Surface CD52, CD84, and PTGER2 mark mature PMN-MDSCs from cancer patients and G-CSF-treated donors.

Precise molecular characterization of circulating polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) is hampered by their mixed composition of mature and immature cells and lack of specific markers. Here, we focus on mature CD66b+CD10+CD16+CD11b+ PMN-MDSCs (mPMN-MDSCs) from either cancer patients or healthy donors receiving G-CSF for stem cell mobilization (GDs). By RNA sequencing (RNA-seq) experiments, we report the identification of a distinct gene signature shared by the different mPMN-MDSC populations under investigation, also validated in mPMN-MDSCs from GDs and tumor-associated neutrophils (TANs) by single-cell RNA-seq (scRNA-seq) experiments. Analysis of such a gene signature uncovers a specific transcriptional program associated with mPMN-MDSC differentiation and allows us to identify that, in patients with either solid or hematologic tumors and in GDs, CD52, CD84, and prostaglandin E receptor 2 (PTGER2) represent potential mPMN-MDSC-associated markers. Altogether, our findings indicate that mature PMN-MDSCs distinctively undergo specific reprogramming during differentiation and lay the groundwork for selective immunomonitoring, and eventually targeting, of mature PMN-MDSCs.

HPV-associated head and neck cancer is characterized by distinct profiles of CD8+ T cells and myeloid-derived suppressor cells.

Patients with HPV--localized head and neck cancer (HNC) show inferior outcomes after surgery and radiochemotherapy compared to HPV-associated cancers. The underlying mechanisms remain elusive, but differences in immune status and immune activity may be implicated. In this study, we analyzed immune profiles of CD8+ T cells and myeloid-derived suppressor cells (MDSC) in HPV+ versus HPV- disease.The overall frequency of CD8+ T cells was reduced in HNC versus healthy donors but substantially increased after curative therapy (surgery and/or radiochemotherapy). In HPV+ patients, this increase was associated with significant induction of peripheral blood CD8+/CD45RA-/CD62L- effector memory cells. The frequency of HPV-antigen-specific CD8+ cells was low even in patients with virally associated tumors and dropped to background levels after curative therapy. Pre-therapeutic counts of circulating monocytic MDSC, but not PMN-MDSC, were increased in patients with HPV- disease. This increase was accompanied by reduced fractions of terminally differentiated CD8+ effector cells. HPV- tumors showed reduced infiltrates of CD8+ and CD45RO+ immune cells compared with HPV+ tumors. Importantly, frequencies of tumor tissue-infiltrating PMN-MDSC were increased, while percentages of Granzyme B+ and Ki-67+ CD8 T cells were reduced in patients with HPV- disease.We report differences in frequencies and relative ratios of MDSC and effector T cells in HPV- HNC compared with more immunogenic HPV-associated disease. Our data provide new insight into the immunological profiles of these two tumor entities and may be utilized for more tailored immunotherapeutic approaches in the future.

Immunotherapy-induced cytotoxic T follicular helper cells reduce numbers of retrovirus-infected reservoir cells in B cell follicles.

Antiretroviral therapy (ART) transformed HIV from a life-threatening disease to a chronic condition. However, eliminating the virus remains an elusive therapy goal. For several decades, Friend virus (FV) infection serves as a murine model to study retrovirus immunity. Similar to HIV, FV persists at low levels in lymph nodes B cell follicles avoiding elimination by immune cells. Such immune-privileged reservoirs exclude cytotoxic T cells from entry. However, CXCR5+ T cells are permitted to traffic through germinal centers. This marker is predominantly expressed by CD4+ follicular helper T cells (Tfh). Therefore, we explored immunotherapy to induce cytotoxic Tfh, which are rarely found under physiological conditions. The TNF receptor family member CD137 was first identified as a promising target for cancer immunotherapy. We demonstrated that FV-infected mice treatment with αCD137 antibody resulted in an induction of the cytotoxic program in Tfh. The therapy significantly increased numbers of cytotoxic Tfh within B cell follicles and contributed to viral load reduction. Moreover, αCD137 antibody combined with ART delayed virus rebound upon treatment termination without disturbing the lymph node architecture or antibody responses. Thus, αCD137 antibody therapy might be a novel strategy to target the retroviral reservoir and an interesting approach for HIV cure research.

