Quantitative phosphoproteomic analysis reveals involvement of PD-1 in multiple T cell functions.

Programmed cell death protein 1 (PD-1) is a critical inhibitory receptor that limits excessive T cell responses. Cancer cells have evolved to evade these immunoregulatory mechanisms by upregulating PD-1 ligands and preventing T cell-mediated anti-tumor responses. Consequently, therapeutic blockade of PD-1 enhances T cell-mediated anti-tumor immunity, but many patients do not respond and a significant proportion develop inflammatory toxicities. To improve anti-cancer therapy, it is critical to reveal the mechanisms by which PD-1 regulates T cell responses. We performed global quantitative phosphoproteomic interrogation of PD-1 signaling in T cells. By complementing our analysis with functional validation assays, we show that PD-1 targets tyrosine phosphosites that mediate proximal T cell receptor signaling, cytoskeletal organization, and immune synapse formation. PD-1 ligation also led to differential phosphorylation of serine and threonine sites within proteins regulating T cell activation, gene expression, and protein translation. In silico predictions revealed that kinase/substrate relationships engaged downstream of PD-1 ligation. These insights uncover the phosphoproteomic landscape of PD-1-triggered pathways and reveal novel PD-1 substrates that modulate diverse T cell functions and may serve as future therapeutic targets. These data are a useful resource in the design of future PD-1-targeting therapeutic approaches.

PD-1 signaling uncovers a pathogenic subset of T cells in inflammatory arthritis.

BACKGROUND: PD-1 is an immune checkpoint on T cells, and interventions to block this receptor result in T cell activation and enhanced immune response to tumors and pathogens. Reciprocally, despite a decade of research, approaches to treat autoimmunity with PD-1 agonists have only had limited successful. To resolve this, new methods must be developed to augment PD-1 function beyond engaging the receptor. METHODS: We conducted a flow cytometry analysis of T cells isolated from the peripheral blood and synovial fluid of patients with rheumatoid arthritis. In addition, we performed a genome-wide CRISPR/Cas9 screen to identify genes associated with PD-1 signaling. We further analyzed genes involved in PD-1 signaling using publicly available bulk and single-cell RNA sequencing datasets. RESULTS: Our screen confirmed known regulators in proximal PD-1 signaling and, importantly, identified an additional 1112 unique genes related to PD-1 ability to inhibit T cell functions. These genes were strongly associated with the response of cancer patients to PD-1 blockades and with high tumor immune dysfunction and exclusion scores, confirming their role downstream of PD-1. Functional annotation revealed that the most significant genes uncovered were those associated with known immune regulation processes. Remarkably, these genes were considerably downregulated in T cells isolated from patients with inflammatory arthritis, supporting their overall inhibitory functions. A study of rheumatoid arthritis single-cell RNA sequencing data demonstrated that five genes, KLRG1, CRTAM, SLAMF7, PTPN2, and KLRD1, were downregulated in activated and effector T cells isolated from synovial fluids. Backgating these genes to canonical cytotoxic T cell signatures revealed PD-1+ HLA-DRHIGH KLRG1LOW T cells as a novel inflammatory subset of T cells. CONCLUSIONS: We concluded that PD-1+ HLA-DRHIGH KLRG1LOW T cells are a potential target for future PD-1 agonists to treat inflammatory diseases. Our study uncovers new genes associated with PD-1 downstream functions and, therefore, provides a comprehensive resource for additional studies that are much needed to characterize the role of PD-1 in the synovial subset of T cells.

SAP-expressing T peripheral helper cells identify systemic lupus erythematosus patients with lupus nephritis.

