Immune privilege or inflammation? Insights into the Fas ligand enigma

Comprehensive narrative review on the analysis of outcomes from cell transplantation clinical trials for discogenic low back pain

Background

Intervertebral disc (IVD) degeneration is one of the primary causes of low back pain (LBP) and despite a prominent prevalence, present treatment options remain inadequate for a large portion of LBP patients. New developments in regenerative therapeutics offer potentially powerful medical tools to modify this pathology, with specific focus on (stem) cell transplantations. Multiple clinical trials have since reported overall beneficial outcomes favoring cell therapy. Nonetheless, the significance of these improvements is often not (clearly) discussed. As such, this narrative review aims to summarize the significance of the reported improvements from human clinical trials on IVD-targeted cell therapy.

Methods

Through a comprehensive narrative review we discuss the improvements in pain, disability, quality of life, and imaging modalities and reported adverse events following cell therapy for discogenic pain.

Results

Most clinical trials were able to report clear and significant improvements in pain and disability outcomes. Imaging and quality of life improvements however were not as clearly reported but did present some enhancements for a select number of patients. Finally, whether cell therapy can outperform placebo treatment remains intangible.

Conclusions

Our review highlights the clinical significance of observed trends in pain and disability improvement. Nevertheless, reporting quality was found unsatisfactory and large-scale randomized controlled studies remain small in number. Future studies and articles should put more emphasis on improvements in imaging modalities and compare outcomes to (placebo) control groups to fully elucidate the efficacy and safety of cellular therapeutics against LBP.

An in-depth analysis of the immunomodulatory mechanisms of intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) is the pathological basis of disc herniation, spinal stenosis, and other related diseases, and the lower back pain it produces lays a heavy financial burden on individuals and society. Thus, it is essential to comprehend IVDD's pathophysiology. Numerous factors, such as inflammatory factors, oxidative stress, apoptosis, matrix metalloproteinases, are linked to IVDD pathogenesis. Despite the fact that many researches has provided explanations for the pathophysiology of IVDD, these studies are typically singular, restricted, and isolated, expound only on one or two components, and do not systematically analyze and summarize the numerous influencing elements. In addition, we discovered that the incidence of many chronic diseases in the field of orthopedics may be thoroughly and systematically defined in terms of immunological systems. In order to provide a theoretical foundation for an in-depth understanding of the pathological process of IVDD and the formulation of more effective prevention and treatment measures, this review provides a comprehensive and systematic account of the pathogenesis of IVDD from the physical to the molecular barriers of the intervertebral disc, from the nucleus pulposus tissue to the cellular to the immune-molecular level.

Bladder Cancer Exhibiting High Immune Infiltration Shows the Lowest Response Rate to Immune Checkpoint Inhibitors

Background: Bladder urothelial cancer (BLCA) treatment using immune checkpoint inhibitors (IMCIs) can result in long-lasting clinical benefits. However, only a fraction of patients respond to such treatment. In this study, we aimed to identify the relationships between immune cell infiltration levels (ICILs) and IMCIs and identify markers for ICILs.

Methods: ICILs were estimated based on single-sample gene set enrichment analysis. The response rates of different ICILs to IMCIs were calculated by combining the ICILs of molecular subtypes in BLCA with the response rates of different molecular subtypes of IMvigor 210 trials to a programmed cell death ligand-1 inhibitor. Weighted gene co-expression network analysis was used to identify modules of interest with ICILs. Functional enrichment analysis was performed to functionally annotate the modules. Screening of key genes and unsupervised clustering were used to identify candidate biomarkers. Tumor IMmune Estimation Resource was used to validate the relationships between the biomarkers and ICILs. Finally, we verified the expression of key genes in molecular subtypes of different response rates for IMCIs.

Findings: The basal squamous subtype and luminal infiltrated subtype, which showed low response rates for IMCIs, had the highest levels of immune infiltration. The neuronal subtypes, which showed the highest response rates to IMCIs, had low ICILs. The modules of interest and key genes were determined based on topological overlap measurement, clustering results, and inclusion criteria. Modules highly correlated with ICILs were mainly enriched in immune responses and epithelial–mesenchymal transition. After screening the key genes in the modules, five candidate biomarkers (CD48, SEPT1, ACAP1, PPP1R16B, and IL16) were selected by unsupervised clustering. The key genes were inversely associated with tumor purity and were mostly expressed in the basal squamous subtype and luminal infiltrated subtypes.

Interpretation: Patients with high ICILs may benefit the least from treatment with IMCIs. Five key genes could predict ICILs in BLCA, and their high expression suggested that the response rate to IMCIs may decrease.

Tumor mutational burden is a determinant of immune-mediated survival in breast cancer

Mounting evidence supports a role for the immune system in breast cancer outcomes. The ability to distinguish highly immunogenic tumors susceptible to anti-tumor immunity from weakly immunogenic or inherently immune-resistant tumors would guide development of therapeutic strategies in breast cancer. Genomic, transcriptomic and clinical data from The Cancer Genome Atlas (TCGA) and Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) breast cancer cohorts were used to examine statistical associations between tumor mutational burden (TMB) and the survival of patients whose tumors were assigned to previously-described prognostic immune subclasses reflecting favorable, weak or poor immune-infiltrate dispositions (FID, WID or PID, respectively). Tumor immune subclasses were associated with survival in patients with high TMB (TMB-Hi, P < 0.001) but not in those with low TMB (TMB-Lo, P = 0.44). This statistical relationship was confirmed in the METABRIC cohort (TMB-Hi, P = 0.047; TMB-Lo, P = 0.39), and also found to hold true in the more-indolent Luminal A tumor subtype (TMB-Hi, P = 0.011; TMB-Lo, P = 0.91). In TMB-Hi tumors, the FID subclass was associated with prolonged survival independent of tumor stage, molecular subtype, age and treatment. Copy number analysis revealed the reproducible, preferential amplification of chromosome 1q immune-regulatory genes in the PID immune subclass. These findings demonstrate a previously unappreciated role for TMB as a determinant of immune-mediated survival of breast cancer patients and identify candidate immune-regulatory mechanisms associated with immunologically cold tumors. Immune subtyping of breast cancers may offer opportunities for therapeutic stratification.

Variation at 2q35 (PNKD and TMBIM1) influences colorectal cancer risk and identifies a pleiotropic effect with inflammatory bowel disease

To identify new risk loci for colorectal cancer (CRC), we conducted a meta-analysis of seven genome-wide association studies (GWAS) with independent replication, totalling 13 656 CRC cases and 21 667 controls of European ancestry. The combined analysis identified a new risk association for CRC at 2q35 marked by rs992157 (P = 3.15 × 10-8, odds ratio = 1.10, 95% confidence interval = 1.06-1.13), which is intronic to PNKD (paroxysmal non-kinesigenic dyskinesia) and TMBIM1 (transmembrane BAX inhibitor motif containing 1). Intriguingly this susceptibility single-nucleotide polymorphism (SNP) is in strong linkage disequilibrium (r2 = 0.90, D' = 0.96) with the previously discovered GWAS SNP rs2382817 for inflammatory bowel disease (IBD). Following on from this observation we examined for pleiotropy, or shared genetic susceptibility, between CRC and the 200 established IBD risk loci, identifying an additional 11 significant associations (false discovery rate [FDR]) < 0.05). Our findings provide further insight into the biological basis of inherited genetic susceptibility to CRC, and identify risk factors that may influence the development of both CRC and IBD.

