The phenotype of the CD4⁺ T cells that mediate the CNS pathology in multiple sclerosis is still unclear, and yet a vital question for developing therapies. One of the conundrums is the role of TGF-β in the development of encephalitogenic Th17 cells. In the present study, TGF-β1 and TGF-β3 were directly compared in their capacity to promote the differentiation of myelin-specific Th17 cells that could induce experimental autoimmune encephalomyelitis (EAE). Myelin-specific CD4⁺ T cell receptor transgenic cells differentiated with antigen in the presence of IL-6+TGF-β1 or IL-6+TGF-β3 generated T cells that produced robust amounts of IL-17, but were incapable of inducing EAE when transferred into mice. Further analysis of these non-encephalitogenic Th17 cells found that they expressed lower amounts of GM-CSF or IL-23R, both molecules necessary for encephalitogenicity. Thus, TGF-β, irrespective of isoform, negatively regulates the differentiation of encephalitogenic Th17 cells.