Tumor-infiltrating Myeloid Cells Research Articles

Overcoming immunotherapeutic resistance by targeting the cancer inflammation cycle.

Inflammation is a hallmark of cancer and supports tumor growth, proliferation, and metastasis, but also inhibits T cell immunosurveillance and the efficacy of immunotherapy. The biology of cancer inflammation is defined by a cycle of distinct immunological steps that begins during disease conception with the release of inflammatory soluble factors. These factors communicate with host organs to trigger bone marrow mobilization of myeloid cells, trafficking of myeloid cells to the tumor, and differentiation of myeloid cells within the tumor bed. Tumor-infiltrating myeloid cells then orchestrate an immunosuppressive microenvironment and assist in sustaining a vicious cycle of inflammation that co-evolves with tumor cells. This Cancer-Inflammation Cycle acts as a rheostat or "inflammostat" that impinges upon T cell immunosurveillance and prevents the development of productive anti-tumor immunity. Here, we define the major nodes of the Cancer-Inflammation Cycle and describe their impact on T cell immunosurveillance in cancer. Additionally, we discuss emerging pre-clinical and clinical data suggesting that intervening upon the Cancer-Inflammation Cycle will be a necessary step for broadening the potential of immunotherapy in cancer.

PD-1 Imposes Qualitative Control of Cellular Transcriptomes in Response to T Cell Activation.

Targeted blockade of programmed cell death 1 (PD-1), an immune-checkpoint receptor that inhibits Tcell activation, provides clinical benefits in various cancers. However, how PD-1 modulates gene expression in Tcells remains enigmatic. Here weinvestigated how PD-1 affects transcriptome changes induced by Tcell receptor (TCR) activation. Intriguingly, we identified a huge variance in PD-1 sensitivity among TCR-inducible genes. When we quantified the half maximal effective concentration (EC50) as the relationship between change in gene expression and TCR signal strength, we found that genes associated with survival and proliferation were efficiently expressed upon TCR activation and resistant to PD-1-mediated inhibition. Conversely, genes encoding cytokines and effector molecules were expressed less efficiently and sensitive to PD-1-mediated inhibition. We further demonstrated that transcription factor binding motifs and CpG frequency in the promoter region affect EC50 and thus the PD-1 sensitivity of genes. Our findings explain how PD-1, dependent on the TCR signal strength, calibrates cellular transcriptomes to shape functional properties of Tcell populations.

Current Strategies to Target Tumor-Associated-Macrophages to Improve Anti-Tumor Immune Responses.

Established evidence demonstrates that tumor-infiltrating myeloid cells promote rather than stop-cancer progression. Tumor-associated macrophages (TAMs) are abundantly present at tumor sites, and here they support cancer proliferation and distant spreading, as well as contribute to an immune-suppressive milieu. Their pro-tumor activities hamper the response of cancer patients to conventional therapies, such as chemotherapy or radiotherapy, and also to immunotherapies based on checkpoint inhibition. Active research frontlines of the last years have investigated novel therapeutic strategies aimed at depleting TAMs and/or at reprogramming their tumor-promoting effects, with the goal of re-establishing a favorable immunological anti-tumor response within the tumor tissue. In recent years, numerous clinical trials have included pharmacological strategies to target TAMs alone or in combination with other therapies. This review summarizes the past and current knowledge available on experimental tumor models and human clinical studies targeting TAMs for cancer treatment.

