Dysregulated hematopoiesis caused by mammary cancer is associated with epigenetic changes and hox gene expression in hematopoietic cells

The crosstalk between lung cancer and the bone marrow niche fuels emergency myelopoiesis

Modest response rates to immunotherapy observed in advanced lung cancer patients underscore the need to identify reliable biomarkers and targets, enhancing both treatment decision-making and efficacy. Factors such as PD-L1 expression, tumor mutation burden, and a 'hot' tumor microenvironment with heightened effector T cell infiltration have consistently been associated with positive responses. In contrast, the predictive role of the abundantly present tumor-infiltrating myeloid cell (TIMs) fraction remains somewhat uncertain, partly explained by their towering variety in terms of ontogeny, phenotype, location, and function. Nevertheless, numerous preclinical and clinical studies established a clear link between lung cancer progression and alterations in intra- and extramedullary hematopoiesis, leading to emergency myelopoiesis at the expense of megakaryocyte/erythroid and lymphoid differentiation. These observations affirm that a continuous crosstalk between solid cancers such as lung cancer and the bone marrow niche (BMN) must take place. However, the BMN, encompassing hematopoietic stem and progenitor cells, differentiated immune and stromal cells, remains inadequately explored in solid cancer patients. Subsequently, no clear consensus has been reached on the exact breadth of tumor installed hematopoiesis perturbing cues nor their predictive power for immunotherapy. As the current era of single-cell omics is reshaping our understanding of the hematopoietic process and the subcluster landscape of lung TIMs, we aim to present an updated overview of the hierarchical differentiation process of TIMs within the BMN of solid cancer bearing subjects. Our comprehensive overview underscores that lung cancer should be regarded as a systemic disease in which the cues governing the lung tumor-BMN crosstalk might bolster the definition of new biomarkers and druggable targets, potentially mitigating the high attrition rate of leading immunotherapies for NSCLC.

Engineering immune response to regulate cardiovascular disease and cancer

Cardiovascular disease (CVD) and cancer are major contributors to global morbidity and mortality. This book chapter delves into the intricate relationship between the immune system and the pathogenesis of both cardiovascular and cancer diseases, exploring the roles of innate and adaptive immunities, immune regulation, and immunotherapy in these complex conditions. The innate immune system acts as the first line of defense against tissue damage and infection, with a significant impact on the initiation and progression of CVD and cancer. Endothelial dysfunction, a hallmark in CVD, shares commonalities with the tumor microenvironment in cancer, emphasizing the parallel involvement of the immune system in both conditions. The adaptive immune system, particularly T cells, contributes to prolonged inflammation in both CVD and cancer. Regulatory T cells and the intricate balance between different T cell subtypes influence disease progression, wound healing, and the outcomes of ischemic injury and cancer immunosurveillance. Dysregulation of immune homeostasis can lead to chronic inflammation, contributing to the development and progression of both CVD and cancer. Thus, immunotherapy emerged as a promising avenue for preventing and managing these diseases, with strategies targeting immune cell modulation, cytokine manipulation, immune checkpoint blockade, and tolerance induction. The impact of gut microbiota on CVD and cancer too is explored in this chapter, highlighting the role of gut leakiness, microbial metabolites, and the potential for microbiome-based interventions in cardiovascular and cancer immunotherapies. In conclusion, immunomodulatory strategies and immunotherapy hold promise in reshaping the landscape of cardiovascular and cancer health. Additionally, harnessing the gut microbiota for immune modulation presents a novel approach to prevent and manage these complex diseases, emphasizing the importance of personalized and precision medicine in healthcare. Ongoing research and clinical trials are expected to further elucidate the complex immunological underpinnings of CVD and cancer thereby refining these innovative approaches.

Systemic administration of STING agonist promotes myeloid cells maturation and antitumor immunity through regulating hematopoietic stem and progenitor cell fate

STING is a pivotal mediator of effective innate and adaptive anti-tumor immunity; however, intratumoral administration of STING agonists have shown limited therapeutic benefit in clinical trials. The systemic effect of the intravenous delivery of STING agonists in cancer is not well-defined. Here, we demonstrated that systemic administration of STING agonist inhibited melanoma growth, improved inflammatory effector cell infiltration, and induced bone marrow mobilization and extramedullary hematopoiesis, causing widespread changes in immune components in the peripheral blood. The systemically administered STING agonist promoted HSC expansion and influenced lineage fate commitment, which was manifested as the differentiation of HSPCs was skewed toward myeloid cells at the expense of B-cell lymphopoiesis and erythropoiesis. Transcriptome analysis revealed upregulation of myeloid lineage differentiation-related and type I interferon-related genes. This myeloid-biased differentiation promoted the production and maturation of myeloid cells toward an activated phenotype. Furthermore, depletion of Gr-1+ myeloid cells attenuated the anti-tumor immunity of STING agonist. Our findings reveal the anti-tumor mechanism of systemic administration of STING agonist that involves modulating HSPC differentiation and promoting myeloid cells maturation. Our study may help explain the limited clinical activity of STING agonists administered intratumorally.

Short-term immune-checkpoint inhibition partially rescues perturbed bone marrow hematopoiesis in mismatch-repair deficient tumors

Wide-spread cancer-related immunosuppression often curtails immune-mediated antitumoral responses. Immune-checkpoint inhibitors (ICIs) have become a state-of-the-art treatment modality for mismatch repair-deficient (dMMR) tumors. Still, the impact of ICI-treatment on bone marrow perturbations is largely unknown. Using anti-PD1 and anti-LAG-3 ICI treatments, we here investigated the effect of bone marrow hematopoiesis in tumor-bearing Msh2loxP/loxP;TgTg(Vil1-cre) mice. The OS under anti-PD1 antibody treatment was 7.0 weeks (vs. 3.3 weeks and 5.0 weeks, control and isotype, respectively). In the anti-LAG-3 antibody group, OS was 13.3 weeks and thus even longer than in the anti-PD1 group (p = 0.13). Both ICIs induced a stable disease and reduced circulating and splenic regulatory T cells. In the bone marrow, a perturbed hematopoiesis was identified in tumor-bearing control mice, which was partially rescued by ICI treatment. In particular, B cell precursors and innate lymphoid progenitors were significantly increased upon anti-LAG-3 therapy to levels seen in tumor-free control mice. Additional normalizing effects of ICI treatment were observed for lin-c-Kit+IRF8+ hematopoietic stem cells, which function as a "master" negative regulator of the formation of polymorphonuclear-myeloid-derived suppressor cell generation. Accompanying immunofluorescence on the TME revealed significantly reduced numbers of CD206+F4/80+ and CD163+ tumor-associated M2 macrophages and CD11b+Gr1+ myeloid-derived suppressor cells especially upon anti-LAG-3 treatment. This study confirms the perturbed hematopoiesis in solid cancer. Anti-LAG-3 treatment partially restores normal hematopoiesis. The interference of anti-LAG-3 with suppressor cell populations in otherwise inaccessible niches renders this ICI very promising for subsequent clinical application.

