Myeloid-derived Regulatory Cells Research Articles

(469) - Lung Microbiome Predicts Myeloid Derived Suppressor Cell Response in Lung Transplant

Recent evidence suggests a role for lung microbiome in the occurrence of bronchiolitis obliterates syndrome (BOS) in lung transplant recipients (LTR); however the mechanism is unclear. In this study, we hypothesized that changes in diversity and/or abundance of the lung microbiome modulate host immune responses and contribute to activation of myeloid derived regulatory cells (MDRCs) leading to BOS. BAL samples from 10 adult LTR were collected. Six serial fractions of BAL return were collected and labeled BAL 1(proximal airway) thru BAL 6 (distal airway). Oral wash (OW) and nasal swabs (N) were collected. 16S rDNA genes were amplified using V4 primers and PCR products sequenced for microbiome analysis. MDRC subsets were enumerated from BAL using multi-parameter flow cytometry. Alpha diversity (Shannon index -SI) was found to be significantly higher in BAL1 (mean SI= 6.6), BAL6 (average SI =6.8) and N (average SI=6.3) as compared to OW (SI=3.6) (p<0.0001). Beta-diversity between (unifrac-weighted distance) was significantly greater between OW microbiome and BAL1, BAL6 and N microbiome (p<0.001). N microbiome was similar to both BAL1 and BAL6. Significant differences in microbiome of BAL1 and BAL6 were noted. BAL1 had a higher proportion of immunosuppressive MDRCs (CD14+HLA-DR−CD11b+CD16−CD66b− (A) and CD14−HLA-DR−CD11b+CD16+CD66b+(B)), while BAL6 had a significantly higher proportion of pro-inflammatory (CD163+HLA-DR+CD11b+CD16−CD66b−(C)) MDRCs (p<0.05). Correlation analysis revealed that in BAL1, phyla Actinobacteria had a significant positive correlation with MDRCs subsets B (p= 0.002) and C (p=0.02). Phyla Chlorobi was positively correlated with subset A (p=0.04) and phyla Planctomycetes (p= 0.02) and TM7 (p=0.04) were positively correlated with subset C. In comparison, in B6 only phyla TM7 had a significant positive correlation with subset B (p=0.003) and C (p=0.01). Additionally, the interaction between proportions of subset B and airway microbiome (B1/B6) was significant in predicting the total gram+ bacterial abundance (p=0.046). In LTR, nasal but not oral microbiome correlates with lung microbiome. There exist negative and positive correlation of certain bacteria with various MDSCs. An imbalance in the ratio of immunosuppressive and pro-inflammatory MDSCs may contribute to the pathogenesis of BOS.

Cancer-Associated Myeloid Regulatory Cells.

Myeloid cells are critically involved in the pathophysiology of cancers. In the tumor microenvironment (TME), they comprise tumor-associated macrophages (TAMs), neutrophils (TANs), dendritic cells, and myeloid-derived suppressor cells, which are further subdivided into a monocytic subset and a granulocytic subset. Some of these myeloid cells, in particular TAMs and TANs, are divided into type 1 or type 2 cells, according to the paradigm of T helper type 1 or type 2 cells. Type 1-activated cells are generally characterized as cells that aid tumor rejection, while all other myeloid cells are shown to favor tumor progression. Moreover, these cells are often at the basis of resistance to various therapies. Much research has been devoted to study the biology of myeloid cells. This endeavor has proven to be challenging, as the markers used to categorize myeloid cells in the TME are not restricted to particular subsets. Also from a functional and metabolic point of view, myeloid cells share many features. Finally, myeloid cells are endowed with a certain level of plasticity, which further complicates studying them outside their environment. In this article, we challenge the exclusive use of cell markers to unambiguously identify myeloid cell subsets in the TME. We further propose to divide myeloid cells into myeloid regulatory or stimulatory cells according to their pro- or antitumor function, because we contend that for therapeutic purposes it is not targeting the cell subsets but rather targeting their protumor traits; hence, myeloid regulatory cells will push antitumor immunotherapy to the next level.

Transplantation Tolerance Induction: Cell Therapies and Their Mechanisms.

