A Legumain-based minigene vaccine targets the tumor stroma and suppresses breast cancer growth and angiogenesis
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Tumor associated macrophages (TAMs) are well known to play a very important role in tumor angiogenesis and metastasis. The suppression of TAMs in the tumor-microenvironment (TME) provides a novel strategy to inhibit tumor growth and dissemination by remodeling the tumor’s stroma. Here, we tested our hypothesis that suppression of TAMs can be achieved in syngeneic BALB/c mice with oral minigene vaccines against murine MHC class I antigen epitopes of Legumain, an asparaginyl endopeptidase and a member of the C13 family of cystine proteases which is overexpressed on TAMs in the tumor stroma. Vaccine vectors were constructed and transformed into attenuated Salmonella typhimurium (Dam−, AroA−) for oral delivery. Groups of mice received either the expression vectors encoding the Legumain H-2D or 2K epitopes or the control empty vector by gavage. The efficacy of the minigene vaccines was determined by their ability to protect mice from lethal tumor cell challenges, the induction of a specific CTL response as well as IFN-γ release, and inhibition of tumor angiogenesis. We demonstrated that the Legumain minigene vaccine provided effective protection against tumor cell challenge by inducing a specific CD8+ T-cell response against Legumain+ TAMs in our breast tumor model. The protection, induced by this T-cell response, mediated by the Legumain Kd minigene, is also responsible for lysing D2F2 breast carcinoma cells in syngeneic BALB/c mice and for suppressing tumor angiogenesis. Importantly, in a prophylactic setting, the minigene vaccine proved to be of similar anti-tumor efficacy as a vaccine encoding the entire Legumain gene. Together, our findings establish proof of concept that a Legumain minigene vaccine provides a more flexible alternative to the whole gene vaccine, which may facilitate the future design and clinical applications of such a vaccine for cancer prevention.
KeywordsLegumain Minigene vaccine Tumor associated macrophages Anti-angiogenesis CTLs
Tumor associated macrophages
Cytotoxic T lymphocytes
Major histocompatibility complex
We thank K. Cairns for editorial assistance. This work was supported by Grant 12RT-0002 from the California Tobacco-Related Disease Research Program (to R.A.R.), and E. Merck, Darmstadt-Lexigen Research Center, Billerica, MA Grant SFP1330 (to R.A.R.). Grants from The National Natural Science Foundation of China No.30672389 and No. 30572116 (to R.X.). This is The Scripps Research Institute’s manuscript number 17696-IMM.
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