Antitumor immune response by CX3CL1 fractalkine gene transfer depends on both NK and T?cells

Immunomodulation of human T cells by microbubble-mediated focused ultrasound

While met with initial and ground-breaking success targeting blood borne cancers, cellular immunotherapy remains significantly hindered in the context of solid tumors by the tumor microenvironment. Focused ultrasound, in conjunction with microbubbles, has found tremendous potential as a targeted and local drug/gene delivery technique for cancer therapy. The specific immunomodulating effects of this technique on immune cells, including T-cells, remain unexplored. Here, with freshly isolated human immune cells, we examine how focused ultrasound can viably modulate immune cell membrane permeability and influence the secretion of over 90 cytokines, chemokines and other analytes relevant to a potent immune response against cancer. We determine that microbubble-mediated focused ultrasound modulates the immune cell secretome in a time-dependent manner - ranging in ~0.1-3.6-fold changes in the concentration of a given cytokine compared to sham controls over 48 hours post-treatment (e.g. IL-1β, TNF-α, CX3CL1, CCL21). Further, we determine the general trend of a negative correlation between secreted cytokine concentration and viable ultrasound-assisted membrane permeability with negligible loss of cell viability. Taken together, the data presented here highlights the potential of microbubble-mediated focused ultrasound to viably enhance T-cell permeability and modulate key pro-immune pathways, offering a novel approach to augment targeted cellular therapies for solid tumors.

Is modulation of immune checkpoints on glioblastoma-infiltrating myeloid cells a viable therapeutic strategy?

The field of immunology has traditionally focused on immune checkpoint modulation of adaptive immune cells. However, many malignancies such as glioblastoma are mostly devoid of T cells and rather are enriched with immunosuppressive myeloid cells of the innate immune system. While some immune checkpoint targets are shared between adaptive and innate immunity, myeloid-specific checkpoints could also serve as potential therapeutics. To better understand the impact of immune checkpoint blockade on myeloid cells, we systematically summarize the current literature focusing on the direct immunological effects of PD-L1/PD-1, CD24/Siglec-10, collagen/LAIR-1, CX3CL1/CX3CR1, and CXCL10/CXCR3. By synthesizing the molecular mechanisms and the translational implications, we aim to prioritize agents in this category of therapeutics for glioblastoma.

CX3CR1+CD8+ T cells: Key players in antitumor immunity

CX3CR1 functions as the specific receptor for the chemokine CX3CL1, demonstrating expression across a broad spectrum of immune cells. This underscores its pivotal role in communication and response mechanisms within the immune system. Upon engagement with CX3CL1, CX3CR1 initiates a cascade of downstream signaling pathways that regulate various biological functions. In the context of tumor progression, the intricate and inhibitory nature of the tumor microenvironment presents a significant challenge to current clinical treatment techniques. This review aims to comprehensively explore the tumor-destructive potential shown by CX3CR1+CD8+ T cells. Simultaneously, it investigates the promising prospects of utilizing CX3CR1 in future tumor immunotherapies.

Fractalkine in Health and Disease

CX3CL1 is one of the 50 up-to-date identified and characterized chemokines. While other chemokines are produced as small, secreted proteins, CX3CL1 (fractalkine) is synthetized as a transmembrane protein which also leads to a soluble form produced as a result of proteolytic cleavage. The membrane-bound protein and the soluble forms exhibit different biological functions. While the role of the fractalkine/CX3CR1 signaling axis was described in the nervous system and was also related to the migration of leukocytes to sites of inflammation, its actions are controversial in cancer progression and anti-tumor immunity. In the present review, we first describe the known biology of fractalkine concerning its action through its cognate receptor, but also its role in the activation of different integrins. The second part of this review is dedicated to its role in cancer where we discuss its role in anti-cancer or procarcinogenic activities.

Generation, Transcriptomic States, and Clinical Relevance of CX3CR1+ CD8 T Cells in Melanoma

Recent progress in single-cell profiling technologies has revealed significant phenotypic and transcriptional heterogeneity in tumor-infiltrating CD8+ T cells. However, the transition between the different states of intratumoral antigen-specific CD8+ T cells remains elusive. Here, we sought to examine the generation, transcriptomic states, and the clinical relevance of melanoma-infiltrating CD8+ T cells expressing a chemokine receptor and T-cell differentiation marker, CX3C chemokine receptor 1 (CX3CR1). Analysis of single-cell datasets revealed distinct human melanoma-infiltrating CD8+ T-cell clusters expressing genes associated with effector T-cell function but with distinguishing expression of CX3CR1 or PDCD1. No obvious impact of CX3CR1 expression in melanoma on the response to immune checkpoint inhibitor therapy was observed while increased pretreatment and on-treatment frequency of a CD8+ T-cell cluster expressing high levels of exhaustion markers was associated with poor response to the treatment. Adoptively transferred antigen-specific CX3CR1- CD8+ T cells differentiated into the CX3CR1+ subset in mice treated with FTY720, which inhibits lymphocyte egress from secondary lymphoid tissues, suggesting the intratumoral generation of CX3CR1+ CD8+ T cells rather than their trafficking from secondary lymphoid organs. Furthermore, analysis of adoptively transferred antigen-specific CD8+ T cells, in which the Cx3cr1 gene was replaced with a marker gene confirmed that CX3CR1+ CD8+ T cells could directly differentiate from the intratumoral CX3CR1- subset. These findings highlight that tumor antigen-specific CX3CR1- CD8+ T cells can fully differentiate outside the secondary lymphoid organs and generate CX3CR1+ CD8+ T cells in the tumor microenvironment, which are distinct from CD8+ T cells that express markers of exhaustion.

SIGNIFICANCE

Intratumoral T cells are composed of heterogeneous subpopulations with various phenotypic and transcriptional states. This study illustrates the intratumoral generation of antigen-specific CX3CR1+ CD8+ T cells that exhibit distinct transcriptomic signatures and clinical relevance from CD8+ T cells expressing markers of exhaustion.

CX3CL1 release during immunogenic apoptosis is associated with enhanced anti-tumour immunity

Introduction

Immunogenic cell death (ICD) has emerged as a novel option for cancer immunotherapy. The key determinants of ICD encompass antigenicity (the presence of antigens) and adjuvanticity, which involves the release of damage-associated molecular patterns (DAMPs) and various cytokines and chemokines. CX3CL1, also known as neurotactin or fractalkine, is a chemokine involved in cellular signalling and immune cell interactions. CX3CL1 has been denoted as a "find me" signal that stimulates chemotaxis of immune cells towards dying cells, facilitating efferocytosis and antigen presentation. However, in the context of ICD, it is uncertain whether CX3CL1 is an important mediator of the effects of ICD.

Methods

In this study, we investigated the intricate role of CX3CL1 in immunogenic apoptosis induced by mitoxantrone (MTX) in cancer cells. The Luminex xMAP technology was used to quantify murine cytokines, chemokines and growth factors to identify pivotal regulatory cytokines released by murine fibrosarcoma MCA205 and melanoma B16-F10 cells undergoing ICD. Moreover, a murine tumour prophylactic vaccination model was employed to analyse the effect of CX3CL1 on the activation of an adaptive immune response against MCA205 cells undergoing ICD. Furthermore, thorough analysis of the TCGA-SKCM public dataset from 98 melanoma patients revealed the role of CX3CL1 and its receptor CX3CR1 in melanoma patients.

Results

Our findings demonstrate enhanced CX3CL1 release from apoptotic MCA205 and B16-F10 cells (regardless of the cell type) but not if they are undergoing ferroptosis or accidental necrosis. Moreover, the addition of recombinant CX3CL1 to non-immunogenic doses of MTX-treated, apoptotically dying cancer cells in the murine prophylactic tumour vaccination model induced a robust immunogenic response, effectively increasing the survival of the mice. Furthermore, analysis of melanoma patient data revealed enhanced survival rates in individuals exhibiting elevated levels of CD8+ T cells expressing CX3CR1.

Conclusion

These data collectively underscore the importance of the release of CX3CL1 in eliciting an immunogenic response against dying cancer cells and suggest that CX3CL1 may serve as a key switch in conferring immunogenicity to apoptosis.

