Role of HLA-G and extracellular vesicles in renal cancer stem cell-induced inhibition of dendritic cell differentiation

Extracellular Vesicle-Dependent Communication Between Mesenchymal Stromal Cells and Immune Effector Cells

Mesenchymal stem/stromal cells (MSCs) are multipotent cells residing in the stromal tissues of the body and capable of promoting tissue repair and attenuating inflammatory processes through their immunomodulatory properties. Preclinical and clinical observations revealed that not only direct intercellular communication mediates MSC properties; in fact, a pivotal role is also played by the release of soluble and bioactive factors, such as cytokines, growth factor and extracellular vesicles (EVs). EVs are membrane-coated vesicles containing a large variety of bioactive molecules, including lipids, proteins, and nucleic acids, such as RNA. EVs release their contents into target cells, thus influencing cell fate through the control of intracellular processes. In addition, MSC-derived EVs can mediate modulatory effects toward different effector cells belonging to both innate and adaptive immunity. In this review, we will discuss the literature data concerning MSC-derived EVs, including the current standardized methods for their isolation and characterization, the mechanisms supporting their immunoregulatory properties, and their potential clinical application as alternative to MSC-based therapy for inflammatory reactions, such as graft-versus-host disease (GvHD).

Cancer stem cell secretome in the tumor microenvironment: a key point for an effective personalized cancer treatment

Cancer stem cells (CSCs) represent a tumor subpopulation responsible for tumor metastasis and resistance to chemo- and radiotherapy, ultimately leading to tumor relapse. As a consequence, the detection and eradication of this cell subpopulation represent a current challenge in oncology medicine. CSC phenotype is dependent on the tumor microenvironment (TME), which involves stem and differentiated tumor cells, as well as different cell types, such as mesenchymal stem cells, endothelial cells, fibroblasts and cells of the immune system, in addition to the extracellular matrix (ECM), different in composition to the ECM in healthy tissues. CSCs regulate multiple cancer hallmarks through the interaction with cells and ECM in their environment by secreting extracellular vesicles including exosomes, and soluble factors such as interleukins, cytokines, growth factors and other metabolites to the TME. Through these factors, CSCs generate and activate their own tumor niche by recruiting stromal cells and modulate angiogenesis, metastasis, resistance to antitumor treatments and their own maintenance by the secretion of different factors such as IL-6, VEGF and TGF-ß. Due to the strong influence of the CSC secretome on disease development, the new antitumor therapies focus on targeting these communication networks to eradicate the tumor and prevent metastasis, tumor relapse and drug resistance. This review summarizes for the first time the main components of the CSC secretome and how they mediate different tumor processes. Lastly, the relevance of the CSC secretome in the development of more precise and personalized antitumor therapies is discussed.

Extracellular Vesicle-Associated Proteins in Tissue Repair

The administration of (stem) cell-derived extracellular vesicles (EVs) promotes tissue repair through management of different inflammatory, proliferative and remodeling processes in the body. Despite the widely observed biological and therapeutic roles of EVs in wound healing and tissue repair, knowledge on how EVs activate recipient cells and which EV cargo is responsible for the subsequent functional effects is limited. Recent studies hint toward an important role for proteins as functional EV cargo. Here, we provide an overview of how EV-associated proteins promote tissue repair processes and discuss current challenges in evaluating their contribution to EV function and future directions for translating fundamental insights into clinically relevant EV therapies.

HLA-G: Function, polymorphisms and pathology

HLA-G immune modulatory genes and molecules are presently being studied by a widespread number of research groups. In the present study, we do not aim to be exhaustive since the number of manuscripts published every year is overwhelming. Instead, our aim is pointing out facts about HLA-G function, polymorphism and pathology that have been confirmed by several different researchers, together with exposing aspects that may have been overlooked or not sufficiently remarked in this productive field of study. On the other hand, we question whether performing mainly studies on HLA-G and disease associations is going to give a clear answer in the future, since 40 years of study of classical HLA molecules association with disease has still given no definite answer on this issue.

Extracellular Vesicles in the Tumour Microenvironment: Eclectic Supervisors

The tumour microenvironment (TME) plays a crucial role in the regulation of cell survival and growth by providing inhibitory or stimulatory signals. Extracellular vesicles (EV) represent one of the most relevant cell-to-cell communication mechanism among cells within the TME. Moreover, EV contribute to the crosstalk among cancerous, immune, endothelial, and stromal cells to establish TME diversity. EV contain proteins, mRNAs and miRNAs, which can be locally delivered in the TME and/or transferred to remote sites to dictate tumour behaviour. EV in the TME impact on cancer cell proliferation, invasion, metastasis, immune-escape, pre-metastatic niche formation and the stimulation of angiogenesis. Moreover, EV can boost or inhibit tumours depending on the TME conditions and their cell of origin. Therefore, to move towards the identification of new targets and the development of a novel generation of EV-based targeting approaches to gain insight into EV mechanism of action in the TME would be of particular relevance. The aim here is to provide an overview of the current knowledge of EV released from different TME cellular components and their role in driving TME diversity. Moreover, recent proposed engineering approaches to targeting cells in the TME via EV are discussed.

