Direct Cell-cell Contact Research Articles

Abstract 4517: Tumor-associated macrophages are reprogrammed by pancreatic ductal adenocarcinoma cells through tumor-induced DNA methylation on metabolic genes

Abstract Metabolism is shifted toward glycolysis with increased glucose uptake in anti-tumor M1 macrophages, and toward oxidative phosphorylation with significant decreased glucose uptake in pro-tumor M2 macrophages in Pancreatic ductal adenocarcinoma (PDA). Current study aims to investigate the mechanism by which tumor cells reprogram tumor associated macrophages metabolically and functionally. Using mouse bone marrow derived macrophages and human macrophages derived from peripheral blood mononuclear cells for contact and non-contact co-culture experiments with PDA tumor cells, we showed PDA tumor cells, through direct cell-cell contact confirmed by Lucifer yellow dye-coupling assay, induced DNA methylation and downregulation of a panel of glucose metabolism and oxidative phosphorylation genes selectively in M1 but not M2 macrophages by methylation specific PCR, methylation microarray analysis and qPCR, RNA-seq analysis. Glucose-response genes such as IL10 were subsequently activated. Through IL10 and its receptor IL-10R on tumor cells, macrophages enhanced the in vitro migration of tumor cells in trans-well migration assay verified by shRNA knockdown of IL10 and IL10R respectively. Exogenous infusion of both M1 and M2 macrophages promoted PDA metastasis in orthotopic mouse model after resident macrophage depletion, although pretreating with DNA demethylating agent Decitabine prevented M1, but not M2 macrophages in promoting metastasis, suggesting M1 macrophages were reprogrammed metabolically and functionally by tumor cells to become pro-cancerous. To interrogate the mechanism that regulates the tumor-induced DNA methylation in macrophages, we first examined chromatin remodeling complex Polycomb Repressive Complex 2 (PRC2), with its major component enhancer of zeste homolog 2 (EZH2) previously shown to recruit DNA methyltransferases to specific chromatin regions for epigenetic gene regulation. We found EZH2 protein was most significantly increased in M1 macrophages while Ser21 phosphorylated EZH2 (pSer21-EZH2) remained constant, indicating a decreased percentage of pSer21-EZH2/EZH2 in M1 macrophages co-cultured with tumor cells. Further identification of potential F-box containing ubiquitin ligases that interact with pSer21-EZH2 by Co-immunoprecipitation suggested EZH2 may be stabilized in M1 macrophages by tumor cells through inhibiting the ubiquitin-dependent proteolysis of pSer21-EZH2 in a phosphorylation dependent manner. This study thus far reveals a novel mechanism that reprograms M1 macrophages phenotypically into M2-like macrophages and functionally into pro-cancerous macrophages. Identification of cell surface receptors that mediate the direct tumor-macrophage contact are actively being sought, which will lead to the development of therapeutic blockades to reverse the macrophage reprogramming. Citation Format: Xingyi Pan, Mengwen Zhang, Kenji Fujiwara, Noelle R. Jurcak, Stephen Muth, Lei Zheng. Tumor-associated macrophages are reprogrammed by pancreatic ductal adenocarcinoma cells through tumor-induced DNA methylation on metabolic genes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4517.

Burkholderia cepacia Complex Contact-Dependent Growth Inhibition Systems Mediate Interbacterial Competition.

Burkholderia species, including opportunistic pathogens in the Burkholderia cepacia complex (Bcc), have genes to produce contact-dependent growth inhibition (CDI) system proteins. CDI is a phenomenon in which Gram-negative bacteria use the toxic C terminus of a polymorphic surface-exposed exoprotein, BcpA, to inhibit the growth of susceptible bacteria upon direct cell-cell contact. Production of a small immunity protein, BcpI, prevents autoinhibition. Although CDI systems appear widespread in Gram-negative bacteria, their function has been primarily examined in several model species. Here we demonstrate that genes encoding predicted CDI systems in Bcc species exhibit considerable diversity. We also show that Burkholderia multivorans, which causes pulmonary infections in patients with cystic fibrosis, expresses genes that encode two CDI systems, both of which appear distinct from the typical Burkholderia-type CDI system. Each system can mediate intrastrain interbacterial competition and contributes to bacterial adherence. Surprisingly, the immunity-protein-encoding bcpI gene of CDI system 1 could be mutated without obvious deleterious effects. We also show that nonpathogenic Burkholderia thailandensis uses CDI to control B. multivorans growth during coculture, providing one of the first examples of interspecies CDI and suggesting that CDI systems could be manipulated to develop therapeutic strategies targeting Bcc pathogens.IMPORTANCE Competition among bacteria affects microbial colonization of environmental niches and host organisms, particularly during polymicrobial infections. The Bcc is a group of environmental bacteria that can cause life-threatening opportunistic infections in patients who have cystic fibrosis or are immunocompromised. Understanding the mechanisms used by these bacterial pathogens to compete with one another may lead to the development of more effective therapies. Findings presented here demonstrate that a Bcc species, Burkholderia multivorans, produces functional CDI system proteins and that growth of this pathogen can be controlled by CDI system proteins produced by neighboring Burkholderia cells.

