摘要Objective To review the recent studies about the role of indoleamine 2,3-dioxygenase (IDO) in tumor induced tolerance.Data sources Published articles (1978-2009) on IDO and tumor induced tolerance were selected from Medline. Study selection Articles selected were relevant to development of IDO in tumor induced tolerance. Of all originally identified articles, 50 specially addressed the stated purpose.Results Recent work has revealed IDO at high levels in tumors and in tumor-draining lymph nodes and a close relationship between IDO activity and the regulatory T cells.Conclusion Up-regulation of IDO is proven to be a mechanism of acquired tolerance in tumors, in which the closely coupled positive feedback system between IDO and regulatory T cells may be considered to play an important role.