Multiple sclerosis-associated HLA demarcates EBV-specific CD8+ T cells with an exhausted and brain residency phenotype

Specific HLA class I subtypes as well as circulating antibodies against Epstein-Barr virus (EBV) have been associated with increased susceptibility to develop multiple sclerosis (MS). It is currently unclear whether and how these risk factors are functionally related. Here, we assessed the impact of MS risk allele HLA-B7 and protective allele HLA-A2 on the effector phenotype of EBV-specific CD8+ T cells and if this corresponds with anti-EBV IgG titers. For this, we selected HLA-A2+ and/or HLA-B7+ donors with and without MS and analyzed HLA-restricted, EBV- specific CD8+ T cells with different fine-specificities using 38 color-based spectral flow cytometry. In contrast to HLA-A2-restricted CD8+ T cells, HLA-B7-restricted CD8+ T cells showed a confined response to EBV, which was mainly directed against latent peptide EBNA3A(379-387). These HLA-B7-restricted EBV-specific CD8+ T cells expressed higher levels of CNS residency markers CXCR3 and CD20 and were most abundant in fresh single-cell suspensions derived from different post-mortem CNS compartments of an HLA-A2+B7+ MS donor. Moreover, HLA-B7- restricted EBV-specific CD8+ T cells displayed a more exhausted phenotype (PD- 1+CD244+CD160+KLRG1+TIGIT+) that stood out in the blood from people with MS (pwMS). Accordingly, in the blood, increased IgG titers against EBV were found for pwMS carrying HLA- B7 but lacking HLA-A2, which seemed to coincide with HLA-B7-restricted EBV-specific CD8+ T cells having such an effector phenotype. These data support a model in which the confined response against EBV makes circulating HLA-B7-restricted CD8+ T cells less able to control EBV and more prone to infiltrate the CNS in pwMS.