Miranda Broz

STAT3 Establishes an Immunosuppressive Microenvironment during the Early Stages of Breast Carcinogenesis to Promote Tumor Growth and Metastasis

Immunosurveillance constitutes the first step of cancer immunoediting in which developing malignant lesions are eliminated by antitumorigenic immune cells. However, the mechanisms by which neoplastic cells induce an immunosuppressive state to evade the immune response are still unclear. The transcription factor STAT3 has been implicated in breast carcinogenesis and tumor immunosuppression in advanced disease, but its involvement in early disease development has not been established. Here, we genetically ablated Stat3 in the tumor epithelia of the inducible PyVmT mammary tumor model and found that Stat3-deficient mice recapitulated the three phases of immunoediting: elimination, equilibrium, and escape. Pathologic analyses revealed that Stat3-deficient mice initially formed hyperplastic and early adenoma-like lesions that later completely regressed, thereby preventing the emergence of mammary tumors in the majority of animals. Furthermore, tumor regression was correlated with massive immune infiltration into the Stat3-deficient lesions, leading to their elimination. In a minority of animals, focal, nonmetastatic Stat3-deficient mammary tumors escaped immune surveillance after a long latency or equilibrium period. Taken together, our findings suggest that tumor epithelial expression of Stat3 plays a critical role in promoting an immunosuppressive tumor microenvironment during breast tumor initiation and progression, and prompt further investigation of Stat3-inhibitory strategies that may reactivate the immunosurveillance program.

The Emerging Understanding of Myeloid Cells as Partners and Targets in Tumor Rejection

Myeloid cells are the most prominent among cells capable of presenting tumor-derived antigens to T cells and thereby maintaining the latter in an activated state. Myeloid populations of the tumor microenvironment prominently include monocytes and neutrophils (sometimes loosely grouped as myeloid-derived suppressor cells), macrophages, and dendritic cells. Although intratumoral myeloid populations, as a whole, have long been considered nonstimulatory or suppressive, it has only recently been appreciated that not all tumor-infiltrating myeloid cells are made equal. Because of advances in high-dimensional flow cytometry as well as more robust transcriptional profiling, we now also understand that the subsets of the tumor-myeloid compartment are far more diverse and notably even contain a rare population of stimulatory dendritic cells. As all of these myeloid populations represent major T-cell–interacting partners for incoming tumor-reactive cytotoxic T lymphocytes, understanding the distinctions in their lineage and function reveals and guides numerous therapeutic avenues targeting these antigen-presenting cells. In this Cancer Immunology at the Crossroads overview, we review the recent progress in this rapidly evolving field and advance the hypothesis that the antigen-presenting compartment within tumor microenvironments may contain significant numbers of potent allies to be leveraged for immune-based tumor clearance. Cancer Immunol Res; 3(4); 313–9. ©2015 AACR.

Antitumor adaptive immunity remains intact following inhibition of autophagy and antimalarial treatment

The rising success of cancer immunotherapy has produced immense interest in defining the clinical contexts that may benefit from this therapeutic approach. To this end, there is a need to ascertain how the therapeutic modulation of intrinsic cancer cell programs influences the anticancer immune response. For example, the role of autophagy as a tumor cell survival and metabolic fitness pathway is being therapeutically targeted in ongoing clinical trials that combine cancer therapies with antimalarial drugs for the treatment of a broad spectrum of cancers, many of which will likely benefit from immunotherapy. However, our current understanding of the interplay between autophagy and the immune response remains incomplete. Here, we have evaluated how autophagy inhibition impacts the antitumor immune response in immune-competent mouse models of melanoma and mammary cancer. We observed equivalent levels of T cell infiltration and function within autophagy-competent and -deficient tumors, even upon treatment with the anthracycline chemotherapeutic doxorubicin. Similarly, we found equivalent T cell responses upon systemic treatment of tumor-bearing mice with antimalarial drugs. Our findings demonstrate that antitumor adaptive immunity is not adversely impaired by autophagy inhibition in these models, allowing for the future possibility of combining autophagy inhibitors with immunotherapy in certain clinical contexts.

