Regulation of tumor metastasis by myeloid-derived suppressor cells.

Accumulation of pathologically activated immature myeloid cells with potent immune-suppressive activity is one of the major immunological hallmarks of cancer. In recent years, it became clear that in addition to their immune-suppressive activity, myeloid-derived suppressor cells (MDSCs) influence tumor progression in a variety of ways. They are directly implicated in the promotion of tumor metastases by participating in the formation of premetastatic niches, promoting angiogenesis and tumor cell invasion. In this review, we discuss recent data describing various roles of MDSCs in the formation of tumor metastases.

Regulation of dendritic cell differentiation in bone marrow during emergency myelopoiesis.

Although accumulation of dendritic cell (DC) precursors occurs in bone marrow, the terminal differentiation of these cells takes place outside bone marrow. The signaling, regulating this process, remains poorly understood. We demonstrated that this process could be differentially regulated by Notch ligands: Jagged-1 (Jag1) and Delta-like ligand 1 (Dll1). In contrast to Dll1, Jag1, in vitro and during induced myelopoiesis in vivo, prevented DC differentiation by promoting the accumulation of their precursors. Although both ligands activated Notch in hematopoietic progenitor cells, they had an opposite effect on Wnt signaling. Dll1 activated Wnt pathways, whereas Jag1 inhibited it via downregulation of the expression of the Wnt receptors Frizzled (Fzd). Jag1 suppressed fzd expression by retaining histone deacetylase 1 in the complex with the transcription factor CSL/CBF-1 on the fzd promoter. Our results suggest that DC differentiation, during induced myelopoiesis, can be regulated by the nature of the Notch ligand expressed on adjacent stroma cells.

Myeloid-derived suppressor cells regulate growth of multiple myeloma by inhibiting T cells in bone marrow.

Myeloid-derived suppressor cells (MDSC) are one of the major factors limiting the immune response in cancer. However, their role in bone marrow (BM), the site of primary localization of multiple myeloma (MM), is poorly understood. In this study, we found a significant accumulation of CD11b(+)CD14(-)CD33(+) immunosuppressive MDSC in BM of patients with newly diagnosed MM. To assess the possible role of MDSC in MM, we used immunocompetent mouse models. Immunosuppressive MDSC accumulated in BM of mice as early as 1 wk after tumor inoculation. S100A9 knockout (KO) mice, which are deficient in their ability to accumulate MDSC in tumor-bearing hosts, demonstrated reduced MDSC accumulation in BM after injection of MM cells compared with wild-type mice. Growth of the immunogenic MM cells was significantly reduced in S100A9KO mice. This effect was associated with the accumulation of Ag-specific CD8(+) T cells in BM and spleens of S100A9KO mice, but not wild-type mice, and was abrogated by the administration of anti-CD8 Ab or adoptive transfer of MDSC. Thus, the accumulation of MDSC at early stages of MM plays a critical role in MM progression and suggests that MDSC can be considered a possible therapeutic target in this disease.

Regulation of plasmacytoid dendritic cell development in mice by aryl hydrocarbon receptor.

Aryl hydrocarbon receptor (AhR) has an important role in the regulation of cell responses to different environmental stimuli, as well as to various endogenous ligands. Although AhR was previously implicated in the regulation of dendritic cell (DC) activation, very little is known about its potential role in the development of these cells. Here we report our unexpected findings that AhR may regulate the differentiation of plasmacytoid DCs (pDCs). Agonist of AhR markedly decreased the generation of pDCs in vitro, whereas the AhR antagonist had an opposite effect. The differentiation of conventional DCs (cDCs) was not affected. AhR-knockout mice had a substantial accumulation of pDCs in peripheral lymphoid organs; whereas no changes in cDCs were seen. Thus, this study has identified AhR as a transcription factor involved in the development of one population of DCs-pDCs.

The phosphatase SRC homology region 2 domain-containing phosphatase-1 is an intrinsic central regulator of dendritic cell function.