Developing drug strategies for the neuroprotective treatment of acute ischemic stroke

Developing new treatment strategies for acute ischemic stroke in the last twenty years has offered some important successes, but also several failures. Most trials of neuroprotective therapies have been uniformly negative to date. Recent research has reported how excitatory amino acids act as the major excitatory neurotransmitters in the cerebral cortex and hippocampus. Furthermore, other therapeutic targets such as free radical scavenger strategies and the anti-inflammatory neuroprotective strategy have been evaluated with conflicting data in animal models and human subjects with acute ischemic stroke. Whereas promising combinations of neuroprotection and neurorecovery, such as citicoline, albumin and cerebrolysin have been tested with findings worthy of further evaluation in larger randomized clinical trials. Understanding the complexities of the ischemic cascade is essential to developing pharmacological targets for acute ischemic stroke in neuroprotective or flow restoration therapeutic strategies.

Mesenchymal stem cells inhibit multiple myeloma cells via the Fas/Fas ligand pathway

Introduction

Cell-based therapy represents a new frontier in the treatment of a wide variety of human diseases traditionally associated with morbidity outcomes, including those involving inflammation, autoimmunity, tissue damage, and cancer. However, the use of mesenchymal stem cells (MSCs) to treat multiple myeloma (MM) bone disease has raised concerns. Specifically, evidence has shown that infused MSCs might support tumor growth and metastasis.

Methods

In this study, we used a standard disseminated MM model in mice to identify the in vivo effects of intravenous MSC infusion. In addition, a series of in vitro co-culture assays were preformed to explore whether Fas/Fas ligand (Fas-L) is involved in the inhibitory effects of MSCs on MM cells.

Results

In the MM mouse model, treatment of MSCs with highly expressed Fas ligand (Fas-L^high MSCs) showed remarkable inhibitory effects on MM indenization in terms of extending the mouse survival rate and inhibiting tumor growth, bone resorption in the lumbus and collum femoris, and MM cell metastasis in the lungs and kidneys. In addition, reduced proliferation and increased apoptosis of MM cells was observed when co-cultured with Fas-L^high MSCs in vitro. Furthermore, mechanistically, the binding between Fas and Fas-L significantly induced apoptosis in MM cells, as evidenced through an increase in the expression of apoptosis marker and Fas in MM cells. In contrast, Fas-L^null MSCs promote MM growth.

Conclusions

These data suggest that Fas/Fas-L-induced MM apoptosis plays a crucial role in the MSC-based inhibition of MM growth. Although whether MSCs inhibit or promote cancer growth remains controversial, the levels of Fas-L expression in MSCs determine, at least partially, the effects of MSCs on MM cell growth.

Persistent degenerative changes in the intervertebral disc after burst fracture in an in vitro model mimicking physiological post-traumatic conditions

PURPOSE

Post-traumatic disc degeneration (DD) is currently investigated with models not fully matching the clinical condition, in particular post-traumatic loading of the disc is not considered. Therefore, the aim was to establish an in vitro burst fracture model that more closely mimics the in vivo situation by including post-traumatic physiological loading and to investigate DD under these conditions.

METHODS

72 rabbit spinal segments (disc/endplates + 1/3 of adjacent vertebrae) were harvested from T8/9 to L5/6 and assigned to control (n = 36) or trauma groups (n = 36). Burst fractures were induced at day 0 in the trauma group using a dropped-weight device. From day 1 to 28, all specimens were cultured at 37 °C and were dynamically loaded daily (~1 MPa nominal pressure, 1 Hz, 2,500 cycles). At day 1, 7, 14, and 28, 9 specimens from each group were taken for analysis: histology (n = 2), total disc glycosaminoglycan (GAG) content (n = 3) normalized to DNA, and qPCR of DD marker genes (n = 4) in the nucleus pulposus and the annulus fibrosus.

RESULTS

Burst fracture with post-traumatic physiological loading resulted in a 65 % loss of GAG/DNA by day 28. Histological sections confirmed the remodeling of the matrix. Catabolic (MMP-1/-3), pro-apoptotic (TNF-α, fas ligand), and pro-inflammatory (IL-1/-6, iNOS) gene transcription was substantially up-regulated in the nucleus after the trauma and did not normalize to control within 28 days. Similar results were found for the annulus on lower levels.

CONCLUSION

An in vitro burst fracture model with physiological post-traumatic loading was established. Under these conditions, burst spinal segments undergo strong and persistent degenerative changes.

Dendritic cell vaccination and immunostimulation in advanced melanoma

The most recent advances in immunology bear witness to the fact that tumors, in particular melanoma, escape recognition by the host's immune system and can locally inactivate its effectors, T-cells and antigen presenting cells. There is, however, preclinical evidence that the immune system, opportunely stimulated, is capable of recognizing and killing tumor cells. It has been verified that the activation of autologous dendritic cells, derived from peripheral blood and pulsed with tumor antigens, results in the specific stimulation of T-cells against the tumor. Preliminary data from dendritic cell vaccination trials, mainly of advanced melanoma, show unequivocal evidence of immunization and of the first clinical responses. Many questions remain to be answered before more effective and widespread use of this type of vaccination is possible, especially in the early stages of the disease.

From biocontrol to cancer, probiotics and beyond

This invited commentary covers the period 1997-2012 and has seen changes in terminology that progressed from "basic" and "applied" to "translational" research. In the context of Bioengineered, these changes map readily onto the processes of identifying microbial characteristics appropriate for specific applications, isolation of suitable cultures, strain or genome manipulation and exploitation of these or their metabolomes across a range of settings.   To a great degree, this commentary and my career reflect an engagement with molecular microbiology and the trialling of bacteria and derived constructs in applications ranging from intensive-scale crop protection to amelioration of gastrointestinal disease. This engagement began with laboratory and field evaluations of biocontrol, specifically use of pseudomonads effective against nematode and fungal plant pathogens, characterization of mechanisms mediating beneficial effects of probiotic lactobacilli and bifidobacteria and assessment of functional foods in multinational clinical trials relating to inflammatory bowel disease. Subsequent work focused on (1) intellectual property (IP)-based medical devices for localized delivery of systemically toxic and gene cancer therapies; (2) growth of the science base supporting expansion of a multinational business including company acquisitions; (3) complementing existing inter-institutional research capabilities through development of a national industry-led collaboration; and, most recently, (4) strategic research programs at Ireland's newest medical school. My activities as outlined above parallel two distinct aspects of translational research: (1) involvement in knowledge-driven (commercial and research) organizations that brought together necessary resources and infrastructure and (2) availability of scale research funding from European Framework and Irish national programs.

