Depletion Of Myeloid-derived Suppressor Cells Research Articles

Myeloid-derived suppressor cell depletion therapy targets IL-17A-expressing mammary carcinomas

Triple-negative breast cancer (TNBC) is an invasive subtype of breast cancer but paradoxically associated with increased tumor-infiltrating leukocytes. The molecular and cellular mechanisms underlying TNBC immunobiology are incompletely understood. Interleukin (IL)-17A is a pro-inflammatory cytokine that has both pro- and anti-tumor effects and found in 40–80% of TNBC samples. We report here that IL-17A mRNA and protein are detectable in some human TNBC cell lines and further upregulated by IL-23 and LPS stimulation. Furthermore, the impact of tumor-derived IL-17A in host immune response and tumor growth was examined using murine TNBC 4T1 mammary carcinoma cells transduced with an adenoviral vector expressing IL-17A (AdIL-17A) or control vector (Addl). Compared to Addl-transduction, AdIL-17A-transduction enhanced 4T1 tumor growth and lung metastasis in vivo, which was associated with a marked expansion of myeloid-derived suppressor cells (MDSCs). However, AdIL-17A-transduction also induced strong organ-specific and time-dependent immune activation indicated by dynamic changes of NK cells, B cells, CD4, and CD8 T cells in peripheral blood, lung, and tumor site, as well as the plasma levels of IFNγ. Such findings highlight that tumor-associated IL-17A induces concurrent immune activation and immune suppression. Administration of anti-Gr1 or anti-G-CSF antibody effectively depleted MDSCs in vivo, markedly reducing the growth of AdIL-17A-transduced 4T1 tumors, and eliminating lung metastasis. Collectively, our study demonstrates that MDSC depletion is an effective and practical approach for treating IL-17A-enriched mammary carcinomas.

Notch signaling contributes to the establishment of sustained unresponsiveness to food allergens by oral immunotherapy

Oral immunotherapy (OIT) aims to establish desensitization and sustained unresponsiveness (SU) in patients with food allergy by ingestion of gradually increasing doses of specific food allergens. However, little is known about the mechanisms by which OIT induces SU to specific allergens. We investigated the role of Notch signaling, which controls cell fate decisions in many types of immune cells in the induction of SU by OIT treatment. Two types of mouse models, ovalbumin-induced food allergy and OIT, were generated. To elucidate the role of Notch signaling in OIT-induced SU, mice were intraperitoneally injected with the Notch signaling inhibitor N-[(3,5-difluorophenyl)acetyl]-l-alanyl-2-phenylglycine-1,1-dimethylethyl ester during the OIT treatment period. Ovalbumin-sensitized mice were desensitized and also had SU induced by OIT treatment, whereas repeated challenges with ovalbumin caused the development of severe allergic reactions in ovalbumin-sensitized mice. Administration of N-[(3,5-difluorophenyl)acetyl]-l-alanyl-2-phenylglycine-1,1-dimethylethyl ester to mice during the OIT treatment period inhibited the establishment of SU to ovalbumin but did not affect the induction of desensitization. OIT induced a systemic expansion of IL-10-producing CD4+ T cells, including TH2 cells, and myeloid-derived suppressor cells (MDSCs), particularly the monocytic MDSC subpopulation. Inhibition of Notch signaling prevented the OIT-induced expansion of those cells. Invitro cultures of bone marrow cells showed that Notch signaling directly promoted the generation of monocytic MDSCs. In addition, the contribution of MDSCs to OIT-induced SU was confirmed by MDSC depletion with the anti-Gr1 antibody. Notch signaling contributes to the establishment of SU induced by OIT through systemic expansion of immunosuppressive cells, such as IL-10-producing CD4+ T cells and MDSCs.

Adipose-resident myeloid-derived suppressor cells modulate immune cell homeostasis in healthy mice.

The metabolically dynamic nature of healthy adipose places this tissue under regular inflammatory stress. A network of adipose-resident anti-inflammatory immune cells modulates and resolves this endogenous inflammation. Previous work in our laboratory identified a CD11b+ Gr1+ subset of these immunosuppressive adipose stromal cells in healthy mice. Myeloid-derived suppressor cells (MDSCs), typically associated with cancer and chronic inflammation, have a similar surface marker phenotype and accumulate in adipose of high-fat diet-fed mice. Given the routine inflammatory stresses on healthy adipose and the suppressive nature of the tissue-resident immune cells, we hypothesized that these CD11b+ Gr1+ cells were a genuine population of MDSCs involved in regulating tissue homeostasis. Flow cytometric analysis of these cells found that they were CD11b+ CD301- Ly6C+ Ly6G+/- and did not express traditional macrophage markers. Moreover, in vitro functional assays demonstrated that these cells suppressed αCD3/αCD28-induced T-cell proliferation, solidifying their identity as bona fide adipose-resident MDSCs. Systemic MDSC depletion altered adipose immune cell dynamics in otherwise healthy mice, increasing the number of CD4+ effector memory T cells and modifying the surface markers expressed by adipose-resident macrophages. In addition, transcription of various immunomodulatory cytokines was clearly dysregulated in the adipose of MDSC-depleted animals compared with controls. Altogether, our findings indicate that there is a population of bona fide MDSCs in the adipose of otherwise healthy mice that actively contribute to the health and immune homeostasis of this tissue.

