Immunomodulatory Properties Of Mesenchymal Stromal Cells Research Articles

IFNγ Primed MSCs Suppress Stimulated T Cells By Inducing Perturbations of Redox Homeostasis

Acute Graft versus host disease (GVHD) remains the primary cause of morbidity and nonrelapse mortality after allogeneic hematopoietic cell transplantation (HCT). Despite the current standard prophylaxis, approximately 50% of patients will develop acute GVHD. the outcome of patients with steroid-refractory and/or severe GVHD is poor; hence, more effective prophylaxis reducing the risk of these scenarios is greatly needed. In recent years, considerable attention has been directed toward mesenchymal stromal cells (MSCs) as prophylaxis and therapy for acute GVHD. Even though the immunosuppressive and immunomodulatory properties of MSCs are enhanced by proinflammatory cytokines such as interferon γ (γMSCs), relatively less attention has been focused on these cells. Our laboratory has shown human γMSCs are effective in GVHD prophylaxis in a fully mismatched murine HCT/GVHD model. When infused IV on day +1 after HCT, γMSCs traffic to the spleen, liver, and gut-associated lymphoid tissue (GALT) which is essential for effective prophylaxis. This may be a key element of the mechanism of prophylaxis as the gut and GALT are thought to be paramount for the development of GVHD. We now sought to understand the mechanism(s) of γMSC suppression of alloreactive T cells suppressive activity in this specific clinical and biological setting. In vivo, control mice transplanted with a fully MHC mismatched graft developed GVHD in 6-8 days (0% GVHD-free survival) while human γMSCs administration at day +1 completely prevented GVHD in the first 17 days (100% GVHD survival) but the animals developed acute GVHD in 21-28 days. Hence, a single dose of γMSCs is 100% effective early but is insufficient for overall GVHD prevention. The mechanism is highly effective but of relatively short duration, and seemingly reversible. In vitro, the reversible T cell suppressive activity was entirely contact-independent, while cell-to-cell contact could induce T cell death. Moreover, γMSC IDO1 expression, alone, was sufficient to suppress T cells. After 24 hours of T cell activation or γMSC suppression in vitro, we found the T cells were arrested in G0 inconsistent with most cell cycle regulation which would arrest cells in late G1 at the so-called restriction point. In scRNA Seq, we identified 16,478 expressed genes in both groups but only 98 genes were significantly differentially expressed (≥20% FC, Padj ≤ 10 -4). ROS response pathways were significantly enriched in the suppressed cells suggesting oxidative stress. Paradoxically, flow cytometric analysis of CM-H2DCFDA stained T cells revealed less ROS in suppressed cells compared to controls. Additionally, total NAD is elevated and the NAD/NADH ratio was 10-fold less in suppressed T cells compared to activated cells indicating an excess of reducing equivalents in the suppressed cells. Collectively these data define reductive stress. On this note, the upregulation of ROS response genes is also consistent with reductive stress. IDO1 activity seems to have induced reductive stress. The IDO1 catalytic activity converts tryptophan (Trp) to kynurenine (Kyn). We then found the addition of Trp (10 µM) to γMSC CM abolished suppression; supplementing fresh media with 15-fold excess Kyn had no effect. Moreover, RPMI without Trp and with dialyzed FBS also conferred suppression to activated T cells. These data suggest that among the many metabolites consumed or generated in γMSC CM, the lack of Trp induces T cell suppression. Trp supplementation of γMSC CM showed the expected level of ROS in activated T cells suggesting the Trp deficiency caused the reduced ROS. Supplementing γMSC CM with a graded concentration of hydrogen peroxide, we found that 100 nM hydrogen peroxide was not toxic to control cells, had ROS similar to activated T cells, and abolished suppression indicating the reduced ROS directly caused suppression. Kyn, nutritional deficiency, or an integrated stress response did not seem to play a measurable role in this setting. Collectively, our data suggest that IDO1-mediated Trp deficiency perturbs redox homeostasis (reductive stress) which suppresses activated T cells. We postulate that once redox homeostasis is restored, T cell activation proceeds. Future efforts will be directed toward identifying the link between Trp deficiency and redox homeostasis in this setting, and the genomic changes that directly mediate the lack of T cell proliferation.

Mesenchymal stromal cells and their small extracellular vesicles in allergic diseases: From immunomodulation to therapy.