Extracellular Vesicles Released by Tumor Endothelial Cells Spread Immunosuppressive and Transforming Signals Through Various Recipient Cells

Head and neck squamous cell carcinoma (HNSCC) has a high recurrence and metastatic rate with an unknown mechanism of cancer spread. Tumor inflammation is the most critical processes of cancer onset, growth, and metastasis. We hypothesize that the release of extracellular vesicles (EVs) by tumor endothelial cells (TECs) induce reprogramming of immune cells as well as stromal cells to create an immunosuppressive microenvironment that favor tumor spread. We call this mechanism as non-metastatic contagious carcinogenesis. Extracellular vesicles were collected from primary HNSCC-derived endothelial cells (TEC-EV) and were used for stimulation of peripheral blood mononuclear cells (PBMCs) and primary adipose mesenchymal stem cells (ASCs). Regulation of ASC gene expression was investigated by RNA sequencing and protein array. PBMC, stimulated with TEC-EV, were analyzed by enzyme-linked immunosorbent assay and fluorescence-activated cell sorting. We validated in vitro the effects of TEC-EV on ASCs or PBMC by measuring invasion, adhesion, and proliferation. We found and confirmed that TEC-EV were able to change ASC inflammatory gene expression signature within 24-48 h. TEC-EV were also able to enhance the secretion of TGF-β1 and IL-10 by PBMC and to increase T regulatory cell (Treg) expansion. TEC-EV carry specific proteins and RNAs that are responsible for Treg differentiation and immune suppression. ASCs and PBMC, treated with TEC-EV, enhanced proliferation, adhesion of tumor cells, and their invasion. These data indicate that TEC-EV exhibit a mechanism of non-metastatic contagious carcinogenesis that regulates tumor microenvironment and reprograms immune cells to sustain tumor growth and progression.

HLA-G Neo-Expression on Tumors

HLA-G is known to modulate the immune system activity in tissues where physiological immune-tolerance is necessary (i.e., maternal-fetal interface, thymus, and cornea). However, the frequent neo-expression of HLA-G in many cancer types has been previously and extensively described and is correlated with a bad prognosis. Despite being an MHC class I molecule, HLA-G is highly present in tumor context and shows unique characteristics of tissue restriction of a Tumor Associated Antigen (TAA), and potent immunosuppressive activity of an Immune CheckPoint (ICP). Consequently, HLA-G appears to be an excellent molecular target for immunotherapy. Although the relevance of HLA-G in cancer incidence and development has been proven in numerous tumors, its neo-expression pattern is still difficult to determine. Indeed, the estimation of HLA-G's actual expression in tumor tissue is limited, particularly concerning the presence and percentage of the new non-canonical isoforms, for which detection antibodies are scarce or inexistent. Here, we summarize the current knowledge about HLA-G neo-expression and implication in various tumor types, pointing out the need for the development of new tools to analyze in-depth the HLA-G neo-expression patterns, opening the way for the generation of new monoclonal antibodies and cell-based immunotherapies.

Biology and therapeutic potential of mesenchymal stem cell-derived exosomes

Mesenchymal stem cells (MSC) are multipotent stromal cells with the potential to differentiate into several cell types. MSC‐based therapy has emerged as a promising strategy for various diseases. Accumulating evidence suggests that the paracrine effects of MSC are partially exerted by the secretion of soluble factors, in particular exosomes. MSC‐derived exosomes are involved in intercellular communication through transfer of proteins, RNA, DNA and bioactive lipids, which might constitute a novel intercellular communication mode. This review illustrates the current knowledge on the composition and biological functions as well as the therapeutic potential of MSC‐derived exosomes in cancer, with a focus on clinical translation opportunities.

Tumor microenvironment-related dendritic cell deficiency: a target to enhance tumor immunotherapy

Dendritic cells (DCs), as specialized antigen-presenting cells, are essential for the initiation of specific T cell responses in innate antitumor immunity and, in certain cases, support humoral responses to inhibit tumor development. Mounting evidence suggests that the DC system displays a broad spectrum of dysfunctional status in the tumor microenvironment (TME), which ultimately affects antitumor immune responses. DC-based therapy can restore the function of DCs in the TME, thus showing a promising potential in tumor therapy. In this review, we provide an overview of the DC deficiency caused by various factors in the TME and discuss proposed strategies to reverse DC deficiency and the applications of novel combinatorial DC-based therapy for immune normalization of the tumor.

Influence of Innate Immunity on Cancer Cell Stemness

Even if cancer stem cells (CSCs) represent only a small proportion of the tumor mass, they significantly account for tumor maintenance, resistance to therapies, relapse and metastatic spread, due to their increased capacity of self-renewal, multipotency, tumorigenicity and quiescence. Emerging evidence suggests that the immune contexture within the tumor microenvironment (TME) determines both the response to therapy and the clinical outcome. In this context, CSCs acquire immune evasion skills by editing immune cell functions and sculpting the immunosuppressive landscape of TME. Reciprocally, infiltrating immune cells influence CSCs self-renewal, tumorigenicity and metastasis. In this review, we summarize the immunomodulatory properties of CSCs, as well as the impact of innate immune cells on cancer cells stemness in the different phases of cancer immunoediting process and neoplastic progression.