The role of cell adhesion in hematopoiesis and leukemogenesis.

The cells of the bone marrow microenvironment are emerging as important contributors and regulators of normal hematopoiesis. This microenvironment is perturbed during leukemogenesis, and evidence points toward a bidirectional communication between leukemia cells and the normal cells of the bone marrow, mediated by direct cell-cell contact as well as soluble factors. These interactions are increasingly appreciated to play a role in leukemogenesis and possibly in resistance to chemotherapy. In fact, several compounds that specifically target the bone marrow microenvironment, including inhibitors of cell adhesion, are being tested as adjuncts to leukemia therapy.

Reciprocal modulation of cell functions upon direct interaction of adipose mesenchymal stromal and activated immune cells.

The interaction of adipose mesenchymal stromal cells (ASCs) and allogeneic peripheral blood mononuclear cells (PBMCs) is regulated either through direct or paracrine mechanisms. Here, we examined the impact of direct contact in reciprocal regulation of ASC-PBMC functions. Activated PBMCs in vitro induced ASC immunomodulatory activity, while direct and paracrine intercellular interactions regulated PBMCs themselves: the functional state of the organelles was altered, and activation decreased. Direct contact with immune cells affected the activity of ASC intracellular compartments, in particular, reactive oxygen species (ROS) production, and decreased the growth rate. Some ASC properties, including motility, intercellular adhesion molecule-1 (ICAM-1), and major histocompatibility complex class I and II antigens (HLA-ABC and HLA-DR, respectively) expression, did not depend on contact with PBMCs and were only regulated by paracrine means. Direct ASC and PBMC contact favoured an angiogenesis-supportive microenvironment, possibly due to the greater production of VEGF by ASCs; this microenvironment also contained a higher leukemia inhibitory factor (LIF) level. Thus, a change in the functional activity of ASCs and PBMCs upon interaction promoted the formation of an immunosuppressive, anti-inflammatory, and proangiogenic microenvironment. This environment could help resolve inflammation and further restore damaged tissue. SIGNIFICANCE OF THE STUDY: Numerous studies have demonstrated the beneficial effects of transplanted mesenchymal stromal cells, particularly ASCs, for the treatment of a number of autoimmune diseases as well as various tissue injuries. To improve the efficiency of these methods, it is necessary to understand the principal events that occur when ASCs are introduced, primarily the molecular mechanisms of interaction between ASCs and the recipient immune system. We demonstrated that an anti-inflammatory, immunosuppressive, and angiostimulatory shift in the paracrine profile upon the interaction of activated PBMCs and ASCs changes the functional activity of both cell types, a phenomenon that is potentiated by direct cell-cell contact.

Saccharomycin, a biocide from S. cerevisiae that kill-off other yeasts

Introduction: Saccharomyces cerevisiae plays an important role in alcoholic fermentation and is involved in the production of wine, beer and bread. Recent studies [1–7] showed that S. cerevisiae secretes antimicrobial peptides (AMPs), named “saccharomycin”, derived from the glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH) that are active against a variety of wine-related microbial species. AMPs are low molecular weight proteins with broad antimicrobial spectrum of action against bacteria, viruses, and fungi [8]. Organisms use AMPs for defence against infection and membrane interaction appears to be the key to this antimicrobial function: generally they adopt amphiphilic structures that interact with the infectious agent’s membrane. AMPs constitute a promising source as alternatives to: i) combat pathogenic bacteria resistant to common antibiotics and ii) substitute chemical preservatives in food-fermented products such as wine. The aim of this study was to discover the mode of action of these peptides by detailed chemical structure characterisation and cell contact mechanism. Materials and methods: Structural characterization of saccharomycin and of its synthetic analogues was performed by NMR. 2D NMR spectra, COSY, TOCSY, ROESY, and 1H-13C-HMQC (Figure 1) for identifying non-peptide components involved in the chemical structure of saccharomycin by comparison with synthetic analogues. Atomic Force Microscopy (Figure 2) was used to observe the surface of different species of yeast cells upon cell-cell contact. Yeast cells were observed after being collected at different growth stages, either from mixed or pure cultures. Differential proteomic studies were performed to identify S.cerevisiae metabolic pathways involved in the production of AMPs using 2D electrophoresis coupled to MS techniques Figure 1. 13C HMQC of native AMPs from S. cerevisiae Figure 2. 13AFM image of S. cerevisiae cell surface. Results: NMR experiments show further support of our previous results indicating the presence of carbohydrate molecules linked to the native peptide. AFM images of pure and mixed cultures were obtained in different growth times, at different dilutions. Discussion and conclusions: AFM imaging shows direct cell-cell contact between different yeast species in mixed cultures. Protemic studies have identified main proteins in this methabolism. 2D NMR spectra of biological active isolated fraction from S. cerevisiae gave evidence of the presence of glycosylated peptides in the native form.

