Human MDSCs derived from the bone marrow maintain their functional ability but have a reduced frequency of induction in the elderly compared to pediatric donors

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immunosuppressive cells developing from myeloid progenitors, which are enriched in pathological conditions such as cancer, and are known to inhibit the functions of effector T cells. During aging, several changes occur both at the adaptive and innate immune system level, in a process defined as immunoscenescence. In particular, the low-grade inflammation state observed in the elderly appears to affect hematopoiesis. We previously demonstrated that the combination of GM-CSF and G-CSF drives the in vitro generation of bone marrow-derived MDSCs (BM-MDSCs) from precursors present in human bone marrow aspirates of healthy donors, and that these cells are endowed with a strong immune suppressive ability, resembling that of cancer-associated MDSCs. In the present work we investigated BM-MDSCs induction and functional ability in a cohort of pediatric versus elderly donors. To this aim, we analyzed the differences in maturation stages and ability to suppress T cell proliferation. We found that the ex vivo distribution of myeloid progenitors is similar between pediatric and elderly individuals, whereas after cytokine treatment a significant reduction in the more immature compartment is observed in the elderly. Despite the decreased frequency, BM-MDSCs maintain their suppressive capacity in aged donors. Taken together, these results indicate that in vitro induction of MDSCs from the BM is reduced with aging and opens new hypotheses on the role of age-related processes in myelopoiesis

Activated T cells sustain myeloid-derived suppressor cell-mediated immune suppression

The expansion of myeloid-derived suppressor cells (MDSCs), a suppressive population able to hamper the immune response against cancer, correlates with tumor progression and overall survival in several cancer types. We have previously shown that MDSCs can be induced in vitro from precursors present in the bone marrow and observed that these cells are able to actively proliferate in the presence of activated T cells, whose activation level is critical to drive the suppressive activity of MDSCs. Here we investigated at molecular level the mechanisms involved in the interplay between MDSCs and activated T cells. We found that activated T cells secrete IL-10 following interaction with MDSCs which, in turn, activates STAT3 phosphorylation on MDSCs then leading to B7-H1 expression. We also demonstrated that B7-H1+ MDSCs are responsible for immune suppression through a mechanism involving ARG-1 and IDO expression. Finally, we show that the expression of ligands B7-H1 and MHC class II both on in vitro-induced MDSCs and on MDSCs in the tumor microenvironment of cancer patients is paralleled by an increased expression of their respective receptors PD-1 and LAG-3 on T cells, two inhibitory molecules associated with T cell dysfunction. These findings highlight key molecules and interactions responsible for the extensive cross-talk between MDSCs and activated T cells that are at the basis of immune suppression

Immunosuppressive activity of tumor-infiltrating myeloid cells in patients with meningioma

Meningiomas WHO grade I and II are common intracranial tumors in adults that normally display a benign outcome, but are characterized by a great clinical heterogeneity and frequent recurrence of the disease. Although the presence of an immune cell infiltrate has been documented in these tumors, a clear phenotypical and functional characterization of the immune web is missing. Here, we performed an extensive immunophenotyping of peripheral blood and fresh tumor tissue at surgery by multiparametric flow cytometry in 34 meningioma patients, along with immunosuppressive activity of sorted cells of myeloid origin. Four subsets of myeloid cells, phenotypically corresponding to myeloid-derived suppressor cells (MDSCs) are detectable in the blood and in the tumor tissue of patients and three of them are significantly expanded in the blood of patients, but show no evidence of suppressive activity. At the tumor site, a large leukocyte infiltrate is present, predominantly constituted by CD33 myeloid cells, largely composed of macrophages endowed with suppressive activity and significantly expanded in grade II meningioma patients as compared to grade I

In vitro characterization of adipose stem cells non-enzymatically extracted from the thigh and abdomen