Introduction: T follicular (TFH) and peripheral helper (TPH) cells have been increasingly recognized as a pathogenic subset of CD4 T cells in systemic lupus erythematosus (SLE). The SLAM Associated Protein (SAP) regulates TFH and TPH function by binding to the co-stimulatory signaling lymphocyte activation molecule family (SLAMF) receptors that mediate T cell - B cell interactions. SAP and SLAMF are critical for TPH-dependent B cell maturation into autoantibody-producing plasma cells that characterize SLE pathogenesis. We hypothesized that SAP-expressing TPH cells are involved in the pathogenesis of lupus nephritis (LN). Methods: Peripheral blood mononuclear cells (PBMC) were isolated using density gradient separation from whole blood. Cells were stained for cell surface markers, followed by permeabilization and staining of intracellular SAP for spectral flow cytometry analysis. We also analyzed SAP expression from renal infiltrating LN T cells using the available single-cell RNA sequencing (scRNA seq) Accelerated Medicines Partnership (AMP) SLE dataset. Results: PBMC from 30 patients with SLE (34 ± 10 years old, 83% female), including 10 patients with LN, were analyzed. We found an increase in total SAP-positive CD4 and CD8 T cells in SLE compared with controls (55.5 ± 2.6 vs. 41.3 ± 3.4, p=0.007, and 52.5 ± 3.0 vs. 39.2 ± 2.8, p=0.007 respectively). In CD4 T cells, the highest SAP expression was in the TPH subset. The frequency of SAP+TPH in circulation correlated with disease activity; SLE patients with renal disease had higher levels of circulating SAP+TPH that remained significant after adjusting for age, sex, race, low complements, and elevated anti-dsDNA (p=0.014). scRNA-seq data of renal infiltrating T cells in LN identified SAP expression to localize to the TFH-like CD4 cluster and GZMK+ CD8 cluster. Increased SAP expression in LN was associated with the differential expression of SLAMF3 and SLAMF7 and granzyme K and EOMES. The existence of two predominant SAP-expressing subsets, the TFH-like CD4 T cells, and GZMK+ effector CD8 T cells, was verified using scRNA-seq data from a human transcriptomic atlas of fifteen major organs. Conclusion: The expansion of SAP-expressing T helper cells was associated with LN in our cohort and verified using scRNA-seq data of renal infiltrating T cells. Improved SLAM and SAP signaling understanding can identify new therapeutic targets in LN.

Inhibition of IL-25/IL-17RA improves immune-related adverse events of checkpoint inhibitors and reveals antitumor activity.

BACKGROUND: Immune checkpoint inhibitors (ICIs) have improved outcomes and extended patient survival in several tumor types. However, ICIs often induce immune-related adverse events (irAEs) that warrant therapy cessation, thereby limiting the overall effectiveness of this class of therapeutic agents. Currently, available therapies used to treat irAEs might also blunt the antitumor activity of the ICI themselves. Therefore, there is an urgent need to identify treatments that have the potential to be administered alongside ICI to optimize their use. METHODS: Using a translationally relevant murine model of anti-PD-1 and anti-CTLA-4 antibodies-induced irAEs, we compared the safety and efficacy of prednisolone, anti-IL-6, anti-TNFɑ, anti-IL-25 (IL-17E), and anti-IL-17RA (the receptor for IL-25) administration to prevent irAEs and to reduce tumor size. RESULTS: While all interventions were adequate to inhibit the onset of irAEs pneumonitis and hepatitis, treatment with anti-IL-25 or anti-IL-17RA antibodies also exerted additional antitumor activity. Mechanistically, IL-25/IL-17RA blockade reduced the number of organ-infiltrating lymphocytes. CONCLUSION: These findings suggest that IL-25/IL-17RA may serve as an additional target when treating ICI-responsive tumors, allowing for better tumor control while suppressing immune-related toxicities.

Exclusion of PD-1 from the immune synapse: a novel strategy to modulate T cell function.

