Sun et al. Journal of Experimental & Clinical Cancer Research 2011, 30:82 http://www.jeccr.com/content/30/1/82 R E S E A R C H Open Access Upregulated expression of indoleamine 2, 3-dioxygenase in CHO cells induces apoptosis of competent T cells and increases proportion of Treg cells Jingyan Sun1†, Jinpu Yu2†, Hui Li2, Lili Yang2, Feng Wei2, Wenwen Yu2, Juntian Liu1* and Xiubao Ren2* Abstract Introduction: The inflammatory enzyme indoleamine 2, 3-dioxygenase (IDO) participates in immune tolerance and promotes immune escape of IDO+ tumors. A recent hypothesis suggested that IDO may contribute to the differentiation of new T regulatory cells (Tregs) from naive CD4+ T cells. In this study we investigated the role of IDO in induction of immunosuppression in breast cancer by increasing the apoptosis of T cells and the proportion of Tregs. Methods: An IDO expression plasmid was constructed and Chinese hamster ovary (CHO) cells were stably transfected with human IDO. Purified CD3+ T cells were isolated from the peripheral blood monouclear cells of breast cancer patients. After co-culturing IDO expressing or untransfected (control) CHO cells with T cells, T cells apoptosis were determined by flow cytometry analysis and annexin-V and PI staining. The proportion of the regulatory T cell (Tregs [CD4 + CD25 + CD127-]) subset was measured by flow cytometry analysis. T cells total RNA and cellular protein samples were isolated for detecting Foxp3 gene and protein expression. Results: IDO transgenic CHO cells yielded high levels of IDO enzymatic activity, resulting in complete depletion of tryptophan from the culture medium. We found that apoptosis occurred in 79.07 ± 8.13% of CD3+T cells after co- cultured with IDO+ CHO cells for 3 days and the proportion of CD4 + CD25 + CD127- T cells increased from 3.43 ± 1.07% to 8.98 ± 1.88% (P < 0.05) as well. The specific inhibitor of IDO,1-MT efficiently reversed enhancement of T cells apoptosis and amplification of Tregs in vitro. Increased expression of Foxp3, a key molecular marker of Tregs, was confirmed by RT-PCR, real-time RT-PCR and Western blot analysis at the same time. Conclusions: These results suggest that IDO helps to create a tolerogenic milieu in breast tumors by directly inducing T cell apoptosis and enhancing Treg-mediated immunosuppression. Keywords: Indoleamine-Pyrrole 2, 3-Dioxygenase, breast neoplasms, immune tolerance, CHO Cells, regulatory T- Lymphocytes * Correspondence: juntian_liu2001@yahoo.com.cn; rwziyi@yahoo.com † Contributed equally 1Department of Breast Oncology, Tianjin Medical University Cancer Institute and Hospital, Tiyuanbei, Huanhuxi Road, Hexi District, Tianjin, 300060, China 2Department of Immunology, Key laboratory of Cancer Prevention and Therapy, Tianjin Medical University Cancer Institute and Hospital, Tiyuanbei, Huanhuxi Road, Hexi District, Tianjin, 300060, China Full list of author information is available at the end of the article © 2011 Sun et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.