Using quantitative proteomics to analyse HCMV manipulation of dendritic cells following cell-cell transfer

Human cytomegalovirus (HCMV) rapidly mutates during in vitro passage, and this strongly alters the way the virus spreads. In vivo HCMV spreads by direct cell-cell contact, as do recent clinical isolates. In contrast, passaged strains spread via cell-free virions. Because of this, cell-cell spread remains largely uncharacterised. We have developed a strain (Merlin) that retains a full length, wildtype genome. As a result, it mimics clinical HCMV and spreads by direct cell-cell contact, a method of spread that is more resistant to neutralising antibodies, and innate and intrinsic immunity. We now show that each cell-cell transfer is equivalent to an extremely high MOI infection, with up to 300 genomes delivered to each cell, potentially providing an explanation for the ‘immune-evasive’ properties of cell-cell transfer. Furthermore, infectious virions accumulate at cell-cell contacts between cells. This may represent a ‘virological synapse’ that protects virions from neutralising antibodies. Not only does Merlin enable us to characterise cell-cell spread, but it enables us to infect a wide range of clinically relevant cells with a virus expressing the complete complement of virus genes. In vivo, HCMV infects dendritic cells (DCs), but is never cleared, implying that it is able to subvert DC function. Therefore, we performed quantitative proteomic analysis of infected primary immature DCs, following cell-cell transfer. This quantified 7992 intracellular proteins, and 703 plasma membrane proteins. Over 99 proteins were downregulated following infection. Many of these are DC-specific, and have roles in regulating adaptive immunity. These viral-manipulations may therefore dramatically impact DC function.

Abstract P4-06-08: The spatial localization of immune cells predicts prognosis and response to therapy in inflammatory breast cancer

Abstract Introduction The mechanisms contributing to the aggressive biology of inflammatory breast cancer (IBC) are still under investigation. Our lab reported a 79-gene signature that is shaped by specific immune response programs and discriminates between IBC and non-IBC (nIBC). Furthermore, the presence of cytotoxic CD8+ immune cells is associated with a better prognosis in proliferative subtypes of breast cancer. However, not only the presence of CD8+ cells, but also the interaction with other immune cells plays a role in the functional immune response. In this study we assessed the spatial associations between immune cells in IBC. Methodology Affymetrix gene expression data of 105 IBC patients were analyzed using CIBERSORT and xCell modules to narrow down the number of stainings for the immunophenotyping. To analyze the composition of the immune infiltrate, we used five validated antibodies: CD79α (B-cell lineage), CD8 (cytotoxic T-cells), FOXP3 (Tregs), CD163 (Tumor associated macrophages, TAMs) and the SP142 PDL1 antibody. A standard H&E stained section was used to mark the tumor area on pretreatment biopsy sections. Subsequently, 5 slides were stained according to a validated protocol, scanned and evaluated using VISIOPHARM® software that makes virtual multiplexing possible after the alignment of the scanned images. Using both point pattern analysis and the Morisita–Horn index (MHI), developed for ecological studies, we assessed the co-localization of the different types of immune cells. Currently, we report the result of our validation cohort (30 patient samples). Results Most of our IBC patients presented with a hormone receptor positive carcinoma (64.7%). Almost a quarter of the patients (23.3%) with initially localized disease achieved complete pathological response (pCR) after neo-adjuvant chemotherapy (NACT). For every staining we report the median relative marker area (RMA), MHI for colocalization with CD8 applying a square tessellation of 100 μm and the number of cells in a radius of 30 μm around CD8+ cells (direct cell-cell contact) in table 1. RMAMHI # X+ cells (30 μm)CD80.33 % CD1630.12 %0.7213.13CD79α0.04 %0.6522.52FOXP30.01 %0.7011.37PDL1 0.7460.70Table 1: Median spatial properties. The RMA of CD8 predicted pCR after NACT (RMA= 1.07% pCR vs 0.35% no pCR, P=0.04), but was not prognostic for OS (P= 0.445). PDL1 positivity predicted neither pCR nor OS in this cohort. However, OS of patients with more PDL1+ cells ( > 0.703) in close contact with the CD8+ cells was significantly shorter (5y OS: 50% vs 68%, P= 0.03). Interestingly, the colocalization of CD8+ cells with TAMs (MHI= 0.69 no pCR vs. 0.75 pCR, P= 0.04) and CD79α+ B-cells (MHI= 0.63 no pCR vs. 0.69 pCR, P= 0.04) was also associated with pCR after NACT, while the number of CD163+ or CD79α+ cells was not. Conclusion In this study we described the dynamic interplay between cancer and immune cells. In a validation cohort of 30 patient samples we showed that the colocalization of TAMs or B-cells with cytotoxic T cells was associated with pCR after NACT. Furthermore, patients with more PDL1+ cells around CD8+ cells (r= 30 μm) had a worse prognosis while solely the number of PDL1+ or CD8+ cells was not prognostic. By December we will present data on 179 IBC patients. Citation Format: Van Berckelaer C, Colpaert C, Rypens C, Marien KM, Waumans Y, Kockx M, Vermeulen P, Dirix L, Van Laere S, Van Dam P. The spatial localization of immune cells predicts prognosis and response to therapy in inflammatory breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-06-08.

