Leukocyte populations and IL-6 in the tumor microenvironment of an orthotopic colorectal cancer model

Abstract

Colorectal cancer (CRC) is a major health problem worldwide. It is often diagnosed late due to its asymptomatic nature. As with all cancers, an immune reaction is involved; however, in CRC, it is unknown if this immune response is favorable or unfavorable for disease progression. In this study, the immune response in mesenteric lymph nodes (MLNs) and Peyer's patches was investigated during development of CRC in an orthotopic mouse model. CRC was induced by injecting CT26 cells into the cecum wall of BALB/c mice. Flow cytometry was used to analyze leukocyte populations involved in tumor immunity in MLNs and Peyer's patches. Cryostat sections for immunohistochemistry were prepared from the caecum and colon from CRC-induced and sham-operated animals. Cytokines produced by mouse CT26 cell line were measured in vitro and in vivo. Significant increases in the number of CD8 + /TCR + and CD49b + /TCR − (natural killer) cells were found in MLNs and Peyer's patches in the CRC group. In addition, γδT cells were present in the lamina propria of the colon tissues from sham-operated mice, but absent in the colon tissues from mice with CRC. Immunohistochemical analysis of tumorous tissues showed eosinophil, CD69 + T cell, and CD11b + cell infiltration. Both in vitro and in vivo CT26 tumor cells were interleukin (IL)-6 positive. In addition, tumor-infiltrating CD45 + cells were also IL-6 positive. In summary, the kinetics of the immune response to CRC and the key effector lymphocytes that are implicated in tumor immunity are demonstrated. Furthermore, IL-6 is a key cytokine present within the tumor microenvironment.

Tumor location impacts immune response in mouse models of colon cancer

“…Orthotopic tumors were better infiltrated with T cells than subcutaneous tumors, same trend was also observed with B cells. Similar results were also observed in a cecum model [ 26 ], in which higher frequency of CD8 + T cells were detected in Peyer's patches in response to tumor challenge. Furthermore, studies have shown that regulatory T-cell (Treg) inhibits the function of cytotoxic T-cell and selectively kills antigen presenting cells including B cells [ 27 ].…”

“…In mice, orthotopic tumors had more NK-cell infiltration than subcutaneous tumors. In a caecum model, higher levels of NK cells were founded in mesenteric lymph nodes (MLNs) of tumor group compared with MLNs of control groups [ 26 ]. Notably, subcutaneous tumors had more immunosuppressive cells such as MDSCs, compared to orthotopic tumors.…”

The Role of Tumor Microenvironment Cells in Colorectal Cancer (CRC) Cachexia

“…Both in vivo tissues (CD45 + TILs) and cells of another murine CRC cell line (CT26), obtained from a BALB/c mouse, showed a positive reaction to IL-6, indicating this cytokine as key for CRC TME. Moreover, it could also potentially participate in CRC-associated cachexia [ 96 ].…”

The Complex Interaction between the Tumor Micro-Environment and Immune Checkpoints in Breast Cancer

“…Advances in the understanding of the TME in pre-invasive and invasive breast cancer have demonstrated strong evidence to suggest that the TME and associated molecules as well as the infiltration of immune cells, soluble factors and altered extracellular matrix, are involved in promoting tumor growth and metastasis [51,52]. These critical elements of the TME have initiated the identification of new breast cancer markers, such as biological, immunological and immunosuppressive which are associated with tumor development and progression [53].…”