Immunological priming of mesenchymal stromal/stem cells and their extracellular vesicles augments their therapeutic benefits in experimental graft-versus-host disease via engagement of PD-1 ligands.

Mesenchymal stromal cells (MSCs) and their extracellular vesicles (EVs) exert profound anti-inflammatory and regenerative effects in inflammation and tissue damage, which makes them an attractive tool for cellular therapies. In this study we have assessed the inducible immunoregulatory properties of MSCs and their EVs upon stimulation with different combinations of cytokines. First, we found that MSCs primed with IFN-γ, TNF-α and IL-1ß, upregulate the expression of PD-1 ligands, as crucial mediators of their immunomodulatory activity. Further, primed MSCs and MSC-EVs, compared to unstimulated MSCs and MSC-EVs, had increased immunosuppressive effects on activated T cells and mediated an enhanced induction of regulatory T cells, in a PD-1 dependent manner. Importantly, EVs derived from primed MSCs reduced the clinical score and prolonged the survival of mice in a model of graft-versus-host disease. These effects could be reversed in vitro and in vivo by adding neutralizing antibodies directed against PD-L1 and PD-L2 to both, MSCs and their EVs. In conclusion, our data reveal a priming strategy that potentiates the immunoregulatory function of MSCs and their EVs. This concept also provides new opportunities to improve the clinical applicability and efficiency of cellular or EV-based therapeutic MSC products.

Macrophage-Orbital Fibroblast Interaction and Hypoxia Promote Inflammation and Adipogenesis in Graves' Orbitopathy.

The inflammatory eye disease Graves' orbitopathy (GO) is the main complication of autoimmune Graves' disease. In previous studies we have shown that hypoxia plays an important role for progression of GO. Hypoxia can maintain inflammation by attracting inflammatory cells such as macrophages (MQ). Herein, we investigated the interaction of MQ and orbital fibroblasts (OF) in context of inflammation and hypoxia. We detected elevated levels of the hypoxia marker HIF-1α, the MQ marker CD68, and inflammatory cytokines TNFα, CCL2, CCL5, and CCL20 in GO biopsies. Hypoxia stimulated GO tissues to release TNFα, CCL2, and CCL20 as measured by multiplex enzyme-linked immunosorbent assay (ELISA). Further, TNFα and hypoxia stimulated the expression of HIF-1α, CCL2, CCL5, and CCL20 in OF derived from GO tissues. Immunofluorescence confirmed that TNFα-positive MQ were present in the GO tissues. Thus, interaction of M1-MQ with OF under hypoxia also induced HIF-1α, CCL2, and CCL20 in OF. Inflammatory inhibitors etanercept or dexamethasone prevented the induction of HIF-1α and release of CCL2 and CCL20. Moreover, co-culture of M1-MQ/OF under hypoxia enhanced adipogenic differentiation and adiponectin secretion. Dexamethasone and HIF-1α inhibitor PX-478 reduced this effect. Our findings indicate that GO fat tissues are characterized by an inflammatory and hypoxic milieu where TNFα-positive MQ are present. Hypoxia and interaction of M1-MQ with OF led to enhanced secretion of chemokines, elevated hypoxic signaling, and adipogenesis. In consequence, M1-MQ/OF interaction results in constant inflammation and tissue remodeling. A combination of anti-inflammatory treatment and HIF-1α reduction could be an effective treatment option.

Proteomic and bioinformatic profiling of neutrophils in CLL reveals functional defects that predispose to bacterial infections.

