Melanoma exosomes deliver a complex biological payload that upregulates PTPN11 to suppress T lymphocyte function

Exosomes as key mediators in immune and cancer cell interactions: insights in melanoma progression and therapy

Exosomes (30-150 nm) are small extracellular vesicles that are secreted by cells into the extracellular environment and are known to mediate cell-to-cell communication. Exosomes contain proteins, lipids, and RNA molecules in relative abundance, capable of modifying the activity of target cells. Melanoma-derived exosomes (MEXs) promote the transfer of oncogenic signals and immunosuppressive factors into immune cells, resulting in a bias of the immune response towards tumor-promoting processes. MEXs could suppress the activation and proliferation of T cells and dendritic cells and induce differentiation of myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs). They can induce apoptosis of antigen-specific CD8 + T cells and promote the transfer of tumor antigens, resulting in immune evasion. Specifically, MEXs can shuttle cytokines like interleukin-10 (IL-10) and transforming growth factor-β (TGF-β) to immune cells or express programmed death-ligand 1 (PD-L1 or CD274), creating an immune-suppressive microenvironment that promotes tumorigenesis. Since exosomes preferentially accumulate in melanoma tissues, this targeted delivery could enhance the bioavailability of treatments while limiting side effects. Here, we review the molecular composition of melanoma-derived exosomes, their mechanisms of action, and their potential as therapeutic targets or biomarkers in melanoma. The summarizations of these mechanisms to appropriately influence exosome-mediated interactions could yield new tactics to elicit anti-melanoma immunity or augment the therapeutic effects of current therapies.

Tumor Microenvironment-Derived Exosomes: A Double-Edged Sword for Advanced T Cell-Based Immunotherapy

The tumor microenvironment (TME) plays a crucial role in cancer progression and immune evasion, partially mediated by the activity of the TME-derived exosomes. These extracellular vesicles are pivotal in shaping immune responses through the transfer of proteins, lipids, and nucleic acids between cells, facilitating a complex interplay that promotes tumor growth and metastasis. This review delves into the dual roles of exosomes in the TME, highlighting both their immunosuppressive functions and their emerging therapeutic potential. Exosomes can inhibit T cell function and promote tumor immune escape by carrying immune-modulatory molecules, such as PD-L1, yet they also hold promise for cancer therapy as vehicles for delivering tumor antigens and costimulatory signals. Additionally, the review discusses the intricate crosstalk mediated by exosomes among various cell types within the TME, influencing both cancer progression and responses to immunotherapies. Moreover, this highlights current challenges and future directions. Collectively, elucidating the detailed mechanisms by which TME-derived exosomes mediate T cell function offers a promising avenue for revolutionizing cancer treatment. Understanding these interactions allows for the development of targeted therapies that manipulate exosomal pathways to enhance the immune system's response to tumors.

Head-to-Head Comparison of CCN4, DNMT3A, PTPN11, and SPARC as Suppressors of Anti-tumor Immunity

Purpose

Emergent cancer cells likely secrete factors that inhibit anti-tumor immunity. To identify such factors, we applied a functional assay with proteomics to an immunotherapy resistant syngeneic mouse melanoma model. Four secreted factors were identified that potentially mediate immunosuppression and could become targets for novel immunotherapies. We tested for consistent clinical correlates in existing human data and verified in vivo whether knocking out tumor cell production of these factors improved immune-mediated control of tumor growth.

Methods

Existing human data was analyzed for clinical correlates. A CRISPR/Cas9 approach to generate knockout cell lines and a kinetic analysis leveraging a Markov Chain Monte Carlo (MCMC) approach quantified the various knockouts' effect on cells' intrinsic growth rate. Flow cytometry was used to characterize differences in immune infiltration.

Results

While all four gene products were produced by malignant melanocytes, only increased CCN4 expression was associated with reduced survival in primary melanoma patients. In immunocompetent C57BL/6 mice the CCN4 knockout increased survival while the other knockouts had no effect. This survival advantage was lost when the CCN4 knockout cells were injected into immunocompromised hosts, indicating that the effect of CCN4 may be immune mediated. Parameter estimation from the MCMC analysis shows that CCN4 was the only knockout tested that decreased the net tumor growth rate in immunocompetent mice. Flow cytometry showed an increase in NK cell infiltration in CCN4 knockout tumors.

Conclusions

The results suggest that CCN4 is a mediator of immunosuppression in the melanoma tumor microenvironment and a potential collateral immunotherapy target.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-023-00787-7.

Tumor-Derived Small Extracellular Vesicles Inhibit the Efficacy of CAR T Cells against Solid Tumors

Chimeric antigen receptor (CAR) T-cell therapy has shown remarkable success in the treatment of hematologic malignancies. Unfortunately, it has limited efficacy against solid tumors, even when the targeted antigens are well expressed. A better understanding of the underlying mechanisms of CAR T-cell therapy resistance in solid tumors is necessary to develop strategies to improve efficacy. Here we report that solid tumors release small extracellular vesicles (sEV) that carry both targeted tumor antigens and the immune checkpoint protein PD-L1. These sEVs acted as cell-free functional units to preferentially interact with cognate CAR T cells and efficiently inhibited their proliferation, migration, and function. In syngeneic mouse tumor models, blocking tumor sEV secretion not only boosted the infiltration and antitumor activity of CAR T cells but also improved endogenous antitumor immunity. These results suggest that solid tumors use sEVs as an active defense mechanism to resist CAR T cells and implicate tumor sEVs as a potential therapeutic target to optimize CAR T-cell therapy against solid tumors.

