A Functionally Distinct CXCR3⁺/IFN-γ⁺/IL-10⁺ Subset Defines Disease-Suppressive Myelin-Specific CD8 T Cells

Multiple sclerosis (MS) is an immune-mediated demyelinating disease of the CNS. We have previously demonstrated that CNS-specific CD8 T cells possess a disease-suppressive function in MS and variations of its animal model, experimental autoimmune encephalomyelitis (EAE), including the highly clinically relevant relapsing-remitting EAE disease course. Regulatory CD8 T cell subsets have been identified in EAE and other autoimmune diseases, but studies vary in defining phenotypic properties of these cells. In relapsing-remitting EAE, PLP_178-191 CD8 T cells suppress disease, whereas PLP_139-151 CD8 T cells lack this function. In this study, we used this model to delineate the unique phenotypic properties of CNS-specific regulatory PLP_178-191 CD8 T cells versus nonregulatory PLP_139-151 or OVA_323-339 CD8 T cells. Using multiparametric flow cytometric analyses of phenotypic marker expression, we identified a CXCR3⁺ subpopulation among activated regulatory CD8 T cells, relative to nonregulatory counterparts. This subset exhibited increased degranulation and IFN-γ and IL-10 coproduction. A similar subset was also identified in C57BL/6 mice within autoregulatory PLP_178-191 CD8 T cells but not within nonregulatory OVA_323-339 CD8 T cells. This disease-suppressing CD8 T cell subpopulation provides better insights into functional regulatory mechanisms, and targeted enhancement of this subset could represent a novel immunotherapeutic approach for MS.