Research Advances on Role of Extracellular Vesicles in the Bone Marrow Microenvironment of Patients with Hematological Malignancies--Review

Bone marrow (BM) microenvironment appears to play an important role in the pathogenesis of hematological malignancies. Apart from soluble factors and direct cell-cell contact, the extracellular vesicles (EVs) were identified as a third mediator for cell communication within BM microenvironment. Recently, more and more evidences have demonstrated that EVs are also involved in the dysregulation of the BM microenvironment in patients with hematological malignancies. Therefore this review focuses on the biological characteristics of EVs, the clinical value of EVs as biomarkers, the BM microenvironment reprogramming in hematological malignancies by EVs, and the potential role of EVs in drug resistance and therapy of hematological malignancies.

Abstract WP351: Lung-Specific Extracellular Superoxide Dismutase Blocks Neutrophil-Mediated Toxicity in Brain Ischemia-Reperfusion

Introduction: Tissue damage and neuroinflammatory responses associated with cerebral ischemia trigger a systemic immune response that exacerbates brain injury during reperfusion and adversely influences functional recovery. Polymorphonuclear neutrophils (PMNs) are the first-line response to inflammation following acute brain injury, and evidence implicates lung-dependent PMN depriming as a critical endogenous protective mechanism against reperfusion injury. Methods: We explored mechanisms of PMN priming and neurotoxicity with in vivo modeling of systemic inflammation after brain ischemia-reperfusion as well as cellular culture experiments. Using transgenic mice overexpressing the human antioxidant gene superoxide dismutase 3 in the lung (TgSOD3), we tested the hypothesis that manipulation of the lung’s redox environment could mitigate PMN activation and post-ischemic brain injury. Injury was induced by occlusion of the common carotid and basilar arteries followed by reperfusion and lipopolysaccharide-induced systemic inflammation. To assess cell interactions using live microscopy, we cultured primary cortical neurons after oxygen-glucose deprivation (OGD) with primed PMNs from wild-type or TgSOD3 mice. Results: Our results show that pulmonary SOD3 protects against peripheral PMN activation, lung injury, brain injury, and neuroinflammation after ischemia/reperfusion with systemic inflammation. We also found that PMNs from TgSOD3 mice are less toxic to post-OGD cultures compared to wild-type PMNs. Our data indicate that direct cell-cell contact is required for PMN-dependent neurotoxicity in mixed cellular cultures and that pre-exposure of neurons to OGD amplifies this response. Analyses reveal that PMNs effect a considerable degree of neuritic damage in vitro , while in vivo modeling demonstrates cortical injury, blood-brain barrier compromise, PMN activation, and lung injury after reperfusion. Conclusion: Collectively, these studies expand our understanding of PMN-dependent mechanisms in post-ischemic toxicity, both directly on neurons and via effects on CNS inflammation, and argue that the inflammatory milieu within the lung may modulate CNS reperfusion injury via manipulation of peripheral PMN priming.

Blockade of Store-Operated Calcium Entry Reduces IL-17/TNF Cytokine-Induced Inflammatory Response in Human Myoblasts.

Muscle inflammation as in idiopathic inflammatory myopathies (IIM) leads to muscle weakness, mononuclear cell infiltration, and myofiber dysfunction affecting calcium channels. The effects of interleukin-17A (IL-17) and tumor necrosis factor-α (TNFα) on inflammation and calcium changes were investigated in human myoblasts. Human myoblasts were exposed to IL-17 and/or TNFα with/without store-operated Ca2+ entry (SOCE) inhibitors (2-ABP or BTP2). For co-cultures, peripheral blood mononuclear cells (PBMC) from healthy donors activated or not with phytohemagglutinin (PHA) were added to myoblasts at a 5:1 ratio. IL-17 and TNFα induced in synergy CCL20 and IL-6 production by myoblasts (>14-fold). PBMC-myoblast co-cultures enhanced CCL20 and IL-6 production in the presence or not of PHA compared to PBMC or myoblast monocultures. Anti-IL-17 and/or anti-TNFα decreased the production of IL-6 in co-cultures (p < 0.05). Transwell system that prevents direct cell-cell contact reduced CCL20 (p < 0.01) but not IL-6 secretion. IL-17 and/or TNFα increased the level of the ER stress marker Grp78, mitochondrial ROS and promoted SOCE activation by 2-fold (p < 0.01) in isolated myoblasts. SOCE inhibitors reduced the IL-6 production induced by IL-17/TNFα. Therefore, muscle inflammation induced by IL-17 and/or TNFα may increase muscle cell dysfunction, which, in turn, increased inflammation. Such close interplay between immune and non-immune mechanisms may drive and increase muscle inflammation and weakness.