Double-faced CX3CL1 enhances lymphangiogenesis-dependent metastasis in an aggressive subclone of oral squamous cell carcinoma

Because cancer cells have a genetically unstable nature, they give rise to genetically different variant subclones inside a single tumor. Understanding cancer heterogeneity and subclone characteristics is crucial for developing more efficacious therapies. Oral squamous cell carcinoma (OSCC) is characterized by high heterogeneity and plasticity. On the other hand, CX3C motif ligand 1 (CX3CL1) is a double-faced chemokine with anti- and pro-tumor functions. Our study reported that CX3CL1 functioned differently in tumors with different cancer phenotypes, both in vivo and in vitro. Mouse OSCC 1 (MOC1) and MOC2 cells responded similarly to CX3CL1 in vitro. However, in vivo, CX3CL1 increased keratinization in indolent MOC1 cancer, while CX3CL1 promoted cervical lymphatic metastasis in aggressive MOC2 cancer. These outcomes were due to double-faced CX3CL1 effects on different immune microenvironments indolent and aggressive cancer created. Furthermore, we established that CX3CL1 promoted cancer metastasis via the lymphatic pathway by stimulating lymphangiogenesis and transendothelial migration of lymph-circulating tumor cells. CX3CL1 enrichment in lymphatic metastasis tissues was observed in aggressive murine and human cell lines. OSCC patient samples with CX3CL1 enrichment exhibited a strong correlation with lower overall survival rates and higher recurrence and distant metastasis rates. In conclusion, CX3CL1 is a pivotal factor that stimulates the metastasis of aggressive cancer subclones within the heterogeneous tumors to metastasize, and our study demonstrates the prognostic value of CX3CL1 enrichment in long-term monitoring in OSCC.

Combined use of NK cells and radiotherapy in the treatment of solid tumors

Natural killer (NK) cells are innate lymphocytes possessing potent tumor surveillance and elimination activity. Increasing attention is being focused on the role of NK cells in integral antitumor strategies (especially immunotherapy). Of note, therapeutic efficacy is considerable dependent on two parameters: the infiltration and cytotoxicity of NK cells in tumor microenvironment (TME), both of which are impaired by several obstacles (e.g., chemokines, hypoxia). Strategies to overcome such barriers are needed. Radiotherapy is a conventional modality employed to cure solid tumors. Recent studies suggest that radiotherapy not only damages tumor cells directly, but also enhances tumor recognition by immune cells through altering molecular expression of tumor or immune cells via the in situ or abscopal effect. Thus, radiotherapy may rebuild a NK cells-favored TME, and thus provide a cost-effective approach to improve the infiltration of NK cells into solid tumors, as well as elevate immune-activity. Moreover, the radioresistance of tumor always hampers the response to radiotherapy. Noteworthy, the puissant cytotoxic activity of NK cells not only kills tumor cells directly, but also increases the response of tumors to radiation via activating several radiosensitization pathways. Herein, we review the mechanisms by which NK cells and radiotherapy mutually promote their killing function against solid malignancies. We also discuss potential strategies harnessing such features in combined anticancer care.

Plasma fractalkine contributes to systemic myeloid diversity and PD-L1/PD-1 blockade in lung cancer

Recent studies highlight the importance of baseline functional immunity for immune checkpoint blockade therapies. High-dimensional systemic immune profiling is performed in a cohort of non-small-cell lung cancer patients undergoing PD-L1/PD-1 blockade immunotherapy. Responders show high baseline myeloid phenotypic diversity in peripheral blood. To quantify it, we define a diversity index as a potential biomarker of response. This parameter correlates with elevated activated monocytic cells and decreased granulocytic phenotypes. High-throughput profiling of soluble factors in plasma identifies fractalkine (FKN), a chemokine involved in immune chemotaxis and adhesion, as a biomarker of response to immunotherapy that also correlates with myeloid cell diversity in human patients and murine models. Secreted FKN inhibits lung adenocarcinoma growth in vivo through a prominent contribution of systemic effector NK cells and increased tumor immune infiltration. FKN sensitizes murine lung cancer models refractory to anti-PD-1 treatment to immune checkpoint blockade immunotherapy. Importantly, recombinant FKN and tumor-expressed FKN are efficacious in delaying tumor growth in vivo locally and systemically, indicating a potential therapeutic use of FKN in combination with immunotherapy.

A systematic pan-cancer analysis reveals the clinical prognosis and immunotherapy value of C-X3-C motif ligand 1 (CX3CL1)

It is now widely known that C-X3-C motif ligand 1 (CX3CL1) plays an essential part in the process of regulating pro-inflammatory cells migration across a wide range of inflammatory disorders, including a number of malignancies. However, there has been no comprehensive study on the correlation between CX3CL1 and cancers on the basis of clinical features. In order to investigate the potential function of CX3CL1 in the clinical prognosis and immunotherapy, I evaluated the expression of CX3CL1 in numerous cancer types, methylation levels and genetic alterations. I found CX3CL1 was differentially expressed in numerous cancer types, which indicated CX3CL1 may plays a potential role in tumor progression. Furthermore, CX3CL1 was variably expressed in methylation levels and gene alterations in most cancers according to The Cancer Genome Atlas (TCGA). CX3CL1 was robustly associated with clinical characteristics and pathological stages, suggesting that it was related to the degree of tumor malignancy and the physical function of patients. As determined by the Kaplan-Meier method of estimating survival, high CX3CL1 expression was associated with either favorable or unfavorable outcomes depending on the different types of cancer. It suggests the correlation between CX3CL1 and tumor prognosis. Significant positive correlations of CX3CL1 expression with CD4+ T cells, M1 macrophage cells and activated mast cells have been established in the majority of TCGA malignancies. Which indicates CX3CL1 plays an important role in tumor immune microenvironment. Gene Ontology (GO) terms and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis suggested that the chemokine signaling pathway may shed light on the pathway for CX3CL1 to exert function. In a conclusion, our study comprehensively summarizes the potential role of CX3CL1 in clinical prognosis and immunotherapy, suggesting that CX3CL1 may represent a promising pharmacological treatment target of tumors.

CX3CL1 promotes cell sensitivity to ferroptosis and is associated with the tumor microenvironment in clear cell renal cell carcinoma

Background

An increasing number of studies have demonstrated that CX3CL1 is involved in the development of tumors and may thus be considered a new potential therapeutic target for them. However, the function of CX3CL1 in clear cell renal cell carcinoma (ccRCC) remains poorly defined.

Methods

The pan-cancer expression pattern and prognostic value of CX3CL1 were evaluated in this study. Moreover, the relationship of CX3CL1 expression with the tumor microenvironment, especially the tumor immune microenvironment, was analyzed. Our analyses employed public repository data. Additionally, we generated stable CX3CL1-overexpressing 786-O cells to determine the role of CX3CL1 in vitro via cell viability and transwell assays. A xenograft tumor model was used to determine the role of CX3CL1 in vivo. The association between CX3CL1 and ferroptosis sensitivity of tumor cells was assessed using Ferrostatin-1.

Results

Our findings indicated the involvement of CX3CL1 in the occurrence and development of ccRCC by acting as a tumor suppressor. We also found that ccRCC patients with high CX3CL1 expression showed better clinical outcomes than those with low CX3CL1 expression. The findings of our epigenetic study suggested that the expression of CX3CL1 in ccRCC is correlated with its DNA methylation level. Furthermore, the CX3CL1 expression level was closely related to the infiltration level of CD8+ T cells into the tumor microenvironment (TME). CX3CL1 showed different predictive values in different immunotherapy cohorts. Finally, CX3CL1 overexpression inhibited tumor cell proliferation and metastasis and promoted tumor ferroptosis sensitivity in ccRCC.

Conclusions

This study revealed the role of CX3CL1 as a tumor suppressor in ccRCC. Our findings indicated that CX3CL1 plays a crucial role in regulating the ccRCC TME and is a potential predictor of immunotherapy outcomes in ccRCC. We also found that CX3CL1 can promote ferroptosis sensitivity in ccRCC cells.