Abstract I03: Immune contexture of human pancreatic cancer

Abstract The concept that leukocytes are critical components of solid tumors is now generally accepted; however, their role(s) in regulating aspects of neoplastic progression, and/or response to cytotoxic, targeted, and/or immune therapy is only beginning to be understood. Utilizing de novo mouse models of organ-specific solid tumor development (mammary, cutaneous, and pancreas carcinomas and mesothelioma), we now appreciate that adaptive leukocytes differentially regulate myeloid cell recruitment, activation, and effector function, and in turn, activated tumor-infiltrating myeloid cells engage tissue-based programs to foster malignancy and repress antitumor immunity by a diversity of mechanisms. Treatment of tumor-bearing mice with therapeutic agents that disrupt lymphocyte-myeloid cell interaction, myeloid cell activation, or myeloid cell functionality generally slow primary tumor growth kinetics when combined with cytotoxic therapy; however, their impact on metastases is variable. Similar to organ-specific regulatory programs co-opted to foster primary tumor growth, regulation of metastatic seeding and outgrowth is also regulated by tissue- and organ-specific mechanisms. Based on this, it stands to reason that therapeutic strategies may not be efficacious in both primary and metastatic locations. To be presented will be our recent insights into organ- and tissue-specific regulation of primary and metastatic cancer development by adaptive and innate immune cells, how systemic regulation of humoral immunity and complement-mediated pathways regulate pro- versus antitumor immune responses, and new studies evaluating how attenuating protumor properties of select lymphoid and myeloid cells can be exploited to enhance therapeutic responses to cytotoxic and immune-based therapy. (LMC acknowledges generous support from the NIH/NCI, the Department of Defense Breast Cancer Research Program, Susan G. Komen Foundation, the Breast Cancer Research Foundation, and the Brenden-Colson Center for Pancreatic Health.) Citation Format: Lisa M. Coussens. Immune contexture of human pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr I03.

Intratumoural MDSC recruitment by chemotherapeutic agent, 5-FU offsets the anti-tumor activity of immune-checkpoint inhibitor in HCC

Abstract Background Current hepatocellular carcinoma (HCC) immunotherapy trials only yield modest outcome, suggesting that possibly strong intrinsic immunosuppressive network needed to be tackled. Conventional chemotherapies are found to exert immunomodulatory effect on the tumor microenvironment (TME). Our study investigated anti-tumor activity of 5-FU in combination with anti-PD-L1, using pre-clinical HCC mouse model, and evaluated the immunomodulation in TME after drug treatments. Methods For the orthotopic HCC in vivo experiment, 6-8-week-old male C57BL/6 mice were injected intrahepatically with 5x10^5 RIL-175 luc+ cells. In order to assess its immunomodulatory effect on HCC TME rather than on direct tumor-killing effect, 5-FU was administrated (i.p.) 3 times per week at a relative low dose—20mg/kg. Whilst, anti-PD-L1(10mg/kg) was delivered (i.p.) every 5 days. Tumor growth was monitored via in vivo imaging. Tumor, liver, spleen and blood was collected afterwards, followed by immune profiling analysis via flow cytometry. Results In terms of in vivo imaging results, mice with single anti-PD-L1 treatment showed significant response in tumor growth amongst other groups. Meanwhile 5-FU monotherapy and combined treatment group showed no difference with vehicle group. We found an increased amounts of T lymphocytes and NK cells in the tumor site after anti-PD-L1 single treatment, suggesting that these immune active cells contributed to the anti-tumor effect. Tumor-infiltrating myeloid cells, particularly P-MDSC, elevated upon 5-FU treatment in both single and combined group, suggesting that they may play a role in mediating immunosuppression. Conclusion This study illustrated that anti-PD-L1 monotherapy enriched tumor-infiltrating T lymphocytes and NK cells, possibly accounting for the deferred tumor growth. However, the accumulation of myeloid cells in 5-FU treated mice hinders the anti-tumor activity of anti-PD-L1 from this orthotopic HCC mouse model. Therefore, low dose of 5-FU may initiate immunosuppressive mechanism to alter the effectiveness of anti-PD-L1 in HCC. Legal entity responsible for the study The authors. Funding Has not received any funding. Disclosure All authors have declared no conflicts of interest.