Mesenchymal stromal cells (MSCs) have long been considered a potential tool for treatment of allergic inflammatory diseases, owing to their immunomodulatory characteristics. In recent decades, the medical utility of MSCs has been evaluated both in vitro and in vivo, providing a foundation for therapeutic applications. However, the existing limitations of MSC therapy indicate the necessity for novel therapies. Notably, small extracellular vesicles (sEV) derived from MSCs have emerged rapidly as candidates instead of their parental cells. The acquisition of abundant and scalable MSC-sEV is an obstacle for clinical applications. The potential application of MSC-sEV in allergic diseases has attracted increasing attention from researchers. By carrying biological microRNAs or active proteins, MSC-sEV can modulate the function of various innate and adaptive immune cells. In this review, we summarise the recent advances in the immunomodulatory properties of MSCs in allergic diseases, the cellular sources of MSC-sEV, and the methods for obtaining high-quality human MSC-sEV. In addition, we discuss the immunoregulatory capacity of MSCs and MSC-sEV for the treatment of asthma, atopic dermatitis, and allergic rhinitis, with a special emphasis on their immunoregulatory effects and the underlying mechanisms of immune cell modulation.

Intravenous Administration of Human Umbilical Cord Mesenchymal Stromal Cells Leads to an Inflammatory Response in the Lung.

Mesenchymal stromal cells (MSCs) administered intravenously (IV) have shown efficacy in preclinical models of various diseases. This is despite the cells not reaching the site of injury due to entrapment in the lungs. The immunomodulatory properties of MSCs are thought to underlie their therapeutic effects, irrespective of whether they are sourced from bone marrow, adipose tissue, or umbilical cord. To better understand how MSCs affect innate immune cell populations in the lung, we evaluated the distribution and phenotype of neutrophils, monocytes, and macrophages by flow cytometry and histological analyses after delivering human umbilical cord-derived MSCs (hUC-MSCs) IV into immunocompetent mice. After 2 hr, we observed a significant increase in neutrophils, and proinflammatory monocytes and macrophages. Moreover, these immune cells localized in close proximity to the MSCs, suggesting an active role in their clearance. By 24 hr, we detected an increase in anti-inflammatory monocytes and macrophages. These results suggest that the IV injection of hUC-MSCs leads to an initial inflammatory phase in the lung shortly after injection, followed by a resolution phase 24 hr later.

Assessment of the therapeutic role of mesenchymal stromal cells in a mouse model of graft-versus-host disease using cryo-imaging

Insights regarding the biodistribution and homing of mesenchymal stromal cells (MSCs), as well as their interaction with alloreactive T-cells are critical for understanding how MSCs can regulate graft-versus-host disease (GVHD) following allogeneic (allo) bone marrow transplantation (BMT). We developed novel assays based on 3D, microscopic, cryo-imaging of whole-mouse-sized volumes to assess the therapeutic potential of human MSCs using an established mouse GVHD model. Following infusion, we quantitatively tracked fluorescently labeled, donor-derived, T-cells and third party MSCs in BMT recipients using multispectral cryo-imaging. Specific MSC homing sites were identified in the marginal zones in the spleen and the lymph nodes, where we believe MSC immunomodulation takes place. The number of MSCs found in spleen of the allo BMT recipients was about 200% more than that observed in the syngeneic group. To more carefully define the effects MSCs had on T cell activation and expansion, we developed novel T-cell proliferation assays including secondary lymphoid organ (SLO) enlargement and Carboxyfluoescein succinimidyl ester (CFSE) dilution. As anticipated, significant SLO volume enlargement and CFSE dilution was observed in allo but not syn BMT recipients due to rapid proliferation and expansion of labeled T-cells. MSC treatment markedly attenuated CFSE dilution and volume enlargement of SLO. These assays confirm evidence of potent, in vivo, immunomodulatory properties of MSC following allo BMT. Our innovative platform includes novel methods for tracking cells of interest as well as assessing therapeutic function of MSCs during GVHD induction. Our results support the use of MSCs treatment or prevention of GVHD and illuminate the wider adoption of MSCs as a standard medicinal cell therapy.

Licensing microgels prolong the immunomodulatory phenotype of mesenchymal stromal cells.