Inflammation, apoptosis, and necrosis induced by neoadjuvant fas ligand gene therapy improves survival of dogs with spontaneous bone cancer

Fas ligand (FasL) gene therapy for cancer has shown promise in rodents; however, its efficacy in higher mammals remains unknown. Here, we used intratumoral FasL gene therapy delivered in an adenovirus vector (Ad-FasL) as neoadjuvant to standard of care in 56 dogs with osteosarcoma. Tumors from treated dogs had greater inflammation, necrosis, apoptosis, and fibrosis at day 10 (amputation) compared to pretreatment biopsies or to tumors from dogs that did not receive Ad-FasL. Survival improvement was apparent in dogs with inflammation or lymphocyte-infiltration scores >1 (in a 3-point scale), as well as in dogs that had apoptosis scores in the top 50th percentile (determined by cleaved caspase-3). Survival was no different than that expected from standard of care alone in dogs with inflammation scores ≤1 or apoptosis scores in the bottom 50th percentile. Reduced Fas expression by tumor cells was associated with prognostically advantageous inflammation, and this was seen only in dogs that received Ad-FasL. Together, the data suggest that Ad-FasL gene therapy improves survival in a subset of large animals with naturally occurring tumors, and that at least in some tumor types like osteosarcoma, it is most effective when tumor cells fail to express Fas.

P2X7 signaling promotes microsphere embolism-triggered microglia activation by maintaining elevation of Fas ligand

Background

The cerebral microvascular occlusion elicits microvascular injury which mimics the different degrees of stroke severity observed in patients, but the mechanisms underlying these embolic injuries are far from understood. The Fas ligand (FasL)-Fas system has been implicated in a number of pathogenic states. Here, we examined the contribution of microglia-derived FasL to brain inflammatory injury, with a focus on the potential to suppress the FasL increase by inhibition of the P2X₇-FasL signaling with pharmacological or genetic approaches during ischemia.

Methods

The cerebral microvascular occlusion was induced by microsphere injection in experimental animals. Morphological changes in microglial cells were studied immunohistochemically. The biochemical analyses were used to examine the intracellular changes of P2X₇/FasL signaling. The BV-2 cells and primary microglia from mice genetically deficient in P2X₇ were used to further establish a linkage between microglia activation and FasL overproduction.

Results

The FasL expression was continuously elevated and was spatiotemporally related to microglia activation following microsphere embolism. Notably, P2X₇ expression concomitantly increased in microglia and presented a distribution pattern that was similar to that of FasL in ED1-positive cells at pathological process of microsphere embolism. Interestingly, FasL generation in cultured microglia cells subjected to oxygen-glucose deprivation-treated neuron-conditioned medium was prevented by the silencing of P2X₇. Furthermore, FasL induced the migration of BV-2 microglia, whereas the neutralization of FasL with a blocking antibody was highly effective in inhibiting ischemia-induced microglial mobility. Similar results were observed in primary microglia from wild-type mice or mice genetically deficient in P2X₇. Finally, the degrees of FasL overproduction and neuronal death were consistently reduced in P2X₇^−/− mice compared with wild-type littermates following microsphere embolism insult.

Conclusion

FasL functions as a key component of an immunoreactive response loop by recruiting microglia to the lesion sites through a P2X₇-dependent mechanism. The specific modulation of P2X₇/FasL signaling and aberrant microglial activation could provide therapeutic benefits in acute and subacute phase of cerebral microembolic injury.

Weapons ovarian epithelial tumors may use in immune escape: an immunohistochemical correlational study

Investigate FasL and survivin expression in a series of primary ovarian surface epithelial tumors, correlate their expression with each other, and characterize the presence of CD3+ T-lymphocytes in studied tumors and determine whether their presence correlates with FasL or survivin expression in malignant cases. FasL and survivin expression was assessed in 54 ovarian epithelial tumors. The results were compared between different tumor types and grades. Correlation between both markers' expression in all studied tumors was done. Either marker's expression was compared to the mean CD3+ T-lymphocytes per HPF in the studied malignant tumors. Either FasL or survivin expression was significantly higher in malignant versus benign ovarian epithelial tumors (p < 0.001 for both) and both markers were strongly correlated to each other (r = 0.877 & p < 0.001). Malignant tumors show significantly higher mean CD3+ T-lymphocytes than benign and borderline tumors. The mean CD3+ T-lymphocytes decrease significantly on increasing malignant tumor grade (p = 0.019) and expression of both FasL and survivin (r = -0.729, -0.582, respectively & p < 0.001 for both). The higher expression of FasL and survivin in malignant as compared to benign ovarian tumors suggest that they have a significant role in pathogenesis of ovarian carcinoma. Both markers are strongly correlated to each other and may contribute to immune escape of ovarian carcinoma as their higher expression is associated with decreased number of CD3 + T-lymphocytes.

Human neuropathological and animal model evidence supporting a role for Fas-mediated apoptosis and inflammation in cervical spondylotic myelopathy

Although cervical spondylotic myelopathy is a common cause of chronic spinal cord dysfunction in humans, little is known about the molecular mechanisms underlying the progressive neural degeneration characterized by this condition. Based on animal models of cervical spondylotic myelopathy and traumatic spinal cord injury, we hypothesized that Fas-mediated apoptosis and inflammation may play an important role in the pathobiology of human cervical spondylotic myelopathy. We further hypothesized that neutralization of the Fas ligand using a function-blocking antibody would reduce cell death, attenuate inflammation, promote axonal repair and enhance functional neurological outcomes in animal models of cervical spondylotic myelopathy. We examined molecular changes in post-mortem human spinal cord tissue from eight patients with cervical spondylotic myelopathy and four control cases. Complementary studies were conducted using a mouse model of cervical spondylotic myelopathy (twy/twy mice that develop spontaneous cord compression at C2-C3). We observed Fas-mediated apoptosis of neurons and oligodendrocytes and an increase in inflammatory cells in the compressed spinal cords of patients with cervical spondylotic myelopathy. Furthermore, neutralization of Fas ligand with a function-blocking antibody in twy/twy mice reduced neural inflammation at the lesion mediated by macrophages and activated microglia, glial scar formation and caspase-9 activation. It was also associated with increased expression of Bcl-2 and promoted dramatic functional neurological recovery. Our data demonstrate, for the first time in humans, the potential contribution of Fas-mediated cell death and inflammation to the pathobiology of cervical spondylotic myelopathy. Complementary data in a murine model of cervical spondylotic myelopathy further suggest that targeting the Fas death receptor pathway is a viable neuroprotective strategy to attenuate neural degeneration and optimize neurological recovery in cervical spondylotic myelopathy. Our findings highlight the possibility of medical treatments for cervical spondylotic myelopathy that are complementary to surgical decompression.

The role of FasL and Fas in health and disease

The FS7-associated cell surface antigen (Fas, also named CD95, APO-1 or TNFRSF6) attracted considerable interest in the field of apoptosis research since its discovery in 1989. The groups of Shin Yonehara and Peter Krammer were the first reporting extensive apoptotic cell death induction upon treating cells with Fas-specific monoclonal antibodies.1,2 Cloning of Fas3 and its ligand,4,5 FasL (also known as CD178, CD95L or TNFSF6), laid the cornerstone in establishing this receptor-ligand system as a central regulator of apoptosis in mammals. Therapeutic exploitation of FasL-Fas-mediated cytotoxicity was soon an ambitous goal and during the last decade numerous strategies have been developed for its realization. In this chapter, we will briefly introduce essential general aspects of the FasL-Fas system before reviewing its physiological and pathophysiological relevance. Finally, FasL-Fas-related therapeutic tools and concepts will be addressed.