SIGNIFICANCE

Small extracellular vesicles secreted by solid tumors inhibit CAR T cells, which provide a molecular explanation for CAR T-cell resistance and suggests that strategies targeting exosome secretion may enhance CAR T-cell efficacy. See related commentary by Ortiz-Espinosa and Srivastava, p. 2637.

Extracellular Vesicles-Based Cell-Cell Communication in Melanoma: New Perspectives in Diagnostics and Therapy

Extracellular vesicles (EVs) are a heterogeneous group of cell-secreted particles that carry cargo of functional biomolecules crucial for cell-to-cell communication with both physiological and pathophysiological consequences. In this review, we focus on evidence demonstrating that the EV-mediated crosstalk between melanoma cells within tumor, between melanoma cells and immune and stromal cells, promotes immune evasion and influences all steps of melanoma development from local progression, pre-metastatic niche formation, to metastatic colonization of distant organs. We also discuss the role of EVs in the development of resistance to immunotherapy and therapy with BRAF^V600/MEK inhibitors, and shortly summarize the recent advances on the potential applications of EVs in melanoma diagnostics and therapy.

Exosomes carrying immune checkpoints, a promising therapeutic approach in cancer treatment

Exosomes are a subgroup of extracellular vesicles generated by distinct cells. Tumor-derived extracellular vesicles convey immunological checkpoint molecules. TEXs as critical mediators in tumor development, metastasis, and immune escape have recently become the focus of scientific research. Exosomes are involved in the regulation of the immune system. Exosomes interact with target cells in the tumor microenvironment, changing their function based on the cargo they contain. Exosomal immune checkpoints might be exploited to track tumor immune evasion, treatment response, and patient prognosis while enhancing tumor cell proliferation and spread. This review focuses on tumor-derived exosomes, their immunosuppressive effects in mice models, and their role in cancer immunotherapy. Exosomes are being studied as possible cancer vaccines, with numerous uses in tumor immunotherapy. Exosomes can carry chemotherapeutics, siRNA, and monoclonal antibodies. Exosomes produced by macrophages might be used to treat cancer. These and other clinical consequences provide new doors for cancer treatment.

Mechanisms of extracellular vesicle-mediated immune evasion in melanoma

Melanoma-derived extracellular vesicles (EVs) have been found to promote tumor growth and progression, and to predict patient responsiveness to immunotherapy. Consequently, EVs have been implicated in tumor immune evasion, and multiple studies reported immune-regulatory activities of melanoma EVs in vitro and in vivo. This review highlights mechanistic insights in EV-mediated regulation of various immune cell types, including effects on inflammatory, apoptotic, stress-sensing and immune checkpoint pathways as well as antigen-dependent responses. Additionally, current challenges in the field are discussed that need to be overcome to determine the clinical relevance of these various mechanisms and to develop corresponding therapeutic approaches to promote tumor immunity and immunotherapy responsiveness in melanoma patients in the future.

Critical roles of PTPN family members regulated by non-coding RNAs in tumorigenesis and immunotherapy

Since tyrosine phosphorylation is reversible and dynamic in vivo, the phosphorylation state of proteins is controlled by the opposing roles of protein tyrosine kinases (PTKs) and protein tyrosine phosphatase (PTPs), both of which perform critical roles in signal transduction. Of these, intracellular non-receptor PTPs (PTPNs), which belong to the largest class I cysteine PTP family, are essential for the regulation of a variety of biological processes, including but not limited to hematopoiesis, inflammatory response, immune system, and glucose homeostasis. Additionally, a substantial amount of PTPNs have been identified to hold crucial roles in tumorigenesis, progression, metastasis, and drug resistance, and inhibitors of PTPNs have promising applications due to striking efficacy in antitumor therapy. Hence, the aim of this review is to summarize the role played by PTPNs, including PTPN1/PTP1B, PTPN2/TC-PTP, PTPN3/PTP-H1, PTPN4/PTPMEG, PTPN6/SHP-1, PTPN9/PTPMEG2, PTPN11/SHP-2, PTPN12/PTP-PEST, PTPN13/PTPL1, PTPN14/PEZ, PTPN18/PTP-HSCF, PTPN22/LYP, and PTPN23/HD-PTP, in human cancer and immunotherapy and to comprehensively describe the molecular pathways in which they are implicated. Given the specific roles of PTPNs, identifying potential regulators of PTPNs is significant for understanding the mechanisms of antitumor therapy. Consequently, this work also provides a review on the role of non-coding RNAs (ncRNAs) in regulating PTPNs in tumorigenesis and progression, which may help us to find effective therapeutic agents for tumor therapy.