Dendritic cells (DCs) initiate proinflammatory or regulatory T cell responses, depending on their activation state. Despite extensive knowledge of DC-activating signals, the understanding of DC inhibitory signals is relatively limited. We show that Src homology region 2 domain-containing phosphatase-1 (SHP-1) is an important inhibitor of DC signaling, targeting multiple activation pathways. Downstream of TLR4, SHP-1 showed increased interaction with several proteins including IL-1R-associated kinase-4, and modulated LPS signaling by inhibiting NF-κB, AP-1, ERK, and JNK activity, while enhancing p38 activity. In addition, SHP-1 inhibited prosurvival signaling through AKT activation. Furthermore, SHP-1 inhibited CCR7 protein expression. Inhibiting SHP-1 in DCs enhanced proinflammatory cytokines, IL-6, IL-12, and IL-1ß production, promoted survival, and increased DC migration to draining lymph nodes. Administration of SHP-1-inhibited DCs in vivo induced expansion of Ag-specific cytotoxic T cells and inhibited Foxp3(+) regulatory T cell induction, resulting in an enhanced immune response against pre-established mouse melanoma and prostate tumors. Taken together, these data demonstrate that SHP-1 is an intrinsic global regulator of DC function, controlling many facets of T cell-mediated immune responses.

Systemic and local immunity following adoptive transfer of NY-ESO-1 SPEAR T cells in synovial sarcoma.

BACKGROUND: Gene-modified autologous T cells expressing NY-ESO-1c259, an affinity-enhanced T-cell receptor (TCR) reactive against the NY-ESO-1-specific HLA-A*02-restricted peptide SLLMWITQC (NY-ESO-1 SPEAR T-cells; GSK 794), have demonstrated clinical activity in patients with advanced synovial sarcoma (SS). The factors contributing to gene-modified T-cell expansion and the changes within the tumor microenvironment (TME) following T-cell infusion remain unclear. These studies address the immunological mechanisms of response and resistance in patients with SS treated with NY-ESO-1 SPEAR T-cells. METHODS: Four cohorts were included to evaluate antigen expression and preconditioning on efficacy. Clinical responses were assessed by RECIST v1.1. Engineered T-cell persistence was determined by qPCR. Serum cytokines were evaluated by immunoassay. Transcriptomic analyses and immunohistochemistry were performed on tumor biopsies from patients before and after T-cell infusion. Gene-modified T-cells were detected within the TME via an RNAish assay. RESULTS: Responses across cohorts were affected by preconditioning and intra-tumoral NY-ESO-1 expression. Of the 42 patients reported (data cut-off 4June2018), 1 patient had a complete response, 14 patients had partial responses, 24 patients had stable disease, and 3 patients had progressive disease. The magnitude of gene-modified T-cell expansion shortly after infusion was associated with response in patients with high intra-tumoral NY-ESO-1 expression. Patients receiving a fludarabine-containing conditioning regimen experienced increases in serum IL-7 and IL-15. Prior to infusion, the TME exhibited minimal leukocyte infiltration; CD163+ tumor-associated macrophages (TAMs) were the dominant population. Modest increases in intra-tumoral leukocytes (≤5%) were observed in a subset of subjects at approximately 8 weeks. Beyond 8 weeks post infusion, the TME was minimally infiltrated with a TAM-dominant leukocyte infiltrate. Tumor-associated antigens and antigen presentation did not significantly change within the tumor post-T-cell infusion. Finally, NY-ESO-1 SPEAR T cells trafficked to the TME and maintained cytotoxicity in a subset of patients. CONCLUSIONS: Our studies elucidate some factors that underpin response and resistance to NY-ESO-1 SPEAR T-cell therapy. From these data, we conclude that a lymphodepletion regimen containing high doses of fludarabine and cyclophosphamide is necessary for SPEAR T-cell persistence and efficacy. Furthermore, these data demonstrate that non-T-cell inflamed tumors, which are resistant to PD-1/PD-L1 inhibitors, can be treated with adoptive T-cell based immunotherapy. TRIAL REGISTRATION: ClinicalTrials.gov, NCT01343043 , Registered 27 April 2011.

Strategies for imaging mitophagy in high-resolution and high-throughput.

