Lessons for the Next Generation of Scientists from the Second Annual Arthur and Sandra Irving Cancer Immunology Symposium

The Arthur and Sandra Irving Cancer Immunology Symposium has been created as a platform for established cancer immunologists to mentor trainees and young investigators as they launch their research career in the field. By sharing their different paths to success, the senior faculty mentors provide an invaluable resource to support the development of the next generation of leaders in the cancer immunology community. This Commentary describes some of the key topics that were discussed during the 2022 symposium: scientific and career trajectory, leadership, mentoring, collaborations, and publishing. For each of these topics, established investigators discussed the elements that facilitate success in these areas as well as mistakes that can hinder progress. Herein, we outline the critical points raised in these discussions for establishing a successful independent research career. These points are highly relevant for the broader scientific community.

Critical role of CD206+ macrophages in organizing anti-tumor immunity

Tumor-associated macrophages (TAMs) are frequently and simplistically categorized as immunosuppressive, and one molecule prominently used to highlight their so-called 'M2' state is the surface protein CD206. However, direct evidence of the impact of macrophages remains impaired by the lack of sufficiently penetrant and specific tools to manipulate them in vivo. We thus made a novel conditional CD206 knock-in mouse to specifically visualize and/or deplete these TAMs. Early depletion of CD206+ macrophages and monocytes (here, 'MonoMacs') strikingly led to an indirect loss of a key anti-tumor network of NK cells, conventional type I dendritic cells (cDC1) and CD8 T cells. Among myeloid cells, we found that the CD206+ TAMs are the primary producers of CXCL9, the well-established chemoattractant for CXCR3-expressing NK and CD8 T cells. In contrast, a population of stress-responsive TAMs ("Hypoxic" or Spp1+) and immature monocytes, which remain following depletion, expressed vastly diminished levels of CXCL9. We confirmed that the missing NK and CD8 T cells are the primary producers of the cDC1-attracting chemokine Xcl1 and cDC1 growth factor Flt3l. Consistent with the loss of this critical network, CD206+ TAM depletion decreased tumor control in mice. Likewise, in humans, the CD206+ MonoMac signature correlated robustly with stimulatory cDC1 signature genes. Together, these findings negate the classification of CD206+ macrophages as immunosuppressive and instead illuminate the role of this majority of TAMs in organizing a critical tumor-reactive archetype of immunity.

Uptake of tumor-derived microparticles induces metabolic reprogramming of macrophages in the early metastatic lung

Pre-metastatic niche formation is a critical step during the metastatic spread of cancer. One way by which primary tumors prime host cells at future metastatic sites is through the shedding of tumor-derived microparticles as a consequence of vascular sheer flow. However, it remains unclear how the uptake of such particles by resident immune cells affects their phenotype and function. Here, we show that ingestion of tumor-derived microparticles by macrophages induces a rapid metabolic and phenotypic switch that is characterized by enhanced mitochondrial mass and function, increased oxidative phosphorylation, and upregulation of adhesion molecules, resulting in reduced motility in the early metastatic lung. This reprogramming event is dependent on signaling through the mTORC1, but not the mTORC2, pathway and is induced by uptake of tumor-derived microparticles. Together, these data support a mechanism by which uptake of tumor-derived microparticles induces reprogramming of macrophages to shape their fate and function in the early metastatic lung.

Tumor cell heterogeneity drives spatial organization of the intratumoral immune response in squamous cell skin carcinoma

Intratumoral heterogeneity (ITH)-defined as genetic and cellular diversity within a tumor-is linked to failure of immunotherapy and an inferior anti-tumor immune response. The underlying mechanism of this association is unknown. To address this question, we modeled heterogeneous tumors comprised of a pro-inflammatory ("hot") and an immunosuppressive ("cold") tumor population, labeled with YFP and RFP tags respectively to enable precise spatial tracking. The resulting mixed-population tumors exhibited distinct regions comprised of YFP+ (hot) cells, RFP+ (cold) cells, or a mixture. We found that tumor regions occupied by hot tumor cells (YFP+) harbored more total T cells and a higher frequency of Th1 cells and IFNγ+ CD8 T cells compared to regions occupied by cold tumor cells (RFP+), whereas immunosuppressive macrophages showed the opposite spatial pattern. We identified the chemokine CX3CL1, produced at higher levels by our cold tumors, as a mediator of intratumoral macrophage accumulation, particularly immunosuppressive CD206Hi macrophages. Furthermore, we examined the response of heterogeneous tumors to a therapeutic combination of PD-1 blockade and CD40 agonist on a region-by-region basis. While the combination successfully increases Th1 abundance in "cold" tumor regions, it fails to bring overall T cell activity to the same level as seen in "hot" regions. The presence of the "cold" cells thus ultimately leads to a failure of the therapy to induce tumor rejection. Collectively, our results demonstrate that the organization of heterogeneous tumor cells has a profound impact on directing the spatial organization and function of tumor-infiltrating immune cells as well as on responses to immunotherapy.

