Mesenchymal Stromal Cell Secretion of Programmed Death-1 Ligands Regulates T Cell Mediated Immunosuppression

Soluble PD-1 ligands regulate T-cell function in Waldenstrom macroglobulinemia

Although immune checkpoint molecules regulate the progression of certain cancers, their significance in malignant development of Waldenstrom macroglobulinemia (WM), an incurable low-grade B-cell lymphoma, remains unknown. Recently, cytokines in the bone marrow (BM) microenvironment are shown to contribute to the pathobiology of WM. Here, we investigated the impact of cytokines, including interleukin-6 (IL-6) and IL-21, on immune regulation and particularly on the programmed death-1 (PD-1) and its ligands PD-L1 and PD-L2. We showed that IL-21, interferon γ, and IL-6 significantly induced PD-L1 and PD-L2 gene expression in WM cell lines. Increased PD-L1 and PD-L2 messenger RNA was also detected in patients' BM cells. Patients' nonmalignant BM cells, including T cells and monocytes, showed increased PD-L1, but minimal or undetectable PD-L2 surface expression. There was also very modest PD-L1 and PD-L2 surface expression by malignant WM cells, suggesting that ligands are cleaved from the cell surface. Levels of soluble ligands were higher in patients' BM plasma and blood serum than controls. Furthermore, IL-21 and IL-6 increased secreted PD-L1 in the culture media of WM cell lines, implying that elevated levels of soluble PD-1 ligands are cytokine mediated. Soluble PD-1 ligands reduced T-cell proliferation, phosphorylated extracellular signal-regulated kinase and cyclin A levels, mitochondrial adenosine triphosphate production, and spare respiratory capacity. In conclusion, we identify that soluble PD-1 ligands are elevated in WM patients and, in addition to surface-bound ligands in WM BM, could regulate T-cell function. Given the capability of secreted forms to be bioactive at distant sites, soluble PD-1 ligands have the potential to promote disease progression in WM.

Comparison of Mesenchymal Stromal Cells From Different Origins for the Treatment of Graft-vs.-Host-Disease in a Humanized Mouse Model

Mesenchymal stromal cells (MSCs) have potent immunomodulatory properties that make them an attractive tool against graft- vs.-host disease (GVHD). However, despite promising results in phase I/II studies, bone marrow (BM-) derived MSCs failed to demonstrate their superiority over placebo in the sole phase III trial reported thus far. MSCs from different tissue origins display different characteristics, but their therapeutic benefits have never been directly compared in GVHD. Here, we compared the impact of BM-, umbilical cord (UC-), and adipose-tissue (AT-) derived MSCs on T-cell function in vitro and assessed their efficacy for the treatment of GVHD induced by injection of human peripheral blood mononuclear cells in NOD-scid IL-2Rγ^null HLA-A2/HHD mice. In vitro, resting BM- and AT-MSCs were more potent than UC-MSCs to inhibit lymphocyte proliferation, whereas UC- and AT-MSCs induced a higher regulatory T-cell (CD4⁺CD25⁺FoxP3⁺)/T helper 17 ratio. Interestingly, AT-MSCs and UC-MSCs activated the coagulation pathway at a higher level than BM-MSCs. In vivo, AT-MSC infusions were complicated by sudden death in 4 of 16 animals, precluding an analysis of their efficacy. Intravenous MSC infusions (UC- or BM- combined) failed to significantly increase overall survival (OS) in an analysis combining data from 80 mice (hazard ratio [HR] = 0.59, 95% confidence interval [CI] 0.32–1.08, P = 0.087). In a sensitivity analysis we also compared OS in control vs. each MSC group separately. The results for the BM-MSC vs. control comparison was HR = 0.63 (95% CI 0.30–1.34, P = 0.24) while the figures for the UC-MSC vs. control comparison was HR = 0.56 (95% CI 0.28–1.10, P = 0.09). Altogether, these results suggest that MSCs from various origins have different effects on immune cells in vitro and in vivo. However, none significantly prevented death from GVHD. Finally, our data suggest that the safety profile of AT-MSC and UC-MSC need to be closely monitored given their pro-coagulant activities in vitro.

Achievement of Tolerance Induction to Prevent Acute Graft-vs.-Host Disease

Acute graft-vs.-host disease (GVHD) limits the efficacy of allogeneic hematopoietic stem cell transplantation (allo-HSCT), a main therapy to treat various hematological disorders. Despite rapid progress in understanding GVHD pathogenesis, broad immunosuppressive agents are most often used to prevent and remain the first line of therapy to treat GVHD. Strategies enhancing immune tolerance in allo-HSCT would permit reductions in immunosuppressant use and their associated undesirable side effects. In this review, we discuss the mechanisms responsible for GVHD and advancement in strategies to achieve immune balance and tolerance thereby avoiding GVHD and its complications.

The mechanism of TDP-43 gene expression on inflammatory factors and the JNK and p38 MAPK signalling pathways in ischaemic hypoxic stress dependence

In this study, the mechanism of TDP-43 gene expression on inflammatory factors and Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) signalling pathways in ischaemic hypoxic stress dependence was investigated. Sixty SD rats were selected and divided into the control group, the osteoarthritis (OA) model group, and the TDP-43-mMSCs+OA group. In the OA model group and the TDP-43-mMSCs+OA group, OA was established by collagenase injection. Western blotting assays were used to detect the expression of TDP-43 in cartilage tissues of each rat. The secretion of tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in the serum of rats was determined by enzyme-linked immunosorbent assay (ELISA). The formation of cytoplasmic stress granules (SGs) and the expression of receptor for activated c-kinase 1 (RACK1) were detected by Western blotting assays in each group of rats. The expression of MTK1 and MAPKKK phosphorylation and changes in the JNK and p38 MAPK signalling pathways were detected by Western blotting assays. Compared with the control group, the expression of TDP-43 in the cartilage tissue of rats in the OA model group was significantly decreased. The expression of TDP-43 in the cartilage tissue of rats in the TDP-43-mMSCs+OA group was significantly higher than that of the control group and the OA model group, which indicates that TDP-43-mMSC transplantation was successful. Enzyme-linked immunosorbent assay results showed that the plasma TNF-α and IL-1β levels in the OA model group were significantly increased (P < 0.01) when compared with the control group. However, the secretion of TNF-α and IL-1β in the serum of the TDP-43-mMSCs+OA group was significantly lower than that of the model group (P < 0.01) but still higher than the control group. This indicates that overexpression of TDP-43 reduces the inflammatory response induced by OA. Western blotting assays showed that the amount of cytoplasmic SGs in the cartilage tissue of rats in the OA model group was significantly decreased when compared with the control group. The amount of SGs in the cartilage of rats in the TDP-43-mMSCs+OA group was significantly higher than that of the model group. The expression of RACK1 in the cartilage tissue of rats in the OA model group was significantly higher than that of the control group. Overexpression of the TDP-43 gene can interfere with the secretion of inflammatory factors and inhibit the activation of the JNK and p38 MAPK signalling pathways by ischaemic hypoxia stress. Thus, the molecular mechanism of chondrocytopathic lesions was reversed, which provided a new theoretical basis for the treatment of OA.