Characterisation of a functional rat hepatocyte spheroid model

Many in vitro liver cell models, such as 2D systems, that are used to assess the hepatotoxic potential of xenobiotics suffer major limitations arising from a lack of preservation of physiological phenotype and metabolic competence. To circumvent some of these limitations there has been increased focus on producing more representative 3D models. Here we have used a novel approach to construct a size-controllable 3D hepatic spheroid model using freshly isolated primary rat hepatocytes (PRH) utilising the liquid-overlay technique whereby PRH spontaneously self-assemble in to 3D microtissues. This system produces viable spheroids with a compact in vivo-like structure for up to 21 days with sustained albumin production for the duration of the culture period. F-actin was seen throughout the spheroid body and P-glycoprotein (P-gp) and multidrug resistance-associated protein 2 (MRP2) transporters had polarised expression on the canalicular membrane of hepatocytes within the spheroids upon formation (day 3). The MRP2 transporter was able to functionally transport 5 μM 5-chloromethylfluorescein diacetate (CMFDA) substrates into these canalicular structures. These PRH spheroids display in vivo characteristics including direct cell-cell contacts, cellular polarisation, 3D cellular morphology, and formation of functional secondary structures throughout the spheroid. Such a well-characterised system could be readily exploited for pre-clinical and non-clinical repeat-dose investigations and could make a significant contribution to replace, reduce and refine the use of animals for applied research.

Human Bone Marrow Derived Mesenchymal Stromal Cells Enhance the Number and Function of Umbilical Cord Blood Peripheral Tregs during IL-2 Driven Ex Vivo Expansion

Tumor growth factor β (TGF-β)-induced peripheral regulatory T cells (pTreg) are a promising therapeutic cell source that exhibit Foxp3 expression and suppressive functions similar to natural regulatory T cells. Nonetheless, their clinical potential is limited by the instability of Foxp3 expression and T cell exhaustion that occurs during ex vivo expansion. We postulated that mesenchymal stromal cells (MSCs) could enhance the number, function and Foxp3 expression stability of pTregs during IL-2 driven 21 day expansion due to their diverse immunomodulatory properties. In this study, we observed that use of a human bone marrow mesenchymal stromal cells (hBM-MSC) platform significantly enhanced the number of pTreg during IL-2 driven 21 day ex vivo expansion vs. standard suspension culture condition (MSC platform: 80.2 x 106 vs. IL2/media: 39.3 x 106, n=6; p<0.01). Also the number of pTreg expressing a naive phenotype (CD4+CD45RA+ and CD4+CD62L+ ) were significantly increased (CD45RA+; MSC platform: 74.4 ± 1.6 x 106 vs. IL2/media: 45.9 ± 2.9 x 106, n=6, p<0.001; CD62L+; MSC platform: 79.1 ± 1.3 x 106 vs. IL2/media: 54.5 ± 2.1 x 106, n=6, p<0.001), as well as stability of Foxp3 expression (IL-2/media: 88.2 ± 1.7% vs. MSC platform: 96.2 ± 1.1%, n=7; p<0.05). In addition, pTreg suppressive function was noted to be more potent during 21 day IL-2 driven ex vivo expansion compared to standard IL-2/media culture condition (MSC platform: 79% vs. media: 35% inhibition of T cell proliferation in 10:1 ratio, n=6; p<0.01). pTreg expanded over a hBM-MSC platform exhibited higher surface CD25, CTLA-4, and ICOS MFI expression (CD25; MSC platform: 1410 vs. Media: 774; p<0.001, CTLA-4; MSC platform: 1084 vs. Media: 318; p<0.001, ICOS; MSC platform: 4386 vs. Media: 2641, p<0.01, n=6). Notably, hBM-MSC enhancement of pTreg ex vivo expansion requires direct cell-cell contact, as Foxp3 expression in pTreg was not enhanced by hBM-MSC conditioned media (CM:73.4 ± 6.8% vs. MSC platform: 96.2 ± 1.0%, p<0.001; and IL2/media: 88.8 ± 1.6% vs. MSC platform: 96.2 ± 1.0%, p<0.01) nor in a trans-well culture experiments (Transwell: 83.4 ± 2.5% vs. IL2/media: 88.8 ± 1.6%; and Transwell: 83.4 ± 2.5% vs. MSC platform: 96.2 ± 1.0%, p<0.01). Importantly, optical sectioning microscopy and flow cytometry revealed that hBM-MSC supports Treg number and function via direct contact-dependent mitochondrial transfer (Figure 1A-B). Cytochalasin B treatment blocked mitochondrial transfer, suggesting that tunneling nanotubes (TNT) facilitate mitochondrial transfer from hBM-MSC to pTreg during IL-2 driven ex vivo expansion (Mock: 2208 ± 122.1 vs. Cyto B: 923.8 ± 89 MFI, n=6, p<0.0001). Moreover, the quantity of ATP (n=6; p<0.01) mitochondrial potential of pTreg (MSC platform: 9010 ± 224.5 vs. media: 7316 ± 122.7 MFI, n=6; p<0.01) were significantly enhanced in pTreg during IL-2 driven ex vivo expansion over a hBM-MSC platform. Taken together, hBM-MSC significantly improves the number, maturation, and function of pTreg during 21 day IL-2 driven ex vivo expansion. We have identified one key mechanism of action of hBM-MSC underlying these favorable effects on pTreg during ex vivo expansion to be mitochondrial transfer via TNT. Notably, these studies identify a novel role of hBM-MSC to overcome current limitations in IL-2/media suspension culture conditions including T cell senescence, and loss of Foxp3 expression. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Human Double-Negative Regulatory T Cells Modulate Effector Functions of Conventional T Cells By Selectively Blocking mTOR Signaling