IL-5-producing CD4+ T cells and eosinophils cooperate to enhance response to immune checkpoint blockade in breast cancer

Immune checkpoint blockade (ICB) has heralded a new era in cancer therapy. Research into the mechanisms underlying response to ICB has predominantly focused on T cells; however, effective immune responses require tightly regulated crosstalk between innate and adaptive immune cells. Here, we combine unbiased analysis of blood and tumors from metastatic breast cancer patients treated with ICB with mechanistic studies in mouse models of breast cancer. We observe an increase in systemic and intratumoral eosinophils in patients and mice responding to ICB treatment. Mechanistically, ICB increased IL-5 production by CD4⁺ T cells, stimulating elevated eosinophil production from the bone marrow, leading to systemic eosinophil expansion. Additional induction of IL-33 by ICB-cisplatin combination or recombinant IL-33 promotes intratumoral eosinophil infiltration and eosinophil-dependent CD8⁺ T cell activation to enhance ICB response. This work demonstrates the critical role of eosinophils in ICB response and provides proof-of-principle for eosinophil engagement to enhance ICB efficacy.

Neoadjuvant immune checkpoint blockade triggers persistent and systemic Treg activation which blunts therapeutic efficacy against metastatic spread of breast tumors

The clinical successes of immune checkpoint blockade (ICB) in advanced cancer patients have recently spurred the clinical implementation of ICB in the neoadjuvant and perioperative setting. However, how neoadjuvant ICB therapy affects the systemic immune landscape and metastatic spread remains to be established. Tumors promote both local and systemic expansion of regulatory T cells (T_regs), which are key orchestrators of tumor-induced immunosuppression, contributing to immune evasion, tumor progression and metastasis. T_regs express inhibitory immune checkpoint molecules and thus may be unintended targets for ICB therapy counteracting its efficacy. Using ICB-refractory models of spontaneous primary and metastatic breast cancer that recapitulate the poor ICB response of breast cancer patients, we observed that combined anti-PD-1 and anti-CTLA-4 therapy inadvertently promotes proliferation and activation of T_regs in the tumor, tumor-draining lymph node and circulation. Also in breast cancer patients, T_reg levels were elevated upon ICB. Depletion of T_regs during neoadjuvant ICB in tumor-bearing mice not only reshaped the intratumoral immune landscape into a state favorable for ICB response but also induced profound and persistent alterations in systemic immunity, characterized by elevated CD8+ T cells and NK cells and durable T cell activation that was maintained after treatment cessation. While depletion of T_regs in combination with neoadjuvant ICB did not inhibit primary tumor growth, it prolonged metastasis-related survival driven predominantly by CD8+ T cells. This study demonstrates that neoadjuvant ICB therapy of breast cancer can be empowered by simultaneous targeting of T_regs, extending metastasis-related survival, independent of a primary tumor response.

Spatiotemporal co-dependency between macrophages and exhausted CD8+ T cells in cancer

T cell exhaustion is a major impediment to antitumor immunity. However, it remains elusive how other immune cells in the tumor microenvironment (TME) contribute to this dysfunctional state. Here, we show that the biology of tumor-associated macrophages (TAMs) and exhausted T cells (T_ex) in the TME is extensively linked. We demonstrate that in vivo depletion of TAMs reduces exhaustion programs in tumor-infiltrating CD8⁺ T cells and reinvigorates their effector potential. Reciprocally, transcriptional and epigenetic profiling reveals that T_ex express factors that actively recruit monocytes to the TME and shape their differentiation. Using lattice light sheet microscopy, we show that TAM and CD8⁺ T cells engage in unique, long-lasting, antigen-specific synaptic interactions that fail to activate T cells but prime them for exhaustion, which is then accelerated in hypoxic conditions. Spatially resolved sequencing supports a spatiotemporal self-enforcing positive feedback circuit that is aligned to protect rather than destroy a tumor.

ZipSeq: barcoding for real-time mapping of single cell transcriptomes

Spatial transcriptomics seeks to integrate single cell transcriptomic data within the three-dimensional space of multicellular biology. Current methods to correlate a cell's position with its transcriptome in living tissues have various limitations. We developed an approach, called 'ZipSeq', that uses patterned illumination and photocaged oligonucleotides to serially print barcodes ('zipcodes') onto live cells in intact tissues, in real time and with an on-the-fly selection of patterns. Using ZipSeq, we mapped gene expression in three settings: in vitro wound healing, live lymph node sections and a live tumor microenvironment. In all cases, we discovered new gene expression patterns associated with histological structures. In the tumor microenvironment, this demonstrated a trajectory of myeloid and T cell differentiation from the periphery inward. A combinatorial variation of ZipSeq efficiently scales in the number of regions defined, providing a pathway for complete mapping of live tissues, subsequent to real-time imaging or perturbation.