NK cells and solid tumors: therapeutic potential and persisting obstacles

Natural killer (NK) cells, which are innate lymphocytes endowed with potent cytotoxic activity, have recently attracted attention as potential anticancer therapeutics. While NK cells mediate encouraging responses in patients with leukemia, the therapeutic effects of NK cell infusion in patients with solid tumors are limited. Preclinical and clinical data suggest that the efficacy of NK cell infusion against solid malignancies is hampered by several factors including inadequate tumor infiltration and persistence/activation in the tumor microenvironment (TME). A number of metabolic features of the TME including hypoxia as well as elevated levels of adenosine, reactive oxygen species, and prostaglandins negatively affect NK cell activity. Moreover, cancer-associated fibroblasts, tumor-associated macrophages, myeloid-derived suppressor cells, and regulatory T cells actively suppress NK cell-dependent anticancer immunity. Here, we review the metabolic and cellular barriers that inhibit NK cells in solid neoplasms as we discuss potential strategies to circumvent such obstacles towards superior therapeutic activity.

Crosstalk between IL-15Rα+ tumor-associated macrophages and breast cancer cells reduces CD8+ T cell recruitment

Background

Interleukin‐15 (IL‐15) is a promising immunotherapeutic agent owing to its powerful immune‐activating effects. However, the clinical benefits of these treatments are limited. Crosstalk between tumor cells and immune cells plays an important role in immune escape and immunotherapy drug resistance. Herein, this study aimed to obtain in‐depth understanding of crosstalk in the tumor microenvironment for providing potential therapeutic strategies to prevent tumor progression.

Methods

T‐cell killing assays and co‐culture models were developed to determine the role of crosstalk between macrophages and tumor cells in breast cancer resistant to IL‐15. Western blotting, histological analysis, CRISPR‐Cas9 knockout, multi‐parameter flow cytometry, and tumor cell‐macrophage co‐injection mouse models were developed to examine the mechanism by which IL‐15Rα⁺ tumor‐associated macrophages (TAMs) regulate breast cancer cell resistance to IL‐15.

Results

We found that macrophages contributed to the resistance of tumor cells to IL‐15, and tumor cells induced macrophages to express high levels of the α subunit of the IL‐15 receptor (IL‐15Rα). Further investigation showed that IL‐15Rα⁺ TAMs reduced the protein levels of chemokine CX3C chemokine ligand 1 (CX3CL1) in tumor cells to inhibit the recruitment of CD8⁺ T cells by releasing the IL‐15/IL‐15Rα complex (IL‐15Rc). Administration of an IL‐15Rc blocking peptide markedly suppressed breast tumor growth and overcame the resistance of cancer cells to anti‐ programmed cell death protein 1 (PD‐1) antibody immunotherapy. Interestingly, Granulocyte‐macrophage colony‐stimulating factor (GMCSF) induced γ chain (γc) expression to promote tumor cell‐macrophage crosstalk, which facilitated tumor resistance to IL‐15. Additionally, we observed that the non‐transcriptional regulatory function of hypoxia inducible factor‐1alpha (HIF‐1α) was essential for IL‐15Rc to regulate CX3CL1 expression in tumor cells.

Conclusions

The IL‐15Rc‐HIF‐1α‐CX3CL1 signaling pathway serves as a crosstalk between macrophages and tumor cells in the tumor microenvironment of breast cancer. Targeting this pathway may provide a potential therapeutic strategy for enhancing the efficacy of cancer immunotherapy.

DNA Hypermethylation-Regulated CX3CL1 Reducing T Cell Infiltration Indicates Poor Prognosis in Wilms Tumour

Objective

To investigate the role of chemokines in Wilms tumours, especially their chemotaxis to immune cells and the role of DNA methylation in regulating the expression level of chemokines.

Methods

RNAseqV2 gene expression and clinical data were downloaded from the TARGET database. DNA methylation data were downloaded from the GEO and cBioPortal database. The difference analysis and Kaplan-Meier(KM) analysis of chemokines were performed by edgeR package. Then predictive model based on chemokines was constructed by lasso regression and multivariate COX regression. ROC curve, DCA curve, Calibration curve, and Nomogram were used to evaluate the prognostic model. MCPcounter and Cibersort algorithm was used to calculate the infiltration of immune cells in Wilms tumour and para-tumour samples. Then the difference analysis of the immune cells was performed. The relationship between chemokines and immune cells were calculated by Pearson correlation. In addition, DNA methylation differences between Wilms tumour and para-tumour samples was performed. The correlation between DNA methylation and mRNA expression was calculated by Pearson correlation. Western blot(WB)and immunofluorescence were used to confirm the differential expression of CX3CL1 and T cells, and the correlation between them.

Results

A total of 16 chemokines were differentially expressed in tumour and para-tumour samples. A total of seven chemokines were associated with survival. CCL2 and CX3CL1 were positively correlated with prognosis, while high expression of CCL3, CCL8, CCL15, CCL18 and CXCL9 predicted poor prognosis. By lasso regression and multivariate COX regression, CCL3, CCL15, CXCL9 and CX3CL1 were finally included to construct a prediction model. The model shows good prediction ability. MCPcounter and Cibersort algorithm both showed that T cells were higher in para-tumour tissues than cancer tissues. Correlation analysis showed that CX3CL1 had a strong correlation with T cells. These were verified by Weston blot and immunofluorescence. DNA methylation analysis showed that various chemokines were different in para-tumours and tumours. CX3CL1 was hypermethylated in tumours, and the degree of methylation was negatively correlated with mRNA expression.

Conclusion

1. There is low T cell infiltration in nephroblastoma. 2. Chemokines such as CX3CL1 indicate a favourable prognosis and positively correlate with the number of T cells. 3. chemokines such as CX3CL1 are negatively regulated by DNA hypermethylation.

CD40 and CD80/86 signaling in cDC1s mediate effective neoantigen vaccination and generation of antigen-specific CX3CR1+ CD8+ T cells

The use of tumor mutation-derived neoantigen represents a promising approach for cancer vaccines. Preclinical and early phase human clinical studies have shown the successful induction of tumor neoepitope-directed responses; however, overall clinical efficacy of neoantigen vaccines has been limited. One major obstacle of this strategy is the prevailing lack of sufficient understanding of the mechanism underlying the generation of neoantigen-specific CD8⁺ T cells. Here, we report a correlation between antitumor efficacy of neoantigen/toll-like receptor 3 (TLR3)/CD40 agonists vaccination and an increased frequency of circulating antigen-specific CD8⁺ T cells expressing CX3C chemokine receptor 1 (CX3CR1) in a preclinical model. Mechanistic studies using mixed bone marrow chimeras identified that CD40 and CD80/86, but not CD70 signaling in Batf3-dependent conventional type 1 dendritic cells (cDC1s) is required for the antitumor efficacy of neoantigen vaccine and generation of neoantigen-specific CX3CR1⁺ CD8⁺ T cells. Although CX3CR1⁺ CD8⁺ T cells exhibited robust in vitro effector function, in vivo depletion of this subset did not alter the antitumor efficacy of neoantigen/TLR3/CD40 agonists vaccination. These findings indicate that the vaccine-primed CX3CR1⁺ subset is dispensable for antitumor CD8⁺ T cell responses, but can be used as a blood-based T-cell biomarker for effective priming of CD8⁺ T cells as post-differentiated T cells. Taken together, our results reveal a critical role of CD40 and CD80/86 signaling in cDC1s in antitumor efficacy of neoantigen-based therapeutic vaccines, and implicate the potential utility of CX3CR1 as a circulating predictive T-cell biomarker in vaccine therapy.

Prognostic and tumor-immune infiltration cell signatures in tamoxifen-resistant breast cancers

BACKGROUND

The cumulative risk of distant recurrence of hormone receptor-positive (HR+) breast cancer in the past 20 years has ranged from 22% to 52% after 5 years of endo-therapy. The TNM stage, histological grade, and age are important clinical factors related to recurrence, however the exact mechanism of tamoxifen resistance is still unclear.

METHODS

Differentially expressed genes (DEGs) were identified in 10 pairs of patients who had relapsed and non-relapsed after tamoxifen treatment based on matching their clinicopathological factors. After analysis of the Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, 10 hub genes were identified using Cytoscape software. Next, real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) and the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) database were used to verify the expression and overall survival (OS) of the 10 hub genes respectively, and GSE96058 and Kaplan-Meier Plotter website were used to further verify the OS of C3, CX3CL1, CXCL2, and SAA1. Finally, Immune Cell Abundance Identifier (ImmuCellAI) and the TIMER database were used to estimate immune cell infiltration and the expression of prognostic genes.

