Myeloid-derived Suppressor Cells Trafficking Research Articles

Enhancing the efficacy of vaccinia-based oncolytic virotherapy by inhibiting CXCR2-mediated MDSC trafficking.

Oncolytic virotherapy is an innovative approach for cancer treatment. However, recruitment of myeloid-derived suppressor cells (MDSCs) into the tumor microenvironment (TME) after oncolysis-mediated local inflammation leads to tumor resistance to the therapy. Using the murine malignant mesothelioma model, we demonstrated that the in situ vaccinia virotherapy recruited primarily polymorphonuclear MDSCs (PMN-MDSCs) into the TME, where they exhibited strong suppression of cytotoxic T lymphocytes in a reactive oxygen species-dependent way. Single-cell RNA sequencing analysis confirmed the suppressive profile of PMN-MDSCs at the transcriptomic level and identified CXCR2 as a therapeutic target expressed on PMN-MDSCs. Abrogating PMN-MDSC trafficking by CXCR2-specific small molecule inhibitor during the vaccinia virotherapy exhibited enhanced antitumor efficacy in 3 syngeneic cancer models, through increasing CD8+/MDSC ratios in the TME, activating cytotoxic T lymphocytes, and skewing suppressive TME into an antitumor environment. Our results warrant clinical development of CXCR2 inhibitor in combination with oncolytic virotherapy.

Targeting Myeloid-Derived Suppressor Cell Trafficking as a Novel Immunotherapeutic Approach in Microsatellite Stable Colorectal Cancer.

Myeloid-derived suppressor cells (MDSCs) are a unique subset of immune cells that promote an immunosuppressive phenotype due to their impacts on CD8 and regulatory T cell function. The inhibition of MDSC trafficking to the tumor microenvironment (TME) may represent a novel target in microsatellite stable (MSS) colorectal cancer with the potential to reprogram the immune system. Here, we review the rationale of inhibiting myeloid suppressor cell trafficking in treatment-refractory MSS colorectal cancer and circulating tumor DNA (ctDNA) positive settings to determine whether this approach can serve as a backbone for promoting immunotherapy response in this difficult-to-treat disease.

Coordination polysaccharide nanomissiles with size/charge dual-transformability and immunomicroenvironment-reeducating activity potentiate PD-1 blockade in hepatocellular carcinoma

PD-1 blockade therapy holds great potential for curing hepatocellular carcinoma (HCC), but its efficacy is severely restrained by inefficient CD8+ T cells and abundant immunosuppressive myeloid-derived suppressor cells (MDSCs) in tumors. Moreover, the solid feature of HCC limits drugs’ penetration depth. Herein, cisplatin/indocyanine green (ICG)-coloaded polysaccharide-based nanomissiles (CIC-Gal) with galactose-mediated tumor targeting ability and tumor microenvironment (TME)-responsive size/charge dual-transformability are constructed by coordination-driven self-assembly. The nanoparticles can efficiently accumulate in tumors and exert antitumor effects on HCC via combinational chemotherapy/phototherapy. Importantly, CIC-Gal nanoparticles may protect cisplatin from glutathione-mediated detoxification by depleting glutathione. Photodynamic therapy rather than photothermal therapy plays a predominant role in ICG-mediated phototherapy. Furthermore, CIC-Gal nanoparticles can induce prominent immunogenic cell death (ICD), promote dendritic cells maturation, and activate robust systemic antitumor immunity in combination with αPD-1, which efficiently eradicates primary tumors, inhibits distant tumor growth and lung metastasis, and prolongs survival of tumor-bearing mice by promoting CD8+ T cell infiltration in tumors, suppressing the expansion and trafficking of MDSCs, and reshaping immunostimulatory TME. Collectively, this study provides a drug-based coordination-driven polysaccharide nanomissile construction approach, and the CIC-Gal nanoparticles display a strong immunomicroenvironment-reeducating ability for potentiating HCC immunotherapy.