Response of metastatic mouse invasive lobular carcinoma to mTOR inhibition is partly mediated by the adaptive immune system

Effective treatment of invasive lobular carcinoma (ILC) of the breast is hampered by late detection, invasive growth, distant metastasis, and poor response to chemotherapy. Phosphoinositide 3-kinase (PI3K) signaling, one of the major druggable oncogenic signaling networks, is frequently activated in ILC. We investigated treatment response and resistance to AZD8055, an inhibitor of mammalian target of rapamycin (mTOR), in the K14-cre;Cdh1^Flox/Flox;Trp53^Flox/Flox (KEP) mouse model of metastatic ILC. Inhibition of mTOR signaling blocked the growth of primary KEP tumors as well as the progression of metastatic disease. However, primary tumors and distant metastases eventually acquired resistance after long-term AZD8055 treatment, despite continued effective suppression of mTOR signaling in cancer cells. Interestingly, therapeutic responses were associated with increased expression of genes related to antigen presentation. Consistent with this observation, increased numbers of tumor-infiltrating major histocompatibility complex class II-positive (MHCII+) immune cells were observed in treatment-responsive KEP tumors. Acquisition of treatment resistance was associated with loss of MHCII+ cells and reduced expression of genes related to the adaptive immune system. The therapeutic efficacy of mTOR inhibition was reduced in Rag1^−/- mice lacking mature T and B lymphocytes, compared to immunocompetent mice. Furthermore, therapy responsiveness could be partially rescued by transplanting AZD8055-resistant KEP tumors into treatment-naïve immunocompetent hosts. Collectively, these data indicate that the PI3K signaling pathway is an attractive therapeutic target in invasive lobular carcinoma, and that part of the therapeutic effect of mTOR inhibition is mediated by the adaptive immune system.

Unleashing Type-2 Dendritic Cells to Drive Protective Antitumor CD4+ T Cell Immunity

Differentiation of proinflammatory CD4⁺ conventional T cells (T_conv) is critical for productive antitumor responses yet their elicitation remains poorly understood. We comprehensively characterized myeloid cells in tumor draining lymph nodes (tdLN) of mice and identified two subsets of conventional type-2 dendritic cells (cDC2) that traffic from tumor to tdLN and present tumor-derived antigens to CD4⁺ T_conv, but then fail to support antitumor CD4⁺ T_conv differentiation. Regulatory T cell (T_reg) depletion enhanced their capacity to elicit strong CD4⁺ T_conv responses and ensuing antitumor protection. Analogous cDC2 populations were identified in patients, and as in mice, their abundance relative to T_reg predicts protective ICOS⁺ PD-1^lo CD4⁺ T_conv phenotypes and survival. Further, in melanoma patients with low T_reg abundance, intratumoral cDC2 density alone correlates with abundant CD4⁺ T_conv and with responsiveness to anti-PD-1 therapy. Together, this highlights a pathway that restrains cDC2 and whose reversal enhances CD4⁺ T_conv abundance and controls tumor growth.

Therapeutic targeting of macrophages enhances chemotherapy efficacy by unleashing type I interferon response

Recent studies have revealed a role for macrophages and neutrophils in limiting chemotherapy efficacy; however, the mechanisms underlying the therapeutic benefit of myeloid-targeting agents in combination with chemotherapy are incompletely understood. Here, we show that targeting tumour-associated macrophages by colony-stimulating factor-1 receptor (CSF-1R) blockade in the K14cre;Cdh1^F/F;Trp53^F/F transgenic mouse model for breast cancer stimulates intratumoural type I interferon (IFN) signalling, which enhances the anticancer efficacy of platinum-based chemotherapeutics. Notably, anti-CSF-1R treatment also increased intratumoural expression of type I IFN-stimulated genes in patients with cancer, confirming that CSF-1R blockade is a powerful strategy to trigger an intratumoural type I IFN response. By inducing an inflamed, type I IFN-enriched tumour microenvironment and by further targeting immunosuppressive neutrophils during cisplatin therapy, antitumour immunity was activated in this poorly immunogenic breast cancer mouse model. These data illustrate the importance of breaching multiple layers of immunosuppression during cytotoxic therapy to successfully engage antitumour immunity in breast cancer.

The Space Physics Environment Data Analysis System (SPEDAS)

With the advent of the Heliophysics/Geospace System Observatory (H/GSO), a complement of multi-spacecraft missions and ground-based observatories to study the space environment, data retrieval, analysis, and visualization of space physics data can be daunting. The Space Physics Environment Data Analysis System (SPEDAS), a grass-roots software development platform (www.spedas.org), is now officially supported by NASA Heliophysics as part of its data environment infrastructure. It serves more than a dozen space missions and ground observatories and can integrate the full complement of past and upcoming space physics missions with minimal resources, following clear, simple, and well-proven guidelines. Free, modular and configurable to the needs of individual missions, it works in both command-line (ideal for experienced users) and Graphical User Interface (GUI) mode (reducing the learning curve for first-time users). Both options have "crib-sheets," user-command sequences in ASCII format that can facilitate record-and-repeat actions, especially for complex operations and plotting. Crib-sheets enhance scientific interactions, as users can move rapidly and accurately from exchanges of technical information on data processing to efficient discussions regarding data interpretation and science. SPEDAS can readily query and ingest all International Solar Terrestrial Physics (ISTP)-compatible products from the Space Physics Data Facility (SPDF), enabling access to a vast collection of historic and current mission data. The planned incorporation of Heliophysics Application Programmer's Interface (HAPI) standards will facilitate data ingestion from distributed datasets that adhere to these standards. Although SPEDAS is currently Interactive Data Language (IDL)-based (and interfaces to Java-based tools such as Autoplot), efforts are under-way to expand it further to work with python (first as an interface tool and potentially even receiving an under-the-hood replacement). We review the SPEDAS development history, goals, and current implementation. We explain its "modes of use" with examples geared for users and outline its technical implementation and requirements with software developers in mind. We also describe SPEDAS personnel and software management, interfaces with other organizations, resources and support structure available to the community, and future development plans.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (10.1007/s11214-018-0576-4) contains supplementary material, which is available to authorized users.

