GPR15 Facilitates Recruitment of Regulatory T Cells to Promote Colorectal Cancer.

Colorectal cancer is one of the most frequent malignancies worldwide. Despite considerable progress in early detection and treatment, there is still an unmet need for novel antitumor therapies, particularly in advanced colorectal cancer. Regulatory T cells (Treg) are increased in the peripheral blood and tumor tissue of patients with colorectal cancer. Recently, transient ablation of tumor-associated Tregs was shown to foster CD8+ T-cell-mediated antitumoral immunity in murine colorectal cancer models. However, before considering therapies on targeting Tregs in patients with cancer, detailed knowledge of the phenotype and features of tumor-associated Tregs is indispensable. Here, we demonstrate in a murine model of inflammation-induced colorectal cancer that tumor-associated Tregs are mainly of thymic origin and equipped with a specific set of molecules strongly associated with enhanced migratory properties. Particularly, a dense infiltration of Tregs in mouse and human colorectal cancer lesions correlated with increased expression of the orphan chemoattractant receptor GPR15 on these cells. Comprehensive gene expression analysis revealed that tumor-associated GPR15+ Tregs have a Th17-like phenotype, thereby producing IL17 and TNFα. Gpr15 deficiency repressed Treg infiltration in colorectal cancer, which paved the way for enhanced antitumoral CD8+ T-cell immunity and reduced tumorigenesis. In conclusion, GPR15 represents a promising novel target for modifying T-cell-mediated antitumoral immunity in colorectal cancer. SIGNIFICANCE: The G protein-coupled receptor 15, an unconventional chemokine receptor, directs Tregs into the colon, thereby modifying the tumor microenvironment and promoting intestinal tumorigenesis.See related commentary by Chakraborty and Zappasodi, p. 2817.

The IL-33/ST2 pathway shapes the regulatory T cell phenotype to promote intestinal cancer.

The composition of immune infiltrates strongly affects the prognosis of patients with colorectal cancer (CRC). Interleukin (IL)-33 and regulatory T cells (Tregs) in the tumor microenvironment have been separately implicated in CRC; however their contribution to intestinal carcinogenesis is still controversial. Here, we reveal that IL-33 signaling promotes CRC by changing the phenotype of Tregs. In mice with CRC, tumor-infiltrating Tregs preferentially upregulate IL-33 receptor (ST2), and IL-33/ST2 signaling positively correlates with tumor number and size. Transcriptomic and flow cytometry analyses demonstrate that ST2 expression induces a more activated and migratory phenotype in FOXP3+ Tregs, which favors their accumulation in the tumor environment. Consequently, genetic ablation of St2 reduces Treg infiltration and concomitantly enhances the frequencies of effector CD8+ T cells, thereby restraining CRC. Mechanistically, IL-33 curtails IL-17 production by FOXP3+ Tregs and inhibits Th17 differentiation. In humans, numbers of activated ST2-expressing Tregs are increased in blood and tumor lesions of CRC patients, suggesting a similar mode of regulation. Together, these data indicate a central role of IL-33/ST2 signaling in shaping an immunosuppressive environment during intestinal tumorigenesis. Blockade of this pathway may provide a strategy to modulate the composition of CRC immune infiltrates.

Targeting CD47 in Anaplastic Thyroid Carcinoma Enhances Tumor Phagocytosis by Macrophages and Is a Promising Therapeutic Strategy.

