Abstract 3651: Phosphatidylserine-targeting antibody induces differentiation of myeloid-derived suppressor cells into M1-like macrophages

Epithelial plasticity of cancer cells is considered to be critical for the metastatic process of cancer cells. Epithelial-mesenchymal transition (EMT) has been proved to associate with cancer metastatic dissemination from primary tumor site to distal metastatic organ. In contrast, accumulated evidence showed that the reversal process of EMT, i.e., mesenchymal-epithelial transition (MET), is critical for metastatic colonization. However, the mechanism for controlling the epithelial plasticity during metastatic process is unclear. Tumor-associated macrophages (TAMs) are the most abundant host immune cells in tumor microenvironments. TAMs have been shown to modulate cancer progression through regulating cancer cell growth and metastasis, and remodeling extracellular matrix. However, it is still unclear about the roles of TAMs in regulating epithelial plasticity during cancer metastasis. Here, we demonstrate the distinct characteristics of that the TAMs in primary and metastatic tumors. The TAMs in metastatic tumors carry a M2-like phenotype; in contrast, the TAMs in primary tumors are composed of heterogeneous population containing both M1-like and M2-like cells. Furthermore, we polarize human monocytes into M1-like and M2-like macrophages and treat cancer cells with M1 and M2 macrophages conditioned medium. We find that different macrophage subtypes have a distinct effect in modulating epithelial plasticity of cancer cells. Interestingly, polarized macrophages regulate cancer cell morphological changes through epigenetic regulation. Therefore, we propose that TAMs in tumor microenvironment may polarize into different subtypes and facilitate cancer metastatic dissemination. These findings have implications for designing alternative strategies aimed at preventing and inhibiting cancer metastasis. Citation Format: CHIH-CHAN LEE, Muh-Hwa Yang. Regulation of epithelial plasticity of cancer cells by tumor-associated macrophages. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 474. doi:10.1158/1538-7445.AM2015-474

Multiple tumor-derived factors are responsible for the accumulation and expansion of immune-suppressing myeloid-derived suppressor cells (MDSC) and M2-like tumor-associated macrophages (TAM) in tumors. Here, we show that treatment of tumor-bearing mice with docetaxel in combination with the phosphatidylserine-targeting antibody 2aG4 potently suppressed the growth and progression of prostate tumors, depleted M2-like TAMs, and MDSCs, and increased the presence of M1-like TAMs and mature dendritic cells in the tumors. In addition, the antibody markedly altered the cytokine balance in the tumor microenvironment from immunosuppressive to immunostimulatory. In vitro studies confirmed that 2aG4 repolarized TAMs from an M2- to an M1-like phenotype and drove the differentiation of MDSCs into M1-like TAMs and functional dendritic cells. These data suggest that phosphatidylserine is responsible for the expansion of MDSCs and M2-like TAMs in tumors, and that bavituximab, a phosphatidylserine-targeting antibody currently in clinical trials for cancer, could reverse this process and reactivate antitumor immunity.

<div>Abstract<p>Multiple tumor-derived factors are responsible for the accumulation and expansion of immune-suppressing myeloid-derived suppressor cells (MDSC) and M2-like tumor-associated macrophages (TAM) in tumors. Here, we show that treatment of tumor-bearing mice with docetaxel in combination with the phosphatidylserine-targeting antibody 2aG4 potently suppressed the growth and progression of prostate tumors, depleted M2-like TAMs, and MDSCs, and increased the presence of M1-like TAMs and mature dendritic cells in the tumors. In addition, the antibody markedly altered the cytokine balance in the tumor microenvironment from immunosuppressive to immunostimulatory. <i>In vitro</i> studies confirmed that 2aG4 repolarized TAMs from an M2- to an M1-like phenotype and drove the differentiation of MDSCs into M1-like TAMs and functional dendritic cells. These data suggest that phosphatidylserine is responsible for the expansion of MDSCs and M2-like TAMs in tumors, and that bavituximab, a phosphatidylserine-targeting antibody currently in clinical trials for cancer, could reverse this process and reactivate antitumor immunity. <i>Cancer Immunol Res; 1(4); 256–68. ©2013 AACR</i>.</p></div>