Extracellular Vesicles in Renal Cell Carcinoma: Multifaceted Roles and Potential Applications Identified by Experimental and Computational Methods

Renal cell carcinoma (RCC) is the most common type of kidney cancer. Increasingly evidences indicate that extracellular vesicles (EVs) orchestrate multiple processes in tumorigenesis, metastasis, immune evasion, and drug response of RCC. EVs are lipid membrane-bound vesicles in nanometer size and secreted by almost all cell types into the extracellular milieu. A myriad of bioactive molecules such as RNA, DNA, protein, and lipid are able to be delivered via EVs for the intercellular communication. Hence, the abundant content of EVs is appealing reservoir for biomarker identification through computational analysis and experimental validation. EVs with excellent biocompatibility and biodistribution are natural platforms that can be engineered to offer achievable drug delivery strategies for RCC therapies. Moreover, the multifaceted roles of EVs in RCC progression also provide substantial targets and facilitate EVs-based drug discovery, which will be accelerated by using artificial intelligence approaches. In this review, we summarized the vital roles of EVs in occurrence, metastasis, immune evasion, and drug resistance of RCC. Furthermore, we also recapitulated and prospected the EVs-based potential applications in RCC, including biomarker identification, drug vehicle development as well as drug target discovery.

Immunoregulatory Effects of Stem Cell-Derived Extracellular Vesicles on Immune Cells

Recent investigations on the regulatory action of extracellular vesicles (EVs) on immune cells in vitro and in vivo have sparked interest on the subject. As commonly known, EVs are subcellular components secreted by a paracellular mechanism and are essentially a group of nanoparticles containing exosomes, microvesicles, and apoptotic bodies. They are double-layer membrane-bound vesicles enriched with proteins, nucleic acids, and other active compounds. EVs are recognized as a novel apparatus for intercellular communication that acts through delivery of signal molecules. EVs are secreted by almost all cell types, including stem/progenitor cells. The EVs derived from stem/progenitor cells are analogous to the parental cells and inhibit or enhance immune response. This review aims to provide its readers a comprehensive overview of the possible mechanisms underlying the immunomodulatory effects exerted by stem/progenitor cell-derived EVs upon natural killer (NK) cells, dendritic cells (DCs), monocytes/macrophages, microglia, T cells, and B cells.

Intercellular transfer of HLA-G: its potential in cancer immunology

Intercellular protein transfer between cancer cells and immune cells is a very common phenomenon that can affect different stages of host antitumor immune responses. HLA-G, a non-classical HLA class I antigen, has been observed to be widely expressed in various malignancies, and its immune-suppressive functions have been well recognised. HLA-G expression in cancer cells can directly mediate immune tolerance by interacting with inhibitory receptors such as ILT2 and ILT4 expressed on immune cells. Moreover, a network of multiple directional intercellular transfers of HLA-G among cancer cells and immune cells through trogocytosis, exosomes and tunnelling nanotubes provides malignant cells with an alternative ploy for antigen sharing and induces more complex heterogeneity, to modulate immune responses, ultimately leading to immune evasion, therapy resistance, disease progression and poor clinical outcome. Herein, we discuss the relative aspects of the intercellular transfer of HLA-G between tumor cells and immune cells and its potential use in tumor immunology research and translational cancer therapy.

Vesicular-Bound HLA-G as a Predictive Marker for Disease Progression in Epithelial Ovarian Cancer

Extracellular vesicles (EV) and their tumor-supporting cargos provide a promising translational potential in liquid biopsies for risk assessment of epithelial ovarian cancer (EOC) patients frequently relapsing, despite initial complete therapy responses. As the immune checkpoint molecule HLA-G, which is operative in immune-escape, can be released by EV, we evaluate the abundance of EV and its vesicular-bound amount of HLA-G (HLA-GEV) as a biomarker in EOC. After enrichment of EV from plasma samples, we determined the EV particle number and amount of HLA-GEV by nanoparticle tracking analysis or ELISA. The association of results with the clinical status/outcome revealed that both, EV particle number and HLA-GEV were significantly elevated in EOC patients, compared to healthy females. However, elevated levels of HLA-GEV, but not EV numbers, were exclusively associated with a disadvantageous clinical status/outcome, including residual tumor, presence of circulating tumor cells, and disease progression. High HLA-GEV status was an independent predictor of progression, besides residual tumor burden and platinum-sensitivity. Especially among patients without residual tumor burden or with platinum-sensitivity, HLA-GEV identified patients with high risk of progression. Thus, this study highlights HLA-GEV as a potential novel biomarker for risk assessment of EOC patients with a rather beneficial prognosis defined by platinum-sensitivity or lack of residual tumor burden.

Tumor-derived exosomes (TDEs): How to avoid the sting in the tail

Exosomes are abundantly secreted extracellular vesicles that accumulate in the circulation and are of great interest for disease diagnosis and evaluation since their contents reflects the phenotype of their cell of origin. Tumor‐derived exosomes (TDEs) are of particular interest for cancer diagnosis and therapy, since most tumor demonstrate highly elevated exosome secretion rates and provide specific information about the genotype of a tumor and its response to treatment. TDEs also contain regulatory factors that can alter the phenotypes of local and distant tissue sites and alter immune cell functions to promote tumor progression. The abundance, information content, regulatory potential, in vivo half‐life, and physical durability of exosomes suggest that TDEs may represent a superior source of diagnostic biomarkers and treatment targets than other materials currently under investigation. This review will summarize current information on mechanisms that may differentially regulate TDE biogenesis, TDE effects on the immune system that promote tumor survival, growth, and metastasis, and new approaches understudy to counteract or utilize TDE properties in cancer therapies.