Abstract 2513: MDSC-derived TNF is a novel regulator of T-cell dysfunction in pancreatic cancer

Abstract Introduction: Abundance of myeloid-derived suppressor cells (MDSC) and a dysfunctional T-cell compartment are defining hallmarks of therapeutic resistance in pancreatic ductal adenocarcinoma (PDAC). Using congenic in vivo murine models to phenocopy extremes of T-cell enrichment or exclusion, we sought to interrogate central MDSC-mediated mechanisms that govern immune tolerance in PDAC. Methods: Orthotopically implanted T-cell-excluded (Tcelllo) vs T-cell-enriched (T-cellhi) congenic KPC tumors, and intratumoral Ly6G+F4/80- MDSCs from both clones, were subjected to RNA sequencing. Ex vivo co-cultures evaluated the effects of intratumoral MDSC on splenic T-cells. Orthotopically injected KPC-T-celllo mice were treated with etanercept vs. vehicle, and immunophenotyping via flow cytometry was performed. Results: RNA-seq of KPC T-celllo vs. T-cellhi tumors revealed enrichment of myeloid immunoregulatory pathways, and downregulation of leukocyte activation/cytotoxicity pathways. Flow cytometry revealed a dramatic increase in MDSCs infiltrating KPC-Tcelllo tumors (P<0.001). To decipher MDSC-intrinsic mechanisms associated with T-cell exclusion, RNA-seq of MDSCs infiltrating T-cellhi clones revealed relative downregulation of MAPK signaling, and cytokine profiling of MDSCs conditioned with MAPK inhibitor trametinib revealed marked reduction in TNF secretion. Confocal microscopy confirmed striking decrease in TNF in MDSCs isolated from KPC- T-cellhi vs. Tcelllo tumors. Ex vivo MDSC-T-cell co-cultures significantly attenuated T-cell proliferation and activation (via IFN-γ release) while favoring T-cell apoptosis, which could be rescued by pre-conditioning MDSCs with either etanercept (TNFR2 decoy receptor) or MAPK pathway inhibitors. Orthotopically injected KPC-T-celllo tumor-bearing mice treated with etanercept demonstrated a remodeled TME vs. vehicle-treated mice, with attenuation in MDSC trafficking, enrichment in CD4+/CD8+ T-cell infiltration, and reduction in T-cell exhaustion. Conclusion: MDSC-derived TNF regulates T-cell dysfunction in PDAC via a MAPK-dependent mechanism. Compartment-specific inhibition of TNF may be a provocative strategy to overcome immune tolerance in PDAC. Citation Format: Anna Bianchi, Iago De Castro Silva, Nilesh U. Deshpande, Siddharth Mehra, Samara Singh, Austin R. Dosch, Vanessa T. Garrido, Christine I. Rafie, Nagaraj Nagathihalli, Nipun Merchant, Jashodeep Datta. MDSC-derived TNF is a novel regulator of T-cell dysfunction in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2513.

Translocation of Helicobacter hepaticus synergizes with myeloid-derived suppressor cells and contributes to breast carcinogenesis

ABSTRACT Microbial dysbiosis plays an important role in the development of intestinal diseases. Recent studies suggest a link between intestinal bacteria and mammary cancer. Here, we report that female ApcMin/+ mice infected with Helicobacter hepaticus exhibited an increased mammary and small/large intestine tumor burden compared with uninfected littermates. H. hepaticus DNA was detected in small/large intestine, mammary tumors, and adjacent lymph nodes, suggesting a migration pathway. CD11b+Gr1+ myeloid-derived suppressor cells (MDSCs) infiltrated and expressed high levels of Wnts, likely enhancing tumorigenesis through activation of Wnt/β-catenin pathway. Our previous studies indicated that histidine decarboxylase (Hdc) marks a population of myeloid-biased hematopoietic stem cells and granulocytic MDSCs. Cytokines/chemokines secreted by IL-17-expressing mast cells and tumor tissues promoted Hdc+ MDSCs expansion and trafficking toward mammary tumors. Adoptive transfer of MDSCs isolated from H. hepaticus-infected mice increased MDSCs frequencies in peripheral blood, mesenteric lymph nodes, mammary gland, and lymph nodes in recipient ApcMin/+ mice. The adoptive transfer of H. hepaticus primed MDSCs also increased the size and number of mammary tumors. Our results demonstrate that H. hepaticus can translocate from the intestine to mammary tissues to promote mammary tumorigenesis with MDSCs. Targeting bacteria and MDSCs may be useful for the prevention and therapy of extraintestinal cancers. Abbreviations: Helicobacter hepaticus, Hh; myeloid-derived suppressor cell, MDSC; histidine decarboxylase, Hdc; Breast cancer, BC; T regulatory, TR; inflammatory bowel disease, IBD; fluorescence in situ hybridization, FISH; myeloid-biased hematopoietic stem cells, MB-HSCs; granulocytic MDSCs, PMN-MDSCs; Lipopolysaccharide, LPS; Toll-like receptors, TLRs; Mast cells, MCs; Granulocyte-macrophage colony-stimulating factor, GM-CSF; epithelial–mesenchymal transition, EMT; Intestinal epithelial cells, IECs.