Blockade of p38 kinase impedes the mobilization of protumorigenic myeloid populations to impact breast cancer metastasis.

Patients with metastatic breast cancer (MBC) have limited therapeutic options and novel treatments are critically needed. Prior research implicates tumor-induced mobilization of myeloid cell populations in metastatic progression, as well as being an unfavorable outcome in MBC; however, the underlying mechanisms for these relationships remain unknown. Here, we provide evidence for a novel mechanism by which p38 promotes metastasis. Using triple-negative breast cancer models, we showed that a selective inhibitor of p38 (p38i) significantly reduced tumor growth, angiogenesis, and lung metastasis. Importantly, p38i decreased the accumulation of myeloid populations, namely, myeloid-derived suppressor cells (MDSCs) and CD163+ tumor-associated macrophages (TAMs). p38 controlled the expression of tumor-derived chemokines/cytokines that facilitated the recruitment of protumor myeloid populations. Depletion of MDSCs was accompanied by reduced TAM infiltration and phenocopied the antimetastatic effects of p38i. Reciprocally, p38i increased tumor infiltration by cytotoxic CD8+ T cells. Furthermore, the CD163+ /CD8+ expression ratio inversely correlated with metastasis-free survival in breast cancer, suggesting that targeting p38 may improve clinical outcomes. Overall, our study highlights a previously unknown p38-driven pathway as a therapeutic target in MBC.

Phase III trial of sitravatinib plus nivolumab vs. docetaxel for treatment of NSCLC after platinum-based chemotherapy and immunotherapy (SAPPHIRE).

TPS9635 Background: Sitravatinib is an oral spectrum-selective tyrosine kinase inhibitor that targets the TAM (TYRO3/AXL/MERTK) and split (VEGFR2/KIT) family receptor tyrosine kinases (RTKs), as well as MET. Inhibition of TAM RTKs may promote the depletion of myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment (TME) and repolarize tumor associated macrophages towards the pro-inflammatory M1 phenotype. Inhibition of the split RTKs may reduce immunosuppressive regulatory T cells in addition to MDSCs within the TME. Given these pleiotropic immune-stimulating effects, sitravatinib may reverse resistance to checkpoint inhibitor therapy (CIT) and augment the antitumor immune response of nivolumab in patients (pts) with non-small cell lung cancer (NSCLC). An ongoing Phase 2 study (MRTX-500) demonstrates clinical activity of this combination in pts with metastatic non-squamous NSCLC after progression on or after CIT. Methods: Global, randomized, open-label, Phase 3 study of sitravatinib in combination with nivolumab vs docetaxel in pts with advanced non-squamous NSCLC who have progressed on or after CIT. Pts must have also received platinum-based chemotherapy either in combination with CIT or prior to CIT. Pts are randomized (1:1) to receive oral sitravatinib 120 mg once daily in continuous 28-day cycles combined with nivolumab IV 240 mg every 2 weeks or 480 mg every 4 weeks vs treatment with docetaxel 75 mg/m2 IV every 3 weeks. Patients are stratified based on number of prior treatment regimens in the advanced setting, ECOG performance status, and presence of brain metastases. Key eligibility criteria include duration of treatment of CIT of at least 4 months, discontinuation of prior treatment with CIT < 90 days prior to the date of randomization, and absence of symptomatic or uncontrolled brain metastases. The primary endpoint is overall survival (OS). Key secondary endpoints include safety and tolerability, ORR, PFS, PROs, and PK. OS will be analyzed using Kaplan-Meier methods and the stratified log-rank test to estimate and compare the median OS between the two treatment arms with 95% CI. An IDMC will review safety at regular intervals and efficacy at a planned interim analysis based on OS. Enrollment is ongoing. Clinical trial information: NCT03906071 .

Myeloid-derived suppressor cells expand after transplantation and their augmentation increases graft survival.