Regulatory T cells play an important role in the maintenance of immune tolerance to self-antigens and are involved in modulating immune responses to promote resolution of inflammation. The population of TCRαβ+ CD4-/CD8- (double-negative, DN) T cells has attracted growing attention as a result of their potent immune regulatory function. In murine models, DN T cells were able to prevent rejection of allogeneic and xenogeneic organ grafts by effectively suppressing reactive T cells. In addition, DN T cells possess the capacity to resolve various inflammatory conditions, including graft-versus-host disease (GvHD) after allogeneic hematopoietic stem cell transplantation. Notably, first clinical studies in patients after stem cell transplantation demonstrated an inverse correlation between the frequency of circulating DN T cells and the severity of acute GvHD, suggesting a therapeutic potential of human DN T cells. To gain a better understanding of the molecular mechanism of suppression, we investigated whether human DN T cells modulate distinct signaling processes in conventional T cells. We found that DN T cells selectively block mTOR signaling but not activation of mitogen-activated protein kinases. Enforced activation of the mTOR pathway by a chemical activator rendered conventional T cells unsusceptible to DN T cell-mediated suppression, confirming the critical function of mTOR signaling. Given that mTOR is a major regulator of cellular metabolism, we further determined the impact of DN T cells on the metabolic framework of conventional T cells. Of interest, DN T cells diminished upregulation of the glycolytic machinery and glucose uptake in conventional T cells, whereas fatty acid uptake was not modified. Next, we investigated the fate and function of effector cells after DN T cell co-culture. Of importance, DN T cells suppressed proliferation but also altered expression of differentiation markers, transcription factors and homing receptors. Further analyses demonstrated that CD4+ T cells failed to produce effector cytokines IL-17 and IFN-γ after coculture with DN T cells, whereas IL-2 secretion was amplified. The selective modification was induced by a direct cell-cell contact dependent mechanism between CD4 and DN T cells and not as a consequence of competition for nutrients or growth factors. Together, our findings expand the understanding of DN T cell functionality and support that human DN T cells represent an interesting opportunity to limit and modulate T-cell reactivity. DisclosuresNo relevant conflicts of interest to declare.

Preconditioning of bone marrow-derived mesenchymal stem cells highly strengthens their potential to promote IL-6-dependent M2b polarization

