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Interleukin 2 expression by tumor cells alters both the immune response and the tumor microenvironment
1Department of Microbiology and Immunology, University of Rochester School of Medicine and Dentistry, New York 14642, USA.
Abstract:
Microenvironmental conditions within solid tumors can have marked effects on the growth of the tumors and their response to therapies. The disorganized growth of tumors and their attendant vascular systems tends to result in areas of the tumors that are deficient in oxygen (hypoxic). Cells within these hypoxic areas are more resistant to conventional therapies such as radiation and chemotherapy. Here, we examine the hypoxic state of EMT6 mouse mammary tumors and the location of host cells within the different areas of the tumors to determine whether such microenvironmental conditions might also affect their ability to be recognized by the immune system. Hypoxia within tumors was quantified by flow cytometry and visualized by immunohistochemistry using a monoclonal antibody (ELK3-51) against cellular adducts of 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)acetam ide (EF5), a nitroimidazole compound that binds selectively to hypoxic cells. Thy-1+ cells, quantified using a monoclonal antibody, were found only in the well-oxygenated areas. The location of these Thy-1+ cells was also examined in EMT6 tumors that had been transfected with the gene for interleukin-2 (IL-2) because these tumors contain greatly increased numbers of host cells. Surprisingly, we found that IL-2-transfected tumors had significantly decreased hypoxia compared to parental tumors. Furthermore, using the fluorescent dye Hoechst 33342, an in vivo marker of perfused vessels, combined with immunochemical staining of PECAM-1 (CD31) as a marker of tumor vasculature, we found increased vascularization in the IL-2-transfected tumors. Thus, expression of IL-2 at the site of tumor growth may enhance tumor immunity not only by inducing the generation of tumor-reactive CTLs but also by allowing increased infiltration of activated T cells into the tumors.
Insights
Tumor hypoxia impacts immune cell location and therapy resistance. Interleukin-2 (IL-2) expression in tumors reduced hypoxia and improved vascularization, potentially enhancing anti-tumor immunity.
Area of Science:
- Tumor microenvironment
- Cancer immunology
- Molecular oncology
Background:
- Solid tumor microenvironments significantly influence tumor growth and therapeutic responses.
- Tumor hypoxia, resulting from disorganized vasculature, leads to therapy resistance.
- Hypoxic conditions may also impair the immune system's ability to recognize tumors.
Purpose of the Study:
- To investigate the relationship between tumor hypoxia and host immune cell location in EMT6 mouse mammary tumors.
- To determine if microenvironmental conditions affect immune recognition of tumors.
- To assess the impact of interleukin-2 (IL-2) gene transfection on tumor hypoxia and vascularization.
Main Methods:
- Quantification and visualization of tumor hypoxia using flow cytometry and immunohistochemistry with an EF5 antibody.
- Identification and localization of Thy-1+ immune cells using monoclonal antibodies.
- Assessment of tumor vascularization using Hoechst 33342 and PECAM-1 (CD31) staining in IL-2 transfected tumors.
Main Results:
- Thy-1+ immune cells were exclusively found in well-oxygenated tumor areas.
- IL-2-transfected tumors exhibited significantly reduced hypoxia compared to parental tumors.
- IL-2 transfection led to increased tumor vascularization.
Conclusions:
- Tumor hypoxia restricts the infiltration of certain immune cells, like Thy-1+ cells, to oxygenated regions.
- IL-2 expression at the tumor site can decrease hypoxia and enhance vascularization.
- IL-2 may boost anti-tumor immunity by promoting T cell infiltration and potentially generating tumor-reactive cytotoxic T lymphocytes (CTLs).