Myeloid-derived suppressor cells (MDSCs) expand in an inflammatory microenvironment such as cancer and autoimmunity. To study if transplantation induces MDSCs and these cells regulate allograft survival, C57BL/6 donor hearts were transplanted into BALB/c recipients and endogenous MDSCs were characterized. The effects of adoptive transfer of transplant (tx), tumor (tm), and granulocyte-colony stimulating factor (g-csf)-expanded MDSCs or depletion of MDSC were assessed. MDSCs expanded after transplantation (1.7-4.6-fold) in the absence of immunosuppression, homed to allografts, and suppressed proliferation of CD4 T cells in vitro. Tx-MDSCs differed phenotypically from tm-MDSCs and g-csf-MDSCs. Among various surface markers, Rae-1 expression was notably low and TGF-β receptor II was high in tx-MDSCs when compared to tm-MDSCs and g-csf-MDSCs. Adoptive transfer of these three MDSCs led to differential graft survival: control (6days), tx-MDSCs (7.5days), tm-MDSCs (9.5days), and g-csf-MDSCs (19.5days). In combination with anti-CD154 mAb, MDSCs synergistically extended graft survival from 40days (anti-CD154 alone) to 86days with tm-MDSCs and 132days with g-csf-MDSCs. Early MDSC depletion (day 0 or 20), however, abrogated graft survival, but late depletion (day 25) did not. In conclusion, MDSCs expanded following transplantation, migrated to cardiac allografts, prolonged graft survival, and were synergistic with anti-CD154 mAb.

Scald Injury-Induced T Cell Dysfunction Can Be Mitigated by Gr1+ Cell Depletion and Blockage of CD47/CD172a Signaling.

Infection is a common and severe complication of burn injury: Sepsis accounts for 47% of postburn mortality. Burn-induced T cell suppression likely contributes to the increased infection susceptibility in burn patients. However, little is known about the kinetics of T cell dysfunction after burn and its underlying mechanisms. In this study, we show in a murine scald injury model that T cell activation of both CD4+ and CD8+ T cells as well as T cell cytokine production is suppressed acutely and persistently for at least 11 days after burn injury. Purified T cells from scald-injured mice exhibit normal T cell functions, indicating an extrinsically mediated defect. We further show that T cell dysfunction after burn appears to be cell-to-cell contact dependent and can be ameliorated by depletion of myeloid-derived suppressor cells. These cells expand after burn injury, particularly a subset expressing the checkpoint inhibitor CD172a, and infiltrate germinal centers. Expression of CD172a appears to be driven by ingestion of immature reticulocytes. Immature reticulocytes are drastically increased in the spleen of scald mice and may contribute to immunosuppression through more direct mechanisms as well. Overall, our study newly identifies two cell populations, myeloid-derived suppressor cells and immature reticulocytes, as well as the CD47/CD172a-signaling pathways as mediators of T cell suppressors after burn and thus opens up new research opportunities in the search for new therapies to combat increased infection susceptibility and the associated morbidity and mortality in burn victims.

Metronomic low dose cyclophosphamide in combination with a DNA methyltransferase inhibitor limits tumor growth in murine triple negative breast cancer

Abstract Many breast cancers are treated with therapies that target herceptin, estrogen, or progesterone receptors; however, for triple-negative breast cancers (TNBC) that lack these receptors, treatment options are limited, and prognosis is often unfavorable. The goal of this study is to design a therapeutic intervention that can elicit an effective immune response against the tumor and instill immunological memory to eradicate primary and metastatic lesions. Guadecitabine (Guad) is a second-generation DNA methyltransferase inhibitor (DMNTi) that has been reported to have several antitumor properties such as increased antigenicity and depletion of myeloid-derived suppressor cells (MDSC’s). Cyclophosphamide is a FDA approved chemotherapy that has been shown, when given as a low-dose treatment, to selectively deplete regulatory T-cells (T-regs). Both MDSCs and T-regs suppress antitumor immunity. We hypothesize that the combination of Guad and Cyp will synergize and promote anticancer immunity through increased expression of de novo tumor antigens and depletion of MDSCs and T-regs in a low-dose setting. To test this hypothesis, BALB/c mice were challenged with murine TNBC 4T1 tumor cells and the 4T1-bearing mice were administered low-dose Guad and Cyp daily for ten consecutive days. This experiment showed a degree of synergy between Guad and Cyp with the dual therapy reducing tumor burden to a greater extent than either monotherapy.