Assessment of PD-L1 expression across breast cancer molecular subtypes, in relation to mutation rate, BRCA1-like status, tumor-infiltrating immune cells and survival

To better understand the expression pattern of programmed death-ligand 1 (PD-L1) expression in different breast cancer types, we characterized PD-L1 expression in tumor and tumor-infiltrating immune cells, in relation to mutation rate, BRCA1-like status and survival. We analyzed 410 primary treatment-naive breast tumors comprising 162 estrogen receptor-positive (ER+) and HER2-, 101 HER2+ and 147 triple-negative (TN) cancers. Pathologists quantified tumor-infiltrating lymphocytes (TILs) and PD-L1 expression in tumor cells and TILs using whole slides and tissue microarray. Mutation rate was assessed by DNA sequencing, BRCA1-like status using multiplex ligation-dependent probe amplification, and immune landscape by multiplex image analyses of CD4, CD68, CD8, FOXP3, cytokeratin, and PD-L1. Half of PD-L1 scores evaluated by tissue microarray were false negatives compared to whole slide evaluations. We observed at least 1% of PD-L1-positive (PD-L1+) cells in 53.1% of ER+HER2-, 73.3% of HER2+, and 84.4% of TN tumors. PD-L1 expression was higher in ductal compared to lobular carcinomas, also within ER+HER2- tumors (p = 0.04). High PD-L1+ TILs score (> 50%) was independently associated with better outcome in TN tumors (HR = 0.27; 95%CI = 0.10-0.69). Within TN tumors, PD-L1 and TIL scores showed a modest but significant positive association with the number of silent mutations, but no association with BRCA1-like status. Multiplex image analyses indicated that PD-L1 is expressed on multiple immune cells (CD68+ macrophages, CD4+, FOXP3+, and CD8+ T cells) in the breast tumor microenvironment, independent of the PD-L1 status of the tumor cells. We found no evidence that levels of PD-L1+ TILs in TN breast cancer are driven by high mutation rate or BRCA1-like status.

Understanding the tumor immune microenvironment (TIME) for effective therapy

The clinical successes in immunotherapy have been both astounding and at the same time unsatisfactory. Countless patients with varied tumor types have seen pronounced clinical response with immunotherapeutic intervention; however, many more patients have experienced minimal or no clinical benefit when provided the same treatment. As technology has advanced, so has the understanding of the complexity and diversity of the immune context of the tumor microenvironment and its influence on response to therapy. It has been possible to identify different subclasses of immune environment that have an influence on tumor initiation and response and therapy; by parsing the unique classes and subclasses of tumor immune microenvironment (TIME) that exist within a patient's tumor, the ability to predict and guide immunotherapeutic responsiveness will improve, and new therapeutic targets will be revealed.

Genetically engineered mouse models in oncology research and cancer medicine

Genetically engineered mouse models (GEMMs) have contributed significantly to the field of cancer research. In contrast to cancer cell inoculation models, GEMMs develop de novo tumors in a natural immune‐proficient microenvironment. Tumors arising in advanced GEMMs closely mimic the histopathological and molecular features of their human counterparts, display genetic heterogeneity, and are able to spontaneously progress toward metastatic disease. As such, GEMMs are generally superior to cancer cell inoculation models, which show no or limited heterogeneity and are often metastatic from the start. Given that GEMMs capture both tumor cell‐intrinsic and cell‐extrinsic factors that drive de novo tumor initiation and progression toward metastatic disease, these models are indispensable for preclinical research. GEMMs have successfully been used to validate candidate cancer genes and drug targets, assess therapy efficacy, dissect the impact of the tumor microenvironment, and evaluate mechanisms of drug resistance. In vivo validation of candidate cancer genes and therapeutic targets is further accelerated by recent advances in genetic engineering that enable fast‐track generation and fine‐tuning of GEMMs to more closely resemble human patients. In addition, aligning preclinical tumor intervention studies in advanced GEMMs with clinical studies in patients is expected to accelerate the development of novel therapeutic strategies and their translation into the clinic.

Abstract 575: PD-L1 positive tumor-infiltrating lymphocytes and mutational load in breast cancer

Background: PD-1 blockade has emerged as an effective treatment for a subset of cancer patients. Studies have shown that PD-L1 expression is associated with likelihood of response to PD-1 blockade. In order to select the right breast cancer patient for immunotherapy, characterization of the immune landscape of breast tumors is required. Therefore, we assessed PD-L1 expression and tumor-infiltrating lymphocytes (TILs) in different breast tumor subtypes and the link with prognosis. We also sequenced a panel of genes to assess the mutational load in triple negative tumors (TNBC) and investigate the association with PD-L1 positive TILs.