Structural insights into human Arginase-1 pH dependence and its inhibition by the small molecule inhibitor CB-1158

Arginase-1 is a manganese-dependent metalloenzyme that catalyzes the hydrolysis of L-arginine into L-ornithine and urea. Arginase-1 is abundantly expressed by tumor-infiltrating myeloid cells that promote tumor immunosuppression, which is relieved by inhibition of Arginase-1. We have characterized the potencies of the Arginase-1 reference inhibitors (2S)-2-amino-6-boronohexanoic acid (ABH) and Nω-hydroxy-nor-L-arginine (nor-NOHA), and studied their pH-dependence and binding kinetics. To gain a better understanding of the structural changes underlying the high pH optimum of Arginase-1 and its pH-dependent inhibition, we determined the crystal structure of the human Arginase-1/ABH complex at pH 7.0 and 9.0. These structures revealed that at increased pH, the manganese cluster assumes a more symmetrical coordination structure, which presumably contributes to its increase in catalytic activity. Furthermore, we show that binding of ABH involves the presence of a sodium ion close to the manganese cluster. We also studied the investigational new drug CB-1158 (INCB001158). This inhibitor has a low-nanomolar potency at pH 7.4 and increases the thermal stability of Arginase-1 more than ABH and nor-NOHA. Moreover, CB-1158 displays slow association and dissociation kinetics at both pH 9.5 and 7.4, as indicated by surface plasmon resonance. The potent character of CB-1158 is presumably due to its increased rigidity compared to ABH as well as the formation of an additional hydrogen-bond network as observed by resolution of the Arginase-1/CB-1158 crystal structure.

A Phase 1b/2 Study of TAK-981, a First-in-Class Sumoylation Inhibitor, in Combination with Rituximab in Patients with Relapsed/Refractory (r/r) CD20-Positive Non-Hodgkin Lymphoma (NHL)

A Phase 1b/2 Study of TAK-981, a First-in-Class Sumoylation Inhibitor, in Combination with Rituximab in Patients with Relapsed/Refractory (r/r) CD20-Positive Non-Hodgkin Lymphoma (NHL)

IMMU-45. CAR-T TREATMENT OF NOVEL MOUSE MODEL OF EGFRVIII+ GBM MIRRORS CLINICAL TRIAL OUTCOMES AND PROVIDES A SYNGENEIC PLATFORM FOR THE INVESTIGATION OF CAR-T MECHANISMS OF ACTION

Abstract Despite the recent successes in cancer immunotherapy, brain tumors continue to present a significant challenge due to the unique relationship between the CNS and the immune system. Adoptive cell transfer of chimeric antigen receptor T-cells (CAR-T cells) targets tumor-associated and tumor-specific antigens. Multiple clinical trials testing CAR-T cells in the brain tumor setting have demonstrated the feasibility and safety, but also highlighted the limitations and continued need for treatment improvement. These challenges include recurrence of tumor cells that do not express the target antigens and induction of immuno-regulatory mechanisms, such as PD-L1 expression within the tumor. In this study, we used a murine GBM cell line (SB28), engineered to express the tumor-specific neoantigen human epidermal growth factor receptor variant III, to study the in vivo effects of EGFRvIII-CAR T-cells in a novel fully immunocompetent mouse model. SB28 cells have been shown to recapitulate key characteristics of human GBM, such as aggressive growth, low mutation burden, and resistance to immune checkpoint blockade therapy, and therefore, allow us to investigate many clinically relevant questions and variations in treatment protocol. Intravenous administration of CAR-transduced murine T-cells in EGFRvIII-expressing SB28 tumors showed survival benefit only when preceded by a lymphodepleting regimen. Despite prolonging survival, EGFRvIII-CAR-T cells were not curative, and the recurrent tumors displayed profound antigen loss, similar to post-treatment human tumor samples. Preliminary mechanistic studies revealed upregulation of IFNγ-inducible molecules, such as PD-L1 on tumor cells and tumor-infiltrating myeloid cells, as well as the emergence of a small, but discreet population of activated antigen presenting cells. Currently ongoing studies are aimed at delineating the exact molecular and cellular changes in the tumor microenvironment in response to the EGFRvIII-CAR T-cell treatment, in combination with clinically relevant therapies targeting the largely immunosuppressive tumor myeloid compartment

Myeloid immunosuppression and immune checkpoints in the tumor microenvironment.