<div>Abstract<p>Multiple tumor-derived factors are responsible for the accumulation and expansion of immune-suppressing myeloid-derived suppressor cells (MDSC) and M2-like tumor-associated macrophages (TAM) in tumors. Here, we show that treatment of tumor-bearing mice with docetaxel in combination with the phosphatidylserine-targeting antibody 2aG4 potently suppressed the growth and progression of prostate tumors, depleted M2-like TAMs, and MDSCs, and increased the presence of M1-like TAMs and mature dendritic cells in the tumors. In addition, the antibody markedly altered the cytokine balance in the tumor microenvironment from immunosuppressive to immunostimulatory. <i>In vitro</i> studies confirmed that 2aG4 repolarized TAMs from an M2- to an M1-like phenotype and drove the differentiation of MDSCs into M1-like TAMs and functional dendritic cells. These data suggest that phosphatidylserine is responsible for the expansion of MDSCs and M2-like TAMs in tumors, and that bavituximab, a phosphatidylserine-targeting antibody currently in clinical trials for cancer, could reverse this process and reactivate antitumor immunity. <i>Cancer Immunol Res; 1(4); 256–68. ©2013 AACR</i>.</p></div>

Key words: CDK20, E4BP4, MDSC, Immunosuppression, T cell immunity The breakthrough in understanding the inhibition of negative immune regulation has paved way for cancer immunotherapy. The immune-checkpoint blockade (ICB) therapy has produced promising and yet modest objective response rates in some solid cancers such as hepatocellular carcinoma (HCC), which have been attributable to the strong immunosuppressive tumor microenvironment (TME). Accumulating evidence has demonstrated that myeloid-derived suppressor cell (MDSC), an immature myeloid population with potent T cell-suppressive activity, is remarkably associated with poor prognosis and ICB resistance of cancer patients. While targeting MDSC can blunt T cell activity, new approach is directed towards driving differentiation of MDSC into antigen presentation cell crucial for T cell priming and activation. Therefore, decoding the molecular pathways that sustain the immunosuppressive MDSCs will be instrumental in deriving strategies for greater anti-tumor immune responses. Given their pivotal roles in cell cycle and transcriptional regulation, deregulation of cyclin-dependent kinases (CDKs) has become a hallmark of several cancer types. We have recently shown that hepatoma-intrinsic CDK20, or more commonly known as cell cycle-related kinase (CCRK), mitigates anti-tumor T cell responses by expanding MDSCs within TME, while tumoral CCRK depletion diminishes MDSC-mediated immunosuppression leading to improved ICB efficacy. As emerging evidence highlights the key roles of CDKs in immune cell signaling and identity, our new findings from tumor-bearing mice and healthy human blood-derived cell models uncovered specific over-expression of CCRK in MDSCs but not lymphocytes. Notably, blockade of MDSC-intrinsic CCRK induced its differentiation into mature macrophage which amplified T cell responses in vitro and in vivo, resulting in reduced tumorigenicity. Mechanistically, CCRK inhibition suppressed signal transducer and activator of transcription 3 (STAT3) signaling to revert E4-binding protein 4 (E4BP4)-dependent interleukin-10 (IL-10)/IL-12 imbalance and arginase I expression for maintenance of immunosuppression. As we also showed CCRK over-expression in HCC patient-derived MDSCs, the findings of this study not only unravel mechanistic insights in MDSC maintenance and differentiation, but also offer a novel therapeutic kinase-target to resolve ICB resistance, thereby conferring durable eradication of solid tumors. Acknowledgement: This project was supported by the University Grants Committee through the General Research Fund 14108219 and the Collaborative Research Fund C4045-18W. The authors declare no conflict of interests. Citation Format: Jingying Zhou, Alfred Sze Lok Cheng. Targeting myeloid cell-cycle related kinase signaling amplifies anti-tumor T cell responses via inducing myeloid derived suppressor cell differentiation [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 400.