HOXB3 drives WNT-activation associated progression in castration-resistant prostate cancer

Enabled resistance or innate insensitiveness to antiandrogen are lethal for castration-resistant prostate cancer (CRPC). Unfortunately, there seems to be little can be done to overcome the antiandrogen resistance because of the largely unknown mechanisms. In prospective cohort study, we found that HOXB3 protein level was an independent risk factor of PSA progression and death in patients with metastatic CRPC. In vivo, upregulated HOXB3 contributed to CRPC xenografts progression and abiraterone resistance. To uncover the mechanism of HOXB3 driving tumor progression, we performed RNA-sequencing in HOXB3 negative (HOXB3-) and HOXB3 high (HOXB3 + ) staining CRPC tumors and determined that HOXB3 activation was associated with the expression of WNT3A and enriched WNT pathway genes. Furthermore, extra WNT3A and APC deficiency led HOXB3 to be isolated from destruction-complex, translocated to nuclei, and then transcriptionally regulated multiple WNT pathway genes. What's more, we also observed that the suppression of HOXB3 could reduce cell proliferation in APC-downregulated CRPC cells and sensitize APC-deficient CRPC xenografts to abiraterone again. Together, our data indicated that HOXB3 served as a downstream transcription factor of WNT pathway and defined a subgroup of CRPC resistant to antiandrogen which would benefit from HOXB3-targeted therapy.

Enniatin B and beauvericin affect intestinal cell function and hematological processes in Atlantic salmon (Salmo salar) after acute exposure

Unintentional use of mold-infested plant-based feed ingredients are sources of mycotoxins in fish feeds. The presence of the emerging mycotoxins ENNB and BEA in Norwegian commercial fish feeds and plant-based feed ingredients has raised concerns regarding the health effects on farmed Atlantic salmon (Salmon salar). Atlantic salmon pre-smolts were exposed to non-lethal doses of BEA and ENNB (ctrl, 50 and 500 μg/kg feed for 12 h), after which total RNA sequencing of the intestine and liver was carried out to evaluate gut health and identify possible hepatological changes after acute dietary exposure. ENNB and BEA did not trigger acute toxicity, however ENNB caused the onset of pathways linked to acute intestinal inflammation and BEA exposures caused the onset of hepatic hematological disruption. The prevalence and concentration of ENNB found in today's commercial feed could affect the fish health if consumed over a longer time-period.

Association of lymphopenia and RDW elevation with risk of mortality in acute aortic dissection

OBJECTIVE

The study aimed to investigate whether lymphopenia and red blood cell distribution width (RDW) elevation are associated with an increased risk of mortality in acute aortic dissection (AAD).

METHODS

This multicenter retrospective cohort study enrolled patients diagnosed with AAD by aortic computed tomographic angiography (CTA) from 2010 to 2021 in five teaching hospitals in central-western China. Cox proportional hazards regression and Kaplan-Meier curves were used in univariable and multivariable models. Clinical outcomes were defined as all-cause in-hospital mortality, while associations were evaluated between lymphopenia, accompanied by an elevated RDW, and risk of mortality.

RESULTS

Of 1903 participants, the median age was 53 (interquartile range [IQR], 46-62) years, and females accounted for 21.9%. Adjusted increased risk of mortality was linearly related to the decreasing lymphocyte percentage (P-non-linearity = 0.942) and increasing RDW (P-non-linearity = 0.612), and per standard deviation (SD) of increment lymphocyte percentage and RDW was associated with the 26% (0.74, 0.64-0.84) decrement and 5% (1.05, 0.95-1.15) increment in hazard ratios (HRs) and 95% confidence intervals (CIs) of mortality, respectively. Importantly, lymphopenia and elevation of RDW exhibited a significant interaction with increasing the risk of AAD mortality (P-value for interaction = 0.037).

CONCLUSIONS

Lymphopenia accompanied by the elevation of RDW, which may reflect the immune dysregulation of AAD patients, is associated with an increased risk of mortality. Assessment of immunological biomarkers derived from routine tests may provide novel perspectives for identifying the risk of mortality.

Hematologic dysfunction in cancer: Mechanisms, effects on antitumor immunity, and roles in disease progression

With the major advances in cancer immunology and immunotherapy, it is critical to consider that most immune cells are short-lived and need to be continuously replenished from hematopoietic stem and progenitor cells. Hematologic abnormalities are prevalent in cancer patients, and many ground-breaking studies over the past decade provide insights into their underlying cellular and molecular mechanisms. Such studies demonstrate that the dysfunction of hematopoiesis is more than a side-effect of cancer pathology, but an important systemic feature of cancer disease. Here we review these many advances, covering the cancer-associated phenotypes of hematopoietic stem and progenitor cells, the dysfunction of myelopoiesis and erythropoiesis, the importance of extramedullary hematopoiesis in cancer disease, and the developmental origins of tumor associated macrophages. We address the roles of many secreted mediators, signaling pathways, and transcriptional and epigenetic mechanisms that mediate such hematopoietic dysfunction. Furthermore, we discuss the important contribution of the hematopoietic dysfunction to cancer immunosuppression, the possible avenues for therapeutic intervention, and highlight the unanswered questions and directions for future work. Overall, hematopoietic dysfunction is established as an active component of the cancer disease mechanisms and an important target for therapeutic intervention.

Physical Activity as the Best Supportive Care in Cancer: The Clinician's and the Researcher's Perspectives

Multidisciplinary supportive care, integrating the dimensions of exercise alongside oncological treatments, is now regarded as a new paradigm to improve patient survival and quality of life. Its impact is important on the factors that control tumor development, such as the immune system, inflammation, tissue perfusion, hypoxia, insulin resistance, metabolism, glucocorticoid levels, and cachexia. An increasing amount of research has been published in the last years on the effects of physical activity within the framework of oncology, marking the appearance of a new medical field, commonly known as "exercise oncology". This emerging research field is trying to determine the biological mechanisms by which, aerobic exercise affects the incidence of cancer, the progression and/or the appearance of metastases. We propose an overview of the current state of the art physical exercise interventions in the management of cancer patients, including a pragmatic perspective with tips for routine practice. We then develop the emerging mechanistic views about physical exercise and their potential clinical applications. Moving toward a more personalized, integrated, patient-centered, and multidisciplinary management, by trying to understand the different interactions between the cancer and the host, as well as the impact of the disease and the treatments on the different organs, this seems to be the most promising method to improve the care of cancer patients.

