Intravital imaging reveals distinct responses of depleting dynamic tumor-associated macrophage and dendritic cell subpopulations

Abstract

Tumor-infiltrating inflammatory cells comprise a major part of the stromal microenvironment and support cancer progression by multiple mechanisms. High numbers of tumor myeloid cells correlate with poor prognosis in breast cancer and are coupled with the angiogenic switch and malignant progression. However, the specific roles and regulation of heterogeneous tumor myeloid populations are incompletely understood. CSF-1 is a major myeloid cell mitogen, and signaling through its receptor CSF-1R is also linked to poor outcomes. To characterize myeloid cell function in tumors, we combined confocal intravital microscopy with depletion of CSF-1R-dependent cells using a neutralizing CSF-1R antibody in the mouse mammary tumor virus long-terminal region-driven polyoma middle T antigen breast cancer model. The depleted cells shared markers of tumor-associated macrophages and dendritic cells (M-DCs), matching the phenotype of tumor dendritic cells that take up antigens and interact with T cells. We defined functional subgroups within the M-DC population by imaging endocytic and matrix metalloproteinase activity. Anti-CSF-1R treatment altered stromal dynamics and impaired both survival of M-DCs and accumulation of new M-DCs, but did not deplete Gr-1 + neutrophils or block doxorubicin-induced myeloid cell recruitment, and had a minimal effect on lung myeloid cells. Nevertheless, prolonged treatment led to delayed tumor growth, reduced vascularity, and decreased lung metastasis. Because the myeloid infiltrate in metastatic lungs differed significantly from that in mammary tumors, the reduction in metastasis may result from the impact on primary tumors. The combination of functional analysis by intravital imaging with cellular characterization has refined our understanding of the effects of experimental targeted therapies on the tumor microenvironment.inflammation | myeloid cells | matrix metalloproteinase | CSF-1 receptor | lung metastasis C ells of the myeloid lineage, including macrophages, monocytes, neutrophils, mast cells, and immature myeloid cells, are major components of the complex stromal microenvironment of solid tumors (1, 2). Abundant evidence from human and experimental tumor types shows that myeloid cells support tumor growth and progression by a wide range of mechanisms, including stimulation of angiogenesis, secretion of factors inducing tumor growth, survival and cell migration, remodeling of the extracellular matrix to facilitate growth and invasion, recruitment of additional support cells, and suppression of the antitumor immune response (3-5). In human breast cancer, as in most other solid tumors, large numbers of myeloid cells, characterized as tumor-associated macrophages (TAMs), correlate with poor prognosis, as does high expression of the myeloid cell mitogen colony-stimulating factor-1 (CSF-1, M-CSF) or its receptor CSF-1R (CD115, c-fms), and gene-expression profiles reflecting myeloid involvement or CSF-1 signaling (3, 5-8).The marked effects of myeloid cells on tumor growth, invasion, and metastasis ...

Tumor-Associated Macrophages Derived from Circulating Inflammatory Monocytes Degrade Collagen through Cellular Uptake

“…Interestingly, these cells also frequently expressed the dendritic cell markers CD11c and MHCII, which were expressed infrequently on collagen- and dextran non-endocytosing cells (Figure 1K). This resemblance of TAMs to dendritic cells is aligned with recent findings (Lohela et al, 2014). …”

The Cancer Stem Cell Niche: How Essential Is the Niche in Regulating Stemness of Tumor Cells?

“…TAMs and TANs are derived from polarized macrophages and neutrophils respectively, which results in their pro-tumor phenotypes that facilitate tumor growth and stimulate angiogenesis (Lohela et al, 2014; Casbon et al, 2015). In addition, TAMs promote ECM breakdown, invasion, and metastasis (reviewed in Noy and Pollard, 2014; Kitamura et al, 2015).…”

“…A positive correlation between TAM infiltration and angiogenesis was found in many human cancers. TAMs become pro-angiogenic through their response to M-CSF (Lohela et al, 2014), secreted by tumor cells, which induces VEGF-A production and suppresses anti-angiogenic factor expression.…”

Imaging innate immune responses at tumour initiation: new insights from fish and flies

“…Intravital imaging, using multiphoton and spinning disc microscopy, is also providing us with new opportunities to step beyond the current complex in vitro three-dimensional human autologous or tumour slice models 56 , in which any immune response is likely to be considerably altered, and to make high-resolution in vivo movies of immune cell-cancer cell interactions in mammalian tissues. When this is in relatively accessible locations -for example, within mouse mammary carcinomas -such new imaging strategies are enabling the viewing of macrophage involvement in metastatic spread and of altered immune cell-cancer cell interactions following chemotherapy and other treatments 57,58 . But for now, the tiny size of zebrafish larvae and D. melanogaster imaginal discs, and their unmatched translucency, means that the earliest moments of cancer initiation, as pre-neoplastic cells first develop, remain best studied in fish and flies.…”