Disease Exacerbation in Multiple Sclerosis Patients is Characterized by Loss of Terminally Differentiated CD8+ T Regulatory Cells

Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the central nervous system (CNS) that afflicts more than 400,000 people in the US. Although the etiology of the disease is unknown, pathogenic T cells are thought to underlie MS immune pathology. In contrast to the current paradigm, we recently showed that MS patients harbor CNS-specific CD8+ T regulatory cells (CD8 Tregs) that are deficient during disease relapse. In the current study, we demonstrate that the neuroantigen-specific CD8 Tregs were cytolytic and eliminated pathogenic CD4+ T cells. Sorting of CD8+ T cells using an array of surface cellular markers revealed that the CD8 Tregs were terminally differentiated (CD27-, CD45RO-). The CD8 Treg-mediated suppression was perforin, granzyme B, and interferon-γ-dependent. Interestingly, we found that MS patients with acute disease exacerbation displayed a significant loss (averaging 25%) in the terminally differentiated CD8+ T cells, with a concurrent loss in perforin and granzyme B expression. In order to restore the regulatory potential of impaired CD8 Tregs during exacerbation, we pre-treated exacerbation-derived bulk CD8+ T cells with the cytokine IL-12 and significantly increased the suppressive capability of the cells by ~48% through upregulation of granzyme B and perforin. Our studies uncover the immune suppressive mechanism of neuroantigen-specific CD8 Tregs, and may contribute to the design of clinically relevant immune therapies for MS patients.