Effect of colorectal cancer-derived extracellular vesicles on the immunophenotype and cytokine secretion profile of monocytes and macrophages

Itraconazole inhibits nuclear delivery of extracellular vesicle cargo by disrupting the entry of late endosomes into the nucleoplasmic reticulum

Extracellular vesicles (EVs) are mediators of intercellular communication under both healthy and pathological conditions, including the induction of pro-metastatic traits, but it is not yet known how and where functional cargoes of EVs are delivered to their targets in host cell compartments. We have described that after endocytosis, EVs reach Rab7+ late endosomes and a fraction of these enter the nucleoplasmic reticulum and transport EV biomaterials to the host cell nucleoplasm. Their entry therein and docking to outer nuclear membrane occur through a tripartite complex formed by the proteins VAP-A, ORP3 and Rab7 (VOR complex). Here, we report that the antifungal compound itraconazole (ICZ), but not its main metabolite hydroxy-ICZ or ketoconazole, disrupts the binding of Rab7 to ORP3-VAP-A complexes, leading to inhibition of EV-mediated pro-metastatic morphological changes including cell migration behaviour of colon cancer cells. With novel, smaller chemical drugs, inhibition of the VOR complex was maintained, although the ICZ moieties responsible for antifungal activity and interference with intracellular cholesterol distribution were removed. Knowing that cancer cells hijack their microenvironment and that EVs derived from them determine the pre-metastatic niche, small-sized inhibitors of nuclear transfer of EV cargo into host cells could find cancer therapeutic applications, particularly in combination with direct targeting of cancer cells.

Extracellular vesicles derived from gut microbiota in inflammatory bowel disease and colorectal cancer: new players?

The human gut microbiome encompasses inter alia, the myriad bacterial species that create the optimal host-microorganism balance essential for normal metabolic and immune function. Various lines of evidence suggest that dysregulation of the microbiota-host interaction is linked to pathologies such as inflammatory bowel disease (IBD) and colorectal cancer (CRC). Extracellular vesicles (EVs), found in virtually all body fluids and produced by both eukaryotic cells and bacteria are involved in cell-cell communication and crosstalk mechanisms, such as the immune response, barrier function and intestinal flora. This review highlights advancements in knowledge of the functional role that EVs may have in IBD and CRC, and discusses the possible use of EVs derived from intestinal microbiota in therapeutic strategies for treating these conditions.

Detection of Immune Checkpoint Receptors - A Current Challenge in Clinical Flow Cytometry

Immunological therapy principles are increasingly determining modern medicine. They are used to treat diseases of the immune system, for tumors, but also for infections, neurological diseases, and many others. Most of these therapies base on antibodies, but small molecules, soluble receptors or cells and modified cells are also used. The development of immune checkpoint inhibitors is amazingly fast. T-cell directed antibody therapies against PD-1 or CTLA-4 are already firmly established in the clinic. Further targets are constantly being added and it is becoming increasingly clear that their expression is not only relevant on T cells. Furthermore, we do not yet have any experience with the long-term systemic effects of the treatment. Flow cytometry can be used for diagnosis, monitoring, and detection of side effects. In this review, we focus on checkpoint molecules as target molecules and functional markers of cells of the innate and acquired immune system. However, for most of the interesting and potentially relevant parameters, there are still no test kits suitable for routine use. Here we give an overview of the detection of checkpoint molecules on immune cells in the peripheral blood and show examples of a possible design of antibody panels.

Extracellular Vesicles: Versatile Nanomediators, Potential Biomarkers and Therapeutic Agents in Atherosclerosis and COVID-19-Related Thrombosis