Targeting immune checkpoint receptors on T cells is a common cancer treatment strategy. Frequently, this is accomplished through antibodies targeting the ligand of inhibitory co-receptors. Blocking the immune checkpoint PD-1 binding to its ligands PD-L1 and PD-L2 prevents downstream signaling and enhances anti-tumor T cell responses. This approach improved cancer patients' outcome. However, only one-third of the patients respond to these treatments. To better understand the mechanism of anti-PD-1 antibodies, we explored the location of PD-1 within the immune synapse. Surprisingly, we discovered that anti-PD-1 antibodies, besides blocking the interaction between PD-1 and its ligands, also removed PD-1 from the synapse. We demonstrated a correlation between removing PD-1 from the synapse by anti-PD-1 antibodies and the extent of T cell activation. Interestingly, a short version of the anti-PD-1 antibody, F(ab') 2 , failed to remove PD-1 from the synapse and activate T cells. Using syngeneic tumor model, we showed a superior anti-tumor effect to anti-PD-1 antibody over the shorter version of the antibody. Our data indicates that anti-PD-1 antibodies activate T cells by removing PD-1 away from the synapse and changing the location of PD-1 or other immune receptors within immune synapse could serve as an alternative, efficient approach to treat cancer.

PD-1 signaling uncovers a pathogenic subset of T cells in inflammatory arthritis.

Background: PD-1 is an immune checkpoint on T cells and interventions to block this receptor result in T cell activation and enhanced immune response to tumors. Paired to that, and despite a decade of research, approaches to treat autoimmunity with PD-1 agonists still need to be more successful. To resolve this, new methods must be developed to augment PD-1 function beyond engaging the receptor. Methods: We conducted a flow cytometry analysis of T cells isolated from the peripheral blood and synovial fluid of patients with rheumatoid arthritis. In addition, we performed a genome-wide CRISPR/Cas9 screen to identify genes associated with PD-1 signaling. We further analyzed genes involved in PD-1 signaling using publicly available bulk and single-cell RNA sequencing datasets. Results: Our screen confirmed known regulators in proximal PD-1 signaling and, importantly, found an additional 1,112 unique genes related to PD-1 ability to inhibit T cell functions. These genes were strongly associated with the response of cancer patients to PD-1 blockades and with high tumor immune dysfunction and exclusion scores, confirming their role downstream of PD-1. Functional annotation revealed that more significant genes uncovered were those associated with known immune regulation processes. Remarkably, these genes were considerably downregulated in T cells isolated from patients with inflammatory arthritis, supporting their overall inhibitory functions. A study of rheumatoid arthritis single-cell RNA sequencing data demonstrated that five genes, KLRG1, CRTAM, SLAMF7, PTPN2, and KLRD1, were downregulated in activated and effector T cells isolated from synovial fluids. Back-gating these genes to canonical cytotoxic T cell signatures revealed PD-1 + HLA-DR HIGH KLRG LOW T cells as a novel inflammatory subset of T cells. Conclusion: We concluded that PD-1 + HLA-DR HIGH KLRG LOW T cells are a potential target for future PD-1 agonists to treat inflammatory diseases. Our study uncovers new genes associated with PD-1 downstream functions and, therefore, provides a comprehensive resource for additional studies that are much needed to characterize the role of PD-1 in the synovial subset of T cells.

Single-cell RNA sequencing reveals distinct T cell populations in immune-related adverse events of checkpoint inhibitors.

PD-1 is an inhibitory receptor in T cells, and antibodies that block its interaction with ligands augment anti-tumor immune responses. The clinical potential of these agents is limited by the fact that half of all patients develop immune-related adverse events (irAEs). To generate insights into the cellular changes that occur during anti-PD-1 treatment, we performed single-cell RNA sequencing of circulating T cells collected from patients with cancer. Using the K-nearest-neighbor-based network graph-drawing layout, we show the involvement of distinctive genes and subpopulations of T cells. We identify that at baseline, patients with arthritis have fewer CD8 TCM cells, patients with pneumonitis have more CD4 TH2 cells, and patients with thyroiditis have more CD4 TH17 cells when compared with patients who do not develop irAEs. These data support the hypothesis that different populations of T cells are associated with different irAEs and that characterization of these cells' pre-treatment has the potential to serve as a toxicity-specific predictive biomarker.

PD-1-stimulated T cell subsets are transcriptionally and functionally distinct.