G-CSF/GM-CSF-induced hematopoietic dysregulation in the progression of solid tumors

There are two types of abnormal hematopoiesis in solid tumor occurrence and treatment: pathological hematopoiesis, and myelosuppression induced by radiotherapy and chemotherapy. In this review, we primarily focus on the abnormal pathological hematopoietic differentiation in cancer induced by tumor-released granulocyte colony stimulating factor (G-CSF) and granulocyte-macrophage colony stimulating factor (GM-CSF). As key factors in hematopoietic development, G-CSF/GM-CSF are well-known facilitators of myelopoiesis and mobilization of hematopoietic stem cells (HSCs). In addition, these two cytokines can also promote or inhibit tumors, dependent on tumor type. In multiple cancer types, hematopoiesis is greatly enhanced and abnormal lineage differentiation is induced by these two cytokines. Here, dysregulated hematopoiesis induced by G-CSF/GM-CSF in solid tumors and its mechanism are summarized, and the prognostic value of G-CSF/GM-CSF-associated dysregulated hematopoiesis for tumor metastasis is also briefly highlighted.

Comprehensive Assessment of Selected Immune Cell Subpopulations Changes in Chemotherapy-Naïve Germ Cell Tumor Patients

The pattern of immune cell distribution in testicular germ cell tumors (GCT) significantly differs from the immune environment in normal testicular tissues. The present study aimed to evaluate the role of different leukocyte subpopulation in GCTs. A cohort of 84 chemotherapy-naïve GCT patients was analyzed. Immunophenotyping of peripheral blood leukocyte subpopulations was carried out by flow cytometry. In addition, the data assessing the immunophenotypes and the baseline clinicopathological characteristics of the included subjects were statistically evaluated. Their prognostic value for the assessment of progression-free survival (PFS) and overall survival (OS) was estimated. The percentage of different innate/adaptive immune cell subpopulations was significantly associated with poor risk-related clinical features, including the number of metastatic sites, presence of retroperitoneal, mediastinal, lung, brain and non-pulmonary visceral metastases as well as with the S-stage and International Germ Cell Consensus Classification Group (IGCCCG) risk groups. In univariate analysis, the percentages of neutrophils, eosinophils, dendritic cells type 2, lymphocytes and T cytotoxic cells were significantly associated with PFS, while the neutrophil, non-classical monocyte and lymphocyte percentage were associated with OS. However, all these outcome correlations were not independent of IGCCCG in multivariate analysis. The data indicated a link among different innate/adaptive peripheral immune cell subpopulations in GCT patients. In addition, the association between these subpopulations and tumor characteristics was also investigated. The findings of the present study may contribute to a deeper understanding of the interactions between cancer and innate/adaptive immune response in GCT patients.

The role of CD71+ erythroid cells in the regulation of the immune response

Complex regulation of the immune response is necessary to support effective defense of an organism against hostile invaders and to maintain tolerance to harmless microorganisms and autoantigens. Recent studies revealed previously unappreciated roles of CD71⁺ erythroid cells (CECs) in regulation of the immune response. CECs physiologically reside in the bone marrow where erythropoiesis takes place. Under stress conditions, CECs are enriched in some organs outside of the bone marrow as a result of extramedullary erythropoiesis. However, the role of CECs goes well beyond the production of erythrocytes. In neonates, increased numbers of CECs contribute to their vulnerability to infectious diseases. On the other side, neonatal CECs suppress activation of immune cells in response to abrupt colonization with commensal microorganisms after delivery. CECs are also enriched in the peripheral blood of pregnant women as well as in the placenta and are responsible for the regulation of feto-maternal tolerance. In patients with cancer, anemia leads to increased frequency of CECs in the peripheral blood contributing to diminished antiviral and antibacterial immunity, as well as to accelerated cancer progression. Moreover, recent studies revealed the role of CECs in HIV and SARS-CoV-2 infections. CECs use a full arsenal of mechanisms to regulate immune response. These cells suppress proinflammatory responses of myeloid cells and T-cell proliferation by the depletion of ʟ-arginine by arginase. Moreover, CECs produce reactive oxygen species to decrease T-cell proliferation. CECs also secrete cytokines, including transforming growth factor β (TGF-β), which promotes T-cell differentiation into regulatory T-cells. Here, we comprehensively describe the role of CECs in orchestrating immune response and indicate some therapeutic approaches that might be used to regulate their effector functions in the treatment of human conditions.

Systemic immunity in cancer

Immunotherapy has revolutionized cancer treatment, but efficacy remains limited in most clinical settings. Cancer is a systemic disease that induces many functional and compositional changes to the immune system as a whole. Immunity is regulated by interactions of diverse cell lineages across tissues. Therefore, an improved understanding of tumour immunology must assess the systemic immune landscape beyond the tumour microenvironment (TME). Importantly, the peripheral immune system is required to drive effective natural and therapeutically induced antitumour immune responses. In fact, emerging evidence suggests that immunotherapy drives new immune responses rather than the reinvigoration of pre-existing immune responses. However, new immune responses in individuals burdened with tumours are compromised even beyond the TME. Herein, we aim to comprehensively outline the current knowledge of systemic immunity in cancer.

Myelopoiesis during Solid Cancers and Strategies for Immunotherapy

Our understanding of the relationship between the immune system and cancers has undergone significant discovery recently. Immunotherapy with T cell therapies and checkpoint blockade has meaningfully changed the oncology landscape. While remarkable clinical advances in adaptive immunity are occurring, modulation of innate immunity has proven more difficult. The myeloid compartment, including macrophages, neutrophils, and dendritic cells, has a significant impact on the persistence or elimination of tumors. Myeloid cells, specifically in the tumor microenvironment, have direct contact with tumor tissue and coordinate with tumor-reactive T cells to either stimulate or antagonize cancer immunity. However, the myeloid compartment comprises a broad array of cells in various stages of development. In addition, hematopoietic stem and progenitor cells at various stages of myelopoiesis in distant sites undergo significant modulation by tumors. Understanding how tumors exert their influence on myeloid progenitors is critical to making clinically meaningful improvements in these pathways. Therefore, this review will cover recent developments in our understanding of how solid tumors modulate myelopoiesis to promote the formation of pro-tumor immature myeloid cells. Then, it will cover some of the potential avenues for capitalizing on these mechanisms to generate antitumor immunity.