A natural killer-dendritic cell axis defines checkpoint therapy-responsive tumor microenvironments.

Intratumoral stimulatory dendritic cells (SDCs) play an important role in stimulating cytotoxic T cells and driving immune responses against cancer. Understanding the mechanisms that regulate their abundance in the tumor microenvironment (TME) could unveil new therapeutic opportunities. We find that in human melanoma, SDC abundance is associated with intratumoral expression of the gene encoding the cytokine FLT3LG. FLT3LG is predominantly produced by lymphocytes, notably natural killer (NK) cells in mouse and human tumors. NK cells stably form conjugates with SDCs in the mouse TME, and genetic and cellular ablation of NK cells in mice demonstrates their importance in positively regulating SDC abundance in tumor through production of FLT3L. Although anti-PD-1 ‘checkpoint’ immunotherapy for cancer largely targets T cells, we find that NK cell frequency correlates with protective SDCs in human cancers, with patient responsiveness to anti-PD-1 immunotherapy, and with increased overall survival. Our studies reveal that innate immune SDCs and NK cells cluster together as an excellent prognostic tool for T cell–directed immunotherapy and that these innate cells are necessary for enhanced T cell tumor responses, suggesting this axis as a target for new therapies.Cross-talk between innate immune cells helps to enhance the antitumor T cell response during checkpoint blockade therapy.

Abstract A02: Stat3 plays a critical role in the establishment of immunosuppressive tumor microenvironment: Implications for tumor immunsurviellance and metastatic progression

Immune surveillance is thought to play a critical role in promoting the elimination of developing malignant lesions through activation of immune response. However, cancer cells eventually acquire the ability to escape immune surveillance by favoring recruitment of immune cell types that exert an inflammatory and immunosuppressive state. Despite the importance of immune surveillance, the molecular mechanisms that promote escape from immune remains poorly defined. Here we demonstrate that expression of the Stat3 transcription factor in the tumor epithelial is involved in promoting an immunosuppressive tumor microenvironment. To investigate the role of Stat3 in modulating the tumor immune-microenvironment, we ablated Stat3 in the tumor epithelia of an inducible PyV mT model of mammary tumor progression. Molecular and pathological analyses of tumor progression revealed that Stat3 deficient tumors were initially able to form hyperplastic and early adenoma–like lesions with no obvious impact on the proliferative or apoptotic status on these epithelial lesions. However, these early premalignant lesions completely regressed, thereby preventing the emergence of mammary tumors in the majority of animals. Tumor regression was correlated with a massive infiltration of T lymphocytes and F4/80 positive macrophages into Stat3 deficient lesions. However focal Stat3 deficient mammary tumors escaped immune surveillance after a long latency period in a minority of the affected animals. Our data argue that tumor epithelial expression of Stat3 plays a critical role in promoting an immune suppressive tumor microenvironment . Note: This abstract was not presented at the conference. Citation Format: Laura M. Jones, Miranda Broz, Jill Ranger, Josie Ursini-Siegel, Matthew Krummel, William J. Muller. Stat3 plays a critical role in the establishment of immunosuppressive tumor microenvironment: Implications for tumor immunsurviellance and metastatic progression. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr A02.

Abstract A098: A role for fibrosis in promoting pro-tumor immune response in breast cancer

