癌症生物学

Three-dimensional (3D) tumor spheroids have the potential to bridge the gap between two-dimensional (2D) monolayer tumor cell cultures and solid tumors with which they share a significant degree of similarity. However, the progression of solid tumors is often influenced by the dynamic and reciprocal interactions between tumor and immune cells. Here we present a 3D tumor spheroid-based model that might shed new light on understanding the mechanisms of tumor and immune cell interactions. The model first utilizes the hanging drop assay, which serves as one of the simplest methods for generating 3D spheroids and requires no specialized equipment. Next, pre-established spheroids can be co-cultured either directly or indirectly with an immune cell population of interest. Using skin melanoma, we provide a detailed description of the model, which might hold a significant importance for the development of successful therapeutic strategies.

Inflammatory Ly6C^hi monocytes can give rise to distinct mononuclear myeloid cells in the tumor microenvironment, such as monocytic myeloid-derived suppressor cells (Mo-MDSC), immature macrophages, M2-like tumor-associated macrophages (TAMs), M1-like TAMs or monocyte-derived dendritic cells (Mo-DCs). This protocol describes a method to assess the fate and recruitment of inflammatory Ly6C^hi monocytes in the tumor microenvironment.

Immunotherapy has demonstrated great therapeutic potential by activating the immune system to fight cancer. However, little is known about the specific dynamics of interactions that occur between tumor and immune cells. In this protocol we describe a novel method to visualize the interaction of tumor and immune cells in the lung of live mice, which can be applied to other organs. In this protocol fluorescent-labeled tumor cells are transferred to recipient mice expressing fluorescently tagged immune cells. Tumor-immune cell interactions in the lung are then imaged by confocal or two photon microscopy. Analysis of tumor interactions with immune cells using this protocol should aid in a better understanding of the importance of these interactions and their role in developing immunotherapies.

Myeloid derived suppressor cells (MDSCs) are a subset of granulocytes (immature myeloid cells) that exploit a variety of mechanism to modulate the innate and adaptive immune system. MDSCs are present normally in the body, but their numbers increase during inflammation and in cancer, promoting an immunosuppressive microenvironment. In addition to MDSCs, macrophages also play an important role during cancer development. There are two subsets of tumor associated macrophages (TAMs): M1 and M2. M1 are “anti-tumor” macrophages that are activated by interferon gamma (IFN-γ) and/or Lipopolysaccharide (LPS) and secrete high amount of interleukin 12 (IL-12) thereby inducing a Th1 anti-tumor immune response. M2 or “pro-tumorigenic” macrophages are activated by interleukin 4 (IL-4) and interleukin 10 (IL-10) and secrete large amounts of IL-10, which promotes tumor progression (Gabrilovich et al., 2012).

Interaction between MDSCs and macrophages in the tumor microenvironment was shown to enhance immune suppression mediated by these subsets. MDSCs influence TAMs by producing IL-10 that, in turn, induces a down-regulation of IL-12 and polarizes M1 into M2 macrophages. In our study, we use the following protocol to evaluate the ability of tumor induced MDSCs to polarize LPS activated M1 into M2 macrophages (Vences-Catalan et al., 2015). This protocol was adapted from a previous study (Sinha et al., 2007).

Regulatory T cells (Tregs), a subset of CD4⁺CD25⁺ T cells, infiltrate tumors and suppress antitumor activity of effector T and NK cells. Depletion of Tregs by anti CD25⁺ antibodies has been shown to reduce tumor growth and metastasis (Olkhanud et al., 2009). Conversely, adoptive transfer of Tregs induced immune suppression and promoted tumor growth (Smyth et al., 2006; Janakiram et al., 2015). We have adoptively transferred Tregs to evaluate their immunosuppressive function in vivo. Our study (Vences-Catalan et al., 2015) compared the immunosuppressive efficacy of Tregs derived from tumor-bearing wild type to those of CD81KO mice. The following protocol could be adapted to any other source of Tregs.

Lymph node or splenic tumor-induced Tregs are isolated and purified by a two-step procedure using CD4⁺CD25⁺ regulatory T cell isolation kit from MACS Miltenyi Biotec. First, CD4⁺ T cells are enriched by negative selection, followed by positive selection of CD25⁺ T cells. Tumor-induced purified Tregs (CD3⁺CD4⁺CD25⁺FoxP3⁺) are then co-injected subcutaneously together with tumor cells into naïve mice (Winn assay) (Winn, 1960). Tregs could also be injected intravenously once or several times, according to the research needs. The effect of the adoptively transferred Tregs on tumor growth is then measured by caliper or by in vivo imaging techniques.

The high migration rate of tumor cells often results in poor prognosis for the survival of the patients. Here, we describe a protocol to measure the migration of cells using a quantitative assay. The relative tumor cell migration was measured using ThinCerts^TM cell culture inserts and a lactate dehydrogenase (LDH) assay to quantify the relative cell number. The quantification of the migration with the LDH kit is much more precise than other methods using i.e. crystal blue to count the cells.

Bone is a primary site of metastasis from prostate and breast cancers. Bone marrow macrophages (BMMs) are mediators of inflammatory processes and are thought to promote tumor growth in the skeletal sites. In order to elucidate how their interactions with tumor cells impact aggressiveness of metastatic tumors in bone in vitro methods are required. By employing a system in which BMMs and tumor cells are grown separately, yet share the media and exchange soluble factors, contribution of each cell type in the context of BMM-tumor cell relationship in the bone marrow can be investigated. Additional advantages of this system include the ability to study: 1) phenotypic changes in BMMs and tumor cells upon co-culture; 2) cell-specific modulation of protein and gene expression; and 3) effects on proliferation and cell survival. It is noteworthy, that this transwell co-culture system is not limited to BMMs and tumor cells and can be easily modified to include other components of bone marrow microenvironment (e.g., adipocytes, stromal cells, osteoblasts).