Role of exosomes in skin diseases

BACKGROUND

Exosomes, as a family member of extracellular vesicles, are cell-secreted nanoscale structures that play pivotal roles in regulating physiological and pathophysiological processes of the skin. Exosomes induce communication between cells and are responsible for transporting cellular components such as microRNAs, mRNAs, DNA, lipids, metabolites, and cell-surface proteins. Numerous preclinical and clinical trials searched the contribution of exosomes to skin functions and disorders. Thus, exosomes are gaining increasing attention within investigational dermatology. In advance, stem-cell-derived exosomes were integrated into the functional cosmetics industry nominated as cell-free regenerative medicine.

OBJECTIVE

This review aims to demonstrate the roles of exosomes in inflammatory skin disorders, stem cell, and tumor biology through a comprehensive evaluation of the diagnostic, prognostic, and therapeutic perspectives.

METHODS

A comprehensive literature search was performed using electronic online databases "PubMed" and "Google Scholar" using key words ''exosomes'', ''skin'', ''wound healing''.

CONCLUSION

Exosomes are regarded as promising diagnostic and prognostic biomarkers for various skin diseases. Future prospects are repurposing exosomes to treat skin disorders, either as drug carriers or drugs themselves.

Tumor-derived exosomes: the emerging orchestrators in melanoma

Cutaneous melanoma is an aggressive cancer type derived from melanocytes and its incidence has rapidly increased worldwide. Despite the vast improvement in therapy, melanoma is still confronted with high invasion, metastasis, and recurrence rate. Recent studies have confirmed that the exosomes are naturally occurring membranous extracellular vesicles with nano-sized lipid bilayers, performing as information messagers within cellular reciprocal action. Exosomes are unquestionably endowed with multifaceted roles in various diseases, including melanoma. Notably, tumor-derived exosomes play a pivotal role in conditioning the tumor microenvironment to promote the growth, metastasis, immune escape, and even drug-resistance of melanoma by transferring carcinogenic nucleic acids and proteins. Clinically, the dynamic expressions of exosomal components and loadings in melanoma patients with different tumor stages confer the clinical application of melanoma exosomes as diagnostic biomarkers. Hence, this review highlights the recent complicated roles and mechanisms of melanoma exosomes, as well as their potential as diagnostic and therapeutic targets in melanoma. The in-depth insights into the properties and behaviors of melanoma exosomes are of great potential to yield attractive therapeutic methods for melanoma.

Liquid Biopsy and Dielectrophoretic Analysis—Complementary Methods in Skin Cancer Monitoring

The incidence and prevalence of skin cancers is currently increasing worldwide, with early detection, adequate treatment, and prevention of recurrences being topics of great interest for researchers nowadays. Although tumor biopsy remains the gold standard of diagnosis, this technique cannot be performed in a significant proportion of cases, so that the use of alternative methods with high sensitivity and specificity is becoming increasingly desirable. In this context, liquid biopsy appears to be a feasible solution for the study of cellular and molecular markers relevant to different types of skin cancers. Circulating tumor cells are just one of the components of interest obtained from performing liquid biopsy, and their study by complementary methods, such as dielectrophoresis, could bring additional benefits in terms of characterizing skin tumors and subsequently applying personalized therapy. One purpose of this review is to demonstrate the utility of liquid biopsy primarily in monitoring the most common types of skin tumors: basal cell carcinoma, squamous cell carcinoma, and malign melanoma. In addition, the originality of the article is based on the detailed presentation of the dielectrophoretic analysis method of the most important elements obtained from liquid biopsy, with direct impact on the clinical and therapeutic approach of skin tumors.

Anti-Metastatic Function of Extracellular Vesicles Derived from Nanog-Overexpressing Melanoma

A metastatic melanoma cell line B16-F10 (F10) was modified to a more undifferentiated state by Nanog overexpression. The produced cell line Nanog⁺F10 showed a higher metastatic potential than F10. Instead of whole cells, the extracellular vesicles (EVs) therefrom were investigated about their possible role as an autovaccine against metastasis. EVs from Nanog⁺F10 cells (Nanog⁺F10-EVs) could suppress the metastasis, contrasting the EVs from less metastatic F10 cells (F10-EVs) enhanced metastasis. The involvement of TGF-β1 in the role of Nanog⁺F10-EVs was analyzed, as TGF-β1 was a secretory cytokine being affected most intensively by Nanog overexpression. It was suggested to be crucial that the TGF-β1 concentration in Nanog⁺F10-EVs should be as low as 1.6 pg/μg for its metastasis-suppressive role. In response to Nanog⁺F10-EVs, immunoreaction was observed in liver, indicating the specific decrease in the number of tumor-promotive CD163-positive macrophages. These indicate a possibility of Nanog⁺F10-EVs as a novel autovaccine candidate against melanoma metastasis.

Strategies for Engineering Exosomes and Their Applications in Drug Delivery

Exosomes are representative of a promising vehicle for delivery of biomolecules. Despite their discovery nearly 40 years, knowledge of exosomes and extracellular vesicles (EVs) and the role they play in etiology of disease and normal cellular physiology remains in its infancy. EVs are produced in almost all cells, containing nucleic acids, lipids, and proteins delivered from donor cells to recipient cells. Consequently, they act as mediators of intercellular communication and molecular transfer. Recent studies have shown that, exosomes are associated with numerous physiological and pathological processes as a small subset of EVs, and they play a significant role in disease progression and treatment. In this review, we discuss several key questions: what are exosomes, why do they matter, and how do we repurpose them in their strategies and applications in drug delivery systems. In addition, opportunities and challenges of exosome-based theranostics are also described and directions for future research are presented.