Mesenchymal stromal cells (MSC) are sensors of inflammation, and they exert immunomodulatory properties through the secretion of cytokines and exosomes and direct cell-cell interactions. MSC are routinely used in clinical trials and effectively resolve inflammatory conditions. Nevertheless, inconsistent clinical outcomes necessitate the need for more robust therapeutic phenotypes. The immunomodulatory properties of MSC can be enhanced and protracted by priming (aka licensing) them with IFNγ and TNFα. Yet these enhanced properties rapidly diminish, and prolonged stimulation could tolerize their response. Hence a balanced approach is needed to enhance the therapeutic potential of the MSC for consistent clinical performance. Here, we investigated the concentration-dependent effects of IFNγ and TNFα and developed gelatin-based microgels to sustain a licensed MSC phenotype. We show that IFNγ treatment is more beneficial than TNFα in promoting an immunomodulatory MSC phenotype. We also show that the microgels possess integrin-binding sites to support adipose tissue-derived MSC (AD-MSC) attachment and a net positive charge to sequester the licensing cytokines electrostatically. Microgels are enzymatically degradable, and the rate is dependent on the enzyme concentration and matrix density. Our studies show that one milligram of microgels by dry mass can sequester up to 641 ± 81 ng of IFNγ. Upon enzymatic degradation, microgels exhibited a sustained release of IFNγ that linearly correlated with their degradation rate. The AD-MSC cultured on the IFNγ sequestered microgels displayed efficient licensing potential comparable to or exceeding the effects of bolus IFNγ treatment. When cultured with proinflammatory M1-like macrophages, the AD-MSC-seeded on licensing microgel showed an enhanced immunomodulatory potential compared to untreated AD-MSC and AD-MSC treated with bolus IFNγ treatment. Specifically, the AD-MSC seeded on licensing microgels significantly upregulated Arg1, Mrc1, and Igf1, and downregulated Tnfα in M1-like macrophages compared to other treatment conditions. These licensing microgels are a potent immunomodulatory approach that shows substantial promise in elevating the efficacy of current MSC therapies and may find utility in treating chronic inflammatory conditions.

Dimethyloxalylglycine, a small molecule, synergistically increases the homing and angiogenic properties of human mesenchymal stromal cells when cultured as 3D spheroids.

Strategies aiming at increasing the survival and paracrine activity of human mesenchymal stromal cells (MSCs) are of utmost importance to achieve the full therapeutic potential of these cells. Herein, we propose both physical and biochemical strategies to enhance the survival, homing, angiogenic, and immunomodulatory properties of MSCs in vitro. To that purpose, we compared the effect of exposing either 2D monolayer or 3D spheroids of MSCs to (i) hypoxia (2% O2 ) or to (ii) a hypoxic-mimetic small molecule, dimethyloxalylglycine (DMOG), with cells cultured at 21% O2 . 3D-cultured MSC spheroids evidenced higher survival upon exposure to oxidative stress and expressed higher levels of factors involved in tissue repair processes, namely tumor necrosis factor-stimulated gene-6, matrix metalloproteinase-2, and vascular endothelial growth factor. MSCs cultured as 3D spheroids and further exposed to hypoxia or hypoxic-mimetic conditions provided by DMOG synergistically favored the expression of the cell surface marker C-X-C chemokine receptor type-4, involved in homing processes to injured tissues, and adhesion to extracellular matrix components as fibronectin. These results highlight the role of ex vivo preconditioning approaches, presenting a novel strategy that combine biochemical stimuli with 3D spheroid organization of MSCs to maximize their tissue regeneration potential.

Titanium Surface Properties Influence the Biological Activity and FasL Expression of Craniofacial Stromal Cells.

Mesenchymal stromal cells (MSCs) can be easily isolated form craniofacial bones during routine dentistry procedures. Due to their embryological origin from neural crest, they represent a suitable cell population to study cell-biomaterial interaction in the craniofacial field, including osteoinductive/osteointegrative processes. The biological and immunomodulatory properties of MSCs may be influenced by chemistry and topography of implant surfaces. We investigated if and how three different titanium surfaces, machined (MCH), sandblasted with resorbable blasting medium (RBM), and Ca++-nanostructured (NCA), may affect biological activity, osseointegration, and immunomodulatory properties of craniofacial MSCs. Cell proliferation, morphology, osteogenic markers, and FasL were evaluated on MSCs isolated from the mandibular bone after seeding on these three different surfaces. No statistically significant differences in cell proliferation were observed whereas different morphologies and growth patterns were detected for each type of surface. No difference in the expression of osteogenic markers was revealed. Interestingly, FasL expression, involved in the immunomodulatory activity of stem cells, was influenced by surface properties. Particularly, immunofluorescence analysis indicated that FasL expression increased on MCH surface compared to the others confirming the suggested role of FasL in promoting osteogenic differentiation. Titanium surface treatments and topography might reflect different biological behaviours of craniofacial MSCs and influence their osseointegration/immunomodulation properties.