ITLN1 inhibits tumor neovascularization and myeloid derived suppressor cells accumulation in colorectal carcinoma.

Low levels of ITLN1 have been correlated with obesity-related colorectal carcinogenesis, however, the specific functions and underlying mechanisms remain unclear. Thus, we sought to explore the inhibitory role of ITLN1 in the tumor-permissive microenvironment that exists during the first occurrence and subsequent development of colorectal carcinoma (CRC). Results indicated that ITLN1 was frequently lost in CRC tissues and ITLN1 to be an independent prognostic predictor of CRC. Orthotopic and subcutaneous tumor xenograft approaches were then used to further confirm the protective role of ITLN1 during tumor progression. Increased ITLN1 expression in CRC cells significantly inhibited local pre-existing vessels sprouting, EPC recruitment and the infiltration of immunosuppressive myeloid-derived suppressor cells (MDSCs) into tumor tissues without affecting the behavior of CRC cells in vitro. Comparatively, ITLN1-derived MDSCs had a lower suppressive effect on T cell proliferation, NOS2 expression, and ROS production. In addition, ITLN1 overexpression markedly suppressed bone marrow (BM)-derived hematopoietic progenitor cells (HPC) differentiation into MDSCs as well as NOS2 activity on MDSCs. Using H-2b+YFP + chimerism through bone marrow transplantation, increased ITLN1 in HCT116 significantly reduced the BM-derived EPCs and MDSCs in vivo mobilization. Mechanistically, results indicated ITLN1 inhibited tumor-derived IL-17D and CXCL2 (MIP2) through the KEAP1/Nrf2/ROS/IL-17D and p65 NF-ĸB/CXCL2 signaling cascades dependent on PI3K/AKT/GSK3ß. This effect was reversed by the PI3K selective inhibitor LY294002. Collectively, ITLN1 synergistically suppressed IL-17D and CXCL2-mediated tumor vascularization, bone marrow derived EPC recruitment, as well as MDSCs generation and trafficking. Thus, ITLN1 potentially serves as a critical prognostic and therapeutic target for CRC.

Low-dose HDACi potentiates anti-tumor activity of macrophages in immunotherapy

ABSTRACT The success of checkpoint immunotherapy has created optimism that cancer may be curable. However, not all patients respond, resistance is common and many patients relapse owing to immune escape. We demonstrate that HDAC inhibition not only decreases the trafficking of myeloid-derived suppressor cells (MDSCs) into tumors but also potentiates tumor-associated macrophages (TAMs) to specify anti-tumoral phenotype and bolster T cells activation within the tumor microenvironment (TME).

EXTH-32. TARGETED STAT3 INHIBITION IMPAIRS MDSC MOBILIZATION AND RECRUITMENT IN GLIOBLASTOMA

Abstract BACKGROUND Glioblastoma tumors (GBM) are comprised upwards of 30 percent by glioma-associated myeloid cells (GAMs). A large fraction of GAMs are myeloid-derived suppressor cells (MDSC) thought to traffic in from peripheral circulation. MDSCs foster a hospitable environment for cancer cells by regulating immune suppression and driving resistance to immunotherapy. While signal transducer and activator of transcription 3 (STAT3) is considered to be a specific marker for MDSCs and is a known player in their phenotypic polarization in cancer, we sought to closely examine its specific role in MDSC trafficking and tumor recruitment. HYPOTHESIS Targeted inhibition of STAT3 blocks MDSC from the bone marrow, mitigating their accumulation within GBM tumors. METHODS Human and murine GBM samples were analyzed for immune-specific STAT3 phosphorylation (P-STAT3). Immune cell characterization and quantification in peripheral and GBM tissue from syngeneic murine models treated with a novel STAT3 inhibitor (LLL12B) was done. Therapeutic responses to LLL12B alone and in combination with immune checkpoint blockade were evaluated. RESULTS We found P-STAT3 to be predominantly expressed by tumor-associated immune cells in both human and murine GBM, particularly MDSCs. Circulating numbers of MDSCs dramatically increase in response to tumor burden. P-STAT3 is elevated in these cells, indicating that its activation occurs prior to tumor infiltration. LLL12B blockade of STAT3 significantly reduced the number of circulating and tumor-infiltrating MDSCs. As a single agent LLL12B reduced tumor volume and extended the survival of murine GBM models. When combined with anti-PD-1 checkpoint blockade, we observed durable survival in a significant fraction of treated mice. CONCLUSIONS These findings advocate a critically important role for STAT3 in regulating MDSC mobilization and trafficking to GBM tumors. It additionally reveals a new therapeutic mechanism of action for LLL12B that may be relevant for other direct inhibitors of STAT3, influencing their clinical applicability to treat GBM.