The Roles of Extracellular Vesicles in Malignant Melanoma

Different types of cells, such as endothelial cells, tumor-associated fibroblasts, pericytes, and immune cells, release extracellular vesicles (EVs) in the tumor microenvironment. The components of EVs include proteins, DNA, RNA, and microRNA. One of the most important functions of EVs is the transfer of aforementioned bioactive molecules, which in cancer cells may affect tumor growth, progression, angiogenesis, and metastatic spread. Furthermore, EVs affect the presentation of antigens to immune cells via the transfer of nucleic acids, peptides, and proteins to recipient cells. Recent studies have also explored the potential application of EVs in cancer treatment. This review summarizes the mechanisms by which EVs regulate melanoma development, progression, and their potentials to be applied in therapy. We initially describe vesicle components; discuss their effects on proliferation, anti-melanoma immunity, and drug resistance; and finally focus on the effects of EV-derived microRNAs on melanoma pathobiology. This work aims to facilitate our understanding of the influence of EVs on melanoma biology and initiate ideas for the development of novel therapeutic strategies.

Tumor-Derived Exosomal Protein Tyrosine Phosphatase Receptor Type O Polarizes Macrophage to Suppress Breast Tumor Cell Invasion and Migration

Tumor-derived exosomes, containing multiple nucleic acids and proteins, have been implicated to participate in the interaction between tumor cells and microenvironment. However, the functional involvement of phosphatases in tumor-derived exosomes is not fully understood. We and others previously demonstrated that protein tyrosine phosphatase receptor type O (PTPRO) acts as a tumor suppressor in multiple cancer types. In addition, its role in tumor immune microenvironment remains elusive. Bioinformatical analyses revealed that PTPRO was closely associated with immune infiltration, and positively correlated to M1-like macrophages, but negatively correlated to M2-like macrophages in breast cancer tissues. Co-cultured with PTPRO-overexpressing breast cancer cells increased the proportion of M1-like tumor-associated macrophages (TAMs) while decreased that of M2-like TAMs. Further, we observed that tumor-derived exosomal PTPRO induced M1-like macrophage polarization, and regulated the corresponding functional phenotypes. Moreover, tumor cell-derived exosomal PTPRO inhibited breast cancer cell invasion and migration, and inactivated STAT signaling in macrophages. Our data suggested that exosomal PTPRO inhibited breast cancer invasion and migration by modulating macrophage polarization. Anti-tumoral effect of exosomal PTPRO was mediated by inactivating STAT family in macrophages. These findings highlight a novel mechanism of tumor invasion regulated by tumor-derived exosomal tyrosine phosphatase, which is of translational potential for the therapeutic strategy against breast cancer.

CML derived exosomes promote tumor favorable functional performance in T cells

BACKGROUND

Leukemic cells facilitate the creation of the tumor-favorable microenvironment in the bone marrow niche using their secreted factors. There are not comprehensive details about immunosuppressive properties of chronic myelogenous leukemia-derived exosomes in the bone marrow stromal and immune compartment. We explained here that K562-derived exosomes could affect the gene expression, cytokine secretion, nitric oxide (NO) production, and redox potential of human primary cord blood-derived T cells (CB T cells).

METHODS

Human primary cord blood-derived T cells were treated with K562-derived exosomes. We evaluated the expression variation of some critical genes activated in suppressor T cells. The alterations of some inflammatory and anti-inflammatory cytokines levels were assessed using ELISA assay and real-time PCR. Finally, NO production and intracellular ROS level in CB T cells were evaluated using Greiss assay and flow cytometry, respectively.

RESULTS

Our results showed the over-expression of the genes involved in inhibitory T cells, including NQO1, PD1, and FoxP3. In contrast, genes involved in T cell activation such as CD3d and NFATc3 have been reduced significantly. Also, the expression of interleukin 10 (IL-10) and interleukin 6 (IL-6) mRNAs were significantly up-regulated in these cells upon exosome treatment. In addition, secretion of the interleukin 10, interleukin 6, and interleukin 17 (IL-17) proteins increased in T cells exposed to K562-derived exosomes. Finally, K562-derived exosomes induce significant changes in the NO production and intracellular ROS levels in CB T cells.

CONCLUSIONS

These results demonstrate that K562-derived exosomes stimulate the immunosuppressive properties in CB-derived T cells by inducing anti-inflammatory cytokines such as IL-10, reducting ROS levels, and arising of NO synthesis in these cells. Moreover, considering the elevation of FOXP3, IL-6, and IL-17 levels in these cells, exosomes secreted by CML cells may induce the fates of T cells toward tumor favorable T cells instead of conventional activated T cells.