Canine placenta: A promising potential source of highly proliferative and immunomodulatory mesenchymal stromal cells?

In veterinary medicine, therapeutic mesenchymal stromal cells (MSC) have been traditionally isolated from adult bone marrow or adipose tissue. Neonatal tissues, normally discarded at birth from all species have become an alternative source of cells for regenerative medicine in the human clinic. These cells have been described as being more primitive, proliferative and immunosuppressive than their adult counterparts. Our objective was to examine if this phenomena holds true in dogs. Little information exists regarding canine neonatal MSC characterisation. In this study, we were able to both isolate, phenotype and assess the differentiation and immunomodulatory properties of MSC from canine foetal adnexa allowing us to compare their characteristics to their more well-known bone marrow (BM) cousins. Neonatal tissues, including amnion (AM), placenta (PL), and umbilical cord matrix (UCM) were collected from 6 canine caesarean sections. Primary cells were expanded in vitro for 5 consecutive passages and their proliferation measured. BM-MSC were isolated from 5 control dogs euthanised from other studies and grown in vitro using an identical protocol. All MSC lines were systematically evaluated for their ability to differentiate into 3 mesodermal lineages (adipocyte, osteocyte and chondrocyte) and phenotyped by cytometry and qPCR. In addition, the enzymatic activity of the key immunomodulatory marker indoleamine 2,3-dioxygenase (IDO) was evaluated for each MSC line.MSC displaying a fibroblastic appearance were successfully grown from all neonatal tissues. PL-MSC exhibited significantly higher proliferation rates than AM- and UCM–MSC (p=0.05). Cytometric analysis showed that all MSC express CD90, CD29, and CD44, while no expression of CD45, CD34 and MHC2 was detected. Molecular profiling showed expression of CD105 and CD73 in all MSC. Low levels of SOX2 mRNA was observed in all MSC, while neither NANOG, nor OCT4 were detected. All MSC differentiate into 3 mesodermal lineages. Following inflammatory stimulation, the activity of the immunomodulatory enzyme IDO was significantly higher in neonatal MSC compared to BM-MSC (p=0.009).Our results show that canine foetal adnexa cells share very similar properties to their adult equivalents but upon stimulation show significantly higher IDO immunomodulatory activity. Further studies will be needed to confirm the potential therapeutic benefits of these cells.

Localization and functions of mesenchymal stromal cells in vivo

Studying mesenchymal stromal cells (MSC) is a very topical problem. Numerous experiments in vitro promoted understanding of MSC biology to a great extent. However, many aspects of their behavior in vivo still remain unclear. This review deals with MSC localization and functioning in an organism. MSC are present in various tissues, changing their numbers and traits during ontogenesis. Pericytes, or adventitial cells, can be considered as possible equivalents of MSC in vivo. Self-maintenance, proliferation, and differentiation of MSC are controlled by their tissue microenvironment that includes surrounding cells, soluble molecules, and extracellular matrix. At early stages of ontogenesis, MSC, probably, migrate throughout an organism. The migration occur also through a mature organism when tissues happen to be damaged. MSC move pointedly to the damaged parts and render a reparative effect which is due, first of all, to paracrine production of bioactive molecules. Immunomodulatory properties of MSC also play their role in tissues regeneration. An important function of MSC consists in creation of hematopoietic microenvironment. They secrete humoral regulators of hemopoiesis such as cytokines and chemoattractants. In addition, they interact with hemopoietic cells via surface molecules. Possibly, MSC sustain the stable functioning of other tissues as well. Their unique features make them quite attractive for clinical use, although successful introduction of MSC into medical practice requires their further studying.