Cells convey information among one another. One instrument employed to transmit data and constituents to specific (target) cells is extracellular vesicles (EVs). They originate from a variety of cells (endothelial, immune cells, platelets, mesenchymal stromal cells, etc.), and consequently, their surface characteristics and cargo vary according to the paternal cell. The cargo could be DNA, mRNA, microRNA, receptors, metabolites, cytoplasmic proteins, or pathological molecules, as a function of which EVs exert different effects upon endocytosis in recipient cells. Recently, EVs have become important participants in a variety of pathologies, including atherogenesis and coronavirus disease 2019 (COVID-19)-associated thrombosis. Herein, we summarize recent advances and some of our own results on the role of EVs in atherosclerotic cardiovascular diseases, and discuss their potential to function as signaling mediators, biomarkers and therapeutic agents. Since COVID-19 patients have a high rate of thrombotic events, a special section of the review is dedicated to the mechanism of thrombosis and the possible therapeutic potential of EVs in COVID-19-related thrombosis. Yet, EV mechanisms and their role in the transfer of information between cells in normal and pathological conditions remain to be explored.

Lung on a Chip Development from Off-Stoichiometry Thiol-Ene Polymer

Current in vitro models have significant limitations for new respiratory disease research and rapid drug repurposing. Lung on a chip (LOAC) technology offers a potential solution to these problems. However, these devices typically are fabricated from polydimethylsiloxane (PDMS), which has small hydrophobic molecule absorption, which hinders the application of this technology in drug repurposing for respiratory diseases. Off-stoichiometry thiol-ene (OSTE) is a promising alternative material class to PDMS. Therefore, this study aimed to test OSTE as an alternative material for LOAC prototype development and compare it to PDMS. We tested OSTE material for light transmission, small molecule absorption, inhibition of enzymatic reactions, membrane particle, and fluorescent dye absorption. Next, we microfabricated LOAC devices from PDMS and OSTE, functionalized with human umbilical vein endothelial cell (HUVEC) and A549 cell lines, and analyzed them with immunofluorescence. We demonstrated that compared to PDMS, OSTE has similar absorption of membrane particles and effect on enzymatic reactions, significantly lower small molecule absorption, and lower light transmission. Consequently, the immunofluorescence of OSTE LOAC was significantly impaired by OSTE optical properties. In conclusion, OSTE is a promising material for LOAC, but optical issues should be addressed in future LOAC prototypes to benefit from the material properties.

Inorganic nanohybrids combat antibiotic-resistant bacteria hiding within human macrophages

Bacterial infections are one of the main health concerns humanity faces today and bacterial resistances and protection mechanisms are set to aggravate the issue in the coming years. An increasing number of bacterial strains evades antibiotic treatment by hiding inside cells. Conventional antimicrobial agents are unable to penetrate or be retained in the infected mammalian cells. Recent approaches to overcome these limitations have focused on load-carrier systems, requiring a triggered discharge leading to complex release kinetics. The unison of potent antimicrobial activity with high mammalian cell compatibility is a prerequisite for intracellular activity, which is not well-met by otherwise well-established inorganic systems, such as silver-based nanoparticles. In this work, load and carrier are combined into one functional inorganic nanoparticle system, which unites antimicrobial activity with mammalian cell compatibility. These multicomponent nanohybrids based on cerium oxide are produced in one step, yet unite complex materials. The nanoparticles form suprastructures of similar size and surface charge as bacteria, therefore facilitating the uptake into the same subcellular compartments, where they unleash their antibacterial effect. Such intrinsically antibacterial nanohybrids significantly reduce bacterial survival inside macrophages without harming the latter. Furthermore, blocking of nanoparticle endocytosis and subcellular electron microscopy elucidate the mechanism of action. Taken together, this work presents the first demonstration of antibacterial activity of ceria-based nanoparticles inside of mammalian cells and offers a route to straightforward and robust intracellular antibacterial agents that do not depend on payload delivery or biological constituents.

