Multiple sclerosis (MS) is an inflammatory, demyelinating disorder of the central nervous system (CNS). A great deal of our understanding about the immunologic processes that underlie MS derives from studies in its autoimmune animal model, experimental autoimmune encephalomyelitis (EAE). However, the vast majority of studies in EAE and MS have focused on evaluating and targeting CD4+ T cell responses, with the general assumption that these diseases are predominantly Th1/Th17-mediated and Th2/Treg-modulated. Recent reports from others and us indicate that CD8+ T cells play a role in the pathogenesis as well as regulation of autoimmune demyelination. Our studies in MS and EAE have provided evidence for a novel and unexpected disease suppressive role for CNS-specific CD8+ T cells (CNS-CD8). Based on our data, we hypothesize that specific functional and phenotypic subsets of CNS-CD8 form an important and exploitable arm of immune regulation during autoimmune demyelinating disease. We propose that this process can be harnessed for the development of effective immunotherapeutic approaches. The experiments proposed in this application will utilize EAE models to address the fundamental cellular and molecular mechanisms of immune modulation (IFNγ and its receptor, trafficking and cytotoxicity, suppression at the site of pathology) by these autoregulatory CD8 T cells, and to define a potent and enhanceable immune suppressive subset of CNS-CD8. Further, a novel vaccination strategy that reliably engages disease-reversing CNS-CD8 will also be investigated as a proof of principle. We believe that achievable results from the proposed experiments will provide greater fundamental insights into CD8 T cell-mediated immune regulation and pave the way for newer intervention strategies for MS and other immune-mediated diseases.