The relapse of cancer after frontline therapies like chemotherapy is a major clinical problem as tumors often grow back at the site of surgical removal and/or as metastases. Tumor-associated macrophages (TAMs) are a major cellular component of both primary and metastatic tumors, and promote such key processes in tumor progression as angiogenesis, immunosuppression, invasion, and metastasis. Gene expression profiling and immunostaining studies have identified both classically (M1) and alternatively (M2) activated TAMs in human and mouse tumors. Heavily M2-skewed TAMs - those expressing the angiopoietin receptor, TIE2 - have been shown to be important for angiogenesis and immunosuppression in mouse tumors. Moreover, high levels of TAMs expressing another M2 marker, CD163, correlate with poor prognosis in various forms of human cancer. TAMs have been shown recently to reduce the sensitivity of mouse mammary tumors to cytotoxic agents like paclitaxel (PTX) and doxorubicin. Here, we report on our use of various mouse tumor models to investigate the role of TAMs in tumor relapse after chemotherapy. Our studies show that a distinct subset of M2-skewed, CXCR4hi VEGF+ TAMs cluster around blood vessels after administration of various cytotoxic agents. This correlated with increased tumor CXCL12 levels - and the selective depletion of this perivascular TAM subset, using the CXCR4 antagonist, AMD3100 (Plerixafor), revealed an important role for these cells in driving revascularisation and regrowth in post-chemotherapy tumors. Additionally, adoptive transfer of this TAM subset into tumor-bearing mice after chemotherapy accelerated tumor regrowth. No such effect was seen with non-M2 skewed TAMs isolated from the same tumors. These studies suggest that combining chemotherapy with inhibitors of the CXCL12-CXCR4 axis could delay tumor relapse in cancer patients. Citation Format: Claire E. Lewis. Perivascular, CXCR4-expressing macrophages in tumors promote relapse following chemotherapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-168. doi:10.1158/1538-7445.AM2014-LB-168

Antiangiogenic therapy is associated with increased radiographic responses in glioblastomas (GBMs), but tumors invariably recur. Because tumor-associated macrophages (TAMs) have been shown to mediate escape from antiangiogenic therapy in preclinical models, we examined the role of TAMs in recurrent glioblastoma (rGBM) patients. We compared autopsy brain specimens from 20 rGBM patients who received antiangiogenic treatment and chemoradiation (AAT+) to 8 patients who received chemotherapy and/or radiotherapy without antiangiogenic therapy, or no treatment (AAT-). TAMs were morphologically and phenotypically analyzed using flow cytometry and immunohistochemistry (IHC) for CD68, CD14, CD163, and CD11b expression. Flow cytometry showed an increase in TAMs in the AAT+ patients. IHC analysis demonstrated an increase in CD68+ TAMs in the tumor bulk (p<0.01) and infiltrative areas (p=0.02) in AAT+ patients. We also observed an increase in CD11b+ cells in the tumor bulk (p<0.01) and an increase in CD163+ TAMs in infiltrative tumor (p=0.02). Of note, an increased number of CD11b+ cells in bulk and infiltrative tumor (p=0.05 and p=0.05, respectively) correlated with poor overall survival in patients who first received antiangiogenic therapy at recurrence. In summary, rGBMs showed an increased infiltration in myeloid populations in the tumor bulk and in the infiltrative regions after antiangiogenic therapy. Higher numbers of CD11b+ cells correlated with poor survival in rGBM patients. These data suggest that TAMs may participate in escape from antiangiogenic therapy and may represent a potential biomarker of resistance and a potential therapeutic target in rGBM. Citation Format: Christine Lu-Emerson, Matija Snuderl, Nathaniel D. Kirkpatrick, Jermaine Goveia, Jennie Taylor, Christian Davidson, Yuhui Huang, Lars Riedemann, S. Percy Ivy, G. Dan Duda, Marek Ancukiewicz3, Scott R. Plotkin, Andrew Chi, Elizabeth R. Gerstner, April F. Eichler, Jorg Dietrich, Anat O. Stemmer-Rachamimov, Tracy T. Batchelor, Rakesh K. Jain. Increase in tumor-associated macrophages (TAMs) after antiangiogenic therapy is associated with poor survival in recurrent glioblastoma (GBM) patients. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-339. doi:10.1158/1538-7445.AM2013-LB-339