Computational Simulation of Exosome Transport in Tumor Microenvironment

Cellular exosome-mediated crosstalk in tumor microenvironment (TME) is a critical component of anti-tumor immune responses. In addition to particle size, exosome transport and uptake by target cells is influenced by physical and physiological factors, including interstitial fluid pressure, and exosome concentration. These variables differ under both normal and pathological conditions, including cancer. The transport of exosomes in TME is governed by interstitial flow and diffusion. Based on these determinants, mathematical models were adapted to simulate the transport of exosomes in the TME with specified exosome release rates from the tumor cells. In this study, the significance of spatial relationship in exosome-mediated intercellular communication was established by treating their movement in the TME as a continuum using a transport equation, with advection due to interstitial flow and diffusion due to concentration gradients. To quantify the rate of release of exosomes by biomechanical forces acting on the tumor cells, we used a transwell platform with confluent triple negative breast cancer cells 4T1.2 seeded in BioFlex plates exposed to an oscillatory force. Exosome release rates were quantified from 4T1.2 cells seeded at the bottom of the well following the application of either no force or an oscillatory force, and these rates were used to model exosome transport in the transwell. The simulations predicted that a larger number of exosomes reached the membrane of the transwell for 4T1.2 cells exposed to the oscillatory force when compared to controls. Additionally, we simulated the interstitial fluid flow and exosome transport in a 2-dimensional TME with macrophages, T cells, and mixtures of these two populations at two different stages of a tumor growth. Computational simulations were carried out using the commercial computational simulation package, ANSYS/Fluent. The results of this study indicated higher exosome concentrations and larger interstitial fluid pressure at the later stages of the tumor growth. Quantifying the release of exosomes by cancer cells, their transport through the TME, and their concentration in TME will afford a deeper understanding of the mechanisms of these interactions and aid in deriving predictive models for therapeutic intervention.

Uptake of circulating extracellular vesicles from rectal cancer patients and differential responses by human monocyte cultures

Extracellular vesicles (EVs) released by tumor cells can directly or indirectly modulate the phenotype and function of the immune cells of the microenvironment locally or at distant sites. The uptake of circulating EVs and the responses by human monocytes in vitro may provide new insights into the underlying biology of the invasive and metastatic processes in cancer. Although a mixed population of vesicles is obtained with most isolation techniques, we predominantly isolated exosomes (small EVs) and microvesicles (medium EVs) from the SW480 colorectal cancer cell line (established from a primary adenocarcinoma of the colon) by sequential centrifugation and ultrafiltration, and plasma EVs were prepared from 22 patients with rectal adenoma polyps or invasive adenocarcinoma by size‐exclusion chromatography. The EVs were thoroughly characterized. The uptake of SW480 EVs was analyzed, and small SW480 EVs were observed to be more potent than medium SW480 EVs in inducing monocyte secretion of cytokines. The plasma EVs were also internalized by monocytes; however, their cytokine‐releasing potency was lower than that of the cell line‐derived vesicles. The transcriptional changes in the monocytes highlighted differences between adenoma and adenocarcinoma patient EVs in their ability to regulate biological functions, whereas the most intriguing changes were found in monocytes receiving EVs from patients with metastatic compared with localized cancer.

Landscape of extracellular vesicles in the tumour microenvironment: Interactions with stromal cells and with non-cell components, and impacts on metabolic reprogramming, horizontal transfer of neoplastic traits, and the emergence of therapeutic resistance

Extracellular vesicles (EVs) are increasingly recognised as a pivotal player in cell-cell communication, an attribute of EVs that derives from their ability to transport bioactive cargoes between cells, resulting in complex intercellular signalling mediated by EVs, which occurs under both physiological and pathological conditions. In the context of cancer, recent studies have demonstrated the versatile and crucial roles of EVs in the tumour microenvironment (TME). Here, we revisit EV biology, and focus on EV-mediated interactions between cancer cells and stromal cells, including fibroblasts, immune cells, endothelial cells and neurons. In addition, we focus on recent reports indicating interactions between EVs and non-cell constituents within the TME, including the extracellular matrix. We also review and summarise the intricate cancer-associated network modulated by EVs, which promotes metabolic reprogramming, horizontal transfer of neoplastic traits, and therapeutic resistance in the TME. We aim to provide a comprehensive and updated landscape of EVs in the TME, focusing on oncogenesis, cancer progression and therapeutic resistance, together with our future perspectives on the field.