Effects of obesity on NK cells in a mouse model of postmenopausal breast cancer

Obesity is a widely spread disease and a crucial risk factor for malign disorders, including breast cancer of women in the postmenopause. Studies demonstrated that in case of obesity crucial natural killer (NK) cell functions like combating tumor cells are affected. This study aims to analyze NK cells and NK cell receptor expression of obese mice in a model for postmenopausal breast cancer. Therefore, female BALB/c mice were fed either a high fat or a standard diet. Thereafter, ovaries were ectomized and a syngeneic and orthotopical injection of 4T1-luc2 mouse mammary tumor cells into the mammary adipose tissue pad was performed. Obese mice showed increased body weights and visceral fat mass as well as increased levels of leptin and IL-6 in plasma. Moreover, compared to the lean littermates, tumor growth was increased and the NKp46-expression on circulating NK cells was decreased. Furthermore, the activating NK cell receptor NKG2D ligand (MULT1) expression was enhanced in adipose tissue of obese tumor bearing mice. The present study gives novel insights into gene expression of NK cell receptors in obesity and aims to promote possible links of the obesity-impaired NK cell physiology and the elevated breast cancer risk in obese women.

Prognostic impact of neutrophils-to-lymphocytes ratio (NLR), PD-L1 expression, and tumor immune microenvironment in laryngeal cancer

PURPOSE

In laryngeal carcinoma (LSCC), tumor immune microenvironment is attracting increasing interest, given the recent progresses in immunotherapy. Immune cells migrate to tumors as a result of a tumor antigen-induced immune reaction and cancer cells recruit immune regulatory cells to induce an immunosuppressive network, resulting in the escape from host immunity. This interaction reflects both on tumor microenvironment and systemic inflammatory status. Blood neutrophil-to-lymphocyte ratio (NLR), reflecting a highly pro-inflammatory status, has been related to worse oncological survival outcomes. The aim of this study was to analyze in LSCC the relationship between circulating inflammatory cells (also in terms of NLR) and tumor immune microenvironment histopathological features (programmed cell death ligand 1 [PD-L1] expression, and tumor-infiltrating lymphocytes [TILs]), also investigating their clinical-pathological and prognostic significance.

METHODS

Blood pre-operative NLR, and, at pathology, PD-L1 (in terms of combined positive score [CPS]) and TILs were assessed on 60 consecutive cases of LSCC.

RESULTS

Blood NLR, neutrophils, and lymphocytes counts showed a significant value in predicting DFS and recurrence risk. Moreover, PD-L1 CPS ≥ 1 and TILs count rate ≥30% were associated with higher disease-free survival (DFS) and reduced recurrence risk. A logistic regression model found a significant positive association between increasing NLR values, and PD-L1 CPS < 1 and TILs count rate <30%.

CONCLUSIONS

Further studies are needed to better characterize the role of pre-operative blood NLR in association with PD-L1 expression and tumor immune microenvironment features as prognostic factors and markers of anti-tumor immune response in LSCCs, also with regard to the effectiveness of immunotherapeutic protocols.

Splenic Hematopoietic and Stromal Cells in Cancer Progression

Tumor-derived secretory factors orchestrate splenic hematopoietic and stromal cells to fuel metastasis. The spleen acts as a reservoir site for hematopoietic stem and progenitor cells, which are rapidly exploited as myeloid-derived suppressor cells at the cost of tumor-reactive lymphoid cells. Splenic erythroid progenitor cells and mesenchymal stromal cells contribute directly and indirectly to both tumor immune escape and the metastatic cascade. Animal models provide valuable mechanistic insights, but their translation to a clinical setting highlights specific challenges and open issues. In this review, we envision the exploitation of the spleen as a source for novel biomarkers and therapeutic approaches.

Exercise and immunometabolic regulation in cancer

Unhealthful lifestyle factors, such as obesity, disrupt organismal homeostasis and accelerate cancer pathogenesis, partly through metabolic and immunological dysregulation. Exercise is a prototypical strategy that maintains and restores homeostasis at the organismal, tissue, cellular and molecular levels and can prevent or inhibit numerous disease conditions, including cancer. Here, we review unhealthful lifestyle factors that contribute to metabolic and immunological dysregulation and drive tumourigenesis, focusing on patient physiology (host)-tissue-tumour microenvironment interactions. We also discuss how exercise may influence distant tissue microenvironments, thereby improving tissue function through both metabolic and immunospecific pathways. Finally, we consider future directions that merit consideration in basic and clinical translational exercise studies.

Contributions of HOX genes to cancer hallmarks: Enrichment pathway analysis and review

Homeobox genes function as master regulatory transcription factors during development, and their expression is often altered in cancer. The HOX gene family was initially studied intensively to understand how the expression of each gene was involved in forming axial patterns and shaping the body plan during embryogenesis. More recent investigations have discovered that HOX genes can also play an important role in cancer. The literature has shown that the expression of HOX genes may be increased or decreased in different tumors and that these alterations may differ depending on the specific HOX gene involved and the type of cancer being investigated. New studies are also emerging, showing the critical role of some members of the HOX gene family in tumor progression and variation in clinical response. However, there has been limited systematic evaluation of the various contributions of each member of the HOX gene family in the pathways that drive the common phenotypic changes (or "hallmarks") and that underlie the transformation of normal cells to cancer cells. In this review, we investigate the context of the engagement of HOX gene targets and their downstream pathways in the acquisition of competence of tumor cells to undergo malignant transformation and tumor progression. We also summarize published findings on the involvement of HOX genes in carcinogenesis and use bioinformatics methods to examine how their downstream targets and pathways are involved in each hallmark of the cancer phenotype.

The DNA methyltransferase inhibitor, guadecitabine, targets tumor-induced myelopoiesis and recovers T cell activity to slow tumor growth in combination with adoptive immunotherapy in a mouse model of breast cancer

Background

Myeloid derived suppressor cells (MDSCs) present a significant obstacle to cancer immunotherapy because they dampen anti-tumor cytotoxic T cell responses. Previous groups, including our own, have reported on the myelo-depletive effects of certain chemotherapy agents. We have shown previously that decitabine increased tumor cell Class I and tumor antigen expression, increased ability of tumor cells to stimulate T lymphocytes, depleted tumor-induced MDSC in vivo and augmented immunotherapy of a murine mammary carcinoma.