Background: Anaplastic thyroid carcinoma (ATC) is one of the most aggressive human cancers, with a median survival of only three to six months. Standard treatment options and even targeted therapies have so far failed to improve long-term overall survival. Thus, novel treatment modalities for ATC, such as immunotherapy, are urgently needed. CD47 is a "don't eat me" signal, which prevents cancer cells from phagocytosis by binding to signal regulatory protein alpha on macrophages. So far, the role of macrophages and the CD47-signal regulatory protein alpha signaling axis in ATC is not well understood. Methods: This study analyzed 19 primary human ATCs for macrophage markers, CD47 expression, and immune checkpoints by immunohistochemistry. ATC cell lines and a fresh ATC sample were assessed by flow cytometry for CD47 expression and macrophage infiltration, respectively. CD47 was blocked in phagocytosis assays of co-cultured macrophages and ATC cell lines. Anti-CD47 antibody treatment was administered to ATC cell line xenotransplanted immunocompromised mice, as well as to tamoxifen-induced ATC double-transgenic mice. Results: Human ATC samples were heavily infiltrated by CD68- and CD163-expressing tumor-associated macrophages (TAMs), and expressed CD47 and calreticulin, the dominant pro-phagocytic molecule. In addition, ATC tissues expressed the immune checkpoint molecules programmed cell death 1 and programmed death ligand 1. Blocking CD47 promoted the phagocytosis of ATC cell lines by macrophages in vitro. Anti-CD47 antibody treatment of ATC xenotransplanted mice increased the frequency of TAMs, enhanced the expression of macrophage activation markers, augmented tumor cell phagocytosis, and suppressed tumor growth. In double-transgenic ATC mice, CD47 was expressed on tumor cells, and blocking CD47 increased TAM frequencies. Conclusions: Targeting CD47 or CD47 in combination with programmed cell death 1 may potentially improve the outcomes of ATC patients and may represent a valuable addition to the current standard of care.

Cytokine-Induced Modulation of Colorectal Cancer.

The emergence of novel immunomodulatory cancer therapies over the last decade, above all immune checkpoint blockade, has significantly advanced tumor treatment. For colorectal cancer (CRC), a novel scoring system based on the immune cell infiltration in tumors has greatly improved disease prognostic evaluation and guidance to more specific therapy. These findings underline the relevance of tumor immunology in the future handling and therapeutic approach of malignant disease. Inflammation can either promote or suppress CRC pathogenesis and inflammatory mediators, mainly cytokines, critically determine the pro- or anti-tumorigenic signals within the tumor environment. Here, we review the current knowledge on the cytokines known to be critically involved in CRC development and illustrate their mechanisms of action. We also highlight similarities and differences between CRC patients and murine models of CRC and point out cytokines with an ambivalent role for intestinal cancer. We also identify some of the future challenges in the field that should be addressed for the development of more effective immunomodulatory therapies.

The IL-33/ST2 pathway contributes to intestinal tumorigenesis in humans and mice.

Colorectal cancer (CRC) develops through a multistep process and is modulated by inflammation. However, the inflammatory pathways that support intestinal tumors at different stages remain incompletely understood. Interleukin (IL)-33 signaling plays a role in intestinal inflammation, yet its contribution to the pathogenesis of CRC is unknown. Using immunohistochemistry on 713 resected human CRC specimens, we show here that IL-33 and its receptor ST2 are expressed in low-grade and early-stage human CRCs, and to a lesser extent in higher-grade and more advanced-stage tumors. In a mouse model of CRC, ST2-deficiency protects from tumor development. Moreover, bone marrow (BM) chimera studies indicate that engagement of the IL-33/ST2 pathway on both the radio-resistant and radio-sensitive compartment is essential for CRC development. Mechanistically, activation of IL-33/ST2 signaling compromises the integrity of the intestinal barrier and triggers the production of pro-tumorigenic IL-6 by immune cells. Together, this data reveals a tumor-promoting role of IL-33/ST2 signaling in CRC.

The Role of IL-33-Dependent Inflammation in the Tumor Microenvironment.

There is compelling evidence that inflammation contributes to tumorigenesis. Inflammatory mediators within the tumor microenvironment can either promote an antitumor immune response or support tumor pathogenesis. Therefore, it is critical to determine the relative contribution of tumor-associated inflammatory pathways to cancer development. Interleukin-33 (IL-33) is a member of the IL-1 family of cytokines that is released upon tissue stress or damage to operate as an alarmin. IL-33 has been primarily implicated in the induction of type-2 immune responses. However, recent findings have shown a role of IL-33 in several cancers where it may exert multiple functions. In this review, we will present the current knowledge on the role of IL-33 in the microenvironment of different tumors. We will highlight which cells produce and which cells are activated by IL-33 in cancer. Furthermore, we will explain how IL-33 modulates the tumor-associated inflammatory microenvironment to restrain or promote tumorigenesis. Finally, we will discuss the issues to be addressed first before potentially targeting the IL-33 pathway for cancer therapy.