RESULTS

The DEGs were mainly enriched in the inflammatory response and cytokine-receptor interaction. The expression and the survival analysis identified CX3CL1, CXCL2, and SAA1 as prognostic factors, whose overexpression in HR+/human epidermal growth factor receptor 2 (HER-2) negative breast cancer possibly predicted a longer disease-free survival. The expression levels of these 3 genes are positively correlated with immune cell infiltration. Their high expression levels may predict longer disease-free survival in breast cancer after tamoxifen treatment and may be biomarkers for tamoxifen-resistant therapy.

CONCLUSIONS

In conclusion, the high expression of CX3CL1, CXCL2, and SAA1 may predict longer disease-free survival in breast cancer after tamoxifen treatment and may be a biomarker for tamoxifen therapy.

Role of the CX3CL1-CX3CR1 axis in renal disease

Excessive infiltration of immune cells into the kidney is a key feature of acute and chronic kidney diseases. The family of chemokines comprises key drivers of this process. Fractalkine [chemokine (C-X3-C motif) ligand 1 (CX3CL1)] is one of two unique chemokines synthesized as a transmembrane protein that undergoes proteolytic cleavage to generate a soluble species. Through interacting with its cognate receptor, chemokine (C-X3-C motif) receptor 1 (CX3CR1), CX3CL1 was originally shown to act as a conventional chemoattractant in the soluble form and as an adhesion molecule in the transmembrane form. Since then, other functions of CX3CL1 beyond leukocyte recruitment have been described, including cell survival, immunosurveillance, and cell-mediated cytotoxicity. This review summarizes diverse roles of CX3CL1 in kidney disease and potential uses as a therapeutic target and novel biomarker. As the CX3CL1-CX3CR1 axis has been shown to contribute to both detrimental and protective effects in various kidney diseases, a thorough understanding of how the expression and function of CX3CL1 are regulated is needed to unlock its therapeutic potential.

Functional heterogeneity of mesenchymal stem cells from natural niches to culture conditions: implications for further clinical uses

Mesenchymal stem cells (MSC) are present in all organs and tissues. Several studies have shown the therapeutic potential effect of MSC or their derived products. However, the functional heterogeneity of MSC constitutes an important barrier for transferring these capabilities to the clinic. MSC heterogeneity depends on their origin (biological niche) or the conditions of potential donors (age, diseases or unknown factors). It is accepted that many culture conditions of the artificial niche to which they are subjected, such as O₂ tension, substrate and extracellular matrix cues, inflammatory stimuli or genetic manipulations can influence their resulting phenotype. Therefore, to attain a more personalized and precise medicine, a correct selection of MSC is mandatory, based on their functional potential, as well as the need to integrate all the existing information to achieve an optimal improvement of MSC features in the artificial niche.

Human Mesenchymal Stem Cells Overexpressing Interleukin 2 Can Suppress Proliferation of Neuroblastoma Cells in Co-Culture and Activate Mononuclear Cells In Vitro

High-dose recombinant interleukin 2 (IL2) therapy has been shown to be successful in renal cell carcinoma and metastatic melanoma. However, systemic administration of high doses of IL2 can be toxic, causing capillary leakage syndrome and stimulating pro-tumor immune response. One of the strategies to reduce the systemic toxicity of IL2 is the use of mesenchymal stem cells (MSCs) as a vehicle for the targeted delivery of IL2. Human adipose tissue-derived MSCs were transduced with lentivirus encoding IL2 (hADSCs-IL2) or blue fluorescent protein (BFP) (hADSCs-BFP). The proliferation, immunophenotype, cytokine profile and ultrastructure of hADSCs-IL2 and hADSCs-BFP were determined. The effect of hADSCs on activation of peripheral blood mononuclear cells (PBMCs) and proliferation and viability of SH-SY5Y neuroblastoma cells after co-culture with native hADSCs, hADSCs-BFP or hADSCs-IL2 on plastic and Matrigel was evaluated. Ultrastructure and cytokine production by hADSCs-IL2 showed modest changes in comparison with hADSCs and hADSCs-BFP. Conditioned medium from hADSC-IL2 affected tumor cell proliferation, increasing the proliferation of SH-SY5Y cells and also increasing the number of late-activated T-cells, natural killer (NK) cells, NKT-cells and activated T-killers. Conversely, hADSC-IL2 co-culture led to a decrease in SH-SY5Y proliferation on plastic and Matrigel. These data show that hADSCs-IL2 can reduce SH-SY5Y proliferation and activate PBMCs in vitro. However, IL2-mediated therapeutic effects of hADSCs could be offset by the increased expression of pro-oncogenes, as well as the natural ability of hADSCs to promote the progression of some tumors.

Fractalkine/CX3CL1 in Neoplastic Processes

Fractalkine/CX3C chemokine ligand 1 (CX3CL1) is a chemokine involved in the anticancer function of lymphocytes-mainly NK cells, T cells and dendritic cells. Its increased levels in tumors improve the prognosis for cancer patients, although it is also associated with a poorer prognosis in some types of cancers, such as pancreatic ductal adenocarcinoma. This work focuses on the 'hallmarks of cancer' involving CX3CL1 and its receptor CX3CR1. First, we describe signal transduction from CX3CR1 and the role of epidermal growth factor receptor (EGFR) in this process. Next, we present the role of CX3CL1 in the context of cancer, with the focus on angiogenesis, apoptosis resistance and migration and invasion of cancer cells. In particular, we discuss perineural invasion, spinal metastasis and bone metastasis of cancers such as breast cancer, pancreatic cancer and prostate cancer. We extensively discuss the importance of CX3CL1 in the interaction with different cells in the tumor niche: tumor-associated macrophages (TAM), myeloid-derived suppressor cells (MDSC) and microglia. We present the role of CX3CL1 in the development of active human cytomegalovirus (HCMV) infection in glioblastoma multiforme (GBM) brain tumors. Finally, we discuss the possible use of CX3CL1 in immunotherapy.

CX3CR1-CD8+ T cells are critical in antitumor efficacy but functionally suppressed in the tumor microenvironment

Although blockade of the programmed cell death 1/programmed cell death ligand 1 (PD-1/PD-L1) immune checkpoint has revolutionized cancer treatment, how it works on tumor-infiltrating CD8+ T cells recognizing the same antigen at various differentiation stages remains elusive. Here, we found that the chemokine receptor CX3CR1 identified 3 distinct differentiation states of intratumor CD8+ T cell subsets. Adoptively transferred antigen-specific CX3CR1-CD8+ T cells generated phenotypically and functionally distinct CX3CR1int and CX3CR1hi subsets in the periphery. Notably, expression of coinhibitory receptors and T cell factor 1 (Tcf1) inversely correlated with the degree of T cell differentiation defined by CX3CR1. Despite lower expression of coinhibitory receptors and potent cytolytic activity, in vivo depletion of the CX3CR1hi subset did not alter the antitumor efficacy of adoptively transferred CD8+ T cells. Furthermore, differentiated CX3CR1int and CX3CR1hi subsets were impaired in their ability to undergo proliferation upon restimulation and had no impact on established tumors upon second adoptive transfer compared with the CX3CR1- subset that remained effective. Accordingly, anti-PD-L1 therapy preferentially rescued proliferation and cytokine production of the CX3CR1- subset and enhanced antitumor efficacy of adoptively transferred CD8+ T cells. These findings provide a better understanding of the phenotypic and functional heterogeneity of tumor-infiltrating CD8+ T cells and can be exploited to develop more effective immunotherapy.