Results

In this study, we expand upon this observation by testing a next-generation DNA methyltransferase inhibitor (DNMTi), guadecitabine, which has increased stability in the circulation. Using the 4 T1 murine mammary carcinoma model, in BALB/cJ female mice, we found that guadecitabine significantly reduces tumor burden in a T cell-dependent manner by preventing excessive myeloid proliferation and systemic accumulation of MDSC. The remaining MDSC were shifted to an antigen-presenting phenotype. Building upon our previous publication, we show that guadecitabine enhances the therapeutic effect of adoptively transferred antigen-experienced lymphocytes to diminish tumor growth and improve overall survival. We also show guadecitabine’s versatility with similar tumor reduction and augmentation of immunotherapy in the C57BL/6 J E0771 murine breast cancer model.

Conclusions

Guadecitabine depleted and altered MDSC, inhibited growth of two different murine mammary carcinomas in vivo, and augmented immunotherapeutic efficacy. Based on these findings, we believe the immune-modulatory effects of guadecitabine can help rescue anti-tumor immune response and contribute to the overall effectiveness of current cancer immunotherapies.

Exercise reduces immune suppression and breast cancer progression in a preclinical model

Exercise is associated with favorable changes in circulating immune cells and improved survival in early-stage breast cancer patients, but the mechansims remain to be fully elucidated. Preclinical studies indicate that physical activity started before tumor injection reduces tumor incidence and progression. Here we tested whether exercise has anti-tumor effects in mice with established 4T1 mammary carcinoma, a mouse model of triple negative breast cancer. Exercise slowed tumor progression and reduced the tumor-induced accumulation of myeloid-derived suppressor cells (MDSCs). The reduction in MDSCs was accompanied by a relative increase in natural killer and CD8 T cell activation, suggesting that exercise restores a favorable immune environment. Consistently, exercise improved responses to a combination of programmed cell death protein 1 (PD-1) blockade and focal radiotherapy. These data support further investigations of exercise in breast cancer patients treated with combinations of immunotherapy and cytotoxic agents to improve cancer outcomes.

Transcriptional Profiles and Stromal Changes Reveal Bone Marrow Adaptation to Early Breast Cancer in Association with Deregulated Circulating microRNAs

The presence of a growing tumor establishes a chronic state of inflammation that acts locally and systemically. Bone marrow responds to stress signals by expanding myeloid cells endowed with immunosuppressive functions, further fostering tumor growth and dissemination. How early in transformation the cross-talk with the bone marrow begins and becomes detectable in blood is unknown. Here, gene expression profiling of the bone marrow along disease progression in a spontaneous model of mammary carcinogenesis demonstrates that transcriptional modifications in the hematopoietic compartment occurred as early as preinvasive disease stages. The transcriptional profile showed downregulation of adaptive immunity and induction of programs related to innate immunity and response to danger signals triggered by activating transcription factor 3. Transcriptional reprogramming was paralleled by the expansion of myeloid populations at the expense of erythroid and B lymphoid fractions. Hematopoietic changes were associated with modifications of the bone marrow stromal architecture through relocalization and increased density in the interstitial area of Nestin⁺ mesenchymal cells expressing CXCL12 and myeloid cells expressing CXCL12 receptor CXCR4. These early events were concomitant with deregulation of circulating miRNAs, which were predicted regulators of transcripts downregulated in the bone marrow and involved in lymphoid differentiation and activation. These data provide a link between sensing of peripheral cancer initiation by the bone marrow and hematopoietic adaptation to distant noxia through transcriptional rewiring toward innate/inflammatory response programs. SIGNIFICANCE: The bone marrow senses distant tissue transformation at premalignant/preinvasive stages, suggesting that circulating messengers, intercepted in the blood, could serve as early diagnostic markers.

CXCR2 expression on granulocyte and macrophage progenitors under tumor conditions contributes to mo-MDSC generation via SAP18/ERK/STAT3

Myeloid-derived suppressor cells (MDSCs) comprise a critical component of the tumor environment and CXCR2 reportedly plays a key role in the pathophysiology of various inflammatory diseases. Here, CXCR2 expression on granulocyte and macrophage progenitor cells (GMPs) was found to participate in myeloid cell differentiation within the tumor environment. In CXCR2-deficient tumor-bearing mice, GMPs exhibited fewer macrophage and dendritic cell progenitor cells than wild-type tumor-bearing mice, thereby decreasing monocytic MDSCs (mo-MDSCs) expansion. CXCR2 deficiency increased SAP18 expression in tumor-bearing mice, which reduced STAT3 phosphorylation through restraining ERK1/2 activation. Our findings reveal a critical role for CXCR2 in regulating hematopoietic progenitor cell differentiation under tumor conditions, and SAP18 is a key negative regulator in this process. Thus, inhibiting CXCR2 expression may alter the tumor microenvironment and attenuate tumor progression.

Predictive value of IL-18 and IL-10 in the prognosis of patients with colorectal cancer

Predictive value of serum interleukin 10 (IL-10) and interleukin 18 (IL-18) expression in patients with colorectal cancer (CRC) was investigated. This study retrospectively analyzed the medical records of 146 patients with CRC admitted to the Binzhou Medical University Hospital as the study group, and collected the physical examination data of 82 volunteers as the control group. The expression levels of IL-10 and IL-18 in the serum were measured by enzyme-linked immunosorbent assay (ELISA). A 60-month follow-up on patients in the study group was performed to make records of their prognosis. The expressions of IL-10 and IL-18 were statistically different in patients with different Dukes stages, tumor sizes, histological grades, and different situations of distant metastasis of cancer cells (P<0.05); with a gradual downward trend following the operation. The expression levels of serum IL-10 and IL-18 in the study group 7 days after the operation were lower than the levels before the operation (P<0.05), and the expression levels of IL-10 and IL-18 of patients in the study group on the day of discharge were lower than the expression levels 7 days after the operation (P<0.05). The expressions of IL-10 and IL-18 of patients with reoccurred CRC after the operation were significantly higher than that of patients without recurrence of CRC in the study group (P<0.05). Thus, IL-10 and IL-18 are highly expressed in the serum of CRC patients, which makes IL-10 and IL-18 useful to serve as indicators to determine the prognosis of CRC patients. The lower the expression levels of IL-10 and IL-18, the lower the cancer recurrence rate, the better the prognosis and the longer the survival time.