An Organoid Approach to Target Her2/PD‐L1 Positive Gastric Cancers

BackgroundTumors can evade immune surveillance by expressing ligands such as programmed cell death 1 (PDL‐1) which interacts with PD‐1 or CTLA‐4, respectively, on CD8+ cytotoxic T lymphocytes (CTLs). These interactions inhibit CTL proliferation, survival, and effector function subsequently leading to immune evasion and cancer persistence. Despite that 40% of gastric cancers express PD‐L1, the response rate to immunotherapy is only 30%. Human epidermal growth factor receptor2 (HER2) is one of the critical regulators of several metastatic cancers, including gastric. Half of PD‐L1‐positive gastric cancers co‐express HER2, but whether HER2‐induced PD‐L1 sustains tumor cell immune evasion has not been determined.HypothesisThe current research tests the hypothesis that targeted anti‐HER2 and immune checkpoint inhibition may provide synergistic effects in gastric cancer treatment.MethodsPatient‐derived gastric cancer organoids, generated from resected tumor tissues or biopsies were co‐cultured with cytotoxic T lymphocytes (CTLs) and tumor antigenloaded dendritic cells and myeloid‐derived suppressor cells (MDSCs).ResultsWhile PD‐L1‐positive tumor organoids co‐expressed HER2, pharmacological inhibition and gene knockdown of HER2 resulted in decreased PD‐L1 expression in tumor organoids. Within the organoid/immune cell co‐culture, decreased PD‐L1 expression in patient‐derived gastric cancer organoids correlated with a significant increase in CTL proliferation and survival, leading to cancer cell death. Similar results were within the co‐culture were observed in response to Nivolumab treatment. MDSCs within the co‐culture counteracted the inhibitory effects of Her2 inhibition by Mubritinib and Nivolumab.ConclusionThus, HER2‐induced PD‐L1 may contribute to tumor immune evasion. Organoid/immune cell co‐cultures may be used to effectively screen for targeted therapy in individual gastric cancer patients. Therapeutic anti‐HER2 antibody and, immune checkpoint inhibition, as well as depletion of MDSCs, may provide synergistic effects in gastric cancer treatment.Support or Funding Information• NIH NIDDK R01DK083402‐08 (Zavros)NIH 1U19AI116491‐01, (PIs: Weiss and Wells, Zavros Project Leader 1

Granulocyte Colony-Stimulating Factor Attenuates Renal Ischemia-Reperfusion Injury by Inducing Myeloid-Derived Suppressor Cells.

Granulocyte colony-stimulating factor (G-CSF) can increase populations of myeloid-derived suppressor cells, innate immune suppressors that play an immunoregulatory role in antitumor immunity. However, the roles of myeloid-derived suppressor cells and G-CSF in renal ischemia-reperfusion injury remain unclear. We used mouse models of ischemia-reperfusion injury to investigate whether G-CSF can attenuate renal injury by increasing infiltration of myeloid-derived suppressor cells into kidney tissue. G-CSF treatment before ischemia-reperfusion injury subsequently attenuated acute renal dysfunction, tissue injury, and tubular apoptosis. Additionally, G-CSF treatment suppressed renal infiltration of macrophages and T cells as well as renal levels of IL-6, MCP-1, IL-12, TNF-α, and IFN-γ, but it increased levels of IL-10, arginase-1, and reactive oxygen species. Moreover, administering G-CSF after ischemia-reperfusion injury improved the recovery of renal function and attenuated renal fibrosis on day 28. G-CSF treatment increased renal infiltration of myeloid-derived suppressor cells (F4/80-CD11b+Gr-1int), especially the granulocytic myeloid-derived suppressor cell population (CD11b+Ly6GintLy6Clow); splenic F4/80-CD11b+Gr-1+ cells sorted from G-CSF-treated mice displayed higher levels of arginase-1, IL-10, and reactive oxygen species relative to those from control mice. Furthermore, these splenic cells effectively suppressed in vitro T cell activation mainly through arginase-1 and reactive oxygen species, and their adoptive transfer attenuated renal injury. Combined treatment with anti-Gr-1 and G-CSF showed better renoprotective effects than G-CSF alone, whereas preferential depletion of myeloid-derived suppressor cells by pep-G3 or gemcitabine abrogated the beneficial effects of G-CSF against renal injury. G-CSF induced renal myeloid-derived suppressor cells, thereby attenuating acute renal injury and chronic renal fibrosis after ischemia-reperfusion injury. These results suggest therapeutic potential of myeloid-derived suppressor cells and G-CSF in renal ischemia-reperfusion injury.

Runx2 Deficiency in Osteoblasts Promotes Myeloma Progression by Altering the Bone Microenvironment at New Bone Sites.