Trophoblast derived extracellular vesicles specifically alter the transcriptome of endometrial cells and may constitute a critical component of embryo-maternal communication

BACKGROUND

The period of time when the embryo and the endometrium undergo significant morphological alterations to facilitate a successful implantation-known as "window of implantation"-is a critical moment in human reproduction. Embryo and the endometrium communicate extensively during this period, and lipid bilayer bound nanoscale extracellular vesicles (EVs) are purported to be integral to this communication.

METHODS

To investigate the nature of the EV-mediated embryo-maternal communication, we have supplemented trophoblast analogue spheroid (JAr) derived EVs to an endometrial analogue (RL 95-2) cell layer and characterized the transcriptomic alterations using RNA sequencing. EVs derived from non-trophoblast cells (HEK293) were used as a negative control. The cargo of the EVs were also investigated through mRNA and miRNA sequencing.

RESULTS

Trophoblast spheroid derived EVs induced drastic transcriptomic alterations in the endometrial cells while the non-trophoblast cell derived EVs failed to induce such changes demonstrating functional specificity in terms of EV origin. Through gene set enrichment analysis (GSEA), we found that the response in endometrial cells was focused on extracellular matrix remodelling and G protein-coupled receptors' signalling, both of which are of known functional relevance to endometrial receptivity. Approximately 9% of genes downregulated in endometrial cells were high-confidence predicted targets of miRNAs detected exclusively in trophoblast analogue-derived EVs, suggesting that only a small proportion of reduced expression in endometrial cells can be attributed directly to gene silencing by miRNAs carried as cargo in the EVs.

CONCLUSION

Our study reveals that trophoblast derived EVs have the ability to modify the endometrial gene expression, potentially with functional importance for embryo-maternal communication during implantation, although the exact underlying signalling mechanisms remain to be elucidated.

Exosomes in Immune Regulation

Exosomes, small extracellular vesicles mediate intercellular communication by transferring their cargo including DNA, RNA, proteins and lipids from cell to cell. Notably, in the immune system, they have protective functions. However in cancer, exosomes acquire new, immunosuppressive properties that cause the dysregulation of immune cells and immune escape of tumor cells supporting cancer progression and metastasis. Therefore, current investigations focus on the regulation of exosome levels for immunotherapeutic interventions. In this review, we discuss the role of exosomes in immunomodulation of lymphoid and myeloid cells, and their use as immune stimulatory agents to elicit specific cytotoxic responses against the tumor.

Oncogenic Tyrosine Phosphatases: Novel Therapeutic Targets for Melanoma Treatment

Despite a large number of therapeutic options available, malignant melanoma remains a highly fatal disease, especially in its metastatic forms. The oncogenic role of protein tyrosine phosphatases (PTPs) is becoming increasingly clear, paving the way for novel antitumor treatments based on their inhibition. In this review, we present the oncogenic PTPs contributing to melanoma progression and we provide, where available, a description of new inhibitory strategies designed against these enzymes and possibly useful in melanoma treatment. Considering the relevance of the immune infiltrate in supporting melanoma progression, we also focus on the role of PTPs in modulating immune cell activity, identifying interesting therapeutic options that may support the currently applied immunomodulating approaches. Collectively, this information highlights the value of going further in the development of new strategies targeting oncogenic PTPs to improve the efficacy of melanoma treatment.

New Insights into the Role of Sphingolipid Metabolism in Melanoma

Cutaneous melanoma is a deadly skin cancer whose aggressiveness is directly linked to its metastatic potency. Despite remarkable breakthroughs in term of treatments with the emergence of targeted therapy and immunotherapy, the prognosis for metastatic patients remains uncertain mainly because of resistances. Better understanding the mechanisms responsible for melanoma progression is therefore essential to uncover new therapeutic targets. Interestingly, the sphingolipid metabolism is dysregulated in melanoma and is associated with melanoma progression and resistance to treatment. This review summarises the impact of the sphingolipid metabolism on melanoma from the initiation to metastatic dissemination with emphasis on melanoma plasticity, immune responses and resistance to treatments.

Signaling of Tumor-Derived sEV Impacts Melanoma Progression

Small extracellular vesicles (sEV or exosomes) are nanovesicles (30–150 nm) released both in vivo and in vitro by most cell types. Tumor cells produce sEV called TEX and disperse them throughout all body fluids. TEX contain a cargo of proteins, lipids, and RNA that is similar but not identical to that of the “parent” producer cell (i.e., the cargo of exosomes released by melanoma cells is similar but not identical to exosomes released by melanocytes), possibly due to selective endosomal packaging. TEX and their role in cancer biology have been intensively investigated largely due to the possibility that TEX might serve as key component of a “liquid tumor biopsy.” TEX are also involved in the crosstalk between cancer and immune cells and play a key role in the suppression of anti-tumor immune responses, thus contributing to the tumor progression. Most of the available information about the TEX molecular composition and functions has been gained using sEV isolated from supernatants of cancer cell lines. However, newer data linking plasma levels of TEX with cancer progression have focused attention on TEX in the patients’ peripheral circulation as potential biomarkers of cancer diagnosis, development, activity, and response to therapy. Here, we consider the molecular cargo and functions of TEX as potential biomarkers of one of the most fatal malignancies—melanoma. Studies of TEX in plasma of patients with melanoma offer the possibility of an in-depth understanding of the melanoma biology and response to immune therapies. This review features melanoma cell-derived exosomes (MTEX) with special emphasis on exosome-mediated signaling between melanoma cells and the host immune system.