Concise Review: Modulating Cancer Immunity with Hematopoietic Stem and Progenitor Cells

Hematopoietic stem and progenitor cells (HSPCs) are the progenitor cells that can regenerate the entire blood compartment, including the immune system. Recent studies have unearthed considerable immune-modulating potential of these cells. They can migrate through chemotactic gradients, differentiate into functional immune cells, and crosstalk with immune cells during infections, autoimmune diseases, and cancers. Although the primary role of HSPCs during solid malignancies is considered immunosuppressive, recent studies have discovered immune-activating HSPCs and progeny. In this review, we will discuss the recent evidence that HSPCs act as immunomodulators during solid cancers and highlight the future directions of discovery. Stem Cells 2019;37:166-175.

Cross-talk between T Cells and Hematopoietic Stem Cells during Adoptive Cellular Therapy for Malignant Glioma

Purpose: Adoptive T-cell immunotherapy (ACT) has emerged as a viable therapeutic for peripheral and central nervous system (CNS) tumors. In peripheral cancers, optimal efficacy of ACT is reliant on dendritic cells (DCs) in the tumor microenvironment. However, the CNS is largely devoid of resident migratory DCs to function as antigen-presenting cells during immunotherapy. Herein, we demonstrate that cellular interactions between adoptively transferred tumor-reactive T cells and bone marrow-derived hematopoietic stem and progenitor cells (HSPCs) lead to the generation of potent intratumoral DCs within the CNS compartment.Experimental Design: We evaluated HSPC differentiation during ACT in vivo in glioma-bearing hosts and HSPC proliferation and differentiation in vitro using a T-cell coculture system. We utilized FACS, ELISAs, and gene expression profiling to study the phenotype and function of HSPC-derived cells ex vivo and in vivo To demonstrate the impact of HSPC differentiation and function on antitumor efficacy, we performed survival experiments.Results: Transfer of HSPCs with concomitant ACT led to the production of activated CD86+CD11c+MHCII+ cells consistent with DC phenotype and function within the brain tumor microenvironment. These intratumoral DCs largely supplanted abundant host myeloid-derived suppressor cells. We determined that during ACT, HSPC-derived cells in gliomas rely on T-cell-released IFNγ to differentiate into DCs, activate T cells, and reject intracranial tumors.Conclusions: Our data support the use of HSPCs as a novel cellular therapy. Although DC vaccines induce robust immune responses in the periphery, our data demonstrate that HSPC transfer uniquely generates intratumoral DCs that potentiate T-cell responses and promote glioma rejection in situClin Cancer Res; 24(16); 3955-66. ©2018 AACR.

Melanoma induced immunosuppression is mediated by hematopoietic dysregulation

Tumors are associated with expansion of immunosuppressive cells such as tumor associated macrophages (TAMs), regulatory T cells (Tregs) and myeloid derived suppressor cells (MDSCs). These cells promote tumor growth, angiogenesis, metastasis and immune escape. Cancer patients frequently present symptoms such as anemia, leukocytosis and/or cytopenia; associated with poor prognosis. To uncover tumor-mediated hematopoietic abnormalities and identify novel targets that can be harnessed to improve tumor-specific immune responses, we investigated the hematopoietic stem and progenitor cell compartment in melanoma bearing mice. We show that melanoma growth results in expansion of myeloid lineages such as MDSCs, macrophages and DCs along with a reduction in mature RBCs and platelets. Mature B lymphocytes in the blood and BM of melanoma mice were also reduced. Mice bearing melanoma showed extramedullary hematopoiesis in the spleen. Increased expansion of myeloid lineages occurred directly at the level of stem and progenitor cells. The reduction in mature B lymphocytes resulted from a block at the Pro-B cell stage in the bone marrow. Addition of recombinant IL-3 to bone marrow cells resulted in the expansion of committed myeloid progenitors including common myeloid precursors, granulocyte-monocyte precursors and megakaryocyte-erythrocyte precursors. In vivo, IL-3 receptor stimulation in melanoma bearing mice using an IL-3 antibody also resulted in a robust expansion of committed myeloid progenitors and hematopoietic stem cells. Collectively our findings demonstrate that tumor growth plays a pivotal role in reprogramming the host immune system by impacting hematopoiesis directly at the level of stem cell compartment.

The protumorigenic potential of FTY720 by promoting extramedullary hematopoiesis and MDSC accumulation

FTY720 (also called fingolimod) is recognized as an immunosuppressant and has been approved by the Food and Drug Administration to treat refractory multiple sclerosis. However, long-term administration of FTY720 potentially increases the risk for cancer in recipients. The underlying mechanisms remain poorly understood. Herein, we provided evidence that FTY720 administration potentiated tumor growth. Mechanistically, FTY720 enhanced extramedullary hematopoiesis and massive accumulation of myeloid-derived suppressor cells (MDSCs), which actively suppressed antitumor immune responses. Granulocyte-macrophage colony-stimulating factor (GM-CSF), mainly produced by MDSCs, was identified as a key factor to mediate these effects of FTY720 in tumor microenvironment. Furthermore, we showed that FTY720 triggers MDSCs to release GM-CSF via S1P receptor 3 (S1pr3) through Rho kinase and extracellular signal-regulated kinase-dependent pathway. Thus, our findings provide mechanistic explanation for the protumorigenic potentials of FTY720 and suggest that targeting S1pr3 simultaneously may be beneficial for the patients receiving FTY720 treatment.