Tumor-promoting inflammation and the avoidance of immune destruction are hallmarks of cancer. While innate immune cells, such as neutrophils, monocytes, and macrophages, are critical mediators for sterile and nonsterile inflammation, persistent inflammation, such as that which occurs in cancer, is known to disturb normal myelopoiesis. This disturbance leads to the generation of immunosuppressive myeloid cells, such as myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs). Due to their potent suppressive activities against effector lymphocytes and their abundance in the tumor microenvironment, immunosuppressive myeloid cells act as a major barrier to cancer immunotherapy. Indeed, various therapeutic approaches directed toward immunosuppressive myeloid cells are actively being tested in preclinical and clinical studies. These include anti-inflammatory agents, therapeutic blockade of the mobilization and survival of myeloid cells, and immunostimulatory adjuvants. More recently, immune checkpoint molecules expressed on tumor-infiltrating myeloid cells have emerged as potential therapeutic targets to redirect these cells to eliminate tumor cells. In this review, we discuss the complex crosstalk between cancer-related inflammation and immunosuppressive myeloid cells and possible therapeutic strategies to harness antitumor immune responses.

A transcriptomic landscape of cancer and TME in early-stage lungadenocarcinomaby single-cell sequencing.

33 Background: Immuno-checkpoint inhibition therapies has been revolutionizing cancer treatment. Yet only a fraction of patients show durable responses , whereas the majority of treated patients show relatively low clinical response. This difference is likely to be caused by the heterogeneity of both cancer cells and cells involved in the tumor microenvironment (TME). However, the extent of this heterogeneity, how it is shaped by other factors in the tumor and vice versa, remains poorly understood. Methods: To explore the heterogeneity of lung adenocarcinoma, we obtained tumor tissuesand peripheral blood froma cohort of 30 treatment-naive patients. For each sample, single-cell RNA sequencingand whole exome sequencing(WES) wereperformed. A graph-based unsupervised clusteringmethod was usedand cell types were assignedto clusters based on marker gene expression. The sub-types of both cancer cells and TME cells along with their gene expression patterns were comparedbetween different cancer stages and mutation status. Results: we presented a landscape of cancer and TME transcriptome in human lung adenocarcinoma at single-cell resolution. We found the expression of cancer cells exhibits distinct characteristics with different TNM stages. For instance, the tumor cells of a patient classified as T1aN2M0 highly express genes enriched in the cell migration pathway. By comparing TME cells among patients with different mutation status, we identified changes in various T cell subtypes and tumor-infiltrating myeloid cells. Conclusions: This study provided a detailed cell atlas of lung adenocarcinoma and identified gene expression patterns that are unique to specific TNM stages. Moreover, single-cell analyses offer valuable knowledgeof immune changes for each patient subgroup, providing ausefultool for the rational design of immunetherapies.

Characterization of Immunosuppressive Cells Using MultiOmyx in Hematological Malignancies