CX3CL1 Signaling in the Tumor Microenvironment

CX3CL1 (Fractalkine) is a multifunctional inflammatory chemokine with a single receptor CX3CR1. The biological effects elicited by CX3CL1 on surrounding cells vary depending on a number of factors including its structure, the expression pattern of CX3CR1, and the cell type. For instance, the transmembrane form of CX3CL1 primarily serves as an adhesion molecule, but when cleaved to a soluble form, CX3CL1 predominantly functions as a chemotactic cytokine (Fig. 1.1). However, the biological functions of CX3CL1 also extend to immune cell survival and retention. The pro-inflammatory nature of CX3CR1-expressing immune cells place the CX3CL1:CX3CR1 axis as a central player in multiple inflammatory disorders and position this chemokine pathway as a potential therapeutic target. However, the emerging role of this chemokine pathway in the maintenance of effector memory cytotoxic T cell populations implicates it as a key chemokine in anti-viral and anti-tumor immunity, and therefore an unsuitable therapeutic target in inflammation. The reported role of CX3CL1 as a key regulator of cytotoxic T cell-mediated immunity is supported by several studies that demonstrate CX3CL1 as an important TIL-recruiting chemokine and a positive prognostic factor in colorectal, breast, and lung cancer. Such reports are conflicting with an overwhelming number of studies demonstrating a pro-tumorigenic and pro-metastatic role of CX3CL1 across multiple blood and solid malignancies.This chapter will review the unique structure, function, and biology of CX3CL1 and address the diversity of its biological effects in the immune system and the tumor microenvironment. Overall, this chapter highlights how we have just scratched the surface of CX3CL1's capabilities and suggests that further in-depth and mechanistic studies incorporating all CX3CL1 interactions must be performed to fully appreciate its role in cancer and its potential as a therapeutic target.

The miR-561-5p/CX3CL1 Signaling Axis Regulates Pulmonary Metastasis in Hepatocellular Carcinoma Involving CX3CR1+ Natural Killer Cells Infiltration

Natural killer (NK) cell can inhibit tumor initiation and regulates metastatic dissemination, acting as key mediators of the innate immune response. Intrinsic factors modulating NK cells infiltration and its anticancer activity remain poorly characterized. We investigated the roles of dysregulation of micro(mi)RNAs and NK cells in progression of hepatocellular carcinoma (HCC).

Methods: Small RNA sequencing were used to detect the miRNA profiles of tumor tissues from HCC patients with (n=14) or without (n=13) pulmonary metastasis and HCC cell lines with different pulmonary metastatic potentials. Chemokine expression profiling and bioinformatics were used to detect the downstream target of candidate target. In gain- and loss-of-function assays were used to investigate the role of miRNA in HCC progression. Different subsets of NK cells were isolated and used for chemotaxis and functional assays in vivo and in vitro. In situ hybridization and immunohistochemical analyses were performed to detect the expression of miRNA in tumor tissues from 242 HCC patients undergoing curative resection from 2010.

Results: Three miRNAs (miR-137, miR-149-5p, and miR-561-5p) were identified to be associated with pulmonary metastasis in patients with HCC. miR-561-5p was most highly overexpressed in metastatic HCC tissues and high-metastatic-potential HCC cell lines. In gain- and loss-of-function assays in a murine model, miR-561-5p promoted tumor growth and spread to the lungs. Yet, miR-561-5p did not appear to affect cellular proliferation and migration in vitro. Bioinformatics and chemokine expression profiling identified chemokine (C-X₃-C motif) ligand 1 (CX₃CL1) as a potential target of miR-561-5p. Furthermore, miR-561-5p promoted tumorigenesis and metastasis via CX₃CL1-dependent regulation of CX₃CR1⁺ NK cell infiltration and function. CX₃CR1⁺ NK cells demonstrated stronger in vivo anti-metastatic activity relative to CX₃CR1^- NK cells. CX₃CL1 stimulated chemotactic migration and cytotoxicity in CX₃CR1⁺ NK cells via STAT3 signaling. Blockade of CX₃CL1, CX₃CR1, or of pSTAT3 signaling pathways attenuated the antitumor responses. Clinical samples exhibited a negative correlation between miR-561-5p expression and levels of CX₃CL1 and CX₃CR1⁺ NK cells. High miR-561-5p abundance, low CX₃CL1 levels, and low numbers of CX₃CR1⁺ NK cells were associated with adverse prognosis.

Conclusion: We delineated a miR-561-5p/CX3CL1/NK cell axis that drives HCC metastasis and demonstrated that CX₃CR1⁺ NK cells serve as potent antitumor therapeutic effectors.

Mesenchymal Stem Cells and Cancer: Clinical Challenges and Opportunities

Stem cell-based therapies exhibit profound therapeutic potential for treating various human diseases, including cancer. Among the cell types that can be used for this purpose, mesenchymal stem cells (MSCs) are considered as promising source of stem cells in personalized cell-based therapies. The inherent tumor-tropic property of MSCs can be used to target cancer cells. Although the impacts of MSCs on tumor progression remain elusive, they have been genetically modified or engineered as targeted anticancer agents which could inhibit tumor growth by blocking different processes of tumor. In addition, there are close interactions between MSCs and cancer stem cells (CSCs). MSCs can regulate the growth of CSCs through paracrine mechanisms. This review aims to focus on the current knowledge about MSCs-based tumor therapies, the opportunities and challenges, as well as the prospective of its further clinical implications.

CX3CR1 identifies PD-1 therapy-responsive CD8+ T cells that withstand chemotherapy during cancer chemoimmunotherapy

Although immune checkpoint inhibitors have resulted in durable clinical benefits in a subset of patients with advanced cancer, some patients who did not respond to initial anti-PD-1 therapy have been found to benefit from the addition of salvage chemotherapy. However, the mechanism responsible for the successful chemoimmunotherapy is not completely understood. Here we show that a subset of circulating CD8+ T cells expressing the chemokine receptor CX3CR1 are able to withstand the toxicity of chemotherapy and are increased in patients with metastatic melanoma who responded to chemoimmunotherapy (paclitaxel and carboplatin plus PD-1 blockade). These CX3CR1+CD8+ T cells have effector memory phenotypes and the ability to efflux chemotherapy drugs via the ABCB1 transporter. In line with clinical observation, our preclinical models identified an optimal sequencing of chemoimmunotherapy that resulted in an increase of CX3CR1+CD8+ T cells. Taken together, we found a subset of PD-1 therapy-responsive CD8+ T cells that were capable of withstanding chemotherapy and executing tumor rejection with their unique abilities of drug efflux (ABCB1), cytolytic activity (granzyme B and perforin), and migration to and retention (CX3CR1 and CD11a) at tumor sites. Future strategies to monitor and increase the frequency of CX3CR1+CD8+ T cells may help to design effective chemoimmunotherapy to overcome cancer resistance to immune checkpoint blockade therapy.

Tissue-specific Role of CX3CR1 Expressing Immune Cells and Their Relationships with Human Disease

Chemokine (C-X3-C motif) ligand 1 (CX₃CL1, also known as fractalkine) and its receptor chemokine (C-X3-C motif) receptor 1 (CX₃CR1) are widely expressed in immune cells and non-immune cells throughout organisms. However, their expression is mostly cell type-specific in each tissue. CX₃CR1 expression can be found in monocytes, macrophages, dendritic cells, T cells, and natural killer (NK) cells. Interaction between CX₃CL1 and CX₃CR1 can mediate chemotaxis of immune cells according to concentration gradient of ligands. CX₃CR1 expressing immune cells have a main role in either pro-inflammatory or anti-inflammatory response depending on environmental condition. In a given tissue such as bone marrow, brain, lung, liver, gut, and cancer, CX₃CR1 expressing cells can maintain tissue homeostasis. Under pathologic conditions, however, CX₃CR1 expressing cells can play a critical role in disease pathogenesis. Here, we discuss recent progresses of CX₃CL1/CX₃CR1 in major tissues and their relationships with human diseases.

Genetic engineering of human NK cells to express CXCR2 improves migration to renal cell carcinoma

Background

Adoptive natural killer (NK) cell transfer is being increasingly used as cancer treatment. However, clinical responses have so far been limited to patients with hematological malignancies. A potential limiting factor in patients with solid tumors is defective homing of the infused NK cells to the tumor site. Chemokines regulate the migration of leukocytes expressing corresponding chemokine receptors. Various solid tumors, including renal cell carcinoma (RCC), readily secrete ligands for the chemokine receptor CXCR2. We hypothesize that infusion of NK cells expressing high levels of the CXCR2 chemokine receptor will result in increased influx of the transferred NK cells into tumors, and improved clinical outcome in patients with cancer.