Abstract 692: Discovery of novel metformin derivatives with potent antitumor activity in combination with immunotherapy for treatment of triple-negative breast cancer

Abstract Triple negative breast cancer (TNBC) occurs in about 15% of breast cancer (BC) patients, yet it accounts for almost 50% of all BC deaths. TNBC is characterized by lack of expression of estrogen, progesterone and HER2 receptors, and it cannot be treated with current targeted therapies. TNBCs are heterogeneous and occur often in younger and African American women. Although initially responsive to some chemotherapies, TNBCs tend to relapse early and metastasize, leading to poor survival. Development of new therapeutic approaches for clinical translation is a high priority. Emerging evidence from epidemiologic and preclinical work suggests that metformin, the most widely used drug to treat type 2 diabetes mellitus, exerts anticancer activity in BC. Diabetic patients treated with metformin have a reduced incidence and better survival from BC. Moreover, TNBC cells are reported to be uniquely sensitive to metformin in vitro, but strong antitumor effects require relatively high metformin doses in vivo. To address this challenge, we used a structure-activity strategy to develop metformin analogues with more potent anticancer action and safety at lower doses in vivo. Using TNBC cell proliferation in vitro to screen drug candidates, selected new metformin analogues were identified that exerted dose-dependent inhibition of cell proliferation at significantly lower concentrations than that of parental metformin (P<0.01). As antitumor effects of metformin are attributed in part to activation of the LKB1-AMPK pathway, we find that metformin analogues also strongly induced phosphorylation of AMPK by Western blot assays and significantly reduced phosphorylation of mTOR downstream signaling pathway components (p70S6K, S6 ribosomal protein, 4E-BP1). Analogues also induced TNBC cell apoptosis at lower doses than metformin. In vivo, metformin analogues were more effective at lower doses given by oral gavage than metformin in suppressing TNBC human tumor xenograft progression in nude mouse models (P<0.001). It is notable that data from clinical trials with immune checkpoint inhibitors (ICI) indicate that TNBCs are susceptible to immunotherapy, but only a minority of patients to date have had clinical benefit. Importantly, our studies indicate that metformin analogues modulate the activity and trafficking of myeloid-derived suppressor cells (MDSC) and tumor infiltrating lymphocytes (TIL) that may significantly impact TNBC responses to ICIs. Thus, combination therapy with metformin analogues and anti-PD-L1 antibodies was more effective at blocking tumor growth in vivo than either treatment given alone using murine 4T1 TNBC implants in syngeneic, immune-competent BALB/C mouse models. In the TNBC microenvironment, analogue treatment with ICIs elicited significant infiltration of predominantly effector T-cells, increased populations of tissue-resident memory T-cells, and a reduction of exhausted T-cells as compared to controls (P<0.01). Moreover, MDSC were significantly decreased after combination therapy as compared to appropriate controls (P<0.05). Since there are currently no specific treatments for TNBC, identification of a new targeted therapeutic approach could ultimately be beneficial for managing patients afflicted with this deadly disease. Funding by California BC RP, NCI U54 CA143930. Citation Format: Diana C. Márquez-Garban, Gang Deng, Begonya Comin-Anduix, Vishaka Muhunthan, Gaoyuan Ma, Jennifer Murphy, Alejandro J. Garcia, Cristian D. Yanes, Lorena R. Burton, Nalo Hamilton, David Shackelford, Michael E. Jung, Richard J. Pietras. Discovery of novel metformin derivatives with potent antitumor activity in combination with immunotherapy for treatment of triple-negative breast cancer [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 692.