IL-33 signaling contributes to the pathogenesis of myeloproliferative neoplasms.

Myeloproliferative neoplasms (MPNs) are characterized by the clonal expansion of one or more myeloid cell lineage. In most cases, proliferation of the malignant clone is ascribed to defined genetic alterations. MPNs are also associated with aberrant expression and activity of multiple cytokines; however, the mechanisms by which these cytokines contribute to disease pathogenesis are poorly understood. Here, we reveal a non-redundant role for steady-state IL-33 in supporting dysregulated myelopoiesis in a murine model of MPN. Genetic ablation of the IL-33 signaling pathway was sufficient and necessary to restore normal hematopoiesis and abrogate MPN-like disease in animals lacking the inositol phosphatase SHIP. Stromal cell-derived IL-33 stimulated the secretion of cytokines and growth factors by myeloid and non-hematopoietic cells of the BM, resulting in myeloproliferation in SHIP-deficient animals. Additionally, in the transgenic JAK2V617F model, the onset of MPN was delayed in animals lacking IL-33 in radio-resistant cells. In human BM, we detected increased numbers of IL-33-expressing cells, specifically in biopsies from MPN patients. Exogenous IL-33 promoted cytokine production and colony formation by primary CD34+ MPN stem/progenitor cells from patients. Moreover, IL-33 improved the survival of JAK2V617F-positive cell lines. Together, these data indicate a central role for IL-33 signaling in the pathogenesis of MPNs.

In situ proliferation contributes to accumulation of tumor-associated macrophages in spontaneous mammary tumors.

Infiltration of a neoplasm with tumor-associated macrophages (TAMs) is considered an important negative prognostic factor and is functionally associated with tumor vascularization, accelerated growth, and dissemination. However, the ontogeny and differentiation pathways of TAMs are only incompletely characterized. Here, we report that intense local proliferation of fully differentiated macrophages rather than low-pace recruitment of blood-borne precursors drives TAM accumulation in a mouse model of spontaneous mammary carcinogenesis, the MMTVneu strain. TAM differentiation and expansion is regulated by CSF1, whose expression is directly controlled by STAT1 at the gene promoter level. These findings appear to be also relevant for human breast cancer, in which an interrelationship between STAT1, CSF1, and macrophage marker expression was identified. We propose that, akin to various MU subtypes in nonmalignant tissues, local proliferation and CSF1 play a vital role in the homeostasis of TAMs.

Lapatinib and doxorubicin enhance the Stat1-dependent antitumor immune response.

The dual erbB1/2 tyrosine kinase inhibitor lapatinib as well as the anthracycline doxorubicin are both used in the therapy of HER2-positive breast cancer. Using MMTV-neu mice as an animal model for HER2-positive breast cancer, we observed enhanced tumor infiltration by IFN-γ-secreting T cells after treatment with doxorubicin and/or lapatinib. Antibody depletion experiments revealed a contribution of CD8⁺ but not CD4⁺ T cells to the antitumor effect of these drugs. Doxorubicin treatment additionally decreased the content of immunosuppressive tumor-associated macrophages (TAMs) in the tumor bed. In contrast, Stat1-deficient mice were resistant to tumor growth inhibition by lapatinib and/or doxorubicin and exhibited impaired T-cell activation and reduced T-cell infiltration of the tumor in response to drug treatment. Furthermore, Stat1-deficiency resulted in reduced expression of the T-cell chemotactic factors CXCL9, CXCL10, and CXCL11 in the tumor epithelium. The inhibition of TAM infiltration of the tumor by doxorubicin and the immunosuppressive function of TAMs were found to be Stat1 independent. Taken together, the results point to an important contribution toward enhancing T-cell and IFN-γ-based immunity by lapatinib as well as doxorubicin and emphasize the role of Stat1 in building an effective antitumor immune response.