Patients With Severe Multiple Sclerosis Exhibit Functionally Altered CD8+Regulatory T Cells

Abstract

Background and ObjectivesMultiple sclerosis (MS) is a chronic inflammatory and demyelinating disease of the CNS. Studies of immune dysfunction in MS have mostly focused on CD4+Tregs, but the role of CD8+Tregs remains largely unexplored. We previously evidenced the suppressive properties of rat and human CD8+CD45RClow/negTregs from healthy individuals, expressing Forkhead box P3 (FOXP3) and acting through interferon-gamma (IFN-γ), transforming growth factor beta (TGFβ), and interleukin-34 (IL-34). secretions to regulate immune responses and control diseases such as transplant rejection. To better understand CD8+CD45RClow/negTregs contribution to MS pathology, we further investigated their phenotype, function, and transcriptome in patients with MS.MethodsWe enrolled adults with relapsing-remitting MS and age-matched and sex-matched healthy volunteers (HVs). CD8+T cells were segregated based on low or lack of expression of CD45RC. First, the frequency in CSF and blood, phenotype, transcriptome, and function of CD8+CD45RClowandnegwere investigated according to exacerbation status and secondarily, according to clinical severity based on the MS severity score (MSSS) in patients with nonexacerbating MS. We then induced active MOG35-55EAE in C57Bl/6 mice and performed adoptive transfer of fresh and expanded CD8+CD45RCnegTregs to assess their ability to mitigate neuroinflammation in vivo.ResultsThirty-one untreated patients with relapsing-remitting MS were compared with 40 age-matched and sex-matched HVs. We demonstrated no difference of CSF CD8+CD45RClowand CD8+CD45RCnegproportions, but blood CD8+CD45RClowfrequency was lower in patients with MS exacerbation when compared with that in HVs. CD8+CD45RCnegTregs but not CD8+CD45RClowshowed higher suppressive capacities in vitro in MS patients with exacerbation than in patients without acute inflammatory attack. In vitro functional assays showed a compromised suppression capacity of CD8+CD45RClowTregs in patients with nonexacerbating severe MS, defined by the MSSS. We then characterized murine CD8+CD45RCnegTregs and demonstrated the potential of CD45RCnegcells to migrate to the CNS and mitigate experimental autoimmune encephalomyelitis in vivo.DiscussionAltogether, these results suggest a defect in the number and function of CD8+CD45RClowTregs during MS relapse and an association of CD8+CD45RClowTregs dysfunction with MS severity. Thus, CD8+CD45RClow/negT cells might bring new insights into the pathophysiology and new therapeutic approaches of MS.