Abstract 2255: Enhancing immunogenicity in immunologically cold ER+ breast cancer using estrogen receptor blockade and radiation therapy

Abstract Metastatic, hormone therapy-resistant breast cancers expressing estrogen receptor (ER+) account for the majority of breast cancer deaths. ER+ breast cancers are immunologically “cold” with low tumor mutation burden and few tumor-infiltrating lymphocytes (TILs). Consequently, application of immune checkpoint inhibitors (ICIs) to ER+ breast cancers has not proven effective. Radiation therapy (RT) can increase immune susceptibility of “cold” tumors, but can also increase recruitment of immunosuppressive myeloid-derived suppressor cells (MDSCs) to the radiated tumor microenvironment (TME). Recent studies demonstrate that ER inhibition may antagonize the trafficking and activation of MDSCs in tumors. We hypothesized that combining RT and a selective ER degrader (SERD), fulvestrant, would cooperate to relieve immunosuppression, increase tumor immune susceptibility, and facilitate response to ICIs in a syngeneic murine model of ER+ breast cancer. Using a murine breast cancer model of ER+ breast cancer developed (TC11), we examined effects in vitro and in vivo. In vitro, TC11 cells were treated with 8Gy RT and/or fulvestrant (1uM) to evaluate cell autonomous effects. In vivo, 25,000 TC11 cells were transplanted to caudal mammary fat pads of female FVB/N mice. When tumors reached ~200mm3, mice were randomized and treated. We initially evaluated the time course of immune responses to 8Gy RT in the TC11 TME, euthanizing mice every 5 days up to 20 days after RT. We subsequently treated mice with vehicle, fulvestrant (250mg/kg sc, weekly), 8Gy RT, and fulvestrant+8Gy RT. Flow cytometry was performed on day 5 and day 10 after RT to examine the innate and adaptive immune cell infiltrates, respectively. A therapeutic intervention study was performed using combinations of fulvestrant, 8Gy RT, and/or anti-PDL1 (200µg, ip, at days 3, 6, and 9 after RT). 8Gy RT elicited a type-1 interferon response in TC11 cells in vitro and in vivo; as measured by upregulated expression of Mx1, Pdl1, Oas2, Oas3, Trex1, and IfnB mRNAs peaking at 3-5 days post RT and persisting to day 10 in TC11 tumors. RT increased MDSCs (Ly6C+Ly6G+) in the TC11 TME compared to vehicle or fulvestrant alone in tumors taken at day 5, but MDSCs were reduced in tumors treated with fulvestrant and RT. Together, fulvestrant and RT increased TILs (CD45+) and CD8+ T cells at day 10 compared to vehicle control and single treatments. Preliminary data indicate RT and fulvestrant together primed a greater response to anti-PDL1 ICI compared to single or dual combinations of these treatments. These results demonstrate a cooperative interaction between RT and fulvestrant in favorably modulating the TME and response to ICIs in an immunologically cold, hormone-therapy resistant, murine ER+ breast cancer model. Further study is warranted to determine whether this combination may elicit a more effective in situ vaccine effect compared to RT alone. Citation Format: Amber M. Bates, Kathleen A. O'Leary, Sarah Emma, Erin Nystuen, Elizabeth G. Sumiec, Linda A. Schuler, Zachary S. Morris. Enhancing immunogenicity in immunologically cold ER+ breast cancer using estrogen receptor blockade and radiation therapy [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 2255.

Type I IFN signaling in T regulatory cells modulates chemokine production and myeloid derived suppressor cells trafficking during EAE

Interferon-β has therapeutic efficacy in Multiple Sclerosis by reducing disease exacerbations and delaying relapses. Previous studies have suggested that the effects of type I IFN in Experimental Autoimmune Encephalomyelitis (EAE) in mice were targeted to myeloid cells. We used mice with a conditional deletion (cKO) of the type I IFN receptor (IFNAR) in T regulatory (Treg) cells to dissect the role of IFN signaling on Tregs. cKO mice developed severe EAE with an earlier onset than control mice. Although Treg cells from cKO mice were more activated, the activation status and effector cytokine production of CD4+Foxp3- T cells in the draining lymph nodes (dLN) was similar in WT and cKO mice during the priming phase. Production of chemokines (CCL8, CCL9, CCL22) by CD4+Foxp3- T cells and LN resident cells from cKO mice was suppressed. Suppression of chemokine production was accompanied by a substantial reduction of myeloid derived suppressor cells (MDSCs) in the dLN of cKO mice, while generation of MDSCs and recruitment to peripheral organs was comparable. This study demonstrates that signaling by type I IFNs in Tregs reduces their capacity to suppress chemokine production, with resultant alteration of the entire microenvironment of draining lymph nodes leading to enhancement of MDSC homing, and beneficial effects on disease outcome.