Autologous fat grafting is a surgical technique in which adipose tissue is transferred from one area of the body to another, in order to reconstruct or regenerate damaged or injured tissues. Before reinjection, adipose tissue needs to be purified from blood and cellular debris to avoid inflammation and preserve the graft viability. To perform this purification, different enzymatic and mechanical methods can be used. In this study, we characterized in vitro the product of a closed automatic device based on mechanical disaggregation, named Rigenera\uae, focusing on two sites of adipose tissue harvesting. At first, we optimized the Rigenera\uae operating timing, demonstrating that 60 s of treatment allows a higher cellular yield, in terms of the cell number and growth rate. This result optimizes the mechanical disaggregation and it can increase the clinical efficiency of the final product. When comparing the extracted adipose samples from the thigh and abdomen, our results showed that the thigh provides a higher number of mesenchymal-like cells, with a faster replication rate and a higher ability to form colonies. We can conclude that by collecting adipose tissue from the thigh and treating it with the Rigenera\uae device for 60 s, it is possible to obtain the most efficient product

Immunosuppression by monocytic myeloid-derived suppressor cells in patients with pancreatic ductal carcinoma is orchestrated by STAT3

Background: Pancreatic ductal adenocarcinoma (PDAC) is a highly devastating disease with an overall 5-year survival rate of less than 8%. New evidence indicates that PDAC cells release pro-inflammatory metabolites that induce a marked alteration of normal hematopoiesis, favoring the expansion and accumulation of myeloid-derived suppressor cells (MDSCs). We report here that PDAC patients show increased levels of both circulating and tumor-infiltrating MDSC-like cells. Methods: The frequency of MDSC subsets in the peripheral blood was determined by flow cytometry in three independent cohorts of PDAC patients (total analyzed patients, n = 117). Frequency of circulating MDSCs was correlated with overall survival of PDAC patients. We also analyzed the frequency of tumor-infiltrating MDSC and the immune landscape in fresh biopsies. Purified myeloid cell subsets were tested in vitro for their T-cell suppressive capacity. Results: Correlation with clinical data revealed that MDSC frequency was significantly associated with a shorter patients' overall survival and metastatic disease. However, the immunosuppressive activity of purified MDSCs was detectable only in some patients and mainly limited to the monocytic subset. A transcriptome analysis of the immunosuppressive M-MDSCs highlighted a distinct gene signature in which STAT3 was crucial for monocyte re-programming. Suppressive M-MDSCs can be characterized as circulating STAT3/arginase1-expressing CD14+ cells. Conclusion: MDSC analysis aids in defining the immune landscape of PDAC patients for a more appropriate diagnosis, stratification and treatment

Induction of immunosuppressive functions and NF-\u3baB by FLIP in monocytes

Immunosuppression is a hallmark of tumor progression, and treatments that inhibit or deplete monocytic myeloid-derived suppressive cells could promote anti-tumor immunity. c-FLIP is a central regulator of caspase-8-mediated apoptosis and necroptosis. Here we show that low-dose cytotoxic chemotherapy agents cause apoptosis linked to c-FLIP down-regulation selectively in monocytes. Enforced expression of c-FLIP or viral FLIP rescues monocytes from cytotoxicity and concurrently induces potent immunosuppressive activity, in T cell cultures and in vivo models of tumor progression and immunotherapy. FLIP-transduced human blood monocytes can suppress graft versus host disease. Neither expression of FLIP in granulocytes nor expression of other anti-apoptotic genes in monocytes conferred immunosuppression, suggesting that FLIP effects on immunosuppression are specific to monocytic lineage and distinct from death inhibition. Mechanistically, FLIP controls a broad transcriptional program, partially by NF-\u3baB activation. Therefore, modulation of FLIP in monocytes offers a means to elicit or block immunosuppressive myeloid cells

Cellule soppressorie di derivazione mieloide: espansione nei pazienti con tumore, induzione in vitro con fattori di crescita ed analisi dei meccanismi molecolari coinvolti nell'immunosoppressione