Cell-based therapies have been studied extensively in the context of transplantation tolerance induction. The most successful protocols have relied on transfusion of bone marrow prior to the transplantation of a renal allograft. However, it is not clear that stem cells found in bone marrow are required in order to render a transplant candidate immunologically tolerant. Accordingly, mesenchymal stem cells, regulatory myeloid cells, T regulatory cells, and other cell types are being tested as possible routes to tolerance induction, in the absence of donor-derived stem cells. Early data with each of these cell types have been encouraging. However, the induction regimen capable of achieving consistent tolerance, while avoiding unwanted sided effects, and which is scalable to the human patient, has yet to be identified. Here, we present the status of investigations of various tolerogenic cell types and the mechanistic rationale for their use in tolerance induction protocols.

Compensatory Regulatory Networks between CD8 T, B, and Myeloid Cells in Organ Transplantation Tolerance.

In transplantation tolerance, numerous regulatory populations have the capacity to inhibit allograft rejection; however, their compensatory capacities have never been clearly evidenced. We have previously demonstrated that the tolerogenic effect mediated by CD8(+)CD45RC(low) regulatory T cells (Tregs) in a model of organ transplantation with CD40Ig could be abrogated by permanent depletion of CD8(+) cells that resulted in allograft rejection in half of the recipients. This result demonstrated that CD8(+) Tregs were essential, but also that half of the recipients still survived indefinitely. We also demonstrated that no other regulatory populations, besides CD8(+) Tregs, could induce and maintain allograft tolerance in CD40Ig-treated tolerant animals. In the current study, we analyzed the mechanisms that arose following CD8(+) Treg depletion and allowed establishment of networks of new regulatory cells to maintain allograft survival. We identified regulatory B cells (Bregs) and regulatory myeloid cells (RegMCs) as being responsible of the maintenance of the long-term allograft survival. We demonstrated that both regulatory cell subsets efficiently inhibited antidonor immune responses in adoptively transferred recipients. Although Bregs were induced, they were not essential for the maintenance of the graft as demonstrated in IgM-deficient recipients. In addition, we showed that RegMCs were the most suppressive and acted alone, whereas Bregs activity was associated with increased suppressive activity of other subsets in adoptively transferred recipients. Altogether, to our knowledge, we demonstrated in this study for the first time the emergence of both Bregs and RegMCs following Tregs depletion and highlighted the importance of regulatory cell networks and their synergistic potential in transplantation.

GM-CSF and the role of myeloid regulatory cells in the pathogenesis and treatment of Crohn's disease.

Background Intestinal monocytes/macrophages sustain the intestinal immune homeostasis and might be an attractive therapeutic target for the management of inflammatory bowel disease (IBD). Granulocyte macrophage colony-stimulating factor (GM-CSF) exerts beneficial effects on intestinal inflammation and promotes signal transducer and activator of transcription 3 (STAT3)-mediated expansion of myeloid-derived suppressor cells (MDSCs). However, the full action mechanism of GM-CSF, and especially whether monocytes mediate its therapeutic effects in vivo, had not been previously elucidated. Conclusions This review article summarizes recent developments in the immunology of mucosal diseases and describes new aspects of the role of myeloid regulatory cells in IBD and the function of GM-CSF in maintaining the intestinal immune homeostasis in Crohn’s disease (CD). This review article highlights the exploration of stimulating in addition to suppressive therapies for patients with IBD and underpins that myeloid regulatory cells might become a promising novel cell-based therapeutic option.

Adoptive cellular therapy containing T cells and CD25+ NKT cells modulates myeloid cells and stimulates endogenous anti-tumor immune function (VAC7P.1038)

Abstract Myeloid-derived suppressor cells (MDSCs) are a type of myeloid regulatory cell (Mreg) that suppresses the anti-tumor activity of immune effector cells. We have previously demonstrated that CD25+ NKT cells function as cellular adjuvants for converting MDSC into immune stimulatory myeloid cells, thereby rescuing anti-tumor T cell function from MDSCs in vitro. Here, we sought to characterize the in vivo efficacy of adoptive cellular therapy (ACT) utilizing reprogrammed T cells and CD25+ NKT cells in modulating MDSCs in FVBN202 mice. We demonstrate a significant 2-fold decrease in the frequency and absolute number of splenic MDSCs in recipients of ACT compared with control mice bearing comparable lung metastases. We also observed a significant 2-fold increase in the frequency and absolute number of mature myeloid cells (CD11b-MHC-II+CD40+CD86+). Functional analysis was performed in which CD11b- myeloid cells from ACT-recipient animals bearing lung metastases were cultured with autologous splenocytes. CD11b- MHC II+ cells induced a significant release of splenocyte-derived IFN-γ; this response was enhanced greater than 20-fold upon the addition of tumor cells. Importantly, ACT recipients of mice bearing Ki-67hi circulating tumor cells experienced extended time to progression compared to control animals. These data suggest CD25+ NKT cells may act to promote ‘vaccination in situ’ of endogenous T cells, in addition to boosting anti-tumor efficacy of ACT.