2B4-SAP signaling is required for the priming of naive CD8+ T cells by antigen-expressing B cells and B lymphoma cells

Mutations in SH2D1A gene that encodes SAP (SLAM-associated protein) result in X-linked lymphoproliferative disease (XLP), a rare primary immunodeficiency disease defined by exquisite sensitivity to the B-lymphotropic Epstein-Barr virus (EBV) and B cell lymphomas. However, the precise mechanism of how the loss of SAP function contributes to extreme vulnerability to EBV and the development of B cell lymphomas remains unclear. Here, we investigate the hypothesis that SAP is critical for CD8⁺ T cell immune surveillance of antigen (Ag)-expressing B cells or B lymphoma cells under conditions of defined T cell receptor (TCR) signaling. Sh2d1a^-/- CD8⁺ T cells exhibited greatly diminished proliferation relative to wild type when Ag-presenting-B cells or -B lymphoma cells served as the primary Ag-presenting cell (APC). By contrast, Sh2d1a^-/- CD8⁺ T cells responded equivalently to wild-type CD8⁺ T cells when B cell-depleted splenocytes, melanoma cells or breast carcinoma cells performed Ag presentation. Through application of signaling lymphocyte activation molecule (SLAM) family receptor blocking antibodies or SLAM family receptor-deficient CD8⁺ T cells and APCs, we found that CD48 engagement on the B cell surface by 2B4 is crucial for initiating SAP-dependent signaling required for the Ag-driven CD8⁺ T cell proliferation and differentiation. Altogether, a pivotal role for SAP in promoting the expansion and differentiation of B cell-primed viral-specific naive CD8⁺ T cells may explain the selective immune deficiency of XLP patients to EBV and B cell lymphomas.

Hypoxia pathway and hypoxia-mediated extensive extramedullary hematopoiesis are involved in ursolic acid's anti-metastatic effect in 4T1 tumor bearing mice

Hypoxic in the tumor mass is leading to the myeloproliferative-like disease (leukemoid reaction) and anemia of body, which characterized by strong extensive extramedullary hematopoiesis (EMH) in spleen. As the key transcription factor of hypoxia, hypoxia-inducible factor-1 (HIF-1) activates the expression of genes essential for EMH processes including enhanced blood cell production and angiogenesis. We found ursolic acid (UA), a natural pentacyclic triterpenoid carboxylic acid, inhibited growth of breast cancer both in vivo and in vitro. The suppression was mediated through the inhibition of multiple cell pathways linked to inflammation, proliferation, angiogenesis, and metastasis. UA also suppressed the leukemoid reaction and the EMH phenomenon of the tumor bearing mice without any significant suppression on body weight (i.p. by 20 mg/kg for 28 days). This is associated with the significant decrease in white blood cells (WBC), platelets (PLT) and spleen weight. During this process, we also detected the down-regulation of cell proliferative genes (PCNA, and β-catenin), and metastatic genes (VEGF, and HIF-1α), as well as the depression of nuclear protein intensity of HIF-1α. Furthermore, the expression of E2F1, p53 and MDM2 genes were increased in UA group when the VEGF and HIF-1α was over-expressed. Cancer cells were sensitive to UA treating after the silencing of HIF-1α and the response of Hypoxic pathway reporter to UA was suppressed when HIF-1α was over expressed. Overall, our results from experimental and predictive studies suggest that the anticancer activity of UA may be at least in part caused by suppressing the cancer hypoxia and hypoxia-mediated EMH.

Tumor-secreted products repress B-cell lymphopoiesis in a murine model of breast cancer

Growing cancers are known to modify immune responses through suppressive mechanisms manifested within the local tumor microenvironment. Accumulating evidence indicates that secreted tumor products can also influence on distant immunological compartments, including myelopoiesis in the bone marrow. However, it is unknown if a similar effect can occur to regulate B-cell lymphopoiesis in breast cancer. Examining the MMTV-PyMT murine model of breast cancer, we show a complete block in bone marrow B-cell lymphopoiesis, which is dependent on tumor burden. We also observed an increase in the total number of splenic B cells and an elevated frequency of marginal zone B cells. By using in vitro assays of B-cell lymphopoiesis, we show that tumor-secreted molecules directly inhibit B-cell progenitor proliferation and favor maturation. These data demonstrate a profound sensitivity of B-cell lymphopoiesis to the accumulation of ectopically produced molecules during tumor growth in PyMT.

EphA4-deleted microenvironment regulates cancer development and leukemoid reaction of the isografted 4T1 murine breast cancer via reduction of an IGF1 signal

EphA4 belongs to the largest family of receptor tyrosine kinases (RTKs). Although EphA4 is highly expressed in the central nervous system, EphA4 has also been implicated in cancer progression. Most of the studies focus on the expression and function in tumor cells. It is unknown whether EphA4‐deleted microenvironment affects tumor progression. Some of cancers in animals and humans, such as 4T1 cancer cells, are known to produce a large amount of granulocyte colony‐stimulating factors (G‐CSF/Csf3) which can stimulate myeloproliferation, such as myeloid‐derived suppressor cells (MDSCs) leading to a poor recipient prognosis. We isografted 4T1 breast cancer cells into both EphA4‐knockout and control wild‐type female littermate mice. The results showed that the EphA4‐deleted host could inhibit primary tumor growth and tumor metastasis mainly by decreasing the amount of IGF1 synthesis in the circulation and locally tissues. The EphA4‐deleted microenvironment and delayed tumor development reduced the production of G‐CSF resulting in the decrease of splenomegaly and leukemoid reaction including MDSCs, which in turn inhibit the tumor progression. This inhibition can be reversed by supplying the mice with IGF1. However, an excess of IGF1 supply over demand to the control mice could not further accelerate the tumor growth and metastasis. A better understanding and re‐evaluation of the main role of IGF1 in regulating tumor progression could further enhance our cognition of the tumor development niche. Our findings demonstrated that EphA4‐deleted microenvironment impairs tumor‐supporting conditions. Conclusion: Host EphA4 expression regulates cancer development mainly via EphA4‐mediated IGF1 synthesis signal. Thus, targeting this signaling pathway may provide a potential therapeutic option for cancer treatment.

VEGF-A/VEGFR Inhibition Restores Hematopoietic Homeostasis in the Bone Marrow and Attenuates Tumor Growth

Antiangiogenesis-based cancer therapies, specifically those targeting the VEGF-A/VEGFR2 pathway, have been approved for subsets of solid tumors. However, these therapies result in an increase in hematologic adverse events. We surmised that both the bone marrow vasculature and VEGF receptor-positive hematopoietic cells could be impacted by VEGF pathway-targeted therapies. We used a mouse model of spontaneous breast cancer to decipher the mechanism by which VEGF pathway inhibition alters hematopoiesis. Tumor-bearing animals, while exhibiting increased angiogenesis at the primary tumor site, showed signs of shrinkage in the sinusoidal bone marrow vasculature accompanied by an increase in the hematopoietic stem cell-containing Lin-cKit(+)Sca1(+) (LKS) progenitor population. Therapeutic intervention by targeting VEGF-A, VEGFR2, and VEGFR3 inhibited tumor growth, consistent with observed alterations in the primary tumor vascular bed. These treatments also displayed systemic effects, including reversal of the tumor-induced shrinkage of sinusoidal vessels and altered population balance of hematopoietic stem cells in the bone marrow, manifested by the restoration of sinusoidal vessel morphology and hematopoietic homeostasis. These data indicate that tumor cells exert an aberrant systemic effect on the bone marrow microenvironment and VEGF-A/VEGFR targeting restores bone marrow function.