We established a positive correlation between a fibrotic phenotype in human breast tumors — especially the Her2 and basal-like breast cancer subtypes — and CD45 and CD68 positive immune cell infiltration. We were interested in elucidating how this fibrotic phenotype may influence the immune response. To address this question, we examined if matrix stiffness alters the function of STAT3, a central regulator of tumor inflammation. We hypothesize that tissue fibrosis promotes STAT3 signaling in mammary tumor cells and alter the cytokine milieu to induce a pro-tumor immune response. We found that ECM stiffness directly enhanced STAT3 phosphorylation in tumor cells both in vitro and in vivo. Our data suggest the fibrotic phenotype promotes STAT3 activity, enhancement of which may drive a pro-tumor immune response. Indeed, we observed several alterations in cytokines and immune cell populations upon STAT3 ablation consistent with anti-tumor immune response. Interestingly, our data also suggest STAT3 knockout in tumor cells doesn9t necessary influence immune cell infiltration, but rather their differentiation in mammary tumors. Finally, we investigated if matrix stiffness has potentiated macrophage differentiation when cultured with specific immunosuppressive cytokines. Overall, our work reveals a novel mechanistic insight into how a pro-tumor immune response stems from the interplay between fibrosis and STAT3 signaling in tumor cells. As such, our findings may stimulate an interest in exploring combinational treatment options with anti-fibrotic agents and immunotherapy. Citation Format: Ori Maller, Luke Cassereau, Allison Drain, Brian Ruffell, Irene Acerbi, Miranda Broz, Jennifer Munson, Melody Swartz, Matthew Krummel, Lisa Coussens, Valerie Weaver. A role for fibrosis in promoting pro-tumor immune response in breast cancer [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A098.

Abstract IA32: Visualizing tumor immune interaction in real time

The nature of an immune response is rarely defined by a unanimous decisions by the participating cells; cells with seemingly opposing functions pervade many immune sites and tumors are no exception. Multiple DC and Macrophage subsets exert push/pull on T cell responses in tumors. Fundamentals of this are gleaned by live-imaging in connection with conventional methods such as flow-cytometry and immunofluorescence. Here, we broadly treat real-time imaging as a discovery tool to understand the tumor microenvironment (TME) and the diversity of cellular interactions that comprise host-tumor interactions. We have advanced this technology from sites of primary, spontaneous and aggressive tumors into sites of metastasis. The results promote the concept of seeking “allies” for tumor therapies within the TME and provide a basis for considering the balance of push/pull signals that determine the consensus immune response. Citation Format: Edward W. Roberts, Mark B. Headley, Miranda Broz, Bijan Boldjipour, Kaitlin Corbin, Mikhail Binnewies, Adriaan Bins, Audrey Audrey Gerard, Matthew Krummel. Visualizing tumor immune interaction in real time [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr IA32.

Abstract B65: Dissecting the tumor myeloid compartment reveals rare activating antigen presenting cells, critical for T cell immunity

Incoming tumor-reactive cytotoxic T lymphocytes (CTL) are modulated by innate immune cells of the tumor microenvironment and we have used intravital live-imaging to characterize the predominant T cell-APC interactions there. To further hone in on the identities of the APC populations, we have extensively examined myeloid subset diversity across multiple spontaneous (GEMM) and ectopic models. Importantly, as a functional counterpart to the abundant tumor infiltrating macrophages, we have identified a small population of rare tumoral Dendritic Cells capable of robust antigen processing and T cell stimulation. We have identified the specific lineage requirements of these cells, dissecting the essential cytokines driving each tumor APC population. In addition we have found that T-cell dependent immune clearance relies upon these rare tumoral Dendritic Cells. Thus, through the dissection of the tumor myeloid compartment we have revealed a rare, yet highly stimulatory and targetable DC subset that could be exploited therapeutically to enhance anti-tumor immune responses locally. This work is supported by the Genentech Foundation and the Margaret A. Cunningham Immune Mechanisms in Cancer Research Fellowship Award. Citation Format: Miranda Broz, Mikhail Binnewies, Bijan Boldajipour, Amanda Nelson, Joshua Pollock, David Erle, Andrea Barczak, Michael Rosenblum, Adil Daud, Diane Barber, Sebastian Amigorena, Laura J. van 9t Veer, Anne Sperling, Denise Wolf, Matthew F. Krummel. Dissecting the tumor myeloid compartment reveals rare activating antigen presenting cells, critical for T cell immunity. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr B65.