Recognition of viral and self-antigens by T_H1 and T_H1/T_H17 central memory cells in patients with multiple sclerosis reveals distinct roles in immune surveillance and relapses

Background Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) that is caused by autoreactive T cells and associated with viral infections. However, the phenotype of pathogenic T cells in peripheral blood remains to be defined, and how viruses promote MS is debated. Objective We aimed to identify and characterize potentially pathogenic autoreactive T cells, as well as protective antiviral T cells, in patients with MS. Methods We analyzed CD4⁺ helper T-cell subsets from peripheral blood or cerebrospinal fluid for cytokine production, gene expression, plasticity, homing potentials, and their reactivity to self-antigens and viral antigens in healthy subjects and patients with MS. Moreover, we monitored their frequencies in untreated and fingolimod- or natalizumab-treated patients with MS. Results T_H1/T_H17 central memory (T_H1/T_H17_CM) cells were selectively increased in peripheral blood of patients with relapsing-remitting MS with a high disease score. T_H1/T_H17_CM cells were closely related to conventional T_H17 cells but had more pathogenic features. In particular, they could shuttle between lymph nodes and the CNS and produced encephalitogenic cytokines. The cerebrospinal fluid of patients with active MS was enriched for CXCL10 and contained mainly CXCR3-expressing T_H1 and T_H1/T_H17 subsets. However, while T_H1 cells responded consistently to viruses, T_H1/T_H17_CM cells reacted strongly with John Cunningham virus in healthy subjects but responded instead to myelin-derived self-antigens in patients with MS. Fingolimod and natalizumab therapies efficiently targeted autoreactive T_H1/T_H17_CM cells but also blocked virus-specific T_H1 cells. Conclusions We propose that autoreactive T_H1/T_H17_CM cells expand in patients with MS and promote relapses after bystander recruitment to the CNS, whereas T_H1 cells perform immune surveillance. Thus the selective targeting of T_H1/T_H17 cells could inhibit relapses without causing John Cunningham virus–dependent progressive multifocal encephalomyelitis.