© 2007 Nature Publishing Group http://www.nature.com/natureimmunology A dominant function for interleukin 27 in generating interleukin 10–producing anti-inflammatory T cells Amit Awasthi 1,5 , Yijun Carrier 2,5 , Jean P S Peron 3 , Estelle Bettelli 2 , Masahito Kamanaka 4 , Richard A Flavell 4 , Vijay K Kuchroo 2 , Mohamed Oukka 1 & Howard L Weiner 2 Regulatory T cells (T reg cells) expressing the transcription factor Foxp3 are key in maintaining the balance of immune homeostasis. However, distinct induced T regulatory type 1 (Tr1) cells that lack Foxp3 expression also regulate T cell function, mainly by producing the immunosuppressive cytokine interleukin 10 (IL-10). However, the factors required for the induction of IL-10-producing suppressive T cells are not fully understood. Here we demonstrate that dendritic cells modified by T reg cells induced the generation of IL-10-producing Tr1 cells. The differentiation of naive CD4 + T cells into IL-10-producing cells was mediated by IL-27 produced by the T reg cell–modified dendritic cells, and transforming growth factor-b amplified the generation of induced IL-10 + Tr1 cells by IL-27. Thus, IL-27 and transforming growth factor-b promote the generation of IL-10-producing Tr1 cells. T cell activation and differentiation are tightly regulated events, as naive T cells can differentiate through the T helper type 1 cell (T H 1 cell), T H 2 cell or interleukin 17 (IL-17)–producing T helper cell (T H -17 cell) pathway to exert specific effector functions during an immune response 1 . Exaggeration of these pathways can lead to inflammation and tissue injury. T regulatory cells (T reg cells) positive for expression of the transcription factor Foxp3 have a dominant function in active immune suppression and the maintenance of immune homeostasis 2 , although other regulatory T cells such as T H 3 cell and T regulatory type 1 (Tr1) cells also contribute substan- tially to active suppression in the periphery 3,4 . Tr1 cells that produce mainly interleukin 10 (IL-10) are efficient regulators of inflammation and autoimmunity 5 . IL-10, a potent anti-inflammatory cytokine, ‘antagonizes’ T H 1 responses by inhibiting the production of inter- feron-g (IFN-g) 6 and also inhibits antigen presentation 7 . IL-10 defi- ciency leads to spontaneous colitis 8 due to excessive activation of dendritic cells (DCs) and Toll-like receptor signaling pathways 9 . Conversely, IL-10-modified DCs maintain an immature phenotype and support IL-10 production by T cells 10,11 . IL-10-producing Tr1 cells can be generated in vitro by repetitive antigen stimulation in the presence of IL-10 (ref. 12). These cells secrete large amounts of IL-10 and variable amounts of IFN-g, IL-2, IL-5 and transforming growth factor-b (TGF-b) but no IL-4. In addition, Tr1 cells generated in vitro in the presence of the immuno- suppressive drugs vitamin D3 and dexamethasone do not express Foxp3 but suppress T cell functions in an IL-10-dependent way 13,14 . Thus, lack of expression of Foxp3, predominant production of IL-10 and suppression of immune responses are hallmarks of Tr1 cells. In contrast to naturally occurring Foxp3 + T reg cells, whose antigen specificity is often unknown, Tr1 cells by definition are antigen specific and therefore may provide therapeutic advantages over Foxp3 + T cells. In addition, the therapeutic efficacy of the Foxp3 + T reg cells is compromised in the presence of inflammatory cytokines because effector T cells may become refractory to Foxp3 + T reg cell–mediated suppression 15,16 . Thus, IL-10-producing Tr1 cells may provide an advantage relative to Foxp3 + T reg cells in mediating suppression of ongoing inflammation. Progress in the study of Tr1 cells has been hampered because of lack of knowledge about growth factors capable of promoting the generation of IL-10-producing Tr1 cells. Although IL-10 can induce Tr1 differentiation, the resulting Tr1 cells do not proliferate because of the suppressive nature of IL-10. This observation suggests that factors other than IL-10 might be important for the differentiation and population expansion of IL-10-secreting Tr1 cells. Here we used induced T reg cells (iT reg cells) to demonstrate that DCs modified by TGF-b-induced T reg cells elicited the generation of Tr1-like cells that produced large amounts of IL-10 and IFN-g and suppressed T cell responses in a Foxp3-independent way. The mod- ified DCs were fully mature and had a plasmacytoid-like phenotype (CD11c int CD11b lo CD8a – CD45RB hi B220 hi ). In addition to IL-10, the modified DCs produced IL-27 and TGF-b. IL-27, a member of the IL-12 family, was the dominant factor involved in the induction of IL-10-producing T cells and worked together with TGF-b to further enhance Tr1 differentiation. Received 22 June; accepted 17 October; published online 11 November 2007; doi:10.1038/ni1541 1 Center for Neurologic Diseases, Brigham and Women’s Hospital, Harvard Medical School, Cambridge, Massachusetts 02139, USA. 2 Center for Neurologic Diseases, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA. 3 Department of Immunology, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil CEP 05508-900. 4 Section of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06520, USA. 5 These authors contributed equally to this work. Correspondence should be addressed to M.O. (moukka@rics.bwh.harvard.edu) and H.L.W. (hweiner@rics.bwh.harvard.edu). 1380 VOLUME 8 NUMBER 12 DECEMBER 2007 NATURE IMMUNOLOGY ARTICLES