Salivary Extracellular Vesicle-Associated exRNA as Cancer Biomarker

Extracellular vesicles (EVs) secreted in biological fluids contain several transcripts of the cell of origin, which may modify the functions and phenotype of proximal and distant cells. Cancer-derived EVs may promote a favorable microenvironment for cancer growth and invasion by acting on stroma and endothelial cells and may favor metastasis formation. The transcripts contained in cancer EVs may be exploited as biomarkers. Protein and extracellular RNA (exRNA) profiling in patient bio-fluids, such as blood and urine, was performed to identify molecular features with potential diagnostic and prognostic values. EVs are concentrated in saliva, and salivary EVs are particularly enriched in exRNAs. Several studies were focused on salivary EVs for the detection of biomarkers either of non-oral or oral cancers. The present paper provides an overview of the available studies on the diagnostic potential of exRNA profiling in salivary EVs.

Role of extracellular vesicles in stem cell biology

The extracellular vesicles (EVs) are membrane vesicles carrying proteins, nucleic acids, and bioactive lipids of the cell of origin. These vesicles released within the extracellular space and entering into the circulation may transfer their cargo to neighboring or distant cells and induce phenotypical and functional changes that may be relevant in several physiopathological conditions. In an attempt to define the biological properties of EVs, several investigations have focused on their cargo and on the effects elicited in recipient cells. EVs have been involved in modulation of tumor microenvironment and behavior, as well as in the immune and inflammatory response. In the present review, we address the paracrine action of EVs released by stem cells and their potential involvement in the activation of regenerative programs in injured cells.

Induction of tolerogenic dendritic cells by activated TGF-β/Akt/Smad2 signaling in RIG-I-deficient stemness-high human liver cancer cells

BACKGROUND

Dendritic cells (DCs) alter their role from being immunostimulatory to immunosuppressive at advanced stages of tumor progression, but the influence of cancer stem cells (CSCs) and their secreted factors on generation and phenotypic change of DCs is unknown. Retinoic acid-inducible gene I (RIG-I) plays a role in regulation of other cellular processes including leukemic stemness besides its antiviral function.

METHODS

Short hairpin RNA-mediated gene silencing was employed to generate stable RIG-I-knocked-down human hepatocellular carcinoma (HCC) cell lines. Expression levels of genes and proteins in spheres of those HCC cells were determined by quantitative real-time PCR and Western bot, respectively. Levels of secreted cytokines were measured by ELISA. The surface molecule expression levels of DCs were analyzed using flow cytometry. The ability of DCs to induce proliferation of T cells was assessed by a mixed lymphocyte reaction (MLR) assay.

RESULTS

RIG-I-knocked-down HCC cells showed upregulated expression of stem cell marker genes, enhanced secretion of factors suppressing in vitro generation of DCs into the conditioned medium (CM), and induction of a phenotype of tumor-infiltrating DCs (TIDCs) with low levels of DC markers in their tumors in nude mice. Those DCs and TIDCs showed reduced MLR, indicating RIG-I deficiency-induced immunotolerance. The RIG-I-deficient HCC cells secreted more TGF-β1 than did reference cells. The tumors formed after injection of RIG-I-deficient HCC cells had higher TGF-β1 contents than did tumors derived from control cells. DC generation and MLR suppressed by the CM of RIG-I-deficient HCC cells were restored by an anti-TGF-β1 antibody. TGF-β1-induced phosphorylation of Smad2 and Akt was enhanced in RIG-I-deficient HCC spheres, knockdown of AKT gene expression abolishing the augmentation of TGF-β1-induced Smad2 phosphorylation. Akt and p-Akt were co-immunoprecipitated with Smad2 in cytoplasmic proteins of RIG-I-deficient spheres but not in those of control spheres, the amounts of co-immunoprecipitated Akt and p-Akt being increased by TGF-β stimulation.

CONCLUSIONS

Our results demonstrate that RIG-I deficiency in HCC cells induced their stemness, enhanced secretion and signaling of TGF-β1, tolerogenic TIDCs and less generation of DCs, and the results suggest involvement of TGF-β1 in those RIG-I deficiency-induced tolerogenic changes and involvement of CSCs in DC-mediated immunotolerance.

Extracellular Vesicles and Carried miRNAs in the Progression of Renal Cell Carcinoma

The formation and maintenance of renal cell carcinomas (RCC) involve many cell types, such as cancer stem and differentiated cells, endothelial cells, fibroblasts and immune cells. These all contribute to the creation of a favorable tumor microenvironment to promote tumor growth and metastasis. Extracellular vesicles (EVs) are considered to be efficient messengers that facilitate the exchange of information within the different tumor cell types. Indeed, tumor EVs display features of their originating cells and force recipient cells towards a pro-tumorigenic phenotype. This review summarizes the recent knowledge related to the biological role of EVs, shed by renal tumor cells and renal cancer stem cells in different aspects of RCC progression, such as angiogenesis, immune escape and tumor growth. Moreover, a specific role for renal cancer stem cell derived EVs is described in the formation of the pre-metastatic niche. We also highlight the tumor EV cargo, especially the oncogenic miRNAs, which are involved in these processes. Finally, the circulating miRNAs appear to be a promising source of biomarkers in RCC.