Interleukin-12 elicits a non-canonical response in B16 melanoma cells to enhance survival

BACKGROUND

Oncogenesis rewires signaling networks to confer a fitness advantage to malignant cells. For instance, the B16F0 melanoma cell model creates a cytokine sink for Interleukin-12 (IL-12) to deprive neighboring cells of this important anti-tumor immune signal. While a cytokine sink provides an indirect fitness advantage, does IL-12 provide an intrinsic advantage to B16F0 cells?

METHODS

Acute in vitro viability assays were used to compare the cytotoxic effect of imatinib on a melanoma cell line of spontaneous origin (B16F0) with a normal melanocyte cell line (Melan-A) in the presence of IL-12. The results were analyzed using a mathematical model coupled with a Markov Chain Monte Carlo approach to obtain a posterior distribution in the parameters that quantified the biological effect of imatinib and IL-12. Intracellular signaling responses to IL-12 were compared using flow cytometry in 2D6 cells, a cell model for canonical signaling, and B16F0 cells, where potential non-canonical signaling occurs. Bayes Factors were used to select among competing signaling mechanisms that were formulated as mathematical models. Analysis of single cell RNAseq data from human melanoma patients was used to explore generalizability.

RESULTS

Functionally, IL-12 enhanced the survival of B16F0 cells but not normal Melan-A melanocytes that were challenged with a cytotoxic agent. Interestingly, the ratio of IL-12 receptor components (IL12RB2:IL12RB1) was increased in B16F0 cells. A similar pattern was observed in human melanoma. To identify a mechanism, we assayed the phosphorylation of proteins involved in canonical IL-12 signaling, STAT4, and cell survival, Akt. In contrast to T cells that exhibited a canonical response to IL-12 by phosphorylating STAT4, IL-12 stimulation of B16F0 cells predominantly phosphorylated Akt. Mechanistically, the differential response in B16F0 cells is explained by both ligand-dependent and ligand-independent aspects to initiate PI3K-AKT signaling upon IL12RB2 homodimerization. Namely, IL-12 promotes IL12RB2 homodimerization with low affinity and IL12RB2 overexpression promotes homodimerization via molecular crowding on the plasma membrane.

CONCLUSIONS

The data suggest that B16F0 cells shifted the intracellular response to IL-12 from engaging immune surveillance to favoring cell survival. Identifying how signaling networks are rewired in model systems of spontaneous origin can inspire therapeutic strategies in humans. Interleukin-12 is a key cytokine that promotes anti-tumor immunity, as it is secreted by antigen presenting cells to activate Natural Killer cells and T cells present within the tumor microenvironment. Thinking of cancer as an evolutionary process implies that an immunosuppressive tumor microenvironment could arise during oncogenesis by interfering with endogenous anti-tumor immune signals, like IL-12. Previously, we found that B16F0 cells, a cell line derived from a spontaneous melanoma, interrupts this secreted heterocellular signal by sequestering IL-12, which provides an indirect fitness advantage. Normally, IL-12 signals via a receptor comprised of two components, IL12RB1 and IL12RB2, that are expressed in a 1:1 ratio and activates STAT4 as a downstream effector. Here, we report that B16F0 cells gain an intrinsic advantage by rewiring the canonical response to IL-12 to instead initiate PI3K-AKT signaling, which promotes cell survival. The data suggest a model where overexpressing one component of the IL-12 receptor, IL12RB2, enables melanoma cells to shift the functional response via both IL-12-mediated and molecular crowding-based IL12RB2 homodimerization. To explore the generalizability of these results, we also found that the expression of IL12RB2:IL12RB1 is similarly skewed in human melanoma based on transcriptional profiles of melanoma cells and tumor-infiltrating lymphocytes. Additional file 6: Video abstract. (MP4 600 kb).

Extracellular vesicle-mediated crosstalk between melanoma and the immune system: Impact on tumor progression and therapy response

Melanoma is a very lethal tumor type that easily spreads and colonizes regional and distant tissues. Crucial phenotypic changes that favor melanoma metastasis are interposed by the tumor microenvironment (TME), representing a complex network in which malignant cells communicate not only with each other but also with stromal and immune cells. This cell-cell communication can be mediated by extracellular vesicles (EVs), which are lipid bilayer-delimited particles capable of carrying a wide variety of bioactive compounds. Both melanoma-derived or TME-derived EVs deliver important pro- and antitumor signals implicated in various stages of tumor progression, such as proliferation, metastasis, and treatment response. In this review, we highlight the recent advances in EV-mediated crosstalk between melanoma and immune cells and other important cells of the TME, and address different aspects of this bidirectional interaction as well as how this may hinder or trigger the development and progression of melanoma. We also discuss the potential of using EVs as biomarkers and therapeutic strategies for melanoma.

