptors at the cellular level, and (c) what are the consequences of the cell death-independent functions of these receptors for their role in cancer and inflammatory diseases.

Pre-existing Fas ligand (FasL) in cancer cells elicits tumor-specific protective immunity, but delayed induction of FasL expression after inoculation facilitates tumor formation

Overexpression of Fas ligand (FasL) in cancer cells elicits potential antitumor effects via recruitment of neutrophils. Conversely, FasL-expressing tumors may counterattack tumor-infiltrating lymphocytes by delivering apoptotic death signals via Fas/FasL interactions, which may lead to tumor escape. In order to distinguish the role of FasL in antitumor activity and tumor progression, Lewis lung carcinoma cells (LLC-1) were used to establish the cell line LLC-FasL, in which FasL expression was repressed by doxycycline (Dox) treatment and induced in the absence of Dox. LLC-FasL cells promote tumor regression when expressing FasL, whereas tumor outgrowth is observed by depletion of FasL expression. To investigate whether initial expression of FasL during tumor formation is critical for FasL-mediated tumor regression, Dox-treated LLC-FasL cells were inoculated into Dox-treated mice, but Dox treatment was stopped 5 days after inoculation. When low cell numbers were inoculated, we observed 80% survival and no tumor formation, whereas no mice survived inoculation with high cell numbers, despite the delayed induction of FasL by Dox withdrawal. The inoculation of a high density of cells may establish a favorable tumor microenvironment before the expression of FasL. Our findings demonstrate that FasL may elicit antitumor activity when it is initially present on injected cancer cells and thus can act prior to tumor microenvironment formation. Furthermore, a well-established tumor microenvironment abrogates FasL-mediated antitumor activity.

Polymorphonuclear neutrophils and cancer: intense and sustained neutrophilia as a treatment against solid tumors

Polymorphonuclear neutrophils (PMN) are the most abundant circulating immune cells and represent the first line of immune defense against infection. This review of the biomedical literature of the last 40 years shows that they also have a powerful antitumoral effect under certain circumstances. Typically, the microenvironment surrounding a solid tumor possesses many of the characteristics of chronic inflammation, a condition considered very favorable for tumor growth and spread. However, there are many circumstances that shift the chronic inflammatory state toward an acute inflammatory response around a tumor. This shift seems to convert PMN into very efficient anticancer effector cells. Clinical reports of unexpected antitumoral effects linked to the prolonged use of granulocyte colony-stimulating factor, which stimulates an intense and sustained neutrophilia, suggest that an easy way to fight solid tumors would be to encourage the development of intense peritumoral PMN infiltrates. Specifically designed clinical trials are urgently needed to evaluate the safety and efficacy of such drug-induced neutrophilia in patients with solid tumors. This antitumoral role of neutrophils may provide new avenues for the clinical treatment of cancer.

Regulatory T cells inhibit Fas ligand-induced innate and adaptive tumour immunity

CD4+CD25+ regulatory T cells (Treg) are known to influence T cell responses to tumours. Here we have explored the role of Treg in inhibiting not only adaptive, but also innate immune responses to tumours. To this end we used a Fas ligand (FasL)-expressing melanoma cell line in a mouse model. In this system, innate immunity is sufficient to reject the tumour. All mice depleted of Treg and challenged with FasL-expressing melanoma remained tumour-free. Investigation of the underlying cellular effector mechanisms revealed that depletion of Treg enhanced an NK cell response capable of tumour lysis. Furthermore, this initial innate immune response primed mice to make an effective adaptive immune response leading to complete rejection of challenge with the parental melanoma. Both antigen-specific antibody and CD4+ T cells were implicated in protection via adaptive immunity. We conclude that removal of Treg and vaccination with whole tumour cells expressing FasL activates multiple arms of the immune system, leading to efficient tumour rejection. These findings highlight a novel role for FasL in inducing innate immune responses that are normally inhibited by Treg and uncover an adjuvant effect of FasL that can be used to stimulate tumour immunity after depletion of Treg.

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

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

Fas ligand-dependent suppression of autoimmunity via recruitment and subsequent termination of activated T cells

Signals transmitted by binding of Fas ligand (FasL) to the Fas receptor (CD95/Apo-1) have pleiotropic effects on cellular function that present opportunities for therapeutic applications. For example, depending on the circumstances, overexpression of FasL can enhance, prevent, or reverse growth of spontaneous or transplantable tumors. Furthermore, local administration of FasL into a single paw in susceptible mice protects from or reduces the severity of collagen-induced arthritis (CIA) in all paws. Here, we define mechanisms that mediate systemic protection induced by locally delivered FasL. Protection is not solely dependent on local interactions between Fas and FasL, but rather requires induction of a paradoxical inflammatory response that not only destroys Fas-resistant tumors, but also recruits motile, activated, Fas-bearing T cells that are Fas sensitive. We demonstrate by following the antigen-specific recruitment and subsequent termination of transgenic T cells that activated T cells, including autoreactive cells responsible for CIA, are eliminated within this inflammatory environment through the overexpressed FasL. The nature of the inflammatory response, which depends on the Fas ligand being cell bound and not soluble, and the magnitude of FasL expression within the inflammatory milieu are essential for this effect, as arthritogenic inflammation alone resulting from CIA induction is insufficient to ameliorate the disease or eliminate antigen-specific T cells, even upon systemic delivery of soluble FasL. These data show that gene delivery of membrane-bound FasL can effectively recruit and eliminate autoreactive T cells.