Methods

Blood and tumor biopsies from 14 primary RCC patients were assessed by flow cytometry and chemokine analysis. Primary NK cells were transduced with human CXCR2 using a retroviral system. CXCR2 receptor functionality was determined by Calcium flux and NK cell migration was evaluated in transwell assays.

Results

We detected higher concentrations of CXCR2 ligands in tumors compared with plasma of RCC patients. In addition, CXCL5 levels correlated with the intratumoral infiltration of CXCR2-positive NK cells. However, tumor-infiltrating NK cells from RCC patients expressed lower CXCR2 compared with peripheral blood NK cells. Moreover, healthy donor NK cells rapidly lost their CXCR2 expression upon in vitro culture and expansion. Genetic modification of human primary NK cells to re-express CXCR2 improved their ability to specifically migrate along a chemokine gradient of recombinant CXCR2 ligands or RCC tumor supernatants compared with controls. The enhanced trafficking resulted in increased killing of target cells. In addition, while their functionality remained unchanged compared with control NK cells, CXCR2-transduced NK cells obtained increased adhesion properties and formed more conjugates with target cells.

Conclusions

To increase the success of NK cell-based therapies of solid tumors, it is of great importance to promote their homing to the tumor site. In this study, we show that stable engineering of human primary NK cells to express a chemokine receptor thereby enhancing their migration is a promising strategy to improve anti-tumor responses following adoptive transfer of NK cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s40425-017-0275-9) contains supplementary material, which is available to authorized users.

CX3CL1/CX3CR1 Axis, as the Therapeutic Potential in Renal Diseases: Friend or Foe?

The fractalkine receptor chemokine (C-X3-C motif) receptor 1 (CX3CR1) and its highly selective ligand CX3CL1 mediate chemotaxis and adhesion of immune cells, which are involved in the pathogenesis and progression of numerous inflammatory disorders and malignancies. The CX3CL1/CX3CR1 axis has recently drawn attention as a potential therapeutic target because it is involved in the ontogeny, homeostatic migration, or colonization of renal phagocytes. We performed a Medline/PubMed search to detect recently published studies that explored the relationship between the CX3CL1/CX3CR1 axis and renal diseases and disorders, including diabetic nephropathy, renal allograft rejection, infectious renal diseases, IgA nephropathy, fibrotic kidney disease, lupus nephritis and glomerulonephritis, acute kidney injury and renal carcinoma. Most studies demonstrated its role in promoting renal pathopoiesis; however, several recent studies showed that the CX3CL1/CX3CR1 axis could also reduce renal pathopoiesis. Thus, the CX3CL1/CX3CR1 axis is now considered to be a double-edged sword that could provide novel perspectives into the pathogenesis and treatment of renal diseases and disorders.

Regulation of cytotoxic T-Lymphocyte trafficking to tumors by chemoattractants: implications for immunotherapy

Cancer immunotherapy has recently emerged as an important treatment modality. FDA approval of provenge, ipilimumab and pembrolizumab has started to deliver on the long awaited promise of cancer immunotherapy. Many new modalities of immunotherapies targeting cytotoxic T lymphocytes (CTLs) responses, such as adoptive cell therapies and vaccines, are in advanced clinical trials. In all these immunotherapies, migration of CTLs to the tumor site is a critical step for achieving therapeutic efficacy. However, inefficient infiltration of activated CTLs into established tumors is increasingly being recognized as one of the major hurdles limiting efficacy. Mechanisms that control migration of CTLs to tumors are poorly defined. In this review, the authors discuss the chemoattractants and their receptors that have been implicated in endogenous- or immunotherapy-induced CTL recruitment to tumors and the potential for targeting these pathways for therapeutic efficacy.

Mutant p53 reprograms TNF signaling in cancer cells through interaction with the tumor suppressor DAB2IP

Inflammation is a significant factor in cancer development, and a molecular understanding of the parameters dictating the impact of inflammation on cancers could significantly improve treatment. The tumor suppressor p53 is frequently mutated in cancer, and p53 missense mutants (mutp53) can acquire oncogenic properties. We report that cancer cells with mutp53 respond to inflammatory cytokines increasing their invasive behavior. Notably, this action is coupled to expression of chemokines that can expose the tumor to host immunity, potentially affecting response to therapy. Mechanistically, mutp53 fuels NF-κB activation while it dampens activation of ASK1/JNK by TNFα, and this action depends on mutp53 binding and inhibiting the tumor suppressor DAB2IP in the cytoplasm. Interfering with such interaction reduced aggressiveness of cancer cells in xenografts. This interaction is an unexplored mechanism by which mutant p53 can influence tumor evolution, with implications for our understanding of the complex role of inflammation in cancer.

Elevated expression of CX3C chemokine receptor 1 mediates recruitment of T cells into bone marrow of patients with acquired aplastic anaemia

OBJECTIVE

Acquired aplastic anaemia (AA) is a T-cell-mediated, organ-specific autoimmune disease characterized by haematopoietic stem cell destruction in the bone marrow. The exact molecular mechanism of T-cell trafficking into the bone marrow is unclear in AA. Very late activation antigen-4 (VLA-4) and CX3C chemokine receptor 1 (CX3CR1) play active roles in many autoimmune diseases. Therefore, we investigated whether VLA-4 and CX3CR1 also contribute to T-cell migration into the bone marrow in acquired AA.

DESIGN, SETTING AND SUBJECTS

Expression levels of CX3CR1 and VLA-4 and their ligands [fractalkine (CX3CL1) and vascular cell adhesion molecule-1 (VCAM-1)] were examined in 63 patients with AA and 21 healthy control subjects. T-cell chemotaxis and adhesion were analysed in 17 patients with severe AA. We also prospectively evaluated the expression pattern of CX3CR1 during treatment with antithymocyte globulin plus cyclosporine in 11 patients with severe AA.

RESULTS

The proportion of peripheral and bone marrow CD4(+) and CD8(+) T cells expressing CX3CR1 and the level of CX3CL1 was increased in patients with AA. However, there was no significant difference in VLA-4 expression or VCAM-1 levels. Functional studies demonstrated that chemotaxis towards autologous bone marrow plasma or soluble CX3CL1 was significantly higher in T cells from AA patients and could be blocked by CX3CR1 inhibitors. CX3CR1-mediated T-cell adhesion was also upregulated in these patients. The expression of CX3CR1 was associated with the efficacy of immunosuppressive therapy.

CONCLUSION

The present findings demonstrate that CX3CR1 plays a pivotal role in recruitment of T cells into the bone marrow in acquired AA and is a potential therapeutic target for treatment of this disorder.

The emerging role of soluble HLA-G in the control of chemotaxis

HLA-G is an immunosuppressive molecule, that impairs the function of different immune cell populations, both in physiological and pathological conditions. Here, we have analyzed data obtained by our group and others regarding sHLA-G concentration in plasma from patients with different diseases. Next, we have summarized novel data regarding the impairment of chemotaxis of different immune effector cells mediated by sHLA-G. Finally, we have discussed the impact of this function on the immune response during cancer, viral infection, autoimmunity, and on B cell differentiation in secondary lymphoid organs. In conclusion, we have delineated a role of sHLA-G in the control of chemotaxis of immune effector cells, that may be relevant to modulate immune responses in different settings.

Enhanced antitumor immunity is elicited by adenovirus-mediated gene transfer of CCL21 and IL-15 in murine colon carcinomas

The chemokine CCL21 is a potent chemoattractant for T cells and dendritic cells. IL-15 elicits powerful antitumor immune responses through the stimulation of natural killer cells. We constructed a CCL21/IL-15-expressing adenovirus (Ad-CCL21-IL-15) and evaluated its antitumor effects in vitro and in vivo. We found that the intratumoral injection of Ad-CCL21-IL-15 into murine colon carcinomas significantly inhibited tumor growth. Splenocytes from mice treated with Ad-CCL21-IL-15 developed tumor-specific cytotoxic T cells and were protected from subsequent challenges with tumor cells. This study indicates that providing cancer therapy by combining CCL21 and IL-15 can induce antitumor immune responses and is an effective strategy for cancer immunotherapy.