Fas ligand expression in lynch syndrome-associated colorectal tumours

Fas Ligand (FasL) expression by cancer cells may contribute to tumour immune escape via the Fas counterattack against tumour-infiltrating lymphocytes (TILs). Whether this plays a role in colorectal carcinogenesis in Lynch syndrome was examined studying FasL expression, tumour cell apoptosis and number of TILs in colorectal neoplasms from Lynch syndrome patients (50 adenomas, 20 carcinomas) compared with sporadic cases (69 adenomas, 52 carcinomas). FasL expression was observed in 94% of Lynch syndrome adenomas and in all carcinomas. FasL expression patterns and apoptotic indices were similar in Lynch syndrome-associated neoplasms and sporadic cases. The number of TILs was higher in Lynch syndrome neoplasms than in sporadic cases. There were no correlations between FasL expression and tumour cell apoptosis or number of TILs in Lynch syndrome-associated neoplasms. So, FasL expression is an early event in Lynch syndrome and sporadic colorectal carcinogenesis, but not related to TIL number. Taken together, our data do not support a role for the Fas counterattack in colorectal carcinogenesis in Lynch syndrome.

Cellular immunotherapy of cancer

Standard therapies for many common cancers remain toxic and are often ineffective. Cellular immunotherapy has the potential to be a highly targeted alternative, with low toxicity to normal tissues but a high capacity to eradicate tumor. In this chapter we describe approaches that generate cellular therapies using active immunization with cells, proteins, peptides, or nucleic acids, as well as efforts that use adoptive transfer of effector cells that directly target antigens on malignant cells. Many of these approaches are proving successful in hematologic malignancy and in melanoma. In this chapter we discuss the advantages and limitations of each and how over the next decade investigators will attempt to broaden their reach, increase their efficacy, and simplify their application.

Mechanisms of local immunoresistance in glioma

Even though the central nervous system (CNS) was conventionally defined as "immunologically privileged", new discoveries have demonstrated the role of the immune system in neurologic disease and illness, including gliomas. Brain tumor immunotherapy is an exciting and revived area of research, in which neurosurgeons have taken a major position. Despite the ability to induce a tumor-specific systemic immune response, the challenge to effectively eradicate intracranial gliomas remains mainly because of tumor-induced immunoresistance. This article gives an overview of the immunologic responses that occur in the CNS and their potential role in brain tumors. The main cellular and molecular mechanisms that mediate tumor escape from natural immune surveillance are also covered in this article. Glioma cells have been shown to diminish the expression of danger signals necessary for immune activation and to increase the concentration of immunosuppressive factors in the tumor microenvironment, which results in T-cell anergy or apoptosis. Finally, the authors discuss most of the over-expressed oncogenic signaling pathways that cause tumor tolerance.

Double role of Fas ligand in the apoptosis of intervertebral disc cells in vitro

Fas ligand (FasL) may play an important role in maintaining the immune privilege of intervertebral disc (IVD). Besides, it is closely related to the apoptosis of degenerative disc cells. Nowadays, lots of reports have described about the paradoxical effects of FasL, although the effect of FasL on IVD cells is still under debate. In this study, we tried to investigate the effects of FasL on Fas expression and on the apoptosis of nucleus pulposus (NP) cells in Sprague-Dawley rats. The results showed that the expression of Fas in NP cells was significantly increased by the recombinant FasL. Meanwhile, the apoptosis of NP cells increased markedly in a FasL dose-dependent manner. Interestingly, RNA interference results indicated that the increase of Fas expression and the NP cell apoptosis described previously were inhibited by Fas siRNA, suggesting that RNA interference might be one of novel strategies to prevent IVD cells from apoptosis.

Marie R, Wang TC, Lyle S, Kurt-Jones E, Houghton J. Human and mouse colon cancer utilizes CD95 signaling for local growth and metastatic spread to liver

BACKGROUND & AIMS

Analysis of clinical colon cancer specimens show alterations in the CD95 (Fas Ag/Fas L) pathway as tumors progress from local to metastatic disease, suggesting that this pathway may play a role in invasive behavior of colon cancer. However, direct causality between these alterations and clinical disease progression has not been shown.

METHODS

Surgically resected metastatic colon cancer samples were evaluated for Fas Ag/L and apoptosis. Alterations in the Fas-signaling pathway found in human samples were recreated through a series of staged transfection experiments in the MC38 mouse colon cancer cell line and the effects on growth tested in vitro and in vivo.

RESULTS

Expression of FLICE-like inhibitory protein confers apoptosis resistance, increasing the incidence of primary tumors through a survival advantage by avoiding apoptosis and inducing Fas-mediated proliferation. Coexpression of Fas L enables colon cancer cells to metastasize to the liver from local tumors as well as from intravenous injection of cells. MC38-FasL/FLICE-like inhibitory protein colon cancer cells induce apoptosis in hepatocytes via activation of type II Fas Ag signaling, thus creating a niche conducive to tumor growth and fueling their own growth via Fas proliferative signaling.

CONCLUSIONS

Alterations in the Fas Ag pathway which inhibit apoptosis and increase Fas-mediated proliferation directly increase local colon cancer growth, and enhance metastasis to the liver. Delineating points in the pathway responsible for growth and metastasis will offer targets that may be exploited for therapy.

Cytotoxicity mediated by the Fas ligand (FasL)-activated apoptotic pathway in stem cells

Whereas it is now clear that human bone marrow stromal cells (BMSCs) can be immunosuppressive and escape cytotoxic lymphocytes (CTLs) in vitro and in vivo, the mechanisms of this phenomenon remain controversial. Here, we test the hypothesis that BMSCs suppress immune responses by Fas-mediated apoptosis of activated lymphocytes and find both Fas and FasL expression by primary BMSCs. Jurkat cells or activated lymphocytes were each killed by BMSCs after 72 h of co-incubation. In comparison, the cytotoxic effect of BMSCs on non-activated lymphocytes and on caspase-8(-/-) Jurkat cells was extremely low. Fas/Fc fusion protein strongly inhibited BMSC-induced lymphocyte apoptosis. Although we detected a high level of Fas expression in BMSCs, stimulation of Fas with anti-Fas antibody did not result in the expected BMSC apoptosis, regardless of concentration, suggesting a disruption of the Fas activation pathway. Thus BMSCs may have an endogenous mechanism to evade Fas-mediated apoptosis. Cumulatively, these data provide a parallel between adult stem/progenitor cells and cancer cells, consistent with the idea that stem/progenitor cells can use FasL to prevent lymphocyte attack by inducing lymphocyte apoptosis during the regeneration of injured tissues.

Tricks tumors use to escape from immune control

Tumor escape from the host immune system has been a major problem in immunotherapy of human malignancies. Human tumors are known to develop escape strategies, which might differ among tumors of the same histology. This suggests that host-tumor interactions create the tumor microenvironment that is unique for every tumor. Recent advances in cancer immunology allow for a better understanding of the mechanisms tumors use to execute immune escape and of the relationship the tumor establishes with immune cells. It is now feasible to obtain an "immune signature" of the tumor, that is to define the genetic, molecular and functional profiles of immune cells in the tumor microenvironment. This knowledge might be critically important for the personalized selection of available therapies and thus for clinical outcome.