Multiple myeloma is a plasma cell malignancy that thrives in the bone marrow (BM), with frequent progression to new local and distant bone sites. Our previous studies demonstrated that multiple myeloma cells at primary sites secrete soluble factors and suppress osteoblastogenesis via the inhibition of Runt-related transcription factor 2 (Runx2) in pre- and immature osteoblasts (OB) in new bone sites, prior to the arrival of metastatic tumor cells. However, it is unknown whether OB-Runx2 suppression in new bone sites feeds back to promote multiple myeloma dissemination to and progression in these areas. Hence, we developed a syngeneic mouse model of multiple myeloma in which Runx2 is specifically deleted in the immature OBs of C57BL6/KaLwRij mice (OB-Runx2-/- mice) to study the effect of OB-Runx2 deficiency on multiple myeloma progression in new bone sites. In vivo studies with this model demonstrated that OB-Runx2 deficiency attracts multiple myeloma cells and promotes multiple myeloma tumor growth in bone. Mechanistic studies further revealed that OB-Runx2 deficiency induces an immunosuppressive microenvironment in BM that is marked by an increase in the concentration and activation of myeloid-derived suppressor cells (MDSC) and the suppression and exhaustion of cytotoxic CD8+ T cells. In contrast, MDSC depletion by either gemcitabine or 5-fluorouracil treatment in OB-Runx2-/- mice prevented these effects and inhibited multiple myeloma tumor growth in BM. These novel discoveries demonstrate that OB-Runx2 deficiency in new bone sites promotes multiple myeloma dissemination and progression by increasing metastatic cytokines and MDSCs in BM and inhibiting BM immunity. Importantly, MDSC depletion can block multiple myeloma progression promoted by OB-Runx2 deficiency.Significance: This study demonstrates that Runx2 deficiency in immature osteoblasts at distant bone sites attracts myeloma cells and allows myeloma progression in new bone sites via OB-secreted metastatic cytokines and MDSC-mediated suppression of bone marrow immunity.

Neutrophil elastase from myeloid cells promotes TSC2-null tumor growth.

Chronic inflammation promotes progression of many cancers, with circulating myeloid-derived suppressor cell (MDSC) levels correlating with poor prognosis. Here we examine effects of MDSCs on lymphangioleiomyomatosis (LAM), a rare disease occurring almost exclusively in women whereby estrogen-sensitive metastatic TSC2-null tumors grow throughout the lungs, markedly reducing pulmonary function. The LAM cell origin remains unknown; however, previous work demonstrated that Tsc2 inactivation in the mouse uterus induced estrogen-dependent myometrial tumors with nearly all features of LAM. Half of these animals developed metastatic myometrial tumors in the lungs, suggesting that LAM cells might originate from the myometrium, possibly explaining its overwhelming female prevalence and estrogen-sensitivity. Here we report that MDSC levels, and in particular granulocytic myeloid cell levels, are elevated in the periphery and in tumors of uterine-specific Tsc2-null mice. Importantly, MDSC depletion or inhibition of their recruitment impairs myometrial tumor growth. RNA and protein analysis of Tsc2-null myometrial tumors and xenografts demonstrate high expression and activity of the serine protease neutrophil elastase (NE), with selective qPCR studies indicating a stromal origin of the NE. Notably, treatment with sivelestat, a known NE inhibitor already approved for human use in some countries, reduces tumor growth similar to MDSC depletion. Furthermore, NE promotes Tsc2-null tumor cell growth, migration, and invasion in vitro. Finally, NE-expressing myeloid cells are present throughout the lungs of LAM patients but not controls. These data suggest that NE derived from granulocytic myeloid cells might directly promote LAM tumor cell progression and could be a novel therapeutic target for LAM.

Deciphering the Crosstalk Between Myeloid-Derived Suppressor Cells and Regulatory T Cells in Pancreatic Ductal Adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) is a fatal disease with rising incidence and a remarkable resistance to current therapies. The reasons for this therapeutic failure include the tumor's extensive infiltration by immunosuppressive cells such as myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs). By using light sheet fluorescent microscopy, we identified here direct interactions between these major immunoregulatory cells in PDAC. The in vivo depletion of MDSCs led to a significant reduction in Tregs in the pancreatic tumors. Through videomicroscopy and ex vivo functional assays we have shown that (i) MDSCs are able to induce Treg cells in a cell-cell dependent manner; (ii) Treg cells affect the survival and/or the proliferation of MDSCs. Furthermore, we have observed contacts between MDSCs and Treg cells at different stages of human cancer. Overall our findings suggest that interactions between MDSCs and Treg cells contribute to PDAC immunosuppressive environment.