Despite the obvious inhibitory outcome of PD-1 signaling, an additional series of functions are activated. We have observed that T cells stimulated through the T cell receptor (TCR) and PD-1 primarily do not proliferate; however, there is a population of cells that proliferates more than through TCR stimulation alone. In this study, we performed flow cytometry and RNA sequencing on individual populations of T cells and discovered that unlike naive T cells, which were inhibited following PD-1 ligation, T cells that proliferated more following PD-1 ligation were associated with effector and central memory phenotypes. We showed that these populations had different gene expression profiles following PD-1 ligation with PD-L1 compared to PD-L2. The presence of transcriptionally and functionally distinct T cell populations responsive to PD-1 ligation provides new insights into the biology of PD-1 and suggest the use of T cell subset-specific approaches to improve the clinical outcome of PD-1 blockade.

SHP2 Targets ITK Downstream of PD-1 to Inhibit T Cell Function.

PD-1 is a critical therapeutic target in cancer immunotherapy and antibodies blocking PD-1 are approved for multiple types of malignancies. The phosphatase SHP2 is the main effector mediating PD-1 downstream signaling and accordingly attempts have been made to target this enzyme as an alternative approach to treat immunogenic tumors. Unfortunately, small molecule inhibitors of SHP2 do not work as expected, suggesting that the role of SHP2 in T cells is more complex than initially hypothesized. To better understand the perplexing role of SHP2 in T cells, we performed interactome mapping of SAP, an adapter protein that is associated with SHP2 downstream signaling. Using genetic and pharmacological approaches, we discovered that SHP2 dephosphorylates ITK specifically downstream of PD-1 and that this event was associated with PD-1 inhibitory cellular functions. This study suggests that ITK is a unique target in this pathway, and since ITK is a SHP2-dependent specific mediator of PD-1 signaling, the combination of ITK inhibitors with PD-1 blockade may improve upon PD-1 monotherapy in the treatment of cancer.

In Vitro Assays to Study PD-1 Biology in Human T Cells.

Our understanding of programmed cell death 1 (PD-1) biology is limited due to technical difficulties in establishing reproducible, yet simple, in vitro assays to study PD-1 signaling in primary human T cells. The protocols in this article were refined to test the consequences of PD-1 ligation on short-term T cell signaling, long-term T cell function, and the structural consequences of PD-1 ligation with PD-1 ligands. Basic Protocol 1 addresses the need for a robust and reproducible short-term assay to examine the signaling cascade triggered by PD-1. We describe a phospho flow cytometry method to determine how PD-1 ligation alters the level of CD3ζ phosphorylation on Tyr142 , which can be easily applied to other proximal signaling proteins. Basic Protocol 2 describes a plate-bound assay that is useful to examine the long-term consequences of PD-1 ligation such as cytokine production and T cell proliferation. Complementary to that, Basic Protocol 3 describes an in vitro superantigen-based assay to evaluate T cell responses to therapeutic agents targeting the PD-1/PD-L axis, as well as immune synapse formation in the presence of PD-1 engagement. Finally, in Basic Protocol 4 we outline a tetramer-based method useful to interrogate the quality of PD-1/PD-L interactions. These protocols can be easily adapted for mouse studies and other inhibitory receptors. They provide a valuable resource to investigate PD-1 signaling in T cells and the functional consequences of various PD-1-based therapeutics on T cell responses. © 2020 Wiley Periodicals LLC. Basic Protocol 1: PD-1 crosslinking assay to determine CD3ζ phosphorylation in primary human T cells Basic Protocol 2: Plate-based ligand binding assay to study PD-1 function in human T cells Support Protocol 1: T cell proliferation assay in the presence of PD-1 ligation Basic Protocol 3: In vitro APC/T cell co-culture system to evaluate therapeutic interventions targeting the PD-1/PD-L1 axis Support Protocol 2: Microscopy-based approach to evaluate the consequences of PD-1 ligation on immune synapse formation Basic Protocol 4: Tetramer-based approach to study PD-1/PD-L1 interactions.

Tumor-Stroma-Inflammation Networks Promote Pro-metastatic Chemokines and Aggressiveness Characteristics in Triple-Negative Breast Cancer.