MicroRNAs in Tumor Exosomes Drive Immune Escape in Melanoma

MicroRNAs (miRNA), small noncoding RNAs that regulate gene expression, exist not only in cells but also in a variety of body fluids. These circulating miRNAs could enable intercellular communication. miRNAs are packaged in membrane-encapsulated vesicles, such as exosomes, or protected by RNA-binding proteins. Here, we report that miRNAs included in human melanoma exosomes regulate the tumor immune response. Using microscopy and flow cytometry, we demonstrate that CD8⁺ T cells internalize exosomes from different tumor types even if these cells do not internalize vesicles as readily as other immune cells. We explored the function of melanoma-derived exosomes in CD8⁺ T cells and showed that these exosomes downregulate T-cell responses through decreased T-cell receptor (TCR) signaling and diminished cytokine and granzyme B secretions. The result reduces the cells' cytotoxic activity. Using mimics, we found that miRNAs enriched in exosomes-such as Homo sapiens (hsa)-miR-3187-3p, hsa-miR-498, hsa-miR-122, hsa-miR149, and hsa-miR-181a/b-regulate TCR signaling and TNFα secretion. Our observations suggest that miRNAs in melanoma-derived exosomes aid tumor immune evasion and could be a therapeutic target.

Purity and yield of melanoma exosomes are dependent on isolation method

Both exosomes and soluble factors have been implicated in the generation of an immunosuppressive tumour microenvironment. Determining the contribution of each requires stringent control of purity of the isolated analytes. The present study compares several conventional exosome isolation methods for the presence of co-enriched soluble factors while isolating exosomes from human melanoma-derived cell lines. The resultant preparations were analysed by multiplex bead array analysis for cytokine profiles, and by electron microscopy and nanotracking analysis for exosome size distribution and concentration. It is demonstrated that the amount and repertoire of soluble factors in exosome preparations is dependent upon the isolation method used. A combination of ultrafiltration and size exclusion chromatography yielded up to 58-fold more exosomes than ultracentrifugation, up to 836-fold lower concentrations of co-purified soluble factors when adjusted for exosome yield, and a greater than two-fold increase in PD-L1 expressing exosomes. Mechanistically, in context of the immunomodulatory effects of exosomes, the exosome isolation method should be carefully considered in order to limit any effects due instead to co-eluted soluble factors.

Roles of exosomes in liver metastases: Novel diagnosis and treatment choices

Tumors tend to metastasize to the liver. Premetastatic niche formation is a vital step in liver metastasis. Tumor-derived exosomes can influence premetastatic niche formation from three aspects: vascular leakiness and angiogenesis, recruitment of nonresident cells, and changes in local resident cells. Exosomes from other tissues, such as mesenchymal stem cell-derived exosomes and engineered exosomes, also have therapeutic potential, but further research on these exosomes is required. Based on the mechanism of premetastatic niche formation, we summarize the therapeutic and diagnostic potential of exosomes in inhibiting liver metastases in this review in an attempt to provide new avenues for the prevention and treatment of liver metastases.

Tumor-derived exosomes modulate T cell function through transfer of RNA

Tumor cells can develop a variety of mechanisms to evade and subvert the immune system for their survival. Bland et al., in this edition of The FEBS Journal, make the novel finding that the tumor line B16F0 can deliver mRNA/miRNA loaded exosomes to cytotoxic T lymphocytes and alter their metabolic function and interferon gamma production.

Molecular and Functional Profiles of Exosomes From HPV(+) and HPV(-) Head and Neck Cancer Cell Lines

Exosomes produced by tumor cells have been shown to reprogram functions of human immune cells. Molecular cargos of exosomes isolated from supernatants of HPV(+) and HPV(−) head and neck cancer (HNC) cell lines or from HNC patients' plasma were compared. The exosome protein profiles resembled those of respective parent tumor cells. Only HPV(+) exosomes carried E6/E7, p16, and survivin. HPV(−) exosomes were negative for cyclin D1 and carried low p53 levels. Immunomodulatory molecules (TGF-β, FasL, OX40, OX40L, and HSP70) were carried by HPV(+) and HPV(−) exosomes. These exosomes co-incubated with human T cells induced apoptosis and suppressed T cell activation and proliferation. HPV(−) exosomes suppressed DC maturation and expression of antigen processing machinery (APM) components. In contrast, HPV(+) exosomes promoted DC maturation and did not suppress expression of APM components in mature DCs. While DCs readily internalized exosomes, T lymphocytes resisted their uptake during the initial 12 h co-culture. Thus, HPV(+) exosomes capable of sustaining DC functions may play a key role in promoting anti-tumor immune responses thereby improving outcome in patients with HPV(+) cancers.