CD11B+ Ly6G+ myeloid derived suppressor cells promote liver regeneration in a murine model of major hepatectomy

Background: Liver regeneration depends on sequential activation of multiple pathways and cell types involving the remaining organ in recovery of mass. Proliferation of parenchyma is dependent on angiogenesis. Understanding liver regeneration associated neovascularization may be useful for future development of clinical interventions. Myeloid Derived Suppressor Cells (MDSCs) promote immune suppression and tumor angiogenesis, and play a role in normal developmental processes that necessitate rapid vascularization. The role of MDSCs in liver regeneration has not been studied. Materials & Methods: The proportion of MDSC populations was assessed within remnant livers following major hepatectomy (Hx). The effect of CD11b+Ly6G+ MDSCs (G-MDSCs) depletion on post-operative mortality, liver injury, regeneration, and angiogenesis was evaluated. Transcriptional and functional characterization of regenerating liver-derived G-MDSCs was performed. All animal studies were conducted according to protocols approved by the institutional animal care and use committee of Tel-Aviv Sourasky Medical Center, strictly observing national, local, and institutional guidelines. Approval no. 13-4-16 Results: G-MDSCs were enriched within regenerating livers, and their depletion led to increased post-operative mortality, reduced liver weights, increased liver injury, decreased hepatic vascularization and hepatocyte proliferation, and to aberrant liver function indices in peripheral blood. Global gene expression profiling of regenerating liver-derived G-MDSCs demonstrated a large-scale transcriptional response, involving key pathways related to angiogenesis. Functionally, enhanced reactive oxygen species production and angiogenic capacities of regenerating liver-derived G-MDSCs were confirmed. A comparative analysis revealed that the transcriptional response of G-MDSCs during liver regeneration highly resembled that of peripheral blood G-MDSCs during progression of abdominal tumors, suggesting a common G-MDSC gene expression profile promoting angiogenesis. Conclusions: This study provides the first evidence that MDSCs contribute to early stages of liver regeneration by exerting pro-angiogenic functions using a unique transcriptional program.

Myeloid-Derived Suppressor Cells: Major Figures that Shape the Immunosuppressive and Angiogenic Network in Cancer.

Myeloid-derived suppressor cells (MDSCs) constitute a vast population of immature myeloid cells implicated in various conditions. Most notably, their role in cancer is of great complexity. They exert immunosuppressive functions like hampering cancer immunity mediated by T lymphocytes and natural killer cells, while simultaneously they can recruit T regulatory cells to further promote immunosuppression, thus shielding tumor cells against the immune defenses. In addition, they were shown to support tumor invasion and metastasis by inducing vascularization. Yet again, in order to exert their angiogenic activities, they do have at their disposal a variety of occasionally overlapping mechanisms, mainly driven by VEGF/JAK/STAT signaling. In this concept, they have risen to be a rather attractive target for therapies, including depletion or maturation, so as to overcome cancer immunity and suppress angiogenic activity. Even though, many studies have been conducted to better understand these cells, there is much to be done yet. This article hopes to shed some light on the paradoxal complexity of these cells, while elucidating some of the key features of MDSCs in relation to immunosuppression and, most importantly, to the vascularization processes, along with current therapeutic options in cancer, in relation to MDSC depletion.

Sequential depletion of myeloid-derived suppressor cells and tumor cells with a dual-pH-sensitive conjugated micelle system for cancer chemoimmunotherapy

Myeloid-derived suppressor cells(MDSCs)are one of the most important immunosuppressive cells in tumor microenvironment, which also promote the development and progression of tumor cells. Nevertheless, due to the different distribution features of MDSCs and tumor cells, selective elimination of MDSCs and tumor cells in tumor microenvironment remain a great challenge. Here we have designed a dual-pH-sensitivity conjugated micelle system (PAH/RGX-104@PDM/PTX) that could deliver liver-X nuclear receptor (LXR) agonist RGX-104 and paclitaxel (PTX) to the perivascular region and tumor cells, respectively. Upon arrival at the acidic tumor microenvironment, the PAH/RGX-104@PDM/PTX undergo structure disintegration and capacitate coinstantaneous release of RGX-104 in the perivascular regions, leaving the intact PTX containing micelles PDM/PTX for tumor deep penetration. The released RGX-104 can be preferentially taken up by leukocytes, endothelial cells and macrophages which are nicely enriched in perivascular regions to active the LXR, and further reduces immunosuppressive MDSC levels. The remained small micelles carrying PTX enable deep tumor penetration as well as rapid specific drug release in the endosomal/lysosomal to kill tumor cells. PAH/RGX-104@PDM/PTX exhibits superior tumor accumulation as well as tumor penetration, and suppresses 74.88% in vivo tumor growth. More importantly, PAH/RGX-104@PDM/PTX has significantly alleviated tumor immunosuppression by eliminating MDSCs and increasing cytotoxic T lymphocytes infiltration. Our studies suggest that the dual-pH-sensitive codelivery nanocarrier not only cause apoptosis of cancer cells but also regulate the tumor immune environment to ultimately enhance the antitumor effect of CTLs through MDSCs depletion.