Apoptosis signaling proteins as prognostic biomarkers in colorectal cancer: a review

Colorectal cancer is a leading cause of cancer related mortality in the Western world. In recent years, combination 5-fluorouracil based adjuvant chemotherapy as first line treatment of this disease has led to improved disease free and overall survival. However drug resistance, both innate and acquired, remains an obstacle in the effective treatment of this disease. Apoptotic pathways are frequently altered in both tumor progression and drug resistance; therefore proteins associated with this pathway may have potential as prognostic biomarkers for this disease. Identification of clinical biomarkers that are able to identify patients who are more likely to respond to specific chemotherapy will lead to more personalized, effective, and less toxic therapy. This review focuses on the current status of apoptosis related proteins as biomarkers for colorectal cancer and discusses the possible application of systems approaches in this context.

Thy1 up-regulates FasL expression in lung myofibroblasts via Src family kinases

We have previously demonstrated that myofibroblasts from lungs with bleomycin-induced fibrosis overexpress FasL molecules. Two subpopulations of fibroblasts, distinguished by their expression of Thy1 molecules, have been shown in the lungs of both mice and humans. Thy1-mediated FasL induction has been reported in T cells through the use of anti-Thy1 (G7). We therefore sought to determine whether FasL expression in lung myofibroblasts is associated with and/or dependent on Thy1 expression, and to examine the underlying mechanism of regulation. We show that myofibroblast Thy1 expression is associated with increased FasL expression. Moreover, we directly show that Thy1 activation induces FasL up-regulation. Initially, Thy1 activation causes translocation of FasL to the membrane surface, and later induces de novo synthesis of FasL at the mRNA and protein levels. In contrast to Thy1 activation, TNF-alpha and IFN-gamma do not induce FasL myofibroblast up-regulation. Using Src family kinase (SFKs) inhibitor (PP2), we show the general involvement of SFKs in Thy1 signal transduction leading to FasL up-regulation; and, using specific siRNA, we show the particular involvement of Fyn, one protein in the SFK family. These results demonstrate that Thy1 in myofibroblasts is not just a marker, but is a functional protein that transmits signals into the cell, up-regulating its FasL expression.

Prostaglandin E2 stimulates Fas ligand expression via the EP1 receptor in colon cancer cells

Fas ligand (FasL/CD95L) is a member of the tumour necrosis factor superfamily that triggers apoptosis following crosslinking of the Fas receptor. Despite studies strongly implicating tumour-expressed FasL as a major inhibitor of the anti-tumour immune response, little is known about the mechanisms that regulate FasL expression in tumours. In this study, we show that the cyclooxygenase (COX) signalling pathway, and in particular prostaglandin E₂ (PGE₂), plays a role in the upregulation of FasL expression in colon cancer. Suppression of either COX-2 or COX-1 by RNA interference in HCA-7 and HT29 colon tumour cells reduced FasL expression at both the mRNA and protein level. Conversely, stimulation with PGE₂ increased FasL expression and these cells showed increased cytotoxicity against Fas-sensitive Jurkat T cells. Prostaglandin E₂-induced FasL expression was mediated by signalling via the EP1 receptor. Moreover, immunohistochemical analysis using serial sections of human colon adenocarcinomas revealed a strong positive correlation between COX-2 and FasL (r=0.722; P<0.0001) expression, and between EP1 receptor and FasL (r=0.740; P<0.0001) expression, in the tumour cells. Thus, these findings indicate that PGE₂ positively regulates FasL expression in colon tumour cells, adding another pro-neoplastic activity to PGE₂.

Is there a role for the Fas-/Fas-Ligand pathway in chemoresistance of human squamous cell carcinomas of the head and neck (SCCHN)?

The aim of the present investigation was to determine the expression of the Fas-receptor/ligand system in established cell lines of squamous cell carcinomas of the head and neck (SCCHN), and to study it's functional impact on chemotherapy-induced apoptosis in these SCCHN cell lines. We observed constitutive expression of Fas and FasL in 13 SCCHN cell lines by RT-PCR, Southern-blotting and immunocytochemistry, respectively. Administration of the agonistic Fas-antibody CH-11 led to a significant reduction of viable cells in the colorimetric MTT-assay in 5 out of 13 (38%) cell lines tested and preincubation with Interferon-gamma (IFN-gamma) rendered 3 (23%) primarily resistant cell lines sensitive. Cisplatin (cDDP) and bleomycin (BLM) caused dose-dependent cytotoxicity in all cell lines as determined by the 50% inhibitory concentration (IC(50)) and induction of apoptosis. Furthermore, both antineoplastic agents led to an enhanced surface expression of Fas and FasL in all cell lines, and this effect was independent of the respective p53-status. This upregulation of Fas/FasL surface expression increased preexisting Fas-sensitivity only, but failed to make primarily resistant cell lines undergo Fas-mediated growth reduction or apoptosis. Vice versa, blockade of Fas-receptor-ligand-interactions by monoclonal antibodies directed against FasL was able to attenuate the cytotoxic effect of cDDP and BLM in 2 out of 5 (40%) cell lines tested only. In conclusion, in contrast to many other solid tumors, the Fas/FasL-system does not seem to play an exclusive role in anticancer drug mediated apoptosis in SCCHN.

Neutrophil-dependent tumor rejection and priming of tumoricidal CD8+ T cell response induced by dendritic cells overexpressing CD95L

Overexpression of CD95 (Fas/Apo-1) ligand (CD95L) has been shown to induce T cell tolerance but also, neutrophilic inflammation and rejection of allogeneic tissue. We explored the capacity of dendritic cells (DCs) genetically engineered to overexpress CD95L to induce an antitumor response. We first found that DCs overexpressing CD95L, in addition to MHC class I-restricted OVA peptides (CD95L-OVA-DCs), induced increased antigen-specific CD8(+) T cell responses as compared with DCs overexpressing OVA peptides alone. The enhanced T cell responses were associated with improved regression of a tumor expressing OVA, allowing survival of all animals. When DCs overexpressing CD95L (CD95L-DCs) were injected with the tumor expressing OVA, in vivo tumor proliferation was strikingly inhibited. A strong cellular apoptosis and a massive neutrophilic infiltrate developed in this setting. Neutrophil depletion prevented tumor regression as well as enhanced IFN-gamma production induced by CD95L-OVA-DCs. Furthermore, the CD8(+) T cell response induced by the coadministration of tumor cells and CD95L-DCs led to rejection of a tumor implanted at a distance from the DC injection site. In summary, DCs expressing CD95L promote tumor rejection involving neutrophil-mediated innate immunity and CD8(+) T cell-dependent adaptative immune responses.

Requirement of inositol 1,4,5-trisphosphate receptors for tumor-mediated lymphocyte apoptosis

Tumor cells strategically down-regulate Fas receptor expression to evade immune attack and up-regulate expression of Fas ligand to promote apoptosis of infiltrating T lymphocytes. Many pathways leading to apoptotic cell death require calcium release from inositol 1,4,5-trisphosphate receptors (IP3Rs). Here, we show that Fas-dependent killing of Jurkat T lymphoma cells by SW620 colon cancer cells requires calcium release from IP3R. General suppression of IP3R signaling significantly reduced SW620-mediated Jurkat cell apoptosis. Significantly, a specific inhibitor of apoptotic calcium release from IP3R strongly blocked lymphocyte apoptosis. Thus, selective pharmacological targeting of apoptotic calcium release from IP3R may enhance tumor cell immunogenicity.

