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Clinical and Developmental Immunology
Volume 2012, Article ID 173029, 12 pages
Research Article

Immunological and Nonimmunological Effects of Indoleamine 2,3-Dioxygenase on Breast Tumor Growth and Spontaneous Metastasis Formation

1Department of Medicine, University of Pittsburgh Cancer Institute, Pittsburgh, PA 15213, USA
2University of Pittsburgh Cancer Institute, Hillman Cancer Center, Pittsburgh, PA 15213, USA
3Department of Immunology, University of Pittsburgh Cancer Institute, Pittsburgh, PA 15213, USA
4Department of Pathology, University of Pittsburgh Cancer Institute, Pittsburgh, PA 15213, USA

Received 27 January 2012; Accepted 6 March 2012

Academic Editor: Masoud H. Manjili

Copyright © 2012 Vera Levina et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The role of the tryptophan-catabolizing enzyme, indoleamine 2,3-dioxygenase (IDO1), in tumor escape and metastasis formation was analyzed using two pairs of Ido1+ and Ido1− murine breast cancer cell lines. Ido1 expression in 4T1 cells was knocked down by shRNA, and Ido1 expression in NT-5 cells was upregulated by stable transfection. Growth of Ido1− tumors and spontaneous metastasis formation were inhibited in immunocompetent mice. A higher level of cytotoxic T lymphocytes was generated by spleen cells from mice bearing Ido1− tumors than Ido1+ tumors. Tumor and metastatic growth was enhanced in immunodeficient mice, confirming an intensified immune response in the absence of Ido1 expression. However, Ido1+ tumors grow faster than Ido1− tumors in immunodeficient SCID/beige mice (lacking T, B, and NK cells) suggesting that some Ido1-controlled nonimmunological mechanisms may be involved in tumor cell growth regulation. In vitro experiments demonstrated that downregulation of Ido1 in tumor cells was associated with decreased cell proliferation, increased apoptosis, and changed expression of cell cycle regulatory genes, whereas upregulation of Ido1 in the cells had the opposite effects. Taken together, our findings indicate that Ido1 expression could exert immunological and nonimmunological effects in murine breast tumor cells.