A single administration of human adipose tissue-derived mesenchymal stromal cells (MSC) induces durable and sustained long-term regulation of inflammatory response in experimental colitis

Current therapies for inflammatory bowel diseases (IBD) are aimed at controlling the exacerbated response in the gut, but no treatment is fully effective for many refractory patients. Mesenchymal stromal cells (MSC) are multi-potent cells with regulatory immunosuppressive activity that may control inflammatory diseases. In this study, we investigated the short- and especially the long-term protective effects of MSC on experimental colitis. We show that MSC elicited protection to acute intestinal inflammation with gain of weight, improvement in the clinical disease score and expressive reduction in the mortality rate of treated mice. MSC changed the population of neutrophils, eosinophils and augmented the frequency of CD4 T lymphocytes in the gut-draining lymph nodes, together with reduced accumulation of these cells in the colon intraepithelial compartment. Interestingly, there were increased levels of programmed death 1 (PD-1) and glucocorticoid-induced tumour necrosis factor receptor family-related receptor (GITR) in the spleen regulatory T cells of mice that received MSC treatment, which also presented a reversal in the pattern of immune response in the gut, with diminished inflammatory, T helper type 1 (Th1) and Th17 profile, in contrast to augmented Th2 responses. Most strikingly, this balanced response elicited by a single administration of MSC during the acute colitis persisted long-term, with restored goblet cells, eosinophils and maintenance of elevated gut interleukin (IL)-4, besides increased CD4⁺ CD25⁺ PD-1⁺ cells in the spleen and reduced Th17 response in mesenteric lymph nodes (MLN) of treated mice on day 60. Taken together, our findings provided a significant contribution to translational immunology by pointing human adipose tissue-derived MSC as a novel therapeutic approach with long-term beneficial regulatory effects in experimental colitis.

Clinical Use of Mesenchymal Stromal Cells in the Treatment of Acute Graft-versus-Host Disease

Acute graft-versus-host disease (aGvHD) continues to impact morbidity and mortality after allogeneic stem cell transplantation (allo-SCT). First-line therapy for aGvHD still remains the use of high-dose corticosteroids. Unfortunately, 40-60% of patients with aGvHD exhibit steroid resistance, which is associated with a very poor prognosis. As no effective second-line therapy existed, in recent decades various treatment options were considered for the treatment of therapy-refractory GvHD. Based on their in vitro immunomodulatory properties, the use of mesenchymal stromal cells (MSCs) in the treatment of aGvHD has been introduced. However, most of the clinical data are generated from uncontrolled trials and case series, showing clinical responses to MSCs. Clinical results are more consistent in children despite the use of MSC preparations of various provenance and manufacturing protocols. While these data support the therapeutic principle, the great variability of outcomes strongly suggests that not all MSC preparations are equal and that the specific manufacturing protocols influence therapeutic success in vivo.

Cymerus™ iPSC-MSCs significantly prolong survival in a pre-clinical, humanized mouse model of Graft-vs-host disease

The immune-mediated tissue destruction of graft-vs-host disease (GvHD) remains a major barrier to greater use of hematopoietic stem cell transplantation (HSCT). Mesenchymal stem cells (MSCs) have intrinsic immunosuppressive qualities and are being actively investigated as a therapeutic strategy for treating GvHD. We characterized Cymerus™ MSCs, which are derived from adult, induced pluripotent stem cells (iPSCs), and show they display surface markers and tri-lineage differentiation consistent with MSCs isolated from bone marrow (BM). Administering iPSC-MSCs altered phosphorylation and cellular localization of the T cell-specific kinase, Protein Kinase C theta (PKCθ), attenuated disease severity, and prolonged survival in a humanized mouse model of GvHD. Finally, we evaluated a constellation of pro-inflammatory molecules on circulating PBMCs that correlated closely with disease progression and which may serve as biomarkers to monitor therapeutic response. Altogether, our data suggest Cymerus iPSC-MSCs offer the potential for an off-the-shelf, cell-based therapy to treat GvHD.

Tumor-infiltrating mesenchymal stem cells: Drivers of the immunosuppressive tumor microenvironment in prostate cancer?

BACKGROUND

Prostate cancer is characterized by T-cell exclusion, which is consistent with their poor responses to immunotherapy. In addition, T-cells restricted to the adjacent stroma and benign areas are characterized by anergic and immunosuppressive phenotypes. In order for immunotherapies to produce robust anti-tumor responses in prostate cancer, this exclusion barrier and immunosuppressive microenvironment must first be overcome. We have previously identified mesenchymal stem cells (MSCs) in primary and metastatic human prostate cancer tissue.

METHODS

An Opal Multiplex immunofluorescence assay based on CD73, CD90, and CD105 staining was used to identify triple-labeled MSCs in human prostate cancer tissue. T-cell suppression assays and flow cytometry were used to demonstrate the immunosuppressive potential of primary MSCs expanded from human bone marrow and prostate cancer tissue from independent donors.

RESULTS

Endogenous MSCs were confirmed to be present at sites of human prostate cancer. These prostate cancer-infiltrating MSCs suppress T-cell proliferation in a dose-dependent manner similar to their bone marrow-derived counterparts. Also similar to bone marrow-derived MSCs, prostate cancer-infiltrating MSCs upregulate expression of PD-L1 and PD-L2 on their cell surface in the presence of IFNγ and TNFα.

CONCLUSION

Prostate cancer-infiltrating MSCs suppress T-cell proliferation similar to canonical bone marrow-derived MSCs, which have well-documented immunosuppressive properties with numerous effects on both innate and adaptive immune system function. Thus, we hypothesize that selective depletion of MSCs infiltrating sites of prostate cancer should restore immunologic recognition and elimination of malignant cells via broad re-activation of cytotoxic pro-inflammatory pathways.