Abstract Background Tumor associated macrophages (TAM) and myeloid-derived suppressor cells (MDSC) can assist tumors to escape immune surveillance within the tumor microenvironment (TME). Based on phenotypical characteristics, MDSC can be further subdivided into granulocytic MDSC (G-MDSC) and monocytic MDSC (M-MDSC). These myeloid cell populations are well characterized and extensively studied in the solid tumors and their immunosuppressive function can be exerted via direct recruitment of Regulatory T cells (Treg). However, the role of these cells has been less studied in hematological malignancies (HM). Methods We report an analysis of MDSC, M2 macrophages and Treg using MultiOmyx multiplexed IF assay in clinical samples diagnosed with AML, HL and DLBCL. MultiOmyx technology enables detection and visualization of up to 60 protein biomarkers on a single FFPE slide. The FFPE sections were stained with a 13-marker panel including Arg1, CD11b, CD14, CD15, CD16, CD33, CD68, CD163, HLA-DR, CD3, CD4, CD8 and FOXP3. Results Both M-MDSC and G-MDSC were found to accumulate within the TME in different HM, with higher frequency of G-MDSC over M-MDSC. The data also revealed an abundant M2 macrophages present in the TME, especially in AML patient samples. Using the MultiOmyx proprietary algorithm, we quantified the counts and density of MDSC, TAM and Treg cells and studied the spatial correlations between different subsets of immunosuppressive cells. The results in the patient samples indicated that Treg was in closer proximity to M2 TAM than MDSC. Conclusions Targeting tumor-infiltrating myeloid cells has emerged as a new immunotherapeutic strategy. MultiOmyx 13-plexed panel has the potential to monitor the changes of immunosuppressive myeloid cells in response to immune modulating drugs such as MDSC-targeting drugs (e.g. PDE-5 inhibitors, COX-2 inhibitors), TAM-targeting agents (e.g. anti-CSF1R) and combination therapy in treatment of HM.

Mechanisms and Functional Significance of Human Tumor-infiltrating Myeloid Cells

Myeloid cells as the major components of tumor-infiltrating leukocytes play critical roles in anti-tumor immunity. However, emerging evidences have revealed that soluble factors produced by tumor/stromal cells skew myeloid cells toward a tumor-promoting phenotype. Tumor-infiltrating myeloid cells (TIMs) including tumor-associated macrophages (TAMs), tumor-associated neutrophils (TANs), myeloid-derived suppressor cells (MDSCs), and tumor-associated dendritic cells (TADCs) are considered as the key mediators of tumor microenvironment (TME). TIMs have been shown to play important roles in various aspects of cancer biology and their presence is often linked to altered patient prognosis and survival. Regarding their critical role in TME, TIMs have been proposed as relevant targets of therapeutic strategies aimed at expanding immunostimulatory myeloid cell populations and depleting or modulating immunosuppressive ones. In this review, we briefly describe TIMs subsets and discuss the mechanisms by which TIMs induce immunosuppression, angiogenesis, and metastasis.

Systemic Interferon-γ Increases MHC Class I Expression and T-cell Infiltration in Cold Tumors: Results of a Phase 0 Clinical Trial.

Interferon-γ (IFNγ) has been studied as a cancer treatment with limited evidence of clinical benefit. However, it could play a role in cancer immunotherapy combination treatments. Despite high expression of immunogenic cancer-testis antigens, synovial sarcoma (SS) and myxoid/round cell liposarcoma (MRCL) have a cold tumor microenvironment (TME), with few infiltrating T cells and low expression of major histocompatibility complex class I (MHC-I). We hypothesized that IFNγ treatment could drive inflammation in a cold TME, facilitating further immunotherapy. We conducted a phase 0 clinical trial treating 8 SS or MRCL patients with weekly systemic IFNγ. We performed pre- and posttreatment biopsies. IFNγ changed the SS and MRCL TME, inducing tumor-surface MHC-I expression and significant T-cell infiltration (P < 0.05). Gene-expression analysis suggested increased tumor antigen presentation and less exhausted phenotypes of the tumor-infiltrating T cells. Newly emergent antigen-specific humoral and/or T-cell responses were found in 3 of 7 evaluable patients. However, increased expression of PD-L1 was observed on tumor-infiltrating myeloid cells and in some cases tumor cells. These findings suggest that systemic IFNγ used to convert SS and MRCL into "hot" tumors will work in concert with anti-PD-1 therapy to provide patient benefit.

Agonism of CD11b reprograms innate immunity to sensitize pancreatic cancer to immunotherapies.