A reproducible immunopotency assay to measure mesenchymal stromal cell–mediated T-cell suppression

Background aimsThe T-cell suppressive property of bone marrow–derived mesenchymal stromal cells (MSCs) has been considered a major mode of action and basis for their utilization in a number of human clinical trials. However, there is no well-established reproducible assay to measure MSC-mediated T-cell suppression. MethodsAt the University of Wisconsin-Madison Production Assistance for Cellular Therapy (PACT) Center, we developed an in vitro quality control T-cell suppression immunopotency assay (IPA) that uses anti-CD3 and anti-CD28 antibodies to stimulate T-cell proliferation. We measured MSC-induced suppression of CD4+ T-cell proliferation at various effector-to-target cell ratios with the use of defined peripheral blood mononuclear cells and in parallel compared with a reference standard MSC product. We calculated an IPA value for suppression of CD4+ T cells for each MSC product. ResultsEleven MSC products generated at three independent PACT centers were evaluated for cell surface phenotypic markers and T-cell suppressive properties. Flow cytometry results demonstrated typical MSC cell surface marker profiles. There was significant variability in the level of suppression of T-cell proliferation, with immunopotency assay values ranging from 27% to 88%. However, MSC suppression did not correlate with human leukocyte antigen–DR expression. ConclusionsWe have developed a reproducible immunopotency assay to measure allogeneic MSC-mediated suppression of CD4+ T cells. Additional studies may be warranted to determine how these in vitro assay results may correlate with other immunomodulatory properties of MSCs, in addition to evaluating the ability of this assay to predict in vivo efficacy.

From Single Nucleotide Polymorphisms to Constant Immunosuppression: Mesenchymal Stem Cell Therapy for Autoimmune Diseases

The regenerative abilities and the immunosuppressive properties of mesenchymal stromal cells (MSCs) make them potentially the ideal cellular product of choice for treatment of autoimmune and other immune mediated disorders. Although the usefulness of MSCs for therapeutic applications is in early phases, their potential clinical use remains of great interest. Current clinical evidence of use of MSCs from both autologous and allogeneic sources to treat autoimmune disorders confers conflicting clinical benefit outcomes. These varied results may possibly be due to MSC use across wide range of autoimmune disorders with clinical heterogeneity or due to variability of the cellular product. In the light of recent genome wide association studies (GWAS), linking predisposition of autoimmune diseases to single nucleotide polymorphisms (SNPs) in the susceptible genetic loci, the clinical relevance of MSCs possessing SNPs in the critical effector molecules of immunosuppression is largely undiscussed. It is of further interest in the allogeneic setting, where SNPs in the target pathway of MSC's intervention may also modulate clinical outcome. In the present review, we have discussed the known critical SNPs predisposing to disease susceptibility in various autoimmune diseases and their significance in the immunomodulatory properties of MSCs.

Immunomodulatory effects of mesenchymal stromal cells revisited in the context of inflammatory cardiomyopathy.

Myocarditis is a common inflammatory cardiomyopathy, associated with cardiomyocyte apoptosis, which can lead to chronic left ventricular dysfunction. Under conventional heart failure therapy, inflammatory cardiomyopathy typically has a progressive course, indicating a need for alternative therapeutic strategies to improve long-term outcomes. Experimental and clinical studies consistently support the application of cellular transplantation as a strategy to improve myocardial function. Mesenchymal stromal cells (MSCs) mediate distinct paracrine effects supporting endogenous regeneration, but most important are their remarkable immunoregulatory properties. In this review, an overview of current knowledge on immunopathology in myocarditis will be given. Furthermore, current research regarding the immunomodulatory properties of MSCs in the context of myocarditis will be discussed. Finally, the impact of MSC priming by the environment on their functionality and the advantages of systemic administration of MSCs under myocarditis are outlined.

Activated T cells modulate immunosuppression by embryonic-and bone marrow-derived mesenchymal stromal cells through a feedback mechanism