Myeloid-derived suppressor cells modulate aortic aneurysm formation via CXCR2 and IL-17 signaling

Abstract Aortic aneurysm formation is associated with vascular inflammation and remodeling mediated via CD4+ T cell-secreted IL-17A production. Our hypothesis is that innate myeloid-derived suppressor cells (MDSCs), which are a heterogeneous population of myeloid precursor and progenitor cells, exhibit an immunoregulatory role in the progression of aortic inflammation during abdominal aortic aneurysm (AAA) formation. The trafficking and migration of MDSCs to the aortic tissue and role of CXCR2 and programmed death-1 (PD-1) receptor signaling was deciphered using an in vivo elastase-treatment model of AAA as well as in vitro co-culture experiments. We used an established murine AAA model of topical elastase-treatment in the present study. Preliminary data showed that elastase-treatment of C57BL/6 (wild-type; WT) mice resulted in significant increase in infrarenal aortic diameter causing AAA formation on day 14 that was significantly inhibited by a combined treatment with anti-CXCR2 and PD-1 antibodies. A multi-fold increase in MDSCs (CD11b+Gr-1+) in aortic tissue of elastase-treated WT mice on days 7 and 14 occurred compared to controls. Co-culture of MDSCs with aortic endothelial cells in the presence of anti-CXCR2 antibody inhibited the transmigration of MDSCs through the endothelial barrier. Moreover, transient elastase treatment of co-cultures of anti-CD3/CD28 treated mononuclear cells with MDSCs significantly enhanced IL-17A secretion compared to cultures without MDSCs. Our results indicate that MDSCs may play a contributory role in aortic inflammation by trafficking in a CXCR2-dependent manner and promotion of IL-17A secretion, signifying the importance of MDSC-mediated immunoregulation of aortic aneurysms.

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Inside the USCAP Journals

Inhibition of MDSC Trafficking with SX-682, a CXCR1/2 Inhibitor, Enhances NK-Cell Immunotherapy in Head and Neck Cancer Models.

Natural killer (NK)-cell-based immunotherapy may overcome obstacles to effective T-cell-based immunotherapy such as the presence of genomic alterations in IFN response genes and antigen presentation machinery. All immunotherapy approaches may be abrogated by the presence of an immunosuppressive tumor microenvironment present in many solid tumor types, including head and neck squamous cell carcinoma (HNSCC). Here, we studied the role of myeloid-derived suppressor cells (MDSC) in suppressing NK-cell function in HNSCC. The ability of peripheral and tumor-infiltrating MDSC from mice bearing murine oral cancer 2 (MOC2) non-T-cell-inflamed tumors and from patients with HNSCC to suppress NK-cell function was studied with real-time impedance and ELISpot assays. The therapeutic efficacy of SX-682, a small-molecule inhibitor of CXCR1 and CXCR2, was assessed in combination with adoptively transferred NK cells. Mice bearing MOC2 tumors pathologically accumulate peripheral CXCR2+ neutrophilic-MDSC (PMN-MDSC) that traffic into tumors and suppress NK-cell function through TGFβ and production of H2O2. Inhibition of MDSC trafficking with orally bioavailable SX-682 significantly abrogated tumor MDSC accumulation and enhanced the tumor infiltration, activation, and therapeutic efficacy of adoptively transferred murine NK cells. Patients with HNSCC harbor significant levels of circulating and tumor-infiltrating CXCR1/2+ CD15+ PMN-MDSC and CD14+ monocytic-MDSC. Tumor MDSC exhibited greater immunosuppression than those in circulation. HNSCC tumor MDSC immunosuppression was mediated by multiple, independent, cell-specific mechanisms including TGFβ and nitric oxide. The clinical study of CXCR1/2 inhibitors in combination with adoptively transferred NK cells is warranted.