BackgroundDuring the last decade, mesenchymal stem cells (MSCs) have gained much attention in the field of regenerative medicine due to their capacity to differentiate into different cell types and to promote immunosuppressive effects. However, the underlying mechanism of MSC-mediated immunoregulation is not fully understood so far. Macrophages are distinguished in classical activated, pro-inflammatory M1 and alternatively activated M2 cells, which possess different functions and transcriptional profiles with respect to inflammatory responses. As polarization is not fixed, macrophage functional plasticity might be modulated by the microenvironment allowing them to rapidly react to danger signals and maintaining tissue homeostasis.MethodsMurine MSCs were preconditioned with IL-1ß and IFN-ɣ to enhance their immunosuppressive capacity regarding macrophage polarization under M1- and M2a-polarizing conditions. Macrophage polarization was analyzed by real-time PCR, flow cytometry, and cytokine detection in culture supernatants. The role of MSC-derived nitric oxide (NO), prostaglandin E2 (PGE2), and IL-6 in this process has been evaluated using siRNA transfection and IL-6 receptor-deficient macrophages, respectively.ResultsPreconditioned, but not unprimed, MSCs secreted high levels of NO, IL-6, and PGE2. Co-culture with macrophages (M0) in the presence of M1 inducers (LPS + IFN-ɣ) led to significant reduction of CD86 and iNOS protein in macrophages and diminished TNF-α secretion. Additionally, CD86 and iNOS protein expression as well as NO and IL-10 secretion were markedly increased under M2a-polarizing culture conditions (IL-4). MSC-dependent macrophage polarization did not depend on direct cell-cell contact. Co-culturing in the presence of LPS and IFN-ɣ resulted in the upregulation of M2a, M2b, and M2c marker genes, whereas in the presence of IL-4 only M2b markers were significantly increased. In turn, IL-10-producing regulatory M2b cells significantly inhibited IFN-ɣ expression in CD4+ T lymphocytes. Finally, we show that MSC-mediated macrophage polarization strongly depends on IL-6, whereas a minor role for NO and PGE2 was found.ConclusionsPreconditioning of MSCs highly strengthens their capacity to regulate macrophage features and to promote immunosuppression. Repression of M1 polarization during inflammation and M2b polarization under anti-inflammatory conditions strongly depend on functional IL-6 signaling in macrophages. The potential benefit of preconditioned MSCs and IL-6 should be considered for future clinical treatment.

Bone Marrow Cells Inhibit BMP-2-Induced Osteoblast Activity in the Marrow Environment.

Bone morphogenetic protein 2 (BMP-2) is widely known as a potent growth factor that promotes bone formation. However, an increasing number of studies have demonstrated side effects of BMP-2 therapy. A deeper understanding of the effect of BMP-2 on cells other than those involved directly in bone remodeling is of fundamental importance to promote a more effective delivery of BMP-2 to patients. In this study, we aimed to investigate the effect of BMP-2 in the marrow environment. First, BMP-2 adsorbed onto titanium implants was delivered at the tooth extraction socket (marrow-absent site) or in the mandible marrow of beagle dogs. BMP-2 could induce marked bone formation around the implant at the tooth extraction socket. Surprisingly, however, no bone formation was observed in the BMP-2-coated titanium implants inserted in the mandible marrow. In C57BL/6 mice, BMP-2 adsorbed in freeze-dried collagen pellets could induce bone formation in marrow-absent calvarial bone. However, similar to the canine model, BMP-2 could not induce bone formation in the femur marrow. Analysis of osteoblast differentiation using Col1a1(2.3)-GFP transgenic mice revealed a scarce number of osteoblasts in BMP-2-treated femurs, whereas in the control group, osteoblasts were abundant. Ablation of femur marrow recovered the BMP-2 ability to induce bone formation. In vitro experiments analyzing luciferase activity of C2C12 cells with the BMP-responsive element and alkaline phosphatase activity of MC3T3-E1 osteoblasts further revealed that bone marrow cells inhibit the BMP-2 effect on osteoblasts by direct cell-cell contact. Collectively, these results showed that the effect of BMP-2 in inducing bone formation is remarkably repressed by marrow cells via direct cell-cell contact with osteoblasts; this opens new perspectives on the clarification of the side-effects associated with BMP-2 application. © 2018 American Society for Bone and Mineral Research.

Eph/ephrin family anchored on exosome facilitate communications between cells.

Interactions of Ephrins and Eph receptors at cell membranes play crucial role in boundary formation and axon guidance. Extracellular vesicles (EVs), such as exosomes, are formed by cells communicating with each other in paracrine or endocrine manner. Until now, it is thought that direct cell-cell contact is necessary for ephrin and Eph receptor signal transduction. In this review, we discuss recent data that indicate the existence of a novel Eph-ephrin family anchored exosome signaling pathway in long-range intercellular communication and provide evidence that this type of signaling elicits cellular responses in cancer cells, independent of juxtacrine interactions. We emphasize that exosome-anchored Eph/ephrin involves a variety of biological processes and transduction signals, which may serve as a potential diagnostic biomarker.