Although checkpoint immunotherapies have revolutionized the treatment of cancer, not all tumor types have seen substantial benefit. Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy in which very limited responses to immunotherapy have been observed. Extensive immunosuppressive myeloid cell infiltration in PDAC tissues has been postulated as a major mechanism of resistance to immunotherapy. Strategies concomitantly targeting monocyte or granulocyte trafficking or macrophage survival, in combination with checkpoint immunotherapies, have shown promise in preclinical studies, and these studies have transitioned into ongoing clinical trials for the treatment of pancreatic and other cancer types. However, compensatory actions by untargeted monocytes, granulocytes, and/or tissue resident macrophages may limit the therapeutic efficacy of such strategies. CD11b/CD18 is an integrin molecule that is highly expressed on the cell surface of these myeloid cell subsets and plays an important role in their trafficking and cellular functions in inflamed tissues. Here, we demonstrate that the partial activation of CD11b by a small-molecule agonist (ADH-503) leads to the repolarization of tumor-associated macrophages, reduction in the number of tumor-infiltrating immunosuppressive myeloid cells, and enhanced dendritic cell responses. These actions, in turn, improve antitumor T cell immunity and render checkpoint inhibitors effective in previously unresponsive PDAC models. These data demonstrate that molecular agonism of CD11b reprograms immunosuppressive myeloid cell responses and potentially bypasses the limitations of current clinical strategies to overcome resistance to immunotherapy.

Abstract 2358: Porphyromonas gingivalis promotes colorectal cancer development by regulating NLRP3 inflammasome signaling

Abstract Metagenomic analyses indicate that Porphyromonas spp. is associated with human colorectal carcinoma (CRC), however, whether this is an indirect or causal link remains unclear. We found that Porphyromonas gingivalis (P. gingivalis) were enriched in human stool or FFPE samples from colorectal carcinoma patients compared to colorectal adenoma or healthy subjects. Two colorectal cohort studies demonstrated that P. gingivalis infection was associated with poor prognosis of CRC. Moreover, in the ApcMin/+ mouse model of colorectal tumorigenesis, P. gingivalis increases tumor counts and in the orthotopic rectal MC38 carcinoma model increases tumor growth. Furthermore, tumors from orthotopic MC38 model exposed to P. gingivalis exhibited a tumor-infiltrating myeloid cells recruiting signature that was confirmed in human P.gingivalis-positive colorectal carcinomas. We next evaluated the role of NLRP3 in P. gingivalis promoting on CRC progression. When comparing with wild type mice, the increased tumor growth was subtracted in Nlrp3-/- mice by the same orthotopic MC38 model exposed to P. gingivalis. To determine relevant cell compartment responsible for NLRP3 function, we generated Nlrp3-/- chimeric mice with adoptive bone marrow transplantation by using the same orthotopic tumor model. The results showed the effect of NLRP3 on P. gingivalis pathogenesis was from both hematopoietic and non-hematopoietic sources. Additionally, we performed expression profile to show that NLRP3 attenuates multiple pathways associated with P. gingivalis promoting colorectal cancer development. Collectively, these data suggest that, through recruitment of tumor-infiltrating immune cells by regulating NLRP3 inflammasome activity, P. gingivalis generates a proinflammatory microenvironment that is conductive for colorectal neoplasia progression. Note: This abstract was not presented at the meeting. Citation Format: Zhi Wang, Xi Wang, Yiqun Jia. Porphyromonas gingivalis promotes colorectal cancer development by regulating NLRP3 inflammasome signaling [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 2358.