Patients with chronic lymphocytic leukemia (CLL) typically suffer from frequent and severe bacterial infections. Although it is well known that neutrophils are critical innate immune cells facilitating the early defense, the underlying phenotypical and functional changes in neutrophils during CLL remain largely elusive. Using a murine adoptive transfer model of CLL, we demonstrate aggravated bacterial burden in CLL-bearing mice upon a urinary tract infection with uropathogenic Escherichia coli. Bioinformatic analyses of the neutrophil proteome revealed increased expression of proteins associated with interferon signaling and decreased protein expression associated with granule composition and neutrophil migration. Functional experiments validated these findings by showing reduced levels of myeloperoxidase and acidification of neutrophil granules after ex vivo phagocytosis of bacteria. Pathway enrichment analysis indicated decreased expression of molecules critical for neutrophil recruitment, and migration of neutrophils into the infected urinary bladder was significantly reduced. These altered migratory properties of neutrophils were also associated with reduced expression of CD62L and CXCR4 and correlated with an increased incidence of infections in patients with CLL. In conclusion, this study describes a molecular signature of neutrophils through proteomic, bioinformatic, and functional analyses that are linked to a reduced migratory ability, potentially leading to increased bacterial infections in patients with CLL.

TNF-α and IL-1ß sensitize human MSC for IFN-γ signaling and enhance neutrophil recruitment.

During inflammatory processes, tissue environmental cues are influencing the immunoregulatory properties of tissue-resident mesenchymal stem/stromal cells (MSC). In this study, we elucidated one of the molecular and cellular responses of human MSC exposed to combinations of inflammatory cytokines. We showed that during multi-cytokine priming by TNF-α, IL-1ß, and IFN-γ, IL-1ß further augmented the well-established immunoregulatory activity induced by TNF-α/IFN-γ. On the molecular level, TNF-α and IL-1ß enhanced the expression of IFN-γ receptor (IFN-γR) via NF 'kappa-light-chain-enhancer' of activated B-cells (NF-κΒ) signaling. In turn, enhanced responsiveness to IFN-γ stimulation activated STAT5 and p38-MAPK signaling. This molecular feedback resulted in an increased IL-8 release and augmented recruitment of polymorphonuclear granulocytes (PMN). Our study suggests the possibility that responses of MSC to multi-cytokine priming regimens may be exploited therapeutically to fine-tune inflammatory activity in tissues. This study elucidates molecular mechanisms underlying the immunological priming of mesenchymal stromal cells (MSC) and their interaction with neutrophils.

Immunophenotyping of Circulating Myeloid-Derived Suppressor Cells (MDSC) in the Peripheral Blood of Cancer Patients.

Myeloid-derived suppressor cells (MDSC) are a heterogeneous group of pathologically expanded myeloid cells with immunosuppressive activity. According to their phenotype, MDSC can be divided into three major subpopulations: early stage MDSC (e-MDSC), lacking myeloid lineage markers, monocytic MDSC (M-MDSC), and granulocytic MDSC (PMN-MDSC). Additionally, PMN-MDSC can be subdivided based on their activation and differentiation status, although it is not clear how this status contributes to immunosuppression and disease pathology. Here, we describe an immunophenotyping and gating strategy for the identification and isolation of MDSC subsets based on fluorescence-activated cell sorting. This method allows direct comparison of MDSC subsets in clinical settings.

Isolation of Human Circulating Myeloid-Derived Suppressor Cells and Analysis of Their Immunosuppressive Activity.

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of myeloid cells with potent immunosuppressive activity and characterized by a pathological state of activation. The T cell suppression assay is the most common method to evaluate the suppressive capacity of MDSC. Identifying the suppressive potential of different MDSC subsets within individual donors is key for understanding the biology of MDSC and their clinical relevance. Here we describe assays to ascertain and quantify the suppression of autologous T cells by human MDSC. These include the dye dilution proliferation assay for flow cytometry and the detection of IFNγ production by T cells using flow cytometry and sandwich ELISA.

Differential expansion of circulating human MDSC subsets in patients with cancer, infection and inflammation.