Material and methods: We analyzed 438 tumor samples from breast cancer patients of all ages treated between 1986 and 2007 with surgery, with or without adjuvant therapy. PD-L1 was stained using whole slide specimens (E1L3N® antibody) after methodological validation. Pathologists quantified TILs based on International TILs Working Group recommendations and scored PD-L1 based on the percentage of positive (tumor and/or immune) cells; as negative if 0%, positive if ≥1%, and high if >50%. Mutational load was assessed based on DNA kinome sequencing. Associations were measured by Cox/logistic regression model, including pathological variables. Multiplex imaging of 20 immune-infiltrated areas from four ER negative tumors were performed using the Vectra® system based on immunofluorescence staining panel of: CD4, CD68, CD8, FOXP3 and PD-L1.

Results: PD-L1 expression and TILs were higher in ductal (compared with lobular), high grade and estrogen receptor (ER)-negative tumors (p<0.001). TILs (density ≥5%) were significantly associated with worse distant metastasis-free survival (DMFS) only in ER-positive tumors (n=204): HR=2.72; 95%CI: 1.07-6.94. PD-L1 positivity (≥1%) followed the same trend: HR=1.66; 95%CI: 0.87-3.15. However, in ER-negative tumors (n=171), high PD-L1 expression (>50%) was significantly associated with better DMFS: HR=0.51; 95%CI: 0.27-0.98. TNBC with high PD-L1 expression of TILs (>50%) showed an association with increased mutation load (p=0.019) and a trend for better DMFS (HR=0.41; 95%CI: 0.16-1.04) compared with tumors lacking TILs. Further characterization of PD-L1 positivity in the immune-infiltrated cells was conducted by a multiplex imaging analysis. Preliminary results indicated that PD-L1 is expressed in CD68+, CD4+, FOXP3+ and CD8+ immune-cells.

Conclusion: Our findings suggest that PD-L1 positive TILs are associated with worse prognosis in ER-positive breast cancer and with better outcome in ER-negative group. In TNBC, high mutational load correlates with high PD-L1 positive TILs.

Citation Format: Marcelo Sobral-Leite, Koen Van de Vijver, Magali Michaut, Hugo M. Horlings, Tesa M. Severson, Philip C. Schouten, Rianne van der Linden, Kelly Kersten, Anna Marie Mulligan, Nayana Weerasooriya, Joyce Sanders, Ashley Cimino-Mathews, Dennis Peters, Gerrit K. Hooijer, Erik Hooijberg, Annegien Broeks, Rene Bernards, Sabine Linn, Irene L. Andrulis, Marc J. van de Vijver, Lodewyk F. Wessels, Marleen Kok, Karin E. de Visser, Marjanka K. Schmidt. PD-L1 positive tumor-infiltrating lymphocytes and mutational load in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 575. doi:10.1158/1538-7445.AM2017-575

Mammary tumor-derived CCL2 enhances pro-metastatic systemic inflammation through upregulation of IL1β in tumor-associated macrophages

Patients with primary solid malignancies frequently exhibit signs of systemic inflammation. Notably, elevated levels of neutrophils and their associated soluble mediators are regularly observed in cancer patients, and correlate with reduced survival and increased metastasis formation. Recently, we demonstrated a mechanistic link between mammary tumor-induced IL17-producing γδ T cells, systemic expansion of immunosuppressive neutrophils and metastasis formation in a genetically engineered mouse model for invasive breast cancer. How tumors orchestrate this systemic inflammatory cascade to facilitate dissemination remains unclear. Here we show that activation of this cascade relies on CCL2-mediated induction of IL1β in tumor-associated macrophages. In line with these findings, expression of CCL2 positively correlates with IL1Β and macrophage markers in human breast tumors. We demonstrate that blockade of CCL2 in mammary tumor-bearing mice results in reduced IL17 production by γδ T cells, decreased neutrophil expansion and enhanced CD8⁺ T cell activity. These results highlight a new role for CCL2 in facilitating the breast cancer-induced pro-metastatic systemic inflammatory γδ T cell – IL17 – neutrophil axis.

Abstract A20: Mammary tumor-derived CCL2 enhances pro-metastatic systemic inflammation through upregulation of macrophage-derived IL1beta

Metastatic breast cancer remains a major cause of cancer-related death among women. Metastasis is regulated by extensive crosstalk between cancer cells and immune cells. Besides the onset of a local inflammatory microenvironment, tumors frequently induce a systemic inflammatory state characterized by the release of various cytokines, chemokines and growth factors to mobilize myeloid cells that support metastasis, emphasizing the notion that cancer should be regarded as a systemic disease. Utilizing the K14cre;Cdh1F/F;Trp53F/F (KEP) conditional mouse model of metastatic breast cancer, we have recently unraveled a novel mechanistic link between mammary tumor-induced IL17-producing gamma delta T cells, systemic expansion of immunosuppressive neutrophils and metastasis formation. We identified tumor-derived IL1beta as one of the drivers of this cascade by inducing IL17 release from gamma delta T cells. However, it remains unclear how other inflammatory mediators are involved in this systemic inflammatory cascade. In the current study, we identified the pro-inflammatory cytokine CCL2 as a key regulator of the gamma delta T cell IL17 neutrophil axis. CCL2 blockade resulted in reduced IL17-production by gamma delta T cells, decreased systemic neutrophil accumulation and enhanced CD8+ T cell activity. We show that activation of this cascade relies on CCL2-mediated release of IL1beta from CCR2+ tumor-associated macrophages. These results indicate that CCL2, via IL1beta, acts as a key player in regulating the pro-metastatic gamma delta T cell IL17 neutrophil systemic inflammatory cascade and might be an interesting candidate for therapeutic targeting.