Myeloid-Derived Suppressor Cells Promote Metastasis in Breast Cancer After the Stress of Operative Removal of the Primary Cancer.

Objective: To investigate the role of myeloid-derived suppressor cells (MDSC) in cancer progression after the stress of operative removal and the potential treatment value of MDSC depletion.Summary Background Data: Surgery is the most important treatment strategy in breast cancer. Recent research has provided evidence that operations may promote cancer metastases under some circumstances.Methods: A mouse model of breast cancer (administration of the murine breast cancer 4T1 cells subcutaneously) and the stress of operation were used to compare immune responses and survival outcomes. Flow cytometry was performed to detect the expression of CD11b and Gr1 MDSCs in tumor tissues and lung metastases. Cytokine levels were detected with three-color flow cytometry and enzyme-linked immunosorbent assay (ELISA). MDSCs were isolated and co-cultured with 4T1 cells to identify any morphological change with immunofluorescence. The anti Gr-1 antibody was used to detect the function of the anti-Gr1 treatment in breast cancer.Results: The operative stress impaired the overall survival, leading to an increased number of MDSCs that preferentially infiltrated the tumor microenvironment and promoted tumor metastasis. In both in vitro and in vivo assays, MDSCs induced the epithelial-mesenchymal transition (EMT) of tumor cells through the up-regulation of TGF-beta1, VEGF, and IL-10. Furthermore, a treatment strategy of MDSC depletion was found to reduce pulmonary metastases after operations.Conclusions: The stress of operation could impair the overall survival in mice. The infiltrated MDSCs appear to induce EMT of tumor cells and increase metastases through the up-regulation of TGF-beta1, VEGF, and IL-10 levels. MDSC depletion could be a promising treatment strategy to prevent immune evasion after operations.

The dysfunction of BP180/collagen XVII in keratinocytes promotes melanoma progression.

BP180, also termed collagen XVII, is a hemidesmosomal transmembrane glycoprotein expressed in basal keratinocytes, and functions as a cell-matrix adhesion molecule in the dermal-epidermal junction of the skin. Its function other than cell-matrix adhesion remains unclear. We generated a mouse strain with BP180 dysfunction (termed ∆NC16A), which develops spontaneous skin inflammation accompanied by an influx of myeloid derived suppressor cells (MDSCs). We utilized the B16 mouse melanoma model to demonstrate that BP180 dysfunction in either skin or basal keratinocytes promotes MDSC influx into skin and tumor progression. MDSC depletion reduced tumor progression in ∆NC16A mice, demonstrating a critical role for BP180 dysfunction-driven MDSCs in melanoma progression. This study provides the first direct evidence that BP180, a cell-cell matrix adhesion molecule, possesses anti-tumor function through modulating infiltration of MDSCs. Basal keratinocytes actively participate in skin microenvironment changes caused by BP180 dysfunction. ∆NC16A mice could be a new animal model to study the melanoma microenvironment.

Myeloid-Derived Suppressor Cells Mediate Immunosuppression After Cardiopulmonary Bypass.