Exosomes in cancer: small vesicular transporters for cancer progression and metastasis, biomarkers in cancer therapeutics

Cancer progression is a polygenic procedure in which the exosomes can function as substantial roles. Exosomes are tiny, phospholipid bilayer membrane nanovesicles of endocytic derivation with a diameter of 40-100 nm. These nanovesicles can transport bioactive molecules containing mRNAs, proteins, DNA fragments, and non-coding RNAs from a donor cell to recipient cells, and cause the alteration in genetic and epigenetic factors and reprogramming of the target cells. Many diverse cell types such as mesenchymal cells, immune cells, and cancer cells can induce the release of exosomes. Increasing evidence illustrated that the exosomes derived from tumor cells might trigger the tumor initiation, tumor cell growth and progression, metastasis, and drug resistance. The secreted nanovesicles of exosomes can play significant roles in cells communicate via shuttling the nucleic acid molecules and proteins to target cells and tissues. In this review, we discussed multiple mechanisms related to biogenesis, load, and shuttle of the exosomes. Also, we illustrated the diverse roles of exosomes in several types of human cancer development, tumor immunology, angiogenesis, and metastasis. The exosomes may act as the promising biomarkers for the prognosis of various types of cancers which suggested a new pathway for anti-tumor therapeutic of these nanovesicles and promoted exosome-based cancer for clinical diagnostic and remedial procedures.

Exosomes in melanoma: a role in tumor progression, metastasis and impaired immune system activity

Exosomes (Exo) are small vesicles produced by melanoma cells and the accessory cells of the tumor microenvironment. They emerge via both classical and direct pathways and actively participate in tumor colonisation of distant tissues. The proteins, nucleic acids, cytokines and growth factors engulfed by Exo are transferred to recipient cells, where they drive numerous functions required for the tumor escape from immune system control and tumor progression. By positively or negatively modulating immune cell properties, Exo provoke immune suppression and, in turn, defective dendritic cell (DC) functions. Together, these effects limit the cytotoxicity of T-cells and expand both T-regulatory and myeloid-derived suppressor populations. They also hinder perforin and granzyme production by natural killer cells. Finally, Exo also control the organotropism of melanoma cells. The distinct phenotypic properties of Exo can be exploited both for diagnostic purposes and in the early identification of melanoma patients likely to respond to immunotherapy. The potential therapeutic application of Exo derived from DCs has been demonstrated in vaccination trials, which showed an increase in anti-melanoma activity with respect to circulating tumor cells. However, additional studies are required before Exo can be effectively used in diagnostic and therapeutic applications in melanoma.

Exosomes derived from B16F0 melanoma cells alter the transcriptome of cytotoxic T cells that impacts mitochondrial respiration

While recent clinical studies demonstrate the promise of cancer immunotherapy, a barrier for broadening the clinical benefit is identifying how tumors locally suppress cytotoxic immunity. As an emerging mode of intercellular communication, exosomes secreted by malignant cells can deliver a complex payload of coding and noncoding RNA to cells within the tumor microenvironment. Here, we quantified the RNA payload within tumor-derived exosomes and the resulting dynamic transcriptomic response to cytotoxic T cells upon exosome delivery to better understand how tumor-derived exosomes can alter immune cell function. Exosomes derived from B16F0 melanoma cells were enriched for a subset of coding and noncoding RNAs that did not reflect the abundance in the parental cell. Upon exosome delivery, RNAseq revealed the dynamic changes in the transcriptome of CTLL2 cytotoxic T cells. In analyzing transiently coexpressed gene clusters, pathway enrichment suggested that the B16F0 exosomal payload altered mitochondrial respiration, which was confirmed independently, and upregulated genes associated with the Notch signaling pathway. Interestingly, exosomal miRNA appeared to have no systematic effect on downregulating target mRNA levels.

DATABASES

Gene expression data are available in the GEO database under the accession SuperSeries number GSE102951.

Exosomes derived from hypoxic epithelial ovarian cancer deliver microRNA-940 to induce macrophage M2 polarization

Hypoxia is a common feature of solid tumors. It is closely related to tumor progression. Exosomal microRNAs derived from cancers are considered to be mediators between cancer cells and the tumor microenvironment. In addition, the number of tumor-associated macrophages (TAMs) in the tumor microenvironment has also been demonstrated to correlate with tumor development. However, the relationship between tumor-secreted exosomes and TAM polarization under hypoxic conditions during tumor progression is not clear. Herein, we demonstrated that hypoxia induces the high expression of microRNA-940 (miR‑940) in exosomes derived from epithelial ovarian cancer (EOC). We also found that miR‑940 is highly expressed in exosomes isolated from ascites of EOC patients. Moreover, the overexpression of miR‑940 in macrophages delivered by exosomes stimulated M2 phenotype polarization, while the M2 subtype macrophages promoted EOC proliferation and migration. These results highlight the function of hypoxia in enhancing the high level of expression of miR‑940 in tumor exosomes taken up by macrophages. We also showed that the tumor-promoting function of miR‑940 is mediated by TAM polarization in EOC. These findings show that tumor-derived exosomal miR‑940 induced by hypoxia plays an important role in stimulating TAM polarization in the progression of EOC.

Emerging applications of exosomes in cancer therapeutics and diagnostics

Exosomes are nanoscale extracellular vesicles that are shed from different cells in the body. Exosomes encapsulate several biomolecules including lipids, proteins, and nucleic acids, and can therefore play a key role in cellular communication. These vesicles can be isolated from different body fluids and their small sizes make them attractive in various biomedical applications. Here, we review state-of-the art approaches in exosome isolation and purification, and describe their potential use in cancer vaccines, drug delivery, and diagnostics.