Pancreatic cancer is the fourth most common cause of cancer-related death in the United States with many patients that are diagnosed dying within one year. Pancreatic ductal adenocarcinoma is an inflammatory disease and includes several stromal elements such as lymphocytes and other immune cells, fibroblasts, and stellate cells. Pancreatic stellate cells (PSC), also known as cancer associated fibroblasts, can provide pro-survival signals to tumor cells, however their interactions with immune cells within the tumor microenvironment have not been explored in detail. We hypothesized that factors produced by human PSC could enhance myeloid-derived suppressor cell (MDSC) differentiation and function, which promotes immunosuppression in the tumor microenvironment. Primary PSC were harvested from human specimens and morphology was confirmed via immunofluorescent microscopy and staining for vimentin, alpha-smooth muscle actin (α SMA), and glial fibrillary acidic protein (GFAP). We analyzed soluble factors from PSC and human fetal primary pancreatic fibroblast cell line (HPPFC; negative controls) using a Luminex assay. Normal donor peripheral blood mononuclear cells (PBMC, n=3 donors) were cultured with 5 and 10% PSC supernatants, 10% HPPFC supernatants (negative control), or IL-6/GM-CSF (positive control) for 7 days, and assessed for MDSC phenotype by flow cytometry. The FLLL32 STAT3 inhibitor was used to determine whether PSC-mediated MDSC differentiation or PSC viability was STAT3-dependent. Stellate cell lines (n=7) were generated from patients and validated. Luminex analysis indicated that PSC produced cytokines involved in MDSC differentiation (IL-6, VEGF, MCSF) and chemotaxis (SDF-1, MCP-1). Culture with PSC supernatants for 7 days promoted PBMC differentiation into an MDSC (CD11b+CD33+) phenotype (p<0.01) and a sub-population of polymorphonuclear CD11b+CD33+CD15+ cells (p<0.05). Supernatants from a HPPFC were used as a negative control, which when cultured with PBMC did not induce an MDSC phenotype. The resulting CD11b+CD33+ cells were functional as they suppressed autologous T cell proliferation (p<0.05). Culture of normal PBMCs with PSC supernatants led to STAT3 but not STAT1 or STAT5 phosphorylation. Finally, the FLLL32 STAT3 inhibitor abrogated PSC-mediated MDSC differentiation, PSC viability, and reduced autocrine IL-6 production indicating these processes are STAT3 dependent (p<0.01). These data demonstrate a novel role for PSC in supporting immunosuppression associated with cancer and suggest that STAT3 within both stromal and immunosuppressive cells represents a therapeutic target. Citation Format: Thomas A. Mace, Zeenath Ameen, Wendy Frankel, Amy Collins, Sylwia Wojcik, Markus Mair, Gregory S. Young, James R. Fuchs, Tim D. Eubank, Tanios Bekaii-Saab, Mark Bloomston, Gregory B. Lesinski. Pancreatic cancer associated stellate cells promote differentiation of myeloid-derived suppressor cells in a STAT3-dependent manner. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2874. doi:10.1158/1538-7445.AM2013-2874