The "Fas counterattack" is not an active mode of tumor immune evasion in colorectal cancer with high-level microsatellite instability

Microsatellite instability (MSI) is an alternative pathway of colorectal carcinogenesis. It is found in 10% to 15% of sporadic colorectal neoplasms and is characterized by failure of the DNA mismatch-repair system. High-level MSI (MSI-H) is associated with tumor-infiltrating lymphocytes (TILs) and a favorable prognosis. Expression of Fas ligand (FasL/CD95L) by cancer cells may mediate tumor immune privilege by inducing apoptosis of antitumor immune cells. The aim of this study was to investigate the relationship between FasL expression and MSI status in primary colon tumors. Using immunohistochemistry, we detected FasL expression in 91 colorectal carcinoma specimens, previously classified according to the level of MSI as MSI-H (n = 26), MSI-low (MSI-L) (n = 29), and microsatellite stable (n = 36). Tumor-infiltrating lymphocyte density was quantified by immunohistochemical staining for CD3. MSI-H tumors were significantly associated with reduced frequency (P = .04) and intensity (P = .066) of FasL expression relative to non-MSI-H (ie, microsatellite stable and MSI-L) tumors. Higher FasL staining intensity correlated with reduced TIL density (P = .059). Together, these findings suggest that the abundance of TILs found in MSI-H tumors may be due to the failure of these tumor cells to up-regulate FasL and may explain, in part, the improved prognosis associated with these tumors.

Intratumoral CRH modulates immuno-escape of ovarian cancer cells through FasL regulation

Although corticotropin-releasing hormone (CRH) and Fas ligand (FasL) have been documented in ovarian carcinoma, a clear association with tumour progression and immuno-escape has not been established. FasL plays an important role in promoting tumour cells' ability to counterattack immune cells. Here, we examined immunohistochemically the expression of CRH, CRHR1, CRHR2 and FasL in 47 human ovarian cancer cases. The ovarian cancer cell lines OvCa3 and A2780 were further used to test the hypothesis that CRH might contribute to the immune privilege of ovarian tumours, by modulating FasL expression on the cancer cells. We found that CRH, CRHR1, CRHR2 and FasL were expressed in 68.1, 70.2, 63.8 and 63.8% of the cases respectively. Positivity for CRH or FasL expression was associated with higher tumour stage. Finally, CRH increased the expression of FasL in OvCa3 and A2780 cells through CRHR1 thereby potentiated their ability to induce apoptosis of activated peripheral blood lymphocytes. Corticotropin-releasing hormone produced by human ovarian cancer might favour survival and progression of the tumour by promoting its immune privilege. These findings support the hypothesis that CRHR1 antagonists could potentially be used against ovarian cancer.

Immunosuppressive strategies that are mediated by tumor cells

Despite major advances in understanding the mechanisms leading to tumor immunity, a number of obstacles hinder the successful translation of mechanistic insights into effective tumor immunotherapy. Such obstacles include the ability of tumors to foster a tolerant microenvironment and the activation of a plethora of immunosuppressive mechanisms, which may act in concert to counteract effective immune responses. Here we discuss different strategies employed by tumors to thwart immune responses, including tumor-induced impairment of antigen presentation, the activation of negative costimulatory signals, and the elaboration of immunosuppressive factors. In addition, we underscore the influence of regulatory cell populations that may contribute to this immunosuppressive network; these include regulatory T cells, natural killer T cells, and distinct subsets of immature and mature dendritic cells. The current wealth of preclinical information promises a future scenario in which the synchronized blockade of immunosuppressive mechanisms may be effective in combination with other conventional strategies to overcome immunological tolerance and promote tumor regression.

Links between innate and cognate tumor immunity

Cancer results from a tumor cell intrinsic dysregulation of oncogenes, tumor suppressor and stability genes as well as from the avoidance of immunosurveillance. A complex network of cellular interactions allows one to mount cognate anti-tumor immune responses. Recently, discoveries have been made regarding the links between innate and cognate antitumor immunity eliciting protective T-cell responses. The intricate differentiation pathway, whereby dendritic cells can efficiently mature in the tumor microenvironment, appears crucial for the priming of T cells. Transformed cells might deliver danger signals directly to the dendritic cell. Alternatively, other cell types belonging to the innate immune system can sense transformed cells through a specific set of receptors and then interact with dendritic cells to modulate their activation state. A novel subset of innate effector cells called interferon-producing killer dendritic cells are multitasking chimeras that can recognize and kill transformed cells, and undergo a maturation state of antigen presentation. Also, evidence has been produced suggesting that cell death promoted by conventional chemotherapy or radiotherapy might elicit interactions between the innate and the cognate immune system that result in anti-tumor immune responses.

The effects of FasL on inflammation and tumor survival are dependent on its expression levels

The apoptosis-inducing Fas ligand (FasL) is expressed in a variety of human cancers and has been implicated in tumor immune evasion. Paradoxically, ectopic expression of FasL in experimental tumors triggers a neutrophil-mediated inflammatory response and tumor rejection. To resolve these conflicting findings, we have established B16 melanoma and P29 Lewis lung carcinoma lines expressing different levels of FasL and examined their tumorigenicity in vivo. While tumors with a high level of FasL were rapidly rejected as previously reported, those expressing a low level of FasL were not rejected but grew faster than did FasL-negative parental cells. The growth enhancement of FasL(low) tumors was not observed in T-cell-deficient nude mice, suggesting that FasL expressed in tumors at low levels counteracted against T-cell-dependent antitumor responses. In support of this notion, FasL(low) tumors were found to grow faster than parental cells in mice that had acquired tumor-specific immunity. Furthermore, histological examinations revealed apoptosis of lymphocytes in tissue sections of FasL(low) tumors. These results collectively suggest that FasL on tumors is a double-edged sword: at high levels it triggers tumor rejection whereas at low levels it facilitates tumor growth possibly by suppressing antitumor immune responses.

Active transcription of the human FASL/CD95L/TNFSF6 promoter region in T lymphocytes involves chromatin remodeling: role of DNA methylation and protein acetylation suggest distinct mechanisms of transcriptional repression

Fas ligand (FasL/CD95L/TNFSF6), a member of the tumor necrosis factor family, initiates apoptosis in lymphoid and nonlymphoid tissues by binding to its receptor Fas (CD95/TNFRSF6). Although the transcriptional control of TNFSF6 gene expression is subjected to intense study, the role of its chromatin organization and accessibility to the transcriptional machinery is not known. Here, we determined the chromatin organization of TNFSF6 gene 5' regulatory regions. Using the indirect end-labeling technique, a unique region named HSS1 and encompassing nucleotides -189 to +185 according to the transcriptional start site, was identified throughout a 20-kilobase nucleosomal DNA domain surrounding the promoter. The HSS1 region displayed hypersensitivity to in vivo DNase I digestion in TNFSF6-expressing cells only, including upon T cell activation. Hypersensitivity to micrococcal nuclease digestion and to specific restriction enzyme digestion suggested the precise positioning of two nucleosomes across the transcription start site and minimal promoter region, likely interfering with TNFSF6 active transcription in T lymphocytes. Indeed, HSS1 hypersensitivity to nuclease digestion strictly correlated with TNFSF6 transcription, including in primary and leukemia T cells. HSS1 chromatin remodeling preceded detectable TNFSF6 mRNA accumulation and was blocked by cycloheximide that also prevented TNFSF6 transcription. However, DNA methylation levels of the TNFSF6 HSS1 region did not correlate with transcriptional activation. Induction of global protein acetylation by treatment with histone deacetylase inhibitors was not accompanied by HSS1 chromatin remodeling and/or TNFSF6 transcription. We conclude that chromatin remodeling is a primary event in the activation of TNFSF6 expression in primary and leukemia T cells and that mechanisms independent of protein deacetylation and of DNA methylation of the TNFSF6 promoter region are involved in the repression of TNFSF6 gene expression.