Abstract 1100: Genetic driver-mutations define composition and properties of tumor-associated myeloid cells in glioblastoma

Abstract The GBM microenvironment is composed of numerous non-neoplastic cells, among which tumor-associated myeloid cells (TAMs) are the most abundant. TAMs are constituted of several different cell types, including brain microglia and bone-marrow-derived infiltrating cells, which can be further divided into inflammatory monocytes, monocyte-derived macrophages, and polymorphnuclear neutrophils. These myeloid cells are believed to promote tumor growth and immune evasion by expressing immune checkpoint proteins. Remarkable progress has been made in treating lung cancer and melanoma by using immune-checkpoint inhibitors; however, mixed results were obtained for its application in GBM. To examine how molecular-subtypes of GBM influence the composition and immunosuppression of tumor-associated myeloid cells, we used the RCAS_tv-a system, a somatic cell-specific gene transfer system, to generate de novo murine GBM (mGBM). By manipulating different known human oncogenic-driver mutations such as overexpressing PDGFB or EGFRVIII, or silencing NF1, we generated Proneural (PN), Classical (CL) and Mesenchymal (MES) GBMs respectively, which phenotypically resemble their human counterparts. We found that the majority (80%) of tumor-infiltrating myeloid cells in PN GBM are bone-marrow derived macrophages, whereas this number is significantly less in CL and MES mGBM. Interestingly, unique to MES, there is a significant presence (16%) of neutrophils in these tumors than in other subtypes (4%). Further characterization for subtype-specific expression of PD-L1, a druggable immune checkpoint molecule, by flow cytometry shows that MES has the highest expression of PD-L1), whereas the expression is lower in PN and CL subtypes. Treating GBM-bearing mice with anti-PDL1 antibodies did not prolong their survival. Concurrent treatment of irradiation and anti-PDL1 antibody did not confer significant survival advantage either compared to controls. These results reflect the unsuccessful trails of recent human clinical studies; however, it also emphasizes the importance of understanding the mechanism of resistance in GBM immunotherapy before effective immune treatment can be established. Our immunocompetent mouse models provide indispensable tools for these studies. Note: This abstract was not presented at the meeting. Citation Format: Zhihong Chen, Cameron J. Hurting, Ben Gabanic, Jyothi Murukuti, Dolores Hambardzumyan. Genetic driver-mutations define composition and properties of tumor-associated myeloid cells in glioblastoma [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 1100.

Glioblastoma-Derived IL6 Induces Immunosuppressive Peripheral Myeloid Cell PD-L1 and Promotes Tumor Growth.

Upregulation of programmed death-ligand 1 (PD-L1) on circulating and tumor-infiltrating myeloid cells is a critical component of GBM-mediated immunosuppression that has been associated with diminished response to vaccine immunotherapy and poor survival. Although GBM-derived soluble factors have been implicated in myeloid PD-L1 expression, the identity of such factors has remained unknown. This study aimed to identify factors responsible for myeloid PD-L1 upregulation as potential targets for immune modulation. Conditioned media from patient-derived GBM explant cell cultures was assessed for cytokine expression and utilized to stimulate naïve myeloid cells. Myeloid PD-L1 induction was quantified by flow cytometry. Candidate cytokines correlated with PD-L1 induction were evaluated in tumor sections and plasma for relationships with survival and myeloid PD-L1 expression. The role of identified cytokines on immunosuppression and survival was investigated in vivo utilizing immunocompetent C57BL/6 mice bearing syngeneic GL261 and CT-2A tumors. GBM-derived IL6 was identified as a cytokine that is necessary and sufficient for myeloid PD-L1 induction in GBM through a STAT3-dependent mechanism. Inhibition of IL6 signaling in orthotopic murine glioma models was associated with reduced myeloid PD-L1 expression, diminished tumor growth, and increased survival. The therapeutic benefit of anti-IL6 therapy proved to be CD8+ T-cell dependent, and the antitumor activity was additive with that provided by programmed death-1 (PD-1)-targeted immunotherapy. Our findings suggest that disruption of IL6 signaling in GBM reduces local and systemic myeloid-driven immunosuppression and enhances immune-mediated antitumor responses against GBM.

The tumor microenvironment in renal cell cancer.