Citation Format: Kelly Kersten, Seth B. Coffelt, Niels J. Verstegen, Kim Vrijland, Metamia Ciampricotti, Chris W. Doornebal, Cheei-Sing Hau, Parul Doshi, Karin E. de Visser. Mammary tumor-derived CCL2 enhances pro-metastatic systemic inflammation through upregulation of macrophage-derived IL1beta. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr A20.

Abstract IA04: Cancer-associated systemic inflammation facilitates breast cancer metastasis

Over 90% of breast cancer deaths are due to complications as a consequence of metastasis formation. Despite its devastating effects, metastatic disease is still poorly understood. Accumulating evidence indicates that cells and mediators of the immune system influence metastasis formation. In our lab, we use preclinical mouse models for metastatic breast cancer to dissect the impact of the immune system on the different steps of the metastatic cascade. Neutrophils make up a significant proportion of the inflammatory infiltrate in many tumors and their systemic accumulation in cancer patients has been associated with metastasis formation. Also in our recently developed spontaneous breast cancer metastasis mouse model that accurately mimics each step of the metastatic cascade in humans, metastasis formation is accompanied by pronounced systemic accumulation of neutrophils. Antibody-mediated depletion of neutrophils did not affect primary breast cancer outgrowth, but profoundly decreased spontaneous metastasis formation in lungs and lymph nodes. Using biological and genetic approaches, we have uncovered a novel mammary tumor-induced systemic communication network between gamma delta T cells and neutrophils that is critical for breast cancer metastasis. Our data indicate that targeting this novel cancer cell-initiated systemic inflammatory cascade represents a viable strategy to inhibit metastatic disease.

Citation Format: Seth B. Coffelt, Kelly Kersten, Max Wellenstein, Chris W. Doornebal, Camilla Salvagno, Kim Vrijland, Cheei-Sing Hau, Jos Jonkers, Karin E. de Visser. Cancer-associated systemic inflammation facilitates breast cancer metastasis. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr IA04.

Exploiting the Immunomodulatory Properties of Chemotherapeutic Drugs to Improve the Success of Cancer Immunotherapy

Cancer immunotherapy is gaining momentum in the clinic. The current challenge is to understand why a proportion of cancer patients do not respond to cancer immunotherapy, and how this can be translated into the rational design of combinatorial cancer immunotherapy strategies aimed at maximizing success of immunotherapy. Here, we discuss how tumors orchestrate an immunosuppressive microenvironment, which contributes to their escape from immune attack. Relieving the immunosuppressive networks in cancer patients is an attractive strategy to extend the clinical success of cancer immunotherapy. Since the clinical availability of drugs specifically targeting immunosuppressive cells or mediators is still limited, an alternative strategy is to use conventional chemotherapy drugs with immunomodulatory properties to improve cancer immunotherapy. We summarize the preclinical and clinical studies that illustrate how the anti-tumor T cell response can be enhanced by chemotherapy-induced relief of immunosuppressive networks. Treatment strategies aimed at combining chemotherapy-induced relief of immunosuppression and T cell-boosting checkpoint inhibitors provide an attractive and clinically feasible approach to overcome intrinsic and acquired resistance to cancer immunotherapy, and to extend the clinical success of cancer immunotherapy.

Adaptive Immune Regulation of Mammary Postnatal Organogenesis

Postnatal organogenesis occurs in an immune competent environment and is tightly controlled by interplay between positive and negative regulators. Innate immune cells have beneficial roles in postnatal tissue remodeling, but roles for the adaptive immune system are currently unexplored. Here we show that adaptive immune responses participate in the normal postnatal development of a non-lymphoid epithelial tissue. Since the mammary gland (MG) is the only organ developing predominantly after birth, we utilized it as a powerful system to study adaptive immune regulation of organogenesis. We found that antigen-mediated interactions between mammary antigen-presenting cells and interferon-γ (IFNγ)-producing CD4+ T helper 1 cells participate in MG postnatal organogenesis as negative regulators, locally orchestrating epithelial rearrangement. IFNγ then affects luminal lineage differentiation. This function of adaptive immune responses, regulating normal development, changes the paradigm for studying players of postnatal organogenesis and provides insights into immune surveillance and cancer transformation.