BACKGROUND: Myeloid-derived suppressor cells (MDSC) are a functional myeloid cell subset that includes myeloid cells with immune suppressive properties. The presence of MDSC has been reported in the peripheral blood of patients with several malignant and non-malignant diseases. So far, direct comparison of MDSC across different diseases and Centers is hindered by technical pitfalls and a lack of standardized methodology. To overcome this issue, we formed a network through the COST Action Mye-EUNITER (www.mye-euniter.eu) with the goal to standardize and facilitate the comparative analysis of human circulating MDSC in cancer, inflammation and infection. In this manuscript, we present the results of the multicenter study Mye-EUNITER MDSC Monitoring Initiative, that involved 13 laboratories and compared circulating MDSC subsets across multiple diseases, using a common protocol for the isolation, identification and characterization of these cells. METHODS: We developed, tested, executed and optimized a standard operating procedure for the isolation and immunophenotyping of MDSC using blood from healthy donors. We applied this procedure to the blood of almost 400 patients and controls with different solid tumors and non-malignant diseases. The latter included viral infections such as HIV and hepatitis B virus, but also psoriasis and cardiovascular disorders. RESULTS: We observed that the frequency of MDSC in healthy donors varied substantially between centers and was influenced by technical aspects such as the anticoagulant and separation method used. Expansion of polymorphonuclear (PMN)-MDSC exceeded the expansion of monocytic MDSC (M-MDSC) in five out of six solid tumors. PMN-MDSC expansion was more pronounced in cancer compared with infection and inflammation. Programmed death-ligand 1 was primarily expressed in M-MDSC and e-MDSC and was not upregulated as a consequence of disease. LOX-1 expression was confined to PMN-MDSC. CONCLUSIONS: This study provides improved technical protocols and workflows for the multi-center analysis of circulating human MDSC subsets. Application of these workflows revealed a predominant expansion of PMN-MDSC in solid tumors that exceeds expansion in chronic infection and inflammation.

Inflammation-driven activation of JAK/STAT signaling reversibly accelerates acute myeloid leukemia in vitro.

Acute myeloid leukemia (AML) is characterized by a high relapse rate and dismal long-term overall survival which is related to persistence of leukemia-initiating cells in their niche. Different animal models of myeloid malignancies reveal how neoplastic cells alter the structural and functional characteristics of the hematopoietic stem cell niche to reinforce malignancy. Understanding and disruption of the microenvironmental interactions with AML cells are a vital need. Malignant niches frequently go along with inflammatory responses, but their impact on cancerogenesis often remains unexplored. Here, we uncovered an aberrant production of inflammatory cytokines in untreated AML bone marrow that was proved to promote the proliferation of leukemia cells. This inflammatory response induced an activation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway in AML blasts as well as bone marrow stromal cells that also fostered leukemia proliferation. Inhibition of JAK/STAT signaling using the selective JAK1/2 inhibitor ruxolitinib resulted in significant antileukemic activity in AML in vitro which is mediated through both cell-autonomous and microenvironment-mediated mechanisms. However, in a xenograft transplantation model, monotherapy with ruxolitinib did not achieve substantial antileukemic activity, possibly suggesting a complementary function of JAK1/2 inhibition in AML.

Protocol to assess the suppression of T-cell proliferation by human MDSC.

Inhibition of T-cell proliferation is the most common approach to assess human myeloid-derived suppressor cell (MDSC) functions. However, diverse methodologies hinder the comparison of results obtained in different laboratories. In this chapter, we present a T-cell proliferation assay procedure based on allogeneic MDSC and T-cells that is potentially suitable to multi-center studies. The T-cells are isolated from non-cancerous donors and frozen for later use in different research groups. We observed that pure thawed T-cells showed poor proliferative capacities. To retain proliferation, T-cell-autologous mature dendritic cells are supplemented after thawing. MDSC are isolated from clinical samples and represent the sole variant between assays. Flow cytometry is used to assess T-cell proliferation by the dilution of a tracking dye.

Multidimensional imaging provides evidence for down-regulation of T cell effector function by MDSC in human cancer tissue.