Efficacy of immunotherapeutic approaches against glioma is limited by the immunosuppressive tumor microenvironment. Tumor derived TGF-β, IL-10 and Prostaglandin E2 along with the presence of regulatory T cells (Tregs) and tumor associated macrophages (TAMs) promote the immune escape in gliomas. Also, tumor derived factors induce the expansion of myeloid derived suppressor cells (MDSCs). MDSCs represent a heterogeneous population of myeloid cells at various stages of differentiation that have the potential to inhibit anti-tumor T cell responses. Herein we demonstrate the accumulation of MDSCs in GL26 brain tumor bearing mice. Absolute numbers of Ly-6G+ (Gr-1high) MDSCs showed a 200 fold increase within the tumor mass 28 days post-tumor implantation. In contrast, the numbers of Ly-6C+ (Gr-1low) MDSCs did not significantly change within the tumor microenvironment. While this massive influx of MDSCs was noted within intracranial tumors, the levels of Ly-6G+ or Ly-6C+ MDSCs did not increase in the tumor draining lymph nodes (dLNs), spleen, bone marrow or blood of intracranial tumor bearing mice. Mice bearing GL26 or B16-F0 tumors in the flank showed a ∼3 fold increased influx of Ly-6G+ MDSCs within the tumor mass, the spleen and circulating MDSCs. Ly-6G+ MDSCs isolated from the brain tumors and spleens of GL26 intracranial tumor bearing mice inhibited tumor antigen-specific CD8+ T cell proliferation and T cell proliferation mediated by CD3 ligation . On the other hand, Ly-6C+ MDSCs did not did not elicit inhibition of T cell proliferation. Preliminary experiments using tumor cells' conditioned media indicate that CXCR2 signaling mediates the migration of MDSCs in a transwell assay and suggest the possibility that it could mediate MDSCs' migration into the tumor microenvironment in vivo. Overall, our data shows that MDSCs accumulate within the glioma mass and inhibit tumor-specific T cell responses. Strategies that inhibit MDSC recruitment to the tumor microenvironment and/or block their activity may therefore enhance the T cell mediated tumor clearance and suppress glioma progression. Supported by National Institutes of Health/ National Institute of Neurological Disorders & Stroke (NIH/NINDS) Grants RO1-NS074387 and RO1-NS054193 Citation Format: Neha Kamran, Hikmat Assi, Marianela Candolfi, Mariela Moreno, Youping Li, Pedro R. Lowenstein, Maria G. Castro. Glioma-infiltrating myeloid derived suppressor cells inhibit anti-tumor T cell responses. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1085. doi:10.1158/1538-7445.AM2014-1085

BackgroundV-domain immunoglobulin suppressor of T cell activation (VISTA) is a B7 family inhibitory immune checkpoint protein and is highly expressed on myeloid cells and T cells.1 VISTA acts as both...

The increasing interest in the tumour microenvironment leads to focus on new bioassays to represent all the players of the cancer immune response. Some of these players like Tumour Associated Macrophages (TAM) and Myeloid Derived Suppressor Cells (MDSC) play an important role by downregulating the anti-tumour response. Their regulation mechanisms constitute an important target for new therapeutics. In order to study these mechanisms in a human model, suppressive bioassays, mimicking the suppressive action of these cells on T cells activations, were developed. One of the important players in the tumor microenvironment are the macrophages which possess important active and regulatory functions in both innate and adaptive immune responses. Classical activated macrophages, also classified as M1-like macrophages, comprise immune effector cells with an acute inflammatory phenotype while the alternatively activated M2-like macrophages have suppressive and healing capacities. Tumor associated macrophages (TAMs) are present at high densities in solid tumors and share many characteristics with so called M2 macrophages. Although distinguished classification and in vitro generation and polarization of M1- and M2-like macrophages is challenging, in vitro assays can be a first step to screen the effect of the test molecules on the phenotype and function of the macrophages. For example, macrophage precursors display extraordinary plasticity in response to exogenous and endogenous stimuli which can lead them to M2-polarized macrophages or towards the M1-activated status. Using in vitro polarization and functional macrophage assays, one can screen molecules with the potential to influence M1 and M2 like macrophage generation and polarization. Next to that, the effect of the test molecules on the function of the macrophages can be evaluated using a macrophage suppressive assay. Here the ability of the molecules to reverse the stimulating effect of the M1-macropahges or suppressive effect of the M2-macrophages on T cells can be determined by measuring their proliferation and cytokine production. Myeloid-derived suppressor cells (MDSC) can also be found in the tumour microenvironment and present a highly suppressive phenotype. Their role in relation to cancer development and progression has shown to be of great importance. Therefore, the ability of molecules to reverse the suppressive function of the MDSC can be evaluated in vitro using these cell-type specific suppressive bioassays. The use of the bioassays contributes to a better understanding of the tumour microenvironment and the steps needed to generate an anti-tumour response by the immune system will help to assess the functional potential of new drugs, design clinical trials and ultimately discover relevant biomarkers. Citation Format: Amin Osmani, Thibaut Janss, Thibault Jonckheere, Séverine Giltaire, Sofie Pattijn, Jana Schockaert. Suppressive bioassays using macrophages and MDSCs [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 414.

Myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) play critical roles in tumorigenesis. However, the mechanisms underlying MDSC and TAM development and function remain unclear. In this study, we find that myeloid-specific activation of Notch/RBP-J signaling downregulates lactate transporter MCT2 transcription via its downstream molecule Hes1, leading to reduced intracellular lactate levels, blunted granulocytic MDSC (G-MDSC) differentiation, and enhanced TAM maturation. We identify c-Jun as a novel intracellular sensor of lactate in myeloid cells using liquid-chromatography-mass spectrometry (LC-MS) followed by CRISPR-Cas9-mediated gene disruption. Meanwhile, lactate interacts with c-Jun to protect from FBW7 ubiquitin-ligase-mediated degradation. Activation of Notch signaling and blockade of lactate import repress tumor progression by remodeling myeloid development. Consistently, the relationship between the Notch-MCT2/lactate-c-Jun axis in myeloid cells and tumorigenesis is also confirmed in clinical lung cancer biopsies. Taken together, our current study shows that lactate metabolism regulated by activated Notch signaling might participate in MDSC differentiation and TAM maturation.

Purpose: Suppressive myeloid cells such as myeloid derived suppressor cells (MDSCs) and tumor associated macrophages (TAMs) are a major barrier of cancer immunotherapy. These populations suppress immune responses, promote angiogenesis, and facilitate cancer progression and metastasis. Tasquinimod is an experimental anti-angiogenic agent tested in prostate cancer. In the current study, we investigated the novel immunomodulatory effects of tasquinimod. We focused on the modulation of myeloid populations by tasquinimod since tasquinimod binds to the inflammatory protein S100A9, which potentially activates MDSCs. Thus, we studied whether tasquinimod affects the induction/function of MDSCs and TAMs, and whether this agent can facilitate vaccine therapy in prostate and kidney cancer models. Experimental Design: The effects of tasquinimod on myeloid cells were tested in Myc-CaP and TRAMP transplantable prostate cancer models, and the RENCA orthotopic model of renal cell carcinoma. Splenocytes, blood cells, and cells from tumor samples were isolated from tumor bearing mice. The samples were subjected to staining with MDSC markers (Gr1 and CD11b) and macrophage markers (F4/80 and CD206), and to flow cytometry analysis. An immunotherapy combining tasquinimod with a modified survivin peptide vaccine, SurVaxM, was administered in Myc-CaP and TRAMP models. Tumor growth, MDSCs, and TAMs accumulation and their function after different treatments were monitored. Tasquinimod's effect on metastases is currently being tested in a LuCaP 23.1 orthotopic prostate cancer model. Results: Tasquinimod treatment reduced peripheral Gr1−CD11b+ monocytes, but did not affect the number of peripheral Gr1+CD11b+ MDSCs. However, tumor infiltrating Gr1+CD11b+ MDSCs significantly decreased following tasquinimod treatment (60% reduction, p = 0.03). In addition, Gr1−CD11b+ monocytes gained the macrophage marker, F4/80, in tumors, and tasquinimod reduced the M2 macrophages (immunosuppressive macrophages) in both peripheral sites and tumors (56% reduction, p = 0.04). Tasquinimod had a modest effect on the suppressive function of MDSCs. In the vaccine therapy, tasquinimod, combined with SurVaxM, improved antitumor immune responses and reduced tumor growth (48% inhibition, p = 0.03), as compared to vehicle and single treatments (no inhibition by SurVaxM, 15% inhibition by tasquinimod). Conclusions: Our study suggests that tasquinimod does not affect the expansion of Gr1+CD11b+ MDSCs induced by tumor, but interferes with the migration of MDSCs to tumor sites. Moreover, tasquinimod targets M2 macrophages, possibly by depleting the monocytic precursor populations such as Gr1−CD11b+ monocytes. By inhibiting MDSCs and TAMs, tasquinimod has an immunomodulatory potential to target cancer progression and metastasis, and to improve immunotherapies. Citation Format: Li Shen, Michael Ciesielski, Kiersten M. Miles, Robert Fenstermaker, Roberto Pili. Modulation of suppressive myeloid populations by tasquinimod. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4746. doi:10.1158/1538-7445.AM2013-4746