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of cells that expands during cancer, inflammation and infection and are potent inhibitors of T-cell-mediated antitumor immunity. MDSC accumulate in the blood, lymph nodes and bone marrow and at tumor sites in most patients and experimental animals with cancer and inhibit both adaptative and innate immunity. Expansion, mobilization and activaction of MDSC is driven by tumors-secreted growth factors, and by a profound alteration of myelopoiesis. In cancer patients the nature of MDSC is still poorly defined since evidence exists for both monocytic and granulocytic features. In the present study we evaluated the phenotype and the suppressive activity of leukocyte subsets freshly isolated from the blood of melanoma and colon cancer patients. Our results indicate that cells with characteristics of MDSC can be found in both mononuclear and polymorphonuclear fraction, and that a useful marker for their identification is the alpha chain of IL4R. Subsequently, we defined growth factors able to generate MDSC in vitro from human bone marrow precursors and to use these cells to characterize better the biology and phenotype of human MDSC. We demonstrated that combinations of some cytokine, such as G-CSF, GM-CSF and IL-6 induce the expansion of bone-marrow immature myeloid populations (BM-MDSC) expressing IL4Ra, with phenotype and inhibitory activity comparable to patients' MDSC. Functional assays revealed that only cytokine-treated bone marrow cells are able to suppress lymphocyte proliferation, while ex-vivo isolated cells and untreated bone marrow cells do not interfere significantly with T lymphocyte proliferation. BM-MDSC suppress activation of both alloactivated and mitogen activated T lymphocytes. We further examined BM-MDSC mechanisms of suppression, and we demonstrated that these cells are able to suppress lymphocyte proliferation by decreasing lymphocyte CD3z chain expression and that suppression requires cell-to-cell contact. Immunoregulatory activity of BM-MDSC is dependent on C/EBPb transcription factor, a key component of the emergency myelopoiesis, because the knock down of C/EBPb leads to a marked decrease in the immunosuppressive activity of BM-MDSC. Since BM-derived MDSC consist of a heterogeneous myeloid population, we separated myeloid fractions with immunomagnetic sorting and we demonstrated that the Lineage negative fraction of BM-MDSC contains the main immunosuppressive activity by inducing a decrease of lymphocyte proliferation and of CD3z expression.Le cellule soppressorie di derivazione mieloide (MDSC) costituiscono una popolazione molto eterogenea che viene espansa in alcune condizioni patologiche, come le neoplasie, le infiammazioni e le infezioni ed ha la capacità di inibire potentemente l'immunità antitumorale mediata dai linfociti T. Le MDSC si accumulano nel sangue, nei linfonodi, nel midollo osseo e nel microambiente tumorale, in pazienti ed in modelli animali portatori di tumore e inibiscono sia la risposta immunitaria innata, che quella adattativa. L'espansione, la mobilizzazione e l'attivazione delle MDSC è indotta da fattori di crescita rilasciati della cellule tumorali e da un'estesa alterazione della mielopoiesi. In pazienti portatori di tumore la caratterizzazione fenotipica e funzionale delle MDSC non è ancora completamente definita, ma esistono evidenze sia sulla natura granulocitaria che su quella monocitaria di tale popolazione. In questo lavoro di tesi abbiamo valutato il fenotipo e l'attività soppressoria di popolazioni leucocitarie isolate dal sangue periferico di pazienti affetti da tumore del colon e melanoma. I nostri risultati indicano che cellule con caratteristiche delle MDSC possono essere trovate sia nella frazione monocitaria che in quella granulocitaria e che un marcatore utile per la loro identificazione è la catena alpha del recettore dell'interleuchina 4 (IL4Ra). Nella seconda parte di questo lavoro abbiamo definito i fattori di crescita necessari per l'induzione in vitro di MDSC da progenitori mieloidi midollari, ed abbiamo usato tali cellule per caratterizzare la biologia ed il fenotipo delle MDSC. Abbiamo dimostrato che le combinazioni di alcune citochine, come G-CSF, GM-CSF e IL-6 inducono l'espansione di popolazioni mieloidi immature midollari (BM-MDSC) che esprimono IL4Ra e dotate di caratteristiche fenotipiche e funzionali simili a quelle delle MDSC espanse nei pazienti. I saggi funzionali hanno mostrato che solo le cellule trattate con le citochine sono in grado di inibire la proliferazione linfocitaria, mentre le cellule isolate ex-vivo o le colture mantenute in vitro senza l'aggiunta dei fattori di crescita, non interferiscono in modo significativo con la proliferazione linfocitaria. Le MDSC derivate da midollo (BM-MDSC) sopprimono sia la proliferazione dei linfociti attivati da alloantigeni, che la proliferazione di linfociti attivati da mitogeni. Abbiamo quindi analizzato i meccanismi di soppressione delle BM-MDSC ed abbiamo dimostrato che tali cellule sono in grado di sopprimere la proliferazione linfocitaria inducendo una diminuzione dell'espressione della catena z del CD3 e che la soppressione mediata dalle BM-MDSC richiede il contatto cellula-cellula. L'attività immunoregolatrice delle BM-MDSC dipende dal fattore di trascrizione C/EBPb, un componente chiave della granulopoiesi di emergenza, dal momento che la diminuzione della proteina induce una marcata inibizione dell'attività soppressoria delle BM-MDSC. Infine abbiamo separato alcune sottopopolazioni mieloidi presenti nelle BM-MDSC, poichè queste sono rappresentate da una popolazione mieloide eterogenea, ed abbiamo dimostrato che la frazione cellulare Lineage- è responsabile della maggiore attività immunosoppressoria inducendo una diminuzione della proliferazione linfocitaria e dell'espressione del CD3z di superficie