Epigenetic therapy inhibits metastases by disrupting premetastatic niches.

Cancer recurrence after surgery remains an unresolved clinical problem1-3. Myeloid cells derived from bone marrow contribute to the formation of the premetastatic microenvironment, which is required for disseminating tumour cells to engraft distant sites4-6. There are currently no effective interventions that prevent the formation of the premetastatic microenvironment6,7. Here we show that, after surgical removal of primary lung, breast and oesophageal cancers, low-dose adjuvant epigenetic therapy disrupts the premetastatic microenvironment and inhibits both the formation and growth of lung metastases through its selective effect on myeloid-derived suppressor cells (MDSCs). In mouse models of pulmonary metastases, MDSCs are key factors in the formation of the premetastatic microenvironment after resection of primary tumours. Adjuvant epigenetic therapy that uses low-dose DNA methyltransferase and histone deacetylase inhibitors, 5-azacytidine and entinostat, disrupts the premetastatic niche by inhibiting the trafficking of MDSCs through the downregulation of CCR2 and CXCR2, and by promoting MDSC differentiation into a more-interstitial macrophage-like phenotype. A decreased accumulation of MDSCs in the premetastatic lung produces longer periods of disease-free survival and increased overall survival, compared with chemotherapy. Our data demonstrate that, even after removal of the primary tumour, MDSCs contribute to the development of premetastatic niches and settlement of residual tumour cells. A combination of low-dose adjuvant epigenetic modifiers that disrupts this premetastatic microenvironment and inhibits metastases may permit an adjuvant approach to cancer therapy.

Pseudoneutrophil Cytokine Sponges Disrupt Myeloid Expansion and Tumor Trafficking to Improve Cancer Immunotherapy.

Myeloid-derived suppressor cells (MDSCs) promote tumor immune escape through multiple mechanisms including suppressing antitumor activities of T lymphocytes. However, therapeutic abrogation of MDSCs often causes severe adverse effects, compensatory recruitment of alternative cell populations, and the multiplicity and complexity of relevant cytokines/receptors. Alternatively, suppressing the expansion and tumor trafficking of MDSCs may be a proficient and safe way for cancer treatment. Here we report that pseudoneutrophil cytokine sponges (pCSs) can disrupt expansion and tumor trafficking of MDSCs and reverse immune tolerance. Coated with plasma membranes of neutrophils phenotypically and morphologically similar to polymorphonuclear MDSCs (PMN-MDSCs), the nanosized pCSs inherited most membrane receptors from the "parental" neutrophils, enabling the neutralization of MDSC-related cytokines. Upon pCSs administration, the expansion of MDSCs and their enrichment in peripheral lymphoid organs and tumors were reduced without the compensatory influx of alternative myeloid subsets. In murine breast cancer and melanoma syngeneic models, pCSs treatment dramatically increased the number of tumor-infiltrating T lymphocytes and restored their antitumor functions. In addition, when pCSs were combined with the programmed cell death protein 1 (PD-1), the immune checkpoint blockade synergistically suppressed tumor progression and prolonged animal survival. Overall, the pseudocell nanoplatform opens up new paths toward effective cancer immunotherapy.

Targeting myeloid-derived suppressor cells in the treatment of hepatocellular carcinoma: current state and future perspectives.

Systemic therapy for advanced hepatocellular carcinoma (HCC) has been focusing on overcoming tumor angiogenesis and immunosuppression. Myeloid-derived suppressor cells (MDSCs) promote both angiogenesis and immunosuppression in the tumor microenvironment (TME). Multiple clinical studies have demonstrated the prognostic implications of and suggested the translational significance of MDSCs in patients with HCC. In preclinical HCC models, targeting MDSCs has been shown to enhance antitumor efficacy of sorafenib or immune checkpoint inhibitors. Reversing the protumor effects of MDSCs could be achieved by depleting MDSCs, blocking MDSC trafficking and migration into TME, and inhibiting the immunosuppressive functions of MDSCs. To date, these strategies have not yet been validated to be clinically useful in patients with malignancy including HCC. Future studies should focus on identifying specific markers for human MDSCs and developing combination approaches incorporating MDSC-targeting therapy in the treatment of HCC.