Matrix metalloproteinase-7 increases resistance to Fas-mediated apoptosis and is a poor prognostic factor of patients with colorectal carcinoma

The ability of tumor cells to resist apoptosis triggered by immune cells results in their escape from immune surveillance of the host. A critical effector of apoptosis is the Fas/Fas ligand (FasL) system that mediates the tumoricidal effects of cytotoxic T cells. Recently, in vitro cleavage of Fas expressed in various tumor cells by matrix metalloproteinase-7 (MMP-7) was demonstrated. In the present study, we first analyzed the influence of this metalloproteinase on Fas signaling in SW480, HCT-15 and HT-29 colorectal carcinoma (CRC) cells by assessing their responses to either an agonistic Fas antibody (CH11) or the FasL-bearing Jurkat cells after they were pretreated with MMP-7. Interestingly, both antibody- and Jurkat cell-induced apoptosis in three different CRC lines were significantly reduced by MMP-7 pretreatment. Additionally, immunohistochemical (IHC) staining was used to examine the expression levels of MMP-7 and Fas in tumor samples of 54 CRC patients. In agreement with our in vitro observation, the expression of MMP-7 in tumor tissues was inversely correlated with those of Fas (P < 0.001; chi2-test). Moreover, shortened survival was found in patients with a higher MMP-7 and a lower Fas expression, respectively, in their tumor tissues (P < 0.0001). Finally, by multivariate analysis, we discovered that MMP-7 (P = 0.001) and Fas levels (P = 0.036) were independent prognostic factors for CRC patients. These results suggest that Fas downregulation and a consequential increased resistance to FasL-triggered apoptosis resulting from upregulated MMP-7 in colorectal cancer cells could be a key mechanism for their escape from the immune surveillance, thereby predicting a poor survival in CRC patients.

Fas ligand expression in human and mouse cancer cell lines; a caveat on over-reliance on mRNA data

Background

During carcinogenesis, tumors develop multiple mechanisms for evading the immune response, including upregulation of Fas ligand (FasL/CD95L) expression. Expression of FasL may help to maintain tumor cells in a state of immune privilege by inducing apoptosis of anti-tumor immune effector cells. Recently this idea has been challenged by studies reporting that tumor cells of varying origin do not express FasL. In the present study, we aimed to comprehensively characterize FasL expression in tumors of both murine and human origin over a 72 hour time period.

Methods

RNA and protein was extracted from six human (SW620, HT29, SW480, KM12SM, HCT116, Jurkat) and three mouse (CMT93, CT26, B16F10) cancer cell lines at regular time intervals over a 72 hour time period. FasL expression was detected at the mRNA level by RT-PCR, using intron spanning primers, and at the protein level by Western Blotting and immunofluorescence, using a polyclonal FasL- specific antibody.

Results

Expression of FasL mRNA and protein was observed in all cell lines analysed. However, expression of FasL mRNA varied dramatically over time, with cells negative for FasL mRNA at many time points. In contrast, 8 of the 9 cell lines constitutively expressed FasL protein. Thus, cells can abundantly express FasL protein at times when FasL mRNA is absent.

Conclusion

These findings demonstrate the importance of complete analysis of FasL expression by tumor cells in order to fully characterize its biological function and may help to resolve the discrepancies present in the literature regarding FasL expression and tumor immune privilege.

Modulation of HLA-G expression in human neural cells after neurotropic viral infections

HLA-G is a nonclassical human major histocompatibility complex class I molecule. It may promote tolerance, leading to acceptance of the semiallogeneic fetus and tumor immune escape. We show here that two viruses-herpes simplex virus type 1 (HSV-1), a neuronotropic virus inducing acute infection and neuron latency; and rabies virus (RABV), a neuronotropic virus triggering acute neuron infection-upregulate the neuronal expression of several HLA-G isoforms, including HLA-G1 and HLA-G5, the two main biologically active isoforms. RABV induces mostly HLA-G1, and HSV-1 induces mostly HLA-G3 and HLA-G5. HLA-G expression is upregulated in infected cells and neighboring uninfected cells. Soluble mediators, such as beta interferon (IFN-beta) and IFN-gamma, upregulate HLA-G expression in uninfected cells. The membrane-bound HLA-G1 isoform was detected on the surface of cultured RABV-infected neurons but not on the surface of HSV-1-infected cells. Thus, neuronotropic viruses that escape the host immune response totally (RABV) or partially (HSV-1) regulate HLA-G expression on human neuronal cells differentially. HLA-G may therefore be involved in the escape of certain viruses from the immune response in the nervous system.

Apoptosis dominant in the periinfarct area of human ischaemic stroke--a possible target of antiapoptotic treatments

Animal experiments have suggested that apoptotic programmed cell death is responsible for an important portion of the delayed ischaemic brain damage. Antiapoptotic signalling through erythropoietin (EPO) binding to its receptor (EPOR) is triggered by systemic or local hypoxia and may exist in the post-ischaemic brain, and a neuroprotective effect by EPO was described recently and proposed for clinical stroke treatment. The objective of the study was to determine whether apoptosis occurs in human ischaemic stroke and to describe its topographical distribution. An autopsy cohort consisting of 13 cases of fatal ischaemic stroke (symptom duration from 15 h to 18 days) treated at the Department of Neurology, Helsinki University Central Hospital and 3 controls were studied. DNA damage was investigated by immunofluorescent TUNEL-labelling in combination with apoptotic cell morphology and by visualization of a major signalling system of apoptosis, Fas-FasL (Fas-ligand), by the immunoperoxidase technique. The relationship of EPO and EPOR in the face of TUNEL-labelled and necrotic cell death was co-registered in human cerebral neurons undergoing different stages of ischaemic change. TUNEL-labelled cells with apoptotic morphology were disproportionately more frequent, 148% (30) [mean (SE)] in the periinfarct versus 97% (22) in the core, as percentage of the cells in the contralateral hemisphere (P = 0.027). The apoptotic cell percentage reached up to 26% (2) of all cells in periinfarct area. A linear correlation was found for Fas and its counterpart FasL expression (r(S) = 0.774, P < 0.001). Ischaemia induced widespread neuronal expression of EPOR, which was inversely related to the severity of ischaemic neuronal necrosis (P < 0.05). To conclude, these data verify the predominance of apoptosis in the periphery of human ischaemic infarctions. Fas and FasL were linearly overexpressed supporting that this 'death-receptor' complex may promote the completion of cell death. Increased EPO signalling may be a cellular response for survival in less severely damaged areas. These results support antiapoptotic therapies against delayed neuronal cell death in human ischaemic stroke.

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

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

Tumor counterattack: fact or fiction?