IL-27 Promotes Human Placenta-Derived Mesenchymal Stromal Cell Ability To Induce the Generation of CD4+IL-10+IFN-γ+ T Cells via the JAK/STAT Pathway in the Treatment of Experimental Graft-versus-Host Disease

Human mesenchymal stromal cells (MSCs) harbor immunomodulatory properties to induce the generation of suppressive T cells. MSCs have been successfully used in treating graft-versus-host disease (GVHD) accompanied by abundant inflammatory cytokines such as IL-27. This study investigated the effects of IL-27 on the human placenta-derived MSCs (hPMSCs) to induce generation of CD4⁺IL-10⁺IFN-γ⁺ T cells in vitro and in the humanized xenogenic GVHD NOD/SCID model. The results showed that the percentages of CD4⁺IL-10⁺IFN-γ⁺ T cells were significantly increased in activated human PBMC from both healthy donors and GVHD patients with hPMSCs and in the liver and spleen of hPMSC-treated GVHD mice, and the level of CD4⁺IL-10⁺IFN-γ⁺ T cells in the liver was greater than that in the spleen in hPMSC-treated GVHD mice. The serum level of IL-27 decreased and the symptoms abated in hPMSC-treated GVHD. Further, in vitro results showed that IL-27 promoted the regulatory effects of hPMSCs by enhancing the generation of CD4⁺IL-10⁺IFN-γ⁺ T cells from activated PBMC. Activation occurred through increases in the expression of programmed death ligand 2 (PDL2) in hPMSCs via the JAK/STAT signaling pathway. These findings indicated that hPMSCs could alleviate GVHD mice symptoms by upregulating the production of CD4⁺IL-10⁺IFN-γ⁺ T cells in the spleen and liver and downregulating serum levels of IL-27. In turn, the ability of hPMSCs to induce the generation of CD4⁺IL-10⁺IFN-γ⁺ T cells could be promoted by IL-27 through increases in PDL2 expression in hPMSCs. The results of this study will be of benefit for the application of hPMSCs in clinical trials.

Trained murine mesenchymal stem cells have anti-inflammatory effect on macrophages, but defective regulation on T-cell proliferation

Mesenchymal stem cell (MSC)-mediated immunomodulation affects both innate and adaptive immune systems. These responses to environmental cues, such as pathogen-associated molecular patterns, damage-associated molecular patterns, or proinflammatory cytokines, are crucial for resolution of inflammation, as well as successful tissue healing and regeneration. We observed that intermittent, repeated exposure of MSCs to LPS induced stronger NF-κB activation than singular stimulation. A similar phenomenon, named innate immune memory or trained immunity, has been reported with macrophages. However, the potential regulation of "immune memory" in nonclassic immune cells, such as MSCs, has not been reported. In the current study, we chose IFN-γ plus TNF-α restimulation-induced iNOS expression as a model of MSC activation, because IFN-γ and TNF-α play crucial roles in MSC-mediated immunomodulation. The iNOS expression was enhanced in LPS-trained MSCs, 3 d after a washout period following primary stimulation. LPS-trained MSCs enhanced the anti-inflammatory (arginase 1 and CD206) marker expression, but decreased the proinflammatory marker (TNF-α, IL-1β, iNOS, and IL-6) expression using an MSC-macrophage coculture model. In contrast, LPS-trained MSCs demonstrated a defective regulation on CD4 T-cell proliferation. Mechanistic studies suggested that histone methylation and the JNK pathway are involved in LPS-trained immunomodulation in MSCs. Our results demonstrate differential immunomodulatory effects of trained MSCs on macrophages and T cells. These immunomodulatory consequences are critical, because they will have a major impact on current MSC-based cell therapies.-Lin, T., Pajarinen, J., Kohno, Y., Huang, J.-F., Maruyama, M., Romero-Lopez, M., Nathan, K., Yao, Z., Goodman, S. B. Trained murine mesenchymal stem cells have anti-inflammatory effect on macrophages, but defective regulation on T-cell proliferation.

Mesenchymal Stem Cells Ameliorate Hepatic Ischemia/Reperfusion Injury via Inhibition of Neutrophil Recruitment

Ischemia/reperfusion injury (IRI) remains a major problem in organ transplantation, which represents the main cause of graft dysfunction posttransplantation. Hepatic IRI is characterized by an excessive inflammatory response within the liver. Mesenchymal stem cells (MSCs) have been shown to be immunomodulatory cells and have the therapeutic action on IRI in several organs. However, the mechanism of regulatory effect of MSCs on IRI remains unclear. In the present study, we examined the impact of MSCs on hepatic inflammatory response such as neutrophil influx and liver damage in a rat model of 70% hepatic IRI. Treatment with MSCs protected rat against hepatic IRI, with significantly decreased serum levels of liver enzymes, attenuated hepatic neutrophil infiltration, reduced expression of apoptosis-associated proteins, and ameliorated liver pathological injury. MSCs also significantly enhanced the intracellular activation of p38 MAPK phosphorylation, which led to decreased expression of CXCR2 on the surface of neutrophils. In addition, MSCs significantly diminished neutrophil chemoattractant CXCL2 production by inhibiting NF-κB p65 phosphorylation in macrophages. These results demonstrate that MSCs significantly ameliorate hepatic IRI predominantly through its inhibitory effect on hepatic neutrophil migration and infiltration.

Human adipose‑derived mesenchymal stem cells promote breast cancer MCF7 cell epithelial‑mesenchymal transition by cross interacting with the TGF‑β/Smad and PI3K/AKT signaling pathways

The influence and underlying mechanisms of human adipose-derived stem cells (Hu-ADSCs) on breast cancer cells in the tumor microenvironment remain unclear. Understanding the association between Hu-ADSCs and cancer cells may provide targets for breast cancer treatment and reference for the clinical application of stem cells. Therefore, a Hu-ADSC and breast cancer MCF7 cell coculture system was established to investigate the paracrine effects of Hu-ADSCs on MCF7 cell migration and invasion, in addition to the potential mechanism of action by reverse transcription-quantitative polymerase chain reaction and western blotting. Hu-ADSCs enhanced MCF7 cell migration and invasion by decreasing the expression of epithelial marker E-cadherin, and increasing the expression of interstitial marker N-cadherin and epithelial-mesenchymal transition (EMT) transcription factors in vitro. The EMT effect of cocultured MCF7 cells was inhibited with the addition of anti-transforming growth factor (TGF)-β1 or phosphoinositide 3-kinase (PI3K) inhibitor LY294002, accompanied by a significant decrease in phosphorylated (p)-mothers against decapentaplegic homolog (Smad) and p-protein kinase B (AKT) expression. The data suggested that the paracrine effect of Hu-ADSCs in the tumor microenvironment promoted the EMT of MCF7 cells by cross interacting with the TGF-β/Smad and PI3K/AKT pathways.

The Rising Era of Immune Checkpoint Inhibitors in Myelodysplastic Syndromes

Myelodysplastic syndromes (MDS) are a heterogeneous group of diseases characterized by ineffective hematopoiesis and a wide spectrum of manifestations ranging from indolent and asymptomatic cytopenias to acute myeloid leukemia (AML). MDS result from genetic and epigenetic derangements in clonal cells and their surrounding microenvironments. Studies have shown associations between MDS and other autoimmune diseases. Several immune mechanisms have been identified in MDS, suggesting that immune dysregulation might be at least partially implicated in its pathogenesis. This has led to rigorous investigations on the role of immunomodulatory drugs as potential treatment options. Epigenetic modification via immune check point inhibition, while well established as a treatment method for advanced solid tumors, is a new approach being considered in hematologic malignancies including high risk MDS. Several trials are looking at the efficacy of these agents in MDS, as frontline therapy and in relapse, both as monotherapy and in combination with other drugs. In this review, we explore the utility of immune checkpoint inhibitors in MDS and current research evaluating their efficacy.