A high intratumoral frequency of neutrophils is associated with poor clinical outcome in most cancer entities. It is hypothesized that immunosuppressive MDSC (myeloid-derived suppressor cell) activity of neutrophils against tumor-reactive T cells contributes to this effect. However, direct evidence for such activity in situ is lacking. Here, we used whole-mount labeling and clearing, three-dimensional (3D) light sheet microscopy and digital image reconstruction supplemented by 2D multiparameter immunofluorescence, for in situ analyses of potential MDSC-T cell interactions in primary human head and neck cancer tissue. We could identify intratumoral hotspots of high polymorphonuclear (PMN)-MDSC and T cell colocalization. In these areas, the expression of effector molecules Granzyme B and Ki67 in T cells was strongly reduced, in particular for T cells that were in close proximity or physically engaged with PMN-MDSC, which expressed LOX-1 and arginase I. Patients with cancer with evidence for strong down-regulation of T cell function by PMN-MDSC had significantly impaired survival. In summary, our approach identifies areas of clinically relevant functional interaction between MDSC and T cells in human cancer tissue and may help to inform patient selection in future combination immunotherapies.

High Salt Inhibits Tumor Growth by Enhancing Anti-tumor Immunity.

Excess salt intake could affect the immune system by shifting the immune cell balance toward a pro-inflammatory state. Since this shift of the immune balance is thought to be beneficial in anti-cancer immunity, we tested the impact of high salt diets on tumor growth in mice. Here we show that high salt significantly inhibited tumor growth in two independent murine tumor transplantation models. Although high salt fed tumor-bearing mice showed alterations in T cell populations, the effect seemed to be largely independent of adaptive immune cells. In contrast, depletion of myeloid-derived suppressor cells (MDSCs) significantly reverted the inhibitory effect on tumor growth. In line with this, high salt conditions almost completely blocked murine MDSC function in vitro. Importantly, similar effects were observed in human MDSCs isolated from cancer patients. Thus, high salt conditions seem to inhibit tumor growth by enabling more pronounced anti-tumor immunity through the functional modulation of MDSCs. Our findings might have critical relevance for cancer immunotherapy.

Chemoirradiated neutrophils and T cells differentially affect immune functions of APCs.

Extracorporeal photopheresis (ECP) is known as an immunomodulatory therapy with few side effects, which is mainly used in the treatment of cutaneous T cell lymphoma, graft-versus-host disease, and allograft rejection. During ECP, leukocytes are separated from whole blood by leukapheresis, subsequently chemoirradiated with 8-methoxypsoralen and UVA light, and re-infused into the patient. Although clinically effective, its mode of action has not been fully elucidated. In the present study, we analyzed the interaction of chemoirradiated neutrophils and CD3+ lymphocytes with APC in an in vitro model. We report that chemoirradiated CD3+ T cells induced increased expression of activation markers on dendritic cells (DC), macrophages, and monocytes. Coculture of chemoirradiated CD3+ T cells with these APC also led to significantly increased secretion of TNF-α. Although less pronounced, additional activation of APC took place when APC were stimulated with LPS or IFN-γ. In contrast, chemoirradiated neutrophils did not show activating effects on APC. The presence of chemoirradiated neutrophils during LPS and IFN-γ stimulation of DC rather diminished DC and macrophage activation. In line with these findings DC cocultured with chemoirradiated CD3+ T cells, but not neutrophils, showed significantly increased activation of CD3+ responder lymphocytes in a mixed lymphocyte reaction. With this study, we demonstrate that chemoirradiated leukocytes have differential indirect immunomodulatory effects. Whereas chemoirradiated CD3+ T cells activate APC, chemoirradiated neutrophils suppress activation of APC in the presence of other activating factors, suggesting that the composition of the ECP-treated buffy coat might be of importance for its immunomodulatory effects.

Clinical Relevance and Suppressive Capacity of Human Myeloid-Derived Suppressor Cell Subsets.