The selective autophagic removal of mitochondria called mitophagy is an essential physiological signaling for clearing damaged mitochondria and thus maintains the functional integrity of mitochondria and cells. Defective mitophagy is implicated in several diseases, placing mitophagy as a target for drug development. The identification of key regulators of mitophagy as well as chemical modulators of mitophagy requires sensitive and reliable quantitative approaches. Since mitophagy is a rapidly progressing event and sub-microscopic in nature, live cell image-based detection tools with high spatial and temporal resolution is preferred over end-stage assays. We describe two approaches for measuring mitophagy in mammalian cells using stable cells expressing EGFP-LC3 - Mito-DsRed to mark early phase of mitophagy and Mitochondria-EGFP - LAMP1-RFP stable cells for late events of mitophagy. Both the assays showed good spatial and temporal resolution in wide-field, confocal and super-resolution microscopy with high-throughput adaptable capability. A limited compound screening allowed us to identify a few new mitophagy inducers. Compared to the current mitophagy tools, mito-Keima or mito-QC, the assay described here determines the direct delivery of mitochondrial components to the lysosome in real time mode with accurate quantification if monoclonal cells expressing a homogenous level of both probes are established. Since the assay described here employs real-time imaging approach in a high-throughput mode, the platform can be used both for siRNA screening or compound screening to identify key regulators of mitophagy at decisive stages.

Antitumor Activity Associated with Prolonged Persistence of Adoptively Transferred NY-ESO-1 c259T Cells in Synovial Sarcoma.

We evaluated the safety and activity of autologous T cells expressing NY-ESO-1c259, an affinity-enhanced T-cell receptor (TCR) recognizing an HLA-A2-restricted NY-ESO-1/LAGE1a-derived peptide, in patients with metastatic synovial sarcoma (NY-ESO-1c259T cells). Confirmed antitumor responses occurred in 50% of patients (6/12) and were characterized by tumor shrinkage over several months. Circulating NY-ESO-1c259T cells were present postinfusion in all patients and persisted for at least 6 months in all responders. Most of the infused NY-ESO-1c259T cells exhibited an effector memory phenotype following ex vivo expansion, but the persisting pools comprised largely central memory and stem-cell memory subsets, which remained polyfunctional and showed no evidence of T-cell exhaustion despite persistent tumor burdens. Next-generation sequencing of endogenous TCRs in CD8+ NY-ESO-1c259T cells revealed clonal diversity without contraction over time. These data suggest that regenerative pools of NY-ESO-1c259T cells produced a continuing supply of effector cells to mediate sustained, clinically meaningful antitumor effects.Significance: Metastatic synovial sarcoma is incurable with standard therapy. We employed engineered T cells targeting NY-ESO-1, and the data suggest that robust, self-regenerating pools of CD8+ NY-ESO-1c259T cells produce a continuing supply of effector cells over several months that mediate clinically meaningful antitumor effects despite prolonged exposure to antigen. Cancer Discov; 8(8); 944-57. ©2018 AACR.See related commentary by Keung and Tawbi, p. 914This article is highlighted in the In This Issue feature, p. 899.

Bone marrow PMN-MDSCs and neutrophils are functionally similar in protection of multiple myeloma from chemotherapy.

Multiple myeloma (MM) is an incurable cancer of plasma cells localized preferentially in the bone marrow (BM). Resistance to chemotherapy represents one of the main challenges in MM management. BM microenvironment is known to play a critical role in protection of MM cells from chemotherapeutics; however, mechanisms responsible for this effect are largely unknown. Development of MM is associated with accumulation of myeloid-derived suppressor cells (MDSCs) mostly represented by pathologically activated relatively immature polymorphonuclear neutrophils (PMN-MDSCs). Here, we investigated whether PMN-MDSCs are responsible for BM microenvironment-mediated MM chemoresistance. Using in vivo mouse models allowing manipulation of myeloid cell number, we demonstrated a critical role for myeloid cells in MM growth and chemoresistance. PMN-MDSCs isolated from MM-bearing host are immunosuppressive and thus, functionally distinct from their counterpart in tumor-free host neutrophils. We found, however, that both PMN-MDSCs and neutrophils equally promote MM survival from doxorubicin and melphalan and that this effect is mediated by soluble factors rather than direct cell-cell contact. Our data indicate that targeting PMN-MDSCs would enhance chemotherapy efficacy in MM.

Myeloid-derived suppressor cells in the development of lung cancer.

