Sun et al. Journal of Experimental & Clinical Cancer Research 2011, 30:82 http://www.jeccr.com/content/30/1/82 Page 9 of 10 Analysis of apoptosis after co-culture of IDO-expres- sing CHO cells and CD3+T cells isolated from the per- ipheral blood of patients with breast cancer showed that a significantly higher proportion of CD3+T cells were apoptotic than in the control group, suggesting that IDO may affect the T cell proliferation and induce T cell apoptosis. In our recent study, we found that cell proliferation and IL-2 synthesis triggered by the TCR activating anti-CD3 monoclonal antibody OKT3 was inhibited in T-cells which were co-cultured with IDO-expressing CHO cells. Furthermore, co-cultured of CHO/IDO with T-cells could inhibit Vav1 mRNA and protein expression in T-cells. However, an inhibi- tor of IDO, 1-MT, attenuated CHO/IDO-induced decrease of T-cell proliferation, IL-2 levels in T-cells and inhibition of Vav1 [11]. These data suggested that Vav1 is a target molecule involved in the regulatory effect of IDO on T-cells. Whether IDO can induce the maturation and differ- entiation of Tregs is unclear. Investigation into the relationship between IDO expression and regulation of Tregs is likely to be key to revealing a tumor immune tolerance-related mechanism [11,25]. A recent experi- ment showed that in patients with acute myeloid leu- kemia, IDO-expressing tumor cells can induce the transformation of CD4+CD25-T cells to CD4+CD25+T cells [12]. In this study, we explored the inductive effect of IDO on Tregs isolated from the solid tumors of patients with breast cancer, and used low expression of CD127 as a more accurate and specific surface molecular marker of inhibitory Tregs [9,10]. We detected an increase in CD4+CD25+CD127- regulatory T cells in the CD3+T cell population from co-cultures of IDO-expressing CHO cells and CD3+T cells isolated from the peripheral blood of patients with breast can- cer. This phenomenon may be due to the IDO induced differentiation of CD3+T into CD4+CD25+CD127- cells, but further study will be needed to confirm this conclusion. Conclusions Endogenous IDO may be involved in a variety of periph- eral tolerance mechanisms and immunosuppressive responses, as well as having a role in other cellular mechanisms. We established a cell line that stably expressed IDO and preliminarily confirmed that active expression of IDO could induce apoptosis in T cells iso- lated from the peripheral blood of patients with breast cancer; we confirm the role of IDO in the maturation and development of Tregs in breast cancer patients. This study provides an experimental basis for further study into the mechanism underlying the interaction between IDO and Tregs in tumor immunity. Acknowledgements We thanked Dr. Sharma’s work in establishment of the vivo model for activated mature Tregs by IDO. We also thanked Yizi Cong and Lijuan Wei of Tianjin Medical University Cancer Hospital and Institute for their technical assistance. This work was supported by grants from the National Natural Science Foundation of China (30972694, 81072159) and Tianjin Municipal Education Commission(20090133, 20090217), P. R. China. Author details 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. Authors’ contributions JS carried out the molecular genetic studies, participated in the sequence alignment and drafted the manuscript. JY carried out the immunoassays and drafted the manuscript. HL and LY participated in the sequence alignment. FW and WY performed the statistical analysis. JL and XR conceived of the study, and participated in its design and coordination. All authors read and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Received: 25 May 2011 Accepted: 14 September 2011 Published: 14 September 2011 References 1. Uyttenhove C, Pilotte L, Theate I, et al: Evidence for a tumoral immune resistance mechanism based on tryptophan degradation by indoleamine 2,3-dioxygenase. Nat Med 2003, 9:1269-74. 2. Mellor AL, Keskin DB, Johnson T, et al: Cells expressing indoleamine 2,3- dioxygenase inhibit T cell responses. J Immunol 2002, 168:3771-6. 3. Munn DH, Zhou M, Attwood JT, et al: Prevention of allogeneic fetal rejection by tryptophan catabolism. Science 1998, 281:1191-3. 4. Munn DH, Mellor AL: Indoleamine 2,3-dioxygenase and tumor-induced tolerance. J Clin Invest 2007, 117:1147-54. 5. Astigiano S, Morandi B, Costa R, et al: Eosinophil granulocytes account for indoleamine 2,3-dioxygenase-mediated immune escape in human non- small cell lung cancer. Neoplasia 2005, 7:390-6. 6. Brandacher G, Perathoner A, Ladurner R, et al: Prognostic value of indoleamine 2,3-dioxygenase expression in colorectal cancer: effect on tumor-infiltrating T cells. Clin Cancer Res 2006, 12:1144-51. 7. Okamoto A, Nikaido T, Ochiai K, et al: Indoleamine 2,3-dioxygenase serves as a marker of poor prognosis in gene expression profiles of serous ovarian cancer cells. Clin Cancer Res 2005, 11:6030-9. 8. Sakurai K, Amano S, Enomoto K, et al: [Study of indoleamine 2,3- dioxygenase expression in patients with breast cancer]. Gan To Kagaku Ryoho 2005, 32:1546-9. 9. Chatila TA: Role of regulatory T cells in human diseases. J Allergy Clin Immunol 2005, 116:949-59, quiz 60. 10. Schwartz RH: Natural regulatory T cells and self-tolerance. Nat Immunol 2005, 6:327-30. 11. Li R, Wei F, Yu J, et al: IDO inhibits T-cell function through suppressing Vav1 expression and activation. Cancer Biol Ther 2009, 8:1402-8. 12. Curti A, Pandolfi S, Valzasina B, et al: Modulation of tryptophan catabolism by human leukemic cells results in the conversion of CD25- into CD25+ T regulatory cells. Blood 2007, 109:2871-7. 13. Mellor AL, Munn DH: Tryptophan catabolism and T-cell tolerance: immunosuppression by starvation? Immunol Today 1999, 20:469-73. 14. Grohmann U, Orabona C, Fallarino F, et al: CTLA-4-Ig regulates tryptophan catabolism in vivo. Nat Immunol 2002, 3:1097-101. 15. Munn DH, Sharma MD, Baban B, et al: GCN2 kinase in T cells mediates proliferative arrest and anergy induction in response to indoleamine 2,3-dioxygenase. Immunity 2005, 22:633-42. 16. Grohmann U, Volpi C, Fallarino F, et al: Reverse signaling through GITR ligand enables dexamethasone to activate IDO in allergy. Nat Med 2007, 13:579-86.