Cardiosphere-derived cells suppress allogeneic lymphocytes by production of PGE2 acting via the EP4 receptor

Cardiosphere-derived cells (CDCs) are a cardiac progenitor cell population, which have been shown to possess cardiac regenerative properties and can improve heart function in a variety of cardiac diseases. Studies in large animal models have predominantly focussed on using autologous cells for safety, however allogeneic cell banks would allow for a practical, cost-effective and efficient use in a clinical setting. The aim of this work was to determine the immunomodulatory status of these cells using CDCs and lymphocytes from 5 dogs. CDCs expressed MHC I but not MHC II molecules and in mixed lymphocyte reactions demonstrated a lack of lymphocyte proliferation in response to MHC-mismatched CDCs. Furthermore, MHC-mismatched CDCs suppressed lymphocyte proliferation and activation in response to Concanavalin A. Transwell experiments demonstrated that this was predominantly due to direct cell-cell contact in addition to soluble mediators whereby CDCs produced high levels of PGE2 under inflammatory conditions. This led to down-regulation of CD25 expression on lymphocytes via the EP4 receptor. Blocking prostaglandin synthesis restored both, proliferation and activation (measured via CD25 expression) of stimulated lymphocytes. We demonstrated for the first time in a large animal model that CDCs inhibit proliferation in allo-reactive lymphocytes and have potent immunosuppressive activity mediated via PGE2.

Human mast cells promote colon cancer growth via bidirectional crosstalk: studies in 2D and 3D coculture models

ABSTRACT Chronic inflammation drives the development of colorectal cancer (CRC), where tumor-infiltrating immune cells interact with cancer cells in a dynamic crosstalk. Mast cells (MC), one of earliest recruited immune cells, accumulate in CRC tissues and their density is correlated with cancer progression. However, the exact contribution of MC in CRC and their interaction with colon cancer cells is poorly understood. Here, we investigated the impact of primary human MC and their mediators on colon cancer growth using 2D and 3D coculture models. Primary human MC were generated from peripheral CD34+ stem cells. Transwell chambers were used to analyze MC chemotaxis to colon cancer. Colon cancer cells HT29 and Caco2 differentially recruited MC by releasing CCL15 or SCF, respectively. Using BrdU proliferation assays, we demonstrated that MC can directly support colon cancer proliferation and this effect was mediated by their cellular crosstalk. 3D coculture models with cancer spheroids further confirmed the pro-tumor effect of MC on colon cancer growth, where direct cell-cell contact is dispensable and increased production of multiple soluble mediators was detected. Moreover, TLR2 stimulation of MC promoted stronger growth of colon cancer spheroids. By examining the transcriptome profile of colon cancer-cocultured MC versus control MC, we identified several MC marker genes, which were deregulated in expression. Our study provides an advanced in vitro model to investigate the role of human MC in cancer. Our data support the detrimental role of MC in CRC development and provide a molecular insight into the cellular crosstalk between MC and colon cancer cells.

Human T cells modulate myeloid-derived suppressor cells through a TNF-α-mediated mechanism

Myeloid-derived suppressor cells (MDSC) represent an innate immune cell subset capable of suppressing T-cell responses in cancer and chronic inflammation. While the effect of MDSC on T cells has been defined thoroughly, the reciprocal impact of T cells on MDSC homeostasis remains poorly understood. Therefore, we comprehensively analyzed the effect of different T-cell subsets on the generation and survival of human MDSC. Using an in vitro MDSC generation assay, we demonstrate that unstimulated CD4+, but not CD8+ T cells, induce polymorphonuclear MDSC (PMN-MDSC) from CD33+ myeloid cells. This effect was dependent on direct cell-cell contact and required TNF-α signaling. Soluble TNF-α was dispensable for PMN-MDSC generation, suggesting that transmembrane TNF-α is involved in that trans-cellular process. Stimulated human CD3+ T cells delayed the apoptosis of PMN-MDSC, which was independent of TNF-α signaling or direct cell-cell contact, but was recapitulated by IL-2. Taken together, our study shows that human T cells modulate MDSC generation and survival through two distinct mechanisms and thereby fine-tune the homeostasis of human MDSC in a regulated manner.

PrgB promotes aggregation, biofilm formation, and conjugation through DNA binding and compaction.

Gram-positive bacteria deploy type IV secretion systems (T4SSs) to facilitate horizontal gene transfer. The T4SSs of Gram-positive bacteria rely on surface adhesins as opposed to conjugative pili to facilitate mating. Enterococcus faecalis PrgB is a surface adhesin that promotes mating pair formation and robust biofilm development in an extracellular DNA (eDNA) dependent manner. Here, we report the structure of the adhesin domain of PrgB. The adhesin domain binds and compacts DNA in vitro. In vivo PrgB deleted of its adhesin domain does not support cellular aggregation, biofilm development and conjugative DNA transfer. PrgB also binds lipoteichoic acid (LTA), which competes with DNA binding. We propose that PrgB binding and compaction of eDNA facilitates cell aggregation and plays an important role in establishment of early biofilms in mono- or polyspecies settings. Within these biofilms, PrgB mediates formation and stabilization of direct cell-cell contacts through alternative binding of cell-bound LTA, which in turn promotes establishment of productive mating junctions and efficient intra- or inter-species T4SS-mediated gene transfer.