To test whether retinal pigment epithelial (RPE) cells are able to induce myeloid-derived suppressor cell (MDSC) differentiation from bone marrow (BM) progenitors. BM cells were cocultured with or without RPE cells in the presence of GM-CSF and IL-4. Numbers of resultant MDSCs were assessed by flow cytometry after 6 days of incubation. The ability of the RPE cell-induced MDSCs to inhibit T cells was evaluated by a CFSE-based T-cell proliferation assay. To explore the mechanism by which RPE cells induce MDSC differentiation, PD-L1-deficient RPE cells and blocking antibodies against TGF-β, CTLA-2α, and IL-6 were used. RPE cell-induced MDSCs were adoptively transferred into mice immunized with interphotoreceptor retinoid-binding protein in complete Freund's adjuvant to test their efficacy in suppressing autoreactive T-cell responses in experimental autoimmune uveitis (EAU). RPE cells induced the differentiation of MDSCs. These RPE cell-induced MDSCs significantly inhibited T-cell proliferation in a dose-dependent manner. PD-L1-deficient RPE cells induced MDSC differentiation as efficiently as wild-type RPE cells, and neutralizing TGF-β or CTLA-2α did not alter the numbers of induced MDSCs. However, blocking IL-6 reduced the efficacy of RPE cell-induced MDSC differentiation. Finally, adoptive transfer of RPE cell-induced MDSCs suppressed IRBP-specific T-cell responses that led to EAU. RPE cells induce the differentiation of MDSCs from bone marrow progenitors. Both cell surface molecules and soluble factors are important in inducing MDSC differentiation. PD-L1, TGF-β, and CTLA-2α were not measurably involved in RPE cell-induced MDSC differentiation, whereas IL-6 was important in the process. The induction of MDSCs could be another mechanism by which RPE cells control immune reactions in the retina, and RPE cell-induced MDSCs should be further investigated as a potential approach to therapy for autoimmune posterior uveitis.

Tumor-associated macrophages (TAMs) are the most abundant inflammatory cells and orchestrate different stages of breast cancer development. TAMs participate in the tumor angiogenesis, matrix remodeling, invasion, immunosuppression, metastasis, and chemoresistance in breast cancer. Several clinical studies indicate the association between the high influx of TAMs in tumor with poor prognosis in hepatocellular, ovarian, cervical, and breast cancer. Previously developed hypotheses have proposed that TAMs participate in antitumor responses of the body, while recently many clinical and experimental studies have revealed that TAMs in tumor microenvironment predominantly resemble with M2-like polarized macrophages and produce a high amount of anti-inflammatory factors which are directly responsible for the development of tumor. Various studies have shown that TAMs in tumor either enhance or antagonize the anti-tumor efficacy of cytotoxic agents, antibodies-targeting cancer cells, and therapeutic agents depending on the nature of treatment. Thereby, multiple roles of TAMs suggests that it is very important to develop novel therapeutic strategies to target TAMs in breast tumor. In this review, we have discussed the functional role of TAMs in breast cancer and summarized available recent advances potential therapeutic strategies that effectively target to TAMs cells. J. Cell. Biochem. 118: 2484-2501, 2017. © 2017 Wiley Periodicals, Inc.