Autoimmune diseases are often characterized by spontaneous remission followed by relapses. Although the mechanism(s) controlling pathogenic self-reactive T cells are not fully understood, recent data in experimental autoimmune encephalomyelitis (EAE), a prototype for CD4 T cell-mediated autoimmune diseases, indicate that spontaneous recovery is mediated by regulatory T cells (Treg) specific for peptides derived from the beta-chain of the TCR. Here we have tested whether recombinant single-chain TCRs (scTCRs) containing Vbeta domains can be used as vaccines for efficient priming of Treg. A single injection of mice with these recombinant proteins leads to efficient in vivo priming of Treg and almost complete protection from Ag-induced EAE. Significantly, administration of scTCRs during ongoing disease at a 10-fold lower dose than that required for prophylactic treatment also reverses established EAE. However, if a higher dose of scTCR is administered during ongoing disease, paralytic symptoms become exacerbated and the majority of treated animals die from severe and chronic EAE. Furthermore, we demonstrate that regulatory determinants are processed and presented from scTCRs resulting in the recruitment of both CD4 and CD8 regulatory T cells which are required for efficient regulation induced by scTCR. Reversal of established disease following an optimum dose of recombinant TCRs suggests that proteins expressing appropriate Vbeta domains could be used for the treatment of a variety of T cell-mediated pathologic conditions.