Immunogenic potential of human bone marrow mesenchymal stromal cells is enhanced by hyperthermia

BACKGROUND AIMS

Bone marrow-derived mesenchymal stromal cells (MSCs) have been reported to suppress T-cell proliferation and used to alleviate the symptoms of graft-versus-host disease (GVHD). MSCs are a mixed cell population and at this time there are no tools to isolate the cells responsible for the T-cell suppression. We wanted to find a way to enhance the immune-modulatory actions of MSCs and tried varying the temperature at which they were cultured.

METHODS

We cultured human MSCs derived from healthy volunteers at different temperatures and tested their ability to switch macrophage character from pro-inflammatory to anti-inflammatory (M1 type to M2 type). Using an enzyme-linked immunosorbent assay (ELISA), we showed that when MSCs are cultured at higher temperatures their ability to induce co-cultured macrophages to produce more interleukin-10, (IL-10) (an anti-inflammatory cytokine) and less tumor necrosis factor alpha, (TNFα) (a pro-inflammatory cytokine) is increased. We performed Western blots and immunocytochemistry to screen for changes that might underlie this effect.

RESULTS

We found that in hyperthermia the heat shock protein, HSF1, translocated into the nucleus of MSCs. It appears to induce the COX2/PGE2 (Cyclooxygenase2/Prostaglandin E2) pathway described earlier as a major mechanism of MSC-directed immune-suppression.

CONCLUSION

Hyperthermia increases the efficacy of MSC-driven immune-suppression. We propose that changing the time of MSC administration to patients to mid-to-late afternoon when the body temperature is naturally highest might be beneficial. Warming the patient could also be considered.

NF-KappaB Pathway Is Involved in Bone Marrow Stromal Cell-Produced Pain Relief

Bone marrow stromal cells (BMSCs) produce long-lasting attenuation of pain hypersensitivity. This effect involves BMSC's ability to interact with the immune system and activation of the endogenous opioid receptors in the pain modulatory circuitry. The nuclear factor kappa B (NF-κB) protein complex is a key transcription factor that regulates gene expression involved in immunity. We tested the hypothesis that the NF-κB signaling plays a role in BMSC-induced pain relief. We focused on the rostral ventromedial medulla (RVM), a key structure in the descending pain modulatory pathway, that has been shown to play an important role in BMSC-produced antihyperalgesia. In Sprague-Dawley rats with a ligation injury of the masseter muscle tendon (TL), BMSCs (1.5 M/rat) from donor rats were infused i.v. at 1 week post-TL. P65 exhibited predominant neuronal localization in the RVM with scattered distribution in glial cells. At 1 week, but not 8 weeks after BMSC infusion, western blot and immunostaining showed that p65 of NF-κB was significantly increased in the RVM. Given that chemokine signaling is critical to BMSCs' pain-relieving effect, we further evaluated a role of chemokine signaling in p65 upregulation. Prior to infusion of BMSCs, we transduced BMSCs with Ccl4 shRNA, incubated BMSCs with RS 102895, a CCR2b antagonist, or maraviroc, a CCR5 antagonist. The antagonism of chemokines significantly reduced BMSC-induced upregulation of p65, suggesting that upregulation of p65 was related to BMSCs' pain-relieving effect. We then tested the effect of a selective NF-κB activation inhibitor, BAY 11-7082. The mechanical hyperalgesia of the rat was assessed with the von Frey method. In the pre-treatment experiment, BAY 11-7082 (2.5 and 25 pmol) was injected into the RVM at 2 h prior to BMSC infusion. Pretreatment with BAY 11-7082 attenuated BMSCs' antihyperalgesia, but post-treatment at 5 weeks post-BMSC was not effective. On the contrary, in TL rats receiving BAY 11-7082 without BMSCs, TL-induced hyperalgesia was attenuated, consistent with dual roles of NF-κB in pain hypersensitivity and BMSC-produced pain relief. These results indicate that the NF-κB signaling pathway in the descending circuitry is involved in initiation of BMSC-produced behavioral antihyperalgesia.

Exosomes in perspective: a potential surrogate for stem cell therapy

Exosomes as a unique subtype of small extracellular vesicles (sEVs) have attracted increasing interest in recent years in the fields of mesenchymal stromal cell (MSC) research. Studies have confirmed that exosomes derived from MSCs preserve immunosuppressive phenotype and can mimic therapeutic benefits of their parent cells. This review briefly summarizes most recent findings on the potential of exosomes as an alternative of therapeutic MSCs, focusing on the role of MSCs and their secreted exosomes in regulation of immune cells, preclinical and clinical evidence of therapeutic outcomes of MSC exosomes, and the biodistribution and pharmacokinetic profile of systemically administered exosomes. It is appreciated that exosomes from MSCs of different sources have variable contents including inflammatory mediators, tropic factors, signaling molecules, and nucleic acids (DNA, mRNA, microRNA and long non-coding RNA). Diverse functions of exosomes derived from different sources are expected. More importantly, exosomes isolated in vitro may not mirror that from in vivo, where donor MSCs are exposed to specific disease or injury-related conditions. Simulating in vivo microenvironment by pretreatment of MSCs with relevant chemical mediators may lead to their secretion of therapeutically more efficient exosomes/sEVs. However, we know very little about the key molecules involved and the differences between exosomes released under different conditions. These issues would be of tremendous interest to preclinical research that pursues exosome biology-underlain therapeutic mechanisms of MSCs. Further studies are expected to demonstrate the superiority of MSC-derived exsomes/sEVs as a pharmaceutical entity with regard to efficacy, safety, and practicability.