In addition to the provision of nutrients and growth factors that facilitate tumor cell proliferation and metastasis, the tumor microenvironment (MEV) restricts immune surveillance of tumor-associated antigens and limits the efficacy of immune checkpoint inhibitors, tumor vaccines, and other immune therapies. This review will focus on the immunosuppressive mechanisms operative within the tumor MVE of renal cell carcinoma. Several of the immunosuppressive mechanisms within the tumor MEV have been identified and are potentially druggable. Clinical trials with agents that target several of these inhibitory pathways are currently underway. Although renal cell carcinoma is one of several tumor types responsive to immune checkpoint inhibitors, the effectiveness of these agents is likely to be limited by the various tumor-infiltrating bone marrow-derived myeloid cells that comprise the MEV. Several strategies to combat the recruitment of these cells into tumor tissue or to neutralize their immunosuppressive function have shown encouraging results in animal tumor models and clinical trials.

Dissecting intratumoral myeloid cell plasticity by single cell RNA-seq.

Tumor‐infiltrating myeloid cells are the most abundant leukocyte population within tumors. Molecular cues from the tumor microenvironment promote the differentiation of immature myeloid cells toward an immunosuppressive phenotype. However, the in situ dynamics of the transcriptional reprogramming underlying this process are poorly understood. Therefore, we applied single cell RNA‐seq (scRNA‐seq) to computationally investigate the cellular composition and transcriptional dynamics of tumor and adjacent normal tissues from 4 early‐stage non‐small cell lung cancer (NSCLC) patients. Our scRNA‐seq analyses identified 11 485 cells that varied in identity and gene expression traits between normal and tumor tissues. Among these, myeloid cell populations exhibited the most diverse changes between tumor and normal tissues, consistent with tumor‐mediated reprogramming. Through trajectory analysis, we identified a differentiation path from CD14+ monocytes to M2 macrophages (monocyte‐to‐M2). This differentiation path was reproducible across patients, accompanied by increased expression of genes (eg, MRC1/CD206, MSR1/CD204, PPARG, TREM2) with significantly enriched functions (Oxidative phosphorylation and P53 pathway) and decreased expression of genes (eg, CXCL2, IL1B) with significantly enriched functions (TNF‐α signaling via NF‐κB and inflammatory response). Our analysis further identified a co‐regulatory network implicating upstream transcription factors (JUN, NFKBIA) in monocyte‐to‐M2 differentiation, and activated ligand‐receptor interactions (eg, SFTPA1‐TLR2, ICAM1‐ITGAM) suggesting intratumoral mechanisms whereby epithelial cells stimulate monocyte‐to‐M2 differentiation. Overall, our study identified the prevalent monocyte‐to‐M2 differentiation in NSCLC, accompanied by an intricate transcriptional reprogramming mediated by specific transcriptional activators and intercellular crosstalk involving ligand‐receptor interactions.

Single-Cell Transcriptomics of Human and Mouse Lung Cancers Reveals Conserved Myeloid Populations across Individuals and Species

Tumor-infiltrating myeloid cells (TIMs) comprise monocytes, macrophages, dendritic cells, and neutrophils, and have emerged as key regulators of cancer growth. These cells can diversify into aspectrum of states, which might promote or limittumor outgrowth but remain poorly understood. Here, we used single-cell RNA sequencing (scRNA-seq) to map TIMs in non-small-cell lung cancer patients. We uncovered 25 TIM states, most of which were reproducibly found across patients. To facilitate translational research of these populations, we also profiled TIMs in mice.In comparing TIMs across species, we identified a near-complete congruence of population structures among dendritic cells and monocytes; conserved neutrophil subsets; and species differences among macrophages. By contrast, myeloidcell population structures in patients' bloodshowed limited overlap with those of TIMs.This study determines the lung TIM landscape and sets the stage for future investigations into the potential of TIMs as immunotherapy targets.