EVs as Potential New Therapeutic Tool/Target in Gastrointestinal Cancer and HCC

For more than a decade, extracellular vesicles (EVs) have been in focus of science. Once thought to be an efficient way to eliminate undesirable cell content, EVs are now well-accepted as being an important alternative to cytokines and chemokines in cell-to-cell communication route. With their cargos, mainly consisting of functional proteins, lipids and nucleic acids, they can activate signalling cascades and thus change the phenotype of recipient cells at local and systemic levels. Their substantial role as modulators of various physiological and pathological processes is acknowledged. Importantly, more and more evidence arises that EVs play a pivotal role in many stages of carcinogenesis. Via EV-mediated communication, tumour cells can manipulate cells from host immune system or from the tumour microenvironment, and, ultimately, they promote tumour progression and modulate host immunity towards tumour's favour. Additionally, the role of EVs in modulating resistance to pharmacological and radiological therapy of many cancer types has become evident lately. Our understanding of EV biology and their role in cancer promotion and drug resistance has evolved considerably in recent years. In this review, we specifically discuss the current knowledge on the association between EVs and gastrointestinal (GI) and liver cancers, including their potential for diagnosis and treatment.

Myeloid Cell Modulation by Tumor-Derived Extracellular Vesicles

Extracellular vesicles (EV) can carry proteins, RNA and DNA, thus serving as communication tools between cells. Tumor cells secrete EV, which can be taken up by surrounding cells in the tumor microenvironment as well as by cells in distant organs. Tumor-derived EV (TEV) contain factors induced by tumor-associated hypoxia such as heat shock proteins or a variety of microRNA (miRNA). The interaction of TEV with tumor and host cells can promote cancer angiogenesis, invasion and metastasis. Myeloid cells are widely presented in tissues, comprise the majority of immune cells and play an essential role in immune reactions and tissue remodeling. However, in cancer, the differentiation of myeloid cells and their functions are impaired, resulting in tumor promotion. Such alterations are due to chronic inflammatory conditions associated with cancer and are mediated by the tumor secretome, including TEV. A high capacity of myeloid cells to clear EV from circulation put them in the central position in EV-mediated formation of pre-metastatic niches. The exposure of myeloid cells to TEV could trigger numerous signaling pathways. Progenitors of myeloid cells alter their differentiation upon the contact with TEV, resulting in the generation of myeloid-derived suppressor cells (MDSC), inhibiting anti-tumor function of T and natural killer (NK) cells and promoting thereby tumor progression. Furthermore, TEV can augment MDSC immunosuppressive capacity. Different subsets of mature myeloid cells such as monocytes, macrophages, dendritic cells (DC) and granulocytes take up TEV and acquire a protumorigenic phenotype. However, the delivery of tumor antigens to DC by TEV was shown to enhance their immunostimulatory capacity. The present review will discuss a diverse and complex EV-mediated crosstalk between tumor and myeloid cells in the context of the tumor type, TEV-associated cargo molecules and type of recipient cells.

Normoxic Tumour Extracellular Vesicles Modulate the Response of Hypoxic Cancer and Stromal Cells to Doxorubicin In Vitro

Extracellular vesicles (EV) secreted in the tumour microenvironment (TME) are emerging as major antagonists of anticancer therapies by orchestrating the therapeutic outcome through altering the behaviour of recipient cells. Recent evidence suggested that chemotherapeutic drugs could be responsible for the EV-mediated tumour-stroma crosstalk associated with cancer cell drug resistance. Here, we investigated the capacity of tumour EV (TEV) secreted by normoxic and hypoxic (1% oxygen) C26 cancer cells after doxorubicin (DOX) treatment to alter the response of naïve C26 cells and RAW 264.7 macrophages to DOX. We observed that C26 cells were less responsive to DOX treatment under normoxia compared to hypoxia, and a minimally cytotoxic DOX concentration that mounted distinct effects on cell viability was selected for TEV harvesting. Homotypic and heterotypic pretreatment of naïve hypoxic cancer and macrophage-like cells with normoxic DOX-elicited TEV rendered these cells slightly less responsive to DOX treatment. The observed effects were associated with strong hypoxia-inducible factor 1-alpha (HIF-1α) induction and B-cell lymphoma-extra-large anti-apoptotic protein (Bcl-xL)-mediated anti-apoptotic response in normoxic DOX-treated TEV donor cells, being also tightly connected to the DOX-TEV-mediated HIF-1α induction, as well as Bcl-xL levels increasing in recipient cells. Altogether, our results could open new perspectives for investigating the role of chemotherapy-elicited TEV in the colorectal cancer TME and their modulatory actions on promoting drug resistance.