Commitment to Aerobic Glycolysis Sustains Immunosuppression of Human Mesenchymal Stem Cells

Human mesenchymal stem cells (hMSCs) promote endogenous tissue repair in part by coordinating multiple components of the host immune system in response to environmental stimuli. Recent studies have shown that hMSCs are metabolically heterogeneous and actively reconfigure metabolism to support the biochemical demands of tissue repair. However, how hMSCs regulate their energy metabolism to support their immunomodulatory properties is largely unknown. This study investigates hMSC metabolic reconfiguration during immune activation and provides evidence that the hMSC metabolic state significantly influences their immunomodulatory properties. Specifically, hMSC immune polarization by interferon‐gamma (IFN‐γ) treatment leads to remodeling of hMSC metabolic pathways toward glycolysis, which is required to sustain the secretion of immunosuppressive factors. IFN‐γ exposure also inhibited mitochondrial electron transport activity, and the accumulation of mitochondrial reactive oxygen species plays an important signaling role in this metabolic reconfiguration. The results also show that activation of the Akt/mTOR signaling pathway is required for metabolic reconfiguration during immune polarization and that interruption of these metabolic changes alters the immune response in IFN‐γ licensed hMSCs. The results demonstrate the potential of altering hMSC metabolism to enhance their immunomodulatory properties and therapeutic efficacy in various diseases. Stem Cells Translational Medicine2019;8:93–106

Mesenchymal Stem Cells in Primary Sjögren's Syndrome: Prospective and Challenges

Primary Sjögren's syndrome (pSS) is a chronic systemic inflammatory autoimmune disease characterized by lymphocytic infiltrates in exocrine glands. Current approaches do not control harmful autoimmune attacks or prevent irreversible damage and have considerable side effects. Mesenchymal stem cells (MSCs) have been effective in the treatment of several autoimmune diseases. The objective of this review is to illustrate the potential therapeutic role of MSCs in pSS. We summarize the recent advances in what is known about their immunomodulatory function and therapeutic applications in pSS. MSC transfusion can suppress autoimmunity and restore salivary gland secretory function in mouse models and patients with pSS by inducing regulatory T cells, suppressing Th1, Th17, and T follicular helper cell responses. In addition, MSCs can differentiate into salivary epithelial cells, presenting an option as a suitable alternative treatment. We also discuss current bioengineering methods which improve functions of MSCs for pSS. However, there remain many challenges to overcome before their wide clinical application.

Expression of Programmed Death-Ligand 1 by Human Colonic CD90+ Stromal Cells Differs Between Ulcerative Colitis and Crohn's Disease and Determines Their Capacity to Suppress Th1 Cells

Background and Aims

The role of programmed cell death protein 1 (PD-1) and its ligands in the dysregulation of T helper immune responses observed in the inflammatory bowel disease (IBD) is unclear. Recently, a novel concept emerged that CD90⁺ colonic (myo)fibroblasts (CMFs), also known as stromal cells, act as immunosuppressors, and are among the key regulators of acute and chronic inflammation. The objective of this study was to determine if the level of the PD-1 ligands is changed in the IBD inflamed colonic mucosa and to test the hypothesis that changes in IBD-CMF-mediated PD-1 ligand-linked immunosuppression is a mechanism promoting the dysregulation of Th1 cell responses.

Methods

Tissues and cells derived from Crohn's disease (CD), ulcerative colitis (UC), and healthy individuals (N) were studied in situ, ex vivo, and in culture.

Results

A significant increase in programmed death-ligand 1 (PD-L1) was observed in the inflamed UC colonic mucosa when compared to the non-inflamed matched tissue samples, CD, and healthy controls. UC-CMFs were among the major populations in the colonic mucosa contributing to the enhanced PD-L1 expression. In contrast, PD-L1 expression was decreased in CD-CMFs. When compared to CD-CMFs and N-CMFs, UC-CMFs demonstrated stronger suppression of IL-2, Th1 transcriptional factor Tbet, and IFN-γ expression by CD3/CD28-activated CD4⁺ T cells, and this process was PD-L1 dependent. Similar observations were made when differentiated Th1 cells were cocultured with UC-CMFs. In contrast, CD-CMFs showed reduced capacity to suppress Th1 cell activity and addition of recombinant PD-L1 Fc to CD-CMF:T cell cocultures partially restored the suppression of the Th1 type responses.

Conclusion

We present evidence showing that increased PD-L1 expression suppresses Th1 cell activity in UC. In contrast, loss of PD-L1 expression observed in CD contributes to the persistence of the Th1 inflammatory milieu in CD. Our data suggest that dysregulation of the Th1 responses in the inflamed colonic mucosa of IBD patients is promoted by the alterations in PD-L1 expression in the mucosal mesenchymal stromal cell compartment.

Bone marrow-derived mesenchymal stem cells promote cell proliferation of multiple myeloma through inhibiting T cell immune responses via PD-1/PD-L1 pathway

OBJECTIVES

This study aims to explore the effect of bone marrow mesenchymal stem cells (BMSCs) on multiple myeloma (MM) development and the underlying mechanism.

MATERIALS AND METHODS

BMSCs from C57BL/6 J mice were isolated and the third passage was used for subsequent experiments. Additionally, a series of in vitro transwell coculture assays were performed to explore the effects of BMSCs on the proliferation of MM cells 5TGM1 and CD4+ T cells. Furthermore, a 5TGM1-induced MM mice model was established. Moreover, PD-L1 shRNA was transfected into BMSCs to investigate whether PD-1/PD-L1 pathway involved in BMSCs-mediated regulation of T cells and MM growth.

RESULTS

Data revealed that BMSCs significantly promoted 5TGM1 proliferation in a dose-dependent manner. Furthermore, BMSCs administration exerted stimulatory effects on MM development in terms of shortening the mouse survival rate, promoting tumor growth, and enhancing inflammatory infiltration in the MM model mice. Moreover, BMSCs decreased the percentage of Th1 and Th17 cells, whereas increased that of Th2 and Treg cells. Their corresponding cytokines of these T cell subsets showed similar alteration in the presence of BMSCs. Additionally, BMSCs significantly suppressed CD4+ T cell proliferation. We also found that PD-L1 shRNA inhibited 5TGM1 proliferation likely through activation of CD4+ T cells. Further in vivo experiments confirmed that PD-L1 inhibition attenuated BMSCs-induced MM growth, inflammation infiltration and imbalance of Th1/Th2 and Th17/Treg.

CONCLUSION

In summary, our findings demonstrated that BMSCs promoted cell proliferation of MM through inhibiting T cell immune responses via PD-1/PD-L1 pathway.

Immune regulatory cell infusion for graft-versus-host disease prevention and therapy

Current approaches to prevent and treat graft-versus-host disease (GVHD) after stem cell transplantation rely principally on pharmacological immune suppression. Such approaches are limited by drug toxicity, nonspecific immune suppression, and a requirement for long-term therapy. Our increased understanding of the regulatory cells and molecular pathways involved in limiting pathogenic immune responses opens the opportunity for the use of these cell subsets to prevent and/or GVHD. The theoretical advantages of this approach is permanency of effect, potential for facilitating tissue repair, and induction of tolerance that obviates a need for ongoing drug therapy. To date, a number of potential cell subsets have been identified, including FoxP3⁺ regulatory T (Treg) and FoxP3^negIL-10⁺ (FoxP3-negative) regulatory T (Tr1), natural killer (NK) and natural killer T (NKT) cells, innate lymphoid cells, and various myeloid suppressor populations of hematopoietic (eg, myeloid derived suppressor cells) and stromal origin (eg, mesenchymal stem cells). Despite initial technical challenges relating to large-scale selection and expansion, these regulatory lineages are now undergoing early phase clinical testing. To date, Treg therapies have shown promising results in preventing clinical GVHD when infused early after transplant. Results from ongoing studies over the next 5 years will delineate the most appropriate cell lineage, source (donor, host, third party), timing, and potential exogenous cytokine support needed to achieve the goal of clinical transplant tolerance.

