Targeting tumor-associated macrophages as a novel strategy against breast cancer
Yunping Luo, He Zhou, Jörg Krueger, Charles Kaplan, Sung-Hyung Lee, Carrie Dolman, Dorothy Markowitz, Wenyuan Wu, Cheng Liu, Ralph A. Reisfeld, Rong Xiang
Yunping Luo, He Zhou, Jörg Krueger, Charles Kaplan, Sung-Hyung Lee, Carrie Dolman, Dorothy Markowitz, Wenyuan Wu, Cheng Liu, Ralph A. Reisfeld, Rong Xiang
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Research Article Oncology

Targeting tumor-associated macrophages as a novel strategy against breast cancer

Abstract

Tumor-associated macrophages (TAMs) are associated with tumor progression and metastasis. Here, we demonstrate for the first time that legumain, a member of the asparaginyl endopeptidase family functioning as a stress protein, overexpressed by TAMs, provides an ideal target molecule. In fact, a legumain-based DNA vaccine served as a tool to prove this point, as it induced a robust CD8+ T cell response against TAMs, which dramatically reduced their density in tumor tissues and resulted in a marked decrease in proangiogenic factors released by TAMs such as TGF-β, TNF-α, MMP-9, and VEGF. This, in turn, led to a suppression of both tumor angiogenesis and tumor growth and metastasis. Importantly, the success of this strategy was demonstrated in murine models of metastatic breast, colon, and non–small cell lung cancers, where 75% of vaccinated mice survived lethal tumor cell challenges and 62% were completely free of metastases. In conclusion, decreasing the number of TAMs in the tumor stroma effectively altered the tumor microenvironment involved in tumor angiogenesis and progression to markedly suppress tumor growth and metastasis. Gaining better insights into the mechanisms required for an effective intervention in tumor growth and metastasis may ultimately lead to new therapeutic targets and better anticancer strategies.

Authors

Yunping Luo, He Zhou, Jörg Krueger, Charles Kaplan, Sung-Hyung Lee, Carrie Dolman, Dorothy Markowitz, Wenyuan Wu, Cheng Liu, Ralph A. Reisfeld, Rong Xiang

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Figure 3

TAM population in the tumor stroma is decreased by CD8+ -specific CTLs induced by the legumain-based DNA vaccine.

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TAM population in the tumor stroma is decreased by CD...
(A) RAW macrophage cells, which highly express legumain after culturing with 10 ng/ml IL-4, IL-10, and IL-13, served as target cells in a 4-hour 51Cr release assay. Splenocytes isolated from mice immunized with the pLegumain vaccine were shown to effectively kill RAW cells treated with these cytokines in vitro at different effector-to-target (E/T) cell ratios but failed to induce cytotoxic killing of unstimulated RAW cells lacking legumain expression. **P < 0.005 compared with control groups. (B) The percentage of TAM populations with specific macrophage markers (CD206 and F4/80) in tumor tissue with or without vaccination was detected by flow cytometry. The percentage of TAM populations among tumor tissue cells isolated from mice treated with our DNA vaccine was shown to be reduced; however, there was no decrease in TAM populations isolated from mice treated with either empty vector or pLegumain following CD8+ T cell depletion (**P < 0.005). (C) The results of flow cytometry were confirmed by immunohistochemical staining evaluated by confocal microscopy. The population of TAMs in the tumor stroma was dramatically decreased after vaccination. 4T1 cancer cells are shown in blue and TAMs in red. Magnification, ×50 (H&E) and ×350 (control, empty vector, and pLegumain).