The transmembrane chemokines CXCL16 and CX3CL1 and their receptors are expressed in human meningiomas

Meningiomas are common slowly growing benign tumors, however, anaplastic meningiomas have an aggressive biological and clinical behavior associated with high rates of recurrence and unfavorable prognosis. Since the molecular mechanisms involved in progression of meningiomas are not yet fully understood and recent investigations have suggested a possible role of chemokines in tumor biology, the aim of the study was to investigate the expression of CX3CL1/CX3CR1 and CXCL16/CXCR6 on mRNA and protein level in human meningiomas. Quantitative reverse-transcription polymerase chain reaction, immunohistochemistry and double immuno-staining techniques were used for the investigations. We showed that mRNA and protein expression of the chemokine/receptor pairs CX3CL1/CX3CR1 and CXCL16/CXCR6 were detectable in human meningioma samples. Double immunostaining revealed that the chemokines/receptors were predominantly expressed in the tumor cells themselves, in infiltrating microglia cells/macrophages and endothelial cells of blood vessels. Nevertheless, not all cells of different kinds were positive for different chemokine/receptors. Of note, in comparison to more benign meningioma samples, CX3CR1 and CXCL16 were found to be expressed at lower levels in anaplastic variants. Moreover, a positive correlation between expression levels of ligands and corresponding receptors could be observed for some malignancy grades. Taken together, these results showed that chemokines and their receptors are involved in the pathogenesis of human meningiomas. Our results provide an interesting basis for further investigations that should be performed to characterize the functional roles of chemokines and their receptors in human meningiomas, and also enhance future therapeutic design.

Fractalkine/CX3CR1: why a single chemokine-receptor duo bears a major and unique therapeutic potential

IMPORTANCE OF THE FIELD

Fractalkine, also known as CX3CL1, is the unique member of the fourth class of chemokines and mediates both chemotaxis and adhesion of inflammatory cells via its highly selective receptor CX3CR1. Fractalkine mediates inflammatory responses and pain sensation and is involved in the pathogenesis and progression of numerous inflammatory disorders and malignancies.

AREAS COVERED IN THIS REVIEW

We performed a Medline/PubMed search to detect all published studies that explored the role of fractalkine and CX3CR1 and the possibilities of therapeutic intervention in the fractalkine/CX3CR1 axis in a wide range of clinical disorders, using CX3CR1 blocking antibodies, different fractalkine antagonists, CX3CR1 depletion or transfection of fractalkine expression vectors.

WHAT THE READER WILL GAIN

This review summarizes the role of fractalkine and its receptor CX3CR1 in various diseases, focusing on their high potential as novel therapeutic targets, with special emphasis on pancreatic diseases.

TAKE HOME MESSAGE

The reviewed studies provide promising results demonstrating fractalkine and CX3CR1 as potential target molecules for future therapeutics that may attenuate pain, inflammation and furthermore serve as an anti-cancer therapy. However, to date, no therapeutics targeting fractalkine or CX3CR1 are in clinical use.

Intra-tumoral dendritic cells increase efficacy of peripheral vaccination by modulation of glioma microenvironment

Pilot data showed that adding intratumoral (IT) injection of dendritic cells (DCs) prolongs survival of patients affected by glioblastoma multiforme (GBM) treated by subcutaneous (SC) delivery of DCs. Using a murine model resembling GBM, we investigated the immunological mechanisms underlying this effect. C57BL6/N mice received brain injections of GL261 glioma cells. Seven days later, mice were treated by 3 SC injections of DCs with or without 1 IT injection of DCs. DC maturation, induced by pulsing with GL261 lysates, was necessary to develop effective immune responses. IT injection of pulsed (pDC), but not unpulsed DCs (uDC), increased significantly the survival, either per se or in combination with SC-pDC (P < .001 vs controls). Mice treated by IT-pDC plus SC-pDC survived longer than mice treated by SC-pDC only (P = .03). Injected pDC were detectable in tumor parenchyma, but not in cervical lymph nodes. In gliomas injected with IT-pDC, CD8+ cells were significantly more abundant and Foxp3+ cells were significantly less abundant than in other groups. Using real-time polymerase chain reaction, we also found enhanced expression of IFN-gamma and TNF-alpha and decreased expression of transforming growth factor-beta (TGF-beta) and Foxp3 in mice treated with SC-pDC and IT-pDC. In vitro, pDC produced more TNF-alpha than uDC: addition of TNF-alpha to the medium decreased the proliferation of glioma cells. Overall, the results suggest that IT-pDC potentiates the anti-tumor immune response elicited by SC-pDC by pro-immune modulation of cytokines in the tumor microenvironment, decrease of Treg cells, and direct inhibition of tumor proliferation by TNF-alpha.

Intratracheal delivery of CX3CL1-expressing mesenchymal stem cells to multiple lung tumors

The lung is one of the organs to which cancers from solid tumors frequently metastasize. Multiple tumors in the lung are usually treated by systemic chemotherapy because of the lack of efficient methods of targeting antitumor agents to the lung. Although intratracheal administration is an ideal route for targeting multiple lung tumors, antitumor agents are often harmful to the organ or induce inflammation. Mesenchymal stem cells (MSCs), nonhematopoietic stem cells capable of differentiating into various mesoderm-type cells, have a propensity to migrate to and proliferate in tumor tissues after systemic administration. We intratracheally injected MSCs expressing CX3CL1 (MSC/RGDFKN) into the lung of lung tumor-bearing mice with multiple metastases of C26 or Lewis lung carcinoma (LLC). Antitumor effects were evaluated by counting the number of lung metastases and survival. We demonstrated the tropism of mouse MSCs to lung tumor tissues after intratracheal administration of GFP-positive MSCs. Intratracheal injection of MSC/RGDFKN strongly inhibited growth of lung metastases of C26 or LLC, and thus prolonged survival. Intratracheal injection of MSC/RGDFKN did not induce an inflammatory reaction in the lung. These results suggest that MSCs expressing antitumor agents can be delivered intratracheally into multiple lung tumor tissues without causing inflammation.

NK cells are migrated and indispensable in the anti-tumor activity induced by CCL27 gene therapy

Natural killer (NK) cells have been demonstrated could play an important role in the treatment of a number of tumors in mice. In the present study, chemokine CCL27, which be considered only selectively chemoattracts cutaneous lymphocyte antigen positive memory T cells and Langerhans cells, firstly demonstrated that it could induce the accumulation of NK cells into tumor by the intratumoral injection of CCL27-encoding fiber-mutant vector, AdRGD-CCL27. Experiments using spleen cell fractionation and RT-PCR showed CCL27 receptor, mCCR10, was strongly expressed in NK cells, suggesting the accumulation of NK cells in tumor was attributed to chemoattractant activity of CCL27 itself. Moreover, the combination of AdRGD-CCL27 and AdRGD-IL-12 induced the synergistic anti-tumor activity via NK-dependent manner and induced more NK cells infiltration into tumor nodule than that induced by AdRGD-CCL27 alone or AdRGD-IL-12 alone.

Polymorphism in the microglial cell-mobilizing CX3CR1 gene is associated with survival in patients with glioblastoma

PURPOSE

Few reliable prognostic molecular markers have been characterized for glioblastoma multiforme (GBM), considered the deadliest of human cancers. We hypothesized that genetic polymorphisms in chemokines and their receptors, which together control microglial cell mobilization, may influence survival.

METHODS

Distributions of one polymorphism of the chemokine CCL2 (-2518A<G) and two polymorphisms of the chemokine receptor CX3CR1 (termed V249I and T280M) were determined in a prospective series of 230 patients with GBM and correlated with overall survival. The replication study used data from a retrospective series of 106 additional patients with GBM. The extent of microglial cell infiltration was assessed by immunochemistry in 102 tumor specimens.

RESULTS

Survival analysis showed that the common CX3CR1-I249 allele was an independent favorable prognostic factor in both groups, prospective and retrospective, with hazard ratios of 0.619 (95% CI, 0.451 to 0.850; P = .0031) and 0.354 (95% CI, 0.217 to 0.580; P < .0001), respectively. This beneficial effect was observed only in patients who underwent surgery. Patients with only this CX3CR1-I249 allele had a substantially longer mean survival (23.5 v 14.1 months; P < .0001). The CCL2-2518G allele was not associated with patient survival. Immunohistochemical analysis of primary tumor biopsies showed that the common CX3CR1 variant allele was associated with reduced microglial cell infiltration.