Bone marrow mesenchymal stromal cells protect allograft lung transplants from acute rejection via the PD-L1/IL-17A axis

PURPOSE

Using a rat model of allograft lung transplantation, we investigated the effectiveness of mesenchymal stromal cells (MSCs) as prophylactic and therapeutic agents against the acute rejection of lung grafts.

METHODS

Lung grafts were harvested from donor rats and transplanted orthotopically into major histocompatibility complex-mismatched rats. MSCs were administered to the recipients once (on day 0) or twice (on days 0 and 3) after transplantation. The grade of acute rejection was evaluated both macroscopically and microscopically 6 days after transplantation. To elucidate the related mechanism, mRNA levels of inflammatory cytokines and immunomodulatory receptors in the transplanted grafts were measured using quantitative RT-PCR.

RESULTS

The lung graft tissue from the rats that received MSCs post-surgically was protected from acute rejection significantly better than that from the untreated controls. Notably, the rats administered MSCs twice after surgery exhibited the least signs of rejection, with a markedly upregulated mRNA level of PD-L1 and a downregulated mRNA level of IL-17A.

CONCLUSION

This study assessed MSC protection of lung allografts from acute rejection by modulating T cell activity via enforced expression of PD-L1 in transplants and downregulation of IL-17A.

Inducible indoleamine 2,3-dioxygenase 1 and programmed death ligand 1 expression as the potency marker for mesenchymal stromal cells

AIM

Establishment of a potency assay in the manufacturing of clinical-grade mesenchymal stromal cells (MSCs) has been a challenge due to issues of relevance to function, timeline and variability of responder cells. In this study, we attempted to develop a potency assay for MSCs.

METHODS

Clinical-grade bone marrow-derived MSCs were manufactured. The phenotype and immunosuppressive functions of the MSCs were evaluated based on the International Society for Cellular Therapy guidelines. Resting MSCs licensed by interferon (IFN)-γ exposure overnight were evaluated for changes in immune suppression and immune-relevant proteins. The relationship of immune-relevant protein expression with immunosuppression of MSCs was analyzed.

RESULTS

MSC supressed third-party T-lymphocyte proliferation with high inter-donor and inter-test variability. The suppression of T-lymphocyte proliferation by IFN-γ-licensed MSCs correlated with that by resting MSCs. Many cellular proteins were up-regulated after IFN-γ exposure, including indoleamine 2,3-dioxygenase 1 (IDO-1), programmed death ligand 1 (PD-L1), vascular cell adhesion molecule 1 (VCAM-1), intercellular adhesion molecule 1 (ICAM-1) and bone marrow stromal antigen 2 (BST-2). The expression levels of IDO-1 and PD-L1 on licensed MSCs, not VCAM-1, ICAM-1 or BST-2 on licensed MSCs, correlated with MSC suppression of third-party T-cell proliferation.

CONCLUSION

A flow cytometry-based assay of MSCs post-IFN-γ exposure measuring expression of intracellular protein IDO-1 and cell surface protein PD-L1 captures two mechanisms of suppression and offers the potential of a relevant, rapid assay for MSC-mediated immune suppression that would fit with the manufacturing process.

The genes involved in asthma with the treatment of human embryonic stem cell-derived mesenchymal stem cells

BACKGROUND

Asthma is affecting more than 300 million people worldwide, which represents the most common chronic disease among children. We previously found that mesenchymal stem cells (MSCs) derived from induced pluripotent stem cells (iPSCs) modulated the immune response on Th2-mediated asthma in vivo and in vitro. This study further evaluated the immunomodulatory effects of MSCs from human embryonic stem cells (hESCs) on asthma.

METHODS

Multipotent hESC-MSCs were obtained using a feeder-free method. The hESC-MSCs were analysed for the expression of stem cell surface markers by flow cytometry, their differentiation potentials were analysed using in vitro trilineage differentiation methods hESC-MSCs were transplanted into the murine model with ovalbumin (OVA)-induced airway allergic inflammation. The expression levels of allergic related genes were measured by the mRNA PCR arrays.

RESULTS

The hESC-MSCs expressed classical MSC markers and held the capability of differentiation into multiple mesoderm-type cell lineages. hESC-MSCs were able to suppress allergic inflammation by modulating Th2 cells and eosinophils in the mice, and reversed the reduction of regulatory T cells. By using PCR array, 5 mRNAs- chemokine (C-C motif) ligand 11 (Ccl11), Ccl24, interleukin13 (Il13), Il33 and eosinophil-associated, ribonuclease A family, member 11 (Ear11) were identified the most relevant in murine airway allergic inflammation and hESC-MSCs treatment.

CONCLUSIONS

The therapeutic effects of hESC-MSCs were identified in the murine model of airway allergic inflammation with key mRNAs involved. This study will provide a better understanding regarding the mechanisms underlying hESC-MSCs therapeutic application in airway allergic inflammation.

How to Hit Mesenchymal Stromal Cells and Make the Tumor Microenvironment Immunostimulant Rather Than Immunosuppressive

Experimental evidence indicates that mesenchymal stromal cells (MSCs) may regulate tumor microenvironment (TME). It is conceivable that the interaction with MSC can influence neoplastic cell functional behavior, remodeling TME and generating a tumor cell niche that supports tissue neovascularization, tumor invasion and metastasization. In addition, MSC can release transforming growth factor-beta that is involved in the epithelial-mesenchymal transition of carcinoma cells; this transition is essential to give rise to aggressive tumor cells and favor cancer progression. Also, MSC can both affect the anti-tumor immune response and limit drug availability surrounding tumor cells, thus creating a sort of barrier. This mechanism, in principle, should limit tumor expansion but, on the contrary, often leads to the impairment of the immune system-mediated recognition of tumor cells. Furthermore, the cross-talk between MSC and anti-tumor lymphocytes of the innate and adaptive arms of the immune system strongly drives TME to become immunosuppressive. Indeed, MSC can trigger the generation of several types of regulatory cells which block immune response and eventually impair the elimination of tumor cells. Based on these considerations, it should be possible to favor the anti-tumor immune response acting on TME. First, we will review the molecular mechanisms involved in MSC-mediated regulation of immune response. Second, we will focus on the experimental data supporting that it is possible to convert TME from immunosuppressive to immunostimulant, specifically targeting MSC.