European Patent in Immunoncology: From Immunological Principles of Implantation to Cancer Treatment

The granted European patent EP 2 561 890 describes a procedure for an immunological treatment of cancer. It is based on the principles of the HLA-supported communication of implantation and pregnancy. These principles ensure that the embryo is not rejected by the mother. In pregnancy, the placenta, more specifically the trophoblast, creates an “interface” between the embryo/fetus and the maternal immune system. Trophoblasts do not express the “original” HLA identification of the embryo/fetus (HLA-A to -DQ), but instead show the non-classical HLA groups E, F, and G. During interaction with specific receptors of NK cells (e.g., killer-immunoglobulin-like receptors (KIR)) and lymphocytes (lymphocyte-immunoglobulin-like receptors (LIL-R)), the non-classical HLA groups inhibit these immunocompetent cells outside pregnancy. However, tumors are known to be able to express these non-classical HLA groups and thus make use of an immuno-communication as in pregnancies. If this occurs, the prognosis usually worsens. This patent describes, in a first step, the profiling of the non-classical HLA groups in primary tumor tissue as well as metastases and recurrent tumors. The second step comprises tailored antibody therapies, which is the subject of this patent. In this review, we analyze the underlying mechanisms and describe the currently known differences between HLA-supported communication of implantation and that of tumors.

HLA-G 3' untranslated region variants +3187G/G, +3196G/G and +3035T define diametrical clinical status and disease outcome in epithelial ovarian cancer

Expression of the non-classical human leukocyte antigen-G (HLA-G) promotes cancer progression in various malignancies including epithelial ovarian cancer (EOC). As single nucleotide polymorphisms (SNPs) in the HLA-G 3' untranslated region (UTR) regulate HLA-G expression, we investigated HLA-G 3'UTR haplotypes arranged by SNPs in healthy controls (n = 75) and primary EOC patients (n = 79) and determined soluble HLA-G (sHLA-G) levels. Results were related to the clinical status and outcome. Although haplotype frequencies were similar in patients and controls, (i) sHLA-G levels were increased in EOC independent of the haplotype, (ii) homozygosity for UTR-1 or UTR-2 genotypes were significantly associated with metastases formation and presence of circulating tumor cells before therapy, whereas (iii) the UTR-5 and UTR-7 haplotypes were significantly associated with a beneficial clinical outcome regarding negative nodal status, early FIGO staging, and improved overall survival. Lastly, (iv) the ambivalent impact on clinical EOC aspects could be deduced to specific SNPs in the HLA-G 3'UTR: +3187G, +3196G and +3035T alleles. Our results give evidence that even if the genetic background of the HLA-G 3'UTR is identical between patients and controls, certain SNPs have the potential to contribute to diametrical clinical status/outcome in EOC.

Extracellular vesicles in onco-nephrology

Extracellular vesicles (EVs) are important mediators of intercellular communication in cancer and in normal tissues. EVs transfer biologically active molecules from the cell of origin to recipient cells. This review summarizes the studies on EVs derived from renal cell carcinoma and from a subpopulation of CD105-positive renal cancer stem cells. While EVs from renal cell carcinoma show mild biological activity, EVs from renal cancer stem cells enhance tumor angiogenesis and metastasis formation. The effect is probably due to the transfer of proangiogenic RNA cargo to endothelial cells, which acquire an activated angiogenic phenotype. In vivo, treatment with EVs favors the formation of a premetastatic niche in the lungs. Moreover, EVs derived from renal cancer stem cells modify gene expression in mesenchymal stromal cells, enhancing the expression of genes involved in matrix remodeling, cell migration, and tumor growth. Mesenchymal stromal cells preconditioned with tumor EVs and then coinjected in vivo with renal cancer cells support tumor growth and vessel formation. Finally, tumor EVs promote tumor immune escape by inhibiting the differentiation process of dendritic cells and the activation of T cells. Thus, tumor-derived EVs act on the microenvironment favoring tumor aggressiveness, may contribute to angiogenesis through both direct and indirect mechanisms and are involved in tumor immune escape.

Membrane-bound packages called extracellular vesicles (EVs) released by kidney cancer stem cells can make tumors more aggressive, promote the onset of cancer at other sites, and help tumors escape the anti-cancer immune response. Giovanni Camussi and colleagues at the University of Turin, Italy, review understanding of EVs from kidney cancer cells. EVs from cancer stem cells are especially effective in promoting cancer, unlike those from mature cancer cells. This is partly due to their ability to promote the formation of new blood vessels to sustain tumor growth. Some of the vesicles’ effects are mediated by transferring small molecules of ribonucleic acid (RNA) into other cells. These RNAs can regulate the activity of specific genes, promoting cancer. Studying patients’ EVs may assist cancer diagnosis and help predict the likely progression of the disease.

Cell communication and signaling: how to turn bad language into positive one

Cell-to-cell communication has a critical role during tumor development and progression, allowing cancer cell to re-program not only the surrounding tumor microenvironment, but also cells located at distant sites. The crosstalk between neoplastic cells and accessory elements, such as immune and stromal cells, fosters several processes that are necessary for tumor progression and dissemination, such as angiogenesis, immune-escape, epithelial-to-mesenchymal transition, invasion and multi-drug resistance. There are several means by which cells communicate to each other, either by direct cell interactions through membrane receptors and ligands, or by releasing soluble molecules, such as growth factors, cytokines and chemokines. More recently, additional means of cell communication have been identified, such as microRNAs and extracellular vesicles. These two peculiar ways of cell-to-cell interaction were the focus of the 31st Annual Conference of the Italian Association of Cell Cultures (AICC).