Human embryonic stem cell (hESC)-derived mesenchymal stromal cells (MSC) (hESC-MSC) are an alternative source of MSC to bone marrow (BM)-derived MSC (BM-MSC), which are being investigated in clinical trials for their immunomodulatory potential. hESC-MSC have the advantage of being consistent because each batch can be generated from hESC under defined conditions. In contrast, BM-MSC have a limited proliferative capacity. The ability to suppress the proliferation of anti-CD3/CD28-stimulated CD4 (+) T cells by hESC-MSC was compared with adult BM-MSC and neonatal foreskin fibroblast (Fb). hESC-MSC suppress the proliferation of CD4 (+) T cells in both contact and transwell systems, although inhibition is less in the transwell system. hESC-MSC are approximately 2-fold less potent (67 cells/100 T cells) than BM-MSC and Fb (37 and 34 cells/100 T cells, respectively) at suppressing T-cell proliferation by 50% in a transwell [inhibitory concentration(IC)(50)]. The anti-proliferative effect is not contact-dependent but requires the presence of factors such as interferon (IFN)-γ produced by activated T cells. IFN-γ induces the expression of indoleamine-2,3-dioxygenase (IDO) in hESC-MSC, BM-MSC and Fb, contributing to their immunosuppressive property. The feedback loop between MSC or Fb and activated T cells may limit the immunosuppressive effects of MSC and Fb to sites containing ongoing immunologic or inflammatory responses where activated T cells induce the up-regulation of IDO and immunomodulatory properties of MSC and Fb. These data demonstrate that hESC-MSC may be evaluated further as an allogeneic cell source for therapeutic applications requiring immunosuppression.

Mesenchymal stromal cells for tissue-engineered tissue and organ replacements.

Mesenchymal stromal cells (MSCs), a rare heterogeneous subset of pluripotent stromal cells that can be easily isolated from different adult tissues, in vitro expanded and differentiated into multiple lineages, are immune privileged and, more important, display immunomodulatory capacities. Because of this, they are the preferred cell source in tissue-engineered replacements, not only in autogeneic conditions, where they do not evoke any immune response, but especially in the setting of allogeneic organ and tissue replacements. However, more preclinical and clinical studies are requested to completely understand MSC's immune biology and possible clinical applications. We herein review the immunogenicity and immunomodulatory properties of MSCs, their possible mechanisms and potential clinical use for tissue-engineered organ and tissue replacement.

Therapeutic Applications of Mesenchymal Stromal Cells: Paracrine Effects and Potential Improvements

Among the various types of cell-to-cell signaling, paracrine signaling comprises those signals that are transmitted over short distances between different cell types. In the human body, secreted growth factors and cytokines instruct, among others, proliferation, differentiation, and migration. In the hematopoietic stem cell (HSC) niche, stromal cells provide instructive cues to stem cells via paracrine signaling and one of these cell types, known to secrete a broad panel of growth factors and cytokines, is mesenchymal stromal cells (MSCs). The factors secreted by MSCs have trophic, immunomodulatory, antiapoptotic, and proangiogenic properties, and their paracrine profile varies according to their initial activation by various stimuli. MSCs are currently studied as treatment for inflammatory diseases such as graft-versus-host disease and Crohn's disease, but also as treatment for myocardial infarct and solid organ transplantation. In addition, MSCs are investigated for their use in tissue engineering applications, in which their differentiation plays an important role, but as we have recently demonstrated, their trophic factors may also be involved. Furthermore, a functional improvement of MSCs might be obtained after preconditioning or tailoring the cells themselves. Also, the way the cells are clinically administered may be specialized for specific therapeutic scenarios. In this review we will first discuss the HSC niche, in which MSCs were recently identified and are thought to play an instructive and supportive role. We will then evaluate therapeutic applications that currently try to utilize the trophic and/or immunomodulatory properties of MSCs, and we will also discuss new options to enhance their therapeutic effects.

Effect of the HDAC inhibitor SAHA on the immunomodulatory properties of MSC and tumor stroma cells

Histone deacetylase inhibitors, like suberoylanilide hydroxamic acid (SAHA), are potential new drugs in oncologic treatment protocols. They can impact on proliferation and function of T cells. We analysed the effects SAHA on T cells directly as well as on mesenchymal stromal cells (MSC), which are known to modulate T cell responses. SAHA reduced the suppressive effects of MSC on PBMC. In previous studies we found that tumor stromal cells (TStrC) impair T cell function. As TStrC share several properties with MSC, we hypothesized that in this particular setting SAHA may facilitate tumorimmunological responses by downregulation of the immune suppression by TStrC. We isolated TStrC from neuroblastoma patients and analysed the effect of SAHA on these TStrC including cytokine patterns. Proliferation TStrC was only slightly affected at the pharmacologically relevant concentration of 1,2µM. After treatment with SAHA, TStrC showed reduced inhibition of the proliferation of PBMC and cytotoxicity of NK cells. These findings suggest, that SAHA may modify the tumor microenvironment to allow for more efficient anti-tumor immune responses.