Antigen specificity of immune suppression by myeloid-derived suppressor cells.

Among the mechanisms set in motion by the tumor to escape the control of the immune system, MDSCs play a central role in inducing tolerance to a variety of antitumor effectors, including T lymphocytes. It has been demonstrated that MDSCs expand in tumor-bearing mice and in cancer patients, leading to an impairment of T cell reactivity against the tumor. However, as the presence of MDSCs is not correlated with a general immune suppression, it was advanced that a mechanism regulating the specificity of MDSC inhibition must be present. In this article, we review the literature showing that MDSCs exert their immune-suppressive function on Ag-specific T cell responses but at times, also on mitogen-activated T lymphocytes, therefore bypassing the Ag dependency. We propose that the features of MDSC-mediated immune suppression might be influenced not only by the specific microenvironment in which MDSCs expand and by the tumor characteristics but also by the levels of activation of the target lymphocytes. J. Leukoc. Biol. 90: 31-36; 2011

Highlights on molecular mechanisms of MDSC-mediated immune suppression:\ua0paving the way for new working hypotheses.

Abstract MDSCs have been recognized in the last years as tolerogenic cells, potentially dangerous in the context of neoplasia, since they are able to induce tolerance to a variety of anti-tumor effectors, including CD4 and CD8 T cells. It is currently believed that the origin of MDSCs is due to an arrest of the myeloid differentiation process caused by tumor-secreted factors released in the tumor microenvironment that are able to exert an effect on myeloid progenitors, rendering them unable to terminally differentiate into dendritic cells, granulocytes and macrophages. As a consequence, these immature myeloid cells acquire suppressive activity through the activation of several mechanisms, controlled by different transcription factors. The lack of consensus about the phenotypical characterization of human MDSCs is the result of the existence of different MDSC subsets, most likely depending on the tumor in which they expand and on the tumor specific cytokine cocktail driving their activation. This, in turn, might also influence the mechanisms of MDSC-mediated immune suppression. In this review article we address the role of tumor-derived factors (TDFs) in MDSC-recruitment and activation, discuss the complex heterogeneity of MDSC phenotype and analyze the crosstalk between activated T cells and MDSCs. \ua9 2012 Informa Healthcare USA, Inc

Myeloid-derived suppressor cell heterogeneity in human cancers

The dynamic interplay between cancer and host immune system often affects the process of myelopoiesis. As a consequence, tumor-derived factors sustain the accumulation and functional differentiation of myeloid cells, including myeloid-derived suppressor cells (MDSCs), which can interfere with T cell-mediated responses. Since both the phenotype and mechanisms of action of MDSCs appear to be tumor-dependent, it is important not only to determine the presence of all MDSC subsets in each cancer patient, but also which MDSC subsets have clinical relevance in each tumor environment. In this review, we describe the differences between MDSC populations expanded within different tumor contexts and evaluate the prognostic significance of MDSC expansion in peripheral blood and within tumor masses of neoplastic patients