Activation of Hematopoietic Stem/Progenitor Cells Promotes Immunosuppression Within the Pre-metastatic Niche

Metastatic tumors have been shown to establish microenvironments in distant tissues that are permissive to disseminated tumor cells. Hematopoietic cells contribute to this microenvironment, yet the precise initiating events responsible for establishing the pre-metastatic niche remain unclear. Here, we tracked the developmental fate of hematopoietic stem and progenitor cells (HSPC) in tumor-bearing mice. We show that a distant primary tumor drives the expansion of HSPCs within the bone marrow and their mobilization to the bloodstream. Treatment of purified HSPCs cultured ex vivo with tumor-conditioned media induced their proliferation as well as their differentiation into immunosuppressive myeloid cells. We furthered tracked purified HSPCs in vivo and found they differentiated into myeloid-derived suppressor cells in early metastatic sites of tumor-bearing mice. The number of CD11b(+)Ly6g(+) cells in metastatic sites was significantly increased by HSPC mobilization and decreased if tumor-mediated mobilization was inhibited. Moreover, pharmacologic mobilization of HSPCs increased metastasis, whereas depletion of Gr1(+) cells abrogated the metastasis-promoting effects of HSPC mobilization. Finally, we detected elevated levels of HSPCs in the circulation of newly diagnosed cancer patients, which correlated with increased risk for metastatic progression. Taken together, our results highlight bone marrow activation as one of the earliest steps of the metastatic process and identify circulating HSPCs as potential clinical indicators of metastatic niche formation.

PD-L1 is highly expressed in Enzalutamide resistant prostate cancer

Efficacy of Enzalutamide (ENZ) in castration resistant prostate cancer (CRPC) patients is short-lived. Immunotherapy like T cell checkpoint blockade may improve patient survival. However, when and where checkpoint molecules are expressed in CRPC and whether immune evasion is a mechanism of ENZ resistance remains unclear. Thus, we investigated whether clinically relevant immunotherapy targets, specifically PD-L1/2, PD-1 and CTLA-4, are upregulated in ENZ resistant (ENZR) patients and in a pre-clinical model of ENZ resistance. We show for the first time that patients progressing on ENZ had significantly increased PD-L1/2⁺ dendritic cells (DC) in blood compared to those naïve or responding to treatment, and a high frequency of PD-1⁺T cells. These data supported our pre-clinical results, in which we found significantly increased circulating PD-L1/2⁺ DCs in mice bearing ENZR tumors compared to CRPC, and ENZR tumors expressed significantly increased levels of tumor-intrinsic PD-L1. Importantly, the expression of PD-L1 on ENZR cells, or the ability to modulate PD-L1/2⁺ DC frequency, was unique to ENZR cell lines and xenografts that did not show classical activation of the androgen receptor. Overall, our results suggest that ENZ resistance is associated with the strong expression of anti-PD-1 therapy targets in circulating immune cells both in patients and in a pre-clinical model that is non-AR driven. Further evaluation of the contribution of tumor vs. immune cell PD-L1 expression in progression of CRPC to anti-androgen resistance and the utility of monitoring circulating cell PD-L1 pathway activity in CRPC patients to predict responsiveness to checkpoint immunotherapy, is warranted.

Macrophages support splenic erythropoiesis in 4T1 tumor-bearing mice

Anemia is a common complication of cancer; a role of spleen in tumor-stress erythropoiesis has been suggested. However, the molecular mechanisms involved in the splenic erythropoiesis following tumor maintenance remain poorly understood. Here we show that tumor development blocks medullar erythropoiesis by granulocyte colony-stimulating factor (G-CSF) and then causes anemia in murine 4T1 breast tumor-bearing mice. Meanwhile, tumor-stress promotes splenic erythropoiesis. Splenectomy worsened tumor-induced anemia, and reduced tumor volume and tumor weight, indicating the essential role of spleen in tumor-stress erythropoiesis and tumor growth. Tumor progression of these mice led to increased amounts of bone morphogenetic protein 4 (BMP4) in spleen. The in vivo role of macrophages in splenic erythropoiesis under tumor-stress conditions was investigated. Macrophage depletion by injecting liposomal clodronate decreased the expression of BMP4, inhibited splenic erythropoiesis, aggravated the tumor-induced anemia and suppressed tumor growth. Our results provide insight that macrophages and BMP4 are positive regulators of splenic erythropoiesis in tumor pathological situations. These findings reveal that during the tumor-stress period, the microenvironment of the spleen is undergoing changes, which contributes to adopt a stress erythropoietic fate and supports the expansion and differentiation of stress erythroid progenitors, thereby replenishing red blood cells and promoting tumor growth.

SOCS3 Deficiency in Myeloid Cells Promotes Tumor Development: Involvement of STAT3 Activation and Myeloid-Derived Suppressor Cells

Suppressor of cytokine signaling (SOCS) proteins are negative regulators of the JAK/STAT pathway and generally function as tumor suppressors. The absence of SOCS3 in particular leads to heightened activation of the STAT3 transcription factor, which has a striking ability to promote tumor survival while suppressing antitumor immunity. We report for the first time that genetic deletion of SOCS3, specifically in myeloid cells, significantly enhances tumor growth, which correlates with elevated levels of myeloid-derived suppressor cells (MDSC) in the tumor microenvironment, and diminishes CD8(+) T-cell infiltration in tumors. The importance of MDSCs in promoting tumor growth is documented by reduced tumor growth upon depletion of MDSCs. Furthermore, SOCS3-deficient bone-marrow-derived cells exhibit heightened STAT3 activation and preferentially differentiate into the Gr-1(+)CD11b(+)Ly6G(+) MDSC phenotype. Importantly, we identify G-CSF as a critical factor secreted by the tumor microenvironment that promotes development of MDSCs via a STAT3-dependent pathway. Abrogation of tumor-derived G-CSF reduces the proliferation and accumulation of Gr-1(+)CD11b(+) MDSCs and inhibits tumor growth. These findings highlight the critical function of SOCS3 as a negative regulator of MDSC development and function via inhibition of STAT3 activation.