CONCLUSION

The common CX3CR1 allelic variant was associated with increased GBM survival and with reduced tumor infiltration by microglia. The CX3CR1 polymorphism does not seem to be a risk factor for GBM but may prove useful in predicting survival.

Natural killer cell accumulation in tumors is dependent on IFN-gamma and CXCR3 ligands

Several studies have correlated high numbers of tumor-infiltrating natural killer (NK) cells with a good prognosis for cancer patients. Our study aimed at identifying factors controlling intratumoral NK cell accumulation in s.c. injected NK cell sensitive tumor models and at studying their effect on survival time of recipient mice. We observed that fewer NK cells infiltrated the tumors in IFN-gamma receptor knockout (IFN-gammaR(-/-)) mice compared with wild-type controls that correlated with decreased survival rate. Exogenous application of IFN-gamma in the tumor augmented levels of ligands of the chemokine receptor CXCR3, increased NK cell accumulation, and prolonged survival. Furthermore, our data show that CD27(high) NK cells, which under steady-state conditions express CXCR3, preferentially accumulated in the tumor tissue. Accordingly, significantly lower numbers of tumor-infiltrating NK cells were detected in CXCR3(-/-) mice, and the capacity of adoptively transferred CXCR3(-/-) NK cells to accumulate in the tumor was severely impaired. Finally, exogenous application of the CXCR3 ligand CXCL10 in the tumor or ectopic expression of CXCL10 by tumor cells increased the numbers of NK cells in the tumors and prolonged NK cell-dependent survival. Our results identify IFN-gamma and the expression of CXCR3 on NK cells as prerequisites for NK cell infiltration into tumors. Exploiting strategies to augment NK cell accumulation in the tumor might lead to the development of effective antitumor therapies.

Enhancement of antitumor radiation efficacy and consistent induction of the abscopal effect in mice by ECI301, an active variant of macrophage inflammatory protein-1alpha

PURPOSE

We studied whether i.v. administration of a chemokine after local tumor site irradiation could prevent remaining, as well as distant, nonirradiated tumor cell growth by leukocyte recruitment.

EXPERIMENTAL DESIGN

Tumors were implanted s.c. in the right or both flanks. After local irradiation at the right flank, ECI301, a human macrophage inflammatory protein-1alpha variant was injected i.v. Tumor volumes were measured every 3 days after treatment.

RESULTS

In Colon26 adenocarcinoma-bearing BALB/c mice, repeated daily administration (over 3-5 consecutive days) of 2 mug per mouse ECI301 after local irradiation of 6 Gy prolonged survival without significant toxicity, and in about half of the treated mice, the tumor was completely eradicated. Three weekly administrations of ECI301 after local irradiation also led to significant, although less effective, antitumor radiation efficacy. ECI301 also inhibited growth of other syngenic tumor grafts, including MethA fibrosarcoma (BALB/c) and Lewis lung carcinoma (C57BL/6). Importantly, tumor growth at the nonirradiated site was inhibited, indicating that ECI301 potentiated the abscopal effect of radiation. This abscopal effect observed in BALB/c and C57BL/6 mice was tumor-type independent. Leukocyte depletion studies suggest that CD8+ and CD4+ lymphocytes and NK1.1 cells were involved.

CONCLUSIONS

Marked inhibition of tumor growth at the irradiated site, with complete tumor eradication and consistent induction of the abscopal effect, was potentiated by i.v. administration of ECI301. The results of this study may offer a new concept for cancer therapy, namely chemokine administration after local irradiation, leading to development of novel therapeutics for the treatment of advanced metastatic cancer.

CX3CL1 and CX3CR1 in the GL261 murine model of glioma: CX3CR1 deficiency does not impact tumor growth or infiltration of microglia and lymphocytes

Human glioblastoma multiforme (GBM) is the most malignant form of human brain tumors. A characteristic of GBM is the marked presence of tumor infiltrated microglia/macrophages and lymphocytes. The goal of this study was directed toward understanding the role of the chemokine system CX3CL1 and its receptor CX3CR1 in the GL261 murine model of malignant glioma. In situ hybridization analysis identified CX3CL1 and CX3CR1 expression in GL261 tumors. The impact of CX3CR1 deletion on the growth of intracranial GL261 gliomas and associated immune cell infiltration was evaluated in CX3CR1 gene-disrupted C57BL/6 mice. A slight increase in the tumor growth rate in CX3CR1-/- mice was evident with similar numbers of microglia and CD4+, CD8+, FoxP3+, or Ly49G2+ lymphocytes within tumors established in CX3CR1 +/- and -/- mice. These data indicate that CX3CR1 has little or no effects on either gliomagenesis or the migration of microglia and lymphocytes into GL261 tumors.

Disrupted expression of CXCL5 in colorectal cancer is associated with rapid tumor formation in rats and poor prognosis in patients

PURPOSE

We isolated a subline (CC531M) from the CC531S rat colon carcinoma cell line, which grows and metastasizes much more rapidly than CC531S. We found, using RNA expression profiling, that one of the major changes in the CC531M cell line was a 5.8-fold reduction of the chemokine CXCL5. The purpose of this study was to determine the effect of CXCL5 expression on colorectal tumor growth and metastasis.

EXPERIMENTAL DESIGN

CC531 clones were generated with either knockdown or restored expression of CXCL5. These clones were inoculated in the liver of rats. In addition, in two independent cohorts of colorectal cancer patients, the level of CXCL5 expression was determined and associated to clinical variables.

RESULTS

Knockdown of CXCL5 expression in CC531S resulted in rapid tumor growth and increased number of metastasis, whereas restored expression of CXCL5 in CC531M resulted in a return of the "mild" tumor growth pattern of the parental cell line CC531S. In vitro, no difference was found in proliferation rate between clones with either high or low expression of CXCL5, suggesting that environmental interactions directed by CXCL5 determine tumor outgrowth. Finally, the importance of our findings was established for patients with colorectal cancer. We found that low expression of CXCL5 was significantly associated with poor prognosis for colorectal cancer patients. CXCL5 showed a trend (P = 0.05) for a positive correlation with intratumoral CD8(+) T-cell infiltration, suggesting a possible explanation for the observed poorer prognosis.

CONCLUSIONS

Our results show that CXCL5 is important in growth and development of colorectal cancer, implicating a future role in both cancer therapy and diagnosis.

Increased expression of fractalkine is correlated with a better prognosis and an increased number of both CD8+ T cells and natural killer cells in gastric adenocarcinoma

BACKGROUND

Fractalkine (CX3CL1) is the only CX3C chemokine that can chemoattract natural killer (NK) cells, CD8+ T cells, monocytes, and dendritic cells. Although experimental studies have demonstrated that Fractalkine expression by tumor cells is related to the infiltrating lymphocytes and initiates antitumor immunity, the clinical significance of Fractalkine remains to be elucidated in gastric adenocarcinoma.

METHODS

Tissue sections from 158 patients with curatively resected T2 or T3 gastric adenocarcinoma were immunohistochemically stained for Fractalkine. Furthermore, to evaluate CD8+ T cells and NK cells infiltration, antibodies to CD8 and CD57 protein were respectively used for immunohistochemistry.

RESULTS

A significant direct correlation was observed between the Fractalkine scores and the number of CD8+ T cells and NK cells using the Spearman rank correlation coefficient test (P = .0080, .0031, respectively). Furthermore, the high Fractalkine expression group (n = 67) showed a significantly better prognosis than the low Fractalkine expression group (n = 91) regarding the disease-free survival (P = .0016). In a multivariate analysis, the Fractalkine expression was identified as one of the independent prognosticators for disease-free survival (risk ratio, 2.5; P = .0147).

CONCLUSIONS

These data suggest that the expression of Fractalkine by tumor cells enhances the recruitment of CD8+ T cells and NK cells and induces both innate and adaptive immunity, thereby yielding a better prognosis in gastric adenocarcinoma. Fractalkine is a new independent predictor of the prognosis and can be a novel candidate for development of a more effective therapeutic strategy for gastric adenocarcinomas.