Entinostat Converts Immune-Resistant Breast and Pancreatic Cancers into Checkpoint-Responsive Tumors by Reprogramming Tumor-Infiltrating MDSCs.

Immune-checkpoint inhibition (ICI) has revolutionized treatment in cancers that are naturally immunogenic by enabling infiltration of T cells into the tumor microenvironment (TME) and promoting cytotoxic signaling pathways. Tumors possessing complex immunosuppressive TMEs such as breast and pancreatic cancers present unique therapeutic obstacles as response rates to ICI remain low. Such tumors often recruit myeloid-derived suppressor cells (MDSCs), whose functioning prohibits both T-cell activation and infiltration. We attempted to sensitize these tumors to ICI using epigenetic modulation to target MDSC trafficking and function to foster a less immunosuppressive TME. We showed that combining a histone deacetylase inhibitor, entinostat (ENT), with anti-PD-1, anti-CTLA-4, or both significantly improved tumor-free survival in both the HER2/neu transgenic breast cancer and the Panc02 metastatic pancreatic cancer mouse models. Using flow cytometry, gene-expression profiling, and ex vivo functional assays, we characterized populations of tumor-infiltrating lymphocytes (TILs) and MDSCs, as well as their functional capabilities. We showed that addition of ENT to checkpoint inhibition led to significantly decreased suppression by granulocytic MDSCs in the TME of both tumor types. We also demonstrated an increase in activated granzyme-B-producing CD8+ T effector cells in mice treated with combination therapy. Gene-expression profiling of both MDSCs and TILs identified significant changes in immune-related pathways. In summary, addition of ENT to ICI significantly altered infiltration and function of innate immune cells, allowing for a more robust adaptive immune response. These findings provide a rationale for combination therapy in patients with immune-resistant tumors, including breast and pancreatic cancers.

Targeting Chemokine Receptors to Modulate MDSCs for Cancer Therapy

Abstract Host anti-tumor responses, including the actions of cytotoxic T cells, play a key role in targeting tumors, but can be hindered by multiple mechanisms active within the tumor microenvironment. One such mechanism involves the recruitment and expansion of immunosuppressive cells such as myeloid derived suppressor cells (MDSCs) in the tumor microenvironment. We have utilized two transplantable lung tumor cell lines (TC1 and LLC) to address the role of certain chemokine receptors in MDSC associated tumor progression. In addition, we used a thioglycolate-induced peritonitis model of inflammation to validate the ability of chemokine receptor antagonists to inhibit trafficking of MDSCs to the site of inflammation. Finally, we tested the compounds for their ability to impair chemokine signaling within established tumors and promote antitumor immunity. In summary, genetic and pharmacologic data indicate that targeting chemokine receptors to modulate MDSCs may be an important new component of immuno-oncology based therapies.

Paradoxical myeloid-derived suppressor cell reduction in the bone marrow of SIV chronically infected macaques.

Myeloid derived suppressor cells (MDSCs), which suppress anti-tumor or anti-viral immune responses, are expanded in the peripheral blood and tissues of patients/animals with cancer or viral infectious diseases. We here show that in chronic SIV infection of Indian rhesus macaques, the frequency of MDSCs in the bone marrow (BM) was paradoxically and unexpectedly decreased, but increased in peripheral blood. Reduction of BM MDSCs was found in both CD14+MDSC and Lin-CD15+MDSC subsets. The reduction of MDSCs correlated with high plasma viral loads and low CD4+ T cell counts, suggesting that depletion of BM MDSCs was associated with SIV/AIDS disease progression. Of note, in SHIVSF162P4-infected macaques, which naturally control viral replication within a few months of infection, the frequency of MDSCs in the bone marrow was unchanged. To investigate the mechanisms by which BM MDSCs were reduced during chronic SIV infection, we tested several hypotheses: depletion due to viral infection, alterations in MDSC trafficking, and/or poor MDSC replenishment. We found that the possible mobilization of MDSCs from BM to peripheral tissues and the slow self-replenishment of MDSCs in the BM, along with the viral infection-induced depletion, all contribute to the observed BM MDSC reduction. We first demonstrate MDSC SIV infection in vivo. Correlation between BM CD14+MDSC reduction and CD8+ T cell activation in tissues is consistent with decreased immune suppression by MDSCs. Thus, depletion of BM MDSCs may contribute to the pathologic immune activation during chronic SIV infection and by extension HIV infection.