Csf2 Attenuated Sepsis-Induced Acute Kidney Injury by Promoting Alternative Macrophage Transition

Sepsis is a systemic inflammatory state that occurs in response to infection and significantly increases mortality in combination with acute kidney injury (AKI). Macrophages accumulate in the kidney after injury and undergo a transition from a proinflammatory (M1) phenotype to an alternatively activated (M2) phenotype that is required for normal repair. However, the specific signals that regulate the transition from the M1 to M2 phenotype in vivo are unknown. Here, we found an unexpected role of Colony stimulating factor 2 (Csf2) in controlling macrophage transition in vitro and in a mouse model of sepsis induced by cecal ligation and puncture (CLP). We first co-cultured human M1 macrophages with HK-2 cells and characterized cytokine/chemokine profiles via Luminex. Of the cytokines and chemokines that were overexpressed in medium from M1 macrophages cocultured with human kidney-2 (HK-2) cells compared with that from M1 macrophages cultured alone, Csf2 and IL6 showed the greatest increases. Csf2 was exclusively secreted by HK-2 cells but not by M1 macrophages. Furthermore, recombinant human Csf2 protein promoted transition of M1 macrophages to the M2 phenotype in a dose and time-dependent manner. The apoptosis and reactive oxygen species (ROS) release induced by M1 macrophages in HK-2 cells was attenuated after exposure to exogenous Csf2. In addition, the switch from the proinflammatory M1 phenotype to the M2 phenotype occurred via the p-Stat5 pathway, which was activated by Csf2. Importantly, we found that intraperitoneal injection of a Csf2-neutralizing antibody after CLP aggravated kidney injury and suppressed tubular proliferation, subsequently decreasing survival. However, administration of recombinant mouse Csf2 protein could rescue mice with sepsis. Together, our results indicate that Csf2 plays critical roles in regulating macrophage transition via activation of p-STAT5. These data form a foundation upon which new therapeutic strategies can be designed to improve the therapeutic efficacy of cytokine-based treatments for sepsis-induced AKI.

microRNA-141-3p-containing small extracellular vesicles derived from epithelial ovarian cancer cells promote endothelial cell angiogenesis through activating the JAK/STAT3 and NF-κB signaling pathways

Paracrine signaling between tumor and surrounding stromal cells is critical for the maintenance of tumor microenvironment during ovarian cancer progression. Small extracellular vesicles (sEVs; exosomes in particular) are nano-sized vesicles secreted actively by many cells including tumor cells and are found to have fundamental roles in intercellular communication through shuttling functional RNAs. Although microRNAs (also called miRNAs or miRs), small non-coding RNAs regulating gene expression, are selectively accumulated in tumor sEVs and can mediate intercellular communication, the exact biological mechanisms underlying the functions of exosomal miRNAs in ovarian tumor angiogenesis remain unclear. In this study, sEVs were isolated from conditioned medium of the human ovarian carcinoma cell line SKOV-3 using ExoQuick Exosome Precipitation Solution, and characterized by scanning electron microscopy, dynamic light scattering, and immunoblotting. To elucidate the possible paracrine effects on ovarian tumor cell-derived sEVs (TD-sEVs), we investigated the angiogenesis-related signaling events triggered by TD-sEVs in endothelial cells. Due to the possible role in ovarian tumor pathogenesis, we focused on miR-141-3p which was detected to be enriched in TD-sEVs compared with their corresponding donor cells. We identified that sEV transfer of miR-141-3p considerably reduced the expression levels of cytokine-inducible suppressors of cytokine signaling (SOCS)-5 leading to up-regulated JAK-STAT3 pathway in endothelial cells. We also observed that sEV-shuttled miR-141-3p may up-regulate the expression of VEGFR-2 in endothelial cells which leads to promoting endothelial cell migration and angiogenesis. The putative role of miR-141-3p shuttled by TD-sEVs in regulating VEGFR-2 expression was demonstrated by the ability of anti-miR-141-3p to rescue the promoting effects of TD-sEVs on the expression of VEGFR-2 in endothelial cells. Our results also revealed that TD-sEVs trigger the intracellular reactive oxygen species (ROS)-dependent activation of NF-κB signaling in endothelial cells. Taken together, our findings propose a novel model in which sEV transfer of epithelial ovarian cancer-secreted miR-141-3p plays as a significant mediator of intercellular communication, promoting endothelial cell angiogenesis.