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

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

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

Anti-Fas mAb-induced apoptosis and cytolysis of airway tissue eosinophils aggravates rather than resolves established inflammation

Background

Fas receptor-mediated eosinophil apoptosis is currently forwarded as a mechanism resolving asthma-like inflammation. This view is based on observations in vitro and in airway lumen with unknown translatability to airway tissues in vivo. In fact, apoptotic eosinophils have not been detected in human diseased airway tissues whereas cytolytic eosinophils abound and constitute a major mode of degranulation of these cells. Also, Fas receptor stimulation may bypass the apoptotic pathway and directly evoke cytolysis of non-apoptotic cells. We thus hypothesized that effects of anti-Fas mAb in vivo may include both apoptosis and cytolysis of eosinophils and, hence, that established eosinophilic inflammation may not resolve by this treatment.

Methods

Weeklong daily allergen challenges of sensitized mice were followed by airway administration of anti-Fas mAb. BAL was performed and airway-pulmonary tissues were examined using light and electron microscopy. Lung tissue analysis for CC-chemokines, apoptosis, mucus production and plasma exudation (fibrinogen) were performed.

Results

Anti-Fas mAb evoked apoptosis of 28% and cytolysis of 4% of eosinophils present in allergen-challenged airway tissues. Furthermore, a majority of the apoptotic eosinophils remained unengulfed and eventually exhibited secondary necrosis. A striking histopathology far beyond the allergic inflammation developed and included degranulated eosinophils, neutrophilia, epithelial derangement, plasma exudation, mucus-plasma plugs, and inducement of 6 CC-chemokines. In animals without eosinophilia anti-Fas evoked no inflammatory response.

Conclusion

An efficient inducer of eosinophil apoptosis in airway tissues in vivo, anti-Fas mAb evoked unprecedented asthma-like inflammation in mouse allergic airways. This outcome may partly reflect the ability of anti-Fas to evoke direct cytolysis of non-apoptotic eosinophils in airway tissues. Additionally, since most apoptotic tissue eosinophils progressed into the pro-inflammatory cellular fate of secondary necrosis this may also explain the aggravated inflammation. Our data indicate that Fas receptor mediated eosinophil apoptosis in airway tissues in vivo may cause severe disease exacerbation due to direct cytolysis and secondary necrosis of eosinophils.

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

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

Verminderung der Lipidperoxidation und der Apoptoserate in kornealen Endothelzellen durch Vitamin A

PURPOSE

The goal of this study was to determine the effects of lipid peroxidation-mediated toxicity of iron ions on corneal endothelial cells leading to apoptosis.

METHODS

Murine corneal endothelial cells were maintained in tissue culture medium supplemented with free iron ions, known to lead to increased lipid peroxidation. Retinoic acid in the cell supernatant and cytoplasm of these cells was determined using HPLC. The rate of apoptosis was assessed by quantification of caspase-3-like activity. The lipid peroxidation was measured using the malondialdehyde method. Supplementation of retinoic acid was tested in the setting of apoptosis.

RESULTS

Free iron ions led to a rapid loss of retinoic acid in the supernatant and the corneal endothelial cells. This was correlated with rising levels of malondialdehyde following oxidative stress and increased apoptosis. Supplementation of retinoic acid alone significantly reduced oxidative stress and apoptosis in the respective cells.

CONCLUSION

In this study the authors present a novel in vitro model to test the direct influence of pro-oxidative species on corneal endothelial cells. The authors also prove that supplementing corneal endothelial cells with retinoic acid sufficiently prevents free radical injury and apoptosis.

Considering Fas ligand as a target for therapy

About a decade ago, the death factor Fas ligand (FasL) was identified as the natural trigger of Fas/CD95-dependent apoptosis and as an inducer of Fas-dependent activation-induced cell death. Meanwhile, it is known that this molecule not only contributes to target cell lysis in the immune system but also to the establishment of immune privilege and tumour survival. Because delivering a specific antiproliferative signal to T lymphocytes is of major biomedical interest, the FasL/Fas system has gained much attention over the last few years. However, only recently it became evident that the biology of FasL is more complex than initially anticipated. FasL displays a complex pattern of inducible and constitutive expression associated with a number of different functions as a death factor or a co-stimulatory/accessory molecule in lymphocyte activation. Thus, side effects are likely to occur following systemic administration of, for example, anti-FasL medication, not only because of the constitutive FasL expression on cells within immune privileged tissues and vascular endothelium. In addition, FasL comes in different forms: as a surface molecule, as a protease-shed soluble variant or secreted in vesicles. Because increased levels of soluble FasL (sFasL) have been determined in various immunological and non-immunological diseases, it has been suggested that sFasL might serve as a prognostic or diagnostic marker even though the pathophysiological cause for its enhanced production is hardly known in most cases. This review summarises the current facts and ideas about the clinical and pharmacological potential of FasL and sFasL as targets for therapeutic interventions.

Up-regulation of Fas ligand (FasL) in the central nervous system: a mechanism of immune evasion by rabies virus

Following its injection into the hindlimbs of mice, CVS, a highly pathogenic strain of rabies virus, invades the spinal cord and brain resulting in the death of the animal. In contrast, central nervous system (CNS) invasion by PV, a strain of attenuated pathogenicity, is restricted to the spinal cord and mice infected with this virus survive. Lymphocytes display transient migration into the infected CNS in fatal rabies and sustained migration in nonfatal rabies. The transient migration of T cells in fatal rabies is associated with an increase in T-cell apoptosis. We found that the early production of Fas ligand (FasL) mRNAs was up-regulated only in fatal rabies. FasL is produced by several neuronal cells and mainly in infected neurons. In mice lacking FasL (gld), infection with the neuroinvasive rabies virus strain was less severe, and the number of CD3 T cells undergoing apoptosis was smaller than that in normal mice. These data provide strong evidence that fatal rabies virus infection involves the early triggering of FasL production leading to the destruction of migratory T cells by the Fas/FasL apoptosis pathway. This mechanism could be in part responsible for the fact that T cells cannot control neuroinvasive rabies infection. Thus, rabies virus seems to use an immunosubversive strategy that takes advantage of the immune privilege status of the CNS.

Fas ligand expression by maternal decidual cells is negatively correlated with the abundance of leukocytes present at the maternal–fetal interface

The abundance of leukocytes at the maternal-fetal interface could influence the fate and invasion of extravillous trophoblasts. However, the mechanism(s) involved in determining the number of leukocytes present at the maternal-fetal interface as well as the nature of the interactions between invading fetal trophoblasts, maternal leukocytes and decidual cells are not well understood. In the present studies, we examined Fas ligand (FasL)/Fas expression at the maternal-fetal interface in human placental tissues of early pregnancy by immunohistochemistry. The types of cells and their localization were also characterized by specific cell markers (cytokeratin, vimentin and CD45 for trophoblast, decidual cells and leukocytes, respectively). The cells undergoing apoptosis and specific apoptotic trophoblasts were detected by TUNEL assay and M30 cytoDEATH immunostaining, respectively. Using single or double immunostaining, we found that FasL expression in decidual cells was negatively correlated with the number of Fas-expressing leukocytes in the same region. Furthermore, the density of leukocytes had an inverse relationship with the number of interstitial trophoblasts present in the same area. We observed also that extravillous trophoblasts are viable despite expressing Fas and being in close proximity to decidual cell-derived FasL. These data support our hypothesis that maternal decidual cell-derived FasL may be involved in preventing the recruitment of Fas-bearing leukocytes at the maternal-fetal interface through apoptosis induction by Fas/FasL interaction, thereby promoting trophoblast invasion.