IL-17-producing γδ T cells and neutrophils conspire to promote breast cancer metastasis

Metastatic disease remains the primary cause of death for patients with breast cancer. The different steps of the metastatic cascade rely on reciprocal interactions between cancer cells and their microenvironment. Within this local microenvironment and in distant organs, immune cells and their mediators are known to facilitate metastasis formation. However, the precise contribution of tumour-induced systemic inflammation to metastasis and the mechanisms regulating systemic inflammation are poorly understood. Here we show that tumours maximize their chance of metastasizing by evoking a systemic inflammatory cascade in mouse models of spontaneous breast cancer metastasis. We mechanistically demonstrate that interleukin (IL)-1β elicits IL-17 expression from gamma delta (γδ) T cells, resulting in systemic, granulocyte colony-stimulating factor (G-CSF)-dependent expansion and polarization of neutrophils in mice bearing mammary tumours. Tumour-induced neutrophils acquire the ability to suppress cytotoxic T lymphocytes carrying the CD8 antigen, which limit the establishment of metastases. Neutralization of IL-17 or G-CSF and absence of γδ T cells prevents neutrophil accumulation and downregulates the T-cell-suppressive phenotype of neutrophils. Moreover, the absence of γδ T cells or neutrophils profoundly reduces pulmonary and lymph node metastases without influencing primary tumour progression. Our data indicate that targeting this novel cancer-cell-initiated domino effect within the immune system--the γδ T cell/IL-17/neutrophil axis--represents a new strategy to inhibit metastatic disease.

Abstract IA07: Cancer-associated inflammation facilitates metastatic breast cancer and counteracts chemoresponsiveness

Over 90% of breast cancer deaths are due to complications as a consequence of metastasis formation. Much progress has been made in understanding primary breast cancer formation; however, metastatic disease is still largely unexplored, poorly understood and incurable. Clearly, there is an urgent need for novel therapies with efficacious anti-metastatic activity. The different steps of the metastatic cascade are largely regulated by reciprocal interactions between cancer cells and their microenvironment. Accumulating evidence indicates that cells and mediators of the immune system can facilitate metastasis formation. To mechanistically study how immune cells and their mediators modulate breast cancer metastasis, we have recently developed a mouse model of spontaneous breast cancer metastasis that mimics the clinical course of metastatic disease in humans. The basis is the K14cre;EcadF/F;p53F/F transgenic mouse that develops breast cancer resembling human invasive lobular carcinoma. We orthotopically transplant invasive lobular carcinoma fragments from these mice into mammary glands of wild-type syngeneic mice. Once primary tumors are established, we mimic the clinical setting and perform a mastectomy. Following surgery, the mice develop clinically overt metastases in lymph nodes, lungs, liver and other distant organs. This novel mouse model of breast cancer metastasis accurately mimics each step of the metastatic cascade in humans. It provides a unique tool to further explore the biology of metastatic breast cancer with the aim to contribute to the development of more effective treatment strategies.

Neutrophils make up a significant proportion of the inflammatory infiltrate in many tumors and their accumulation in breast cancer patients has been associated with metastasis formation. Also in our spontaneous breast cancer metastasis mouse model, metastasis formation is accompanied by a very pronounced accumulation of neutrophils in circulation and distant organs. Antibody-mediated depletion of neutrophils did not affect primary breast cancer outgrowth, but did result in a profound decrease in lung and lymph node metastasis. Using biological and genomic approaches, we have uncovered a novel communication network between gamma delta T cells and neutrophils that is critical for breast cancer metastasis. We are currently dissecting the mechanisms by which neutrophils facilitate breast cancer metastasis formation.

Besides regulating metastatic disease, the immune system also modulates responsiveness of cancer to conventional forms of therapy. Using the K14cre;EcdF/F;p53F/F mouse mammary tumor model, we study the ability of the immune system to influence the anti-cancer efficacy of chemotherapy. We have observed that it is very important to optimally match chemotherapeutic drugs with immunomodulatory compounds. In addition, combining chemotherapy with an immunomodulatory drug can trigger a rewiring of the inflammatory tumor microenvironment resulting in immune-dependent therapy resistance. Taken together, through mechanistic understanding of the crosstalk between the immune system and cancer, we aim to contribute to the design of novel immunomodulatory strategies to fight metastatic breast cancer and to increase the efficacy of conventional anti-cancer therapies.

(Supported by the Dutch Cancer Society grant 2011-5004, NWO/VIDI 91796307, AICR 11-0677 and FP7 MCA-ITN 317445)

Citation Format: Seth B. Coffelt, Chris W. Doornebal, Metamia Ciampricotti, Camilla Salvagno, Kelly Kersten, Kim Vrijland, Cheei-Sing Hau, Jos Jonkers, Karin E. De Visser. Cancer-associated inflammation facilitates metastatic breast cancer and counteracts chemoresponsiveness. [abstract]. In: Abstracts: AACR Special Conference on Cellular Heterogeneity in the Tumor Microenvironment; 2014 Feb 26-Mar 1; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(1 Suppl):Abstract nr IA07. doi:10.1158/1538-7445.CHTME14-IA07