Similarities Between Embryo Development and Cancer Process Suggest New Strategies for Research and Therapy of Tumors: A New Point of View

Here, I propose that cancer stem cells (CSCs) would be equivalent to para-embryonic stem cells (p-ESCs), derived from adult cells de-re-programmed to a ground state. p-ESCs would differ from ESCs by the absence of genomic homeostasis. A p-ESC would constitute the cancer cell of origin (i-CSC or CSC0), capable of generating an initial tumor, corresponding to a pre-implantation blastocyst. In a niche with proper signals, it would engraft as a primary tumor, corresponding to a post-implantation blastocyst. i-CSC progeny would form primary pluripotent and slow self-renewing CSCs (CSC1s), blocked in an undifferentiated state, corresponding to epiblast cells; CSC1s would be tumor-initiating cells (TICs). CSC1s would generate secondary CSCs (CSC2s), corresponding to hypoblast cells; CSC2s would be tumor growth cells (TGCs). CSC1s/CSC2s would generate tertiary CSCs (CSC3s), with a mesenchymal phenotype; CSC3s would be tumor migrating cells (TMCs), corresponding to mesodermal precursors at primitive streak. CSC3s with more favorable conditions (normoxia), by asymmetrical division, would differentiate into cancer progenitor cells (CPCs), and these into cancer differentiated cells (CDCs), thus generating a defined cell hierarchy and tumor progression, mimicking somito-histo-organogenesis. CSC3s with less favorable conditions (hypoxia) would delaminate and migrate as quiescent circulating micro-metastases, mimicking mesenchymal cells in gastrula morphogenetic movements. In metastatic niches, these CSC3s would install and remain dormant in the presence of epithelial/mesenchymal transition (EMT) signals and hypoxia. But, in the presence of mesenchymal/epithelial transition (MET) signals and normoxia, they would revert to self-renewing CSC1s, reproducing the same cell hierarchy of the primary tumor as macro-metastases. Further similarities between ontogenesis and oncogenesis involving crucial factors, such as ID, HSP70, HLA-G, CD44, LIF, and STAT3, are strongly evident at molecular, physiological and immunological levels. Much experimental data about these factors led to considering the cancer process as ectopic rudimentary ontogenesis, where CSCs have privileged immunological conditions. These would consent to CSC development in an adverse environment, just like an embryo, which is tolerated, accepted and favored by the maternal organism in spite of its paternal semi-allogeneicity. From all these considerations, novel research directions, potential innovative tumor therapy and prophylaxis strategies might, theoretically, result.

Application potential of stem/progenitor cell-derived extracellular vesicles in renal diseases

Extracellular vesicles (EVs) are nanometer-sized and membrane-bound vesicles, including exosomes and microvesicles. EVs can deliver bioactive macromolecules such as proteins, lipids, and nucleic acids, allowing intercellular communication in multicellular organisms. EVs are secreted by all cell types including stem/progenitor cells. Stem/progenitor cell-derived EVs have been identified to exert immunomodulatory effects on target cells through transferring protein molecules as well as regulatory effects on the phenotype of target cells through fusion with the target cells membrane and/or through direct endocytosis by target cells to transfer nucleic acid substances (such as mRNA, miRNA) to the target cells. In both human and animal models, the use of stem/progenitor cells (such as bone marrow mesenchymal stromal cells) has been shown to promote the recovery of kidney diseases such as acute kidney injury and chronic kidney disease. Stem/progenitor cell-derived extracellular vesicles are an important mechanism by which stem/progenitor cells might repair kidney injury. Here, this review will discuss the latest advances concerning the application potential of stem/progenitor cell-derived extracellular vesicles in renal diseases, including the aspects as follows: anti-inflammatory, proliferation-promoting and anti-apoptotic, proangiogenic, antifibrotic and renal cancer progression-promoting. Therefore, stem/progenitor cell-derived extracellular vesicles may be a promising treatment tool for renal diseases.

HLA-G, -E and -F regulatory and coding region variability and haplotypes in the Beninese Toffin population sample

HLA-G/E/F genes exhibit immunomodulatory properties and are expressed in placenta. Little attention has been devoted to the study of these genes in sub-Saharan African populations, which are yet the most diverse. To fill this gap, we evaluated the complete gene variability, approximately 5.1 kb for HLA-G (n = 149), 7.7 kb for HLA-E (n = 150) and 6.2 kb for HLA-F (n = 152) in the remote Beninese Toffin population, using massive parallel sequencing. Overall, 96, 37 and 68 variable sites were detected along the entire HLA-G, -E and -F, respectively, arranged into region-specific haplotypes; i.e., promoter haplotypes (16, 19, and 15 respectively), coding haplotypes (19, 15, and 29 respectively), 3' untranslated region (3'UTR) haplotypes (12, 7 and 2, respectively) and extended haplotypes (33, 31 and 32 respectively). All promoter/coding/3'UTR haplotypes followed the patterns already described in worldwide populations. HLA-E was the most conserved, exhibiting mainly two full-length encoded-molecules (E*01:01 and E*01:03), followed by HLA-F, three full-length proteins (F*01:01, F*01:02 and F*01:03) and HLA-G, four proteins: three full-length (G*01:01, G*01:03 and G*01:04) and one truncated (G*01:05N). Although HLA-G/E/F alleles in the Toffin population were the most frequently observed worldwide, the frequencies of the coding haplotypes were closely similar to those described for other African populations (Guinea-Conakry and Burkina-Faso), when compared to non-African ones (Brazilian), indicating that variable sites along these genes were present in Africa before human dispersion.