Immunomodulatory plasticity of mesenchymal stem cells: a potential key to successful solid organ transplantation

Organ transplantation remains to be a treatment of choice for patients suffering from irreversible organ failure. Immunosuppressive (IS) drugs employed to maintain the allograft have shown excellent short-term graft survival, but, their long-term use could contribute to immunological and non-immunological risk factors, resulting in graft dysfunctionalities. Upcoming IS regimes have highlighted the use of cell-based therapies, which can eliminate the risk of drug-borne toxicities while maintaining efficacy of the treatment. Mesenchymal stem cells (MSCs) have been considered as an invaluable cell type, owing to their unique immunomodulatory properties, which makes them desirable for application in transplant settings, where hyper-activation of the immune system is evident. The immunoregulatory potential of MSCs holds true for preclinical studies while achieving it in clinical studies continues to be a challenge. Understanding the biological factors responsible for subdued responses of MSCs in vivo would allow uninhibited use of this therapy for countless conditions. In this review, we summarize the variations in the preclinical and clinical studies utilizing MSCs, discuss the factors which might be responsible for variability in outcome and propose the advancements likely to occur in future for using this as a "boutique/personalised therapy" for patient care.

Differentiation of Mesenchymal Stem Cells from Human Induced Pluripotent Stem Cells Results in Downregulation of c-Myc and DNA Replication Pathways with Immunomodulation Toward CD4 and CD8 Cells

Multilineage tissue-source mesenchymal stem cells (MSCs) possess strong immunomodulatory properties and are excellent therapeutic agents, but require constant isolation from donors to combat replicative senescence. The differentiation of human induced pluripotent stem cells (iPSCs) into MSCs offers a renewable source of MSCs; however, reports on their immunomodulatory capacity have been discrepant. Using MSCs differentiated from iPSCs reprogrammed using diverse cell types and protocols, and in comparison to human embryonic stem cell (ESC)-MSCs and bone marrow (BM)-MSCs, we performed transcriptome analyses and assessed for functional immunomodulatory properties. Differentiation of MSCs from iPSCs results in decreased c-Myc expression and its downstream pathway along with a concomitant downregulation in the DNA replication pathway. All four lines of iPSC-MSCs can significantly suppress in vitro activated human peripheral blood mononuclear cell (PBMC) proliferation to a similar degree as ESC-MSCs and BM-MSCs, and modulate CD4 T lymphocyte fate from a type 1 helper T cell (Th1) and IL-17A-expressing (Th17) cell fate to a regulatory T cell (Treg) phenotype. Moreover, iPSC-MSCs significantly suppress cytotoxic CD8 T proliferation, activation, and differentiation into type 1 cytotoxic T (Tc1) and IL-17-expressing CD8 T (Tc17) cells. Coculture of activated PBMCs with human iPSC-MSCs results in an overall shift of secreted cytokine profile from a pro-inflammatory environment to a more immunotolerant milieu. iPSC-MSC immunomodulation was also validated in vivo in a mouse model of induced inflammation. These findings support that iPSC-MSCs possess low oncogenicity and strong immunomodulatory properties regardless of cell-of-origin or reprogramming method and are good potential candidates for therapeutic use. Stem Cells 2018;36:903-914.

Perspective on immune oncology with liquid biopsy, peripheral blood mononuclear cells, and microbiome with non-invasive biomarkers in cancer patients

Antibodies against immune checkpoint inhibitors such as anti-programmed cell death protein 1 (PD-1) and anti-programmed death ligand 1 (PD-L1) play a key role in the treatment of advanced lung cancer. To examine the clinical benefits of these agents, preclinical and clinical studies have been conducted to identify definitive biomarkers associated with cancer status. Analysis of the blood and feces of tumor patients has attracted attention in recent studies attempting to identify non-invasive biomarkers such as cytokines, soluble PD-L1, peripheral blood mononuclear cells, and gut microbiota. These factors are believed to interact with each other to produce synergistic effects and contribute to the formation of the tumor immune microenvironment through the seven steps of the cancer immunity cycle. The immunogram was first introduced as a novel indicator to define the immunity status of cancer patients. In this review, we discuss the progress in the identification of predictive biomarkers as well as future prospects for anti-PD-1/PD-L1 therapy.

Mesenchymal Stem Cells and Calcium Phosphate Bioceramics: Implications in Periodontal Bone Regeneration

In orthopedic medicine, a feasible reconstruction of bone structures remains one of the main challenges both for healthcare and for improvement of patients' quality of life. There is a growing interest in mesenchymal stem cells (MSCs) medical application, due to their multilineage differentiation potential, and tissue engineering integration to improve bone repair and regeneration. In this review we will describe the main characteristics of MSCs, such as osteogenesis, immunomodulation and antibacterial properties, key parameters to consider during bone repair strategies. Moreover, we describe the properties of calcium phosphate (CaP) bioceramics, which demonstrate to be useful tools in combination with MSCs, due to their biocompatibility, osseointegration and osteoconduction for bone repair and regeneration. Also, we overview the main characteristics of dental cavity MSCs, which are promising candidates, in combination with CaP bioceramics, for bone regeneration and tissue engineering. The understanding of MSCs biology and their interaction with CaP bioceramics and other biomaterials is critical for orthopedic surgical bone replacement, reconstruction and regeneration, which is an integrative and dynamic medical, scientific and bioengineering field of research and biotechnology.

Regenerative approaches for cartilage repair in the treatment of osteoarthritis

Osteoarthritis (OA) as a debilitating affliction of joints currently affects millions of people and remains an unsolved problem. The disease involves multiple cellular and molecular pathways that converge on the progressive destruction of cartilage. Activation of cartilage regenerative potential and specific targeting pathogenic mediators have been the major focus of research efforts aimed at slowing the progression of cartilage degeneration and preserve joint function. This review will summarize recent key discoveries toward better understanding of the complex mechanisms behind OA development and highlight the latest advances in basic and clinical research in the approach for cartilage regeneration. Prospectively, more potent therapeutic strategies against progressive cartilage deterioration may use a combination of cytotherapy, pharmacotherapy, and bioscaffoldings for improved chondrogenic differentiation and stem/progenitor cell homing as well as the concomitant reduced enzymatic matrix degradation and inflammation. Further, treatments need to be provided with increased preciseness of targeted therapy. One might expect that the regenerative therapies could potentially control or even possibly cure OA if performed at early stages of the disease.