Cardiopulmonary bypass is associated with severe immune dysfunctions. Particularly, a cardiopulmonary bypass-related long-lasting immunosuppressive state predisposes patients to a higher risk of postoperative complications, such as persistent bacterial infections. This study was conducted to elucidate mechanisms of post-cardiopulmonary bypass immunosuppression. In vitro studies with human peripheral blood mononuclear cells. Cardiosurgical ICU, University Research Laboratory. Seventy-one patients undergoing cardiac surgery with cardiopulmonary bypass (enrolled May 2017 to August 2018). Peripheral blood mononuclear cells before and after cardiopulmonary bypass were analyzed for the expression of immunomodulatory cell markers by real-time quantitative reverse transcription polymerase chain reaction. T cell effector functions were determined by enzyme-linked immunosorbent assay, carboxyfluorescein succinimidyl ester staining, and cytotoxicity assays. Expression of cell surface markers was assessed by flow cytometry. CD15 cells were depleted by microbead separation. Serum arginine was measured by mass spectrometry. Patient peripheral blood mononuclear cells were incubated in different arginine concentrations, and T cell functions were tested. After cardiopulmonary bypass, peripheral blood mononuclear cells exhibited significantly reduced levels of costimulatory receptors (inducible T-cell costimulator, interleukin 7 receptor), whereas inhibitory receptors (programmed cell death protein 1 and programmed cell death 1 ligand 1) were induced. T cell effector functions (interferon γ secretion, proliferation, and CD8-specific cell lysis) were markedly repressed. In 66 of 71 patients, a not yet described cell population was found, which could be characterized as myeloid-derived suppressor cells. Myeloid-derived suppressor cells are known to impair immune cell functions by expression of the arginine-degrading enzyme arginase-1. Accordingly, we found dramatically increased arginase-1 levels in post-cardiopulmonary bypass peripheral blood mononuclear cells, whereas serum arginine levels were significantly reduced. Depletion of myeloid-derived suppressor cells from post-cardiopulmonary bypass peripheral blood mononuclear cells remarkably improved T cell effector function in vitro. Additionally, in vitro supplementation of arginine enhanced T cell immunocompetence. Cardiopulmonary bypass strongly impairs the adaptive immune system by triggering the accumulation of myeloid-derived suppressor cells. These myeloid-derived suppressor cells induce an immunosuppressive T cell phenotype by increasing serum arginine breakdown. Supplementation with L-arginine may be an effective measure to counteract the onset of immunoparalysis in the setting of cardiopulmonary bypass.

Abstract 2710: Depletion of CXCR2-dependent myeloid-derived suppressor cells (MDSCs) overcomes anti-PD-1 resistance in a murine model of LKB1-deficient non-small cell lung cancer (NSCLC) with high mutational load

Abstract Checkpoint inhibitors such as PD-L1/PD-1 blockade have rapidly integrated into the paradigm of NSCLC treatment. However, a majority of patients do not benefit from monotherapy with checkpoint inhibitors. High tumor mutational burden (TMB), along with pre-existing intratumoral T cell infiltration and baseline high PD-L1 expression, predicts response to checkpoint blockade. Furthermore, a recent retrospective study identified LKB1 alterations as the most prevalent genomic driver of resistance to PD-1 axis inhibitors in KRAS-mutant lung adenocarcinoma. In this study, we investigate the mechanisms underlying LKB1-mediated immunosuppression in NSCLC. We show that loss of LKB1 in human bronchial epithelial cells (HBECs) and NSCLC cells leads to increased secretion of CXCR2 ligands, including CXCL1, CXCL2, CXCL3, CXCL5 and CXCL8. These CXCR2 ligands are also elevated in LKB1-deficient tumors from patient-derived xenografts and genetically-engineered murine models. We find abundant tumor infiltrating MDSCs in murine Lkb1-deficient NSCLC, consistent with the capacity for CXCR2 ligands to recruit MDSCs. MDSCs mediate potent immune suppressive activities at multiple levels including release of immunosuppressive cytokines, recruitment of regulatory T cells (Tregs), inhibition of CD8 T cell tumor infiltration and upregulation of PD-L1 expression. Although MDSC depletion activates interferon gamma signaling and decreases systemic Tregs in murine KrasK12D;Tp53-/-;Lkb1-/- (KPL) tumors, it does not sensitize KPL tumors to anti-PD-1 therapy. One of the major challenges in the preclinical assessment of lung cancer immunotherapy is that the commonly utilized murine models lack the mutational burden of human NSCLC. To assess this combination therapy in the context of a mutational burden that more accurately reflects the clinical disease, we generated tumors with high TMB by exposing KPL cells in vitroto the tobacco carcinogen N-methyl-N-nitrosourea. In the context of high TMB, MDSC depletion demonstrates remarkable anti-tumor effects in combination with anti-PD-1 therapy. Finally, we delineate the regulation of CXCR2 ligands by LKB1 which is dependent on the MARK-mediated NF-κB pathway. In conclusion, we find that LKB1 deficiency leads to increased CXCR2 ligand production and tumor infiltrating MDSCs. MDSC depletion enhances the efficacy of anti-PD-1 blockade in LKB1-deficient tumors bearing high TMB. Citation Format: Rui Li, Ramin Salehi-Rad, Stephanie Ong, Milica Momcilovic, Bin Liu, Raymond Lim, Linh Tran, Ziling Huang, Zhe Jing, Manash Paul, Kostyantyn Krysan, Stacy Park, John Minna, Michael Teitell, David Shackelford, Steven Dubinett. Depletion of CXCR2-dependent myeloid-derived suppressor cells (MDSCs) overcomes anti-PD-1 resistance in a murine model of LKB1-deficient non-small cell lung cancer (NSCLC) with high mutational load [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2710.