Purpose: Myeloid-derived suppressor cells (MDSC) are a heterogeneous group of pathologically expanded myeloid cells with immunosuppressive activity. In human disease, three major MDSC subpopulations can be defined as monocytic (M-MDSC), granulocytic [polymorphonuclear-MDSC (PMN-MDSC)], and early stage (e-MDSC), which lacks myeloid lineage markers of the former two subsets. The purpose of this study was to determine and compare the immunosuppressive capacity and clinical relevance of each of these subsets in patients with solid cancer.Experimental Design: The frequency of MDSC subsets in the peripheral blood was determined by flow cytometry in a cohort of 49 patients with advanced head and neck cancer (HNC) and 22 patients with urological cancers. Sorted and purified MDSC subsets were tested in vitro for their T-cell-suppressive capacity. Frequency of circulating MDSC was correlated with overall survival of patients with HNC.Results: A high frequency of PMN-MDSC most strongly correlated with poor overall survival in HNC. T-cell-suppressive activity was higher in PMN-MDSC compared with M-MDSC and e-MDSC. A subset of CD66b+/CD11b+/CD16+ mature PMN-MDSC displayed high expression and activity of arginase I, and was superior to the other subsets in suppressing proliferation and cytokine production of T cells in both cancer types. High levels of this CD11b+/CD16+ PMN-MDSC, but not other PMN-MDSC subsets, strongly correlated with adverse outcome in HNC.Conclusions: A subset of mature CD11b+/CD16+ PMN-MDSC was identified as the MDSC subset with the strongest immunosuppressive activity and the highest clinical relevance. Clin Cancer Res; 24(19); 4834-44. ©2018 AACR.

Activated Tissue-Resident Mesenchymal Stromal Cells Regulate Natural Killer Cell Immune and Tissue-Regenerative Function.

The interaction of mesenchymal stromal cells (MSCs) with natural killer (NK) cells is traditionally thought of as a static inhibitory model, whereby resting MSCs inhibit NK cell effector function. Here, we use a dynamic in vitro system of poly(I:C) stimulation to model the interaction of NK cells and tissue-resident MSCs in the context of infection or tissue injury. The experiments suggest a time-dependent system of regulation and feedback, where, at early time points, activated MSCs secrete type I interferon to enhance NK cell effector function, while at later time points TGF-ß and IL-6 limit NK cell effector function and terminate inflammatory responses by induction of a regulatory senescent-like NK cell phenotype. Importantly, feedback of these regulatory NK cells to MSCs promotes survival, proliferation, and pro-angiogenic properties. Our data provide additional insight into the interaction of stromal cells and innate immune cells and suggest a model of time-dependent MSC polarization and licensing.

Adenosine metabolism of human mesenchymal stromal cells isolated from patients with head and neck squamous cell carcinoma.

BACKGROUND: Mesenchymal stromal cells (MSC) are a major component of the tumor microenvironment in patients with head and neck squamous cell carcinoma (HNSCC). MSC display innate and regulatory immunologic functions, very similar to many hematopoietic 'classical' immune cells. Conversion of ATP to immunosuppressive adenosine is an immunosuppressive mechanism utilized by other hematopoietic immune cells. The present study explores the adenosine metabolism of tumor derived MSC in comparison to autologous MSC from non-malignant tissue. METHODS: From HNSCC patients (n=10), paired MSC were generated from tumor tissue (tMSC) and autologous healthy control tissue (cMSC). Differentiation properties and phenotype (CD105, CD73, CD39, CD90, CD26, CD29) were compared by flow cytometry. Production of immunosuppressive adenosine (ADO) by functionally active ectonucleotidases, CD39 and CD73, was determined by luminescence and mass spectrometry. Suppressive activity of ADO was tested in CFSE proliferation assays of isolated T-cells. Plasticity of cMSC was explored after incubation with tumor-cell conditioned media. RESULTS: Differentiation into osteogenic, chondrogenic and adipogenic directions was comparable in tMSC and cMSC. Expression of ectonucleotidases, CD39 and CD73, was decreased in tMSC as compared to corresponding cMSC, which correlated with decreased ATP metabolism in mass spectrometry. Proliferation of CD4+ T-cells was significantly suppressed by exogenous ADO. Tumor-conditioned medium was unable to down-regulate ADO production in cMSC. CONCLUSION: We identified MSC of the oropharyngeal mucosa as an important producer of exogenous ADO. In patients with HNSCC, reduced expression of ADO may contribute to excessive inflammation and tumor growth.

Human mesenchymal stromal/stem cells acquire immunostimulatory capacity upon cross-talk with natural killer cells and might improve the NK cell function of immunocompromised patients.