Heterogeneity of HLA-G Expression in Cancers: Facing the Challenges

Phenotypic heterogeneity has been observed in most malignancies, which represents a considerable challenge for tumor therapy. In recent decades, the biological function and clinical significance of the human leukocyte antigen (HLA)-G have been intensively explored. It is now widely accepted that HLA-G is a critical marker of immunotolerance in cancer cell immune evasion and is strongly associated with disease progress and prognosis for cancer patients. Moreover, it has recently been emphasized that the signaling pathway linking HLA-G and immunoglobulin-like transcripts (ILTs) is considered an immune checkpoint. In addition, HLA-G itself can generate at least seven distinct isoforms, and intertumor and intratumor heterogeneity of HLA-G expression is common across different tumor types. Furthermore, HLA-G heterogeneity in cancers has been related to disease stage and outcomes, metastatic status and response to different therapies. This review focuses on the heterogeneity of HLA-G expression in malignant lesions, and clinical implications of this heterogeneity that might be relevant to personalized treatments are also discussed.

Biomarker discovery for renal cancer stem cells

Characterised by high intra- and inter-tumor heterogeneity, metastatic renal cell carcinoma (RCC) is resistant to chemo- and radiotherapy. Therefore, the development of new prognostic and diagnostic markers for RCC patients is needed. Cancer stem cells (CSCs) are a small population of neoplastic cells within a tumor which present characteristics reminiscent of normal stem cells. CSCs are characterised by unlimited cell division, maintenance of the stem cell pool (self-renewal), and capability to give rise to all cell types within a tumor; and contribute to metastasis in vivo (tumourigenicity), treatment resistance and recurrence. So far, many studies have tried to establish unique biomarkers to identify CSC populations in RCC. At the same time, different approaches have been developed with the aim to isolate CSCs. Consequently, several markers were found to be specifically expressed in CSCs and cancer stem-like cells derived from RCC such as CD105, ALDH1, OCT4, CD133, and CXCR4. However, the contribution of genetic and epigenetic mechanisms, and tumor microenvironment, to cellular plasticity have made the discovery of unique biomarkers a very difficult task. In fact, contrasting results regarding the applicability of such markers to the isolation of renal CSCs have been reported in the literature. Therefore, a better understanding of the mechanism underlying CSC may help dissecting tumor heterogeneity and drug treatment efficiency.

Extracellular vesicles as regulators of tumor fate: crosstalk among cancer stem cells, tumor cells and mesenchymal stem cells

The tumor microenvironment comprises a heterogeneous population of tumorigenic and non-tumorigenic cells. Cancer stem cells (CSCs) and mesenchymal stem cells (MSCs) are components of this microenvironment and have been described as key regulators of different aspects of tumor physiology. They act differently on the tumor: CSCs are described as tumor initiators and are associated with tumor growth, drug resistance and metastasis; MSCs can integrate the tumor microenvironment after recruitment and interact with cancer cells to promote tumor modifications. Extracellular vesicles (EVs) have emerged as an important mechanism of cell communication under the physiological and pathological conditions. In cancer, secretion of EVs seems to be one of the main mechanisms by which stem cells interact with other tumor and non-tumor cells. The transfer of bioactive molecules (lipids, proteins and RNAs) compartmentalized into EVs triggers different responses in the target cells, regulating several processes in the tumor as angiogenesis, tumor invasiveness and immune escape. This review focuses on the role of CSCs and MSCs in modulating the tumor microenvironment through secretion of EVs, addressing different aspects of the multidirectional interactions among stem cells, tumor and tumor-associated cells.

Extracellular Vesicles in Renal Pathophysiology

Extracellular vesicles are a heterogeneous population of microparticles released by virtually all living cells which have been recently widely investigated in different biological fields. They are typically composed of two primary types (exosomes and microvesicles) and are recently commanding increasing attention as mediators of cellular signaling. Indeed, these vesicles can affect recipient cells by carrying and delivering complex cargos of biomolecules (including proteins, lipids and nucleic acids), protected from enzymatic degradation in the environment. Their importance has been demonstrated in the pathophysiology of several organs, in particular in kidney, where different cell types secrete extracellular vesicles that mediate their communication with downstream urinary tract cells. Over the past few years, evidence has been shown that vesicles participate in kidney development and normal physiology. Moreover, EVs are widely demonstrated to be implicated in cellular signaling during renal regenerative and pathological processes. Although many EV mechanisms are still poorly understood, in particular in kidney, the discovery of their role could help to shed light on renal biological processes which are so far elusive. Lastly, extracellular vesicles secreted by renal cells gather in urine, thus becoming a great resource for disease or recovery markers and a promising non-invasive diagnostic instrument for renal disease. In the present review, we discuss the most recent findings on the role of extracellular vesicles in renal physiopathology and their potential implication in diagnosis and therapy.