The tumor microenvironment (TME) plays key roles in promoting disease progression in the aggressive triple-negative subtype of breast cancer (TNBC; Basal/Basal-like). Here, we took an integrative approach and determined the impact of tumor-stroma-inflammation networks on pro-metastatic phenotypes in TNBC. With the TCGA dataset we found that the pro-inflammatory cytokines tumor necrosis factor α (TNFα) and interleukin 1ß (IL-1ß), as well as their target pro-metastatic chemokines CXCL8 (IL-8), CCL2 (MCP-1), and CCL5 (RANTES) were expressed at significantly higher levels in basal patients than luminal-A patients. Then, we found that TNFα- or IL-1ß-stimulated co-cultures of TNBC cells (MDA-MB-231, MDA-MB-468, BT-549) with mesenchymal stem cells (MSCs) expressed significantly higher levels of CXCL8 compared to non-stimulated co-cultures or each cell type alone, with or without cytokine stimulation. CXCL8 was also up-regulated in TNBC co-cultures with breast cancer-associated fibroblasts (CAFs) derived from patients. CCL2 and CCL5 also reached the highest expression levels in TNFα/IL-1ß-stimulated TNBC:MSC/CAF co-cultures. The elevations in CXCL8 and CCL2 expression partly depended on direct physical contacts between the tumor cells and the MSCs/CAFs, whereas CCL5 up-regulation was entirely dependent on cell-to-cell contacts. Supernatants of TNFα-stimulated TNBC:MSC "Contact" co-cultures induced robust endothelial cell migration and sprouting. TNBC cells co-cultured with MSCs and TNFα gained migration-related morphology and potent migratory properties; they also became more invasive when co-cultured with MSCs/CAFs in the presence of TNFα. Using siRNA to CXCL8, we found that CXCL8 was significantly involved in mediating the pro-metastatic activities gained by TNFα-stimulated TNBC:MSC "Contact" co-cultures: angiogenesis, migration-related morphology of the tumor cells, as well as cancer cell migration and invasion. Importantly, TNFα stimulation of TNBC:MSC "Contact" co-cultures in vitro has increased the aggressiveness of the tumor cells in vivo, leading to higher incidence of mice with lung metastases than non-stimulated TNBC:MSC co-cultures. Similar tumor-stromal-inflammation networks established in-culture with luminal-A cells demonstrated less effective or differently-active pro-metastatic functions than those of TNBC cells. Overall, our studies identify novel tumor-stroma-inflammation networks that may promote TNBC aggressiveness by increasing the pro-malignancy potential of the TME and of the tumor cells themselves, and reveal key roles for CXCL8 in mediating these metastasis-promoting activities.

Notch-Mediated Tumor-Stroma-Inflammation Networks Promote Invasive Properties and CXCL8 Expression in Triple-Negative Breast Cancer.