Small-molecule inhibitors of PD-1/PD-L1 immune checkpoint alleviate the PD-L1-induced exhaustion of T-cells

Antibodies targeting the PD-1/PD-L1 immune checkpoint achieved spectacular success in anticancer therapy in the recent years. In contrast, no small molecules with cellular activity have been reported so far. Here we provide evidence that small molecules are capable of alleviating the PD-1/PD-L1 immune checkpoint-mediated exhaustion of Jurkat T-lymphocytes. The two optimized small-molecule inhibitors of the PD-1/PD-L1 interaction, BMS-1001 and BMS-1166, developed by Bristol-Myers Squibb, bind to human PD-L1 and block its interaction with PD-1, when tested on isolated proteins. The compounds present low toxicity towards tested cell lines and block the interaction of soluble PD-L1 with the cell surface-expressed PD-1. As a result, BMS-1001 and BMS-1166 alleviate the inhibitory effect of the soluble PD-L1 on the T-cell receptor-mediated activation of T-lymphocytes. Moreover, the compounds were effective in attenuating the inhibitory effect of the cell surface-associated PD-L1. We also determined the X-ray structures of the complexes of BMS-1001 and BMS-1166 with PD-L1, which revealed features that may be responsible for increased potency of the compounds compared to their predecessors. Further development may lead to the design of an anticancer therapy based on the orally delivered immune checkpoint inhibition.

Adipose Extracellular Matrix/Stromal Vascular Fraction Gel Secretes Angiogenic Factors and Enhances Skin Wound Healing in a Murine Model

Mesenchymal stem cells are an attractive cell type for cytotherapy in wound healing. The authors recently developed a novel, adipose-tissue-derived, injectable extracellular matrix/stromal vascular fraction gel (ECM/SVF-gel) for stem cell therapy. This study was designed to assess the therapeutic effects of ECM/SVF-gel on wound healing and potential mechanisms. ECM/SVF-gel was prepared for use in nude mouse excisional wound healing model. An SVF cell suspension and phosphate-buffered saline injection served as the control. The expression levels of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and monocyte chemotactic protein-1 (MCP-1) in ECM/SVF-gel were analyzed at different time points. Angiogenesis (tube formation) assays of ECM/SVF-gel extracts were evaluated, and vessels density in skin was determined. The ECM/SVF-gel extract promoted tube formation in vitro and increased the expression of the angiogenic factors VEGF and bFGF compared with those in the control. The expression of the inflammatory chemoattractant MCP-1 was high in ECM/SVF-gel at the early stage and decreased sharply during the late stage of wound healing. The potent angiogenic effects exerted by ECM/SVF-gel may contribute to the improvement of wound healing, and these effects could be related to the enhanced inflammatory response in ECM/SVF-gel during the early stage of wound healing.

Mesenchymal Stromal Cells: What Is the Mechanism in Acute Graft-Versus-Host Disease?

After more than a decade of preclinical and clinical development, therapeutic infusion of mesenchymal stromal cells is now a leading investigational strategy for the treatment of acute graft-versus-host disease (GVHD). While their clinical use continues to expand, it is still unknown which of their immunomodulatory properties contributes most to their therapeutic activity. Herein we describe the proposed mechanisms, focusing on the inhibitory activity of mesenchymal stromal cells (MSCs) at immunologic checkpoints. A deeper understanding of the mechanism of action will allow us to design more effective treatment strategies.

Granulocytic myeloid-derived suppressor cells from human cord blood modulate T-helper cell response towards an anti-inflammatory phenotype

Infections are a leading cause of perinatal morbidity and mortality. The outstandingly high susceptibility to infections early in life is mainly attributable to the compromised state of the neonatal immune system. One important difference to the adult immune system is a bias towards T helper type 2 (Th2) responses in newborns. However, mechanisms regulating neonatal T-cell responses are incompletely understood. Granulocytic myeloid-derived suppressor cells (GR-MDSC) are myeloid cells with a granulocytic phenotype that suppress various functions of other immune cells and accumulate under physiological conditions during pregnancy in maternal and fetal blood. Although it has been hypothesized that GR-MDSC accumulation during fetal life could be important for the maintenance of maternal-fetal tolerance, the influence of GR-MDSC on the immunological phenotype of neonates is still unclear. Here, we investigated the impact of GR-MDSC isolated from cord blood (CB-MDSC) on the polarization of Th cells. We demonstrate that CB-MDSC inhibit Th1 responses and induced Th2 responses and regulatory T (Treg) cells. Th1 inhibition was cell-contact dependent and occurred independent of other cell types, while Th2 induction was mediated independently of cell contact through expression of ArgI and reactive oxygen species by CB-MDSC and partially needed the presence of monocytes. Treg cell induction by CB-MDSC also occurred cell-contact independently but was partially mediated through inducible nitric oxide synthase. These results point towards a role of MDSC in regulating neonatal immune responses. Targeting MDSC function in neonates could be a therapeutic opportunity to improve neonatal host defence.

Antitumor Activity of a Mesenchymal Stem Cell Line Stably Secreting a Tumor-Targeted TNF-Related Apoptosis-Inducing Ligand Fusion Protein

Mesenchymal stem cells (MSCs) are currently exploited as gene delivery systems for transient in situ expression of cancer therapeutics. As an alternative to the prevailing viral expression, we here describe a murine MSC line stably expressing a therapeutic protein for up to 42 passages, yet fully maintaining MSC features. Because of superior antitumoral activity of hexavalent TNF-related apoptosis-inducing ligand (TRAIL) formats and the advantage of a tumor-targeted action, we choose expression of a dimeric EGFR-specific diabody single-chain TRAIL (Db-scTRAIL) as a model. The bioactivity of Db-scTRAIL produced from an isolated clone (MSC.TRAIL) was revealed from cell death induction in Colo205 cells treated with either culture supernatants from or cocultured with MSC.TRAIL. In vivo, therapeutic activity of MSC.TRAIL was shown upon peritumoral injection in a Colo205 xenograft tumor model. Best antitumor activity in vitro and in vivo was observed upon combined treatment of MSC.TRAIL with bortezomib. Importantly, in vivo combination treatment did not cause apparent hepatotoxicity, weight loss, or behavioral changes. The development of well characterized stocks of stable drug-producing human MSC lines has the potential to establish standardized protocols of cell-based therapy broadly applicable in cancer treatment.

Tumor-associated fibrosis as a regulator of tumor immunity and response to immunotherapy

Tumor-associated fibrosis is characterized by unchecked pro-fibrotic and pro-inflammatory signaling. The components of fibrosis including significant numbers of cancer-associated fibroblasts, dense collagen deposition, and extracellular matrix stiffness, are well appreciated regulators of tumor progression but may also be critical regulators of immune surveillance. While this suggests that the efficacy of immunotherapy may be limited in highly fibrotic cancers like pancreas, it also suggests a therapeutic opportunity to target fibrosis in these tumor types to reawaken anti-tumor immunity. This review discusses the mechanisms by which fibrosis might subvert tumor immunity and how to overcome these mechanisms.