Soluble monomers, dimers and HLA-G-expressing extracellular vesicles: the three dimensions of structural complexity to use HLA-G as a clinical biomarker

The HLA-G molecule belongs to the family of nonclassical human leukocyte antigen (HLA) class I. At variance to classical HLA class I, HLA-G displays (i) a low number of nucleotide variations within the coding region, (ii) a high structural diversity, (iii) a restricted peptide repertoire, (iv) a limited tissue distribution and (v) strong immune-suppressive properties. The physiological HLA-G surface expression is restricted to the maternal-fetal interface and to immune-privileged adult tissues. Soluble forms of HLA-G (sHLA-G) are detectable in various body fluids. Cellular activation and pathological processes are associated with an aberrant or a neo-expression of HLA-G/sHLA-G. Functionally, HLA-G and its secreted forms are considered to be key players in the induction of short- and long-term tolerance. Thus, its unique expression profile and tolerance-inducing functions render HLA-G/sHLA-G an attractive biomarker to monitor the systemic health/disease status and disease activity/progression for clinical approaches in disease management and treatments. Here, we place emphasis on (i) the current status of the tolerance-inducing functions by HLA-G/sHLA-G, (ii) the current complexity to implement this molecule as a meaningful clinical biomarker regarding the three dimensions of structural diversity (monomers, dimers and HLA-G-expressing extracellular vesicles) with its functional implications, and (iii) novel and future approaches to detect and quantify sHLA-G structures and functions.

Cross Talk between Cancer and Mesenchymal Stem Cells through Extracellular Vesicles Carrying Nucleic Acids

Extracellular vesicles (EVs) are considered to be a novel complex mechanism of cell communication within the tumor microenvironment. EVs may act as vehicles for transcription factors and nucleic acids inducing epigenetic changes in recipient cells. Since tumor EVs may be present in patient biological fluids, it is important to investigate their function and molecular mechanisms of action. It has been shown that tumor cells release EVs, which are capable of regulating cell apoptosis, proliferation, invasion, and epithelial-mesenchymal transition, as well as to suppress activity of immune cells, to enhance angiogenesis, and to prepare a favorable microenvironment for metastasis. On the other hand, EVs derived from stromal cells, such as mesenchymal stem cells (MSCs), may influence the phenotype of tumor cells through reciprocal cross talk greatly influenced by the transcription factors and nucleic acids they carry. In particular, non-coding RNAs (ncRNAs), including microRNAs and long ncRNAs, have recently been identified as the main candidates for the phenotypic changes induced in the recipient cells by EVs. ncRNAs, which are important regulators of mRNA and protein expression, can function either as tumor suppressors or as oncogenes, depending on their targets. Herein, we have attempted to revise actual evidence reported in the literature on the role of EVs in tumor biology with particular regard to the cross talk of ncRNAs between cancer cells and MSCs.

Renal Cancer Stem Cells: Characterization and Targeted Therapies

Renal cell carcinoma (RCC) is a major neoplasm with high incidence in western countries. Tumors are heterogeneous and are composed of differentiated cancer cells, stromal cells, and cancer stem cells (CSCs). CSCs possess two main properties: self-renewal and proliferation. Additionally, they can generate new tumors once transplanted into immunodeficient mice. Several approaches have been described to identify them, through the expression of cell markers, functional assays, or a combination of both. As CSCs are involved in the resistance mechanisms to radio- and chemotherapies, several new strategies have been proposed to directly target CSCs in RCC. One approach drives CSCs to differentiate into cancer cells sensitive to conventional treatments, while the other proposes to eradicate them selectively. A series of innovative therapies aiming at eliminating CSCs have been designed to treat other types of cancer and have not been experimented with on RCC yet, but they reveal themselves to be promising. In conclusion, CSCs are an important player in carcinogenesis and represent a valid target for therapy in RCC patients.

The Potential of HLA-G-Bearing Extracellular Vesicles as a Future Element in HLA-G Immune Biology

The HLA-G molecule is a member of the non-classical HLA class I family. Its surface expression is physiologically restricted to the maternal–fetal interface and to immune privileged adult tissues. Despite the restricted tissue expression, HLA-G is detectable in body fluids as secreted soluble molecules. A unique feature of HLA-G is the structural diversity as surface expressed and as secreted molecules. Secreted HLA-G can be found in various body fluids either as free soluble HLA-G or as part of extracellular vesicles (EVs), which are composed of various antigens/ligands/receptors, bioactive lipids, cytokines, growth factors, and genetic information, such as mRNA and microRNA. Functionally, HLA-G and its secreted forms are considered to play a crucial role in the network of immune-regulatory tolerance mechanisms, preferentially interacting with the cognate inhibitory receptors LILRB1 and LILRB2. The HLA-G mediated tolerance is described in processes of pregnancy, inflammation, and cancer. However, almost all functional and clinical implications of HLA-G in vivo and in vitro have been established based on simple single ligand/receptor interactions at the cell surface, whereas HLA-G-bearing EVs were in minor research focus. Indeed, cytotrophoblast cells, mesenchymal stem cells, and cancer cells were recently described to secrete HLA-G-bearing EVs, displaying immunosuppressive effects and modulating the tumor microenvironment. However, numerous functional and clinical open questions persist. Here, we (i) introduce basic aspects of EVs biology, (ii) summarize the functional knowledge, clinical implications and open questions of HLA-G-bearing EVs, and (iii) discuss HLA-G-bearing EVs as a future element in HLA-G biology.