Stromal cells and pro-inflammatory cytokines play key roles in promoting the aggressiveness of triple-negative breast cancers (TNBC; Basal/Basal-like). In our previous study we demonstrated that stimulation of TNBC and mesenchymal stem cells (MSCs) co-cultures by the pro-inflammatory cytokine tumor necrosis factor α (TNFα) has led to increased metastasis-related properties in vitro and in vivo. In this context, elevated release of the pro-metastatic chemokines CXCL8 (IL-8) and CCL5 (RANTES) was noted in TNFα- and interleukin-1ß (IL-1ß)-stimulated TNBC:MSC co-cultures; the process was partly (CXCL8) and entirely (CCL5) dependent on physical contacts between the two cell types. Here, we demonstrate that DAPT, inhibitor of γ-secretase that participates in activation of Notch receptors, inhibited the migration and invasion of TNBC cells that were grown in "Contact" co-cultures with MSCs or with patient-derived cancer-associated fibroblasts (CAFs), in the presence of TNFα. DAPT also inhibited the contact-dependent induction of CXCL8, but not of CCL5, in TNFα- and IL-1ß-stimulated TNBC:MSC/CAF co-cultures; some level of heterogeneity between the responses of different TNBC cell lines was noted, with MDA-MB-231:MSC/CAF co-cultures being the most sensitive to DAPT. Patient dataset studies comparing basal tumors to luminal-A tumors, and mRNA analyses of Notch receptors in TNBC and luminal-A cells pointed at Notch1 as possible mediator of CXCL8 increase in TNFα-stimulated TNBC:stroma "Contact" co-cultures. Accordingly, down-regulation of Notch1 in TNBC cells by siRNA has substantially reduced the contact-dependent elevation in CXCL8 in TNFα- and also in IL-1ß-stimulated TNBC:MSC "Contact" co-cultures. Then, studies in which CXCL8 or p65 (NF-κB pathway) were down-regulated (siRNAs; CRISPR/Cas9) in TNBC cells and/or MSCs, indicated that upon TNFα stimulation of "Contact" co-cultures, p65 was activated and led to CXCL8 production mainly in TNBC cells. Moreover, our findings indicated that when tumor cells interacted with stromal cells in the presence of pro-inflammatory stimuli, TNFα-induced p65 activation has led to elevated Notch1 expression and activation, which then gave rise to elevated production of CXCL8. Overall, tumor:stroma interactions set the stage for Notch1 activation by pro-inflammatory signals, leading to CXCL8 induction and consequently to pro-metastatic activities. These observations may have important clinical implications in designing novel therapy combinations in TNBC.

miRNA-1246 induces pro-inflammatory responses in mesenchymal stem/stromal cells by regulating PKA and PP2A.

The tumor microenvironment (TME) has an impact on breast cancer progression by creating a pro-inflammatory milieu within the tumor. However, little is known about the roles of miRNAs in cells of the TME during this process. We identified six putative oncomiRs in a breast cancer dataset, all strongly correlating with poor overall patient survival. Out of the six candidates, miR-1246 was upregulated in aggressive breast cancer subtypes and expressed at highest levels in mesenchymal stem/stroma cells (MSCs). Functionally, miR-1246 led to a p65-dependent increase in transcription and release of pro-inflammatory mediators IL-6, CCL2 and CCL5 in MSCs, and increased NF-κB activity. The pro-inflammatory phenotype of miR-1246 in MSCs was independent of TNFα stimulations and mediated by direct targeting of the tumor-suppressors PRKAR1A and PPP2CB. In vitro recapitulation of the TME revealed increased Stat3 phosphorylation in breast epithelial (MCF10A) and cancer cells (SK-BR-3, MCF7, T47D) upon incubation with conditioned medium (CM) of MSCs overexpressing miR-1246. Additionally, this stimulation enhanced proliferation of MCF10A cells, increased migration of MDA-MB-231 cells and induced attraction of THP-1 monocytic cells. Our data shows that miR-1246 acts as both key-enhancer of pro-inflammatory responses in MSCs and putative oncomiR in breast cancer, suggesting its influence on cancer-related inflammation and breast cancer progression.

Co-Inflammatory Roles of TGFß1 in the Presence of TNFα Drive a Pro-inflammatory Fate in Mesenchymal Stem Cells.