Myeloid-derived suppressor cells (MDSC) are widely implicated in immune suppression associated with tumor progression and chronic inflammation. However, very little is known about their possible role in tumor development. Here, we evaluated the role of MDSC in two experimental models of lung cancer: inflammation-associated lung cancer caused by chemical carcinogen urethane in combination with exposure to cigarette smoke; and a transgenic CC10Tg model not associated with inflammation. Exposure of mice to cigarette smoke alone resulted in significant accumulation in various organs of cells with typical MDSC phenotype (Gr-1(+)CD11b(+)). However, these cells lacked immunosuppressive activity and could not be defined as MDSC. When cigarette smoke was combined with a single dose of urethane, it led to the development of tumor lesions in lungs within 4 months. By that time, Gr-1(+)CD11b(+) cells accumulated in the spleen and lung and had potent immunosuppressive activity, and thus could be defined as MDSC. In the CC10Tg model, accumulation of immunosuppressive MDSC was observed only at 4 months of age, after the appearance of tumor lesions in the lungs. Accumulation of MDSC in both models was abrogated in S100A9 knockout mice. This resulted in a dramatic improvement in survival of mice in both models. Thus, cigarette smoke results in the expansion of immature myeloid cells lacking suppressive activity. Accumulation of bona fide MDSC in both models was observed only after the development of tumor lesions. However, MDSC played a major role in tumor progression and survival, which suggests that their targeting may provide clinical benefits in lung cancer.

ER stress regulates myeloid-derived suppressor cell fate through TRAIL-R-mediated apoptosis.

Myeloid-derived suppressor cells (MDSCs) dampen the immune response thorough inhibition of T cell activation and proliferation and often are expanded in pathological conditions. Here, we studied the fate of MDSCs in cancer. Unexpectedly, MDSCs had lower viability and a shorter half-life in tumor-bearing mice compared with neutrophils and monocytes. The reduction of MDSC viability was due to increased apoptosis, which was mediated by increased expression of TNF-related apoptosis-induced ligand receptors (TRAIL-Rs) in these cells. Targeting TRAIL-Rs in naive mice did not affect myeloid cell populations, but it dramatically reduced the presence of MDSCs and improved immune responses in tumor-bearing mice. Treatment of myeloid cells with proinflammatory cytokines did not affect TRAIL-R expression; however, induction of ER stress in myeloid cells recapitulated changes in TRAIL-R expression observed in tumor-bearing hosts. The ER stress response was detected in MDSCs isolated from cancer patients and tumor-bearing mice, but not in control neutrophils or monocytes, and blockade of ER stress abrogated tumor-associated changes in TRAIL-Rs. Together, these data indicate that MDSC pathophysiology is linked to ER stress, which shortens the lifespan of these cells in the periphery and promotes expansion in BM. Furthermore, TRAIL-Rs can be considered as potential targets for selectively inhibiting MDSCs.

Skeletal muscle myosin cross-bridge cycling is necessary for myofibrillogenesis.

A major stimulus affecting myofibrillogenesis in both embryonic and mature striated muscle is contractile activity. There are two major signals associated with contractile activity: a physiological signal, the transient increase in intracellular calcium, and a physical signal, the transient increase in tension production. However, dissociating these two signals to examine their relative contributions to myofibrillogenesis has proven difficult. In this study, we have used two different myosin inhibitors to determine the importance of myosin cross-bridge cycling in sarcomere assembly. We find that the small-molecule inhibitor 2,3-butanedione monoxime (BDM), which inhibits myosin ATPase, disrupts myofibrillogenesis in amphibian myocytes, consistent with results from avian studies. However, BDM is a weak myosin inhibitor and it is non-specific; concentrations that inhibit contraction and disrupt myofibrillogenesis also disrupt calcium signaling. Therefore, we also used the recently identified skeletal muscle myosin II inhibitor, N-benzyl-p-toluenesulphonamide (BTS), which has high affinity and specificity for skeletal muscle fast myosin. BTS inhibits contraction and results in myofibrillar disruption that phenocopies our results with BDM. However, BTS does not affect either spontaneous or induced calcium transients. Furthermore, BTS is reversible and does not significantly affect the expression levels of myosin or actin. Thus, our convergent results with BDM and BTS suggest that sarcomere assembly depends on active regulation of tension in the forming myofibril.