Circulating Extracellular Vesicle MicroRNA as Diagnostic Biomarkers in Early Colorectal Cancer-A Review

Colorectal cancer (CRC) is one of the most common malignancies in the developed world, with global deaths expected to double in the next decade. Disease stage at diagnosis is the single greatest prognostic indicator for long-term survival. Unfortunately, early stage CRC is often asymptomatic and diagnosis frequently occurs at an advanced stage, where long-term survival can be as low as 14%. Circulating microRNAs encapsulated in extracellular vesicles (EVs) have recently come to prominence as novel diagnostic markers for cancer. EV-miRNAs are dysregulated in the circulation of CRC patients compared to healthy controls, and several specific miRNA candidates have been posited as diagnostic markers, including miR-21, miR-23a, miR-1246, and miR-92a. This review outlines the current landscape of EV-miRNAs as potential diagnostic markers for CRC, with a specific focus on those able to detect early stage disease.

Molecular model linking Th2 polarized M2 tumour-associated macrophages with deaminase-mediated cancer progression mutation signatures

A new and diverse range of somatic mutation signatures are observed in late-stage cancers, but the underlying reasons are not fully understood. We advance a "combinatorial association model" for deaminase binding domain (DBD) diversification to explain the generation of previously observed cancer-progression associated mutation signatures. We also propose that changes in the polarization of tumour-associated macrophages (TAMs) are accompanied by the expression of deaminases with a new and diverse range of DBDs, and thus accounting for the generation of new somatic mutation signatures. The mechanism proposed is molecularly reminiscent of combinatorial association of heavy (H) and light (L) protein chains following V(D)J recombination of immunoglobulin molecules (and similarly for protein chains in heterodimers α/β and γ/δ of V(D)Js of T Cell Receptors) required for pathogen antigen recognition by B cells and T cells, respectively. We also discuss whether extracellular vesicles (EVs) emanating from tumour enhancing M2-polarized macrophages represent a likely source of the de novo deaminase DBDs. We conclude that M2-polarized macrophages extruding EVs loaded with deaminase proteins or deaminase-specific transcription/translation regulatory factors and like information may directly trigger deaminase diversification within cancer cells, and thus account for the many new somatic mutation signatures that are indicative of cancer progression. This hypothesis now has a plausible evidentiary base, and it is worth direct testing in future investigations. A long-term objective would be to identify molecular biomarkers predicting cancer progression (or metastatic disease) and to support the development of new drug targets before metastatic pathways are activated.

Gut microbiota-stimulated cathepsin K secretion mediates TLR4-dependent M2 macrophage polarization and promotes tumor metastasis in colorectal cancer