Heme oxygenase and the immune system in normal and pathological pregnancies.

Normal pregnancy is an immunotolerant state. Many factors, including environmental, socioeconomic, genetic, and immunologic changes by infection and/or other causes of inflammation, may contribute to inter-individual differences resulting in a normal or pathologic pregnancy. In particular, imbalances in the immune system can cause many pregnancy-related diseases, such as infertility, abortions, pre-eclampsia, and preterm labor, which result in maternal/fetal death, prematurity, or small-for-gestational age newborns. New findings imply that myeloid regulatory cells and regulatory T cells (Tregs) may mediate immunotolerance during normal pregnancy. Effector T cells (Teffs) have, in contrast, been implicated to cause adverse pregnancy outcomes. Furthermore, feto-maternal tolerance affects the developing fetus. It has been shown that the Treg/Teff balance affects litter size and adoptive transfer of pregnancy-induced Tregs can prevent fetal rejection in the mouse. Heme oxygenase-1 (HO-1) has a protective role in many conditions through its anti-inflammatory, anti-apoptotic, antioxidative, and anti-proliferative actions. HO-1 is highly expressed in the placenta and plays a role in angiogenesis and placental vascular development and in regulating vascular tone in pregnancy. In addition, HO-1 is a major regulator of immune homeostasis by mediating crosstalk between innate and adaptive immune systems. Moreover, HO-1 can inhibit inflammation-induced phenotypic maturation of immune effector cells and pro-inflammatory cytokine secretion and promote anti-inflammatory cytokine production. HO-1 may also be associated with T-cell activation and can limit immune-based tissue injury by promoting Treg suppression of effector responses. Thus, HO-1 and its byproducts may protect against pregnancy complications by its immunomodulatory effects, and the regulation of HO-1 or its downstream effects has the potential to prevent or treat pregnancy complications and prematurity.

Permanent acceptance of mouse cardiac allografts with CD40 siRNA to induce regulatory myeloid cells by use of a novel polysaccharide siRNA delivery system.

The CD40/CD154 co-stimulatory pathway is crucial in alloimmune response. We developed a novel small interfering RNA (siRNA) delivery system with a poly-dA extension at the 5'-end of the siRNA sense strand that was stably incorporated into 1,3-β-glucan (schizophyllan, SPG). This was captured and incorporated into dendritic cells (DCs) through its receptor, Dectin-1, specifically silencing CD40 genes (siCD40) to exert immunoregulatory activity. siCD40/SPG-treated CBA mice permanently accepted B10 fully mismatched cardiac allografts. Consistent with graft survival, the infiltration of CD4(+), CD8(+) T cells into the graft was lower, and that the numbers of CD40(low)CD11c(+) DCs cells and CD4(+)Foxp3(+)cells were increased in both the graft and in the recipient spleen. In addition, naive CBA recipients given an adoptive transfer of splenocytes from the primary recipients with siCD40/SPG accepted a heart graft from donor-type B10, but not third-party Balb/c mice. In conclusion, the treatment with siCD40/SPG targeting DCs could generate antigen-specific Tregs, resulting in the permanent acceptance of mouse cardiac allografts. These findings have important implications for clarifying the mechanism underlying the induction of tolerance in DCs, and also highlight the potential of immunomodulation and the feasibility of siRNA-based clinical therapy in the transplantation field.