BACKGROUND: The suppressive effect of mesenchymal stromal/stem cells (MSCs) on diverse immune cells is well known, but it is unclear whether MSCs additionally possess immunostimulatory properties. We investigated the impact of human MSCs on the responsiveness of primary natural killer (NK) cells in terms of cytokine secretion. METHODS: Human MSCs were generated from bone marrow and nasal mucosa. NK cells were isolated from peripheral blood of healthy volunteers or of immunocompromised patients after severe injury. NK cells were cultured with MSCs or with MSC-derived conditioned media in the absence or presence of IL-12 and IL-18. C-C chemokine receptor (CCR) 2, C-C chemokine ligand (CCL) 2, and the interferon (IFN)-γ receptor was blocked by specific inhibitors or antibodies. The synthesis of IFN-γ and CCL2 was determined. RESULTS: In the absence of exogenous cytokines, trace amounts of NK cell-derived IFN-γ licensed MSCs for enhanced synthesis of CCL2. In turn, MSCs primed NK cells for increased release of IFN-γ in response to IL-12 and IL-18. Priming of NK cells by MSCs occurred in a cell-cell contact-independent manner and was impaired by inhibition of the CCR2, the receptor of CCL2, on NK cells. CD56(bright) NK cells expressed higher levels of CCR2 and were more sensitive to CCL2-mediated priming by MSCs and by recombinant CCR2 ligands than cytotoxic CD56(dim) NK cells. NK cells from severely injured patients were impaired in cytokine-induced IFN-γ synthesis. Co-culture with MSCs or with conditioned media from MSCs and MSC/NK cell co-cultures from healthy donors improved the IFN-γ production of the patients' NK cells in a CCR2-dependent manner. CONCLUSIONS: A positive feedback loop driven by NK cell-derived IFN-γ and MSC-derived CCL2 increases the inflammatory response of cytokine-stimulated NK cells not only from healthy donors but also from immunocompromised patients. Therapeutic application of MSCs or their soluble factors might thus improve the NK function after severe injury.

Orbital Fibroblasts From Graves' Orbitopathy Patients Share Functional and Immunophenotypic Properties With Mesenchymal Stem/Stromal Cells.

PURPOSE: In Graves' orbitopathy (GO), inflammation and expansion of the retrobulbar tissue are the result of a pathophysiologic process in which orbital fibroblasts (GO-Fs) are considered the central cell type. However, in a previous study we observed that GO-Fs expressed some of the consensus surface markers described for mesenchymal stem/stromal cells (MSC). In this study, we further elucidate the stem cell characteristics of GO-Fs by comparing them with orbital fat-derived mesenchymal stem cells. METHODS: We enriched primary human GO-MSCs and GO-Fs simultaneously from the same retrobulbar fat biopsies obtained during decompression surgery of GO patients. The biological characteristics of donor-matched GO-MSCs and -Fs were compared along criteria that define MSC: fibroblast-like growth, MSC surface marker profile, multilineage differentiation potential, and immunomodulatory functions. RESULTS: Application of a standardized isolation and expansion protocol yielded GO-MSCs, which showed plastic adherent fibroblast-like morphology and proliferated and produced hyaluronan similarly to GO-Fs. Both GO-MSCs and GO-Fs expressed orbital fat-derived stem cell surface markers CD29, CD44, CD71, CD73, CD90, CD105, and CD166 and were negative for CD31, CD34, CD45, CD146, and Stro-1 after ex vivo expansion. Further, GO-MSCs and GO-Fs displayed adipogenic, osteogenic, chondrogenic, myogenic, and neuronal differentiation, although GO-Fs with a lower capacity. In addition, when compared to GO-MSCs, the GO-Fs showed reduced T-cell suppression and secreted reduced amounts of IL-6, suggesting a lower immunosuppressive potential. CONCLUSIONS: The in vitro data obtained in this study provide the first experimental evidence that orbital fibroblasts derived from retrobulbar fat of GO patients share biological characteristics with MSCs. These findings provide new insight into the biology of key cells in GO.