Abstract PL03-03: Inflammation and cancer: Repolarizing the immune microenvironment as a therapeutic anticancer strategy

Abstract

Abstract Clinical and experimental studies have established that chronic infiltration of neoplastic tissue by leukocytes, i.e., chronic inflammation, promotes development and/or progression of various solid tumors [1, 2]; however, the organ-specific cellular and molecular programs that favor pro-tumor, as opposed to anti-tumor immunity by leukocytes are incompletely understood. While some leukocytes certainly exhibit anti-tumor activity, i.e., cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells [3-5], other leukocytes, most notably mast cells, CD4+ T cells, B lymphocytes, dendritic cells (DCs), granulocytes, immature monocytes and macrophages exhibit more bipolar roles, by virtue of their capacity to either hinder or potentiate tumor progression [1, 2]. A major question regarding these disparate leukocytes bioactivities is the degree to which their various pro- or anti-cancer activities are regulated by tissue-specificity and/or are responsive to individual oncogenic or tumor suppressive gene programming in early neoplastic tissue. Leukocytes and Breast Carcinogenesis: In the breast, cancer development is in part characterized by a significant increase in the presence of both innate and adaptive immune cells, with B and T lymphocytes as well as macrophages representing the most abundant leukocytes present in neoplastic stroma [6]. Retrospective clinical studies examining identity of leukocytes in human breast cancer have revealed that high immunoglobulin (Ig) levels in tumor stoma (and serum), and increased presence of extra follicular B cells, T regulatory (Treg) cells, high ratios of CD4/CD8 or TH2/TH1 T lymphocytes in primary tumors or in draining lymph nodes correlates with tumor grade, stage and overall patient survival [7-11]; thus, some facets of adaptive immunity may indeed be involved in fostering cancer development. On the other hand, experimental studies have demonstrated that macrophages in primary mammary adenocarcinomas regulate late-stage carcinogenesis by virtue of their pro-angiogenic properties [12, 13], as well as fostering pulmonary metastasis by providing epidermal growth factor (EGF) and cathepsin proteases [14] to malignant mammary epithelial cells (MECs) and thereby enhancing their invasive (and metastatic) behavior [15, 16]. Based on these seemingly disparate observations, we sought to determine if adaptive immunity also fostered malignancy in the breast by regulating the phenotype or effector functions of tumor-associated macrophages (TAMs) and either activated their pro-tumor properties or alternatively by suppressing their anti-tumor capabilities. Utilizing the MMTV-PyMT mouse model of mammary carcinogenesis [17], we revealed a provocative and functional role for CD4+ T effector cells as potentiators of peripheral blood dissemination and pulmonary metastasis of malignant mammary adenocarcinomas through their ability to regulate the pro-tumor properties of TAMs [18]. Specifically, TH2-polarized CD4+ T lymphocytes secrete high levels of interleukin (IL)-4 and thereby regulate M1 and M2-type TAM bioactivity by activation of IL4Ra-signaling cascades. M2-TAMs in turn promote invasive behavior of malignant MECs by high level production of cathepsin protease activity [14] and EGF that subsequently activates MEC invasion and EGF receptor signaling programs, activities that are essential for entry into peripheral blood, dissemination and outgrowth in the lung. These findings indicate that when CD4+ T lymphocytes are present in a TH2-type tumor microenvironment, they promote metastasis by regulating the pro-tumor properties of TAMs mediated by IL4Ra-signaling, as opposed to limiting or eradicating malignant cells by engaging cytotoxic mechanisms. These provocative realizations provide rational for development of anti-cancer therapeutics that neutralize the pro-tumor properties of IL4Ra-based signaling in both adaptive and innate immune cells in the tumor microenvironment and periphery, that when delivered in combination with cytotoxic drugs or therapeutics bolstering anti-tumor immunity, may thereby extend survival of cancer patients with advanced disease. Leukocytes and Squamous Carcinogenesis: B lymphocytes constitute a central component of adaptive immunity and not only serve in antibody production but also as antigen-presenting cell; thus, B lymphocyte expression of major histocompatability complex (MHC) and co-stimulatory molecules as well as secretion of pro-inflammatory cytokines induces optimal CD4+ and CD8+ T cells activation, expansion, memory T lymphocyte formation and antigenic spreading. As such, B cells have been historically associated with anti-tumor immunity. More recently, the heterogeneity of B lymphocyte responses has been recognized and diverse B cell subtypes with either pro-immune or regulatory properties have been identified in vivo. In particular, regulatory B lymphocytes, which include various flavors of IL-10 producing cells, have been identified in the context of autoimmune diseases that exert anti-inflammatory activities [19, 20]. However, the role of these individual B lymphocyte subpopulations in malignant disease has yet to be fully elucidated. Using a transgenic mouse model of multi-stage epithelial carcinogenesis, i.e., K14-HPV16 mice [21], we previously revealed that adaptive immunity is an important regulator of inflammation-associated cancer development [22]. Combined B and T lymphocyte-deficiency in HPV16 mice, e.g. HPV16/RAG1-/- mice, resulted in a failure to initiate and/or sustain leukocyte infiltration during premalignancy [22]. As a consequence, tissue remodeling, angiogenesis and epithelial hyperproliferation were significantly reduced, culminating in attenuated premalignant progression and a 43% reduction in carcinoma incidence [22]. Importantly, adoptive transfer of B lymphocytes or serum from HPV16 mice into HPV16/RAG1-/- mice reinstated chronic inflammation in premalignant tissues, indicating that B cell-derived soluble mediators were necessary to potentiate malignant progression. More recently, we revealed that B cell-derived IgGs regulate neoplastic progression and subsequent carcinoma development by engagement of Fcg[[Unsupported Character - ]]receptors (FcgR) expressed on resident and recruited immune cells [23]. Specifically, we found that that immune complex (IC)-stimulation of leukocyte FcRg is critical for establishing a pro-tumor microenvironment in premalignant tissue that directs not only recruitment of leukocytes from peripheral blood, but also leukocyte composition, phenotype and bioeffector functions once within neoplastic tissue. As such, proangiogenic and protumorigenic functions of mast cells and macrophages are differentially regulated by humoral immunity and functionally contribute to squamous carcinogenesis. These findings have broad clinical implications as they reveal critical signaling pathways regulated by humoral immunity and FcRg to target therapeutically in patients at risk for cancer development, e.g., patients suffering from chronic inflammatory diseases, as well as individuals harboring premalignant lesions where chronic inflammation compromises tissue integrity and enhances risk of malignancy. Summary: While many factors regulate the propensity of leukocytes to promote or repress primary tumor development and metastasis, some of which may be tissue- and/or oncogene-specific, polarized TH2-type adaptive immune responses by B and T lymphocytes foster pro- as opposed to anti- tumor programming of myeloid cells that in turn directly regulate many of the “hallmarks” of solid tumor development [24]. Neutralizing these various “pro-tumor” regulatory pathways may provide relief for some aspects of late-stage cancer development as monotherapy, but more likely when combined with cytotoxic-, targeted- and/or immuno-therapy will provide a survival advantage by bolstering induction of anti-tumor bioactivities of tumor-associated leukocytes that extend efficacy of therapy.