Myeloid regulatory cells: cross talk of innate and adaptive immunity to maintain the intestinal immune homeostasis in inflammatory bowel disease

Meeting abstract Intestinal monocytes/macrophages sustain the intestinal immune homeostasis and might be an attractive therapeutic target for the management of inflammatory bowel disease (IBD). Granulocyte macrophage colonystimulating factor (GM-CSF) exerts beneficial effects in intestinal inflammation and promotes STAT3-mediated expansion of myeloid-derived suppressor cells (MDSCs). We explored whether GM-CSF mediates its beneficial effects in IBD via myeloid regulatory cells (Mreg). Here we show that GM-CSF i) provokes non-classical monocyte activation; ii) drives monocytes towards an antiinflammatory phenotype; iii) enhances innate immune functions; iv) primes monocyte responses to secondary microbial stimuli; and v) accelerates epithelial healing via monocytes. GM-CSF-activated monocytes (GMaM) show therapeutic activity in T cell-induced colitis in Rag1 mice with increased production of IL-4, IL-10, IL-13 and decreased production of IFNg in LPMCs. Confirming this finding, GMaM attract T cells and shape their differentiation towards Th2 cells in vitro. In addition, GMaM induce regulatory (Foxp3) T cells (Treg) in vitro and adoptive transfer of GMaM in chronic DSS-induced colitis ameliorates disease in vivo with accelerated gut homing of GMaM and induction of colonic Treg. Myeloid-cell specific STAT3 activation protects gp130 mice from colitis via MDSC expansion and increased production of suppressive and protective cytokines. LysMcre/STAT3 mice with myeloid-specific STAT3-deficiency show opposite effects and are not protected from colitis. Additionally, MDSCs of gp130 mice produce significantly more IL-4, IL-10 and IL-13. In summary, beneficial effects of GM-CSF in IBD may possibly be mediated through reprogramming of monocytes and MDSCs via enhanced innate immune functions as well as regulation of adaptive immunity. Our findings support the exploration of stimulating rather than suppressive therapies for patients with IBD and underpin that Mreg might become a promising novel cell-based therapeutic option.

Payload drug vs. nanocarrier biodegradation by myeloperoxidase- and peroxynitrite-mediated oxidations: pharmacokinetic implications.

With the advancement of nanocarriers for drug delivery into biomedical practice, assessments of drug susceptibility to oxidative degradation by enzymatic mechanisms of inflammatory cells become important. Here, we investigate oxidative degradation of a carbon nanotube-based drug carrier loaded with Doxorubicin. We employed myeloperoxidase-catalysed and peroxynitrite-mediated oxidative conditions to mimic the respiratory burst of neutrophils and macrophages, respectively. In addition, we revealed that the cytostatic and cytotoxic effects of free Doxorubicin, but not nanotube-carried drug, on melanoma and lung carcinoma cell lines were abolished in the presence of tumor-activated myeloid regulatory cells that create unique myeloperoxidase- and peroxynitrite-induced oxidative conditions. Both ex vivo and in vitro studies demonstrate that the nanocarrier protects the drug against oxidative biodegradation.

Exposure to cigarette smoke impacts myeloid-derived regulatory cell function and exacerbates airway hyper-responsiveness

Cigarette smoking enhances oxidative stress and airway inflammation in asthma, the mechanisms of which are largely unknown. Myeloid-derived regulatory cells (MDRC) are free radical producing immature myeloid cells with immunoregulatory properties that have recently been demonstrated as critical regulators of allergic airway inflammation. NO (nitric oxide)-producing immunosuppressive MDRC suppress T-cell proliferation and airway-hyper responsiveness (AHR), while the O2•− (superoxide)-producing MDRC are proinflammatory. We hypothesized that cigarette smoke (CS) exposure may impact MDRC function and contribute to exacerbations in asthma. Exposure of bone marrow (BM)-derived NO-producing MDRC to CS reduced the production of NO and its metabolites and inhibited their potential to suppress T-cell proliferation. Production of immunoregulatory cytokine IL-10 was significantly inhibited, while proinflammatory cytokines IL-6, IL-1β, TNF-α and IL-33 were enhanced in CS-exposed BM-MDRC. Additionally, CS exposure increased NF-κB activation and induced BM-MDRC-mediated production of O2•−, via NF-κB-dependent pathway. Intratracheal transfer of smoke-exposed MDRC-producing proinflammatory cytokines increased NF-κB activation, reactive oxygen species and mucin production in vivo and exacerbated AHR in C57BL/6 mice, mice deficient in Type I IFNR and MyD88, both with reduced numbers of endogenous MDRC. Thus CS exposure modulates MDRC function and contributes to asthma exacerbation and identifies MDRC as potential targets for asthma therapy.