High plasticity is a hallmark of mesenchymal stem cells (MSCs), and as such, their differentiation and activities may be shaped by factors of their microenvironment. Bones, tumors, and cardiomyopathy are examples of niches and conditions that contain MSCs and are enriched with tumor necrosis factor α (TNFα) and transforming growth factor ß1 (TGFß1). These two cytokines are generally considered as having opposing roles in regulating immunity and inflammation (pro- and anti-inflammatory, respectively). Here, we performed global gene expression analysis of human bone marrow-derived MSCs and identified overlap in half of the transcriptional programs that were modified by TNFα and TGFß1. The two cytokines elevated the mRNA expression of soluble factors, including mRNAs of pro-inflammatory mediators. Accordingly, the typical pro-inflammatory factor TNFα prominently induced the protein expression levels of the pro-inflammatory mediators CCL2, CXCL8 (IL-8), and cyclooxygenase-2 (Cox-2) in MSCs, through the NF-κB/p65 pathway. In parallel, TGFß1 did not elevate CXCL8 protein levels and induced the protein expression of CCL2 at much lower levels than TNFα; yet, TGFß1 readily induced Cox-2 and acted predominantly via the Smad3 pathway. Interestingly, combined stimulation of MSCs by TNFα + TGFß1 led to a cooperative induction of all three inflammatory mediators, indicating that TGFß1 functioned as a co-inflammatory cytokine in the presence of TNFα. The cooperative activities of TNFα + TGFß1 that have led to CCL2 and CXCL8 induction were almost exclusively dependent on p65 activation and were not regulated by Smad3 or by the upstream regulator TGFß-activated kinase 1 (TAK1). In contrast, the TNFα + TGFß1-induced cooperative elevation in Cox-2 was mostly dependent on Smad3 (demonstrating cooperativity with activated NF-κB) and was partly regulated by TAK1. Studies with MSCs activated by TNFα + TGFß1 revealed that they release factors that can affect other cells in their microenvironment and induce breast tumor cell elongation, migration, and scattering out of spheroid tumor masses. Thus, our findings demonstrate a TNFα + TGFß1-driven pro-inflammatory fate in MSCs, identify specific molecular mechanisms involved, and propose that TNFα + TGFß1-stimulated MSCs influence the tumor niche. These observations suggest key roles for the microenvironment in regulating MSC functions, which in turn may affect different health-related conditions.

Regulation of the inflammatory profile of stromal cells in human breast cancer: prominent roles for TNF-α and the NF-κB pathway.

INTRODUCTION: Breast cancer progression is promoted by stromal cells that populate the tumors, including cancer-associated fibroblasts (CAFs) and mesenchymal stem/stromal cells (MSCs). The activities of CAFs and MSCs in breast cancer are integrated within an intimate inflammatory tumor microenvironment (TME) that includes high levels of tumor necrosis factor α (TNF-α) and interleukin 1ß (IL-1ß). Here, we identified the impact of TNF-α and IL-1ß on the inflammatory phenotype of CAFs and MSCs by determining the expression of inflammatory chemokines that are well-characterized as pro-tumorigenic in breast cancer: CCL2 (MCP-1), CXCL8 (IL-8) and CCL5 (RANTES). METHODS: Chemokine expression was determined in breast cancer patient-derived CAFs by ELISA and in patient biopsies by immunohistochemistry. Chemokine levels were determined by ELISA in (1) human bone marrow-derived MSCs stimulated by tumor conditioned media (Tumor CM) of breast tumor cells (MDA-MB-231 and MCF-7) at the end of MSC-to-CAF-conversion process; (2) Tumor CM-derived CAFs, patient CAFs and MSCs stimulated by TNF-α (and IL-1ß). The roles of AP-1 and NF-κB in chemokine secretion were analyzed by Western blotting and by siRNAs to c-Jun and p65, respectively. Migration of monocytic cells was determined in modified Boyden chambers. RESULTS: TNF-α (and IL-1ß) induced the release of CCL2, CXCL8 and CCL5 by MSCs and CAFs generated by prolonged stimulation of MSCs with Tumor CM of MDA-MB-231 and MCF-7 cells. Patient-derived CAFs expressed CCL2 and CXCL8, and secreted CCL5 following TNF-α (and IL-1ß) stimulation. CCL2 was expressed in CAFs residing in proximity to breast tumor cells in biopsies of patients diagnosed with invasive ductal carcinoma. CCL2 release by TNF-α-stimulated MSCs was mediated by TNF-RI and TNF-RII, through the NF-κB but not via the AP-1 pathway. Exposure of MSCs to TNF-α led to potent CCL2-induced migration of monocytic cells, a process that may yield pro-cancerous myeloid infiltrates in breast tumors. CONCLUSIONS: Our novel results emphasize the important roles of inflammation-stroma interactions in breast cancer, and suggest that NF-κB may be a potential target for inhibition in tumor-adjacent stromal cells, enabling improved tumor control in inflammation-driven malignancies.