Modification of tumor cells with Fas (CD95) antigen gene and Fas ligand (CD95L) gene transfection by electroporation for immunotherapy of cancer

Electroporation is a method for introducing DNA into cells by using a high-voltage electric field. This method is very simple and easily manipulated. We describe here a method for the modification of tumor cells with the Fas/Apo-1 (CD95) antigen-gene and Fas ligand (FasL)-gene transfection through the use of electroporation, and suggest that the Fas-FasL system is a good target for the induction of apoptosis-mediated antitumor activity. The Fas receptor/ligand system induces apoptosis and plays an important role in regulation of the immune system. In the method described, hepatoma MH134 (Fas- and FasL-) is transfected with murine Fas and FasL cDNA. A single administration of monoclonal anti-Fas antibody efficiently suppresses the growth of F6b (MH134+Neo+Fas) tumors but not that of N1d (MH134+Neo) tumors in gld/gld lpr/lpr mice. MH134+Neo+FasL tumor cells were rejected after the induction of inflammation with infiltration of neutrophils in mice. These results suggest that electroporation and Fas-mediated apoptosis are a good method for inducing of antitumor activity.

Enhancing antimelanoma immune responses through apoptosis

We examined the feasibility of using tumor apoptosis at accessible sites to enhance antimelanoma immune responses in a model of spontaneous canine melanoma. We show that priming peripheral blood mononuclear cells with apoptotic melanoma cells significantly enhanced autologous and allogeneic lymphokine-activated killing of tumor cells. Since various pathways required for intrinsic apoptosis are often inactivated in melanoma, we used Fas ligand (FasL) overexpression to promote extrinsic apoptosis. FasL induced apoptosis in five of six cell lines. Each of the susceptible lines, but not the resistant one, expressed Fas mRNA. In addition, direct intratumoral administration of FasL DNA to tumor-bearing dogs was safe, with no adverse events reported over 7 days of observation. A reduction of tumor burden was seen in three of five dogs treated. The reduction of tumor volume was correlated with Fas expression by the tumors, although one dog with a Fas-negative tumor survived for 82 weeks after treatment. Our data show that overexpression of FasL is suitable to promote apoptosis of Fas(+) melanomas, and support the notion that priming immune responder cells with apoptotic tumor cells may enhance antitumor responses. The results also suggest that intratumoral administration of FasL offers a safe route for therapeutic gene delivery.

Fas ligand breaks tolerance to self-antigens and induces tumor immunity mediated by antibodies

The role of Fas ligand (FasL) in programmed cell death via interaction with its receptor Fas is well characterized. It has been proposed that expression of FasL can confer immune privilege to some organs, allowing them to kill infiltrating lymphocytes and inflammatory cells. However, a number of studies have shown that when tumors or transplants express FasL, rejection often occurs as a consequence of proinflammatory functions of FasL. Here we demonstrate that FasL elicits tumor immunity in a murine melanoma model with weak immunogenicity and low expression of major histocompatibility complex (MHC) class I. We show that protected mice recognize melanocyte differentiation self-antigens. Importantly, tumor immunity is mediated by antibodies, as it can be transferred by serum from protected mice.

Cell death and immune privilege

The host response to pathogens involves complex inflammatory responses and immune reactions. While these are central to host defense and vital to clearing infections, they are often accompanied by injury to surrounding tissue. Most organ systems can tolerate these responses without permanent consequences. However, there are sites that limit the spread of inflammation because it can threaten organ function. The most prominent examples of these are the eye, brain, and reproductive organs (testis, ovary), where even minor bouts of inflammation can have long-term consequences for the survival of the organism. In these organs immune responses either do not proceed, or proceed in a manner different from other areas; thus, they are called "immunologically privileged." Here a functioning immune response can be the culprit that leads to disease.

Neutrophils in anti-cancer immunological strategies: old players in new games

This review highlights the new "immunological identity" of neutrophils within the cytokine network and their role in biology of diseases, particularly in tumor biology. The latest preclinical evidence of their involvement in anti-cancer immunotherapeutic and prophylactic strategies will be discussed with particular reference to the real possibilities of transferring experimental results to a clinical setting.

The role of Fas ligand in immune privilege

Immune privilege is a property of some sites in the body, whereby immune responses are limited or prevented. One explanation that has been proposed for this phenomenon is engagement of the pro-apoptotic molecule Fas by its ligand (FasL), which leads to apoptosis, and consequently limits an inflammatory response. This idea has recently been challenged, and here we review the evidence for and against a role for FasL in immune privilege.