Subsets of airway myeloid-derived regulatory cells distinguish mild asthma from chronic obstructive pulmonary disease

Subsets of myeloid-derived regulatory cells (MDRCs), which are phenotypically similar to the myeloid-derived suppressor cells found in patients with cancer, have recently been appreciated as critical regulators of airway inflammation in mouse models of asthma. We test the hypothesis that subsets of airway MDRCs contribute differentially to the inflammatory milieu in human asthma and chronic obstructive pulmonary disease (COPD). We used bronchoalveolar lavage to identify and characterize human airway MDRCs from 10 healthy subjects, 9 patients with mild asthma, and 8 patients with COPD, none of whom were treated with inhaled or systemic corticosteroids. We defined subsets of airway MDRCs using flow cytometry, the molecular mediators they produce, and their abilities to regulate proliferation of polyclonally activated autologous T lymphocytes. We found substantial differences in the functional potential of MDRC subsets in healthy subjects, patients with asthma, and patients with COPD, with these differences regulated by the nitrosative and oxidative free radicals and cytokines they produced. Nitric oxide-producing MDRCs suppressed and superoxide-producing MDRCs enhanced proliferation of polyclonally activated autologous CD4 T cells. HLA-DR(+)CD11b(+)CD11c(+)CD163(-) superoxide-producing MDRCs, which stimulated proliferation of autologous T cells, comprised a high fraction of MDRCs in the airways of patients with mild asthma or COPD but not those of healthy control subjects. CD11b(+)CD14(+)CD16(-)HLA-DR(-) nitric oxide-producing MDRCs, which suppressed T-cell proliferation, were present in high numbers in airways of patients with mild asthma but not patients with COPD or healthy control subjects. Subsets of airway MDRCs conclusively discriminate patients with mild asthma, patients with COPD, and healthy subjects from each other. The distinctive activities of these MDRCs in patients with asthma or COPD might provide novel targets for new therapeutics for these common disorders. [Corrected]

480P - Phase Ii, Multicenter, Open-Label, Proof of Concept Study of Tasquinimod in Patients with Advanced Hepatocellular (Hcc), Ovarian (Oc), Renal Cell (Rcc) and Gastric (Gc) Carcinomas

ABSTRACT Aim: Tumor immunosuppression and angiogenesis play a role in disease progression in HCC, OC, RCC and GC. Tasquinimod is a novel, small molecule compound that targets the tumor microenvironment by binding to S100A9, modulating accumulation and function of regulatory myeloid cells (myeloid derived suppressor cells [MDSCs] and tumor associated macrophages [TAMs]). Tasquinimod is an immunomodulator, antiangiogenic and antimetastatic agent. Antiangiogenic effects may be partly explained by action on MDSCs and TAMs, and through interaction with histone deacetylase-4, reducing the hypoxic response and down regulating HIF1a genes. Tasquinimod significantly improves median PFS (7.6 v 3.3 months) in patients with metastatic hormone resistant prostate cancer1 and is currently in late stage development in this indication. Its unique mode of action makes tasquinimod an attractive compound to be evaluated in other tumors. The primary objective was to determine the clinical activity of tasquinimod in advanced HCC pre-treated with sorafenib, platinum-resistant OC, RCC pre-treated with VEGF inhibitor and GC pre-treated with platinum therapy. Methods: The study design has been previously reported2. The primary endpoint was the PFS rate at a predefined time for each cohort. Secondary objectives included PFS, response rate, OS, safety, pharmacokinetics and biomarkers. Results: Cohort Pts PFS rate*, % Median PFS, w (95% CI) Pts with stable disease*, N (%) Median OS, w (95% CI) OC 55 24w: 7 8 (8-17) 27 (49) NR (31-NR) RCC 38 16w: 13 15 (8-17) 18 (47) 33 (26-41) GC 21 12w: 10 6 (5-7) 5 (24) 22 (14-33) HCC** 45 N/A *Central reading; **Ongoing; NA, not assessed; NR, not reached The most frequent treatment-emergent adverse events (all grade incidence >15%) were nausea (44%), vomiting (34%), constipation (32%), abdominal pain (32%), diarrhea (22%), fatigue (47%), decreased appetite (40%), back pain (27%), cough (22%), peripheral edema (20%), and insomnia (18%). Conclusions: The data did not support further development of tasquinimod mono therapy in heavily pretreated patients with OC, RCC and GC. Pharmacokinetic and biomarkers analyses are ongoing.HCC cohort is continuing with results expected 2015. Pili R et al, J Clin Oncol. 2011; 29:4022-8. Escudier B et al, J Clin Oncol. 2013;31(abstract TPS2622). Disclosure: R. Plummer: Ipsen funding to institution for present study; I.B. Vergote: Amgen, AstraZeneca, Boehringer Ingelheim, Bristol Myers Squibb, Chugai, Eisai, Eli Lilly, GE, GSK, Ipsen, Janssen, Menarini, MSD, Novartis, Novo Nordisk, Pfizer, Quintiles, Roche, Sanofi, Sandoz, Shering-Plough, Vifor, Wyett; R.J. Jones: Ipsen research funding GSK research funding, speaker honoraria, advisory board Pfizer research funding, speaker honoraria, advisory board Novartis research funding, speaker honoraria, advisory board Roche research funding; E. Van Cutsem: Ipsen funding to institution for present study; S. Faivre: Ipsen: research funding, advisory board; C. Descot: Ipsen employee; N. Germann: Ipsen employee. All other authors have declared no conflicts of interest.