Metastasis is a complex process that requires the interaction between tumor cells and their microenvironment. As an important regulator of intestinal microenvironment, gut microbiota plays a significant role in the initiation and progression of colorectal cancer (CRC), but the underlying mechanisms remain elusive. In this study, a metastasis-related secretory protein cathepsin K (CTSK) was identified as a vital mediator between the imbalance of intestinal microbiota and CRC metastasis. We implanted MC38 cells into the cecal mesentry of antibiotic-treated mice with intragastrically administration of E. coli to mimic gut microbiota imbalance. The bigger primary tumors and more liver metastatic foci were detected in the E. coli group accompanied with high LPS secretion and CTSK overexpression compared with that in the control group. CTSK contributes to the aggressive phenotype of CRC cells both in vitro and in vivo. Silencing CTSK or administration of Odanacatib, a CTSK-specific inhibitor, totally abolished the CTSK-enhanced migration and motility of CRC cells. Interestingly, the tumor-secreted CTSK could bind to toll-like receptor 4 (TLR4) to stimulate the M2 polarization of tumor-associated macrophages (TAMs) via an mTOR-dependent pathway. Recombinant CTSK could neither stimulate CRC growth and metastasis, nor induce M2 macrophage polarization in TRL4^-/- mice. Meanwhile, CTSK could stimulate the secretion of cytokines by M2 TAMs including IL10 and IL17, which, in turn, promote the invasion and metastasis of CRC cells through NFκB pathway. Clinically, overexpression of CTSK in human CRC tissues is always accompanied with high M2 TAMs in the stroma, and correlated with CRC metastasis and poor prognosis. Our current research identified CTSK as a mediator between the imbalance of gut microbiota and CRC metastasis. More importantly, we illustrated a CTSK-mediated-positive feedback loop between CRC cells and TAMs during metastasis, prompting CTSK as a novel predictive biomarker and feasible therapeutic target for CRC.

Tumor cell-released autophagosomes (TRAPs) promote immunosuppression through induction of M2-like macrophages with increased expression of PD-L1

Background

Tumor-associated macrophages (TAMs) facilitate tumor progression via establishment of an immunosuppressive tumor microenvironment (TME). However, it is poorly understood how tumor cells could functionally modulate TAMs. Our previous work indicated that tumor cell-released autophagosomes (TRAPs), a type of LC3-II⁺ double-membrane extracellular vesicles (EVs) was sufficient to suppress anti-tumor immune responses by inducing IL-10-producing B cells and immune suppressive neutrophils. Here, we hypothesized that TRAPs may participate in regulating macrophage polarization.

Methods

TRAPs isolated from multiple murine tumor cell lines and pleural effusions or ascites of cancer patients were incubated with bone marrow-derived macrophages (BMDMs) and monocytes, respectively. Cellular phenotypes were examined by flow cytometry, ELISA and quantitative PCR. TRAPs treated BMDMs were tested for the ability to suppress T-cell proliferation in vitro, and for promotion of tumor growth in vivo. Transwell chamber and neutralization antibodies were added to ascertain the inhibitory molecules expressed on BMDMs exposed to TRAPs. Knockout mice were used to identify the receptors responsible for TRAPs-induced BMDMs polarization and the signaling mechanism was examined by western blot. Autophagy-deficient tumors were profiled for phenotypic changes of TAMs and IFN-γ secretion of T cells by flow cytometry. The phenotype of monocytes from pleural effusions or ascites of cancer patients was assessed by flow cytometry.

Results

TRAPs converted macrophages into an immunosuppressive M2-like phenotype characterized by the expression of PD-L1 and IL-10. These macrophages inhibited the proliferation of both CD4⁺ and CD8⁺ T cells in vitro, and promoted tumor growth mainly through PD-L1 in vivo. TRAPs-induced macrophage polarization was dependent on TLR4-mediated MyD88-p38-STAT3 signaling. In vivo studies indicated that disruption of autophagosome formation in B16F10 cells by silencing the autophagy gene Beclin1 resulted in a remarkable delay in tumor growth, which was associated with reduced autophagosome secretion, TAMs reprogramming and enhanced T cell activation. Moreover, the levels of LC3B⁺ EVs appeared to correlate significantly with up-regulation of PD-L1 and IL-10 in matched monocytes from effusions or ascites of cancer patients, and TRAPs isolated from these samples could also polarize monocytes to an M2-like phenotype with increased expression of PD-L1, CD163 and IL-10, decreased expression of HLA-DR, and T cell-suppressive function.

Conclusions

These findings suggest the TRAPs-PD-L1 axis as a major driver of immunosuppression in the TME by eliciting macrophage polarization towards an M2-like phenotype, and highlight the potential novel therapeutic approach of simultaneously targeting autophagy and PD-L1.

Electronic supplementary material

The online version of this article (10.1186/s40425-018-0452-5) contains supplementary material, which is available to authorized users.