Abstract A083: Neutrophils promote metastasis of invasive lobular carcinoma

The multistep process of metastasis is highly dependent on the intrinsic mutations that accumulate in cancer cells. However, recent experimental evidence has shown that these mutations are not sufficient to facilitate metastatic disease. Cues from the tumor microenvironment are also required. In order to understand how systemic changes might affect metastasis formation, we profiled the cellular and molecular alterations in various organs of K14cre;EcdF/F;p53F/F mammary tumor-bearing mice – a model of invasive lobular breast cancer. Among all immune cells, increased neutrophil accumulation was the most pronounced. To test the functional importance of neutrophils in the metastatic process, we utilized our recently described model of spontaneous metastasis. This model is based on the transplantation of K14cre;EcdF/F;p53F/F tumor pieces into wild-type recipient mice, and subsequent surgical removal of the primary tumor, permitting us to investigate neutrophil function in both the neoadjuvant and adjuvant settings. Interestingly, mice treated with neutrophil-depleting antibodies in the neoadjuvant setting displayed a profound reduction in pulmonary metastasis, whereas metastases in the adjuvant group were equivalent to controls. These data indicate that neutrophils play a prominent role during the very early stages of the metastatic cascade. Our preliminary data suggest that these tumor-educated neutrophils can suppress the activation of T cells, as one mechanism by which they may promote metastasis. In addition, cytokine analysis of K14cre;EcdF/F;p53F/F mammary tumors demonstrated an increase in the IL17 pathway when compared to wild-type mammary glands. Subsets of T cells are known producers of IL17 and this pathway regulates neutrophil expansion indirectly. In accordance with this, K14cre;EcdF/F;p53F/F mice lacking the adaptive immune system displayed reduced IL17 levels and reduced circulating neutrophils. Current efforts are underway to determine whether T cells play a role in the pro-metastatic function of neutrophils. Together, these findings indicate that neutrophils are crucial for the establishment of breast cancer metastasis.

Citation Format: Seth B. Coffelt, Chris W. Doornebal, Kelly Kersten, Metamia Ciampricotti, Cheei-Sing Hau, Kim Vrijland, Jorieke Weiden, Jos Jonkers, Karin E. de Visser. Neutrophils promote metastasis of invasive lobular carcinoma. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A083.

Abstract A96: The impact of the inflammatory microenvironment on breast cancer metastasis and chemotherapy responsiveness

After decades of research, breast cancer still remains the leading cause of cancer mortality in women. The majority of these breast cancer deaths is due to metastasis, which is still poorly understood and incurable. Recently it has been appreciated that the tumor microenvironment plays a significant role in both tumor progression and response to chemotherapy. However, its role in metastasis formation is still largely unclear. In this project we focus on the role of the inflammatory microenvironment on metastatic breast cancer and chemotherapy responsiveness.

In our research we make use of the conditional K14cre;EcdF/F;P53F/F breast cancer mouse model that spontaneously develops mammary tumors resembling human invasive lobular carcinomas (ILC). These tumors reside in an inflammatory microenvironment which is characterized by expression of inflammatory cytokines resulting in infiltration of large numbers of immune cells. About 50% of K14cre;EcdF/F;P53F/F animals develop micrometastases in distant organs like lung, lymph node and spleen, however they do not succumb to metastatic disease. We hypothesize that the inflammatory tumor microenvironment plays a role in breast cancer metastasis formation and possibly in chemotherapy efficacy. Exploiting the K14cre;EcdF/F;P53F/F model, mouse ILC (mILC) pieces are transplanted into the 4th mammary gland of wild type recipient mice. Tumors are allowed to grow to a specific size upon which a mastectomy is performed mimicking the clinical situation. Mice are sacrificed as soon as they show clinical signs of metastatic disease. This transplantable model allows us to study the effect of the microenvironment on breast cancer metastasis and chemotherapy responsiveness in two distinct settings: a neo-adjuvant setting (treatment targeting primary tumor growth) and an adjuvant setting (treatment after mastectomy specifically targeting metastatic outgrowth). Using this model we set out to study the effect of the inflammatory microenvironment in breast cancer metastasis formation and chemotherapy responsiveness. We found that neo-adjuvant chemotherapy treatment resulted in a significant delay of primary tumor growth. As a result, metastasis-free survival was significantly increased compared to controls. Also adjuvant chemotherapy treatment resulted in a survival benefit compared to controls. We are currently studying the effect of inflammatory cytokine inhibition on chemotherapy responsiveness and formation of distant metastases. Therefore we are analyzing different populations of immune cells in the inflammatory tumor microenvironment by flow cytometry. Subsequently, we are looking into the pattern of metastasis formation throughout the body. This research is funded by the Dutch Cancer Society; 2011-5004.

Citation Format: Kelly Kersten, Metamia Ciampricotti, Chris W. Doornebal, Cheei-Sing Hau, Seth B. Coffelt, Karin de Visser. The impact of the inflammatory microenvironment on breast cancer metastasis and chemotherapy responsiveness. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr A96.

Waves in interplanetary shocks: a wind/WAVES study

We describe results from the first statistical study of waveform capture data during 67 interplanetary (IP) shocks with Mach numbers ranging from approximately 1-6. Most of the waveform captures and nearly 100% of the large amplitude waves were in the ramp region. Although solitary waves, Langmuir waves, and ion acoustic waves (IAWs) are all observed in the ramp region of the IP shocks, large amplitude IAWs dominate. The wave amplitude is correlated with the fast mode Mach number and with the shock strength. The observed waves produced anomalous resistivities from approximately 1-856 Omega.m (approximately 10(7) times greater than classical estimates.) The results are consistent with theory suggesting IAWs provide the primary dissipation for low Mach number shocks.