Evolution of Our Understanding of Myeloid Regulatory Cells: From MDSCs to Mregs.

The term myeloid-derived suppressor cells (MDSCs) was first suggested in 2007 in order to reflect the origin and function of myeloid cells during immunosuppression in cancer and other pathologic conditions. Emerging evidence suggests that MDSCs suppress CTL and Th1 responses in malignant diseases while they regulate effective immune responses in parasitic and helminth infections as well as Th17 inflammatory response during autoimmune diseases. Based on these data, the term myeloid regulatory cells (Mregs) more accurately reflects their function and interactions with different cells of the immune system during diseased conditions. Here, we provide evidence on the multifaceted function of Mregs during diseased states.

31: Understanding transcriptional regulation of myeloid cells in the tumor microenvironment

31: Understanding transcriptional regulation of myeloid cells in the tumor microenvironment

Actelated dextran microparticle delivery as a means to generate regulatory myeloid cells (IRC5P.470)

Abstract Myeloid cells (MC) have potent regulatory abilities but factors influencing the development of such regulatory myeloid cells (MC-regs) remain poorly understood. Retinoic acid (RA) is a metabolite of vitamin A that has regulatory abilities and impacts myeloid cell differentiation. We have previously shown that RA produces MC-regs that expressed increased IL-10, regulatory T (Treg) cells, and were able to suppress the proliferation and cytotoxicity of CD4+ and CD8+ T cells, respectively. We hypothesize that encapsulation of RA within acetalated dextran (AC-DEX) microparticles (MPs) can be used for targeted generation of MC-regs in vivo. We used MPs containing encapsulated FITC-labeled BSA to determine the relative uptake of Ac-DEX MPs by myeloid cell populations in vitro and in vivo. We found that labeled MPs were readily taken up by macrophages, DCs and myeloid progenitors in vitro. Following in vivo injection, increased percentage of FITC+ cells was seen in both CD11c+CD11b- and CD11c-CD11b+ cells in draining lymph nodes (DLN) over controls of free FITC or empty MP administration. When RA was encapsulated into MPs, CD11b+ cells within the DLNs had a increased PD-L1 expression and proliferation in DLNs was decreased. These results suggest that in vivo targeted delivery of regulatory compounds by Ac-DEX MPs can induce MC-regs which may be useful to treat inlammatory and immune-mediated diseases.

Continuous retinoic acid induces the differentiation of mature regulatory monocytes but fails to induce regulatory dendritic cells

BackgroundMyeloid cells (MC) have potent immunoregulatory abilities that can be therapeutically useful to treat inflammatory disease. However, the factors which promote regulatory myeloid cell differentiation remain poorly understood. We have previously shown that estriol (E3) induces mature regulatory dendritic cells in vivo. To determine whether additional steroid hormones could induce mature regulatory myeloid cells, we investigated the effects of retinoic acid (RA) on MCs. Retinoic acid is a steroid hormone important in regulating mucosal immunity in the gut and promoting myeloid differentiation. We hypothesized that the presence of RA during differentiation would promote the formation of mature regulatory myeloid cells (MCregs).MethodsTo determine RA’s ability to induce regulatory myeloid cells, we differentiated bone marrow progenitor cells with granulocytic-macrophage colony-stimulating factor (GM-CSF) under the influence of RA. We found that day 7 MCs differentiated in the presence of RA had an increase in the percent positive and relative expression levels of both maturation (CD80, CD86, and MHCII) and inhibitory (PD-L1 and PD-L2) markers compared to control cells. Functionally, these day 7 RA MCs expressed increased intracellular IL-10, induced regulatory T cells in vitro compared to controls and suppressed the proliferation of responder immune cells even after inflammatory challenge with LPS.ConclusionRA induced mature regulatory myeloid cells that were suppressive and had a CD11b+ CD11c-Ly6C low/intermediate monocyte phenotype. Surprisingly, RA CD11c+ dendritic cells were not suppressive and could contribute to enhanced proliferation. These results suggest that continuous RA has unique effects on different myeloid populations during monopoeisis and dendropoiesis and promotes a population of regulatory monocytes.

Origin and pharmacological modulation of tumor‐associated regulatory dendritic cells

Protumorigenic activity of immune regulatory cells has been proven to play a major role in precluding immunosurveillance and limiting the efficacy of anticancer therapies. Although several approaches have been offered to deplete myeloid-derived suppressor cells (MDSC) and regulatory T cells, there are no data on how to control suppressive dendritic cell (DC) accumulation or function in the tumor environment. Although immunosuppressive function of DC in cancer was implicated to immature and plasmacytoid DC, details of how conventional DC (cDC) develop immunosuppressive properties remain less understood. Here, we show that the development of lung cancer in mice was associated with fast accumulation of regulatory DC (regDC) prior to the appearance of MDSC. Using the in vitro and in vivo approaches, we demonstrated that (i)both cDC and MDSC could be polarized into protumor regDC in the lung cancer environment; (ii) cDC → regDC polarization was mediated by the small Rho GTPase signaling, which could be controlled by noncytotoxic doses of paclitaxel; and (iii) prevention of regDC appearance increased the antitumor potential of DC vaccine in lung cancer. These findings not only bring new players to the family of myeloid regulatory cells and provide new targets for cancer therapy, but offer novel insights into the immunomodulatory capacity of chemotherapeutic agents used in low, noncytotoxic doses.

Mechanisms of action of tasquinimod on the tumour microenvironment

Tasquinimod is a small molecule with pleiotropic effects on the tumour microenvironment. Tasquinimod inhibits the growth and metastasis of tumour cells in vitro and in vivo. It targets the tumour microenvironment, enhancing the host immune response and inhibiting the angiogenic response. Tasquinimod influences infiltrating myeloid cells in the tumour milieu shifting the balance towards a less immunosuppressive phenotype. Myeloid-derived suppressor cells and tumour-associated macrophages are major components of the immunosuppressive microenvironment and as a result promote tumour growth and favour angiogenesis and metastasis formation. Growing evidence indicates that tasquinimod targets these myeloid cells and modulates local tumour immunity by blocking the interaction between the multifunctional protein S100A9 and its ligands receptor of advanced glycation end products and Toll-like receptor 4. Its anti-angiogenic effects are achieved at least in part through these effects on regulatory myeloid cells and also potentially through inactivating histone deacetylase-4 and reducing expression of hypoxia-inducible factor 1-controlled genes. The aim is to comprehensively review the mode of action of tasquinimod as a novel oral anti-cancer agent. Based on its unique combination of effects, tasquinimod is a novel agent with clinical therapeutic potential in various solid tumours, both alone and as part of rational combination therapy.

CD8+ T Cells Are Required For Glatiramer Acetate Therapy in Autoimmune Demyelinating Disease

The exact mechanism of glatiramer acetate (GA, Copaxone®), an FDA-approved immunomodulatory therapy for multiple sclerosis (MS), remains unclear after decades of research. Previously, we have shown that GA therapy of MS induces CD8+ T cell responses that can potentially suppress pathogenic CD4+ T cell responses. Using a murine model of MS, experimental autoimmune encephalomyelitis (EAE), we now demonstrate that CD8+ T cells are necessary in mediating the therapeutic effects of GA. Further, adoptive transfer of GA-induced CD8+ T cells resulted in amelioration of EAE, establishing a role as a viable immunotherapy in demyelinating disease. Generation of these cells required indoleamine-2,3-dioxygenase (IDO), while suppressive function depended on non-classical MHC class I, IFN-γ, and perforin expression. GA-induced regulatory myeloid cells, previously shown to activate CD4+ regulatory T cells in an antigen-independent manner, required CD8+ T cells for disease suppression in vivo. These studies demonstrate an essential role for CD8+ T cells in GA therapy and identify their potential as an adoptive immunotherapeutic agent.